Virtual image display device and optical unit

Abstract

To improve the light utilization efficiency of a virtual image display device.SOLUTION: A virtual image display device comprises: a display panel 11a that emits video light ML; a projection optical system 20 that collimates the video light ML from the display panel 11a; and a light guide member 50 including a light guide plate 51a that guides the video light ML, an input diffraction optical element DI that makes the video light ML incident on the light guide plate 51a, and an output diffraction optical element DO that makes the video light ML emitted from the light guide plate 51a. A diffraction region Dr of the input diffraction optical element DI covers an incident region Lr of the video light ML in the light guide member 50, and is set within a range where the video light ML diffracted by the input diffraction optical element DI is reflected on an opposite surface of the light guide plate 51a and incident on the outside of the input diffraction optical element DI.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a virtual image display device and an optical unit that enable observation of a virtual image.

Background Art

[0002] As a video display device that enables observation of a virtual image, there is one including a video projection module, a video light duplication unit, and a light guide plate having a light input unit and a light output unit (Patent Document 1). In the device of Patent Document 1, in order to display a video with uniform brightness, the video light incident from the video projection module is uniformly duplicated by the video light duplication unit and then incident on the light input unit.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the device of Patent Document 1, since the size of the light input unit becomes large, there is a possibility that the light rays diffracted by the input grating of the light input unit are reflected on the facing side and incident on the input grating again. That is, in the device of Patent Document 1, there is a problem that the light utilization efficiency decreases because the light rays come out of the light guide plate again.

Means for Solving the Problems

[0005] In one aspect of the present invention, a virtual image display device or an optical unit includes a display panel that emits image light, a projection optical system that collimates the image light from the display panel, a light guide plate that guides the image light, an input diffractive optical element that causes the image light to enter the light guide plate, and an output diffractive optical element that causes the image light to exit the light guide plate. The diffractive region of the input diffractive optical element covers the incident region of the image light in the light guide member, and is set within a range where the image light diffracted by the input diffractive optical element is reflected by the opposing surface of the light guide plate and enters the outside of the input diffractive optical element.

Brief Description of the Drawings

[0006]

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Embodiments for Carrying Out the Invention

[0007] 〔First Embodiment〕 Hereinafter, with reference to FIGS. 1 to 3 and the like, a first embodiment of a virtual image display device according to the present invention will be described.

[0008] FIG. 1 is a diagram for explaining the wearing state of a head-mounted display device (hereinafter, also referred to as a head-mounted display or HMD) 200. The HMD 200 causes an observer or wearer US wearing it to recognize an image as a virtual image. In FIG. 1 and the like, X, Y, and Z are a rectangular coordinate system. The +X direction corresponds to the horizontal direction in which both eyes EY of the observer or wearer US wearing the HMD 200 are arranged. The +Y direction corresponds to the upward direction perpendicular to the horizontal direction in which both eyes EY are arranged for the wearer US. The +Z direction corresponds to the forward direction or the front direction for the wearer US. The ±Y directions are parallel to the vertical axis or the vertical direction.

[0009] The HMD200 includes a first virtual image display device 100A for the right eye, a second virtual image display device 100B for the left eye, a pair of temple-shaped support devices 100C that support the virtual image display devices 100A and 100B, and a user terminal 90 that is an information terminal. The first virtual image display device 100A functions as an HMD alone and is composed of a first display driving unit 102a arranged at the upper part and a first light guide optical system 103a in the shape of a spectacle lens that covers in front of the eyes. Similarly, the second virtual image display device 100B functions as an HMD alone and is composed of a second display driving unit 102b arranged at the upper part and a second light guide optical system 103b in the shape of a spectacle lens that covers in front of the eyes. The HMD200 combining the first virtual image display device 100A and the second virtual image display device 100B is also a virtual image display device in a broad sense. The support device 100C is a wearing member that is worn on the head of the wearer US, and supports the upper end sides of the pair of light guide optical systems 103a and 103b through the display driving units 102a and 102b that are integrated in appearance. The combination of the pair of display driving units 102a and 102b is called a driving device 102. The first virtual image display device 100A and the second virtual image display device 100B are optically reversed left and right. For the second virtual image display device 100B, detailed description is omitted.

[0010] FIG. 2 is a side view specifically explaining the first display driving unit 102a and the first light guide optical system 103a of the first virtual image display device 100A. FIG. 3 is a plan view specifically explaining the first display driving unit 102a and the first light guide optical system 103a.

[0011] As shown in FIGS. 2 and 3, the first display driving unit 102a includes an image light generating device 10, a projection optical system 20, and a drive circuit member 88. The image light generating device 10 is an optical engine including a display panel 11a. The projection optical system 20 is a collimator including a plurality of lens elements 21. The image light ML generated by the image light generating device 10 is collimated by the projection optical system 20 and coupled to a first light guiding optical system 103a including a light guiding member 50. Collimation means optically adjusting diffused light to be parallel by an optical element to obtain collimated light, that is, parallel light. The drive circuit member 88 causes the display panel 11a to perform a display operation. In the first virtual image display device 100A, the optical device excluding the drive circuit member 88 is referred to as an optical unit 100. The first virtual image display device 100A guides the image light ML to the eyes EY of the wearer US, allowing the wearer US to visually recognize a virtual image.

[0012] FIG. 4 is a diagram mainly for explaining the optical system of the first display driving unit 102a. In the first display driving unit 102a, the image light generating device 10 includes only one display panel 11a. That is, the display panel 11a includes pixels of three colors, RGB, and in the display panel 11a, the pixels of each color are two-dimensionally arranged. The projection optical system 20 includes a plurality of lens elements 21. The display panel 11a and the projection optical system 20 are fixed in a state of being positioned relative to each other by a lens barrel 30. The lens barrel 30 is supported in a state of being positioned relative to each other by a holder 35 (see FIG. 2) that also serves as a cover, together with the drive circuit member 88, and is adhesively fixed to the first light guiding optical system 103a, specifically, the light guiding member 50.

[0013] The display panel 11a is a display element or a display device that emits image light ML to form an image corresponding to a virtual image. Specifically, the display panel 11a is, for example, a display of various light-emitting element arrays such as an OLED (Organic Light Emitting Diode), a micro OLED, an organic EL (Organic Electro-Luminescence), an inorganic EL, an LED, or a micro LED, and forms a still image or a moving image on a two-dimensional display surface parallel to the XY plane. The display panel 11a has a light-emitting element 14a. The light-emitting element 14a has a large number of pixel elements two-dimensionally arranged along the XY plane on a substrate. When the display panel 11a is an OLED display, each pixel element constituting the light-emitting element 14a includes, in order from the substrate side, a cathode, an electron transport layer, a light-emitting layer, a hole layer, and a transparent electrode layer.

[0014] The display panel 11a is not limited to the self-luminous type video light generation device 10, and may be composed of an LCD or other light modulation elements, and an image may be formed by illuminating the light modulation elements with a light source such as a background. As the display panel 11a, instead of an LCD, an LCOS (Liquid crystal on silicon, LCoS is a registered trademark), a digital micro mirror device (specifically, DLP: registered trademark), a laser beam scan, etc. can also be used.

[0015] The projection optical system 20 includes a first lens 21a and a second lens 21b as lens elements 21 that collimate, that is, parallelize, the incident light. The projection optical system 20 has a function substantially equivalent to that of a single lens 20i, collimates the image light ML emitted from the display surface 11d of the display panel 11a in a state having a predetermined light beam width, and emits it toward the incident diffraction layer 51b.

[0016] The projection optical system 20 may include optical elements such as a reflection mirror in addition to one or more lens elements made of resin or glass. The optical surfaces of the optical elements constituting the projection optical system 20 may be any of a spherical surface, an aspherical surface, and a free-form surface.

[0017] As shown in FIGS. 2 to 4, the first light guide optical system 103a includes a light guide member 50 that enables color display and extends substantially parallel to the XY plane. In the present embodiment, the first light guide optical system 103a has a light guide member 50 and a cover member 60. The light guide member 50 is disposed on the side of the projection optical system 20, and the cover member 60 is disposed on the outside world side. The light guide member 50 and the cover member 60 are fixed with a predetermined interval therebetween. As described above, the light guide member 50 is adhesively fixed to the lens barrel 30.

[0018] The light guide member 50 has a light guide plate 51a, an incident diffraction layer 51b, a pupil expansion grating layer 51e, and an exit diffraction layer 51c.

[0019] The light guide plate 51a is a member formed from a parallel plate and has a first total reflection surface 51i and a second total reflection surface 51o that are a pair of planes extending in the XY plane.

[0020] The incident diffraction layer 51b, the pupil expansion grating layer 51e, and the exit diffraction layer 51c perform diffraction according to the wavelength of the video light ML. The incident diffraction layer 51b, the exit diffraction layer 51c, and the pupil expansion grating layer 51e are formed on the second total reflection surface 51o disposed on the outside world side, that is, the +Z side of the light guide plate 51a. The incident diffraction layer 51b, the exit diffraction layer 51c, and the pupil expansion grating layer 51e are designed to function as reflection type diffraction gratings that partially transmit outside light.

[0021] FIG. 5 is a rear view mainly for explaining the first light guide optical system 103a. The incident diffraction layer 51b is an input diffraction optical element DI, and folds back the video light ML emitted from the display panel 11a of the video light generation device 10 and incident through the lens element 21 of the projection optical system 20 so as to propagate inside the light guide member 50. The video light ML collimated around the optical axis AX (see FIG. 2) perpendicular to the light guide plate 51a is incident on the incident diffraction layer 51b. The incident diffraction layer 51b is formed with a diffraction pattern that linearly extends in the vertical Y direction and periodically repeats in the horizontal X direction.

[0022] The pupil enlargement grating layer 51e is a pupil enlargement diffractive optical element DD, which is provided on the +X side of the incident diffraction layer 51b, guided into the light guide plate 51a, and bends the optical path of the video light ML that travels in the +X direction as a whole so as to travel in the -Y direction as a whole. The pupil enlargement grating layer 51e is configured such that while switching the diffraction direction, the angular information of the video light ML in the left-right X direction and the angular information of the video light ML in the up-down Y direction are not substantially impaired. The pupil enlargement grating layer 51e guides the video light ML guided from the incident diffraction layer 51b into the light guide plate 51a to the exit diffraction layer 51c while enlarging the pupil of the exit diffraction layer 51c. More specifically, the pupil enlargement grating layer 51e is interposed between the incident diffraction layer 51b and the exit diffraction layer 51c, guides the video light ML in a direction (-Y direction) intersecting the diffraction direction (+X direction) of the incident diffraction layer 51b, and splits the light beam, and has a role of expanding the lateral light beam width. The pupil enlargement grating layer 51e is formed of a diffraction pattern that linearly extends in the DS1 direction oblique and parallel to the XY plane and periodically repeats in the DS2 direction perpendicular to the DS1 direction and parallel to the XY plane. The DS1 direction is a direction rotated 45° clockwise with respect to the +Y direction and is an intermediate direction between the -X direction and the +Y direction. The grating period or pitch in the X direction and the Y direction of the pattern formed on the pupil enlargement grating layer 51e coincides with the grating period in the X direction of the pattern formed on the incident diffraction layer 51b and coincides with the grating period in the Y direction of the pattern formed on the exit diffraction layer 51c.

[0023] The emission diffraction layer 51c is an output diffractive optical element that guides the image light ML in the -Y direction while splitting the light rays and has the role of expanding the light ray width in the vertical direction. As a result, the light ray widths of the image light ML incident on the pupil position PP shown in FIG. 2 in the X and Y directions have a spread corresponding to the emission diffraction layer 51c, and the pupil sizes in the vertical and horizontal directions increase through the pupil expansion grating layer 51e, the emission diffraction layer 51c, etc. From the emission diffraction layer 51c, collimated image light ML is emitted around the emission optical axis OX (see FIG. 2) perpendicular to the light guide plate 51a. The image light ML emitted from the emission diffraction layer 51c is about ±25° with respect to the emission optical axis OX. That is, the angular field of view of the first virtual image display device 100A is about 50°. The emission diffraction layer 51c is formed with a diffraction pattern that linearly extends in the horizontal X direction and periodically repeats in the vertical Y direction.

[0024] The incident diffraction layer 51b, the emission diffraction layer 51c, and the pupil expansion grating layer 51e are formed from, for example, surface relief type diffraction elements or diffraction gratings. The surface relief type diffraction grating is formed by nanoimprinting, but is not limited thereto, and can also be formed by etching the surface of the light guide plate 51a, or may be such that a diffraction element or diffraction grating is attached. The material of the diffraction grating is a nanoimprint material when produced by nanoimprinting, and the same material as the light guide plate 51a when produced by etching. The material of the light guide plate 51a is, for example, glass, resin, etc.

[0025] The cover member 60 is disposed on the outer side of the light guide member 50, that is, on the outside with respect to the light guide member 50, extends along the light guide member 50, and covers the entire light guide member 50. The cover member 60 protects the incident diffraction layer 51b, the pupil expansion grating layer 51e, and the emission diffraction layer 51c of the light guide member 50. Since the thickness of the incident diffraction layer 51b, etc. is several tens of μm, an air layer is provided as a space between the light guide member 50 and the cover member 60. The thickness of the cover member 60 is, for example, about 0.4 mm. The cover member 60 is formed of glass or resin.

[0026] Hereinafter, with reference to FIG. 5 and the like, the light guiding of the image light ML using the light guiding member 50 and the formation of a virtual image will be described. The image light ML from the image light generation device 10 enters the incident diffraction layer 51b via the light guide plate 51a, and is diffracted in the angular direction corresponding to the grating period of the pattern formed in the incident diffraction layer 51b, so that it is propagated while being totally reflected in the light guide plate 51a and advances in the +X direction as a whole. The image light ML propagated in the +X direction in the light guide plate 51a is diffracted by the pupil expansion grating layer 51e and bent in the -Y direction as a whole, and is shifted to the position in the +X direction reflecting the number of reflections until it is diffracted by the pupil expansion grating layer 51e. That is, the pupil expansion grating layer 51e has a role of expanding the horizontal pupil size corresponding to the lateral or X-direction light beam width at which the image light ML enters the eye EY. The image light ML propagated in the -Y direction as a whole in the light guide plate 51a after passing through the pupil expansion grating layer 51e is diffracted by the emission diffraction layer 51c and emitted toward the eye EY. The image light ML emitted from the emission diffraction layer 51c is reproduced in the angular state before being emitted from the image light generation device 10 and entering the light guiding member 50 with respect to the X direction and the Y direction, and the pupil size is enlarged with respect to the X direction and the Y direction. That is, the light guiding member 50 enlarges the pupil size in the vertical and horizontal directions while maintaining the image information. Thereby, even if the position of the wearer US is shifted, the wearer US can observe the virtual image by the image light ML.

[0027] FIG. 6 is a partially enlarged rear view of the input diffractive optical element DI (incident diffraction layer 51b). Hereinafter, the relationship between the incident diffraction layer 51b of the light guiding member 50 and the image light ML incident on the incident diffraction layer 51b will be described.

[0028] The input diffractive optical element DI (incident diffraction layer 51b) is an incident light limiting member 70 that limits the image light ML incident on the light guide plate 51a. The limiting region of the incident light is defined by the diffraction region Dr of the incident diffraction layer 51b. That is, the incident diffraction layer 51b has a function as a diaphragm. The diffraction region Dr is a region where a diffraction pattern is formed when the incident diffraction layer 51b is viewed in plan view.

[0029] The diffraction region Dr of the incident diffraction layer 51b covers the incident region Lr of the video light ML in the light guide member 50. Here, the incident region Lr of the video light ML is the effective region where the video light ML is incident from the incident diffraction layer 51b into the light guide plate 51a. Further, the diffraction region Dr is set to a range where the video light ML diffracted by the incident diffraction layer 51b is reflected by the opposing surface of the light guide plate 51a (in this embodiment, the first total reflection surface 51i) and enters the outside of the incident diffraction layer 51b on the surface where the incident diffraction layer 51b is formed (in this embodiment, the second total reflection surface 51o).

[0030] In this embodiment, the exit pupil Lx of the projection optical system 20 is disposed between the light guide plate 51a and the cover member 60, and specifically, at the position of the incident diffraction layer 51b on the light guide plate 51a. Therefore, the incident region Lr of the video light ML in this embodiment has the same size and shape as the exit pupil Lx of the projection optical system 20. The diffraction region Dr of the incident diffraction layer 51b and the incident region Lr of the video light ML are substantially equal. That is, the size and shape of the diffraction region Dr are substantially the same as the size and shape of the incident region Lr. In other words, the size and shape of the incident diffraction layer 51b are substantially the same as the size and shape of the light beam of the video light ML (in this embodiment, the exit pupil Lx) incident on the incident diffraction layer 51b of each light guide plate 51a. The diffraction region Dr and the incident region Lr are circular. Note that the diffraction region Dr and the incident region Lr do not necessarily have exactly the same size. The diffraction region Dr may have a margin with respect to the incident region Lr. In the example of FIG. 6, the diffraction region Dr extends concentrically with respect to the incident region Lr. That is, in the diffraction region Dr, the expansion size Va on the light guide side and the expansion size Vb on the anti-light guide side are substantially equal.

[0031] The size and shape of the incident diffraction layer 51b need only be such that it can absorb all of the light beam of the image light ML incident on the incident diffraction layer 51b. In other words, the incident diffraction layer 51b should be formed to have the smallest size possible without being smaller than the size of the light beam of the image light ML incident on the incident diffraction layer 51b. As a result, the size of the incident diffraction layer 51b is the same as or larger than the ray width of the image light ML incident on the incident diffraction layer 51b. The exit pupil Lx of the projection optical system 20 is set based on the size of the incident diffraction layer 51b.

[0032] FIG. 7 illustrates the size of the diffraction region Dr and the incident region Lr of the incident diffraction layer 51b. A light ray LL diffracted by the incident diffraction layer 51b and incident on the light guide plate 51a is totally reflected within the light guide plate 51a at a propagation angle Wm. For the light ray LL to be totally reflected, the angle must be equal to or greater than the critical angle θm. The size Dw of the incident diffraction layer 51b, i.e., the diffraction region Dr, is defined by the thickness tw of the light guide plate 51a and the critical angle θm. When the refractive index of the light guide plate 51a is nw and the refractive index of air is ni, sinθm = ni / nw is satisfied. Essentially, the larger the incident diffraction layer 51b, the greater the amount of captured image light ML. However, if the incident diffraction layer 51b is too large, the totally reflected light ray LL re-enters the incident diffraction layer 51b. Therefore, the size Di of the incident region Lr (in this embodiment, the size of the exit pupil Lx of the projection optical system 20) is set so that the size Dw of the incident diffraction layer 51b is equal to or smaller than the width W of the folded light beam in the light guiding direction GA. The width W of the folded light beam is expressed by the following equation: W=2×tw×tanθm

[0033] By setting the size Dw of the incident diffraction layer 51b (diffraction region Dr) to match the width W up to the light ray folding back, and by setting the size Di of the incident region Lr to match the size Dw of the incident diffraction layer 51b, it is possible to maximize the amount of image light ML that is incident on the light-guiding member 50 or light-guiding plate 51a.

[0034] The light beam width of the video light ML incident on the incident diffraction layer 51b, that is, the size Di of the incident region Lr (the size of the exit pupil Lx of the projection optical system 20), is set to a desired size by the configuration of the projection optical system 20, a diaphragm (not shown), control for narrowing the viewing angle of the display panel 11a, and the like. In this case, the configuration of the projection optical system 20, the diaphragm, and the viewing angle control of the display panel 11a correspond to the region limiting member 75 that limits the incident region Lr of the video light ML in the incident diffraction layer 51b. Note that the viewing angle may be adjusted with a lens for each pixel of the display panel 11a, or may be adjusted by shifting the light emitting element and a color filter (not shown).

[0035] The range in which the above-described video light ML is incident outside the incident diffraction layer 51b is defined by an outer incident structure OI in which the size Di of the incident region Lr is set so that the size Dw of the diffraction region Dr is equal to or less than the width W up to the light beam folding in the light guiding direction GA. The outer incident structure OI is a combination of the incident light limiting member 70 or the incident light limiting member 70 and the region limiting member 75 (see FIG. 4).

[0036] As described above, when the light guiding member 50 functions as a reflective diffraction grating and the lens barrel 30 and the light guide plate 51a are in contact with each other, the position of the exit pupil Lx of the projection optical system 20 is defined by the thickness tw of the light guide plate 51a from the contact surface between the lens barrel 30 and the light guide plate 51a.

[0037] The position of the exit pupil Lx of the projection optical system 20 is the position where the light beam of the video light ML is most restricted. By aligning the position of the exit pupil Lx and the position of the incident diffraction layer 51b, the size of the incident diffraction layer 51b can be minimized. By minimizing the incident diffraction layer 51b, the incident light rays reflected on the opposite surface side of the light guide plate 51a are less likely to be incident on the input diffractive optical element DI again, so that the light utilization efficiency of the virtual image display device 100A can be improved. Since the improvement in light utilization efficiency is easy to maintain even when the light guide plate 51a is made thinner, the virtual image display device 100A can be made smaller and lighter.

[0038] As described above, the position of the exit pupil Lx of the projection optical system 20 is optimized by the position of the incident diffraction layer 51b on the light guide plate 51a. Further, the size and shape of the incident diffraction layer 51b are optimized by the size and shape of the exit pupil Lx of the projection optical system 20.

[0039] Although not shown, the virtual image display devices 100A and 100B may not be provided with the cover member 60.

[0040] The virtual image display devices 100A and 100B according to the first embodiment include a display panel 11a that emits image light ML, a projection optical system 20 that collimates the image light ML from the display panel 11a, a light guide plate 51a that guides the image light ML, an input diffractive optical element DI that causes the image light ML to enter the light guide plate 51a, and an output diffractive optical element DO that causes the image light ML to exit the light guide plate 51a. The diffraction region Dr of the input diffractive optical element DI covers the incident region Lr of the image light ML in the light guide member 50, and is set to a range in which the image light ML diffracted by the input diffractive optical element DI is reflected by the opposing surface of the light guide plate 51a and enters the outside of the input diffractive optical element DI.

[0041] In the virtual image display devices 100A and 100B, the diffraction region Dr of the input diffractive optical element DI covers the incident region Lr of the image light ML in the light guide member 50, thereby preventing the generation of stray light. Further, since the image light ML reflected by the opposing surface of the input diffractive optical element DI of the light guide plate 51a enters the outside of the input diffractive optical element DI, it is possible to prevent the image light ML from re-entering the input diffractive optical element DI and reducing the light utilization efficiency.

[0042] 〔Second Embodiment〕 Hereinafter, a virtual image display device according to the second embodiment of the present invention will be described. The virtual image display device according to the second embodiment is a partial modification of the virtual image display device according to the first embodiment, and the description of the common parts will be omitted.

[0043] As shown in FIG. 8, in the virtual image display device 100A of the present embodiment, the cover member 60 constituting the first light guide optical system 103a is disposed between the projection optical system 20 and the light guide member 50. That is, the light guide member 50 is disposed on the outermost side with respect to the outside world. The cover member 60 is adhesively fixed to the lens barrel 30.

[0044] In the first light guide optical system 103a or the light guide member 50 of the present embodiment, the incident diffraction layer 51b, the exit diffraction layer 51c, and the pupil expansion grating layer 51e are formed on a first total reflection surface 51i disposed on the projection optical system 20 side, that is, the -Z side. The incident diffraction layer 51b, the exit diffraction layer 51c, and the pupil expansion grating layer 51e are designed to function as transmissive diffraction gratings that partially transmit external light. In the present embodiment, the incident diffraction layer 51b is disposed at the position of the exit pupil Lx of the projection optical system 20.

[0045] FIG. 9 is a diagram for explaining the sizes of the diffraction region Dr and the incident region Lr of the incident diffraction layer 51b. The light ray LL diffracted by the incident diffraction layer 51b and incident on the light guide plate 51a totally reflects inside the light guide plate 51a at a propagation angle Wm. In order to prevent the totally reflected light ray LL from re-entering the incident diffraction layer 51b, the size Di of the incident region Lr (in the present embodiment, the size of the exit pupil Lx of the projection optical system 20) is set so that the size Dw of the incident diffraction layer 51b is equal to or less than the width W up to the light ray folding back.

[0046] As described above, when the light guide member 50 functions as a transmissive diffraction grating and the lens barrel 30 and the cover member 60 are in contact with each other, the position of the exit pupil Lx of the projection optical system 20 is defined by the sum (tc + ta) of the thickness tc of the cover member 60 and the distance ta between the space between the cover member 60 and the light guide plate 51a from the contact surface between the lens barrel 30 and the cover member 60.

[0047] 〔Third Embodiment〕 Hereinafter, a virtual image display device according to a third embodiment of the present invention will be described. The virtual image display device of the third embodiment is a partial modification of the virtual image display device of the first embodiment, and the description of the common parts will be omitted.

[0048] As shown in FIG. 10, in the virtual image display device 100A of the present embodiment, the first light guide optical system 103a stacks a plurality of light guide plates 51a in parallel. Specifically, the first light guide optical system 103a includes a first light guide member 150 and a second light guide member 250 that diffracts image light ML in a wavelength range different from that of the first light guide member 150. The first and second light guide members 150 and 250 each include a light guide plate 51a, an incident diffraction layer 51b, an emission diffraction layer 51c, and a pupil expansion grating layer 51e.

[0049] The first light guide member 150 and the second light guide member 250 are optimized according to the wavelength range of the image light ML. The first and second light guide members 150 and 250 can be, for example, those corresponding to the three colors of RBG. By sharing the colors responsible for each light guide plate 51a of the first and second light guide members 150 and 250, the diffraction efficiency and the luminance uniformity can be further improved. Specifically, in the first light guide member 150, the grating period of the incident diffraction layer 51b is set so that, for example, blue light and green light propagate. In the second light guide member 250, the grating period of the incident diffraction layer 51b is set so that, for example, red light propagates.

[0050] Note that three light guide members may be provided corresponding to each of the three colors. Each light guide plate 51a of the light guide member may be divided by the angle of view in addition to the wavelength range in which the light is guided.

[0051] When the first light guide optical system 103a is composed of a plurality of light guide plates 51a, since the positions of the input diffractive optical elements DI (incident diffraction layers 51b) provided on each light guide plate 51a are shifted in the optical axis AX direction, that is, in the stacking direction of the light guide plates 51a, when the position of the exit pupil Lx of the projection optical system 20 is adjusted to the position of one of the incident diffraction layers 51b, the light rays spread when the image light ML enters the other incident diffraction layer 51b. Therefore, when the light guide plate 51a is composed of a plurality of plates, the exit pupil Lx of the projection optical system 20 is set at a position where the average values of the light ray widths Wa and Wb of the image light ML incident on the incident diffraction layers 51b of each light guide plate 51a are minimized. That is, in the present embodiment, the position of the exit pupil Lx is arranged at a position shifted from the incident diffraction layer 51b in the optical axis AX direction. The size and shape of the incident diffraction layer 51b are substantially the same as the size and shape of the light beam of the image light ML incident on the incident diffraction layer 51b of each light guide plate 51a. Note that the incident diffraction layer 51b may be formed to have a minimum size within a range not smaller than the size of the light beam of the image light ML incident on the incident diffraction layer 51b.

[0052] As shown in FIG. 11, even when the light guide plate 51a is composed of a plurality of plates, by setting the exit pupil Lx so that the light ray width of the image light ML incident on each light guide plate 51a becomes equal to or less than the width W up to the light ray folding in each light guide plate 51a, the capture of the incident image light ML can be maximized.

[0053] 〔Fourth Embodiment〕 Hereinafter, a virtual image display device according to the fourth embodiment of the present invention will be described. The virtual image display device of the fourth embodiment is a partially modified version of the virtual image display device of the first embodiment, and descriptions of common parts will be omitted.

[0054] As shown in FIG. 12, in the virtual image display device 100A of the present embodiment, the image light generation device 10 of the first display drive unit 102a includes three display panels 11r, 11b, and 11g, and a cross dichroic prism 18. The projection optical system 20 is a collimator including a plurality of lenses 21a and 21b which are lens elements 21.

[0055] The display panel 11r for red is the first display panel and emits red video light MLr which is the first video light. The display panel 11r is, for example, an OLED display, forms a still image or a moving image on a two-dimensional display surface parallel to the YZ plane, and emits red video light MLr.

[0056] The display panel 11b for blue is the second display panel and emits blue video light MLb which is the second video light. The display panel 11b is, for example, an OLED display like the display panel 11r for red, forms a still image or a moving image on a two-dimensional display surface parallel to the YZ plane, and emits blue video light MLb. The light-emitting element 14a incorporated in the display panel 11b for blue has a different emission wavelength from the light-emitting element 14a of the display panel 11r for red. That is, the blue video light MLb which is the second video light and the red video light MLr which is the first video light have different wavelength ranges.

[0057] The display panel 11g for green is the third display panel and emits green video light MLg which is the third video light. The display panel 11g is, for example, an OLED display like the display panel 11r for red, forms a still image or a moving image on a two-dimensional display surface parallel to the XY plane, and emits green video light MLg. The light-emitting element 14a incorporated in the display panel 11g for green has a different emission wavelength from the light-emitting elements 14a of the display panels 11r and 11b for red and blue. That is, the red video light MLr which is the first video light and the blue video light MLb which is the second video light have different wavelength ranges. That is, the green video light MLg which is the third video light and the red video light MLr which is the first video light and the blue video light MLb which is the second video light have different wavelength ranges.

[0058] The light-emitting elements 14a incorporated in the display panels 11r, 11b, and 11g are all OLED displays provided with a first resonance type cavity. Therefore, the alignment characteristics of the display panels 11r, 11b, and 11g are such that the light intensity is large in the front direction parallel to the optical axis AX, and rapidly decreases in a direction slightly inclined with respect to the front direction. Taking the angle at which the light intensity becomes half as the radiation angle, the radiation angle from the pixels of the red video light MLr, the radiation angle from the pixels of the blue video light MLb, and the radiation angle from the pixels of the green video light MLg are within about 20°. Based on the radiation angles of these video lights MLr, MLb, and MLg, the dichroic mirrors 18r and 18b of the cross-dichroic prism 18 described later are designed.

[0059] The display panel 11r for red is fixed so as to be attached to the first light incident surface 18ib of the cross-dichroic prism 18. The first display panel 11r for red causes the red video light MLr, which is the first video light, to enter the cross-dichroic prism 18 from the first light incident surface 18ib. The display panel 11b for blue is fixed so as to be attached to the second light incident surface 18ic of the cross-dichroic prism 18. The second display panel 11b for blue causes the blue video light MLb, which is the second video light, to enter the cross-dichroic prism 18 from the second light incident surface 18ic. The display panel 11g for green is fixed so as to be attached to the third light incident surface 18ia of the cross-dichroic prism 18. The third display panel 11g for green causes the green video light MLg, which is the third video light, to enter the cross-dichroic prism 18 from the third light incident surface 18ia.

[0060] The cross-dichroic prism 18 is formed by joining four right-angled triangular prisms made of a glass material or the like so that their right-angled edges coincide, and has a structure in which two dichroic mirrors 18r and 18b orthogonal to these joints are embedded. One of the dichroic mirrors 18r is arranged at an angle of 45° with respect to the first incident surface 18ib. The dichroic mirror 18r forms a plane connecting the diagonals of a square contour when viewed from the direction of the cross axis CX of the cross-dichroic prism 18. The other dichroic mirror 18b is arranged at an angle of 45° with respect to the second incident surface 18ic. The dichroic mirror 18b forms a plane connecting the diagonals of a square contour when viewed from the direction of the cross axis CX of the cross-dichroic prism 18.

[0061] The red video light MLr incident from the first display panel 11r for red on the first incident surface 18ib of the cross-dichroic prism 18 is reflected by the dichroic mirror 18r and bent toward the emission side, that is, toward the projection optical system 20, and is emitted from the light emission surface 18o in the external +Z direction. The blue video light MLb incident from the second display panel 11b for blue on the second incident surface 18ic of the cross-dichroic prism 18 is reflected by the dichroic mirror 18b and bent toward the emission side, that is, toward the projection optical system 20, and is emitted from the light emission surface 18o in the external +Z direction. The green video light MLg incident from the third display panel 11g for green on the third incident surface 18ia of the cross-dichroic prism 18 passes through toward the projection optical system 20 without being reflected by the dichroic mirrors 18r and 18b, and is emitted from the light emission surface 18o in the external +Z direction. That is, the cross-dichroic prism 18 transmits the green video light MLg. As a result, the cross-dichroic prism 18 synthesizes an image in which the red video light MLr, the blue video light MLb, and the green video light MLg are superimposed, and emits it as the video light ML, which can be made incident on the projection optical system 20.

[0062] In the cross dichroic prism 18, the cross axis CX extends along the intersection line of the two dichroic mirrors 18r and 18b and is parallel to the Y direction. The optical axis AX passing through the light emitting surface 18o of the cross dichroic prism 18 extends in the lateral direction perpendicular to the light guide plate 51a, that is, the Z direction.

[0063] The projection optical system 20 is an optical system that is substantially telecentric with respect to the display panels 11r, 11b, and 11g on the object side. That is, among the image lights MLr, MLb, and MLg emitted from each location of the light emitting element 14a which is the display surface of each display panel 11r, 11b, and 11g, the chief rays pass through the light incident surfaces 18ib, 18ic, and 18ia of the cross dichroic prism 18 in a state substantially parallel to the optical axis AX, enter the cross dichroic prism 18, and are emitted from the cross dichroic prism 18 substantially parallel to the optical axis AX. Thereby, red image light MLr, blue image light MLb, and green image light MLg within a predetermined angle range or less are incident on the dichroic mirrors 18r and 18b, and light loss due to the dichroic mirrors 18r and 18b can be suppressed.

[0064] Note that the arrangement of the display panels 11r, 11b, and 11g can be changed as appropriate.

[0065] Also, the virtual image display device 100A of the present embodiment may have the same configuration as the first light guiding optical system 103a of the second or third embodiment.

[0066] Also, the display panels 11r, 11b, and 11g of the present embodiment can be appropriately changed in addition to the OLED display, and for example, a micro OLED display, a micro LED display, etc. may also be used.

[0067] 〔Other matters〕 The structures described above are examples, and various changes can be made within the range where the same functions can be achieved.

[0068] FIG. 13 is a diagram for explaining a modification of the arrangement of the diffraction region Dr and the incident region Lr. In FIG. 13, the diffraction region Dr does not make the expansion sizes Va and Vb with respect to the incident region Lr the same as shown in FIG. 6. Instead, the expansion size Va on the light guiding side with respect to the incident region Lr is made narrow, and the expansion size Vb on the anti-light guiding side is made wide. That is, in the diffraction region Dr, the expansion size Va is small on the light guiding side with respect to the incident region Lr. Thereby, re-incidence of the video light ML at the input diffractive optical element DI can be further prevented.

[0069] Due to the design of the projection optical system 20, the aperture stop, etc., the diffraction region Dr and the exit pupil Lx (incident region Lr) of the input diffractive optical element DI are not limited to a circular shape, and can be appropriately changed to other shapes such as a rectangular shape, for example.

[0070] As will be described later, an aperture stop ST may be separately provided as the region limiting member 75 that limits the incident region Lr (see FIGS. 14 and 15). When the aperture stop ST is provided in the first display driving unit 102a, it is desirable to incorporate it into the projection optical system 20. Further, in the input diffractive optical element DI, since there is a possibility that the light beam incident from the anti-light guiding side re-enters the input diffractive optical element DI, the aperture stop ST may be provided only on the anti-light guiding side.

[0071] FIG. 14 is a conceptual diagram for explaining a modification of the optical system constituting the virtual image display device 100A. As shown in FIG. 14, the projection optical system 20 may be an optical system of a relay system. As a specific example, the projection optical system 20 has, as a lens element 21, the first to third lenses 21a to 21c as an optical system of a relay system, and an aperture stop ST is arranged between the first lens 21a and the second lens 21b. The aperture stop ST forms the shape of the light beam of the video light ML. The aperture stop ST is the region limiting member 75 and functions as stray light prevention.

[0072] FIG. 15 is a conceptual diagram for explaining a modified example of the optical system that constitutes the virtual image display device 100A. In FIG. 15, region AR1 is a conceptual diagram mainly for explaining the optical system of the first display driving unit 102a, and region AR2 is a partially enlarged rear view mainly for explaining the first light guide optical system 103a. As shown in FIG. 15, an aperture ST may be provided in the cover member 60. In a specific example, the aperture ST is provided on the outer surface of the cover member 60 (in the illustrated example, the surface facing the light guide member 50) in a configuration where the cover member 60 is adhered to the lens barrel 30 and the light guide member 50 is disposed on the outside. The aperture ST is formed by applying a light absorbing material such as black paint. In the illustrated example, the position of the exit pupil Lx is disposed at a position shifted from the incident diffraction layer 51b in the direction of the optical axis AX. Since the position of the aperture ST is away from the input diffractive optical element DI, when attempting to restrict the light incident obliquely, the light beam width (incident region Lr) of the video light ML becomes smaller than the diffraction region Dr of the input diffractive optical element DI. The aperture ST is a region restricting member and functions to prevent stray light.

[0073] In the above, the arrangements of the incident diffraction layer 51b, the exit diffraction layer 51c, and the pupil expansion grating layer 51e, the orientations and angles of the diffraction gratings, the propagation directions, etc. can be changed as appropriate.

[0074] The incident diffraction layer 51b, the exit diffraction layer 51c, and the pupil expansion grating layer 51e may be formed from a volume hologram. The incident diffraction layer 51b, the exit diffraction layer 51c, and the pupil expansion grating layer 51e are not limited to being composed of a single layer, and may also be a laminate of a plurality of functional layers adapted to the wavelength of the video light ML and the like.

[0075] The light guide member 50 is not limited to including the incident diffraction layer 51b, the exit diffraction layer 51c, and the pupil expansion grating layer 51e. For example, the pupil expansion grating layer 51e can also be omitted. In this case, the collimated video light ML is guided into the light guide plate 51a by the incident diffraction layer 51b and propagated laterally, and is emitted by the exit diffraction layer 51c toward the pupil position PP inside the video light ML propagating laterally in the light guide plate 51a.

[0076] In the above description, the virtual image display devices 100A and 100B are made available for use as an HMD. However, the present invention is not limited thereto and can be applied to various optical devices. For example, the present invention can also be applied to a head-up display (HUD).

[0077] The virtual image display device in a specific embodiment includes a display panel that emits image light, a projection optical system that collimates the image light from the display panel, a light guide plate that guides the image light, an input diffractive optical element that makes the image light enter the light guide plate, and an output diffractive optical element that emits the image light from the light guide plate, and a light guide member including the above components. The diffraction region of the input diffractive optical element covers the incident region of the image light in the light guide member, and the range is set such that the image light diffracted by the input diffractive optical element is reflected by the opposite surface of the light guide plate and enters the outside of the input diffractive optical element.

[0078] In the above virtual image display device, the generation of stray light can be prevented by covering the incident region of the image light in the light guide member with the diffraction region of the input diffractive optical element. Further, since the image light reflected by the opposite surface of the input diffractive optical element of the light guide plate enters the outside of the input diffractive optical element, it is possible to prevent the image light from re-entering the input diffractive optical element and reduce the light utilization efficiency.

[0079] In the virtual image display device in a specific embodiment, the range where the image light enters the outside of the input diffractive optical element is defined by an outer incident structure in which the size of the incident region is set such that the size of the diffraction region is equal to or less than the width up to the light beam folding in the light guide direction.

[0080] The virtual image display device in a specific embodiment includes a region limiting member that limits the incident region. In this case, the light beam width of the image light incident on the light guide plate can be limited. As a result, the input diffractive optical element can be made smaller, and it becomes easier to prevent the image light from re-entering the input diffractive optical element.

[0081] In the virtual image display device in a specific embodiment, the diffraction region has a smaller expanded size on the light guide side with respect to the incident region. In this case, re-incidence of the video light on the input diffractive optical element can be further prevented.

[0082] In the virtual image display device in a specific embodiment, the diffraction region and the incident region are substantially equal. In this case, while preventing re-incidence of the video light on the input diffractive optical element, the video light can be efficiently taken into the light guide plate.

[0083] In the virtual image display device in a specific embodiment, the input diffractive optical element is disposed at the position of the exit pupil of the projection optical system. In this case, while preventing re-incidence of the video light on the input diffractive optical element, the maximum amount of video light from the projection optical system can be taken into the light guide plate.

[0084] In the virtual image display device in a specific embodiment, a cover member is provided either between the projection optical system and the light guide member or outside the light guide member. In this case, the diffraction element such as the input diffractive optical element of the light guide member can be protected by the cover member.

[0085] In the virtual image display device in a specific embodiment, a first display panel which is a display panel that emits first video light among the video light, a second display panel that emits second video light having a wavelength range different from that of the first video light, a third display panel that emits third video light having a wavelength range different from those of the first video light and the second video light, and a cross dichroic prism that synthesizes the first video light, the second video light, and the third video light are provided. In this way, by synthesizing the first video light, the second video light, and the third video light, a high-brightness virtual image can be displayed.

[0086] In the virtual image display device in a specific embodiment, a first light guide member which is a light guide member, and a second light guide member that diffracts video light in a wavelength range different from that of the first light guide member are provided. In this case, optimization of the diffraction efficiency can be achieved according to the wavelength range of the video light.

[0087] In the virtual image display device in a specific embodiment, the diffraction region is circular.

[0088] In a specific embodiment, the optical unit includes a display panel that emits image light, a projection optical system that collimates the image light from the display panel, a light guide plate that guides the image light, an input diffractive optical element that causes the image light to enter the light guide plate, and an output diffractive optical element that causes the image light to exit the light guide plate. The diffractive region of the input diffractive optical element covers the incident region of the image light in the light guide member, and is set within a range where the image light diffracted by the input diffractive optical element is reflected by the opposing surface of the light guide plate and enters the outside of the input diffractive optical element.

Description of Reference Numerals

[0089] 10…Image light generation device, 11a, 11r, 11b, 11g…Display panel, 18…Cross dichroic prism, 20…Projection optical system, 21…Lens element, 30…Lens barrel, 50…Light guide member, 51a…Light guide plate, 51b…Incident diffraction layer, 51c…Emission diffraction layer, 51e…Pupil expansion grating layer, 60…Cover member, 70…Incident light limiting member, 75…Region limiting member, 88…Drive circuit member, 90…User terminal, 100…Optical unit, 100A, 100B…Virtual image display device, 100C…Support device, 102a, 102b…Display drive unit, 103a, 103b…Light guide optical system, AX…Optical axis, DD…Pupil expansion diffractive optical element, DI…Input diffractive optical element, DO…Output diffractive optical element, Dr…Diffractive region, EY…Eye, Lr…Incident region, Lx…Exit pupil, ML…Image light, OX…Emission optical axis, PP…Pupil position, ST…Aperture, US…Wearer

Claims

1. A display panel that emits image light, a projection optical system that collimates the image light from the display panel, a light guide plate that guides the image light, a light guide member including an input diffractive optical element that makes the image light enter the light guide plate, and an output diffractive optical element that makes the image light exit from the light guide plate, comprising: The diffraction region of the input diffractive optical element covers the incident region of the image light in the light guide member, and is set to a range in which the image light diffracted by the input diffractive optical element is reflected by the opposing surface of the light guide plate and enters outside the input diffractive optical element. A virtual image display device.

2. The range in which the image light enters outside the input diffractive optical element is defined by an outer incident structure that sets the size of the incident region so that the size of the diffraction region is equal to or less than the width to the light ray folding in the light guiding direction. The virtual image display device according to claim 1.

3. Comprising a region limiting member that limits the incident region. The virtual image display device according to claim 1.

4. The diffraction region has a smaller extended size on the light guiding side with respect to the incident region. The virtual image display device according to claim 1.

5. The diffraction region and the incident region are substantially equal. The virtual image display device according to claim 1.

6. The input diffractive optical element is disposed at the position of the exit pupil of the projection optical system. The virtual image display device according to claim 1.

7. Comprising a cover member either between the projection optical system and the light guide member or outside the light guide member. The virtual image display device according to claim 1.

8. A first display panel that is the display panel that emits first image light among the image light, a second display panel that emits second image light having a different wavelength range from the first image light, a third display panel that emits third image light having a different wavelength range from the first image light and the second image light, and a cross dichroic prism that synthesizes the first image light, the second image light, and the third image light. The virtual image display device according to claim 1.

9. A first light guide member that is the light guide member, and a second light guide member that diffracts the image light in a wavelength range different from that of the first light guide member. The virtual image display device according to claim 1.

10. The diffraction region is circular. The virtual image display device according to claim 1.

11. A display panel that emits image light, a projection optical system that collimates the image light from the display panel, A light guide member including a light guide plate for guiding the image light, an input diffractive optical element for causing the image light to enter the light guide plate, and an output diffractive optical element for emitting the image light from the light guide plate, comprising, wherein a diffraction region of the input diffractive optical element covers an incident region of the image light in the light guide member, and is set to a range in which the image light diffracted by the input diffractive optical element is reflected by an opposing surface of the light guide plate and enters outside the input diffractive optical element, an optical unit.

Images