Image display device

An image display device includes an image light generation device configured to generate image light, and a deflection member configured to deflect the image light to form an exit pupil, in which the image light generation device includes a first light source unit configured to emit first light, a second light source unit configured to emit second light within a same frequency band as the first light and having a wavelength band different from a wavelength band of the first light, and a combining optical member configured to at least partially superimpose the first light and the second light, the deflection member includes a first diffraction member corresponding to the wavelength band of the first light and a second diffraction member corresponding to the wavelength band of the second light, and the first diffraction member and the second diffraction member overlap when viewed from the exit pupil.

The present application is based on, and claims priority from JP Application Serial Number 2019-216448, filed Nov. 29, 2019, the disclosure of which is hereby incorporated by reference herein in its entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to an image display device.

2. Related Art

In recent years, image display devices of a head-mounted type such as a head-mounted display have attracted attention. Such a head-mounted display is designed to form an exit pupil that rays of image light intersect at a pupil position of an observer. In consideration of a change in the pupil position due to eyeball movement when the observer views an image, it is desired for a size of the exit pupil to be expanded to prevent the viewed image from causing missing portions or defects. In JP 2016-517036 T (Translation of PCT Application), a technology for expanding the size of the exit pupil is disclosed, in which a MEMS mirror is caused to scan light rays emitted from a plurality of light sources with different wavelengths, while collimating the light rays, with shifting timings for each of the light sources to generate pupils at a plurality of positions.

Unfortunately, in the technology of JP 2016-517036 T, an image light generation device grows in size because 21 pieces of the laser light sources are required per one eye when providing seven pieces of the exit pupils, for example. In addition, it is necessary to compensate for a distortion and the like of the image light because an incident angle of the image light varies depending on positions of the exit pupils, and, a processing using a large-scale CPU is required when providing the plurality of pupils as described above. When providing a space for installing the large-scale CPU, there is a risk that the device configuration may further grow in size.

SUMMARY

In order to resolve the above-described issue, a first aspect of the present disclosure provides an image display device including an image light generation device configured to generate image light, and a deflection member of a reflective-type configured to deflect the image light emitted from the image light generation device to form an exit pupil, in which the image light generation device includes a first light source unit configured to emit first light, a second light source unit configured to emit second light that is within a same frequency band as the first light and has a wavelength band different from a wavelength band of the first light, and a combining optical member configured to at least partially superimpose the first light and the second light, in which the deflection member includes a first diffraction member including a first diffraction element corresponding to the wavelength band of the first light and a second diffraction member including a second diffraction element corresponding to the wavelength band of the second light, and in which the first diffraction member and the second diffraction member overlap when viewed from the exit pupil.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

First Embodiment

Embodiments of the present disclosure will be described below with reference to the accompanying drawings. Note that, in each of the drawings below, to make each of layers and each of members a recognizable size, each of the layers and each of the members are illustrated to be different from an actual scale and an actual angle.

FIG. 1is an external view illustrating an aspect of an external appearance of an image display device100of the first embodiment.FIG. 2is an explanatory diagram illustrating an aspect of an optical system10of the image display device100illustrated inFIG. 1. Note that, as necessary in the drawings used in the following description, a front and rear direction of an observer wearing the image display device is designated as a direction along a Z axis, the front of the observer wearing the image display device is designated as a front side Z1 as one side in the front and rear direction, and the rear of the observer wearing the image display device is designated as a rear side Z2 as the other side in the front and rear direction. In addition, a left-right direction with respect to the observer wearing the image display device is designated as a direction along an X axis, one side in the left-right direction corresponding to the right direction of the observer wearing the image display device is designated as a right side X1, and the other side in the left-right direction corresponding to the left direction of the observer wearing the image display device is designated as a left side X2. Further, an up and down direction with respect to the observer wearing the image display device is designated as a direction along a Y axis, one side in the up and down direction corresponding to the up direction of the observer wearing the image display device is designated as an up side Y1, and the other side in the up and down direction corresponding to the down direction of the observer wearing the image display device is designated as a down side Y2.

The image display device100illustrated inFIG. 1serves as an image display device of a head-mounted type. The image display device100includes an optical system for right eye10athat allows image light L0ato enter a right eye Ea and an optical system for left eye10bthat allows image light L0bto enter a left eye Eb. The image display device100is formed in a glasses-like shape, for example. Specifically, the image display device100further includes a chassis90for holding both the optical system for right eye10aand the optical system for left eye10b. The image display device100is mounted onto the head of the observer by the chassis90.

The image display device100includes, as the chassis90, a frame91, a temple92aprovided at the right side of the frame91and hooked on the right ear of the observer, and a temple92bprovided at the left side of the frame91and hooked on the left ear of the observer. The frame91includes storage spaces91son both sides of the frame91, where the storage spaces91sstore components such as an image light projection device that constitute the optical system10described later. The temples92aand92bare coupled to the frame91by hinges95in a foldable manner.

Next, a basic configuration of the optical system10of the image display device100will be described. The optical system for right eye10ahas the same basic configuration as the optical system for left eye10b. Thus, the optical system for right eye10aand the optical system for left eye10bwill be simply described as the optical system10when no particular distinction is made in the description below.

FIG. 2is a diagram illustrating a schematic configuration of the optical system10. Note thatFIG. 2illustrates the optical system for right eye10aas an example.

As illustrated inFIG. 2, the optical system10of the first embodiment includes an image light generation device11and a deflection member20. The image light generation device11includes a prism unit (a combining optical member)12, a first display panel (a first light source unit)13, a second display panel (a second light source unit)14, and a projection optical system15.

The prism unit12includes a optical combining film12bbetween a pair of triangular prisms12a. The prism unit12, which has a substantially square or substantially rectangular planar shape, has a first side face12a1and a second side face12a2that are orthogonal to each other. The prism unit12has a light emission surface12cfacing opposite to the second side face12a2. The optical combining film12bis constituted by a dichroic film, for example. The prism unit12combines first light G1emitted from the first display panel13and the second light G2emitted from the second display panel14to generate image light G.

The first display panel13is provided facing the first side face12a1of the prism unit12. The second display panel14is provided facing the second side face12a2of the prism unit12. The first display panel13and the second display panel14are constituted, for example, by a self-luminous panel such as an organic electroluminescence display element, or a liquid crystal panel formed by combining a backlight with a liquid crystal display element. Note that a laser backlight using a MEMS or the like may also be used as the backlight. The first display panel13and the second display panel14have a plurality of pixels.

The first display panel13is configured to emit the first light G1from each of the pixels corresponding to image angles of the image light G. The second display panel14is configured to emit the second light G2from each of the pixels corresponding to the image angles of the image light G.

The optical combining film12bof the prism unit12has characteristics of reflecting the first light G1and transmitting the second light G2.

Note that inFIG. 2, for making the drawings easily viewable, as the first light G1emitted from the first display panel13and the second light G2emitted from the second display panel14, a light ray corresponding to a single image angle, for example, the center image angle of the image light G are illustrated.

The first light G1is light containing red light LR1, green light LG1, and blue light LB1. The red light LR1is light having a wavelength band ranging from 580 nm to 700 nm, the green light LG1is light having a wavelength band ranging from 495 nm to 580 nm, and the blue light LB1is light having a wavelength band ranging from 400 nm to 500 nm.

The first light G1of the first embodiment is light containing the red light LR1having a peak wavelength of 630 nm, the green light LG1having a peak wavelength of 520 nm, and the blue light LB1having a peak wavelength of 440 nm, for example. Note that the half widths of the red light LR1, the green light LG1, and the blue light LB1are all 10 nm. In the first embodiment, the first light G1emitted from the first display panel13is reflected by the optical combining film12bof the prism unit12.

The second light G2is light containing red light LR2, green light LG2, and blue light LB2. The red light LR2is light having a wavelength band ranging from 580 nm to 700 nm, the green light LG2is light having a wavelength band ranging from 495 nm to 580 nm, and the blue light LB2is light having a wavelength band ranging from 400 nm to 500 nm.

The second light G2is light within a same frequency band as the first light G1and having a wavelength band different from the wavelength band of the first light G1. That is, the red light LR2, the green light LG2, and the blue light LB2of the second light G2have peak wavelengths different from the red light LR1, the green light LG1, and the blue light LB1of the first light G1, respectively.

Specifically, the second light G2of the first embodiment is light containing the red light LR2having a peak wavelength of 670 nm, the green light LG2having a peak wavelength of 560 nm, and the blue light LB2having a peak wavelength of 480 nm, for example. Note that the half widths of the red light LR2, the green light LG2, and the blue light LB2are all 10 nm. In the first embodiment, the second light G2emitted from the second display panel14is transmissive of the optical combining film12bof the prism unit12.

The first light G1emitted from the first display panel13is reflected by the optical combining film12bof the prism unit12, to then travel toward the light emission surface12c. The second light G2emitted from the second display panel14is transmitted through the optical combining film12bof the prism unit12, to then travel toward the light emission surface12c. Note that polarized light may be used for combining the first light G1and the second light G2at the optical combining film12b. In this case, the first light G1may be caused to enter, as S-polarized light, the optical combining film12bconstituted as a polarizing beam splitter, and the second light G2may be caused to enter, as P-polarized light, the optical combining film12b.

As illustrated inFIG. 2, the prism unit12is configured to at least partially superimpose the first light G1and the second light G2that have passed through the optical combining film12bto generate the image light G. The prism unit12is configured to emit the image light G from the light emission surface12ctoward the projection optical system15.

The projection optical system15is constituted by combining a plurality of free curved lenses or rotationally symmetric lenses. The projection optical system15is configured to emit the image light G toward the deflection member20.

As such, the image light generation device11of the first embodiment is configured to emit the image light G generated by combining the first light G1and the second light G2that are emitted from the first display panel13and the second display panel14toward the deflection member20. The image light G is incident on the deflection member20in an oblique direction.

The deflection member20is configured to deflect the image light G emitted from the image light generation device11to form an exit pupil H near an eye E of the observer. Specifically, the deflection member20has a structure of layering reflective diffraction elements. In the first embodiment, the deflection member20has a structure of layering two reflective diffraction elements. Note that inFIG. 2, the deflection member20is configured in a plate shape, and may also have a concave curved shape concaved away from the eye E. The deflection member20, by employing the concave curved shape, can have a positive power for converging the image light G toward the eye E of the observer.

The deflection member20includes an internal surface side diffraction member (a second diffraction member)21disposed on a side of a light incidence surface on which the image light G is incident, an external surface side diffraction member (a first diffraction member)22layered on a back surface side opposite to the light incidence surface of the internal surface side diffraction member21, and a light transmissive member23that covers the internal surface side diffraction member21. That is, the internal surface side diffraction member21overlaps, when viewing the front side Z1 from the exit pupil H, with the external surface side diffraction member22. AlthoughFIG. 2illustrates a case where the internal surface side diffraction member21is the same in size as the external surface side diffraction member22, and the internal surface side diffraction member21may be different in size from the external surface side diffraction member22. For example, the external surface side diffraction member22may be greater in size than the internal surface side diffraction member21.

In the first embodiment, the internal surface side diffraction member21and the external surface side diffraction member22are constituted by a reflective volume hologram. The light transmissive member23has light transmissivity of transmitting external light.

The internal surface side diffraction member21includes a base material21aand a diffraction portion21b. Similarly, the external surface side diffraction member22includes a base material22aand a diffraction portion22b. The base material21a, the base material22a, and the light transmissive member23are composed, for example, of plastic (for example, PMMA, polycarbonate resin, acrylic resin, amorphous polypropylene resin, styrene resin containing AS resin, or the like), or glass (for example, quartz, BK7, or the like). Note that the internal surface side diffraction member21and the external surface side diffraction member22may be formed into a concave curved surface concaved away from the eye E. This allows the image light G to be efficiently converged toward the eye E of the observer.

The diffraction portion (a second diffraction element)21band the diffraction portion (a first diffraction element)22bare formed, for example, of a photopolymer material, and interference fringes are formed from the interior portion to the surface. In the first embodiment, the diffraction portion21bof the internal surface side diffraction member21have a wavelength different from the diffraction portion22bof the external surface side diffraction member22.

Specifically, the diffraction portion21bof the internal surface side diffraction member21has second interference fringes121formed at a pitch corresponding to a wavelength band of the second light G2emitted from the second display panel14.

The second interference fringes121are formed by superimposing interference fringes121R,121G, and121B that are formed at a pitch corresponding to the red light LR2, the green light LG2, and the blue light LB2that are contained in the second light G2. For example, the interference fringes121R are formed at a pitch corresponding to light of 670 nm, which is the peak wavelength of the red light LR2. The interference fringes121G are formed at a pitch corresponding to light of 560 nm, which is the peak wavelength of the green light LG2. The interference fringes121B are formed at a pitch corresponding to light of 480 nm, which is the peak wavelength of the blue light LB2. The second interference fringes121can be formed, in a state of forming a holographic photosensitive layer having sensitivity corresponding to the respective wavelengths of the red light LR2, the green light LG2, and the blue light LB2, by performing interference exposure on the holographic photosensitive layer by using reference light and object light that correspond to the respective wavelengths.

According to the internal surface side diffraction member21of the first embodiment, the red light LR2, the green light LG2, and the blue light LB2that are contained in the second light G2can be deflected to enter the eye E of the observer. In addition, the internal surface side diffraction member21of the first embodiment is configured to transmit light having a wavelength band different from a wavelength of the second light G2in the external light.

Further, the diffraction portion22bof the external surface side diffraction member22has first interference fringes122formed at a pitch corresponding to a wavelength band of the first light G1emitted from the first display panel13.

The first interference fringes122are formed by superimposing interference fringes122R,122G, and122B that are formed at a pitch corresponding to the red light LR1, the green light LG1, and the blue light LB1that are contained in the first light G1. For example, the interference fringes122R are formed at a pitch corresponding to light of 630 nm, which is the peak wavelength of the red light LR1. The interference fringes122G are formed at a pitch corresponding to light of 520 nm, which is the peak wavelength of the green light LG1. The interference fringes122B are formed at a pitch corresponding to light of 440 nm, which is the peak wavelength of the blue light LB1. The first interference fringes122can be formed, in a state of forming a holographic photosensitive layer having sensitivity corresponding to the respective wavelengths of the red light LR2, the green light LG2, and the blue light LB2, by performing interference exposure on the holographic photosensitive layer by using reference light and object light that correspond to the respective wavelengths.

According to the external surface side diffraction member22of the first embodiment, the red light LR1, the green light LG1, and the blue light LB1that are contained in the first light G1can be deflected to enter the eye E of the observer. The external surface side diffraction member22of the first embodiment is also configured to transmit light having a wavelength band different from the wavelength band of the first light G1in the external light.

Accordingly, the internal surface side diffraction member21and the external surface side diffraction member22cause the image light G to be efficiently converged into the eye E of the observer, and have see-through properties of transmitting the external light.

Thus, the deflection member20of the first embodiment can cause the observer to recognize an image formed by superimposing the image light G on the external light (background) formed at the image light generation device11.

Next, functions and advantageous effects of the deflection member20will be described.

As illustrated inFIG. 2, when the image light G is incident on the deflection member20, the image light G is refracted by the light transmissive member23to enter the internal surface side diffraction member21. As described above, the diffraction portion21bof the internal surface side diffraction member21has the second interference fringes121corresponding to the wavelength bands of the red light LR2, the green light LG2, and the blue light LB2that are contained in the second light G2. Accordingly, the second light G2included in the image light G is diffracted by the diffraction portion21bof the internal surface side diffraction member21to be emitted toward the eye E of the observer. On the other hand, the first light G1contained in the image light G is not diffracted by the diffraction portion21b, thus the first light G1is transmitted through the internal surface side diffraction member21.

In the deflection member20of the first embodiment, the external surface side diffraction member22overlaps, when viewing the front side Z1 from the exit pupil H, with the internal surface side diffraction member21. Accordingly, the first light G1transmitted through the internal surface side diffraction member21is incident on the external surface side diffraction member22.

Specifically, the first light G1is transmitted through the base material21aof the internal surface side diffraction member21to reach the external surface side diffraction member22. As described above, the diffraction portion22bof the external surface side diffraction member22has first interference fringes122corresponding to the wavelength bands of the red light LR1, the green light LG1, and the blue light LB1that are contained in the first light G1. Accordingly, the first light G1is diffracted by the diffraction portion22bof the external surface side diffraction member22to be emitted toward the eye E of the observer. The first light G1diffracted by the diffraction portion22bis transmitted through the internal surface side diffraction member21. In the first embodiment, the second interference fringes121of the diffraction portion21bof the internal surface side diffraction member21correspond to the wavelength band of the second light G2, and thus the second interference fringes121does not act on the first light G1having a different wavelength band. This suppresses the occurrence of a ghost caused by the diffraction when the first light G1is transmitted through the internal surface side diffraction member21.

In the deflection member20of the first embodiment, diffraction positions at which the first light G1and the second light G2that are contained in the image light G are diffracted differ from each other. That is, the first light G1travels, inside the base material21a, obliquely with respect to a thickness direction of the base material21ato be diffracted at the front side Z1 of the second light G2. Accordingly, the diffraction position at which the first light G1is diffracted is displaced to the left side X2 by an optical path length that the first light G1is transmitted through the base material21awith respect to the diffraction position at which the second light G2is diffracted.

According to the deflection member20of the first embodiment, the second light G2diffracted by the internal surface side diffraction member21and the first light G1diffracted by the external surface side diffraction member22are separated in the left-right direction, and the first light G1and the second light G2are emitted toward the eye E in a state of being parallel to each other, to thus form the exit pupil H of the image light G. The first light G1and the second light G2are separated in the left-right direction, thus the image light G having been deflected by the deflection member20comes into a state where a luminous flux width of the image light G, that is, a size of the exit pupil H formed by the image light G is expanded.

Note that inFIG. 2, only the light ray corresponding to the center image angle of the image light G are illustrated as the first light G1and the second light G2, and the same relationship as this holds true for light rays corresponding to other image angles of the image light G. That is, according to the optical system10of the first embodiment, the exit pupil H can be expanded in width at the entire image angle of the image light G.

The optical system10of the first embodiment, when causing the image light G emitted from the image light generation device11to travel along a horizontal plane (an XZ plane) to be guided to the eye E of the observer, can expand the size of the exit pupil H in the left-right direction.

As described above, according to the optical system10of the first embodiment, the diffraction positions at which the first light G1and the second light G2are diffracted, which correspond to a single image angle of the image light G are caused to differ in a thickness direction of the deflection member20, to thus expand the width of the exit pupil H of the image light G.

The image light generation device11of the first embodiment, which is constituted by the first display panel13, the second display panel14, the prism unit12, and the projection optical system15, helps suppress the device configuration from growing in size in the optical system10, compared to when forming a plurality of the exit pupils using a large number of laser light sources.

According to the optical system10of the first embodiment, a spacing between the first light G1and the second light G2is widened to expand the exit pupil H, thus preventing the occurrence of a distortion of the image light, unlike when forming the plurality of the exit pupils using the large number of laser light sources. Accordingly, the optical system10of the first embodiment can avoid the need for performing a complicated processing such as a correction of the distortion of the image light G. Thus, in the optical system10of the first embodiment, an installing of a large-scale CPU to perform processing of the image light generation device11does not cause the device configuration to grow in size.

Consequently, according to the image display device100of the first embodiment, the exit pupil H can be expanded in size while suppressing the device configuration from growing in size.

Second Embodiment

Next, an optical system according to the second embodiment will be described. Note that components common to the first embodiment will be given identical reference signs and detailed description of these will be omitted.

FIG. 3is a diagram illustrating a configuration of an optical system according to the second embodiment. As illustrated inFIG. 3, an optical system210of the second embodiment includes an image light generation device11A and the deflection member20. The image light generation device11A includes a prism unit112, the first display panel13, the second display panel14, the projection optical system15, and a detector16.

The prism unit112includes four triangular prisms12aand the optical combining film12band a dichroic mirror12dthat are provided in a manner crossing between the triangular prisms12awhen viewed in plan view. The prism unit112, which has a substantially square planar shape, has the first side face12a1and the second side face12a2that are orthogonal to each other, a third side face12a3orthogonal to the second side face12a2, and the light emission surface12cfacing opposite to the second side face12a2. The dichroic mirror12dhas characteristics of transmitting both the first light G1and the second light G2and reflecting detection light described later.

The prism unit112is configured to combine the first light G1emitted from the first display panel13and the second light G2emitted from the second display panel14to generate the image light G.

The detector16is provided facing the third side face12a3of the prism unit112. The detector16serves as a sensor configured to detect light emitted from the eye E of the observer disposed near the exit pupil H.

The detector16is configured to emit light toward the eye E of the observer and to detect the light reflected by the eye E. That is, the detector16is configured to detect the light emitted from the exit pupil H. For example, the detection light emitted from the detector16to enter the eye E of the observer is reflected by a corneal surface E1of the eye E. Reflected detection light R reflected by the corneal surface E1travels through an optical path opposite to the image light G, to reach the prism unit112. The reflected detection light R being incident on the prism unit112is reflected by the dichroic mirror12dand enters the detector16. The detector16is configured to detect a position of the eye E of the observer based on a detection result of the reflected detection light R. For example, the detector16is configured to move a position of the projection optical system15based on the detection result to change a traveling direction in which the image light G travels, thus allowing the image light G to efficiently enter the eye E of the observer.

The detector16may also be configured to detect the reflected detection light R reflected by a retina E2of the eye E of the observer.

In the optical system210of the second embodiment, an optical path length of the reflected detection light R emitted from the exit pupil H (the eye E of the observer) and entering the detector16is equal to optical path lengths of the first light G1and the second light G2that are emitted from the first display panel13and the second display panel14and enter the eye E of the observer.

Accordingly, an image of the reflected detection light R that forms an image on the detector16is the same as images of the first light G1or the second light G2, which forms an image on the retina E2. Thus, the detector16can detect the reflected detection light R to detect an image forming state of the first light G1or the second light G2on the retina E2. The detector16can detect a degree of blur of the image light G, and thus, for example, the detector16, by moving the position of the projection optical system15, can adjust the image to be clearly viewed to the observer.

Note that in the above description, an example is given of a case where the reflected detection light R of the detection light emitted from the detector16is used, and the image light G (the first light G1and the second light G2) reflected by the eye E of the observer may also be used as the detection light.

According to the optical system210of the second embodiment, the detector16can detect the position of the eye E of the observer and the degree of blur on the retina E2, thus allowing the image light G having higher quality to be viewed by the observer.

Third Embodiment

Next, an optical system according to the third embodiment will be described. Note that components common to the first embodiment will be given identical reference signs and detailed description of these will be omitted.

FIG. 4is a diagram illustrating a configuration of an optical system according to the third embodiment. As illustrated inFIG. 4, an optical system310of the third embodiment includes an image light generation device11B and the deflection member20. The image light generation device11B includes the prism unit12, a first light source unit113, a second light source unit114, a MEMS mirror17, and the projection optical system15.

The first light source unit113is provided facing the first side face12a1of the prism unit12. The second light source unit114is provided facing the second side face12a2of the prism unit12. In the third embodiment, the first light source unit113and the second light source unit114are constituted by a laser light source configured to emit laser light of RGB colors. That is, the third embodiment is different from the first embodiment in that the first light G1and the second light G2emitted from the first light source unit113and the second light source unit114serve as laser light. Note that inFIG. 4, as the first light G1emitted from the first light source unit113and the second light G2emitted from the second light source unit114, the light ray corresponding to a single image angle, for example, the center image angle of the image light G is illustrated.

The prism unit12is configured to combine the first light G1emitted from the first light source unit113and the second light G2emitted from the second light source unit114.

The MEMS mirror17is constituted by a micromirror. The MEMS mirror17is configured to rotate about a predetermined rotation axis to control a reflection direction of the combined light of the first light G1and the second light G2that are emitted from the prism unit12. The image light generation device11B of the third embodiment is configured to cause the MEMS mirror to scan the combined light of the first light G1and the second light G2to generate the image light G corresponding to the image angles.

According to the optical system310of the third embodiment, even with a structure of combining the first light source unit113and the second light source unit114that are composed of a laser light source, with the MEMS mirror17, the exit pupil can be expanded in size while suppressing the device from growing in size.

Fourth Embodiment

Next, an optical system according to the fourth embodiment will be described. The optical system of the fourth embodiment has a configuration of combining the second embodiment with the third embodiment. Note that components common to the above-described embodiments will be given identical reference signs and detailed description of these will be omitted.

FIG. 5is a diagram illustrating a configuration of an optical system according to the fourth embodiment. As illustrated inFIG. 5, an optical system410of the fourth embodiment includes an image light generation device11C and the deflection member20. The image light generation device11C includes the prism unit112, the first light source unit113, the second light source unit114, the MEMS mirror17, the projection optical system15, and the detector16.

The first light source unit113is provided facing the first side face12a1of the prism unit112. The second light source unit114is provided facing the second side face12a2of the prism unit112. The detector16is provided facing the third side face12a3of the prism unit112.

According to the optical system410of the fourth embodiment, in the structure of combining the laser light source with the MEMS mirror17to generate the image light G, the detector16is caused to detect the position of the eye E of the observer, that is, a position of the corneal surface E1or the degree of blur on the retina E2, thus allowing the image light G having higher quality to be viewed.

InFIG. 5, the reflected detection light R is transmitted through the center portion of the prism unit112composed of a cross prism, where a gap may occur at the center portion of the cross prism. Accordingly, the reflected detection light R may be caused to pass through a position shifted from the center portion of the prism unit112to enter the detector16.

Note that when using the laser light as the image light G as in the fourth embodiment, the shape of the prism unit112is not limited to the above-described embodiments.

FIG. 6is a diagram illustrating a structure of a prism unit112A according to a modified example. As illustrated inFIG. 6, the prism unit112A may be configured by bonding a first prism115and a second prism116together. The first prism115has a structure provided with a dichroic mirror12ebetween the pair of triangular prisms12a. The dichroic mirror12ehas characteristics of reflecting the first light G1and transmitting the second light G2. The second prism116has a structure provided with a half mirror12fbetween the pair of triangular prisms12a.

The prism unit112A having the structure according to the modified example is configured by bonding two prisms having a simple shape together, compared to the cross prism that constitutes the above-described prism unit112. This improves the assembly accuracy when manufacturing the prism unit, to thus provide the prism unit112A with high accuracy while achieving cost reduction.

Fifth Embodiment

Next, an optical system according to the fifth embodiment will be described. Note that components common to the first embodiment will be given identical reference signs and detailed description of these will be omitted.

FIG. 7is a diagram illustrating a configuration of an optical system according to the fifth embodiment. As illustrated inFIG. 7, an optical system510of the fifth embodiment includes an image light generation device11D, a light-guiding portion18, and the deflection member20. The image light generation device11D includes the prism unit12, the first display panel13, and the second display panel14. That is, the image light generation device11D of the fifth embodiment includes the light-guiding portion18in place of the projection optical system15.

In the fifth embodiment, the image light G emitted from the image light generation device11D is incident on the light-guiding portion18. The light-guiding portion18includes a light-guiding body24, a light incidence portion25, and a light emission portion26. The light-guiding body24includes a parallel light-guiding plate40of a plate-like shape extending in the left-right direction of the observer. The parallel light-guiding plate40includes a pair of a first surface40aand a second surface40bthat are parallel to each other. The first surface40aand the second surface40bare configured to function as a totally reflecting surface for totally reflecting the image light G propagating inside, and to guide the image light G to the light emission portion26with less loss.

The light incidence portion25is for capturing the image light G into the inside of the light-guiding body24, and the light emission portion26is for extracting the image light G traveling inside the light-guiding body24to the outside. The light incidence portion25is constituted by a diffractive optical element25aof a plate-like shape affixed to one end side of the second surface40bof the parallel light-guiding plate40. The diffractive optical element25ais constituted by the reflective volume hologram. Note that the diffractive optical element25amay be constituted by a surface relief diffractive element, for example, a blazed diffraction grating.

The deflection member20is provided at the light emission portion26. In the fifth embodiment, the deflection member20is provided directly at the second surface40bof the parallel light-guiding plate40, and thus the light transmissive member23is omitted.

The optical system510of the fifth embodiment can cause the deflection member20to correct a color deviation caused by a difference in diffraction angle occurring depending on the wavelength at the diffractive optical element25aprovided at the light incidence portion25. Note that the diffractive optical element25amay be omitted as necessary.

The image light G propagating inside the light-guiding body24propagates along the lengthwise direction of the deflection member20by total internal reflection of the light-guiding body24. In addition, zero-order light is transmitted through, at a plurality of locations, the internal surface side diffraction member21and first-order light is reflected by the external surface side diffraction member22, and thus the image light G is emitted toward the eye E of the observer in a state where the first light G1and the second light G2are separated in the left-right direction.

According to the optical system510of the fifth embodiment, the exit pupil H can be efficiently expanded in size by a synergistic effect of a total reflection inside the light-guiding body24and an expansion of a light ray width of the deflection member20.

The light-guiding body24of the fifth embodiment is constituted by the parallel light-guiding plate40, and the light-guiding body24may also have a curved shape. When the light-guiding body24has the curved shape as such, the effect of widening the light ray width due to a plurality of the total reflections is not achieved unlike the parallel light-guiding plate40. Even when using the light-guiding body24having the curved shape as such, the exit pupil H can be expanded in size by providing the deflection member20at the light emission portion26.

Note that the configuration of the optical system510of the fifth embodiment may be combined with the configuration of the second embodiment. That is, the prism unit12of the image light generation device11D may be replaced by the prism unit112including the detector16illustrated inFIG. 3.

Further, the configuration of the optical system510of the fifth embodiment may be combined with the configuration of the third embodiment. That is, the image light generation device11D may be replaced by the image light generation device11B illustrated inFIG. 4.

Further, the configuration of the optical system510of the fifth embodiment may be combined with the configuration of the fourth embodiment. That is, the image light generation device11D may be replaced by the image light generation device11C illustrated inFIG. 5.

Further, in the configurations of the above-described first to fourth embodiments, the image light G may be caused to enter the deflection member20via the diffractive optical element25a. In this case as well, the deflection member20can correct the color deviation caused by the difference in diffraction angle occurring depending on the wavelength at the diffractive optical element25a.

Note that the present disclosure is not limited to the aspects of the above-described embodiments, and various modifications can be appropriately made to the above-described embodiments within a scope not departing from the gist of the present disclosure. In the above-described embodiments and modified examples, an example is given of a case where the external surface side diffraction member22and the internal surface side diffraction member21that constitute the deflection member20are layered, however, the external surface side diffraction member22and the internal surface side diffraction member21may be disposed in a manner spaced apart from each other. That is, a gap may be provided between the external surface side diffraction member22and the internal surface side diffraction member21.

In addition, in the above-described embodiments and modified examples, an example is given of a case when causing the image light G emitted from the image light generation device to travel along the horizontal plane to be guided to the eye E of the observer, however, the optical system of an aspect of the present disclosure can also be applicable when causing the image light G to travel along the vertical plane to be guided to the eye E of the observer. In this case, the optical system of an aspect of the present disclosure may be expanded in size of the exit pupil H in the up and down direction. Further, the optical system of an aspect of the present disclosure can also be applicable when causing the image light G to travel along a plane intersecting the vertical plane to be guided to the eye E of the observer. In this case, the optical system of an aspect of the present disclosure can be expanded in size of the exit pupil H in an oblique direction intersecting both the up and down direction and the left-right direction.

Application to Other Image Display Device

In the above-described embodiments, the image display device100of a head-mounted type is exemplified, and the present disclosure may also be applied to a head-up display, a handheld display, and the like.