JP2021117480A - Image display device - Google Patents

Abstract

To provide an image display device capable of achieving virtual image display having reality.SOLUTION: An image display device according to an aspect of the present technique comprises a plurality of display units. Each of the plurality of display units includes: a screen on which an object image is formed; and a diffraction optical element having a first surface and a second surface opposite the first surface, diffracting image light of the object image entering the first surface and emitting the light from the first surface, and displaying a virtual image of the object image on the second surface so as to be superimposed with background. The plurality of diffraction optical elements included in the plurality of display units are respectively arranged to surround at least part of the periphery of a predetermined axis with the second surface being opposite the predetermined axis.SELECTED DRAWING: Figure 1

Description

The present technology relates to an image display device that displays an image using a virtual image.

Patent Document 1 describes a head-mounted display that displays a virtual image. In this head-mounted display, a partial display image is projected from a plurality of projection units onto one screen to form a composite display image. The image display light that constitutes the composite display image is guided to the eyes of an observer wearing a head-mounted display by a combiner that is a virtual image optical system. This allows the observer to visually recognize the real object in front of the observer together with the virtual image of the composite display image (paragraphs [0002] [0011] [0017] [0022] of Patent Document 1. Fig. 1 etc.).

Japanese Unexamined Patent Publication No. 2010-32615

As described above, by displaying the virtual image superimposed on the background, it is possible to provide various viewing experiences, and there is a demand for a technique capable of realizing a virtual image display with a sense of reality.

In view of the above circumstances, an object of the present technology is to provide an image display device capable of realizing a virtual image display with a sense of reality.

In order to achieve the above object, the image display device according to one embodiment of the present technology includes a plurality of display units.
Each of the plurality of display units has a screen forming an object image, a first surface, and a second surface opposite to the first surface, and is incident on the first surface. It has a diffractive optical element that diffracts the image light of the object image and emits it from the first surface, and displays a virtual image of the object image on the second surface side so as to overlap the background.
The plurality of diffractive optical elements included in the plurality of display units are arranged so as to face at least a part of the periphery of the predetermined axis with the second surface facing the predetermined axis.

The image display device is provided with a plurality of display units having a screen and diffractive optical elements, and each diffractive optical element is arranged so as to cover at least a part around a predetermined axis. The image light of the object image formed on the screen is diffracted by the diffractive optical element, emitted from the first surface opposite to the predetermined axis, and is directed to the second surface side toward the predetermined axis. A virtual image of the object image is displayed so as to overlap the background. As a result, it is possible to display a virtual image toward the periphery of a predetermined axis, and it is possible to realize a virtual image display with a sense of reality.

It is a schematic diagram which shows the structural example of the image display device which concerns on 1st Embodiment of this technique. It is a schematic diagram which shows the structural example of the display unit. It is a graph which shows the reflectance and the transmittance of the Fresnel reflection of the light incident on the interface. It is a schematic diagram which shows the structural example of a reflective hologram. It is a graph which shows the relationship between the incident angle and the exit angle of a reflection type hologram. It is an optical path diagram which shows an example of the optical path of the image light which displays a virtual image. It is a schematic diagram for demonstrating the virtual image displayed by a single reflective hologram. It is a schematic diagram for demonstrating the virtual image displayed by an image display device. It is a schematic diagram which shows the display device given as a comparative example. It is a schematic diagram which shows the structural example of the reflective hologram which concerns on 2nd Embodiment. It is a map which shows an example of the diffraction efficiency distribution of a hologram part. It is a schematic diagram which shows the structural example of the display unit which concerns on 3rd Embodiment. It is a graph which shows the diffraction characteristic of the 1st reflection type hologram 71. It is a graph which shows the diffraction characteristic of the 2nd reflection type hologram 72. It is a schematic diagram which shows the structural example of the image display device which concerns on 3rd Embodiment. It is a schematic diagram for demonstrating the reflection type hologram lens. It is a schematic diagram which shows the virtual image display by the linear hologram given as a comparative example. It is a schematic diagram which shows the structural example of the display unit using the reflective hologram lens. It is a schematic diagram which shows an example of the optical path of the image light diffracted by a reflective hologram lens. It is a schematic diagram which shows the relationship between the display position on the object image plane, and the diffraction position by a reflective hologram lens. It is a map which shows an example of the diffraction efficiency distribution about each display position shown in FIG. It is a figure for demonstrating the virtual image position in a reflective hologram lens and a linear hologram. This is an exposure apparatus that exposes interference fringes on a hologram. This is an exposure device that exposes a hologram lens.

Hereinafter, embodiments relating to the present technology will be described with reference to the drawings.

<First Embodiment>
[Configuration of image display device]
FIG. 1 is a schematic view showing a configuration example of an image display device according to a first embodiment of the present technology. FIG. 1A is a perspective view showing the appearance of the image display device 100. FIG. 1B is a top view of the image display device 100 when viewed from above. Hereinafter, the direction of the surface (XY plane) on which the image display device 100 is arranged will be described as the horizontal direction, and the direction perpendicular to the horizontal direction (Z direction) will be described as the vertical direction.

The image display device 100 has a plurality of display units 10. The display unit 10 is a unit that displays a virtual image of an image to be displayed (target image). The image display device 100 is configured by arranging a plurality of display units 10 in the circumferential direction centered on the reference axis O parallel to the vertical direction. Therefore, the image display device 100 is a device that uses a plurality of display units 10 to display a virtual image of the target image toward the periphery of the reference axis O. In the present embodiment, the reference axis O corresponds to a predetermined axis.

Each of the plurality of display units 10 has a screen 20 and a reflective hologram 30. That is, one display unit 10 is composed of a set of screen 20 and a reflective hologram 30. Therefore, the same number of screens 20 and reflective holograms 30 as the number of display units 10 are arranged around the reference axis O. Note that in FIGS. 1A and 1B, the thicknesses of the screen 20 and the reflective hologram 30 are omitted.

The screen 20 has a planar object image plane 21 and forms an object image. Here, the object image is an image of the target image to be displayed, and is typically an image. The object image surface 21 is a surface on which an object image is formed. In the present embodiment, the screen 20 is arranged with the object image plane 21 facing the reference axis O so that the object image plane 21 is parallel to the reference axis O. That is, the object image plane 21 is directed to the inside of the image display device 100 (reference axis O side). Hereinafter, the direction orthogonal to the screen 20 of the display unit 10a is defined as the X direction, and the plane parallel to the screen 20 (object image plane 21) of the display unit 10a is defined as the YZ plane.

The screen 20 avoids the optical path of the light displaying the virtual image formed by the reflective hologram 30, and is displaced from the position facing the first surface 31 along the direction of the reference axis O (lower side in the figure). Is placed in. Further, the screen 20 is arranged at a position (outer peripheral side of the first surface 31) away from the reference axis O from the outer surface (first surface 31) of the reflective hologram 30.

From each point on the object image plane 21, image light 1 displaying the pixels of the target image corresponding to each point is emitted so as to be diffused at a predetermined diffusion angle. That is, the screen 20 diffuses and emits the image light 1 of the object image. The direction in which the image light 1 is emitted is directed to the first surface 31 of the reflective hologram 30. In FIG. 1, an example of the optical path of the image light 1 emitted from the point P on the object image plane 21 (screen 20) of the display unit 10a to the first plane 31 is schematically shown. In this way, the screen 20 is arranged on the first surface 31 side so as not to block the display of the virtual image 4, and emits the image light 1 to the first surface 31. The diffusion angle and the like when the screen 20 emits the image light 1 will be described in detail later.

The specific configuration of the screen 20 is not limited. For example, a transmission type or reflection type diffusion screen that diffuses light projected from a projection type display device (not shown) such as a projector to display an image is used as the screen 20 (see FIG. 2). In this case, the surface that diffuses and emits the projected light is the object image surface 21. Further, for example, a self-luminous display such as a liquid crystal display, an organic EL display, and a plasma display may be used as the screen 20. In this case, the display surface of each display is the object image surface 21. In addition, any screen 20 capable of forming an object image such as a target image may be used.

The reflective hologram 30 has a first surface 31 and a second surface 32 opposite to the first surface 31. The first surface 31 is a surface directed to the side opposite to the reference axis O, and the second surface 32 is a surface directed to the reference axis O. Therefore, in the image display device 100, the first surface 31 is an outer surface and the second surface 32 is an inner surface. In the present embodiment, the reflective hologram 30 has a flat plate shape. Therefore, both the first surface 31 and the second surface 32 are flat.

The reflective hologram 30 is a reflective holographic optical element (HOE). The HOE is an optical element using hologram technology, and realizes control of the traveling direction of light (optical path control) by diffracting light by interference fringes 2 recorded in advance. In the reflection type HOE, the direction of diffraction reflection that diffracts and reflects light can be controlled. In this embodiment, the reflective hologram 30 corresponds to a diffractive optical element.

The reflective hologram 30 is configured to diffract and reflect light incident in a specific angle range and transmit light in another angle range. For example, light incident on the first surface 31 in a specific angle range is emitted from the first surface 31 at an emission angle corresponding to the incident angle. Further, the light incident at an incident angle other than the specific angle range passes through the reflective hologram 30 with almost no diffraction by the interference fringes 2.

As the reflective hologram 30, a HOE exposed with interference fringes 2 having a period in one direction is used. Specifically, a plurality of band-shaped interference fringes 2 parallel to each other are formed along the first surface 31 (second surface 32). For example, the direction orthogonal to each of the interference fringes 2 formed in parallel with each other is the direction in which the interference fringes 2 have a period (periodic direction). The interference fringes 2 function as a one-dimensional diffraction grating. That is, the reflective hologram 30 has a one-dimensional diffraction grating. In FIG. 1A, the interference fringes 2 formed on the reflective hologram 30 of the display unit 10a are schematically illustrated by a striped pattern. Such a pattern of interference fringes 2 (one-dimensional diffraction grating) having a period in one direction can be formed by using a technique such as scan exposure that scans a laser beam to generate interference fringes.

The method of constructing the reflective hologram 30 is not limited. For example, when color display or the like is performed, three types of reflective holograms 30 exposed by each of RGB lights are laminated and used. Further, for example, a photopolymer capable of multiple exposure may be used. In this case, the reflective hologram 30 includes interference fringes 2 exposed to light having different wavelengths from each other.

The reflective hologram 30 is arranged so that the one-dimensional diffraction grating (interference fringe 2) is orthogonal to the plane including the reference axis O. Specifically, in the reflective hologram 30, the direction in which the interference fringes 2 (one-dimensional diffraction grating) extend is the horizontal direction, and the first surface 31 (second surface 32) and the surface including the reference axis O are included. Are arranged so that they are orthogonal to each other. For example, the reflective hologram 30 of the display unit 10a is arranged so that the interference fringes 2 have a period in the direction orthogonal to the Y direction (Z direction in FIG. 1). Therefore, in the reflective hologram 30 of the display unit 10a, the interference fringes 2 extend along the Y direction and are orthogonal to the XZ plane including the reference axis O. In the other display unit 10, each reflective hologram 30 is arranged so that the extending direction of the interference fringes 2 is the horizontal direction. This makes it possible to avoid a situation in which the diffraction efficiency of the adjacent reflective hologram 30 changes discontinuously. This point will be described in detail later.

The reflective hologram 30 diffracts the image light 1 of the object image incident on the first surface 31 and emits it from the first surface 31, and creates a virtual image of the object image on the second surface 32 side so as to overlap the background. indicate. That is, the interference fringes 2 are exposed on the reflective hologram 30 so as to diffract and reflect the image light of the object image formed on the screen 20 and to transmit the background light.

For example, as shown in FIG. 1, the image light 1 (diffused light) emitted from the point P on the screen 20 (object image surface 21) and incident on the first surface 31 is diffracted and reflected by the interference fringes 2, and the first It is emitted from the first surface 31 along an optical path connecting the incident position on the surface 31 and the point P'(virtual image focal point) on the second surface 32 side. As a result, the image light 1 incident on the observer's pupil 5 directed to the first surface 31 is observed as if it was emitted from the point P'on the second surface 32 side. Further, the background light incident from the second surface 32 side is directly incident on the pupil 5. This makes it possible to display an image such as a target image by superimposing it on the background. As described above, the display unit 10 is a display device that uses a reflective hologram 30 for displaying an image superimposed on the background, diffracts the image on the screen 20 and delivers it to the pupil 5.

A method of using a transmissive mirror such as a half mirror as an optical system (combiner) for displaying a virtual image 1 superimposed on a background is known. Here, the ratio (transmittance) at which the reflective hologram 30 transmits the background light will be described as compared with the case where the transmissive mirror is used. In the transmissive mirror, light is turned back by regular reflection (Fresnel reflection). Therefore, the transmissive mirror is arranged at an angle with respect to the observation direction (see FIG. 9). On the other hand, in this configuration using the reflective hologram 30, the reflective hologram 30 can be arranged vertically as shown in FIG.

For example, when the virtual image 1 is displayed over the entire circumference, the background light perceived by the user is the light that has passed through the virtual image screens (reflective hologram 30 or transmissive screen) arranged on the front side and the back side when viewed from the user. .. In this case, the brightness of the background light perceived together with the virtual image 1 is represented by the square of the transmittance of the virtual image screen seen from the position of the pupil.

Here, it is assumed that the reflective hologram 30 and the transmissive mirror can display the virtual image 1 with the same brightness as each other. This is, for example, the diffraction efficiency of the reflective hologram 30 that diffracts the light from the object image plane 21 into the pupil, and the reflection of the transmissive mirror arranged so as to reflect the light from the object image plane 21 at the same pupil position. When the rate is the same. In such a case, the thickness of the reflective hologram 20 is set so that the square of the white light transmittance of the reflective hologram 30 is equal to or greater than the square of the white light transmittance of the transmissive mirror. Here, the white light transmittance is, for example, the transmittance of visible light contained in the background light.

In this way, the thickness of the reflective hologram 30 is set so that more background light can be transmitted than the Fresnel reflecting surface (transmissive mirror) capable of displaying the virtual image 1 with the same brightness. As a result, the background light looks brighter when the virtual image 1 is viewed through the reflective hologram 30 than when the virtual image is viewed through the transmissive mirror. As a result, it is possible to superimpose the virtual image 1 on a background closer to the actual brightness and display it, so that it is possible to realize a display with a high sense of reality as if a character or the like were there. It becomes.

In the image display device 100, the plurality of reflective holograms 30 included in the plurality of display units 10 are arranged so as to face at least a part around the reference axis O with the second surface 32 facing the reference axis O. NS. Therefore, an inner peripheral surface 34 composed of the second surfaces 32 of the plurality of reflective holograms 30 is arranged around the reference axis O. Further, the observer can observe the virtual image 4 displayed on the reference axis O side from multiple directions through the outer peripheral surface 35 composed of the first surface 31 of the plurality of reflective holograms 30.

In this embodiment, three or more reflective holograms 30 arranged adjacent to each other and surrounding the reference axis O are used. Specifically, three or more display units 10 are arranged in the circumferential direction so that the reflective holograms 30 are adjacent to each other, and a closed outer peripheral surface 35 surrounding the reference axis O is configured. This makes it possible to observe the virtual image superimposed on the background from all directions of 360 °. In the example shown in FIG. 1, the image display device 100 is configured by using the six display units 10a to 10f.

The number of display units 10 is not limited, and can be appropriately set according to the design of the image display device 100 and the like. Further, the case is not limited to the case where the outer peripheral surface 35 is configured so as to completely surround the reference axis O, and for example, two or more reflective holograms 30 (display unit 10) are arranged so as to surround a part around the reference axis O. May be good. Even in such a case, it is possible to configure an image display device 100 that displays a virtual image in different directions.

Further, in the present embodiment, each reflective hologram 30 is arranged so that the first surface 31 and the reference axis O are parallel to each other, and form a prismatic structure surrounding the reference axis O. As shown in FIG. 1A, in the image display device 100, the outer peripheral surface 35 (inner peripheral surface 34) of the hexagonal column structure centered on the reference axis O is formed by the six reflective holograms 30. As a result, the first surface 31 on which diffraction reflection occurs can be observed from the front, and the transparency of the background can be significantly improved. Further, since the first surface 31 that diffracts and reflects the image light 1 has a rectangular shape, it is possible to secure a certain display range for displaying a virtual image regardless of, for example, the upper and lower positions.

Further, as shown in FIG. 1B, in the present embodiment, the reflective holograms 30 are configured so that the widths in the horizontal direction have the same values as each other. Therefore, the outer peripheral surface 35 has a regular hexagonal column structure in contact with the inscribed circle 11a having a radius R centered on the reference axis O. Further, the six screens 20 form a regular hexagonal column structure in contact with the inscribed circle 11b having a radius R'larger than the radius R of the inscribed circle 11a.

The reflective hologram 30 may be arranged so as to be inclined with respect to the reference axis O. For example, each reflective hologram 30 is inclined and arranged so that the first surface 31 faces downward in the device, and the outer peripheral surface 35 (inner peripheral surface 34) has a pyramid structure. Even in such a case, the one-dimensional interference fringes 2 can be arranged along the horizontal direction. Further, each screen 20 may be arranged so as to be inclined with respect to the reference axis O. The tilt angles of the reflective hologram 30 and the screen 20 are not limited, and may be set within a range in which the observer can properly observe the virtual image, for example.

Here, the angle formed by the optical path of the image light 1 with the orthogonal plane orthogonal to the reference axis O is defined as the elevation angle α, and the angle indicating the direction of the optical path of the image light projected on the orthogonal plane is defined as the azimuth angle β. For example, in FIG. 1, the XY plane (horizontal plane) is an orthogonal plane orthogonal to the reference axis O. That is, the elevation angle α is an angle representing an inclination angle with respect to the horizontal plane in the image display device 100. Further, the azimuth angle β is an angle representing the azimuth in the horizontal plane (horizontal direction) in the image display device 100.

In the following, the elevation angle α and the azimuth angle β are represented with reference to the first surface 31 of each reflective hologram 30. That is, on the first surface 31, the angle component in the vertical direction with respect to the perpendicular line of the first surface 31 is defined as the elevation angle α, and the angle component in the horizontal direction with respect to the reference axis O is defined as the azimuth angle β. Further, the elevation angle α and the azimuth angle β representing the direction of the perpendicular line of the first surface 31 are set to 0 degrees, respectively.

As shown in FIG. 1, when a plurality of reflective holograms 30 are continuously arranged in the circumferential direction about the reference axis O to form a polygonal column, the angle formed by the adjacent first surface 31 is It is set according to the diffraction characteristics in the elevation angle direction and the azimuth angle direction of the reflective hologram 30.

For example, the reflective hologram 30 diffracts light with a diffraction efficiency corresponding to an elevation angle α and an azimuth angle β in the light emitting direction (or incident direction). As described above, each reflective hologram 30 has a one-dimensional diffraction grating extending in the horizontal direction. In this case, the reflective hologram 30 shows a symmetrical distribution centered on the azimuth angle β = 0 in the diffraction efficiency in the azimuth direction in a certain range in the elevation angle direction (see FIG. 7 and the like). The angle formed by the adjacent first surface 31 is set according to the distribution of the diffraction efficiency in the azimuth direction.

In the image display device 100, the angle θ formed by the perpendicular of the adjacent first surface 31 determines the diffraction efficiency in the azimuth direction _{at the elevation angle (assumed pupil elevation angle α 0) assuming the position of the observer's pupil 5.} It is set to the _{angle β 0} or less represented by the angle range of the azimuth angle β that is greater than or equal to the value. In the present embodiment, the assumed pupil elevation angle α ₀ corresponds to a predetermined elevation angle, and the predetermined value corresponds to the first value.

In the present embodiment, the predetermined value is set to a value that is half of the peak value of the diffraction efficiency. Therefore, the angle β ₀ is an angle representing the full width at half maximum (full width at half maximum) in the distribution of diffraction efficiency in the azimuth direction. That is, the angle θ formed by the perpendicular line of the adjacent first surface 31 is set to an angle equal to or less than the _{half-value full width β 0} of the diffraction efficiency in the azimuth direction at the _{assumed pupil elevation angle α 0 (θ ≦ β 0} ). _{As a result, the diffraction efficiency of the image light 1 emitted at the assumed pupil elevation angle α 0} with respect to the pupil 5 directed to the reference axis O becomes a diffraction efficiency of half or more of the peak value. As described above, in the plurality of reflective holograms 30, the diffraction efficiency of the image light 1 emitted from the first surface 31 along the surface including the reference axis O at the assumed pupil elevation angle α _{0 is at least half the peak value.} It is arranged so as to be.

FIG. 1B shows, as an example, the perpendiculars 6b and 6c of the first surface 31 of the adjacent display units 10b and 10c. As shown in FIG. 1B, when a regular polygonal prism is formed, the angle θ formed by the perpendiculars 6b and 6c is an angle at which the center of the reflective hologram 30 adjacent to the reference axis O (the intersection with the inscribed circle 11a) is expected. It can be said that. The angle θ formed by the perpendicular line is equal to the outer angle (supplementary angle) of the angle formed by the adjacent first surface 31.

Further, in the image display device 100, the radius R of the inscribed circle 11a internally provided in the prismatic structure composed of the reflective holograms 30 and the distance from the virtual image focal point in the horizontal direction seen from the pupil 5 to the first surface 31. The distance between the first surface 31 and the object image surface 21 is set so as to coincide with. That is, the plurality of reflective holograms 30 have a radius R equal to the distance from the first surface 31 to the virtual image focal point in the horizontal direction orthogonal to the reference axis O, and are formed on the inscribed circle 11a centered on the reference axis O. The surface 31 of 1 is arranged so as to be inscribed. Here, the distance between the first surface 31 and the object image surface 21 includes the horizontal and vertical distances. As a result, when the pupil 5 moves in the circumferential direction at the assumed pupil elevation angle α ₀ , the virtual image of the object image is always displayed centered on the reference axis O.

The focal length due to convergence seen from the left and right pupils 5 of the observer is the same as the focal length of the monocular focus in the horizontal direction. Therefore, the position where the virtual image is recognized by the convergence angle (angle difference between the left and right pupils 5) is also the position centered on the reference axis O. As a result, even when the pupil 5 moves in the circumferential direction, a continuous virtual image can be displayed. Further, since the position where the virtual image is displayed coincides with the reference axis O as the center, it is possible to display a virtual image such as a character with a sense of substance and a three-dimensional effect.

The image height of the displayed virtual image 4 is determined according to, for example, the position of the screen 20 arranged so as not to block the image light 1 (virtual image ray) displaying the virtual image. In reality, it is conceivable that the distance of the virtual image focal point changes slightly depending on the image height (vertical virtual image position). Therefore, for example, the focal length according to the range of the image height is set so that a virtual image of a desired height is displayed. Typically, the position of the screen 20 is appropriately set so that the position of the virtual image focal point in the horizontal direction of the center of the virtual image (center of the object image) coincides with the reference axis O.

[Construction of reflective hologram and screen]
FIG. 2 is a schematic view showing a configuration example of the display unit 10. FIG. 2 schematically shows a cross section of the display unit 10a shown in FIG. 1 cut along the XZ plane. The display unit 10 has a projector 15 that projects an object image 3 on a screen 20. In this embodiment, the projector 15 corresponds to a projection unit.

The projector 15 emits image light 1 constituting an object image to be an object image 3 at a predetermined radiation angle (angle of view). As shown in FIG. 2, the projector 15 is arranged on the outside of the screen 20 so as to project the image light 1 at a predetermined projection angle (launch angle). This projection angle is the central angle of the radiation angle. By projecting the image light 1 obliquely in this way, it is possible to improve the brightness of the image light 1 emitted from the screen 20.

As the projector 15, a laser projector or the like using a laser light source is used. In this embodiment, a scan-type laser projector that scans RGB laser light and projects an image is used. A projection type laser projector using a liquid crystal light bulb or the like may be used.

By using the laser light source, it is possible to project the target image using RGB light having a narrow band, and it is possible to narrow the band of the image light 1. This makes it possible to exhibit high diffraction performance. As the light source, a projector 15 using an LED light source, a lamp light source, or the like may be used. In this case, it is possible to project the image light 1 having a narrow band by combining a narrow band filter or the like that narrows the band of light.

The screen 20 is a transmissive diffusion screen and has an incident surface 22 that is opposite to the object image surface 21. The incident surface 22 is a surface on which the image light 1 emitted from the projector 15 is incident. The image light 1 incident on the incident surface 22 passes through the screen 20 and is diffused and emitted from the object image surface 21. As a result, the object image 3 of the target image composed of the image light 1 emitted from the projector 15 is formed on the object image surface 21. In FIG. 2, an object image 3 formed on the object image surface 21 of the screen 20 and a virtual image 4 formed on the second surface 32 side of the reflective hologram 30 are schematically illustrated by shaded areas. There is.

As the screen 20, a reflective diffusion screen may be used. In this case, the inner surface of the screen 20 (the surface facing the reflective hologram 30) is the incident surface on which the image light 1 is incident and the exit surface on which the image light 1 is emitted. As a result, for example, the projector 15 can be arranged inside the device with respect to the screen 20, and the size of the device can be reduced.

Hereinafter, the configuration of the reflective hologram 30 for delivering the object image 3 to the pupil 5 will be described. Here, the assumed pupil elevation angle α ₀ is 0 degrees, the distance between the first surface 31 and the pupil 5 is L, and a configuration is assumed in which a virtual image can be observed through the first surface 31. The distance L is set to a value in the range of, for example, 100 mm to 1000 mm. Of course, it is not limited to this. In FIG. 2, the elevation angle α is an angle of the first surface 31 with respect to the perpendicular line 6.

As shown in FIG. 2, on the first surface 31 of the reflective hologram 30, image light 1 (incident light) emitted from the object image surface 21 of the screen 20 arranged below the device is projected at various angles of incidence. Incident. Further, the image light 1 (diffracted light) diffracted by the interference fringes 2 is emitted from the first surface 31 toward the pupil 5. At this time, the direction in which the diffracted light is emitted is the direction along the straight line connecting the virtual image focal point and the incident position. This allows the observer to observe the virtual image 4 formed on the second surface 32 side of the reflective hologram 30.

In this way, considering that the image light 1 of the object image 3 is delivered to the pupil by being incident from a certain angle of the object image surface 21, the specularly reflected light of the incident light on the first surface 31 does not enter the pupil 5. It is desirable to do so. Here, the specularly reflected light is, for example, light reflected by Frenel reflection (interfacial reflection) generated on the first surface 31, and is reflected at the same reflection angle as the incident angle.

FIG. 3 is a graph showing the reflectance and transmittance of Fresnel reflection of light incident on the interface. The vertical axis of the graph is the transmittance and the reflectance, and the horizontal axis is the angle of incidence of light with respect to the interface. FIG. 3 shows the reflectances of S-polarized light and P-polarized light (Rs and Rp) and the transmittances of S-polarized light and P-polarized light (Ts and Tp). For example, a part of the incident light incident on the interface (first surface 31 or the like) is reflected at the interface, and the other part passes through the interface and penetrates into the inside. The reflectance and transmittance at this time are values according to the incident angle of the incident light and the ratio of S-polarized light and P-polarized light contained in the incident light.

In order to prevent the specularly reflected light from entering the pupil 5, it is desirable that the image light 1 is incident on the first surface 31 at an angle as much as possible (increasing the incident angle). On the other hand, as shown in the graph of FIG. 3, the reflectance of Fresnel reflection increases as the incident angle increases. Therefore, if the incident angle is increased, the amount of light incident on the first surface 31 may decrease, and the brightness of the virtual image 4 may decrease.

In the present embodiment, the incident angle at the center of the angle of view is set based on the permissible range of the level at which the light source intensity (brightness of the virtual image) decreases due to Fresnel reflection and the assumed range of the elevation angle of the pupil 5. Here, the incident angle at the center of the angle of view is the center angle (projection angle) of the radiation angle of the image light 1 projected from the projector 15. Further, the assumed range of the elevation angle of the pupil 5 is a range assuming an elevation angle at which a virtual image can be seen when the pupil 5 moves. For example, the incident angle at the center of the angle of view is set so that the specular reflected light is reflected in a direction outside the assumed range of the elevation angle of the pupil 5 and the reflectance of the Frenel reflection is as low as possible.

For example, the assumed range of the elevation angle of the pupil 5 is set to 0 ± 10 degrees. As a result, the viewing range of the virtual image is secured even when the elevation angle moves within a range of ± 10 degrees from the assumed pupil elevation angle α _0. The maximum value of the amount of decrease in the light source intensity due to Fresnel reflection is set to 30%. From the graph shown in FIG. 3, the maximum incident angle is set to about 70 °. The incident angle at the center of the angle of view is set so that the incident angle of the image light 1 with respect to the first surface 31 is equal to or less than the maximum incident angle. The assumed range of the elevation angle of the pupil 5 and the maximum value of the amount of decrease in the light source intensity are not limited to the above examples.

FIG. 4 is a schematic view showing a configuration example of the reflective hologram 30. FIG. 4A is a schematic view showing a cross section of the reflective hologram 30 in the thickness direction. FIG. 4B is a schematic view showing the first surface 31 of the reflective hologram 30.

As shown in FIG. 4A, interference fringes 2 having a slant angle φ are formed at regular intervals inside the reflective hologram 30. Here, the slant angle φ is an angle between the interference fringes 2 and the surfaces of the reflective hologram 30 (first surface 31 and second surface 32). For example, the light incident on the reflective hologram 30 is reflected at an angle corresponding to the incident angle and the slant angle φ. The slant angle φ can be set to a desired angle by adjusting the incident direction of the laser beam when exposing the interference fringes 2.

As described above, in the reflective hologram 30, a one-dimensional diffraction grating is formed by the interference fringes 2. In FIG. 4A, the grating vector 36 of the interference fringe 2 is schematically illustrated by a thick arrow. The grating vector is a vector orthogonal to each interference fringe 2. In the present embodiment, the interference fringes 2 having a grating vector (slant angle φ) that diffracts the object image 3 at the assumed pupil elevation angle α _{0 are exposed.}

The direction in which the interference fringes 2 extend is a horizontal direction orthogonal to the reference axis O. Therefore, as shown in FIG. 4B, on the surface of the reflective hologram 30 (first surface 31 or second surface 32), the grating vector is a vector having only vertical components.

In the following, the period of the interference fringes 2 in the reflective hologram 30 will be referred to as a grating pitch P, and the period of the interference fringes 2 on the surface of the reflective hologram 30 will be referred to as a boundary pitch Λ. The grating pitch P is a pitch determined by the wavelength of the laser beam and the exposure angle when exposing the interference fringes 2. For example, a reflective hologram 30 having a different grating pitch P is exposed for each wavelength of RGB light. In this case, the reflective holograms 30 corresponding to RGB are laminated and used. When multiple exposures can be performed using light having a plurality of wavelengths, the interference fringes 2 corresponding to the plurality of wavelengths may be exposed on one reflective hologram 30.

The relationship between the angle of incidence on the first surface 31 from the object image plane 21 and the emission angle of the diffracted light emitted from the first surface 31 follows the following equation.
Sinθ _in + mλ / Λ = Sinθ _out (1)
Here, θ _in is the incident angle, and θ _out is the exit angle (exit diffraction angle). Further, Λ is the boundary pitch, λ is the main wavelength of the image light 1 serving as the reproduction light source, and m is an integer of 1 or more.

For example, in order to display the virtual image 4 at a high resolution of about 100 ppi (pixel per inch), it is desirable that the wavelength half width of the image light 1 is about 2 nm from the above equation (1). Therefore, by using the projector 15 provided with the laser light source described with reference to FIG. 2, it is possible to use RGB light in a narrow band as the image light 1, and it is possible to realize a high-resolution virtual image display. be. In the following, as RGB light emitted from the projector 15, red light R having a wavelength of 647 nm, green light G having a wavelength of 524 nm, and blue light B having a wavelength of 446 nm are used.

[Diffraction angle of reflective hologram]
FIG. 5 is a graph showing the relationship between _{the incident angle θ in} and the exit angle θ _out of the reflective hologram 30. The vertical axis of the graph is the incident angle θ _in , and the horizontal axis of the graph is the exit angle θ _out . FIG. 5 shows the relationship between the _{incident angle θ in} and the emitted angle θ _out with respect to the reflective hologram 30 when the exit diffraction angle to the pupil elevation angle is 0 ± 10 degrees and the incident angle is designed to be 70 degrees or more. It is shown. Here, the graph is calculated assuming a configuration in which the first surface 31 (or the second surface), which is the grating surface, is installed parallel to the reference axis O. The boundary pitch Λ in the vertical direction on the first surface 31 was set as follows for each RGB. That is, the boundary pitch Λ for red light R was set to 851.6 nm, the boundary pitch Λ for green light G was set to 689 nm, and the boundary pitch Λ for blue light B was set to 587 nm.

As shown in FIG. 5, the relationship between the _{incident angle θ in} and the exit angle θ _out is the same for each of the red light R, the green light G, and the blue light B. For example, when the incident angle θ _in of the image light 1 is −50 degrees, the emission angle θ _out is about 0 degrees. When the incident angle θ _in is −35 degrees, the exit angle θ _out is about 10 degrees, and when the incident angle θ _in is −70 degrees, the exit angle θ _out is about −10 degrees. Note that −70 degrees corresponds to the maximum incident angle set with reference to FIG. Therefore, when the incident angle θ _{in is set} to 50 degrees, an emission angle θ _out of ± 10 degrees can be obtained. That is, for the image light 1 emitted from a certain point on the object image plane 21 displaying the virtual image 4, the range of the _{incident angle θ in} that can be seen when the pupil 5 moves ± 10 degrees from the _{assumed pupil elevation angle α 0 is −35 degrees.} Therefore, it is -70 degrees.

[Screen diffusion angle]
Hereinafter, a method of setting the diffusion angle of the screen 20 will be described. The diffusion angle of the screen 20 is set based on the relationship between the radiation angle of the projector 15 and the incident angle θ _in and the exit angle θ _{out described above.} In the following, it is assumed that the diffusion angle of the screen 20 is set by taking the case where the reflective hologram 30 having the characteristics of the graph shown in FIG. 5 is used as an example.

For example, assume that the projection angle (launch angle at the center of the angle of view) of the projector 15 is set to −50 degrees and the radiation angle is set to ± 5 degrees. In this case, the range of the incident angle of the image light 1 incident on the incident surface 22 of the screen 20 is −50 ± 5 degrees. Therefore, in order to diffuse the image light 1 without reducing the amount of light and suppress unnecessary diffusion, it is sufficient that the diffusion angle of the screen 20 is −30 degrees to −75 degrees.

In this case, the magnitude of the diffusion angle is 45 degrees, and the screen 20 is set to a diffusion angle of about ± 23 degrees with respect to the center angle in the diffusion direction. The angle range of the diffusion angle is within the range of the incident angle θ _in (-35 degrees to -70 degrees) _{that realizes the emission angle θ out} of the assumed range (± 0 degrees) of the elevation angle of the pupil 5. The radiation angle (± 5 degrees) is added. As a result, the image light 1 incident on the screen 20 at an elevation angle of, for example, −45 degrees or −55 degrees can be diffused without reducing the amount of light. In the above, the assumed pupil elevation angle α ₀ is set to 0 degrees, but the assumed pupil elevation angle α ₀ may be set to an angle other than 0 degrees.

Hereinafter, a method of correcting the diffusion angle and the like of the screen 20 set by using the above method will be described.

First, the assumed range of the elevation angle of the pupil 5 (the pupil movement range in the elevation angle direction) is corrected. For example, when the pitch (grating pitch or boundary pitch) set by the above method is used, the diffraction efficiency of the diffracted light emitted from the first surface 31 of the reflective hologram 30 with respect to the elevation angle in the emitting direction is calculated. NS. As will be described later, in the reflective hologram 30, the diffraction efficiency with respect to the elevation angle in the emission direction shows a distribution with a predetermined elevation angle as a peak when the azimuth angle is 0 degrees (see FIG. 7). The range of the elevation angle (exit elevation angle range) represented by the half-width full-width of the diffraction efficiency with respect to the elevation angle in the emission direction is set again as the assumed range of the elevation angle of the pupil 5. This makes it possible to set other parameters (such as the diffusion angle of the screen 20 and the projection angle of the projector 15) with reference to the elevation angle range in which a bright virtual image can be observed.

As described with reference to FIGS. 5 and (1), in the reflective hologram 30, there is a one-to-one correspondence _{between the incident angle θ in} and the exit angle θ _{out with respect to the first surface 31.} Therefore, the diffraction efficiency according to the emission direction of the diffracted light can be read as the diffraction efficiency according to the incident direction of the incident light with respect to the first surface 31. For example, the diffraction efficiency of the reflective hologram 30 according to the incident direction peaks at a predetermined elevation angle (black angle) when the azimuth angle is 0 degrees. The range of the elevation angle (incident elevation range) represented by the half-width full-width of this peak distribution corresponds to the assumed range of the corrected elevation angle of the pupil 5 (exit elevation range).

In the present embodiment, the diffusion angle in the elevation angle direction of the screen 20 is corrected to the incident elevation angle range. That is, the diffusion angle of the screen 20 in the elevation angle direction is such that the diffraction efficiency is at least half the peak value when the azimuth angle component of the image light 1 with respect to the first surface 31 in the incident direction is orthogonal to the first surface 31. It is set to the angle represented by the incident elevation angle range, which is the range of the elevation angle in the incident direction. In the present embodiment, the incident elevation angle range corresponds to the third angle range.

Further, the diffusion angle in the azimuth angle direction of the screen 20 is set based on the diffraction efficiency of the reflective hologram 30. Specifically, the diffusion angle in the azimuth angle direction is set in the range of the azimuth angle (incident azimuth angle range) represented by the half value full angle of the diffraction efficiency with respect to the azimuth angle in the incident direction within the incident angle range. That is, the diffusion angle in the azimuth angle direction of the screen 20 is set to the angle represented by the incident azimuth angle range, which is the range of the azimuth angle in the incident direction in which the diffraction efficiency is equal to or more than half the peak value in the incident elevation angle range. In the present embodiment, the incident azimuth range corresponds to the fourth angle range.

In this way, the diffusion angle of the screen 20 is set based on the diffraction efficiency according to the incident direction. As a result, the image light 1 incident on the screen 20 can be diffracted with a diffraction efficiency equal to or higher than half the peak value, and a bright virtual image display can be realized.

The diffusion angle of the screen 20 may be set based on the radiation angle of the projector 15. For example, the elevation angle component of the radiation angle is added to the diffusion angle in the elevation angle direction set in the incident elevation angle range. Further, the azimuth component of the radiation angle is added to the diffusion angle in the azimuth direction set in the incident azimuth range. Therefore, the screen 20 diffuses and emits the image light 1 in an angle range obtained by adding the radiation angle by the projector 15 to the incident elevation angle range and the incident azimuth angle range.

As a result, the image light 1 can be incident on the reflective hologram 30 in an angle range with high diffraction efficiency without being diffused in an unnecessary direction, and the brightness of the virtual image display can be significantly improved. .. In the above, the method of correcting the diffusion angle has been described stepwise, but the diffusion angle calculated in each step can be used as an actual design value.

Further, the projection angle of the projector 15 may be corrected. For example, in the reflective hologram 30, when it is desired to shift the elevation angle at which the diffraction efficiency peaks, the peak angle of the diffraction efficiency is shifted from the Bragg angle by changing the slant angle while fixing the pitch of the interference fringes 2. It is possible. In this case, it is desirable to change the projection angle of the projector 15 according to the peak angle at the changed slant angle. This makes it possible to maintain the brightness of the virtual image display even when the peak angle is shifted.

A screen 20 having perfect diffusion characteristics may be used. The perfect diffusion characteristic is a characteristic that evenly diffuses incident light. In this case, the image light 1 incident on the screen 20 in the range of the radiation angle is evenly diffused from the object image plane 21 side. This makes it possible to easily expand the assumed range of the elevation angle of the pupil 5, for example.

As the screen 20, for example, a diffusion sheet is used. The diffusion sheet is used by being attached to a transparent member such as glass or an acrylic plate with a light-transmitting optical adhesive (OCA: Optical Clear Adhesive) or the like. This constitutes a transmissive diffusion screen. Alternatively, a reflective diffusion sheet may be formed by attaching a diffusion sheet on the mirror. Further, a diffusion plate formed by sanding a glass plate or the like may be used as the screen 20.

Further, for example, a volume scattering type diffusion plate or a diffusion type hologram having a diffusion angle may be used as the screen 20. The diffusion type hologram is a hologram in which interference fringes are exposed using diffused light as object light, and has an angle-selective diffusion function. A diffusion type hologram is created by, for example, two-luminous flux exposure using object light (diffuse light) emitted from a diffusion sheet having a diffusion angle of ± 23 degrees and reference light of 50 degrees. At this time, it is desirable to use light having the same wavelength as the image light 1 of the projector 15 as the object light and the diffused light. This makes it possible to realize a screen 20 that diffuses the image light 1 to a degree of composition. In addition, a projection type laser projector or a liquid crystal panel using a laser light source as a backlight may be used as the light source of the object image 3.

[Arrangement of reflective holograms and screens]
FIG. 6 is an optical path diagram showing an example of the optical path of the image light 1 displaying the virtual image 4. The upper view of FIG. 6 is an optical path diagram when the display unit 10 is viewed from the horizontal direction, and the lower diagram is an optical path diagram when the display unit 10 is viewed from the vertical direction.

The distance L in the figure is the distance from the first surface 31 to the pupil 5 position. Note that in FIG. 6, the illustration of the pupil is omitted. The distance D is the distance between the first surface 31 and the object image surface 21. S is the amount of shift along the reference axis O of the center of the object image 3 with respect to the center of the first surface 31. I is the size of the object image 3. The distance Fv is the vertical virtual image focal length of the reflective hologram 30, and the distance Fh is the horizontal virtual focal length of the reflective hologram 30.

Further, in FIG. 6, the assumed pupil elevation angle α ₀ is set to 0 degrees, and the projection angle of the projector 15 is set to 50 degrees. A pupil 5 (not shown) is arranged at a position (left side in the drawing) separated from the first surface 31 by a distance L. In the lower figure, it is assumed that the left and right pupils 5 are arranged. The distance between the pupils 5 is represented by the interpupillary distance (IPD). The aperture diameter of the pupil 5 is about 3 mm, and the IPD is about 70 mm. The optical path shown in FIG. 6 is an object image 3 when an observer who sees the reflective hologram 30 under the above conditions visually recognizes a virtual image at a position of a virtual image focal length Fh in the horizontal direction from the first surface 31. This is a ray trace of the image light 1.

The reflective hologram 30 is configured so that the diffraction efficiency reaches a peak value when the assumed pupil elevation angle α ₀ is 0 degrees, and the projection angle of the projector 15 is set to 50 degrees. Further, the screen 20 is arranged so that the center of the object image plane 21 is shifted from the first plane 31 and the center by the distance D on the pupil 5 side in the vertical direction by the shift amount S. With this arrangement, the virtual image is displayed at the position of the virtual image focal length Fh in the horizontal direction.

Further, the virtual image focal length Fv in the vertical direction has a value of about twice that of Fh due to the aberration of the reflective hologram 30. Therefore, the reflective hologram 30 focuses the virtual image 4 at a position farther than the virtual image focal length Fv in the horizontal direction when viewed from the pupil 5. In this case, for example, the monocular focal position is about halfway between the vertical and horizontal virtual image positions, and may not match the focal position due to the convergence angle. On the other hand, when the convergence angle and the focal position do not match, as in the case of 3D display using the parallax barrier method using the convergence angle, the focal point of the solid is recognized by the focal position of the convergence angle. Therefore, even in the method shown in FIG. 6, the virtual image is recognized by the virtual image focal point in the horizontal direction.

The horizontal focal length (virtual image focal length) differs slightly depending on the vertical virtual image height. In this case, it is desirable to determine the position of the object image plane 21 (screen 20) so that the center of the virtual image 4 coincides with the reference axis O. As a result, the virtual image 4 can be displayed around the reference axis O, and even when the orientation of the pupil 5 changes, it is possible to realize a virtual image display without a sense of discomfort.

[Virtual image display by reflective hologram]
FIG. 7 is a schematic diagram for explaining a virtual image displayed by a single reflective hologram 30. FIG. 7A is a map showing an example of the diffraction efficiency distribution of the reflective hologram 30 according to the elevation angle and the azimuth angle in the emission direction. The vertical axis of the map is the elevation angle of the image light 1 (diffracted light) emitted from the first surface 31 in the emission direction, and the horizontal axis of the map is the azimuth in the emission direction. The color of each point represents the diffraction efficiency according to the elevation angle and the azimuth angle in the emission direction.

The map shown in FIG. 7A is the distribution of diffraction efficiency in the reflective hologram 30 for green light G. The refractive index of the reflective hologram 30 is 1.51, and the refractive index difference Δn is 0.035. The slant angle is set to about 78 degrees. The thickness of the reflective hologram 30 is set, for example, in the range of several μm to several tens of μm.

In this diffraction efficiency distribution, the band-shaped region A that is convex upward is a region having higher diffraction efficiency than other regions. Further, the band-shaped region A has a distribution symmetrical in the azimuth direction with the azimuth angle β = 0 degrees as an axis.

When the azimuth angle β = 0 degrees, the range of the elevation angle (exit elevation angle range) represented by the half-width full-width of the diffraction efficiency in the elevation angle direction is about 0 degrees to about 6 degrees. Here, the azimuth angle β = 0 degrees is when the azimuth angle component in the emission direction is orthogonal to the first surface 31. Therefore, the emission angle range is the elevation angle in the emission direction in which the diffraction efficiency is equal to or higher than the first value in a state where the azimuth component of the image light 1 emitted from the first surface 31 is orthogonal to the first surface 31. Is in the range of. In the present embodiment, the exit elevation angle range corresponds to the first angle range.

In FIG. 7A, the central angle of the exit elevation angle range is 3 degrees, and the angle represented by the exit elevation angle range is about 6 degrees. Therefore, in the emission elevation angle range of α = 3 ± 3 degrees, the virtual image 4 is reproduced with a diffraction efficiency equal to or more than half the peak value of the diffraction efficiency. Further, in the example shown in FIG. 7A, the half-width full-width of the diffraction efficiency in the azimuth direction is maximized at the center angle (about 3 degrees) of the emission elevation angle range.

The range of the azimuth angle (exit azimuth angle range) represented by the half-value full angle of the diffraction efficiency in the azimuth angle direction at the central angle of the emission angle range is about -15 degrees to about 15 degrees. It should be noted that the half-width full-width in the azimuth direction is not always the maximum at the center angle of the exit elevation angle range. In this case, the emission azimuth range may be appropriately set so that the half-width full-width of the diffraction efficiency in the azimuth direction is maximized in the emission elevation range. As described above, the emission azimuth angle range is the range of the azimuth angle in the emission direction in which the diffraction efficiency is equal to or more than half the peak value in the emission elevation angle range. In the present embodiment, the exit azimuth range corresponds to the second angle range.

In FIG. 7A, the angle represented by the emission azimuth range is about 30 °. Therefore, in the central angle (about 3 degrees) of the emission elevation angle range, in the emission azimuth angle range of β = ± 15 degrees, the virtual image 4 is reproduced with a diffraction efficiency equal to or more than half the peak value of the diffraction efficiency. In FIG. 7A, the exit elevation angle range and the exit azimuth angle range are illustrated by rectangular regions.

Further, when the assumed pupil elevation angle α ₀ was changed to 3 degrees and the virtual image focal length Fh in the horizontal direction was recalculated, the virtual image focal length at the elevation angle of 3 degrees became a value longer than Fh (Fh'). As described above, in the present embodiment, the assumed pupil elevation angle and the virtual image focal length are corrected according to the diffraction efficiency of the reflective hologram 30.

FIG. 7B is a schematic view showing an example of a virtual image display by a single reflective hologram 30. FIG. 7B schematically illustrates a display unit 10 including a set of reflective holograms 30 and a screen 20 (object image plane 21). Further, an example of the visual images 7a to 7e (virtual image 4) visually recognized by the observer when the first surface 31 is viewed by changing the direction at an elevation angle of 3 degrees is shown. The color of the visual image 7 represents the brightness, and the darker the gray, the brighter the image.

The visual image 7c is an image when the virtual image 4 is viewed at an azimuth angle of 0 degrees, and is a bright image displayed by the image light 1 diffracted with a high diffraction efficiency close to the peak value. The visual images 7b and 7d are images when the virtual image 4 is viewed at azimuth angles of −15 degrees and +15 degrees. In this case, the diffraction efficiency is about half the peak value, and the displayed image is displayed with recognizable brightness. The visual images 7b and 7d are images when the virtual image 4 is viewed at an azimuth angle of −15 degrees or less and +15 degrees or more, and the images are darkened to the extent that it is difficult to visually recognize them.

In this way, in the virtual image display using the single reflective hologram 30, the observer moves because the half-value full angle (exit azimuth angle range) of the diffraction efficiency in the azimuth direction at an elevation angle of 3 degrees is ± 15 degrees. When the azimuth changes by 15 degrees or more, the brightness of the virtual image 4 becomes half or less.

[Virtual image display by image display device]
In the present embodiment, a plurality of reflective holograms 30 are arranged around the reference axis O so that the virtual image 4 can be continuously visually recognized even when the azimuth angle is changed. Specifically, the angle formed by the perpendiculars 6 of the first surfaces 31 adjacent to each other of the plurality of reflective holograms 30 is the range of the azimuth angle in the exit direction in which the diffraction efficiency is equal to or higher than the first value in the emission elevation angle range. It is set to be less than or equal to the angle represented by the incident elevation angle range.

For example, when the reflective hologram 30 showing the diffraction efficiency distribution shown in FIG. 7A is used, the angle formed by the perpendicular line 6 of the first surface 31 of the reflective hologram 30 adjacent in the circumferential direction is the angle represented by the emission azimuth range. It is set to (30 degrees). In this case, a polygonal prism having 12 reflective holograms 30 (first surface 31) in the circumferential direction centered on the reference axis O is configured.

Further, the radius of the inscribed circle 11a of the polygonal prism formed by the first surface 31 is set to the horizontal virtual image focal length Fh'recalculated with the change of the _{assumed pupil elevation angle α 0.} This makes it possible to accurately match the position where the virtual image 4 is displayed with the reference axis O. As a result, even if the pupil 5 moves 360 degrees in the azimuth direction at an elevation angle of 3 degrees, the situation in which the virtual image displayed in the adjacent hologram plane cannot be seen is avoided. This makes it possible to continuously display the virtual image 4 of the object image 3 centered on the reference axis O over all directions of 360 degrees.

When Δn is changed or the thickness of the reflective hologram 30 (photopolymer) is changed, the half-value full angle (exit azimuth angle) in the azimuth direction is obtained at the diffraction efficiency peak angle in the elevation angle direction at an azimuth angle of 0 degrees. Range) changes. Therefore, the angle formed by the perpendicular may be appropriately changed according to the full-width diffraction half value. Further, the angle formed by the perpendicular may be set in advance to be equal to or less than the emission azimuth angle range. This makes it unnecessary to change the design even when the emission azimuth angle range is reduced, for example.

FIG. 8 is a schematic diagram for explaining a virtual image displayed by the image display device 100. FIG. 8A is a map showing an example of the diffraction efficiency distribution of a plurality of reflective holograms 30 arranged in the image display device 100. FIG. 8B is a schematic view showing an example of virtual image display by the image display device 100. FIG. 8B schematically shows a part of an image display device 100 including three reflective holograms 30a to 30c arranged adjacent to each other. The reflective holograms 30a to 30c are arranged so that the angle formed by the perpendiculars of the first surfaces 31 adjacent to each other is the angle (30 degrees) represented by the emission azimuth range.

The map shown in FIG. 8A shows the diffraction efficiency distributions of the three reflective holograms 30a to 30c shown in FIG. 8B according to the emission direction. The vertical axis is the elevation angle in the emission direction of each reflective hologram 30, and the horizontal axis is the azimuth angle centered on the reference axis O in the emission direction. In FIG. 8A, the direction orthogonal to the central reflective hologram 30b is an azimuth of 0 degrees. The diffraction efficiency distribution of each of the reflective holograms 30a to 30c is the same as the diffraction efficiency distribution shown in FIG. 7A.

As shown in FIG. 8A, in the image display device 100, the emission azimuth angle range of each reflective hologram 30 is continuous. Therefore, in the range of the azimuth angle of ± 45 degrees, _{the diffraction efficiency at the assumed pupil elevation angle α 0} (3 degrees) is maintained at a value of half or more of the peak value. Therefore, in the range of the azimuth angle of ± 45 degrees, the image light 1 can be diffracted with high diffraction efficiency regardless of the azimuth angle.

The azimuth (display azimuth) at which the central reflective hologram 30b displays the virtual image 4 is in the range of ± 15 degrees. Similarly, the display azimuth of the reflective hologram 30a arranged on the left side of the reflective hologram 30b when viewed from the pupil 5 position is -45 degrees to -15 degrees, and the reflection arranged on the right side of the reflective hologram 30b. The display azimuth of the type hologram 30c is 15 to 45 degrees.

For example, suppose an observer looking at the central reflective hologram 30b moves to the left. In this case, the virtual image 4 formed by the reflective hologram 30b can be visually recognized at an azimuth angle of up to −15 degrees. Further, at an azimuth angle β = -15 degrees, a virtual image 4 formed with a diffraction efficiency of half the peak value is displayed by the reflective holograms 30b and a. Further, at an azimuth angle of −15 degrees or less, the virtual image 4 displayed by the reflective hologram 30a can be visually recognized.

In this way, when the pupil 5 moves in the azimuth direction with the elevation angle of 3 degrees, the diffraction efficiency continues on the adjacent reflective hologram 30 (first surface 31). As a result, the virtual image 4 of the object image 3 can be continuously displayed, and the virtual image display with a three-dimensional effect can be observed from the entire circumference. Further, the reflective hologram 30 has a limitation in diffraction efficiency. Therefore, a situation in which an image of the screen 20 paired with the adjacent reflective hologram 30 is reflected is avoided. This makes it possible to realize a high-quality virtual image display.

As described above, the image display device 100 according to the present embodiment is provided with a plurality of display units 10 having a screen 20 and a reflective hologram 30, and each reflective hologram 30 covers at least a part around the reference axis O. Arranged like this. The image light 1 of the object image 3 formed on the screen 20 is diffracted by the reflective hologram 30, emitted from the first surface 31 on the side opposite to the reference axis O, and directed to the reference axis O. A virtual image 4 of the object image 3 is displayed on the surface 32 side so as to overlap the background. As a result, the virtual image 4 can be displayed toward the periphery of the reference axis O, and the virtual image display with a sense of reality can be realized.

As a method of superimposing the background and the image, there is a method using a phenomenon called Pepper's ghost. In this method, the image on the display is folded back by the observer using a half mirror to display a virtual image of the image. A method is conceivable in which the display and the half mirror are paired and a plurality of pairs are arranged in the azimuth direction to display a virtual image.

FIG. 9 is a schematic view showing a display device 40 given as a comparative example. The display device 40 shown in FIG. 9 is an example of a device that displays a virtual image using the above-mentioned Pepper's ghost. The display device 40 includes a display 41 and a half mirror 42. The half mirror 42 has a shape in which the apex of the quadrangular pyramid is cut, and the cut surface is arranged toward the display 41. For example, the image 43 displayed on the display 41 is reflected by the half mirror 42 toward the outer periphery of the device. As a result, the virtual image 44 of the image 43 is displayed inside the quadrangular pyramid-shaped half mirror 42.

In order to ensure visibility in the light field, it is desirable that the brightness of the image in which the background and the virtual image are superimposed is high. However, in a method such as the display device 40, there is a trade-off between the transmittance of the half mirror 42 and the display brightness. As a result, it may be difficult to secure the display brightness while maintaining a high background brightness.

Further, in order to display the image superimposed on the background, for example, it is necessary to set the perpendicular line of the half mirror 42 in a direction intermediate between the perpendicular line of the display 41 and the line-of-sight direction to which the observer's eyes are directed. Therefore, when the half mirrors 42 are installed in each direction so as to be observed from the circumferential direction, it becomes necessary to arrange the half mirrors 42 in a conical shape or a pyramid shape as shown in FIG.

Therefore, the virtual image 44 displayed by the half mirror near the apex needs to be displayed small, and when displaying the virtual image 44 or the like along the axial direction of the pyramid, the virtual image 44 depends on the width of the half mirror 42 near the apex. The size of is constrained. Further, when the width near the apex is increased, the base of the pyramid becomes large and the device size increases. Further, when the angle with the adjacent surface is small, it is conceivable that an unintended image is reflected.

In the present embodiment, a plurality of reflective holograms 30 are arranged so as to cover the periphery of the reference axis O. Further, each reflective hologram 30 is arranged parallel to the reference axis O to form a polygonal prism structure. As a result, a highly transparent virtual image display that sufficiently transmits the background light becomes possible. Further, by using the reflective hologram 30, it is possible to selectively diffract the image light 1 of the object image 3 with high efficiency. As a result, the display brightness of the background and the virtual image is greatly improved, and high visibility can be exhibited. Further, since each reflective hologram 30 has a rectangular shape, the size of the virtual image that can be displayed does not differ depending on the position in the vertical direction, for example, and a highly versatile virtual image can be displayed.

Further, as described with reference to FIG. 8 and the like, the peak of the diffraction efficiency is set with respect _{to the assumed pupil elevation angle α 0.} Further, the adjacent first surface 31 is arranged so that the diffraction efficiency is continuous in the azimuth angle direction. As a result, the situation in which the virtual image 4 disappears when the pupil 5 moves in the azimuth angle direction is avoided. Further, since the diffraction efficiency is maintained at a high value, it is possible to display a bright virtual image 4 over the entire circumference.

Further, the radius of the inscribed circle 11a inscribed in the reflective hologram 30 is set to the virtual image focal length at the elevation angle at which the diffraction efficiency peaks. This makes it possible to suppress fluctuations in the virtual image position due to the movement of the pupil 5. As a result, it is possible to observe the bright virtual image 4 displayed superimposed on the background centering on the reference axis O from any direction, and it is possible to greatly improve the realism and stereoscopic effect of the virtual image display. It is possible.

<Second embodiment>
The image display device of the second embodiment according to the present technology will be described. In the following description, the description of the same parts as those of the configuration and operation in the image display device 100 described in the above embodiment will be omitted or simplified.

FIG. 10 is a schematic view showing a configuration example of the reflective hologram 50 according to the second embodiment. In the present embodiment, in order to continuously maintain the diffraction efficiencies in the elevation angle direction and the azimuth angle direction in the same plane, the reflective holograms 50 generated under different exposure conditions are laminated. Specifically, several types of reflective holograms 50 (photopolymers) exposed by changing only the slant angle φ while keeping the boundary pitch Λ constant are used.

As shown in FIG. 10, in the present embodiment, nine types of reflective holograms 50 are laminated and used. In the following, the nine types of laminated reflective holograms 50 will be referred to as the hologram unit 51. FIG. 10 schematically shows a cross section of the hologram portion 51 cut in the stacking direction.

The hologram unit 51 includes three types of reflective holograms R1 to R3 that diffract red light, three types of reflective holograms G1 to G3 that diffract green light, and three types of reflective holograms B1 to diffract blue light. It has B3 and. In the example shown in FIG. 10, the order is from the left side in the figure. Reflective holograms R1 to R3, reflective holograms G1 to G3, and reflective holograms B1 to B3 are laminated in this order. In the following, the laminated reflective holograms R1 to R3 will be referred to as a red hologram 52R, the stacked reflective holograms G1 to G3 will be referred to as a green hologram 52G, and the laminated reflective holograms B1 to B3 will be referred to as blue. The hologram 52B is described, and the order in which the reflective holograms 50 are laminated is not limited.

FIG. 11 is a map showing an example of the diffraction efficiency distribution of the hologram unit 51. In the left column of the figure, the diffraction efficiency distributions of the red hologram 52R and the reflective holograms R1 to R3 that diffract red light are shown in order from the top. Further, in the center column, the diffraction efficiency distributions of the green hologram 52G and the reflective holograms G1 to G3 that diffract the green light are shown in this order. Further, in the right column, the diffraction efficiency distributions of the blue hologram 52B and the reflective holograms B1 to B3 that diffract the blue light are shown in this order. The exposure wavelengths of red light, green light, and blue light are 647 nm, 524 nm, and 446 nm, respectively.

Further, in the second, third, and fourth stages from the top in the figure, the slant angles are set to 74.25 degrees, 74.7 degrees, and 75.1 degrees, respectively. For example, in the reflective hologram R1 having a smaller slant angle than the reflective hologram R2, the band-shaped region A that is convex upward is shifted in the positive elevation angle direction and spreads in the positive and negative azimuth angles. Further, in the reflective hologram R1 having a larger slant angle than the reflective hologram R2, the region A is shifted in the negative elevation angle direction and reduced in the positive / negative azimuth angle direction. In this way, the range in which the diffraction efficiency is relatively high changes depending on the slant angle.

The diffraction efficiency distribution of the red hologram 52R is the diffraction efficiency distribution when the reflective holograms R1 to R3 are laminated. In the red hologram 52R, the region A having high diffraction efficiency in each of the reflective holograms R1 to R3 overlaps, so that the region having high diffraction efficiency is expanded. In this way, by stacking the reflective holograms 50 having the same boundary pitch Λ and exposed only by changing the slant angle, it is possible to expand the half-width full-width of the diffraction efficiency. The reflection holograms 50 corresponding to green light and blue light are also laminated with each other to expand the half-width full-width of the diffraction efficiency.

The hologram unit 51 is configured by laminating a red hologram 52R, a green hologram 52G, and a blue hologram 52B. As a result, the hologram unit 51 becomes an optical element in which the half-width full-width of the diffraction efficiency is enlarged for each RGB light. As described above, in the present embodiment, the reflective hologram 50 has a laminated structure in which a plurality of holographic optical elements having different slant angles of interference fringes are laminated.

By expanding the diffractable angle range with high efficiency, it is conceivable that another object image plane may be diffracted and reflected on the adjacent first plane. In such a case, it is possible to prevent reflection by making the diffusion angle of the screen (diffusion sheet or diffusion hologram) smaller than the diffraction width in the azimuth direction.

Further, although the case where a plurality of reflective holograms 50 are laminated has been described above, it is possible to expand the half-width full-width of the diffraction efficiency by another method. For example, a photopolymer capable of multiple exposure may be used. By exposing different slants to the same surface a plurality of times and making them continuous, it is possible to widen the diffraction angle in the elevation angle direction and the azimuth angle direction. Further, by setting the refractive index difference Δn of the reflective hologram 50 to be high or setting the film thickness of the reflective hologram 50 to be thin, it is possible to widen the diffraction angle in the elevation angle direction and the azimuth angle direction.

<Third embodiment>
FIG. 12 is a schematic view showing a configuration example of the display unit 60 according to the third embodiment. The display unit 60 includes a screen 61, a transparent substrate 70, a first reflective hologram 71, and a second reflective hologram 72. In this embodiment, the screen 61 is located inside the device rather than the first reflective hologram 71.

The screen 61 has an object image plane 62 that forms an object image. The screen 61 has a flat plate shape, and is arranged so that the object image plane 62 faces the outside of the device and does not overlap with the virtual image. The transparent substrate 70 is a flat plate-shaped transparent member having light transmission. As the transparent substrate 70, for example, a glass substrate or a plastic substrate such as acrylic is used.

The first reflective hologram 71 has a first surface 81 and a second surface 82 opposite to the first surface 81, and is transparent with the second surface 82 directed to the reference axis O. It is bonded to the surface of the substrate 70 facing the reference axis O. The first reflective hologram 71 diffracts the image light 1 of the object image and emits it toward the pupil 5. More specifically, the light incident from the first surface 81 at a predetermined angle is diffracted through the transparent substrate 70. The predetermined angle is the angle of incidence through the transparent medium (transparent substrate). In this embodiment, the first reflective hologram 71 corresponds to a diffractive optical element.

The second reflective hologram 72 has a third surface 83 and a fourth surface 84 opposite to the third surface 83. The second reflective hologram 72 is attached to the surface of the transparent substrate 70 opposite to the surface facing the reference axis O with the third surface 83 facing. As described above, in the present embodiment, the second reflective hologram 72 is arranged so as to face the first surface 81 of the first reflective hologram 71. Further, the second reflective hologram 72 is formed with interference fringes (grating vectors) that reflect and diffract the light incident from the third surface 83 with respect to the angle range diffracted by the first reflective hologram 71. Will be done. In this embodiment, the second reflective hologram 72 corresponds to another diffractive optical element.

13 and 14 are graphs showing the diffraction characteristics of the first reflective hologram 71 and the second reflective hologram 72. The vertical axis of each graph is the diffraction efficiency, and the horizontal axis is the angle of incidence in the medium. The in-medium incident angle is an incident angle when light is incident through the transparent substrate 70. For example, as shown in FIG. 12, the first surface 81 of the first reflective hologram 71 and the third surface 83 of the second reflective hologram 72 are both bonded to the transparent substrate 70. Therefore, light is incident on the first surface 81 and the third surface 83 via the transparent substrate 70 (medium).

As shown in FIG. 13, the diffraction efficiency of the first reflective hologram 71 (first surface 81) peaks when the incident angles in the medium are about 0 degrees and about 35 degrees. Further, as shown in FIG. 14, the diffraction efficiency of the second reflective hologram 72 (third surface 83) peaks when the incident angle in the medium is about ± 30 degrees. As described above, each of the reflection holograms 71 and 72 has a reflection diffraction characteristic with respect to a predetermined angle of incidence in the medium.

As shown in FIG. 12, the screen 61 is arranged on the second surface 82 side of the first reflective hologram 71 so as not to block the display of the virtual image, and emits the image light 1 to the second surface 82. For example, the image light 1 is emitted from the object image plane 62 with respect to the second plane 82 at an incident angle of 50 degrees. The image light 1 incident on the second surface 82 is refracted at the interface of the second surface 82 and penetrates into the first reflective hologram 71. The image light 1 that has passed through the first surface 81 passes through the transparent substrate 70 and is incident on the third surface 83 of the second reflective hologram 72 at an incident angle of 30 degrees.

The image light 1 incident at an incident angle of 30 degrees is diffracted and reflected by the second reflective hologram 72, and is emitted toward the first surface 81 of the first reflective hologram 71. In this way, the second reflective hologram 72 diffracts the image light 1 emitted from the screen 61 and passed through the second surface 82 and the first surface 81, and is emitted to the first surface 81.

At this time, the angle of incidence of the image light 1 diffracted and reflected with respect to the first surface 81 in the medium is 35 degrees, which is the angle diffracted and reflected by the first reflective hologram 71. The image light 1 incident on the first surface 81 is diffracted and reflected by the first reflective hologram 71, and is emitted from the first surface 81 at a predetermined elevation angle (about 0 degrees). The image light 1 emitted from the first surface 81 passes through the transparent substrate 70 and the second reflective hologram 72, and is emitted toward the pupil 5 outside the apparatus.

Since the image light 1 propagating in the medium (transparent substrate) from the second reflective hologram 72 is incident on the first reflective hologram 71, the incident angle is not affected by Fresnel reflection. The same applies to the second reflective hologram 72. Therefore, for example, it is possible to change the incident angle from outside the medium to a large angle such as 50 degrees to 60 degrees.

As described above, when the first reflective hologram 71 is incident at an incident angle of 35 degrees in the medium, the first reflective hologram 71 is diffracted to an elevation angle of 0 degrees. Further, when the second reflective hologram 72 is incident at an out-of-medium incident angle of 50 degrees, the second reflective hologram 72 is reflected at an incident angle of 35 degrees corresponding to the first reflective hologram 71. That is, the second reflective hologram 72 is an optical element that diffracts the image light 1 and emits it at a predetermined angle (35 degrees) with respect to the first surface 81. This makes it possible to arrange the screen 61 inside the device, for example, to reduce the size of the device.

The specific configuration of the second reflective hologram 72 is not limited. The angle range in which the second reflective hologram 72 can be diffracted by a predetermined value may include the incident angle corresponding to the first reflective hologram 71. In this case, the second reflective hologram 72 is an optical element that includes a predetermined angle in an angle range in which the diffraction efficiency of the image light 1 is equal to or higher than a predetermined value. Here, the predetermined value is typically half the peak value of the diffraction efficiency. In the present embodiment, the predetermined value corresponds to the second value.

<Fourth Embodiment>
FIG. 15 is a schematic view showing a configuration example of the image display device 300 according to the third embodiment. FIG. 15A is a perspective view showing the appearance of the image display device 300. As shown in FIG. 15A, the image display device 300 is configured by arranging a plurality of display units 310 so as to surround the reference axis O.
In the present embodiment, the reflective hologram lens 330 is used as the diffractive optical element used for each display unit 310. That is, the image display device 300 is provided with a plurality of reflective hologram lenses 330.
The image display device 300 shown in FIG. 15A is provided with six display units 310a to 310f. These display units 310a to 310f are configured by using a screen 320 and a reflective hologram lens 330, respectively.

The reflective hologram lens 330 is a reflective holographic optical element (HOE) having a lens function. The reflective hologram lens 330 has a flat plate shape, and has a first surface 331 directed to the side opposite to the reference axis O (outside the device) and a second surface 331 directed to the reference axis O side (inside the device). It has a surface of 332 and.
For example, the image light 1 of the object image displayed on the screen 320 is emitted toward the first surface 331. The image light 1 incident on the first surface 331 is diffracted by the interference fringes exposed on the reflective hologram lens 330, and is emitted from the first surface 331. That is, the image light 1 of the object image 3 is reflected by the first surface 331. At this time, a virtual image of an object image enlarged according to the magnification of the reflective hologram lens 330 is formed on the second surface 332 side. Therefore, the reflective hologram lens 330 functions as a reflective lens (hologram mirror lens).

Further, the reflective hologram lens 330 is configured to selectively diffract the incident light in a predetermined angle range. Therefore, light incident at an angle outside the predetermined angle range (for example, background light) is transmitted without being diffracted by the reflective hologram lens 330. This makes it possible to display a virtual image superimposed on the background.

As will be described later, the reflective hologram lens 330 is exposed to interference fringes by interfering with the light emitted from the two points (see FIG. 16A). These points are arranged on both sides of the main body of the reflective hologram lens 330. In the following, the point arranged on the first surface 331 side will be referred to as the first point Q, and the point arranged on the second surface 332 side will be referred to as the second point Q'. FIG. 15A schematically illustrates a first point Q and a second point Q'corresponding to the reflective hologram lens 330 constituting the display unit 310a.
As described above, in the image display device 300, the interference fringes are caused by the light emitted from the first point Q arranged on the first surface 331 side and the second point Q'arranged on the second surface 332 side. A plurality of reflective hologram lenses 330 exposed to the light are used.

FIG. 16 is a schematic diagram for explaining the reflective hologram lens 330. FIG. 16A is a schematic view showing a state when the interference fringes of the reflective hologram lens 330 are exposed. FIG. 16B is a schematic diagram showing the diffraction of light by the interference fringes exposed by the method shown in FIG. 16A.
Here, a method for generating the reflective hologram lens 330 and its characteristics will be described.

As shown in FIG. 16A, when the interference fringes are exposed, the photopolymer 335 serving as the reflective hologram lens 330 is irradiated with light from the reference point 8 and the object point 9.
The photopolymer 335 is bonded to a transparent flat plate member such as a glass plate or an acrylic plate.
The reference point 8 is a starting point for emitting the reference light 90. Here, the reference point 8 is arranged below the side to be observed by the observer (the first surface 331 side), and becomes the above-mentioned first point Q.
The object point 9 is a point that serves as a starting point for emitting the object light 91. Here, the object point 9 is arranged on the side opposite to the side observed by the observer (the second surface 332 side), and becomes the above-mentioned second point Q'.

The reference light 90 and the object light 91 are synchrotron radiation emitted radially from the reference point 8 and the object point 9. In the following, the optical axes of the reference light 90 and the object light 91 will be referred to as an optical axis 92a and an optical axis 92b. Here, the optical axis is, for example, the central axis of synchrotron radiation (reference light 90 and object light 91).
The optical axis 92a of the reference light 90 is set so that, for example, the observation range by the observer and the reference point 8 do not overlap. The optical axis 92b of the object light 91 is set so as to coincide with the elevation angle (assumed pupil elevation angle α _{0) assuming the position of the observer's pupil 5.}
Further, the reference point 8 and the object point 9 are arranged so that the optical axis 92a and the optical axis 92b intersect on the photopolymer 335. The light spots of the optical axis 92a and the optical axis 92b serve as the lens center C of the reflective hologram lens 330.
In the present embodiment, the optical axis 92a and the optical axis 92b are set so as not to be parallel to each other. Therefore, the reflective hologram lens 330 is an off-axis lens in which the optical axes of the incident light and the emitted light are different.

As shown in FIG. 16A, the angle at which the synchrotron radiation (reference light 90 and object light 91) emitted from the reference point 8 and the object point 9 is incident on the photopolymer 335 differs depending on the position. Therefore, the photopolymer 335 is exposed to the interference fringes by the light incident on both sides of the photopolymer 335 at different angles for each position.
As described above, the grating vector of the interference fringes formed on the reflective hologram lens 330 is determined by the positions of the reference point 8 and the object point 9 at the time of exposure and the angles of the optical axes 92a and 92b corresponding to the respective points. .. The grating vector of the interference fringes to be exposed differs depending on the position of the reflective hologram lens 330.

FIG. 16B schematically shows the optical path of the image light 1 when the image light 1 is emitted radially from the reference point 8 along the optical axis 92a.
The image light 1 radially emitted from the reference point 8 along the optical axis 92a and incident on the first surface 331 is diffracted (reflected) by the reflective hologram lens 330 and emitted from the first surface 331. At this time, the direction in which the image light 1 is reflected is the same as the light emitted from the object point 9 along the optical axis 92b (object light 91 in FIG. 16A). As a result, a virtual image 4 of the reference point 8 is formed at the object point 9 on the second surface 332 side.
Similarly, the image light 1 emitted from each point of the image plane including the reference point 8 is diffracted by the reflective hologram lens 330, so that the virtual image plane including the object point 9 is formed on the second surface 332 side. It is formed.

In the present embodiment, the object point 9 is set at the point where the optical axis 92b intersects the reference axis O, with the intersection angle between the optical axis 92b and the reflective hologram lens 330 as a desired viewing angle (assumed pupil elevation angle). That is, a virtual image point (object point 9) on which the virtual image of the reference point 8 is displayed when the virtual image 4 is reproduced is set on the reference axis O. Further, the reference point 8 is set to be a point on the screen 320 (for example, the center point of the screen 320). This makes it possible to align the virtual image plane with the reference axis O.

In the example shown in FIG. 16, the reference point 8 is the first point Q arranged on the first surface 331 side, and the object point 9 is the second point Q'arranged on the second surface 332 side. The case where becomes is explained. Not limited to this, the reference point 8 and the object point 9 can be interchanged with each other.
For example, it is possible to diffract (reflect) the light incident from the object point 9 to form a virtual image of the object point 9 at the reference point 8. In this case, the object point 9 becomes the first point Q, and the surface on the object point 9 side becomes the first surface 331. Further, the reference point 8 becomes the second point Q', and the surface on the reference point 8 side becomes the second surface 332.

As described above, one of the first point Q and the second point Q'is the reference point 8 that emits the reference light 90, and the other of the first point Q and the second point Q'is the object light. It is an object point 9 that emits 91.
Hereinafter, as shown in FIG. 16, a case where the first point Q is the reference point 8 and the second point Q'is the object point 9 will be described. Further, the first point Q and the second point Q'may be described as a reference point Q and an object point Q'.

As shown in FIG. 15A, the plurality of reflective hologram lenses 330 are arranged so as to surround the reference axis O so that the first surface 331 (second surface 332) is parallel to the reference axis O. Each reflective hologram lens 330 is arranged continuously in the circumferential direction, for example, to form a polygonal prism.
Further, the plurality of reflective hologram lenses 330 are arranged so that each object point Q'overlaps with the reference axis O. Typically, each reflective hologram lens 330 is arranged so that each object point Q'consists at one point on the reference axis O.
As described above, in the present embodiment, the plurality of reflective hologram lenses 330 are arranged so that the first surface 331 and the reference axis O are parallel to each other and the object point Q'overlaps the reference axis O. This makes it possible to form a virtual image plane by each reflective hologram lens 330 along the reference axis O.

FIG. 15B is a schematic view showing a cross section of the image display device 300 cut along the reference axis O along the XZ plane. This cross section is a cross section of the display unit 310a shown in FIG. 15A and the display unit 310d arranged on the opposite side of the display unit 310a with the reference axis O interposed therebetween.
In FIG. 15B, a line segment 93 connecting the object point Q'of the reflective hologram lens 330 and the lens center C is shown by a thick dotted line. The line segment 93 corresponds to the optical axis 92b of the object light 91 described above.
The distance between each reflective hologram lens 330 and the reference axis O depends on the length of the line segment 93 corresponding to the optical axis 92b and the elevation angle (assumed pupil elevation angle) of the line segment 93 with respect to the reflective hologram lens 330. It will be decided. For example, the larger the length of the line segment 93 and the smaller the elevation angle of the line segment 93, the larger the distance between each reflective hologram lens 330 and the reference axis O.

In the present embodiment, in the plurality of reflective hologram lenses 330, the length and elevation angle of the line segment 93 connecting the object point Q'and the lens center C are set to be equal to each other. That is, when the interference fringes are exposed to each reflective hologram lens 330, the relative arrangement position of the object point Q'and the elevation angle of the optical axis 92b of the object light 91 are set to be equal to each other.
This makes it possible to set the distance between each reflective hologram lens 330 and the reference axis O equally. As a result, the plurality of reflective hologram lenses 330 form a polygonal prism inscribed in the inner circumference circle having a radius R centered on the reference axis O. This makes it possible to realize, for example, an all-around display in which virtual images are switched at regular intervals.

In each reflective hologram lens 330, the length and elevation angle of the line segment 93 may be set individually. In this case, the distance between each reflective hologram lens 330 and the reference axis O is appropriately set so that, for example, the virtual image plane coincides with the reference axis O. In this case, it is possible to individually set the assumed pupil elevation angle depending on the viewing direction, and it is possible to improve the degree of freedom in design.

The screen 320 has a flat object image plane 321 and forms an object image. Further, the screen 320 is arranged so that the object image surface 321 is directed toward the first surface 331 and the optical path of the light displaying the virtual image 4 formed by the reflective hologram lens 330 is avoided.
The position and orientation of the screen 320 are set according to, for example, the characteristics of the corresponding reflective hologram lens 330. Specifically, the reference point Q of the reflective hologram lens 330 is arranged so as to coincide with a point (for example, a center point) on the screen 320 (object image plane 321). As a result, the virtual image of the object image 3 formed on the screen 320 can be clearly displayed on the reference axis O. The orientation of the screen 320 is set so as to be orthogonal to, for example, the optical axis 92 of the reference light 90. This makes it possible to avoid a situation in which the virtual image is tilted.
The position and orientation of the screen 320 are not limited, and may be appropriately set so that the virtual image 4 of the object image is properly displayed.

As the screen 320, for example, a transmissive diffusion screen or the like is used. In this case, the display unit 310 is provided with a projector (see FIG. 2) that projects an image (object image) onto the screen 320 from the side opposite to the object image plane 321.
Further, the projection direction in which the projector projects the object image (for example, the direction in which the central pixel of the object image is projected) is set so as to coincide with the optical axis 92a of the reference light 90 described above. That is, the projector projects an object image on the screen 320 along the same direction as the optical axis 92a of the light emitted from the reference point Q. As a result, the diffraction efficiency of the object image is improved, and a bright image can be displayed.
The specific configuration of the screen 320 is not limited, and for example, a reflective diffusion screen may be used. Further, a self-luminous display or the like may be used as the screen 320.

As described above, in the image display device 300, the plurality of reflective hologram lenses have the object point Q'allocated to coincide with the axis (reference axis O) passing through the center of the inner peripheral circle inscribed in each reflective hologram lens 330. 330 is placed. Further, a plurality of screens 320 are arranged so that the reference point Q coincides with a point in the object image plane 321 of the corresponding screen 320.
This makes it possible to display a clear virtual image along the reference axis O.

FIG. 17 is a schematic view showing a virtual image display by a linear hologram given as a comparative example.
Here, the difference between the reflective hologram (linear hologram 350) exposed with interference fringes having a period in one direction and the reflective hologram lens 330 will be described.
17A and 17B schematically show an optical path of light diffracted by two types of linear holograms 350 having different values of boundary pitch Λ. Further, in each figure, an exit point 95 from which light is emitted and a virtual image point 96 corresponding to the emission point 95 are schematically illustrated.

As shown in FIG. 17A, when the exit point 95 and the virtual image point 96 are plane symmetric with respect to the linear hologram 350, the incident angle θ _in and the exit angle θ _out are equal. Therefore, the boundary pitch Λ becomes infinite due to the relationship of the above equation (1) (Sinθ _in + mλ / Λ = Sinθ _out).
In this way, when the boundary pitch Λ is infinite, even if the observer's pupil 5 moves in the elevation angle direction, the amount of change _in the incident angle θ in and the exit angle θ _{out corresponding to the position of each pupil 5 is equal.} The position of the virtual image point 96, that is, the position of the virtual image 4 does not change.

On the other hand, as shown in FIG. 17B, when the exit point 95 and the virtual image point 96 are not plane-symmetric with respect to the linear hologram 350, the incident angle θ _in and the exit angle θ _out are different angles from each other. In this case, the boundary pitch Λ takes a finite value.
When the boundary pitch Λ becomes small, the position of the virtual image point 96 changes because the change _in the incident angle θ _{in is small with respect to the change in the diffraction angle (exit angle θ out) accompanying the movement of the pupil 5.} Image distortion or the like that distorts the virtual image itself may occur.

When the linear hologram 350 is used as the hologram combiner in this way, it is conceivable that the virtual image position moves with the movement of the pupil 5 (movement of the viewpoint). As a result, for example, when the viewpoint is moved in the azimuth direction and the virtual image 4 is viewed across the adjacent linear hologram 350, the virtual image display may shift. Further, for example, when the viewpoint is moved in the elevation angle direction, the virtual image position with respect to each linear hologram 350 changes, so that the center position may shift. Due to the movement of the virtual image accompanying the movement of the viewpoint, the sense of reality of the virtual image 4 may be impaired.

On the other hand, when the reflective hologram lens 330 is used, the image light 1 is diffracted as if the light is emitted from the same point even when the observer's pupil 5 moves. It is possible.
As described above, the grating vector of the interference fringes formed on the reflective hologram lens 330 differs for each position. By appropriately correcting the change in the diffraction angle described in FIG. 17B by the interference fringes, the virtual image movement and the like that occur in the linear hologram 350 are suppressed.
For example, as shown in FIG. 16B, the image light 1 emitted from the reference point Q is diffracted so as to be emitted from the object point Q'(virtual image point) regardless of the position of the pupil 5. As a result, it is possible to suppress virtual image movement, image distortion, and the like, and it is possible to realize a virtual image display with a sense of reality.

Further, it is desirable that the distance between the reference point Q and the lens center C and the distance between the object point Q'and the lens center C are set to the same magnification. That is, the distances of the reference point Q and the object point Q'with respect to the lens center C are set to be equal to each other. In this case, the magnification of the reflective hologram lens 330 is 1.
In this way, the plurality of reflective hologram lenses 330 are configured as the same magnification lens. This makes it possible to reduce the change in the optical path of the image light 1 due to the movement of the pupil 5. As a result, for example, distortion of the virtual image plane (curvature of field) can be sufficiently suppressed.

Further, it is desirable that the distance between the reference point Q and the lens center C and the distance between the object point Q'and the lens center C be set as small as possible. That is, it is desirable that the reference point Q and the object point Q'are set close to each other. As a result, the amount of change in the optical path of the image light 1 becomes small, and it becomes possible to sufficiently suppress virtual image movement, image distortion, and the like.

The positions of the reference point Q and the object point Q', the angles of the optical axis 92a and the optical axis 92b, etc. are set so that the object image surface 321 of the screen 320 does not cover the visual field of the pupil 5 when the virtual image 4 is reproduced. Is set to.
If the distance from the lens center C of the reflective hologram lens 330 to the reference point Q and the object point Q'is not the same magnification, the reflective hologram lens 330 and the screen 320 (object image plane 321) correspond to the magnification. By appropriately arranging the above, it is possible to realize an appropriate holographic display.

FIG. 18 is a schematic view showing a configuration example of the display unit 310 using the reflective hologram lens 330. FIG. 18 shows the display unit 310 in the image display device 300 when the diameter of the inner peripheral circle of the polygonal prism composed of the plurality of reflective hologram lenses 330 is set to 200 mm and the image height of the object image is 40 mm. A configuration example is shown.
In this case, the distance from the lens center C to the reference point Q (for example, the center point of the screen 320) is set to 126.9 mm. The elevation angle of the optical axis 92a from the reference point Q toward the lens center C is set to 38 deg.
Further, the distance from the lens center C to the object point Q'on the reference axis O is set to 101.5 mm. The elevation angle (assumed pupil elevation angle) of the optical axis 92b from the object point Q'to the lens center C is set to 10 deg.
By configuring the display unit 310 in this way, it is possible to properly display the virtual image 4 of the object image 3 along the reference axis O.
Note that FIG. 18 shows an optical path of the image light 1 emitted from the reference point Q and an optical path of the image light 1 emitted from a point below the reference point Q, respectively.

FIG. 19 is a schematic view showing an example of the optical path of the image light 1 diffracted by the reflective hologram lens 330. 19A and 19B are schematic views showing the optical path of the image light 1 when the display unit 310 is viewed from the side and above.
Since the reflective hologram lens 330 has an object point Q'and a reference point Q as described above, the grating vector differs depending on the position of the reflective hologram lens 330 (lens surface). Therefore, the diffraction efficiency of the image light 1 in the reflective hologram lens 330 differs depending on the position of the lens surface.

For example, as shown in FIG. 19A, if the elevation angle of the pupil 5 looking into the reflective hologram lens 330 changes, the position on the lens surface that reflects the light rays reaching the pupil 5 from the object image plane 321 of the screen 320 changes in the vertical direction. Change. That is, the diffraction position (reflection position) at which the image light 1 displaying each point on the object image plane 321 is diffracted changes. As a result, the image light 1 that reaches the pupil 5 becomes light diffracted by the interference fringes of different grating vectors as the pupil 5 moves. That is, when the pupil 5 moves, the grating vector of the interference fringes diffracting the image light 1 changes.
Further, as shown in FIG. 19B, the grating vector of the interference fringes diffracting the image light 1 also changes when the azimuth angle of the pupil 5 looking into the reflective hologram lens 330 changes.

FIG. 20 is a schematic view showing the relationship between the display position on the object image plane and the diffraction position by the reflective hologram lens. FIG. 21 is a map showing an example of the diffraction efficiency distribution for each display position shown in FIG.
In FIG. 20, an image of a black arrow is shown as an example of the object image 3 displayed on the object image plane 321. Further, the display position 97 on the object image plane 321 is shown using white circles. For example, when the observer moves the pupil 5, the diffraction position on the reflective hologram lens 330 changes. The diffraction position also differs depending on the display position 97.
In the following, the coordinates of the display position 97 on the object image plane 321 will be described as (x [mm], y [mm]). The display position 97a is, for example, the center position (0,0) of the object image plane 321. The coordinates of the display positions 97b, 97c, 97d, and 97e are (0,15), (0,-15), (15,0), and (-15,0), respectively.

The map shown in FIG. 21 is a map showing the angular distribution of diffraction efficiency corresponding to the display positions 97a to 97e shown in FIG. In each map, the diffraction efficiency distribution when the observer moves the pupil 5 to anticipate each display position 97 of the object image plane 321 (that is, the diffraction when the pupil 5 is moved while looking at each display position 97). The angular distribution of efficiency) is shown.
The map shown in FIG. 21 is a simulation result using the arrangement of the display units 310 shown in FIG. In this simulation, the thickness of the reflective hologram lens 330 was set to 16 μm, and the refractive index difference Δn = 0.035. The wavelength of the image light 1 (reproduction wavelength) was set to 524 nm.

The vertical and horizontal axes of each map are the elevation and azimuth angles of pupil movement. The range of elevation angle is 0 deg to 20 deg, and the range of azimuth angle is -15 deg to +15 deg. Grayscale shades on each map indicate diffraction efficiency. In all these maps, the maximum value of diffraction efficiency is close to 100%. The map with the lowest diffraction efficiency is the map at the display position 97c (-15,0), and the value is about 50%.

For example, the diffraction efficiency of the image light 1 emitted from the display position 97a (0,0) hardly changes even if the azimuth angle of the pupil 5 changes. Further, although the diffraction efficiency decreases as the elevation angle of the pupil 5 increases, a high value of 50% or more is maintained in the range where the elevation angle is up to 20 deg.
Further, the diffraction efficiency for the other display positions 97b to 87e is also maintained at a high value of 50% or more regardless of the movement of the pupil 5. Therefore, even if the observation direction changes, it is possible to display the virtual image of each point on the object image plane 321 with sufficient brightness.

As described above, in the reflective hologram lens 330, the brightness of the virtual image 4 may not be easily reduced by the movement of the pupil 5 in the azimuth angle direction. In this case, depending on the arrangement angle of the reflective hologram lens 330 (for example, the angle formed by the perpendiculars of the first surfaces 331 adjacent to each other), the virtual image 4 may be reflected. In the reflection of the virtual image 4, for example, the virtual image 4 generated by the adjacent reflective hologram lens 330 is superimposed on the virtual image 4 generated by the reflective hologram lens 330 to be observed.

Such reflection of the virtual image 4 can be avoided, for example, by appropriately setting the diffusion angle of the image light 1 emitted from the screen 320.
Specifically, the half-value diffusion angle of the image light 1 emitted from the screen 320 (object image plane 321) in the azimuth direction is set to be approximately the same as the arrangement angle of the reflective hologram lens 330. Here, the diffuse half-width full-width is an angle range in which the brightness of the diffused light is reduced to 50% of the maximum value.
This makes it possible to prevent the reflection of the object image 3 (virtual image 4) formed on the adjacent screen 320.
In this case, the arrangement angle of the reflective hologram lens 330 is set to, for example, an angle determined by the assumed number of strokes of the polygonal prism. Alternatively, the arrangement angle of the reflective hologram lens 330 may be freely set, and the number of strokes of the polygonal prism or the like may be set according to the arrangement angle.

When the angle range (half-value full angle) in the azimuth direction at which the diffraction efficiency in the azimuth direction is 50% or less is determined, the arrangement angle of the reflective hologram lens 330 is set according to the half-value full angle.
This makes it possible to avoid reflection of the virtual image 4. Further, it is possible to avoid a situation in which the virtual image 4 becomes invisible when the observation direction changes and the reflective hologram lens 330 is switched. As a result, it is possible to realize a virtual image display with a sense of reality.

Further, it is conceivable that the virtual image 4 created by the reflective hologram lens 330 has astigmatism in the elevation angle direction and the azimuth angle direction. In this case, the position where the virtual image is formed may deviate between the elevation angle direction and the azimuth angle direction. In such a case, the radius of the inscribed circle is set with reference to the virtual image focal point in the azimuth direction in which congestion is dominant. As a result, the virtual image 4 can be properly displayed along the reference axis O even when the observer moves in the congestion direction (azimuth angle direction) where the position shift or the like is easily perceived.

FIG. 22 is a diagram for explaining virtual image positions in the reflective hologram lens 330 and the linear hologram 350.
FIG. 22A is a schematic view showing pupil movement in the azimuth direction. Here, it is assumed that the pupil 5 located at a position 500 mm away from the HOE (reflective hologram lens 330 or linear hologram) moves in the azimuth direction within a range of ± 20 deg. Further, it is assumed that the elevation angle of the pupil 5 in the observation direction with respect to the HOE is 10 deg.

FIG. 22B is a graph showing a change in the virtual image position in the reflective hologram lens 330 with the movement of the pupil in the azimuth direction. Further, FIG. 22C is a graph showing a change in the virtual image position in the linear hologram 350 due to the movement of the pupil in the azimuth direction. Hereinafter, the depth of the virtual image position is described as X, and the height Z is described. Further, the angle in the azimuth direction is described as a horizontal angle.
22B and 22C show virtual image positions when the horizontal angles of the pupil 5 are 0 deg, 5 deg, 10 deg, 15 deg, and 20 deg, respectively. The horizontal and vertical axes of each graph are depth X and height Z.

As shown in FIG. 22B, the depth and height of the virtual image 4 displayed by the reflective hologram lens 330 hardly move even if the horizontal angle of the pupil 5 changes from 0 deg to 20 deg. Therefore, for example, when the observer observes the virtual image 4 while moving around the image display device 300, the virtual image 4 is fixedly displayed at a fixed display position (a position intersecting the reference axis O).
On the other hand, as shown in FIG. 22C, in the virtual image 4 displayed by the linear hologram 350, the depth X shifts backward and the height Z shifts upward as the horizontal angle of the pupil 5 increases. Therefore, when the linear hologram 350 is used, for example, the position of the virtual image 4 changes depending on the position where the image display device 300 is observed, which may impair the sense of reality.

As described above, in the reflective hologram lens 330, the virtual image fluctuation with respect to the change in the azimuth direction of the pupil 5 (change in the azimuth angle of the viewpoint) is sufficiently suppressed and the virtual image position is fixed as compared with, for example, the linear hologram 350. .. Similarly, in the reflective hologram lens 330, the virtual image fluctuation with respect to the change in the elevation angle direction of the pupil 5 (change in the viewpoint elevation angle) is also suppressed.
As a result, for example, by moving the pupil 5 in the azimuth direction, it is possible to match the virtual image positions even when observing the virtual image 4 across the adjacent reflective hologram lenses 330.
Further, the position of the virtual image seen from each surface hardly changes regardless of the elevation angle of the pupil 5. By fixing the virtual image position in this way, it is possible to avoid fluctuations in the virtual image due to movement of the viewpoint, and to realize a virtual image display with a sufficient sense of reality.

<Other Embodiments>
The present technology is not limited to the embodiments described above, and various other embodiments can be realized.

In the above embodiment, the case where the reflective holograms are adjacent to each other is mainly described. Not limited to this, reflective holograms may be placed apart. For example, a part of a surface of a regular polygon may be formed by using a structural member or the like. Alternatively, a gap may be provided between the reflective holograms. As described above, the plurality of reflective holograms constituting the image display device may be arranged with a gap from each other. Even in such a case, it is possible to realize a virtual image display with a sense of reality by appropriately setting the relative angle of each reflective hologram as described above.

In the above, the case where the reflective hologram is a plane has been described. For example, the reflective hologram may be composed of curved surfaces. Specifically, the reflective hologram constitutes a cylindrical surface centered on a reference axis. In this case, the plurality of reflective holograms form, for example, a cylindrical structure surrounding a reference axis. This enables a virtual image display that can be observed from multiple directions through the cylindrical surface.

For example, when the image light is emitted along a certain direction with respect to the cylindrical surface (first surface), the larger the radius of the cylindrical surface, the smaller the azimuth component in the incident direction with respect to the cylindrical surface. On the contrary, the smaller the radius of the cylindrical surface, the larger the azimuth component in the incident direction. Therefore, the azimuth component of the light diffracted and reflected on the cylindrical surface becomes smaller as the radius is larger, and becomes larger as the radius is smaller.

Therefore, in order to properly display the virtual image of the object image displayed on the screen, it is necessary to appropriately set the radius of the cylindrical surface. In the present disclosure, the radius of the cylindrical surface is equal to or less than half the angle represented by the range of the azimuth angle in the emission direction in which the azimuth angle of the image light emitted from the first surface is equal to or higher than a predetermined value. Is set to be. Here, the predetermined value is, for example, half of the peak value. Since the azimuth angle of diffraction reflection is either positive or negative, half of the angle represented by the azimuth angle is used as a reference. As a result, the diffraction efficiency of the image light (light that forms a virtual image) reflected on the cylindrical surface becomes at least a predetermined value or more. In this way, the radius of the cylindrical surface is set according to the diffraction efficiency of the reflective hologram.

FIG. 23 is an exposure apparatus that exposes interference fringes on the hologram. The exposure apparatus 200 is an apparatus that generates a reflective hologram (linear hologram) having interference fringes having a period in one direction. The exposure apparatus 200 includes a light source unit 210 and an exposure unit 220. The light source unit 210 includes RGB laser light sources 211r, 211g, 211b, beam expanders 212r, 212g, 212b, mirror 213, and half mirrors 214a and 214b.

The RGB laser light sources 211r, 211g, and 211b emit red, green, and blue laser beams 230r, 230g, and 230b, respectively. The beam expanders 212r, 212g and 212b expand the laser beams 230r, 230g and 230b emitted from each laser light source. The mirror 213 reflects the magnified red laser beam 230r along a predetermined optical path. The half mirror 214a is arranged on a predetermined optical path and reflects 230 g of magnified green laser light along the predetermined optical path. The half mirror 214b is arranged on a predetermined optical path and reflects the enlarged blue laser light 230b along the predetermined optical path. Therefore, the beam light 231 to which the laser light 230 is combined is emitted from the predetermined optical path.

The exposure unit 220 includes a beam splitter 221, a fixed mirror 222, movable mirrors 223a and 223b, and first to third stages 224a to 224c. The beam splitter 221 splits the beam light 231 incident along a predetermined optical path from the light source unit 210 into a fixed mirror 222 and a movable mirror 223a and emits the beam light 231. The fixed mirror 222 emits the incident beam light to the movable mirror 223b. The movable mirror 223a is rotatable and reflects the beam light 231 toward one surface of the sample 232. The movable mirror 223b is rotatable and reflects the beam light 231 toward the other surface of the sample 232.

The first to third stages 224a to 224c can move along a direction parallel to each other (Y direction). The first stage 224a supports the movable mirror 223a, and the second stage 224b supports the movable mirror 223b. The third stage 224c also supports the sample 232 and is capable of moving the sample 232 along the Z-axis direction. Here, as the sample 232, for example, a transparent substrate such as glass to which a photosensitive photopolymer is attached is used.

Each RGB laser beam 230 is expanded by a beam expander to make the beam wave surface uniform. Each color laser beam 230 is combined by the mirror 213 and the half mirrors 214a and 214b and emitted as beam light. The beam light 231 is split into two beams using a beam splitter, and the movable mirrors 223a and 223b are used to irradiate each surface of the sample 232 as reference light and object light, respectively. At this time, the angles of the reference light and the object light are deflected, and the interference fringes are exposed at a desired exposure angle. The exposed sample 232 may be used as it is attached to the glass, or the photopolymer may be peeled off and reattached to another substrate such as an acrylic plate. The substrate may be a curved surface as well as a flat surface.

By moving the third stage 224c in the Y direction and the Z direction, it is possible to increase the area where the interference fringes are exposed. Further, by changing the mirror angle according to the exposure position, it is possible to perform exposure while changing the slant angle in the hologram surface. In this case, in the reflective hologram, the slant angle of the interference fringes differs depending on the exposure position. For example, this method is used when the slant angle is changed for each elevation angle with respect to the position of the pupil for exposure. This makes it possible to control the direction in which light is diffracted and reflected for each position.

FIG. 24 is an exposure apparatus that exposes a hologram lens. The exposure apparatus 400 is an apparatus for generating a reflective hologram lens having interference fringes that functions as a reflective lens.
The exposure apparatus 400 includes, for example, the exposure apparatus 200 shown in FIG. 23, as well as a reference optical lens 410 and an object optical lens 420. Hereinafter, the same configuration as the exposure apparatus 200 of FIG. 23 will be described with reference to the same reference numerals.

The reference light lens 410 is a lens that produces the reference light 90. For example, the beam light 231 incident on the reference light lens 410 is focused on the focal point of the reference light lens 410 and then emitted radially from the focal point. The focal point of the reference optical lens 410 is the reference point 8 described with reference to FIG. 16 and the like. The optical axis of the reference light lens 410 is the optical axis 92a of the reference light 90, and is set parallel to the traveling direction of the beam light 231 reflected by the movable mirror 223a.
The object light lens 420 is a lens that generates the object light 91. For example, the beam light 231 incident on the object light lens 420 is focused on the focal point of the object light lens 420 and then emitted radially from the focal point. The focal point of the object light lens 420 is the object point 9 described with reference to FIG. 16 and the like. The optical axis of the object light lens 420 is the optical axis 92b of the object light 91, and is set parallel to the traveling direction of the beam light 231 reflected by the movable mirror 223b.
The reference optical lens 410 and the object optical lens 420 are fixed independently of the first to third stages 224a to 224c by using, for example, a holding portion (not shown).

The exposure apparatus 400 uses a reflective hologram lens 330 with red, green, and blue laser beams 230r, 230g, and 230b, and is a two-luminous flux exposure optical system for simultaneously exposing interference fringes corresponding to each color light to a photopolymer. Is configured.
The red, green, and blue laser beams 230r, 230g, and 230b emitted from the RGB laser light sources 211r, 211g, and 211b are magnified by the corresponding beam expanders 212r, 212g, and 212b, and the beam wave plane of each laser beam is expanded. Be homogenized. The homogenized laser beams 230r, 230g, and 230b are reflected by the mirror 213, the half mirror 214a, and the half mirror 214b along a predetermined optical path, respectively. In this process, the laser beams of each color are combined. The combined laser light (beam light 231) is split into two beams using a beam splitter.

One of the demultiplexed beam lights 231 is deflected by the movable mirror 223a and is incident on the reference optical lens 410 along the optical axis 92a. The other side of the demultiplexed beam light 231 is reflected by the mirror 222, then deflected by the movable mirror 223b, and is incident on the object light lens 420 along the optical axis 92b. Each beam light 231 focused on the reference point 8 and the object point 9 by the reference light lens 410 and the object light lens 420 irradiates the sample 232 as synchrotron radiation (reference light 90 and object light 91).
The sample is constructed by, for example, attaching a photopolymer to glass. After the exposure, it may be used as it is attached to the glass, or the photopolymer may be peeled off and reattached to an acrylic plate or the like. The base to be attached may be a curved surface.

The optical axis 92a of the reference optical lens 410 and the optical axis 92b of the object optical lens 420 are set to desired exposure angles. Further, it is desirable that the optical axes 92a and 92b are installed so as to form an intersection on the photopolymer attached to the sample 232. This intersection is the center of the lens. For example, by moving the third stage holding the sample 232, it is possible to adjust the exposure position in the photopolymer.

It is conceivable that the exposure wavelength for exposing the interference fringes and the reproduction wavelength for reproducing the virtual image may be different. In such a case, each lens may be shifted so that the object point or the reference point becomes a desired point. Further, for example, the deviation between the exposure wavelength and the reproduction wavelength may be corrected by controlling the wave surface using an SLM (spatial light modulation) element or the like.

In the above, a reflective hologram and a reflective hologram lens, which are reflective HOEs, are used. Not limited to this, any diffractive optical element capable of diffracting the image light and displaying a virtual image may be used. Here, the diffractive optical element (DOE) is an optical element that diffracts light. For example, the above-mentioned HOE is an example of a diffractive optical element.

The specific configuration of the diffractive optical element is not limited. For example, a volumetric HOE in which interference fringes are recorded inside the device described with reference to FIG. 4 and the like is used. Further, a relief type (embossed type) HOE or the like in which interference fringes are recorded due to irregularities on the surface of the element or the like may be used. For these HOEs, for example, a material such as a photopolymer (photosensitive material or the like) or a UV curable resin can be used. Further, in addition to diffraction by interference fringes, a diffractive optical element of a type that diffracts light using a diffraction grating or the like having a predetermined pattern may be used.

It is also possible to combine at least two feature parts among the feature parts according to the present technology described above. That is, the various feature portions described in each embodiment may be arbitrarily combined without distinction between the respective embodiments. Further, the various effects described above are merely examples and are not limited, and other effects may be exhibited.

In the present disclosure, "same", "equal", "orthogonal", etc. are concepts including "substantially the same", "substantially equal", "substantially orthogonal", and the like. For example, a state included in a predetermined range (for example, a range of ± 10%) based on "exactly the same", "exactly equal", "exactly orthogonal", etc. is also included.

The present technology can also adopt the following configurations.
(1) Each
The screen that forms the object image and
It has a first surface and a second surface opposite to the first surface, and diffracts the image light of the object image incident on the first surface and emits it from the first surface. A plurality of display units having a diffractive optical element for displaying a virtual image of the object image so as to overlap the background are provided on the second surface side.
An image display device in which a plurality of diffractive optical elements included in the plurality of display units are respectively arranged so that the second surface faces a predetermined axis and covers at least a part of the periphery of the predetermined axis.
(2) The image display device according to (1).
The diffraction optical element is an image display device having a one-dimensional diffraction grating and arranging the one-dimensional diffraction grating so as to be orthogonal to a surface including the predetermined axis.
(3) The image display device according to (1) or (2).
An image display device in which the plurality of diffractive optical elements are arranged adjacent to each other and include three or more diffractive optical elements surrounding the predetermined axis.
(4) The image display device according to (3).
An image display device in which the three or more diffractive optical elements have a flat plate shape and are arranged so that the first surface and the predetermined axis are parallel to each other to form a prismatic structure surrounding the predetermined axis.
(5) The image display device according to any one of (1) to (4).
The angle formed by the optical path of the image light with an orthogonal plane orthogonal to the predetermined axis is defined as an elevation angle.
An azimuth is an angle indicating the direction of the optical path of the image light projected on the orthogonal plane.
The plurality of diffractive optical elements are arranged so that the diffraction efficiency of the image light emitted from the first surface at a predetermined elevation angle along a surface including the predetermined axis is equal to or higher than the first value. Image display device.
(6) The image display device according to (5).
The diffractive optical element has a flat plate shape and has a flat plate shape.
The angle formed by the perpendiculars of the first surface of the plurality of diffraction optical elements adjacent to each other is a state in which the azimuth component of the image light emitted from the first surface is orthogonal to the first surface. In the first angle range which is the range of the elevation angle in the exit direction where the diffraction efficiency is equal to or higher than the first value, and in the range of the azimuth angle in the exit direction where the diffraction efficiency is equal to or higher than the first value. An image display device set to be less than or equal to the angle represented by a second angle range.
(7) The image display device according to (5) or (6).
The first value is an image display device that is half the value of the peak value of the diffraction efficiency.
(8) The image display device according to (5) to (7).
The plurality of diffractive optical elements have a radius equal to the distance from the first surface to the virtual image focal point in a direction orthogonal to the predetermined axis, and the first one is formed on an inner circumference circle centered on the predetermined axis. An image display device arranged so that the surfaces are inscribed.
(9) The image display device according to any one of (5) to (8).
The screen diffuses and emits the image light of the object image.
The diffusion angle in the elevation angle direction of the screen is such that the diffraction efficiency becomes equal to or higher than the first value in a state where the azimuth angle component in the incident direction of the image light with respect to the first surface is orthogonal to the first surface. This is the angle represented by the third angle range, which is the range of elevation angles in the incident direction.
The diffusion angle in the azimuth direction of the screen is an angle represented by a fourth angle range which is a range of the azimuth angle in the incident direction in which the diffraction efficiency is equal to or higher than the first value in the third angle range. Image display device.
(10) The image display device according to (9).
The display unit has a projection unit that projects the object image on the screen.
The screen is an image display device that diffuses and emits the image light in an angle range obtained by adding the radiation angle by the projection unit to the third and fourth angle ranges.
(11) The image display device according to any one of (5) to (10).
The diffractive optical element constitutes a cylindrical surface centered on the predetermined axis.
The radius of the cylindrical surface is the angle represented by the range of the azimuth angle in the emission direction in which the azimuth angle of the image light emitted from the first surface is equal to or higher than the first value. An image display device that is set to be less than half.
(11) The image display device according to any one of (1) to (11).
An image display device in which the plurality of diffractive optical elements are arranged with a gap between them.
(13) The image display device according to any one of (1) to (12).
An image display device in which the screen is arranged on the first surface side so as not to block the display of the virtual image, and emits the image light to the first surface.
(14) The image display device according to any one of (1) to (12).
The screen is arranged on the second surface side so as not to block the display of the virtual image, and emits the image light to the second surface.
The display unit is arranged so as to face the first surface, diffracts the image light emitted from the screen and passed through the second surface and the first surface, and is emitted to the first surface. An image display device having another diffractive optical element.
(15) The image display device according to (14).
The diffractive optical element diffracts light incident on the first surface at a predetermined angle.
The other diffractive optical element is an optical element that diffracts the image light and emits it at the predetermined angle with respect to the first surface, or an angle at which the diffraction efficiency of the image light becomes equal to or higher than a second value. An image display device that is one of the optical elements whose range includes the predetermined angle.
(16) The image display device according to any one of (1) to (15).
The diffractive optical element is an image display device including a holographic optical element exposed with interference fringes having a period in one direction.
(17) The image display device according to (16).
The holographic optical element is an image display device in which the slant angle of the interference fringes differs depending on the exposure position.
(18) The image display device according to (16) or (17).
The holographic optical element is an image display device including interference fringes exposed to light having different wavelengths from each other.
(19) The image display device according to any one of (1) to (18).
The diffractive optical element is an image display device having a laminated structure in which a plurality of holographic optical elements having different slant angles of the interference fringes are laminated.
(20) The image display device according to (1).
The plurality of diffractive optical elements are such that interference fringes are exposed by light emitted from a first point arranged on the first surface side and a second point arranged on the second surface side. An image display device that includes a reflective hologram lens.
(21) The image display device according to (20).
One of the first point and the second point is a reference point that emits reference light.
The other of the first point and the second point is an image display device which is an object point that emits object light.
(22) The image display device according to (20) or (21).
The plurality of reflective hologram lenses have a flat plate shape, and are arranged so that the first surface and the predetermined axis are parallel to each other and the second point overlaps the predetermined axis.
(23) The image display device according to (22).
The angle formed by the optical path of the image light with an orthogonal plane orthogonal to the predetermined axis is defined as an elevation angle.
The plurality of reflective hologram lenses are image display devices in which the length and elevation angle of a line segment connecting the second point and the center of the lens are set to be equal to each other.
(24) The image display device according to any one of (20) to (23).
The display unit is an image display device having a projection unit that projects the object image on the screen along the same direction as the optical axis of the light emitted from the first point.
(25) The image display device according to any one of (20) to (24).
The plurality of reflective hologram lenses are an image display device configured as a 1x lens.

O ... Reference axis C ... Lens center 1 ... Image light 2 ... Interference fringes 3 ... Object image 4 ... Virtual image 6, 6b, 6c ... Vertical line 8, Q ... Reference point 9, Q'... Object points 10, 10a to 10f, 60 , 310 ... Display units 11a, 11b ... Inscribed circles 15 ... Projectors 20, 61, 320 ... Screens 21, 62, 321 ... Object image planes 30, 30a to 30c, 50 ... Reflective holograms 31, 81, 331 ... First Surfaces 32, 82, 332 ... Second surface 71 ... First reflective hologram 72 ... Second reflective hologram 100, 300 ... Image display device 330 ... Reflective hologram lens

Claims (25)

Each one
The screen that forms the object image and
It has a first surface and a second surface opposite to the first surface, and diffracts the image light of the object image incident on the first surface and emits it from the first surface. A plurality of display units having a diffractive optical element for displaying a virtual image of the object image so as to overlap the background are provided on the second surface side.
An image display device in which a plurality of diffractive optical elements included in the plurality of display units are respectively arranged so that the second surface faces a predetermined axis and covers at least a part of the periphery of the predetermined axis. The image display device according to claim 1.
The diffraction optical element is an image display device having a one-dimensional diffraction grating and arranging the one-dimensional diffraction grating so as to be orthogonal to a surface including the predetermined axis. The image display device according to claim 1.
An image display device in which the plurality of diffractive optical elements are arranged adjacent to each other and include three or more diffractive optical elements surrounding the predetermined axis. The image display device according to claim 3.
An image display device in which the three or more diffractive optical elements have a flat plate shape and are arranged so that the first surface and the predetermined axis are parallel to each other to form a prismatic structure surrounding the predetermined axis. The image display device according to claim 1.
The angle formed by the optical path of the image light with an orthogonal plane orthogonal to the predetermined axis is defined as an elevation angle.
An azimuth is an angle indicating the direction of the optical path of the image light projected on the orthogonal plane.
The plurality of diffractive optical elements are arranged so that the diffraction efficiency of the image light emitted from the first surface at a predetermined elevation angle along a surface including the predetermined axis is equal to or higher than the first value. Image display device. The image display device according to claim 5.
The diffractive optical element has a flat plate shape and has a flat plate shape.
The angle formed by the perpendiculars of the first surface of the plurality of diffraction optical elements adjacent to each other is a state in which the azimuth component of the image light emitted from the first surface is orthogonal to the first surface. In the first angle range which is the range of the elevation angle in the exit direction where the diffraction efficiency is equal to or higher than the first value, and in the range of the azimuth angle in the exit direction where the diffraction efficiency is equal to or higher than the first value. An image display device set to be less than or equal to the angle represented by a second angle range. The image display device according to claim 5.
The first value is an image display device that is half the value of the peak value of the diffraction efficiency. The image display device according to claim 5.
The plurality of diffractive optical elements have a radius equal to the distance from the first surface to the virtual image focal point in a direction orthogonal to the predetermined axis, and the first one is formed on an inner circumference circle centered on the predetermined axis. An image display device arranged so that the surfaces are inscribed. The image display device according to claim 5.
The screen diffuses and emits the image light of the object image.
The diffusion angle in the elevation angle direction of the screen is such that the diffraction efficiency becomes equal to or higher than the first value in a state where the azimuth angle component in the incident direction of the image light with respect to the first surface is orthogonal to the first surface. This is the angle represented by the third angle range, which is the range of elevation angles in the incident direction.
The diffusion angle in the azimuth direction of the screen is an angle represented by a fourth angle range which is a range of the azimuth angle in the incident direction in which the diffraction efficiency is equal to or higher than the first value in the third angle range. Image display device. The image display device according to claim 9.
The display unit has a projection unit that projects the object image on the screen.
The screen is an image display device that diffuses and emits the image light in an angle range obtained by adding the radiation angle by the projection unit to the third and fourth angle ranges. The image display device according to claim 5.
The diffractive optical element constitutes a cylindrical surface centered on the predetermined axis.
The radius of the cylindrical surface is the angle represented by the range of the azimuth angle in the emission direction in which the azimuth angle of the image light emitted from the first surface is equal to or higher than the first value. An image display device that is set to be less than half. The image display device according to claim 1.
An image display device in which the plurality of diffractive optical elements are arranged with a gap between them. The image display device according to claim 1.
An image display device in which the screen is arranged on the first surface side so as not to block the display of the virtual image, and emits the image light to the first surface. The image display device according to claim 1.
The screen is arranged on the second surface side so as not to block the display of the virtual image, and emits the image light to the second surface.
The display unit is arranged so as to face the first surface, diffracts the image light emitted from the screen and passed through the second surface and the first surface, and is emitted to the first surface. An image display device having another diffractive optical element. The image display device according to claim 14.
The diffractive optical element diffracts light incident on the first surface at a predetermined angle.
The other diffractive optical element is an optical element that diffracts the image light and emits it at the predetermined angle with respect to the first surface, or an angle at which the diffraction efficiency of the image light becomes equal to or higher than a second value. An image display device that is one of the optical elements whose range includes the predetermined angle. The image display device according to claim 1.
The diffractive optical element is an image display device including a holographic optical element exposed with interference fringes having a period in one direction. The image display device according to claim 16.
The holographic optical element is an image display device in which the slant angle of the interference fringes differs depending on the exposure position. The image display device according to claim 16.
The holographic optical element is an image display device including interference fringes exposed to light having different wavelengths from each other. The image display device according to claim 1.
The diffractive optical element is an image display device having a laminated structure in which a plurality of holographic optical elements having different slant angles of the interference fringes are laminated. The image display device according to claim 1.
The plurality of diffractive optical elements are such that interference fringes are exposed by light emitted from a first point arranged on the first surface side and a second point arranged on the second surface side. An image display device that includes a reflective hologram lens. The image display device according to claim 20.
One of the first point and the second point is a reference point that emits reference light.
The other of the first point and the second point is an image display device which is an object point that emits object light. The image display device according to claim 20.
The plurality of reflective hologram lenses have a flat plate shape, and are arranged so that the first surface and the predetermined axis are parallel to each other and the second point overlaps the predetermined axis. The image display device according to claim 22.
The angle formed by the optical path of the image light with an orthogonal plane orthogonal to the predetermined axis is defined as an elevation angle.
The plurality of reflective hologram lenses are image display devices in which the length and elevation angle of a line segment connecting the second point and the center of the lens are set to be equal to each other. The image display device according to claim 20.
The display unit is an image display device having a projection unit that projects the object image on the screen along the same direction as the optical axis of the light emitted from the first point. The image display device according to claim 20.
The plurality of reflective hologram lenses are an image display device configured as a 1x lens.

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