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

Abstract

The present invention enables the display of two images based on a display image. This display device comprises: a display panel that displays a display image; an optical system that can form an image based on the display image at a position different from that of the display panel; and a housing in which the optical system is located. A first image based on the display image and a second image based on the display image are visibly displayed at different positions.

Description

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

[0001] The present disclosure relates to a display device and the like.

[0002] Conventionally, for example, a display device described in Patent Document 1 is known.

[0003] Japanese Patent Application Laid-Open No. 2022-63533

[0004] A display device according to one aspect of the present disclosure includes a display panel that displays a display image, an optical system that can form an image of an image based on the display image at a position different from the display panel, and a housing in which the optical system is located inside, and displays a first image based on the display image and a second image based on the display image so as to be visible at different positions.

[0005] This figure schematically shows the configuration of the display device according to the present disclosure. This is a cross-sectional view showing an example of a specific configuration of the display device according to the present 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 according to the present disclosure. This is a cross-sectional view showing a different example of the main components of the display device according to the present 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 according to the present disclosure, other than that shown in Figures 5 and 6. This figure shows an example of the application of an imaging device equipped with the display device according to the present disclosure. This figure shows an example of the interior of a moving body, which is a vehicle to which an imaging device equipped with the display device according to the present disclosure is applied. This is a schematic diagram schematically showing the configuration of a display device according to one embodiment of the present disclosure. This figure shows the positional relationship between the first retard axis of the first phase difference plate and the second retard axis of the second phase difference plate, and the polarization state in the Poincaré sphere due to differences in viewing direction. This figure shows the positional relationship between the first retard axis of the first phase difference plate and the second retard axis of the second phase difference plate, and the polarization state in the Poincaré sphere due to differences in viewing direction. This figure shows the positional relationship between the first retard axis of the first phase difference plate and the second retard axis of the second phase difference plate, and the polarization state in the Poincaré sphere due to differences in viewing direction. This is a schematic diagram illustrating the configuration of a display device according to one embodiment of the present disclosure. This is a schematic diagram illustrating the configuration of a display device according to one embodiment of the present disclosure. This is a schematic diagram illustrating the configuration of a display device according to one embodiment of the present disclosure. This is a schematic diagram illustrating the configuration of a display device according to one embodiment of the present disclosure. This is a cross-sectional view showing an example of an optical element. This is a schematic diagram illustrating the configuration of a display device according to one embodiment of the present disclosure. This is a schematic diagram illustrating the projection of a virtual image in a display device according to one embodiment of the present disclosure.

[0006] A display device capable of displaying two images based on a displayed image is desired. According to one aspect of this disclosure, it is possible to display two images based on a displayed image.

[0007] [Basic Configuration of Display Device] 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 38, and an optical system 3.

[0008] 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 closer to the display panel 2. The virtual image V may be formed on the side of the user 22 that is further away from the viewing window 38 or closer to the viewing window 38.

[0009] 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.

[0010] 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.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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).

[0021] The housing 36 may be a housing in which the display panel 2 is located on the 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. 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.

[0022] 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.

[0023] The viewing window 38 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.

[0024] The optical system 3 may project the display light emitted from the display panel 2 as an image based on the display image into the user's field of view 22. The image based on the display image into the user's field of view 22 may be formed at a position different from the display panel. For example, the optical system 3 may project the display light emitted from the display panel 2 as a virtual image V into 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 formed by the optical system 3. The virtual image V may be formed at a position different from the display panel 2. The optical system 3 may be configured to include a first phase difference plate 5, a semi-transparent mirror 6, a second phase difference plate 7, and a reflective polarizing plate 8, as shown in Figure 5. The optical system 3 may be located inside the housing 36. If the display device 1 has a viewing window 38, the optical system 3 may be positioned so as to be surrounded by the housing 36 and the viewing window 38. 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 arranged in this order in the direction of emission of display light from the display panel 2 (positive direction in the Z-axis direction).

[0025] Here, the optical system 3 may be capable of forming a virtual image V in a way that makes it visible through the viewing window 38. In other words, the virtual image V may be visible by looking through the viewing window 38. To put it another way, the virtual image V cannot be seen without the viewing window 38. As will be explained in detail below, if the display device of this disclosure does not have a viewing window 38, the optical system 3 may be capable of forming a virtual image V in a way that makes it visible through the aperture 37.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] The semi-transparent mirror 6 may be positioned between the first phase difference plate 5 and the second phase difference plate 7. The semi-transparent mirror 6 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 6 are not limited to 50%. The semi-transparent mirror 6 may have a function to collect or focus light. Specifically, the semi-transparent mirror 6 may have a function to collect or focus light that has been incident on and reflected by the semi-transparent mirror 6. The semi-transparent mirror 6 reflects a portion of the display light reflected by the reflective polarizer 8 and directs it into the eyes of the user 22. This makes it possible for the user 22 to see the virtual image V. The semi-transparent mirror 6 may be a concave mirror having a concave reflective surface 6a, as shown in Figure 5. The reflective surface 6a of the semi-transparent mirror 6 may be positioned on the side of the second phase difference plate 7. The semi-transparent mirror 6 may include a spherical, aspherical, or free-form shape in at least a portion of its reflective surface 6a. The semi-transparent mirror 6 may focus or concentrate light more effectively than other components of the optical system 3. In other words, the semi-transparent mirror 6 may have a larger degree of focusing, convergence, or an index expressed as the reciprocal of the focal length than other components of the optical system 3. The reflective surface 6a of the semi-transparent mirror 6 may have a greater curvature than other components of the optical system 3. The optical system 3 may have only the semi-transparent mirror 6 as a component with a focusing or converging function. Furthermore, the semi-transparent mirror 6 may be composed of a holographic optical element (HOE), or its surface shape may have a Fresnel shape.

[0031] The semi-transparent mirror 6 is 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, a resin material, a glass material, etc. The resin material may be, for example, an acrylic resin, a 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. The semi-transparent mirror 6 may be configured to reflect light with the semi-transparent reflective layer. The semi-transparent reflective layer may be formed on the surface of the substrate located on the side of the second phase difference plate 7.

[0032] 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.

[0033] 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.

[0034] The reflective polarizer 8 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 8 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.

[0035] The display device 1 may include a controller 50. The controller 50 may be connected to each component of the display device 1 and control each component. The controller 50 may control the irradiator 4. The controller 50 may control the display image displayed on the display panel 2 and the irradiator 4. The controller 50 may control the irradiator 4 based on the display image displayed on the display panel 2. The controller 50 may be configured to include one or more processors. The processors 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 processors 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, which may store various information or programs for operating each component of the display device 1. The storage unit may be composed of, for example, a semiconductor memory. The memory unit may function as the work memory of the controller 50.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] In FIG. 5, for ease of illustration, the optical path of the light incident on the reflective polarizing plate 8 and the optical path of the light reflected by the reflective polarizing plate 8 are shifted in the height direction (Y-axis direction) and shown. Also, the optical path of the light incident on the semi-transmissive mirror 6 and the optical path of the light reflected by the semi-transmissive mirror 6 are shifted in the height direction (Y-axis direction) and shown. However, in reality, the display light emitted from the display panel 2 propagates substantially on a single axis. Regarding the optical paths shown in FIGS. 6 and 7 as well, the display light emitted from the display panel 2 propagates substantially on a single axis.

[0042] FIG. 6 is a cross-sectional view showing another example, different from FIG. 5, of the main configuration of the display device 1. Other examples of the display device 1 will be described below. In the following description, the display device 1 shown in FIG. 6 as an example will be referred to as the display device 1A. The display device 1A is different from the display device 1 in that it includes an optical system 10 instead of the optical system 3.

[0043] The optical system 10 may be configured to include a first semi-transmissive mirror 11, a first retardation plate 12, a second semi-transmissive mirror 13, a second retardation plate 14, and a polarizing plate 15. The first semi-transmissive mirror 11, the first retardation plate 12, the second semi-transmissive mirror 13, the second retardation plate 14, and the polarizing plate 15 may be arranged in this order in the emission direction of the display light from the display panel 2.

[0044] The first retardation plate 12 may be located on the side of the reflection surface 11a of the first semi-transmissive mirror 11. The first retardation plate 12 may be located at a distance from the display surface 2a in the emission direction of the display light from the display panel 2. The second retardation plate 14 may be located at a distance from the first retardation plate 12 in the emission direction of the display light. The first retardation plate 12 and the second retardation plate 14 may be quarter-wave plates. The positional relationship between the first retardation plate 12 and the second retardation plate 14 may be defined such that when the first retardation plate 12 and the second retardation plate 14 are viewed along the Z-axis direction, the slow axis of the second retardation plate 14 is orthogonal to the slow axis of the first retardation plate 12. The positional relationship between the first retardation plate 12 and the second retardation plate 14 may also be defined such that when the first retardation plate 12 and the second retardation plate 14 are viewed along the Z-axis direction, the slow axis of the second retardation plate 14 is parallel to the slow axis of the first retardation plate 12.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] The second semi-transmissive mirror 13 may have a function of diverging the light that is incident on and reflected by the second semi-transmissive mirror 13. The second semi-transmissive mirror 13 may have a convex reflective surface 13a, and the reflective surface 13a may be located on the side of the first retardation plate 12. The second semi-transmissive mirror 13 is also referred to as a convex half mirror. The second semi-transmissive mirror 13 may transmit a part of the incident light (for example, approximately 50%) and reflect the remaining part (for example, approximately 50%). The transmittance and reflectance of the light incident on the second semi-transmissive mirror 13 are not limited to 50%. The second semi-transmissive mirror 13 may also have a function of condensing or converging the light that is incident on and reflected by the second semi-transmissive mirror 13. Specifically, the second semi-transmissive mirror 13 may have a concave shape located on the display panel 2 side. Further, the second semi-transmissive mirror 13 may be configured to include a holographic optical element (HOE), or may have a surface shape with a Fresnel shape.

[0049] The second semi-transmissive mirror 13 may be configured to include, for example, a substrate and a semi-transmissive reflective layer located 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, inorganic glass, resin 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 a metal thin film, and may be, for example, a dielectric multilayer film, etc.

[0050] 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.

[0051] 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.

[0052] 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%) passes through the second semi-transparent mirror 13. The third circularly polarized light C3 that has passed through the second semi-transparent mirror 13 may pass through the second phase difference plate 14 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 15 and be emitted to the outside.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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 light of the third linearly polarized light L3, whose polarization direction is perpendicular to that of the first linearly polarized light L1 (i.e., P-wave polarized light). The third linearly polarized light L3 may be transmitted through the first phase difference plate 18 and converted into light of the third circularly polarized light C3. The light of the third circularly polarized light C3 is 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 may be transmitted through the second phase difference plate 20 and converted into light of the fourth linearly polarized light L4, whose polarization direction is perpendicular to that of the first linearly polarized light L1 (i.e., P-wave polarized light). The light of the fourth linearly polarized light L4 may be transmitted through the third semi-transparent mirror 21 and emitted to the outside.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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).

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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 speed, and fuel level as virtual images V (hereinafter also referred to as virtual images V4).

[0082] 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).

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] [Overview of the Display Device of the Disclosure] As described above, the display device of the Disclosure may include a display panel for displaying a display image, and an optical system capable of forming an image based on the display image at a position different from the display panel. Furthermore, as will be described below, the display device of the Disclosure may display a first image based on the display image and a second image based on the display image in a viewable manner at different positions. As a result, the display device of the Disclosure can display two images based on the display image. The specific configuration of such a display device will be described in the following embodiments.

[0088] In the following description, the position from which the first image displayed by the display device of this disclosure can be viewed will be referred to as the first position P11, and the position from which the second image displayed by the display device of this disclosure can be viewed will be referred to as the second position P12. Furthermore, a user 22 located at the first position P11 will be referred to as the first user 22A, and a user 22 located at the second position will be referred to as the second user 22B.

[0089] The imaging device 100 equipped with the display device of this disclosure may be applied as a digital rearview mirror. In this case, the first position P11 may be the driver's seat and the second position P12 may be the passenger seat. However, as described above, the imaging device 100 may also be applied as, for example, a digital side mirror (left-side display device 1L, right-side display device 1R) or a cluster 29. In this case as well, the first position P11 may be the driver's seat and the second position P12 may be the passenger seat. The imaging device 100 may also be applied as, for example, a CID 30 or a PID 31. In this case, the first position P11 may be the driver's seat and the second position P12 may be the passenger seat, or the first position P11 may be the passenger seat and the second position P12 may be the driver's seat. The imaging device 100 may also be applied as, for example, an RSE system 32. In this case, the first position P11 and the second position P12 may be any two locations in the rear seats.

[0090] Furthermore, in the following description, the display device of this disclosure will be described as having a viewing window 38, but it is not required to have a viewing window 38. In this case, the second phase difference plate 7 and the reflective polarizing plate 8 may be supported by the opening 37. In the following description, the viewing window 38 may be read as the opening 37.

[0091] [Embodiment 1] First, we will explain how the first image and the second image can be displayed in a visible manner in the configuration of the display devices 1, 1A, and 1B described as the basic configuration. In this embodiment, we will explain using the display device 1 as an example. Figure 10 is a schematic diagram showing the configuration of the display device 1.

[0092] As shown in Figure 10, the first angle α, which is the angle between the normal direction ND of the display panel 2 and the first direction FD, which is the direction in which the first image can be viewed, may be smaller than the second angle β, which is the angle between the normal direction ND and the second direction SD, which is the direction in which the second image can be viewed. The first angle α may have a predetermined range. The second angle β may have a predetermined range. If the first angle α and the second angle β have predetermined ranges, the ranges of the first angle α and the second angle β may partially overlap.

[0093] Here, the statement that the first angle α is smaller than the second angle β means, for example, that the maximum value of the first angle α is smaller than the maximum value of the second angle β. Specifically, for example, the first angle α may range from 0° to 50°, and the second angle β may range from 60° to 80°, in which case the maximum value of the first angle α, which is 50°, may be smaller than the maximum value of the second angle β, which is 80°.

[0094] Furthermore, the statement that the first angle α is smaller than the second angle β may mean, for example, that the median of the first angle α is smaller than the median of the second angle β. Specifically, for example, if the first angle α is between 0° and 50°, and the second angle β is between 60° and 80°, then the median of the first angle α, (0 + 50) / 2 = 25°, may be smaller than (60 + 80) / 2 = 70°.

[0095] Furthermore, the statement that the first angle α is smaller than the second angle β may mean, for example, that the maximum value of the first angle α is smaller than the minimum value of the second angle β. Specifically, for example, the first angle α may range from 0° to 50°, and the second angle β may range from 60° to 80°, and the maximum value of the first angle α, which is 50°, may be smaller than the minimum value of the second angle β, which is 60°.

[0096] The first angle α may be set to an angle at which the first image can be seen from the first position P11, while the second image is not visible at all or is barely visible. Here, "barely visible" of the second image may mean, for example, that the brightness of the second image is 5 percent or less compared to the brightness of the display panel 2. Brightness may refer to the brightness of the image. Brightness may be measured using, for example, a BM-5A manufactured by Topcon Techno House. The measurement angle may be 1°. The brightness measurement point may be the center position of the display surface 2a. The measurement direction may coincide with the normal direction ND at the center position of the display surface 2a. The measurement distance may be 500 mm. The measurement distance may be the distance from the front lens of the BM-5A to the display surface 2a. That is, brightness may be measured with the BM-5A positioned relative to the display panel such that the front lens is located 500 mm from the display surface 2a.

[0097] The first image may be a virtual image V formed by the optical system 3. When the second angle β is set to be larger than the first angle α, not only the first image but also the second image can be seen from the second position P12. In this case, the second image may be an image that corresponds to at least a part of the display image I displayed by the display panel 2. For example, the second image may be an image that displays all of the display image I displayed by the display panel 2, or an image that displays a part of the display image I displayed by the display panel 2. The second angle β may be set to an angle in which the second image can be seen from the second position P12, while the first image cannot be seen at all or is almost invisible. Here, "almost invisible" of the first image may mean, for example, that the brightness of the first image is 5 percent or less compared to the brightness of the display panel 2.

[0098] The difference between the first angle α and the second angle β can result in different images being visible from the first position P11 and the second position P12, as will be explained using Figures 11 to 13.

[0099] Figures 11 to 13 show the positional relationship between the first retard axis 5AX of the first phase difference plate 5 and the second retard axis 7AX of the second phase difference plate 7, and the polarization state in the Poincaré sphere depending on the viewing direction. Figure 11 shows the above positional relationship and polarization state when the first phase difference plate 5 and the second phase difference plate 7 are viewed along the normal direction ND (i.e., the Z-axis direction). Figure 12 shows the above positional relationship and polarization state when the first phase difference plate 5 and the second phase difference plate 7 are viewed from a position shifted vertically from the normal direction ND (i.e., the Y-axis direction). Figure 13 shows the above positional relationship and polarization state when the first phase difference plate 5 and the second phase difference plate 7 are viewed from a position shifted horizontally from the normal direction ND (i.e., the X-axis direction). In the explanation of Figures 11 to 13, it is assumed that the vibration direction of light is the X-axis direction and the Y-axis direction.

[0100] As shown in Figure 11, when the display device 1 is viewed from the normal direction ND, the angles from the X-axis are 45° and 135°, respectively, and the first lagging axis 5AX and the second lagging axis 7AX are orthogonal. The X-axis and Y-axis are also orthogonal. Therefore, as shown in the Poincaré sphere in Figure 11, the light incident on the first phase difference plate 5 is converted by the first phase difference plate 5 from a linearly polarized state (polarization state PO1) to a circularly polarized state (polarization state PO2). Consequently, the light incident on the second phase difference plate 7 is converted by the second phase difference plate 7 from a circularly polarized state (polarization state PO2) back to a linearly polarized state (polarization state PO1). Therefore, the light incident on the second phase difference plate 7 is either S-wave polarized or P-wave polarized, and the user 22 can only see the light that has passed through the reflective polarizer 8 and constitutes the virtual image V.

[0101] On the other hand, as shown in Figure 12, when the display device 1 is viewed from a position shifted vertically from the normal direction ND, the X and Y axes are orthogonal, but the angles from the X axis become γ1 > 45° and γ2 < 135°, so the first lagging axis 5AX and the second lagging axis 7AX are no longer orthogonal. Therefore, as shown in the Poincaré sphere of Figure 12, the light incident on the first phase difference plate 5 is not converted from a linearly polarized state (polarization state PO1) to a circularly polarized state (polarization state PO2) by the first phase difference plate 5, but is converted to an elliptically polarized state (polarization state PO3). Consequently, the light incident on the second phase difference plate 7 is converted from an elliptically polarized state (polarization state PO3) to a state containing an elliptically polarized component (polarization state PO4) by the second phase difference plate 7. Therefore, the light incident on the second phase difference plate 7 contains components of light with polarization states other than S-wave polarization or P-wave polarization. Since this component is less than the P-wave polarized component transmitted through the reflective polarizer 8, the user 22 is able to see a display image I with lower resolution in addition to the virtual image V.

[0102] Furthermore, as shown in Figure 13, when the display device 1 is viewed from a position shifted horizontally from the normal direction ND, the first retard axis 5AX and the second retard axis 7AX are orthogonal, but the X and Y axes are no longer orthogonal. Therefore, as shown in the Poincaré sphere in Figure 13, the light incident on the first phase difference plate 5 is shifted horizontally from a linearly polarized state (polarization state PO1) to a state (polarization state PO5) by the first phase difference plate 5. Consequently, the component of the light incident on the first phase difference plate 5 is not converted to a circularly polarized state (polarization state PO2), but to an elliptically polarized state (polarization state PO6). Consequently, the light incident on the second phase difference plate 7 is returned by the second phase difference plate 7 from an elliptically polarized state (polarization state PO6) to a state containing an elliptically polarized component (polarization state PO5). Therefore, the light incident on the second phase difference plate 7 contains a component of light with a polarization state other than S-wave polarization or P-wave polarization. Since this component is less than the P-wave polarized component transmitted through the reflective polarizer 8, the user 22 is able to see a display image I with lower resolution in addition to the virtual image V.

[0103] The larger the angle from the normal direction ND, the more pronounced the phenomena shown in Figures 12 and 13 become. In other words, the smaller the angle from the normal direction ND, the less pronounced the phenomena shown in Figures 12 and 13 become. Therefore, when the display device 1 is viewed from a direction with a relatively small angle from the normal direction ND, the user 22 may not be able to see the displayed image I, or may hardly be able to see it at all.

[0104] In this embodiment, the positional relationship between the display device 1 and the first position P11 may be defined such that the first angle α is 0 degrees or close to 0 degrees. Furthermore, the positional relationship between the display device 1 and the second position P12 may be defined such that the second angle β is a larger angle than the first angle α. As a result, the display device 1 can emit light in the first direction FD that constitutes the virtual image V as the first image, and emit light in the second direction SD that constitutes the display image I as the second image, in addition to the virtual image V. As a result, the first user 22A located at the first position P11 can view the first image based on the display image I, and the second user 22B located at the second position P12 can view the first image and the second image displayed at a different position from the first image.

[0105] In this embodiment, the display device 1 may project a virtual image V onto a first position P11 using light emitted from the display panel 2, passing through the semi-transparent mirror 6, being reflected by the reflective polarizer 8, and being reflected again by the semi-transparent mirror 6. That is, the display device 1 may have an optical system 3, which is an optical system for projecting a virtual image V onto the first position P11. The optical path length of the light emitted from the display panel 2, passing through the semi-transparent mirror 6, being reflected by the reflective polarizer 8, and reaching the semi-transparent mirror 6 is referred to as the first optical path length FL. On the other hand, for a second position P12, the display image I may be projected using light emitted from the display panel 2, passing through the semi-transparent mirror 6, and further passing through the reflective polarizer 8. The optical path length of the light emitted from the display panel 2, passing through the semi-transparent mirror 6, and reaching the reflective polarizer 8 is referred to as the second optical path length SL.

[0106] However, the second optical path length may be the length of an optical path formed at a different position from the optical path constituted by the first optical path length FL, which is the optical path of light emitted from the display panel 2, passing through the semi-transparent mirror 6, being reflected by the reflective polarizer 8, and returning to the semi-transparent mirror 6. In this case, the second optical path length is referred to as the second optical path length SL1.

[0107] As can be seen from Figure 5, the length indicated by the first optical path length FL and the length indicated by the second optical path length SL may be different from each other. For example, the first optical path length FL may be longer than the second optical path length SL.

[0108] Furthermore, the first image and the second image may be viewed from different locations. In other words, the distance to the first image viewed by the first user 22A at the first position P11 may be different from the distance to the second image viewed by the second user 22B at the second position P12. For example, the first image may be located further from the display panel 2 than the second image. Also, for example, the distance to the first image viewed by the first user 22A at the first position P11 may be longer than the distance to the second image viewed by the second user 22B at the second position P12.

[0109] Furthermore, the size of the first image and the size of the second image may be different from each other. In other words, the first magnification, which is the magnification of the first image relative to the display image I, and the second magnification, which is the magnification of the second image relative to the display image I, may be different from each other.

[0110] In this embodiment, since the second image is the display image I, the second magnification can be 1. That is, by having the length indicated by the first optical path length FL and the length indicated by the second optical path length SL be different from each other, the size and magnification of the first image and the second image can be made different. This allows two images of different sizes to be viewed.

[0111] In this embodiment, the first optical path length FL may be longer than the second optical path length SL. Therefore, the size of the first image, the virtual image V, may be larger than the size of the second image, the displayed image I. In other words, the first magnification may be larger than the second magnification. Therefore, the first image can be made to appear larger than the second image.

[0112] Here, the projection of the first image, the virtual image V, in the display device 1 will be explained using Figure 20. In Figure 20, the illuminator 4 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 5 and second phase difference plate 7) are omitted. The distance between the display panel 2 and the semi-transparent mirror 6 may be considered as "0". In the following explanation, the focal length of the concave mirror, the semi-transparent mirror 6, will be denoted as f, the distance between the display panel 2 and the reflective polarizer 8 will be denoted as a1, and the distance between the semi-transparent mirror 6 and the reflective polarizer 8 will be denoted as a2.

[0113] The display device 1 may be configured to project a virtual image V by magnifying the virtual image Q of the display surface 2a formed by the reflective polarizing plate 8 using a concave mirror, which is a semi-transparent mirror 6. As shown in Figure 20, the virtual image Q is located on the opposite side of the concave mirror, which is the semi-transparent mirror 6, from the reflective polarizing plate 8, and the distance from the reflective polarizing plate 8 may be a1. The virtual image Q may be an image of the display surface 2a magnified to 1x.

[0114] 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). The virtual image distance b is the distance between the virtual image V and the semitransparent mirror 6, and the virtual image magnification m may be the magnification ratio of the virtual image V relative to the display surface 2a. b = 1 / (1 / (a1 + a2) - 1 / f) ... (1) m = b / (a1 + a2) = f / (f - (a1 + a2)) ... (2)

[0115] In this embodiment, for example, as shown in Figure 20, the first optical path length FL is a1 + a2 and the second optical path length SL is a1, and the first optical path length FL may be longer than the second optical path length SL.

[0116] In this embodiment, for example, as shown in Figure 20, the first image may be located behind the display panel 2 at a distance of b = 1 / (1 / (a1+a2)-1 / f). On the other hand, the second image is the display image I and may be located at the position of the display panel 2. As a result, the first image may be located behind the second image at a distance of b = 1 / (1 / (a1+a2)-1 / f).

[0117] In this embodiment, since the second image is the display image I, the second magnification can be 1. On the other hand, in this embodiment, for example, as in Figure 20, the first magnification is f / (f - (a1 + a2)), and since a1 + a2 > 0, the magnification can be greater than the second magnification (magnification 1). In other words, the first image can be larger than the second image.

[0118] In other words, by having the lengths indicated by the first optical path length FL and the second optical path length SL differ from each other, the size and magnification of the first and second images can be made different. This allows two images of different sizes to be viewed.

[0119] Furthermore, the brightness of the first image and the brightness of the second image may be different from each other. In this embodiment, the brightness of the first image, which is the virtual image V, and the brightness of the second image, which is the displayed image I, may be different from each other. This makes it possible to make the viewing conditions of the first image and the second image different.

[0120] Specifically, the brightness of the first image may be higher than that of the second image. The first image can be made to appear brighter than the second image. As described above, in this embodiment, the display image I projected in the second direction SD may be composed of light having fewer components than the P-wave polarized light transmitted through the reflective polarizer 8. Therefore, in this embodiment, the brightness of the display image I may be darker than that of the virtual image V composed of P-wave polarized light transmitted through the reflective polarizer 8. In other words, the brightness of the virtual image V (first image) may be brighter than that of the display image I (second image).

[0121] [Embodiment 2] Another embodiment of the present disclosure is described below. For convenience of explanation, components having the same function as those described in the above embodiments are denoted by the same reference numerals, and their descriptions are not repeated.

[0122] Figure 14 is a schematic diagram illustrating the configuration of the display device 1C according to this embodiment. As shown in Figure 14, the display device 1C may include an optical system 3C. The optical system 3C may include a first phase difference plate 5, a semi-transparent mirror 6, a second phase difference plate 7, and a reflective polarizing plate 8. However, the optical system C may be configured such that the second phase difference plate 7 and the reflective polarizing plate 8 are located only in a portion of the viewing window 38. That is, when the display device 1C is viewed from the front, the second phase difference plate 7 and the reflective polarizing plate 8 are not located in almost the entire area, but rather in a portion of the area. In other words, when the display device 1C is viewed from the front, the display device 1C may have an area comprising the optical system 3C and an area comprising a portion of the configuration of the optical system 3C. Here, a portion of the configuration of the optical system 3C may mean that at least one component is less than that of the optical system 3C.

[0123] For example, the second phase difference plate 7 and the reflective polarizing plate 8 may be located in at least a portion of the first region AR1 on the side of the first end 38A, one of the two ends of the viewing window 38 in the longitudinal direction (X-axis direction). In this embodiment, the second phase difference plate 7 and the reflective polarizing plate 8 may be located in at least a portion of the region of the viewing window 38 from the first end 38A to the center position. That is, the second phase difference plate 7 and the reflective polarizing plate 8 do not need to be located in the second region AR2 on the side of the second end 38B, one of the two ends of the viewing window 38. In this embodiment, the second phase difference plate 7 and the reflective polarizing plate 8 may be located only on the side of the first position P11. In other words, when the display device 1C is viewed from the front, the region comprising the optical system 3C and the region comprising a part of the configuration of the optical system 3C may be arranged along the longitudinal direction of the display device 1C.

[0124] The optical system 3C may include a first phase difference plate 5, a semi-transparent mirror 6, a second phase difference plate 7, and a reflective polarizer 8. Therefore, in the region where the optical system 3C has the second phase difference plate 7 and the reflective polarizer 8, the virtual image V may be imaged as the first image by the same principle as the optical system 3. Consequently, the virtual image V is projected onto the first position P11 located in the first direction FD, and the display image I does not need to be projected. Here, "the display image I is not projected" means that the display image I is not visible or is almost invisible. Here, "almost invisible" means, for example, that the brightness of the display image I is 5 percent or less compared to the brightness of the display panel 2. Therefore, the first position P11 may be a position where only the first image is visible and the second image is not visible.

[0125] On the other hand, in regions where the second phase difference plate 7 and the reflective polarizer 8 are not present, the light transmitted through the semi-transparent mirror 6 (the first circularly polarized light C1 shown in Figure 5) may pass through the viewing window 38. Therefore, in these regions, the optical system 3C may project the display image I as the second image. On the other hand, in these regions, since the second phase difference plate 7 and the reflective polarizer 8 are not present, the virtual image V does not need to be formed. That is, the display image I is projected onto the second position P12 located in the second direction SD, and the virtual image V does not need to be projected. Therefore, the second position P12 may be a position where the first image cannot be seen, and only the second image can be seen.

[0126] Thus, with the display device 1C, the first user 22A, positioned at the first position P11, can view the first image based on the display image I, and the second user 22B, positioned at the second position P12, can view the second image displayed at a different position from the first image. Furthermore, the possibility of the second user 22B viewing the display image I with low resolution can be reduced.

[0127] In this embodiment, the first image, the virtual image V, may be P-wave polarized light, and the second image, the displayed image I, may be circularly polarized light. Thus, the polarization state of the first image may differ from the polarization state of the second image.

[0128] In this embodiment as well, the size of the first image and the size of the second image may be different from each other. In other words, the first magnification and the second magnification may be different from each other. In this embodiment, since the second image is the display image I, the second magnification may be 1.

[0129] Specifically, the first optical path length FL may be longer than the second optical path length SL. In this embodiment, the first optical path length FL may be the optical path length of the light constituting the virtual image V, and the second optical path length SL may be the optical path length of the light constituting the display image I. Therefore, the size of the first image, the virtual image V, may be larger than the size of the second image, the display image I. In other words, the first magnification may be larger than the second magnification.

[0130] Furthermore, the brightness of the first image and the brightness of the second image may be different from each other. In this embodiment, the brightness of the first image, which is the virtual image V, and the brightness of the second image, which is the displayed image I, may be different from each other.

[0131] As described above, the amount of light (luminance) of the light constituting the virtual image V emitted from the display device 1C may be, for example, approximately 25% of the amount of light (luminance) of the display light emitted from the display panel 2. On the other hand, the display image I projected in the second direction SD may be composed of light emitted from the display panel 2, transmitted through the semi-transparent mirror 6, and further transmitted through the reflective polarizing plate 8. Therefore, the amount of light (luminance) of the light constituting the display image I emitted from the display device 1C may be, for example, approximately 50% of the amount of light (luminance) of the display light emitted from the display panel 2. Therefore, in this embodiment, the luminance of the first image may be lower than that of the second image. In other words, the luminance of the second image may be higher than that of the first image. Therefore, the second image can be made to appear brighter than the first image. When the second position P12 is located further from the display device 1C than the first position P11, the second image can be made easier for the second user 22B to see.

[0132] [Embodiment 3] Another embodiment of the present disclosure is described below. For convenience of explanation, components having the same function as those described in the above embodiments are denoted by the same reference numerals, and their descriptions are not repeated.

[0133] Figure 15 is a schematic diagram illustrating the configuration of the display device 1D according to this embodiment. As shown in Figure 15, the display device 1D may include an optical system 3D. The optical system 3D may have a first optical system 3D1 and a second optical system 3D2. The first optical system 3D1 may have a first phase difference plate 5, a semi-transparent mirror 6, a second phase difference plate 7, and a first reflective polarizer 8D1. The second optical system 3D2 may have a first phase difference plate 5, a semi-transparent mirror 6, a second phase difference plate 7, and a second reflective polarizer 8D2. The second optical system 3D2 may be a different optical system from the first optical system 3D1. The first optical system 3D1 and the second optical system 3D2 may, for example, be optical systems having different components, or they may be optical systems in which the same components are positioned in different arrangements, or they may be optical systems in which different components are positioned in different arrangements.

[0134] The first reflective polarizer 8D1 may be the reflective polarizer 8. The second reflective polarizer 8D2 may have the same structure as the first reflective polarizer 8D1. However, the second reflective polarizer 8D2 may be positioned relative to the viewing window 38 with the first reflective polarizer 8D1 rotated around an axis perpendicular to the surface of the first reflective polarizer 8D1. In this embodiment, the second reflective polarizer 8D2 may be positioned relative to the viewing window 38 with the first reflective polarizer 8D1 rotated by 90°. Therefore, while the first reflective polarizer 8D1 transmits P-wave polarized light and reflects S-wave polarized light, the second reflective polarizer 8D2 transmits S-wave polarized light and reflects P-wave polarized light. In other words, in this embodiment, the first optical system 3D1 and the second optical system 3D2 may be optical systems in which the same components are positioned in different arrangements. Here, "the same components are positioned in different arrangements" may mean that the distances between components in the first optical system 3D1 and the distances between components in the second optical system 3D2 are different. Furthermore, "the same components are positioned in different arrangements" may mean that, compared to the first optical system 3D1, at least one component of the second optical system 3D2 is positioned in a state where it has rotated around an axis along the direction in which the components are aligned. In addition, the first optical system 3D1 and the second optical system 3D2 may share components. For example, in this embodiment, the first optical system 3D1 and the second optical system 3D2 may share a semi-transparent mirror 6 and a reflective polarizing plate 8.

[0135] The optical system 3D may have, in the viewing window 38, a region where the second phase difference plate 7 and the first reflective polarizer 8D1 are located, and a region where the second phase difference plate 7 and the second reflective polarizer 8D2 are located. In other words, the first optical system 3D1 and the second optical system 3D2 may be located at different positions relative to the viewing window 38. To put it another way, when the display device 1D is viewed from the front, the region comprising the first optical system 3D1 and the region comprising the second optical system 3D2 may be located at different positions.

[0136] For example, the second phase difference plate 7 and the first reflective polarizer 8D1 may be located in at least a portion of the first region AR1. Specifically, the second phase difference plate 7 and the first reflective polarizer 8D1 may be located in at least a portion of the region of the viewing window 38 from the first end 38A to the center position. Also, the second phase difference plate 7 and the second reflective polarizer 8D2 may be located in at least a portion of the second region AR2. Specifically, the second phase difference plate 7 and the second reflective polarizer 8D2 may be located in at least a portion of the region of the viewing window 38 from the second end 38B to the center position. In this embodiment, the second phase difference plate 7 and the first reflective polarizer 8D1 may be located on the first position P11 side, and the second phase difference plate 7 and the second reflective polarizer 8D2 may be located on the second position P12 side. In other words, when the display device 1D is viewed from the front, the region comprising the first optical system 3D1 and the region comprising the second optical system 3D2 may be positioned along the longitudinal direction of the display device 1D. In this embodiment, when the display device 1D is viewed from the front, the region comprising the first optical system 3D1 may be located on the first position P11 side, and the region comprising the second optical system 3D2 may be located on the second position P12 side.

[0137] The reflectivity of the viewing window 38 and the reflective polarizer may be different from each other. Therefore, the reflection of light in the viewing window 38 may differ between the region where the reflective polarizer is located and the region where the reflective polarizer is not located. In this embodiment, the first reflective polarizer 8D1 and the second reflective polarizer 8D2 are located relative to the viewing window 38. Therefore, the region where the reflective polarizer is not located can be made smaller. Consequently, the possibility that the reflection of light in the viewing window 38 differs from region to region of the viewing window 38 can be reduced. Therefore, the appearance of the display device 1C can be improved. The larger the ratio of the area of ​​the first reflective polarizer 8D1 and the second reflective polarizer 8D2 to the area of ​​the viewing window 38, the more the possibility that the reflection of light in the viewing window 38 differs from region to region of the viewing window 38 can be reduced. In addition to the display device 1D, in display devices other than the display device 1C of Embodiment 1, the possibility that the reflection of light in the viewing window 38 differs from region to region of the viewing window 38 can be reduced.

[0138] The first optical system 3D1 may be an optical system that forms a first image. In this embodiment, the first optical system 3D1 has the same configuration as the optical system 3. Therefore, in the region having the first reflective polarizer 8D1, a virtual image V may be formed as the first image by the same principle as the optical system 3. Consequently, the virtual image V is projected onto the first position P11 located in the first direction FD, and the display image I does not need to be projected. Here, "the display image I is not projected" means that the display image I is not visible or is almost invisible. Here, "almost invisible" means, for example, that the brightness of the display image I is 5 percent or less compared to the brightness of the display panel 2.

[0139] The second optical system 3D2 may be an optical system for forming a second image. As described above, the second optical system 3D2 may include a first phase difference plate 5, a semitransparent mirror 6, a second phase difference plate 7, and a second reflective polarizer 8D2. The second reflective polarizer 8D2 may transmit S-wave polarized light converted from circularly polarized light by the second phase difference plate 7. Therefore, the second optical system 3D2 may project the display image I as the second image in the region where the second reflective polarizer 8D2 is located. On the other hand, the second reflective polarizer 8D2 may reflect P-wave polarized light. Therefore, the second optical system 3D2 does not need to form a virtual image V composed of P-wave polarized light in that region. That is, the display image I is projected onto the second position P12 located in the second direction SD, and the virtual image V does not need to be projected. Therefore, the second position P12 may be a position where the first image cannot be seen and only the second image can be seen.

[0140] Thus, with the display device 1D, the first user 22A, positioned at the first position P11, can view the first image based on the display image I, and the second user 22B, positioned at the second position P12, can view the second image displayed at a different position from the first image. Furthermore, the possibility of the second user 22B viewing the display image I with low resolution can be reduced.

[0141] In this embodiment, the first image, the virtual image V, may be P-wave polarized light, and the second image, the displayed image I, may be S-wave polarized light. Thus, the polarization state of the first image may differ from that of the second image.

[0142] In this embodiment, the first optical path length FL described above may be the optical path length of the first optical system 3D1, and the second optical path length SL described above may be the optical path length of the second optical system 3D2. As described above, the length indicated by the first optical path length FL and the length indicated by the second optical path length SL may be different from each other. In other words, in this embodiment as well, the size of the first image and the size of the second image may be different from each other. In other words, the first magnification and the second magnification may be different from each other. In this embodiment, since the second image is the display image I, the second magnification may be 1.

[0143] Specifically, the first optical path length FL may be longer than the second optical path length SL. In this embodiment, the first optical path length FL may be the optical path length of the light constituting the virtual image V, and the second optical path length SL may be the optical path length of the light constituting the display image I. Therefore, the size of the first image, the virtual image V, may be larger than the size of the second image, the display image I. In other words, the first magnification may be larger than the second magnification.

[0144] Furthermore, the brightness of the first image and the brightness of the second image may be different from each other. In this embodiment, the brightness of the first image, which is the virtual image V, and the brightness of the second image, which is the displayed image I, may be different from each other. In this embodiment as well, the brightness of the first image may be lower than the brightness of the second image.

[0145] [Embodiment 4] Another embodiment of the present disclosure is described below. For convenience of explanation, components having the same function as those described in the above embodiments are denoted by the same reference numerals, and their descriptions are not repeated.

[0146] Figure 16 is a schematic diagram illustrating the configuration of the display device 1E according to this embodiment. As shown in Figure 16, the display device 1E may include an optical system 3E. The optical system 3E may have a first optical system 3E1 and a second optical system 3E2. The first optical system 3E1 may have a first phase difference plate 5, a semi-transparent mirror 6, a third phase difference plate 7E1, and a reflective polarizing plate 8. The second optical system 3E2 may have a first phase difference plate 5, a semi-transparent mirror 6, a fourth phase difference plate 7E2, and a reflective polarizing plate 8. The second optical system 3E2 may be a different optical system from the first optical system 3E1. In this embodiment, the first optical system 3E1 and the second optical system 3E2 may be optical systems having different components. In this embodiment, the first optical system 3E1 and the second optical system 3E2 may have a third phase difference plate 7E1 and a fourth phase difference plate 7E2 as different phase difference plates. Furthermore, the first optical system 3E1 and the second optical system 3E2 may share some common components. For example, in this embodiment, the first optical system 3E1 and the second optical system 3E2 may share a semi-transparent mirror 6 and a reflective polarizing plate 8.

[0147] The third phase difference plate 7E1 may be the second phase difference plate 7. That is, the third phase difference plate 7E1 may be positioned relative to the reflective polarizer 8 such that the lagging axis of the third phase difference plate 7E1 (the second lagging axis 7AX of the second phase difference plate 7) is perpendicular to the first lagging axis 5AX of the first phase difference plate 5. Therefore, the circularly polarized light converted by the first phase difference plate 5 is converted by the third phase difference plate 7E1 into S-wave polarized light, which is the same as the light emitted by the display panel 2. Therefore, the S-wave polarized light emitted from the third phase difference plate 7E1 may be reflected by the reflective polarizer 8.

[0148] The fourth phase difference plate 7E2 may be the first phase difference plate 5. That is, the fourth phase difference plate 7E2 may be positioned relative to the reflective polarizer 8 such that the lagging axis of the fourth phase difference plate 7E2 is parallel to the first lagging axis 5AX of the first phase difference plate 5. Therefore, the circularly polarized light converted by the first phase difference plate 5 is converted by the fourth phase difference plate 7E2 into P-wave polarized light having a vibration direction perpendicular to the vibration direction of the light emitted from the display panel 2. Therefore, the P-wave polarized light emitted from the fourth phase difference plate 7E2 may pass through the reflective polarizer 8.

[0149] The optical system 3E may have, in the viewing window 38, a region where the third phase difference plate 7E1 and the reflective polarizer 8 are located, and a region where the fourth phase difference plate 7E2 and the reflective polarizer 8 are located. In other words, the first optical system 3E1 and the second optical system 3E2 may be located at different positions relative to the viewing window 38. To put it another way, when the display device 1E is viewed from the front, the region comprising the first optical system 3E1 and the region comprising the second optical system 3E2 may be located at different positions.

[0150] In this embodiment, the reflective polarizing plate 8 may be located over substantially the entire area of ​​the viewing window 38. In this embodiment, the third phase difference plate 7E1 may be located in at least a part of the first area AR1. Specifically, the third phase difference plate 7E1 may be located in at least a part of the area of ​​the viewing window 38 from the first end 38A to the center position. Also, the fourth phase difference plate 7E2 may be located in at least a part of the second area AR2. Specifically, the fourth phase difference plate 7E2 may be located in at least a part of the area of ​​the viewing window 38 from the second end 38B to the center position. In this embodiment, the third phase difference plate 7E1 may be located on the first position P11 side, and the fourth phase difference plate 7E2 may be located on the second position P12 side. Furthermore, the reflective polarizing plate 8 may not be a single plate, but may be divided and located on the side of the third phase difference plate 7E1 and the side of the fourth phase difference plate 7E2, respectively. In other words, when the display device 1E is viewed from the front, the region comprising the first optical system 3E1 and the region comprising the second optical system 3E2 may be positioned along the longitudinal direction of the display device 1E. In this embodiment, when the display device 1E is viewed from the front, the region comprising the first optical system 3E1 may be located on the first position P11 side, and the region comprising the second optical system 3E2 may be located on the second position P12 side.

[0151] The first optical system 3E1 may be an optical system that forms a first image. In this embodiment, the first optical system 3E1 may have the same configuration as the optical system 3. Therefore, in the region having the third phase difference plate 7E1, a virtual image V may be formed as the first image by the same principle as the optical system 3. Consequently, the virtual image V is projected onto the first position P11 located in the first direction FD, and the display image I does not need to be projected. Here, "the display image I is not projected" means that the display image I is not visible or is almost invisible. Here, "almost invisible" means, for example, that the brightness of the display image I is 5 percent or less compared to the brightness of the display panel 2.

[0152] The second optical system 3E2 may be an optical system for forming a second image. As described above, the second optical system 3E2 may include a first phase difference plate 5, a semi-transparent mirror 6, a fourth phase difference plate 7E2, and a reflective polarizer 8. The reflective polarizer 8 may transmit P-wave polarized light converted from circularly polarized light by the fourth phase difference plate 7E2. This P-wave polarized light is light converted from S-wave polarized light emitted from the display panel 2, and may be light that is not projected onto the semi-transparent mirror 6 (i.e., not reflected by the semi-transparent mirror 6). Therefore, in the region where the fourth phase difference plate 7E2 is located, the second optical system 3E2 may project the display image I as the second image. Furthermore, in this region, since no reflection of light occurs by the semi-transparent mirror 6, the second optical system 3E2 does not need to form a virtual image V. That is, at the second position P12 located in the second direction SD, the display image I is projected, and the virtual image V does not need to be projected.

[0153] Thus, with the display device 1E, the first user 22A, positioned at the first position P11, can view the first image based on the display image I, and the second user 22B, positioned at the second position P12, can view the second image displayed at a different position from the first image. Furthermore, the possibility of the second user 22B viewing the display image I with low resolution can be reduced.

[0154] In this embodiment as well, the length indicated by the first optical path length FL and the length indicated by the second optical path length SL may be different from each other. That is, the size of the first image and the size of the second image may be different from each other. In other words, the first magnification and the second magnification may be different from each other. In this embodiment, since the second image is the display image I, the second magnification may be 1.

[0155] Specifically, the first optical path length FL may be longer than the second optical path length SL. In this embodiment, the first optical path length FL may be the optical path length of the light constituting the virtual image V, and the second optical path length SL may be the optical path length of the light constituting the display image I. Therefore, the size of the first image, the virtual image V, may be larger than the size of the second image, the display image I. In other words, the first magnification may be larger than the second magnification.

[0156] Furthermore, the brightness of the first image and the brightness of the second image may be different from each other. In this embodiment, the brightness of the first image, which is the virtual image V, and the brightness of the second image, which is the displayed image I, may be different from each other. In this embodiment as well, the brightness of the first image may be lower than the brightness of the second image.

[0157] [Embodiment 5] Another embodiment of the present disclosure is described below. For convenience of explanation, components having the same function as those described in the above embodiments are denoted by the same reference numerals, and their descriptions are not repeated.

[0158] Figure 17 is a schematic diagram illustrating the configuration of the display device 1F according to this embodiment. As shown in Figure 17, the display device 1F may include an optical system 3F. The optical system 3F may have a first optical system 3F1 and a second optical system 3F2. The second optical system 3F2 may be a different optical system from the first optical system 3F1. The first optical system 3F1 and the second optical system 3F2 may be optical systems having different components. For example, the first optical system 3F1 and the second optical system 3F2 may have different optical elements. The first optical system 3F1 may have a first optical element 452A, a first phase difference plate 5, a semi-transparent mirror 6, a second phase difference plate 7, and a reflective polarizing plate 8. The second optical system 3F2 may have a second optical element 452B, a first phase difference plate 5, a semi-transparent mirror 6, a second phase difference plate 7, and a reflective polarizing plate 8. In other words, in this embodiment, the first optical system 3F1 and the second optical system 3F2 may have different optical elements, namely the first optical element 452A and the second optical element 452B.

[0159] In this embodiment, an example in which the first optical element 452A and the second optical element 452B are realized by an optical element 45 will be described. Figure 18 is a cross-sectional view showing an example of an optical element 45. As shown in Figure 18, the irradiator 4 of this embodiment may include a prism sheet 45A as the optical element 45. The prism sheet 45A may be a member that changes the direction of incident light to two different directions and emits the light. Examples of materials for the prism sheet 45A include acrylic, polycarbonate, polyethylene terephthalate, or polyvinyl chloride. The prism sheet 45A may have a base material 451, a first optical element 452A, and a second optical element 452B.

[0160] The first optical element 452A may change the direction of light incident on the substrate 451 substantially perpendicularly toward the third end 451A and emit the light. The first optical element 452A may be a first prism in which the incident surface 4521 is inclined with respect to the light emission surface 4511 such that the normal direction of the incident surface 4521 is toward the third end 451A. The second optical element 452B may change the direction of light incident on the substrate 451 substantially perpendicularly toward the fourth end 451B and emit the light. The second optical element 452B may be a second prism in which the incident surface 4521 is inclined with respect to the emission surface 4511 such that the normal direction of the incident surface 4521 is toward the fourth end 451B.

[0161] For example, multiple first optical elements 452A may be located in at least a portion of the third region AR3, which is the region on the third end 451A side of the two ends in the longitudinal direction of the substrate 451. Specifically, multiple first optical elements 452A may be located in at least a portion of the region of the substrate 451 from the third end 451A to the center position. Also, multiple second optical elements 452B may be located in at least a portion of the fourth region AR4, which is the region on the fourth end 451B side of the two ends of the substrate 451. Specifically, multiple second optical elements 452B may be located in at least a portion of the region of the substrate 451 from the fourth end 451B to the center position. In other words, when the display device 1F is viewed from the front, the region comprising the first optical system 3F1 and the region comprising the second optical system 3F2 may be arranged along the longitudinal direction of the display device 1F. In this case, the region comprising the first optical system 3F1, the center position when the display device 1F is viewed from the front, and the region comprising the second optical system 3F2 may be arranged in that order. The region comprising the first optical system 3F1 and the region comprising the second optical system 3F2 may be located in contact with each other or at a distance from each other.

[0162] The prism sheet 45A may be positioned such that the first optical element 452A and the second optical element 452B face the diffuser plate 44 (see Figures 3 and 4). Therefore, of the light emitted from the light source 42, the light that passes through the first optical element 452A may proceed towards the first region AR1, and the light that passes through the second optical element 452B may proceed towards the second region AR2.

[0163] In this embodiment, the display panel 2 may display multiple display images as display image I. Specifically, as shown in Figure 17, the display panel 2 may display a first display image IP1 and a second display image IP2 as display image I. The first display image IP1 and the second display image IP2 may be different images or the same image.

[0164] The prism sheet 45A may be positioned such that the third region AR3 side, where the first optical element 452A is located, faces the display area of ​​the first display image IP1, and the fourth region AR4 side, where the second optical element 452B is located, faces the display area of ​​the second display image IP2. Therefore, the light constituting the first display image IP1 may be emitted towards the first region AR1 side (first direction FD), and the light constituting the second display image IP2 may be emitted towards the second region AR2 side (second direction SD).

[0165] The first optical system 3F1 may be an optical system that forms a first image. In this embodiment, the first optical system 3F1 may have the same configuration as the optical system 3, such as the first phase difference plate 5, the semi-transparent mirror 6, the second phase difference plate 7, and the reflective polarizer 8, as described above. The light constituting the first display image IP1 may be transmitted or reflected by the first optical element 452A on the display area side (i.e., the first area AR1 side) of the first phase difference plate 5, the semi-transparent mirror 6, the second phase difference plate 7, and the reflective polarizer 8 of the first display image IP1. Therefore, the first optical system 3F1 may form a first virtual image VP1 of the first display image IP1 as the first image on the first area AR1 side, using the same principle as the optical system 3. Consequently, at the first position P11 located in the first direction FD, the first virtual image VP1 of the first display image IP1 is projected, and the display image I does not need to be projected. Furthermore, since the first display image IP1 is a part of the display image I, the first image may be an image corresponding to a part of the display image I.

[0166] The second optical system 3F2 may be an optical system for forming a second image. In this embodiment, the second optical system 3F2 may have the same configuration as the optical system 3, as described above, including the first phase difference plate 5, the semi-transparent mirror 6, the second phase difference plate 7, and the reflective polarizer 8. The light constituting the second display image IP2 may be transmitted or reflected by the second optical element 452B on the display area side (i.e., the second region AR2 side) of the first phase difference plate 5, the semi-transparent mirror 6, the second phase difference plate 7, and the reflective polarizer 8 of the second display image IP2. Therefore, on the second region AR2 side, the second optical system 3F2 may form a second virtual image VP2 of the second display image IP2 as a second image using the same principle as the optical system 3. Accordingly, at the second position P12 located in the second direction SD, the second virtual image VP2 of the second display image IP2 may be projected. Since the second display image IP2 is a part of the display image I, the second image may be an image corresponding to a part of the display image I.

[0167] Furthermore, as described in Embodiment 1, the second angle β may be larger than the first angle α. Therefore, the second optical system 3F2 may project the second display image IP2 as the second image on the second region AR2 side.

[0168] Thus, the display device 1F can project only the first image based on the first display image IP1 to the first position P11, and only the second image based on the second display image IP2 to the second position P12. Therefore, with the display device 1F, the first user 22A located at the first position P11 can perceive the first virtual image VP1 as the first image based on the first display image IP1. In addition, the second user 22B located at the second position P12 can perceive the second virtual image VP2 based on the second display image IP2 and the second display image IP2 as second images displayed at a different position from the first image.

[0169] In this embodiment as well, the length indicated by the first optical path length FL and the lengths indicated by the second optical path lengths SL and SL1 may be different from each other. That is, the size of the first image and the size of the second image may be different from each other. In other words, the first magnification and the second magnification may be different from each other.

[0170] For example, the angle of the incident surface 4521 of the first optical element 452A with respect to the exit surface 4511 may be different from the angle of the incident surface 4521 of the second optical element 452B with respect to the exit surface 4511. Also, the materials of the first optical element 452A and the second optical element 452B may be different from each other. This makes it possible to make the length indicated by the first optical path length FL of the light constituting the first virtual image VP1 as the first image and the length indicated by the second optical path length SL1 of the light constituting the second virtual image VP2 as the second image different from each other.

[0171] As described above, the second image may be the second display image IP2. The second optical path length SL of the light constituting the second display image IP2 may be the optical path length of the light emitted from the display panel 2, passing through the semi-transparent mirror 6, and reaching the reflective polarizer 8. Therefore, the first optical path length FL of the light constituting the first virtual image VP1 may be longer than the second optical path length SL of the light constituting the second display image IP2. Consequently, the size of the first virtual image VP1, which is the first image, may be larger than the size of the second display image IP2, which is the second image. In other words, the first magnification may be larger than the second magnification. Furthermore, the brightness of the first image and the brightness of the second image may be different from each other. In this embodiment, the brightness of the first virtual image VP1, which is the first image, and the brightness of the second display image IP2, which is the second image, may be different from each other. In this embodiment, the second display image IP2 is composed of light having fewer components than the P-wave polarized component that passes through the reflective polarizer 8. Therefore, the brightness of the first image can be higher than that of the second image.

[0172] In this embodiment, the case in which the optical element 45 is a prism sheet 45A was described as an example, but the invention is not limited to this. The direction of the incident light may be changed to two different directions, and a diffraction grating may be applied as the member that emits the light.

[0173] In this embodiment, the case in which the display panel 2 displays a first display image IP1 and a second display image IP2 has been described as an example, but a single display image I may be displayed. Therefore, the second image may be an image corresponding to the second display image IP2 which constitutes a part of the display image I, or it may be an image corresponding to the entire display image I. That is, the second image may be an image corresponding to at least a part of the display image I. Similarly, the first image may be an image corresponding to the first display image IP1 which constitutes a part of the display image I, or it may be an image corresponding to the entire display image I. That is, the first image may be an image corresponding to at least a part of the display image I.

[0174] [Embodiment 6] Another embodiment of the present disclosure is described below. For convenience of explanation, components having the same function as those described in the above embodiments are denoted by the same reference numerals, and their descriptions are not repeated.

[0175] Figure 19 is a schematic diagram illustrating the configuration of the display device 1G according to this embodiment. As shown in Figure 19, the display device 1G may include an optical system 3G. The optical system 3G may have a first optical system 3G1 and a second optical system 3G2. Here, the first optical system 3G1 and the second optical system 3G2 may be different optical systems. For example, the first optical system 3G1 and the second optical system 3G2 may be optical systems having different components, or the same components may be positioned in different arrangements, or different components may be positioned in different arrangements. The first optical system 3G1 may have a first phase difference plate 5, a fourth semi-transparent mirror 61, a second phase difference plate 7, and a reflective polarizer 8. The second optical system 3G2 may have a first phase difference plate 5, a fifth semi-transparent mirror 62, a second phase difference plate 7, and a reflective polarizer 8. The fourth semi-transparent mirror 61 and the fifth semi-transparent mirror 62 may differ in size from the semi-transparent mirror 6, but may have the same structure as the semi-transparent mirror 6.

[0176] The first optical system 3G1 and the second optical system 3G2 may be optical systems in which the same components are positioned in different arrangements. Here, "the same components are positioned in different arrangements" may mean that the distances between components in the first optical system 3G1 and the distances between components in the second optical system 3G2 are different. Furthermore, "the same components are positioned in different arrangements" may mean that, compared to the first optical system 3G1, at least one component of the second optical system 3G2 is positioned in a state where it has rotated around an axis along the direction in which the components are aligned. In this embodiment, the distances between components in the first optical system 3G1 and the distances between components in the second optical system 3G2 may be different. Specifically, the first distance D11, which is the distance between the fourth semi-transparent mirror 61 and the second phase difference plate 7 of the first optical system 3G1, and the second distance D12, which is the distance between the fifth semi-transparent mirror 62 and the second phase difference plate 7 of the second optical system 3G2, may be different.

[0177] Here, the first optical system 3G1 and the second optical system 3G2 may share some common components. For example, in this embodiment, the first optical system 3D1 and the second optical system 3D2 may share the first phase difference plate 5, the second phase difference plate 7, and the reflective polarizing plate 8.

[0178] The fourth semi-transparent mirror 61 and the fifth semi-transparent mirror 62 are positioned between the first phase difference plate 5 and the second phase difference plate 7, and their concave reflective surfaces may be located on the side of the second phase difference plate 7. The fourth semi-transparent mirror 61 may be positioned such that its concave reflective surface is located on the side of the second phase difference plate 7 on the first region AR1 side. The fifth semi-transparent mirror 62 may be positioned such that its concave reflective surface is located on the side of the second phase difference plate 7 on the second region AR2 side.

[0179] The first optical system 3G1 may be an optical system for forming a first image. In this embodiment, the first optical system 3G1 may include a first phase difference plate 5, a fourth semi-transparent mirror 61 located on the first region AR1 side, a second phase difference plate 7, and a reflective polarizer 8. Since the fourth semi-transparent mirror 61 has the same structure as the semi-transparent mirror 6, on the first region AR1 side, the first virtual image VP1 may be formed as the first image by the same principle as the optical system 3. Therefore, at the first position P11 located in the first direction FD, the first virtual image VP1 is projected, and the display image I does not need to be projected. The first image may be an image corresponding to the display image I.

[0180] The second optical system 3G2 may be an optical system for forming a second image. In this embodiment, the second optical system 3G2 may include a first phase difference plate 5, a fifth semi-transparent mirror 62 located on the second region AR2 side, a second phase difference plate 7, and a reflective polarizer 8. Since the fifth semi-transparent mirror 62 has the same structure as the semi-transparent mirror 6, on the second region AR2 side, a second virtual image VP2 may be formed as a second image by the same principle as the optical system 3. Therefore, the second virtual image VP2 may be projected at the second position P12 located in the second direction SD. The second image may be an image corresponding to the display image I.

[0181] Furthermore, as described in Embodiment 1, the second angle β may be larger than the first angle α. Therefore, the second optical system 3G2 may project the display image I as the second image on the second region AR2 side.

[0182] Thus, the display device 1G can project a first image based on the display image I to the first position P11 and a second image based on the display image I to the second position P12. In other words, when the display device 1G is viewed from the front, the region equipped with the first optical system 3G1 and the region equipped with the second optical system 3G2 may be located at different positions. In this embodiment, when the display device 1G is viewed from the front, the region equipped with the first optical system 3G1 may be located to the first position P11, and the region equipped with the second optical system 3G2 may be located to the second position P12. Therefore, with the display device 1G, the first user 22A located at the first position P11 can perceive the first virtual image VP1 as the first image based on the display image I. Also, the second user 22B located at the second position P12 can perceive the second virtual image VP2 based on the display image I and the display image I as a second image displayed at a different position from the first image.

[0183] In this embodiment as well, the length indicated by the first optical path length FL and the lengths indicated by the second optical path lengths SL and SL1 may be different from each other. That is, the size of the first image and the size of the second image may be different from each other. In other words, the first magnification and the second magnification may be different from each other.

[0184] The optical path length of light emitted from the display panel 2, passing through the fourth semi-transparent mirror 61, reflected by the reflective polarizer 8, and returning to the fourth semi-transparent mirror 61 may be the first optical path length FL. Therefore, the first optical path length FL may include the first distance D11 between the fourth semi-transparent mirror 61 and the second phase difference plate 7. Also, the optical path length of light emitted from the display panel 2, passing through the fifth semi-transparent mirror 62, reflected by the reflective polarizer 8, and returning to the fifth semi-transparent mirror 62 may be the second optical path length SL1. Therefore, the second optical path length SL1 may include the second distance D12 between the fifth semi-transparent mirror 62 and the second phase difference plate 7.

[0185] The first distance D11 can be changed by changing the positional relationship between the fourth semi-transparent mirror 61 and the second phase difference plate 7. Also, the second distance D12 can be changed by changing the positional relationship between the fifth semi-transparent mirror 62 and the second phase difference plate 7. Therefore, by changing the relationship between the first distance D11 and the second distance D12, the relationship between the first optical path length FL and the second optical path length SL1 can be changed. Consequently, the relationship between the size of the first image and the size of the second image, in other words, the relationship between the first magnification and the second magnification can be changed.

[0186] In this embodiment, the positions of the fourth semi-transparent mirror 61 and the fifth semi-transparent mirror 62 may be defined such that the first distance D11 is longer than the second distance D12. Therefore, in this embodiment, the first optical path length FL may be longer than the second optical path length SL1. Consequently, the first virtual image VP1, which is the first image, may be imaged further back on the display device 1G than the second virtual image VP2, which is the second image. That is, the third distance D21 from the reference line BL, which virtually connects the first position P11 and the second position P12, to the first virtual image VP1 may be longer than the fourth distance D22 from the reference line BL to the second virtual image VP2. Therefore, the size of the first virtual image VP1, which is the first image, may be larger than the size of the second virtual image VP2, which is the second image. That is, the first magnification may be larger than the second magnification.

[0187] As described above, the second image may be the display image I. The second optical path length SL of the light constituting the display image I may be the optical path length of the light emitted from the display panel 2, passing through the semi-transparent mirror 6, and reaching the reflective polarizer 8. Therefore, the first optical path length FL of the light constituting the first virtual image VP1 may be longer than the second optical path length SL of the light constituting the display image I. Consequently, the size of the first virtual image VP1, which is the first image, may be larger than the size of the display image I, which is the second image. In other words, the first magnification may be larger than the second magnification. Furthermore, the brightness of the first image and the brightness of the second image may be different from each other. In this embodiment, the brightness of the first virtual image VP1, which is the first image, and the brightness of the display image I, which is the second image, may be different from each other. In this embodiment, the display image I is composed of light having fewer components than the P-wave polarized component that passes through the reflective polarizer 8. Therefore, the brightness of the first image may be higher than the brightness of the second image.

[0188] In this embodiment, the optical system 3G has a fourth semi-transparent mirror 61 and a fifth semi-transparent mirror 62 having the same structure, but is not limited to this. The fourth semi-transparent mirror 61 and the fifth semi-transparent mirror 62 may be semi-transparent mirrors with different focal lengths. In this case, even if the first distance D11 and the second distance D12 are the same, the size of the first virtual image VP1, which is the first image, and the size of the second virtual image VP2, which is the second image, can be made different.

[0189] In this embodiment, the display device 1G may also include a first optical element 452A and a second optical element 452B. In this case, the display device 1G can project a first virtual image VP1 based on a first display image IP1 onto the first region AR1 side, and a second virtual image VP2 based on a second display image IP2 onto the second region AR2 side. Therefore, the display device 1G can project different display images as virtual images of different sizes.

[0190] [Summary] The display device according to Embodiment 1 of the present disclosure comprises a display panel for displaying a display image, an optical system capable of forming an image based on the display image at a position different from the display panel, and a housing in which the optical system is located on the inside, and displays a first image based on the display image and a second image based on the display image in a viewable manner at different positions.

[0191] In the display device according to Embodiment 2 of this disclosure, in Embodiment 1, the second image is an image corresponding to at least a part of the display image.

[0192] A display device according to aspect 3 of the present disclosure, in aspect 1 or 2, further comprises a first optical system and a second optical system, wherein the first optical system is an optical system for forming a first image, and the second optical system is an optical system for forming a second image.

[0193] In the display device according to aspect 4 of the present disclosure, in aspect 3, the length indicated by the first optical path length, which is the optical path length of the first optical system, and the length indicated by the second optical path length, which is the optical path length of the second optical system, are different from each other.

[0194] In the display device according to aspect 5 of this disclosure, in aspect 4, the first optical path length is longer than the second optical path length.

[0195] In the display device according to embodiment 6 of the present disclosure, in any of embodiments 1 to 5, the size of the first image and the size of the second image are different from each other.

[0196] In the display device according to embodiment 7 of this disclosure, in embodiment 6, the size of the first image is larger than the size of the second image.

[0197] In the display device according to embodiment 8 of the present disclosure, in any of embodiments 1 to 7, the first magnification, which is the magnification of the first image relative to the display image, and the second magnification, which is the magnification of the second image relative to the display image, are different from each other.

[0198] In the display device according to embodiment 9 of this disclosure, in embodiment 8, the first magnification is greater than the second magnification.

[0199] In the display device according to embodiment 10 of the present disclosure, in any of embodiments 1 to 9, the brightness of the first image and the brightness of the second image are different from each other.

[0200] In the display device according to embodiment 11 of this disclosure, in embodiment 10, the brightness of the first image is lower than that of the second image.

[0201] In the display device according to embodiment 12 of this disclosure, in embodiment 10, the brightness of the first image is higher than the brightness of the second image.

[0202] In the display device according to aspect 13 of this disclosure, in any of aspects 1 to 12, the first image is a virtual image.

[0203] In any of embodiments 1 to 13, the display device according to embodiment 14 of the present disclosure has a first angle, which is the angle between the normal direction of the display panel and the first direction in which the first image can be viewed, which is smaller than the second angle, which is the angle between the normal direction and the second direction in which the second image can be viewed.

[0204] In the display device according to embodiment 15 of the present disclosure, in any of embodiments 1 to 14, the polarization state of the first image is different from the polarization state of the second image.

[0205] [Additional Notes] Although embodiments of this disclosure have been described in detail above, this disclosure is not limited to the embodiments described above.

[0206] 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.

[0207] 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.

[0208] 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 modifications or alterations based on this disclosure. Furthermore, it should be noted that these modifications or alterations are included in the scope of this disclosure.

[0209] 1, 1A-1G Display device 2 Display panel 3, 3C-3G, 10, 16 Optical system 3D1-3G1 First optical system 3D2-3G2 Second optical system I Display image (second image) IP1 First display image (display image) IP2 Second display image (display image, second image) V Virtual image (first image) VP1 First virtual image (first image) VP2 Second virtual image (second image) FL First optical path length SL, SL1 Second optical path length ND Normal direction FD First direction SD Second direction α First angle β Second angle

Claims

1. A display device comprising: a display panel for displaying an image; an optical system capable of forming an image based on the display image at a position different from the display panel; and a housing in which the optical system is located on the inside, wherein a first image based on the display image and a second image based on the display image are displayed in a manner that is visible at different positions.

2. The display device according to claim 1, wherein the second image is an image corresponding to at least a part of the display image.

3. The display device according to claim 1 or 2, wherein the optical system further comprises a first optical system and a second optical system, the first optical system being an optical system for forming a first image, and the second optical system being an optical system for forming a second image.

4. The display device according to claim 3, wherein the length indicated by the first optical path length, which is the optical path length of the first optical system, and the length indicated by the second optical path length, which is the optical path length of the second optical system, are different from each other.

5. The display device according to claim 4, wherein the first optical path length is longer than the second optical path length.

6. The display device according to any one of claims 1 to 5, wherein the size of the first image and the size of the second image are different from each other.

7. The display device according to claim 6, wherein the size of the first image is larger than the size of the second image.

8. The display device according to any one of claims 1 to 7, wherein the first magnification, which is the magnification of the first image relative to the display image, and the second magnification, which is the magnification of the second image relative to the display image, are different from each other.

9. The display device according to claim 8, wherein the first magnification is greater than the second magnification.

10. The display device according to any one of claims 1 to 9, wherein the brightness of the first image and the brightness of the second image are different from each other.

11. The display device according to claim 10, wherein the brightness of the first image is lower than that of the second image.

12. The display device according to claim 10, wherein the brightness of the first image is higher than that of the second image.

13. The display device according to any one of claims 1 to 12, wherein the first image is a virtual image.

14. The display device according to any one of claims 1 to 13, wherein the first angle, which is the angle between the normal direction of the display panel and the first direction in which the first image can be viewed, is smaller than the second angle, which is the angle between the normal direction and the second direction in which the second image can be viewed.

15. The display device according to any one of claims 1 to 14, wherein the polarization state of the first image is different from the polarization state of the second image.

16. A display system comprising a display device according to any one of claims 1 to 15, and a camera capable of communicating with the display device, wherein the display panel displays an image captured by the camera.

17. A mobile body comprising the display system described in claim 16.

18. A display panel housing device comprising: a display panel mounting section capable of installing a display panel having a display surface for displaying a display image; an optical system capable of forming an image based on the display image at a position different from the display panel; and a housing in which the optical system is located on the inside, wherein a first image based on the display image and a second image based on the display image are displayed in a manner that is visible at different positions.

Images