Display device, display system, mobile body, and display panel housing device

Abstract

The present invention expands the viewing area in a display device. This display device comprises: a visual confirmation window that enables the inside of a housing to be viewed from the outside of the housing; and an optical system capable of forming an image based on a display image, which is displayed by a display panel positioned inside the housing, so as to be viewable via the visual confirmation window. A first lower end of the visual confirmation window is positioned forward or rearward of a first upper end of the visual confirmation window, or a first left end (38z) of the visual confirmation window is positioned forward or rearward of a first right end of the visual confirmation window.

Description

Display device, display system, mobile unit, and display panel housing device

[0001] This disclosure relates to a display device for displaying images, and a mobile device equipped with such a display device. Furthermore, this disclosure relates to a display device, a display system, and a mobile device.

[0002] Conventionally, a display device, such as the one described in Patent Document 1, is known. In addition, various display systems have been proposed that are mounted on vehicles and allow the driver to view images of the area behind the vehicle (see, for example, Patent Document 1).

[0003] Japanese Patent Publication No. 2022-63533, Japanese Patent Publication No. 2010-208372

[0004] A display device according to one aspect of the present disclosure comprises: a display panel for displaying a display image; a housing in which the display panel is located inside; a viewing section located in front of the display panel in the housing when the direction in which the display panel displays the display image is considered as the forward direction, and which makes the inside of the housing visible from the outside of the housing; and an optical system capable of forming an image based on the display image so as to be visible through the viewing section, wherein when the vertically upward direction in the operating state of the display device is considered as the upward direction, the direction opposite to the upward direction is considered as the downward direction, and the direction perpendicular to the upward direction, the downward direction, and the forward direction is considered as the left-right direction, the first lower end of the viewing section is located in front of or behind the first upper end of the viewing section, or the first left end of the viewing section is located in front of or behind the first right end of the viewing section.

[0005] This is a diagram illustrating the schematic configuration of the display device relating to this disclosure. This is a cross-sectional view showing an example of a specific configuration of the display device relating to this disclosure. This is a schematic diagram showing an example of an edge-lit backlight. This is a schematic diagram showing an example of a direct-lit backlight. This is a cross-sectional view showing an example of the main components of the display device relating to this disclosure. This is a cross-sectional view showing a different example of the main components of the display device relating to this disclosure, other than that shown in Figure 5. This is a cross-sectional view showing a different example of the main components of the display device relating to this disclosure, other than that shown in Figures 5 and 6. This is a diagram showing an example of the application of an imaging device equipped with the display device relating to this disclosure. This is a diagram showing an example of the interior of a mobile body, which is a vehicle to which an imaging device equipped with the display device relating to this disclosure is applied. This is a diagram showing an example of the arrangement of components in a display device provided in a mobile body. This is a diagram illustrating variations in the arrangement of each component in the display device relating to this disclosure. This is a diagram illustrating variations in the arrangement of each component in the display device relating to this disclosure. This is a diagram illustrating variations in the arrangement of each component in the display device relating to this disclosure. This is a diagram illustrating variations in the arrangement of each component in the display device relating to this disclosure. This is a diagram illustrating variations in the arrangement of each component in the display device relating to this disclosure. This is a diagram illustrating variations in the arrangement of each component in the display device relating to this disclosure. This figure illustrates variations in the arrangement of each component in the display device according to this disclosure. This figure shows an example of the display device according to this disclosure being applied to a digital rearview mirror. This figure shows an example of the display device according to this disclosure being applied to a CID. This figure shows an example of the display device according to this disclosure being applied to a digital side mirror. This figure shows an example of the optical path when the display device according to this disclosure is applied to a digital rearview mirror. This figure shows an example of the optical path when the display device according to this disclosure is applied to a CID display device according to this disclosure. This figure shows an example of the optical path when the display device according to this disclosure is applied to a digital side mirror. This figure illustrates variations in the shape of the housing in the display device according to this disclosure. This figure shows an example of a vehicle equipped with a display system. This figure schematically shows an example of the configuration of a display device. This figure schematically shows the configuration of a display system. This figure schematically shows an example of the configuration of a display device.This is a schematic diagram showing the configuration of a dimming member. This is a diagram explaining the reflection of ambient light in a display device. This is a schematic diagram showing an example of a virtual image seen by a user. This is a schematic diagram showing an example of a virtual image seen by a user. This is a flowchart showing the control of the display device by the control unit. This is a flowchart showing the control of the display device by the control unit. This is a flowchart showing the control of the display device by the control unit. This is a schematic diagram showing another example of the configuration of a display device. This is a schematic diagram showing another example of the configuration of a display device. This is a schematic diagram showing another example of the configuration of a display device. This is a schematic diagram showing another example of the configuration of a display device. This is a diagram explaining the projection of a virtual image in the display device of Figure 35. This is a diagram explaining the projection of a virtual image in the display device of Figure 36. This is a schematic diagram explaining the projection of a virtual image in the display device of Figure 36. This is a schematic diagram showing another example of the configuration of a display device. This is a schematic diagram showing another example of the configuration of a display device. This is a schematic diagram showing another example of the configuration of a display device. This is a diagram explaining the function of an optical system having a third phase difference plate and a fourth phase difference plate. This is a diagram explaining the function of an optical system having a third phase difference plate and a fourth phase difference plate. This is a diagram illustrating the function of an optical system having a third phase difference plate and a fourth phase difference plate. This is a diagram illustrating the function of an optical system having a third phase difference plate and a fourth phase difference plate. This is a diagram illustrating the function of an optical system having a third phase difference plate and a fourth phase difference plate. This is a diagram illustrating the function of an optical system having a third phase difference plate and a fourth phase difference plate. This is a diagram illustrating the function of an optical system having a third phase difference plate and a fourth phase difference plate. This is a graph illustrating the function of an optical system having a third phase difference plate and a fourth phase difference plate. This is a diagram schematically showing another example of the configuration of a display device. This is a diagram schematically showing another example of the configuration of a display device. This is a diagram illustrating an example of a vehicle equipped with a display system. This is a diagram schematically showing another example of the configuration of a display device. This is a diagram schematically showing another example of the configuration of a display device. This is a diagram schematically showing another example of the configuration of a display device. This is a diagram schematically showing another example of the configuration of a display device. This is a perspective view schematically showing a cross-section of another example of a display device. This is a cross-sectional view schematically showing a cross-section of another example of a display device. This is a diagram illustrating the optical path of the display light in the display device of Figure 27.

[0006] [Embodiment 1] One aspect of the present disclosure expands the viewing area in a display device.

[0007] A display device according to one aspect of the present disclosure comprises: a display panel for displaying a display image; a housing in which the display panel is located on the inside; a viewing section located in front of the display panel in the housing when the direction in which the display panel displays the display image is considered as the forward direction, and which makes the inside of the housing visible from the outside of the housing; and an optical system capable of forming an image based on the display image so as to be visible through the viewing section, wherein when the vertically upward direction in the operating state of the display device is considered as the upward direction, the direction opposite to the upward direction is considered as the downward direction, and the direction perpendicular to the upward direction, the downward direction, and the forward direction is considered as the left-right direction, the first lower end of the viewing section is located in front of or behind the first upper end of the viewing section, or the first left end of the viewing section is located in front of or behind the first right end of the viewing section.

[0008] According to one aspect of this disclosure, the viewing area in a display device is expanded.

[0009] Hereinafter, one embodiment of the present disclosure will be described in detail. (Basic Configuration) Figure 1 is a schematic diagram showing the configuration of the display device 1 according to the present disclosure. Figure 2 is a cross-sectional view showing an example of a specific configuration of the display device 1. Figure 5 is a cross-sectional view showing an example of the main components of the display device 1. As shown in Figures 1, 2 and 5, the display device 1 may include a display panel 2, a housing 36, a viewing window 38P, and an optical system 3.

[0010] The display device 1 may direct a portion of the display light emitted from the display panel 2 into the eyes of the user 22, allowing the user 22 to view it as an image, picture, or aerial image. The display device 1 can allow the user 22 to view the display on the display panel 2 at a position different from the position of the display panel 2, using the display light emitted from the display panel 2. In one embodiment of this disclosure, the display device 1 may allow the user 22 to view the display light as a virtual image V. The virtual image V may be formed on the side of the display device 1 that is further away from the user 22. The virtual image V may be an upright virtual image that is an enlarged version of the display image displayed on the display panel 2. The virtual image V may be formed inside the housing 36 or outside the housing 36. The virtual image V may be formed on the side of the user 22 that is further away from the display panel 2 or on the side that is closer to the display panel 2. The virtual image V may be formed on the side farther from the viewing window 38P, or on the side closer to the viewing window 38P, as viewed from the user 22.

[0011] The display device 1 in one embodiment of this disclosure may be a non-attachable device to the user 22. That is, it may not be attached to the user 22 but may be fixed to the environment. The display device 1 may be fixed to, for example, a wall, column, or ceiling. The display device 1 may also be fixed to the interior of a vehicle. The display device 1 may be attached to the user 22. When attached to the user 22, the display device 1 may have a mounting part (not shown) so that the window 37 is fixed at the position of the user 22's eyes.

[0012] The display panel 2 has a display surface 2a, and a display image may be displayed on the display surface 2a. In other words, the display panel 2 may emit display light of the display image from the display surface 2a. The display panel 2 may be configured to emit linearly polarized display light. The following description will focus on, but is not limited to, the case in which the display panel 2 emits S-wave polarized display light. For example, if the display panel 2 emits P-wave polarized display light, then S-wave polarization in the following description may be read as P-wave polarization, and P-wave polarization may be read as S-wave polarization.

[0013] The display panel 2 may be a liquid crystal panel. The liquid crystal panel may have a known liquid crystal panel configuration. Known liquid crystal panels may be, for example, IPS (In-Plane Switching), FFS (Fringe Field Switching), VA (Vertical Alignment), ECB (Electrically Controlled Birefringence), and the like.

[0014] The display device 1 may include an irradiator 4 that illuminates the display panel 2 with light over a surface. The irradiator 4 is also called a backlight. The irradiator 4 may be an edge-lit backlight 4A or a direct-lit backlight 4B.

[0015] Figure 3 is a schematic diagram showing an example of an edge-lit backlight 4A. Reference numeral 301 in Figure 3 is a plan view of the edge-lit backlight 4A as seen from the display panel 2 side, and reference numeral 302 is a cross-sectional view taken along the line III-III. Figure 4 is a schematic diagram showing an example of a direct-lit backlight 4B. Reference numeral 401 in Figure 4 is a plan view of the direct-lit backlight 4B as seen from the display panel 2 side, and reference numeral 402 is a cross-sectional view taken along the line IV-IV. Reference numerals 301 and 401 only show the substrate 41 and the light source 42.

[0016] The edge-lit backlight 4A may comprise a substrate 41, a light source 42, a light guide plate 43, a diffuser plate 44, and an optical element 45, as shown in Figure 3. The substrate 41 may have substantially the same size and shape as the display panel 2.

[0017] The light source 42 may be, for example, a cold cathode fluorescent lamp, a halogen lamp, or a xenon lamp. Alternatively, the light source 42 may be, for example, a light-emitting diode (LED), an organic light-emitting diode (OLED), or a semiconductor laser (LD). In the edge-lit backlight 4A, the light source 42 may be located in a part of the periphery of the substrate 41. As shown in reference numeral 301, a plurality of light sources 42 may be located in a line along one side of the substrate 41.

[0018] The light guide plate 43 may be a component that guides the light emitted by the light source 42. The light guide plate 43 may be positioned on the substrate 41 adjacent to the light source 42 and covering most of the substrate 41. In this way, the light guide plate 43 may disperse the light emitted by the light source 42 across the entire surface of the substrate 41 and emit it towards the display panel 2.

[0019] The diffuser plate 44 may be a component that diffuses and emits light emitted from the light guide plate 43 toward the display panel 2. The diffuser plate 44 may be positioned on the light source 42 and the light guide plate 43 so as to cover the entire light source 42 and the light guide plate 43. The optical element 45 may be a component that changes the direction of light emitted from the diffuser plate 44. The optical element 45 may be positioned on the diffuser plate 44 so as to cover the entire diffuser plate 44.

[0020] As shown in Figure 4, the direct-lit backlight 4B may include a substrate 41, a light source 42, a diffuser plate 44, and an optical element 45. In the direct-lit backlight 4A, as shown by reference numeral 401, a plurality of light sources 42 may be positioned across the entire surface of the substrate 41. The diffuser plate 44 may be positioned on the plurality of light sources 42 so as to cover the plurality of light sources 42.

[0021] In this embodiment, the irradiator 4 is described as having an optical element 45, but it does not necessarily have to have an optical element 45.

[0022] The display panel 2 is not limited to a liquid crystal panel (transmissive display panel). The display panel 2 may be a self-emissive display panel that includes self-emissive elements such as a light-emitting diode (LED), an organic light-emitting diode (OLED), or a semiconductor laser (LD).

[0023] The housing 36 may be a housing in which the display panel 2 is located on the inside. Alternatively, the housing 36 may be a housing in which the display panel 2 is located inside. The housing 36 may have an opening 37 in which a part of the wall surface is cut out. The housing 36 may have a viewing area that allows the inside of the housing 36 to be seen from the outside of the housing 36. Alternatively, the housing 36 may have a viewing area that allows the inside of the housing 36 to be seen from the outside of the housing 36. The opening 37 may function as a viewing area.

[0024] The housing 36 may have a member that makes the inside of the housing 36, which is positioned in the opening 37, visible from the outside of the housing 36. The housing 36 may have a member that makes the inside of the housing 36, which is positioned in the opening 37, visible from the outside of the housing 36. The viewing window 38 may be positioned so as to block at least a portion of the opening 37. The viewing window 38 may be a light-transmitting plate. The viewing window 38 may transmit light emitted from the optical system 3. The viewing window 38 may be formed of light-transmitting glass or resin or the like. The member that makes the inside of the housing 36, which is positioned in the opening 37, visible from the outside of the housing 36 (for example, the viewing window 38) may function as a viewing part. The member that makes the inside of the housing 36, which is positioned in the opening 37, visible from the outside of the housing 36 (for example, the viewing window 38) may function as a viewing part.

[0025] The viewing window 38P may be located in front of the display panel 2 in the housing 36 when the direction in which the display panel 2 displays the display image is considered to be forward. The direction in which the display panel 2 displays the display image may be, for example, the direction from the display panel 2 toward the user 22 when the display device 1 is in use.

[0026] The optical system 3 may project the display light emitted from the display panel 2 as a virtual image V within the user's field of view 22. In other words, the virtual image V may be an example of an image based on the display image displayed by the display panel 2, which is imaged by the optical system 3. The virtual image V may be imaged at a position different from the display panel 2. The optical system 3 may be able to image the virtual image V in a way that makes it visible through the viewing window 38P. In other words, the virtual image V may be visible by looking through the viewing window 38P. To put it another way, the virtual image V cannot be seen without the viewing window 38P. As shown in Figure 5, the optical system 3 may be composed of a first phase difference plate 5, a semi-transparent mirror 6, a second phase difference plate 7, and a reflective polarizer 8. The first phase difference plate 5, the semi-transparent mirror 6, the second phase difference plate 7, and the reflective polarizer 8 may be arranged in this order in the direction of emission of the display light from the display panel 2 (positive direction in the Z-axis direction).

[0027] The first phase difference plate 5 may be located on the side of the display surface 2a of the display panel 2. The second phase difference plate 7 may be located away from the first phase difference plate 5 in the direction of emission of display light from the display panel 2. The first phase difference plate 5 and the second phase difference plate 7 may be quarter-wave plates. The first phase difference plate 5 and the second phase difference plate 7 may give a phase difference of 1 / 4 wavelength to the polarization plane (polarization plane in the direction of electric field oscillation) of the incident light. This makes it possible to reflect a portion of the display light emitted from the display panel 2 with the reflective polarizer 8 and have it incident on the semi-transparent mirror 6. The positional relationship between the first phase difference plate 5 and the second phase difference plate 7 may be defined such that when the first phase difference plate 5 and the second phase difference plate 7 are viewed along the Z-axis direction, the lagging axis of the second phase difference plate 7 is perpendicular to the lagging axis of the first phase difference plate 5. The positional relationship between the first phase difference plate 5 and the second phase difference plate 7 may be defined such that, when viewed along the Z-axis direction, the lagging axis of the second phase difference plate 7 is parallel to the lagging axis of the first phase difference plate 5.

[0028] The first phase difference plate 5 and the second phase difference plate 7 only need to be able to provide the necessary phase difference to the light transmitted through them so that the light transmitted through them is reflected by the reflective polarizer plate 8. That is, for example, when the polarization obtained by transmitting through the first phase difference plate 5 and the second phase difference plate 7 is taken as the second polarization, the first phase difference plate 5 and the second phase difference plate 7 may be other wavelength plates or combinations thereof, rather than quarter-wave plates, as long as the second polarization is obtained. In this disclosure, the case where the first phase difference plate 5 and the second phase difference plate 7 are quarter-wave plates will be explained as an example. Furthermore, the first phase difference plate and the second phase difference plate may be film-like members.

[0029] Furthermore, the second phase difference plate 7 only needs to be able to provide the necessary phase difference to the light that has passed through the second phase difference plate 7 so that the light that has been reflected by the reflective polarizer 8 and passed through the second phase difference plate 7 passes through the reflective polarizer 8 again when it reaches the reflective polarizer 8. In other words, for example, if the polarization obtained after being reflected by the reflective polarizer 8 and passed through the second phase difference plate 7 is taken as the first polarization, the second phase difference plate 7 may be a wave plate other than a quarter wave plate, as long as the first polarization can be obtained.

[0030] The first phase difference plate 5 may be integrated with the display panel 2. "Integration" may mean that the two members are arranged in contact with each other, or that the two members are joined to each other by an optically transparent adhesive such as OCA (Optically Clear Adhesive). However, the first phase difference plate 5 may be positioned away from the display surface 2a in the direction of emission of display light from the display panel 2.

[0031] The semi-transmissive mirror 6 may be positioned between the first retardation plate 5 and the second retardation plate 7. The semi-transmissive mirror 6 may transmit a part of the incident light (e.g., approximately 50%) and reflect the remaining part (e.g., approximately 50%). The transmittance and reflectance of the light incident on the semi-transmissive mirror 6 are not limited to 50%. The semi-transmissive mirror 6 may have a function of condensing or converging light. Specifically, the semi-transmissive mirror 6 may have a function of condensing or converging the light incident on and reflected by the semi-transmissive mirror 6. The semi-transmissive mirror 6 reflects a part of the display light reflected by the reflective polarizing plate 8 and makes it incident on the eyes of the user 22. Thereby, the user 22 can visually recognize the virtual image V. As shown in FIG. 5, the semi-transmissive mirror 6 may be a concave mirror having a concave reflective surface 6a. The reflective surface 6a of the semi-transmissive mirror 6 may be positioned on the side of the second retardation plate 7. The semi-transmissive mirror 6 may include at least a part of the reflective surface 6a having a spherical shape, an aspherical shape, or a free-form surface shape. The semi-transmissive mirror 6 may condense or converge light more effectively than other members of the optical system 3. In other words, for example, the semi-transmissive mirror 6 may be set with a large index such as the condensing degree, the converging degree, or the reciprocal of the focal length compared to other members of the optical system 3. The reflective surface 6a of the semi-transmissive mirror 6 may have a larger curvature than other members of the optical system 3. The optical system 3 may have only the semi-transmissive mirror 6 as a member having a condensing or converging function. Further, the semi-transmissive mirror 6 may be configured to include a holographic optical element (HOE), or the surface shape may have a Fresnel shape.

[0032] The semi-transmissive mirror 6 is, for example, configured to include a substrate and a semi-transmissive reflective layer positioned on the surface of the substrate. The substrate may have a transmittance of 100% or nearly 100% with respect to light in the visible light band. The substrate may be made of, for example, a resin material, a glass material, etc. The resin material may be, for example, an acrylic resin, a polycarbonate resin, etc. The semi-transmissive reflective layer may be a metal thin film. The metal thin film may be made of a metal material such as aluminum, chromium, etc. The semi-transmissive reflective layer is not limited to the metal thin film and may be, for example, a dielectric multilayer film, etc. The semi-transmissive mirror 6 may be configured to reflect light by the semi-transmissive reflective layer. The semi-transmissive reflective layer may be formed on the surface of the substrate positioned on the side of the second retardation plate 7.

[0033] The reflective polarizer 8 may be located on the side of the second phase difference plate 7 opposite to the side of the semi-transparent mirror 6. In other words, the reflective polarizer 8 may be located downstream of the second phase difference plate 7 in the direction of emission of display light from the display panel 2. The reflective polarizer 8 may transmit a portion of the incident light and reflect the remainder. In this embodiment, the reflective polarizer 8 may be configured to reflect polarized light having a polarization axis parallel to the polarization axis of the display light (also called S-wave polarized light or second polarized light) and transmit polarized light having a polarization axis perpendicular to the polarization axis of the display light (also called P-wave polarized light or first polarized light). In this case, the positional relationship between the first phase difference plate 5 and the second phase difference plate 7 may be defined such that, when the first phase difference plate 5 and the second phase difference plate 7 are viewed along the Z-axis direction, the lagging axis of the second phase difference plate 7 is perpendicular to the lagging axis of the first phase difference plate 5. Furthermore, for example, the reflective polarizer 8 may be configured to reflect polarized light having a polarization axis perpendicular to the polarization axis of the display light (also called P-wave polarized light or second polarized light) and transmit polarized light having a polarization axis parallel to the polarization axis of the display light (also called S-wave polarized light or first polarized light). In this case, the positional relationship between the first phase difference plate 5 and the second phase difference plate 7 may be defined such that when the first phase difference plate 5 and the second phase difference plate 7 are viewed along the Z-axis direction, the lagging axis of the second phase difference plate 7 and the lagging axis of the first phase difference plate 5 are parallel. This makes it possible for the user 22 to view the virtual image V. The reflective polarizer 8 may be integrated with the second phase difference plate 7.

[0034] The reflective polarizer 8 may have the function of diverging the light that is incident on the semi-transparent mirror 6 and reflected. The reflective polarizer 8 may have the function of focusing or converging the light that is incident on the semi-transparent mirror 6 and reflected. The reflective polarizer 8 may be flat, or it may have a concave shape located on the display panel 2 side, or it may have a convex shape located on the display panel 2 side. Furthermore, the reflective polarizer 8 may be composed of a holographic optical element (HOE), or its surface shape may have a Fresnel shape.

[0035] The reflective polarizing plate 8 may be, for example, a wire grid polarizer including a base material and a plurality of metal fine wires (also referred to as a metal nanowire grid) located on the surface of the base material. The base material may have a transmittance of 100% or nearly 100% with respect to light in the visible light band. The base material may be composed of, for example, a resin material, a glass material, or the like. The metal fine wires may be composed of a metal material such as aluminum, chromium, titanium oxide, or the like. The metal fine wires may be arranged along one direction. The reflective polarizing plate 8 can transmit a light component vibrating in a direction orthogonal to the grid and can reflect a light component vibrating in a direction parallel to the grid.

[0036] The display device 1 may include a controller 50. The controller 50 is connected to each component of the display device 1 and may control each component. The controller 50 may control the irradiator 4. The controller 50 may control the display image to be displayed on the display panel 2 and the irradiator 4. The controller 50 may control the irradiator 4 based on the display image to be displayed on the display panel 2. The controller 50 may include one or more processors. The processor may include a general-purpose processor configured to load a specific program and execute a specific function, and a dedicated processor specialized for a specific process. The processor may include a PLD (Programmable Logic Device). The controller 50 may be either a SoC (System-on-a-Chip) or a SiP (System In a Package) in which one or more processors cooperate. The controller 50 includes a storage unit and may store various information or a program for operating each component of the display device 1 in the storage unit. The storage unit may be composed of, for example, a semiconductor memory or the like. The storage unit may function as a work memory of the controller 50.

[0037] The optical function of the optical system 3 will now be described. The display panel 2 may emit display light that is S-wave polarized (first linearly polarized light L1). The display light of the first linearly polarized light L1 emitted from the display panel 2 may pass through the first phase difference plate 5 and be converted into light of the first circularly polarized light C1. A portion of the first circularly polarized light C1 that has passed through the first phase difference plate 5 (for example, approximately 50%) may pass through the semi-transparent mirror 6. The first circularly polarized light C1 that has passed through the semi-transparent mirror 6 may pass through the second phase difference plate 7 and be converted into light of the second linearly polarized light L2, whose polarization direction is parallel to the first linearly polarized light L1 (i.e., S-wave polarized light). The light of the second linearly polarized light L2 may be incident on the reflective polarizer 8. As described above, the reflective polarizer 8 may reflect S-wave polarized light and transmit P-wave polarized light. The light of the second linearly polarized light L2 incident on the reflective polarizer 8 may be reflected by the reflective polarizer 8 and converted into light of the third linearly polarized light L3. The light of the third linearly polarized light L3 may pass through the second phase difference plate 7 and be converted into the light of the second circularly polarized light C2. A portion of the light of the second circularly polarized light C2 that has passed through the second phase difference plate 7 (for example, about 50%) may be reflected by the semitransparent mirror 6 and converted into the light of the third circularly polarized light C3. The light of the third circularly polarized light C3 may pass through the second phase difference plate 7 and be converted into the light of the fourth linearly polarized light L4 whose polarization direction is perpendicular to the first linearly polarized light L1 (i.e., it is P-wave polarized). The light of the fourth linearly polarized light L4 may pass through the reflective polarizer 8 and be emitted to the outside. The amount of light (luminance) emitted from the display device 1 may be, for example, about 25% of the amount of light (luminance) of the display light emitted from the display panel 2.

[0038] Next, another optical function of the optical system 3 will be described. The display panel 2 may emit display light that is S-wave polarized (first linearly polarized light L1). The display light of the first linearly polarized light L1 emitted from the display panel 2 may pass through the first phase difference plate 5 and be converted into light of the first circularly polarized light C1. A portion of the first circularly polarized light C1 that has passed through the first phase difference plate 5 (for example, approximately 50%) may pass through the semi-transparent mirror 6. The first circularly polarized light C1 that has passed through the semi-transparent mirror 6 may pass through the second phase difference plate 7 and be converted into light of the second linearly polarized light L2, whose polarization direction is orthogonal to the first linearly polarized light L1 (i.e., P-wave polarized light). The light of the second linearly polarized light L2 may be incident on the reflective polarizer 8. As described above, the reflective polarizer 8 may reflect P-wave polarized light and transmit S-wave polarized light. The light of the second linearly polarized light L2 incident on the reflective polarizer 8 may be reflected by the reflective polarizer 8 and converted into light of the third linearly polarized light L3. The light of the third linearly polarized light L3 may pass through the second phase difference plate 7 and be converted into the light of the second circularly polarized light C2. A portion of the light of the second circularly polarized light C2 that has passed through the second phase difference plate 7 (for example, about 50%) may be reflected by the semitransparent mirror 6 and converted into the light of the third circularly polarized light C3. The light of the third circularly polarized light C3 may pass through the second phase difference plate 7 and be converted into the light of the fourth linearly polarized light L4 whose polarization direction is parallel to the first linearly polarized light L1 (i.e., S-wave polarized). The light of the fourth linearly polarized light L4 may pass through the reflective polarizer 8 and be emitted to the outside. The amount of light emitted from the display device 1 may be, for example, about 25% of the amount of display light emitted from the display panel 2.

[0039] The first phase difference plate 5, the semi-transparent mirror 6, the second phase difference plate 7, and the reflective polarizing plate 8 may be held by a holding member (not shown) to maintain their relative positions. Air may be interposed between the first phase difference plate 5 and the second phase difference plate 7 (i.e., between the first phase difference plate 5 and the semi-transparent mirror 6, and between the semi-transparent mirror 6 and the second phase difference plate 7). The display device 1 may be configured without a member made of a resin material such as polymer between the first phase difference plate 5 and the second phase difference plate 7. This reduces the risk of deformation of the semi-transparent mirror 6 when the resin material is cured during the manufacturing process of the display device 1, and positional misalignment between the semi-transparent mirror 6 and the first phase difference plate 5 and the second phase difference plate 7. Furthermore, resin materials such as polymers have material-specific retardation, which can reduce the risk of changing the polarization state of light transmitted through the resin material. As a result, a decrease in display quality can be reduced.

[0040] Since the optical system 3 is an on-axis type optical system in which the optical axis of the incident light and the optical axis of the emitted light substantially coincide, the space occupied by the optical system 3 can be reduced, and as a result, the display device 1 can be miniaturized. In addition, because the optical system 3 is on-axis, distortion and brightness unevenness of the virtual image V seen by the user 22 can be reduced, and the design of the optical system 3 is simplified.

[0041] In the display device 1, the optical path length of the light emitted from the display panel 2, passing through the semi-transparent mirror 6, reflected by the reflective polarizer 8, and returning to the semi-transparent mirror 6 may be smaller than the focal length of the semi-transparent mirror 6. In this case, a virtual image V can be made visible to the user 22. In the display device 1, the optical path length of the light emitted from the display panel 2, passing through the semi-transparent mirror 6, reflected by the reflective polarizer 8, and returning to the semi-transparent mirror 6 may be larger than the focal length of the semi-transparent mirror 6. In this case, a real image can be made visible to the user 22.

[0042] In Figure 5, for the sake of illustration, the optical path of light incident on the reflective polarizer 8 and the optical path of light reflected by the reflective polarizer 8 are shown shifted in the height direction (Y-axis direction). Similarly, the optical path of light incident on the semi-transparent mirror 6 and the optical path of light reflected by the semi-transparent mirror 6 are shown shifted in the height direction (Y-axis direction). However, in reality, the display light emitted from the display panel 2 propagates substantially along a single axis. The same applies to the optical paths shown in Figures 6 and 7; the display light emitted from the display panel 2 propagates substantially along a single axis.

[0043] Figure 6 is a cross-sectional view showing a different example of the main components of the display device 1 from that shown in Figure 5. Other examples of the display device 1 will be described below. In the following description, the display device 1 shown as an example in Figure 6 will be referred to as display device 1A. Display device 1A differs from display device 1 in that it has an optical system 10 instead of an optical system 3.

[0044] The optical system 10 may include a first semi-transparent mirror 11, a first phase difference plate 12, a second semi-transparent mirror 13, a second phase difference plate 14, and a polarizing plate 15. The first semi-transparent mirror 11, the first phase difference plate 12, the second semi-transparent mirror 13, the second phase difference plate 14, and the polarizing plate 15 may be arranged in this order in the direction of emission of display light from the display panel 2.

[0045] The first phase difference plate 12 may be located on the side of the reflective surface 11a of the first semi-transparent mirror 11. The first phase difference plate 12 may be located away from the display surface 2a in the direction of emission of display light from the display panel 2. The second phase difference plate 14 may be located away from the first phase difference plate 12 in the direction of emission of display light. The first phase difference plate 12 and the second phase difference plate 14 may be quarter-wave plates. The positional relationship between the first phase difference plate 12 and the second phase difference plate 14 may be defined such that, when viewed along the Z-axis direction, the lagging axis of the second phase difference plate 14 is perpendicular to the lagging axis of the first phase difference plate 12. The positional relationship between the first phase difference plate 12 and the second phase difference plate 14 may be defined such that, when the first phase difference plate 12 and the second phase difference plate 14 are viewed along the Z-axis direction, the lagging axis of the second phase difference plate 14 is parallel to the lagging axis of the first phase difference plate 12.

[0046] The first semi-transparent mirror 11 may be positioned between the display panel 2 and the first phase difference plate 12. The first semi-transparent mirror 11 may transmit a portion of the incident light and reflect the remainder. The first semi-transparent mirror 11 may have a function of focusing or converging light. Specifically, the first semi-transparent mirror 11 may have a function of focusing or converging light that is incident on and reflected by the first semi-transparent mirror 11. The first semi-transparent mirror 11 may be a concave mirror having a concave reflective surface 11a, as shown in Figure 6. The reflective surface 11a of the first semi-transparent mirror 11 may be positioned on the side of the first phase difference plate 12. The first semi-transparent mirror 11 may focus or converge light more effectively than other members of the optical system 10. In other words, the first semi-transparent mirror 11 may have a larger focusing degree, converging degree, or index expressed as the reciprocal of the focal length than other members of the optical system 10. The reflective surface 11a of the first semi-transparent mirror 11 may have a greater curvature than other members of the optical system 10. The optical system 10 may have only the first semi-transparent mirror 11 as a member having a light-gathering or focusing function. The first semi-transparent mirror 11 may also be composed of a holographic optical element (HOE), or its surface shape may have a Fresnel shape. In this embodiment, the first semi-transparent mirror 11 may be configured to transmit polarized light having a polarization axis parallel to the polarization axis of the display light and to reflect polarized light having a polarization axis perpendicular to the polarization axis of the display light. The first semi-transparent mirror 11 may be configured to transmit S-wave polarized light and reflect P-wave polarized light. Alternatively, the first semi-transparent mirror 11 may be configured to reflect S-wave polarized light and transmit P-wave polarized light. At least a portion of the reflective surface 11a of the first semi-transparent mirror 11 may include a spherical shape, an aspherical shape, or a free-form surface shape.

[0047] The first semi-transparent mirror 11 may be composed of, for example, a substrate and a plurality of metal nanowires (metal nanowire grids) located on the surface of the substrate. The substrate may have a transmittance of 100% or close to 100% for light in the visible light band. The substrate may be composed of, for example, a resin material, a glass material, etc. The resin material may be, for example, an acrylic resin, a polycarbonate resin, etc. The metal nanowires may be composed of, for example, a metal material such as aluminum, chromium, or titanium oxide. The metal nanowires may be arranged along one direction. The first semi-transparent mirror 11 can transmit light components vibrating in a direction perpendicular to the grid and can reflect light components vibrating in a direction parallel to the grid. The metal nanowire grid may be formed on the surface of the substrate on the side of the first phase difference plate 12. In this example, the metal nanowire grid is used to impart a reflective polarization function to the first semi-transparent mirror 11, but the first semi-transparent mirror 11 may be used as a simple half-mirror and a separate reflective polarizing plate may be provided.

[0048] The second semi-transparent mirror 13 may be positioned between the first phase difference plate 12 and the second phase difference plate 14. The second semi-transparent mirror 13 may transmit a portion of the incident light (for example, approximately 50%) and reflect the remainder (for example, approximately 50%). The transmittance and reflectance of the light incident on the second semi-transparent mirror 13 are not limited to 50%. The second semi-transparent mirror 13 may be positioned on the opposite side of the first semi-transparent mirror 11 from the first phase difference plate 12, and more specifically, as shown in Figure 6, the reflective surface 13a may be positioned on the side of the first phase difference plate 12. The second semi-transparent mirror 13 may be a plane mirror. The second semi-transparent mirror 13 is also called a plane half-mirror. The second semi-transparent mirror 13 may be integrated with the first phase difference plate 12 and / or the second phase difference plate 14.

[0049] The second semi-transparent mirror 13 may have a function to diverge the light that is incident on and reflected by the second semi-transparent mirror 13. The second semi-transparent mirror 13 may have a convex reflective surface 13a, and the reflective surface 13a may be located on the side of the first phase difference plate 12. The second semi-transparent mirror 13 is also called a convex half mirror. The second semi-transparent mirror 13 may transmit a portion of the incident light (for example, approximately 50%) and reflect the remainder (for example, approximately 50%). The transmittance and reflectance of the light incident on the second semi-transparent mirror 13 are not limited to 50%. The second semi-transparent mirror 13 may have a function to collect or focus the light that is incident on and reflected by the second semi-transparent mirror 13. Specifically, the second semi-transparent mirror 13 may have a concave shape located on the side of the display panel 2. Furthermore, the second semi-transparent mirror 13 may be composed of a holographic optical element (HOE), or its surface shape may have a Fresnel shape.

[0050] The second semi-transparent mirror 13 may be composed of, for example, a substrate and a semi-transparent reflective layer located on the surface of the substrate. The substrate may have a transmittance of 100% or close to 100% for light in the visible light band. The substrate may be made of, for example, inorganic glass, a resin material, etc. The resin material may be, for example, acrylic resin, polycarbonate resin, etc. The semi-transparent reflective layer may be a thin metal film. The thin metal film may be made of, for example, a metal material such as aluminum or chromium. The semi-transparent reflective layer is not limited to a thin metal film, and may be, for example, a dielectric multilayer film, etc.

[0051] The polarizing plate 15 may be located on the side of the second phase difference plate 14 opposite to the side of the second semitransparent mirror 13. In other words, the polarizing plate 15 may be located downstream of the second phase difference plate 14 in the direction of emission of display light from the display panel 2. The polarizing plate 15 may transmit a portion of the incident light and absorb or reflect the remainder. In this embodiment, the polarizing plate 15 may be configured to transmit P-wave polarized light and absorb S-wave polarized light. The polarizing plate 15 may be configured to absorb or reflect polarized light having a polarization axis parallel to the polarization axis of the display light (for example, S-wave polarized light, also called third-wave polarized light) and transmit polarized light having a polarization axis perpendicular to the polarization axis of the display light (for example, P-wave polarized light, also called fourth-wave polarized light). In this case, the positional relationship between the first phase difference plate 12 and the second phase difference plate 14 may be defined such that, when viewed along the Z-axis direction, the lagging axis of the second phase difference plate 14 is perpendicular to the lagging axis of the first phase difference plate 12. Furthermore, the polarizing plate 15 may be configured to absorb or reflect polarized light having a polarization axis perpendicular to the polarization axis of the display light, and transmit polarized light having a polarization axis parallel to the polarization axis of the display light. In this case, the positional relationship between the first phase difference plate 12 and the second phase difference plate 14 may be defined such that, when viewed along the Z-axis direction, the lagging axis of the second phase difference plate 14 is parallel to the lagging axis of the first phase difference plate 12. Furthermore, the polarizing plate 15 may be integrated with the second phase difference plate 14.

[0052] The polarizing plate 15 may have the configuration of a known absorption polarizing plate. Known absorption polarizing plates may be, for example, an iodine-based polarizing plate in which an iodine compound is adsorbed and oriented on a polyvinyl alcohol (PVA) film, or a dye-based polarizing plate in which a dichroic organic dye is adsorbed and oriented on a PVA film. Alternatively, the polarizing plate 15 may have the configuration of a reflective polarizing plate.

[0053] The optical function of the optical system 10 will now be described. The display light of S-wave polarized light (first linearly polarized light L1) emitted from the display panel 2 may pass through the first semi-transparent mirror 11. The display light of the first linearly polarized light L1 may pass through the first phase difference plate 12 and be converted into light of first circularly polarized light C1. The light of first circularly polarized light C1 may be incident on the second semi-transparent mirror 13. A portion of the light of first circularly polarized light C1 (for example, approximately 50%) may be reflected by the second semi-transparent mirror 13 and converted into light of second circularly polarized light C2. The light of second circularly polarized light C2 may pass through the first phase difference plate 12 and be converted into light of second linearly polarized light L2 whose polarization direction is perpendicular to that of first linearly polarized light L1 (i.e., P-wave polarized light). The light of second linearly polarized light L2 may be reflected by the first semi-transparent mirror 11 and converted into light of third linearly polarized light L3 whose polarization direction is perpendicular to that of first linearly polarized light L1. The third linearly polarized light L3 may pass through the first phase difference plate 12 and be converted into the third circularly polarized light C3. A portion of the third circularly polarized light C3 (for example, approximately 50%) may pass through the second semi-transparent mirror 13. The third circularly polarized light C3 that has passed through the second semi-transparent mirror 13 passes through the second phase difference plate 14 and is converted into the fourth linearly polarized light L4, whose polarization direction is perpendicular to the first linearly polarized light L1 (i.e., it is P-wave polarized). The fourth linearly polarized light L4 may pass through the polarizer 15 and be emitted to the outside.

[0054] The remaining portion of the light of the first circularly polarized light C1 (for example, about 50%) may pass through the second semi-transparent mirror 13, then through the second phase difference plate 14, and be converted into light of the fifth linearly polarized light L5, whose polarization direction is parallel to the first linearly polarized light L1 (i.e., S-wave polarized light). The light of the fifth linearly polarized light L5 does not need to be emitted to the outside because it is absorbed or reflected by the polarizer plate 15. In other words, the light of the fifth linearly polarized light L5 may be light that is not transmitted through the polarizer plate 15. Therefore, the amount of light (luminance) emitted from the display device 1A may be, for example, about 25% of the amount of display light (luminance) emitted from the display panel 2.

[0055] In the above, an example was described in which the first phase difference plate 12 and the second phase difference plate 14 are quarter-wave plates. However, the first phase difference plate 12 and the second phase difference plate 14 may be other wave plates or combinations thereof, as long as some of the light is absorbed or reflected by the polarizer plate 15 and other light is transmitted through the polarizer plate 15. For example, the first phase difference plate and the second phase difference plate only need to be able to provide the necessary phase difference to the light that is transmitted through the first phase difference plate and the second phase difference plate without being reflected by the second semi-transparent mirror 13, so that some of the light that is transmitted through the first phase difference plate and the second phase difference plate without being reflected by the second semi-transparent mirror 13 is absorbed or reflected by the polarizer plate 15. In other words, for example, when the polarization obtained by passing through the first and second phase difference plates without being reflected by the second semi-transparent mirror 13 is taken as the third polarization, the first and second phase difference plates may be other wave plates or combinations thereof, rather than quarter-wave plates, as long as the third polarization is obtained. In this disclosure, the case where the first and second phase difference plates are quarter-wave plates will be explained as an example. Furthermore, the first and second phase difference plates should be such that the light reflected by the second semi-transparent mirror 13 and the first semi-transparent mirror 11 and transmitted through the first and second phase difference plates is transmitted through the polarizer plate 15, and the necessary phase difference is given to the light reflected by the second semi-transparent mirror 13 and the first semi-transparent mirror 11 and transmitted through the first and second phase difference plates. In other words, for example, when the polarization obtained by reflecting light from the second semi-transparent mirror 13 and the first semi-transparent mirror 11 and passing through the first phase difference plate and the second phase difference plate is defined as the fourth polarization, the first phase difference plate and the second phase difference plate may be other wave plates instead of quarter-wave plates, as long as the fourth polarization is obtained. Also, the first phase difference plate 12 and the second phase difference plate 14 may be other wave plates or a combination thereof, instead of quarter-wave plates, as long as some of the light is reflected by the first semi-transparent mirror 11 and the other light is passed through the first semi-transparent mirror 11. The first phase difference plate only needs to be given the necessary phase difference to the light that has passed through the first phase difference plate, reflected by the second semi-transparent mirror 13, and then passed through the first phase difference plate again, before being reflected by the first semi-transparent mirror 11.That is, for example, when polarization obtained by passing through the first phase difference plate, reflecting off the second semi-transparent mirror 13, and then passing through the first phase difference plate again is defined as the fifth polarization, the first and second phase difference plates may be other wave plates instead of quarter-wave plates, as long as the fifth polarization is obtained. Also, the first and second phase difference plates may be film-like materials.

[0056] The first semi-transparent mirror 11, the first phase difference plate 12, the second semi-transparent mirror 13, the second phase difference plate 14, and the polarizing plate 15 may be held by a holding member (not shown) to maintain their relative positions. Air may be interposed between the first semi-transparent mirror 11 and the first phase difference plate 12. The display device 1A may be configured without a member made of a resin material such as polymer between the first semi-transparent mirror 11 and the first phase difference plate 12. Therefore, the risk of deformation of the first semi-transparent mirror 11 when the resin material is cured during the manufacturing process of the display device 1A, and misalignment of the first semi-transparent mirror 11 and the first phase difference plate 12 can be reduced. As a result, a decrease in display quality can be reduced.

[0057] Since the optical system 10 is an on-axis type optical system in which the optical axis of the incident light and the optical axis of the emitted light substantially coincide, the space occupied by the optical system 10 can be reduced, and as a result, the display device 1A can be miniaturized. In addition, because the optical system 10 is on-axis, distortion and brightness unevenness of the virtual image V seen by the user 22 can be reduced, and the design of the optical system 10 is simplified.

[0058] Figure 7 is a cross-sectional view showing a different example of the main components of the display device 1 from those shown in Figures 5 and 6. Further examples of the display device 1 will be described below. In the following description, the display device 1 shown as an example in Figure 7 will be referred to as display device 1B. Display device 1B differs from display device 1 in that it has an optical system 16 instead of an optical system 3.

[0059] The optical system 16 may include a first semi-transparent mirror 17, a first phase difference plate 18, a second semi-transparent mirror 19, a second phase difference plate 20, and a third semi-transparent mirror 21. The first semi-transparent mirror 17, the first phase difference plate 18, the second semi-transparent mirror 19, the second phase difference plate 20, and the third semi-transparent mirror 21 may be arranged in this order in the direction of emission of display light from the display panel 2.

[0060] The first phase difference plate 18 may be located on the side of the reflective surface 17a of the first semi-transparent mirror 17. The first phase difference plate 18 may be located away from the display surface 2a in the direction of emission of display light from the display panel 2. The second phase difference plate 20 may be located away from the first phase difference plate 12 in the direction of emission of display light. The first phase difference plate 18 and the second phase difference plate 20 may be quarter-wave plates. The positional relationship between the first phase difference plate 18 and the second phase difference plate 20 may be defined such that, when viewed along the Z-axis direction, the lagging axis of the second phase difference plate 20 is perpendicular to the lagging axis of the first phase difference plate 18. The positional relationship between the first phase difference plate 18 and the second phase difference plate 20 may be defined such that, when the first phase difference plate 18 and the second phase difference plate 20 are viewed along the Z-axis direction, the lagging axis of the second phase difference plate 20 is parallel to the lagging axis of the first phase difference plate 18.

[0061] The first semi-transparent mirror 17 may be positioned between the display panel 2 and the first phase difference plate 18. The first semi-transparent mirror 17 may transmit a portion of the incident light and reflect the remainder. In this embodiment, the first semi-transparent mirror 17 may be configured to transmit S-wave polarized light and reflect P-wave polarized light. Alternatively, the first semi-transparent mirror 17 may be configured to reflect S-wave polarized light and transmit P-wave polarized light. As shown in Figure 7, the first semi-transparent mirror 17 may be a concave mirror having a concave reflective surface 17a located on the side of the first phase difference plate 18. At least a portion of the reflective surface 17a of the first semi-transparent mirror 17 may include a spherical shape, an aspherical shape, or a free-form surface shape.

[0062] The first semi-transparent mirror 17 may be composed of, for example, a substrate and a plurality of metal nanowires (metal nanowire grids) located on the surface of the substrate. The substrate may have a transmittance of 100% or close to 100% for light in the visible light band. The substrate may be composed of, for example, a resin material, a glass material, etc. The resin material may be, for example, acrylic resin, polycarbonate resin, etc. The metal nanowires may be composed of, for example, a metal material such as aluminum, chromium, titanium oxide, etc. The metal nanowires may be arranged along one direction. The first semi-transparent mirror 17 can transmit light components vibrating in a direction perpendicular to the grid and can reflect light components vibrating in a direction parallel to the grid. The metal nanowire grid may be formed on the surface of the substrate located on the side of the first phase difference plate 18. In this example, the metal nanowire grid provides the first semi-transparent mirror 11 with a reflective polarization function, but the first semi-transparent mirror 11 may be used as a simple half-mirror and a separate reflective polarizer may be provided.

[0063] The second semi-transparent mirror 19 may be positioned between the first phase difference plate 18 and the second phase difference plate 20. The second semi-transparent mirror 19 may transmit a portion of the incident light (for example, approximately 50%) and reflect the remainder (for example, approximately 50%). The transmittance and reflectance of the light incident on the second semi-transparent mirror 19 are not limited to 50%. The second semi-transparent mirror 19 may be a plane mirror having a reflective surface 19a located on the side of the first phase difference plate 18 and a reflective surface 19b located on the side of the second phase difference plate 20, as shown in Figure 7. The second semi-transparent mirror 19 is also called a plane half-mirror. The second semi-transparent mirror 19 may be integrated with the first phase difference plate 18 and / or the second phase difference plate 20.

[0064] The second semi-transparent mirror 19 may be composed of, for example, a substrate and a semi-transparent layer located on the surface of the substrate. The substrate may have a transmittance of 100% or close to 100% for light in the visible light band. The substrate may be made of, for example, inorganic glass, a resin material, etc. The resin material may be, for example, acrylic resin, polycarbonate resin, etc. The semi-transparent layer may be a thin metal film. The thin metal film may be made of, for example, a metal material such as aluminum or chromium. The semi-transparent layer is not limited to a thin metal film, and may be, for example, a dielectric multilayer film. The first phase difference plate 18 and the second phase difference plate 20 may be fixed to the second semi-transparent mirror 19 with an optically transparent adhesive such as OCA (Optically Clear Adhesive). The adhesive may be a material with low retardation.

[0065] The third semi-transparent mirror 21 may be located on the side of the second phase difference plate 20 opposite to the side of the second semi-transparent mirror 19. The third semi-transparent mirror 21 may be located downstream of the second phase difference plate 20 in the direction of emission of display light from the display panel 2. The third semi-transparent mirror 21 may transmit a portion of the incident light and reflect the remainder. In this embodiment, the third semi-transparent mirror 21 may be configured to reflect S-wave polarized light and transmit P-wave polarized light. Alternatively, the third semi-transparent mirror 21 may be configured to transmit S-wave polarized light and reflect P-wave polarized light. As shown in Figure 7, the third semi-transparent mirror 21 may be a concave mirror having a concave reflective surface 21a located on the side of the second phase difference plate 20. At least a portion of the reflective surface 21a of the third semi-transparent mirror 21 may include a spherical shape, an aspherical shape, or a free-form shape.

[0066] The third semi-transparent mirror 21 may be composed of, for example, a substrate and a plurality of metal nanowires (metal nanowire grids) located on the surface of the substrate. The substrate may have a transmittance of 100% or close to 100% for light in the visible light band. The substrate may be composed of, for example, a resin material, a glass material, etc. The resin material may be, for example, an acrylic resin, a polycarbonate resin, etc. The metal nanowires may be composed of, for example, a metal material such as aluminum, chromium, or titanium oxide. The metal nanowires may be arranged along one direction. The third semi-transparent mirror 21 can transmit light components vibrating in a direction perpendicular to the grid and can reflect light components vibrating in a direction parallel to the grid. The metal nanowire grid may be formed on the surface of the substrate located on the side of the second phase difference plate 20. In this example, the metal nanowire grid provides the third semi-transparent mirror 21 with a reflective polarization function, but the third semi-transparent mirror 21 may be used as a simple half-mirror and a separate reflective polarizer may be provided.

[0067] The optical functions of the optical system 16 will now be described. In the display device 1B, the display light emitted from the display panel 2 may travel along path P1 or path P2 and be emitted to the outside. First, the light traveling along path P1 will be described. The S-wave polarized (first linearly polarized L1) display light emitted from the display panel 2 may pass through the first semi-transparent mirror 17. The light of the first linearly polarized L1 may pass through the first phase difference plate 18 and be converted into light of the first circularly polarized C1. The light of the first circularly polarized C1 may be incident on the second semi-transparent mirror 19. A portion of the light of the first circularly polarized C1 (for example, approximately 50%) may be reflected by the second semi-transparent mirror 19 and converted into light of the second circularly polarized C2. The light of the second circularly polarized C2 may pass through the first phase difference plate 18 and be converted into light of the second linearly polarized L2, whose polarization direction is perpendicular to that of the first linearly polarized L1 (i.e., P-wave polarized). The light of the second linearly polarized light L2 may be reflected by the first semi-transparent mirror 17 and converted into the light of the third linearly polarized light L3, whose polarization direction is perpendicular to the first linearly polarized light L1 (i.e., it is P-wave polarized). The third linearly polarized light L3 may be transmitted through the first phase difference plate 18 and converted into the light of the third circularly polarized light C3. The light of the third circularly polarized light C3 may be incident on the second semi-transparent mirror 19. A portion of the light of the third circularly polarized light C3 (for example, approximately 50%) may be transmitted through the second semi-transparent mirror 19. The light of the third circularly polarized light C3 that has been transmitted through the second semi-transparent mirror 19 is transmitted through the second phase difference plate 20 and converted into the light of the fourth linearly polarized light L4, whose polarization direction is perpendicular to the first linearly polarized light L1 (i.e., it is P-wave polarized). The light of the fourth linearly polarized light L4 may be transmitted through the third semi-transparent mirror 21 and emitted to the outside.

[0068] Next, we will describe the light traveling along path P2. The remainder (for example, approximately 50%) of the light of the first circularly polarized light C1 incident on the second semi-transparent mirror 19 may pass through the second semi-transparent mirror 19. The light of the first circularly polarized light C1 that has passed through the second semi-transparent mirror 19 may pass through the second phase difference plate 20 and be converted into light of the fifth linearly polarized light L5, whose polarization direction is parallel to the first linearly polarized light L1 (i.e., S-wave polarized light). The light of the fifth linearly polarized light L5 may be reflected by the third semi-transparent mirror 21 and converted into light of the sixth linearly polarized light L6, whose polarization direction is parallel to the first linearly polarized light L1 (i.e., S-wave polarized light). The light of the sixth linearly polarized light L6 may pass through the second phase difference plate 20 and be converted into light of the fourth circularly polarized light C4. The light of the fourth circularly polarized light C4 may be incident on the second semi-transparent mirror 19. A portion of the light from the fourth circularly polarized light C4 (for example, approximately 50%) may be reflected by the second semi-transparent mirror 19 and converted into the light from the fifth circularly polarized light C5. The light from the fifth circularly polarized light C5 may pass through the second phase difference plate 20 and be converted into the light from the seventh linearly polarized light L7, whose polarization direction is perpendicular to the first linearly polarized light L1 (i.e., it is P-wave polarized). The light from the seventh linearly polarized light L7 may pass through the third semi-transparent mirror 21 and be emitted to the outside.

[0069] As described above, in the display device 1B, the display light emitted from the display panel 2 may travel along path P1 or path P2 and be emitted to the outside. As a result, the amount of light (luminance) emitted from the display device 1B may be, for example, approximately 50% of the amount of light (luminance) of the display light emitted from the display panel 2. The display device 1B can improve light utilization efficiency and improve the luminance of the light emitted to the outside.

[0070] In the above, an example was described in which the first phase difference plate 18 and the second phase difference plate 20 are quarter-wave plates. However, the first phase difference plate 18 and the second phase difference plate 20 may be other wave plates or a combination thereof, as long as some of the light is reflected by the first semi-transparent mirror 17 and other light is transmitted through the first semi-transparent mirror 17. Furthermore, the first phase difference plate 18 and the second phase difference plate 20 may be other wave plates or a combination thereof, as long as some of the light is reflected by the third semi-transparent mirror 21 and other light is transmitted through the third semi-transparent mirror 21.

[0071] The first semi-transparent mirror 17, the first phase difference plate 18, the second semi-transparent mirror 19, the second phase difference plate 20, and the third semi-transparent mirror 21 may be held by a holding member (not shown) to maintain their relative positions. Air may be interposed between the first semi-transparent mirror 17 and the first phase difference plate 18, and between the third semi-transparent mirror 21 and the second phase difference plate 20. The display device 1B may be configured without providing members made of resin material such as polymer between the first semi-transparent mirror 17 and the first phase difference plate 18, and between the third semi-transparent mirror 21 and the second phase difference plate 20. This reduces the risk of deformation of the first semi-transparent mirror 11, misalignment between the first semi-transparent mirror 11 and the first phase difference plate 12, etc. As a result, a decrease in display quality can be reduced.

[0072] Since the optical system 16 is an on-axis type optical system in which the optical axis of the incident light and the optical axis of the emitted light substantially coincide, the space occupied by the optical system 16 can be reduced, and as a result, the display device 1B can be miniaturized. In addition, because the optical system 16 is on-axis, distortion and brightness unevenness of the virtual image V seen by the user 22 can be reduced, and the design of the optical system 16 is simplified.

[0073] The display device 1B may be configured such that the focal length of the first semi-transparent mirror 17 is equal to the focal length of the third semi-transparent mirror 21, and the second semi-transparent mirror 19 is a plane mirror. In this case, in the imaging device including the display device 1B, the virtual image formed by light traveling along path P1 and the virtual image formed by light traveling along path P2 substantially coincide, thereby improving the display quality.

[0074] In the display device 1B, the optical path length of light emitted from the display panel 2, passing through the first semi-transparent mirror 17, reflected by the second semi-transparent mirror 19, and returning to the first semi-transparent mirror 17 may be smaller than the focal length of the first semi-transparent mirror 17. In addition, the optical path length of light emitted from the display panel 2, passing through the first semi-transparent mirror 17, passing through the second semi-transparent mirror 19, and returning to the third semi-transparent mirror 21 may be smaller than the focal length of the first semi-transparent mirror 17. In this case, the user 22 can be made to see the virtual image V. In the display device 1B, the optical path length of light emitted from the display panel 2, passing through the first semi-transparent mirror 17, reflected by the second semi-transparent mirror 19, and returning to the first semi-transparent mirror 17 may be larger than the focal length of the first semi-transparent mirror 17. In addition, the optical path length of the light emitted from the display panel 2, passing through the first semi-transparent mirror 17, the second semi-transparent mirror 19, and reaching the third semi-transparent mirror 21 may be greater than the focal length of the first semi-transparent mirror 17. In this case, the user 22 can see a real image.

[0075] Next, an imaging device according to one embodiment of the present disclosure will be described. The imaging device 100 of this embodiment may include a display device 1. The imaging device 100 may cause the user 22 to view the display light emitted from the display panel 2 as a virtual image V. Since the imaging device 100 includes the display device 1, a compact imaging device can be realized, and the user 22 can view a virtual image V with improved display quality. The imaging device 100 may also cause the user 22 to view the display light emitted from the display panel 2 as a real image.

[0076] Figure 8 shows an example of the application of the imaging device 100. The imaging device 100 may be mounted on a vehicle 23, as shown in Figure 8. The vehicle 23 may be an example of a mobile body on which the imaging device 100 is mounted. However, the mobile body on which the imaging device 100 is mounted is not limited to a vehicle 23. The mobile body may be an aircraft or a ship, etc. Figure 8 shows the case where the vehicle 23 is a passenger car, but the vehicle 23 is not limited to a passenger car and may be an automobile such as a truck, bus, or trolleybus, or a motorcycle. The position of the display device 1 is arbitrary inside the vehicle 23. The display device 1 may be located on the dashboard (instrument panel), inside the dashboard, on the ceiling of the passenger compartment, on the A-pillar, etc. The imaging device 100 may share some of its components with other devices and parts provided by the vehicle 23.

[0077] As an example of this disclosure, the imaging device 100 may constitute a display system comprising a display device 1 and a camera 102 that captures images of the scenery around the vehicle 23, as shown in Figure 8. Here, the scenery around the vehicle 23 may be at least one of the front, rear, sides, above, and below the vehicle 23. The camera 102 may include, for example, a CCD (Charge Coupled Device) image sensor or a CMOS (Complementary Metal Oxide Semiconductor) image sensor. The display device 1 and the camera 102 may be connected by wired communication and / or wireless communication. In the vehicle 23, the display device 1 and the camera 102 may be connected via a vehicle network such as a CAN (Control Area Network).

[0078] The display device 1 may be configured to display at least a portion of the captured image captured by the camera 102 on the display panel 2. In this case, the imaging device 100 can allow the user 22 (driver of the vehicle 23) to view the scenery behind the vehicle 23 as a virtual image V (hereinafter also referred to as virtual image V1) formed on a side farther from the imaging device 100. As a result, the user 22 can view the scenery behind the vehicle 23 without significantly changing the viewing distance (point of gaze) while driving the vehicle 23, making it easier to see the virtual image V1 and improving driving safety. Furthermore, since the imaging device 100 is a small imaging device, even if it is placed in the driver's cab of the vehicle 23, it does not occupy a large volume in the driver's cab and is less likely to interfere with driving. The display device 1, which is mounted on the vehicle 23 and configured to allow the user 22 to view the scenery behind the vehicle 23 as a virtual image V1, is also called a digital rearview mirror.

[0079] Figure 9 shows an example of the interior of a vehicle 23 to which the imaging device 100 is applied. The imaging device 100 may also be applied to a digital side mirror. In this case, as shown in Figure 9, the imaging device 100 may include a display device 1 located on the left A-pillar of the vehicle 23 (hereinafter also referred to as the left-side display device 1L) and a camera 102 that captures the left rear of the vehicle 23 (hereinafter also referred to as the left-side camera 102L). Alternatively, the imaging device 100 may include a display device 1 located on the right A-pillar of the vehicle 23 (hereinafter also referred to as the right-side display device 1R) and a camera 102 that captures the right rear of the vehicle 23 (hereinafter also referred to as the right-side camera 102R). The left-side display device 1L may allow the user 22 to view the image of the left rear of the vehicle 23 captured by the left-side camera 102L as a virtual image V (hereinafter also referred to as the virtual image V2). The right-side display device 1R may allow the user 22 to view a virtual image V (hereinafter also referred to as virtual image V3) of the right rear of the vehicle 23 captured by the right-side camera 102R. The image may be a moving image (also referred to as a video) or a still image. The left-side camera 102L may be positioned in the same position as the left-side door mirror, and the right-side camera 102R may be positioned in the same position as the right-side door mirror.

[0080] The imaging device 100 may be configured such that the distances between the user's eye (or eyebox) and the virtual images V2 and V3 are approximately equal. In this case, the user 22 can check the situation on the left rear and right rear of the vehicle 23 without significantly changing the fixation distance (the distance between the user's eye and the point of fixation that the user 22 is fixating on). Therefore, driving safety can be improved. The eyebox may refer to the real-space region where the user's eye is assumed to be located.

[0081] The imaging device 100 may be configured such that the distance between the user's eye (or eyebox) and each of the virtual images V1 to V3 is approximately equal to each other. In this case, the user 22 can check the situation immediately behind, to the left rear, and to the right rear of the vehicle 23 without significantly changing the gaze distance. Therefore, driving safety can be improved.

[0082] The imaging device 100 may be applied to the cluster 29 in the dashboard of the vehicle 23 (see Figure 9). In this case, the display device 1 may allow the user 22 to view images showing driving information such as vehicle speed, engine rotation speed, and remaining fuel as virtual images V (hereinafter also referred to as virtual images V4).

[0083] The imaging device 100 may be applied to a CID (Center Information Display) 30 (see Figure 9). In this case, the display device 1 is located in the center cluster of the vehicle 23 and may display images showing information related to navigation, the in-vehicle environment (for example, settings for the air conditioning system, audio system, etc.) to the user 22 as a virtual image V (hereinafter also referred to as virtual image V5).

[0084] The imaging device 100 may be configured such that the distance between the user's eye (or eyebox) and the virtual images V4 and V5 are approximately equal. In this case, the user 22 can view information related to the operation of the vehicle 23, as well as information related to navigation, the in-vehicle environment, etc., without significantly changing the viewing distance. Therefore, driving safety can be improved.

[0085] The imaging device 100 may be configured such that the distance between the user's eye (or eyebox) and each of the virtual images V1 to V5 is approximately the same. In this case, the user 22 can check the area directly behind, to the left rear, and to the right rear of the vehicle 23 without significantly changing the gaze distance, and can also check information related to the vehicle's operation, navigation, and in-vehicle environment. Therefore, driving safety can be improved.

[0086] The imaging device 100 may be applied to a PID (Passenger Information Display) 31 (see Figure 9). In this case, the display device 1 is placed near the passenger seat on the dashboard, and can display images of entertainment content and images showing information about audio equipment, air conditioning equipment, etc., as virtual images V for the passenger.

[0087] The imaging device 100 may be applied to the RSE (Rear Seat Entertainment) system 32 (see Figure 8). In this case, the display device 1 is positioned on the back of the front seat and may display images of entertainment content and images showing information about audio equipment, air conditioning equipment, etc., as virtual images V for passengers seated in the rear seats of the vehicle 23.

[0088] (Arrangement of Components) Figure 10 shows an example of the arrangement of components in the display device 1 installed in the vehicle 23. For simplicity, the illuminator 4 and controller 50 of the components of the display device 1 are omitted in Figure 10. Also, the optical system 3 is simplified and only the semi-transparent mirror 6 is shown.

[0089] Furthermore, in the following explanation, the ends of each component are assigned ordinal numbers from 1st to 3rd. Specifically, the ends of the viewing window 38P are designated as "1st", the ends of the display panel 2 as "2nd", and the ends of the semi-transparent mirror 6 as "3rd".

[0090] In the operating state of the display device 1, the vertically upward direction is defined as the upward direction, and the direction opposite to the upward direction is defined as the downward direction. Furthermore, the direction perpendicular to the upward direction, the downward direction, and the forward direction described above is defined as the left-right direction. In the display device 1, the first lower end 38x of the viewing window 38P may be located in front of or behind the first upper end 38y of the viewing window 38P. Alternatively, the first left end 38z of the viewing window 38P may be located in front of or behind the first right end 38w of the viewing window 38P.

[0091] Here, if the first lower end 38x is a side, then the statement that the first lower end 38x is located in front of or behind the first upper end 38y means that a virtual line extended vertically upward from any point on the side is located in front of or behind the point on the first upper end 38y that is closest to that point on the side. In this case, the virtual line may be located in front of or behind all points on the first upper end 38y, but there may be some places where the front-to-back relationship is reversed. Similarly, there may be some places where the front-to-back relationship is reversed at the ends of the display panel 2 and the ends of the semi-transparent mirror 6.

[0092] Furthermore, if the first left end 38z is an edge, then the statement that the first left end 38z is located in front of or behind the first right end 38w of the viewing window 38P means that a virtual line extended horizontally from any point on the edge is located in front of or behind the point on the first right end 38w that is closest to that point on the edge. In this case, the virtual line may be located in front of or behind all points on the first right end 38w, but there may be some places where the front-to-back relationship is reversed. Similarly, in the front-to-back relationship of the ends of the display panel 2 and the semi-transparent mirror 6, which will be described below, there may also be some places where the front-to-back relationship is reversed.

[0093] Figure 10 shows a state in which the first lower end 38x of the viewing window 38P is located behind the first upper end 38y of the viewing window 38P, or a state in which the first left end 38z of the viewing window 38P is located behind the first right end 38w. However, the relative positions of these ends in the front-to-back direction may be reversed. That is, in the display device 1, the positions of at least one of the pairs of the first lower end 38x and the first upper end 38y and the first left end 38z and the first right end 38w of the viewing window 38P do not have to coincide in the front-to-back direction.

[0094] In the housing 36, the surface on which the opening 37 is located is referred to as the front surface 36a. The surface opposite to the front surface 36a is referred to as the rear surface 36b. In the display device 1, the housing 36 may be inclined vertically or horizontally so that the end of the viewing window 38P has the above-described positional relationship. In the housing 36, the front surface 36a may be larger than the rear surface 36b, as long as the dimensions of the housing 36 in the vertical or horizontal direction are not changed compared to the case where the housing 36 is a rectangular parallelepiped. For this reason, in Figure 10, the housing 36 may be represented as a trapezoid in which the line representing the front surface 36a is longer than the line representing the rear surface 36b. By having the end of the viewing window 38P have the above-described positional relationship, the front surface 36a of the housing 36 can be widened. Furthermore, the opening 37 can be enlarged, and the viewing area in the display device 1 can be expanded.

[0095] Figure 24 illustrates variations in the shape of the housing 36 in the display device 1. In Figure 24, reference numerals 2401 and 2402 indicate different variations in the shape of the housing 36. The housing 36 may have a shape in which surfaces other than the front surface 36a are parallel in the vertical or horizontal direction, as shown by reference numerals 2401 and 2402.

[0096] Furthermore, in the display device 1, the second lower end 2x of the display panel 2 may be located in front of or behind the second upper end 2y of the display panel 2. Alternatively, the second left end 2z of the display panel 2 may be located in front of or behind the second right end 2w of the display panel 2.

[0097] Figure 10 shows a state in which the second lower end 2x of the display panel 2 is located behind the second upper end 2y of the display panel 2, or a state in which the second left end 2z of the display panel 2 is located behind the second right end 2w of the display panel 2. However, the relative positions of these ends in the front-to-back direction may be reversed. That is, in the display device 1, the positions of at least one of the pairs of the second lower end 2x and the second upper end 2y, and the pairs of the second left end 2z and the second right end 2w, do not have to coincide in the front-to-back direction.

[0098] In the display device 1, as shown in Figure 10, the distance D1 between the first lower end 38x of the viewing window 38P and the second lower end 2x of the display panel 2, and the distance D2 between the first upper end 38y of the viewing window 38P and the second upper end 2y of the display panel 2, may be equal to each other. Here, "equal to each other" means that they can be considered equal from an optical standpoint, and they may have tolerances that are negligible from an optical standpoint. In the following description, the notation "equal" may also have tolerances that are negligible from an optical standpoint.

[0099] Furthermore, if the first lower end 38x is a side, then distance D1 may be the distance between any point on that side and the point on the second lower end 2x that is closest to any point on that side. Distance D2 may be the distance between the point on the first upper end 38y that is closest to any point on that side and the point on the second upper end 2y that is closest to the point on the first upper end 38y. In the following explanation, the descriptions of distance may also be (i) the distance between any point on the side that is the lower end of one component and the point on the side that is the lower end of the other component that is closest to the aforementioned point, or (ii) the distance between any point on the side that is the upper end of one component and the point on the side that is the upper end of the other component that is closest to the aforementioned point.

[0100] Alternatively, the distance D3 between the first left end 38z of the viewing window 38P and the second left end 2z of the display panel 2, and the distance D4 between the first right end 38w of the viewing window 38P and the second right end 2w of the display panel 2, may be equal to each other. Here, if the first left end 38z is an edge, the distance D3 may be the distance between any point on that edge and the point on the second left end 2z that is closest to any point on that edge. The distance D4 may be the distance between the point on the first right end 38w that is closest to any point on that edge and the point on the second right end 2w that is closest to the point on the first right end 38w. In the following explanation, the description of distance may also refer to (i) the distance between any point on the leftmost edge of one component and the point on the leftmost edge of the other component that is closest to the aforementioned point, or (ii) the distance between any point on the rightmost edge of one component and the point on the rightmost edge of the other component that is closest to the aforementioned point.

[0101] Furthermore, in the display device 1, the third lower end 6x of the semi-transparent mirror 6 may be located in front of or behind the third upper end 6y of the semi-transparent mirror 6. Alternatively, the third left end 6z of the semi-transparent mirror 6 may be located in front of or behind the third right end 6w of the semi-transparent mirror 6. Figure 10 shows a state in which the third lower end 6x of the semi-transparent mirror 6 is located behind the third upper end 6y of the semi-transparent mirror 6, or a state in which the third left end 6z of the semi-transparent mirror 6 is located behind the third right end 6w of the semi-transparent mirror 6. However, the positional relationship of these ends in the front-to-back direction may be reversed. That is, in the display device 1, the positions in the front-to-back direction do not have to coincide for at least one of the pairs of the third lower end 6x and the third upper end 6y of the semi-transparent mirror 6 and the pair of the third left end 6z and the third right end 6w of the semi-transparent mirror 6.

[0102] In the display device 1, as shown in Figure 10, the distance D5 between the first lower end 38x of the viewing window 38P and the third lower end 6x of the semi-transparent mirror 6, and the distance D6 between the first upper end 38y of the viewing window 38P and the third upper end 6y of the semi-transparent mirror 6, may be equal to each other. Alternatively, the distance D7 between the first left end 38z of the viewing window 38P and the third left end 6z of the semi-transparent mirror 6, and the distance D8 between the first right end 38w of the viewing window 38P and the third right end 6w of the semi-transparent mirror 6, may be equal to each other.

[0103] Furthermore, as shown in Figure 10, in the display device 1, the distance between the third lower end 6x of the semi-transparent mirror 6 and the second lower end 2x of the display panel 2, and the distance between the third upper end 6y of the semi-transparent mirror 6 and the second upper end 2y of the display panel 2 may be equal to each other. Alternatively, the distance between the third left end 6z of the semi-transparent mirror 6 and the second left end 2z of the display panel 2, and the distance between the third right end 6w of the semi-transparent mirror 6 and the second right end 2w of the display panel 2 may be equal to each other.

[0104] In the display device 1, the virtual image V may be formed at a position different from the display panel 2. Specifically, as shown in Figure 10, the virtual image V may be formed behind the display panel 2.

[0105] Figures 11 to 17 illustrate variations in the arrangement of each component in the display device 1. Examples of arrangements of each component in the display device 1 that differ from those in Figure 10 are described below. For simplicity, the shape of the housing 36 is shown as a rectangle in Figures 11 to 17. In all of the examples in Figures 11 to 17, the viewing area of ​​the display device 1 can be enlarged, just as in the example shown in Figure 10.

[0106] As shown in Figure 11, the distance D9 between the first lower end 38x of the viewing window 38P and the second lower end 2x of the display panel 2 may be shorter than the distance D10 between the first upper end 38y of the viewing window 38P and the second upper end 2y of the display panel 2. Alternatively, the distance D11 between the first left end 38z of the viewing window 38P and the second left end 2z of the display panel 2 may be shorter than the distance D12 between the first right end 38w of the viewing window 38P and the second right end 2w of the display panel 2.

[0107] As shown in Figure 12, the distance D13 between the first lower end 38x of the viewing window 38P and the second lower end 2x of the display panel 2 may be longer than the distance D14 between the first upper end 38y of the viewing window 38P and the second upper end 2y of the display panel 2. Alternatively, the distance D15 between the first left end 38z of the viewing window 38P and the second left end 2z of the display panel 2 may be longer than the distance D16 between the first right end 38w of the viewing window 38P and the second right end 2w of the display panel 2.

[0108] As shown in Figure 13, the second lower end 2x of the display panel 2 may be located below the first lower end 38x of the viewing window 38P. Alternatively, as shown in Figure 14, the second lower end 2x of the display panel 2 may be located above the first lower end 38x of the viewing window 38P.

[0109] As shown in Figure 15, the distance D17 between the first lower end 38x of the viewing window 38P and the third lower end 6x of the semi-transparent mirror 6 may be shorter than the distance D18 between the first upper end 38y of the viewing window 38P and the third upper end 6y of the semi-transparent mirror 6. Alternatively, the distance D19 between the first left end 38z of the viewing window 38P and the third left end 6z of the semi-transparent mirror 6 may be shorter than the distance D20 between the first right end 38w of the viewing window 38P and the third right end 6w of the semi-transparent mirror 6.

[0110] Furthermore, as shown in Figure 16, the distance D21 between the first lower end 38x of the viewing window 38P and the third lower end 6x of the semi-transparent mirror 6 may be longer than the distance D22 between the first upper end 38y of the viewing window 38P and the third upper end 6y of the semi-transparent mirror 6. Alternatively, the distance D23 between the first left end 38z of the viewing window 38P and the third left end 6z of the semi-transparent mirror 6 may be longer than the distance D24 between the first right end 38w of the viewing window 38P and the third right end 6w of the semi-transparent mirror 6.

[0111] As shown in Figure 15, the distance D25 between the third lower end 6x of the semi-transparent mirror 6 and the second lower end 2x of the display panel 2 may be longer than the distance D26 between the third upper end 6y of the semi-transparent mirror 6 and the second upper end 2y of the display panel 2. Alternatively, the distance D27 between the third left end 6z of the semi-transparent mirror 6 and the second left end 2z of the display panel 2 may be longer than the distance D28 between the third right end 6w of the semi-transparent mirror 6 and the second right end 2w of the display panel 2.

[0112] As shown in Figure 11, the distance D29 between the third lower end 6x of the semi-transparent mirror 6 and the second lower end 2x of the display panel 2 may be shorter than the distance D31 between the third upper end 6y of the semi-transparent mirror 6 and the second upper end 2y of the display panel 2. Alternatively, the distance D30 between the third left end 6z of the semi-transparent mirror 6 and the second left end 2z of the display panel 2 may be shorter than the distance D32 between the third right end 6w of the semi-transparent mirror 6 and the second right end 2w of the display panel 2.

[0113] As shown in Figure 17, the third lower end 6x of the semi-transparent mirror 6 may be located below the first lower end 38x of the viewing window 38P. Alternatively, as shown in Figure 13, the third lower end 6x of the semi-transparent mirror 6 may be located above the first lower end 38x of the viewing window 38P.

[0114] Furthermore, as shown in Figure 17, the third lower end 6x of the semi-transparent mirror 6 may be located below the second lower end 2x of the display panel 2. Alternatively, as shown in Figure 13, the third lower end 6x of the semi-transparent mirror 6 may be located above the second lower end 2x of the display panel 2.

[0115] In Figures 10 to 17, the first normal vector 38L is the normal vector of the viewing window 38P. The second normal vector 2L is the normal vector of the display panel 2. The third normal vector 6L is the normal vector of the semi-transparent mirror 6. Here, the first normal vector 38L may be along the direction obtained by averaging the forward normal directions on the surface of the viewing window 38P. The average of the normal directions may be calculated by determining the direction of the vector obtained by adding up multiple unit vectors along the multiple normal directions to be averaged. For example, if the viewing window 38P is a plane, the first normal vector 38L may be the normal vector to the center of the viewing window 38P. Here, the center may be the centroid. For example, if the viewing window 38P is a paraboloid, the first normal vector 38L may be a line along the axis of symmetry. The second normal 2L of the display panel 2 and the third normal 6L of the semi-transparent mirror 6 may be the centroid if the display panel 2 or the semi-transparent mirror 6 is a plane, or a line along the axis of symmetry if it is a parabolic surface. Also, for example, if the semi-transparent mirror 6 is a concave mirror, the normal of the semi-transparent mirror 6 may be along the optical axis.

[0116] The direction of the second normal 2L of the display panel 2 may be the same as the direction of the first normal 38L of the viewing window 38P. The direction of the second normal 2L of the display panel 2 may be different from the direction of the first normal 38L of the viewing window 38P. The direction of the third normal 6L of the semi-transparent mirror 6 may be different from the direction of the first normal 38L of the viewing window 38P. In this case, the possibility of the image outside the housing 36 reflected by the semi-transparent mirror 6 being reflected in the viewing window 38P can be reduced.

[0117] The direction of the third normal 6L of the semi-transparent mirror 6 may be the same as the direction of the second normal 2L of the display panel 2. The direction of the third normal 6L of the semi-transparent mirror 6 may be different from the direction of the second normal 2L of the display panel 2.

[0118] Furthermore, the direction of the third normal 6L of the semi-transparent mirror 6 may be the same as the direction of the first normal 38L of the viewing window 38P. In this case, the optical path lengths can be made the same.

[0119] (Digital rearview mirror, CID and digital side mirror) Figure 18 shows an example in which the display device 1 is applied to a digital rearview mirror. The vehicle to which the display device 1 is applied to a digital rearview mirror is referred to as vehicle 23A. When the display device 1 is applied to the digital rearview mirror described above, the display device 1 may be located above the dashboard of vehicle 23A. In this case, the user's line of sight will be directed diagonally upward. Furthermore, as shown in Figure 18, the first lower end 38x of the viewing window 38P may be located behind the first upper end 38y of the viewing window 38P. In this case, the second lower end 2x of the display panel 2 may be located behind the second upper end 2y of the display panel 2. Also in this case, the third lower end 6x of the semi-transparent mirror 6 may be located in front of the third upper end 6y of the semi-transparent mirror 6. Also in this case, the second upper end 2y of the display panel 2 may be located above the first upper end 38y of the viewing window 38P. In vehicle 23A, when the display device 1 is used as a digital rearview mirror, the display device 1 and its components may be arranged as described above.

[0120] In this case, in vehicle 23A, the brightness of the component located below the dashboard may be lower than the brightness of the component located above the bottom edge of the dashboard. Here, brightness may be an index described in the method of indicating color—indication by three attributes (JIS Z 8781-6:2017).

[0121] In vehicle 23A, components located below the dashboard may include, for example, the center console, seat cushion, or floor mat. Components located above the lower edge of the dashboard may include the dashboard, sun visor, or ceiling. In vehicle 23A, for example, the brightness of at least one of the components—the center console, seat cushion, and floor mat—may be lower than the brightness of the dashboard.

[0122] The brightness of components located below the dashboard may be, for example, 3 or less.

[0123] Furthermore, the brightness of components located below the dashboard may be lower than the brightness of the display image shown on the display panel 2. In other words, the brightness of the display image shown on the display panel 2 may be adjusted to be higher than the brightness of components located below the dashboard. The brightness of the display image shown on the display panel 2 may be determined by the average brightness of the entire display screen.

[0124] Figure 19 shows an example of the display device 1 being applied to a CID 30. The vehicle to which the display device 1 is applied to a digital rearview mirror is referred to as vehicle 23B. When the display device 1 is applied to the CID 30 described above, the display device 1 may be located below the upper edge of the dashboard of vehicle 23B. In this case, the user's line of sight will be directed diagonally downward. Furthermore, as shown in Figure 19, the first lower end 38x of the viewing window 38P may be located in front of the first upper end 38y of the viewing window 38P. In this case, the second lower end 2x of the display panel 2 may be located in front of the second upper end 2y of the display panel 2. Also in this case, the third lower end 6x of the semi-transparent mirror 6 may be located behind the third upper end 6y of the semi-transparent mirror 6. Also in this case, the second lower end 2x of the display panel 2 may be located below the first lower end 38x of the viewing window 38P. When the display device 1 is used as a CID 30 in vehicle 23B, the display device 1 and its components may be arranged as described above.

[0125] In this case, in vehicle 23B, the brightness of components located above the dashboard may be lower than the brightness of components located below the top edge of the dashboard. Examples of components located below the top edge of the dashboard in vehicle 23B include the center console, seat cushion, or floor mat. Examples of components located above the dashboard include the sun visor or ceiling. In vehicle 23B, for example, the brightness of at least one of the components, the sun visor and the ceiling, may be lower than the brightness of the dashboard.

[0126] The brightness of components located above the dashboard may be, for example, 3 or less.

[0127] Furthermore, the brightness of components located above the dashboard may be lower than the brightness of the display image shown on the display panel 2. In other words, the brightness of the display image shown on the display panel 2 may be adjusted to be higher than the brightness of components located above the dashboard. The brightness of the display image shown on the display panel 2 may be determined by the average brightness of the entire display screen.

[0128] Figure 20 shows an example in which the display device 1 is applied to a digital side mirror. When the display device 1 is applied to the digital side mirror described above, the display device 1 may be located to the left or right of the steering wheel of the vehicle 23. In Figure 20, the display device 1 is located to the right of the steering wheel. Therefore, the user's line of sight is diagonally to the right. Of the first left end 38z and the first right end 38w of the viewing window 38P, the one located closer to the steering wheel is called the first window end, and the one located further away from the steering wheel is called the second window end. In this case, the first window end may be located behind the second window end. In the example shown in Figure 20, since the display device 1 is located to the right of the steering wheel, the first left end 38z is the first window end, and the first right end 38w is the second window end. When the display device 1 is located to the left of the steering wheel, the first right end 38w is the first window end, and the first left end 38z is the second window end. Furthermore, of the second left end 2z and second right end 2w of the display panel 2, the one located closer to the steering wheel is referred to as the first panel end, and the one located further away from the steering wheel is referred to as the second panel end. In this case, the first panel end may be located behind the second panel end. In the example shown in Figure 20, since the display device 1 is located to the right of the steering wheel, the second left end 2z is the first panel end and the second right end 2w is the second panel end. If the display device 1 is located to the left of the steering wheel, the second right end 2w is the first panel end and the second left end 2z is the second panel end. When the display device 1 is used as a digital side mirror in the vehicle 23, the display device 1 and its components may be arranged as described above.

[0129] Figures 21 to 23 show examples of optical paths when the display device 1 is applied to a vehicle. Figure 21 shows an example of an optical path when the display device 1 is applied to a digital rearview mirror. Figure 22 shows an example of an optical path when the display device 1 is applied to a CID 30. Figure 23 shows an example of an optical path when the display device 1 is applied to a digital side mirror. Figures 21 and 22 show the optical path viewed from a direction parallel to the horizontal plane. Figure 23 shows the optical path viewed from a direction perpendicular to the horizontal plane. In Figures 21 to 23, for simplicity, only the display panel 2, the semi-transparent mirror 6, and the viewing window 38P of the display device 1 are shown.

[0130] The display device 1 may be configured to magnify the display image on the display panel 2 using a semi-transparent mirror 6 and project it as a virtual image V. In other words, the virtual image V may be larger than the display image on the display panel 2. It may also be larger than at least one of the components of the display device 1. For example, as shown in Figures 21 to 23, the virtual image V may be larger than the display panel 2. The virtual image V may be larger than the semi-transparent mirror 6. The virtual image V may be larger than the viewing window 38P. Furthermore, the virtual image V may be larger than the housing 36 of the display device 1.

[0131] Here, the fourth lower end Vx, which is the lower end of the virtual image V, may be located below the lower end of at least one of the components of the display device 1. The fourth upper end Vy, which is the upper end of the virtual image V, may be located above the upper end of at least one of the components of the display device 1. The fourth left end Vz, which is the left end of the virtual image V, may be located to the left of at least one of the components of the display device 1. The fourth right end Vw, which is the right end of the virtual image V, may be located to the right of at least one of the components of the display device 1.

[0132] Furthermore, the fourth lower end Vx, which is the lower end of the virtual image V, may be located below the lower end of the housing 36. The fourth upper end Vy, which is the upper end of the virtual image V, may be located above the upper end of the housing 36. The fourth left end Vz, which is the left end of the virtual image V, may be located to the left of the left end of the housing 36. The fourth right end Vw, which is the right end of the virtual image V, may be located to the right of the housing 36.

[0133] For example, as shown in Figure 21, the fourth upper end Vy of the virtual image V may be located above the first upper end 38y of the viewing window 38P. Also, the fourth upper end Vy of the virtual image V may be located above the second upper end 2y of the display panel 2. Furthermore, the fourth upper end Vy of the virtual image V may be located above the third upper end 6y of the semi-transparent mirror 6.

[0134] For example, as shown in Figure 22, the fourth lower end Vx of the virtual image V may be located below the first lower end 38x of the viewing window 38P. Also, the fourth lower end Vx of the virtual image V may be located below the second lower end 2x of the display panel 2. Furthermore, the fourth lower end Vx of the virtual image V may be located below the third lower end 6x of the semi-transparent mirror 6.

[0135] Furthermore, as shown in Figure 23, for example, the fourth right end Vw of the virtual image V may be located to the right of the first right end 38w of the viewing window 38P. Also, the fourth right end Vw of the virtual image V may be located to the right of the second right end 2w of the display panel 2. Furthermore, the fourth right end Vw of the virtual image V may be located to the right of the third right end 6w of the semi-transparent mirror 6.

[0136] In the display device 1, the fourth lower end Vx, which is the lower end of the virtual image V, may be located in front of or behind the fourth upper end Vy, which is the upper end of the virtual image V. Alternatively, the fourth left end Vz, which is the left end of the virtual image V, may be located in front of or behind the fourth right end Vw, which is the right end of the virtual image V. For example, in Figure 21, the fourth lower end Vx of the virtual image V is located in front of the fourth upper end Vy of the virtual image V. Also, for example, in Figure 22, the fourth lower end Vx of the virtual image V is located behind the fourth upper end Vy of the virtual image V. Also, for example, in Figure 23, the fourth left end Vz of the virtual image V is located in front of the fourth right end Vw of the virtual image V.

[0137] Furthermore, as shown in Figures 21 to 23, the distance between the lower end of at least one component of the display device 1 and the fourth lower end Vx of the virtual image V may be different from the distance between the upper end of the component and the fourth upper end Vy of the virtual image V. Also, as shown in Figures 21 to 23, the distance between the left end of at least one component of the display device 1 and the fourth left end Vz of the virtual image V may be different from the distance between the right end of the component and the fourth right end Vw of the virtual image V. Specifically, in the display device 1, the distance between the first lower end 38x of the viewing window 38P and the fourth lower end Vx of the virtual image V may be different from the distance between the first upper end 38y of the viewing window 38P and the fourth upper end Vy of the virtual image V. Furthermore, the distance between the first left end 38z of the viewing window 38P and the fourth left end Vz of the virtual image V, and the distance between the first right end 38w of the viewing window 38P and the fourth right end Vw of the virtual image V, may be different from each other. The viewing section (e.g., the viewing window 38P) may be inclined with respect to the virtual image V. In other words, the virtual image V may be inclined with respect to the viewing section (e.g., the viewing window 38P). More specifically, for example, the viewing section (e.g., the viewing window 38P) may have a viewing surface located on the opposite side from the display panel 2, and the viewing surface of the viewing section may be inclined with respect to the direction normal to the virtual image surface of the virtual image V. In other words, the virtual image surface of the virtual image V may be inclined with respect to the direction normal to the direction normal to the viewing surface of the viewing section. Furthermore, in the display device 1, the distance between the second lower end 2x of the display panel 2 and the fourth lower end Vx of the virtual image V, and the distance between the second upper end 2y of the display panel 2 and the fourth upper end Vy of the virtual image V, may be different from each other. Also, the distance between the third lower end 6x of the semi-transparent mirror 6 and the fourth lower end Vx of the virtual image V, and the distance between the third upper end 6y of the semi-transparent mirror 6 and the fourth upper end Vy of the virtual image V, may be different from each other.

[0138] For example, in Figure 21, the distance between the first lower end 38x of the viewing window 38P and the fourth lower end Vx of the virtual image V is shorter than the distance between the first upper end 38y of the viewing window 38P and the fourth upper end Vy of the virtual image V. Also in Figure 21, the distance between the second lower end 2x of the display panel 2 and the fourth lower end Vx of the virtual image V is shorter than the distance between the second upper end 2y of the display panel 2 and the fourth upper end Vy of the virtual image V. Also, for example, in Figure 22, the distance between the first lower end 38x of the viewing window 38P and the fourth lower end Vx of the virtual image V is longer than the distance between the first upper end 38y of the viewing window 38P and the fourth upper end Vy of the virtual image V. Also in Figure 22, the distance between the second lower end 2x of the display panel 2 and the fourth lower end Vx of the virtual image V is longer than the distance between the second upper end 2y of the display panel 2 and the fourth upper end Vy of the virtual image V. Furthermore, for example, in Figure 23, the distance between the first left end 38z of the viewing window 38P and the fourth left end Vz of the virtual image V is shorter than the distance between the first right end 38w of the viewing window 38P and the fourth right end Vw of the virtual image V. Also, in Figure 23, the distance between the second left end 2z of the display panel 2 and the fourth left end Vz of the virtual image V is shorter than the distance between the second right end 2w of the display panel 2 and the fourth right end Vw of the virtual image V.

[0139] Furthermore, the direction of the normal to at least one of the components of the display device 1 may be different from the direction of the normal to the virtual image V. Specifically, in the display device 1, the direction of the normal to the viewing window 38P and the direction of the normal to the virtual image V may be different from each other. Also, in the display device 1, the direction of the normal to the display panel 2 and the direction of the normal to the virtual image V may be different. Furthermore, the direction of the normal to the semi-transparent mirror 6 and the direction of the normal to the virtual image V may be different from each other.

[0140] Reference numeral 2101 in Figure 21, 2201 in Figure 22, and 2301 in Figure 23 indicate the optical paths for the reflected image 22R of the user 22 through the viewing window 38P. In each figure, range R may be the range in which the reflected image 22R is visible. By arranging the display device 1 as described above, the user 22's viewpoint will be outside range R, as shown by reference numerals 2101, 2201, and 2301. Therefore, the reflected image 22R will be less visible to the user 22 in the display device 1.

[0141] Furthermore, reference numeral 2102 in Figure 21, reference numeral 2202 in Figure 22, and reference numeral 2302 in Figure 23 indicate the optical paths for the inverted image 22I of the user 22 formed by the semi-transparent mirror 6. If light from the user 22 were to enter the semi-transparent mirror 6 and the reflected light were to be emitted, as shown in each figure, the user 22 could potentially see the inverted image 22I formed by the semi-transparent mirror 6. However, in the display device 1, the light from the user 22 is blocked by the reflective polarizer 8 in either the path toward the semi-transparent mirror 6 or the path toward the user 22 after being reflected by the semi-transparent mirror 6. Therefore, in the display device 1, the inverted image 22I is less likely to be seen by the user 22.

[0142] As described above, when the display device 1 is applied to a digital rearview mirror, CID 30, or digital side mirror, arranging the display device 1 and its components as described above makes it difficult for the user 22 to see the reflected image 22R and the inverted image 22I. Therefore, the visibility of the virtual image V is improved.

[0143] [Summary] This disclosure can also be expressed as follows:

[0144] A display device according to Embodiment 1 of the present disclosure comprises: a display panel for displaying a display image; a housing in which the display panel is located on the inside; a viewing section located in front of the display panel in the housing when the direction in which the display panel displays the display image is the forward direction, and which makes the inside of the housing visible from the outside of the housing; and an optical system capable of forming an image based on the display image so that it can be viewed through the viewing section. When the vertically upward direction in the operating state of the display device is defined as the upward direction, the direction opposite to the upward direction is defined as the downward direction, and the direction perpendicular to the upward direction, the downward direction, and the forward direction is defined as the left-right direction, the first lower end of the viewing section is located in front of or behind the first upper end of the viewing section, or the first left end of the viewing section is located in front of or behind the first right end of the viewing section.

[0145] In the display device according to aspect 2 of the present disclosure, in aspect 1, (i) the second lower end of the display panel is located in front of or behind the second upper end of the display panel, or (ii) the second left end of the display panel is located in front of or behind the second right end of the display panel.

[0146] In the display device according to aspect 3 of the present disclosure, in aspect 1 or 2, (i) the distance between the first lower end of the viewing section and the second lower end of the display panel and the distance between the first upper end of the viewing section and the second upper end of the display panel are equal to each other, or (ii) the distance between the first left end of the viewing section and the second left end of the display panel and the distance between the first right end of the viewing section and the second right end of the display panel are equal to each other.

[0147] In the display device according to aspect 4 of the present disclosure, in aspect 1 or 2, (i) the distance between the first lower end of the viewing section and the second lower end of the display panel is shorter than the distance between the first upper end of the viewing section and the second upper end of the display panel, or (ii) the distance between the first left end of the viewing section and the second left end of the display panel is shorter than the distance between the first right end of the viewing section and the second right end of the display panel.

[0148] In the display device according to aspect 5 of the present disclosure, in aspect 1 or 2, (i) the distance between the first lower end of the viewing section and the second lower end of the display panel is longer than the distance between the first upper end of the viewing section and the second upper end of the display panel, or (ii) the distance between the first left end of the viewing section and the second left end of the display panel is longer than the distance between the first right end of the viewing section and the second right end of the display panel.

[0149] In any of embodiments 1 to 5, the display device according to embodiment 6 of the present disclosure is configured such that the second lower end of the display panel is located above or below the first lower end of the viewing section.

[0150] In the display device according to embodiment 7 of the present disclosure, in any of embodiments 1 to 6, the direction of the second normal of the display panel is different from the direction of the first normal of the viewing section.

[0151] A display device according to aspect 8 of the present disclosure, in any of aspects 1 to 7, wherein the optical system has a semi-transparent mirror, and (i) the third lower end of the semi-transparent mirror is located in front of or behind the third upper end of the semi-transparent mirror, or (ii) the third left end of the semi-transparent mirror is located in front of or behind the third right end of the semi-transparent mirror.

[0152] In the display device according to aspect 9 of the present disclosure, in aspect 8, (i) the distance between the first lower end of the viewing section and the third lower end of the semi-transparent mirror and the distance between the first upper end of the viewing section and the third upper end of the semi-transparent mirror are equal to each other, or (ii) the distance between the first left end of the viewing section and the third left end of the semi-transparent mirror and the distance between the first right end of the viewing section and the third right end of the semi-transparent mirror are equal to each other.

[0153] In the display device according to aspect 10 of the present disclosure, in aspect 8, (i) the distance between the first lower end of the viewing section and the third lower end of the semi-transparent mirror is shorter than the distance between the first upper end of the viewing section and the third upper end of the semi-transparent mirror, or (ii) the distance between the first left end of the viewing section and the third left end of the semi-transparent mirror is shorter than the distance between the first right end of the viewing section and the third right end of the semi-transparent mirror.

[0154] In the display device according to aspect 11 of the present disclosure, in aspect 8, (i) the distance between the first lower end of the viewing unit and the third lower end of the semi-transparent mirror is longer than the distance between the first lower end of the viewing unit and the third upper end of the semi-transparent mirror, or (ii) the distance between the first left end of the viewing unit and the third left end of the semi-transparent mirror is longer than the distance between the first right end of the viewing unit and the third right end of the semi-transparent mirror.

[0155] In the display device according to embodiment 12 of the present disclosure, in any of embodiments 8 to 11, the third lower end of the semi-transparent mirror is located above or below the first lower end of the viewing section.

[0156] In the display device according to embodiment 13 of this disclosure, in any of embodiments 8 to 12, the direction of the third normal of the semitransparent mirror is the same as the direction of the first normal of the viewing section.

[0157] In the display device according to embodiment 14 of this disclosure, in any of embodiments 8 to 12, the direction of the third normal of the semitransparent mirror is different from the direction of the first normal of the viewing section.

[0158] In any of embodiments 8 to 14, the display device according to embodiment 15 of the present disclosure is characterized in that (i) the distance between the third lower end of the semitransparent mirror and the second lower end of the display panel is equal to the distance between the third upper end of the semitransparent mirror and the second upper end of the display panel, or (ii) the distance between the third left end of the semitransparent mirror and the second left end of the display panel is equal to the distance between the third right end of the semitransparent mirror and the second right end of the display panel.

[0159] In any of embodiments 8 to 14, the display device according to embodiment 16 of the present disclosure is such that (i) the distance between the third lower end of the semitransparent mirror and the second lower end of the display panel is shorter than the distance between the third upper end of the semitransparent mirror and the second upper end of the display panel, or (ii) the distance between the third left end of the semitransparent mirror and the second left end of the display panel is shorter than the distance between the third right end of the semitransparent mirror and the second right end of the display panel.

[0160] In any of embodiments 8 to 14, the display device according to embodiment 17 of the present disclosure is such that (i) the distance between the third lower end of the semitransparent mirror and the second lower end of the display panel is longer than the distance between the third upper end of the semitransparent mirror and the second upper end of the display panel, or (ii) the distance between the third left end of the semitransparent mirror and the second left end of the display panel is longer than the distance between the third right end of the semitransparent mirror and the second right end of the display panel.

[0161] In the display device according to aspect 18 of the present disclosure, in any of aspects 8 to 17, the third lower end of the semitransparent mirror is located above or below the second lower end of the display panel.

[0162] In the display device according to aspect 19 of this disclosure, in any of aspects 8 to 18, the direction of the third normal of the semitransparent mirror is the same as the direction of the second normal of the display panel.

[0163] In the display device according to aspect 20 of the present disclosure, in any of aspects 8 to 18, the direction of the third normal of the semitransparent mirror is different from the direction of the second normal of the display panel.

[0164] In the display device according to embodiment 21 of the present disclosure, in any of embodiments 1 to 20, the optical system forms the image at a position different from the display panel.

[0165] In the display device according to aspect 22 of this disclosure, in aspect 21, the optical system forms the image behind the display panel.

[0166] The display device according to embodiment 23 of the present disclosure is located above the dashboard of the mobile body in any of embodiments 1 to 22, and the first lower end of the viewing section is located behind the first upper end of the viewing section.

[0167] In the display device according to aspect 24 of the present disclosure, in aspect 23, the second lower end of the display panel is located rearward relative to the second upper end of the display panel.

[0168] In the display device according to aspect 25 of the present disclosure, in aspect 23 or 24, the optical system has a semi-transparent mirror, and the third lower end of the semi-transparent mirror is located in front of the third upper end of the semi-transparent mirror.

[0169] In the display device according to embodiment 26 of the present disclosure, in embodiment 25, the second upper end of the display panel is located above the first upper end of the viewing section.

[0170] A mobile body according to embodiment 27 of the present disclosure comprises a dashboard and a display device according to any of embodiments 1 to 22 located above the dashboard, wherein the second lower end of the display panel is located rearward relative to the second upper end of the display panel.

[0171] In any of embodiments 1 to 22, the display device according to embodiment 28 of the present disclosure is located below the upper end of the dashboard of the mobile body, and the first lower end of the viewing section is located in front of the first upper end of the viewing section.

[0172] In the display device according to aspect 29 of the present disclosure, in aspect 28, the second lower end of the display panel is located in front of the second upper end of the display panel.

[0173] In the display device according to embodiment 30 of the present disclosure, in embodiment 28 or 29, the optical system has a semi-transparent mirror, and the third lower end of the semi-transparent mirror is located behind the third upper end of the semi-transparent mirror.

[0174] In the display device according to embodiment 31 of the present disclosure, in embodiment 30, the second lower end of the display panel is located below the first lower end of the viewing portion.

[0175] A mobile body according to embodiment 32 of the present disclosure comprises a dashboard and a display device according to any of embodiments 1 to 22 located below the upper end of the dashboard, wherein the second lower end of the display panel is located in front of the second upper end of the display panel.

[0176] In the display device according to embodiment 33 of the present disclosure, in any embodiment 1 to 22, the display device is located to the left or right of the steering wheel of the moving body, and of the first left end and the first right end of the viewing section, the one located closer to the steering wheel is referred to as the first window end, and the one located further away from the steering wheel is referred to as the second window end, in which case the first window end is located behind the second window end.

[0177] In the display device according to embodiment 34 of the present disclosure, in embodiment 33, if the second left end and second right end of the display panel, the one located closer to the steering wheel, are referred to as the first panel end, and the one located further away from the steering wheel, are referred to as the second panel end, then the first panel end is located behind the second panel end.

[0178] A mobile body according to embodiment 35 of the present disclosure comprises a steering wheel and a display device according to any of embodiments 1 to 22 located to the left or to the right of the steering wheel, wherein, of the first left end and the first right end of the viewing section, the one located closer to the steering wheel is referred to as the first window end, and the one located further away from the steering wheel is referred to as the second window end, the first window end is located behind the second window end.

[0179] This disclosure is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of this disclosure. [Embodiment 2]

[0180] Conventional display systems may reflect high-intensity ambient light (for example, light emitted from the headlights of a following vehicle) towards the driver's eyes, potentially causing glare and making it difficult for the driver to clearly see the image displayed on the display device.

[0181] The display device of this disclosure comprises a housing having a wall member capable of housing a display panel that emits display light, and a light-transmitting plate through which the display light passes, and a dimming member disposed outside the light-transmitting plate and having a light transmittance smaller than that of the light-transmitting plate.

[0182] The mobile device of this disclosure includes the above-described display device.

[0183] The display system disclosed herein is a display system mounted on a mobile body and comprises a housing having a wall member capable of housing a display panel that emits display light, and a light-transmitting plate through which the display light passes; a dimming member disposed outside the light-transmitting plate and having a light transmittance smaller than that of the light-transmitting plate, a detection unit for detecting the brightness of ambient light incident on the dimming member, and a control unit, wherein the control unit controls the transmittance of the dimming member based on the brightness detected by the detection unit.

[0184] According to this disclosure, it is possible to reduce the glare that users experience from reflected ambient light and to allow users to clearly perceive the image as a virtual or real image.

[0185] Embodiments of this disclosure will be described below with reference to the drawings. The figures used in the following description are schematic, and the dimensional ratios and other details shown in the drawings do not necessarily correspond to those of reality. In this specification, for convenience, a Cartesian coordinate system XYZ is defined in some of the drawings. The X-axis direction is also referred to as the first direction. The Y-axis direction is also referred to as the second direction. The Z-axis direction is also referred to as the third direction.

[0186] Figure 25 is a diagram showing an example of a vehicle equipped with a display system. Figure 26A is a schematic diagram showing an example of the configuration of a display device, and Figure 26B is a schematic diagram showing the configuration of a display system. Figure 27 is a schematic diagram showing an example of the configuration of a display device. Figure 28 is a schematic diagram showing the configuration of a dimming member. Figure 29 is a diagram illustrating the reflection of ambient light in a display device. Figures 30A and 30B are schematic diagrams showing examples of virtual images seen by a user. Figures 31 to 33 are flowcharts showing the control of the display device by the control unit. Figures 34 to 37 are schematic diagrams showing other examples of the configuration of a display device. Figure 38 is a diagram illustrating the projection of a virtual image in the display device of Figure 36. Figures 39 and 40 are diagrams illustrating the projection of a virtual image in the display device of Figure 37. Figures 41 to 43 are schematic diagrams showing other examples of the configuration of a display device. Figures 44A, 44B, 44C, 44D, 45A, 45B, 45C, and 45D illustrate the function of an optical system having a third phase difference plate and a fourth phase difference plate. Figure 46 is a graph illustrating the function of an optical system having a third phase difference plate and a fourth phase difference plate. Figures 47 and 48 schematically show other examples of the configuration of a display device. Figure 49 is a diagram showing an example of a vehicle equipped with a display system. Figures 50 to 52 schematically show other examples of the configuration of a display device. Figure 53 is a schematic perspective view showing a cross-section of another example of a display device, and Figure 54 is a schematic cross-sectional view showing a cross-section of another example of a display device. Figure 55 is a diagram showing the optical path of the display light in the display device of Figure 27. Note that in Figures 27, 29, 34 to 37, 41 to 43, and 47 to 54, the acquisition unit, detection unit, and control unit are omitted from the illustration.

[0187] One embodiment of the display system 1P of this disclosure may be mounted on a vehicle 50P, as shown in Figure 25. The vehicle 50P may be an example of a mobile body. The vehicle 50P includes, but is not limited to, automobiles and industrial vehicles, and may also include railway vehicles, passenger vehicles, fixed-wing aircraft that travel on runways, or ships. Automobiles may include, for example, passenger cars, trucks, buses, motorcycles and trolleybuses, and may also include motorcycles. Industrial vehicles may include, for example, industrial vehicles for agriculture and construction. Industrial vehicles may include, for example, forklifts and golf carts. Industrial vehicles for agriculture may include tractors, cultivators, transplanters, binders, combines and lawnmowers. Industrial vehicles for construction may include, for example, bulldozers, scrapers, excavators, cranes, dump trucks and road rollers. Vehicles may include those that are powered by human effort. In the following description, the vehicle 50P will be assumed to be a passenger car.

[0188] The display system 1P may include a display device 8P, as shown in Figures 25 and 26B. The display system 1P may be configured as an electronic rearview mirror (digital rearview mirror) that displays the scenery around the vehicle 50P, captured by a camera or the like, as a virtual image V for the user 11P, who is the driver of the vehicle 50P. Here, the area around the vehicle 50P may be at least one of the areas in front of, behind, to the side of, above, and below the vehicle 50P.

[0189] The display device 8P in one embodiment of this disclosure may be a non-attachable device to the user 11P. That is, it may not be attached to the user 11P but may be fixed to the environment. The display device 8P may be fixed to, for example, a wall, column, or ceiling. The display device 8P may also be fixed to the interior of a vehicle. The display device 8P may be attached to the user 11P. When attached to the user 11P, the display device 8P may have a mounting portion (not shown) such that the opening 42Pa is fixed at the position of the user 11P's eyes.

[0190] The display device 8P may allow the user 11P to clearly perceive the display light emitted from the display panel 2P as an image, virtual image, or real image. The display device 8P may include a housing 41P and a dimming member 4P, as shown in Figure 26A. The housing 41P may have a wall member 42P and a light-transmitting plate 43P. The wall member 42P may be capable of housing the display panel 2P that emits the display light. The wall member 42P may be, for example, a box with one side open. The wall member 42P may be a light-shielding member that blocks visible light. The light-transmitting plate 43P may be located in the opening (also called a window) 42Pa of the wall member 42P. The display light emitted from the display panel 2P can pass through (be transmitted through) the light-transmitting plate 43P. That is, the light-transmitting plate 43P may transmit light emitted from the optical system 3. The light-transmitting plate 43P may at least partially block the opening. The light-transmitting plate 43P may be made of a material that transmits visible light. The light-transmitting plate 43P may be made of, for example, glass, resin, etc. The light-transmitting plate 43P may have a light transmittance of, for example, 90 to 100% for visible light, or 95 to 100% for visible light.

[0191] The housing 41P may have a viewing area that allows the inside of the housing 41P to be seen from the outside of the housing 41P. The housing 41P may also have a viewing area that allows the inside of the housing 41P to be seen from the outside of the housing 41P. The opening in the wall member 42P may function as a viewing area. The housing 41P may also have a member placed in the opening that allows the inside of the housing 41P to be seen from the outside of the housing 41P. The housing 41P may also have a member placed in the opening that allows the inside of the housing 41P to be seen from the outside of the housing 41P. Such a member (for example, a light-transmitting plate 43P) may function as a viewing area.

[0192] The dimming member 4P may be positioned outside the light-transmitting plate 43P. The dimming member 4P may be located in the window 42Pa of the wall member 42P. The dimming member 4P may have a lower transmittance of visible light than the light-transmitting plate 43P.

[0193] The display device 8P may include a reflective member 44P. The reflective member 44P is housed in the housing 41P and may reflect at least a portion of the display light emitted from the display panel 2P. The reflective member 44P may have polarization selectivity. The reflective member 44P may be, for example, a reflective polarizing member that transmits polarized light having a polarization axis in a predetermined direction (also called a transmitted polarization axis) and reflects polarized light having a polarization axis perpendicular to the transmitted polarization axis. The reflective polarizing member may transmit polarized light having a transmitted polarization axis with a transmittance of 100% or close to 100% (e.g., 95% or more or 98% or more). The reflective member 44P may reflect polarized light having a polarization axis perpendicular to the transmitted polarization axis with a reflectance of 100% or close to 100% (e.g., 95% or more or 98% or more).

[0194] The reflective member 44P may be a component of the optical systems 3P, 3P', 3P'', 3P''' described later. The reflective member 44P may be, for example, a reflective polarizer 15P (see Figure 27), but is not limited thereto. The reflective member 44P may be housed in the wall member 42P and reflect at least a portion of the ambient light toward the eyes of the user 11P.

[0195] The dimming member 4P may be positioned outside the reflective member 44P. In this case, the reduction in brightness of the display light can be reduced while also reducing the glare experienced by the user 11P from ambient light reflected by the reflective member 44P. The light transmitting plate 43P may be positioned outside the reflective member 44P. In this case, the display panel 2P and the reflective member 44P can be protected from external environmental factors such as moisture and dust.

[0196] The light-adjusting member 4P may have a transmittance to visible light that is lower than the transmittance to visible light of the reflective member 44P. If the reflective member 44P has polarization selectivity, the transmittance to visible light of the reflective member 44P may mean the transmittance to polarizations having a transmitted polarization axis.

[0197] The display device 8P may include a display panel 2P. The display panel 2P is housed in a housing 41P and may emit display light.

[0198] The dimming member 4P may have a light transmittance of, for example, 0% or more and less than 95% with respect to visible light, or a light transmittance of 0% or more and less than 90%.

[0199] The transmittance of the dimming member 4P to visible light may be variable. In this case, by adjusting the transmittance of the dimming member 4P to visible light according to the luminance of ambient light incident on the display device 8P (especially the dimming member 4P) and / or the illuminance of the surrounding environment of the display device 8P, it is possible to reduce the decrease in the luminance of the display light incident on the user 11P's eyes while reducing the glare the user 11P experiences from reflected ambient light. As a result, it becomes possible for the user 11P to clearly perceive the display light emitted from the display panel 2P as a virtual or real image. The transmittance of the dimming member 4P to visible light may be variable in a range of, for example, 0 to 95%.

[0200] As will be described in more detail later, the dimming member 4P may be composed of a liquid crystal composition. When the dimming member 4P is composed of a liquid crystal composition, the transmittance of the dimming member 4P to visible light can be changed by controlling the voltage applied to the liquid crystal composition.

[0201] The display device 8P may include an optical system 3P, for example, as shown in Figure 26B.

[0202] The optical system 3P may project the display light emitted from the display panel 2P as a virtual image V or a real image. The display panel 2P has a display surface 2Pa, on which an image G is displayed. The display panel 2P emits display light of the image G from the display surface 2Pa in the positive direction of the third direction. The image G may be a moving image (also called a video) or a still image. Hereinafter, the positive direction of the third direction will also be referred to as the "direction of display light emission". The display panel 2P may be configured to emit linearly polarized display light. In this specification, it is assumed that the display panel 2P emits S-wave polarized display light, but it is not limited to this. The display panel 2P may emit P-wave polarized display light. For example, if the display panel 2 emits P-wave polarized display light, then S-wave polarization in the following description may be read as P-wave polarization, and P-wave polarization may be read as S-wave polarization.

[0203] The display panel 2P may be a liquid crystal panel. The liquid crystal panel may be a known liquid crystal panel. Known liquid crystal panels may be, for example, IPS (In-Plane Switching), FFS (Fringe Field Switching), VA (Vertical Alignment), or ECB (Electrically Controlled Birefringence) liquid crystal panels. The display surface 2Pa may be the side (front) of the liquid crystal panel facing the user 11P. In the following description, for each component of the display device 8P, the side facing the user 11P may be referred to as the "front," and the side opposite the front may be referred to as the "back."

[0204] The display device 8P may include an irradiator 10P that illuminates the display panel 2P surfacely. The irradiator 10P is also called a backlight. The irradiator 10P may be an edge-lit backlight or a direct-lit backlight. An edge-lit backlight has one or more light sources arranged on the outer periphery of the display panel 2P, and the light emitted from the light sources may be guided by a light guide plate to the entire back surface of the display panel 2P and uniformly dispersed. A direct-lit backlight has multiple light sources arranged on the back side of the display panel 2P, and the display panel 2P may be illuminated by light emitted from the multiple light sources. The light sources of the irradiator 10P may be cold cathode fluorescent lamps, halogen lamps, or xenon lamps, or they may be light-emitting diodes (LEDs), organic light-emitting diodes (OLEDs), semiconductor lasers (LDs), etc. If the light source of the irradiator 10P is an LD with excellent monochromatic properties, the design of the optical system 3P becomes easier.

[0205] The display panel 2P is not limited to a liquid crystal panel. The display panel 2P may be a self-emissive display panel including, for example, self-emissive elements such as LEDs, OLEDs, or LDs.

[0206] The optical system 3P may image the display light of image G as a virtual image V or a real image. The optical system 3P can image the display light emitted from display panel 2P at a position different from the display surface 2Pa, and allow the user 11P to view it as a virtual image V or a real image. The user 11P may be positioned away from the display device 8P in the direction of emission of the display light. The virtual image V may be formed at a distance from display panel 2P (negative direction side of the third direction) or at a distance from display panel 2P (positive direction side of the third direction) within the user 11P's field of view. The virtual image V may be an upright virtual image which is an enlarged version of the image G displayed on display panel 2P. The real image may be formed at a distance from display panel 2P or at a distance from display panel 2P as seen from the user 11P.

[0207] The optical system 3P may be configured to include a first phase difference plate 12P, a semi-transparent mirror 13P, a second phase difference plate 14P, and a reflective polarizing plate 15P, as shown in Figure 27. The first phase difference plate 12P, the semi-transparent mirror 13P, the second phase difference plate 14P, and the reflective polarizing plate 15P may be arranged in this order in the direction of emission of the display light.

[0208] The first phase difference plate 12P may be located on the side of the display surface 2Pa of the display panel 2P. The first phase difference plate 12P may be located away from the display surface 2Pa in the direction of emission of the display light L. The first phase difference plate 12P may be located in contact with the display panel 2P. The second phase difference plate 14P may be located away from the first phase difference plate 12P in the direction of emission of the display light L.

[0209] The first phase difference plate 12P and the second phase difference plate 14P may be quarter-wave plates. The first phase difference plate 12P and the second phase difference plate 14P may give a phase difference of 1 / 4 wavelength to the polarization plane (polarization plane in the direction of electric field vibration) of the incident light. This makes it possible to reflect a portion of the display light emitted from the display panel 2P by the reflective polarizer plate 15P and direct it onto the semi-transparent mirror 13P.

[0210] The first phase difference plate 12P and the second phase difference plate 14P should be provided with the necessary phase difference for the display light transmitted through them, such that the light transmitted through them is reflected by the reflective polarizer plate 15P. That is, for example, when the polarization obtained by transmitting through the first phase difference plate 12P and the second phase difference plate 14P is called the second polarization, the first phase difference plate 12P and the second phase difference plate 14P may be other wavelength plates or combinations thereof, rather than quarter-wave plates, as long as the second polarization is obtained. In this disclosure, the case where the first phase difference plate 12P and the second phase difference plate 14P are quarter-wave plates will be explained as an example. Furthermore, the first phase difference plate and the second phase difference plate may be film-like members.

[0211] Furthermore, the second phase difference plate 14P only needs to be able to provide the necessary phase difference to the light that has been transmitted through the second phase difference plate 14P so that the light that has been reflected by the reflective polarizer 15P and transmitted through the second phase difference plate 14P is transmitted through the reflective polarizer 15P again when it reaches the reflective polarizer 15P. In other words, for example, if the polarization obtained by being reflected by the reflective polarizer 15P and transmitted through the second phase difference plate 14P is taken as the first polarization, the second phase difference plate 14P may be a wave plate other than a quarter wave plate, as long as the first polarization can be obtained.

[0212] The semi-transparent mirror 13P may be positioned between the first phase difference plate 12P and the second phase difference plate 14P. The semi-transparent mirror 13P may transmit a portion of the incident light (for example, approximately 50%) and reflect the remainder (for example, approximately 50%). The transmittance and reflectance of light incident on the semi-transparent mirror 13P are not limited to 50%. The semi-transparent mirror 13P may have a function to collect or focus light. Specifically, the semi-transparent mirror 13P may have a function to collect or focus light that has been incident on and reflected from the semi-transparent mirror 13P. The semi-transparent mirror 13P may reflect a portion of the display light reflected by the reflective polarizer 15P and direct it into the eyes of the user 11P. This makes it possible for the user 11P to see a virtual image V or a real image. The semi-transparent mirror 13P may be a concave mirror having a concave reflective surface 13Pa, as shown in Figure 27. The reflective surface 13Pa of the semi-transparent mirror 13P may be located on the side of the second phase difference plate 14P. The semi-transparent mirror 13P may include a spherical shape, an aspherical shape, or a free-form shape in at least a portion of the reflective surface 13Pa. The semi-transparent mirror 13P may focus or concentrate light more effectively than other members of the optical system 3P. In other words, the semi-transparent mirror 13P may have a larger degree of focusing, convergence, or an index expressed as the reciprocal of the focal length than other members of the optical system 3P. The reflective surface 13Pa of the semi-transparent mirror 13P may have a larger curvature than other members of the optical system 3P. The optical system 3P may have only the semi-transparent mirror 13P as a member having a focusing or converging function. The semi-transparent mirror 13P may also be composed of a holographic optical element (HOE), or its surface shape may have a Fresnel shape.

[0213] The semi-transparent mirror 13P may be composed of, for example, a substrate and a semi-transparent reflective layer located on the surface of the substrate. The substrate may have a transmittance of 100% or nearly 100% for light in the visible light band. The substrate may be made of, for example, a resin material, a glass material, etc. The resin material may be, for example, acrylic resin, polycarbonate resin, etc. The semi-transparent reflective layer may transmit a portion of the incident light (for example, approximately 50%) and reflect the remainder (for example, approximately 50%). The semi-transparent reflective layer may be a thin metal film. The thin metal film may be made of, for example, a metal material such as aluminum or chromium. The semi-transparent reflective layer is not limited to a thin metal film, and may be, for example, a dielectric multilayer film, etc.

[0214] The reflective polarizer 15P may be positioned on the opposite side of the semi-transparent mirror 13P from the second phase difference plate 14P. In other words, the reflective polarizer 15P may be positioned after the second phase difference plate 14P in the direction of emission of the display light. The reflective polarizer 15P may transmit a portion of the incident light and reflect the remainder. The reflective polarizer 15P may be configured to reflect polarized light having a polarization axis perpendicular to the polarization axis of the display light L (also called P-wave polarized light or second polarized light) and transmit polarized light having a polarization axis parallel to the polarization axis of the display light L (also called S-wave polarized light or first polarized light). In this case, the positional relationship between the first phase difference plate 12P and the second phase difference plate 14P may be defined such that when the first phase difference plate 12P and the second phase difference plate 14P are viewed along the Z-axis direction, the lagging axis of the second phase difference plate 14P and the lagging axis of the first phase difference plate 12P are parallel. The reflective polarizer 15P may be configured to transmit polarized light having a polarization axis perpendicular to the polarization axis of the display light L (also called P-wave polarized light or first polarized light) and to reflect polarized light having a polarization axis parallel to the polarization axis of the display light L (also called S-wave polarized light or second polarized light). In this case, the positional relationship between the first phase difference plate 12P and the second phase difference plate 14P may be defined such that when the first phase difference plate 12P and the second phase difference plate 14P are viewed along the Z-axis direction, the lagging axis of the second phase difference plate 14P is perpendicular to the lagging axis of the first phase difference plate 12P. This makes it possible for the user 11P to view a virtual image V or a real image.

[0215] The reflective polarizer 15P may have a function to diverge the light that is incident on and reflected by the semi-transparent mirror 13P. The reflective polarizer 15P may have a function to collect or focus the light that is incident on and reflected by the semi-transparent mirror 13P. The reflective polarizer 15P may be flat, or it may have a concave shape located on the display panel 2 side, or it may have a convex shape located on the display panel 2 side. Furthermore, the reflective polarizer 15P may be composed of a holographic optical element (HOE), or its surface shape may have a Fresnel shape.

[0216] The reflective polarizer 15P may be a wire grid polarizer comprising, for example, a substrate and a plurality of metal nanowires (also called a metal nanowire grid) located on the surface of the substrate. The substrate may have a transmittance of 100% or nearly 100% for light in the visible light band. The substrate may be made of, for example, a resin material, a glass material, etc. The metal nanowires may be made of, for example, a metal material such as aluminum, chromium, or titanium oxide. The metal nanowires may be arranged along one direction. The reflective polarizer 15P can transmit light components vibrating in a direction perpendicular to the grid and can reflect light components vibrating in a direction parallel to the grid.

[0217] The dimming member 4P may be located in the optical path of the display light between the optical system 3P and the user 11P. The dimming member 4P may transmit a portion of the incident light and scatter and / or absorb the remainder. The dimming member 4P may be configured to have a variable transmittance of visible light.

[0218] The dimming member 4P may be composed of, for example, a dimming layer 17P, a first transparent support layer 18P, and a second transparent support layer 19P, as shown in Figure 28. The first transparent support layer 18P and the second transparent support layer 19P may be arranged parallel to each other with a gap between them. The dimming layer 17P may be located between the first transparent support layer 18P and the second transparent support layer 19P. The dimming layer 17P may contain a transparent polymer layer 17Pa and a liquid crystal composition 17Pb. The transparent polymer layer 17Pa may have a number of voids. The liquid crystal composition 17Pb may fill the voids in the transparent polymer layer 17Pa. The first transparent support layer 18P and the second transparent support layer 19P may each contain support films 18Pa, 19Pa and transparent conductive films 18Pb, 19Pb. By controlling the potential difference between the transparent conductive films 18Pb and 19Pb, the orientation and refractive index of the liquid crystal composition 17Pb can be changed, thereby changing the transmittance of the dimming member 4P.

[0219] The dimming member 4P may be configured such that when no potential difference is applied between the transparent conductive films 18Pb and 19Pb, it becomes black with a transmittance of about 5%, and when a potential difference is applied between the transparent conductive films 18Pb and 19Pb, it becomes transparent with a transmittance of substantially 100%. The dimming member 4P may be configured such that when a potential difference is applied between the transparent conductive films 18Pb and 19Pb, it becomes black with a transmittance of about 5%, and when no potential difference is applied between the transparent conductive films 18Pb and 19Pb, it becomes transparent with a transmittance of substantially 100%. The dimming member 4P may be configured such that when no potential difference is applied between the transparent conductive films 18Pb and 19Pb, it becomes white with a transmittance of about 5%, and when a potential difference is applied between the transparent conductive films 18Pb and 19Pb, it becomes transparent with a transmittance of substantially 100%. The dimming member 4P may be configured such that when a potential difference is applied between the transparent conductive films 18Pb and 19Pb, it becomes white with a transmittance of about 5%, and when no potential difference is applied between the transparent conductive films 18Pb and 19Pb, it becomes transparent with a transmittance of substantially 100%.

[0220] As shown in Figure 50, the display device 8P may have a display panel 2P and a first phase difference plate 12P integrated together, or a reflective polarizing plate 15P and a second phase difference plate 14P integrated together. The reflective polarizing plate 15P may also be integrated with the dimming member 4P. Note that "integrated" may include cases where two members are arranged in contact with each other, and cases where two members are joined together with an adhesive such as OCA (Optically Clear Adhesive).

[0221] In the display device 8P, the display light emitted from the display panel 2P can reach the user 11P's eyes after passing through the dimming member 4P once. In contrast, when ambient light enters the display device 8P via the light-transmitting plate 43P (for example, when the display device 8P is used as an electronic rearview mirror in a vehicle, and light emitted from the headlights of a following vehicle enters the display device 8P via the light-transmitting plate 43P), the ambient light is reflected within the display device 8P and must pass through the dimming member 4P twice before reaching the user 11P's eyes. By appropriately setting the transmittance of the dimming member 4P to visible light, it is possible to reduce the decrease in brightness of the display light that enters the user 11P's eyes while reducing the glare the user 11P experiences from the reflected ambient light. As a result, the display light emitted from the display panel 2P can be clearly viewed by the user 11P as an image, virtual image, or real image.

[0222] The display device 8P may include an acquisition unit 5P, a detection unit 6P, and a control unit 7P.

[0223] The acquisition unit 5P may acquire the illuminance of the surrounding environment of the vehicle 50P and output it to the control unit 7P. The acquisition unit 5P may include a communication interface that can communicate with an external device. The external device may include an illuminance sensor that detects the illuminance of the surrounding environment of the vehicle 50P. The acquisition unit 5P may acquire information from the external device indicating the illuminance of the surrounding environment of the vehicle 50P. The communication interface may include, for example, a physical connector and a wireless communication device. The physical connector may include an electrical connector that supports transmission by electrical signals, an optical connector that supports transmission by optical signals, and an electromagnetic connector that supports transmission by electromagnetic waves. The wireless communication device may include at least one antenna.

[0224] The vehicle 50P may be configured to control the illumination state of its headlights according to the illumination level of the surrounding environment. In such cases, the acquisition unit 5P may acquire the illumination level detected by an illumination sensor attached to the vehicle 50P from the ECU (electronic control unit) that controls the illumination state of the headlights.

[0225] The acquisition unit 5P may include an illuminance sensor that detects the illuminance of the surrounding environment of the vehicle 50P. The acquisition unit 5P may output the illuminance detected by the illuminance sensor to the control unit 7P. The illuminance sensor may be a known illuminance sensor. The position of the illuminance sensor is arbitrary, both inside and outside the vehicle 50P. The illuminance sensor may be located, for example, on the dashboard of the vehicle 50P, on the ceiling of the passenger compartment, etc.

[0226] The acquisition unit 5P may acquire illuminance information around the vehicle 50P from an illuminance sensor installed outside the vehicle 50P. The acquisition unit 5P may acquire illuminance information around the vehicle 50P from a roadside unit around the vehicle 50P. The acquisition unit 5P may acquire illuminance information around the vehicle 50P from a cloud server connected via a network. The acquisition unit 5P may use illuminance estimated based on at least one of the following: weather, time of day, natural light illuminance, and artificial light illuminance around the vehicle 50P as illuminance information around the vehicle 50P.

[0227] The detection unit 6P may detect the luminance of ambient light incident on the display device 8P and output it to the control unit 7P. The detection unit 6P may, for example, detect the luminance of ambient light incident on the front surface of the dimming member 4P and output it to the control unit 7P. The detection unit 6P may include a known luminance sensor. The detection unit 6P may be located in front of the dimming member 4P. The detection unit 6P may be located in front of the reflective polarizing plate 15P. In this case, the control unit 7P may correct the luminance detected by the detection unit 6P according to the transmittance of the dimming member 4P and calculate the luminance of ambient light incident on the front surface of the dimming member 4P.

[0228] Ambient light may be, for example, light emitted from the headlights of a following vehicle and incident on the display device 8P. The ambient light is reflected by the reflective polarizer 15P, semi-transparent mirror 13P, and display panel 2P of the display device 8P, and incident on the user's eyes 11P together with the display light. If the brightness of the ambient light emitted from the display device 8P is higher than the brightness of the display light emitted from the display device 8P, the user 11P may feel dazzled and have difficulty seeing the virtual image V. In particular, when the illumination of the surrounding environment of the vehicle 50P is low, the user 11P is more likely to feel dazzled by the ambient light and have difficulty seeing the virtual image V.

[0229] The control unit 7P is connected to and controls each component of the display device 8P. The components of the display device 8P may be connected to each other via, for example, wired, wireless, or CAN (Controller Area Network). The control unit 7P may be configured to include one or more processors. The processors may include general-purpose processors configured to load specific programs and execute specific functions, and dedicated processors specialized for specific processing. The processors may include PLDs (Programmable Logic Devices). The control unit 7P may be either a SoC (System-on-a-Chip) or a SiP (System In a Package) in which one or more processors cooperate. The control unit 7P includes a storage unit, which may store various information or programs for operating each component of the display device 8P. The storage unit may be composed of, for example, semiconductor memory. The storage unit may function as the work memory of the control unit 7P.

[0230] Referring to Figure 27, the optical function of the optical system 3P will be described. The display panel 2P may emit display light L of S-wave polarized (first linearly polarized) form. The display light L of the first linearly polarized form emitted from the display panel 2P may pass through the first phase difference plate 12P and be converted into light of the first circularly polarized form C1 form. A portion (for example, approximately 50%) of the light of the first circularly polarized form C1 that has passed through the first phase difference plate 12P may pass through the semi-transparent mirror 13P. The light of the first circularly polarized form C1 that has passed through the semi-transparent mirror 13P may pass through the second phase difference plate 14P and be converted into light of the second linearly polarized form L2 form whose polarization direction is perpendicular to that of the first linearly polarized form L1 (i.e., it is P-wave polarized). The light of the second linearly polarized form L2 may be incident on the reflective polarizer 15P. Since the reflective polarizer 15P reflects P-wave polarized light and transmits S-wave polarized light, the second linearly polarized light L2 incident on the reflective polarizer 15P may be reflected by the reflective polarizer 15P and converted into third linearly polarized light L3. The third linearly polarized light L3 may be transmitted through the second phase difference plate 14P and converted into second circularly polarized light C2. A portion of the second circularly polarized light C2 transmitted through the second phase difference plate 14P (for example, approximately 50%) may be reflected by the semi-transparent mirror 13P and converted into third circularly polarized light C3. The third circularly polarized light C3 may be transmitted through the second phase difference plate 14P and converted into fourth linearly polarized light L4 whose polarization direction is parallel to the first linearly polarized light L1 (i.e., S-wave polarized). The fourth linearly polarized light L4 may be transmitted through the reflective polarizer 15P and emitted from the optical system 3P. The amount of light (luminance) of the display light emitted from the optical system 3P may be, for example, approximately 25% of the amount of light (luminance) of the display light emitted from the display panel 2P.

[0231] Next, another optical function of the optical system 3P will be described. The display panel 2P may emit display light that is S-wave polarized (first linearly polarized L1). The display light of the first linearly polarized L1 emitted from the display panel 2P may pass through the first phase difference plate 12P and be converted into light of the first circularly polarized C1. A portion of the first circularly polarized C1 that has passed through the first phase difference plate 12P (for example, approximately 50%) may pass through the semi-transparent mirror 13P. The first circularly polarized C1 that has passed through the semi-transparent mirror 13P may pass through the second phase difference plate 14P and be converted into light of the second linearly polarized L2 whose polarization direction is parallel to the first linearly polarized L1 (i.e., S-wave polarized). The light of the second linearly polarized L2 may be incident on the reflective polarizer 15P. As described above, the reflective polarizer 15P may reflect S-wave polarized light and transmit P-wave polarized light. The second linearly polarized light L2 incident on the reflective polarizer 15P may be reflected by the reflective polarizer 15P and converted into third linearly polarized light L3. The third linearly polarized light L3 may pass through the second phase difference plate 14P and be converted into second circularly polarized light C2. A portion of the second circularly polarized light C2 that has passed through the second phase difference plate 14P (for example, about 50%) may be reflected by the semi-transparent mirror 13P and converted into third circularly polarized light C3. The third circularly polarized light C3 may pass through the second phase difference plate 14P and be converted into fourth linearly polarized light L4 whose polarization direction is perpendicular to the first linearly polarized light L1 (i.e., P-wave polarized). The fourth linearly polarized light L4 may pass through the reflective polarizer 15P and be emitted to the outside. The amount of light (luminance) emitted from the display device 8P may be, for example, about 25% of the amount of display light (luminance) emitted from the display panel 2P.

[0232] In Figure 27, for the sake of illustration, the optical path of light incident on the reflective polarizer 15P and the optical path of light reflected by the reflective polarizer 15P are shown shifted in the height direction (Y-axis direction), and the optical path of light incident on the semi-transparent mirror 13P and the optical path of light reflected by the semi-transparent mirror 13P are also shown shifted in the height direction (Y-axis direction). However, in reality, the display light emitted from the display panel 2P may propagate substantially along a single axis, as shown in Figure 55. This is also true for the optical paths shown in Figures 34-37, 41-43, 47, 48, and 50-52.

[0233] Each component of the optical system 3P may maintain its relative position to one another by being held by a holding member (not shown). Air may be interposed between the first phase difference plate 12P and the second phase difference plate 14P (i.e., between the first phase difference plate 12P and the semi-transparent mirror 13P and between the semi-transparent mirror 13P and the second phase difference plate 14P). The optical system 3P may be configured without a component made of a resin material such as polymer between the first phase difference plate 12P and the second phase difference plate 14P. Therefore, during the manufacturing process of the optical system 3P, deformation of the semi-transparent mirror 13P when the resin material is cured, and positional displacement between the semi-transparent mirror 13P and the first phase difference plate 12P and / or the second phase difference plate 14P can be reduced. In addition, since resin materials such as polymers have material-specific retardation, by not providing a component made of resin material in the optical path of the display light, changes in the polarization state of the display light can be reduced. As a result, the deterioration of the display quality of the display device 8P can be reduced.

[0234] Since the optical system 3P is an on-axis type optical system in which the optical axis of the incident light and the optical axis of the emitted light substantially coincide, the space occupied by the optical system 3P can be reduced, and as a result, the display device 8P can be miniaturized. In addition, because the optical system 3P is on-axis, distortion and brightness unevenness of the virtual image V seen by the user 11P can be reduced, and the design of the optical system 3P is simplified.

[0235] The reflection of ambient light in the display device 8P will be explained with reference to Figure 29. Ambient light incident on the display device 8P may be reflected by the reflective polarizer 15P, the semi-transparent mirror 13P, or the display panel 2P and emitted from the display device 8P, as shown in Figure 29. Note that the optical path shown in Figure 29 shows that the reflective polarizer 15P, the semi-transparent mirror 13P, and the display panel 2P can reflect ambient light, and does not represent the actual optical path of ambient light incident on the display device 8P.

[0236] First, let's explain the case where the transmittance of the dimming member 4P is 100%. Ambient light may pass through the dimming member 4P and be incident on the reflective polarizing plate 15P. A portion of the ambient light incident on the reflective polarizing plate 15P (for example, about 50%) may pass through the reflective polarizing plate 15P. The remaining portion of the ambient light incident on the reflective polarizing plate 15P (for example, about 50%) may be reflected by the reflective polarizing plate 15P, as shown in the ambient light DP1 in Figure 29, pass through the dimming member 4P, and be emitted to the outside.

[0237] The ambient light transmitted through the reflective polarizing plate 15P may pass through the second phase difference plate 14P and be incident on the semi-transparent mirror 13P. A portion of the ambient light incident on the semi-transparent mirror 13P (for example, approximately 50%) may pass through the semi-transparent mirror 13P. A portion of the remaining ambient light incident on the semi-transparent mirror 13P (for example, approximately 50%) may be reflected by the semi-transparent mirror 13P, as shown in the ambient light DP2 in Figure 29, and may pass through the second phase difference plate 14P, the reflective polarizing plate 15P, and the dimming member 4P and be emitted to the outside. Since the second phase difference plate 14P is located between the semi-transparent mirror 13P and the reflective polarizer 15P, for the ambient light DP2 to pass through the reflective polarizer 15P and exit to the outside, it is necessary to travel back and forth between the reflective polarizer 15P and the semi-transparent mirror 13P at least twice. Due to the losses such as scattering and absorption that occur during this time, the brightness of the ambient light DP2 that exits to the outside may be about 1% of the brightness of the ambient light incident on the optical system 3P. The brightness of the ambient light DP2 may be negligibly small compared to the brightness of the ambient light DP1.

[0238] The ambient light that has passed through the reflective polarizer 15P and the semitransparent mirror 13P may pass through the first phase difference plate 12P and be incident on the display panel 2P. A portion of the ambient light incident on the display panel 2P may be reflected by the display panel 2P, as shown in the ambient light DP3 in Figure 29, and pass through the reflective polarizer 15P and the dimming member 4P and be emitted to the outside. Similar to ambient light DP2, due to losses such as scattering and absorption that occur before passing through the reflective polarizer 15P, the brightness of ambient light DP2 emitted to the outside may be about 1% of the brightness of ambient light incident on the optical system 3P. The brightness of ambient light DP3 may be negligibly small compared to the brightness of ambient light DP1.

[0239] As described above, the ambient light that substantially affects the visibility of the virtual image V may be ambient light DP1 that is reflected by the reflective polarizer 15P and emitted to the outside. The brightness of the ambient light DP1 emitted from the display device 8P may be, for example, approximately 50% of the brightness of the ambient light incident on the display device 8P. The brightness of the display light emitted from the display device 8P may be, for example, approximately 25% of the brightness of the display light emitted from the display panel 2P. Therefore, if the transmittance of the dimming member 4P is substantially 100%, the brightness of the ambient light emitted from the display device 8P and incident on the user 11P's eyes may be higher than the brightness of the display light emitted from the display device 8P and incident on the user 11P's eyes. As a result, the user 11P may perceive the ambient light as dazzling and may not be able to see the virtual image V clearly.

[0240] Next, let's consider the case where the transmittance of the dimming member 4P is 50%. For ambient light incident on the display device 8P to be emitted from the display device 8P, it needs to pass through the dimming member 4P twice. In contrast, for display light emitted from the display panel 2P to be emitted from the display device 8P, it only needs to pass through the dimming member 4P once. Therefore, the brightness of the ambient light DP1 emitted from the display device 8P can be, for example, approximately 12.5% ​​of the brightness of the ambient light incident on the display device 8P, and the brightness of the display light emitted from the display device 8P can be, for example, approximately 12.5% ​​of the brightness of the display light emitted from the display panel 2P. Thus, the influence of the dimming member 4P on the brightness of ambient light is greater than the influence of the dimming member 4P on the brightness of display light. Therefore, by setting the transmittance of the dimming member 4P to less than 100%, it is possible to reduce the glare felt by the user 11P from the ambient light emitted from the display device 8P. Furthermore, by setting the transmittance of the dimming element 4P to less than 100%, the brightness of the display light emitted from the display device 8P is reduced. However, by increasing the luminescence of the illuminator 10P, the reduction in the brightness of the display light emitted from the display device 8P can be mitigated. In this way, by controlling the transmittance of the dimming element 4P and the luminescence of the illuminator 10P, it is possible to reduce the glare experienced by the user 11P and the difficulty in seeing the virtual image V when high-luminosity ambient light is incident on the display device 8P. As a result, the virtual image V can be seen clearly by the user 11P, improving the driving safety of the vehicle 50P.

[0241] As an example of this disclosure, the display system 1P may be configured as a display system comprising a display device 8P and an imaging unit 22P that captures the scenery around the vehicle 50P, as shown in Figure 25. Here, the scenery around the vehicle 23 may be at least one of the front, rear, side, above, and below the vehicle 23. The display system 1P may allow the user 11P, who is the driver of the vehicle 50P, to view the scenery behind the vehicle 50P captured by the imaging unit 22P as a virtual image V formed on a side farther from the display device 8P. Since the user 11P can view the scenery behind the vehicle 50P without significantly changing the viewing distance (point of gaze) while driving the vehicle 50P, the virtual image V becomes easier to see, and driving safety can be improved.

[0242] The imaging unit 22P may include a camera. The camera may include, for example, a CMOS (Complementary Metal Oxide Semiconductor) image sensor or a CCD (Charge Coupled Device) image sensor. The imaging unit 22P may output imaging data obtained by imaging the area behind the vehicle 50P to the control unit 7P. The control unit 7P may generate image data for the image G to be displayed on the display panel 2P based on the imaging data acquired from the imaging unit 22P. The image G may include the scenery behind the vehicle 50P, as shown in Figures 30A and 30B. The image G may further include icons 16P indicating the distance to a following vehicle, etc. The imaging unit 22P does not have to include a camera. The imaging unit 22P may be connected to an external camera that images the area behind the vehicle 50P. The imaging unit 22P may acquire imaging data of the area behind the vehicle 50P from the external camera.

[0243] The control of the display panel 2P and dimming member 4P by the control unit 7P will be described below. First, the case in which the control unit 7P does not control the display panel 2P and dimming member 4P will be described. Figure 30A shows an example of a virtual image that the user 11P sees when the control unit 7P does not control the display panel 2P and dimming member 4P. As shown in Figure 30A, when high-luminosity ambient light (for example, light emitted from the headlights of a following vehicle) is incident on the display device 8P, the ambient light reflected by the display device 8P (especially the reflective polarizing plate 15P of the optical system 3P) increases the luminance of region VD within the virtual image V. As a result, the user 11P may feel dazzled and be unable to see the virtual image V clearly. In particular, as shown in Figure 30A, when the surrounding environment of the vehicle 50P is generally dark, the user 11P is more likely to feel dazzled and will have difficulty seeing the virtual image V.

[0244] The following describes the case where the control unit 7P controls the display panel 2P and the dimming member 4P. The control unit 7P may acquire ambient illuminance from the acquisition unit 5P and ambient light luminance from the detection unit 6P. Ambient illuminance refers to the illuminance (brightness) of the environment surrounding the vehicle 50P, and ambient light luminance refers to the luminance of ambient light incident on the display device 8P. Based on the ambient illuminance acquired from the acquisition unit 5P and the ambient light luminance acquired from the detection unit 6P, the control unit 7P may change the transmittance of the dimming member 4P and change the brightness of the image G displayed on the display panel 2P. This reduces the likelihood that the user 11P will feel glare and have difficulty seeing the virtual image V, regardless of the ambient illuminance and ambient light luminance. As a result, as shown in Figure 30B, the user 11P can see the virtual image V clearly. The transmittance of the dimming member 4P can be changed by controlling the potential difference between the transparent conductive films 18Pb and 19Pb. Furthermore, the brightness of image G can be changed by controlling the light emission brightness of the illuminator 10P.

[0245] The control unit 7P may control the light dimming member 4P to lower its transmittance as the ambient light intensity detected by the detection unit 6P increases. In this case, the user 11P may experience reduced glare when the ambient light intensity is high. The control unit 7P may control the light dimming member 4P to increase the brightness of the image displayed on the display panel 2P and lower its transmittance as the ambient light intensity detected by the detection unit 6P increases. In this case, the user 11P may experience reduced glare when the ambient light intensity is high, and the user 11P may be able to clearly see the virtual image V. The control unit 7P may control the light dimming member 4P to lower the brightness of the image displayed on the display panel 2P and increase its transmittance as the ambient illuminance detected by the acquisition unit 5P increases, and also control the light dimming member 4P to increase the brightness of the image displayed on the display panel 2P and lower its transmittance as the ambient light intensity detected by the detection unit 6P increases. In this case, regardless of ambient illuminance and ambient light intensity, the user 11P can experience reduced glare, and the virtual image V can be clearly seen by the user 11P.

[0246] The control of the display device 8P by the control unit 7P will be explained below with reference to the flowcharts shown in Figures 31 to 33. In the flowcharts, "step" is abbreviated as "S," and within the chart, "positive" (computer flag = 1) in the decision control is represented by [Yes], and "negative" (computer flag = 0) is represented by [No].

[0247] The irradiator 10P can vary its luminescence within a predetermined luminance range. The predetermined luminance range is, for example, 0 to 20,000 cd / m². ２ It may be 0 to 30000 cd / m². ２ It may be 0 to 40,000 cd / m². ２ This may be the case. In the flowcharts of Figures 31 to 33, setting the luminescence of the irradiator 10P to the upper limit of a predetermined brightness range is described as "luminescence 100%", and setting the luminescence of the irradiator 10P to the lower limit of a predetermined brightness range is described as "luminescence 0%". Note that the luminescence luminescence M% (0 < M < 100) may mean luminescence that changes linearly between the lower and upper limits of a predetermined brightness range, or it may mean luminescence that changes non-linearly.

[0248] The dimming element 4P can change its transmittance within a predetermined transmittance range. The predetermined transmittance range may be, for example, 5 to 100%, 10 to 100%, or 20 to 100%. In the flowcharts of Figures 31 to 33, setting the transmittance of the dimming element 4P to the lower limit of the predetermined transmittance range is described as "dimming rate 100%", and setting the transmittance of the dimming element 4P to the upper limit of the predetermined transmittance range is described as "dimming rate 0%". Therefore, "dimming rate 100%" does not mean setting the transmittance of the dimming element 4P to 0%. Note that the dimming rate N% (0 < N < 100) may mean a transmittance that changes linearly between the upper and lower limits of the predetermined transmittance range, or it may mean a transmittance that changes non-linearly.

[0249] The flowcharts in Figures 31-33 may start, for example, when user 11P boards vehicle 50P and starts the engine of vehicle 50P. In [S1], ambient illuminance thresholds A1, A2, A3 and ambient light luminance thresholds B1, B2, B3 used to control the irradiator 10P and dimming member 4P may be set. In the flowchart of Figure 31, ambient illuminance thresholds A1, A2, A3 and ambient light luminance thresholds B1, B2, B3 are simply referred to as "thresholds A, B". Ambient illuminance thresholds A1, A2, A3 and ambient light luminance thresholds B1, B2, B3 may be set according to the weather around vehicle 50P, time of day, natural light illuminance and artificial light illuminance around vehicle 50P, etc. Natural light may be light coming from, for example, the sun, moon, etc. Artificial light may be light coming from, for example, road lighting, streetlights, etc. For example, ambient illuminance thresholds A1, A2, and A3 may be set to 1000 (lx), 300 (lx), and 50 (lx), respectively, and ambient light intensity thresholds B1, B2, and B3 may be set to 10000 (cd / m²). ２ ), 8000 (cd / m ２ ) and 5000 (cd / m²) ２ It may be set to ).

[0250] In [S2], ambient illuminance X (lx) may be obtained from the acquisition unit 5P. Subsequently, in [S3], ambient light intensity Y (cd / m) may be obtained from the detection unit 6P. ２) may be obtained. In the following explanation, the units of ambient illuminance X and ambient illuminance thresholds A1, A2, A3, as well as the units of ambient light luminance Y and ambient light luminance thresholds B1, B2, B3 may be omitted.

[0251] In [S4], it may be determined whether the operating mode of the irradiator 10P is in automatic mode. If the operating mode of the irradiator 10P is in automatic mode [Yes] in [S4], the process may proceed to [S5]. If the operating mode of the irradiator 10P is not in automatic mode [No] in [S4], the process may return to [S1].

[0252] In [S5], it is possible to determine whether the ambient illuminance X is less than the ambient illuminance threshold A3. In [S5], if the ambient illuminance X is less than the ambient illuminance threshold A3 [Yes], the process may proceed to [S6]. In [S5], if the ambient illuminance X is not less than the ambient illuminance threshold A3 [No], the process may proceed to [S13].

[0253] In [S6], it is possible to determine whether the ambient light intensity Y is greater than the ambient light intensity threshold B1. If in [S6] the ambient light intensity Y is greater than the ambient light intensity threshold B1 [Yes], the process may proceed to [S7]. If in [S6] the ambient light intensity Y is not greater than the ambient light intensity threshold B1 [No], the process may proceed to [S8].

[0254] In [S7], the luminescence of the irradiator 10P is set to 100%, and the dimming rate of the dimming member 4P is set to 100%, and the flowchart may be terminated.

[0255] In [S8], it is possible to determine whether the ambient light intensity Y is greater than the ambient light intensity threshold B2. If in [S8] the ambient light intensity Y is greater than the ambient light intensity threshold B2 [Yes], the process may proceed to [S9]. If in [S8] the ambient light intensity Y is not greater than the ambient light intensity threshold B2 [No], the process may proceed to [S10].

[0256] In [S9], the luminescence rate of the irradiator 10P is set to 80%, and the dimming rate of the dimming member 4P is set to 90%, and the flowchart may be terminated.

[0257] In [S10], it is possible to determine whether the ambient light intensity Y is greater than the ambient light intensity threshold B3. If in [S10] the ambient light intensity Y is greater than the ambient light intensity threshold B3 [Yes], the process may proceed to [S11]. If in [S10] the ambient light intensity Y is not greater than the ambient light intensity threshold B3 [No], the process may proceed to [S12].

[0258] In [S11], the luminescence rate of the irradiator 10P is set to 70%, and the dimming rate of the dimming member 4P is set to 90%, and the flowchart may be terminated.

[0259] In [S12], the luminescence rate of the irradiator 10P is set to 60%, and the dimming rate of the dimming member 4P is set to 90%, and the flowchart may be terminated.

[0260] In [S5], if the ambient illuminance X is not less than the ambient illuminance threshold A3 [No], then in [S13], it may be determined whether the ambient illuminance X is less than the ambient illuminance threshold A2. In [S13], if the ambient illuminance X is less than the ambient illuminance threshold A2 [Yes], then the process may proceed to [S14]. In [S13], if the ambient illuminance X is not less than the ambient illuminance threshold A2 [No], then the process may proceed to [S21].

[0261] In [S14], it is possible to determine whether the ambient light intensity Y is greater than the ambient light intensity threshold B1. If in [S14] the ambient light intensity Y is greater than the ambient light intensity threshold B1 [Yes], the process may proceed to [S15]. If in [S14] the ambient light intensity Y is not greater than the ambient light intensity threshold B1 [No], the process may proceed to [S16].

[0262] In [S15], the luminescence rate of the irradiator 10P is set to 70%, and the dimming rate of the dimming member 4P is set to 70%, and the flowchart may be terminated.

[0263] In [S16], it is possible to determine whether the ambient light intensity Y is greater than the ambient light intensity threshold B2. If in [S16] the ambient light intensity Y is greater than the ambient light intensity threshold B2 [Yes], the process may proceed to [S17]. If in [S16] the ambient light intensity Y is not greater than the ambient light intensity threshold B2 [No], the process may proceed to [S18].

[0264] In [S17], the luminescence rate of the irradiator 10P is set to 70%, and the dimming rate of the dimming member 4P is set to 60%, and the flowchart may be terminated.

[0265] In [S18], it is possible to determine whether the ambient light intensity Y is greater than the ambient light intensity threshold B3. If in [S18] the ambient light intensity Y is greater than the ambient light intensity threshold B3 [Yes], the process may proceed to [S19]. If in [S18] the ambient light intensity Y is not greater than the ambient light intensity threshold B3 [No], the process may proceed to [S20].

[0266] In [S19], the luminescence rate of the irradiator 10P is set to 60%, and the dimming rate of the dimming member 4P is set to 50%, and the flowchart may be terminated.

[0267] In [S20], the luminescence rate of the irradiator 10P is set to 60%, and the dimming rate of the dimming member 4P is set to 40%, and the flowchart may be terminated.

[0268] In [S13], if the ambient illuminance X is not less than the ambient illuminance threshold A2 [No], then in [S21], it may be determined whether the ambient illuminance X is less than the ambient illuminance threshold A1. In [S21], if the ambient illuminance X is less than the ambient illuminance threshold A1 [Yes], then the process may proceed to [S22]. In [S21], if the ambient illuminance X is not less than the ambient illuminance threshold A1 [No], then the process may proceed to [S24].

[0269] In [S22], it is possible to determine whether the ambient light intensity Y is greater than the ambient light intensity threshold B1. If in [S22] the ambient light intensity Y is greater than the ambient light intensity threshold B1 [Yes], the process may proceed to [S23]. If in [S22] the ambient light intensity Y is not greater than the ambient light intensity threshold B3 [No], the process may proceed to [S25].

[0270] In [S23], the luminescence rate of the irradiator 10P is set to 60%, and the dimming rate of the dimming member 4P is set to 30%, and the flowchart may be terminated.

[0271] In [S25], it is possible to determine whether the ambient light intensity Y is greater than the ambient light intensity threshold B2. If in [S25] the ambient light intensity Y is greater than the ambient light intensity threshold B2 [Yes], the process may proceed to [S26]. If in [S25] the ambient light intensity Y is not greater than the ambient light intensity threshold B2 [No], the process may proceed to [S27].

[0272] In [S26], the luminescence rate of the irradiator 10P is set to 60%, and the dimming rate of the dimming member 4P is set to 20%, and the flowchart may be terminated.

[0273] In [S27], it is possible to determine whether the ambient light intensity Y is greater than the ambient light intensity threshold B3. If in [S27] the ambient light intensity Y is greater than the ambient light intensity threshold B3 [Yes], proceed to [S28]. If in [S27] the ambient light intensity Y is not greater than the ambient light intensity threshold B3 [No], proceed to [S29].

[0274] In [S28], the luminescence rate of the irradiator 10P is set to 60%, and the dimming rate of the dimming member 4P is set to 10%, and the flowchart may be terminated.

[0275] In [S29], the luminescence rate of the irradiator 10P is set to 60%, and the dimming rate of the dimming member 4P is set to 15%, and the flowchart may be terminated.

[0276] In [S21], if the ambient illuminance X is not less than the ambient illuminance threshold A1 [No], then in [S24], the luminous flux of the irradiator 10P is set to 60%, and the dimming rate of the dimming member 4P is set to 0%, and the flowchart may be terminated.

[0277] According to the flowcharts in Figures 31-33, the control unit 7P can enable the user 11P to clearly see the virtual image V regardless of the ambient illuminance X and ambient light luminance Y. The control unit 7P may repeatedly execute the control shown in the flowcharts in Figures 31-33. Furthermore, although the flowcharts in Figures 31-33 describe an example in which three ambient illuminance thresholds and three ambient light luminance thresholds are set in [S1], the control unit 7P is not limited to this, and two or fewer ambient illuminance thresholds and ambient light luminance thresholds may be set, or four or more ambient illuminance thresholds may be set. The number of ambient illuminance thresholds and the number of ambient light luminance thresholds may be the same or different. The flowcharts in Figures 31-33 show an example of control of the display device 8P by the control unit 7P, and the control of the display device 8P by the control unit 7P is not limited to the flowcharts in Figures 31-33.

[0278] The following describes other examples of the display device 8P with reference to Figures 34 to 48.

[0279] The display panel 2P may display a mixed image including a left-eye image and a right-eye image having parallax with respect to each other, and may emit display light of the mixed image. The display device 8P may include an optical element 20P located in the optical path of the display light emitted from the display panel 2P, as shown in Figure 34. The optical element 20P may be configured to define the direction of the light rays of the left-eye image and the right-eye image, so that the display light of the left-eye image reaches the left eye of the user 11P and the display light of the right-eye image reaches the right eye of the user 11P. This makes it possible for the user 11P to view a three-dimensional virtual image using the display device 8P.

[0280] The optical element 20P only needs to direct a portion of the display light of the mixed image to one of the user's left and right eyes, and the other portion of the display light to the other of the user's left and right eyes. It may be a parallax barrier or a lenticular lens. The parallax barrier may be made of a liquid crystal panel. The position of the optical element 20P may be arbitrary within the display device 8P. The optical element 20P may be located between the illuminator 10P and the display panel 2P, between the display panel 2P and the first phase difference plate 12P, or between the reflective polarizing plate 15P and the dimming member 4P.

[0281] As shown in Figure 35, the display device 8P may include a moth-eye structure film (anti-reflective film) 21P located between the first phase difference plate 12P and the semi-transparent mirror 13P. The moth-eye structure film 21P may have a fine uneven structure on the surface facing the semi-transparent mirror 13P. The moth-eye structure film 21P can attenuate reflected light from light incident from the semi-transparent mirror 13P side. When the optical system 3P includes the moth-eye structure film 21P, the amount of ambient light incident on the display device 8P that is reflected by the display panel 2P and emitted from the display device 8P can be further reduced.

[0282] As shown in Figure 36, the display device 8P may have an optical system 3P' instead of the optical system 3P. The optical system 3P' may project the display light emitted from the display panel 2P as a virtual image V or a real image. The optical system 3P' may consist of a first semi-transparent mirror 23P, a first phase difference plate 24P, a second semi-transparent mirror 25P, a second phase difference plate 26P, and a polarizing plate 27P. The first semi-transparent mirror 23P, the first phase difference plate 24P, the second semi-transparent mirror 25P, the second phase difference plate 26P, and the polarizing plate 27P may be arranged in this order in the direction of emission of the display light (i.e., the positive direction of the third direction).

[0283] The first phase difference plate 24P may be positioned at a distance from the display panel 2P in the direction of emission of the display light. The second phase difference plate 26P may be positioned at a distance from the first phase difference plate 24P in the direction of emission of the display light. The first phase difference plate 24P and the second phase difference plate 26P may be quarter-wave plates.

[0284] The first semi-transparent mirror 23P may be positioned between the display panel 2P and the first phase difference plate 24P. The first semi-transparent mirror 23P may transmit a portion of the incident light and reflect the remainder. The first semi-transparent mirror 23P may have a function of focusing or converging light. Specifically, the first semi-transparent mirror 23P may have a function of focusing or converging light that is incident on and reflected by the first semi-transparent mirror 23P. The first semi-transparent mirror 23P may be a concave mirror having a concave reflective surface 23Pa, as shown in Figure 36. The reflective surface 23Pa of the first semi-transparent mirror 23P may be positioned on the side of the first phase difference plate 24P. The first semi-transparent mirror 23P may focus or converge light more effectively than other members of the optical system 3P'. In other words, the first semi-transparent mirror 23P may have a larger focusing degree, converging degree, or index expressed as the reciprocal of the focal length than other members of the optical system 3P'. The reflective surface 23Pa of the first semi-transparent mirror 23P may have a greater curvature than other members of the optical system 3P'. The optical system 3P' may have only the first semi-transparent mirror 23P as a member having a light-gathering or focusing function. The first semi-transparent mirror 23P may also be composed of a holographic optical element (HOE), or its surface shape may have a Fresnel shape. In this embodiment, the first semi-transparent mirror 23P may be configured to transmit polarized light having a polarization axis parallel to the polarization axis of the display light and to reflect polarized light having a polarization axis perpendicular to the polarization axis of the display light. The first semi-transparent mirror 23P may be configured to transmit S-wave polarized light and reflect P-wave polarized light. Alternatively, the first semi-transparent mirror 23P may be configured to reflect S-wave polarized light and transmit P-wave polarized light. At least a portion of the reflective surface 23Pa of the first semi-transparent mirror 23P may include a spherical shape, an aspherical shape, or a free-form surface shape.

[0285] The first semi-transparent mirror 23P may be composed of, for example, a substrate and a plurality of metal nanowires (metal nanowire grids) located on the surface of the substrate. The substrate may have a transmittance of 100% or close to 100% for light in the visible light band. The substrate may be composed of, for example, a resin material, a glass material, etc. The resin material may be, for example, acrylic resin, polycarbonate resin, etc. The metal nanowires may be composed of, for example, a metal material such as aluminum, chromium, titanium oxide, etc. The metal nanowires may be arranged along one direction. The first semi-transparent mirror 23P can transmit light components vibrating in a direction perpendicular to the grid and can reflect light components vibrating in a direction parallel to the grid. The metal nanowire grid may be formed on the surface of the substrate on the side of the first phase difference plate 24P. In this example, the metal nanowire grid is used to impart a reflective polarization function to the first semi-transparent mirror 23P, but the first semi-transparent mirror 23P may be used as a simple half-mirror and a separate reflective polarizer may be provided.

[0286] The second semi-transparent mirror 25P may be positioned between the first phase difference plate 24P and the second phase difference plate 26P. The second semi-transparent mirror 25P may transmit a portion of the incident light (for example, approximately 50%) and reflect the remainder (for example, approximately 50%). The transmittance and reflectance of the light incident on the second semi-transparent mirror 25P are not limited to 50%. The second semi-transparent mirror 25P may be positioned on the opposite side of the first semi-transparent mirror 23P from the first phase difference plate 24P, and more specifically, as shown in Figure 36, the reflective surface 25Pa may be positioned on the side of the first phase difference plate 24P. The second semi-transparent mirror 25P may be a plane mirror. The second semi-transparent mirror 25P is also called a plane half-mirror.

[0287] The second semi-transparent mirror 25P may have a function to diverge the light that is incident on and reflected by the second semi-transparent mirror 25P. The second semi-transparent mirror 25P may have a convex reflective surface 25Pa, and the reflective surface 25Pa may be located on the side of the first phase difference plate 24P. The second semi-transparent mirror 25P is also called a convex half mirror. The second semi-transparent mirror 25P may transmit a portion of the incident light (for example, approximately 50%) and reflect the remainder (for example, approximately 50%). The transmittance and reflectance of the light incident on the second semi-transparent mirror 25P are not limited to 50%. The second semi-transparent mirror 25P may have a function to collect or focus the light that is incident on and reflected by the second semi-transparent mirror 25P. Specifically, the second semi-transparent mirror 25P may have a concave shape located on the side of the display panel 2. Furthermore, the second semi-transparent mirror 13 may be composed of a holographic optical element (HOE), or its surface shape may have a Fresnel shape.

[0288] The second semi-transparent mirror 25P may be composed of, for example, a substrate and a semi-transparent reflective layer located on the surface of the substrate. The substrate may have a transmittance of 100% or nearly 100% for light in the visible light band. The substrate may be made of, for example, inorganic glass, a resin material, etc. The resin material may be, for example, acrylic resin, polycarbonate resin, etc. The semi-transparent reflective layer may transmit a portion of the incident light (for example, approximately 50%) and reflect the remainder (for example, approximately 50%). The semi-transparent reflective layer may be a thin metal film. The thin metal film may be made of, for example, a metal material such as aluminum or chromium. The semi-transparent reflective layer is not limited to a thin metal film, but may be, for example, a dielectric multilayer film, etc.

[0289] The polarizing plate 27P may be located on the side of the second phase difference plate 26P opposite to the side of the second semi-transparent mirror 25P. In other words, the polarizing plate 27P may be located downstream of the second phase difference plate 26P in the direction of emission of the display light. The polarizing plate 27P may transmit a portion of the incident light and absorb or reflect the remainder. In this embodiment, the polarizing plate 27P may be configured to transmit P-wave polarized light and absorb S-wave polarized light. The polarizing plate 27P may be configured to absorb or reflect polarized light having a polarization axis parallel to the polarization axis of the display light (for example, S-wave polarized light, also called third polarization) and transmit polarized light having a polarization axis perpendicular to the polarization axis of the display light (for example, P-wave polarized light, also called fourth polarization). In this case, the positional relationship between the first phase difference plate 24P and the second phase difference plate 26P may be defined such that, when the first phase difference plate 24P and the second phase difference plate 26P are viewed along the Z-axis direction, the lagging axis of the second phase difference plate 26P is perpendicular to the lagging axis of the first phase difference plate 24P. Furthermore, the polarizing plate 27P may be configured to absorb or reflect polarized light having a polarization axis perpendicular to the polarization axis of the display light, and to transmit polarized light having a polarization axis parallel to the polarization axis of the display light. In this case, the positional relationship between the first phase difference plate 24P and the second phase difference plate 26P may be defined such that, when the first phase difference plate 24P and the second phase difference plate 26P are viewed along the Z-axis direction, the lagging axis of the second phase difference plate 26P is parallel to the lagging axis of the first phase difference plate 24P.

[0290] The polarizing plate 27P may have the configuration of a known absorption polarizing plate. Known absorption polarizing plates may be, for example, an iodine-based polarizing plate in which an iodine compound is adsorbed and oriented on a polyvinyl alcohol (PVA) film, or a dye-based polarizing plate in which a dichroic organic dye is adsorbed and oriented on a PVA film. Alternatively, the polarizing plate 27P may have the configuration of a reflective polarizing plate.

[0291] As shown in Figure 51, the display device 8P may have a second semi-transparent mirror 25P and a first phase difference plate 24P and / or a second phase difference plate 26P integrated together, or a polarizing plate 27P and a second phase difference plate 26P integrated together. The polarizing plate 27P may be integrated with the dimming member 4P.

[0292] The optical function of the optical system 3P' will be explained with reference to Figure 36. The display light of S-wave polarized light (first linearly polarized light L1) emitted from the display panel 2P may be transmitted through the first semi-transparent mirror 23P. The display light of the first linearly polarized light L1 may be transmitted through the first phase difference plate 24P and converted into light of first circularly polarized light C1. The light of first circularly polarized light C1 may be incident on the second semi-transparent mirror 25P. A portion of the light of first circularly polarized light C1 (for example, approximately 50%) may be reflected by the second semi-transparent mirror 25P and converted into light of second circularly polarized light C2. The light of second circularly polarized light C2 may be transmitted through the first phase difference plate 24P and converted into light of second linearly polarized light L2 whose polarization direction is perpendicular to that of first linearly polarized light L1 (i.e., P-wave polarized light). The light of second linearly polarized light L2 may be reflected by the first semi-transparent mirror 23P and converted into light of third linearly polarized light L3 whose polarization direction is perpendicular to that of first linearly polarized light L1. The third linearly polarized light L3 may pass through the first phase difference plate 24P and be converted into the third circularly polarized light C3. A portion of the third circularly polarized light C3 (for example, approximately 50%) may pass through the second semi-transparent mirror 25P. The third circularly polarized light C3 that has passed through the second semi-transparent mirror 25P may pass through the second phase difference plate 26P and be converted into the fourth linearly polarized light L4 whose polarization direction is perpendicular to the first linearly polarized light L1 (i.e., it is P-wave polarized). The fourth linearly polarized light L4 may pass through the polarizer 27P and be emitted from the optical system 3P'.

[0293] The remaining portion of the light of the first circularly polarized light C1 (for example, approximately 50%) may pass through the second semi-transparent mirror 25P, then through the second phase difference plate 26P, and be converted into light of the fifth linearly polarized light L5, whose polarization direction is parallel to the first linearly polarized light L1 (i.e., S-wave polarized light). The light of the fifth linearly polarized light L5 is absorbed or reflected by the polarizer plate 27P and does not need to be emitted to the outside. The amount of light (luminance) of the display light emitted from the optical system 3P' may be, for example, approximately 25% of the amount of light (luminance) of the display light emitted from the display panel 2P.

[0294] In the above example, the first phase difference plate 24P and the second phase difference plate 26P are described as quarter-wave plates. However, the first phase difference plate 24P and the second phase difference plate 26P may be other wave plates or combinations thereof, as long as some of the light is absorbed or reflected by the polarizer plate 27P and other light is transmitted through the polarizer plate 27P. For example, the first phase difference plate and the second phase difference plate should be designed to provide the necessary phase difference to the light that is transmitted through the first phase difference plate and the second phase difference plate without being reflected by the second semi-transparent mirror 25P, so that some of the light that is transmitted through the first phase difference plate and the second phase difference plate without being reflected by the second semi-transparent mirror 25P is absorbed or reflected by the polarizer plate 27P. In other words, for example, when the polarization obtained by passing through the first and second phase difference plates without being reflected by the second semi-transparent mirror 25P is taken as the third polarization, the first and second phase difference plates may be other wave plates or combinations thereof, rather than quarter-wave plates, as long as the third polarization is obtained. In this disclosure, the case where the first and second phase difference plates are quarter-wave plates will be explained as an example. Furthermore, the first and second phase difference plates should be such that the light reflected by the second semi-transparent mirror 25P and the first semi-transparent mirror 23P and transmitted through the first and second phase difference plates is transmitted through the polarizer plate 27P, and the necessary phase difference is given to the light reflected by the second semi-transparent mirror 25P and the first semi-transparent mirror 23P and transmitted through the first and second phase difference plates. That is, for example, when the polarization obtained by reflecting light from the second semi-transparent mirror 25P and the first semi-transparent mirror 23P and passing through the first phase difference plate and the second phase difference plate is defined as the fourth polarization, the first phase difference plate and the second phase difference plate may be other wave plates instead of quarter-wave plates, as long as the fourth polarization is obtained. Also, the first phase difference plate 24P and the second phase difference plate 26P may be other wave plates or a combination thereof, instead of quarter-wave plates, as long as some of the light is reflected by the first semi-transparent mirror 23P and the other light is passed through the first semi-transparent mirror 23P. The first phase difference plate only needs to be designed to give the light that has passed through the first phase difference plate the necessary phase difference so that the light that has passed through the first phase difference plate, reflected by the second semi-transparent mirror 25P, and then passed through the first phase difference plate again is reflected by the first semi-transparent mirror 23P.That is, for example, when polarization obtained by passing through the first phase difference plate, reflecting off the second semi-transparent mirror 25P, and then passing through the first phase difference plate again is defined as the fifth polarization, the first and second phase difference plates may be other wave plates instead of quarter-wave plates, as long as the fifth polarization is obtained. Also, the first and second phase difference plates may be film-like materials.

[0295] Each component of the optical system 3P' may maintain its relative position by being held by a holding member (not shown). Air may be interposed between the first semi-transparent mirror 23P and the first phase difference plate 24P. The optical system 3P' may be configured without a component made of a resin material such as polymer between the first semi-transparent mirror 23P and the first phase difference plate 24P. Therefore, deformation of the first semi-transparent mirror 23P when the resin material is cured during the manufacturing process of the optical system 3P' can be reduced, as can positional misalignment between the first semi-transparent mirror 23P and the first phase difference plate 24P. In addition, since resin materials such as polymers have material-specific retardation, not providing a component made of resin material in the optical path of the display light can reduce changes in the polarization state of the display light. As a result, the deterioration of the display quality of the display device 8P can be reduced.

[0296] Even when the display device 8P has an optical system 3P', the transmittance of the dimming member 4P and the luminous intensity of the illuminator 10P can be controlled to reduce the glare experienced by the user 11P and the difficulty in seeing the virtual image V when high-luminosity ambient light is incident on the display device 8P. As a result, the virtual image V can be seen clearly by the user 11P, and the driving safety of the vehicle 50P can be improved.

[0297] Since the optical system 3P' is an on-axis type optical system in which the optical axis of the incident light and the optical axis of the emitted light substantially coincide, the space occupied by the optical system 3P' can be reduced, and as a result, the display device 8P can be miniaturized. In addition, because the optical system 3P' is on-axis, distortion and brightness unevenness of the virtual image V seen by the user 11P can be reduced, and the design of the optical system 3P' is simplified.

[0298] As shown in Figure 37, the display device 8P may have an optical system 3P'' instead of optical system 3P'. The optical system 3P'' differs from optical system 3P' in the configuration of the second semi-transparent mirror, and otherwise has the same configuration as optical system 3P'. Therefore, the same reference numerals are used for components similar to those in optical system 3P', and detailed explanations are omitted.

[0299] The optical system 3P'' may project the display light emitted from the display panel 2P as a virtual image V or a real image. The optical system 3P'' may consist of a first semi-transparent mirror 23P, a first phase difference plate 24P, a second semi-transparent mirror 25P', a second phase difference plate 26P, and a polarizing plate 27P. The first semi-transparent mirror 23P, the first phase difference plate 24P, the second semi-transparent mirror 25P', the second phase difference plate 26P, and the polarizing plate 27P may be arranged in this order in the direction of emission of the display light.

[0300] The second semi-transparent mirror 25P' may have a convex reflective surface 25P'a. The reflective surface 25P'a may be located on the side of the first phase difference plate 24P. The second semi-transparent mirror 25P' is also called a convex half-mirror. The second semi-transparent mirror 25P' may transmit a portion of the incident light (for example, approximately 50%) and reflect the remainder (for example, approximately 50%). The transmittance and reflectance of light incident on the second semi-transparent mirror 25P' are not limited to 50%.

[0301] The second semi-transparent mirror 25P' may be composed of, for example, a substrate and a semi-transparent reflective layer located on the surface of the substrate. The substrate may have a transmittance of 100% or close to 100% for light in the visible light band. The substrate may be made of, for example, inorganic glass, a resin material, etc. The resin material may be, for example, acrylic resin, polycarbonate resin, etc. The semi-transparent reflective layer may be a thin metal film. The thin metal film may be made of, for example, a metal material such as aluminum or chromium. The semi-transparent reflective layer is not limited to a thin metal film, and may be, for example, a dielectric multilayer film, etc.

[0302] The optical system 3P'' may have a polarizing plate 27P and a second phase difference plate 26P and / or a dimming member 4P integrated into it.

[0303] Even when the display device 8P has an optical system 3P'', the transmittance of the dimming member 4P and the luminous brightness of the illuminator 10P can be controlled to reduce the glare experienced by the user 11P and the difficulty in seeing the virtual image V when high-luminosity ambient light is incident on the display device 8P. As a result, the virtual image V can be seen clearly by the user 11P, and the driving safety of the vehicle 50P can be improved.

[0304] The optical system 3P'' may be configured such that the focal length of the second semi-transparent mirror 25P' is greater than the distance between the display panel 2P and the second semi-transparent mirror 25P'. In other words, the optical system 3P'' may be configured such that the second semi-transparent mirror 25P' projects a reduced virtual image Q' (see Figure 39) of the object (i.e., the display surface 2Pa). Furthermore, the optical system 3P'' may be configured such that the focal length of the first semi-transparent mirror 23P is greater than the distance between the virtual image Q' and the first semi-transparent mirror 23P. In other words, the optical system 3P'' may be configured such that the first semi-transparent mirror 23P projects an enlarged virtual image V of the object (i.e., the virtual image Q'). In this case, it becomes possible to adjust the magnification and projection distance of the virtual image V while reducing the thickness of the optical system 3P'' in the third direction (Z-axis direction).

[0305] When the display device 8P has an optical system 3P'', the optical system 3P'' can be made thinner in the third direction (Z-axis direction), thereby providing a thin display device. The thinning of the optical system 3P'' will be explained below with reference to Figures 38 and 39. The first semi-transparent mirror 23P has a concave reflective surface 23Pa, the second semi-transparent mirror 25P has a planar reflective surface 25Pa, and the second semi-transparent mirror 25P' has a convex reflective surface 25P'a. Therefore, in the following explanation, the first semi-transparent mirror 23P may be referred to as a concave mirror, the second semi-transparent mirror 25P as a planar mirror, and the second semi-transparent mirror 25P' as a convex mirror. In addition, the dimensions of the optical systems 3P' and 3P'' in the third direction (Z-axis direction) may be referred to as the thickness of the optical systems 3P' and 3P''.

[0306] Figure 38 illustrates the projection of the virtual image V by the optical system 3P'. In Figure 38, the illuminator 10P and optical components that do not contribute to the projection distance (virtual image distance) and magnification of the virtual image V (first phase difference plate 24P, second phase difference plate 26P, and polarizer plate 27P) are omitted. Also, the concave mirror 23P is positioned in contact with the display panel 2P so that the distance between the display panel 2P and the concave mirror 23P can be considered as "0". In the following explanation, the focal length of the concave mirror 23P is denoted as f, and the distance between the concave mirror 23P and the plane mirror 25P is denoted as a / 2. The distance a / 2 corresponds to the thickness of the optical system 3P'.

[0307] The optical system 3P' may be configured to project a virtual image V by magnifying the virtual image Q of the display surface 2Pa formed by the plane mirror 25P using the concave mirror 23P. As shown in Figure 38, the virtual image Q is located on the opposite side of the concave mirror 23P from the plane mirror 25P, and the distance from the plane mirror 25P may be a / 2. The virtual image Q may be an image of the display surface 2Pa magnified to 1x.

[0308] The virtual image distance b and virtual image magnification m of the virtual image V may be expressed by the following equations (1) and (2), respectively. The virtual image distance b is the distance between the virtual image V and the concave mirror 23P, and the virtual image magnification m may be the magnification ratio of the virtual image V relative to the display surface 2Pa. b = 1 / (1 / a - 1 / f) ... (1) m = b / a ... (2)

[0309]

[0310] Table 1 shows two configuration examples of the optical system 3P'. The units for focal length f, thickness a / 2, and virtual image distance b shown in Table 1 are "mm". Configuration examples 1 and 2 are configured so that the virtual image distance b is 200 mm and the virtual image magnification m is 2 or 3. As shown in Table 1, in order to set the virtual image distance b to 200 mm and the virtual image magnification m to 2, the thickness a / 2 of the optical system 3P' must be 50 mm (see Configuration Example 1). Also, in order to set the virtual image distance b to 200 mm and the virtual image magnification m to 3, the thickness a / 2 of the optical system 3P' must be 33.5 mm (see Configuration Example 2).

[0311] Figure 39 illustrates the projection of a virtual image V by the optical system 3P''. In Figure 39, the illuminator 10P and optical components that do not contribute to the projection distance (virtual image distance) and magnification of the virtual image V (first phase difference plate 24P, second phase difference plate 26P, and polarizer 27P) are omitted. Also, the concave mirror 23P is positioned in contact with the display panel 2P so that the distance between the display panel 2P and the concave mirror 23P can be considered as "0". In the following explanation, the focal length of the convex mirror 25P' is denoted as f', the focal length of the concave mirror 23P is denoted as f'', and the distance between the concave mirror 23P and the convex mirror 25P' is denoted as a' / 2. The distance a' / 2 corresponds to the thickness of the optical system 3P''.

[0312] The optical system 3P'' may be configured to project a virtual image V by magnifying the virtual image Q' of the display surface 2Pa, which is projected by a convex mirror 25P', using a concave mirror 23P. As shown in Figure 39, the virtual image Q' may be located on the opposite side of the concave mirror 23P from the convex mirror 25P'. The distance b' between the virtual image Q' and the convex mirror 25P' may be expressed by the following equation (3). The magnification factor m' of the virtual image Q' relative to the display surface 2Pa may be expressed by the following equation (4). As is clear from equation (3), since b' < a' / 2, the magnification factor m' of the virtual image Q' may be less than 1. Therefore, the virtual image Q' may be a reduced virtual image of the display surface 2Pa. b' = 1 / {1 / f' + 1 / (a' / 2)} ... (3) m' = b' / (a' / 2) ... (4)

[0313] The virtual image distance b'' and virtual image magnification m'' of the virtual image V may be expressed by the following equations (5) and (6). Note that the virtual image distance b'' is the distance between the virtual image V and the concave mirror 23P, and the virtual image magnification m'' may be the magnification ratio of the virtual image V relative to the display surface 2Pa. b'' = 1 / {1 / (a' / 2 + b') - 1 / f''} ... (5) m'' = (b' / (a' / 2)) × b'' / (a' / 2 + b') ... (6)

[0314] Table 2 shows configuration examples 3 and 4 of the optical system 3P''. The units for the focal lengths f', f'', thickness a' / 2, and virtual image distance b'' shown in Table 2 are "mm". Configuration examples 3 and 4 are configured to have a virtual image distance b'' of 200 mm and a virtual image magnification m'' of 2 or 3, similar to configuration examples 1 and 2. As shown in Table 2, with an optical system 3P'' having a thickness a' / 2 of 32 mm, it is possible to have a virtual image distance b'' of 200 mm and a virtual image magnification m'' of 2, similar to configuration example 1 (see configuration example 3). Also, with an optical system 3P'' having a thickness a' / 2 of 25.5 mm, it is possible to have a virtual image distance b'' of 200 mm and a virtual image magnification m'' of 3, similar to configuration example 2 (see configuration example 4). With the optical system 3P'', the thickness can be reduced compared to the optical system 3P''. Therefore, if the display device 8P includes the optical system 3P'', it is possible to make the display device 8P thinner.

[0315]

[0316] The optical system 3P'' may be designed to achieve the given virtual image distance b'', virtual image magnification m'', and thickness a' / 2.

[0317] The design of the optical system 3P'' will be described below with reference to Figure 40. In Figure 40, as in Figure 39, the illuminator 10P, the first phase difference plate 24P, the second phase difference plate 26P, and the polarizer 27P are omitted. Also, the concave mirror 23P is positioned in contact with the display panel 2P so that the distance between the display panel 2P and the concave mirror 23P can be considered as "0". In the following description, the thickness of the optical system 3P'' will be a1, the distance between the convex mirror 25P' and the virtual image Q' will be b1, and the distance between the concave mirror 23P and the virtual image V will be b2. Furthermore, the magnification ratio of the virtual image Q' relative to the display surface 2Pa will be m1, and the magnification ratio of the virtual image V relative to the virtual image Q' will be m2. In addition, the focal length of the convex mirror 25P' will be f1, and the focal length of the concave mirror 23P will be f2.

[0318] The magnification M of the virtual image V on the display surface 2Pa may be expressed as the product of magnification m1 and magnification m2, as shown in equation (7) below. Furthermore, the distance a2 between the concave mirror 23P and the virtual image Q' may be expressed as the sum of thickness a1 and distance b1, as shown in equation (8) below. M = m1 × m2 …(7) a2 = a1 + b1 …(8)

[0319] If we define the thickness a1 of the optical system 3P'' as T and the virtual image distance (i.e., the distance b1 between the concave mirror 23P and the virtual image V) as DP, then the magnification M can be expressed by the following equation (9): M = m1 × m2 = (b1 / a1) × (b2 / a2) = (b1 / T) × (DP / a2) ... (9)

[0320] Substituting equation (10), which holds true for the distance b1 between the convex mirror 25P' and the virtual image Q', into equation (9), we obtain the following equation (11): 1 / a1 = 1 / b1 + 1 / f1 …(10) M = f1 × (1 + D / f2) / (T + f1) …(11)

[0321] Furthermore, substituting the following equation (12), which holds true for the distance b2 between the concave mirror 23P and the virtual image V, into equation (8), we obtain the following equation (13): 1 / a2 = 1 / b2 + 1 / f2 …(12) D × f2 / (D + f2) = T + T × f1 / (T + f1) …(13)

[0322] From equations (9) and (13), the focal length f1 of the convex mirror 25P' and the focal length f2 of the concave mirror 23P can be determined as shown in equations (14) and (15) below. In equation (15), A may be expressed as in equation (16) below. f1 = M × T × T / (D - 2 × M × T) ... (14) f2 = D × A / (M - A) ... (15) A = f1 / (T + f1) ... (16)

[0323] As can be seen from the above calculations, the optical system 3P'' can determine the focal lengths f1 and f2 to achieve the given values ​​of magnification M, thickness T, and virtual image distance D.

[0324] As shown in Figure 41, the display device 8P may have an optical system 3P''' instead of optical systems 3P, 3P', and 3P''. The optical system 3P''' may project the display light emitted from the display panel 2P as a virtual image V or a real image. The optical system 3P''' may consist of a first semi-transparent mirror 28P, a first phase difference plate 29P, a second semi-transparent mirror 30P, a second phase difference plate 31P, and a third semi-transparent mirror 32P. The first semi-transparent mirror 28P, the first phase difference plate 29P, the second semi-transparent mirror 30P, the second phase difference plate 31P, and the third semi-transparent mirror 32P may be arranged in this order in the direction of emission of the display light.

[0325] The first phase difference plate 29P may be located on the side of the reflective surface 28Pa (first reflective surface) of the first semi-transparent mirror 28P. The first phase difference plate 29P may be located away from the display panel 2P in the direction of emission of the display light. The second phase difference plate 31P may be located away from the first phase difference plate 29P in the direction of emission of the display light. The first phase difference plate 29P and the second phase difference plate 31P may be quarter-wave plates.

[0326] The first semi-transparent mirror 28P may be positioned between the display panel 2P and the first phase difference plate 29P. The first semi-transparent mirror 28P may transmit a portion of the incident light and reflect the remainder. The first semi-transparent mirror 28P may transmit S-wave polarized light and reflect P-wave polarized light. The first semi-transparent mirror 17 may also be configured to reflect S-wave polarized light and transmit P-wave polarized light. The first semi-transparent mirror 28P may be a concave mirror having a concave reflective surface 28Pa located on the side of the first phase difference plate 29P, as shown in Figure 41. The first semi-transparent mirror 28P may include a spherical shape, an aspherical shape, or a free-form shape in at least a portion of the reflective surface 28Pa.

[0327] The first semi-transparent mirror 28P may be composed of, for example, a substrate and a plurality of metal nanowires (metal nanowire grids) located on the surface of the substrate. The substrate may have a transmittance of 100% or close to 100% for light in the visible light band. The substrate may be composed of, for example, a resin material, a glass material, etc. The resin material may be, for example, an acrylic resin, a polycarbonate resin, etc. The metal nanowires may be composed of, for example, a metal material such as aluminum, chromium, or titanium oxide. The metal nanowires may be arranged along one direction. The first semi-transparent mirror 28P can transmit light components vibrating in a direction perpendicular to the grid and can reflect light components vibrating in a direction parallel to the grid. The metal nanowire grid may be formed on the surface of the substrate located on the side of the first phase difference plate 29P. In this example, the metal nanowire grid is used to impart a reflective polarization function to the first semi-transparent mirror 28P, but the first semi-transparent mirror 28P may be used as a simple half-mirror and a separate reflective polarizer may be provided.

[0328] The second semi-transparent mirror 30P may be positioned between the first phase difference plate 29P and the second phase difference plate 31P. The second semi-transparent mirror 30P may transmit a portion of the incident light (for example, approximately 50%) and reflect the remainder (for example, approximately 50%). The transmittance and reflectance of the light incident on the second semi-transparent mirror 30P are not limited to 50%. The second semi-transparent mirror 30P may be a plane mirror having a reflective surface 30Pa (second reflective surface) located on the side of the first phase difference plate 29P and a reflective surface 30Pb (third reflective surface) located on the side of the second phase difference plate 31P, as shown in Figure 41. The second semi-transparent mirror 30P is also called a plane half-mirror.

[0329] The second semi-transparent mirror 30P may be composed of, for example, a substrate and a semi-transparent reflective layer located on the surface of the substrate. The substrate may have a transmittance of 100% or close to 100% for light in the visible light band. The substrate may be made of, for example, inorganic glass, a resin material, etc. The resin material may be, for example, acrylic resin, polycarbonate resin, etc. The semi-transparent reflective layer may transmit a portion of the incident light (for example, approximately 50%) and reflect the remainder (for example, approximately 50%). The semi-transparent reflective layer may be a thin metal film. The thin metal film may be made of, for example, a metal material such as aluminum or chromium. The semi-transparent reflective layer is not limited to a thin metal film, but may be, for example, a dielectric multilayer film. The first phase difference plate 29P and the second phase difference plate 31P may be fixed to the second semi-transparent mirror 30P with an optically transparent adhesive such as OCA (Optically Clear Adhesive). The adhesive may be a material with low retardation.

[0330] The third semi-transparent mirror 32P may be located on the side of the second phase difference plate 31P opposite to the side of the second semi-transparent mirror 30P. The third semi-transparent mirror 32P may be located downstream of the second phase difference plate 31P in the direction of emission of the display light. The third semi-transparent mirror 32P may transmit a portion of the incident light and reflect the remainder. The third semi-transparent mirror 32P may reflect S-wave polarized light and transmit P-wave polarized light. Alternatively, the third semi-transparent mirror 32P may be configured to transmit S-wave polarized light and reflect P-wave polarized light. As shown in Figure 41, the third semi-transparent mirror 32P may be a concave mirror having a concave reflective surface 32Pa (fourth reflective surface) located on the side of the second phase difference plate 31P. At least a portion of the reflective surface 32Pa of the third semi-transparent mirror 32P may include a spherical shape, an aspherical shape, or a free-form surface shape.

[0331] The third semi-transparent mirror 32P may be composed of, for example, a substrate and a plurality of metal nanowires (metal nanowire grids) located on the surface of the substrate. The substrate may have a transmittance of 100% or close to 100% for light in the visible light band. The substrate may be composed of, for example, a resin material, a glass material, etc. The resin material may be, for example, acrylic resin, polycarbonate resin, etc. The metal nanowires may be composed of, for example, a metal material such as aluminum, chromium, titanium oxide, etc. The metal nanowires may be arranged along one direction. The third semi-transparent mirror 32P can transmit light components vibrating in a direction perpendicular to the grid and can reflect light components vibrating in a direction parallel to the grid. The metal nanowire grid may be formed on the surface of the substrate located on the side of the second phase difference plate 31P. In this example, the metal nanowire grid is used to impart a reflective polarization function to the third semi-transparent mirror 32P, but the third semi-transparent mirror 32P may be used as a simple half-mirror and a separate reflective polarizer may be provided.

[0332] The optical system 3P''' may be formed by integrating the second semi-transparent mirror 30P and the first phase difference plate 29P and / or the second phase difference plate 31P, as shown in Figure 52.

[0333] Referring to Figure 41, the optical function of the optical system 3P'''' will be explained. Display light emitted from the display panel 2P may travel along path P1 or path P2 and be emitted to the outside. First, the light traveling along path P1 will be explained. The S-wave polarized (first linearly polarized) display light emitted from the display panel 2P may pass through the first semi-transparent mirror 28P. The light of the first linearly polarized L1 passes through the first phase difference plate 29P and is converted into light of the first circularly polarized C1. The light of the first circularly polarized C1 may be incident on the second semi-transparent mirror 30P. A portion of the light of the first circularly polarized C1 (for example, approximately 50%) may be reflected by the second semi-transparent mirror 30P and converted into light of the second circularly polarized C2. The light of the second circularly polarized C2 may pass through the first phase difference plate 29P and be converted into light of the second linearly polarized L2, whose polarization direction is perpendicular to the first linearly polarized L1 (i.e., P-wave polarized). The light of the second linearly polarized light L2 may be reflected by the first semi-transparent mirror 28P and converted into the light of the third linearly polarized light L3, whose polarization direction is perpendicular to the first linearly polarized light L1 (i.e., it is P-wave polarized). The third linearly polarized light L3 may be transmitted through the first phase difference plate 29P and converted into the light of the third circularly polarized light C3. The light of the third circularly polarized light C3 may be incident on the second semi-transparent mirror 30P. A portion of the light of the third circularly polarized light C3 (for example, approximately 50%) may be transmitted through the second semi-transparent mirror 30P. The light of the third circularly polarized light C3 that has been transmitted through the second semi-transparent mirror 30P may be transmitted through the second phase difference plate 31P and converted into the light of the fourth linearly polarized light L4, whose polarization direction is perpendicular to the first linearly polarized light L1 (i.e., it is P-wave polarized). The light of the fourth linearly polarized light L4 may be transmitted through the third semi-transparent mirror 32P and emitted from the optical system 3P'''.

[0334] Next, we will describe the light traveling along path P2. The remainder (for example, approximately 50%) of the light of the first circularly polarized light C1 incident on the second semi-transparent mirror 30P may pass through the second semi-transparent mirror 30P. The light of the first circularly polarized light C1 that has passed through the second semi-transparent mirror 30P may pass through the second phase difference plate 31P and be converted into light of the fifth linearly polarized light L5, whose polarization direction is parallel to the first linearly polarized light L1 (i.e., S-wave polarized light). The light of the fifth linearly polarized light L5 may be reflected by the third semi-transparent mirror 32P and converted into light of the sixth linearly polarized light L6, whose polarization direction is parallel to the first linearly polarized light L1 (i.e., S-wave polarized light). The light of the sixth linearly polarized light L6 may pass through the second phase difference plate 31P and be converted into light of the fourth circularly polarized light C4. The light of the fourth circularly polarized light C4 is incident on the second semi-transparent mirror 30P. A portion of the light from the fourth circularly polarized light C4 (for example, approximately 50%) may be reflected by the second semi-transparent mirror 30P and converted into the light from the fifth circularly polarized light C5. The light from the fifth circularly polarized light C5 may pass through the second phase difference plate 31P and be converted into the light from the seventh linearly polarized light L7, whose polarization direction is perpendicular to the first linearly polarized light L1 (i.e., it is P-wave polarized). The light from the seventh linearly polarized light L7 may pass through the third semi-transparent mirror 32P and exit from the optical system 3P'''.

[0335] As described above, in the optical system 3P''', the display light emitted from the display panel 2P may travel along path P1 or path P2 and be emitted from the optical system 3P'''. For this reason, the amount of light (luminance) emitted from the optical system 3P''' may be, for example, approximately 50% of the amount of light (luminance) of the display light emitted from the display panel 2P. The optical system 3P''' can improve light utilization efficiency compared to optical systems 3P, 3P', and 3P'', and can improve the luminance of the light emitted from the optical system 3P'''.

[0336] The first phase difference plate 29P and the second phase difference plate 31P only need to be given the necessary phase difference to the display light transmitted through the first phase difference plate 29P and the second phase difference plate 31P so that the light transmitted through the first phase difference plate 29P and the second phase difference plate 31P is reflected by the first semi-transparent mirror 28P, the second semi-transparent mirror 30P, and the third semi-transparent mirror 32P. For example, a phase difference of 1 / 4 wavelength may be given to the polarization plane of the incident light (the polarization plane in the direction of electric field vibration). As a result, a portion of the display light emitted from the display panel 2P can be reflected by the first semi-transparent mirror 28P and the second semi-transparent mirror 30P, transmitted through the second semi-transparent mirror 30P, reflected again by the third semi-transparent mirror 32P, and transmitted through the third semi-transparent mirror 32P.

[0337] In the above example, the first phase difference plate 29P and the second phase difference plate 31P are described as quarter-wave plates. However, the first phase difference plate 29P and the second phase difference plate 31P may be other wave plates or a combination thereof, as long as some of the light is reflected by the first semi-transparent mirror 28P and the other light is transmitted through the first semi-transparent mirror 28P. Furthermore, the first phase difference plate 29P and the second phase difference plate 31P may be other wave plates or a combination thereof, as long as some of the light is reflected by the third semi-transparent mirror 32P and the other light is transmitted through the third semi-transparent mirror 32P.

[0338] Even when the display device 8P has an optical system 3P'''', by controlling the transmittance of the dimming member 4P and the luminous intensity of the illuminator 10P, the glare experienced by the user 11P and the difficulty in seeing the virtual image V when high-luminosity ambient light is incident on the display device 8P can be reduced. As a result, the virtual image V can be seen clearly by the user 11P, and the driving safety of the vehicle 50P can be improved.

[0339] The first semi-transparent mirror 28P, the first phase difference plate 29P, the second semi-transparent mirror 30P, the second phase difference plate 31P, and the third semi-transparent mirror 32P may be held by a holding member (not shown) to maintain their relative positions. Air may be interposed between the first semi-transparent mirror 28P and the first phase difference plate 29P, and between the third semi-transparent mirror 32P and the second phase difference plate 31P. The optical system 3P''' may be configured without providing members made of resin material such as polymer between the first semi-transparent mirror 28P and the first phase difference plate 29P, and between the third semi-transparent mirror 32P and the second phase difference plate 31P. This reduces deformation of the first semi-transparent mirror 28P and the third semi-transparent mirror 32P, misalignment between the first semi-transparent mirror 28P and the first phase difference plate 29P, misalignment between the third semi-transparent mirror 32P and the second phase difference plate 31P, etc. As a result, the deterioration of the display quality of the display device 8P can be reduced.

[0340] Since the optical system 3P''' is an on-axis type optical system in which the optical axis of the incident light and the optical axis of the emitted light substantially coincide, the space occupied by the optical system 3P''' can be reduced, and as a result, the display device 8P can be miniaturized. In addition, because the optical system 3P''' is on-axis, distortion and brightness unevenness of the virtual image V seen by the user 11P can be reduced, and the design of the optical system 3P''' becomes easier.

[0341] The optical system 3P''' may be configured such that the focal length of the first semi-transparent mirror 28P and the focal length of the third semi-transparent mirror 32P are approximately equal, and the second semi-transparent mirror 30P is a plane mirror. In this case, the virtual image formed by light traveling along path P1 and the virtual image formed by light traveling along path P2 substantially coincide, thereby improving the display quality of the display device 8P. The focal lengths of the first semi-transparent mirror 28P and the third semi-transparent mirror 32P may be 0.9 times or more and 1.1 times or less than or equal to the other, or 0.95 times or more and 1.05 times or less.

[0342] The following describes another example of a display device 8P having an optical system 3P (see Figure 27). The display device 8P may be configured such that, when the user 11P is positioned in front of the display device 8P, the light of the second linearly polarized element L2 is reflected by the reflective polarizer 15P and not emitted from the display device 8P. The display device 8P having an optical system 3P may be configured such that, when viewed from the front of the display device 8P, the transmission axis of the polarizer on the front side (user 11P side) of the display panel 2P and the transmission axis of the reflective polarizer 15P are orthogonal (in a crossed nicol arrangement). As a result, the light of the second linearly polarized element L2 may be emitted from the display device 8P, and the light of the fourth linearly polarized element L4 may be emitted from the display device 8P. In other words, the user 11P may not directly view the display panel 2P, but may view the reflected image reflected by the semitransparent mirror 13P as a virtual image V.

[0343] If the user 11P is not positioned directly in front of the display device 8P, the crossed nicol arrangement between the transmission axis of the front polarizer of the display panel 2P and the transmission axis of the reflective polarizer 15P may be disrupted, causing some of the light of the second linearly polarized L2 to pass through the reflective polarizer 15P. As a result, the user 11P may be able to see both the real image directly on the display panel 2P and the virtual image V reflected by the semitransparent mirror 13P, which may degrade the display quality of the display device 8P.

[0344] As shown in Figures 42 and 43, the display device 8P may have a third phase difference plate 33P located between the display panel 2P and the reflective polarizing plate 15P. In this case, even when the user 11P is not positioned in front of the display device 8P, the relative angle between the transmission axis of the front polarizing plate of the display panel 2P and the transmission axis of the reflective polarizing plate 15P can be brought closer to a crossed nicol arrangement, thereby reducing the degradation of the display quality of the display device 8P. The third phase difference plate 33P may be a half-wave plate, a quarter-wave plate, an eighth-wave plate, a sixteenth-wave plate, or any other wave plate that imparts a phase difference. A half-wave plate is also called a half-wave plate. The optical axis of the third phase difference plate 33P may be approximately parallel or approximately perpendicular to the transmission axis of the reflective polarizing plate 15P.

[0345] As shown in Figures 42 and 43, the display device 8P may further have a fourth phase difference plate 34P located between the display panel 2P and the reflective polarizing plate 15P. In this case, even when the user 11P is not positioned in front of the display device 8P, the relative angle between the transmission axis of the front polarizing plate of the display panel 2P and the transmission axis of the reflective polarizing plate 15P can be brought closer by the crossed nicol arrangement, further reducing the deterioration of the display quality of the display device 8P. The fourth phase difference plate 34P may be a half-wave plate, a quarter-wave plate, an eighth-wave plate, a sixteenth-wave plate, etc., or any other wave plate that imparts a phase difference. The optical axis of the fourth phase difference plate 34P may be substantially parallel or substantially perpendicular to the transmission axis of the reflective polarizing plate 15P.

[0346] The third phase difference plate 33P and the fourth phase difference plate 34P only need to be positioned between the display panel 2P and the reflective polarizing plate 15P, and their positions can be arbitrary. If no other optical elements are positioned between the third phase difference plate 33P and the fourth phase difference plate 34P, the third phase difference plate 33P and the fourth phase difference plate 34P may be in contact with each other. This reduces the thickness of the optical system 3P.

[0347] The third phase difference plate 33P and the fourth phase difference plate 34P may be a quarter-wave plate and the other a half-wave plate. In this case, the deterioration of the display quality of the display device 8P can be effectively reduced. The third phase difference plate 33P and the fourth phase difference plate 34P may both be half-wave plates. In this case, the deterioration of the display quality of the display device 8P can be reduced more effectively.

[0348] Figures 44A, 44B, 44C, and 44D show a Poincaré sphere illustrating the optical functions (effects on the polarization state of light) of the third phase difference plate 33P and the fourth phase difference plate 34P when the third phase difference plate 33P and the fourth phase difference plate 34P are half-wave plates. Figures 44A and 44B illustrate the optical function of the third phase difference plate 33P, and Figures 44C and 44D illustrate the optical function of the fourth phase difference plate 34P. Figures 44A and 44C show the Poincaré sphere viewed from the North Pole (S3 axis direction), and Figures 44B and 44D show the Poincaré sphere viewed from the side (S1 axis direction). In Figures 44A, 44B, 44C, and 44D, S ＬＣＤshows the polarization state of light immediately after it exits the display panel 2P. S ３３ shows the polarization state of light that has passed through the third retardation plate 33P, S ３４ shows the polarization state of light that has passed through the fourth retardation plate 34P. S ３４ It can be said that it shows the polarization state of light immediately before entering the reflective polarizing plate 15P. S ＲＰ shows the polarization state of light that passes through the reflective polarizing plate 15P with a substantially 100% transmittance, S ＡＰ is S ＲＰ is the antipodal point of S (a point symmetric with respect to the center of the Poincare sphere). S ３４ When S ＡＰ is located at S ＡＰ or in the vicinity of S

[0349] As shown in FIGS. 44C and 44D, when the third retardation plate 33P and the fourth retardation plate 34P are half-wave plates, S ３４ is substantially located at S ＡＰ Therefore, it is possible to reduce the user 11P from visually recognizing the real image directly viewing the display panel 2P, and to reduce the degradation of the display quality of the display device 8P.

[0350] FIGS. 45A, 45B, 45C, and 45D are Poincare spheres showing the optical functions of the third retardation plate 33P and the fourth retardation plate 34P when the third retardation plate 33P is a quarter-wave plate and the fourth retardation plate 34P is a half-wave plate. FIGS. 45A and 45B are diagrams for explaining the optical function of the third retardation plate 33P, and FIGS. 45C and 45D are diagrams for explaining the optical function of the fourth retardation plate 34P. FIGS. 45A and 45C show views of the Poincare sphere seen from the north pole (S3 axis direction), and FIGS. 45B and 45D show views of the Poincare sphere seen from the side (S1 axis direction). S ＬＣＤ S ３３ S ３４ S ＲＰ S ＡＰ and S

[0351] As shown in Figures 45C and 45D, when the third phase difference plate 33P is a quarter-wave plate and the fourth phase difference plate 34P is a half-wave plate, S ３４ is, S ＡＰ It is located in the vicinity of the display panel 2P. Therefore, the likelihood of the user 11P directly viewing the actual image on the display panel 2P can be reduced, and the degradation of the display quality of the display device 8P can be reduced.

[0352] Figure 46 is a graph showing the relationship between the light transmittance of an optical system formed by inserting a third phase difference plate 33P and a fourth phase difference plate 34P between polarizing plates PP1 and PP2 whose transmission axes are mutually orthogonal, and the phase difference between the third phase difference plate 33P and the fourth phase difference plate 34P. Figure 46 shows the results obtained by simulation. The incident light was green light with a wavelength λ of 550 nm. Polarizing plate PP1, the third phase difference plate 33P, the fourth phase difference plate 34P, and polarizing plate PP2 are arranged in this order in the direction of propagation of the incident light. Polarizing plate PP1 is modeled after the front polarizing plate of the display panel 2P, and polarizing plate PP2 is modeled after the reflective polarizing plate 15P.

[0353] The solid line in the graph of Figure 46 shows the transmittance when the phase difference of the fourth phase difference plate 34P is fixed at 0 nm and the phase difference of the third phase difference plate 33P is varied, with the transmittance being minimum when the phase difference of the third phase difference plate 33P is approximately 275 nm (half the wavelength λ of the incident light). The dashed line in the graph of Figure 46 shows the transmittance when the phase difference of the third phase difference plate 33P is fixed at 270 nm and the phase difference of the fourth phase difference plate 34P is varied, with the transmittance being minimum when the phase difference of the fourth phase difference plate 34P is approximately 275 nm (half the wavelength of the incident light).

[0354] From the simulation results shown in Figure 46, it can be seen that when the third phase difference plate 33P and the fourth phase difference plate 34P are half-wave plates, the display device 8P can effectively reduce the amount of real images that the user 11P directly sees on the display panel 2P, and thus effectively reduce the degradation of the display quality of the display device 8P. Furthermore, even when the phase difference of the fourth phase difference plate 34P is fixed to 0 nm (i.e., when only the third phase difference plate 33P is present), if the third phase difference plate 33P can impart a phase difference greater than 0 nm (not 0 nm) to the light incident on the third phase difference plate 33P, it can effectively reduce the amount of real images that the user 11P directly sees on the display panel 2P, and thus effectively reduce the degradation of the display quality of the display device 8P.

[0355] The same may apply to the display device 8P (see Figures 36 and 37) having optical systems 3P' and 3P'' as to the optical system 3P. The display device 8P in Figures 36 and 37 may have a third phase difference plate 33P located between the display panel 2P and the polarizing plate 27P. In this case, the likelihood of the user 11P directly viewing the real image on the display panel 2P can be reduced, and the deterioration of the display quality of the display device 8P can be reduced. The display device 8P in Figures 36 and 37 may further have a fourth phase difference plate 34P located between the display panel 2P and the polarizing plate 27P. In this case, the likelihood of the user 11P directly viewing the real image on the display panel 2P can be further reduced, and the deterioration of the display quality of the display device 8P can be further reduced. The third phase difference plate 33P and the fourth phase difference plate 34P may be a half-wave plate, a quarter-wave plate, an eighth-wave plate, a sixteenth-wave plate, etc., or other wave plates that impart phase difference. The third phase difference plate 33P and the fourth phase difference plate 34P may be a quarter-wave plate and the other a half-wave plate. In this case, the degradation of the display quality of the display device 8P can be effectively reduced. The third phase difference plate 33P and the fourth phase difference plate 34P may both be half-wave plates. In this case, the degradation of the display quality of the display device 8P can be reduced more effectively. The third phase difference plate 33P and the fourth phase difference plate 34P only need to be located between the display panel 2P and the polarizing plate 27P, and their positions can be arbitrary.

[0356] The second semi-transparent mirror 25P' of the optical system 3P'' (see Figure 37) may be composed of a holographic optical element. In this case, as shown in Figure 47, the optical function of the second semi-transparent mirror 25P' can be realized by a flat optical element, and the thickness of the second semi-transparent mirror 25P' in the third direction (Z-axis direction) can be reduced. As a result, the display device 8P can be miniaturized in the third direction. Furthermore, because the second semi-transparent mirror 25P' is a flat optical element, the distance between the second semi-transparent mirror 25P' and the first phase difference plate 24P and / or the second phase difference plate 26P can be reduced, or the second semi-transparent mirror 25P' and the first phase difference plate 24P and / or the second phase difference plate 26P can be brought into contact, so the display device 8P can be further miniaturized in the third direction. The first semi-transparent mirror 23P of the display device 8P in Figure 37 may be composed of a holographic optical element. In this case, as shown in Figure 47, the optical function of the first semi-transparent mirror 23P can be realized by a flat optical element, and the thickness of the first semi-transparent mirror 23P in the third direction can be reduced. As a result, the display device 8P can be miniaturized in the third direction.

[0357] The first semi-transparent mirror 23P (see Figure 36) of the optical system 3P' may be composed of a holographic optical element. In this case, as shown in Figure 48, the optical function of the first semi-transparent mirror 23P can be realized by a flat optical element, and the thickness of the first semi-transparent mirror 23P in the third direction can be reduced. As a result, the display device 8P in Figure 36 can be miniaturized in the third direction.

[0358] The semi-transparent mirror 13P of the optical system 3P (see Figure 27) may be composed of a holographic optical element. In this case, the optical function of the semi-transparent mirror 13P can be realized by a flat optical element, and the thickness of the semi-transparent mirror 13P in the third direction can be reduced. As a result, the display device 8P in Figure 27 can be miniaturized in the third direction.

[0359] The first semi-transparent mirror 28P and the third semi-transparent mirror 32P (see Figure 41) of the optical system 3P''' may be composed of holographic optical elements. In this case, the optical functions of the first semi-transparent mirror 28P and the third semi-transparent mirror 32P can be realized by flat optical elements, and the thickness of the first semi-transparent mirror 28P and the third semi-transparent mirror 32P in the third direction can be reduced. As a result, the display device 8P in Figure 41 can be miniaturized in the third direction.

[0360] A holographic optical element may, for example, have an interference fringe pattern and be configured to diffract incident light in a predetermined direction.

[0361] Other examples of the display devices of this disclosure will be described. Configurations similar to those of display device 8P are given the same reference numerals as those of display device 8P, and detailed descriptions will be omitted.

[0362] The display device 35P in this example may include a display panel 2P, an optical system 36P, a dimming member 4P, and a housing 37P, as shown in Figures 53 and 54.

[0363] The display panel 2P has a display surface 2Pa, and an image may be displayed on the display surface 2Pa. The optical system 36P may project the display light emitted from the display panel 2P as a virtual image V or a real image into the field of view of the user 11P. The optical system 36P may be the optical system 3P (see Figures 27, 29, 34, 35, 42, 43, 50), the optical system 3P' (see Figures 36, 48, 51), the optical system 3P'' (see Figures 37, 47), or the optical system 3P''' (see Figures 41, 52). Figures 53 and 54 show the case where the optical system 36P is the optical system 3P shown in Figures 42 and 43.

[0364] The housing 37P may house the display panel 2P and the optical system 36P. The housing 37P may hold the display panel 2P and the optical system 36P. If the display device 35P includes an irradiator 10P, the housing 37P may house the irradiator 10P and hold the irradiator 10P. The housing 37P may have a viewing section that allows the inside of the housing 37P to be seen from the outside of the housing 37P. The housing 37P may have a viewing section that allows the inside of the housing 37P to be seen from the outside of the housing 37P. The housing 37P may have a window (aperture) 38P that transmits light emitted from the optical system 36P. The window 38P may function as a viewing section. The display device 35P may be positioned such that when the window 38P of the housing 37P is viewed, the window 38P and the display panel 2P overlap. The display device 35P may be positioned such that when the window 38P of the housing 37P is viewed, the window 38P and the optical system 36P overlap. Alternatively, the display device 35P may be positioned such that when the window 38P of the housing 37P is viewed, the display panel 2P and the optical system 36P overlap. In this case, the space occupied by the display device 35P can be reduced, and as a result, the display device 35P can be miniaturized. Furthermore, in the display device 35P, the display light emitted from the display panel 2P propagates substantially along one axis and is formed as a virtual image V or a real image. Therefore, distortion, brightness unevenness, etc. of the virtual image V or real image viewed by the user 11P can be reduced, and the design of the optical system 36P can be simplified.

[0365] The optical system 36P may have a third phase difference plate 33P and a fourth phase difference plate 34P. This allows the relative angle between the transmission axis of the front polarizer plate of the display panel 2P and the transmission axis of the reflective polarizer plate 15P to be brought closer to a cross-nicol arrangement, even when the user 11P is not positioned in front of the display device 35P, thereby reducing the degradation of the display quality of the display device 35P. The third phase difference plate 33P and the fourth phase difference plate 34P may be integrated with each other as shown in Figures 53 and 54, and may be located on the side of the semi-transparent mirror 13P of the second phase difference plate 14P, but are not limited to this. The third phase difference plate 33P and the fourth phase difference plate 34P may be located at different positions in the optical system 36P.

[0366] The third phase difference plate 33P and the fourth phase difference plate 34P may be, but are not limited to, half-wave plates. The third phase difference plate 33P and the fourth phase difference plate 34P may be quarter-wave plates, eighth-wave plates, sixteenth-wave plates, etc., or other wave plates that impart a phase difference. The third phase difference plate 33P and the fourth phase difference plate 34P may be wave plates that impart the same phase difference, or they may be wave plates that impart different phase differences. The optical axis of the third phase difference plate 33P may be substantially parallel or substantially perpendicular to the transmission axis of the reflective polarizer 15P.

[0367] The housing 37P may have a member positioned in the window 38P that makes the inside of the housing 37P visible from the outside of the housing 37P. The housing 37P may have a member positioned in the window 38P that makes the inside of the housing 37P visible from the outside of the housing 37P. The housing 37P may have a light-transmitting plate 39P positioned in the window 38P, as shown in Figures 53 and 54. The light-transmitting plate 39P may transmit light emitted from the optical system 36P. The light-transmitting plate 39P may at least partially block the window 38P. The light-transmitting plate 39P may be made of, for example, glass, resin, etc. The member positioned in the window 38P that makes the inside of the housing 37P visible from the outside of the housing 37P (for example, the light-transmitting plate 39P) may function as a viewing section. A component (for example, a light-transmitting plate 39P) that makes the inside of the housing 37P, located in the window 38P, visible from the outside of the housing 37P may function as a viewing section.

[0368] The dimming member 4P may be attached to the housing 37P. The dimming member 4P may be located downstream of the light-transmitting plate 39P in the direction of light emission of the display light, as shown in Figures 53 and 54, but is not limited to this. The dimming member 4P may be located downstream of the optical system 36P and upstream of the light-transmitting plate 39P in the direction of light emission of the display light.

[0369] The optical system 36P may have at least one moth-eye structure film (anti-reflective film) 40P. Figures 53 and 54 show a case where the optical system 36P has a moth-eye structure film 40P located on the side of the semi-transparent mirror 13P of the first phase difference plate 12P (moth-eye structure film 21P shown in Figure 35) and a moth-eye structure film 40P located on the side of the semi-transparent mirror 13P of the fourth phase difference plate 34P. By having the moth-eye structure film 40P in the optical system 36P, unwanted light and ambient light are reflected by the optical system 36P and the incidence of them into the eyes of the user 11P can be reduced.

[0370] The reflective polarizing plate 15P, the second phase difference plate 14P, the third phase difference plate 33P, the fourth phase difference plate 34P, and the moth-eye structure film 40P may be integrated with the light-transmitting plate 39P. This makes it possible to make the display device 35P thinner in the depth direction (Z-axis direction). Furthermore, deformation of the reflective polarizing plate 15P, the second phase difference plate 14P, the third phase difference plate 33P, the fourth phase difference plate 34P, the moth-eye structure film 40P, and the light-transmitting plate 39P can be reduced.

[0371] The virtual image V may be formed on the side farther from the display device 35P as viewed from the user 11P. The virtual image V may be formed inside the housing 37P or outside the housing 37P. The virtual image V may be formed on the side farther from the display panel 2P as viewed from the user 11P, or on the side closer to the display panel 2P. The virtual image V may be formed on the side farther from the window 38P as viewed from the user 11P, or on the side closer to the window 38P. The virtual image V may be formed on the side farther from the dimming member 4P as viewed from the user 11P, or on the side closer to the dimming member 4P.

[0372] The real image may be formed on the side closer to the display device 35P as viewed from the user 11P. The real image may be formed inside the housing 37P or outside the housing 37P. The real image may be formed on the side farther from the display panel 2P as viewed from the user 11P, or on the side closer to the display panel 2P. The real image may be formed on the side farther from the window 38P as viewed from the user 11P, or on the side closer to the window 38P. The real image may be formed on the side farther from the dimming member 4P as viewed from the user 11P, or on the side closer to the dimming member 4P.

[0373] The above describes the case where the display system 1P is an electronic rearview mirror, but it is not limited to this. The display system 1P may be configured as an electronic side mirror, as shown in Figure 49. The display system 1P may display an image of the rear side of the vehicle 50P, captured by the imaging unit 22P, as a virtual image V for the user 11P. The display device 8P may be placed on the left and right A-pillars of the vehicle 50P. The imaging unit 22P may be placed in the same position as a mirror-type door mirror. The display system 1P may be mounted on the cluster in the instrument panel and configured to display an image showing driving-related information such as vehicle speed and engine speed as a virtual image V for the user 11P. The display system 1P may constitute the CID (Center Information Display) of the vehicle 50P and display an image showing information such as navigation, audio equipment, air conditioning equipment, etc., as a virtual image V for the user 11P. Display system 1P constitutes the PID (Passenger Information Display) of vehicle 50P and may allow passengers of vehicle 50P to view entertainment content as virtual images V, and may also allow passengers to view images showing information related to audio equipment, air conditioning equipment, etc., as virtual images V. Display system 1P constitutes the RSE (Rear Seat Entertainment) of vehicle 50P and may allow passengers in the rear seats of vehicle 50P to view entertainment content as virtual images V, and may also allow passengers in the rear seats to view images showing information related to audio equipment, air conditioning equipment, etc., as virtual images V.

[0374] Although embodiments of the present disclosure have been described in detail above, the present disclosure is not limited to the embodiments described above. Various modifications and improvements are possible without departing from the gist of the present disclosure, and embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the invention of the present disclosure. For example, the functions etc. included in each component etc. can be rearranged in a logically consistent manner, and multiple components etc. can be combined into one or divided. In other words, it should be noted that it is easy for those skilled in the art to make various modifications or alterations based on the present disclosure. Furthermore, it should be noted that these modifications, alterations or alterations are included in the scope of the present disclosure.

[0375] The display device, display system, and vehicle of this disclosure can be implemented in the following embodiments (1) to (20).

[0376] (1) A display device comprising a wall member capable of housing a display panel that emits display light, and a housing having a light-transmitting plate through which the display light passes as a viewing section, and a dimming member disposed outside the light-transmitting plate and having a light transmittance smaller than that of the light-transmitting plate.

[0377] (2) The display device according to (1) above, further comprising a reflective member that reflects at least a portion of the display light and is housed in the housing, wherein the dimming member is positioned outside the reflective member and has a light transmittance lower than that of the reflective member.

[0378] (3) The display device according to (1) or (2), further comprising a display panel that emits the display light and is housed in the housing.

[0379] (4) The display device according to any one of (1) to (3) above, wherein the transmittance of the dimming member is variable.

[0380] (5) The display device according to (2) above, wherein the reflective member is a reflective polarizing member.

[0381] (6) The display device according to (4) above, comprising a detection unit for detecting the brightness of ambient light incident on the dimming member, and a control unit, wherein the control unit has a function for controlling the transmittance of the dimming member based on the brightness detected by the detection unit.

[0382] (7) The display device according to (6), wherein the control unit controls the transmittance of the dimming member to be lower as the brightness detected by the detection unit increases.

[0383] (8) The display device according to (4) above, comprising: a detection unit for detecting the brightness of ambient light incident on the dimming member; and a control unit, wherein the control unit has a function for controlling the brightness of the image displayed on the display panel and the transmittance of the dimming member based on the brightness detected by the detection unit.

[0384] (9) The display device according to (4) above, comprising a detection unit for detecting the brightness of ambient light incident on the dimming member and a control unit, wherein the control unit controls the brightness of the image displayed on the display panel to be increased and the transmittance of the dimming member to be decreased as the brightness detected by the detection unit increases.

[0385] (10) The display device according to (4) above, comprising: an acquisition unit for acquiring the illuminance of the surrounding environment of the display device; a detection unit for detecting the brightness of ambient light incident on the dimming member; and a control unit, wherein the control unit has a function for controlling the brightness of the image to be displayed on the display panel and the transmittance of the dimming member based on the illuminance acquired by the acquisition unit and the brightness detected by the detection unit.

[0386] (11) The display device according to (10), wherein the control unit controls the brightness of the image displayed on the display panel to be lowered and the transmittance of the dimming member to be higher the higher the illuminance detected by the acquisition unit, and controls the brightness of the image displayed on the display panel to be higher and the transmittance of the dimming member to be lower the higher the brightness detected by the detection unit.

[0387] (12) The display device according to any one of (1) to (11) above, further comprising an irradiator that irradiates light onto the side of the display panel opposite to the display surface.

[0388] (13) The display device according to (12), further comprising a control unit having a function for controlling at least one of the image displayed on the display panel and the irradiator.

[0389] (14) A mobile body equipped with the display device described in (13) above.

[0390] (15) A display device according to any one of (2) to (9) above, comprising: a first phase difference plate located on the side of the display surface of the display panel; a second phase difference plate located on the opposite side of the first phase difference plate from the display panel; and a semi-transparent mirror disposed between the first phase difference plate and the second phase difference plate and having a reflective surface on the side of the second phase difference plate, wherein the reflective member is located on the opposite side of the semi-transparent mirror from the second phase difference plate, transmits first linearly polarized light and reflects second linearly polarized light, the first phase difference plate and the second phase difference plate convert the display light to the second linearly polarized light, and the second phase difference plate converts the second linearly polarized light, reflected by the reflective member, to the first linearly polarized light before it is reflected by the semi-transparent mirror and incident on the reflective member again.

[0391] (16) The display panel emits display light and is located on the display surface side of the display panel and transmits first linearly polarized light and reflects second linearly polarized light; a second semi-transparent mirror is located on the opposite side of the display panel from the first semi-transparent mirror and has a reflective surface; a first phase difference plate is located between the first semi-transparent mirror and the second semi-transparent mirror and converts the display light that has passed from the side of the first semi-transparent mirror and reflected by the second semi-transparent mirror into the second linearly polarized light; a second phase difference plate is located on the opposite side of the first phase difference plate from the second semi-transparent mirror and converts the light that has been reflected by the second semi-transparent mirror and passed through the first phase difference plate into the third linearly polarized light, and the light that has passed through the display light without being reflected by the second semi-transparent mirror into the fourth linearly polarized light; and a second phase difference plate is located on the opposite side of the second semi-transparent mirror from the second phase difference plate and has the fourth A display device according to any one of (2) to (9) above, comprising a polarizing plate that transmits the third linearly polarized light more than linearly polarized light.

[0392] (17) A display device according to any one of (2) to (9) above, comprising: a first phase difference plate located on the side of the display surface of the display panel; a second phase difference plate located on the opposite side of the display panel from the first phase difference plate; a first semi-transparent mirror disposed between the display panel and the first phase difference plate and having a first reflective surface on the side of the first phase difference plate; a second semi-transparent mirror disposed between the first phase difference plate and the second phase difference plate and having a second reflective surface on the side of the first phase difference plate and a third reflective surface on the side of the second phase difference plate; and a third semi-transparent mirror having a fourth reflective surface on the side of the second phase difference plate.

[0393] (18) A display system mounted on a mobile body, comprising: a housing having a wall member capable of housing a display panel that emits display light, and a light-transmitting plate through which the display light passes; a dimming member disposed outside the light-transmitting plate and having a light transmittance smaller than that of the light-transmitting plate; a detection unit for detecting the brightness of ambient light incident on the dimming member; and a control unit, wherein the control unit controls the transmittance of the dimming member based on the brightness detected by the detection unit.

[0394] (19) The display system according to (18), further comprising an imaging unit that images the rear and at least one of the side rear of the moving body, wherein the display panel displays the image captured by the imaging unit.

[0395] (20) A mobile body equipped with the display system described in (18) or (19) above.

[0396] [Additional Note 1] For example, the configuration of the display device disclosed in Embodiment 1 can be applied to the configuration of the display device disclosed in Embodiment 2. It can also be said that the configuration of the display device disclosed in Embodiment 2 can be applied to the configuration of the display device disclosed in Embodiment 1.

[0397] For example, the display devices 1, 1A, and 1B of Embodiment 1 may have the configuration of the display devices 8P and 35 of Embodiment 2.

[0398] For example, the housing 36 of Embodiment 1 may be the housings 37P, 41P of Embodiment 2. The opening 37 of Embodiment 1 may be the opening (window) 42Pa of Embodiment 2. The viewing window 38 of Embodiment 1 may be the light-transmitting plates 39P, 43P of Embodiment 2. The display panel 2 of Embodiment 1 may be the display panel 2P of Embodiment 2. The controller 50 of Embodiment 1 may be the control unit 7P of Embodiment 2. The irradiator 4 of Embodiment 1 may be the irradiator 10P of Embodiment 2.

[0399] For example, the optical system 3 of Embodiment 1 may be the optical systems 3P and 36P of Embodiment 2, the optical system 10 of Embodiment 1 may be the optical systems 3P', 3P'', and 36P of Embodiment 2, and the optical system 16 of Embodiment 1 may be the optical systems 3P'' and 36P of Embodiment 2.

[0400] For example, the first phase difference plate 5 in Embodiment 1 may be the first phase difference plate 12P in Embodiment 2, the first phase difference plate 12 in Embodiment 1 may be the first phase difference plate 24P in Embodiment 2, and the first phase difference plate 18 in Embodiment 1 may be the first phase difference plate 29P in Embodiment 2.

[0401] For example, the second phase difference plate 7 in Embodiment 1 may be the second phase difference plate 14P in Embodiment 2, the second phase difference plate 14 in Embodiment 1 may be the second phase difference plate 26P in Embodiment 2, and the second phase difference plate 20 in Embodiment 1 may be the second phase difference plate 31P in Embodiment 2.

[0402] For example, the semi-transparent mirror 6 in Embodiment 1 may be the semi-transparent mirror 13P in Embodiment 2, and the first semi-transparent mirrors 11 and 17 in Embodiment 1 may be the first semi-transparent mirrors 23P and 28P in Embodiment 2. Also, for example, the second semi-transparent mirror 13 in Embodiment 1 may be the second semi-transparent mirrors 25P and 25P' in Embodiment 2, and the second semi-transparent mirror 19 in Embodiment 1 may be the second semi-transparent mirror 30P in Embodiment 2. Also, for example, the third semi-transparent mirror 21 in Embodiment 1 may be the third semi-transparent mirror 32P in Embodiment 2.

[0403] For example, the reflective polarizing plate 8 in Embodiment 1 may be the reflective polarizing plate 15P in Embodiment 2. Also, for example, the polarizing plate 15 in Embodiment 1 may be the polarizing plate 27P in Embodiment 2.

[0404] For example, the imaging device 100 in Embodiment 1, which includes a display device 1 and a camera 102, may be a display system 1P that includes a display device 8P and an imaging unit 22P. Also, for example, the vehicles 23, 23A, and 23B in Embodiment 1 may be the vehicle 50P in Embodiment 2. Furthermore, for example, the user 22 in Embodiment 1 may be the user 11P in Embodiment 2.

[0405] [Addendum 2] Although embodiments of the present disclosure have been described in detail above, the present disclosure is not limited to the embodiments described above.

[0406] For example, while the above describes a display device equipped with a display panel, it is not limited to this. For instance, this disclosure may describe a device that does not have a display panel but is equipped with an optical system.

[0407] For example, the housing of a display device may include a display panel mounting section. The display panel mounting section may be capable of mounting a display panel. The display panel mounting section may be located on a part of the wall surface of the housing, on the inside of the housing, or inside the housing. In this case, the display panel may be located on the inside of the housing or inside the housing. Also, the display panel mounting section may be located on the outside of the housing or outside the housing. That is, the display panel may be located on the outside of the housing or outside the housing. In this case, the housing may have an opening in which a part of the wall surface is cut out. The display panel mounting section may be positioned relative to the housing so that display light emitted from the display panel installed in the display panel mounting section is guided to the inside of the housing through the opening. The display panel mounting section may be positioned relative to the housing so that display light emitted from the display panel installed in the display panel mounting section is guided to the inside of the housing through the opening. The display panel mounting section may be connected to the outer wall of the housing, or it may be connected to the outer wall of the housing so as to close at least a part of the opening. A light-transmitting member may be placed in the opening, and this member may be, for example, glass or resin. For example, Figures 1 and 2 show a display device in which a display panel is installed in the display panel installation section, but the device may not have a display panel installed in the display panel installation section. In this case, the device may be a display panel housing having a housing that includes a viewing section, an optical system, and a display panel installation section on which a display panel can be installed. The display panel housing may also realize the configuration of the display device of each embodiment described above. That is, the position of the display panel installation section of the display panel housing may be defined so that when a display panel is installed in the display panel installation section, it will have the configuration of each embodiment described above. Furthermore, the housing of the display panel housing may have an opening, and the display panel may be insertable through the opening. In this case, the display panel housing may have the same configuration as the display device, except that the housing has an opening and the display panel can be inserted from the outside or from the outside.

[0408] The inventions described in this disclosure have been explained above based on the drawings and embodiments. However, the inventions described in this disclosure are not limited to the embodiments described above. That is, the inventions described in this disclosure can be modified in various ways within the scope shown in this disclosure, and embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the inventions described in this disclosure. In other words, it should be noted that it is easy for those skilled in the art to make various mod...

Claims

A display device, A display panel that displays the image, The housing, in which the aforementioned display panel is located on the inside, When the display panel is oriented to display the display image in the forward direction, the housing includes a viewing section located in front of the display panel, which allows the inside of the housing to be visible from the outside of the housing, The system comprises an optical system capable of forming an image based on the aforementioned display image so that it can be viewed through the viewing unit, A display device in which, when the vertically upward direction in the operating state of the display device is defined as the upward direction, the direction opposite to the upward direction is defined as the downward direction, and the direction perpendicular to the upward direction, the downward direction, and the forward direction is defined as the left-right direction, the first lower end of the viewing section is located in front of or behind the first upper end of the viewing section, or the first left end of the viewing section is located in front of or behind the first right end of the viewing section. (i) The second lower end of the display panel is located in front of or behind the second upper end of the display panel, or (ii) The second left end of the display panel is located in front of or behind the second right end of the display panel, according to claim 1. 　 (i) The distance between the first lower end of the viewing section and the second lower end of the display panel is equal to the distance between the first upper end of the viewing section and the second upper end of the display panel, or (ii) The distance between the first left end of the viewing section and the second left end of the display panel is equal to the distance between the first right end of the viewing section and the second right end of the display panel, the display device according to claim 1 or 2. 　 (i) The distance between the first lower end of the viewing section and the second lower end of the display panel is shorter than the distance between the first upper end of the viewing section and the second upper end of the display panel, or (ii) The distance between the first left end of the viewing section and the second left end of the display panel is shorter than the distance between the first right end of the viewing section and the second right end of the display panel, according to claim 1 or 2. 　 (i) The distance between the first lower end of the viewing section and the second lower end of the display panel is longer than the distance between the first upper end of the viewing section and the second upper end of the display panel, or (ii) The distance between the first left end of the viewing section and the second left end of the display panel is longer than the distance between the first right end of the viewing section and the second right end of the display panel, according to claim 1 or 2. 　 The display device according to any one of claims 1 to 5, wherein the second lower end of the display panel is located above or below the first lower end of the viewing section. 　 The display device according to any one of claims 1 to 6, wherein the direction of the second normal of the display panel is different from the direction of the first normal of the viewing section. 　 The optical system has a semi-transparent mirror, (i) The third lower end of the semitransparent mirror is located in front of or behind the third upper end of the semitransparent mirror, or (ii) The third left end of the semitransparent mirror is located in front of or behind the third right end of the semitransparent mirror, according to any one of claims 1 to 7. 　 (i) The distance between the first lower end of the viewing section and the third lower end of the semi-transparent mirror is equal to the distance between the first upper end of the viewing section and the third upper end of the semi-transparent mirror, or (ii) The distance between the first left end of the viewing section and the third left end of the semi-transparent mirror is equal to the distance between the first right end of the viewing section and the third right end of the semi-transparent mirror, the display device according to claim 8. 　 (i) The distance between the first lower end of the viewing section and the third lower end of the semi-transparent mirror is shorter than the distance between the first upper end of the viewing section and the third upper end of the semi-transparent mirror, or (ii) The distance between the first left end of the viewing section and the third left end of the semi-transparent mirror is shorter than the distance between the first right end of the viewing section and the third right end of the semi-transparent mirror, as described in claim 8. 　 (i) The distance between the first lower end of the viewing section and the third lower end of the semi-transparent mirror is longer than the distance between the first upper end of the viewing section and the third upper end of the semi-transparent mirror, or (ii) The distance between the first left end of the viewing section and the third left end of the semi-transparent mirror is longer than the distance between the first right end of the viewing section and the third right end of the semi-transparent mirror, as described in claim 8. 　 The display device according to any one of claims 8 to 11, wherein the third lower end of the semi-transparent mirror is located above or below the first lower end of the viewing section. 　 The display device according to any one of claims 8 to 12, wherein the direction of the third normal of the semi-transparent mirror is the same as the direction of the first normal of the viewing section. 　 The display device according to any one of claims 8 to 12, wherein the direction of the third normal of the semi-transparent mirror is different from the direction of the first normal of the viewing section. (i) The distance between the third lower end of the semitransparent mirror and the second lower end of the display panel is equal to the distance between the third upper end of the semitransparent mirror and the second upper end of the display panel, or (ii) The distance between the third left end of the semitransparent mirror and the second left end of the display panel is equal to the distance between the third right end of the semitransparent mirror and the second right end of the display panel, the display device according to any one of claims 8 to 14. (i) The distance between the third lower end of the semitransparent mirror and the second lower end of the display panel is shorter than the distance between the third upper end of the semitransparent mirror and the second upper end of the display panel, or (ii) The distance between the third left end of the semitransparent mirror and the second left end of the display panel is shorter than the distance between the third right end of the semitransparent mirror and the second right end of the display panel, according to any one of claims 8 to 14. (i) The distance between the third lower end of the semitransparent mirror and the second lower end of the display panel is longer than the distance between the third upper end of the semitransparent mirror and the second upper end of the display panel, or (ii) The distance between the third left end of the semitransparent mirror and the second left end of the display panel is longer than the distance between the third right end of the semitransparent mirror and the second right end of the display panel, according to any one of claims 8 to 14. 　 The display device according to any one of claims 8 to 17, wherein the third lower end of the semi-transparent mirror is located above or below the second lower end of the display panel. 　 The display device according to any one of claims 8 to 18, wherein the direction of the third normal of the semitransparent mirror is the same as the direction of the second normal of the display panel. 　 The display device according to any one of claims 8 to 19, wherein the direction of the third normal of the semitransparent mirror is different from the direction of the second normal of the display panel. 　 The display device according to any one of claims 1 to 20, wherein the optical system forms the image at a position different from the display panel. 　 The display device according to claim 21, wherein the optical system forms the image behind the display panel. 　 It is located above the dashboard of the vehicle. The display device according to any one of claims 1 to 22, wherein the first lower end of the viewing portion is located rearward relative to the first upper end of the viewing portion. 　 The display device according to claim 23, wherein the second lower end of the display panel is located rearward relative to the second upper end of the display panel. 　 The optical system has a semi-transparent mirror, The display device according to claim 23 or 24, wherein the third lower end of the semi-transparent mirror is located in front of the third upper end of the semi-transparent mirror. 　 The display device according to claim 25, wherein the second upper end of the display panel is located above the first upper end of the viewing section. 　 Dashboard and The system comprises a display device according to any one of claims 1 to 22, located above the dashboard, The second lower end of the display panel is a movable body located rearward relative to the second upper end of the display panel. 　 It is located below the top edge of the vehicle's dashboard. The display device according to any one of claims 1 to 22, wherein the first lower end of the viewing portion is located in front of the first upper end of the viewing portion. 　 The display device according to claim 28, wherein the second lower end of the display panel is located in front of the second upper end of the display panel. 　 The optical system has a semi-transparent mirror, The display device according to claim 28 or 29, wherein the third lower end of the semi-transparent mirror is located behind the third upper end of the semi-transparent mirror. 　 The display device according to claim 30, wherein the second lower end of the display panel is located below the first lower end of the viewing section. Dashboard and The system comprises a display device according to any one of claims 1 to 22, which is located below the upper end of the dashboard, The second lower end of the display panel is a movable body located in front of the second upper end of the display panel. 　 Located to the left or right of the vehicle's steering wheel, The display device according to any one of claims 1 to 22, wherein, of the first left end and the first right end of the viewing section, the one located closer to the steering wheel is referred to as the first window end, and the one located further away from the steering wheel is referred to as the second window end, the first window end is located further back than the second window end. 　 The display device according to claim 33, wherein, of the second left end and second right end of the display panel, the one located closer to the steering wheel is referred to as the first panel end, and the one located further away from the steering wheel is referred to as the second panel end, the first panel end is located further back than the second panel end. 　 The steering wheel and A movable body comprising a display device according to any one of claims 1 to 22, which is located to the left or to the right of the steering wheel, wherein, of the first left end and the first right end of the viewing section, the one located closer to the steering wheel is referred to as the first window end, and the one located further away from the steering wheel is referred to as the second window end, the first window end is located behind the second window end. 　 The housing comprises a wall member capable of housing the display panel that emits display light, and a light-transmitting plate through which the display light passes, which serves as the viewing section, and further, The display device according to claim 1, further comprising a dimming member disposed outside the light-transmitting plate and having a transmittance to visible light less than that of the light-transmitting plate. 　 The casing further comprises a reflective member that reflects at least a portion of the aforementioned display light and is housed within the casing, The display device according to claim 36, wherein the dimming member is positioned outside the reflective member and has a transmittance to visible light smaller than that of the reflective member. 　 The display device according to claim 36 or 37, wherein the display panel emits the display light and is housed in the housing. 　 The display device according to any one of claims 36 to 38, wherein the transmittance of the dimming member is variable. 　 The display device according to claim 37, wherein the reflective member is a reflective polarizing member. 　 A detection unit for detecting the brightness of ambient light incident on the dimming member, It comprises a control unit and, The display device according to claim 39, wherein the control unit has a function to control the transmittance of the dimming member based on the brightness detected by the detection unit. 　 The display device according to claim 41, wherein the control unit controls the transmittance of the dimming member to decrease as the brightness detected by the detection unit increases. 　 A detection unit for detecting the brightness of ambient light incident on the dimming member, It comprises a control unit and, The display device according to claim 39, wherein the control unit has a function to control the brightness of the image displayed on the display panel and the transmittance of the dimming member based on the brightness detected by the detection unit. 　 A detection unit for detecting the brightness of ambient light incident on the dimming member, It comprises a control unit and, The display device according to claim 39, wherein the control unit controls the brightness of the image displayed on the display panel to be increased and the transmittance of the dimming member to be decreased as the brightness detected by the detection unit increases. 　 An acquisition unit that acquires the illuminance of the surrounding environment of the display device, A detection unit for detecting the brightness of ambient light incident on the dimming member, It comprises a control unit and, The display device according to claim 39, wherein the control unit has a function to control the brightness of the image displayed on the display panel and the transmittance of the dimming member based on the illuminance acquired by the acquisition unit and the brightness detected by the detection unit. 　 The display device according to claim 45, wherein the control unit controls the brightness of the image displayed on the display panel to be lowered and the transmittance of the dimming member to be higher the higher the illuminance detected by the acquisition unit, and controls the brightness of the image displayed on the display panel to be higher and the transmittance of the dimming member to be lowered the higher the brightness detected by the detection unit. 　 The display device according to any one of claims 36 to 46, further comprising an irradiator that irradiates light onto the side of the display panel opposite to the display surface. 　 The display device according to claim 47, further comprising a control unit having a function for controlling at least one of the image displayed on the display panel and the irradiator. A mobile body comprising the display device described in claim 48. 　 A first phase difference plate located on the display surface side of the display panel, A second phase difference plate is located on the opposite side of the display panel from the first phase difference plate, The system includes a semi-transparent mirror positioned between the first phase difference plate and the second phase difference plate, with a reflective surface on the side of the second phase difference plate, The reflective member is located on the opposite side of the semi-transparent mirror from the second phase difference plate, transmits the first linearly polarized light, and reflects the second linearly polarized light. The first phase difference plate and the second phase difference plate convert the display light into the second linearly polarized light, The display device according to claim 37, wherein the second phase difference plate converts the second linearly polarized light reflected by the reflecting member into the first linearly polarized light before it is reflected by the semitransparent mirror and re-enters the reflecting member. 　 The aforementioned display panel emits display light, A first semi-transparent mirror is located on the display surface side of the display panel and transmits first linearly polarized light and reflects second linearly polarized light, A second semi-transparent mirror is located on the opposite side of the display panel from the first semi-transparent mirror and has a reflective surface, A first phase difference plate is positioned between the first semi-transparent mirror and the second semi-transparent mirror, and converts the display light that has passed from the first semi-transparent mirror side and been reflected by the second semi-transparent mirror into the second linearly polarized light, A second phase difference plate is located on the opposite side of the first phase difference plate from the second semi-transparent mirror, and the second phase difference plate polarizes the light that is reflected by the second semi-transparent mirror and the first semi-transparent mirror and passes through the first phase difference plate into a third linearly polarized state, and the light that passes through the second semi-transparent mirror without being reflected into a fourth linearly polarized state. The display device according to any one of claims 36 to 48, further comprising a polarizing plate positioned on the opposite side of the second semitransparent mirror from the second phase difference plate, and which transmits the third linearly polarized light more than the fourth linearly polarized light. 　 A first phase difference plate located on the display surface side of the display panel, A second phase difference plate is located on the opposite side of the display panel from the first phase difference plate, A first semi-transparent mirror is positioned between the display panel and the first phase difference plate, and has a first reflective surface on the side of the first phase difference plate. A second semi-transparent mirror is positioned between the first phase difference plate and the second phase difference plate, and has a second reflective surface on the side of the first phase difference plate and a third reflective surface on the side of the second phase difference plate. A display device according to any one of claims 36 to 48, comprising a third semi-transparent mirror having a fourth reflective surface on the side of the second phase difference plate. 　 A display system mounted on a mobile body, comprising a display device according to any one of claims 36 to 48 or 50 to 52, A detection unit for detecting the brightness of ambient light incident on the dimming member, It comprises a control unit and, The control unit controls the transmittance of the dimming member based on the brightness detected by the detection unit, and is part of a display system. 　 The system further includes an imaging unit that images at least one of the rear and side rear of the moving body, The display system according to claim 53, wherein the display panel displays an image captured by the imaging unit. 　 A mobile body comprising the display system according to claim 53 or 54. 　 A display device according to any one of claims 1 to 26, 28 to 31, 33, or 34, The system includes a camera capable of communicating with the aforementioned display device. The display panel is a display system that displays images captured by the camera. 　 A mobile body comprising the display system described in claim 56. 　 A display panel housing device, A display panel mounting section capable of installing a display panel having a display surface for displaying images, The housing, in which the aforementioned display panel is located on the inside, When the display panel is oriented to display the display image in the forward direction, the housing includes a viewing section located in front of the display panel, which allows the inside of the housing to be visible from the outside of the housing, The system comprises an optical system capable of forming an image based on the aforementioned display image so that it can be viewed through the viewing unit, A display panel housing device in which, when the vertically upward direction in the operating state of the display panel housing device is defined as the upward direction, the direction opposite to the upward direction is defined as the downward direction, and the direction perpendicular to the upward direction, the downward direction, and the forward direction is defined as the left-right direction, the first lower end of the viewing section is located in front of or behind the first upper end of the viewing section, or the first left end of the viewing section is located in front of or behind the first right end of the viewing section.

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