Image projection device

Abstract

To provide an image projection device with which it is possible to project a plurality of images while suppressing an increase in the number of components of a projection optical member and achieving a reduction in the size of the optical member.SOLUTION: Provided is an image projection device (100) for projecting a projection image onto a display unit (WS) for displaying virtual images (P1, P2). The image projection device (100) comprises: an image irradiation unit (10) for emitting first image light which is a circularly polarized light in a first direction of rotation, and second image light which is a circularly polarized light rotating in a reverse direction to the first direction of rotation; a first polarization holographic optical element (50) having a refractive index distribution which varies with the direction of polarization; a projection optical unit (30) on which the first image light and the second image light are incident via the first polarization holographic optical element (50), and which projects the first image light and the second image light to a display unit (WS); and a multiplexing member (20) for multiplexing the first image light and the second image light at the position of the first polarization holographic optical element (50).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an image projection device, and more particularly to an image projection device for projecting a plurality of images. [Background technology]

[0002] Conventionally, dashboards that light up icons have been used as devices for displaying various types of information inside a vehicle. 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 a conventional image projection device, an image projection unit projects light containing an image, and the light is reflected by a free-form mirror or the like to reach the viewpoint of the passenger so that the image is formed in space via a display unit such as a windshield. This allows the passenger to perceive the image as being displayed at the imaging position in the depth direction by the light incident on the viewpoint. In addition, it has been proposed to project multiple images onto the windshield using a driving assistance HUD device in order to present more information.

[0005] However, in order to project and form multiple images as virtual images at different distances, multiple image projection units and projection optical systems are required, which limits the degree of freedom in design when fitting them within an instrument panel. Therefore, the applicant of the present application has proposed an image projection device that displays multiple images within a single image projection unit and branches the optical paths of each image to save space. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2019-119248 A [Patent Document 2] JP 2019-119262 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, in conventional image projection devices that project multiple images, the optical path of each image is changed to separate the imaging positions of the virtual images, which increases the number of optical components required.In addition, optical components must be positioned away from the optical paths for projecting other images, which makes it difficult to reduce the size of the device.

[0008] Therefore, the present invention has been made in consideration of the above-mentioned conventional problems, and aims to provide an image projection device capable of projecting multiple images while suppressing an increase in the number of parts in the projection optical components and achieving miniaturization of the optical components. [Means for solving the problem]

[0009] In order to solve the above problems, the image projection device of the present invention is an image projection device that projects a projection image onto a display unit for displaying a virtual image, and is characterized in having an image irradiation unit that irradiates first image light that is circularly polarized in a first rotation direction and second image light that is circularly polarized in the opposite rotation direction to the first rotation direction, a first polarizing holographic optical element having a refractive index distribution that differs depending on the polarization direction, a projection optical unit into which the first image light and the second image light are incident via the first polarizing holographic optical element and which projects the first image light and the second image light onto the display unit, and a combining member that combines the first image light and the second image light at the position of the first polarizing holographic optical element.

[0010] In the image projection device of the present invention, the first image light and the second image light are irradiated as counter-rotating circularly polarized light and are combined at the position of the first polarizing holographic optical element, so that the paths of the first image light and the second image light can be designed according to the grating period of the first polarizing holographic optical element, making it possible to project multiple images while suppressing an increase in the number of parts and miniaturizing the optical components.

[0011] In one embodiment of the present invention, the first polarizing holographic optical element has a lens function and a diffraction grating function.

[0012] In one aspect of the invention, the beam combining member is a reflecting mirror that reflects the first image light and the second image light irradiated from the image irradiating section.

[0013] In one aspect of the invention, the reflecting mirror forms an intermediate image of the first image light and the second image light at an intermediate imaging position, and the first polarizing holographic optical element is disposed at the intermediate imaging position.

[0014] In one aspect of the present invention, the beam combining member is a second polarizing holographic optical element having a refractive index distribution that varies depending on the polarization direction.

[0015] In one aspect of the present invention, the second polarizing holographic optical element has the same grating period as the first polarizing holographic optical element.

[0016] In addition, in one aspect of the present invention, the beam combining member is a prism.

[0017] In one aspect of the present invention, the polarization holographic optical element is a transmissive liquid crystal holographic element.

[0018] In addition, in one embodiment of the present invention, the image irradiation unit has an image display unit that displays a first image and a second image and emits polarized light in a predetermined direction, and the image display unit has a first region that displays the first image and a second region that displays the second image, a first circular polarization conversion unit arranged opposite the first region, and a second circular polarization conversion unit arranged opposite the second region.

[0019] In one embodiment of the present invention, the image display unit is a liquid crystal display device, and the first circular polarization conversion unit and the second circular polarization conversion unit are each a quarter-wave plate or a three-quarter-wave plate, and are arranged so that their fast axes and slow axes intersect the specified direction. Effect of the Invention

[0020] The present invention can provide an image projection device capable of projecting a plurality of images while suppressing an increase in the number of parts in the projection optical members and achieving miniaturization of the optical members. [Brief description of the drawings]

[0021] [Figure 1] 3 is a schematic cross-sectional view illustrating the projection of virtual images P1 and P2 using the image projection device 100 according to the first embodiment. FIG. [Diagram 2]2A and 2B are diagrams showing an example of the positional relationship between the image display area in the image display unit 12 and the first circular polarization conversion unit 13a and the second circular polarization conversion unit 13b, where FIG. 2(a) is a schematic plan view of the image display unit 12 and FIG. 2(b) is a schematic plan view of the first circular polarization conversion unit 13a and the second circular polarization conversion unit 13b. [Diagram 3] 3A and 3B are diagrams for explaining the direction of propagation of circularly polarized light in the polarized holographic optical element 50, where FIG. 3(a) shows the lens function for left-handed circularly polarized light, FIG. 3(b) shows the lens function for right-handed circularly polarized light, FIG. 3(c) shows the diffraction grating function for left-handed circularly polarized light, and FIG. 3(d) shows the diffraction grating function for right-handed circularly polarized light. [Figure 4] 2 is a schematic diagram illustrating the combining of a first image light and a second image light by a reflecting mirror 20 in the image projection device 100 according to the first embodiment. FIG. [Diagram 5] 10 is a schematic diagram illustrating the focal lengths of a first image light and a second image light transmitted through a polarization holographic optical element 50. FIG. [Figure 6] FIG. 11 is a schematic diagram illustrating the focal lengths of a first image light and a second image light transmitted through a polarization holographic optical element 50 in a modified example of the first embodiment. [Figure 7] 13 is a schematic diagram illustrating the combining of a first image light and a second image light by a polarization holographic optical element 60 in an image projector 100 according to a second embodiment. FIG. [Figure 8] 13 is a schematic diagram illustrating the combining of the first image light and the second image light by the prisms 70a and 70b in the image projection device 100 according to the third embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] (First embodiment) Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. The same or equivalent components, members, and processes shown in each drawing are given the same reference numerals, and duplicated descriptions will be omitted as appropriate. Fig. 1 is a schematic cross-sectional view for explaining the projection of virtual images P1 and P2 using an image projection device 100. The dashed line shown in Fig. 1 indicates the optical path of a first image light, which will be described later, and the dashed line indicates the optical path of a second image light.

[0023] As shown in Fig. 1, the image projection device 100 includes an image projection unit 10, a reflection mirror 20, a projection mirror 30, an external light cut filter 40, and a polarizing holographic optical element 50. As shown in Fig. 1, the first image light and the second image light projected from the image projection device 100 are reflected by a windshield (display unit) WS and irradiated to the driver's viewpoint. The driver visually recognizes virtual images P1 and P2 formed on the extension of the optical path along which the first image light and the second image light are incident.

[0024] 1, the optical paths of the first image light and the second image light are drawn as a straight line. However, the actual first image light and the second image light 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. The first image light and the second image light may be reflected by the projection mirror 30 and travel with their light diameters reduced, and may be imaged between the projection mirror 30 and the windshield WS.

[0025] In the image projection device 100 shown in Fig. 1, each part is controlled by a control unit connected to each part so as to be able to communicate information with the other parts. The configuration of the control unit is not limited, but an example includes a CPU (Central Processing Unit) for performing information processing, a memory device, a recording medium, an information communication device, and the like. The control unit controls the operation of each part according to a predetermined program, and sends information including an image (image information) to the image projection unit 10.

[0026] The image projection unit 10 is a part that projects light including an image based on image information from the control unit. In the example shown in FIG. 1, the image projection unit 10 includes a backlight 11, an image display unit 12, a first circular polarization conversion unit 13a, and a second circular polarization conversion unit 13b. The backlight 11 is a part that projects light onto the image display unit 12, and may be, for example, a light emitting diode (LED) that projects light. The light projected by the backlight 11 is preferably white, but a light that emits a single color such as blue, green, or red may also be used.

[0027] The image display unit 12 is a part that displays a projection image in response to an image signal from the control unit. When the projection image displayed on the image display unit 12 is irradiated with light from the backlight 11, the first image light and the second image light are irradiated from the image display unit 12. The specific configuration of the image display unit 12 is not limited, and for example, a liquid crystal display device or the like can be used. As described later, the image display unit 12 is configured to include a far display area (first area) 12a and a near display area (second area) 12b that display a far image and a near image, respectively.

[0028] The first circular polarization conversion unit 13a and the second circular polarization conversion unit 13b are units that transmit the first image light and the second image light irradiated from the image display unit 12 and convert them into circularly polarized light. The first circular polarization conversion unit 13a and the second circular polarization conversion unit 13b are set to convert the light into circularly polarized light with opposite rotations to each other.

[0029] When the first image light and the second image light from the image display unit 12 are not linearly polarized, the first circular polarization conversion unit 13a and the second circular polarization conversion unit 13b are configured by combining a polarizing plate that transmits only linearly polarized light in a predetermined direction with a quarter-wave plate or a three-quarter-wave plate. When a liquid crystal display device is used as the image display unit 12, the first image light and the second image light irradiated from the image display unit 12 are both linearly polarized in a predetermined direction, so that the first circular polarization conversion unit 13a and the second circular polarization conversion unit 13b are configured with a quarter-wave plate or a three-quarter-wave plate without using a separate polarizing plate.

[0030] As an example, quarter-wave plates are used for the first circular polarization conversion unit 13a and the second circular polarization conversion unit 13b, and are arranged so that the fast axis and slow axis of the quarter-wave plate are inclined at 45 degrees and -45 degrees, respectively, to cross the predetermined polarization direction. Alternatively, a quarter-wave plate may be used for one of the first circular polarization conversion unit 13a and the second circular polarization conversion unit 13b, and a three-quarter-wave plate may be used for the other, and the fast axis and slow axis of each may be inclined at 45 degrees to cross the predetermined polarization direction.

[0031] The reflecting mirror 20 is an optical member that receives the first image light transmitted through the first circular polarization conversion unit 13a and the second image light transmitted through the second circular polarization conversion unit 13b, and reflects the first image light and the second image light toward the projection mirror 30 via the polarizing holographic optical element 50. In the example shown in FIG. 1, a free-form mirror with a concave shape is shown as the reflecting mirror 20. The reflecting mirror 20 has a reflecting surface shape that combines the first image light and the second image light that are incident on different regions so as to overlap in the same region at the position of the polarizing holographic optical element 50. Although an example in which one reflecting mirror 20 is used is shown here, a combination of multiple reflecting mirrors 20 may be used.

[0032] The reflecting mirror 20 may have a predetermined focal length and may intermediately image the first and second image lights at a predetermined intermediate image position. In this case, the area of ​​the polarizing holographic optical element 50 can be reduced by disposing the polarizing holographic optical element 50 at the intermediate image position.

[0033] The projection mirror 30 is an optical member that receives the first image light and the second image light that have passed through the polarizing holographic optical element 50 and reflects the first image light and the second image light in the direction of the windshield WS via the external light cut filter 40. The projection mirror 30 corresponds to the projection optical unit in the present invention. Here, an example is shown in which the projection mirror 30 is used as the projection optical unit, but a combination of multiple projection mirrors 30 may be used, and optical members such as lenses and prisms may also be included.

[0034] In the example shown in Fig. 1, a free-form mirror having a concave shape is used as the projection mirror 30. The reflecting surface of the projection mirror 30 is designed to expand the light diameter in the driver's viewpoint direction in order to project the first image light and the second image light as virtual images P1, P2 through the windshield WS. Here, the expansion of the light diameter in the viewpoint direction includes not only the case where the light diameter expands consistently after reflection, but also the case where the light diameter shrinks and expands after forming an image at an intermediate point.

[0035] The external light cut filter 40 is disposed between the projection mirror 30 and the windshield WS, and is a part that cuts out a part of the external light that reaches the inside of the image projection device 100 from the outside. In particular, to prevent sunlight from reaching the image projection unit 10 from above the windshield WS and causing a rise in temperature of the image display unit 12, it is preferable to use a wavelength filter that transmits visible light and cuts infrared light and ultraviolet light.

[0036] The polarizing holographic optical element 50 is an optical member having a refractive index distribution that varies depending on the polarization direction. The polarizing holographic optical element 50 of this embodiment corresponds to the first polarizing holographic optical element of the present invention. Although a specific example of the polarizing holographic optical element 50 is not limited, a known liquid crystal holographic element described in APPLIED PHYSICS LETTERS Vol. 82, No. 3, pages 328-330 can be used as an example. Although FIG. 1 shows an example in which a transmission type liquid crystal holographic element is used as the polarizing holographic optical element 50, a reflection type liquid crystal holographic element may also be used. Circularly polarized light that has passed through the first circular polarization conversion unit 13a and the second circular polarization conversion unit 13b is incident on the polarizing holographic optical element 50, and the first image light and the second image light interfere with each other due to the refractive index according to the polarization direction, and the traveling direction is changed. The conversion of the traveling direction of the first image light and the second image light by the polarizing holographic optical element 50 will be described in detail later.

[0037] The windshield WS is a part provided in front of the driver's seat of the vehicle and transmits visible light. The windshield WS corresponds to the display unit in the present invention because the windshield WS reflects the first image light and the second image light incident from the projection mirror 30 toward the viewpoint on the inner surface of the vehicle and transmits light from the outside of the vehicle toward the viewpoint. Here, an example is shown in which the windshield WS is used as the display unit, but a combiner may be prepared as a display unit separate from the windshield WS and may reflect light from the projection mirror 30 toward the viewpoint. In addition, the display unit is not limited to being located in front of the vehicle, and may be located to the side or rear as long as it projects an image toward the viewpoint of the passenger.

[0038] The virtual images P1 and P2 are images that are displayed as if they were formed in space when the first image light and the second image light reflected by the windshield WS reach the viewpoint (eyebox) of the driver, etc. The positions at which the virtual images P1 and P2 are formed depend on the composite focal length of the light irradiated from the image irradiation unit 10, the polarizing holographic optical element 50, the projection mirror 30, and the windshield WS.

[0039] In the image projection device 100, a far image displayed in the far display area 12a of the image display unit 12 is irradiated as a first image light, and a near image displayed in the near display area 12b is irradiated as a second image light. Examples of the far image displayed in the far display area 12a include images calling attention and auxiliary information related to driving, such as emergency information. Examples of the near image displayed in the near display area 12b include a speed and volume indicator, a driving direction guide, and the like.

[0040] 2 is a diagram showing an example of the positional relationship between the image display area in the image display unit 12 and the first circular polarization conversion unit 13a and the second circular polarization conversion unit 13b, where FIG. 2(a) is a schematic plan view of the image display unit 12 and FIG. 2(b) is a schematic plan view of the first circular polarization conversion unit 13a and the second circular polarization conversion unit 13b. As shown in FIG. 2(a), in the image display unit 12, a far image (first image) and a near image (second image) are displayed in the far display area (first area) 12a and the near display area (second area) 12b, respectively, with respect to the entire display area capable of displaying images. Also, as shown in FIG. 1 and FIG. 2(b), the first circular polarization conversion unit 13a and the second circular polarization conversion unit 13b are arranged to overlap the far display area 12a and the near display area 12b of the image display unit 12, respectively.

[0041] Here, arranging the first circular polarization conversion unit 13a and the second circular polarization conversion unit 13b so as to overlap with the image display unit 12 means that the area in which the first circular polarization conversion unit 13a and the second circular polarization conversion unit 13b are arranged overlaps with the image display area of ​​the image display unit 12 in a planar view. In addition, the overlapping arrangement includes both cases in which the first circular polarization conversion unit 13a and the second circular polarization conversion unit 13b are in contact with the image display unit 12 and cases in which they are not in contact with the image display unit 12. In addition, the overlapping arrangement also includes cases in which an optical member that transmits light or a holding member for maintaining the distance between the first circular polarization conversion unit 13a and the second circular polarization conversion unit 13b and the image display unit 12 is interposed.

[0042] In this embodiment, an element having a lens function and a diffraction grating function is used as the polarizing holographic optical element 50. A polarizing holographic optical element 50 having a lens function has a refractive index distribution in which the refractive index varies depending on the polarization direction, and the refractive index distribution causes light to be diffracted at various points within the plane, resulting in the light diameter being converted into a traveling direction that expands or contracts.

[0043] A polarized holographic optical element 50 having a diffraction grating function has a refractive index distribution in which the refractive index varies depending on the polarization direction, and the light is diffracted at various points in the plane due to the refractive index distribution, resulting in a change in the traveling direction of the light. In such a polarized holographic optical element 50 having a diffraction grating function, if the traveling direction of the light emitted when right-handed circularly polarized light is incident perpendicularly to the plane is +θ, the traveling direction of the light emitted when left-handed circularly polarized light is incident is -θ. Conversely, left-handed circularly polarized light incident from the direction of +θ and right-handed circularly polarized light incident from the direction of -θ are emitted along the same optical path.

[0044] 3 is a diagram for explaining the traveling direction of circularly polarized light in the polarizing holographic optical element 50, in which FIG. 3(a) shows the lens function of left-handed circularly polarized light, FIG. 3(b) shows the lens function of right-handed circularly polarized light, FIG. 3(c) shows the diffraction grating function of left-handed circularly polarized light, and FIG. 3(d) shows the diffraction grating function of right-handed circularly polarized light. As shown in FIG. 3(a), when left-handed circularly polarized light is incident on the polarizing holographic optical element 50, the light diameter of the transmitted circularly polarized light is reduced, and after being focused at the focal point F2, the light diameter is expanded and a real image is formed. In other words, the polarizing holographic optical element 50 becomes equivalent to one that gives positive optical power to left-handed circularly polarized light.

[0045] 3(b), when right-handed circularly polarized light is incident on the polarization holographic optical element 50, the light diameter of the transmitted circularly polarized light expands. In this case, the light is focused at a virtual focal point F1 before passing through the polarization holographic optical element 50, and a virtual image of the light emitted from the focal point F1 is formed. In other words, the polarization holographic optical element 50 is equivalent to one that imparts negative optical power to right-handed circularly polarized light.

[0046] In the example shown in Figures 3(a) and (b), the polarization holographic optical element 50 is shown to impart positive optical power to left-handed circularly polarized light and negative optical power to right-handed circularly polarized light, but the rotation direction of the circularly polarized light and the positive and negative of the power may be reversed. Also, in Figures 3(a) and (b), right-handed and left-handed circularly polarized light are incident on separate polarization holographic optical elements 50, but right-handed and left-handed circularly polarized light may be incident on different regions of a common polarization holographic optical element 50.

[0047] As shown in Fig. 3(c), by making left-handed circularly polarized light incident on the polarizing holographic optical element 50 from the direction of +θ, the transmitted light is converted to right-handed circularly polarized light and travels in a direction perpendicular to the surface. Also, as shown in Fig. 3(d), by making right-handed circularly polarized light incident on the polarizing holographic optical element 50 from the direction of -θ, the transmitted light is converted to left-handed circularly polarized light and travels in a direction perpendicular to the surface.

[0048] By incorporating both a lens function and a diffraction grating function into the polarizing holographic optical element 50, it is possible to realize, with a single polarizing holographic optical element 50, the effect of creating a difference in the imaging position due to the lens function, and the effect of superimposing optical paths due to the diffraction grating function.

[0049] Fig. 4 is a schematic diagram for explaining the multiplexing of the first image light and the second image light by the reflecting mirror 20 in the image projection device 100 according to this embodiment. In Fig. 4, the width of the area through which the first image light passes is typically indicated by a dashed line, and the width of the area through which the second image light passes is typically indicated by a dashed line.

[0050] In this embodiment, the first image light and the second image light are irradiated from the far display region 12a and the near display region 12b, which are different regions of the image display unit 12, and are converted into circularly polarized light with opposite rotations to each other by passing through the first circular polarization conversion unit 13a and the second circular polarization conversion unit 13b, respectively. The first image light and the second image light converted into circularly polarized light are reflected by different regions on the reflecting surface of the reflecting mirror 20, and are combined so as to overlap in the same region at the position of the polarizing holographic optical element 50. At this time, the first image light and the second image light are incident on the polarizing holographic optical element 50 at different incident angles.

[0051] The polarizing holographic optical element 50 has a refractive index distribution that varies depending on the polarization direction, and has the diffraction grating function described in Fig. 3(c) and (d). Therefore, by appropriately setting the refractive index distribution of the polarizing holographic optical element 50, the first image light and the second image light that are incident at different angles can be transmitted in the same direction. The first image light and the second image light that are combined at the position of the polarizing holographic optical element 50 are reflected by the projection mirror 30 and travel toward the windshield WS. The first image light and the second image light that reach the windshield WS are reflected toward the driver's viewpoint, and the driver visually recognizes virtual images P1 and P2 on the extension of the direction in which the first image light and the second image light reach.

[0052] Fig. 5 is a schematic diagram for explaining the focal lengths of the first image light and the second image light transmitted through the polarizing holographic optical element 50. Fig. 5 shows the paths of the first image light and the second image light when the reflecting mirror 20, the polarizing holographic optical element 50, and the projection mirror 30 are viewed in a plan view from above. In Fig. 5, the width of the area through which the first image light passes is typically shown using a dashed line, and the width of the area through which the second image light passes is typically shown using a dashed line.

[0053] The polarizing holographic optical element 50 has a refractive index distribution that differs depending on the polarization direction, and has the lens function described in FIG. 3(a)(b). Therefore, by appropriately setting the refractive index distribution of the polarizing holographic optical element 50, the optical power acting on the first image light and the second image light can be made different, and the light diameter can be condensed or expanded so that the focal positions of each light are different. In the example shown in FIG. 6, a negative optical power acts on the first image light, and the light diameter expands as the first image light reaches the projection mirror 30 so that the virtual focal position (not shown) is located between the reflection mirror 20 and the polarizing holographic optical element 50. A positive optical power acts on the second image light, and the second image light is condensed so that the focal position is located between the polarizing holographic optical element 50 and the projection mirror 30, and the second image light reaches the projection mirror 30 while expanding its light diameter after intermediate imaging.

[0054] The first and second image lights transmitted through the polarizing holographic optical element 50 are reflected by the projection mirror 30 and the windshield WS, and the driver visually recognizes virtual images P1 and P2 on an extension of the direction in which the first and second image lights reach. At this time, the focal positions of the first and second image lights are different due to the lens function of the polarizing holographic optical element 50, so that the virtual images P1 and P2 are visually recognized as being formed at different positions. Specifically, as shown in Figures 1 and 2, the imaging positions of the virtual images P1 and P2 are farther from the viewpoint position for the first image than for the second image.

[0055] 4 and 5 show an example in which only the diffraction grating function of the polarizing holographic optical element 50 is applied to the height direction of the first image light and the second image light, but the lens function may also be applied in the height direction. Also, an example in which the first image light and the second image light are irradiated onto different regions in the height direction of the reflecting mirror 20 is shown, but the first image light and the second image light may be irradiated onto different regions in the width direction, and the diffraction grating function may be applied in the width direction of the polarizing holographic optical element 50.

[0056] As described above, in the image projection device 100 of this embodiment, the first image light and the second image light are converted into circularly polarized light with reverse rotation, and are made to enter the same region of the polarizing holographic optical element 50 at different angles using the reflecting mirror 20. Since the polarizing holographic optical element 50 has a diffraction grating function, the optical paths of the transmitted first image light and the second image light can be overlapped. In addition, the first image light and the second image light transmitted through the polarizing holographic optical element 50 reach the same region of the projection mirror 30 with their optical paths overlapped and are reflected. This makes it possible to reduce the reflecting surface of the projection mirror 30 and achieve miniaturization, compared to the case where the first image light and the second image light are reflected at different regions of the projection mirror 30. In addition, since the polarizing holographic optical element 50 has a lens function, it is possible to differentiate the focal positions of the first image light and the second image light, provide an optical path difference, and differentiate the imaging positions of the virtual images P1 and P2, without using a separate lens or mirror. This makes it possible to project a plurality of images while suppressing an increase in the number of parts and reducing the size of the optical components.

[0057] (Modification of the first embodiment) Next, a modified example of the first embodiment of the present invention will be described with reference to FIG. 6. Descriptions of contents overlapping with the first embodiment will be omitted. FIG. 6 is a schematic diagram for explaining the focal lengths of the first image light and the second image light transmitted through the polarized holographic optical element 50 in this modified example. FIG. 6 shows the paths of the first image light and the second image light when the reflecting mirror 20, the polarized holographic optical element 50, and the projection mirror 30 are viewed in plan from above. In FIG. 6, the width of the area through which the first image light passes is typically shown by using a dashed line, and the width of the area through which the second image light passes is typically shown by using a dashed line.

[0058] This modified example differs from the example shown in Fig. 5 in that different positive optical powers are applied to the first image light and the second image light. As shown in Fig. 6, positive optical power is applied to the first image light, and the light reaches the projection mirror 30 while expanding in diameter after being condensed to form an intermediate image so that the focal position is located between the polarization holographic optical element 50 and the projection mirror 30. Positive optical power is also applied to the second image light, and the light reaches the projection mirror 30 while shrinking in diameter so that the virtual focal position (not shown) is located between the projection mirror 30 and the windshield WS.

[0059] In this modification, the driver also visually recognizes the virtual images P1 and P2 on the extension of the direction in which the first image light and the second image light reach. At this time, the focal positions of the first image light and the second image light are different due to the lens function of the polarized holographic optical element 50, so that the imaging positions of the virtual images P1 and P2 are visually recognized as different. Specifically, as shown in FIG. 1 and FIG. 2, the imaging positions of the virtual images P1 and P2 are farther from the viewpoint position in the first image than in the second image. In FIG. 6, different positive optical powers are applied to the first image light and the second image light, but different negative optical powers may be applied to make the focal positions of the first image light and the second image light different, and the imaging positions of the virtual images P1 and P2 may be made different.

[0060] Second embodiment Next, a second embodiment of the present invention will be described with reference to FIG. 7. Description of the contents overlapping with the first embodiment will be omitted. FIG. 7 is a schematic diagram for explaining the multiplexing of the first image light and the second image light by the polarizing holographic optical element 60 in the image projector 100 according to the second embodiment. As shown in FIG. 7, the image projector 100 includes an image irradiation unit 10, a reflecting mirror 20, a projection mirror 30, an external light cut filter 40, and polarizing holographic optical elements 50 and 60.

[0061] The polarizing holographic optical element 60 is an optical member having a refractive index distribution that varies depending on the polarization direction. The polarizing holographic optical element 60 has at least a diffraction grating function. The grating period of the polarizing holographic optical element 60 is preferably the same as that of the polarizing holographic optical element 50. The polarizing holographic optical element 60 of this embodiment corresponds to the combining member and the second polarizing holographic optical element of the present invention. Figure 7 shows an example in which the polarized holographic optical element 60 is placed in contact with the first circular polarization conversion unit 13a and the second circular polarization conversion unit 13b, but the position is not limited as long as it is on the path of the first image light and the second image light that have passed through the first circular polarization conversion unit 13a and the second circular polarization conversion unit 13b.

[0062] In this embodiment, the first image light and the second image light are irradiated from the far display area 12a and the near display area 12b, which are different areas of the image display unit 12, and are converted into circularly polarized light with opposite rotations to each other by passing through the first circular polarization conversion unit 13a and the second circular polarization conversion unit 13b, respectively. The first image light and the second image light converted into circularly polarized light are bent in opposite directions by the diffraction grating function of the polarizing holographic optical element 60 as shown in Figures 3(c) and (d), and are combined so as to overlap in the same area at the position of the polarizing holographic optical element 50. Here, the first image light and the second image light transmitted through the polarizing holographic optical element 60 are circularly polarized light with opposite rotations to the rotation direction before entering the polarizing holographic optical element 60.

[0063] The first and second image lights bent by the polarizing holographic optical element 60 are incident on the same region of the polarizing holographic optical element 50 at different angles of incidence. As shown in FIG. 3(c) and (d), the bending direction is reversed depending on the rotation direction of the circularly polarized light, so the first and second image lights incident on the polarizing holographic optical element 50 are bent in the opposite direction to the polarizing holographic optical element 60. When the lattice period of the polarizing holographic optical element 60 is the same, the diffraction angle of the same wavelength is the same, so the first and second image lights combined by the polarizing holographic optical element 60 proceed in the same direction. The first and second image lights combined by the polarizing holographic optical element 50 are reflected by the projection mirror 30 and proceed in the direction of the windshield WS. The first and second image lights that reach the windshield WS are reflected in the direction of the driver's viewpoint, and the driver visually recognizes virtual images P1 and P2 on the extension of the direction in which the first and second image lights reach.

[0064] In this embodiment, since the polarizing holographic optical element 60 is used as the beam combining member, the beam combining member can be made smaller and lighter. In addition, by making the grating periods of the polarizing holographic optical elements 50 and 60 the same and making the diffraction angles the same, it becomes easy to overlap the paths of the first image light and the second image light transmitted through the polarizing holographic optical element 50.

[0065] Furthermore, when the first image light and the second image light contain light of multiple wavelengths, the diffraction angle at the polarizing holographic optical elements 50, 60 differs for each wavelength. However, the circular polarization of the first image light and the second image light rotates in opposite directions when passing through the polarizing holographic optical element 60, so the diffraction direction at the polarizing holographic optical element 50 is opposite to that of the polarizing holographic optical element 60. As a result, even if the diffraction angles differ for each wavelength, the difference in diffraction angle due to wavelength is canceled out by bending in the opposite directions at the polarizing holographic optical elements 50, 60, and color shift can be corrected.

[0066] In the image projection device 100 of this embodiment, the reflection surface of the projection mirror 30 can be made smaller to achieve miniaturization, compared to the case where the first image light and the second image light are reflected in different areas of the projection mirror 30. In addition, it is possible to project multiple images while suppressing an increase in the number of parts and miniaturizing the optical members.

[0067] Third embodiment Next, a third embodiment of the present invention will be described with reference to FIG. 8. Descriptions of contents overlapping with the first embodiment will be omitted. FIG. 8 is a schematic diagram for explaining the multiplexing of the first image light and the second image light by the prisms 70a and 70b in the image projection device 100 according to the third embodiment. As shown in FIG. 8, the image projection device 100 includes an image irradiation unit 10, a reflection mirror 20, a projection mirror 30, an external light cut filter 40, a polarizing holographic optical element 50, and the prisms 70a and 70b.

[0068] The prisms 70a and 70b are optical members that are made of a material that transmits light and has a refractive index greater than that of air, and that change the angle of incidence and the angle of emission of light depending on the difference in refractive index with air. As shown in FIG. 8, the prisms 70a and 70b are disposed opposite the first circular polarization conversion unit 13a and the second circular polarization conversion unit 13b, respectively. The prisms 70a and 70b are disposed so that the directions of refracting light are opposite to each other, and the first image light refracted by the prism 70a and the second image light refracted by the prism 70b are combined so as to overlap in the same region of the polarized holographic optical element 50. Therefore, the prisms 70a and 70b in this embodiment correspond to the combining member in the present invention.

[0069] In this embodiment, the first image light and the second image light are irradiated from the far display region 12a and the near display region 12b, which are different regions of the image display unit 12, and are converted into circularly polarized light with opposite rotations to each other by passing through the first circular polarization conversion unit 13a and the second circular polarization conversion unit 13b, respectively. The first image light and the second image light converted into circularly polarized light are bent in opposite directions by the prisms 70a and 70b, respectively, and are combined so as to overlap in the same region at the position of the polarizing holographic optical element 50. At this time, the first image light and the second image light are incident on the polarizing holographic optical element 50 at different incident angles.

[0070] The polarizing holographic optical element 50 has a diffraction grating function, and the first and second image lights combined at the position of the polarizing holographic optical element 50 reach the projection mirror 30 along the same path, are reflected, and travel in the direction of the windshield WS. The first and second image lights that reach the windshield WS are reflected in the direction of the driver's viewpoint, and the driver visually recognizes virtual images P1 and P2 on an extension of the direction in which the first and second image lights arrived.

[0071] In the image projection device 100 of this embodiment, the reflection surface of the projection mirror 30 can be made smaller to achieve miniaturization, compared to the case where the first image light and the second image light are reflected in different areas of the projection mirror 30. In addition, it is possible to project multiple images while suppressing an increase in the number of parts and miniaturizing the optical members.

[0072] The present invention 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 invention. [Explanation of symbols]

[0073] 100...Image projection device 10...Image irradiation unit 20…Reflective mirror 30…Projection mirror 40…External light cut filter 50,60...Polarizing holographic optical element 70a, 70b...Prism 11…Backlight 12...Image display section 12a…Far display area 12b…Near display area 13a...First circular polarization conversion unit 13b...Second circular polarization conversion unit

Claims

1. An image projection device that projects a projection image onto a display unit for displaying a virtual image, an image irradiation unit that irradiates a first image light that is circularly polarized in a first rotation direction and a second image light that is circularly polarized in a direction opposite to the first rotation direction; a first polarizing holographic optical element having a refractive index distribution that varies depending on the polarization direction; a projection optical unit to which the first image light and the second image light are incident via the first polarizing holographic optical element and which projects the first image light and the second image light onto the display unit; an optical element for projecting an image from the first polarizing holographic optical element to the second polarizing holographic optical element;

2. 2. The image projection device according to claim 1, The first polarizing holographic optical element has a lens function and a diffraction grating function.

3. 2. The image projection device according to claim 1, The image projection device, wherein the combining member is a reflection mirror that reflects the first image light and the second image light irradiated from the image irradiation unit.

4. 4. The image projection device according to claim 3, the reflecting mirror forms an intermediate image of the first image light and the second image light at an intermediate image forming position; An image projection device, characterized in that the first polarizing holographic optical element is disposed at the intermediate image forming position.

5. 2. The image projection device according to claim 1, 11. An image projection device, wherein the combining member is a second polarizing holographic optical element having a refractive index distribution that varies depending on the polarization direction.

6. 6. The image projection device according to claim 5, 11. An image projection device, comprising: a first polarizing holographic optical element and a second polarizing holographic optical element, the second polarizing holographic optical element having the same grating period as the first polarizing holographic optical element.

7. 2. The image projection device according to claim 1, The image projection device, wherein the beam combining member is a prism.

8. 2. The image projection device according to claim 1, 13. An image projection device, wherein the polarization holographic optical element is a transmissive liquid crystal holographic element.

9. 9. The image projection device according to claim 1, the image projection unit has an image display unit that displays a first image and a second image and emits polarized light in a predetermined direction; the image display unit includes a first area for displaying the first image and a second area for displaying the second image; a first circular polarization conversion unit disposed opposite the first region; and a second circular polarization conversion unit disposed opposite the second region.

10. 10. The image projection device according to claim 9, the image display unit is a liquid crystal display device, The image projection device, characterized in that the first circular polarization conversion unit and the second circular polarization conversion unit are each a quarter-wave plate or a three-quarter-wave plate, and are arranged so that their fast axes and slow axes intersect with the specified direction.

Images