Projection apparatus and mobile body

Abstract

A projection apparatus according to an embodiment of the present disclosure comprises: a display device; a first polarization optical element that rectifies polarization of light emitted from the display device; a reflection mirror; and a special retroreflection group that includes an anisotropic prism sheet having refractive index anisotropy, a second polarization optical element, and a retroreflective element, and reflects the light having undergone rectification by the first polarization optical element toward the reflection mirror by setting a prescribed offset angle relative to the incident direction.

Description

Projection device and moving object

[0001] The present disclosure relates to a projection device used as, for example, a head-mounted display, and a moving object equipped with the same.

[0002] For example, Patent Document 1 discloses an information display device that uses a reflector having a plurality of unit areas arranged two-dimensionally on its main surface, thereby alleviating restrictions on installation locations.

[0003] International Publication No. 2018 / 061444

[0004] Meanwhile, a projection device that displays driving assistance information to a vehicle driver is required to display a virtual image with a wide viewing angle.

[0005] It is desirable to provide a projection device and a mobile object that can display a virtual image with a wide viewing angle.

[0006] A projection device according to one embodiment of the present disclosure includes a display device, a first polarizing optical element that rectifies the polarization of light emitted from the display device, a reflecting mirror, an anisotropic prism sheet having refractive index anisotropy, a second polarizing optical element, and a special retroreflective group that reflects the light rectified by the first polarizing optical element toward the reflecting mirror at a predetermined offset angle relative to the incident direction.

[0007] A moving object according to an embodiment of the present disclosure includes a vehicle body and the projection device according to the embodiment attached to the vehicle body.

[0008] In a projection device and a moving object according to an embodiment of the present disclosure, light emitted from a display device is guided to a special retroreflection group via a first polarizing optical element and a reflecting mirror. The special retroreflection group includes an anisotropic prism sheet, a second polarizing optical element, and a retroreflection element. Light incident on the special retroreflection group is reflected at an offset angle in a predetermined direction. This allows a wide-angle virtual image to be created without using, for example, a large mirror optical system.

[0009] FIG. 1 is a schematic diagram illustrating an example configuration of a projection device according to an embodiment of the present disclosure. FIG. 2 is a functional block diagram illustrating the configuration of the display device shown in FIG. 1. FIG. 3 is a perspective view illustrating the configuration of an anisotropic prism sheet. FIG. 4 is a cross-sectional schematic diagram illustrating an example configuration of the anisotropic prism sheet shown in FIG. 3. FIG. 5 is a diagram illustrating an example manufacturing process of the anisotropic prism sheet shown in FIG. 3. FIG. 6 is a plan view schematic diagram of a retroreflector. FIG. 7 is a schematic diagram illustrating retroreflective elements constituting the retroreflector shown in FIG. 6. FIG. 8 is a cross-sectional schematic diagram illustrating the retroreflector shown in FIG. 6. FIG. 9 is a diagram illustrating an example behavior of light incident on the special retroreflector group shown in FIG. 1. FIG. 10 is a schematic diagram illustrating an example configuration of the projection device shown in FIG. 1 mounted on a vehicle. FIG. 11 is a schematic diagram illustrating an example configuration of a general projection device. FIG. 12 is a perspective view illustrating the configuration of an anisotropic prism sheet according to Variation 1 of the present disclosure. FIG. 13 is a cross-sectional schematic diagram illustrating an example configuration of the anisotropic prism sheet shown in FIG. 12. FIG. 14A is a perspective view illustrating an example of a manufacturing process for the anisotropic prism sheet illustrated in FIG. 12 . FIG. 14B is a perspective view illustrating a process subsequent to FIG. 14A . FIG. 14C is a perspective view illustrating a process subsequent to FIG. 14B . FIG. 14D is a perspective view illustrating a process subsequent to FIG. 14C . FIG. 14E is a perspective view illustrating a process subsequent to FIG. 14D . FIG. 15 is a schematic diagram illustrating an example configuration of a projection device according to Modification 2 of the present disclosure. FIG. 16 is a diagram illustrating an example of an optical simulation result of the behavior of light rays entering the human eye in the projection device illustrated in FIG. 1 . FIG. 17 is a diagram illustrating another example of an optical simulation result of the behavior of light rays entering the human eye in the projection device illustrated in FIG. 1 . FIG. 18 is a diagram illustrating another example of an optical simulation result of the behavior of light rays entering the human eye in the projection device illustrated in FIG. 1 . FIG. 19 is a characteristics diagram illustrating the relationship between the angle of incidence of P-polarized light and S-polarized light components on a windshield and the reflectance. FIG. 20 is a schematic diagram illustrating an example configuration of a projection device according to Modification 3 of the present disclosure. Fig. 1 is a diagram illustrating the state of each color component in the projection device shown in Fig. 1. Fig. 22 is a diagram illustrating an example of the configuration of the diffraction element shown in Fig. 20. Fig. 23 is a diagram illustrating another example of the configuration of the diffraction element shown in Fig. 20. Fig. 24 is a schematic diagram illustrating an example of the planar configuration of a PBG.FIG. 25 is a diagram illustrating the state of each color component in the projection device shown in FIG. 20 . FIG. 26 is a schematic diagram illustrating another example of the configuration of a projection device according to Modification 3 of the present disclosure. FIG. 27 is a schematic diagram illustrating an example of the configuration of a projection device according to Modification 4 of the present disclosure. FIG. 28 is a diagram illustrating the configuration of the louver film shown in FIG. 27 . FIG. 29 is a perspective view illustrating the configuration of the louver film shown in FIG. 27 . FIG. 30 is a diagram illustrating a region in a retroreflective element that becomes stray light. FIG. 31 is a diagram illustrating the absorption of stray light generated in a retroreflector by a louver film. FIG. 32 is a schematic diagram illustrating an example of the configuration of a projection device according to Other Modification 1 of the present disclosure. FIG. 33 is a schematic diagram illustrating an example of the configuration of a projection device according to Other Modification 2 of the present disclosure. FIG. 34 is a diagram illustrating an example of the behavior of light incident on the special retroreflector group of the projection device shown in FIG. 33 . FIG. 35 is a schematic diagram illustrating an example of the configuration of the special retroreflector group according to Other Modification 2 of the present disclosure. FIG. 36 is a schematic diagram illustrating an example of the configuration of a projection device according to Other Modification 3 of the present disclosure.

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The following description is one specific example of the present disclosure, and the present disclosure is not limited to the following aspects. Furthermore, the present disclosure is not limited to the arrangement, dimensions, dimensional ratios, etc. of each component shown in each drawing. The order of description is as follows: 1. Embodiment (Example of a projection device using a special retroreflection group including an anisotropic prism sheet) 2. Modifications 2-1. Modification 1 (Another example of the configuration of an anisotropic prism sheet) 2-2. Modification 2 (Another example of a projection device) 2-3. Modification 3 (Another example of a projection device) 2-4. Modification 4 (Another example of a projection device) 2-5. Other modifications

[0011] 1 illustrates an example of the configuration of a projection device (projection device 1) according to an embodiment of the present disclosure. The projection device 1 is used in a head-up display (HUD) system that displays speed, navigation, and the like to a driver in the front seat of a vehicle 40 (see, for example, FIG. 10 ) and displays virtual images including driving support information and attention-grabbing information by using light reflected on the windshield.

[0012] [Configuration of Projection Device] The projection device 1 includes a display device 10, a polarizing plate 11, a reflecting mirror 20, and a special retroreflection group 30. The special retroreflection group 30 includes an anisotropic prism sheet 31, a λ / 4 wavelength plate 32, and a retroreflection plate 33.

[0013] Here, the display device 10 corresponds to a specific example of a "display device" according to one embodiment of the present disclosure. The polarizing plate 11 corresponds to a specific example of a "first polarizing optical element" according to one embodiment of the present disclosure. The reflecting mirror 20 corresponds to a specific example of a "reflecting mirror" according to one embodiment of the present disclosure. The special retroreflecting group 30 corresponds to a specific example of a "special retroreflecting group" according to one embodiment of the present disclosure. The anisotropic prism sheet 31 corresponds to a specific example of an "anisotropic prism sheet" according to one embodiment of the present disclosure. The λ / 4 wave plate 32 corresponds to a specific example of a "second polarizing optical element" according to one embodiment of the present disclosure. The retroreflecting plate 33 corresponds to a specific example of a "retroreflecting element" according to one embodiment of the present disclosure.

[0014] 2 is a functional block diagram showing an example of the configuration of the display device 10. The display device 10 projects a virtual image in front of the observer 100. The display device 10 is connected to an external image supply device, such as a computer such as a PC (not shown) or various image players, via an I / F (interface), and projects the virtual image based on an image signal input to this interface.

[0015] The display device 10 includes, for example, a light source device 111, a control unit 112, a light source driving unit 113, a light modulation device 114, an image processing unit 115, a frame memory 116, a panel driving unit 117, a projection optical system driving unit 118, and a projection optical system 119.

[0016] Although not shown, the light source device 111 includes a light source driver that drives the light source and a current value setting unit that sets the current value when driving the light source. The light source driver generates a current having a current value set by the current value setting unit based on power supplied from a power supply circuit (not shown) in synchronization with a signal input from the light source drive unit 113. The generated current is supplied to each of the light sources.

[0017] The control unit 112 controls the light source driving unit 113 , the image processing unit 115 , the panel driving unit 117 and the projection optical system driving unit 118 .

[0018] The light source driving unit 113 outputs a signal for controlling the light emission timing of the light source arranged in the light source device 111. The light source driving unit 113 includes, for example, a PWM setting unit, a PWM signal generating unit, and a limiter (not shown), and controls the light source driver of the light source device 111 based on the control of the control unit 112, and PWM controls the light source to turn the light source on and off or adjust the brightness.

[0019] The light modulation device 114 modulates the light (illumination light) output from the light source device 111 based on an image signal to generate image light. The light modulation device 114 is configured to include, for example, three light valves corresponding to the respective colors of RGB (described later). Examples of the light modulation device 114 include a liquid crystal display panel (panel (B)) that modulates blue light (B), a liquid crystal display panel (panel (R)) that modulates red light (R), and a liquid crystal display panel (panel (G)) that modulates green light (G). The RGB color lights modulated by the light modulation device 114 are combined by a cross dichroic prism or the like (not shown) and guided to the projection optical system 119.

[0020] The image processing unit 115 acquires an image signal input from outside and performs tasks such as determining the image size, the resolution, and whether the image is a still image or a moving image. If the image is a moving image, it also determines image data attributes such as the frame rate. If the resolution of the acquired image signal differs from the display resolution of the light modulation device 114, it performs resolution conversion processing. The image processing unit 115 loads the images after each of these processes into the frame memory 116 for each frame, and outputs the image for each frame loaded in the frame memory 116 to the panel driving unit 117 as a display signal.

[0021] The panel driver 117 drives the light modulator 114. When the panel driver 117 is driven, the light transmittance of each pixel arranged in the light modulator 114 changes, and an image is formed.

[0022] The projection optical system driving unit 118 includes a motor that drives a lens arranged in the projection optical system 119. Under the control of the control unit 112, the projection optical system driving unit 118 drives, for example, the projection optical system 119, and performs, for example, zoom adjustment, focus adjustment, and aperture adjustment.

[0023] The projection optical system 119 includes a group of lenses for forming an image using the light modulated by the light modulator 114 .

[0024] In addition, the display device 10 may be configured as a three-panel type projector using three liquid crystal display panels as the light modulation device 114, as well as a single-panel type time-division projector using one liquid crystal display panel.

[0025] The polarizing plate 11 includes a polarizer having a polarization axis in a predetermined direction and rectifies the polarization of the light L emitted from the display device 10. The polarizing plate 11 selectively transmits light L polarized in a predetermined direction or a predetermined polarized light from the light L emitted from the display device 10. Specifically, the polarizing plate 11 has a transmission axis in a direction (X-axis direction) perpendicular to the paper surface (YZ plane) of FIG. 1 , for example, and selectively transmits the S-polarized component of the light L including an S-polarized component and a P-polarized component emitted from the display device 10.

[0026] When the polarized light L is emitted directly from the display device 10, the polarizing plate 11 can be omitted.

[0027] The reflective mirror 20 reflects, for example, the light L emitted from the display device 10 in a predetermined direction. Here, the reflective mirror 20 reflects the light L emitted from the display device 10 toward the special retroreflection group 30, and also reflects the light (returned light) emitted from the special retroreflection group 30 toward the vicinity of the eyes of the observer 100 by partial reflection.

[0028] The special retroreflecting group 30 reflects the light L incident via the reflecting mirror 20 in a predetermined direction with an offset angle. The special retroreflecting group 30 is composed of, for example, an anisotropic prism sheet 31, a λ / 4 wavelength plate 32, and a retroreflector 33.

[0029] The anisotropic prism sheet 31 is an optical member having refractive index anisotropy. Fig. 3 is a perspective view showing an example of the configuration of the anisotropic prism sheet 31. Fig. 4 is a schematic view showing an example of the cross-sectional configuration of the anisotropic prism sheet 31. As shown in Fig. 3, the anisotropic prism sheet 31 is formed by arranging a plurality of prisms, each having a ridgeline extending in the X-axis direction, in parallel in the Y-axis direction.

[0030] As described above, the anisotropic prism sheet 31 has refractive index anisotropy. Specifically, when the refractive index in the prism ridge direction (X-axis direction) is nx, the refractive index in the parallel direction of the prisms (Y-axis direction) is ny, and the refractive index in the thickness direction of the prisms (Z-axis direction) is nz, the refractive index nx is the largest, and the refractive index ny and the refractive index nz are approximately equal (nx > ny ≈ nz).

[0031] Here, the refractive index nx corresponds to a specific example of a "first refractive index" as an embodiment of the present disclosure. The refractive index ny corresponds to a specific example of a "second refractive index" as an embodiment of the present disclosure. The refractive index nz corresponds to a specific example of a "third refractive index" as an embodiment of the present disclosure. Furthermore, the X-axis direction corresponds to a specific example of a "first direction" as an embodiment of the present disclosure, the Y-axis direction corresponds to a specific positional example of a "second direction" as an embodiment of the present disclosure, and the Z-axis direction corresponds to a specific positional example of a "third direction" as an embodiment of the present disclosure.

[0032] The refractive index nx and the refractive index ny (or the refractive index nz) preferably have a refractive index difference Δn of 0.1 or more (Δn = nx - ny ≧ 0.1). Furthermore, the refractive index nx and the refractive index ny (or the refractive index nz) preferably have a refractive index difference Δn of 0.2 or more (Δn = nx - ny ≧ 0.2). The refractive index difference Δn between the refractive index nx and the refractive index ny (or the refractive index nz) determines the offset amount of the exit angle of the light L exiting the special retroreflection group 30 relative to the incident angle of the light L incident on the special retroreflection group 30, as will be described later. The larger the refractive index difference Δn, the greater the offset amount can be. On the other hand, increasing the refractive index difference Δn poses challenges, such as difficult manufacturing processes and difficult material selection.

[0033] The pitch (W) of the multiple prisms constituting the anisotropic prism sheet 31 is preferably, for example, 10 μm or more and 200 μm or less. This is because if the prism pitch (W) is too small, light will be diffracted. On the other hand, if the prism pitch (W) is too large, there is a concern that it will be difficult to manufacture.

[0034] The anisotropic prism sheet 31 can be formed using, for example, a crystalline resin material that exhibits anisotropy in refractive index when stretched, such as polyethylene naphthalate (PEN), polyethylene terephthalate (PET), and aramid.

[0035] The anisotropic prism sheet 31 using the above resin material can be manufactured, for example, as follows. Fig. 5 is a schematic diagram showing an example of the manufacturing process for the anisotropic prism sheet 31. The anisotropic prism sheet 31 using the resin material is manufactured through a heat pressing process (area A shown in Fig. 5) and a uniaxial stretching process (area B shown in Fig. 5).

[0036] The heat pressing process uses a mold to impart a desired shape to one side of the film. This mold is flexible and held by two or more rolls, and has the desired shape. Specifically, the heat pressing process includes, for example, a high-temperature roll 1011 and a low-temperature roll 1012. These two rolls 1011 and 1012 hold a forming die 1013 on the surface, the forming die having a shape that is an inverse of the shape corresponding to the anisotropic prism sheet 31 (a shape in which the direction of movement of the resin film 311X (the direction of the arrow in FIG. 5) and the prism ridge direction are approximately the same). The temperatures of the high-temperature roll 1011 and the low-temperature roll 1012 are set relative to the glass transition temperature Tg of the film (resin film 311X) used. The high-temperature roll 1011 is set at a temperature higher than the glass transition temperature Tg (for example, about 150°C), and the low-temperature roll 1012 is set at a temperature lower than the glass transition temperature Tg (for example, about 100°C). This is because the crystalline resin film 311X may crystallize if it is cooled slowly (gradually cooled) after reaching a temperature higher than the glass transition temperature Tg, and may not be able to be stretched well in the subsequent stretching step.

[0037] When resin film 311X comes into contact with mold 1013 heated by high-temperature roll 1011 while moving in the direction of the arrow, the surface shape of mold 1013 is transferred to resin film 311X by the heat and the pressure of high-temperature roll 1011 and roll 1014 arranged opposite to each other. Resin film 311X to which the surface shape of mold 1013 has been transferred is rapidly cooled when passing between low-temperature roll 1012 and roll 1014 arranged opposite to each other, and becomes amorphous without crystallizing.

[0038] The amorphous resin film 311X, to which the surface shape of the mold 1013 has been transferred, is then uniaxially stretched in the prism ridge direction in region B. One example of a stretching method is to hold the resin film 311X between rolls 1015 and 1016 with different gear ratios, and stretch the resin film 311X at a stretching ratio corresponding to the gear ratio. The temperatures of the rolls 1015 and 1016 are higher than the glass transition temperature Tg (e.g., 140°C). Uniaxially stretching the resin film 311X in the ridge direction reduces the shape of the prisms similarly, increasing the refractive index nx in the prism ridge direction while substantially maintaining the triangular shape of the prisms. For example, when PEN is used, an anisotropic prism sheet 31 can be obtained with refractive index anisotropy of nx = 1.79, ny = 1.56, and nz = 1.56.

[0039] The λ / 4 wave plate 32 is a polarizing optical element that corrects the polarization state of light passing through it, and is designed to generate a phase difference of λ / 4 wavelength in the light passing through it. The axis of the λ / 4 wave plate 32 is in the XY plane and is tilted 45° from the X-axis. In this example, the λ / 4 wave plate 32 imparts a phase difference of λ / 4 wavelength to the S-polarized light L selected by the polarizing plate 11 and transmitted through the anisotropic prism sheet 31, causing the light to exit as right-handed circularly polarized light.

[0040] The retroreflector 33 has a mechanism for returning reflected light directly to the optical axis of the incident light. The retroreflector 33 has a plurality of unit elements 331 periodically arranged in a two-dimensional array.

[0041] FIG. 6 is a schematic diagram showing the planar configuration of the retroreflector 33. FIG. 7 is a schematic diagram showing the configuration of a plurality of unit elements 331 constituting the retroreflector 33. The unit element 331 is, for example, three plane mirrors combined at right angles to each other with their reflective surfaces facing inward, like the vertices of a cube. Specifically, as shown in FIG. 7, the unit element 331 is combined so that the three surfaces 331S1, 331S2, and 331S3 are perpendicular to each other, thereby forming a triangular pyramidal recess 331c on the inside of the three surfaces 331S1, 331S2, and 331S3. When viewed from directly above, the retroreflector 33, in which such unit elements 331 are arranged in a two-dimensional array, has a close-packed arrangement of equilateral triangles, as shown in FIG. 6, for example. Light that reaches any of the reflective surfaces is reflected by the corner deflectors on the three surfaces and returns to the direction of incidence (retroreflected).

[0042] Figure 8 is a schematic diagram showing the cross-sectional structure of the retroreflector 33 corresponding to line II' shown in Figure 6. The retroreflector 33 has a pair of opposing surfaces 30S1 and 30S2. As shown in Figure 8, for example, a light ray (right-handed circularly polarized light) incident on each unit element 331 is sequentially and repeatedly specularly reflected by a reflecting surface 331S consisting of three surfaces 331S1, 331S2, and 331S3 arranged at right angles to each other, and ultimately returns to the incident direction as left-handed circularly polarized light.

[0043] The retroreflector 33 preferably has a transparent layer 330B formed on a base material 330A on which the reflective surface 331S, including the three surfaces 331S1, 331S2, and 331S3, is formed. This is because the light L incident on the retroreflector 33 is refracted by the transparent layer 330B, allowing for more efficient retroreflection than when the transparent layer 330B is not present and no refraction occurs. The transparent layer 330B preferably has a high refractive index and is highly transparent. Examples of materials that can be used for the transparent layer 330B include acrylic resin, polycarbonate resin, and epoxy resin.

[0044] In actual retroreflectors, when circularly polarized light is reflected once, most of it becomes reverse circularly polarized light, and a small amount of light remains circularly polarized. However, this technology still works without any problems in such cases.

[0045] The behavior of light L emitted from the display device 10 will be described with reference to FIG.

[0046] First, the outbound path will be described. Light L emitted from the display device 10 becomes linearly polarized (S-polarized) light by passing through the polarizing plate 11, and then passes through the reflecting mirror 20 and enters the anisotropic prism sheet 31 that constitutes the special retroreflection group 30. The refractive index nx in the ridge direction of the anisotropic prism sheet 31 becomes the effective refractive index of the S-polarized light L, and the light exits the anisotropic prism sheet 31 with a refraction angle corresponding to the refractive index nx and the prism angle, while maintaining its polarization. The S-polarized light L exiting the anisotropic prism sheet 31 enters the λ / 4 wave plate 32, where it is exited as right-handed circularly polarized light. This completes the outbound path.

[0047] 7, for example, the right-handed circularly polarized light L is reflected three times, once by each of the three surfaces 331S1, 331S2, and 331S3 of the unit element 331, and is emitted as left-handed circularly polarized light. This is because, in an ideal reflection, circularly polarized light becomes reverse-handed circularly polarized light after being reflected once, and when this is repeated three times, the light emitted is left-handed circularly polarized light in response to the right-handed circularly polarized light.

[0048] Next, the return path will be described. The left-handed circularly polarized light L emitted from the retroreflector 33 is incident on the λ / 4 wavelength plate 32, where it is output as linearly polarized light (P-polarized light) parallel to the paper surface. When the P-polarized light L emitted from the λ / 4 wavelength plate 32 enters the anisotropic prism sheet 31, the refractive index ny in the parallel direction of the prisms and the refractive index nz in the thickness direction of the prisms become the effective refractive index, and the light is output from the anisotropic prism sheet 31 at a refraction angle corresponding to the refractive indexes ny and nz and the angle of incidence, while maintaining its polarization. Here, because the refractive indexes ny and nz are smaller than the refractive index nx, the degree of refraction of the light L incident on the anisotropic prism sheet 31 is smaller on the return path than on the outward path. This offsets the angle of the light L (return light) emitted from the special retroreflector group 30 relative to the angle of the light L (incident light) incident on the special retroreflector group 30. The P-polarized light L emitted from the anisotropic prism sheet 31 passes through the reflecting mirror 20 and enters the eye of the observer 100 .

[0049] Figure 9 illustrates the behavior of light incident on the special retroreflector group 30 shown in Figure 1, using specific numerical examples. The anisotropic prism sheet 31 shown in Figure 9 has, for example, a refractive index in the ridge direction of nx = 1.79, a refractive index in the parallel direction of the prisms of ny = 1.56, and a refractive index in the thickness direction of the prisms of nz = 1.56. The angles of the prism triangle are: apex angle θ1 = 59°, angle θ2 of the surface from which the light exits = 46°, and the remaining angle θ3 = 75°. In the anisotropic prism sheet 31 shown in Figure 9, the effective refractive index on the outgoing path is 1.79, and the effective refractive index on the return path is 1.56. Therefore, as shown in FIG. 9 , S-polarized light L incident on surface 31S2 opposite the prism surface (surface 31S1) of the anisotropic prism sheet 31 at an angle of 43° is emitted from surface 31S1 toward the λ / 4 wave plate 32 at an angle of 22° while maintaining its polarization, and upon entering the λ / 4 wave plate 32, it is emitted as right-handed circularly polarized light toward the retroreflector 33. As described above, the right-handed circularly polarized light L incident on the retroreflector 33 is reflected three times, once each by the three surfaces 331S1, 331S2, and 331S3 of the unit element 331, and is emitted as left-handed circularly polarized light. The left-handed circularly polarized light L emitted from the retroreflector 33 is incident on the λ / 4 wave plate 32 and is emitted as P-polarized light toward the anisotropic prism sheet 31. The P-polarized light L emitted from the λ / 4 wave plate 32 is incident on the surface 31S1 of the anisotropic prism sheet 31 at an angle of 22°, just as it was when it was emitted, and is emitted from the surface 31S2 at an angle of 29° while maintaining its polarization, as shown in Figure 9. In this way, it can be seen that the light L incident on the special retroreflecting group 30 is given a predetermined offset angle with respect to the incident direction and is emitted from the special retroreflecting group 30.

[0050] 10 shows a configuration example (projection device 1A) in which the above-described projection device 1 is mounted on a vehicle 40. In the projection device 1A, for example, the display device 10 is installed on the ceiling inside the vehicle, the special retroreflective group 30 is arranged on the dashboard 42, and the windshield 41 also serves as the reflective mirror 20.

[0051] Here, the vehicle 40 corresponds to a specific example of a "mobile body" according to an embodiment of the present disclosure.

[0052] In the projection device 1 of this embodiment, light is emitted from a display device 10 located above the driver (observer 100) (on the vehicle ceiling) and passes through a polarizing plate 11. The light is reflected by a windshield 41 positioned diagonally in front of the observer 100 toward a special retroreflecting group 30 located below the observer 100 (on the dashboard 42). Before forming an image as converging light, the light from each image height enters the special retroreflecting group 30 and, as a result of repeated specular reflections at each unit element 331 constituting the retroreflector 33, returns to the incident direction as divergent light. The divergent light emitted from the special retroreflecting group 30 is partially reflected by the windshield 41 and enters the vicinity of the observer 100's eyes. This displays a wide-angle (wide FOV) distant virtual image in front of the driver. In other words, the driver can see a wide FOV virtual image in the distance.

[0053] [Functions and Effects] In the projection device 1 of this embodiment, light emitted from the display device 10 is guided to the special retroreflection group 30 via the polarizing plate 11 and the reflecting mirror 20. The special retroreflection group 30 includes an anisotropic prism sheet 31, a λ / 4 wavelength plate 32, and a retroreflection plate 33. Light L incident on the special retroreflection group 30 is reflected with an offset angle in a predetermined direction. This allows a wide-angle virtual image to be displayed without using, for example, a huge mirror optical system. This is described below.

[0054] In recent years, development has been progressing on HUD systems that display speed, navigation, etc. to the driver in the front seat of a vehicle and display virtual images including driving support information and cautionary information using light reflection on the windshield.

[0055] Generally, due to the size constraints of display devices, existing HUDs are limited to displaying only an area with a viewing angle of about 10 degrees (the central area in front). Meanwhile, in the world of computer graphics (CG), there are many examples of warning information and augmented reality (AR) information superimposed over the entire windshield. However, in reality, no device that can achieve this yet exists, and none has been installed in an actual vehicle.

[0056] For example, when a display device is placed in the dashboard area, a method called Pepper's Ghost is used to create a virtual image that appears floating over a wide area. With this method, the virtual image is only visible from the distance between the display device and the windshield, so it is not possible to display a virtual image from a distance. Therefore, conventional technology does not have a technology that can display a virtual image over a wide FOV and at a distance, and there was no technology that could realize the ideal CG world.

[0057] Fig. 11 shows an example of the configuration of a typical projection device (projection device 1000). Typical projection device 1000 uses a light source unit located under a dashboard 1042 in the front seat of a vehicle, a mirror optical system including a display panel 1043 and a mirror 1044 that magnify the light (light L) emitted from the unit, and a concave mirror optical system to deliver light to the eyes of the driver (observer 100). As shown in Fig. 11, divergent light reaching observer 100 gives the impression that a virtual image is floating at the position of the virtual light-emitting point, but as described above, projection device 1000 has a limited FOV of about 10 degrees.

[0058] In contrast to this, in the present embodiment, the light emitted from the display device 10 is guided via a polarizing plate 11 and a reflecting mirror 20 to a special retroreflection group 30 including an anisotropic prism sheet 31, a λ / 4 wavelength plate 32, and a retroreflection plate 33.

[0059] For example, when the refractive index of the anisotropic prism sheet 31 is nx, the refractive index of the prism ridge direction is ny, and the refractive index of the prism thickness direction is nz, the refractive index nx is the largest, and the refractive index ny and the refractive index nz are approximately equal (nx > ny ≒ nz). For light L (outbound) incident on the surface (surface 31S2) opposite the prism surface (surface 31S1), the refractive index nx in the prism ridge direction becomes the effective refractive index. Light L with a refraction angle corresponding to the refractive index nx and the angle of the prism is emitted from the surface 31S1 side and enters the retroreflector 33 via the λ / 4 wave plate 32. The light incident on the retroreflector 33 is repeatedly mirror-reflected sequentially on the three surfaces 331S1, 331S2, and 331S3 of the unit elements 331 that make up the retroreflector 33, and is ultimately emitted in the direction of incidence. Light L emitted from the retroreflector 33 is incident on surface 31S1 of the anisotropic prism sheet 31 via the λ / 4 wavelength plate 32. For light L (returning) incident on surface 31S1, the effective refractive index is the refractive index ny in the parallel direction of the prisms and the refractive index nz in the thickness direction of the prisms. Light L with a refraction angle corresponding to the refractive index ny and the refractive index nz and the angle of incidence is emitted from surface 31S2. As described above, because the refractive indices ny and nz are smaller than the refractive index nx, the degree of refraction of light L incident on the anisotropic prism sheet 31 is smaller on the return path than on the forward path. As a result, light L incident on the special retroreflector group 30 is given a predetermined offset angle with respect to the incident direction and is emitted from the special retroreflector group 30, reflected by the reflecting mirror 20, and enters the eye of the observer 100.

[0060] As described above, when the projection device 1 of this embodiment is mounted on a vehicle 40, light from each image height enters the special retroreflection group 30 before being formed as convergent light, and as a result of repeated specular reflection at each unit element 331 constituting the retroreflector 33, the light is given a predetermined offset angle and is emitted from the special retroreflection group 30 as divergent light. The divergent light emitted from the special retroreflection group 30 is partially reflected by the windshield 41 and enters the vicinity of the eyes of the observer 100. As a result, a wide FOV virtual image is rendered in the distance from the observer 100.

[0061] As a result, it is possible to provide a projection device 1 that can display a wide FOV virtual image.

[0062] Next, modified examples 1 to 4 and other modified examples of the present disclosure will be described. In the following, the same components as those in the above embodiment will be given the same reference numerals, and the description thereof will be omitted as appropriate.

[0063] <2. Modifications> (2-1. Modification 1) Fig. 12 is a perspective view showing an example of the configuration of an anisotropic prism sheet 31A that constitutes the special retroreflective group (special retroreflective group 30) according to Modification 1 of the present disclosure. Fig. 13 is a schematic diagram showing an example of the cross-sectional configuration of the anisotropic prism sheet 31A shown in Fig. 12.

[0064] In the above embodiment, the anisotropic prism sheet 31 is formed using a crystalline resin material such as PEN, PET, or aramid, but is not limited to these. The anisotropic prism sheet 31A of this modified example is formed using a liquid crystal polymer.

[0065] Similar to the above-described embodiment, the anisotropic prism sheet 31A is composed of multiple prisms with ridges extending in the X-axis direction, arranged in parallel in the Y-axis direction. The anisotropic prism sheet 31A has refractive index anisotropy, where nx is the refractive index in the ridge direction of the prisms, ny is the refractive index in the parallel direction of the prisms, and nz is the refractive index in the thickness direction of the prisms. The refractive index nx is the largest, and the refractive indexes ny and nz are substantially equal (nx > ny ≈ nz). The refractive index difference Δn between the refractive index nx and the refractive index ny (or the refractive index nz) is preferably 0.1 or greater (Δn = nx - ny ≧ 0.1). Furthermore, the refractive index difference Δn between the refractive index nx and the refractive index ny (or the refractive index nz) is preferably 0.2 or greater (Δn = nx - ny ≧ 0.2).

[0066] The anisotropic prism sheet 31A includes a flat substrate 310 and a prism layer 311 disposed on the substrate 310. The substrate 310 is, for example, a substrate with no birefringence, or a film with a controlled slow axis that maintains linearly polarized light. The prism layer 311 includes multiple prisms with ridges extending in the X-axis direction, arranged in parallel in the Y-axis direction, and is formed, for example, with nematic liquid crystal 312. The nematic liquid crystal 312 has a large refractive index in the longitudinal direction and is oriented so that the longitudinal direction coincides with the prism ridge direction. This results in the refractive index nx in the prism ridge direction being greater than the refractive index ny in the parallel direction of the multiple prisms and the refractive index nz in the prism thickness direction.

[0067] The pitch (W) of the prisms constituting the anisotropic prism sheet 31A is preferably, for example, 10 μm or more and 200 μm or less.

[0068] The anisotropic prism sheet 31A formed using a liquid crystal polymer can be manufactured, for example, as follows: Figures 14A to 14E schematically show an example of a manufacturing process for the anisotropic prism sheet 31A.

[0069] First, as shown in Figure 14A, a master 313 having a prism structure is prepared. The master 313 has a prism structure that is an inverted version of the prisms of the anisotropic prism sheet 31A, and a plurality of minute grooves 313c are formed on the prism surface along the ridge line direction. The prism structure can be formed by cutting with a diamond cutting tool or a carbide cutting tool. Then, the minute grooves 313c can be formed on the prism by laser cutting using a femtosecond laser.

[0070] 14B , after applying uncured liquid crystal monomer 311A ​​to master 313, the temperature is raised to the liquid crystal transition temperature of liquid crystal monomer 311A, whereby liquid crystal monomer 311A ​​changes to a liquid crystal phase. Then, liquid crystal monomer 311A ​​is slowly cooled (gradually cooled). As a result, liquid crystal monomer 311A, which has now reached or below its liquid crystal transition temperature, begins to exhibit the properties of a liquid crystal phase, and is oriented in the direction of minute grooves 313c formed in master 313.

[0071] Next, as shown in Fig. 14C, the substrate 310 is placed on the liquid crystal monomer 311A, and then, as shown in Fig. 14D, the liquid crystal monomer 311A ​​is cured by ultraviolet (UV) irradiation to form a polymer film. This forms the prism layer 311 adhered to the substrate 310. Thereafter, the master 313 is peeled off as shown in Fig. 14E, thereby obtaining the anisotropic prism sheet 31A shown in Fig. 12.

[0072] In this modified example, the anisotropic prism sheet 31A is formed using a liquid crystal polymer. Even when this anisotropic prism sheet 31A is used in place of the anisotropic prism sheet 31 made of a crystalline resin material in the projection device 1 described above, the same effects as those of the above embodiment can be obtained.

[0073] 15 illustrates a configuration example of a projection device (projection device 2) according to Modification 2 of the present disclosure. As in the above embodiment, projection device 2 is used in a HUD system that displays speed, navigation, and the like to a driver in the front seat of a vehicle, and displays virtual images including driving support information and cautionary information using light reflected on the windshield.

[0074] In the projection device 2 of this modification, a −λ / 4 wave plate 51 and a +λ / 4 wave plate 52 are respectively arranged after the display device 10 and before the special retroreflection group 30. Except for this point, the projection device 2 has the same configuration as the projection device 1 of the above embodiment.

[0075] In the configuration of the projection device 1 of the above embodiment, the linearly polarized light reflected by the reflecting mirror 20 (for example, the windshield 41) on the return path is P-polarized light, which poses a problem of low reflectivity at the windshield 41.

[0076] 16 to 18 show the results of an optical simulation of the behavior of light rays (light L) incident on the eye of a person (e.g., observer 100) at angles of +10° (FIG. 16), 0° (FIG. 17), and −10° (FIG. 18) when the field of view (FOV) of the human eye in the vertical direction (Z-axis direction) is ±10°. Fig. 19 is a characteristic diagram showing the relationship between the angle of incidence of the P-polarized component and the S-polarized component on windshield 41 and the reflectance.

[0077] Light L incident on the human eye at an angle of +10° is incident on the windshield 41 at an incident angle θ1 = 58° on the outbound path, and at an incident angle θ2 = 50° on the return path. Light L incident on the human eye at an angle of 0° is incident on the windshield 41 at an incident angle θ1 = 73° on the outbound path, and at an incident angle θ2 = 60° on the return path. Light L incident on the human eye at an angle of -10° is incident on the windshield 41 at an incident angle θ1 = 82° on the outbound path, and at an incident angle θ2 = 68° on the return path.

[0078] As described above, in the configuration of the projection device 1, the light L that is incident on the windshield 41 on the outbound path is S-polarized, and the light L that is incident on the windshield on the return path is P-polarized. As shown in the graph in Figure 19, the angle of incidence of light L that is incident on the windshield 41 on the return path at a viewing angle of ±10° with respect to the human eye is close to the angle (Brewster's angle) at which the reflectance of P-polarized light is nearly zero, and therefore the reflectance is very small.

[0079] The problem of low reflectance of P-polarized light on windshield 41 can be solved by taking measures such as forming an optical multilayer film on windshield 41 itself to increase the reflectance of P-polarized light, but in this modified example, as described above, a −λ / 4 wave plate 51 and a +λ / 4 wave plate 52 are arranged respectively after display device 10 and before special retroreflection group 30. Specifically, as shown in FIG. 15 , −λ / 4 wave plate 51 is arranged between polarizing plate 11 and reflection mirror 20, and +λ / 4 wave plate 52 is arranged between reflection mirror 20 and special retroreflection group 30.

[0080] As a result, light L emitted from display device 10 and converted to S-polarized light by passing through polarizing plate 11 passes through -λ / 4 wave plate 51 to become left-handed circularly polarized light, and then passes through reflecting mirror 20 to enter +λ / 4 wave plate 52. Left-handed circularly polarized light L that entered +λ / 4 wave plate 52 passes through +λ / 4 wave plate 52 to become S-polarized light, and then enters anisotropic prism sheet 31 that constitutes special retroreflection group 30. Light L then passes through right-handed circularly polarized light and left-handed circularly polarized light, as in the above embodiment, and exits anisotropic prism sheet 31 as P-polarized light L. P-polarized light L that exits anisotropic prism sheet 31 passes through +λ / 4 wave plate 52 to become right-handed circularly polarized light, and then enters reflecting mirror 20.

[0081] Table 1 summarizes the amount of light incident on the human eye at a viewing angle of ±10° in the projection device 1 of the above embodiment (Example 1) and the projection device 2 of this modified example (Example 2). Table 1 shows that Example 2, in which a −λ / 4 wave plate 51 and a +λ / 4 wave plate 52 are arranged after the display device 10 and before the special retroreflecting group 30, respectively, can significantly improve the amount of light incident on the human eye compared to Example 1.

[0082]

[0083] In this way, in the projection device 2 of this modification, the −λ / 4 wave plate 51 and the +λ / 4 wave plate 52 are respectively arranged after the display device 10 and before the special retroreflecting group 30. Therefore, in addition to the effects of the above embodiment, an effect of being able to display a clearer virtual image is achieved.

[0084] 20 illustrates a configuration example of a projection device (projection device 3) according to Modification 3 of the present disclosure. As in the above embodiment, projection device 3 is used in a HUD system that displays speed, navigation, and the like to a driver in the front seat of a vehicle, and displays virtual images including driving support information and cautionary information using light reflected on the windshield.

[0085] In the projection device 3 of this modification, a diffraction element 53 is disposed on the optical path of the light L emitted from the display device 10 between the display device 10 and the special retroreflection group 30. Except for this point, the projection device 3 has the same configuration as the projection device 1 of the above embodiment.

[0086] In the above embodiment and variant 1, the anisotropic prism sheet 31 (stretched crystalline resin film 311X) formed using a crystalline resin material and the anisotropic prism sheet 31A formed using a liquid crystal polymer are shown as specific examples of the "anisotropic prism sheet" of one embodiment of the present disclosure. However, anisotropic prism sheets made of stretched crystalline resin film 311X or liquid crystal polymer often have refractive index anisotropy, i.e., the refractive index difference Δn between the refractive index nx and the refractive index ny (or the refractive index nz), that is, wavelength-dependent.

[0087] When an anisotropic prism sheet has wavelength dependency, there is a problem in that the angle of incidence on the human eye (e.g., observer 100) varies depending on the wavelength. For example, as shown in FIG. 21 , of the light L emitted from the display device 10, a difference (angle deviation) occurs in the angle of incidence on the human eye between red component light (red light) Lr around 630 nm and blue component light (blue light) Lb around 460 nm. When an angle deviation occurs, the image is perceived by the human eye as color breakup. To compensate for the angle deviation, signal processing is required, such as shifting the image for each color in advance in the display device 10.

[0088] In contrast to this, in this modified example, a diffraction element 53 is arranged on the optical path of the light L emitted from the display device 10 between the display device 10 and the special retroreflection group 30. Examples of the diffraction element 53 include the blazed diffraction element 53A shown in Fig. 22 and the PBG group 53B shown in Fig. 23.

[0089] 22, the blazed diffraction element 53A generates diffracted light only on one side (+1st order light, red light Lr, green light Lg, and blue light Lb). However, since the blazed diffraction element 53A generates unnecessary 0th order light (unnecessary light L0), it is preferable to also provide an absorber or the like that absorbs the unnecessary light L0.

[0090] As shown in FIG. 23 , the PBG group 53B includes a Pankaratnam-Berry phase grating (PBG) 531, an input polarizer 532, a −λ / 4 waveplate 533, a +λ / 4 waveplate 534, and an output polarizer 535. The PBG 531 is a type of phase diffraction element that diffracts light based on an in-plane distribution of phase difference. The PBG 531 is formed, for example, using a liquid crystal polymer. Because liquid crystal polymers (liquid crystal polymers 531X) have birefringence, a phase difference distribution can be achieved by changing the orientation angle within the plane of the PBG 531, as shown in FIG. 24 . The PBG 531 has a structure in which an alignment film and a liquid crystal polymer layer are stacked on a transparent substrate, for example. Because the PBG 531 is a polarizing optical element, the transparent substrate is preferably a substrate that has no birefringence, such as glass, or has very little birefringence. The PBG 531 may have, for example, a Twist structure in which multiple liquid crystal polymers 531X arranged in the thickness direction (Z-axis direction) within the liquid crystal polymer layer are twisted with respect to each other, or an UnTwist structure in which there is no twist. A PBG with a Twist structure is more difficult to manufacture, but has the advantage of being able to reduce the wavelength dependency of the diffraction efficiency. A PBG with an UnTwist structure is relatively easy to manufacture, but has the characteristic of having wavelength dependency of the diffraction efficiency. As shown in FIG. 23 , the PBG group 53B can emit only +1st-order light (red light Lr, green light Lg, and blue light Lb).

[0091] The diffracted light (e.g., +1st-order light) by the diffraction element 53 is wavelength-dependent, meaning that the longer the wavelength, the easier it is to diffract it. In other words, the longer the wavelength, the greater the angle of bending. On the other hand, the wavelength dependence of the anisotropic prism sheet described above typically increases with shorter wavelengths. In other words, the shorter the wavelength, the greater the angle of bending. In this way, the diffraction element 53 and the anisotropic prism sheet (e.g., the anisotropic prism sheet 31) have opposite wavelength dependencies, making it possible to compensate for wavelength dispersion. Specifically, as shown in FIG. 25, when light L emitted from the display device 10 is diffracted by the diffraction element 53, red light Lr is diffracted at a larger angle than blue light Lb. This compensates for the wavelength dependence of the anisotropic prism sheet 31 that constitutes the special retroreflective group 30, reducing the angular deviation between the red light Lr and blue light Lb incident on the human eye.

[0092] 22 and other figures, the red light Lr and the blue light Lb are each shown as a single line, but in reality, they are surfaces, so all wavelengths including the red and blue components can be incident on the human eye. However, as shown in Figure 25, the fact that the red light Lr and the blue light Lb are misaligned in the Z-axis direction means that the range (eye box) in which the human eye can receive all colors of light emitted from the display device 10 and can view a correct image is narrowed.

[0093] In light of this, the diffraction element 53 may be arranged above the anisotropic prism sheet 31 that constitutes the special retroreflective group 30, as in the projection device 3A shown in Fig. 26. By arranging the diffraction element 53 above the anisotropic prism sheet 31, it is possible to reduce both the angle deviation and the position deviation, and to enlarge the eyebox.

[0094] As described above, in the projection device 3 and the projection device 3A of this modification, the diffraction element 53 is arranged on the optical path of the light L emitted from the display device 10 between the display device 10 and the special retroreflecting group 30. This makes it possible to compensate for the wavelength dependency of the anisotropic prism sheet 31 that occurs in the projection device of the above embodiment (for example, the projection device 1). Therefore, in addition to the effects of the above embodiment, it is possible to achieve the effect of making it possible to view a virtual image in a wide eyebox without performing signal processing within the display device 10.

[0095] 27 illustrates a configuration example of a projection device (projection device 4) according to modification 4 of the present disclosure. Similar to the above embodiment, projection device 4 is used in a HUD system that displays speed, navigation, and the like to a driver in the front seat of a vehicle, and displays virtual images including driving support information and cautionary information using light reflected on the windshield.

[0096] In the projection device 4 of this modification, a louver film 34 is disposed between the λ / 4 wavelength plate 32 and the retroreflector 33 that constitute the special retroreflection group 30A. Except for this point, the projection device 2 has the same configuration as the projection device 2 of the modification 2 described above.

[0097] 27, the polarization state of light L on the outward path before it enters the anisotropic prism sheet 31 is ideally linearly polarized light (S-polarized light) perpendicular to the paper surface. However, in reality, considering that the −λ / 4 wave plate 51 and the +λ / 4 wave plate 52 have incidence angle dependency and wavelength dependency, light L before it enters the anisotropic prism sheet 31 contains linearly polarized light (P-polarized light) parallel to the paper surface. If this P-polarized light enters the anisotropic prism sheet 31, it will become stray light.

[0098] In contrast to this, in this modified example, a louver film 34 is arranged between the λ / 4 wave plate 32 and the retroreflector 33. The louver film 34 is an optical member that controls the viewing angle, and, for example, as shown in Figures 28 and 29, transparent portions 341 and absorbing portions 342 are arranged alternately in the XY in-plane direction. The extension directions of the transparent portions 341 and absorbing portions 342 approximately coincide with the ridge direction of the multiple prisms of the anisotropic prism sheet 31.

[0099] 28 , when light inclined in the Y-axis direction is incident on the louver film 34, light with a small incident angle has a high transmittance, whereas light with a larger incident angle has a lower transmittance, and the transmittance of light above a certain incident angle is nearly zero. The incident angle of light at which the transmittance becomes nearly zero is determined by the relationship between the thickness of the louver film 34 and the width of the transparent portions 231. Therefore, by adjusting the thickness of the louver film 34 and the width of the transparent portions 231, stray light emitted from the anisotropic prism sheet 31 can be absorbed by the absorbing portions 342.

[0100] Furthermore, the louver film 34 can also absorb stray light generated in the retroreflector 33 with the absorbing portions 342. Figure 30 is a schematic diagram showing the planar configuration of the multiple unit elements 331 that make up the retroreflector 33. The multiple unit elements 331 that make up the retroreflector 33 cannot actually retroreflect all incident light, and some light becomes stray light. Specifically, light that is incident on the region X near each vertex of adjacent unit elements 331 shown in Figure 30 cannot be reflected by the three surfaces 331S1, 331S2, and 331S3, and is not retroreflected but is emitted from the retroreflector 33 as stray light Lx. This stray light Lx is emitted in a direction significantly different from the retroreflected light L, as shown in Figure 31, for example, and can therefore be absorbed by the absorbing portions 342 of the louver film 34.

[0101] As described above, in the projection device 4 of this modified example, the louver film 34 is disposed between the λ / 4 wavelength plate 32 and the retroreflector 33 that constitute the special retroreflector group 30A. This reduces stray light generated in the anisotropic prism sheet 31 and the retroreflector 33. Therefore, in addition to the effects of the above-described embodiment, it is possible to suppress unnecessary stray light from being recognized by a person (e.g., the observer 100), thereby enabling a clearer virtual image to be displayed.

[0102] (2-5. Other Modifications) (Other Modification 1) The windshield (windshield 41A) of an actual vehicle is often a curved surface. Fig. 32 shows a configuration example of a projection device (projection device 5) according to Other Modification 1 of the present disclosure, where the field of view (FOV) in the vertical direction (Z-axis direction) of the eyes of a person (e.g., observer 100) is ±10°.

[0103] Light L emitted from display device 10 passes, for example, through polarizing plate 11, −λ / 4 wave plate 51, windshield 41A, +λ / 4 wave plate 52, special retroreflector group 30, +λ / 4 wave plate 52, and windshield 41A in this order before entering the eye of observer 100. The emission angle distribution of light L emitted from display device 10 can be controlled to enter the eye of observer 100 at ±10°, taking into account the inclination at each location on the curved surface of windshield 41A, and is set to ±6° in this modified example, for example.

[0104] In this way, the present technology can obtain the same effect even when the windshield 41A has a curved surface.

[0105] (Other Modification 2) Fig. 33 shows a configuration example of a projection device (projection device 6A) according to Other Modification 2 of the present disclosure. In the above-described embodiments, an example has been shown in which light passes through the reflecting mirror 20 (windshield 41) on both the outbound and inbound journeys, but reflection on the reflecting mirror 20 may occur only on the inbound journey. The windshield of a vehicle generally has a low reflectivity. Therefore, reflecting light L only once on the windshield 41 allows a higher amount of light L to reach the eyes of the observer 100, thereby reducing power consumption of the display device 10 and enabling a brighter image to be viewed.

[0106] However, if the light is only allowed to pass through the reflecting mirror 20 (windshield 41) on the return journey, a large offset angle is required between the outbound and return journeys. Figure 34 illustrates, using specific numerical examples, the behavior of light incident on a special retroreflective group 30B including an anisotropic prism sheet 31A having, for example, a refractive index nx = 2.0 in the ridge direction, a refractive index ny = 1.5 in the parallel direction of the prisms, and a refractive index nz = 1.5 in the thickness direction of the prisms. The angles of the prism triangles are, respectively, an apex angle θ1 = 55°, an angle θ2 = 45° of the surface from which the light exits, and a remaining angle θ3 = 80°. If the light is only allowed to pass through the reflecting mirror 20 (windshield 41) on the return journey, a very large refractive index anisotropy is required, such as a refractive index difference Δn = 0.5 between the refractive index nx and the refractive index ny (or the refractive index nz), as shown in Figure 34.

[0107] If a single anisotropic prism sheet 31 does not provide sufficient refractive index anisotropy, multiple anisotropic prism sheets may be used. Figure 35 illustrates, using specific numerical examples, the behavior of light incident on a special retroreflective group 30C including two anisotropic prism sheets 31B and 31C, each of which has a refractive index in the ridge direction of nx = 1.86, a refractive index in the parallel direction of the prisms of ny = 1.56, and a refractive index in the thickness direction of the prisms of nz = 1.56. The angles of the prism triangles of the anisotropic prism sheets 31B and 31C are, respectively, apex angle θ1 = θ1' = 59°, angle θ2 = θ2' = 46° of the light-emitting surface, and remaining angle θ3 = θ3' = 75°. Even if the refractive index difference Δn between the refractive index nx and the refractive index ny (or the refractive index nz) is small, by combining two or more anisotropic prism sheets, it is possible to provide a large offset angle between the forward and backward paths, which increases the freedom of selection of the constituent materials of the anisotropic prism sheet and the design of the prisms.

[0108] 36 illustrates a configuration example of a projection device (projection device 6B) according to another modification 3 of the present disclosure. The configuration in which reflection by the reflecting mirror 20 is limited to the return path is also effective for a windshield 41 having a curved surface.

[0109] 36, similar to the above-described Other Modification 1, illustrates a case where the field of view (FOV) in the vertical direction (Z-axis direction) of the human eye (e.g., observer 100) is ±10°. Light L emitted from display device 10 passes, for example, through polarizing plate 11, −λ / 4 wavelength plate 51, windshield 41A, +λ / 4 wavelength plate 52, special retroreflector group 30, +λ / 4 wavelength plate 52, and windshield 41A in this order before entering the eye of observer 100. The emission angle distribution of light L emitted from display device 10 can be controlled to enter the eye of observer 100 at ±10°, taking into account the inclination at each location on the curved surface of windshield 41A; for example, this is set to ±6° in this modification.

[0110] In this way, even when reflection from the curved windshield 41A is limited to the return path, the present technology can obtain the same effect.

[0111] Although the present disclosure has been described above with reference to the embodiment and modifications 1 to 4 and other modifications, it should be understood that various modifications are possible and that the present disclosure is not limited to the above-described embodiment, etc. For example, the arrangement and number of components of the optical system exemplified in the above-described embodiment, etc. are merely examples, and it is not necessary to include all of the components, and other components may also be included.

[0112] The effects described in this specification are merely examples and are not limited to those described, and other effects may also be obtained.

[0113] The present technology can also be configured as follows. According to the present technology configured as follows, light emitted from a display device is guided via a first polarizing optical element and a reflecting mirror to a special retroreflection group including an anisotropic prism sheet, a second polarizing optical element, and a retroreflection element. The light incident on the special retroreflection group is reflected with an offset angle in a predetermined direction, making it possible to create a wide-angle virtual image without using, for example, a huge mirror optical system. This makes it possible to provide a projection device capable of displaying a wide-FOV virtual image, and a mobile object equipped with the same. (1) A projection device comprising: a display device; a first polarizing optical element that rectifies the polarization of light emitted from the display device; a reflecting mirror; and a special retroreflection group that includes an anisotropic prism sheet having refractive index anisotropy, a second polarizing optical element, and a retroreflection element, and that reflects the light rectified by the first polarizing optical element toward the reflecting mirror at a predetermined offset angle relative to the incident direction. (2) The anisotropic prism sheet has ridge lines extending in approximately the same direction and includes a plurality of prisms arranged in a direction perpendicular to the extension direction of the ridge lines, where the extension direction of the ridge lines is defined as a first direction, the arrangement direction of the plurality of prisms is defined as a second direction, and the thickness direction of the anisotropic prism sheet is defined as a third direction, and the refractive index in the first direction is defined as a first refractive index, the refractive index in the second direction is defined as a second refractive index, and the refractive index in the third direction is defined as a third refractive index, the first refractive index is greater than the second refractive index and the third refractive index. (3) The projection device described in (2), where the first refractive index and the second refractive index have a refractive index difference of 0.2 or more. (4) The projection device described in (2) or (3), where the second refractive index and the third refractive index are equal. (5) The projection device described in any one of (1) to (4), where the second polarizing optical element is disposed between the anisotropic prism sheet and the retroreflective element. (6) The projection device according to any one of (1) to (5), wherein the first polarizing optical element is a polarizing plate that polarizes the light emitted from the display device in a predetermined direction or selectively transmits predetermined polarized light.(7) The projection device according to any one of (1) to (6), wherein the second polarizing optical element is a λ / 4 wave plate. (8) The projection device according to any one of (1) to (7), further comprising a -λ / 4 wave plate and a +λ / 4 wave plate, wherein the -λ / 4 wave plate is arranged after the display device, and the +λ / 4 wave plate is arranged before the special retroreflection group. (9) The projection device according to any one of (1) to (8), further comprising a diffraction element, wherein the diffraction element is arranged on the optical path of the light between the display device and the special retroreflection group. (10) The projection device according to any one of (1) to (9), wherein the special retroreflection group further comprises a louver film in which absorbing portions and transparent portions, each extending in one direction, are arranged alternately, and the louver film is arranged between the second polarizing optical element and the retroreflection element. (11) The projection device according to (10), wherein the extension direction of the absorbing portion and the transparent portion substantially coincides with the extension direction of the ridge lines of the plurality of prisms. (12) The projection device according to any one of (1) to (11), wherein the special retroreflection group has a plurality of the anisotropic prism sheets on the optical path of the light. (13) The projection device according to any one of (1) to (12), wherein the reflective surface of the reflective mirror is curved. (14) The projection device according to any one of (1) to (13), wherein the light emitted from the display device enters the special retroreflection group via the reflective mirror. (15) The projection device according to any one of (1) to (14), wherein the light emitted from the display device enters the special retroreflection group without passing through the reflective mirror. (16) The projection device according to any one of (1) to (15), wherein the anisotropic prism sheet is formed using a crystalline resin material or a liquid crystal polymer. (17) The projection device according to (16), wherein the resin material is polyethylene naphthalate, polyethylene terephthalate, or aramid.(18) A mobile body comprising: a vehicle body; and a projection device attached to the vehicle body, wherein the projection device comprises: a display device; a first polarizing optical element that rectifies the polarization of light emitted from the display device; a reflecting mirror; and a special retroreflection group that includes an anisotropic prism sheet having refractive index anisotropy, a second polarizing optical element, and a retroreflection element, and that reflects the light rectified by the first polarizing optical element toward the reflecting mirror at a predetermined offset angle with respect to the incident direction.

[0114] This application claims priority based on Japanese Patent Application No. 2024-031599, filed on March 1, 2024, in the Japan Patent Office, the entire contents of which are incorporated herein by reference.

[0115] Those skilled in the art will recognize that various modifications, combinations, subcombinations, and variations may occur depending on design requirements and other factors, and are intended to be within the scope of the appended claims and their equivalents.

Claims

1. A projection device comprising: a display device; a first polarizing optical element that rectifies the polarization of light emitted from the display device; a reflecting mirror; and a special retroreflection group that includes an anisotropic prism sheet having refractive index anisotropy, a second polarizing optical element, and a retroreflection element, and that reflects the light rectified by the first polarizing optical element toward the reflecting mirror at a predetermined offset angle with respect to the incident direction.

2. The projection device described in claim 1, wherein the anisotropic prism sheet has ridge lines that extend in approximately the same direction and includes a plurality of prisms arranged in a direction perpendicular to the extension direction of the ridge lines, and wherein the extension direction of the ridge lines is defined as a first direction, the arrangement direction of the plurality of prisms is defined as a second direction, and the thickness direction of the anisotropic prism sheet is defined as a third direction, and the refractive index in the first direction is defined as a first refractive index, the refractive index in the second direction is defined as a second refractive index, and the refractive index in the third direction is defined as a third refractive index, the first refractive index is greater than the second refractive index and the third refractive index.

3. The projection device according to claim 2, wherein the difference between the first refractive index and the second refractive index is 0.2 or more.

4. The projection device of claim 2, wherein the second refractive index and the third refractive index are equal.

5. The projection device of claim 1, wherein the second polarizing optical element is disposed between the anisotropic prism sheet and the retroreflective element.

6. The projection device according to claim 1, wherein the first polarizing optical element is a polarizing plate that polarizes the light emitted from the display device in a predetermined direction or selectively transmits predetermined polarized light.

7. The projection device of claim 1, wherein the second polarizing optical element is a λ / 4 wave plate.

8. The projection device of claim 1, further comprising a -λ / 4 wave plate and a +λ / 4 wave plate, wherein the -λ / 4 wave plate is disposed after the display device, and the +λ / 4 wave plate is disposed before the special retroreflecting group.

9. The projection device according to claim 1, further comprising a diffraction element, said diffraction element being disposed on the optical path of said light between said display device and said special retroreflection group.

10. The projection device of claim 1, wherein the special retroreflective group further comprises a louver film in which absorbing sections and transparent sections, each extending in one direction, are arranged alternately, and the louver film is arranged between the second polarizing optical element and the retroreflective element.

11. The projection device according to claim 10, wherein the extending direction of said absorbing portion and said transparent portion substantially coincides with the extending direction of the ridge lines of said plurality of prisms.

12. The projection device according to claim 1, wherein the special retroreflection group has a plurality of the anisotropic prism sheets on the optical path of the light.

13. The projection device according to claim 1, wherein the reflecting surface of said reflecting mirror is curved.

14. The projection device according to claim 1, wherein the light emitted from the display device is incident on the special retroreflection group via the reflecting mirror.

15. The projection device according to claim 1, wherein the light emitted from the display device is incident on the special retroreflection group without passing through the reflecting mirror.

16. The projection device according to claim 1, wherein the anisotropic prism sheet is formed using a crystalline resin material or a liquid crystal polymer.

17. The projection apparatus according to claim 16, wherein the resin material is polyethylene naphthalate, polyethylene terephthalate, or aramid.

18. A mobile body comprising: a vehicle body; and a projection device attached to the vehicle body, wherein the projection device comprises: a display device; a first polarizing optical element that rectifies the polarization of light emitted from the display device; a reflecting mirror; and a special retroreflecting group that includes an anisotropic prism sheet having refractive index anisotropy, a second polarizing optical element, and a retroreflecting element, and that reflects the light rectified by the first polarizing optical element toward the reflecting mirror at a predetermined offset angle with respect to the incident direction.

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