Polarization conversion element and image projection device

Abstract

This polarization conversion element comprises: a translucent holding part (13) which is constituted of a material that transmits light; a reflection-type polarization part (14) which is formed on one surface of the translucent holding part (13), reflects polarized-light in a prescribed direction as reflection light, and transmits polarized-light in a direction intersecting the prescribed direction as transmission light; a half-wave plate (15) which is formed on the other surface of the translucent holding part (13) and converts the polarization direction of the transmission light to the prescribed direction; and a reflection mirror which reflects the reflection light or the transmission light. The translucent holding part (13) has one end surface formed as an inclined surface (13a) which is non-perpendicular to the one surface.

Description

Polarization conversion element and image projection device

[0001] The present disclosure relates to a polarization conversion element and an image projection device.

[0002] Conventionally, dashboards that illuminate icons have been used to display various types of information inside vehicles. As the amount of information to be displayed increases, it has been proposed to embed an image display device in the dashboard or to configure the entire dashboard with an image display device.

[0003] However, since the instrument panel is located below the windshield of the vehicle, in order for a driver or other passenger to view the information displayed on the instrument panel, the driver or other passenger must move his or her eyes downward while driving, which is undesirable. Therefore, image projection devices such as head-up displays (hereinafter referred to as HUDs) have been proposed that project images onto the windshield so that passengers can read information when they view the area ahead of the vehicle (see, for example, Patent Documents 1 and 2).

[0004] In the image projection devices of Patent Documents 1 and 2, an image display unit emits light containing an image, and the light is reflected by a free-form mirror or the like, and the light reaches the viewpoint of the occupant so that the image is formed in space via a display unit such as a windshield. This allows the occupant to perceive the image as being displayed at the imaging position in the depth direction due to the light incident on the viewpoint.

[0005] However, in an image projection device, when sunlight or other external light enters from the outside, the external light is concentrated on the surface of the image display unit by the free-form surface mirror, which can cause the temperature of the image display unit to rise and deteriorate. Therefore, it has been proposed to place an external light filter on the path of the external light to cut out ultraviolet and infrared light contained in the external light, thereby reducing the energy of the external light that reaches the image display unit and suppressing the temperature rise of the image display unit (see, for example, Patent Document 3).

[0006] Japanese Patent Publication No. 2019-119248 Japanese Patent Publication No. 2019-119262 Japanese Patent Publication No. 2023-055057

[0007] In conventional image projection devices, image display units such as liquid crystal display devices transmit only light polarized in a specific direction. Therefore, when unpolarized light is incident on the image display unit from a light source, light polarized in other directions is not used to project an image, resulting in reduced light utilization efficiency. Furthermore, the unpolarized light is absorbed by the image display unit, causing an increase in temperature in the image display unit, potentially adversely affecting its product lifespan. In particular, HUD devices project image light through the windshield and superimpose a virtual image onto the background outside the vehicle. Therefore, the amount of light emitted from the light source is much stronger than in monitor devices where the display screen is viewed directly, and the impact of temperature rise is greater.

[0008] Therefore, we considered placing a polarization conversion element between the light source and the image display unit to convert unpolarized light into polarized light in a specific direction to improve light utilization efficiency. However, polarization conversion elements have the problem of easily causing uneven brightness due to overlap or lack of light at the boundary between the area where polarization is converted and the area where it is not converted.

[0009] An object of the present disclosure is to provide a polarization conversion element and an image projection device that can increase the utilization efficiency of irradiated light and suppress brightness unevenness.

[0010] Furthermore, in conventional image projection devices, temperature rise in the image display unit can be suppressed by using an external light cut filter to cut out some wavelengths of external light, but because visible light is transmitted, there is a limit to how much temperature rise can be suppressed. Therefore, the inventors of the present application investigated using a polarizing plate as an external light cut filter, which transmits the light emitted from the image display unit and cuts light perpendicular to the polarization direction of the light. However, they found that the light transmitted through the polarizing plate has a difference in brightness between the center and edge regions of the polarizing plate, which can cause uneven brightness in the projected virtual image and reduce the visibility of the virtual image.

[0011] An object of the present disclosure is to provide an image projection device that can suppress brightness unevenness.

[0012] Furthermore, conventional image projection devices display a projection image using an image display unit such as a liquid crystal display device, and project the image light by irradiating it from the rear side of the image display unit. However, image display units such as liquid crystal display devices transmit only light polarized in a specific direction, so when unpolarized light is incident, light polarized in directions other than the specific direction is not used to project the image, resulting in a decrease in light utilization efficiency.

[0013] An object of the present disclosure is to provide an image projection device that can improve the utilization efficiency of irradiated light.

[0014] In order to solve the above problems, the polarization conversion element of the present disclosure comprises a translucency maintaining section made of a light-transmitting material, a reflective polarizing section formed on one surface of the translucency maintaining section and reflecting polarized light in a predetermined direction as reflected light and transmitting polarized light in a direction intersecting the predetermined direction as transmitted light, a half-wave plate formed on the other surface of the translucency maintaining section and converting the polarization direction of the transmitted light to the predetermined direction, and a reflecting mirror that reflects the reflected light or the transmitted light, and one end face of the translucency maintaining section is an inclined surface that is not perpendicular to the one surface.

[0015] In the polarization conversion element of the present disclosure, one end face of the translucency maintaining portion is made into an inclined surface, thereby preventing light from being refracted or reflected at the end face of the translucency maintaining portion at the boundary region between the half-wave plate and the reflecting mirror, thereby increasing the utilization efficiency of the irradiated light and suppressing brightness unevenness.

[0016] In order to solve the above problem, the image projection device disclosed herein is an image projection device that projects illumination light onto a display unit for displaying a virtual image, and includes an image illumination unit that irradiates the illumination light, and a polarizing unit that is arranged on the optical path of the illumination light and transmits polarized light in a predetermined direction and absorbs or reflects polarized light in a direction intersecting the predetermined direction, and the polarizing unit is curved in a concave shape on the incident side of the illumination light in the direction intersecting the predetermined direction.

[0017] In the image projection device of the present disclosure, the polarizing section is curved into a concave shape, which reduces the difference in transmittance of the irradiated light incident on the central region and the end region of the polarizing section, thereby making it possible to reduce uneven brightness of the virtual image.

[0018] In order to solve the above-described problems, the image projection device of the present disclosure includes a light source that emits unpolarized irradiation light, an image display unit that receives the irradiation light from a rear surface and emits image light from a display surface, a reflective polarizing unit that reflects light polarized in a first direction as a first light and transmits light polarized in a second direction intersecting the first direction as a second light, and a half-wave plate that is disposed on an optical path of the first light or the second light, wherein the first light is irradiated onto a first display region of the image display unit, the second light is irradiated onto a second display region, and the area of ​​the first display region is reduced to S １ and the area of ​​the second display region is S ２ where Pr is the reflectance of the first light in the reflective polarizing unit, Pt is the transmittance of the second light, and Pr / Pt is ２ / S １ is proportional to.

[0019] In the image projection device of the present disclosure, the reflective polarizing unit polarizes and separates the light emitted from the light source, and the half-wave plate rotates the polarization direction of one of the separated light beams. The ratio Pr / Pt of the reflectance Pr of the first light to the transmittance Pt of the second light in the reflective polarizing unit is adjusted to a value smaller than the area S of the first display region. １ and the area S of the second display area ２ Ratio S ２ / S １ By making the luminance proportional to the first display region, it is possible to improve the efficiency of use of the irradiated light and make the luminance of the first display region and the second display region uniform.

[0020] The present disclosure can provide a polarization conversion element and an image projection device that can increase the utilization efficiency of irradiated light and suppress brightness unevenness.

[0021] Furthermore, the present disclosure can provide an image projection device that can suppress uneven brightness.

[0022] Furthermore, the present disclosure can provide an image projection device that can improve the utilization efficiency of irradiated light.

[0023] 1 is a schematic diagram illustrating projection of a virtual image using an image projection device according to a first embodiment. FIG. 1 is a schematic cross-sectional view illustrating an overview of an image projection device according to a first embodiment. FIG. 2 is a schematic cross-sectional view illustrating an overview of an image projection unit according to a first embodiment. FIG. 3 is a partially enlarged schematic view illustrating an enlarged view of the vicinity of an end of a translucency maintaining unit located on the side closer to a first lens. FIG. 4 is a schematic cross-sectional view illustrating an overview of an image projection unit according to a second embodiment. FIG. 5 is a schematic cross-sectional view illustrating an overview of an image projection unit according to a third embodiment. FIG. 6 is an image showing a front view of image light in the image projection unit. FIG. 7 is a schematic cross-sectional view illustrating an overview of an image projection device according to a fourth embodiment. FIG. 8 is a schematic view illustrating the positional relationship between the curved shape of a polarizing unit and the image projection unit. FIG. 9 is a schematic view illustrating the inclination angle of the polarizing unit. FIG. 10 is a schematic view illustrating the curved shape of a polarizing unit and transmission of irradiation light. FIG. 11 is an image illustrating reduction of brightness unevenness by the polarizing unit. FIG. 12 is a schematic cross-sectional view illustrating a modification of the fourth embodiment. FIG. 13 is a schematic cross-sectional view illustrating an overview of an image projection unit according to a fifth embodiment. FIG. 14 is a schematic view illustrating details of a polarization conversion unit. FIG. 15 is a schematic cross-sectional view illustrating a modification of the fifth embodiment. FIG. 16 is a schematic cross-sectional view illustrating an overview of an image projection unit according to a sixth embodiment. FIG. 17 is a schematic cross-sectional view illustrating an overview of an image projection unit according to a seventh embodiment. FIG. 18 is a schematic cross-sectional view illustrating an overview of an image projection unit according to an eighth embodiment. Fig. 13 is a schematic cross-sectional view illustrating an overview of an image irradiation unit according to a ninth embodiment; Fig. 14 is a schematic cross-sectional view illustrating an overview of an image irradiation unit according to a tenth embodiment; Fig. 15 is a schematic cross-sectional view illustrating an overview of an image irradiation unit according to an eleventh embodiment;

[0024] First Embodiment Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the drawings. The same or equivalent components, members, and processes shown in each drawing will be denoted by the same reference numerals, and redundant explanations will be omitted as appropriate. In the following description, an example will be described in which an image projection device 100 according to the present disclosure is applied to a HUD mounted on a vehicle or the like.

[0025] FIG. 1 is a schematic diagram illustrating the projection of a virtual image using an image projection device 100 according to this embodiment. The dashed line in FIG. 1 indicates the optical path of a first image light L1 (described later), and the dashed-dotted line indicates the optical path of a second image light L2. As shown in FIG. 1, the first image light L1 and the second image light L2 projected from the image projection device 100 are reflected by a windshield (display unit) WS and irradiated toward the driver's viewpoint. The driver visually recognizes virtual images P10 and P20 formed on the extension of the optical paths from which the first image light L1 and the second image light L2 are incident. In this embodiment, the image projection device 100 projects the first image light L1 and the second image light L2, forming two images P10 and P20. However, the number of virtual images is not limited. The first image light L1 and the second image light L2 correspond to the irradiated light in this disclosure.

[0026] The windshield WS is a portion of the vehicle that is provided in front of the driver's seat and transmits visible light. The windshield WS reflects the first image light L1 and the second image light L2 incident from the image projection device 100 toward the viewpoint on the interior surface of the vehicle and transmits light from outside the vehicle toward the viewpoint. The windshield WS corresponds to the display unit in this disclosure. While an example in which the windshield WS is used as the display unit has been shown here, a combiner may be provided as a display unit separate from the windshield WS and reflect light from the image projection device 100 toward the viewpoint. Furthermore, the display unit is not limited to being located at the front of the vehicle, and may be located to the side or rear of the vehicle as long as it projects an image toward the viewpoint of the passenger.

[0027] The virtual images P10 and P20 are images that are displayed as if they were formed in space when the first image light L1 and the second image light L2 reflected by the windshield WS reach the viewpoint (eyebox) of the occupant. The positions at which the virtual images P10 and P20 are formed are determined by the combined focal length of the projection optical unit included in the image projection device 100 and the windshield WS.

[0028] In the image projection device 100 of this embodiment, a far image displayed in the far display area of ​​the image projection unit 10 is irradiated as a first image light L1, and a near image displayed in the near display area is irradiated as a second image light L2. Examples of far images displayed in the far display area include images calling attention to driving, emergency information, and other auxiliary information related to driving. Examples of near images displayed in the near display area include a speed and volume indicator, a driving direction guide, and the like.

[0029] FIG. 2 is a schematic cross-sectional view illustrating an overview of an image projection device 100 according to this embodiment. As shown in FIG. 2, the image projection device 100 includes an image projection unit 10, a first mirror 20, a second mirror 30, and a housing 40. In the image projection device 100, each unit is controlled using a control unit (not shown) connected to each unit so as to be able to communicate information with the unit. The configuration of the control unit is not limited, but an example includes a CPU (Central Processing Unit) for information processing, a memory device, a recording medium, an information communication device, and the like. The control unit controls the operation of each unit according to a predetermined program and sends information including an image (image information) to the image projection unit 10.

[0030] The image projection unit 10 is a part that, based on image information from the control unit, projects light containing an image onto the first mirror 20 as image light. In this embodiment, an example is shown in which two image lights displayed in two image display areas are projected onto the first mirror 20 as first image light L1 and second image light L2.

[0031] The first mirror 20 is an optical member that reflects the first image light L1 and the second image light L2 arriving from the image irradiation unit 10 toward the second mirror 30. In the example shown in Fig. 2, the first mirror 20 is a flat reflecting mirror, but a concave or convex reflecting mirror may also be used. Furthermore, when the first mirror 20 is configured with a curved surface, it is not limited to one with a constant curvature, and a paraboloid of revolution, an ellipsoid, a free-form surface mirror, or the like may be used.

[0032] The second mirror 30 is an optical member that reflects the first image light L1 and the second image light L2 that have arrived from the first mirror 20 toward the windshield WS. In the example shown in Fig. 1, the second mirror 30 is a free-form mirror with an optically designed concave shape necessary for projecting the first image light L1 and the second image light L2 as virtual images P10 and P20.

[0033] The reflective surfaces of the first mirror 20 and the second mirror 30 are designed to expand the light diameter in the driver's viewing direction in order to project the first image light L1 and the second image light L2 as virtual images P10 and P20 through the windshield WS. Here, "expanding the light diameter in the viewing direction" refers not only to the case where the light diameter consistently expands after reflection, but also to the case where the light diameter shrinks and then expands after forming an image at an intermediate point. The combination of the first mirror 20 and the second mirror 30 functions to project the first image light L1 and the second image light L2 through the windshield WS. The combination of the first mirror 20 and the second mirror 30 corresponds to the illumination optical unit in this disclosure.

[0034] 1 and 2, the optical paths of the first image light L1 and the second image light L2 are depicted as a single straight line. However, the actual first image light L1 and the second image light L2 are displayed in a predetermined area in the image projection unit 10, and have a predetermined area in a direction perpendicular to the traveling direction. Furthermore, the first image light L1 and the second image light L2 may be reflected by the first mirror 20, and their light diameters may be reduced as they travel, and they may form intermediate images at an intermediate image position F (not shown) between the first mirror 20 and the second mirror 30.

[0035] The housing 40 constitutes the outer shape of the image projection device 100 and is a container that houses each component. The housing 40 is provided with a light exit port for emitting the first image light L1 and the second image light L2. An angle adjustment unit for adjusting the angle of the second mirror 30 may be provided within the housing 40 to adjust the irradiation angle of the first image light L1 and the second image light L2 projected onto the windshield WS and change the imaging height of the virtual images P10 and P20. The housing 40 may also be provided with an optical filter that cuts out ultraviolet light and infrared light contained in light (external light) arriving from outside.

[0036] 3 is a schematic diagram illustrating an overview of the image projection unit 10 according to this embodiment. As shown in FIG. 3 , the image projection unit 10 according to this embodiment includes a light source 11, a first lens 12, a translucency maintaining unit 13, a reflective polarizing unit 14, a half-wave plate 15, a reflecting mirror 16, a second lens 17, a polarization-maintaining diffusion unit 18, and an image display unit 19. The combination of the translucency maintaining unit 13, the reflective polarizing unit 14, the half-wave plate 15, and the reflecting mirror 16 constitutes a polarization conversion element according to this disclosure. In the figure, the solid arrows indicate the optical paths of unpolarized light emitted from the light source 11, and the dashed arrows indicate the optical paths of light polarized in a predetermined direction and light polarized perpendicular to the predetermined direction.

[0037] The light source 11 is a component that irradiates unpolarized light onto the image display unit 19 via the first lens 12, the light-transmitting unit 13, the reflective polarizing unit 14, the half-wave plate 15, the reflecting mirror 16, the second lens 17, and the polarization-maintaining diffusion unit 18. The light source 11 is, for example, a semiconductor light-emitting element such as an LED (Light Emitting Diode), and is arranged in a predetermined direction (a direction perpendicular to the plane of the paper in FIG. 3 ). The color of light emitted by the light source 11 is not particularly limited, but in this embodiment, white light is used as an example. In this embodiment, the light source 11 is arranged in one row, but may be arranged in two or more rows. The light source 11 is not limited to an LED, and may be an organic EL (Electro Luminescence) element, for example.

[0038] The first lens 12 is an optical element disposed in the light emission direction of the plurality of light sources 11 and functions to condense the light emitted from the light sources 11 and emit the light as, for example, parallel light or light close to parallel light (hereinafter, both of these will be collectively referred to as "substantially parallel light"). The first lens 12 extends along the arrangement direction of the plurality of light sources 11. In this embodiment, as an example of the first lens 12, a TIR (Total Internal Reflection) lens (not shown) is used, which has a refracting portion at the center that refracts light and reflective portions that reflect light on both sides of the refracting portion. While FIG. 3 illustrates the first lens 12 as extending in the arrangement direction of the light sources 11, multiple collimating lenses may be provided for each light source 11. Furthermore, the first lens 12 is not limited to a lens as long as it can convert the light from the light sources 11 into substantially parallel light. A combination of a reflector and a lens, or a configuration in which a reflector alone can convert the light into substantially parallel light, may also be used.

[0039] The polarization conversion element, which is composed of a combination of translucency maintaining unit 13, reflective polarizing unit 14, half-wave plate 15, and reflecting mirror 16, is an optical component that is disposed on the light exit side of first lens 12 and converts unpolarized irradiated light into a polarization direction along a predetermined direction (first direction) and emits the light as backlight. Here, an example is shown in which sheet-like members are used as half-wave plate 15 and reflective polarizing unit 14 and attached to translucency maintaining unit 13, but they may also be formed directly on the surface of translucency maintaining unit 13 by vapor deposition or the like.

[0040] The translucency maintaining unit 13 is a member made of a material that transmits light. A reflective polarizing unit 14 is attached to the incident surface of the translucency maintaining unit 13, and a half-wave plate 15 is attached to the surface opposite the reflective polarizing unit 14. While FIG. 3 shows an example in which the translucency maintaining unit 13 is plate-shaped and tilted at a 45-degree angle with respect to the direction of travel of the light irradiated from the first lens 12, the shape and tilt angle are not limited as long as the translucency maintaining unit 13 has a shape that can hold the reflective polarizing unit 14 on one surface and the half-wave plate 15 on the other surface. The material constituting the translucency maintaining unit 13 is not limited, and glass, acrylic resin, polycarbonate resin, etc. can be used. However, it is preferable to use a retardation-free material that does not cause a phase difference in the transmitted light. The thickness of the translucency maintaining unit 13 is not limited, and a thickness of approximately 0.5 mm to 3.0 mm can be used, for example.

[0041] The reflective polarizer 14 is an optical element attached to one surface of the translucency maintaining unit 13, which transmits polarized light in a predetermined direction as transmitted light and reflects polarized light perpendicular to the predetermined direction as reflected light. The polarization direction of the light transmitted by the reflective polarizer 14 is not limited, and must be matched to the polarization direction required for the backlight ultimately irradiated onto the image display unit 19. As an example, the reflective polarizer 14 may transmit polarized light in the horizontal direction (e.g., p-polarized light) in FIG. 3 and reflect polarized light perpendicular to the paper surface (e.g., s-polarized light). The specific configuration of the reflective polarizer 14 is not limited, but it is preferable to use a plate- or sheet-shaped polarizer that can be attached to the surface of the translucency maintaining unit 13. Examples that can be used include the reflective polarizing film WGF manufactured by Asahi Kasei Corporation and a reflective polarizing plate film manufactured by 3M Japan Ltd.

[0042] The half-wave plate 15 is an optical element made of a birefringent material having different refractive indices in the slow axis and the fast axis and is attached to the other surface of the translucency maintaining unit 13. The half-wave plate 15 is designed so that a phase difference of half the wavelength of incident light occurs between the slow axis and the fast axis before the light is emitted. The slow axis and the fast axis of the half-wave plate 15 are oriented 45 degrees apart from the polarization direction of the irradiated light transmitted through the reflective polarizing unit 14. Therefore, the polarization of the irradiated light transmitted through the half-wave plate 15 is rotated 90 degrees in-plane. As a result, the light transmitted through the reflective polarizing unit 14 and the half-wave plate 15 and the light reflected by the reflective polarizing unit 14 and the half-wave plate 15 are irradiated as backlight light having the same predetermined polarization direction. Furthermore, the half-wave plate 15 does not need to have a phase difference of exactly 50% with respect to the wavelength of light; as long as it generates a phase difference close to 50%, it can perform the function of rotating the polarization direction in the plane. There are no specific limitations on the configuration of the half-wave plate 15, but it is preferable to use a plate- or sheet-shaped plate that can be attached to the surface of the translucency maintaining unit 13. As an example, an achromatic half-wave plate manufactured by Dexerials Corporation can be used.

[0043] 3, the reflecting mirror 16 is disposed opposite the reflective polarizing unit 14, and reflects the light reflected by the reflective polarizing unit 14 toward the second lens 17. The reflecting mirror 16 is disposed at an angle of 45 degrees with respect to the traveling direction of the light reflected from the reflective polarizing unit 14, and the reflecting mirror 16 and the reflective polarizing unit 14 are substantially parallel to each other.

[0044] The second lens 17 controls the light flux of the backlight irradiated through the polarization conversion element so that the entire illumination area is uniformly illuminated. Therefore, the shape and positive / negative power of the second lens 17 are selected to suit this purpose. In this embodiment, a concave lens is used as an example of the second lens 17. If the entire illumination area is configured to be uniformly illuminated using only the first lens 12, the second lens 17 may be omitted. The first lens 12 and the second lens 17 are formed of, for example, a resin such as acrylic resin, glass, or the like. The first lens 12 and the second lens 17 function together to guide light emitted from the light source 11 to the illumination area of ​​the image display unit 19. In this embodiment, the illumination area is, for example, the rear surface of the polarization-maintaining diffusion unit 18 (the surface facing the light source 11). However, the illumination area may be determined taking into account the specifications of the light source device, and may be, for example, the rear surface of the image display unit 19.

[0045] The polarization-maintaining diffuser 18 is an optical element disposed on the rear side of the image display unit 19, which diffuses and transmits backlight converted by the polarization conversion element while maintaining its polarization direction. The polarization-maintaining diffuser 18 diffuses the highly directional light polarized by the first lens 12 and the second lens 17 and outputs the light to the image display unit 19, thereby illuminating the image display unit 19 more uniformly. The polarization-maintaining diffuser 18 may diffuse only light polarized in a first direction while maintaining its polarization, or may diffuse light polarized in all directions while maintaining its polarization. The specific configuration of the polarization-maintaining diffuser 18 is not limited, but an example of such a diffuser is a sheet manufactured by Lintec Corporation under the trade name HH120.

[0046] The image display unit 19 functions as a spatial light modulation unit that receives backlight that has passed through the polarization-maintaining diffusion unit 18 from the rear surface, modulates the light according to image information, and emits the modulated light from the emission surface. The specific configuration of the image display unit 19 is not limited, but one example is a transmissive liquid crystal display device that transmits light that enters from the rear surface and emits it from the front surface. In a transmissive liquid crystal display device, only light polarized in a specific direction that enters the rear surface is transmitted, and therefore the polarization direction in the polarization conversion element and polarization-maintaining diffusion unit 18 is made to coincide with this specific direction.

[0047] In the image projection device 100 described above, the illumination light emitted from the light source 11 is unpolarized, with no limitation on the polarization direction. The illumination light emitted from the light source 11 is incident on the first lens 12, where it is collimated, and then incident on the reflective polarization unit 14. A portion of the illumination light incident on the reflective polarization unit 14 is transmitted, and another portion is reflected toward the reflecting mirror 16. Here, the polarization of the illumination light reflected by the reflective polarization unit 14 is polarized in a first direction, which is the direction of transmission through the image display unit 19. Furthermore, the polarization of the illumination light that transmits through the reflective polarization unit 14 is polarized in a second direction that is approximately perpendicular to the first direction.

[0048] The transmitted light that has passed through reflective polarizing unit 14 passes through translucency maintaining unit 13 and enters half-wave plate 15, where its polarization direction is rotated by 90 degrees, and the light is irradiated onto second lens 17 as backlight light polarized in the first direction. In addition, the reflected light that has reached reflecting mirror 16 is reflected and irradiated onto second lens 17 as backlight light polarized in the first direction. The backlight light that has reached second lens 17 has its light distribution adjusted and reaches polarization-maintaining diffusion unit 18.

[0049] In polarization-maintaining diffusion section 18, backlight polarized in the first direction is diffused and transmitted as light polarized in the first direction while maintaining its polarization direction, thereby uniformly irradiating the back surface of image display section 19 with backlight polarized in the first direction. Here, "maintaining the polarization direction" means that the polarization state at the time of incidence is maintained at more than 50% on an energy basis before and after transmission through polarization-maintaining diffusion section 18, and more preferably at least 90%.

[0050] 4 is a partially enlarged schematic diagram showing the vicinity of the end of the translucency maintaining unit 13 located closer to the second lens 17. As shown in Fig. 4, the end face of the translucency maintaining unit 13 is chamfered to form an inclined surface 13a that is inclined non-perpendicularly with respect to the surface to which the reflective polarizing unit 14 is attached. Here, the end face on which the inclined surface 13a is formed is the end face of the translucency maintaining unit 13 closer to the second lens 17, and is located at the boundary between the region irradiated with the light reflected by the reflecting mirror 16 and the region whose polarization direction is converted by the half-wave plate 15.

[0051] In FIG. 4 , the translucency maintaining unit 13 is disposed at a 45-degree angle with respect to the traveling direction of light from the light source 11, and therefore the inclined surface 13a is formed by inclining it at 45 degrees with respect to one surface of the translucency maintaining unit 13 to which the reflective polarizing unit 14 is attached. Here, the inclined surface 13a is inclined at 45 degrees with respect to the one surface, but the angle of inclination is not limited as long as it is provided along the traveling direction of light incident on the reflective polarizing unit 14. Also, as shown in FIG. 4 , the reflective polarizing unit 14 and the half-wave plate 15 may have end positions that are different from each other in a plan view of the translucency maintaining unit 13. In this case, the inclination angle of the inclined surface 13a may be provided along the direction connecting the end of the reflective polarizing unit 14 and the end of the half-wave plate 15.

[0052] 4 shows an example in which the inclined surface 13a is formed as a flat surface, but the shape is not limited as long as it can prevent the irradiated light L from reaching the end of the translucency maintaining unit 13. As an example, the inclined surface 13a may be a curved surface with a predetermined curvature, or the inclined surface 13a may be composed of a plurality of surfaces with a plurality of inclination angles. Furthermore, while FIG. 4 shows an example in which the inclined surface 13a is formed from one surface to the other surface of the translucency maintaining unit 13, the inclined surface 13a may be formed only at the corner on the light incident side.

[0053] In Figure 4, the shape of the end face of the translucency preserving unit 13 without chamfering the inclined surface 13a is shown by a dashed line. The optical path of part of the irradiated light L emitted from the light source 11 is also shown by a dashed arrow. As shown in Figure 4, in the polarization conversion element and image projection unit 10 of this embodiment, the end of the translucency preserving unit 13 is chamfered to form the inclined surface 13a, so that the irradiated light L traveling at a position outside the reflective polarization unit 14 does not reach the translucency preserving unit 13. This prevents the irradiated light L from directly entering the end of the translucency preserving unit 13 and being refracted or reflected to become stray light. This prevents the generation of bright or dark lines in the boundary region between the half-wave plate 15 and the reflecting mirror 16, thereby improving the utilization efficiency of the irradiated light and suppressing brightness unevenness.

[0054] As described above, in the polarization conversion element and image projection device 100 of this embodiment, one end face of the translucency maintaining portion 13 is formed as an inclined surface 13a, which prevents light from being refracted or reflected at the end face of the translucency maintaining portion 13 in the boundary region between transmitted light and reflected light in the reflective polarization portion 14, thereby increasing the utilization efficiency of the irradiated light and suppressing brightness unevenness.

[0055] Second Embodiment Next, a second embodiment of the present disclosure will be described with reference to FIG. 5. Description of content that overlaps with the first embodiment will be omitted. FIG. 5 is a schematic diagram illustrating an overview of an image projection unit 10 according to this embodiment. This embodiment differs from the first embodiment in the arrangement of a light source 11 and a first lens 12, and the arrangement of a light transmissivity maintaining unit 13, a reflective polarizing unit 14, a half-wave plate 15, and a reflecting mirror 16 in the polarization conversion element.

[0056] As shown in Fig. 5, image projection device 100 includes light source 11, first lens 12, translucency maintaining unit 13, reflective polarizing unit 14, half-wave plate 15, reflecting mirror 16, second lens 17, polarization-maintaining diffusion unit 18, and image display unit 19. As shown in Fig. 2, in image projection device 100 of this embodiment, the light entrance surface and light exit surface of the polarization conversion element are substantially perpendicular to each other. Therefore, the traveling direction of the illumination light emitted from light source 11 and first lens 12 is perpendicular to the traveling direction of the backlight emitted from the polarization conversion element.

[0057] 5, the light emitted from the light source 11 is unpolarized, enters the first lens 12 and is collimated, and then enters the reflective polarizing unit 14 provided on the incident surface of the translucency maintaining unit 13. A portion of the light incident on the reflective polarizing unit 14 is transmitted toward the reflecting mirror 16, and another portion is reflected. Here, the polarization of the reflected light reflected by the reflective polarizing unit 14 is polarized in a first direction in which light is transmitted through the image display unit 19. Furthermore, the polarization of the transmitted light that passes through the reflective polarizing unit 14 is polarized in a second direction that is approximately perpendicular to the first direction.

[0058] The transmitted light that has passed through the reflective polarizing unit 14 passes through the translucency maintaining unit 13 and enters the half-wave plate 15. The half-wave plate 15 rotates the polarization direction of the transmitted light by 90 degrees, converting it into light polarized in a first direction and reaching the reflecting mirror 16. The transmitted light that has reached the reflecting mirror 16 is reflected and irradiated onto the second lens 17 as backlight polarized in the first direction. In addition, the reflected light reflected by the reflective polarizing unit 14 is irradiated onto the second lens 17 as backlight polarized in the first direction.

[0059] In the polarization conversion element and image projection device 100 of this embodiment, one end face of the translucency maintaining unit 13 is chamfered to form an inclined surface 13a. In this embodiment, the traveling direction of the light emitted from the light source 11 is the horizontal direction in the figure, so the inclined surface 13a is also formed along the horizontal direction in the figure. Also in this embodiment, the end face on which the inclined surface 13a is formed is the side of the end faces of the translucency maintaining unit 13 that is closer to the second lens 17, and is located at the boundary between the area irradiated with the light reflected by the reflecting mirror 16 and the area whose polarization direction is converted by the half-wave plate 15.

[0060] As described above, in the polarization conversion element and image projection device 100 of this embodiment, one end face of the translucency maintaining portion 13 is formed as an inclined surface 13a, which prevents light from being refracted or reflected at the end face of the translucency maintaining portion 13 in the boundary region between transmitted light and reflected light in the reflective polarization portion 14, thereby increasing the utilization efficiency of the irradiated light and suppressing brightness unevenness.

[0061] Third Embodiment Next, a third embodiment of the present disclosure will be described with reference to Figs. 6 and 7. Description of content that overlaps with the first embodiment will be omitted. Fig. 6 is a schematic diagram illustrating an overview of an image projection unit 10 according to the embodiment. This embodiment differs from the first embodiment in that a lenticular lens portion 17a is formed on the light incident surface side of the second lens 17.

[0062] Lenticular lens portion 17a has an uneven shape formed on the light incident surface side of second lens 17, and the unevenness extends in a direction perpendicular to the plane of paper in Fig. 6. The extending direction of lenticular lens portion 17a is along the boundary between the area irradiated with the reflected light reflected by reflecting mirror 16 and the area whose polarization direction is converted by half-wave plate 15, and is also along the extending direction of inclined surface 13a.

[0063] In the polarization conversion element and image projection device 100 of this embodiment, transmitted light that has passed through the reflective polarization unit 14 also passes through the translucency maintaining unit 13 and enters the half-wave plate 15, where its polarization direction is rotated by 90 degrees and the light is irradiated onto the second lens 17 as backlight light polarized in the first direction. Furthermore, reflected light that reaches the reflecting mirror 16 is reflected and irradiated onto the second lens 17 as backlight light polarized in the first direction. The backlight light that has reached the second lens 17 has its light distribution adjusted and reaches the polarization-maintaining diffusion unit 18. At this time, the backlight light polarized in the first direction is refracted and spread in the left-right direction of the page by the lenticular lens unit 17a, thereby reducing brightness unevenness at the boundary between the area irradiated with the reflected light and the area whose polarization direction has been converted by the half-wave plate 15.

[0064] The shape and size of the lenticular lens portion 17a are not limited, but the pitch of the concaves and convexes may be designed to correspond to the size of the inclined surface 13a. As an example, when the chamfer width of the inclined surface 13a shown in FIG. 4 is D, the pitch may be set to a range of 0.3D to 1.8D. Here, the chamfer width of the inclined surface 13a is the width in the left-right direction of the region indicated by the dashed line in FIG. 4, and corresponds to the width of the virtual translucency maintaining portion 13 removed by the inclined surface 13a. By setting the concave-convex pitch of the lenticular lens portion 17a within this numerical range, brightness unevenness can be effectively improved.

[0065] 7A and 7B are images showing a front view of the image light in the image projection unit 10, with (a) of FIG. 7A showing a case where the lenticular lens unit 17a is not provided, and (b) of FIG. 7A showing a case where the lenticular lens unit 17a is provided. In (a) and (b) of FIG. 7A, the vertical direction of the image corresponds to the horizontal direction in FIG. 6, and the longitudinal direction of the image corresponds to the direction perpendicular to the paper surface in FIG. 6. In the example shown in (a) of FIG. 7A, bright and dark lines appear along the longitudinal direction of the image near the vertical center of the figure, causing brightness unevenness. In the example shown in (b) of FIG. 7A, the bright and dark lines along the longitudinal direction of the image have disappeared, suppressing brightness unevenness.

[0066] As described above, in the polarization conversion element and image projection device 100 of this embodiment, one end face of the translucency maintaining unit 13 is formed as the inclined face 13a, which prevents light from being refracted or reflected at the end face of the translucency maintaining unit 13 in the boundary region between transmitted light and reflected light in the reflective polarizing unit 14, thereby improving the utilization efficiency of the irradiated light and suppressing brightness unevenness. Furthermore, the provision of the lenticular lens portion 17a in the second lens 17 reduces bright lines and dark lines that appear in the boundary region between transmitted light and reflected light in the reflective polarizing unit 14, thereby further suppressing brightness unevenness.

[0067] (Fourth embodiment)

[0068] Next, a fourth embodiment of the present disclosure will be described with reference to Fig. 8 to Fig. 13. Fig. 8 is a schematic cross-sectional view illustrating an overview of an image projection device 100 according to this embodiment. As shown in Fig. 8, the image projection device 100 includes an image irradiation unit 10, a first mirror 20, a second mirror 30, a housing 40, and a polarization unit 50.

[0069] The image projection unit 10 is a part that projects light containing an image onto the first mirror 20 as image light based on image information from the control unit. In this embodiment, an example is shown in which two image lights displayed in two image display areas are projected onto the first mirror 20 as first image light L1 and second image light L2 (see FIG. 1 ). Hereinafter, the first image light L1 and the second image light L2 may be simply referred to as image light.

[0070] The first mirror 20 is an optical member that reflects the first image light L1 and the second image light L2 that arrive from the image projection unit 10 toward the second mirror 30. The second mirror 30 is an optical member that reflects the first image light L1 and the second image light L2 that arrive from the first mirror 20 toward the windshield WS. The housing 40 constitutes the outer shape of the image projection device 100 and is a container that houses each component. Note that the image projection unit 10, the first mirror 20, the second mirror 30, and the housing 40 have the same configurations as in the first embodiment, and therefore detailed description thereof will be omitted.

[0071] The polarizing unit 50 is an optical element having optical properties of transmitting polarized light in the transmission axis direction and reflecting or absorbing polarized light perpendicular to the transmission axis direction, and a known polarizing plate or polarizing film can be used. Furthermore, it is preferable that the transmittance of the transmission axis is uniform within the plane of the polarizing unit 50. The polarizing unit 50 is fixed to the image irradiation unit 10 or the housing 40 by a fixing member or the like (not shown). Here, the transmission axis direction of the polarizing unit 50 corresponds to the predetermined direction in this disclosure, and the direction perpendicular to the transmission axis direction corresponds to the direction intersecting the predetermined direction in this disclosure.

[0072] As shown in FIG. 8 , in this embodiment, the polarizing unit 50 is disposed between the image irradiating unit 10 and the first mirror 20. The polarizing unit 50 is disposed at an angle with respect to the traveling direction of the first image light L1 and the second image light L2 emitted from the image irradiating unit 10. The polarizing unit 50 is curved and extends in a direction perpendicular to the plane of the paper in FIG. 8 . The curved shape of the polarizing unit 50 will be described later. While FIG. 8 shows an example in which the polarizing unit 50 is configured from a single plate-like member, the polarizing unit 50 may also have a structure in which a polarizing sheet is bonded to a light-transmitting substrate such as a glass plate. Sheets that perform other optical functions may also be bonded to the polarizing unit 50 to achieve multiple functions. For example, an infrared light blocking filter or an ultraviolet light blocking filter may be bonded to the polarizing unit 50.

[0073] 8 shows an example in which the polarizing unit 50 is disposed between the image projection unit 10 and the first mirror 20, but the position of the polarizing unit 50 is not limited as long as it is on the optical path of the first image light L1 and the second image light L2 from the image projection unit 10 to the windshield WS. The transmission axis of the polarizing unit 50 is oriented in a direction corresponding to the polarization direction of the first image light L1 and the second image light L2 emitted from the image projection unit 10. The transmission axis of the polarizing unit 50 is preferably disposed so as to transmit P-polarized light with respect to the windshield WS.

[0074] FIG. 9 is a schematic diagram showing the positional relationship between the curved shape of the polarizing unit 50 and the image projection unit 10, with FIG. 9(a) being a schematic perspective view and FIG. 9(b) being a schematic plan view. The opening provided in the image projection unit 10 is a portion through which image light is projected toward the first mirror 20, and the polarizing unit 50 is disposed at a position corresponding to the opening. As shown in FIG. 9 , the polarizing unit 50 has a shape curved along the longitudinal direction and is disposed so that its concave shape faces the side onto which the image light projected from the image projection unit 10 is incident. Here, the transmission axis of the polarizing unit 50 is in the lateral direction, which is perpendicular to the curved longitudinal direction. Therefore, the polarizing unit 50 is curved in a concave shape toward the side onto which the image light (projected light) is incident in a direction (longitudinal direction) intersecting the polarization direction (predetermined direction) of the image light (projected light).

[0075] The curved shape of the polarizing unit 50 depends on the spread angle of the image light (illumination light) emitted from the opening of the image projection unit 10, and examples thereof include an arc, an ellipse, a parabola, a hyperbola, and a free curve. The curvature may vary partially depending on the spread angle of the image light. The average curvature of the polarizing unit 50 is preferably in the range of 25 mm to 200 mm.

[0076] 10 is a schematic diagram illustrating the tilt angle of the polarization unit 50, where (a) of FIG. 10 shows a case where the irradiation light from the image irradiation unit 10 is irradiated at an angle, and (b) of FIG. 10 shows a case where the irradiation light from the image irradiation unit 10 is irradiated perpendicularly. The dashed line in the figure schematically shows the traveling direction of the image light irradiated from the image irradiation unit 10. The arrow perpendicular to the dashed line in the figure shows the polarization direction of the image light. Here, the traveling direction of the image light is the path of the light located at the center of the image light, and is, for example, a line connecting the center position of the image display unit provided in the image irradiation unit 10 and the center position of the area that reflects the image light on the first mirror 20.

[0077] As shown in (a) of Figure 10, the polarizing unit 50 is disposed at a predetermined angle θ1 with respect to the traveling direction and polarization direction (predetermined direction) of the image light (illumination light). When the image light is emitted perpendicularly from an image display unit such as a liquid crystal display device provided in the image projection unit 10, the polarization direction of the image light coincides with the display surface of the image display unit. Therefore, as shown in (b) of Figure 10, the predetermined angle θ1 can be regarded as the angle formed by the image display unit and the polarizing unit 50. Here, the predetermined angle θ1 is preferably in the range of 0 degrees or more and 55 degrees or less. By setting the predetermined angle θ1 in this range, it is possible to suppress the occurrence of double images and to dissipate heat from the image projection unit 10.

[0078] FIG. 11 is a schematic diagram illustrating the curved shape of the polarizing unit 50 and the transmission of irradiated light. The arrows in the figure schematically indicate the spread of image light irradiated from the image irradiating unit 10 at each position. In the polarizing unit 50, the transmittance of polarized light in the transmission axis direction depends on the angle of incidence, and the transmittance tends to decrease when the angle of incidence is large (a large deviation from the perpendicular). However, in this embodiment, as shown in FIG. 11 , the polarizing unit 50 is curved in a concave shape toward the image light incident side. Therefore, the angle of incidence of the expanding image light on the polarizing unit 50 becomes small at each position, and the image light reaches the polarizing unit 50 at an angle close to the perpendicular. This reduces the difference in transmittance between the central region and the end region of the polarizing unit 50, making it possible to suppress uneven brightness in the formed virtual image.

[0079] 12 are images illustrating the reduction of brightness unevenness by the polarizing unit 50, where (a) in FIG. 12 shows a case where no polarizing unit 50 is provided, (b) in FIG. 12 shows a case where a flat polarizing unit 50 is provided, and (c) in FIG. 12 shows a case where a curved polarizing unit 50 is provided. The transmittance in the transmission axis direction of the polarizing unit 50 is the same in (a) to (c) in FIG. 12. In addition, in (b) and (c) in FIG. 12, the polarizing unit 50 is positioned so as to be inclined at a predetermined angle θ1 = 45 degrees with respect to the image light.

[0080] 12(a) to 12(c) show images of the image light projected onto the windshield WS when the entire display area of ​​the image projection unit 10 is displayed at maximum brightness. The circle P1 shown in the figure is located in the center of the figure, the circle P2 is located at the right end of the figure, and the circle P3 is located at the left end of the figure. The brightness was measured at the positions of the circles P1 to P3, and the results are shown in Table 1, expressed as relative brightness with the brightness at the P1 position in each example being 100. In the table, "with polarizer" refers to the case where a flat polarizer 50 was used, and "polarizer_bent" refers to the case where a curved polarizer 50 was used.

[0081] As shown in Table 1, when the polarizing unit 50 was not provided, the relative luminance at both ends was 44 to 45%. When a flat polarizing unit 50 was used, the relative luminance at both ends decreased to approximately 22 to 36%, resulting in luminance unevenness. In contrast, when a curved polarizing unit 50 was used, the relative luminance at both ends was approximately 38 to 43%, which is higher than when a flat polarizing unit 50 was used, and luminance unevenness was reduced.

[0082] As described above, in the image projection device 100 of this embodiment, the polarizing unit 50 is curved into a concave shape, which reduces the difference in transmittance of the irradiated light incident on the central region and the end region of the polarizing unit 50, thereby making it possible to reduce uneven brightness of the virtual image.

[0083] (Modification of the Fourth Embodiment) FIG. 13 is a schematic diagram illustrating a modification of the fourth embodiment. FIG. 13A illustrates an example in which the polarizing unit 50 is disposed between the first mirror 20 and the second mirror 30, and FIG. 13B illustrates an example in which the polarizing unit 50 is disposed between the second mirror 30 and the windshield WS. As shown in FIGS. 13A and 13B, the polarizing unit 50 is preferably disposed at an angle with respect to the traveling direction of the image light. Furthermore, as shown in FIG. 9, the polarizing unit 50 has a curved shape. In FIG. 13A, the polarizing unit 50 is concave toward the first mirror 20, and in FIG. 13B, the polarizing unit 50 is concave toward the second mirror 30. In both cases, the polarizing unit 50 has a concave shape toward the incident side of the image light. In this modification, the average curvature of the polarizing unit 50 is set depending on the spread angle of the image light traveling from the first mirror 20 to the second mirror 30 and the spread angle of the image light traveling from the second mirror 30 to the windshield WS.

[0084] In the image projection device 100 of this modified example, the polarizing unit 50 is also curved into a concave shape, which reduces the difference in transmittance of the irradiated light incident on the central region and the end region of the polarizing unit 50, thereby making it possible to reduce uneven brightness of the virtual image.

[0085] Fifth Embodiment Next, a fifth embodiment of the present disclosure will be described with reference to FIGS. 14 to 16. Description of content that overlaps with the fourth embodiment will be omitted. FIG. 14 is a schematic diagram illustrating an overview of an image projection unit 10 according to this embodiment. As shown in FIG. 14, the image projection unit 10 of this embodiment includes a light source 11, a first lens 12, a polarization conversion unit 60, a reflecting mirror 16, a second lens 17, a polarization-maintaining diffusion unit 18, and an image display unit 19.

[0086] Fig. 15 is a schematic diagram illustrating the details of the polarization conversion unit 60. As shown in Fig. 15, the polarization conversion unit 60 includes a light-transmittance maintaining unit 13, a reflective polarizing unit 14, and a half-wave plate 15. Here, the polarization conversion unit 60 is shown as a combination of the light-transmittance maintaining unit 13, the reflective polarizing unit 14, and the half-wave plate 15. However, the reflective polarizing unit 14 and the half-wave plate 15 may be directly bonded together as long as the curved shape described below can be maintained. In Fig. 15, the arrows shown by solid lines indicate the optical paths of unpolarized light emitted from the light source 11, and the arrows shown by dashed lines indicate the optical paths of light polarized in a predetermined direction and light polarized orthogonal to the predetermined direction.

[0087] The light source 11 is a component that irradiates the image display unit 19 with unpolarized illumination light via the first lens 12, the polarization conversion unit 60, the reflecting mirror 16, the second lens 17, and the polarization-maintaining diffusion unit 18. The first lens 12 is an optical component that is disposed in the light emission direction of the plurality of light sources 11 and has the function of concentrating the illumination light emitted from the light sources 11 and emitting it as, for example, parallel light or light close to parallel light (hereinafter, both of these will be collectively referred to as "substantially parallel light"). Note that the light source 11 and the first lens 12 have the same configuration as in the first embodiment, and therefore detailed description thereof will be omitted.

[0088] The polarization conversion unit 60 is an optical element that transmits light polarized in a predetermined direction, reflects light polarized in a direction perpendicular to the predetermined direction, and rotates the polarization of the transmitted light by 90 degrees. Both the reflected light reflected by the polarization conversion unit 60 and the transmitted light that has passed through the polarization conversion unit 60 are polarized in a direction perpendicular to the predetermined direction, and are incident on the second lens 17. As shown in Figure 14, the polarization conversion unit 60 is curved along the longitudinal direction and has a concave shape on the side on which the irradiated light is incident.

[0089] The translucency maintaining unit 13 is a member made of a material that transmits light. A reflective polarizing unit 14 is attached to the incident surface of the translucency maintaining unit 13, and a half-wave plate 15 is attached to the surface opposite the reflective polarizing unit 14. Here, an example is shown in which sheet-like half-wave plate 15 and reflective polarizing unit 14 are used and attached to the translucency maintaining unit 13, but they may also be formed directly on the surface of the translucency maintaining unit 13 by vapor deposition or the like. The translucency maintaining unit 13 has the function of maintaining the shape of the polarization conversion unit 60, and is therefore curved along the longitudinal direction like the polarization conversion unit 60, and has a concave shape on the incident side of the irradiated light.

[0090] 15 shows an example in which a plate-shaped member is used as the translucency maintaining unit 13 and is arranged at an angle of 45 degrees relative to the traveling direction of the light irradiated from the first lens 12, but the angle of inclination is not limited as long as the shape can hold the reflective polarizing unit 14 on one surface and the half-wave plate 15 on the other surface. The material constituting the translucency maintaining unit 13 is not limited, and glass, acrylic resin, polycarbonate resin, etc. can be used, but it is preferable to use a retardation-free material that does not cause a phase difference in the transmitted light. Furthermore, the thickness of the translucency maintaining unit 13 is not limited, and a thickness of approximately 0.5 mm to 3.0 mm can be used, for example.

[0091] The reflective polarizing unit 14 is an optical element attached to one surface of the translucency maintaining unit 13, which transmits polarized light in a predetermined direction as transmitted light and reflects polarized light perpendicular to the predetermined direction as reflected light. Because the reflective polarizing unit 14 is attached to the translucency maintaining unit 13, it is curved along the longitudinal direction, similar to the polarization conversion unit 60, and has a concave shape on the side on which the irradiated light is incident. The curved shape of the reflective polarizing unit 14 depends on the spread angle of the irradiated light emitted from the first lens 12, and examples of such curves include an arc, an ellipse, a parabola, a hyperbola, and a free curve. The curvature may vary depending on the spread angle of the irradiated light. The average curvature of the reflective polarizing unit 14 is preferably in the range of 10 mm to 500 mm.

[0092] The polarization direction transmitted by the reflective polarizer 14 is not limited, and must match the polarization direction required for the backlight ultimately irradiated onto the image display unit 19. As an example, the reflective polarizer 14 may transmit light polarized in the horizontal direction (e.g., p-polarized light) in FIG. 15 and reflect light polarized in a direction perpendicular to the paper surface (e.g., s-polarized light). The specific configuration of the reflective polarizer 14 is not limited, but it is preferable to use a plate- or sheet-shaped polarizer that can be attached to the surface of the translucency maintaining unit 13. Examples that can be used include the reflective polarizing film WGF manufactured by Asahi Kasei Corporation and a reflective polarizing plate film manufactured by 3M Japan Ltd. The reflective polarizer 14 is disposed on the optical path of the irradiated light and transmits light polarized in a predetermined direction and reflects light polarized in a direction intersecting the predetermined direction, and therefore corresponds to the polarizer in the present disclosure.

[0093] The half-wave plate 15 is an optical element made of a birefringent material having different refractive indices in the slow axis and the fast axis and is attached to the other surface of the translucency maintaining unit 13. The half-wave plate 15 is designed so that a phase difference of half the wavelength of incident light occurs between the slow axis and the fast axis before the incident light is emitted. The slow axis and the fast axis of the half-wave plate 15 are oriented 45 degrees apart from the polarization direction of the irradiated light transmitted through the reflective polarizing unit 14. Therefore, the polarization of the irradiated light transmitted through the half-wave plate 15 is rotated by 90 degrees in-plane. Because the half-wave plate 15 is attached to the translucency maintaining unit 13, it is curved along the longitudinal direction, similar to the polarization conversion unit 60, and has a concave shape on the side on which the irradiated light is incident.

[0094] As a result, the light transmitted through the reflective polarizing unit 14 and the half-wave plate 15 and the light reflected by the reflective polarizing unit 14 and the half-wave plate 15 are irradiated as backlight light having a polarization direction perpendicular to the predetermined direction. The half-wave plate 15 does not need to have a phase difference of exactly 50% with respect to the wavelength of the light; as long as it generates a phase difference close to 50%, it can perform the function of rotating the polarization direction in-plane. The specific configuration of the half-wave plate 15 is not limited, but it is preferable to use a plate- or sheet-shaped plate that can be attached to the surface of the translucency maintaining unit 13. As an example, an achromatic half-wave plate manufactured by Dexerials Corporation can be used.

[0095] The reflecting mirror 16 is an optical element that reflects incident light. In the example shown in Fig. 15, the reflecting mirror 16 is disposed opposite the reflective polarizing unit 14, and reflects the light reflected by the reflective polarizing unit 14 toward the second lens 17. As shown in Fig. 14, the reflecting mirror 16 is curved along the longitudinal direction and has a concave shape on the side on which the irradiated light is incident. The reflecting mirror 16 is disposed at an angle of 45 degrees with respect to the traveling direction of the reflected light from the polarization conversion unit 60. The curvature of the reflecting mirror 16 may be different from the curvature of the polarization conversion unit 60.

[0096] The second lens 17 controls the light flux of the backlight irradiated through the reflector 16 and the polarization converter 60 so that the entire display area is uniformly illuminated. Therefore, the shape and positive / negative power of the second lens 17 are selected to suit this purpose. In this embodiment, a concave lens is used as an example of the second lens 17. If the entire display area is configured to be uniformly illuminated using only the first lens 12, the second lens 17 may be omitted. The first lens 12 and the second lens 17 are formed of, for example, a resin such as acrylic resin, glass, or the like. The first lens 12 and the second lens 17 function together to guide light emitted from the light source 11 to the display area of ​​the image display unit 19. In this embodiment, the display area is, for example, the rear surface of the polarization-maintaining diffusion unit 18 (the surface facing the light source 11). However, the display area may be determined taking into account the specifications of the light source device, and may be, for example, the rear surface of the image display unit 19.

[0097] The polarization-maintaining diffuser 18 is an optical element disposed on the rear side of the image display unit 19, which diffuses and transmits backlight converted by the polarization conversion element while maintaining its polarization direction. The polarization-maintaining diffuser 18 diffuses the highly directional light polarized by the first lens 12 and the second lens 17 and outputs the light to the image display unit 19, thereby illuminating the image display unit 19 more uniformly. The polarization-maintaining diffuser 18 may diffuse only light polarized perpendicular to a predetermined direction while maintaining its polarization, or may diffuse light polarized in all directions while maintaining its polarization. The specific configuration of the polarization-maintaining diffuser 18 is not limited, but an example of such a diffuser is a sheet manufactured by Lintec Corporation under the trade name HH120.

[0098] The image display unit 19 functions as a spatial light modulation unit that receives backlight that has passed through the polarization-maintaining diffusion unit 18 from the rear surface, modulates the light according to image information, and emits the modulated light from the emission surface. The specific configuration of the image display unit 19 is not limited, but one example is a transmissive liquid crystal display device that transmits light that has entered from the rear surface and emits it from the front surface. In a transmissive liquid crystal display device, only light polarized perpendicular to a predetermined direction that has entered the rear surface is transmitted, and therefore the polarization direction in the polarization-maintaining diffusion unit 18 is made to coincide with the direction perpendicular to the predetermined direction.

[0099] In the image projection device 100 described above, the illumination light emitted from the light source 11 is unpolarized, with no limitation on the polarization direction. The illumination light emitted from the light source 11 is incident on the first lens 12, where it is collimated, and then incident on the reflective polarization unit 14. A portion of the illumination light incident on the reflective polarization unit 14 is transmitted, and another portion is reflected toward the reflecting mirror 16. Here, the polarization of the illumination light reflected by the reflective polarization unit 14 is polarized in a first direction, which is the direction of transmission through the image display unit 19. Furthermore, the polarization of the illumination light that transmits through the reflective polarization unit 14 is polarized in a second direction that is approximately perpendicular to the first direction.

[0100] The transmitted light that has passed through reflective polarizing unit 14 passes through translucency maintaining unit 13 and enters half-wave plate 15, where its polarization direction is rotated by 90 degrees, and the light is irradiated onto second lens 17 as backlight light polarized in the first direction. In addition, the reflected light that has reached reflecting mirror 16 is reflected and irradiated onto second lens 17 as backlight light polarized in the first direction. The backlight light that has reached second lens 17 has its light distribution adjusted and reaches polarization-maintaining diffusion unit 18.

[0101] In polarization-maintaining diffusion section 18, backlight polarized in the first direction is diffused and transmitted as light polarized in the first direction while maintaining its polarization direction, thereby uniformly irradiating the back surface of image display section 19 with backlight polarized in the first direction. Here, "maintaining the polarization direction" means that the polarization state at the time of incidence is maintained at more than 50% on an energy basis before and after transmission through polarization-maintaining diffusion section 18, and more preferably at least 90%.

[0102] In the reflective polarizing unit 14, the transmittance of light polarized in the transmission axis direction depends on the angle of incidence, and the transmittance tends to decrease when the angle of incidence is large (large deviation from perpendicular). However, in this embodiment, as shown in Figure 14, the polarization conversion unit 60 is curved in a concave shape on the side on which the irradiated light is incident, so that the angle of incidence of the expanding irradiated light on the reflective polarizing unit 14 becomes smaller at each position, and the irradiated light reaches the reflective polarizing unit 14 at an angle close to perpendicular. This makes it possible to suppress the difference in transmittance between the central region and the edge region of the reflective polarizing unit 14 and suppress uneven brightness of the backlight light irradiated on the image display unit 19.

[0103] As described above, in the image projection device 100 of this embodiment, the reflective polarizing unit 14 is curved into a concave shape, which reduces the difference in transmittance of the irradiated light incident on the central region and the end region of the reflective polarizing unit 14, thereby making it possible to reduce uneven brightness of the virtual image.

[0104] 16 is a schematic diagram illustrating a modification of the fifth embodiment. This modification differs from the fifth embodiment in the arrangement of the light source 11 and the first lens 12, and the arrangement of the transparency maintaining unit 13, the reflective polarizing unit 14, the half-wave plate 15, and the reflecting mirror 16 in the polarization conversion unit 60.

[0105] As shown in Fig. 16 , image projection device 100 includes light source 11, first lens 12, polarization conversion unit 60, and reflecting mirror 16. Second lens 17, polarization-maintaining diffusion unit 18, and image display unit 19 are not shown. Furthermore, polarization conversion unit 60 includes translucency maintaining unit 13, reflective polarizer 14, and half-wave plate 15. As shown in Fig. 16 , in image projection device 100 of this modified example, the light entrance and light exit surfaces of polarization conversion unit 60 and reflecting mirror 16 are substantially perpendicular to each other. Therefore, the traveling direction of the light emitted from light source 11 and first lens 12 is perpendicular to the traveling direction of the backlight emitted from polarization conversion unit 60 and reflecting mirror 16.

[0106] In the image projection device 100 of this modification, the polarization conversion unit 60, the light-transmitting unit 13, the reflective polarizing unit 14, the half-wave plate 15, and the reflecting mirror 16 are also curved along the longitudinal direction and are concave on the incident side of the irradiated light. In addition, since the reflective polarizing unit 14 is curved in a concave shape, it is possible to reduce the difference in transmittance of the irradiated light incident on the central region and the end region of the reflective polarizing unit 14, and to reduce uneven brightness of the virtual image.

[0107] Sixth Embodiment

[0108] Next, a sixth embodiment of the present disclosure will be described with reference to Fig. 17 . Fig. 17 is a schematic cross-sectional view illustrating an overview of an image projection unit 10 according to this embodiment. As shown in Fig. 17 , the image projection unit 10 of this embodiment includes a light source 21, a primary lens 22, a reflective polarizing unit 23, a half-wave plate 24, a reflecting mirror 25, a diffuser 27, an image display unit 28, and a meniscus lens 29. Here, the combination of the reflective polarizing unit 23, the half-wave plate 24, and the reflecting mirror 25 constitutes a polarization conversion element 70 according to this disclosure.

[0109] The light source 21 is a component that irradiates light onto the image display unit 28 via a primary lens 22, a reflective polarizing unit 23, a half-wave plate 24, a reflecting mirror 25, a meniscus lens 29, and a diffuser 27. The light source 21 is, for example, a semiconductor light-emitting element such as an LED, and is arranged in a predetermined direction (the depth direction of the paper in FIG. 17 ). The light emitted by the light source 21 is not particularly limited, but in this embodiment, white light is used as an example. Note that, in this embodiment, the number of light sources 21 arranged is one, but two or more rows may be used. Furthermore, the light emitted from the light source 21 is unpolarized.

[0110] The primary lens 22 is an optical element disposed in the light emission direction of the plurality of light sources 21 and has the function of concentrating the light emitted from the light sources 21 and emitting it as, for example, parallel light or light close to parallel light (hereinafter, both of these will be collectively referred to as "substantially parallel light"). The primary lens 22 extends along the arrangement direction of the plurality of light sources 21. In this embodiment, as an example of the primary lens 22, a TIR lens is used, which has a refractive portion at the center that refracts light and reflective portions on both sides of the refractive portion that reflect light. While FIG. 17 shows the primary lens 22 as extending in the arrangement direction of the light sources 21, multiple collimating lenses may be provided for each light source 21. Furthermore, the primary lens 22 is not limited to a lens as long as it can convert the light from the light sources 21 into substantially parallel light. A combination of a reflector and a lens, or a configuration in which a reflector alone can convert the light into substantially parallel light, may also be used.

[0111] The polarization conversion element 70 is an optical element disposed on the light exit side of the primary lens 22, and converts the unpolarized irradiated light into a polarized light along a specific direction, and emits the polarized light as backlight. The specific configuration of the polarization conversion element 70 is not limited, but Fig. 17 shows an example in which a reflective polarizing unit 23, a half-wave plate 24, and a reflecting mirror 25 are attached to each surface of the prism.

[0112] The reflective polarizing unit 23 is an optical element that reflects light polarized in a first direction and transmits light polarized in a second direction orthogonal to the first direction. The polarization direction of light transmitted by the reflective polarizing unit 23 is not limited, and must be matched to the polarization direction required for the backlight ultimately irradiated onto the image display unit 28. As an example, the reflective polarizing unit 23 may transmit light polarized in the horizontal direction (e.g., p-polarized light) in FIG. 17 and reflect light polarized in a direction perpendicular to the paper surface (e.g., s-polarized light). The reflective polarizing unit 23 is disposed at a predetermined angle with respect to the traveling direction of light emitted from the light source 21. Here, the light reflected by the reflective polarizing unit 23 of the irradiated light corresponds to the first light in this disclosure, and the light transmitted through the reflective polarizing unit 23 corresponds to the second light in this disclosure.

[0113] The half-wave plate 24 is an optical element disposed between the reflecting mirror 25 and the meniscus lens 29, and is made of a birefringent material having different refractive indices in the slow axis and the fast axis. The half-wave plate 24 is designed so that a phase difference of half the wavelength of the incident light occurs between the slow axis and the fast axis before the incident light is emitted. The slow axis and the fast axis of the half-wave plate 24 are oriented at 45 degrees different from the polarization direction of the irradiated light transmitted through the reflective polarizing unit 23.

[0114] The reflecting mirror 25 is an optical member that reflects incident light. In the example shown in Fig. 17 , the reflecting mirror 25 is arranged so as to be inclined at a predetermined angle with respect to the traveling direction of light that has passed through the reflective polarizing unit 23. In the example shown in Fig. 17 , the inclination angles of the reflective polarizing unit 23 and the reflecting mirror 25 with respect to the traveling direction of light emitted from the light source 21 are different. More specifically, the reflective polarizing unit 23 and the reflecting mirror 25 are arranged so that the traveling directions of light reflected by them are different, and the inclination angles are set so as to reflect light in a direction away from the center of the image display unit 28.

[0115] 17 shows an example in which the inclination angles of the reflective polarizing unit 23 and the reflecting mirror 25 are different, but the reflective polarizing unit 23 and the reflecting mirror 25 may be arranged substantially parallel to each other. In this case, the reflective polarizing unit 23 and the reflecting mirror 25 are arranged at an angle of, for example, 45 degrees with respect to the traveling direction of the light emitted from the light source 21, and the traveling direction of the light reflected by the reflective polarizing unit 23 in the backlight light is the same as that of the light reflected by the reflecting mirror 25.

[0116] The diffuser plate 27 is an optical member disposed on the rear side of the image display unit 28, and diffuses and transmits backlight. The diffuser plate 27 diffuses the highly directional light deflected by the primary lens 22 and the meniscus lens 29 and outputs it to the image display unit 28, thereby functioning to more uniformly illuminate the image display unit 28. It is preferable to use an optical member as the diffuser plate 27 that diffuses and transmits the backlight converted by the polarization conversion element 70 while maintaining the polarization direction of the backlight.

[0117] The image display unit 28 functions as a spatial light modulation unit that receives backlight emitted from the polarization conversion element 70 from the rear surface, modulates the light according to image information, and emits the light from the emission surface. The specific configuration of the image display unit 28 is not limited, but one example is a transmissive liquid crystal display device that transmits light incident from the rear surface and emits it from the front surface. In a transmissive liquid crystal display device, only light polarized in a predetermined direction that is incident on the rear surface is transmitted, so the polarization direction in the polarization conversion element 70 is made to coincide with the predetermined direction.

[0118] The meniscus lens 29 is an optical element that adjusts the light distribution of backlight emitted from the polarization conversion element 70. The meniscus lens 29 is formed by extending in a direction perpendicular to the plane of the paper in FIG. 17 . In the example shown in FIG. 17 , the meniscus lens 29 includes a first lens region 29 a and a second lens region 29 b. Light reflected by the reflective polarizing unit 23 enters the first lens region 29 a, and light reflected by the reflecting mirror 25 enters the second lens region 29 b. Although the optical characteristics of the first lens region 29 a and the second lens region 29 b are not limited, the example shown in FIG. 17 illustrates an example in which the light reflected by the reflective polarizing unit 23 and the reflecting mirror 25 is refracted so that the traveling direction of the light is further away from the center of the image display unit 28.

[0119] In the image projection device 100 described above, the illumination light emitted from the light source 21 is unpolarized, with no restriction on the polarization direction. The illumination light emitted from the light source 21 is incident on the primary lens 22, where it is collimated, and then incident on the incident surface of the polarization conversion element 70. Of the illumination light incident on the polarization conversion element 70, the light polarized in a first direction is reflected by the reflective polarization unit 23 toward the first lens region 29a of the meniscus lens 29, and the light polarized in a second direction is transmitted through the reflective polarization unit 23. Here, the polarization of the illumination light reflected by the reflective polarization unit 23 is polarized in the first direction, which is transmitted through the image display unit 28. Furthermore, the polarization of the illumination light transmitted through the reflective polarization unit 23 is polarized in a second direction that is approximately perpendicular to the first direction.

[0120] Furthermore, light irradiated from light source 21 is polarized in the second direction (second light) and passes through reflective polarizing unit 23, is reflected by reflecting mirror 25, and passes through half-wave plate 24. At this time, the polarization of the irradiated light that has passed through half-wave plate 24 is rotated 90 degrees in-plane and converted to polarization in the first direction. As a result, the first light reflected by reflective polarizing unit 23 and the second light that has passed through reflective polarizing unit 23, been reflected by reflecting mirror 25, and passed through half-wave plate 24 are irradiated as backlight light having the same polarization direction, the first direction. Furthermore, half-wave plate 24 does not need to have a phase difference of exactly 50% with respect to the wavelength of light; as long as it generates a phase difference close to 50%, it can perform the function of rotating the polarization direction in-plane.

[0121] The second light that has passed through the half-wave plate 24 is irradiated in the direction of the second lens region 29b of the meniscus lens 29 as backlight light polarized in the first direction. The backlight light that has reached the first lens region 29a or the second lens region 29b of the meniscus lens 29 has its light distribution adjusted and reaches the diffuser plate 27, respectively. The diffuser plate 27 diffuses and transmits the backlight light polarized in the first direction. As a result, the backlight light polarized in the first direction is uniformly irradiated onto the rear surface of the image display unit 28.

[0122] 17 , backlight refracted by the first lens region 29 a and backlight refracted by the second lens region 29 b are irradiated onto different regions of the image display unit 28 and travel in directions away from each other. Therefore, by irradiating the light transmitted through the first lens region 29 a and the light transmitted through the second lens region 29 b onto the far display region and the near display region of the image display unit 28, respectively, the first image light L1 transmitted through the far display region and the second image light L2 transmitted through the near display region can be separated. This eliminates the need for additional optical components for separating the first image light L1 and the second image light L2, thereby enabling the image projection device 100 to be miniaturized. Here, the near display region and the far display region each correspond to either the first display region or the second display region in the present disclosure.

[0123] 17 shows an example in which the inclination angles of the reflective polarizer 23 and the reflector 25 are different, but the reflective polarizer 23 and the reflector 25 may be arranged substantially parallel to each other. In this case, the reflective polarizer 23 and the reflector 25 are arranged at an angle of, for example, 45 degrees with respect to the traveling direction of light emitted from the light source 21, and the traveling direction of the backlight light reflected by the reflective polarizer 23 and the light reflected by the reflector 25 is the same. Furthermore, the backlight light refracted by the first lens region 29 a and the backlight light refracted by the second lens region 29 b are irradiated onto the adjacent first and second display regions of the image display unit 28.

[0124] In the example shown in FIG. 17 , the second light that passes through the reflective polarizing unit 23 and is reflected by the reflecting mirror 25 has a longer optical path length before reaching the image display unit 28 than the first light that is reflected by the reflective polarizing unit 23. Furthermore, although the light emitted from the light source 21 is converted into substantially parallel light by the primary lens 22, it is not a strictly parallel beam and travels with a varying light diameter. Therefore, the illumination area of ​​the first light that illuminates the first display region of the image display unit 28 is different from the illumination area of ​​the second light that illuminates the second display region. Furthermore, the second light is partially attenuated when passing through the half-wave plate 24. This may result in a difference in brightness between the first light that illuminates the first display region of the image display unit 28 and the second light that illuminates the second display region.

[0125] Therefore, in the image projection device 100 of this embodiment, the difference in brightness between the first display area and the second display area is suppressed by appropriately setting the relationship between the reflectance Pr of the first light and the transmittance Pt of the second light in the reflective polarizing unit 23, and display is performed at approximately the same brightness. １ and the area of ​​the second display region is S ２ The ratio Pr / Pt is S ２ / S １ be proportional to.

[0126] Here, the reflectance of the reflecting mirror 25 is Rm, the transmittance of the half-wave plate 24 is Ph, and the amount of light emitted from the light source 21 is LA. The solid angle of the first light emitted from the first display area is ω. １ and the solid angle of the second light emitted from the second display area is ω ２ The amount of the first light reflected by the reflective polarizing unit 23 is Lr=LA·Pr. The amount of the second light transmitted through the reflective polarizing unit 23, reflected by the reflecting mirror 25, and transmitted through the half-wave plate 24 is Lt=LA·Pt·Rm·Ph. The luminance of the first display area is Lr / (S １ ・ω １ ), and the luminance of the second display area is Lt / (S ２ ・ω ２ )

[0127] Therefore, in order to make the luminance of the first display area and the luminance of the second display area the same, the following formula is used: Lr / (S １ ・ω １ ) = Lt / (S ２ ・ω ２ ) This can be transformed into (Equation 2) LA·Pr / (S １ ・ω １ )=LA・Pt・Rm・Ph / (S ２ ・ω ２ ) Further transformation gives: (Equation 3) Pr / Pt = Rm Ph (S ２ ・ω ２ / S １ ・ω １ ) where (ω ２ / ω １) is a constant α, (Equation 4) Pr / Pt = α Rm Ph (S ２ / S １ Therefore, when the relationship between the reflectance Pr of the first light and the transmittance Pt of the second light in the reflective polarizing unit 23 satisfies the above-mentioned formula 4, even if the optical paths of the first light and the second light are different and the areas of the first display region and the second display region are different, the virtual images P10 and P20 can be projected with the same brightness.

[0128] In addition, the solid angle ω in the first display area and the second display area is １ , ω ２ If it is considered that there is no significant difference between the two, the constant α is assumed to be 1, and the following equation (5) is used: Pr / Pt = Rm Ph (S ２ / S １ ) alone can set the relationship between the reflectance Pr of the first light and the transmittance Pt of the second light in the reflective polarizing unit 23, thereby simplifying the optical design.

[0129] As described above, in the image projection device 100 of this embodiment, the light emitted from the light source 21 is converted by the polarization conversion element 70 into backlight light polarized in the first direction. Furthermore, the polarization direction of the backlight light reaching the image display unit 28 matches the polarization direction used for image display on the image display unit 28, so that the amount of polarized light component in the second direction that is absorbed by the image display unit 28 is small, thereby improving the light utilization efficiency. Furthermore, by reflecting the light from the light source 21 by the reflective polarization unit 23 and the reflecting mirror 25, the light irradiation area can be expanded, and the image irradiation unit 10 can be made smaller.

[0130] Furthermore, the reflective polarizing unit 23 polarizes and separates the light emitted from the light source 21, and the half-wave plate 24 rotates the polarization direction of one of the separated light beams. The ratio Pr / Pt of the reflectance Pr of the first light to the transmittance Pt of the second light in the reflective polarizing unit 23 is adjusted to be equal to or larger than the area S of the first display region. １ and the area S of the second display area ２ Ratio S ２ / S １ By making the luminance proportional to the first display region, it is possible to improve the efficiency of use of the irradiated light and make the luminance of the first display region and the second display region uniform.

[0131] Seventh Embodiment Next, a seventh embodiment of the present disclosure will be described with reference to Fig. 18. Description of content that overlaps with the sixth embodiment will be omitted. Fig. 18 is a schematic cross-sectional view illustrating an overview of the image projection unit 10 according to this embodiment. This embodiment differs from the sixth embodiment in that a half-wave plate 24 is disposed between the reflective polarizing unit 23 and the meniscus lens 29.

[0132] In this embodiment, the light emitted from the light source 21 is incident on the primary lens 22, where it is collimated, and then incident on the incident surface of the polarization conversion element 70. Of the light incident on the polarization conversion element 70, the light polarized in a first direction (first light) is reflected by the reflective polarizing unit 23 toward the half-wave plate 24, and the light polarized in a second direction (second light) is transmitted through the reflective polarizing unit 23. The second light transmitted through the reflective polarizing unit 23 is irradiated toward the second lens region 29b of the meniscus lens 29 as backlight polarized in the second direction.

[0133] Light emitted from light source 21 is polarized in a first direction and reflected by reflective polarizing unit 23, and then passes through half-wave plate 24. At this time, the polarization of the irradiated light that has passed through half-wave plate 24 is rotated 90 degrees in-plane and converted into polarization in a second direction. As a result, the first light that has been reflected by reflective polarizing unit 23 and passed through half-wave plate 24 and the second light that has passed through reflective polarizing unit 23 and reflected by reflecting mirror 25 are irradiated as backlight light having the same polarization direction, that is, the second direction.

[0134] In this embodiment, the amount of the first light reflected by the reflective polarizing unit 23 and transmitted through the half-wave plate 24 is Lr=LA·Pr·Ph. The amount of the second light transmitted through the reflective polarizing unit 23 and reflected by the reflecting mirror 25 is Lt=LA·Pt·Rm. The luminance of the first display area is Lr / (S １ ・ω １ ), and the luminance of the second display area is Lt / (S ２ ・ω ２ )

[0135] Therefore, the condition for making the luminance of the first display area and the second display area the same is (Formula 6): Pr / Pt=Rm·(1 / Ph)·(S ２ ・ω ２ / S １ ・ω１ ) where (ω ２ / ω １ ) is a constant α, (Equation 7) Pr / Pt = α Rm (1 / Ph) (S ２ / S １ Therefore, when the relationship between the reflectance Pr of the first light and the transmittance Pt of the second light in the reflective polarizing unit 23 satisfies the above-mentioned formula 7, even if the optical paths of the first light and the second light are different and the areas of the first display region and the second display region are different, the virtual images P10 and P20 can be projected with the same brightness.

[0136] In addition, the solid angle ω in the first display area and the second display area is １ , ω ２ If it is considered that there is no significant difference between the two, then the constant α is assumed to be 1, and the following equation is used: Pr / Pt = Rm (1 / Ph) (S ２ / S １ ) alone can set the relationship between the reflectance Pr of the first light and the transmittance Pt of the second light in the reflective polarizing unit 23, thereby simplifying the optical design.

[0137] Eighth Embodiment Next, an eighth embodiment of the present disclosure will be described with reference to FIG. 19 . Description of content that overlaps with the sixth embodiment will be omitted. FIG. 19 is a schematic cross-sectional view illustrating an overview of an image projection unit 10 according to this embodiment. This embodiment differs from the sixth embodiment in that the light source 21 and the primary lens 22 are disposed below the polarization conversion element 70. Therefore, the second light transmitted through the reflective polarization unit 23 is incident on the first lens region 29 a of the meniscus lens 29. Furthermore, the first light reflected by the reflective polarization unit 23 reaches the reflecting mirror 25.

[0138] In this embodiment, the light emitted from the light source 21 is incident on the primary lens 22, where it is collimated, and then incident on the incident surface of the polarization conversion element 70. Of the light incident on the polarization conversion element 70, the light polarized in a first direction (first light) is reflected by the reflective polarizing unit 23 toward the reflecting mirror 25, and the light polarized in a second direction (second light) is transmitted through the reflective polarizing unit 23. The second light transmitted through the reflective polarizing unit 23 is irradiated toward the first lens region 29a of the meniscus lens 29 as backlight polarized in the second direction.

[0139] Light emitted from light source 21 is polarized in a first direction and reflected by reflective polarizing unit 23, then reflected by reflecting mirror 25, and transmitted through half-wave plate 24. At this time, the polarization of the irradiated light transmitted through half-wave plate 24 is rotated 90 degrees in-plane and converted into polarization in a second direction. As a result, the first light reflected by reflective polarizing unit 23 and transmitted through half-wave plate 24 and the second light transmitted through reflective polarizing unit 23 are irradiated as backlight light having the same polarization direction, the second direction.

[0140] In this embodiment, the amount of the first light reflected by the reflective polarizing unit 23, reflected by the reflecting mirror 25, and transmitted through the half-wave plate 24 is Lr=LA·Pr·Rm·Ph. The amount of the second light transmitted through the reflective polarizing unit 23 is Lt=LA·Pt. The luminance of the first display area is Lr / (S １ ・ω １ ), and the luminance of the second display area is Lt / (S ２ ・ω ２ )

[0141] Therefore, the condition for making the luminance of the first display area and the second display area the same is (Formula 9): Pr / Pt=(1 / Rm)·(1 / Ph)·(S ２ ・ω ２ / S １ ・ω １ ) where (ω ２ / ω １ ) is a constant α, (Equation 10) Pr / Pt=α·(1 / Rm)·(1 / Ph)·(S ２ / S １ Therefore, when the relationship between the reflectance Pr of the first light and the transmittance Pt of the second light in the reflective polarizing unit 23 satisfies the above-described formula 10, even if the optical paths of the first light and the second light are different and the areas of the first display region and the second display region are different, the virtual images P10 and P20 can be projected with the same brightness.

[0142] In addition, the solid angle ω in the first display area and the second display area is １ , ω ２ If it is considered that there is no significant difference between the two, the constant α is assumed to be 1, and the following equation (11) is obtained: Pr / Pt=(1 / Rm)·(1 / Ph)·(S２ / S １ ) alone can set the relationship between the reflectance Pr of the first light and the transmittance Pt of the second light in the reflective polarizing unit 23, thereby simplifying the optical design.

[0143] Ninth Embodiment Next, a ninth embodiment of the present disclosure will be described with reference to Fig. 20. Description of content that overlaps with the eighth embodiment will be omitted. Fig. 20 is a schematic cross-sectional view illustrating an overview of the image projection unit 10 according to this embodiment. This embodiment differs from the eighth embodiment in that a half-wave plate 24 is disposed between the reflective polarizing unit 23 and the meniscus lens 29.

[0144] In this embodiment, the illumination light emitted from the light source 21 is incident on the primary lens 22, where it is collimated, and then incident on the incident surface of the polarization conversion element 70. Of the illumination light incident on the polarization conversion element 70, the polarized light in the first direction (first light) is reflected by the reflective polarizing unit 23 toward the reflecting mirror 25, and the polarized light in the second direction (second light) is transmitted through the reflective polarizing unit 23. The second light transmitted through the reflective polarizing unit 23 is transmitted through the half-wave plate 24 and is irradiated in the direction of the first lens region 29a of the meniscus lens 29. At this time, the polarization of the illumination light transmitted through the half-wave plate 24 is rotated 90 degrees in-plane and converted into polarization in the first direction.

[0145] The light emitted from the light source 21 is polarized in the first direction and reflected by the reflective polarizing unit 23, reflected by the reflecting mirror 25, and directed toward the second lens region 29b of the meniscus lens 29. As a result, the first light reflected by the reflective polarizing unit 23 and the second light transmitted through the reflective polarizing unit 23 and the half-wave plate 24 are irradiated as backlight light having the same polarization direction, the first direction.

[0146] In this embodiment, the amount of the first light reflected by the reflective polarizing unit 23 and then reflected by the reflecting mirror 25 is Lr=LA·Pr·Rm. The amount of the second light transmitted through the reflective polarizing unit 23 and then transmitted through the half-wave plate 24 is Lt=LA·Pt·Ph. The luminance of the first display area is Lr / (S １ ・ω １ ), and the luminance of the second display area is Lt / (S ２ ・ω ２ )

[0147] Therefore, the condition for making the luminance of the first display area and the second display area the same is expressed by the following formula (12): Pr / Pt=(1 / Rm)·Ph·(S ２ ・ω ２ / S １ ・ω １ ) where (ω ２ / ω １ ) is a constant α, (Equation 13) Pr / Pt=α·(1 / Rm)·Ph·(S ２ / S １ Therefore, when the relationship between the reflectance Pr of the first light and the transmittance Pt of the second light in the reflective polarizing unit 23 satisfies the above-mentioned formula 13, even if the optical paths of the first light and the second light are different and the areas of the first display region and the second display region are different, the virtual images P1 and P2 can be projected with the same luminance.

[0148] In addition, the solid angle ω in the first display area and the second display area is １ , ω ２ If it is considered that there is no significant difference between the two, then the constant α is assumed to be 1, and the following equation is obtained: Pr / Pt=(1 / Rm)·Ph·(S ２ / S １ ) alone can set the relationship between the reflectance Pr of the first light and the transmittance Pt of the second light in the reflective polarizing unit 23, thereby simplifying the optical design.

[0149] Tenth Embodiment Next, a tenth embodiment of the present disclosure will be described with reference to FIG. 21. Description of content that overlaps with the sixth embodiment will be omitted. FIG. 21 is a schematic cross-sectional view illustrating an overview of an image projection unit 10 according to this embodiment. This embodiment differs from the sixth embodiment in that the polarization conversion element 70 is separated into a first portion 70a and a second portion 70b, and a half-wave plate 24 is disposed between the first portion 70a and the second portion 70b.

[0150] In this embodiment, the light emitted from the light source 21 is incident on the primary lens 22, where it is collimated, and then incident on the incident surface of the polarization conversion element 70. Of the light incident on the polarization conversion element 70, the light polarized in the first direction (first light) is reflected by the reflective polarizing unit 23 toward the first lens region 29 a of the meniscus lens 29.

[0151] Of the light emitted from the light source 21, the second light polarized in the second direction is transmitted through the reflective polarizing unit 23. The second light transmitted through the reflective polarizing unit 23 is transmitted through the half-wave plate 24 and reflected by the reflecting mirror 25 to be emitted toward the second lens region 29b of the meniscus lens 29 as backlight light polarized in the second direction. At this time, the polarization of the irradiated light transmitted through the half-wave plate 24 is rotated 90 degrees in-plane and converted into polarization in the first direction. As a result, the first light reflected by the reflective polarizing unit 23 and the second light transmitted through the reflective polarizing unit 23, transmitted through the half-wave plate 24, and reflected by the reflecting mirror 25 are irradiated as backlight light polarized in the same first direction.

[0152] In this embodiment, the amount of the first light reflected by the reflective polarizing unit 23 is Lr=LA·Pr. The amount of the second light transmitted through the reflective polarizing unit 23, transmitted through the half-wave plate 24, and reflected by the reflecting mirror 25 is Lt=LA·Pt·Ph·Rm. The luminance of the first display area is Lr / (S １ ・ω １ ), and the luminance of the second display area is Lt / (S ２ ・ω ２ )

[0153] Therefore, the condition for making the luminance of the first display area and the second display area the same is (Equation 3) Pr / Pt=Rm·Ph·(S ２ ・ω ２ / S １ ・ω １ ) where (ω ２ / ω １ ) is a constant α, (Equation 4) Pr / Pt = α Rm Ph (S ２ / S １ ) can be expressed as

[0154] In addition, the solid angle ω in the first display area and the second display area is １ , ω ２ If it is considered that there is no significant difference between the two, the constant α is assumed to be 1, and the following equation (5) is used: Pr / Pt=Rm·(1 / Ph)·(S ２ / S １) alone can set the relationship between the reflectance Pr of the first light and the transmittance Pt of the second light in the reflective polarizing unit 23, thereby simplifying the optical design.

[0155] Eleventh Embodiment Next, an eleventh embodiment of the present disclosure will be described with reference to FIG. 22 . Description of content that overlaps with the tenth embodiment will be omitted. FIG. 22 is a schematic cross-sectional view illustrating an overview of an image projection unit 10 according to this embodiment. This embodiment is similar to the tenth embodiment except that the light source 21 and the primary lens 22 are disposed below the polarization conversion element 70. Therefore, the second light transmitted through the reflective polarization unit 23 is incident on the first lens region 29 a of the meniscus lens 29. Furthermore, the first light reflected by the reflective polarization unit 23 transmits through the half-wave plate 24 and reaches the reflecting mirror 25.

[0156] In this embodiment, the light emitted from the light source 21 is incident on the primary lens 22, where it is collimated, and then incident on the incident surface of the polarization conversion element 70. Of the light incident on the polarization conversion element 70, the light polarized in a first direction (first light) is reflected by the reflective polarizing unit 23 toward the half-wave plate 24, and the light polarized in a second direction (second light) is transmitted through the reflective polarizing unit 23. The second light transmitted through the reflective polarizing unit 23 is irradiated toward the first lens region 29a of the meniscus lens 29 as backlight polarized in the second direction.

[0157] Light emitted from the light source 21 is polarized in a first direction and reflected by the reflective polarizing unit 23, passes through the half-wave plate 24, and is reflected by the reflecting mirror 25 to be emitted toward the second lens region 29b of the meniscus lens 29. At this time, the polarization of the irradiated light that has passed through the half-wave plate 24 is rotated 90 degrees in-plane and converted into polarization in a second direction. As a result, the first light that has been reflected by the reflective polarizing unit 23 and passed through the half-wave plate 24 and the second light that has passed through the reflective polarizing unit 23 and reflected by the reflecting mirror 25 are irradiated as backlight light having the same polarization direction, that is, the second direction.

[0158] In this embodiment, the amount of the first light reflected by the reflective polarizing unit 23, transmitted through the half-wave plate 24, and reflected by the reflecting mirror 25 is Lr=LA·Pr·Ph·Rm. The amount of the second light transmitted through the reflective polarizing unit 23 is Lt=LA·Pt. The luminance of the first display area is Lr / (S １ ・ω １ ), and the luminance of the second display area is Lt / (S ２ ・ω ２ )

[0159] Therefore, the condition for making the luminance of the first display area and the second display area the same is (Equation 9) Pr / Pt=(1 / Rm)·(1 / Ph)·(S ２ ・ω ２ / S １ ・ω １ ) where (ω ２ / ω １ ) is a constant α, (Equation 10) Pr / Pt = α (1 / Rm) (1 / Ph) (S ２ / S １ ) can be expressed as

[0160] In addition, the solid angle ω in the first display area and the second display area is １ , ω ２ If it is considered that there is no significant difference between the two, the constant α is assumed to be 1, and the following equation (11) is obtained: Pr / Pt=(1 / Rm)·(1 / Ph)·(S ２ / S １ ) alone can set the relationship between the reflectance Pr of the first light and the transmittance Pt of the second light in the reflective polarizing unit 23, thereby simplifying the optical design.

[0161] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present disclosure.

[0162] The following configurations also constitute part of the present disclosure. Item 1: A polarization conversion element comprising: a translucency maintaining unit made of a light-transmitting material; a reflective polarizing unit formed on one surface of the translucency maintaining unit, which reflects light polarized in a predetermined direction as reflected light and transmits light polarized in a direction intersecting the predetermined direction as transmitted light; a half-wave plate formed on the other surface of the translucency maintaining unit, which converts the polarization direction of the transmitted light to the predetermined direction; and a reflecting mirror that reflects the reflected light or the transmitted light, wherein one end surface of the translucency maintaining unit is an inclined surface that is not perpendicular to the one surface. Item 2: The polarization conversion element according to item 1, wherein the inclined surface is provided along the traveling direction of light incident on the reflective polarizing unit. Item 3: The polarization conversion element according to Item 1 or 2, wherein, in a plan view of the translucency maintaining unit, the reflective polarizing unit and the half-wave plate have end positions that are different near the one end face, and the inclined surface is provided along a direction connecting the end of the reflective polarizing unit and the end of the half-wave plate. Item 4: The polarization conversion element according to any one of Items 1 to 3, wherein the inclined surface is provided at an angle of 45 degrees with respect to the one face. Item 5: An image projection device comprising the polarization conversion element according to any one of Items 1 to 4, a light source that irradiates the reflective polarizing unit with unpolarized light, and an image display unit that receives light polarized in the predetermined direction from the polarization conversion element from a back surface and emits image light from a display surface. Item 6: The image projection device according to Item 5, further comprising a lens arranged between the polarization conversion element and the image display unit, and the lens having a lenticular lens portion formed along the direction in which the inclined surface extends. Item 7: An image projection device that projects illumination light onto a display unit for displaying a virtual image, the image projection device comprising: an image illumination unit that illuminates the illumination light; and a polarization unit that is arranged on an optical path of the illumination light and transmits polarized light in a predetermined direction and absorbs or reflects polarized light in a direction intersecting the predetermined direction, the polarization unit being curved in a concave shape toward the incident side of the illumination light in the direction intersecting the predetermined direction. Item 8: The image projection device according to Item 7, wherein the polarization unit is arranged to be inclined at a predetermined angle with respect to the predetermined direction of the illumination light. Item 9: The image projection device according to Item 8, wherein the predetermined angle is in the range of 0 degrees or more and 55 degrees or less.Item 10: The image projection device according to any one of items 7 to 9, wherein the image irradiation unit has an image display unit that displays an image, and the polarization unit is disposed between the image display units. Item 11: The image projection device according to item 10, wherein the polarization unit is curved with an average curvature in the range of 25 mm to 200 mm. Item 12: The image projection device according to any one of items 7 to 11, wherein the image irradiation unit has an image display unit that displays an image and a light source that irradiates the image display unit with unpolarized irradiation light, and the polarization unit is disposed between the light source and the image display unit. Item 13: The image projection device according to item 12, wherein the polarization unit is curved with an average curvature in the range of 10 mm to 500 mm. Item 14: An optical display device comprising: a light source that emits unpolarized illumination light; an image display unit that receives the illumination light from a rear surface and emits image light from a display surface; a reflective polarizing unit that reflects light polarized in a first direction as first light and transmits light polarized in a second direction intersecting the first direction as second light; and a half-wave plate that is arranged on an optical path of the first light or the second light, wherein the first light is illuminated onto a first display region of the image display unit and the second light is illuminated onto a second display region, and an area of ​​the first display region is S. １ and the area of ​​the second display region is S ２ where Pr is the reflectance of the first light in the reflective polarizing unit, Pt is the transmittance of the second light, and Pr / Pt is ２ / S １ Item 15: An image projection device, wherein the half-wave plate is disposed on the optical path of the first light, a reflecting portion that reflects the second light is provided on the optical path of the second light, and when a transmittance of the half-wave plate is Ph, a reflectance of the reflecting portion is Rm, and a constant is α, Pr / Pt=α·Rm·(1 / Ph)·(S ２ / S １ Item 16: The image projection device according to item 14, wherein the half-wave plate is disposed on the optical path of the second light, a reflecting portion that reflects the second light is provided on the optical path of the second light, and when a reflectance of the reflecting portion is Rm, a transmittance of the half-wave plate is Ph, and a constant is α, the relationship Pr / Pt=α Rm Ph (S ２ / S１ Item 17: The image projection device according to item 14, wherein the half-wave plate is disposed on the optical path of the first light, a reflecting portion that reflects the first light is provided on the optical path of the first light, and when a transmittance of the half-wave plate is Ph, a reflectance of the reflecting portion is Rm, and a constant is α, the relationship Pr / Pt=α(1 / Rm)(1 / Ph)(S ２ / S １ Item 18: The image projection device according to item 14, wherein the half-wave plate is disposed on the optical path of the second light, a reflecting portion that reflects the first light is provided on the optical path of the first light, and when a reflectance of the reflecting portion is Rm, a transmittance of the half-wave plate is Ph, and a constant is α, the relationship Pr / Pt=α(1 / Rm)Ph(S ２ / S １ Item 19: The image projection device according to item 14, wherein the solid angle of the first light emitted from the first display area is defined as ω １ and the solid angle of the second light emitted from the second display region is ω ２ When the constant α is ２ / ω １ Item 20: The image projection device according to any one of items 14 to 19, wherein the first display area and the second display area are provided adjacent to each other on one image display unit. Item 21: The image projection device according to any one of items 14 to 19, wherein the first display area and the second display area are provided separately on one image display unit.

[0163] This application is based on Japanese Patent Application No. 2023-124222 filed on July 31, 2023, Japanese Patent Application No. 2023-124225 filed on July 31, 2023, and Japanese Patent Application No. 2023-126439 filed on August 2, 2023, the contents of which are incorporated herein by reference.

Claims

1. A polarization conversion element comprising: a light-transmitting portion made of a material that transmits light; a reflective polarizing portion formed on one surface of the light-transmitting portion and reflecting light polarized in a predetermined direction as reflected light and transmitting light polarized in a direction intersecting the predetermined direction as transmitted light; a half-wave plate formed on the other surface of the light-transmitting portion and converting the polarization direction of the transmitted light to the predetermined direction; and a reflecting mirror that reflects the reflected light or the transmitted light, wherein one end face of the light-transmitting portion is an inclined surface that is not perpendicular to the one surface.

2. The polarization conversion element according to claim 1, wherein the inclined surface is provided along the traveling direction of light incident on the reflective polarizing section.

3. A polarization conversion element as described in claim 1, wherein, in a planar view of the translucency maintaining section, the reflective polarizing section and the half-wave plate have end positions that are different near the one end face, and the inclined surface is provided along a direction connecting the end of the reflective polarizing section and the end of the half-wave plate.

4. The polarization conversion element according to claim 1, wherein the inclined surface is inclined at 45 degrees with respect to the one surface.

5. An image projection device comprising: a polarization conversion element according to any one of claims 1 to 4; a light source which irradiates the reflective polarizing section with unpolarized light; and an image display section which receives polarized light in the specified direction from the polarization conversion element from its rear surface and emits image light from its display surface.

6. An image projection device as described in claim 5, further comprising a lens disposed between said polarization conversion element and said image display section, said lens being formed with a lenticular lens section aligned along the direction in which said inclined surface extends.

7. An image projection device that projects illumination light onto a display unit for displaying a virtual image, comprising: an image illumination unit that illuminates the illumination light; and a polarizing unit that is disposed on an optical path of the illumination light, transmits polarized light in a predetermined direction, and absorbs or reflects polarized light in a direction intersecting the predetermined direction, the polarizing unit being curved in a concave shape toward the incident side of the illumination light in a direction intersecting the predetermined direction.

8. The image projection device according to claim 7, wherein the polarizing section is disposed so as to be inclined at a predetermined angle with respect to the predetermined direction of the irradiated light.

9. The image projection device according to claim 8, wherein the predetermined angle is in the range of 0 degrees to 55 degrees.

10. The image projection device according to claim 7, wherein the image irradiation unit has an image display unit that displays an image, and the polarization unit is disposed between the image display unit and the display unit.

11. The image projection device according to claim 10, wherein the polarizing section is curved with an average curvature in the range of 25 mm to 200 mm.

12. The image projection device of claim 7, wherein the image irradiation unit has an image display unit that displays an image, and a light source that irradiates the image display unit with unpolarized irradiation light, and the polarization unit is disposed between the light source and the image display unit.

13. The image projection device according to claim 12, wherein the polarizing section is curved with an average curvature in the range of 10 mm to 500 mm.

14. A liquid crystal display device comprising: a light source which emits unpolarized irradiation light; an image display unit to which the irradiation light is incident from a rear surface and which emits image light from a display surface; a reflective polarizing unit which reflects polarized light in a first direction as a first light and transmits polarized light in a second direction intersecting the first direction as a second light; and a half-wave plate which is disposed on an optical path of the first light or the second light, wherein the first light is irradiated onto a first display region of the image display unit and the second light is irradiated onto a second display region, and the area of ​​the first display region is defined as S １ and the area of ​​the second display region is S ２ The reflectance of the first light in the reflective polarizing unit is Pr, the transmittance of the second light is Pt, and Pr / Pt is S ２ / S １ An image projection device.

15. The half-wave plate is disposed on the optical path of the first light, and a reflecting portion that reflects the second light is provided on the optical path of the second light, and when the transmittance of the half-wave plate is Ph, the reflectance of the reflecting portion is Rm, and a constant is α, Pr / Pt=α·Rm·(1 / Ph)·(S ２ / S １ 15. The image projection device according to claim 14, wherein the following relationship is satisfied:

16. The half-wave plate is disposed on the optical path of the second light, and a reflecting portion that reflects the second light is provided on the optical path of the second light, and when the reflectance of the reflecting portion is Rm, the transmittance of the half-wave plate is Ph, and a constant is α, Pr / Pt=α·Rm·Ph·(S ２ / S １ 15. The image projection device according to claim 14, wherein the following relationship is satisfied:

17. The half-wave plate is disposed on the optical path of the first light, and a reflecting portion that reflects the first light is provided on the optical path of the first light, and when the transmittance of the half-wave plate is Ph, the reflectance of the reflecting portion is Rm, and a constant is α, Pr / Pt=α·(1 / Rm)·(1 / Ph)·(S ２ / S １ 15. The image projection device according to claim 14, wherein the following relationship is satisfied:

18. The half-wave plate is disposed on the optical path of the second light, and a reflecting portion that reflects the first light is provided on the optical path of the first light, and when the reflectance of the reflecting portion is Rm, the transmittance of the half-wave plate is Ph, and a constant is α, Pr / Pt=α·(1 / Rm)·Ph·(S ２ / S １ 15. The image projection device according to claim 14, wherein the following relationship is satisfied:

19. The solid angle of the first light irradiated from the first display area is ω １ and the solid angle of the second light emitted from the second display region is ω ２ Then, the constant α=ω ２ / ω １ 19. The image projection device according to claim 15, wherein:

20. The image projection device according to claim 14, wherein the first display area and the second display area are provided adjacent to each other on one of the image display sections.

21. The image projection device according to claim 14, wherein the first display area and the second display area are provided separately on one of the image display sections.

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