Display device, display panel housing, and mobile unit

Abstract

The display device improves the visibility of images based on the displayed image. The display device comprises a housing having a viewing section and an inner region; a display panel having a display surface for displaying a display image, with the display surface facing the inner region of the housing; a first reflector located inside the housing and having a first reflective surface facing the inner region; a second reflector located inside the housing and having a second reflective surface facing the inner region; and a semi-reflector located inside the inner region of the housing and having a first optical surface positioned to face either the viewing section and the display surface, the first reflective surface, or the second reflective surface, and a second optical surface positioned to face the other of the display surface, the first reflective surface, or the second reflective surface.

Description

Technical Field

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

Background Art

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

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

[0004] A display device according to one aspect of the present disclosure includes a housing having a viewing portion and an inner region, a display panel having a display surface for displaying a display image, the display surface being arranged so as to face the inner region of the housing, a first mirror located within the housing and having a first reflecting surface facing the inner region, a second mirror located within the housing and having a second reflecting surface facing the inner region, a first optical surface located within the inner region of the housing and arranged so as to face either one of the viewing portion, the display surface, the first reflecting surface, and the second reflecting surface, and a second optical surface arranged so as to face the other of the display surface, the first reflecting surface, and the second reflecting surface, and a semi-reflecting plate having the second optical surface.

[0005] A display panel housing device according to one aspect of the present disclosure comprises a housing having a viewing section, an inner region, and a display panel installation section on which a display panel can be installed such that the display surface faces the inner region; a first reflector located inside the housing and having a first reflective surface facing the inner region; a second reflector located inside the housing and having a second reflective surface facing the inner region; and a semi-reflector located inside the inner region within the housing and having a first optical surface arranged to face the viewing section and either the display surface, the first reflective surface, or the second reflective surface; and a second optical surface arranged to face the other of the display surface, the first reflective surface, or the second reflective surface. [Brief explanation of the drawing]

[0006] [Figure 1] This is a schematic diagram illustrating the configuration of the display device related to this disclosure. [Figure 2] This is a cross-sectional view showing the configuration of the vehicle related to this disclosure. [Figure 3] This is a schematic diagram showing the internal configuration of the vehicle related to this disclosure. [Figure 4] This is a schematic diagram illustrating the configuration of a display device related to a comparative example. [Figure 5] This is a cross-sectional view showing an example of the configuration of a display device according to one embodiment. [Figure 6] This is a schematic diagram illustrating the configuration of a display device according to one embodiment. [Figure 7] This is a cross-sectional view showing an example of the configuration of a display device according to one embodiment. [Figure 8] This is a schematic diagram illustrating the configuration of a display device according to one embodiment. [Figure 9] This is a schematic diagram illustrating the configuration of a display device according to one embodiment. [Figure 10] This is a cross-sectional view showing an example of the configuration of a display device according to one embodiment. [Figure 11] This is a schematic diagram illustrating the configuration of a display device according to one embodiment. [Figure 12] This is a cross-sectional view showing an example of the configuration of a display device according to one embodiment. [Figure 13] It is a schematic diagram schematically showing the configuration of a display device according to an embodiment. [Figure 14] It is a cross-sectional view showing an example of the configuration of a display device according to an embodiment. [Figure 15] It is a schematic diagram schematically showing the configuration of a display device according to an embodiment. [Figure 16] It is a cross-sectional view showing an example of the configuration of a display device according to an embodiment. [Figure 17] It is a schematic diagram schematically showing the configuration of a display device according to an embodiment. [Figure 18] It is a schematic diagram schematically showing the configuration of a display device according to an embodiment. [Figure 19] It is a schematic diagram schematically showing the configuration of a display device according to an embodiment. [Figure 20] It is a schematic diagram schematically showing the configuration of a display device according to an embodiment. [Figure 21] It is a schematic diagram schematically showing the configuration of a display device according to an embodiment. [Figure 22] It is a cross-sectional view schematically showing the configuration of a display device according to an embodiment. [Figure 23] It is a schematic cross-sectional view showing an example of the arrangement position of a retardation plate. [Figure 24] It is a schematic diagram showing an example of the size relationship of each member included in the display device. [Figure 25] It is a schematic diagram showing an example of the traveling direction of light emitted from the display panel. [Figure 26] It is a plan view showing an example of an image formed by the display device. [Figure 27] It is a top view for explaining looking directly at the viewing part. [Figure 28] It is a schematic diagram comparing the length of the viewing part and the length of the second mirror in the longitudinal direction of the viewing part. [Figure 29] It is a schematic diagram showing an example of the traveling direction of light emitted from the display panel. [Figure 30] It is a schematic diagram showing an example of the traveling direction of light emitted from the display panel. [Figure 31]It is a schematic diagram showing an example of the traveling direction of light emitted from a display panel. [Figure 32] It is a schematic diagram showing a first example in which a first mirror forms an image of display light to form a first image. [Figure 33] In FIG. 32, it is a schematic diagram showing a first example in which a second mirror forms an image of the first image to form a second image. [Figure 34] In FIG. 32, it is a schematic diagram showing a second example in which a second mirror forms an image of the first image to form a second image. [Figure 35] It is a schematic diagram showing a second example in which a first mirror forms an image of display light to form a first image. [Figure 36] In FIG. 35, it is a schematic diagram showing a first example in which a second mirror forms an image of the first image to form a second image. [Figure 37] In FIG. 35, it is a schematic diagram showing a second example in which a second mirror forms an image of the first image to form a second image. [Figure 38] It is a schematic diagram showing a third example in which a first mirror forms an image of display light to form a first image. [Figure 39] In FIG. 38, it is a schematic diagram showing a first example in which a second mirror forms an image of the first image to form a second image. [Figure 40] In FIG. 38, it is a schematic diagram showing a second example in which a second mirror forms an image of the first image to form a second image. [Figure 41] In FIG. 38, it is a schematic diagram showing a third example in which a second mirror forms an image of the first image to form a second image. [Figure 42] It is a schematic diagram explaining the conditions according to the example of FIG. 40 and the conditions according to the example of FIG. 41. [Figure 43] It is a cross-sectional view schematically showing the configuration of a display device according to an embodiment. [Figure 44] It is a cross-sectional view schematically showing the configuration of a display device according to an embodiment. [Figure 45] It is a cross-sectional view schematically showing the configuration of a display device according to an embodiment. [Figure 46] It is a graph showing an example of the relationship between θ1 and the ellipticity of light in the wavelength bands of red, green, and blue. [Figure 47] This is an external view showing an example of the configuration of a display device according to one embodiment, and a schematic cross-sectional view showing an example of the configuration of a display device according to one embodiment. [Figure 48] This is an exploded view of a specific configuration example of a display device according to one embodiment. [Figure 49] This is a schematic diagram illustrating the configuration of a display device according to one embodiment. [Figure 50] This is a schematic diagram illustrating the configuration of a display device according to one embodiment. [Figure 51] This is a schematic diagram illustrating an example of the direction of light propagation. [Figure 52] This is a schematic diagram illustrating the size of the viewing section and the second reflector. [Modes for carrying out the invention]

[0007] There is a desire to improve the visibility of images based on displayed images. According to one aspect of this disclosure, the visibility of images based on displayed images can be improved.

[0008] [Basic configuration of the display device] Figure 1 is a schematic diagram illustrating the configuration of the display device 1 according to this disclosure. As shown in Figure 1, the display device 1 may include, for example, a housing 2, a viewing window 3, a display panel 4, an irradiator 5, an optical system 6, a controller 7, and a display panel mounting section 8. The specific positional relationships of the display panel 4, the irradiator 5, and the optical system 6 in the housing 2 will be described in each embodiment later.

[0009] The display device 1 in one embodiment of this disclosure may be a non-attachable device for the user Us who uses the display device 1. That is, it may not be attached to the user Us, but may be fixed to the environment and used. 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 Us. When attached to the user Us, the display device 1 may have an attachment part (not shown) so that the viewing part of the housing 2 is fixed at the position of the user Us's eyes.

[0010] The display device 1 directs a portion of the display light emitted from the display panel 4 into the eyes of the user Us using the display device 1, allowing the user Us to view it as an image, picture, or aerial image. The display device 1 can allow the user Us to view the display on the display panel 4 at a position different from the position of the display panel 4, using the display light emitted from the display panel 4. In one embodiment of this disclosure, the display device 1 may allow the user Us to view the display light as a virtual image V. The virtual image V may be formed on a side farther from the display device 1 as seen from the user Us. The virtual image V may be an upright virtual image that is an enlarged version of the display image displayed on the display panel 4. The virtual image V may be formed inside the housing 2 or outside the housing 2. The virtual image V may be formed on a side farther from the display panel 4 as seen from the user Us, or on a side closer to the display panel 4. The virtual image V may be formed on a side farther from the viewing window 3 as seen from the user Us, or on a side closer to the viewing window 3.

[0011] The display panel 4 may display a display image. This may mean that the display panel 4 is for displaying a display image. Specifically, the display panel 4 has a display surface 4a, and the display image may be displayed on the display surface 4a. In other words, the display panel 4 may emit display light of the display image from the display surface 4a. The display panel 4 may be configured to emit linearly polarized display light. The display panel 4 may emit, for example, S-wave polarized display light or P-wave polarized display light. The following description will focus on the case where the display panel 4 emits S-wave polarized display light, but is not limited to this. For example, if the display panel 4 emits P-wave polarized display light, then S-wave polarized light may be read as P-wave polarized light, and P-wave polarized light may be read as S-wave polarized light.

[0012] The display panel 4 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), or ECB (Electrically Controlled Birefringence) liquid crystal panels.

[0013] The display device 1 may include an illuminator 5 that illuminates the display panel 4 in a planar manner. The illuminator 5 is also called a backlight. The illuminator 5 may be an edge-lit backlight or a direct-lit backlight.

[0014] The display panel 4 is not limited to a liquid crystal panel (transmissive display panel). The display panel 4 may be a self-emissive display panel including, for example, a light-emitting diode (LED), an organic light-emitting diode (OLED), or a semiconductor laser (LD). If the display panel 4 is a self-emissive display panel, the irradiator 5 does not need to be provided.

[0015] The enclosure 2 may have an inner region 22. The inner region 22 may be a space contained inside the enclosure 2. The inner region 22 may be defined, for example, by the wall surface of the enclosure 2. In this case, it may be a space along the wall surface of the enclosure 2. The enclosure 2 may have an opening in which a part of the wall surface is cut out. The inner region 22 may be defined, for example, by the opening of the enclosure 2. In this case, it may be a space along the opening of the enclosure 2. However, the inner region 22 does not have to be a space that includes the entire inside of the enclosure 2, but may be a space that includes a part of the inside of the enclosure 2. The shape of the inner region 22 may be any shape. The shape of the inner region 22 may be, for example, a rectangular parallelepiped, a cube, or a sphere. Also, the shape of the inner region 22 may include, for example, at least a part of a planar shape, or at least a part of a curved shape. Also, the material of the wall surface may be any material, and may be a translucent member, which may be, for example, glass or resin.

[0016] The enclosure 2 may have an internal region as a space contained within the enclosure 2. The internal region may be, for example, a space along the walls of the enclosure 2, or a space along an opening in the enclosure 2. The internal region does not have to include the entire interior of the enclosure 2, but may include a part of the interior of the enclosure 2. The shape of the internal region may be any shape.

[0017] The housing 2 may include a display panel mounting section 8. The display panel mounting section 8 may be capable of mounting a display panel 4 such that its display surface 4a faces the inner region 22. That is, the display panel 4 mounted on the display panel mounting section 8 may be positioned so that its display surface 4a faces the inner region 22. The display panel mounting section 8 may be located on a part of the wall surface of the housing 2, or it may be located inside the housing 2. In this case, the display panel 4 may be located inside the housing 2. Alternatively, the display panel mounting section 8 may be located outside the housing 2. That is, the display panel 4 may be located outside the housing 2. In this case, the housing 2 may have an opening in which a part of the wall surface is cut out. The display panel mounting section 8 may be positioned relative to the housing 2 so that the display light emitted from the display panel 4 mounted on the display panel mounting section 8 is guided to the inside of the housing 2 through the opening. The display panel mounting section 8 may be connected to the outer wall of the housing 2, or it may be connected to the outer wall of the housing 2 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.

[0018] The display panel mounting section 8 may be capable of mounting a display panel 4 such that its display surface 4a faces an internal area. That is, the display panel 4 mounted on the display panel mounting section 8 may be positioned so that its display surface 4a faces an internal area. The display panel mounting section 8 may be located on a part of the wall surface of the housing 2, or it may be located inside the housing 2. In this case, the display panel 4 may be located inside the housing 2. Alternatively, the display panel mounting section 8 may be located outside the housing 2. That is, the display panel 4 may be located outside the housing 2. The display panel mounting section 8 may be positioned relative to the housing 2 such that the display light emitted from the display panel 4 mounted on the display panel mounting section 8 is guided into the interior of the housing 2 through the opening.

[0019] Furthermore, the housing 2 may have an opening 21 in which a portion of the wall surface is cut out. The opening 21 may function as a viewing area of ​​the housing 2. The opening 21 may be referred to as the first opening. The opening 21 may extend substantially perpendicular to the bottom of the housing 2.

[0020] The viewing window 3 may be a component that makes the inside of the housing 2 visible from the outside of the housing 2. The viewing window 3 may also be a component that makes the inside of the housing 2 visible from the outside of the housing 2. The viewing window 3 may be positioned to cover the opening 21. The material of the viewing window 3 may be a light-transmitting component, such as glass or resin. The viewing window 3 may function as a viewing section of the housing 2. That is, the viewing section may be the viewing window 3, or it may be a space where no component exists (for example, the opening 21).

[0021] The housing 2 may have a second opening, separate from the opening 21, which is formed by cutting out a portion of the wall surface. The second opening may be inclined with respect to the opening 21. In this case, the viewing window 3 may be positioned to block the second opening. The second opening may function as a viewing section of the housing 2.

[0022] The optical system 6 may form an image based on the display image. This may mean an optical system 6 for forming an image based on the display image. The optical system 6 may form an image of the display light emitted from the display panel 4. The optical system 6 may project the display light emitted from the display panel 4 as an image based on the display image into the user Us's field of view. The image based on the display image may be formed at a position different from the display panel 4. For example, the optical system 6 may project the display light emitted from the display panel 4 as a virtual image V into the user Us's field of view. In this way, the optical system 6 may form an image of the display light as a virtual image V. The virtual image V may be an example of an image based on the display image displayed by the display panel 4. Alternatively, for example, the optical system 6 may project the display light emitted from the display panel 4 as a real image into the user Us's field of view. In this way, the optical system 6 may form an image of the display light as a real image. The specific positional relationship of the optical system 6 will be explained in each embodiment described later.

[0023] Here, the optical system 6 may be capable of forming a virtual image V in a way that makes it visible through a viewing section (e.g., a viewing window 3, an aperture 21, or a second aperture). In other words, the virtual image V may be visible by looking through the viewing section. To put it another way, the virtual image V cannot be seen without the viewing section. The display device 1 does not have to have a viewing window 3. If the display device 1 does not have a viewing window 3, the optical system 6 may be capable of forming a virtual image V in a way that makes it visible through the aperture 21, or through the aperture 21 and the second aperture.

[0024] The controller 7 may be connected to and control each component of the display device 1. The controller 7 may control the irradiator 5. The controller 7 may control the display image displayed on the display panel 4 and the irradiator 5. The controller 7 may control the irradiator 5 based on the display image displayed on the display panel 4. The controller 7 may be configured to include one or more processors. The processors may include general-purpose processors configured to load specific programs and execute specific functions, and dedicated processors specialized for specific processing. The processors may include PLDs (Programmable Logic Devices). The controller 7 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 7 includes a memory unit, which may store various information or programs for operating each component of the display device 1. The memory unit may be composed of, for example, semiconductor memory. The memory unit may function as the work memory of the controller 7.

[0025] [Examples of applications for display devices] Figure 2 is a cross-sectional view showing the configuration of vehicle 50. As shown in Figure 2, vehicle 50 may be equipped with an imaging device 100. Vehicle 50 may be an example of a mobile body equipped with an imaging device 100. However, the mobile body equipped with the imaging device 100 is not limited to vehicle 50, but may be, for example, an aircraft or a ship. Vehicle 50 is not limited to a passenger car, but may be a truck, bus, trolleybus or other automobile, or a motorcycle. The position of the display device 1 may be arbitrary inside vehicle 50. The position of the display device 1 may be arbitrary inside vehicle 50. 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 equipped in vehicle 50.

[0026] The imaging device 100 may include a display system comprising a display device 1 and a camera 102. The imaging device 100 may be an example of a display system comprising a display device 1 and a camera 102. The camera 102 may capture images of the scenery around the vehicle 50. Here, the scenery around the vehicle 50 may be at least one of the front, rear, sides, above, and below the vehicle 50. 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 50, the display device 1 and the camera 102 may be connected via a vehicle network such as a CAN (Control Area Network).

[0027] 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 4. In this case, the imaging device 100 can make the scenery around the vehicle 50 visible to the user Us, who is the driver of the vehicle 50, as a virtual image V1. As a result, the user Us can view the scenery around the vehicle 50 without significantly changing the gaze distance and gaze point while driving the vehicle 50, 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 50, it will not occupy a large volume in the driver's cab and will not interfere with driving. The display device 1, which is mounted on the vehicle 50 and configured to make the scenery around the vehicle 50 (for example, the scenery behind the vehicle 50) visible to the user Us as a virtual image V1, may also be called a digital rearview mirror.

[0028] The imaging device 100 may include a reflective optical element. The imaging device 100 may be configured such that the display device 1 emits display light toward the reflective optical element, and the reflective optical element allows a portion of the display light to reach the eyes of the user Us. If the imaging device 100 is mounted on a vehicle 50, the imaging device 100 may also use the windshield 51 of the vehicle 50 as a reflective optical element.

[0029] Figure 3 is a schematic diagram showing the internal configuration of vehicle 50. The imaging device 100 may be applied to a digital side mirror. In this case, as shown in Figure 3, the imaging device 100 may include a display device 1(1L) located on the left A-pillar of vehicle 50 and a camera 102L that captures the left rear of vehicle 50. Alternatively, the imaging device 100 may include a display device 1(1R) located on the right A-pillar of vehicle 50 and a camera 102R that captures the right rear of vehicle 50. Display device 1L may display the image of the left rear of vehicle 50 captured by camera 102L as a virtual image V2 for the user Us to view. Display device 1R may display the image of the right rear of vehicle 50 captured by camera 102R as a virtual image V3 for the user Us to view. The image may be a moving image or a still image. Camera 102L may be positioned in the same location as the left-side door mirror, and camera 102R may be positioned in the same location as the right-side door mirror.

[0030] The imaging device 100 may be configured such that the distances between the user Us's eye or eyebox and the virtual images V2 and V3 are approximately equal. In this case, the user Us can check the situation on the left rear and right rear of the vehicle 50 without significantly changing the gaze distance. Therefore, driving safety can be improved. The eyebox may refer to the real-space region where the user Us's eye is assumed to be located.

[0031] The imaging device 100 may be configured such that the distance between the user Us's eye or eyebox and each of the virtual images V1 to V3 is approximately equal to each other. In this case, the user Us can check the situation immediately behind, to the left rear, and to the right rear of the vehicle 50 without significantly changing the gaze distance. Therefore, driving safety can be improved.

[0032] The imaging device 100 may be applied to a cluster 52 in the dashboard of the vehicle 50. In this case, the display device 1 may allow the user Us to view an image V4 that shows information related to driving, such as vehicle speed, engine speed, and fuel level.

[0033] The imaging device 100 may be applied to the CID (Center Information Display) 53. In this case, the display device 1 is located in the center cluster of the vehicle 50 and may display images showing information related to navigation, the in-vehicle environment (e.g., settings for the air conditioning system, audio system, etc.) as virtual images V5 for the user Us to view.

[0034] The imaging device 100 may be configured such that the distance between the user Us's eye or eyebox and the virtual images V4 and V5 are approximately equal. In this case, the user Us can view information related to the operation of the vehicle 50, as well as information related to navigation, the in-vehicle environment, etc., without significantly changing the gaze distance. Therefore, driving safety can be improved.

[0035] The imaging device 100 may be configured such that the distance between the user Us's eye or eyebox and each of the virtual images V1 to V5 is approximately equal. In this case, the user Us can check the area directly behind, to the left rear, and to the right rear of the vehicle 50 without significantly changing the gaze distance, and can also check information related to the vehicle 50's operation, navigation, and in-vehicle environment. Therefore, driving safety can be improved.

[0036] The imaging device 100 may be applied to a PID (Passenger Information Display) 54. In this case, the display device 1 is positioned near the passenger seat on the dashboard and may display images of entertainment content and images showing information about audio equipment, air conditioning equipment, etc., as virtual images V6 for the passenger user Us to view.

[0037] The imaging device 100 may be applied to the RSE (Rear Seat Entertainment) system 55. 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 50 to view.

[0038] [Display device related to the comparative example] Figure 4 is a schematic diagram illustrating the configuration of a comparative example display device 200. In the diagram showing the optical paths, for the sake of ease of illustration, the axis of the optical path of light incident approximately perpendicularly to the reflective surface of a certain member and the axis of the optical path of light reflected approximately perpendicularly by the same member are shown offset. However, in reality, these two optical paths may be located approximately on the same axis.

[0039] As shown in Figure 4, the display device 200 may include a display panel 210 and an optical system 211. The optical system 211 may include a first phase difference plate 212, a semi-transparent mirror 213, a second phase difference plate 214, and a reflective polarizer 215. The optical system 211 may be located inside the housing of the display device 200. The optical system 211 may be located inside the housing of the display device 200. The first phase difference plate 212, the semi-transparent mirror 213, the second phase difference plate 214, and the reflective polarizer 215 may be arranged in this order in the direction of emission of display light from the display panel 210.

[0040] The first phase difference plate 212 and the second phase difference plate 214 may be, for example, quarter-wave plates, i.e., λ / 4-wave plates. In this case, the first phase difference plate 212 and the second phase difference plate 214 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 210 by the reflective polarizer plate 215 and direct it onto the semi-transparent mirror 213. The positional relationship between the first phase difference plate 212 and the second phase difference plate 214 may be defined such that, when viewed along the Z-axis, the lagging axis of the second phase difference plate 214 is perpendicular to the lagging axis of the first phase difference plate 212. Furthermore, the positional relationship between the first phase difference plate 212 and the second phase difference plate 214 may be defined such that, when the first phase difference plate 212 and the second phase difference plate 214 are viewed along the Z-axis direction, the lagging axis of the second phase difference plate 214 and the lagging axis of the first phase difference plate 212 are parallel.

[0041] The first phase difference plate 212 and the second phase difference plate 214 only need 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 215. As long as such a phase difference can be provided, the first phase difference plate 212 and the second phase difference plate 214 may be other wave plates or combinations thereof, rather than quarter-wave plates. The first phase difference plate 212 and the second phase difference plate 214 may be film-like members.

[0042] Furthermore, the second phase difference plate 214 only needs to be able to provide the necessary phase difference to the light that has passed through the second phase difference plate 214, so that the light that has been reflected by the reflective polarizing plate 215 and passed through the second phase difference plate 214 passes through the reflective polarizing plate 215 again when it reaches the reflective polarizing plate 215. As long as such a phase difference can be provided, the second phase difference plate 214 may be a wave plate other than a quarter wave plate.

[0043] The semi-transparent mirror 213 may be positioned between the first phase difference plate 212 and the second phase difference plate 214. The semi-transparent mirror 213 may transmit a portion of the incident light (e.g., approximately 50%) and reflect the remainder (e.g., approximately 50%). However, the transmittance and reflectance of the light incident on the semi-transparent mirror 213 are not limited to 50%. The semi-transparent mirror 213 may reflect a portion of the display light reflected by the reflective polarizer 215 and direct it into the user Us's eyes. This makes it possible for the user Us to see the virtual image V. The semi-transparent mirror 213 may be a concave mirror having a concave reflective surface on the second phase difference plate 214 side. At least a portion of the reflective surface 6a may include a spherical shape, an aspherical shape, or a free-form surface shape. Furthermore, the semi-transparent mirror 213 may be composed of a holographic optical element (HOE), or its surface shape may have a Fresnel shape.

[0044] The reflective polarizer 215 may be positioned on the opposite side of the first phase difference plate 212 from the second phase difference plate 214. The reflective polarizer 215 may transmit a portion of the incident light and reflect the remainder. The reflective polarizer 215 may be configured to reflect polarized light having a polarization axis parallel to the polarization axis of the display light and transmit polarized light having a polarization axis perpendicular to the polarization axis of the display light. In this case, the positional relationship between the first phase difference plate 212 and the second phase difference plate 214 may be defined such that, when the first phase difference plate 212 and the second phase difference plate 214 are viewed along the Z-axis direction, the lagging axis of the second phase difference plate 214 is perpendicular to the lagging axis of the first phase difference plate 212. The reflective polarizer 215 may be configured to 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 212 and the second phase difference plate 214 may be defined such that when the first phase difference plate 212 and the second phase difference plate 214 are viewed along the Z-axis, the lagging axis of the second phase difference plate 214 and the lagging axis of the first phase difference plate 212 are parallel. This makes it possible for the user Us to view the virtual image V. The reflective polarizing plate 215 may be flat, or it may have a concave shape located on the display panel 210 side, or it may have a convex shape located on the display panel 210 side. Furthermore, the reflective polarizing plate 215 may be composed of a holographic optical element, or its surface shape may have a Fresnel shape.

[0045] In the example shown in Figure 4, the display panel 210 may emit S-wave polarized display light. The first phase difference plate 212 and the second phase difference plate 214 may change S-wave polarized light to left-handed circularly polarized light, or left-handed circularly polarized light to S-wave polarized light. That is, the first phase difference plate 212 and the second phase difference plate 214 may change P-wave polarized light to right-handed circularly polarized light, or right-handed circularly polarized light to P-wave polarized light. The reflective polarizer 215 may reflect S-wave polarized light and transmit P-wave polarized light. In the diagram showing the optical path, "S", "P", "L", and "R" may represent S-wave polarized light, P-wave polarized light, left-handed circularly polarized light, and right-handed circularly polarized light, respectively.

[0046] The first phase difference plate 212 and the second phase difference plate 214 may transmit incident light with almost no attenuation. The reflective polarizer 215 may transmit or reflect incident light with almost no attenuation. On the other hand, the semi-transparent mirror 213 may transmit a portion of the incident light and reflect the remainder. In the semi-transparent mirror 213, the display light emitted from the display panel 210 may be attenuated when incident from the first phase difference plate 212 side and when incident from the second phase difference plate 214 side. In the example in Figure 4, approximately 50% of the light incident from the first phase difference plate 212 side may be transmitted through the semi-transparent mirror 213, and approximately 50% of the light incident from the second phase difference plate 214 side may be reflected by the semi-transparent mirror 213. Therefore, the amount of light reflected by the semi-transparent mirror 213 and transmitted through the reflective polarizer 215 may be approximately 25% of the display light emitted by the display panel 210.

[0047] The display device 1 of this disclosure may emit light from the aperture 21 having approximately the same amount of light as the display light emitted by the display panel 4, by appropriately defining, for example, the positional relationship between the display panel 4 and the optical system 6, and the positions of each component constituting the optical system 6. Hereinafter, an example of the display device 1 of this disclosure will be described. The display device 1 of this disclosure differs from the display device 200 of the comparative example above, for example, in the configuration of the optical system, but other identical components are given the same reference numerals and detailed descriptions are omitted.

[0048] [Embodiment 1] Figure 5 is a cross-sectional view showing an example of the configuration of the display device 1A according to this embodiment. Figure 6 is a schematic diagram illustrating the configuration of the display device 1A according to this embodiment. In the diagram showing the optical path, the optical path from the light emitted from the display panel 4 to the second reflector 64 is shown by a dashed line.

[0049] Display device 1A may be an example of display device 1. Before giving a specific description of display device 1A, we will mainly describe the components of display device 1 that are common to each embodiment.

[0050] <Basic configuration of the display device in this disclosure> As shown in Figure 5, the display device 1 may include, for example, a viewing window 3, an inner region 22, a display panel 4, a semi-reflector 62, a first reflector 63, and a second reflector 64. As described above, the viewing window 3 is located in the opening 21 and may function together with the opening 21 as a viewing section. Hereafter, the viewing window 3 will be described as an example of a viewing section. The display panel 4 has a display surface 4a for displaying a display image, and the display surface 4a may be arranged so as to face the inner region 22 of the housing 2. The semi-reflector 62, the first reflector 63, and the second reflector 64 may be located inside the housing 2. The semi-reflector 62, the first reflector 63, and the second reflector 64 may function as an optical system 6.

[0051] The display panel 4 may be located inside the housing 2. The display panel 4 may also be located outside the housing 2. In this case, the housing 2 may have an opening in which a part of the wall surface is cut out. The display panel may be positioned relative to the housing 2 such that the display light emitted from the display panel 4 is guided to the inside of the housing 2 through the opening. The display panel 4 may be positioned along the opening, or positioned so as to block at least a part of the opening, or may be connected to the outer wall of the housing 2. A light-transmitting member may be placed in the opening, and this member may be, for example, glass or resin.

[0052] The semi-reflector 62 may be located in the inner region 22. The semi-reflector 62 may be located in the internal region. The semi-reflector 62 may have a first optical surface 62a and a second optical surface 62b. The first optical surface 62a may be positioned to face the viewing window 3, and one of the display surface 4a, the first reflective surface 63a, and the second reflective surface 64a. The second optical surface 62b may be positioned to face the other of the display surface 4a, the first reflective surface 63a, and the second reflective surface 64a. The first reflective surface 63a and the second reflective surface 64a will be described later.

[0053] The semi-reflector 62 may have a first optical surface 62a on the side of the viewing window 3 and a second optical surface 62b on the opposite side of the first optical surface 62a. The semi-reflector 62 may be a member that transmits first polarized light and reflects second polarized light, or it may be a reflective polarizer that transmits first polarized light and reflects second polarized light.

[0054] The first and second polarizations may have different polarization states. For example, if the first polarization is left-handed circularly polarized light, the second polarization may be right-handed circularly polarized light. For example, if the first polarization is right-handed circularly polarized light, the second polarization may be left-handed circularly polarized light. The semi-reflector 62 may be a first reflective polarizer 621 that transmits the first circularly polarized light as the first polarization and reflects the second circularly polarized light as the second polarization. In this case, the first reflective polarizer 621 may include, for example, a cholesteric liquid crystal film. Also, for example, if the first polarization is S-wave polarized light, the second polarization may be P-wave polarized light. For example, if the first polarization is P-wave polarized light, the second polarization may be S-wave polarized light. The semi-reflector 62 may be a second reflective polarizer 622 that transmits the first linearly polarized light as the first polarization and reflects the second linearly polarized light as the second polarization.

[0055] The first reflector 63 may have a first reflective surface 63a facing the inner region 22. The first reflector 63 may have a first reflective surface 63a facing the interior region. The first reflector 63 may be positioned to face the first optical surface 62a or the second optical surface 62b. That is, the first reflector 63 may be positioned so that its first reflective surface 63a faces the semi-reflector 62 side. The first reflector 63 may, for example, reflect all of the incident light, reflect 95% or more, or reflect 90% or more. Alternatively, for example, the first reflector 63 may be a plane mirror whose first reflective surface 63a is planar. In this case, the first reflector 63 may be called a planar full mirror. In this disclosure, "planar" means that it is not a curved surface at a visible level, or that it does not have visible irregularities, and it is not required to be strictly flat.

[0056] The first reflector 63 may be composed of, for example, a substrate and a reflective layer located on the surface of the substrate. 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 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 reflective layer is not limited to a thin metal film, and may be, for example, a dielectric multilayer film. The surface of the reflective layer is the first reflective surface 63a, and light may be reflected by the first reflective surface 63a.

[0057] The second reflector 64 may have a second reflective surface 64a facing the inner region 22. The second reflector 64 may have a second reflective surface 64a facing the interior region. The second reflector 64 may be positioned to face the first optical surface 62a or the second optical surface 62b. That is, the second reflector 64 may be positioned so that its second reflective surface 64a faces the semi-reflector 62 side. The second reflector 64 may, for example, reflect all of the incident light, or reflect 95% or more of it, or reflect 90% or more of it. Also, for example, the second reflector 64 may have a function to collect or focus light. Specifically, the second reflector 64 may have a function to collect or focus light that has been incident on and reflected by the second reflector 64. The second reflector 64 may be a concave mirror in which the second reflective surface 64a is concave. In other words, the second reflector 64 may have a shape that is recessed towards the semi-reflector 62 side. In this case, the second reflector 64 may be called a concave full mirror.

[0058] If the second reflective surface 64a is concave, the second reflector 64 can focus or concentrate light. In this case, the second reflector 64 can also form an image based on the displayed image, which can be viewed by the user Us. If the length of the optical path of the light emitted from the display panel 4 to the second reflector 64, i.e., the optical path length of the light, is less than the focal length of the second reflector 64, the second reflector 64 can make a virtual image V, based on the displayed image, visible to the user Us. If the optical path length of the light is greater than the focal length of the second reflector 64, the second reflector 64 can make a real image, based on the displayed image, visible to the user Us.

[0059] The second reflector 64 may be composed of, for example, a substrate and a reflective layer located on the surface of the substrate. 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 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 reflective layer is not limited to a thin metal film, and may be, for example, a dielectric multilayer film. The surface of the reflective layer is the second reflective surface 64a, and light may be reflected by the second reflective surface 64a.

[0060] Furthermore, the second reflector 64 may have the function of reflecting and diverging light. Specifically, the second reflector 64 may have the function of reflecting and diverging light incident on the second reflector 64. The second reflector 64 may be a convex mirror in which the second reflective surface 64a is convex. In this case, the second reflector 64 may be called a convex full mirror. The second reflector 64 may be a reflector in which at least a part of the second reflective surface 64a has a curved shape. The second reflector 64 may include a spherical shape, an aspherical shape, or a free-form shape in at least a part of the second reflective surface 64a. In addition, the second reflector 64 may be composed of a holographic optical element, or its surface shape may have a Fresnel shape.

[0061] Furthermore, the display panel 4 may be positioned to face either the first optical surface 62a or the second optical surface 62b. That is, the display panel 4 may be positioned so that its display surface 4a faces the semi-reflector 62 side.

[0062] As described above, the display surface 4a, the first reflective surface 63a, and the second reflective surface 64a may face the inner region 22. The display panel 4, the first reflector 63, and the second reflector 64 may be positioned along the inner region 22 so as not to overlap each other. Alternatively, it can be said that the display panel 4, the first reflector 63, and the second reflector 64 are positioned to surround the inner region 22. The display panel 4, the first reflector 63, and the second reflector 64 may be positioned along the inner region so as not to overlap each other. Alternatively, it can be said that the display panel 4, the first reflector 63, and the second reflector 64 are positioned to surround the inner region.

[0063] Here, the normal passing through the center of the display surface 4a may be referred to as the first normal NL1, the normal passing through the center of the first reflective surface 63a as the second normal NL2, the normal passing through the center of the second reflective surface 64a as the third normal NL3, and the normal passing through the centers of the first optical surface 62a and the second optical surface 62b as the fourth normal NL4. In the display device 1 of this disclosure, the display panel 4, the first reflector 63, the second reflector 64, and the semi-reflector 62 may be positioned such that the first normal NL1, the second normal NL2, the third normal NL3 and the fourth normal NL4 face different directions. Furthermore, the first normal NL1 may be the optical axis of the display surface 4a, the second normal NL2 may be the optical axis of the first reflective surface 63a, the third normal NL3 may be the optical axis of the second reflective surface 64a, and the fourth normal NL4 may be the optical axes of the first optical surface 62a and the second optical surface 62b.

[0064] With the above configuration, the first reflector 63 and the second reflector 64 reflect almost all of the incident light, so that almost all of the light emitted from the display panel 4 can be guided to the viewing window 3. Therefore, the display device 1 can increase the brightness efficiency of the image based on the display image. Consequently, the display device 1 can improve the visibility of the image based on the display image. That is, the display device 1 can achieve this effect because the display surface 4a, the first optical surface 62a, the second optical surface 62b, the first reflective surface 63a, and the second reflective surface 64a are positioned as described above. Furthermore, because the positional relationship between the display panel 4, the first reflector 63, the second reflector 64, and the semi-reflector 62 is defined as described above, the display device 1 of this disclosure can be miniaturized.

[0065] Furthermore, as shown in Figure 5, the semi-reflector 62 may be inclined with respect to the viewing window 3. That is, the semi-reflector 62 may be positioned within the housing 2 such that the fourth normal NL4 is inclined with respect to the viewing window 3. With this configuration, even if ambient light is incident on the semi-reflector 62 in the opposite direction to the direction in which the light emitted from the display panel 4 travels to the outside of the housing 2, the semi-reflector 62 can reflect the ambient light in a different direction. Therefore, the possibility of an image based on ambient light being seen by the user Us can be reduced.

[0066] Furthermore, in the display device 1, if the length in the X-axis direction is referred to as the horizontal length, the length in the Y-axis direction as the height, and the length in the Z-axis direction as the depth length, the horizontal length may be longer than the height or depth length. In this case, the display device 1 may have a horizontally elongated viewing section. Also, for example, at least one of the display panel 4, the first reflector 63, the second reflector 64, and the semi-reflector 62 may be horizontally elongated. That is, for example, in Figure 5, the horizontal length of at least one of the display panel 4, the first reflector 63, the second reflector 64, and the semi-reflector 62 may be longer than the height or depth length. More specifically, for example, in Figure 5, the length in the X-axis direction (horizontal length) of at least one of the display panel 4, the first reflector 63, and the semi-reflector 62 may be longer than the length in the Z-axis direction (depth length).

[0067] <Configuration of the display device in this embodiment> As shown in Figure 5, the display device 1A of this embodiment may include a first reflective polarizing plate 621 as an example of a semi-reflective plate 62. In this case, the semi-reflective plate 62 may include a substrate and a film that transmits first circularly polarized light and reflects second circularly polarized light. The film may be, for example, a cholesteric liquid crystal film. The substrate and the film may be integrated. "Integrated" 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 OCR (Optical Clear Resin) or OCA (Optical Clear Adhesive).

[0068] A cholesteric liquid crystal film may be a film having multiple layers in which liquid crystal molecules are arranged in the same direction, and the direction of this arrangement is slightly twisted in adjacent layers, forming a helical structure of liquid crystal molecules in the stacking direction. 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.

[0069] In the display device 1A, the first optical surface 62a may be positioned to face the viewing window 3 and the display surface 4a, and the second optical surface 62b may be positioned to face the first reflective surface 63a and the second reflective surface 64a. That is, the display panel 4 may be positioned to face the first optical surface 62a. The first reflector 63 may be positioned to face the second optical surface 62b. The second reflector 64 may be positioned to face the second optical surface 62b. The second reflector 64 may be positioned to face the surface opposite to the surface of the first reflective polarizing plate 621 that the display panel 4 faces.

[0070] Specifically, as shown in Figure 5, the display panel 4 and the second reflector 64 may be positioned such that the first normal NL1 and the third normal NL3 face in different directions. The first reflector 63 and the second reflector 64 may be positioned such that the second normal NL2 and the third normal NL3 face in different directions. Furthermore, the display surface 4a may be positioned to face the first optical surface 62a, the first reflective surface 63a may be positioned to face the second optical surface 62b and the display surface 4a, and the second reflective surface 64a may be positioned to face the second optical surface 62b and the viewing window 3.

[0071] When the display device 1A is placed on a horizontal surface, if the upward direction is considered to be the +Y axis, then in the display device 1A, the display panel 4 may be located at the top of the housing 2. The first reflector 63 may be located at the bottom of the housing 2. However, in the display device 1A, the display panel 4 may be located at the bottom of the housing 2, and the first reflector 63 may be located at the top of the housing 2. In other words, the positional relationship of each component of the display device 1A may be inverted vertically. Also, the positional relationship of each component of the display device in other embodiments of this disclosure may be inverted vertically. The second reflector 64 may be located on the housing 2 on the side opposite to the viewing window 3. The first reflective polarizing plate 621 may be located within the housing 2 between the viewing window 3 and the second reflector 64, and between the display panel 4 and the first reflector 63. The first reflective polarizing plate 621 may be positioned such that the first optical surface 62a faces the display surface 4a and the viewing window 3, and the second optical surface 62b faces the first reflective surface 63a and the second reflective surface 64a. The first reflective polarizing plate 621 may be positioned at an angle of approximately 45° with respect to a plane parallel to the viewing window 3.

[0072] Approximately 45° may be, for example, 35° to 55°, 40° to 50°, or 43° to 48°. This inclination angle may be adjusted to allow the propagation of light as shown in Figure 6, and is not limited to approximately 45°. Furthermore, the first reflective polarizer 621 may be positioned at an angle of approximately 45° with respect to at least one of the first normal NL1, second normal NL2, and third normal NL3. For example, the angle between at least one of the first normal NL1, second normal NL2, and third normal NL3 and the fourth normal NL4 may be approximately 45°. These angle details can also be applied to the display device 1 according to other embodiments described later. That is, for example, they can be applied not only to the case of the first reflective polarizer 621, but also to the case of the second reflective polarizer 622.

[0073] The display device 1A may include a display panel 4, a first reflector 63, a second reflector 64, and a first reflective polarizer 621, in addition to a first phase difference plate 611. In this case, the first reflector 63, the second reflector 64, the first reflective polarizer 621, and the first phase difference plate 611 may function as an optical system 6.

[0074] The first phase difference plate 611 may be located between the display panel 4 and the first reflective polarizer 621. The first phase difference plate 611 may face the display surface 4a and be integrated with the display panel 4. However, the first phase difference plate 611 may be located separately from the display panel 4. Also, the first phase difference plate 611 may face the first optical surface 62a and be integrated with the first reflective polarizer 621.

[0075] In the display device 1A, as shown in Figure 6, the first phase difference plate 611 is designed so that the light emitted from the display panel 4 and transmitted through the first phase difference plate 611 is transmitted through the first reflective polarizing plate 621, and the light transmitted through the first phase difference plate 611 is given the necessary phase difference. As long as such a phase difference can be given, the first phase difference plate 611 may be a quarter-wave plate, or it may be a different type of wave plate, or a combination thereof.

[0076] In this disclosure, the first phase difference plate 611 may be a quarter-wave plate, or it may be a different type of wave plate, or a combination thereof, as long as it can provide the necessary phase difference to the light transmitted through the first phase difference plate 611. In this disclosure, the case where the first phase difference plate 611 is a quarter-wave plate will be explained as an example. The first phase difference plate 611 may be a film-like member.

[0077] In the display device 1A, as shown in Figure 6, the display panel 4 may emit S-wave polarized light as display light. The first reflective polarizer 621 may transmit left-handed circularly polarized light and reflect right-handed circularly polarized light. In this case, the first phase difference plate 611 may be a phase difference plate that converts S-wave polarized light into left-handed circularly polarized light.

[0078] However, for example, if the display panel 4 emits P-wave polarized light, the first phase difference plate 611 may be a phase difference plate that converts P-wave polarized light into left-handed circularly polarized light. Also, for example, if the first reflective polarizer 621 transmits right-handed circularly polarized light and reflects left-handed circularly polarized light, the first phase difference plate 611 may be a phase difference plate that converts S-wave polarized light into right-handed circularly polarized light. Also, for example, if the display panel 4 emits P-wave polarized light and the first reflective polarizer 621 transmits right-handed circularly polarized light, the first phase difference plate 611 may be a phase difference plate that converts P-wave polarized light into right-handed circularly polarized light.

[0079] An example of the propagation of light emitted from the display panel 4 will be explained using Figure 6. Linearly polarized display light emitted from the display panel 4 may be converted into first circularly polarized light by passing through the first phase difference plate 611 and guided to the first reflective polarizer 621. The first reflective polarizer 621 may transmit the first circularly polarized light as the first polarization and reflect the second circularly polarized light, which has a different polarization state from the first circularly polarized light, as the second polarization. The display light may be, for example, S-wave polarized light. Also, the first circularly polarized light may be, for example, left-handed circularly polarized light, and the second circularly polarized light may be, for example, right-handed circularly polarized light.

[0080] Therefore, the first circularly polarized light converted by the first phase difference plate 611 may pass through the first reflective polarizer plate 621 and be guided to the first reflecting mirror 63. The first circularly polarized light incident on the first reflecting mirror 63 may be converted into second circularly polarized light by reflection at the first reflective surface 63a and guided to the first reflective polarizer plate 621.

[0081] Light of second circular polarization incident on the first reflective polarizer 621 may be reflected at the second optical surface 62b and guided to the second reflector 64. Light of second circular polarization incident on the second reflector 64 may be reflected at the second reflective surface 64a, converted into light of first circular polarization, and guided to the first reflective polarizer 621. Light of first circular polarization incident on the first reflective polarizer 621 may pass through the first reflective polarizer 621 and be guided to the viewing window 3.

[0082] Thus, in the display device 1A, the first reflective polarizing plate 621 may transmit light emitted from the display panel 4 to the first reflector 63, and then reflect the light reflected by the first reflector 63 to the second reflector 64. The light reflected by the second reflector 64 may then be transmitted to the viewing window 3.

[0083] By defining the positional relationship between the display panel 4, the first reflector 63, and the second reflector 64, and guiding the light emitted from the display panel 4 to the viewing window 3, the brightness efficiency of the image based on the displayed image can be increased.

[0084] Furthermore, the light emitted from the display panel 4 may be guided to the second reflector 64 via the first reflective polarizer 621 and the first reflector 63, as shown by the dashed line in Figure 6. Therefore, even when the display panel 4 and optical system 6 are miniaturized, a sufficient optical path length can be secured for the light emitted from the display panel 4 to the second reflector 64. For example, an optical path length equivalent to that of a structure in which each component is included on the same straight line, as shown in Figure 4, can be secured. Therefore, the display position of the image based on the display image can be moved away from the user Us. In addition, since the display surface 4a is not facing the viewing window 3, the possibility of external light being reflected by the display surface 4a can be reduced.

[0085] The optical path length can be changed, for example, by changing the position of the display panel 4, the position of the first reflector 63, or the position of the second reflector 64. In particular, for the optical path of the light emitted from the display panel 4 to the second reflector 64, the optical path length can be effectively increased by moving the member that forms the optical path back and forth between the member and the semi-reflector 62, as far as the member is farther away from the semi-reflector 62. In this embodiment, the optical path length can be effectively increased as farther the first reflector 63 is farther away from the first reflective polarizer 621.

[0086] As mentioned above, when forming a virtual image V as an image based on a display image, the focal length of the second reflector 64 may be greater than the optical path length. Therefore, when forming a virtual image V, the longer the optical path length, the greater the focal length of the second reflector 64 can be, and the larger the virtual image V can be. Also, the larger the focal length of the second reflector 64, the smaller the distortion of the image based on the display image can be. Therefore, by ensuring a sufficient optical path length as described above, the focal length of the second reflector can be increased, and an image based on a display image with less distortion can be formed. In addition, by ensuring a sufficient optical path length, a large virtual image V can be formed.

[0087] Furthermore, by positioning the image based on the displayed image at a distance from the user Us, the strain on the user Us's eyes when viewing the image can be reduced. The distance from the display position of the image based on the displayed image to the user Us may be referred to as VID (Virtual Image Distance).

[0088] [Embodiment 2] Other embodiments of the present disclosure are 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. Figure 7 is a cross-sectional view showing an example of the configuration of the display device 1B according to this embodiment. Figure 8 is a schematic diagram showing a general configuration of the display device 1B according to this embodiment. The display device 1B may be an example of the display device 1.

[0089] As shown in Figure 7, the display device 1B may include a second reflective polarizer 622 instead of the first reflective polarizer 621 as an example of a semi-reflective plate 62. The second reflective polarizer 622 may be a wire grid polarizer composed of a substrate and a plurality of metal nanowires (also called a metal nanowire grid) located on the surface of the substrate. The metal nanowires may be made of a metal material such as aluminum, chromium, or titanium oxide. The metal nanowires may be arranged in one direction. 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 a resin material, a glass material, or the like. The second reflective polarizer 622 can transmit light components vibrating in a direction perpendicular to the grid and reflect light components vibrating in a direction parallel to the grid.

[0090] In the display device 1B, the first optical surface 62a may be positioned to face the viewing window 3 and the display surface 4a, and the second optical surface 62b may be positioned to face the first reflective surface 63a and the second reflective surface 64a. That is, the display panel 4 may be positioned to face the first optical surface 62a. The first reflector 63 may be positioned to face the second optical surface 62b. The second reflector 64 may also be positioned to face the second optical surface 62b. The second reflector 64 may be positioned to face the side opposite to the side of the second reflective polarizing plate 622 that the display panel 4 faces.

[0091] Specifically, as shown in Figure 7, the display panel 4 and the second reflector 64 may be positioned such that the first normal NL1 and the third normal NL3 face in different directions. The first reflector 63 and the second reflector 64 may be positioned such that the second normal NL2 and the third normal NL3 face in different directions. The display surface 4a may be positioned to face the first optical surface 62a, the first reflective surface 63a may be positioned to face the second optical surface 62b and the display surface 4a, and the second reflective surface 64a may be positioned to face the second optical surface 62b and the viewing window 3. In other words, the positional relationship of the display panel 4, the first reflector 63, the second reflector 64 and the second reflective polarizer 622 of the display device 1B may be the same as the positional relationship of the display panel 4, the first reflector 63, the second reflector 64 and the first reflective polarizer 621 of the display device 1A shown in Figure 5.

[0092] The display device 1B may include a display panel 4, a first reflector 63, a second reflector 64, and a second reflecting polarizer 622, in addition to a first phase difference plate 611. In this case, the first reflector 63, the second reflector 64, the second reflecting polarizer 622, and the first phase difference plate 611 may function as an optical system 6.

[0093] The first phase difference plate 611 may be located between the second reflective polarizer 622 and the first reflector 63 and the second reflector 64. As shown in Figure 8, the first phase difference plate 611 may be located on the optical path between the second reflective polarizer 622 and the first reflector 63, and on the optical path between the second reflective polarizer 622 and the second reflector 64.

[0094] As shown in Figure 7, the first phase difference plate 611 may face the second optical surface 62b and be integrated with the second reflective polarizer 622. In this case, the first phase difference plate 611 may be bonded to the base material of the second reflective polarizer 622. However, the first phase difference plate 611 may be positioned separately from the second reflective polarizer 622, as long as it is located on the two optical paths.

[0095] In the display device 1B, as shown in Figure 8, the first phase difference plate 611 should be configured such that the light transmitted through the first phase difference plate 611 is reflected by the first reflector 63, and then the light transmitted through the first phase difference plate 611 again is reflected by the second reflective polarizer 622.

[0096] In the display device 1B, as shown in Figure 8, the display panel 4 may emit S-wave polarized light as display light. The second reflective polarizer 622 may transmit S-wave polarized light and reflect P-wave polarized light. In this case, the first phase difference plate 611 may be a phase difference plate that converts S-wave polarized light to left-handed circularly polarized light. Such a first phase difference plate 611 may have the functions of converting left-handed circularly polarized light to S-wave polarized light, converting P-wave polarized light to right-handed circularly polarized light, and converting right-handed circularly polarized light to P-wave polarized light.

[0097] However, for example, the display panel 4 may emit P-wave polarized light, and the second reflective polarizer 622 may transmit P-wave polarized light and reflect S-wave polarized light. In this case as well, the first phase difference plate 611 may have the above functions. Alternatively, the first phase difference plate 611 may be a phase difference plate that converts P-wave polarized light to left-handed circularly polarized light. In this case, the first phase difference plate 611 may have the functions of converting left-handed circularly polarized light to P-wave polarized light, converting S-wave polarized light to right-handed circularly polarized light, and converting right-handed circularly polarized light to S-wave polarized light.

[0098] An example of the propagation of light emitted from the display panel 4 will be explained using Figure 8. The second reflective polarizer 622 may transmit light with first linear polarization as first polarization and reflect light with second linear polarization, which has a different polarization state from the first linear polarization, as second polarization. Also, the linearly polarized display light emitted from the display panel 4 may be light with first linear polarization. Therefore, the linearly polarized display light emitted from the display panel 4 may pass through the second reflective polarizer 622 and be guided to the first phase difference plate 611. The first linearly polarized light may be, for example, S-wave polarized light, and the second linearly polarized light may be, for example, P-wave polarized light.

[0099] The first phase difference plate 611 may convert first linearly polarized light to first circularly polarized light, or first circularly polarized light to first linearly polarized light. The first phase difference plate 611 may also convert second linearly polarized light to second circularly polarized light, or second circularly polarized light to second linearly polarized light. Therefore, first linearly polarized light incident on the first phase difference plate 611 may be converted to first circularly polarized light by passing through the first phase difference plate 611 and guided to the first reflector 63. The first circularly polarized light may be, for example, left-handed circularly polarized light, and the second circularly polarized light may be, for example, right-handed circularly polarized light. Also, the first circularly polarized light may be, for example, right-handed circularly polarized light, and the second circularly polarized light may be, for example, left-handed circularly polarized light.

[0100] The first circularly polarized light incident on the first reflector 63 may be converted into second circularly polarized light by reflection at the first reflective surface 63a and guided to the first phase difference plate 611. The second circularly polarized light incident on the first phase difference plate 611 may be converted into second linearly polarized light by transmission through the first phase difference plate 611 and guided to the second reflective polarizer plate 622.

[0101] Light of the second linear polarization incident on the second reflective polarizer 622 may be reflected by the second optical surface 62b of the second reflective polarizer 622 and guided to the first phase difference plate 611. Light of the second linear polarization incident on the first phase difference plate 611 may be converted into light of the second circular polarization by passing through the first phase difference plate 611 and guided to the second reflector 64. Light of the second circular polarization incident on the second reflector 64 may be converted into light of the first circular polarization by reflecting at the second reflective surface 64a and guided to the first phase difference plate 611. Light of the first circular polarization incident on the first phase difference plate 611 may be converted into light of the first linear polarization by passing through the first phase difference plate 611 and guided to the second reflective polarizer 622. Light of the first linear polarization incident on the second reflective polarizer 622 may be passed through the second reflective polarizer 622 and guided to the viewing window 3.

[0102] Thus, in the display device 1B, the second reflective polarizing plate 622 may transmit light emitted from the display panel 4 to the first reflector 63, and then reflect the light reflected by the first reflector 63 to the second reflector 64. The light reflected by the second reflector 64 may then be transmitted to the viewing window 3.

[0103] <Another example of display device 1B> In the display device 1B, one first phase difference plate 611 may be located in the optical path between the second reflective polarizing plate 622 and the first reflector 63, and in the optical path between the second reflective polarizing plate 622 and the second reflector 64. Alternatively, phase difference plates may be located in the optical path between the second reflective polarizing plate 622 and the first reflector 63, and in the optical path between the second reflective polarizing plate 622 and the second reflector 64.

[0104] Figure 9 is a schematic diagram illustrating the configuration of the display device 1C according to this embodiment. The display device 1C may be an example of the display device 1. As shown in Figure 9, in the display device 1C, the first phase difference plate 611 may be located between the second reflective polarizing plate 622 and the first reflecting mirror 63, and the second phase difference plate 612 may be located between the second reflective polarizing plate 622 and the second reflecting mirror 64. The first reflecting mirror 63, the second reflecting mirror 64, the second reflective polarizing plate 622, the first phase difference plate 611, and the second phase difference plate 612 may function as an optical system 6.

[0105] The first phase difference plate 611 may face the first reflective surface 63a and be integrated with the first reflector 63. The second phase difference plate 612 may face the second reflective surface 64a and be integrated with the second reflector 64. However, the first phase difference plate 611 may be positioned separately from the first reflector 63. The second phase difference plate 612 may be positioned separately from the second reflector 64.

[0106] In the display device 1C, the first phase difference plate 611 should be configured such that the light transmitted through the first phase difference plate 611 is reflected by the first reflector 63, and then the light transmitted through the first phase difference plate 611 again is reflected by the second reflecting polarizer 622, thereby providing the necessary phase difference to the light.

[0107] In the display device 1C, the second phase difference plate 612 only needs to be configured such that the light transmitted through the second phase difference plate 612, after being reflected by the second reflector 64, is transmitted through the second phase difference plate 612 again and then transmits through the second reflecting polarizer 622. As long as such a phase difference can be provided, the second phase difference plate 612 may be a quarter-wave plate, or it may be a different type of wave plate, or a combination thereof.

[0108] In this disclosure, the second phase difference plate 612 may be a quarter-wave plate, or it may be a different type of wave plate, or a combination thereof, as long as it can provide the necessary phase difference to the light transmitted through the second phase difference plate 612. In this disclosure, the case where the second phase difference plate 612 is a quarter-wave plate will be explained as an example. The second phase difference plate 612 may be a film-like member.

[0109] In the display device 1C, the display panel 4 may emit S-wave polarized light as display light. The second reflective polarizer 622 may transmit S-wave polarized light and reflect P-wave polarized light. In this case, the first phase difference plate 611 may be a phase difference plate that converts S-wave polarized light into left-handed circularly polarized light. Such a first phase difference plate 611 may have the function of converting right-handed circularly polarized light into P-wave polarized light. The second phase difference plate 612 may be a phase difference plate that converts P-wave polarized light into right-handed circularly polarized light. Such a second phase difference plate 612 may have the function of converting left-handed circularly polarized light into S-wave polarized light. That is, when the first phase difference plate 611 and the second phase difference plate 612 are viewed along the path of light transmitted through each phase difference plate, the direction of the lagging axis of the first phase difference plate 611 and the direction of the lagging axis of the second phase difference plate 612 may be in the same direction.

[0110] However, for example, the display panel 4 may emit P-wave polarized light, and the second reflective polarizer 622 may transmit P-wave polarized light and reflect S-wave polarized light. In this case as well, the first phase difference plate 611 and the second phase difference plate 612 may have the above functions. The first phase difference plate 611 may convert P-wave polarized light into right-handed circularly polarized light and left-handed circularly polarized light into S-wave polarized light. The second phase difference plate 612 may convert S-wave polarized light into left-handed circularly polarized light and right-handed circularly polarized light into P-wave polarized light. In this case, the first phase difference plate 611 may be a phase difference plate that converts P-wave polarized light into left-handed circularly polarized light. In this case, the first phase difference plate 611 may have the function of converting right-handed circularly polarized light into S-wave polarized light. In addition, the second phase difference plate 612 may be a phase difference plate that converts S-wave polarized light into right-handed circularly polarized light. In this case, the second phase difference plate 612 may have the function of converting left-handed circularly polarized light into P-wave polarized light.

[0111] An example of the propagation of light emitted from the display panel 4 will be explained using Figure 9. The second reflective polarizer 622 may transmit light with first linear polarization as first polarization and reflect light with second linear polarization as second polarization. Also, the linearly polarized display light emitted from the display panel 4 may be light with first linear polarization. Therefore, the linearly polarized display light emitted from the display panel 4 may pass through the second reflective polarizer 622 and be guided to the first phase difference plate 611. The first linearly polarized light may be, for example, S-wave polarized light, and the second linearly polarized light may be, for example, P-wave polarized light. Also, the first linearly polarized light may be, for example, P-wave polarized light, and the second linearly polarized light may be, for example, S-wave polarized light.

[0112] The first phase difference plate 611 may convert first linearly polarized light to first circularly polarized light, or second circularly polarized light to second linearly polarized light. The second phase difference plate 612 may convert second linearly polarized light to second circularly polarized light, or first circularly polarized light to first linearly polarized light. Therefore, first linearly polarized light incident on the first phase difference plate 611 may be converted to first circularly polarized light by passing through the first phase difference plate 611 and guided to the first reflector 63. The first circularly polarized light may be, for example, left-handed circularly polarized light, and the second circularly polarized light may be, for example, right-handed circularly polarized light. Also, the first circularly polarized light may be, for example, right-handed circularly polarized light, and the second circularly polarized light may be, for example, left-handed circularly polarized light.

[0113] The first circularly polarized light incident on the first reflector 63 may be converted into second circularly polarized light by reflection at the first reflective surface 63a and guided to the first phase difference plate 611. The second circularly polarized light incident on the first phase difference plate 611 may be converted into second linearly polarized light by transmission through the first phase difference plate 611 and guided to the second reflective polarizer plate 622.

[0114] Light of the second linear polarization incident on the second reflective polarizer 622 may be reflected by the second optical surface 62b of the second reflective polarizer 622 and guided to the second phase difference plate 612. Light of the second linear polarization incident on the second phase difference plate 612 may be converted into light of the second circular polarization by passing through the second phase difference plate 612 and guided to the second reflector 64. Light of the second circular polarization incident on the second reflector 64 may be converted into light of the first circular polarization by reflecting at the second reflective surface 64a and guided to the second phase difference plate 612. Light of the first circular polarization incident on the second phase difference plate 612 may be converted into light of the first linear polarization by passing through the second phase difference plate 612 and guided to the second reflective polarizer 622. Light of the first linear polarization incident on the second reflective polarizer 622 may be passed through the second reflective polarizer 622 and guided to the viewing window 3.

[0115] Thus, in the display device 1C, the second reflective polarizing plate 622 may transmit light emitted from the display panel 4 to the first reflector 63, and then reflect the light reflected by the first reflector 63 to the second reflector 64. The light reflected by the second reflector 64 may then be transmitted to the viewing window 3.

[0116] [Embodiment 3] Other embodiments of this disclosure are 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. Figure 10 is a cross-sectional view showing an example of the configuration of the display device 1D according to this embodiment. Figure 11 is a schematic diagram showing a general configuration of the display device 1D according to this embodiment. The display device 1D may be an example of the display device 1.

[0117] As shown in Figure 11, the display device 1D of this embodiment may include a first reflective polarizing plate 621 as an example of a semi-reflective plate 62. In the display device 1D, the first optical surface 62a may be positioned to face the viewing window 3 and the second reflective surface 64a, and the second optical surface 62b may be positioned to face the display surface 4a and the first reflective surface 63a. That is, the display panel 4 may be positioned to face the second optical surface 62b. The first reflector 63 may be positioned to face the second optical surface 62b. The second reflector 64 may be positioned to face the first optical surface 62a. The second reflector 64 may be positioned to face the surface opposite to the surface of the first reflective polarizing plate 621 that the display panel 4 faces.

[0118] Specifically, as shown in Figure 10, the display panel 4 and the first reflector 63 may be positioned such that the first normal NL1 and the second normal NL2 face in different directions. The display panel 4 and the second reflector 64 may be positioned such that the first normal NL1 and the third normal NL3 face in different directions. Furthermore, the display surface 4a may be positioned to face the second optical surface 62b and the viewing window 3, the first reflector 63a may be positioned to face the second optical surface 62b and the second reflector 64a, and the second reflector 64a may be positioned to face the first optical surface 62a.

[0119] When the display device 1D is placed on a horizontal surface, if the upward direction is considered to be the +Y axis, then in the display device 1D, the display panel 4 may be located on the part of the housing 2 opposite to the viewing window 3. The first reflector 63 may be located at the bottom of the housing 2. The second reflector 64 may be located at the top of the housing 2. Alternatively, the first reflector 63 may be located at the top of the housing 2, and the second reflector 64 may be located at the bottom of the housing 2. The first reflective polarizer 621 may be located within the housing 2 between the viewing window 3 and the display panel 4, and between the second reflector 64 and the first reflector 63. The first reflective polarizer 621 may be positioned such that the first optical surface 62a faces the second reflective surface 64a and the viewing window 3, and the second optical surface 62b faces the first reflective surface 63a and the display surface 4a. In other words, the display device 1D may be the same as the display device 1A shown in Figure 5, but with the positional relationship between the display panel 4 and the second reflector 64 reversed.

[0120] The display device 1D may include a display panel 4, a first reflector 63, a second reflector 64, and a first reflective polarizer 621, in addition to a first phase difference plate 611. In this case, the first reflector 63, the second reflector 64, the first reflective polarizer 621, and the first phase difference plate 611 may function as an optical system 6.

[0121] The first phase difference plate 611 may be located between the display panel 4 and the first reflective polarizing plate 621. The first phase difference plate 611 may face the display surface 4a and be integrated with the display panel 4. However, the first phase difference plate 611 may be located separately from the display panel 4.

[0122] In the display device 1D, as shown in Figure 11, the first phase difference plate 611 is designed so that the light emitted from the display panel 4 and transmitted through the first phase difference plate 611 is reflected by the first reflective polarizing plate 621, and the necessary phase difference is given to the light transmitted through the first phase difference plate 611.

[0123] In the display device 1D, as shown in Figure 11, the display panel 4 may emit S-wave polarized light as display light. The first reflective polarizer 621 may transmit left-handed circularly polarized light and reflect right-handed circularly polarized light. In this case, the first phase difference plate 611 may be a phase difference plate that converts S-wave polarized light into right-handed circularly polarized light.

[0124] However, for example, if the display panel 4 emits P-wave polarized light, the first phase difference plate 611 may be a phase difference plate that converts P-wave polarized light into right-handed circularly polarized light. Also, for example, if the first reflective polarizer 621 transmits right-handed circularly polarized light and reflects left-handed circularly polarized light, the first phase difference plate 611 may be a phase difference plate that converts S-wave polarized light into left-handed circularly polarized light. Also, for example, if the display panel 4 emits P-wave polarized light and the first reflective polarizer 621 transmits right-handed circularly polarized light, the first phase difference plate 611 may be a phase difference plate that converts P-wave polarized light into left-handed circularly polarized light.

[0125] An example of the propagation of light emitted from the display panel 4 will be explained using Figure 11. Linearly polarized display light emitted from the display panel 4 may be converted into second circularly polarized light by passing through the first phase difference plate 611 and guided to the first reflective polarizer 621. The first reflective polarizer 621 may transmit the first circularly polarized light as the first polarization and reflect the second circularly polarized light as the second polarization. The display light may be, for example, S-wave polarized light. The display light may also be, for example, P-wave polarized light. Furthermore, the first circularly polarized light may be, for example, left-handed circularly polarized light, and the second circularly polarized light may be, for example, right-handed circularly polarized light. Furthermore, the first circularly polarized light may be, for example, right-handed circularly polarized light, and the second circularly polarized light may be, for example, left-handed circularly polarized light.

[0126] Therefore, the second circularly polarized light converted by the first phase difference plate 611 may be reflected by the second optical surface 62b of the first reflecting polarizer and guided to the first reflecting mirror 63. The second circularly polarized light incident on the first reflecting mirror 63 may be converted into first circularly polarized light by reflection at the first reflecting surface 63a and guided to the first reflecting polarizer 621.

[0127] Light of first circular polarization incident on the first reflecting polarizer may pass through the first reflecting polarizer 621 and be guided to the second reflector 64. Light of first circular polarization incident on the second reflector 64 may be converted into light of second circular polarization by reflection at the second reflecting surface 64a and guided to the first reflecting polarizer 621. Light of second circular polarization incident on the first reflecting polarizer 621 may be guided to the viewing window 3 by reflection at the first optical surface 62a.

[0128] Thus, in the display device 1D, the first reflective polarizing plate 621 may reflect the light emitted from the display panel 4 and guide it to the first reflector 63, and then transmit the light reflected by the first reflector 63 to the second reflector 64. Then, the light reflected by the second reflector 64 may be reflected and guided to the viewing window 3.

[0129] By defining the positional relationship between the display panel 4, the first reflector 63, and the second reflector 64, and guiding the light emitted from the display panel 4 to the viewing window 3, the brightness efficiency of the image based on the displayed image can be increased.

[0130] Furthermore, the light emitted from the display panel 4 may be guided to the second reflector 64 via the first reflecting polarizer 621 and the first reflector 63, as shown by the dashed line in Figure 11. Therefore, even when the display panel 4 and the optical system 6 are miniaturized, a sufficient optical path length can be secured for the light emitted from the display panel 4 to the second reflector 64.

[0131] [Embodiment 4] Other embodiments of this disclosure are 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. Figure 12 is a cross-sectional view showing an example of the configuration of the display device 1E according to this embodiment. Figure 13 is a schematic diagram showing a general configuration of the display device 1E according to this embodiment. The display device 1E may be an example of the display device 1.

[0132] As shown in Figure 12, the display device 1E may include a second reflective polarizer 622 instead of the first reflective polarizer 621 as an example of a semi-reflective plate 62. In addition, in the display device 1E, the first optical surface 62a may be positioned to face the viewing window 3 and the second reflective surface 64a, and the second optical surface 62b may be positioned to face the display surface 4a and the first reflective surface 63a. That is, the display panel 4 may be positioned to face the second optical surface 62b. The first reflector 63 may be positioned to face the second optical surface 62b. The second reflector 64 may be positioned to face the first optical surface 62a. The second reflector 64 may be positioned to face the side opposite to the side of the second reflective polarizer 622 that the display panel 4 faces.

[0133] Specifically, as shown in Figure 12, the display panel 4 and the first reflector 63 may be positioned such that the first normal NL1 and the second normal NL2 face in different directions. The display panel 4 and the second reflector 64 may be positioned such that the first normal NL1 and the third normal NL3 face in different directions. Furthermore, the display surface 4a may be positioned to face the second optical surface 62b and the viewing window 3, the first reflector 63a may be positioned to face the second optical surface 62b and the second reflector 64a, and the second reflector 64a may be positioned to face the first optical surface 62a. In other words, the positional relationship of the display panel 4, the first reflector 63, the second reflector 64, and the second reflective polarizer 622 of the display device 1E may be the same as the positional relationship of the display panel 4, the first reflector 63, the second reflector 64, and the first reflective polarizer 621 of the display device 1D shown in Figure 10.

[0134] The display device 1E may include a display panel 4, a first reflector 63, a second reflector 64, and a second reflecting polarizer 622, as well as a first phase difference plate 611 and a second phase difference plate 612. In this case, the first reflector 63, the second reflector 64, the second reflecting polarizer 622, the first phase difference plate 611, and the second phase difference plate 612 may function as an optical system 6.

[0135] The first phase difference plate 611 may be located between the second reflective polarizer 622 and the first reflector 63. The first phase difference plate 611 may face the first reflective surface 63a and be integrated with the first reflector 63. However, the first phase difference plate 611 may be located at a distance from the first reflector 63. The second phase difference plate 612 may be located between the second reflective polarizer 622 and the second reflector 64. The second phase difference plate 612 may be located at a distance from the second reflective polarizer 622 and the second reflector 64. However, the second phase difference plate 612 may face the first optical surface 62a and be integrated with the second reflective polarizer 622. The second phase difference plate 612 may face the second reflective surface 64a and be integrated with the second reflector 64.

[0136] In the display device 1E, as shown in Figure 13, the first phase difference plate 611 should be configured such that the light transmitted through the first phase difference plate 611 is reflected by the first reflector 63, and then the light transmitted through the first phase difference plate 611 again is reflected by the second reflective polarizer plate 622.

[0137] In the display device 1E, as shown in Figure 13, the display panel 4 may emit S-wave polarized light as display light. The second reflective polarizer 622 may reflect S-wave polarized light and transmit P-wave polarized light. In this case, the first phase difference plate 611 may be a phase difference plate that converts S-wave polarized light into left-handed circularly polarized light. Such a first phase difference plate 611 may have the function of converting right-handed circularly polarized light into P-wave polarized light. The second phase difference plate 612 may be a phase difference plate that converts P-wave polarized light into left-handed circularly polarized light. Such a second phase difference plate 612 may have the function of converting right-handed circularly polarized light into S-wave polarized light. That is, when the first phase difference plate 611 and the second phase difference plate 612 are viewed along the path of light transmitted through each phase difference plate, the direction of the lagging axis of the first phase difference plate 611 and the direction of the lagging axis of the second phase difference plate 612 may be in different directions. These two lagging axes may, for example, be orthogonal.

[0138] However, for example, the display panel 4 may emit P-wave polarized light, and the second reflective polarizer 622 may transmit S-wave polarized light and reflect P-wave polarized light. In this case as well, the first phase difference plate 611 and the second phase difference plate 612 may have the above functions. The first phase difference plate 611 may convert P-wave polarized light into right-handed circularly polarized light and left-handed circularly polarized light into S-wave polarized light. The second phase difference plate 612 may convert S-wave polarized light into right-handed circularly polarized light and left-handed circularly polarized light into P-wave polarized light. In this case, the first phase difference plate 611 may be a phase difference plate that converts P-wave polarized light into left-handed circularly polarized light. In this case, the first phase difference plate 611 may have the function of converting right-handed circularly polarized light into S-wave polarized light. In addition, the second phase difference plate 612 may be a phase difference plate that converts S-wave polarized light into left-handed circularly polarized light. In this case, the second phase difference plate 612 may have the function of converting right-handed circularly polarized light into P-wave polarized light.

[0139] An example of the propagation of light emitted from the display panel 4 will be explained using Figure 13. The second reflective polarizer 622 may reflect second linearly polarized light as second polarization and transmit first linearly polarized light as first polarization. Also, the linearly polarized display light emitted from the display panel 4 may be second linearly polarized light. Therefore, the linearly polarized display light emitted from the display panel 4 may be reflected by the second optical surface 62b of the second reflective polarizer 622 and guided to the first phase difference plate 611. The second linearly polarized light may be, for example, S-wave polarized light, and the first linearly polarized light may be, for example, P-wave polarized light. Also, the second linearly polarized light may be, for example, P-wave polarized light, and the first linearly polarized light may be, for example, S-wave polarized light.

[0140] The first phase difference plate 611 may convert second linearly polarized light to first circularly polarized light, or second circularly polarized light to first linearly polarized light. The second phase difference plate 612 may convert first linearly polarized light to first circularly polarized light, or second circularly polarized light to second linearly polarized light. Therefore, second linearly polarized light incident on the first phase difference plate 611 may be converted to first circularly polarized light by passing through the first phase difference plate 611 and guided to the first reflector 63. The first circularly polarized light may be, for example, left-handed circularly polarized light, and the second circularly polarized light may be, for example, right-handed circularly polarized light. Also, the first circularly polarized light may be, for example, right-handed circularly polarized light, and the second circularly polarized light may be, for example, left-handed circularly polarized light.

[0141] The first circularly polarized light incident on the first reflector 63 may be converted into second circularly polarized light by reflection at the first reflective surface 63a and guided to the first phase difference plate 611. The second circularly polarized light incident on the first phase difference plate 611 may be converted into first linearly polarized light by transmission through the first phase difference plate 611 and guided to the second reflective polarizer plate 622.

[0142] Light of first linear polarization incident on the second reflective polarizer 622 may be transmitted through the second reflective polarizer 622 and guided to the second phase difference plate 612. Light of first linear polarization incident on the second phase difference plate 612 may be transmitted through the second phase difference plate 612 and converted into light of first circular polarization, and guided to the second reflector 64. Light of first circular polarization incident on the second reflector 64 may be reflected at the second reflective surface 64a and converted into light of second circular polarization, and guided to the second phase difference plate 612. Light of second circular polarization incident on the second phase difference plate 612 may be transmitted through the second phase difference plate 612 and converted into light of second linear polarization, and guided to the second reflective polarizer 622. Light of second linear polarization incident on the second reflective polarizer 622 may be reflected at the first optical surface 62a of the second reflective polarizer 622 and guided to the viewing window 3.

[0143] Thus, in the display device 1E, the second reflective polarizing plate 622 may reflect the light emitted from the display panel 4 and guide it to the first reflector 63, and then transmit the light reflected by the first reflector 63 to the second reflector 64. The light reflected by the second reflector 64 may then be reflected and guided to the viewing window 3.

[0144] [Embodiment 5] Other embodiments of the present disclosure are 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. Figure 14 is a cross-sectional view showing an example of the configuration of the display device 1F according to this embodiment. Figure 15 is a schematic diagram showing a general configuration of the display device 1F according to this embodiment. The display device 1F may be an example of the display device 1.

[0145] As shown in Figure 14, the display device 1F of this embodiment may include a first reflective polarizing plate 621 as an example of a semi-reflective plate 62. In addition, in the display device 1F, the first optical surface 62a may be positioned to face the viewing window 3 and the first reflective surface 63a, and the second optical surface 62b may be positioned to face the display surface 4a and the second reflective surface 64a. That is, the display panel 4 may be positioned to face the second optical surface 62b. The first reflector 63 may be positioned to face the first optical surface 62a. The second reflector 64 may be positioned to face the second optical surface 62b.

[0146] Specifically, as shown in Figure 14, the display panel 4 and the first reflector 63 may be positioned such that the first normal NL1 and the second normal NL2 face in different directions. The display panel 4 and the second reflector 64 may be positioned such that the first normal NL1 and the third normal NL3 face in different directions. The display surface 4a may be positioned to face the second optical surface 62b and the viewing window 3, the first reflector 63a may be positioned to face the first optical surface 62a and the second reflector 64a, and the second reflector 64a may be positioned to face the second optical surface 62b.

[0147] The positional relationship between the display panel 4, the first reflector 63, and the second reflector 64 of the display device 1F may be the same as the positional relationship between the display panel 4, the first reflector 63, and the second reflector 64 of the display device 1D shown in Figure 10. In the display device 1F, the first reflective polarizer 621 may be positioned such that the first optical surface 62a faces the first reflective surface 63a and the viewing window 3, and the second optical surface 62b faces the second reflective surface 64a and the display surface 4a. That is, in the display device 1F, the first reflective polarizer 621 may be rotated by approximately 90° around the X axis as the axis of rotation in the display device 1D. In the display device 1D, as shown in Figure 10, the bottom end of the housing 2 of the first reflective polarizer 621 may be located on the viewing window 3 side. On the other hand, in the display device 1F, as shown in Figure 14, the upper end of the housing 2 of the first reflective polarizer 621 may be located on the viewing window 3 side. Therefore, in the display device 1F, the first reflective polarizing plate 621 may reflect the light incident from the display panel 4 side towards the second reflector 64 side, rather than towards the first reflector 63 side.

[0148] The display device 1F may include a display panel 4, a first reflector 63, a second reflector 64, and a first reflective polarizer 621, in addition to a first phase difference plate 611. In this case, the first reflector 63, the second reflector 64, the first reflective polarizer 621, and the first phase difference plate 611 may function as an optical system 6.

[0149] The first phase difference plate 611 may be located between the display panel 4 and the first reflective polarizing plate 621. The first phase difference plate 611 may face the display surface 4a and be integrated with the display panel 4. However, the first phase difference plate 611 may be located separately from the display panel 4.

[0150] In the display device 1E, as shown in Figure 15, the first phase difference plate 611 is provided with the necessary phase difference so that the light emitted from the display panel 4 and transmitted through the first phase difference plate 611 is reflected by the first reflective polarizing plate 621.

[0151] In the display device 1E, as shown in Figure 15, the display panel 4 may emit S-wave polarized light as display light. The first reflective polarizer 621 may transmit left-handed circularly polarized light and reflect right-handed circularly polarized light. In this case, the first phase difference plate 611 may be a phase difference plate that converts S-wave polarized light into right-handed circularly polarized light.

[0152] However, for example, if the display panel 4 emits P-wave polarized light, the first phase difference plate 611 may be a phase difference plate that converts P-wave polarized light into right-handed circularly polarized light. Also, for example, if the first reflective polarizer 621 transmits right-handed circularly polarized light and reflects left-handed circularly polarized light, the first phase difference plate 611 may be a phase difference plate that converts S-wave polarized light into left-handed circularly polarized light. Also, for example, if the display panel 4 emits P-wave polarized light and the first reflective polarizer 621 transmits right-handed circularly polarized light, the first phase difference plate 611 may be a phase difference plate that converts P-wave polarized light into left-handed circularly polarized light.

[0153] An example of the propagation of light emitted from the display panel 4 will be explained using Figure 15. Linearly polarized display light emitted from the display panel 4 may be converted into second circularly polarized light by passing through the first phase difference plate 611 and guided to the first reflective polarizer 621. The first reflective polarizer 621 may transmit the first circularly polarized light as the first polarization and reflect the second circularly polarized light as the second polarization. The display light may be, for example, S-wave polarized light. Also, the first circularly polarized light may be, for example, left-handed circularly polarized light, and the second circularly polarized light may be, for example, right-handed circularly polarized light. The display light may also be, for example, P-wave polarized light. Also, the first circularly polarized light may be, for example, right-handed circularly polarized light, and the second circularly polarized light may be, for example, left-handed circularly polarized light.

[0154] Therefore, the second circularly polarized light converted by the first phase difference plate 611 may be reflected by the second optical surface 62b of the first reflecting polarizer plate 621 and guided to the second reflecting mirror 64. The second circularly polarized light incident on the second reflecting mirror 64 may be converted into first circularly polarized light by reflection at the second reflecting surface 64a and guided to the first reflecting polarizer plate 621.

[0155] Light of first circular polarization incident on the first reflective polarizer 621 may pass through the first reflective polarizer 621 and be guided to the first reflector 63. Light of first circular polarization incident on the first reflector 63 may be converted into light of second circular polarization by reflection at the first reflective surface 63a and guided to the first reflective polarizer 621. Light of second circular polarization incident on the first reflective polarizer 621 may be guided to the viewing window 3 by reflection at the first optical surface 62a.

[0156] Thus, the first reflective polarizing plate 621 may reflect the light emitted from the display panel 4 and guide it to the second reflector 64, and then transmit the light reflected by the second reflector 64 and guide it to the first reflector 63. Then, it may reflect the light reflected by the first reflector 63 and guide it to the viewing window 3. In the display device 1D, the light incident from the display panel 4 travels from the first reflector 63 to the second reflector 64, whereas in the display device 1F, it may travel from the second reflector 64 to the first reflector 63.

[0157] By defining the positional relationship between the display panel 4, the first reflector 63, and the second reflector 64, and guiding the light emitted from the display panel 4 to the viewing window 3, the brightness efficiency of the image based on the displayed image can be increased.

[0158] Furthermore, the light emitted from the display panel 4 may be guided to the second reflector 64 via the first reflecting polarizer 621, as shown by the dashed line in Figure 15. Therefore, even when the display panel 4 and optical system 6 are miniaturized, a certain amount of optical path length can be secured from the light emitted from the display panel 4 to the second reflector 64. As a result, even in the display device 1F, the display position of the image based on the display image can be moved away from the user Us.

[0159] [Embodiment 6] Other embodiments of this disclosure are 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. Figure 16 is a cross-sectional view showing an example of the configuration of the display device 1G according to this embodiment. Figure 17 is a schematic diagram showing a general configuration of the display device 1G according to this embodiment. The display device 1G may be an example of the display device 1.

[0160] As shown in Figure 16, the display device 1G may include a second reflective polarizer 622 instead of the first reflective polarizer 621 as an example of a semi-reflective plate 62. In addition, in the display device 1G, the first optical surface 62a may be positioned to face the viewing window 3 and the first reflective surface 63a, and the second optical surface 62b may be positioned to face the display surface 4a and the second reflective surface 64a. That is, the display panel 4 may be positioned to face the second optical surface 62b. The first reflector 63 may be positioned to face the first optical surface 62a. The second reflector 64 may be positioned to face the second optical surface 62b.

[0161] Specifically, as shown in Figure 16, the display panel 4 and the first reflector 63 may be positioned such that the first normal NL1 and the second normal NL2 face in different directions. The display panel 4 and the second reflector 64 may be positioned such that the first normal NL1 and the third normal NL3 face in different directions. The display surface 4a may be positioned to face the second optical surface 62b and the viewing window 3, the first reflective surface 63a may be positioned to face the first optical surface 62a and the second reflective surface 64a, and the second reflective surface 64a may be positioned to face the second optical surface 62b. In other words, the positional relationship of the display panel 4, the first reflector 63, the second reflector 64 and the second reflective polarizer 622 of the display device 1G may be the same as the positional relationship of the display panel 4, the first reflector 63, the second reflector 64 and the first reflective polarizer 621 of the display device 1F shown in Figure 14.

[0162] The display device 1G may include a display panel 4, a first reflector 63, a second reflector 64, and a second reflecting polarizer 622, as well as a first phase difference plate 611 and a second phase difference plate 612. In this case, the first reflector 63, the second reflector 64, the second reflecting polarizer 622, the first phase difference plate 611, and the second phase difference plate 612 may function as an optical system 6.

[0163] The first phase difference plate 611 may be located between the second reflective polarizer 622 and the second reflector 64. The first phase difference plate 611 may be located away from the second reflective polarizer 622 and the second reflector 64. However, the first phase difference plate 611 may face the second reflective surface 64a and be integrated with the second reflector 64. The second phase difference plate 612 may be located between the second reflective polarizer 622 and the first reflector 63. The second phase difference plate 612 may face the first reflective surface 63a and be integrated with the first reflector 63. However, the second phase difference plate 612 may be located away from the first reflector 63. Also, the second phase difference plate 612 may face the first optical surface 62a and be integrated with the second reflective polarizer 622.

[0164] In the display device 1G, as shown in Figure 17, the first phase difference plate 611 should be configured such that the light transmitted through the first phase difference plate 611 is reflected by the second reflector 64, and then the light transmitted through the first phase difference plate 611 again is reflected by the second reflective polarizer 622.

[0165] In the display device 1G, as shown in Figure 17, the display panel 4 may emit S-wave polarized light as display light. The second reflective polarizer 622 may reflect S-wave polarized light and transmit P-wave polarized light. In this case, the first phase difference plate 611 may be a phase difference plate that converts S-wave polarized light to left-handed circularly polarized light. Such a first phase difference plate 611 may have the function of converting right-handed circularly polarized light to P-wave polarized light. The second phase difference plate 612 may be a phase difference plate that converts P-wave polarized light to left-handed circularly polarized light. Such a second phase difference plate 612 may have the function of converting right-handed circularly polarized light to S-wave polarized light. That is, when the first phase difference plate 611 and the second phase difference plate 612 are viewed along the path of light transmitted through each phase difference plate, the direction of the lagging axis of the first phase difference plate 611 and the direction of the lagging axis of the second phase difference plate 612 may be in different directions. These two lagging axes may, for example, be orthogonal.

[0166] However, for example, the display panel 4 may emit P-wave polarized light, and the second reflective polarizer 622 may transmit S-wave polarized light and reflect P-wave polarized light. In this case as well, the first phase difference plate 611 and the second phase difference plate 612 may have the above functions. The first phase difference plate 611 may convert P-wave polarized light into right-handed circularly polarized light and left-handed circularly polarized light into S-wave polarized light. The second phase difference plate 612 may convert S-wave polarized light into right-handed circularly polarized light and left-handed circularly polarized light into P-wave polarized light. In this case, the first phase difference plate 611 may be a phase difference plate that converts P-wave polarized light into left-handed circularly polarized light. In this case, the first phase difference plate 611 may have the function of converting right-handed circularly polarized light into S-wave polarized light. In addition, the second phase difference plate 612 may be a phase difference plate that converts S-wave polarized light into left-handed circularly polarized light. In this case, the second phase difference plate 612 may have the function of converting right-handed circularly polarized light into P-wave polarized light.

[0167] An example of the propagation of light emitted from the display panel 4 will be explained using Figure 17. The second reflective polarizer 622 may transmit light of the first linear polarization as the first polarization and reflect light of the second linear polarization as the second polarization. Also, the linearly polarized display light emitted from the display panel 4 may be light of the second linear polarization. Therefore, the linearly polarized display light emitted from the display panel 4 may be reflected by the second optical surface 62b of the second reflective polarizer 622 and guided to the first phase difference plate 611. The second linearly polarized light may be, for example, S-wave polarized light, and the first linearly polarized light may be, for example, P-wave polarized light. Also, the second linearly polarized light may be, for example, P-wave polarized light, and the first linearly polarized light may be, for example, S-wave polarized light.

[0168] The first phase difference plate 611 may convert second linearly polarized light to first circularly polarized light, or second circularly polarized light to first linearly polarized light. The second phase difference plate 612 may convert first linearly polarized light to first circularly polarized light, or second circularly polarized light to second linearly polarized light. Therefore, second linearly polarized light incident on the first phase difference plate 611 may be converted to first circularly polarized light by passing through the first phase difference plate 611 and guided to the second reflector 64. The first circularly polarized light may be, for example, left-handed circularly polarized light, and the second circularly polarized light may be, for example, right-handed circularly polarized light. Also, the first circularly polarized light may be, for example, right-handed circularly polarized light, and the second circularly polarized light may be, for example, left-handed circularly polarized light.

[0169] The first circularly polarized light incident on the second reflector 64 may be converted into second circularly polarized light by reflection at the second reflecting surface 64a and guided to the first phase difference plate 611. The second circularly polarized light incident on the first phase difference plate 611 may be converted into first linearly polarized light by passing through the first phase difference plate 611 and guided to the second reflecting polarizer plate 622.

[0170] Light of first linear polarization incident on the second reflective polarizer 622 may pass through the second reflective polarizer 622 and be guided to the second phase difference plate 612. Light of first linear polarization incident on the second phase difference plate 612 may be converted into light of first circular polarization by passing through the second phase difference plate 612 and guided to the first reflector 63. Light of first circular polarization incident on the first reflector 63 may be converted into light of second circular polarization by being reflected at the first reflective surface 63a and guided to the second phase difference plate 612. Light of second circular polarization incident on the second phase difference plate 612 may be converted into light of second linear polarization by being passed through the second phase difference plate 612 and guided to the second reflective polarizer 622. Light of second linear polarization incident on the second reflective polarizer 622 may be reflected at the first optical surface 62a of the second reflective polarizer 622 and guided to the viewing window 3.

[0171] Thus, the second reflective polarizing plate 622 may reflect the light emitted from the display panel 4 and guide it to the second reflector 64, and then transmit the light reflected by the second reflector 64 to the first reflector 63. Then, it may reflect the light reflected by the first reflector 63 and guide it to the viewing window 3.

[0172] [Embodiment 7] Other embodiments of the present disclosure are 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. Figure 18 is a schematic diagram illustrating the configuration of the display device 1H according to this embodiment. The display device 1H may be an example of the display device 1.

[0173] As shown in Figure 18, the display device 1H of this embodiment may include a first reflective polarizing plate 621 as an example of a semi-reflective plate 62. In addition, in the display device 1H, the first optical surface 62a may be positioned to face the viewing window 3 and the display surface 4a, and the second optical surface 62b may be positioned to face the first reflective surface 63a and the second reflective surface 64a. That is, the display panel 4 may be positioned to face the first optical surface 62a. The first reflector 63 may be positioned to face the second optical surface 62b. The second reflector 64 may be positioned to face the second optical surface 62b.

[0174] Specifically, as shown in Figure 18, the display panel 4 and the first reflector 63 may be positioned such that the first normal NL1 and the second normal NL2 face in different directions. The first reflector 63 and the second reflector 64 may be positioned such that the second normal NL2 and the third normal NL3 face in different directions. The display surface 4a may be positioned to face the first optical surface 62a, the first reflective surface 63a may be positioned to face the second optical surface 62b and the viewing window 3, and the second reflective surface 64a may be positioned to face the second optical surface 62b and the display surface 4a.

[0175] When the display device 1H is placed on a horizontal surface, if the upward direction is considered to be the +Y axis, then in the display device 1H, the display panel 4 may be located at the bottom of the housing 2. The first reflector 63 may be located on the part of the housing 2 opposite to the viewing window 3. The second reflector 64 may be located at the top of the housing 2. Alternatively, the display panel 4 may be located at the top of the housing 2, and the second reflector 64 may be located at the bottom of the housing 2. The first reflective polarizer 621 may be positioned such that the first optical surface 62a faces the display surface 4a and the viewing window 3, and the second optical surface 62b faces the first reflective surface 63a and the second reflective surface 64a. In other words, the display device 1H may be the same as the display device 1F shown in Figure 14, but with the positional relationship between the display panel 4 and the first reflector 63 reversed. In the display device 1H, the first reflective polarizer 621 may transmit light incident from the display panel 4 side to the second reflector 64 side.

[0176] The display device 1H may include a display panel 4, a first reflector 63, a second reflector 64, and a first reflective polarizer 621, in addition to a first phase difference plate 611. In this case, the first reflector 63, the second reflector 64, the first reflective polarizer 621, and the first phase difference plate 611 may function as an optical system 6.

[0177] The first phase difference plate 611 may be located between the display panel 4 and the first reflective polarizing plate 621. The first phase difference plate 611 may face the display surface 4a and be integrated with the display panel 4. However, the first phase difference plate 611 may be located separately from the display panel 4.

[0178] In the display device 1H, the first phase difference plate 611 is provided with the necessary phase difference so that the light emitted from the display panel 4 and transmitted through the first phase difference plate 611 is transmitted through the first reflective polarizing plate 621.

[0179] In the display device 1H, the display panel 4 may emit S-wave polarized light as display light. The first reflective polarizer 621 may transmit left-handed circularly polarized light and reflect right-handed circularly polarized light. In this case, the first phase difference plate 611 may be a phase difference plate that converts S-wave polarized light into left-handed circularly polarized light.

[0180] However, for example, if the display panel 4 emits P-wave polarized light, the first phase difference plate 611 may be a phase difference plate that converts P-wave polarized light into left-handed circularly polarized light. Also, for example, if the first reflective polarizer 621 transmits right-handed circularly polarized light and reflects left-handed circularly polarized light, the first phase difference plate 611 may be a phase difference plate that converts S-wave polarized light into right-handed circularly polarized light. Also, for example, if the display panel 4 emits P-wave polarized light and the first reflective polarizer 621 transmits right-handed circularly polarized light, the first phase difference plate 611 may be a phase difference plate that converts P-wave polarized light into right-handed circularly polarized light.

[0181] An example of the propagation of light emitted from the display panel 4 will be explained using Figure 18. Linearly polarized display light emitted from the display panel 4 may be converted into first circularly polarized light by passing through the first phase difference plate 611 and guided to the first reflective polarizer 621. The first reflective polarizer 621 may transmit the first circularly polarized light as the first polarization and reflect the second circularly polarized light as the second polarization. The display light may be, for example, S-wave polarized light. Also, the first circularly polarized light may be, for example, left-handed circularly polarized light, and the second circularly polarized light may be, for example, right-handed circularly polarized light. The display light may also be, for example, P-wave polarized light. Also, the first circularly polarized light may be, for example, right-handed circularly polarized light, and the second circularly polarized light may be, for example, left-handed circularly polarized light.

[0182] Therefore, the first circularly polarized light converted by the first phase difference plate 611 may pass through the first reflective polarizer plate 621 and be guided to the second reflector 64. The first circularly polarized light incident on the second reflector 64 may be converted into second circularly polarized light by reflection at the second reflective surface 64a and guided to the first reflective polarizer plate 621.

[0183] Light of second circular polarization incident on the first reflective polarizer 621 may be reflected by the second optical surface 62b of the first reflective polarizer 621 and guided to the first reflector 63. Light of second circular polarization incident on the first reflector 63 may be converted into light of first circular polarization by reflection at the first reflective surface 63a and guided to the first reflective polarizer 621. Light of first circular polarization incident on the first reflective polarizer 621 may pass through the first reflective polarizer 621 and be guided to the viewing window 3.

[0184] Thus, the first reflective polarizing plate 621 may transmit light emitted from the display panel 4 to the second reflector 64, and then reflect the light reflected by the second reflector 64 to the first reflector 63. The light reflected by the first reflector 63 may then be transmitted to the viewing window 3. In the display device 1H, the light incident from the display panel 4 may also proceed from the second reflector 64 to the first reflector 63.

[0185] By defining the positional relationship between the display panel 4, the first reflector 63, and the second reflector 64, and guiding the light emitted from the display panel 4 to the viewing window 3, the brightness efficiency of the image based on the displayed image can be increased.

[0186] Furthermore, the light emitted from the display panel 4 may be guided to the second reflector 64 via the first reflecting polarizer 621, as shown by the dashed line in Figure 18. Therefore, even when the display panel 4 and optical system 6 are miniaturized, a certain amount of optical path length can be secured from the light emitted from the display panel 4 to the second reflector 64. As a result, even in the display device 1H, the display position of the image based on the display image can be separated from the user Us. In addition, since the display surface 4a is not facing the viewing window 3, the possibility of external light being reflected by the display surface 4a can be reduced.

[0187] [Embodiment 8] Other embodiments of this disclosure are 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. Figure 19 is a schematic diagram illustrating the configuration of the display device 1I according to this embodiment. The display device 1I may be an example of the display device 1.

[0188] As shown in Figure 19, the display device 1I may include a second reflective polarizing plate 622 instead of the first reflective polarizing plate 621 as an example of a semi-reflective plate 62. In addition, in the display device 1I, the first optical surface 62a may be positioned to face the viewing window 3 and the display surface 4a, and the second optical surface 62b may be positioned to face the first reflective surface 63a and the second reflective surface 64a. That is, the display panel 4 may be positioned to face the first optical surface 62a. The first reflector 63 may be positioned to face the second optical surface 62b. Also, the second reflector 64 may be positioned to face the second optical surface 62b.

[0189] Specifically, as shown in Figure 19, the display panel 4 and the first reflector 63 may be positioned such that the first normal NL1 and the second normal NL2 face in different directions. The first reflector 63 and the second reflector 64 may be positioned such that the second normal NL2 and the third normal NL3 face in different directions. The display surface 4a may be positioned to face the first optical surface 62a, the first reflective surface 63a may be positioned to face the second optical surface 62b and the viewing window 3, and the second reflective surface 64a may be positioned to face the second optical surface 62b and the display surface 4a. In other words, the positional relationship of the display panel 4, the first reflector 63, the second reflector 64 and the second reflective polarizer 622 of the display device 1I may be the same as the positional relationship of the display panel 4, the first reflector 63, the second reflector 64 and the first reflective polarizer 621 of the display device 1H shown in Figure 18.

[0190] The display device 1I may include a display panel 4, a first reflector 63, a second reflector 64, and a second reflecting polarizer 622, in addition to a first phase difference plate 611. In this case, the first reflector 63, the second reflector 64, the second reflecting polarizer 622, and the first phase difference plate 611 may function as an optical system 6.

[0191] The first phase difference plate 611 may be located between the second reflective polarizer 622 and the first reflector 63 and the second reflector 64. As shown in Figure 19, the first phase difference plate 611 may be located on the optical path between the second reflective polarizer 622 and the first reflector 63, and on the optical path between the second reflective polarizer 622 and the second reflector 64.

[0192] The first phase difference plate 611 may face the second optical surface 62b and be integrated with the second reflective polarizer 622. In this case, the first phase difference plate 611 may be bonded to the base material of the second reflective polarizer 622. However, the first phase difference plate 611 may be positioned separately from the second reflective polarizer 622, as long as it is located on the two optical paths.

[0193] In the display device 1I, the first phase difference plate 611 should be configured such that the light transmitted through the first phase difference plate 611 is reflected by the second reflector 64, and then the light transmitted through the first phase difference plate 611 again is reflected by the second reflective polarizer 622.

[0194] In this embodiment, the display panel 4 may emit P-wave polarized light as display light. The second reflective polarizer 622 may transmit P-wave polarized light and reflect S-wave polarized light. In this case, the first phase difference plate 611 may be a phase difference plate that converts P-wave polarized light to left-handed circularly polarized light. Such a first phase difference plate 611 may have the functions of converting left-handed circularly polarized light to P-wave polarized light, converting S-wave polarized light to right-handed circularly polarized light, and converting right-handed circularly polarized light to S-wave polarized light.

[0195] However, for example, the display panel 4 may emit S-wave polarized light, and the second reflective polarizer 622 may transmit S-wave polarized light and reflect P-wave polarized light. In this case as well, the first phase difference plate 611 may have the above functions. The first phase difference plate 611 may, for example, convert S-wave polarized light into right-handed circularly polarized light. In this case, the first phase difference plate 611 may be a phase difference plate that converts S-wave polarized light into left-handed circularly polarized light. In this case, the first phase difference plate 611 may have the functions of converting right-handed circularly polarized light into P-wave polarized light, converting P-wave polarized light into right-handed circularly polarized light, and converting left-handed circularly polarized light into S-wave polarized light.

[0196] An example of the propagation of light emitted from the display panel 4 will be explained using Figure 19. The second reflective polarizer 622 may transmit light with first linear polarization as first polarization and reflect light with second linear polarization as second polarization. Also, the linearly polarized display light emitted from the display panel 4 may be light with first linear polarization. Therefore, the linearly polarized display light emitted from the display panel 4 may pass through the second reflective polarizer 622 and be guided to the first phase difference plate 611. The first linearly polarized light may be, for example, P-wave polarized light, and the second linearly polarized light may be, for example, S-wave polarized light. Also, the first linearly polarized light may be, for example, S-wave polarized light, and the second linearly polarized light may be, for example, P-wave polarized light.

[0197] The first phase difference plate 611 may convert first linearly polarized light to first circularly polarized light, or first circularly polarized light to first linearly polarized light. The first phase difference plate 611 may also convert second linearly polarized light to second circularly polarized light, or second circularly polarized light to second linearly polarized light. Therefore, first linearly polarized light incident on the first phase difference plate 611 may be converted to first circularly polarized light by passing through the first phase difference plate 611 and guided to the second reflector 64. The first circularly polarized light may be, for example, left-handed circularly polarized light, and the second circularly polarized light may be, for example, right-handed circularly polarized light. Also, the first circularly polarized light may be, for example, right-handed circularly polarized light, and the second circularly polarized light may be, for example, left-handed circularly polarized light.

[0198] The first circularly polarized light incident on the second reflector 64 may be converted into second circularly polarized light by reflection at the second reflecting surface 64a and guided to the first phase difference plate 611. The second circularly polarized light incident on the first phase difference plate 611 may be converted into second linearly polarized light by transmission through the first phase difference plate 611 and guided to the second reflecting polarizer plate 622.

[0199] Light of the second linear polarization incident on the second reflecting polarizer 622 may be reflected by the second optical surface 62b of the second reflecting polarizer 622 and guided to the first phase difference plate 611. Light of the second linear polarization incident on the first phase difference plate 611 may be converted into light of the second circular polarization by passing through the first phase difference plate 611 and guided to the first reflector 63. Light of the second circular polarization incident on the first reflector 63 may be converted into light of the first circular polarization by reflecting at the first reflecting surface 63a and guided to the first phase difference plate 611. Light of the first circular polarization incident on the first phase difference plate 611 may be converted into light of the first linear polarization by passing through the first phase difference plate 611 and guided to the second reflecting polarizer 622. Light of the first linear polarization incident on the second reflecting polarizer 622 may be passed through the second reflecting polarizer 622 and guided to the viewing window 3.

[0200] Thus, the second reflective polarizing plate 622 may transmit light emitted from the display panel 4 to the second reflector 64, and then reflect the light reflected by the second reflector 64 to the first reflector 63. Finally, it may transmit the light reflected by the first reflector 63 to the viewing window 3.

[0201] [Embodiment 9] Other embodiments of this disclosure are 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. Figure 20 is a schematic diagram illustrating the configuration of the display device 1J according to this embodiment. The display device 1J may be an example of the display device 1.

[0202] As shown in Figure 20, the display device 1J of this embodiment may be the same as the display device 1H shown in Figure 18, but with the positional relationship between the first reflector 63 and the second reflector 64 reversed. That is, the positional relationship between the members other than the first reflector 63 and the second reflector 64 may be the same in the display device 1J and the display device 1H.

[0203] As shown in Figure 20, the display panel 4 and the second reflector 64 may be positioned such that the first normal NL1 and the third normal NL3 face in different directions. The first reflector 63 and the second reflector 64 may be positioned such that the second normal NL2 and the third normal NL3 face in different directions. The display surface 4a may be positioned to face the first optical surface 62a, the first reflector 63a may be positioned to face the second optical surface 62b and the display surface 4a, and the second reflector 64a may be positioned to face the second optical surface 62b and the viewing window 3.

[0204] When the display device 1J is placed on a horizontal surface, if the upward direction is considered to be the +Y axis, then in the display device 1J, the display panel 4 may be located at the bottom of the housing 2. The first reflector 63 may be located at the top of the housing 2. Alternatively, the display panel 4 may be located at the top of the housing 2, and the first reflector 63 may be located at the bottom of the housing 2. The second reflector 64 may be located on the part of the housing 2 opposite to the viewing window 3. The first reflective polarizing plate 621 may be positioned such that the first optical surface 62a faces the display surface 4a and the viewing window 3, and the second optical surface 62b faces the first reflective surface 63a and the second reflective surface 64a.

[0205] For an example of the propagation of light emitted from the display panel 4, the first reflector 63 and the second reflector 64, and the first reflective surface 63a and the second reflective surface 64a can be swapped in the example of light propagation in the display device 1H described in Embodiment 7.

[0206] Thus, the first reflective polarizer 621 may transmit light emitted from the display panel 4 to the first reflector 63, and then reflect the light reflected by the first reflector 63 to the second reflector 64. The light reflected by the second reflector 64 may then be transmitted to the viewing window 3. In the display device 1J, the light emitted from the display panel 4 may be guided to the second reflector 64 via the first reflective polarizer 621 and the first reflector 63, as shown by the dashed line in Figure 20. Therefore, even when the display panel 4 and the optical system 6 are miniaturized, a sufficient optical path length can be secured for the light emitted from the display panel 4 to the second reflector 64.

[0207] [Embodiment 10] Other embodiments of this disclosure are 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. Figure 21 is a schematic diagram illustrating the configuration of the display device 1K according to this embodiment. The display device 1K may be an example of the display device 1.

[0208] As shown in Figure 21, the display device 1K of this embodiment may be the same as the display device 1I shown in Figure 19, but with the positional relationship of the first reflector 63 and the second reflector 64 reversed. That is, the positional relationship of members other than the first reflector 63 and the second reflector 64 may be the same in the display device 1K and the display device 1I.

[0209] As shown in Figure 21, the display panel 4 and the second reflector 64 may be positioned such that the first normal NL1 and the third normal NL3 face in different directions. The first reflector 63 and the second reflector 64 may be positioned such that the second normal NL2 and the third normal NL3 face in different directions. The display surface 4a may be positioned to face the first optical surface 62a, the first reflector 63a may be positioned to face the second optical surface 62b and the display surface 4a, and the second reflector 64a may be positioned to face the second optical surface 62b and the viewing window 3.

[0210] When the display device 1K is placed on a horizontal surface, if the upward direction is considered to be the +Y axis, then in the display device 1K, the display panel 4 may be located at the bottom of the housing 2. The first reflector 63 may be located at the top of the housing 2. Alternatively, the display panel 4 may be located at the top of the housing 2, and the first reflector 63 may be located at the bottom of the housing 2. The second reflector 64 may be located on the part of the housing 2 opposite to the viewing window 3. The second reflective polarizing plate 622 may be positioned such that the first optical surface 62a faces the display surface 4a and the viewing window 3, and the second optical surface 62b faces the first reflective surface 63a and the second reflective surface 64a.

[0211] In this embodiment, the first phase difference plate 611 should be configured such that the light transmitted through the first phase difference plate 611 is reflected by the first reflector 63, and then the light transmitted through the first phase difference plate 611 again is reflected by the second reflective polarizer 622.

[0212] For an example of the propagation of light emitted from the display panel 4, the first reflector 63 and the second reflector 64, and the first reflective surface 63a and the second reflective surface 64a can be swapped in the example of light propagation in the display device 1I described in Embodiment 8.

[0213] Thus, the second reflective polarizer 622 may transmit light emitted from the display panel 4 to the first reflector 63, and then reflect the light reflected by the first reflector 63 to the second reflector 64. The light reflected by the second reflector 64 may then be transmitted to the viewing window 3. In the display device 1K, the light emitted from the display panel 4 may be guided to the second reflector 64 via the second reflective polarizer 622 and the first reflector 63, as shown by the dashed line in Figure 21. Therefore, even when the display panel 4 and optical system 6 are miniaturized, a sufficient optical path length from the light emitted from the display panel 4 to the second reflector 64 can be ensured.

[0214] [Embodiment 11] Other embodiments of this disclosure are 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.

[0215] In the embodiments described above, the display device 1, which includes a display panel 4, is described as having an optical system 6. However, a device without a display panel 4 may also have an optical system 6. Figure 2 shows a display device 1 in which a display panel 4 is installed in a display panel installation section 8. However, a device in which a display panel 4 is not installed in a display panel installation section 8 may also exist. In this case, the device may be a display panel housing device 11 having a housing 2 that includes a viewing window 3, an inner region 22, and a display panel installation section 8 in which a display panel 4 can be installed so that its display surface 4a faces the inner region 22. The device may also be a display panel housing device 11 having a housing 2 that includes a viewing window 3, an internal region, and a display panel installation section 8 in which a display panel 4 can be installed so that its display surface 4a faces the internal region. The configuration of the display device 1 of each embodiment described above may also be realized in the display panel housing device 11. That is, the position of the display panel installation section 8 of the display panel housing device 11 may be defined such that when a display panel 4 is installed in the display panel installation section 8, the configuration of each embodiment described above is achieved.

[0216] [Embodiment 12] Other embodiments of this disclosure are 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.

[0217] Figure 22 is a schematic cross-sectional view showing the configuration of the display device 1 according to this embodiment. Figure 22 may show a display device equivalent to the display device 1E shown in Figures 12 and 13. In Figures 12 and 13, if the upward direction when the display device 1E is placed on a horizontal surface is considered to be the +Y axis direction, the display device 1E may be an example in which the first reflector 63 is located at the bottom of the housing 2 and the second reflector 64 is located at the top of the housing 2. However, the first reflector 63 may be located at the top of the housing 2, and the second reflector 64 may be located at the bottom of the housing 2.

[0218] In the display device 1 shown in Figure 22, the first reflector 63 may be located at the top of the housing 2, and the second reflector 64 may be located at the bottom of the housing 2. However, the first reflector 63 may also be located at the bottom of the housing 2, and the second reflector 64 may be located at the top of the housing 2. Also, the display device 1 shown in Figure 22 may be an example in which the first reflector 63 is a convex mirror with a convex first reflective surface 63a, and the second reflector 64 is a concave mirror with a concave second reflective surface 64a. As will be described later, the first reflector 63 may be, for example, a plane mirror with a planar first reflective surface 63a, or a concave mirror with a concave first reflective surface 63a. Also, the second reflector 64 may be, for example, a plane mirror with a planar second reflective surface 64a, or a convex mirror with a convex second reflective surface 64a. Furthermore, Figure 22 may show the base material 6221 and the wire grid polarizer 6222 that constitute the second reflective polarizer 622.

[0219] The display device 1 may be configured such that, when the user Us is positioned in front of the display device 1, the light emitted from the display panel 4 is reflected by, for example, the components of the optical system 6, and not emitted directly from the viewing window 3. In other words, the user Us may not directly view the display panel 4, but view the image reflected by the second reflector 64 as a virtual image V or a real image. Such light emission may be achieved by appropriately defining the relationship between the angles of the transmission axes of the front polarizer of the display panel 4 (the polarizer on the display surface 4a side) and the components of the optical system 6.

[0220] On the other hand, if the user Us is not positioned directly in front of the display device 1, the above-mentioned angle relationship may be disrupted, and some of the light emitted from the display panel 4 may directly pass through the viewing window 3. As a result, the user Us may be able to see both the display image displayed on the display panel 4 and the virtual image V or real image reflected by the second reflector 64, which may degrade the display quality of the display device 1.

[0221] The display device 1 may be equipped with a phase difference plate located within the housing 2, which reduces the amount of light emitted from the display panel 4 that is directly visible through the viewing window 3 from positions other than the front of the viewing window 3. By providing such a phase difference plate, even when the viewing window 3 is viewed from a position other than the front of the viewing window 3, the angle relationship can be brought closer to the specified one, so that the light emitted from the display panel 4 does not directly emit from the viewing window 3. Therefore, even if the user Us is not positioned in front of the display device 1, the possibility of the user Us directly seeing the light emitted from the display panel 4 can be reduced. Consequently, the possibility of a decrease in the display quality of the display device 1 can be reduced.

[0222] As shown in Figure 22, the display device 1 may have, for example, a third phase difference plate 613 as the phase difference plate. The third phase difference plate 613 may be a half-wave plate, a quarter-wave plate, an eighth-wave plate, a sixteenth-wave plate, or any other wave plate that imparts a phase difference. The optical axis of the third phase difference plate 613 may be approximately parallel or perpendicular to the transmission axis of the reflective polarizer (for example, the second reflective polarizer 622), which is a semi-reflector plate 62. The optical axis of the third phase difference plate 613 may be approximately parallel or perpendicular to the transmission axis of the display panel 4.

[0223] The display device 1 may further include, for example, a fourth phase difference plate 614 as the phase difference plate. The fourth phase difference plate 614 may be a half-wave plate, a quarter-wave plate, an eighth-wave plate, a sixteenth-wave plate, or any other wave plate that imparts a phase difference. The optical axis of the fourth phase difference plate 614 may be approximately parallel or perpendicular to the transmission axis of the reflective polarizer (for example, the second reflective polarizer 622), which is a semi-reflector plate 62. The optical axis of the third phase difference plate 613 may be approximately parallel or perpendicular to the transmission axis of the display panel 4.

[0224] If the display device 1 includes a third phase difference plate 613 and a fourth phase difference plate 614, one of the third phase difference plate 613 and the fourth phase difference plate 614 may be a quarter-wave plate and the other a half-wave plate. In this case, the deterioration of the display quality of the display device 1 can be effectively reduced. Both the third phase difference plate 613 and the fourth phase difference plate 614 may be half-wave plates. In this case, the deterioration of the display quality of the display device 1 can be reduced more effectively. The third phase difference plate 613 and the fourth phase difference plate 614 may provide the same phase difference with respect to transmitted light. In this case, the optical axis of the third phase difference plate 613 may be approximately perpendicular to the optical axis of the fourth phase difference plate 614.

[0225] The display device 1 may have only the third phase difference plate 613, or only the fourth phase difference plate 614. Alternatively, the display device 1 may have three or more phase difference plates. For example, when the phase difference plate functions as a half-wave plate, the phase difference plate may be one half-wave plate, two quarter-wave plates, or four eighth-wave plates. The phase difference plate may also be a film-like material.

[0226] In the example shown in Figure 22, the third phase difference plate 613 and the fourth phase difference plate 614 may be positioned between the second reflective polarizing plate 622 and the viewing area (e.g., the viewing window 3 or opening). In the example shown in Figure 22, the third phase difference plate 613 and the fourth phase difference plate 614 may be positioned in contact with each other and also in contact with the viewing window 3. However, the third phase difference plate 613 and the fourth phase difference plate 614 may be positioned spaced apart from each other, or spaced apart from the viewing window 3. By arranging the phase difference plates closer to the viewing window 3 on the path of light emitted from the display panel 4, the degradation of the display quality of the display device 1 can be more effectively reduced.

[0227] Figure 23 is a schematic cross-sectional view showing an example of the placement position of the phase difference plate. The dotted line frame in Figure 23 indicates a possible position for the phase difference plate. As shown in Figure 23, the phase difference plate may be located at any position along the path of light emitted from the display panel 4. As shown in Figure 22, the phase difference plate may be located between the semi-reflector 62 and the viewing window 3. The phase difference plate may be located between the display panel 4 and the semi-reflector 62, between the first reflector 63 and the first phase difference plate 611, between the first phase difference plate 611 and the semi-reflector 62, between the semi-reflector 62 and the second phase difference plate 612, or between the second phase difference plate 612 and the second reflector 64.

[0228] Furthermore, if at least one of the third phase difference plate 613 and the fourth phase difference plate 614 is located between the semi-reflective plate 62 and the viewing area, the display device 1 may also include a polarizing plate between at least one of the third phase difference plate 613 and the fourth phase difference plate 614 located between the semi-reflective plate 62 and the viewing area and the viewing area. The polarizing plate 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. The polarizing plate may also have the configuration of a reflective polarizing plate.

[0229] If the viewing area is a viewing window 3, the polarizing plate may be located on the surface of the viewing window 3 on the side of the semi-reflector 62. However, it may also be located on the surface of the viewing window 3 opposite to the surface on the side of the semi-reflector 62. The polarizing plate may transmit or reflect light through the semi-reflector 62, transmit light emitted from the viewing area, and absorb or reflect light with a polarization state different from that of the light. The optical axis of the polarizing plate may be approximately parallel or perpendicular to the transmission axis of the reflective polarizing plate (e.g., second reflective polarizing plate 622), which is the semi-reflector 62. The optical axis of the polarizing plate may be approximately parallel or perpendicular to the transmission axis of the display panel 4.

[0230] For example, the phase difference plate may be located in positions other than those shown in Figure 22, such as on the display surface 4a side of the display panel 4, on the first optical surface 62a side of the semi-reflector 62, or on the second optical surface 62b side of the semi-reflector 62. Furthermore, the phase difference plate may be located on the surface side of the first phase difference plate 611 that is on the side of the first reflector 63, or on the surface side of the first phase difference plate 611 that is on the side of the semi-reflector 62. Furthermore, the phase difference plate may be located on the surface side of the second phase difference plate 612 that is on the side of the second reflector 64, or on the surface side of the second phase difference plate 612 that is on the side of the semi-reflector 62.

[0231] For example, along the path of linearly polarized light, at least one of the third phase difference plate 613 and the fourth phase difference plate 614 may be located at any of the positions described above. Here, along the path of linearly polarized light may mean, for example, between the display panel 4 and the semi-reflector 62, between the first phase difference plate 611 and the semi-reflector 62, or between the semi-reflector 62 and the second phase difference plate 612, as shown in Figure 22. Also, both the third phase difference plate 613 and the fourth phase difference plate 614 may be located at any of the positions described above. Furthermore, the third phase difference plate 613 and the fourth phase difference plate 614 may each be located at different positions among the positions described above. That is, both the third phase difference plate 613 and the fourth phase difference plate 614 may be located at any position between two members, or the third phase difference plate 613 and the fourth phase difference plate 614 may each be located separately at different positions among multiple positions between two members.

[0232] Furthermore, for example, both the third phase difference plate 613 and the fourth phase difference plate 614 may be located together in the path of circularly polarized light. In the example shown in Figure 23, both the third phase difference plate 613 and the fourth phase difference plate 614 may be located between the first reflector 63 and the first phase difference plate 611. Also, both the third phase difference plate 613 and the fourth phase difference plate 614 may be located between the second phase difference plate 612 and the second reflector 64.

[0233] The above phase difference plate may include a film having the relationship refractive index nx = refractive index ny > refractive index nz, which is called a negative c plate or negative c plate. The above phase difference plate may include a film having the relationship refractive index nx = refractive index ny < refractive index nz, which is called a positive c plate or positive c plate. The above phase difference plate may include a film having different refractive indices nx, refractive index ny, and refractive index nz, which is called a biaxial phase difference plate. The refractive indices nx and ny are refractive indices in the direction within the film plane, where the x-direction corresponding to refractive index nx and the y-direction corresponding to refractive index ny are orthogonal, and the refractive index nz is the refractive index in the z-direction perpendicular to the film plane.

[0234] The above phase difference plate may include two phase difference plates (third phase difference plate 613 and fourth phase difference plate 614) that provide the same phase difference to transmitted light. The optical axis of the third phase difference plate 613 may be approximately perpendicular to the optical axis of the fourth phase difference plate 614. Furthermore, when the optical axis of the third phase difference plate 613 is approximately perpendicular to the optical axis of the fourth phase difference plate 614, the phase difference plate may be replaced with a film in which the refractive index nx and refractive index ny are the same, and the refractive index nz is different from the refractive index nx and refractive index ny. In other words, it may be replaced with a film having the relationship refractive index nx = refractive index ny > refractive index nz or refractive index nx = refractive index ny < refractive index nz. In this case, the orientation in the x-direction corresponding to the refractive index nx with respect to the transmission axis of the reflective polarizer which is the semi-reflector 62 or the transmission axis of the display panel 4, and the orientation in the y-direction corresponding to the refractive index ny with respect to the transmission axis of the reflective polarizer which is the semi-reflector 62 or the transmission axis of the display panel 4 are not particularly limited. In this case, either the x-direction corresponding to the refractive index nx or the y-direction corresponding to the refractive index ny may be substantially parallel or substantially perpendicular to at least one of the transmission axis of the reflective polarizer which is the semi-reflector 62 and the transmission axis of the display panel 4.

[0235] Furthermore, the phase difference plate may include two phase difference plates (third phase difference plate 613 and fourth phase difference plate 614) that provide different phase differences to transmitted light. The phase difference plate may also include a biaxial phase difference plate. The phase difference plate may include two phase difference plates (third phase difference plate 613 and fourth phase difference plate 614) that provide different phase differences to transmitted light. In this case, if the optical axis of the third phase difference plate 613 is substantially perpendicular to the optical axis of the fourth phase difference plate 614, the phase difference plate may be replaced with a biaxial phase difference plate with different refractive indices nx, ny, and nz. In this case, either the x-direction corresponding to refractive index nx or the y-direction corresponding to refractive index ny may be substantially parallel or substantially perpendicular to at least one of the transmission axis of the reflective polarizer which is the semi-reflector plate 62 and the transmission axis of the display panel 4. Furthermore, in this case, the relationship between refractive index nx, refractive index ny, and refractive index nz can be any one of the following: refractive index nx > refractive index ny > refractive index nz, refractive index ny > refractive index nx > refractive index nz, refractive index nx > refractive index nz > refractive index ny, refractive index ny > refractive index nz > refractive index nx, refractive index nz > refractive index nx > refractive index ny, or refractive index nz > refractive index ny > refractive index nx.

[0236] Regarding the general method of manufacturing a phase difference plate, by stretching the film in one axial direction, the stretched side may have a higher refractive index and become the slow phase axis of the phase difference plate. Regarding the method of manufacturing a negative c plate, by stretching the film equally in two vertical axes (in-plane x and y directions), the stretched x and y axes may have a higher refractive index and the z axis may have a lower refractive index. Regarding the method of manufacturing a biaxial phase difference plate, by stretching the film with a difference in the vertical axes (in-plane x and y directions), the stretched x and y axes will have a higher refractive index, but a refractive index difference may occur between them.

[0237] In the case of the third phase difference plate and the fourth phase difference plate described herein, the third phase difference plate may be replaced with the fourth phase difference plate, or the fourth phase difference plate may be replaced with the third phase difference plate.

[0238] In this embodiment, the case in which the display device 1 corresponding to the display device 1E includes a third phase difference plate 613 and / or a fourth phase difference plate 614 is described, but the invention is not limited to this and may be applied to other embodiments of the present disclosure. For example, the third phase difference plate 613 and / or the fourth phase difference plate 614 may be provided in the display device 1A shown in Figures 5 and 6, the display device 1B shown in Figures 7 and 8, the display device 1C shown in Figure 9, the display device 1D shown in Figures 10 and 11, or the display device 1F shown in Figures 14 and 15. In addition, the third phase difference plate 613 and / or the fourth phase difference plate 614 may be provided in the display device 1G shown in Figures 16 and 17, the display device 1H shown in Figure 18, the display device 1I shown in Figure 19, the display device 1J shown in Figure 20, or the display device 1K shown in Figure 21.

[0239] In these cases as well, the third phase difference plate 613 and / or the fourth phase difference plate 614 may be located at any position along the path of light emitted from the display panel 4. For example, along the path of linearly polarized light, both the third phase difference plate 613 and the fourth phase difference plate 614 may be located at any of the positions described above, or each of the third phase difference plate 613 and the fourth phase difference plate 614 may be located at different positions among those described above. On the other hand, along the path of circularly polarized light, both the third phase difference plate 613 and the fourth phase difference plate 614 may be located together.

[0240] [Embodiment 13] Other embodiments of this disclosure are 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.

[0241] In Figure 22, the size of the first reflective surface 63a when viewed from the first optical surface 62a side or the second optical surface 62b side may be referred to as the first dimension L63. The size of the second reflective surface 64a when viewed from the first optical surface 62a side or the second optical surface 62b side may be referred to as the second dimension L64. The size of the first optical surface 62a or the second optical surface 62b when viewed from the first reflective surface 63a side or the second reflective surface 64a side may be referred to as the third dimension L62. Furthermore, the size of the display panel 4 when viewed from above may be referred to as the fourth dimension L4.

[0242] In Figure 22, the first dimension L63, second dimension L64, third dimension L62, and fourth dimension L4 represent the lengths of each member when viewed from the X-axis direction, but are not limited to this. The first dimension L63, second dimension L64, third dimension L62, and fourth dimension L4 may also represent the size (e.g., area) of each member when viewed from the direction described above.

[0243] Figure 24 is a schematic diagram showing an example of the relative sizes of the components of the display device 1. As shown by reference numeral 1001 in Figure 24, the second dimension L64 may be larger than the third dimension L62. The second dimension L64 may be larger than the fourth dimension L4. The second dimension L64 may be larger than the first dimension L63. The third dimension L62 may be larger than the fourth dimension L4. The third dimension L62 may be larger than the first dimension L63. The fourth dimension L4 may be larger than the first dimension L63.

[0244] Furthermore, as shown by reference numeral 1002 in Figure 24, the second dimension L64 may be larger than the third dimension L62. The second dimension L64 may be larger than the first dimension L63. The second dimension L64 may be larger than the fourth dimension L4. The third dimension L62 may be larger than the first dimension L63. The third dimension L62 may be larger than the fourth dimension L4. The first dimension L63 may be larger than the fourth dimension L4.

[0245] Thus, the second dimension L64 and the third dimension L62 may be larger than the first dimension L63. Also, the second dimension L64 may be larger than the third dimension L62.

[0246] Figure 25 is a schematic diagram showing an example of the direction of propagation of light emitted from the display panel 4. As shown in Figure 25, the light emitted from the display panel 4 may be reflected by the semi-reflector 62 toward the first reflector 63. The light reflected by the first reflector 63 may pass through the semi-reflector 62 and be guided to the second reflector 64, where it may be reflected. The light reflected by the second reflector 64 may be reflected by the semi-reflector 62 and guided toward the viewing window 3. Then, a virtual image V may be formed on the extension of the real ray of light guided from the viewing window 3 to the user Us's eye. In Figure 25, the user Us's eye may be positioned directly in front of the viewing window 3.

[0247] Here, the light emitted from the display panel 4 may travel while converging or while diverging. Light reflected from a convex surface may travel while diverging more than the incident light. Light reflected from a concave surface may travel while converging more than the incident light. Light incident on a planar surface while converging may continue to travel while converging after being reflected from that surface. Light incident on a planar surface while diverging may continue to travel while diverging after being reflected from that surface.

[0248] In this embodiment, the relative sizes of at least the first dimension L63, the second dimension L64, and the third dimension L62 are defined as described above, which enables the formation of a virtual image V as shown in Figure 25.

[0249] Furthermore, the distance from the position of the display panel 4 to the position where the virtual image V is formed, and the magnification ratio of the virtual image V relative to the displayed image, may be defined, for example, as follows.

[0250] (Distance from the position of display panel 4 to the position where the virtual image V is formed) =f2{-f1(a+b) / (-f1+a+b)+(b+c)} / [f2-{-f1(a+b) / (-f1+a+b)+(b+c)}]+(ca) (Magnification) ={(-f1 + a + b) / (-f1)} × {f2 / [f2 - {-f1(a + b) / (-f1 + a + b) + (b + c)}]} In the above formula, -f1 may be the focal length of the first reflector 63, and f2 may be the focal length of the second reflector 64. For example, when the focal length of the first reflector 63 is a concave mirror, it may be f1, and when the focal length of the second reflector 64 is a convex mirror, it may be -f2. For example, a may be the distance from the center of the display panel 4 to the center of the half-reflecting plate 62, b may be the distance from the center of the first reflector 63 to the center of the half-reflecting plate 62, and c may be the distance from the center of the second reflector 64 to the center of the half-reflecting plate 62.

[0251] Also, in this embodiment, taking the display device 1 corresponding to the display device 1E as an example, the size relationship among the half-reflecting plate 62, the first reflector 63, the second reflector 64, and the display panel 4 has been described, but it is not limited to this. This size relationship may also be applied to each of the display devices 1A to 1K. However, in the display devices 1F to 1I in which the light emitted from the display panel 4 is reflected by the second reflector 64 and then reflected by the first reflector 63, the second reflector 64 and the first reflector 63 may be interchanged. That is, in the display devices 1F to 1I, the second reflector 64 may be a convex mirror and the first reflector 63 may be a concave mirror.

[0252] 〔Embodiment 14〕 Other embodiments of the present disclosure will be described below. For convenience of explanation, members having the same functions as those described in the above embodiments are denoted by the same reference numerals, and the description thereof will not be repeated.

[0253] FIG. 26 is a plan view showing an example of an image formed by the display device 1. The virtual image V may have a first region 401 that is visible from the viewing portion and a second region 402 that is not visible from the viewing portion and is smaller than the first region 401 when viewed from the viewing portion while being away from the viewing portion and facing the viewing portion. In the longitudinal direction of the virtual image V, the length of the virtual image V may be larger than the length of the viewing portion. Also, in the short-side direction of the virtual image V, the length of the virtual image V may be longer than the length of the viewing portion.

[0254] In this case, the second region 402 may be located at least on one of the left and right sides of the first region 401, or may be located at least on one of the upper and lower sides of the first region 401. Also, the second region 402 may be located on all of the left and right sides and the upper and lower sides of the first region 401. In other words, the second region 402 may be located at least on one of the left, right, upper, and lower sides of the first region 401. The first region 401 and the second region 402 may be calculated based on the size of the display image displayed on the display panel 4, the magnification when this display image is imaged on the virtual image V, the positional relationship between the virtual image V and the viewing unit, and the size of the viewing unit.

[0255] The sizes of the first region 401 and the second region 402 can be compared by the area of each region. For example, it is sufficient that 60% or more of the virtual image V is the first region 401 and 40% or less of the virtual image V is the second region 402. Also, the first region 401 may have an area twice or more that of the second region 402.

[0256] When looking at the virtual image V from a position away from the viewing unit, for example, it may be viewed from a position where the background around the housing 2 enters the direct viewing range of the user Us. In this case, for example, the housing 2 and the background around it may be included within a range of 70 degrees in the vertical and horizontal directions from the position of the user Us. In the present embodiment, for example, the user Us may view the viewing window 3 while facing it from a position 30 cm or more away from the viewing unit (viewing window 3).

[0257] Figure 27 is a top view illustrating the act of viewing the viewing area directly. Viewing the viewing area directly may mean that the user Us views the viewing area from above the normal 404 to the center 403 of the virtual image V. That is, for example, if the viewing window 3 is installed at an angle to the housing 2, and the viewing area is viewed from above the normal 404, the user Us does not need to view the virtual image V from a position parallel to the inclined surface of the viewing window 3, but may view the virtual image V from a position non-parallel to the inclined surface of the viewing window 3. In this disclosure, when the viewing area is not viewed directly (when the virtual image V is viewed from a position off the normal 404), the virtual image V may have an area that is not visible from the viewing area that is larger than the area that is visible from the viewing area, or it may not have an area that is not visible from the viewing area.

[0258] According to the above configuration, a user Us who is viewing the viewing unit from a distance and directly facing it can see most of the virtual image V, making it easy to recognize the content of the video that is flowing as a virtual image V.

[0259] Furthermore, the second region 402, which should be located above and below the first region 401, may be smaller than the second region 402, which should be located on the side of the first region 401. In this case, the second region 402 may exist on the side of the first region 401, but it is not necessary for the second region 402 to exist above and below the first region 401. In this embodiment, the second region 402 is located above, below, and on the side of the first region 401, and the first portion 406 of the second region 402, which is located above and below the first region 401, may be set to be smaller than the second portion 407 of the second region 402, which is located on the side of the first region 401.

[0260] The second region 402 can be seen from the viewing area when viewed from a distance and without directly facing the viewing area. The first part 406 of the second region 402 can be seen from the viewing window 3 when viewed from above or below, and the second part 407 of the second region 402 can be seen from the viewing window 3 when viewed from the side. In this case, the user Us can more easily see the virtual image V.

[0261] Furthermore, the vertical magnification of the virtual image V may be smaller than the horizontal magnification of the virtual image V. For example, the horizontal magnification of the virtual image V may be twice or more than the vertical magnification. According to the above configuration, a virtual image V with a large width can be formed, making it easier for the user Us to see the virtual image V.

[0262] Figure 28 is a schematic diagram comparing the length of the viewing section with the length of the second reflector 64 in the longitudinal direction of the viewing section. The optical system 6 has a second reflector 64, and in the longitudinal direction WL of the viewing section (viewing window 3), the length L31 of the viewing section (viewing window 3) may be greater than the length L641 of the second reflector 64. The size of the viewing window 3 when viewed from the front position (directly facing position) of the display device 1 may be referred to as the fifth dimension L3. The length L31 of the viewing section (viewing window 3) may be an example of the fifth dimension L3. Also, the length L641 of the second reflector may be an example of the second dimension L64. According to the above configuration, the visible area of ​​the virtual image V can be increased.

[0263] If the viewing area (viewing window 3) is parallel to the XY plane, the longitudinal direction WL of the viewing area (viewing window 3) may be, for example, the X direction or the Y direction. If the viewing area (viewing window 3) is not parallel to the XY plane, the longitudinal direction WL of the viewing area (viewing window 3) may be along the X direction or the Y direction, and the length L3 of the viewing area (viewing window 3) may be the X component or the Y component. Furthermore, the longitudinal direction WL of the viewing area (viewing window 3) may correspond to the longitudinal direction of the second reflecting mirror 64. If a plane substantially perpendicular to the central axis of the second reflecting mirror 64 is parallel to the XZ plane, the longitudinal direction of the second reflecting mirror 64 may be, for example, the X direction or the Z direction. Furthermore, if the plane substantially perpendicular to the central axis of the second reflector 64 is not parallel to the XZ plane, the longitudinal direction of the second reflector 64 is, for example, along the X or Z direction, and the length L641 of the second reflector 64 may be the X component or the Z component.

[0264] Furthermore, as shown in Figure 27, the angle θa between the first straight line 410 connecting the first end 408 in the longitudinal direction of the virtual image V and the center 409 of the viewing window 3, and the second straight line 412 connecting the second end 411 in the longitudinal direction of the virtual image V and the center 409 of the viewing window 3, may be 70 degrees or less.

[0265] An example of an angle θa is shown in Figure 27. Figure 27 may be an example where the longitudinal direction of the virtual image V is the X direction. The longitudinal direction of the virtual image V is not limited to the X direction, but may also be the Y direction or other direction parallel to the XY plane.

[0266] Since the effective field of view of a human being is approximately 70 degrees, the above configuration makes it easy for the user Us to recognize the content of the video that is flowing as a virtual image V.

[0267] The virtual image V may have a size such that more than half of it is visible from the viewing area when viewed by the user Us at a position further away from the focal point of the optical system 6. This makes it easier for the user Us to recognize the content of the image flowing as the virtual image V. If the optical system 6 diverges, focuses, or converges light using multiple optical elements (first reflector 63 and second reflector 64), the focal point of the optical system 6 may be a position based on the combined focal length of the multiple optical elements.

[0268] Figure 52 is a schematic diagram illustrating the size of the viewing section and the second reflector 64. Reference numeral 1031 in Figure 52 is a schematic diagram showing the case where the second reflector 64 is positioned directly facing the viewing section, and reference numeral 1032 is a schematic diagram showing the case where the second reflector 64 is positioned not directly facing the viewing section. In reference numeral 1032, the second reflector 64 is located on the bottom side of the display device 1, but it may also be located on the top side of the display device 1. Figure 52 may be a schematic diagram showing a general cross-section of the display device 1 as viewed from the X-axis direction. In the explanation of Figure 52, a viewing window 3 is given as an example of the viewing section, but the viewing section may be, for example, an opening 21.

[0269] In Figure 52, the first angle α may be the angle between two straight lines 421 and 422 that connect an arbitrary point 415 on the opposite side of the inner region 22 from the viewing window 3 in a cross-sectional view to the respective endpoints 416 and 417 of the viewing window 3. The second angle β may be the angle between two straight lines 423 and 424 that connect an arbitrary point 415 to the respective endpoints 418 and 419 of the second reflector 64 along the optical path of the display light in a cross-sectional view. As shown in Figure 52, the first angle α may be larger than the second angle β. That is, the relative sizes and positions of the viewing window 3 and the second reflector 64 may be defined such that the first angle α is larger than the second angle β. Also, the first angle α may be, for example, 70 degrees or less.

[0270] Any point 415 may be in front of the viewing window 3 (on the user Us side). Any point 415 may be located, for example, on the normal line passing through the center of the viewing window 3. Any point 415 may be the position of user Us facing directly toward the viewing window 3. Any point 415 may be located, for example, 30 cm away from the viewing window 3, or more than 30 cm away. Any point 415 may be located in front of the viewing window 3 (on the user Us side) and 30 cm away from the viewing window 3 on the normal line passing through the center of the viewing window 3.

[0271] The two endpoints 416 and 417 of the viewing window 3, and the two endpoints 418 and 419 of the second reflector 64, may be two points that are directly opposite each other in a cross-sectional view, among the points that constitute the outer edge of each member.

[0272] As shown by reference numeral 1031, if the second reflector 64 is located on the opposite side of any point 415 from the viewing window 3, the viewing window 3 and the second reflector 64 may have their centers coaxial. The path of the display light from the second reflector 64 through the viewing window 3 to any point 415 may be formed along this axis. In this case, the second angle β may be the angle between one straight line 423 and another straight line 424 along this path of display light.

[0273] On the one hand, as shown by reference sign 1032, when the second reflector 64 is not located on the opposite side of an arbitrary point 415 with respect to the viewing window 3, the path of the display light may be refracted by the half-reflector 62. In this case, the second angle β may be an angle formed by a straight line 423 formed by two straight lines and a straight line 424 formed by two straight lines along the path of the display light. When the positional relationship between the viewing window 3 and the second reflector 64 shown by reference sign 1032 is changed coaxially so as to satisfy the optical path of the display light formed by the positional relationship, straight lines 423 and 424 as shown by reference sign 1031 may be formed.

[0274] When another member (for example, the first reflector 63) is arranged on the optical path of the display light, the straight lines 423 and 424 may each be formed by a plurality of straight lines. Also in this case, when the positional relationship among the viewing window 3, the second reflector 64, and the members located between these members is changed coaxially so as to satisfy the optical path of the display light formed by the positional relationship, straight lines 423 and 424 as shown by reference sign 1031 may be formed.

[0275] In the above, an example when the display device 1 is viewed from the X-axis direction has been described, but it is not limited thereto. For example, it can also be applied to the case when the display device 1 is viewed from the Y-axis direction or the Z-axis direction. For example, the magnitude relationship between the first angle α and the second angle β when the display device 1 is viewed from the Y-axis direction or the Z-axis direction may be the same as the magnitude relationship between the first angle α and the second angle β when the display device 1 is viewed from the X-axis direction. That is, when the display device 1 is viewed from the Y-axis direction or the Z-axis direction, the first angle α may also be larger than the second angle β.

[0276] Figs. 29 to 31 are schematic diagrams showing an example of the traveling direction of the light emitted from the display panel 4. In the display device 1 shown in Figs. 29 to 31, in the longitudinal direction WL of the viewing portion (viewing window 3), the length L31 of the viewing portion (viewing window 3) may be larger than the length L641 of the second reflector 64. That is, in the display device 1 shown in Figs. 29 to 31, the size (the fifth dimension L3) of the viewing window 3 may be larger than the size (the second dimension L64) of the second reflector 64 when viewed from the half-reflector 62.

[0277] The size of the second region 402 in the virtual image V can also be changed by adjusting the size of each component of the optical system 6. Figure 29 may show an example where the second dimension L64 is smaller than the second dimension L64 in the display device 1 shown in Figure 25. In this case, it is possible that some of the real light rays emitted from the display panel 4 are not reflected by the second reflector 64. In the example of Figure 29, it is possible that real light rays are not reflected in a portion of the second reflector 64R where real light rays were reflected in Figure 25. In this case, the real light rays of the light emitted from the display panel 4 may be reflected at the end 64E. That is, as shown in Figure 29, the real light rays of the light emitted from the display panel 4 that are transmitted or reflected by each component of the optical system 6 may form paths represented by thick solid lines and thick dashed lines. The virtual image V may then be formed on the extension of these real light rays of the light guided from the viewing window 3 to the eye of the user Us located in front of the viewing window 3.

[0278] As a result, as shown in Figure 29, the size of the virtual image V seen by the user Us, who is positioned directly in front of the viewing window 3, may be smaller than the size of the virtual image V in the case of the display device 1 shown in Figure 25. The smaller area in the virtual image V may become the second area 402.

[0279] Figure 30 may show an example where the size of the semi-reflector 62 (third dimension L62) is smaller than the third dimension L62 in the display device 1 shown in Figure 25. In the display device 1 of Figure 30, the size of the viewing window 3 (fifth dimension L3) may be larger than the size of the semi-reflector 62 (third dimension L62) as seen from the first reflector 63 or the second reflector 64.

[0280] If the third dimension L62 is reduced, it is possible that some of the real light rays emitted from the display panel 4 may not be reflected by the semi-reflector 62. In the example of Figure 30, it is possible that real light rays may not be reflected in a portion of the semi-reflector 62R where real light rays were reflected in Figure 25. In this case, the real light rays of the light emitted from the display panel 4 may be reflected at the end 62E. That is, as shown in Figure 30, the real light rays of the light emitted from the display panel 4 that are transmitted or reflected by each component of the optical system 6 may form paths represented by the thick solid lines and the thick dashed lines. Then, a virtual image V may be formed on the extension of the real light rays of the light that are guided from the viewing window 3 to the eye of the user Us located in front of the viewing window 3.

[0281] As a result, as shown in Figure 30, the size of the virtual image V seen by the user Us, who is positioned directly in front of the viewing window 3, may be smaller than the size of the virtual image V in the case of the display device 1 shown in Figure 25. The smaller area in the virtual image V may become the second area 402.

[0282] Figure 31 may show an example where the size of the first reflector 63 (first dimension L63) is smaller than the first dimension L63 in the display device 1 shown in Figure 25. In the display device 1 of Figure 31, the size of the viewing window 3 (fifth dimension L3) may be larger than the size of the first reflector 63 (first dimension L63) as seen from the semi-reflector 62.

[0283] If the first dimension L63 is reduced, it is possible that some of the real light rays emitted from the display panel 4 will not be reflected by the first reflector 63. In the example of Figure 31, it is possible that real light rays will not be reflected in a portion of the first reflector 63R where real light rays were reflected in Figure 25. In this case, the real light rays of the light emitted from the display panel 4 may be reflected at the end 63E. That is, as shown in Figure 31, the real light rays of the light emitted from the display panel 4 that are transmitted or reflected by each component of the optical system 6 may form paths represented by thick solid lines and thick dashed lines. Then, a virtual image V may be formed on the extension of the real light rays of the light guided from the viewing window 3 to the eye of the user Us located in front of the viewing window 3.

[0284] As a result, as shown in Figure 31, the size of the virtual image V seen by the user Us positioned in front of the viewing window 3 may be smaller than the size of the virtual image V in the case of the display device 1 shown in Figure 25. The smaller area in the virtual image V may become the second area 402.

[0285] Here, the optical system 6 may include an absorbing polarizer. The absorbing polarizer may be located, for example, near the viewing window 3. In this case, the size of the second region 402 may be adjusted by adjusting the size of the absorbing polarizer when viewed from above. The absorbing polarizer may be an example of a polarizer 69, which will be described later.

[0286] In this embodiment, the relationship between the size of the viewing window 3 and the second reflector 64 has been explained using the display device 1 corresponding to the display device 1E as an example, but it is not limited to this. This example of the size relationship may also be applied to each of the display devices 1A to 1K. However, if an image based on the display image is formed by the first reflector 63, the second reflector 64 may be read as the first reflector 63.

[0287] In this embodiment, the example of forming the second region 402 was described using the display device 1 corresponding to the display device 1E as an example, but it is not limited to this. The example of forming the second region 402 may also be applied to each of the display devices 1A to 1K. However, in the display devices 1F to 1I in which light emitted from the display panel 4 is reflected by the second reflector 64 and then by the first reflector 63, the second reflector 64 and the first reflector 63 may be interchangeable. That is, in the display devices 1F to 1I, the second reflector 64 may be a convex mirror and the first reflector 63 may be a concave mirror.

[0288] [Embodiment 15] Other embodiments of this disclosure are 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.

[0289] In this embodiment, the relationship between the focal length of the first reflector 601 and the distance between the display panel 4 and the first reflector 601 will be explained using Figures 32 to 42. The first reflector 601 in the following description may be the first reflector 63 described herein. Also, the second reflector 603 in the following description may be the second reflector 64 described herein. In Figures 32 to 42, for the sake of simplicity, it is assumed that the display panel 4, the first reflector 601 and the second reflector 603 are arranged on the same axis. In addition, in Figures 32 to 42, a semi-reflector 62 is located between the first reflector 601 and the second reflector 603, but the illustration of the semi-reflector 62 is omitted.

[0290] Figure 32 shows a first example in which the first reflector 601 images the display light to form a first image 602. The display panel 4 may emit the display light. The first reflector 601 may have the function of reflecting and diverting light toward the semi-reflector 62, and may image the display light to form a first image 602. The first image 602 may be formed on the side opposite the semi-reflector 62 to the first reflector 601, with the display image of the display panel 4 reduced in size. That is, the first image 602 may be formed on the side opposite to the first reflective surface 63a (the surface to which the display light is incident). In this embodiment, the first reflector 601 can reflect and diverge the light that is incident on and reflected by the first reflector 601. For example, the first reflector 601 may have a convex shape located toward the semi-reflector 62. As a result, the first reflector 601 can reflect and diverge light. The first reflector 601 may also be described as having a convex shape that protrudes toward the semi-reflector 62. Alternatively, the first reflector 601 may also be described as having a concave shape located on the opposite side of the semi-reflector 62. The first reflector 601 may also be described as having a concave shape that opens toward the opposite side of the semi-reflector 62. The first reflector 601 may also be described as having a concave shape that is recessed toward the semi-reflector 62. The first reflector 601 may also be flat. In this case, the first reflector 601 may be a holographic optical element or its surface shape may be Fresnel-shaped. The focal length f601 of the first reflector 601 may be greater than the distance d60B between the display panel 4 and the first reflector 601. The focal length f601 of the first reflector 601 may also be less than the distance d60B between the display panel 4 and the first reflector 601.

[0291] Figure 33 shows a first example in Figure 32 in which the second reflector 603 forms the first image 602 to form the second image 604. The second reflector 603 may have the function of focusing or converging light toward the first image 602 side (semi-reflector 62 side) and forming the first image 602 to form the second image 604. In this embodiment, the second reflector 603 can focus or converge the light that is incident on and reflected by the second reflector 603. For example, the second reflector 603 may have a concave shape located toward the semi-reflector 62 side. As a result, the second reflector 603 can focus or converge the light. It can also be said that the second reflector 603 has a concave shape that opens toward the semi-reflector 62 side. It can also be said that the second reflector 603 has a concave shape that is recessed toward the opposite side from the semi-reflector 62. Furthermore, the second reflector 603 may have a convex shape that protrudes on the opposite side from the semi-reflector 62. The second reflector 603 may also be flat. In this case, the second reflector 603 may be a holographic optical element or have a Fresnel shape on its surface. The focal length f603 of the second reflector 603 may be greater than the separation distance d60A between the first image 602 and the second reflector 603. The second image 604 may be a virtual image formed on the side of the display panel 4 by magnification of the first image 602. The focal point of the second reflector 603 is indicated by the reference numeral 603'.

[0292] The definitions of each separation distance d60A and separation distance d60B are described below. Each separation distance d60A and separation distance d60B may be a distance in a direction parallel to at least one of the following: the optical axis of incident light to the first reflector 601, the optical axis of emitted light to the first reflector 601, the optical axis of incident light to the second reflector 603, and the optical axis of emitted light to the second reflector 603. Alternatively, each separation distance d60A and separation distance d60B may be a distance in a direction parallel to at least one of the following: the optical axis of the first reflector 601, the optical axis of the second reflector 603, the optical axis of the display panel 4 (for example, the normal direction of the display surface of the display panel 4), the normal direction of the reflective surface of the optical component (for example, the first reflector 601 or the second reflector 603), or a direction parallel to that at least one direction. With respect to that direction, each separation distance d60A and separation distance d60B may be a distance that can determine whether the optical component forms a real image or a virtual image in comparison to the focal position of the corresponding optical component. Therefore, at each separation distance d60A and separation distance d60B, the starting point on the optical component side may be the position of the center of the optical component, and the starting point on the image side may be the position of the display surface in the case of the display panel 4, or the image formation position in the case of each first image 602 and second image 604.

[0293] Furthermore, if the display panel 4 and the first reflector 601 are not located coaxially with the semi-reflector 62 in between, the separation distance d60B may be defined, for example, as follows: The separation distance d60B may be the sum of, for example, the distance between the display panel 4 and the semi-reflector 62 in a direction parallel to the optical axis of the display panel 4, and the distance between the first reflector 601 and the semi-reflector 62 in a direction parallel to the optical axis of the incident or emitted light to the first reflector 601.

[0294] Furthermore, if the first image 602 and the second reflector 603 are not located coaxially with the semi-reflector 62 in between, the separation distance d60A may be defined, for example, as follows: The separation distance d60A may be the sum of, for example, the distance between the first image 602 and the semi-reflector 62 in a direction parallel to the optical axis of the first reflector 601 that forms the first image 602, and the distance between the second reflector 603 and the semi-reflector 62 in a direction parallel to the optical axis of the incident or emitted light for the second reflector 603.

[0295] Figure 34 shows a second example in Figure 32 in which the second reflector 603 forms the first image 602 to form the second image 604. The second reflector 603 may have the function of focusing or converging light toward the first image 602 side (semi-reflector 62 side) and forming the first image 602 to form the second image 604. The focal length f603 of the second reflector 603 may be smaller than the separation distance d60A between the first image 602 and the second reflector 603. The second image 604 may be a real image formed by enlarging or reducing the first image 602 toward the user Us side relative to the semi-reflector 62. The second image 604 may be inverted relative to the first image 602.

[0296] Figure 35 shows a second example in which the first reflector 601 images the display light to form the first image 602. The display panel 4 may emit the display light. The first reflector 601 may have the function of focusing or converging light toward the semi-reflector 62 and forming the display light to form the first image 602. In this embodiment, the first reflector 601 can focus or converge the light that is incident on and reflected by the first reflector 601. For example, the first reflector 601 may have a concave shape located toward the semi-reflector 62. As a result, the first reflector 601 can focus or converge the light. It can also be said that the first reflector 601 has a convex shape that protrudes toward the opposite side of the semi-reflector 62 (opposite side of the first optical surface 62a). It can also be said that the first reflector 601 has a concave shape that opens toward the semi-reflector 62. The first reflector 601 can also be described as having a concave shape that is recessed toward the opposite side from the semi-reflector 62. The first reflector 601 may also be flat. In this case, the first reflector 601 may be a holographic optical element or its surface shape may have a Fresnel shape. The focal length f601 of the first reflector 601 may be greater than the separation distance d60B between the display panel 4 and the first reflector 601. The first image 602 may be formed on the opposite side of the semi-reflector 62 from the first reflector 601 by magnifying the display image of the display panel 4. The focal point of the first reflector 601 is indicated by the reference numeral 601'.

[0297] Figure 36 shows a first example in Figure 35 in which the second reflector 603 forms the first image 602 to form the second image 604. The second reflector 603 may have the function of focusing or converging light toward the first image 602 side (semi-reflector 62 side) and forming the first image 602 to form the second image 604. In this embodiment, the second reflector 603 can focus or converge the light that is incident on and reflected by the second reflector 603. For example, the second reflector 603 may have a concave shape located toward the semi-reflector 62 side. As a result, the second reflector 603 can focus or converge the light. It can also be said that the second reflector 603 has a concave shape that opens toward the semi-reflector 62 side. It can also be said that the second reflector 603 has a concave shape that is recessed toward the opposite side from the semi-reflector 62. Furthermore, the second reflector 603 may have a convex shape that protrudes on the opposite side from the semi-reflector 62. The second reflector 603 may also be flat. In this case, the second reflector 603 may be a holographic optical element or have a Fresnel shape on its surface. The focal length f603 of the second reflector 603 may be greater than the separation distance d60A between the first image 602 and the second reflector 603. The second image 604 may be a virtual image formed on the side of the display panel 4 by magnifying the first image 602.

[0298] Figure 37 shows a second example in Figure 35 in which the second reflector 603 forms the first image 602 to form the second image 604. The second reflector 603 may have the function of focusing or converging light toward the first image 602 side (semi-reflector 62 side) and forming the first image 602 to form the second image 604. In this embodiment, the second reflector 603 can focus or converge the light that is incident on and reflected by the second reflector 603. For example, the second reflector 603 may have a concave shape located toward the semi-reflector 62 side. As a result, the second reflector 603 can focus or converge the light. It can also be said that the second reflector 603 has a concave shape that opens toward the semi-reflector 62 side. It can also be said that the second reflector 603 has a concave shape that is recessed toward the opposite side from the semi-reflector 62. Furthermore, the second reflector 603 may have a convex shape that protrudes on the opposite side from the semi-reflector 62. The second reflector 603 may also be flat. In this case, the second reflector 603 may be a holographic optical element or have a Fresnel shape on its surface. The focal length f603 of the second reflector 603 may be smaller than the separation distance d60A between the first image 602 and the second reflector 603. The second image 604 may be a real image formed by enlarging or reducing the first image 602 on the user Us side relative to the semi-reflector 62. The second image 604 may be inverted relative to the first image 602.

[0299] Figure 38 shows a third example in which the first reflector 601 images the display light to form the first image 602. The display panel 4 may emit the display light. The first reflector 601 may have the function of focusing or converging light toward the semi-reflector 62 and forming the display light to form the first image 602. In this embodiment, the first reflector 601 can focus or converge the light that is incident on and reflected by the first reflector 601. For example, the first reflector 601 may have a concave shape located toward the semi-reflector 62. As a result, the first reflector 601 can focus or converge the light. It can also be said that the first reflector 601 has a convex shape that protrudes toward the opposite side of the semi-reflector 62. It can also be said that the first reflector 601 has a concave shape that opens toward the semi-reflector 62. It can also be said that the first reflector 601 has a concave shape that is recessed toward the opposite side of the semi-reflector 62. The first reflector 601 may be flat. In this case, the first reflector 601 may be a holographic optical element or have a Fresnel shape. The focal length f601 of the first reflector 601 may be smaller than the distance d60B between the display panel 4 and the first reflector 601. The first image 602 may be formed on the side of the semi-reflector 62 (or on the side of the display panel 4 via the semi-reflector 62) relative to the first reflector 601, by enlarging or reducing the display image of the display panel 4. The first image 602 may be inverted relative to the display image of the display panel 4.

[0300] Figure 39 shows a first example in Figure 38 where the second reflector 603 forms the first image 602 to form the second image 604. The second reflector 603 may have the function of focusing or converging light toward the first image 602 side (semi-reflector 62 side) and forming the first image 602 to form the second image 604. In this embodiment, the second reflector 603 can focus or converge light that is incident on and reflected by the second reflector 603. For example, the second reflector 603 has a concave shape located on the opposite side from the semi-reflector 62. As a result, the second reflector 603 can focus or converge light. It can also be said that the second reflector 603 has a concave shape that opens toward the semi-reflector 62 side. It can also be said that the second reflector 603 has a concave shape that is recessed toward the opposite side from the semi-reflector 62. Furthermore, the second reflector 603 may have a convex shape that protrudes on the opposite side from the semi-reflector 62. The second reflector 603 may also be flat. In this case, the second reflector 603 may be a holographic optical element or have a Fresnel shape on its surface. The first image 602 may be located on the side of the semi-reflector 62 (or on the side of the display panel 4 via the semi-reflector 62). The focal length f603 of the second reflector 603 may be greater than the separation distance d60A between the first image 602 and the second reflector 603. The second image 604 may be a virtual image formed on the side of the display panel 4 by an enlargement of the first image 602.

[0301] Figure 40 shows a second example in Figure 38 in which the second reflector 603 forms the first image 602 to form the second image 604. The second reflector 603 may have the function of focusing or converging light toward the first image 602 side (semi-reflector 62 side) and forming the first image 602 to form the second image 604. In this embodiment, the second reflector 603 can focus or converge light that is incident on and reflected by the second reflector 603. For example, the second reflector 603 has a concave shape located toward the semi-reflector 62 side. As a result, the second reflector 603 can focus or converge light. It can also be said that the second reflector 603 has a concave shape that opens toward the semi-reflector 62 side. It can also be said that the second reflector 603 has a concave shape that is recessed toward the semi-reflector 62 side. Furthermore, the second reflector 603 may have a convex shape that protrudes on the opposite side from the semi-reflector 62. The second reflector 603 may also be flat. In this case, the second reflector 603 may be a holographic optical element or have a Fresnel shape on its surface. The first image 602 may be located on the side of the semi-reflector 62 (or on the side of the display panel 4 via the semi-reflector 62). The focal length f603 of the second reflector 603 may be smaller than the separation distance d60A between the first image 602 and the second reflector 603. The second image 604 may be a real image formed by enlarging or reducing the first image 602 on the user Us side relative to the semi-reflector 62 or the first image 602. The second image 604 may be inverted relative to the first image 602, in other words, upright relative to the display image of the display panel 4.

[0302] Figure 41 shows a third example in Figure 38 in which the second reflector 603 forms the first image 602 to form the second image 604. The display panel 4 may emit display light. The first reflector 601 may have the function of focusing or converging light toward the semi-reflector 62 and forming the display light to form the first image 602. In this embodiment, the first reflector 601 can focus or converge light that is incident on and reflected by the first reflector 601. For example, the first reflector 601 may have a concave shape located toward the semi-reflector 62. As a result, the first reflector 601 can focus or converge light. It can also be said that the first reflector 601 has a convex shape that protrudes toward the opposite side from the semi-reflector 62. It can also be said that the first reflector 601 has a concave shape that opens toward the semi-reflector 62. The first reflector 601 can also be described as having a concave shape that is recessed toward the opposite side from the semi-reflector 62. The first reflector 601 may also be flat. In this case, the first reflector 601 may be a holographic optical element or may have a Fresnel shape on its surface. The second reflector 603 has the function of focusing or converging light toward the opposite side from the first image 602 (towards the semi-reflector 62), and may form a second image 604 by imaging the first image 602. In this embodiment, the second reflector 603 can focus or converge light that is incident on and reflected by the second reflector 603. For example, the second reflector 603 may have a concave shape located toward the semi-reflector 62. As a result, the second reflector 603 can focus or converge light. The second reflector 603 can also be described as having a concave shape that opens toward the semi-reflector 62. The second reflector 603 may also be described as having a concave shape that is recessed toward the opposite side from the semi-reflector 62. Alternatively, the second reflector 603 may also be described as having a convex shape that protrudes toward the opposite side from the semi-reflector 62. The second reflector 603 may also be flat. In this case, the second reflector 603 may be a holographic optical element or may have a Fresnel shape on its surface. The focal length f601 of the first reflector 601 may be smaller than the distance d60B between the display panel 4 and the first reflector 601 (see Figure 38). The first image 602 may be located on the opposite side of the second reflector 603 from the semi-reflector 62 (or on the side of the display panel 4 via the semi-reflector 62).The second image 604 may be a real image formed by reducing the first image 602 on the opposite side of the first image 602 with respect to the second mirror 603 (the half mirror 62 side or the user Us side). The first image 602 may be inverted with respect to the display image of the display panel 4. The second image 604 may be upright with respect to the first image 602, or in other words, may be inverted with respect to the display image of the display panel 4.

[0303] FIG. 42 is a diagram for explaining the conditions according to the example of FIG. 40 and the conditions according to the example of FIG. 41. Regarding the focal length f601, the separation distance d60B, and the separation distance L60 between the first mirror 601 and the first image 602, (X) may hold.

[0304] L60:d60B=f601:(d60B - f601) That is, L60 = d60B × f601 / (d60B - f601) ···(X) In (X), when the separation distance L60 is greater than the separation distance d60 between the first mirror 601 and the second mirror 603, that is, when d60B × f601 / (d60B - f601) > d60, it may correspond to the example of FIG. 41. In (X), when the separation distance L60 is smaller than the separation distance d60, that is, when d60B × f601 / (d60B - f601) < d60, it may correspond to the example of FIG. 40.

[0305] The separation distance L60 may be, for example, the sum of the distance between the first mirror 601 and the half mirror 62 in a direction parallel to the optical axis of the incident light or the outgoing light with respect to the first mirror 601 and the distance between the first image 602 and the half mirror 62 in a direction parallel to the optical axis of the display panel 4. The separation distance d60 may be, for example, the sum of the distance between the first mirror 601 and the half mirror 62 in a direction parallel to the optical axis of the incident light or the outgoing light with respect to the first mirror 601 and the distance between the second mirror 603 and the half mirror 62 in a direction parallel to the optical axis of the incident light or the outgoing light with respect to the second mirror 603.

[0306] In each example in Figures 32 to 41, the focal length f603 of the second reflector 603 may be greater than the focal length f601 of the first reflector 601. In each example in Figures 32 to 41, the focal length f603 of the second reflector 603 may be less than the focal length f601 of the first reflector 601.

[0307] By applying an example related to any of Figures 33, 34, 36, 37, or 39-41 to the display device 1, the display device 1 can be miniaturized relative to the size of the image by combining two reflectors to form the image seen by the user Us.

[0308] In this embodiment, the relationship between focal length and separation distance has been explained using display device 1 corresponding to display device 1E as an example, but it is not limited to this. This relationship may also be applied to each of the display devices 1A to 1K. However, in display devices 1F to 1I in which light emitted from the display panel 4 is reflected by the second reflector 64 and then by the first reflector 63, the second reflector 64 and the first reflector 63 may be interchanged. That is, in display devices 1F to 1I, the second reflector 64 may correspond to the first reflector 601, and the first reflector 63 may correspond to the second reflector 603.

[0309] [Embodiment 16] Other embodiments of this disclosure are 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.

[0310] Figure 43 is a schematic cross-sectional view showing the configuration of the display device 1 according to this embodiment. Reference numeral 1011 in Figure 43 may be the display device 1 shown in Figure 22. In the example of Figure 22, the first reflecting mirror 63 may be a convex mirror, and the second reflecting mirror 64 may be a concave mirror.

[0311] As shown by reference numeral 1012 in Figure 43, the first reflecting mirror 63 may be a plane mirror. In this case, the first reflecting mirror 63 may be a holographic optical element. The first reflecting mirror 63 may also have a Fresnel shape as its surface shape. The second reflecting mirror 64 may also be a plane mirror. In this case, the second reflecting mirror 64 may be a holographic optical element. The second reflecting mirror 64 may also have a Fresnel shape as its surface shape.

[0312] In this way, by using plane mirrors as the first reflector 63 and the second reflector 64, the display device 1 can be miniaturized. In the example of Figure 43, both the first reflector 63 and the second reflector 64 are plane mirrors, but either the first reflector 63 or the second reflector 64 may be a plane mirror. Even in this case, the display device 1 can be miniaturized.

[0313] In this embodiment, a configuration in which at least one of the first reflector 63 and the second reflector 64 is a plane mirror has been described using the display device 1 corresponding to the display device 1E as an example, but the embodiment is not limited to this. In each of the display devices 1A to 1K, at least one of the first reflector 63 and the second reflector 64 may be a plane mirror. In this case, in the display devices 1A to 1C, 1H to 1K, where the first reflector 63 or the second reflector 64 is located on the opposite side of the viewing window 3 with the semi-reflector 62 in between, the display device 1 can be miniaturized in the Z-axis direction.

[0314] [Embodiment 17] Other embodiments of this disclosure are 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.

[0315] Figure 44 is a schematic cross-sectional view showing the configuration of the display device 1 according to this embodiment. As shown in Figure 44, the display device 1 may include a lens 68. The lens 68 may be located on a path in which light travels in only one direction among the paths of light emitted from the display panel 4 and reflected or transmitted by each member of the optical system 6. In the example of Figure 44, the lens 68 may be located between the viewing window 3 and the semi-reflector 62. In this case, for example, the lens 68 may be located in contact with the viewing window 3, but is not limited to this, and may be located away from the viewing window 3. Also in the example of Figure 44, it may be located between the display panel 4 and the semi-reflector 62. In this case, for example, the lens 68 may be located in contact with the display panel 4, but is not limited to this, and may be located away from the display panel 4.

[0316] The lens 68 may, for example, be a Fresnel lens with a Fresnel-shaped surface. However, it is not limited to this. For example, the lens 68 may be a holographic optical element. In the case of these lenses, the thickness of the lens 68 can be reduced, thus allowing the display device 1 to be miniaturized. For example, the lens 68 may be a biconcave lens, a plano-concave lens, a concave-convex lens, or a biconvex lens, a plano-convex lens, etc. In addition, the lens 68 may be an aspherical lens, a cylindrical lens, a meniscus lens, etc.

[0317] The lens 68 may have a function to diverge the incident light. In this case, the optical system 6 can magnify and form an image based on the display image (virtual image V or real image). Specifically, the lens 68 may have a function to magnify the light emitted from the display panel 4 and reflected by the first reflector 63 and the second reflector 64. In this case, as shown in Figure 44, the lens 68 may be located between the viewing window 3 and the semi-reflector 62. The lens 68 may also have a function to magnify the light emitted from the display panel 4. In this case, the lens 68 may be located between the display panel 4 and the semi-reflector 62.

[0318] Furthermore, the lens 68 may have the function of collecting or focusing incident light. In this case, the optical system 6 can reduce the size of the image based on the display image and form an image. Specifically, the lens 68 may have the function of collecting or focusing light emitted from the display panel 4 and reflected by the first reflector 63 and the second reflector 64. In this case, as shown in Figure 44, the lens 68 may be located between the viewing window 3 and the semi-reflector 62. Also, the lens 68 may have the function of collecting or focusing light emitted from the display panel 4. In this case, the lens 68 may be located between the display panel 4 and the semi-reflector 62.

[0319] Magnification or reduction of the image based on the display image can be enhanced more effectively by magnifying or reducing the light reflected by the reflectors (second reflector 64 and / or first reflector 63) that form an image based on the display image, rather than by magnifying or reducing the light emitted by the display panel 4. In other words, when the lens 68 is located on the viewing window 3 side, the magnification or reduction effect on the image based on the display image can be enhanced.

[0320] In this embodiment, a configuration including a lens 68 has been described using a display device 1 corresponding to display device 1E as an example, but the embodiment is not limited to this. Each of the display devices 1A to 1K may be provided with a lens 68. Furthermore, the display device 1 does not have to have a viewing window 3. In this case, the lens 68 may be placed in the opening 21, and the lens 68 may function as a viewing section.

[0321] [Embodiment 18] Other embodiments of this disclosure are 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.

[0322] Figure 49 is a schematic diagram illustrating the configuration of the display device 1 according to this embodiment. The display device 1 shown in Figure 49 may be the same as the display device 1E shown in Figure 13, but with a change in the position of the second phase difference plate 612. Also, as shown in Figure 49, the display device 1 may include a lens 68, as shown in the display device 1 in Figure 44. In the example of Figure 49, the lens 68 may be located on the viewing side of the semi-reflector 62. Also, as shown in Figure 49, the display device 1 may include a polarizing plate 632. The polarizing plate 632 may be located on the opposite side of the lens 68 from the semi-reflector 62. Also, as shown in Figure 49, the display device 1 may include a seventh phase difference plate 631. The seventh phase difference plate 631 may be located between the lens 68 and the polarizing plate 632.

[0323] The lens 68 and the seventh phase difference plate 631 may be in contact or separated. The seventh phase difference plate 631 and the polarizing plate 632 may be in contact or separated. The polarizing plate 632 may be in contact with the viewing window 3 or separated from the viewing window 3. In this embodiment as well, the display device 1 does not have to be equipped with the viewing window 3.

[0324] The second phase difference plate 612 may be located on the path of light between the semi-reflector 62 and the second reflector 64, as well as on the path of light between the semi-reflector 62 and the lens 68.

[0325] The second phase difference plate 612 may be configured to impart the necessary phase difference to the light transmitted through it, such that the light transmitted through the second phase difference plate 612 is reflected by the second reflector 64, and then the light transmitted through the second phase difference plate 612 again is reflected by the semi-reflector 62. Alternatively, the second phase difference plate 612 may be configured to impart the necessary phase difference to the light transmitted through it, such that the light transmitted through it is transmitted through the polarizer 632 via the seventh phase difference plate 631.

[0326] The polarizing plate 632 may transmit a portion of the incident light and reflect or absorb the remainder. The polarizing plate 632 may transmit light in a first polarization state (polarization characteristics) and reflect or absorb light in a second polarization state different from the first polarization state. The polarizing plate 632 may transmit light in a second polarization state and reflect or absorb light in a first polarization state. In other words, the polarizing plate 632 may function as a reflective polarizing plate or an absorbing polarizing plate.

[0327] If the polarizing plate 632 has the function of a reflective polarizing plate, it may be configured to transmit polarized light having a polarization axis parallel to the polarization axis of the display light and reflect polarized light having a polarization axis perpendicular to the polarization axis of the display light. The polarizing plate 632 may be configured to transmit polarized light having a polarization axis perpendicular to the polarization axis of the display light and reflect polarized light having a polarization axis parallel to the polarization axis of the display light. Furthermore, the transmission axis of the polarizing plate 632 may be substantially parallel or substantially perpendicular to the transmission axis of the reflective polarizing plate (e.g., second reflective polarizing plate 622), which is a semi-reflective plate 62.

[0328] In this case, the polarizing plate 632 may be a wire grid polarizer comprising a substrate and a plurality of metal nanowires (also called a metal nanowire grid) located on the surface of the substrate. The material and function of the substrate and metal nanowires, as well as the arrangement of the metal nanowires, may be the same as those of the second reflective polarizing plate 622.

[0329] The polarizing plate 632 may be flat, or it may have a concave shape located on the lens 68 side, or it may have a convex shape located on the lens 68 side. Furthermore, the polarizing plate 632 may be composed of a holographic optical element, or its surface shape may have a Fresnel shape.

[0330] Furthermore, if the polarizing plate 632 has the function of an absorbing polarizing plate, it may be configured to transmit polarized light having a polarization axis parallel to the polarization axis of the display light and to absorb polarized light having a polarization axis perpendicular to the polarization axis of the display light. The polarizing plate 632 may be configured to transmit polarized light having a polarization axis perpendicular to the polarization axis of the display light and to absorb polarized light having a polarization axis parallel to the polarization axis of the display light. Also, the transmission axis of the polarizing plate 632 may be substantially parallel or substantially perpendicular to the transmission axis of the reflective polarizing plate (for example, the second reflective polarizing plate 622), which is the semi-reflective plate 62.

[0331] In this case, the polarizing plate 632 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.

[0332] The polarizing plate 632 may have the functions of both a reflective polarizing plate and an absorbing polarizing plate. If the polarizing plate 632 has the function of a reflective polarizing plate, it may function as a mirror that forms a reflected image of an object by reflecting ambient light when no display light is emitted from the display panel 4.

[0333] The seventh phase difference plate 631 may be a phase difference plate that converts linearly polarized light to circularly polarized light. The seventh phase difference plate 631 may impart the necessary phase difference to the light that has passed through the seventh phase difference plate 631 so that the light that has been reflected by or transmitted through the semi-reflector plate 62 then passes through the polarizer plate 632. In other words, the seventh phase difference plate 631 may convert the light that has passed through the seventh phase difference plate 631 into light in a first polarization state that can be transmitted through the polarizer plate 632.

[0334] The seventh phase difference plate 631 may have the same structure as the first phase difference plate 611 and the second phase difference plate 612. As long as the above-described phase difference can be provided, the seventh phase difference plate 631 may be, for example, a quarter-wave plate, or it may be a different type of wave plate, or a combination thereof. The seventh phase difference plate 631 may be a film-like material.

[0335] In the example of Figure 49, as explained in the example of Figure 13, the light emitted from the display panel 4 may be reflected by the first reflector 63 and the second reflector 64, and then reflected towards the viewing window 3 by the semi-reflector 62. The same may apply to the example of Figure 50, which will be explained below. For an example of the propagation of light until it is reflected towards the viewing window 3 by the semi-reflector 62, please refer to the explanation using Figure 13.

[0336] In the example shown in Figure 49, the light from the second reflector 64 side, which is second linearly polarized light reflected by the semi-reflector 62, may be converted to second circularly polarized light by passing through the second phase difference plate 612 and guided to the lens 68. The second circularly polarized light that passes through the lens 68 and is incident on the seventh phase difference plate 631 may be converted to second linearly polarized light by passing through the seventh phase difference plate 631 and guided to the polarizer 632. The second linearly polarized light that is incident on the polarizer 632 may be passed through the polarizer 632 and guided to the viewing window 3.

[0337] In the example in Figure 49, the second linearly polarized light may be S-wave polarized, and the first linearly polarized light may be P-wave polarized. The display light may be S-wave polarized. Also, the second circularly polarized light may be right-handed circularly polarized, and the first circularly polarized light may be left-handed polarized. However, the second linearly polarized light may be P-wave polarized, and the first linearly polarized light may be S-wave polarized. The display light may be P-wave polarized. Also, the second circularly polarized light may be left-handed circularly polarized, and the first circularly polarized light may be right-handed polarized. These relationships may also be the same in Figures 50 and 51, which will be explained below.

[0338] Figure 50 is a schematic diagram illustrating the configuration of the display device 1 according to this embodiment. In the display device 1 shown in Figure 50, the position of the second phase difference plate 612 may differ from that of the display device 1 shown in Figure 49. In the display device 1 shown in Figure 50, the position of the second phase difference plate 612 may be the same as that of the display device 1E shown in Figure 13. That is, the second phase difference plate 612 may be located on the path of light between the semi-reflector 62 and the second reflector 64.

[0339] Furthermore, the display device 1 shown in Figure 50 may include an eighth phase difference plate 633. The eighth phase difference plate 633 may be located on the path of light between the semi-reflector 62 and the lens 68. The eighth phase difference plate 633 may provide the necessary phase difference to the light transmitted through it, such that the light transmitted through the eighth phase difference plate 633 is transmitted through the seventh phase difference plate 631 to the polarizer 632. As long as such a phase difference can be provided, the eighth phase difference plate 633 may be, for example, a quarter-wave plate, or it may be a different wave plate, or a combination thereof. The eighth phase difference plate 633 may be a film-like material. That is, the eighth phase difference plate 633 may have the function of the second phase difference plate 612 located on the path of light between the semi-reflector 62 and the lens 68 in the display device 1 shown in Figure 49.

[0340] In the example shown in Figure 49, the light from the second reflector 64 side, which is second linearly polarized light reflected by the semi-reflector 62, may be converted to second circularly polarized light by passing through the second phase difference plate 612 and guided to the lens 68. On the other hand, in the example shown in Figure 50, the light from the second reflector 64 side, which is second linearly polarized light reflected by the semi-reflector 62, may be converted to second circularly polarized light by passing through the eighth phase difference plate 633 and guided to the lens 68.

[0341] Figure 51 is a schematic diagram showing an example of the direction of propagation of ambient light. As described above, the polarizing plate 632 may transmit light in the first polarization state and reflect or absorb light in the second polarization state. In the example of Figure 51, the polarizing plate 632 may transmit light in the second linear polarization state as light in the first polarization state and reflect or absorb light in the first linear polarization state as light in the second polarization state.

[0342] In the example shown in Figure 51, the polarizing plate 632 may transmit second linearly polarized light from the ambient light incident on the polarizing plate 632. This second linearly polarized light may then be converted into second circularly polarized light by passing through the seventh phase difference plate 631 and guided to the lens 68. At least a portion of the second circularly polarized light incident on the lens 68 may be reflected by the lens 68 and converted into first circularly polarized light and guided to the seventh phase difference plate 631. The first circularly polarized light incident on the seventh phase difference plate 631 may be converted into first linearly polarized light by passing through the seventh phase difference plate 631 and guided to the polarizing plate 632. As described above, the polarizing plate 632 may reflect or absorb the first linearly polarized light. Therefore, the first linearly polarized light incident on the polarizing plate 632 from the seventh phase difference plate 631 may be reflected or absorbed by the polarizing plate 632 and not guided to the viewing window 3 side (user Us side).

[0343] Thus, in the display device 1, the seventh phase difference plate 631 and the polarizing plate 632 may be arranged in order from the lens 68 side, on the side opposite the semi-reflector 62 to the lens 68. This reduces the possibility that ambient light reflected by the lens 68 will be emitted to the polarizing plate 632 on the side opposite the lens 68 (in front of the display device 1). Therefore, the possibility of the visibility of the image based on the displayed image being reduced by ambient light can be reduced.

[0344] In this embodiment, a configuration comprising a lens 68, a seventh phase difference plate 631, and a polarizing plate 632 has been described using a display device 1 corresponding to a display device 1E as an example, but the embodiment is not limited to this. The display device 1 of this embodiment may be applied to each of the display devices 1A to 1K.

[0345] For example, for display devices 1A, 1D, 1F, 1H, and 1J in which the light guided from the semi-reflector 62 to the viewing area is circularly polarized light, it is sufficient to provide a lens 68, a seventh phase difference plate 631, and a polarizing plate 632.

[0346] Furthermore, for example, in the display devices 1B, 1C, 1G, 1I, and 1K, including the display device 1E, where the light guided from the semi-reflector 62 to the viewing area is linearly polarized light, the display devices 1K may have the following configuration in addition to the lens 68, the seventh phase difference plate 631, and the polarizer 632. That is, these display devices 1 may be equipped with a phase difference plate on the path of light between the semi-reflector 62 and the lens 68, which gives the light transmitted through the phase difference plate the necessary phase difference so that the light transmitted through the phase difference plate is transmitted through the polarizer 632 via the seventh phase difference plate 631. The phase difference plate may be a part of the second phase difference plate 612 or the eighth phase difference plate 633 in the display device 1 of this embodiment. For example, in the display devices 1A, 1H, and 1J, a part of the first phase difference plate 611 may function as the phase difference plate instead of a part of the second phase difference plate 612.

[0347] [Embodiment 19] Other embodiments of this disclosure are 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.

[0348] Figure 45 is a schematic cross-sectional view showing the configuration of the display device 1 according to this embodiment. The display device 1 according to this embodiment may be the display device 1E.

[0349] As shown in Figure 45, the display device 1 may include a first phase difference plate 611A. The first phase difference plate 611A may be located on the surface of the base material 617. The material of the base material 617 may be light-transmitting glass or resin, etc. The first phase difference plate 611A may include a fifth phase difference plate 615 and a sixth phase difference plate 616. They may be positioned in the order of fifth phase difference plate 615, sixth phase difference plate 616 and base material 617, starting from the side where light from the display panel 4 first enters. Alternatively, they may be positioned in the order of base material 617, fifth phase difference plate 615 and sixth phase difference plate 616, starting from the side where light from the display panel 4 first enters.

[0350] The display device 1 may also include a second phase difference plate 612A. The second phase difference plate 612A may be located on the surface of the base material 618. The material of the base material 618 may be light-transmitting glass or resin, etc. The second phase difference plate 612A may include a fifth phase difference plate 615 and a sixth phase difference plate 616. They may be positioned in the order of fifth phase difference plate 615, sixth phase difference plate 616 and base material 618, starting from the side where light from the display panel 4 first enters. Alternatively, they may be positioned in the order of base material 618, fifth phase difference plate 615 and sixth phase difference plate 616, starting from the side where light from the display panel 4 first enters.

[0351] The fifth phase difference plate 615 may be a half-wave plate, a quarter-wave plate, an eighth-wave plate, a sixteenth-wave plate, or any other wave plate that imparts a phase difference. The sixth phase difference plate 616 may be a half-wave plate, a quarter-wave plate, an eighth-wave plate, a sixteenth-wave plate, or any other wave plate that imparts a phase difference. The fifth phase difference plate 615 and the sixth phase difference plate 616 may each be a single wave plate or composed of multiple wave plates. The fifth phase difference plate 615 and the sixth phase difference plate 616 may be film-like members.

[0352] The fifth phase plate 615 and the sixth phase plate 616 may have the same function as the first phase plate 611, which is a phase plate that converts linearly polarized light to circularly polarized light. To achieve this function, the angle of the retard axis with respect to the polarization direction of the incident light may be defined in relation to each other for the fifth phase plate 615 and the sixth phase plate 616. That is, the direction of the retard axis of the fifth phase plate 615 and the sixth phase plate 616 may be defined in relation to each other.

[0353] When quarter-wave plates are used as phase difference plates (first phase difference plate 611 and second phase difference plate 612) that convert linearly polarized light to circularly polarized light, wavelength dispersion can occur, where the phase difference obtained changes depending on the wavelength of the incident light. In this case, the phase difference plates can convert linearly polarized light to circularly polarized light for some wavelengths, while converting linearly polarized light to elliptically polarized light for other wavelengths. For example, linearly polarized light can be converted to circularly polarized light for the green wavelength band, but linearly polarized light can be converted to elliptically polarized light for the red and blue wavelength bands. That is, for the green wavelength band, the ellipticity, which is the ratio of the minor axis to the major axis, is relatively high (close to 1), while the ellipticity of light in the red and blue wavelength bands can be lower than that of light in the green wavelength band. In particular, the ellipticity of light in the blue wavelength band can be significantly lower than that of light in the green wavelength band than that of light in the red wavelength band. In this case, the transmittance of light with a blue wavelength band becomes low in the phase difference plate, so the wavelength band of that light can be shifted to the complementary color, the yellow wavelength band. As a result, the image based on the displayed image may appear yellowish.

[0354] By using two phase difference plates (fifth phase difference plate 615 and sixth phase difference plate 616) whose lagging axis angles with respect to the polarization direction of the incident light are defined in relation to each other, as phase difference plates for converting linearly polarized light to circularly polarized light, the possibility of wavelength dispersion can be reduced. As a result, the ellipticity of light in the blue wavelength band can be brought closer to the ellipticity of light in the green and red wavelength bands. Consequently, the possibility of images based on the displayed image appearing yellowish can be reduced.

[0355] Let θ1 be the angle of the lagging axis of the fifth phase difference plate 615 with respect to the polarization direction of the incident light, and let θ2 be the angle of the lagging axis of the sixth phase difference plate 616 with respect to the polarization direction of the incident light. The inventors of the present invention, 2θ2≒4θ1+90°…Equation (1) We found that by setting θ1 and θ2 such that the ellipticity of light in the red, green, and blue wavelength bands can be brought closer together. In this case, the fifth phase difference plate 615 may be a half-wave plate. Also, the sixth phase difference plate 616 may be a quarter-wave plate. The fifth phase difference plate 615 and the sixth phase difference plate 616 may each be a single wave plate or composed of multiple wave plates.

[0356] Figure 46 is a graph showing an example of the relationship between θ1 and the ellipticity of light in the red, green, and blue wavelength bands. In Figure 46, θ1 was set in 5° increments from 0° to 35°, and θ2 was calculated from equation (1) above for each value of θ1, and the ellipticity of light for each value of θ1 and θ2 was calculated.

[0357] In this experiment, a half-wave plate was used as the fifth phase difference plate 615, and a quarter-wave plate was used as the sixth phase difference plate 616. The light source, fifth phase difference plate 615, sixth phase difference plate 616, and analyzer were arranged in that order. The light source emitted blue light with a peak wavelength of 450 nm, green light with a peak wavelength of 550 nm, and red light with a peak wavelength of 620 nm. The ellipticity of the light was calculated by measuring the polarization state of the light transmitted through the sixth phase difference plate 616 using the analyzer.

[0358] As shown in Figure 46, it was found that the difference in ellipticity of light in the red, green, and blue wavelength bands is small within the area enclosed by the dotted line frame. As shown in Figure 46, it can be seen that when θ1 is 15° to 20°, each ellipticity falls within a range of approximately 0.05. Therefore, θ1 can be set to 15° to 20°. θ2 can be set to 75° to 85° from equation (1) above. Considering the height of the ellipticity, θ1 can be set to 15° and θ2 to 75°.

[0359] The display device 1 may also include a polarizing plate 69. The polarizing plate 69 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. The polarizing plate 69 may also have the configuration of a reflective polarizing plate.

[0360] The polarizing plate 69 may be located between the semi-reflector 62 and the viewing window 3. In the example of Figure 45, it may be located on the surface of the viewing window 3 on the side of the semi-reflector 62. However, it may also be located on the surface of the viewing window 3 opposite to the surface on the side of the semi-reflector 62. The polarizing plate 69 may transmit or reflect light from the semi-reflector 62, transmit light emitted from the viewing window 3, and absorb light with a polarization state different from that of the transmitted light.

[0361] Furthermore, the display device 1 may include an attenuation member 70. The attenuation member 70 may attenuate the amount of reflected incident light. The attenuation member 70 may be, for example, a moth-eye structure film.

[0362] The attenuating member 70 may be located on the surface of the member that emits, transmits, or reflects light, on which light is incident. The attenuating member 70 may be located on the surface from which light is emitted, on which light is emitted. The attenuating member 70 may be located on either one surface or on both surfaces. If two or more members are integrated with a member that emits, transmits, or reflects light, the attenuating member 70 may be located on at least one of the surfaces from which light is incident and the surface from which light is emitted within the integrated member. Furthermore, the attenuating member 70 may be provided for all members that emit, transmit, or reflect light (including integrated members), or for only a portion of such members.

[0363] In the example of Figure 45, the damping member 70 may be located on the display surface 4a. Alternatively, the damping member 70 may be located on the first optical surface 62a or the second optical surface 62b of the semi-reflector 62. It may also be located on the surface of the base material 617 opposite to the first phase difference plate 611A, or on the surface of the first phase difference plate 611A opposite to the base material 617. It may also be located on the surface of the base material 618 opposite to the second phase difference plate 612A, or on the surface of the second phase difference plate 612A opposite to the base material 618. Furthermore, it may be located on the surface of the third phase difference plate 613 on the semi-reflector 62 side, or on the surface of the viewing window 3 opposite to the semi-reflector 62.

[0364] In this embodiment, the configuration comprising a first phase difference plate 611A and a second phase difference plate 612A was described using an example in which the display device 1 as a display device 1E comprises a third phase difference plate 613 and a fourth phase difference plate 614. Furthermore, the configuration comprising a damping member 70 was described using an example in which the display device 1 as a display device 1E comprises a damping member 70. However, a display device 1 comprising only a third phase difference plate 613, a display device 1 comprising only a fourth phase difference plate 614, or a display device 1 that does not comprise either the third phase difference plate 613 or the fourth phase difference plate 614 may still be equipped with a first phase difference plate 611A and a second phase difference plate 612A. In addition, these display devices 1 may also be equipped with a damping member 70.

[0365] In this embodiment, a configuration comprising a first phase difference plate 611A and a second phase difference plate 612A has been described using display device 1E as an example, but the embodiment is not limited to this. A first phase difference plate 611A may be provided in each of the display devices 1A to 1K. Also, a second phase difference plate 612A may be provided in each of the display devices 1C, 1E, and 1G. In these cases as well, the fifth phase difference plate 615 and the sixth phase difference plate 616 may be positioned in order from the side where light from the display panel 4 first enters.

[0366] In this embodiment, a configuration including the attenuating member 70 has been described using display device 1 as display device 1E as an example, but it is not limited to this. Attenuating members 70 may be provided in each of the display devices 1A to 1K. In this case as well, the attenuating member 70 may be located on the surface to which light is incident, or on the surface to which light is emitted, of the member that emits, transmits, or reflects light. The attenuating member 70 may be located on either one surface, or on both surfaces. If two or more members are integrated with respect to a member that emits, transmits, or reflects light, the attenuating member 70 may be located on at least one of the surfaces to which light is incident and the surface to which light is emitted, in the integrated member. Furthermore, the attenuating member 70 may be provided for all of the members that emit, transmit, or reflect light (including integrated members), or for only a part of the members.

[0367] [Embodiment 20] Other embodiments of this disclosure are 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.

[0368] Reference numeral 1021 in Figure 47 is an external view showing an example configuration of the display device 101. Reference numeral 1021 is a perspective view of the display device 101 as seen from the front. Reference numeral 1022 in Figure 47 is a schematic cross-sectional view showing an example configuration of the display devices 1,101. Reference numeral 1022 may indicate the display device 1 shown in Figure 22 as an example of the display device 1 supported by the display device 101. However, reference numeral 1022 may indicate only the display panel 4, the semi-reflector 62, the first reflector 63, and the second reflector 64. Also, in the display device 1 shown in Figure 22, the viewing window 3 is located in the opening 21 of the housing 2, but in reference numeral 1022, the viewing window 3 does not need to be located in the opening 21.

[0369] As shown in Figure 47, the display device 101 may include an outer housing 112, and the display device 1 may be located inside the outer housing 112. That is, the housing 2 may be located inside the outer housing 112. In this positional relationship, the housing 2 may be referred to as the inner housing, and the viewing section may be referred to as the inner viewing section. The outer housing 112 may contain resin or metal. The optical system 6 of the display device 1 may form an image based on the display image inside the outer housing 112, or it may form an image outside the outer housing 112. The display device 1 may also be referred to as the display device unit 1.

[0370] The outer casing 112 may comprise a first outer casing 121 and a second outer casing 122. The outer casing 112 may be formed by the connection of the first outer casing 121 and the second outer casing 122. The second outer casing 122 may be located on the front side, i.e., the side into which the user Us looks.

[0371] The outer housing 112 may have an external viewing section. In this embodiment, the second outer housing 122 may have an external opening 113 as an external viewing section. The external opening 113 may be located on the front side of the second outer housing 122, opposite to the first outer housing 121.

[0372] An external viewing window 114 may be located in the external opening 113. The external viewing window 114 may be a component that makes the inside of the external housing 112 visible from the outside of the external housing 112. The external viewing window 114 may also be a component that makes the inside of the external housing 112 visible from the outside of the external housing 112. The external viewing window 114 may be positioned to block at least a part of the external opening 113. The material of the external viewing window 114 may be light-transmitting glass or resin, etc. The external viewing window 114 may function as an external viewing area. That is, the external viewing area may be the external viewing window 114, or it may be a space where no component exists (for example, the external opening 113).

[0373] The positional relationship between the outer opening 113 and the opening 21 of the housing 2 may be adjusted so that, when viewed from the front of the display device 101 along the Z-axis, at least a portion of the outer opening 113 coincides with at least a portion of the opening 21 of the housing 2. In other words, the positional relationship between the outer opening 113 and the opening 21 may be adjusted so that the image formed by the optical system 6 can be viewed through the viewing section and the outer viewing section.

[0374] The housing 2 of the display device 1 may be supported within the outer housing 112. The housing 2 may be integrally formed or formed by connecting multiple members. In the example of reference numeral 1022, the housing 2 may include a first support base 151, a second support base 152, and a third support base 153. In this case, the housing 2 having an opening 21 may be formed by connecting the first support base 151, the second support base 152, and the third support base 153.

[0375] The display device 101 shown by reference numeral 1021 is a non-mounted device and may represent an example configuration when applied to a digital rearview mirror. In this case, as shown by reference numeral 1021, the display device 101 may be elongated in shape, such that the distance between its two sides (distance in the X-axis direction) is greater than the distance in the vertical direction (distance in the Y-axis direction) when viewed from the front side of the display device 101 (the side of the outer viewing window 114). Specifically, the display device 101 may be rectangular in shape.

[0376] In this case, the display device 1 may be housed in an outer casing 112 having the shape shown in reference numeral 1021. The display device 1 may be elongated in shape, such that the distance between its two sides (distance in the X-axis direction) is greater than the distance in the vertical direction (distance in the Y-axis direction) when viewed from the front side (viewing window 3 side) of the display device 1. Specifically, the display device 1 may be rectangular in shape.

[0377] In this way, a display device 101 can be realized in which a housing 2 supporting the display panel 4 and optical system 6 is housed within various outer housings 112 with different specifications depending on the application.

[0378] Furthermore, in the manufacturing of the display device 101, it is also possible to provide the manufacturer of the display device 101 with a housing 2 (display device 1) that supports the display panel 4 and the optical system 6, and for that manufacturer to house the display device 1 in the outer housing 112. If there are multiple manufacturers of the display device 101 that manufacture outer housings 112 of different shapes, it is also possible to provide each manufacturer with a display device 1. For example, even in a specific application such as a digital rearview mirror, the shape of the outer housing 112 may differ depending on the type of vehicle 50. It is also possible to manufacture the display device 1 uniformly, taking into account such differences in the shape of the outer housing 112, and provide the display device 1 to each manufacturer of the display device 101.

[0379] Furthermore, the display device 101 may be configured such that the first outer housing 121 and the second outer housing 122 are connected. Therefore, the display device 101 can be realized through simple manufacturing, such as connecting the first outer housing 121 and the second outer housing 122.

[0380] Figure 48 is an exploded view of a specific configuration example of the display device 1 and the display device 101. The first support base 151 may have a frame that constitutes the second aperture 23 and a side surface connected to the frame. In the example of Figure 48, the illuminator 5 and the display panel 4 may be mounted in the second aperture 23. For example, a first reflector 63 or a second reflector 64 may be mounted in the second aperture 23. Alternatively, for example, a first phase difference plate 611, a first phase difference plate 611A, a second phase difference plate 612, or a second phase difference plate 612A may be mounted in the second aperture 23. Alternatively, for example, a third phase difference plate 613 and / or a fourth phase difference plate 614 may be mounted in the second aperture 23.

[0381] The first support base 151 may include a first support region 24. The first support region 24 may be a region that supports the semi-reflector 62. The first support base 151 may include a second support region 25. In the example of Figure 48, the second support region 25 may support the first phase difference plate 611. The second support region 25 may support, for example, the first phase difference plate 611A, the second phase difference plate 612, or the second phase difference plate 612A. Alternatively, for example, the second support region 25 may support the third phase difference plate 613 and / or the fourth phase difference plate 614. If there is no member to be supported by the second support region 25, the second support region 25 may not be provided.

[0382] The second support base 152 may be mounted on top of the first support base 151. In the example of Figure 48, the second support base 152 may support the first reflector 63. The second support base 152 may, for example, support the display panel 4 and the illuminator 5. Alternatively, for example, the second support base 152 may support the second reflector 64. Alternatively, for example, the second support base 152 may support the first phase difference plate 611, the first phase difference plate 611A, the second phase difference plate 612, or the second phase difference plate 612A. Alternatively, for example, the second support base 152 may support the third phase difference plate 613 and / or the fourth phase difference plate 614.

[0383] The third support base 153 may be attached to the bottom of the first support base 151. In the example of Figure 48, the third support base 153 may support the second reflector 64 and the second phase difference plate 612. The third support base 153 may also support, for example, the display panel 4 and the illuminator 5. Alternatively, for example, the third support base 153 may support the first reflector 63. Alternatively, for example, the third support base 153 may support the first phase difference plate 611, the first phase difference plate 611A, or the second phase difference plate 612A. Alternatively, for example, the third support base 153 may support the third phase difference plate 613 and / or the fourth phase difference plate 614.

[0384] With each component supported, the second support base 152 and the third support base 153 may be attached to the first support base 151 to form a display device 1 comprising a housing 2 that supports the display panel 4 and the optical system 6. Alternatively, by attaching the second support base 152 and the third support base 153 to the first support base 151, an opening 21 may be formed in front of the second opening 23. A viewing window 3 may be attached to the opening 21.

[0385] A second outer housing 122, which has an external viewing window 114 attached, may be attached to the front side of the display device 1 formed in this manner, and the first outer housing 121 may be attached to the rear side of the display device 1. The external viewing window 114 does not have to be attached to the second outer housing 122. The first outer housing 121 and the second outer housing 122 may be connected. This may form a display device 101 that houses the display device 1.

[0386] In this embodiment, a display device 101 in which the display device 1 is housed in an outer casing 112 has been described using the display device 1 corresponding to the display device 1E as an example, but the invention is not limited to this. The display device 101 may also be realized by housing any of the display devices 1A to 1K in the outer casing 112.

[0387] 〔summary〕 A display device according to Embodiment 1 of the present disclosure comprises a housing having a viewing section and an inner region; a display panel having a display surface for displaying a display image, wherein the display surface is arranged to face the inner region of the housing; a first reflector located inside the housing and having a first reflective surface facing the inner region; a second reflector located inside the housing and having a second reflective surface facing the inner region; and a semi-reflector located inside the inner region within the housing and having a first optical surface arranged to face the viewing section and either the display surface, the first reflective surface, or the second reflective surface, and a second optical surface arranged to face the other of the display surface, the first reflective surface, or the second reflective surface.

[0388] In the display device according to aspect 2 of this disclosure, in aspect 1, the semi-reflective plate is inclined with respect to the viewing portion.

[0389] In the display device according to aspect 3 of the present disclosure, in aspect 1 or 2, the display panel and the second reflector are positioned such that a first normal passing through the center of the display surface and a third normal passing through the center of the second reflecting surface face in different directions, the first reflector and the second reflector are positioned such that a second normal passing through the center of the first reflecting surface and a third normal face in different directions, the display surface is positioned to face the first optical surface, the first reflecting surface is positioned to face the second optical surface and the display surface, the second reflecting surface is positioned to face the first optical surface and the viewing area, and the semi-reflector transmits light emitted from the display panel and guides it to the first reflector, reflects the light reflected by the first reflector and guides it to the second reflector, and transmits the light reflected by the second reflector and guides it to the viewing area.

[0390] In the display device according to aspect 4 of the present disclosure, in aspect 1 or 2, the display panel and the first reflector are positioned such that a first normal passing through the center of the display surface and a second normal passing through the center of the first reflecting surface face in different directions, the display panel and the second reflector are positioned such that a first normal and a third normal passing through the center of the second reflecting surface face in different directions, the display surface is positioned to face the second optical surface and the viewing area, the first reflecting surface is positioned to face the second optical surface and the second reflecting surface, the second reflecting surface is positioned to face the first optical surface, and the semi-reflector reflects light emitted from the display panel and guides it to the first reflector, transmits the light reflected by the first reflector and guides it to the second reflector, and reflects the light reflected by the second reflector and guides it to the viewing area.

[0391] In the display device according to aspect 5 of the present disclosure, in aspect 1 or 2, the display panel and the first reflector are positioned such that a first normal passing through the center of the display surface and a second normal passing through the center of the first reflecting surface face in different directions, the display panel and the second reflector are positioned such that a first normal passing through the center of the second reflecting surface face in different directions, the display surface is positioned to face the second optical surface and the viewing area, the first reflecting surface is positioned to face the first optical surface and the second reflecting surface, the second reflecting surface is positioned to face the second optical surface, and the semi-reflector reflects light emitted from the display panel and guides it to the second reflector, transmits the light reflected by the second reflector and guides it to the first reflector, and reflects the light reflected by the first reflector and guides it to the viewing area.

[0392] In the display device according to aspect 6 of the present disclosure, in aspect 1 or 2, the display panel and the first reflector are positioned such that a first normal passing through the center of the display surface and a second normal passing through the center of the first reflecting surface face in different directions, the first reflector and the second reflector are positioned such that a second normal passing through the center of the second reflecting surface face in different directions, the display surface is positioned to face the first optical surface, the first reflecting surface is positioned to face the second optical surface and the viewing area, the second reflecting surface is positioned to face the second optical surface and the display surface, and the semi-reflector transmits light emitted from the display panel to the second reflector, reflects the light reflected by the second reflector to the first reflector, and transmits the light reflected by the first reflector to the viewing area.

[0393] In any of embodiments 1 to 6, the display device according to embodiment 7 of the present disclosure is a first reflective polarizing plate that transmits first circularly polarized light and reflects second circularly polarized light.

[0394] In any of embodiments 1 to 6, the display device according to embodiment 8 of the present disclosure is a second reflective polarizer that transmits first linearly polarized light and reflects second linearly polarized light.

[0395] The display device according to aspect 9 of the present disclosure, in any of aspects 1 to 8, includes a phase difference plate located within the housing that reduces the amount of light emitted from the display panel that is directly visible through the viewing section from a position other than the front position of the viewing section.

[0396] In any of embodiments 1 to 9, the display device according to embodiment 10 of the present disclosure is configured such that, when the size of the first reflective surface as viewed from the first optical surface side or the second optical surface side is defined as the first dimension, the size of the second reflective surface as viewed from the first optical surface side or the second optical surface side is defined as the second dimension, and the size of the first optical surface or the second optical surface as viewed from the first reflective surface side or the second reflective surface side is defined as the third dimension, the second and third dimensions are larger than the first dimension, and the second dimension is larger than the third dimension.

[0397] In any of embodiments 1 to 10, the display device according to embodiment 11 of the present disclosure has the following characteristics: the first reflector reflects light toward the semi-reflector and has the function of diverging, concentrating, or focusing light; the second reflector reflects light toward the semi-reflector and has the function of concentrating or focusing light; the focal length of the first reflector is greater than the distance between the display panel and the first reflector; or the focal length of the first reflector is less than the distance between the display panel and the first reflector.

[0398] In any of embodiments 1 to 11, the display device according to embodiment 12 of the present disclosure is such that, in a cross-sectional view, the angle between two straight lines connecting an arbitrary point on the opposite side of the inner region from the viewing portion and each of the endpoints of the viewing portion is greater than the angle between two straight lines connecting the arbitrary point and each of the endpoints of the second reflector along the optical path of the display light.

[0399] The display device according to aspect 13 of the present disclosure, in any of aspects 1 to 12, has two phase difference plates located within the housing and used as phase difference plates for converting linearly polarized light into circularly polarized light, wherein the angle of the lagging axis with respect to the polarization direction of the incident light is defined in relation to each other.

[0400] A display device according to aspect 14 of the present disclosure comprises, in any of aspects 1 to 13, an outer housing having an external viewing section, and an inner housing located within the outer housing as the housing.

[0401] The mobile device according to aspect 15 of this disclosure comprises a display device according to any of aspects 1 to 14.

[0402] A display panel housing device according to aspect 16 of the present disclosure comprises a housing having a viewing section, an inner region, and a display panel installation section capable of installing a display panel such that the display surface faces the inner region; a first reflector located inside the housing and having a first reflective surface facing the inner region; a second reflector located inside the housing and having a second reflective surface facing the inner region; and a semi-reflector located inside the inner region within the housing and having a first optical surface arranged to face the viewing section and either the display surface, the first reflective surface, or the second reflective surface, and a second optical surface arranged to face the other of the display surface, the first reflective surface, or the second reflective surface.

[0403] [Additional Notes] 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.

[0404] For example, in the above description, the first reflecting mirror 63 was described as a plane mirror with a planar shape for the first reflective surface 63a, but the first reflecting mirror 63 may be a reflecting mirror with a curved shape for at least a part of the first reflective surface 63a. In this case, the first reflecting mirror 63 may form a virtual image V or a real image as an image based on the displayed image. The first reflecting mirror 63 may have a function of collecting or focusing light. Specifically, the first reflecting mirror 63 may have a function of collecting or focusing light that has been incident on and reflected by the first reflecting mirror 63. For example, the first reflecting mirror 63 may be a concave mirror with a concave shape for the first reflective surface 63a. In this case, the first reflecting mirror 63 may be called a concave full mirror. Furthermore, the first reflecting mirror 63 may have a function of reflecting and diverging light. Specifically, the first reflecting mirror 63 may have a function of reflecting and diverging light that has been incident on the first reflecting mirror 63. For example, the first reflecting mirror 63 may be a convex mirror in which the first reflective surface 63a is convex. In this case, the first reflecting mirror 63 may be called a convex full mirror. Furthermore, the first reflecting mirror 63 may be composed of a holographic optical element, or its surface shape may have a Fresnel shape.

[0405] For example, in the above description, the second reflector 64 was described as a reflector with a curved second reflective surface 64a, but it may also be a plane mirror with a planar second reflective surface 64a. The second reflector 64 may have a function of focusing or converging light. Specifically, the second reflector 64 may have a function of focusing or converging light that is incident on the second reflector 64 and reflected. For example, the second reflector 64 may be a concave mirror with a concave second reflective surface 64a. In this case, the second reflector 64 may be called a concave full mirror. The second reflector 64 may also have a function of reflecting and diverging light. Specifically, the second reflector 64 may have a function of reflecting and diverging light that is incident on the second reflector 64. For example, the second reflector 64 may be a convex mirror with a convex second reflective surface 64a. In this case, the second reflector 64 may be called a convex full mirror. At least one of the first reflector 63 and the second reflector 64 may have a curved reflective surface. At least one of the first reflector 63 and the second reflector 64 may be composed of a holographic optical element, or its surface shape may have a Fresnel shape. In addition, either the first reflector 63 or the second reflector 64 may have a planar reflective surface.

[0406] Furthermore, the phase difference plate described herein may be a film-like member. [Explanation of Symbols]

[0407] 1,1A~1K,101 Display device 2 enclosures (inner enclosure) 3. Viewing window (viewing section) 4 Display Panel 4a Display surface 8 Display panel mounting section 11 Display panel housing 21. Opening (Viewing area) 22 Inner area 50 vehicles (mobile vehicles) 62 Semi-reflector 62a 1st optical surface 62b Second optical surface 63 1st reflector 63a 1st reflective surface 64 Second reflector 64a 2nd reflective surface 68 lenses 112 Outer housing 415 Any point 416,417 Both ends of the viewing window (Both ends of the viewing area) 418,419 Endpoints of the second reflecting mirror 421,422 Two straight lines 423,424 Two straight lines 613 Third retardation plate (retardation plate) 614 4th retardation plate (retardation plate) 615 5th retardation plate (retardation plate) 616 6th retardation plate (retardation plate) 621 First Reflecting Polarizer 622 Second Reflecting Polarizer 631 7th retardation plate (retardation plate) 632 Polarizing plate NL1 First Normal NL2 2nd normal NL3 3rd normal NL4 4th normal L31 Length of the visible area L62 Third Dimension L63 1st dimension L64 Second Dimension L641 Length of the second reflector Distance between the d60B display panel and the first reflector f601 Focal length of the first reflecting mirror α 1st angle β second angle

Claims

1. A housing having a viewing area and an inner area, A display panel having a display surface for displaying an image, and the display surface being arranged to face the inner region of the housing, A first reflector located inside the housing and having a first reflecting surface facing the inner region, A second reflector located within the housing and having a second reflecting surface facing the inner region, A semi-reflective plate having a first optical surface located within the inner region of the housing and arranged to face the viewing portion and one of the display surface, the first reflective surface, and the second reflective surface, and a second optical surface arranged to face the other of the display surface, the first reflective surface, and the second reflective surface, Equipped with, A display device wherein, in a cross-sectional view, the angle between two straight lines connecting an arbitrary point on the opposite side of the inner region from the viewing portion and each of the endpoints of the viewing portion is greater than the angle between two straight lines connecting the arbitrary point and each of the endpoints of the second reflector along the optical path of the display light.

2. The display device according to claim 1, wherein the semi-reflective plate is inclined with respect to the viewing portion.

3. The display panel and the second reflector are positioned such that the first normal passing through the center of the display surface and the third normal passing through the center of the second reflecting surface point in different directions. The first and second reflectors are positioned such that the second normal and the third normal passing through the center of the first reflecting surface point in different directions. The display surface is positioned to face the first optical surface, the first reflective surface is positioned to face the second optical surface and the display surface, and the second reflective surface is positioned to face the first optical surface and the viewing area. The display device according to claim 1, wherein the semi-reflector transmits light emitted from the display panel and guides it to the first reflector, reflects the light reflected by the first reflector and guides it to the second reflector, and transmits the light reflected by the second reflector and guides it to the viewing section.

4. The display panel and the first reflector are positioned such that the first normal passing through the center of the display surface and the second normal passing through the center of the first reflecting surface point in different directions. The display panel and the second reflector are positioned such that the first normal and the third normal passing through the center of the second reflecting surface point in different directions. The display surface is positioned to face the second optical surface and the viewing area, the first reflective surface is positioned to face the second optical surface and the second reflective surface, and the second reflective surface is positioned to face the first optical surface. The display device according to claim 1, wherein the semi-reflector reflects light emitted from the display panel and guides it to the first reflector, transmits the light reflected by the first reflector and guides it to the second reflector, and reflects the light reflected by the second reflector and guides it to the viewing section.

5. The display panel and the first reflector are positioned such that the first normal passing through the center of the display surface and the second normal passing through the center of the first reflecting surface point in different directions. The display panel and the second reflector are positioned such that the first normal and the third normal passing through the center of the second reflecting surface point in different directions. The display surface is positioned to face the second optical surface and the viewing area, the first reflective surface is positioned to face the first optical surface and the second reflective surface, and the second reflective surface is positioned to face the second optical surface. The display device according to claim 1, wherein the semi-reflector reflects light emitted from the display panel and guides it to the second reflector, transmits the light reflected by the second reflector and guides it to the first reflector, and reflects the light reflected by the first reflector and guides it to the viewing section.

6. The display panel and the first reflector are positioned such that the first normal passing through the center of the display surface and the second normal passing through the center of the first reflecting surface point in different directions. The first and second reflectors are positioned such that the second normal and the third normal passing through the center of the second reflecting surface point in different directions. The display surface is positioned to face the first optical surface, the first reflective surface is positioned to face the second optical surface and the viewing area, and the second reflective surface is positioned to face the second optical surface and the display surface. The display device according to claim 1, wherein the semi-reflector transmits light emitted from the display panel and guides it to the second reflector, reflects the light reflected by the second reflector and guides it to the first reflector, and transmits the light reflected by the first reflector and guides it to the viewing section.

7. The display device according to claim 1, wherein the semi-reflecting plate is a first reflective polarizing plate that transmits first circularly polarized light and reflects second circularly polarized light.

8. The display device according to claim 1, wherein the semi-reflecting plate is a second reflective polarizing plate that transmits first linearly polarized light and reflects second linearly polarized light.

9. The display device according to claim 1, further comprising a phase difference plate located within the housing, which reduces the amount of light emitted from the display panel that is directly visible through the viewing unit from a position other than the front position of the viewing unit.

10. The size of the first reflective surface when viewed from the first optical surface side or the second optical surface side is defined as the first dimension. The size of the second reflective surface when viewed from the first optical surface side or the second optical surface side is defined as the second dimension. When the size of the first optical surface or the second optical surface as viewed from the first reflective surface side or the second reflective surface side is defined as the third dimension, The second and third dimensions are larger than the first dimension. The display device according to claim 1, wherein the second dimension is larger than the third dimension.

11. The first reflector has the function of reflecting light toward the semi-reflector and also diverging, concentrating, or focusing the light. The second reflector has the function of reflecting light toward the semi-reflector and also concentrating or focusing the light. The focal length of the first reflector is greater than the distance between the display panel and the first reflector, or The display device according to claim 1, wherein the focal length of the first reflector is smaller than the distance between the display panel and the first reflector.

12. The display device according to claim 1, wherein the device has two phase difference plates located within the housing, which convert linearly polarized light into circularly polarized light, and the angle of the lagging axis with respect to the polarization direction of the incident light is defined in relation to each other.

13. An outer housing having an external viewing section, The display device according to claim 1, wherein the housing comprises an inner housing located within the outer housing.

14. A mobile body comprising the display device described in claim 1.

15. A housing having a viewing area, an inner area, and a display panel mounting area on which a display panel can be installed so that its display surface faces the inner area, A first reflector located inside the housing and having a first reflecting surface facing the inner region, A second reflector located within the housing and having a second reflecting surface facing the inner region, A semi-reflective plate having a first optical surface located within the inner region of the housing and arranged to face the viewing portion and one of the display surface, the first reflective surface, and the second reflective surface, and a second optical surface arranged to face the other of the display surface, the first reflective surface, and the second reflective surface, Equipped with, A display panel housing device, wherein, in a cross-sectional view, the angle between two straight lines connecting an arbitrary point on the opposite side of the inner region from the viewing portion and each of the endpoints of the viewing portion is greater than the angle between two straight lines connecting the arbitrary point and each of the endpoints of the second reflector along the optical path of the display light.

Images