HK1250790B - Diffractive backlight display and system - Google Patents

Description

Diffraction-backlit displays and systems

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application No. 62/214,976, filed on September 5, 2015, International (PCT) Application No. PCT/US2016/40904, filed on July 2, 2016, and International (PCT) Application No. PCT/US2016/40582, filed on June 30, 2016, the entire contents of which are incorporated herein by reference.

Background Art

In recent years, head-mounted display (HMD) technology has become increasingly popular in virtual and augmented reality applications. An HMD is a display device that is typically worn on a user's head in the form of glasses, goggles, a helmet, or a visor. The display device can be a single small electronic display unit that is located within the field of view of one of the user's eyes when the user is wearing the HMD, or the display device can be implemented as two separate small electronic display units that are located within the field of view of both eyes of the user when the user is wearing the HMD. For example, the small electronic display unit can be implemented using a small plasma display panel or a liquid crystal display. The small display unit used in the HMD can also be implemented using one or more lenses, collimating reflectors, and semi-transparent mirrors, and the image created is focused using a display panel. The HMD can use one display unit to create an augmented reality viewing experience, or the HMD can use two display units to create a virtual reality viewing experience.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features of examples and embodiments according to the principles described herein may be more readily understood by reference to the following detailed description taken in conjunction with the accompanying drawings, in which like reference numerals represent like structural elements, and in which:

FIG. 1A shows a plan view of a plate light guide provided with a diffraction grating.

FIG1B shows an enlarged cross-sectional view of the diffraction grating.

FIG1C shows a graph of the diffraction feature spacing of a diffraction grating as a function of distance.

2A-2C illustrate cross-sectional views of different diffraction grating structures.

FIG3A shows a plan view of a diffractive backlight system.

FIG3B shows a cross-sectional view of the light guide plate near the edge of the light entrance.

FIG4 shows an isometric view of a diffractive backlight system.

FIG5 shows a side view of a light guide plate that focuses light into a localized spatial region.

FIG6 shows an isometric view of the display.

FIG7 shows a side view of the display.

8-9 show side views of two different displays.

10A-10C show plan views of different light guide plate structures.

FIG11 shows a side view of a diffractive backlight system.

FIG12 shows a flow chart of a method for displaying an image in a local spatial region.

FIG13 shows a head mounted display for displaying augmented reality images.

FIG14 shows a head mounted display for displaying virtual reality images.

Certain examples and embodiments may have other features in addition to or instead of the features illustrated in the above-referenced drawings. These and other features are described below with reference to the above-referenced drawings.

DETAILED DESCRIPTION

Embodiments based on the principles described herein provide a diffraction grating-based backlit display implemented with a diffraction backlight system. The diffraction backlight system includes a light source and a light guide plate. A diffraction grating is disposed on a surface of the light guide plate. According to some embodiments, the diffraction grating may include curved diffraction features (e.g., curved ridges and grooves). Light generated by the light source may be coupled into the light guide plate along an edge of the light guide plate. The diffraction grating is configured to couple light out of the light guide plate and concentrate the light in a localized spatial region located a distance from the diffraction grating. For example, the diffraction grating may couple out a portion of the light coupled into the light guide plate. A first light valve array (e.g., a liquid crystal display) may be disposed in the path of light output from the diffraction grating to form a display that concentrates an image for viewing in the localized spatial region. In some embodiments, the display may include a second light valve array disposed in the light path through the first light valve array to provide eye accommodation in the localized spatial region. In one embodiment, the second light valve array may be a planar light valve array. In another embodiment, the second light valve array may be a pixelated contact lens worn by a viewer. One or two diffraction grating-based backlit displays can be used in a head-mounted display to generate focused augmented or virtual reality images for the wearer.

FIG1A illustrates a plan view of a diffraction grating pattern of a diffraction grating 102 formed on the surface of a light guide plate 100. A Cartesian coordinate system with orthogonal x, y, and z axes is used below to describe different orientations of the light guide plate 100. As shown in FIG1A , concentric black and white curves (e.g., black curve 104 and white curve 106) represent curved diffraction features. In some embodiments, the curved diffraction features represented by curves 104 and 106 may include alternating curved ridges and grooves on the surface of the light guide plate 100. As shown, the alternating curved ridges and grooves may have or share a common center of curvature 110 located at a distance from the edge 180. Thus, the alternating curved ridges and grooves may be alternating concentric curved ridges and grooves and represent concentric curved diffraction features. According to various embodiments, the alternating curved ridges and grooves, or more generally, curved diffraction features, form the diffraction grating pattern of the diffraction grating 102.

In some embodiments, the curved diffractive features may take the form of or be defined by a hyperbola (i.e., be defined by or based on a hyperbola), and thus may be "hyperbolic-shaped." Specifically, in some embodiments, the curved diffractive features may be concentric hyperbolic-shaped curvilinear diffractive features (e.g., alternating curved ridges and grooves of concentric hyperbolic shapes). In other embodiments, the curvilinear diffractive features or curved ridges and grooves forming the diffraction grating 102 may take the form of semicircles or concentric semicircles (e.g., semicircles located at a common center of curvature 110 away from the edge 108). In still other embodiments, the curve of the curvilinear diffractive feature may be defined by another curvilinear shape that is substantially neither hyperbolic nor semicircular.

FIG1B shows an enlarged xz plane, which is a cross-sectional view of light guide plate 100. In this view, diffraction grating 102 includes ridges (such as ridge 114) extending in the z direction and separated by grooves (such as groove 116). The width of the grooves is represented by _wg , and the width of the ridges is represented by _wr . The sum of the groove width _wg and the ridge width _wr is called the "feature spacing", denoted by Λ. As shown in FIG1A, the width of the grooves and ridges is substantially constant along the length of the grooves and ridges. Each pair of adjacent grooves and ridges is called a "diffraction feature", and the feature spacing Λ is substantially constant along the length of the diffraction feature.

FIG1C shows a graph of the diffraction feature spacing as a function of radial distance from a common center 110. Horizontal axis 118 represents radial distance from the common center 110 along a radius (e.g., radius 120 extending from the common center 110 in FIG1A ). Vertical axis 122 represents the feature spacing Λ. Curves 124-126 illustrate how the feature spacing varies with increasing distance from the common center 110. Curve 124 illustrates that the feature spacing decreases exponentially with increasing distance from the common center 110. Curve 125 illustrates that f decreases linearly with increasing distance from the common center 110. Curve 126 illustrates that f decreases exponentially with increasing distance from the common center 110.

In the example of FIG1B , and in subsequent illustrations, the cross-sectional view of the diffractive features is represented by rectangular grooves and ridges. In other embodiments, the ridges and grooves of the diffraction grating 102 may have sawtooth, trapezoidal, or hemispherical cross-sectional shapes. For example, the diffractive features of the diffraction grating 102 may have ridges with trapezoidal cross-sections.

The light guide plate 100 can be a plate-shaped optical waveguide in the form of an extended, substantially flat sheet or plate of optically transparent, dielectric material. The light guide plate 100 can include any of a variety of different optically transparent materials, or any of a variety of dielectric materials, including but not limited to one or more of various types of glass, such as silica glass, alkali metal aluminosilicate glass, borosilicate glass, and substantially optically transparent plastics or polymers, such as poly(methyl methacrylate) or acrylic glass and polycarbonate. In some embodiments, the light guide plate 100 can include a cladding layer (not shown) on at least a portion of the surface of the light guide plate 100 to promote total internal reflection.

The diffraction grating 102 can be formed using any of a number of different microfabrication techniques, including but not limited to wet etching, ion milling, photolithography, anisotropic etching, and plasma etching. For example, as shown in FIG1B , the diffraction grating 102 of the light guide plate 100 can be formed using a plate of dielectric material that has been ion milled. In one embodiment, the diffraction grating 102 of the light guide plate 100 can be formed by depositing a dielectric material layer or a metal layer on a surface of the dielectric material plate, and then etching the deposited layer to form the diffraction grating 102.

FIG2A shows a magnified xz plane, a cross-sectional view of a light guide plate 100 formed from a plate 202 of dielectric material, having ridges 204 of a diffraction grating formed on the top surface of plate 202, which is a material different from that of plate 202 (i.e., a dielectric material or metal). In other embodiments, diffraction grating 102 may be formed in the bottom surface of light guide plate 100. FIG2B shows a magnified xz plane, a cross-sectional view of light guide plate 100 having diffraction grating 102 formed in the bottom surface of plate 206 of dielectric material. In this embodiment, a bottom layer 208 of material covers diffraction grating 102 and substantially fills the grooves between the ridges. Bottom layer 208 may be a metal, a reflective material, or a dielectric material with a lower refractive index than plate 206. FIG2C shows a magnified xz plane, a cross-sectional view of light guide plate 100 having diffraction grating 102 formed in the bottom surface of plate 210 of dielectric material. In this embodiment, grooves such as groove 212 are filled with a metal or dielectric material having a lower refractive index than the plate 210. A reflective layer 214 covers the bottom surface of the light guide plate 100.

FIG3A shows a plan view of a diffractive backlight system 300. The diffractive backlight system 300 includes a light source 302 and a light guide plate 100. Light generated by the light source 302 is coupled into the light guide plate 100 along an edge 108, referred to as a "light entry edge." The light source 302 and the light guide plate 100 form a diffractive backlight system. For example, the light source 302 may be a light emitting diode ("LED"), an organic LED, a polymer LED, a plasma optical emitter, a fluorescent lamp, or an incandescent lamp. The light output from the light source 302 may be white light (i.e., including nearly all wavelengths in the visible spectrum) or a specific color within a narrow wavelength band of the visible spectrum. As shown in FIG3A , the light coupled into the light guide plate 100 along the light entry edge 108 propagates within the light guide plate 100 in a direction 304 away from the light entry edge 108. In other words, the light is coupled into the light guide plate 100 along the light entry edge 108 such that the light propagates within the light guide plate 100 in a general direction in which the characteristic spacing of the diffractive features decreases.

FIG3B illustrates the xz plane, which is a cross-sectional view of the light guide plate 100 near the light inlet edge 108. Light is coupled into the light guide plate 100 along the light inlet edge 108 and along a direction generally decreasing in feature spacing within the light guide plate 100. Light coupled into the light guide plate 100 within the range of angles denoted by σ (and referred to as the "internal reflection angular spread") undergoes total internal reflection and is confined within the light guide plate 100. For example, curve 306 represents the internal reflection angular spread σ, and directional arrows 308-310 represent the optical path of light input to the light guide plate 100 within the internal reflection angular spread σ. At each reflection point from opposing top and bottom surfaces (e.g., top surface 312 and bottom surface 314), the light strikes the opposing surface at an angle less than the critical angle and is confined within the light guide plate 100. However, at least a portion of the light confined within the light guide plate 100 interacts with the diffraction grating 102, such as light propagating along optical path 316. Light that interacts with the diffraction grating 102 is coupled out of the light guide plate 100 as a first-order diffracted beam. For example, the zeroth-order and higher-order diffracted beams of light can be suppressed. For example, light 318 represents first-order diffracted light coupled out of the light guide plate 100 at a diffraction angle θ relative to the normal direction 320 of the light guide plate 100.

The pattern and feature spacing of the diffraction grating 102 causes first-order diffracted light to be diffractively coupled out of the light guide plate 100 and focused into a substantially localized spatial region known as the "eyebox." FIG4 illustrates an isometric view of a diffractive backlight system 300, wherein light generated by a light source 302 is coupled into the light guide plate 100. The diffraction grating 102 causes at least a portion of the light input to the light guide plate 100 to be diffractively coupled out of the light guide plate 100 within a pyramidal or conical light transmission region 404 within an internal reflection angular divergence σ and focused into the eyebox 406. Directional arrows 401-403 represent first-order diffracted light that is coupled out of the light guide plate 100 at different points on the diffraction grating 102 in the light transmission region 404 and into the eyebox 406. Light diverges beyond the eyebox 406 and away from the light guide plate 100.

5 shows the xz plane, which is a side view of light output from the light guide plate 100 and entering the viewer's eye 502 located within the eyebox 406. The approximate width of the eyebox 406 is given by the product of the distance f from the light guide plate 100 to the eyebox 406 and the internal reflection angular spread σ:

Eyebox width = f × σ

5 , the feature spacing and internal reflection angular divergence σ of the diffraction features, which decrease as they move away from the light entrance edge 108, focus the light coupled out of the diffraction grating 102 into an eyebox 406 located at a distance f from the light guide plate 100. As a result, when a viewer is located in the eyebox 406, at least a portion of the light field coupled out of the light guide plate 100 can be focused on the retina of the viewer's eye 502.

It should also be noted that the coupling out of the diffraction grating 102 is effectively confined to the light transmission region 404 and the eyebox 406. As a result, when the viewer's eye 502 is located outside the eyebox 406 or outside the light transmission region 404, the light output from the diffraction grating 102 does not enter the viewer's eye 502 and the diffraction grating 102 appears black.

When a viewer's eye is positioned in the eyebox 406, the diffractive backlight system 300 can be combined with the planar light valve array to form a display that projects an image onto the retina of the viewer's eye. FIG6 shows an isometric view of the display 600, which includes the light guide plate 100, the planar light valve array 602, and the light source 302. The light valve array 602 is positioned substantially parallel to the light guide plate 100 (i.e., lies in the xy plane) and intersects the light transmission region 404, so that light coupled out of the diffraction grating 102 passes through the light valve array 602 and is focused in the eyebox 406.

FIG7 illustrates the xz plane, which is a side view of the display 600, with the light valve array 602 positioned at a distance d from the eyebox 406. As shown in FIG7 , the light valve array 602 is oriented substantially parallel to the light guide plate 100 so as to intersect the light transmission region 404. The light valve array 602 includes an array of individually operated light valves, such as light valve 702. The light valve array 602 can be formed from an array of liquid crystal light valves, each of which can individually operate as a pixel to adjust the amount of light passing through the light valve. The light valve 702 can be switched between opaque and transparent to control the amount of light passing through the light valve 702. The light valves can be color light valves, such as red, green, and blue light valves, for creating full-color images. Light passing through each light valve in the light valve array 602 can be selectively adjusted to create a full-color or black-and-white image for viewing in the eyebox 406.

FIG8 illustrates a near-eye diffraction grating-based backlit display 800 that provides eye accommodation. The near-eye diffraction grating-based backlit display 800 is similar to the near-eye diffraction grating-based backlit display 700, except that the near-eye diffraction grating-based backlit display 800 includes a second planar light valve array 802 oriented substantially parallel to the light guide plate 100 and located between the first light valve array 602 and the eye box 406. In FIG8 , the second light valve array 802 is located at a distance d1 from the eye box 406, and the first light valve array 602 is located at a distance d2 from the eye box 406 and between the second light valve array 802 and the light guide plate 100. Light passes through the light valves in the first light valve array 602 and the light valves in the second light valve array 802. The first and second light valve arrays 602 and 802 can operate to provide eye accommodation. For example, the first and second light valve arrays 602, 802 can be operated in a multiplicative manner (e.g., to implement factored light field synthesis) to obtain an image that helps the eye accommodate. For example, the viewer's eye focuses on an image created by the combined operation of the operation of the first light valve array 602 and the second light valve array 802 based on a virtual depth of field created by the multiplication of the transmission characteristics of the two light valve arrays 602, 802.

FIG9 shows a near-eye diffraction grating-based backlit display 900 that provides eye accommodation. The near-eye diffraction grating-based backlit display 900 is operated using a second light valve array in the form of a pixelated contact lens 902 disposed over the viewer's eye 502. The pixelated contact lens 902 includes a plurality of individually operated pixels configured to control the amount of light entering the viewer's eye when the viewer's eye is positioned in the eye box. For example, the pixelated contact lens 902 may include an array of 2-9 light valves (i.e., pixels) per pupil region, and may be individually "opened" by turning only one light valve on at a time (i.e., transparent) while the remaining light valves are "closed" (i.e., opaque). For example, the pixelated contact lens 902 may be a bionic lens with independently controlled light valves. The pixelated contact lens 902 may include liquid crystal light valves that adjust the amount of light that passes through the pixelated contact lens 902 and into the viewer's eye 502. The light valves in the first light valve array 602 and the pixelated contact lens 902 can be independently adjusted to control the light entering the viewer's eye 502 to facilitate eye adaptation. For example, by "opening" only one light valve at a time, the direction of light entering the viewer's eye is changed. This allows different images displayed by the first light valve array 602 to enter the viewer's eye from different directions, which can trigger a focusing response in the viewer's eye 502, creating the effect of objects being displayed in different images and at different distances from the viewer. For example, the adaptation response time of the viewer's eye can be approximately 0.3 seconds, which can reduce the effective refresh rate of the first light valve array 602 that may be required to support the adaptation response.

In other embodiments, the light guide plate may include multiple diffraction grating segments corresponding to different regions of the diffraction grating 102 and separated by unpatterned spaces. For example, the multiple diffraction grating segments may be two-dimensional diffraction grating segments. Although the diffraction grating segments correspond to different regions of the diffraction grating 102 and are separated by unpatterned spaces, the diffraction grating segments collectively couple out light and concentrate light in the same manner as the diffraction grating 102.

10A-10C illustrate light guides that include diffraction grating segments corresponding to different regions of the diffraction grating 102. FIG10A illustrates a light guide 1002 similar to the light guide 100 described above, but including five diffraction grating segments 1004-1008 corresponding to different regions of the diffraction grating 102 separated in one dimension by unpatterned spaces 1010-1013. FIG10B illustrates a light guide 1020 similar to the light guide 100 described above, but including diffraction grating segments (e.g., diffraction grating segment 1022) separated by unpatterned spaces in two dimensions (i.e., the diffraction grating segments are two-dimensional). The diffraction grating patterns of the diffraction grating segments also correspond to different regions of the diffraction grating 102. In other embodiments, the diffraction grating segments may include straight features. 10C shows a light guide plate 1024 that is similar to light guide plate 1020 described above, but light guide plate 1020 includes twenty-five diffraction grating segments formed from straight features, such as diffraction grating segment 1026. Light guide plates 1002, 1020, and 1024 couple less light out than light guide plate 100 due to the surface area occupied by the spaces between the diffraction grating segments.

It should be noted that the light guide plate formed by the diffraction grating segments corresponding to different regions of the diffraction grating 102 is not limited to the rectangular diffraction grating segments shown in Figures 10A-10C. In other embodiments, the light guide plate can be configured with circular, elliptical, triangular, or irregularly shaped diffraction grating segments corresponding to different regions of the diffraction grating 102, and separated by unpatterned spaces.

A light guide plate configured with diffraction grating segments corresponding to different regions of diffraction grating 102 concentrates light into localized spatial regions in the same manner as light guide plate 100 described above with reference to Figures 5 and 6. Figure 11 shows the xz plane, a side view of light guide plate 1102 with diffraction grating segments 1104-1108 configured to concentrate light into an eyebox 1110 located at a distance f from light guide plate 1102. Light enters light guide plate 1102 along light entry edge 1112 within an internal reflection angular divergence σ. A portion of the light is coupled out of diffraction grating segments 1104-1108 and concentrated in eyebox 1110. Because light is not coupled out through unpatterned spaces 1116-1119, less light is concentrated in eyebox 1110 than the light created by light guide plate 100 and concentrated in eyebox 406. For example, light transmission region 1114 (shown by dashed lines) can result from a combination of light collected by diffraction grating segments 1104-1108 and light not coupled out through the unpatterned spaces. In some embodiments, light guide plate 1102 can be replaced with light guide plate 100 in the diffractive backlight system 300 described above to form a portion of a near-eye diffractive backlight system.

FIG12 illustrates a flow chart of a method for displaying an image in a localized spatial region. In block 1201, light is coupled into a light guide, as described above with reference to FIG3A and 3B. The light guide is configured with a two-dimensional diffraction grating, as described above with reference to FIG1A-1C and 10A-10C. In block 1202, a portion of the light propagating in the light guide is diffractively coupled out of the light guide by the diffraction grating and focused in a localized spatial region referred to as an "eye box," as described above with reference to FIG4 and FIG5. In block 1203, the portion of the coupled-out light is adjusted using one or more light valve arrays to form a viewable image in the eye box, as described above with reference to FIG6-9. When a viewer's eye is positioned in the eye box, the image is focused on the viewer's retina, enabling the viewer to see the image.

Any of the above-described displays can be included in a head-mounted display ("HMD") to display virtual or augmented reality images. FIG13 shows an example of an HMD 1300 for displaying augmented reality images. HMD 1300 includes a frame 1302, a display 1304, and a display controller 1306. Display 1304 includes a light guide plate 1308 and a light valve array 1310. Light guide plate 1308 can be transparent, such as light guide plate 100 described above with reference to FIG1B. As described above with reference to FIG3A-3B, light guide plate 1308 and light valve array 1310 are connected to display controller 1306, which includes a light source (not shown) that couples light into light guide plate 1308 along light inlet edge 1312 to form a diffractive backlight system for display 1304. Light valve array 1310 is connected to display controller 1306. Display controller 1306 sends signals to adjust the light valves of light valve array 1310. As shown in FIG13 , a display 1304 and a display controller 1306 are suspended from the frame 1302 so that the display 1304 is within the field of view of the right eye of the person wearing the HMD 1300. The display controller 1306 may include a wireless communication unit that wirelessly connects the display controller 1306 to a broadcasting device, such as a mobile phone, capable of transmitting signals to the wireless communication unit. The display controller 1306 creates an augmented reality viewing experience by focusing the image displayed on the light valve array 1310 on the right eye of the person wearing the HMD 1300. For example, the display 1304 can be used to create an augmented reality viewing experience by displaying the phone number of a person calling the mobile phone of the person wearing the HMD 1300. Because the light guide 1308 is transparent, the person wearing the HMD 1300 can still see their surroundings when not focusing on the image displayed on the display 1304.

FIG14 shows an example of an HMD 1400 in the form of goggles for displaying virtual reality images. HMD 1400 includes eye shields 1402 and straps 1404. Eye shields 1402 surround the eyes of the person wearing HMD 1400, and straps 1404 secure eye shields 1402 to the person's head. Eye shields 1402 include a left-eye display 1406, a right-eye display 1408, and a display controller (not shown), which can be located within eye shields 1402. Each of displays 1406 and 1408 includes a light guide plate, such as light guide plate 1410, and a light valve array 1412. The light guide plate can be configured as described above with reference to FIG1B and FIG2A-2C. The light guide plate and light valve array are connected to the display controller, which includes at least one light source (not shown) that couples light into the light inlet edge of the light guide plate, as described above with reference to FIG3A-3B, to form a diffractive backlight system for each of displays 1408 and 1406. The display's light valve array is also connected to the display controller and receives control signals that adjust the light valves of the light valve array. As shown in FIG14 , displays 1406 and 1408 are located entirely within eye mask 1402 and within the field of view of both eyes of the person wearing HMD 1400. The display controller can create two-dimensional and three-dimensional virtual reality viewing experiences by generating images in the light valve arrays of displays 1406 and 1408, and the light guides of displays 1406 and 1408 focus the images on both eyes of the person wearing HMD 1400. In other embodiments, the left-eye display 1406 and the right-eye display 1408 can each include a second light valve array, as described above with reference to FIG8 , to create an eye-accommodating viewing experience. In other embodiments, the person wearing HMD 1400 can wear bionic contact lenses, as described above with reference to FIG9 , to create an eye-accommodating viewing experience.

It should be understood that the previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present disclosure. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments without departing from the spirit or scope of the present disclosure. Therefore, the present disclosure is not intended to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (20)

1. A display, comprising A light guide plate, having a diffraction grating on its surface, the diffraction grating having curved diffraction features configured to diffractically couple light out of the light guide plate and focus the coupled light into an eyeglass case; and A first light valve array is oriented substantially parallel to the light guide plate and positioned such that light coupled out of the light guide plate passes through the first light valve array to form an image in the eyeglass case. The width of the eyeglass case is equal to the product of the distance from the eyeglass case to the light guide plate and the internal reflection angular divergence of the light propagating within the light guide plate. 2. The display of claim 1, wherein the curved diffraction feature comprises alternating concentric curved ridges and grooves, the ridges and grooves sharing a common center located at a distance outside the edge of the light guide plate. 3. The display of claim 1, wherein the curved diffraction feature has a hyperbolic curve. 4. The display of claim 3, wherein the curved diffraction feature comprises a concentric hyperbolic curved diffraction feature. 5. The display of claim 1, further comprising a light source configured to provide light, the provided light being coupled into a light guide plate along an edge. 6. The display of claim 1, wherein the feature spacing of the curved diffraction features decreases with increasing distance from the edge of the light guide plate, and light is coupled into the light guide plate along the edge of the light guide plate. 7. The display of claim 1, wherein the diffraction grating causes light confined within the light guide plate to diffract and couples first-order diffracted light out of the light guide plate, and focuses the first-order diffracted light into the eyepiece. 8. The display of claim 1, further comprising a second light valve array oriented substantially parallel to the light guide plate and positioned such that light emanating from the first light valve array passes through the second light valve array. 9. The display of claim 1, further comprising a pixelated contact lens configured to be worn on a viewer's eye, wherein the pixelated contact lens comprises a plurality of individually operating pixels that control the amount of light entering the viewer's eye when the viewer's eye is in an eyeglass case. 10. The display of claim 1, wherein the diffraction grating comprises a plurality of two-dimensional diffraction grating segments configured to focus light coupled out of the light guide plate into the eyepiece. 11. A method for displaying an image, the method comprising: Light is coupled into a light guide plate, the light being generated by a light source; A portion of the light is coupled out of the light guide plate via a diffraction grating on its surface, and the diffraction grating focuses the coupled portion of the light into the eyeglass case; and A first light valve array, oriented substantially parallel to the light guide plate, is used to adjust a portion of the diffracted, coupled light to form a viewable image within the eyeglass case. The width of the eyeglass case is equal to the product of the distance from the eyeglass case to the light guide plate and the internal reflection angular divergence of the light propagating within the light guide plate. 12. The method of claim 11, wherein the diffraction grating includes curved diffraction features having a feature spacing that decreases with increasing distance from the edge of the light guide plate, light being coupled into the light guide plate along the edge of the light guide plate. 13. A head-mounted display, comprising: A light guide plate with a diffraction grating is configured to diffractically couple out a portion of the light input to the light guide plate and focus the coupled light into an eyeglass case; and A first light valve array is oriented substantially parallel to the light guide plate and positioned such that light coupled out of the light guide plate passes through the first light valve array; and A display controller connected to the first light valve array operates the first light valve array to form an image in the eyeglass case. The width of the eyeglass case is equal to the product of the distance from the eyeglass case to the light guide plate and the internal reflection angular divergence of the light propagating within the light guide plate. 14. The head-mounted display of claim 13, wherein the diffraction grating includes a curved diffraction feature on the surface of the light guide plate. 15. The head-mounted display of claim 14, wherein the curved diffraction feature is a concentric hyperbolic curved diffraction feature. 16. The head-mounted display of claim 14, wherein the curved diffraction feature comprises alternating curved ridges and grooves, the ridges and grooves sharing a common center located at a distance outside the edge of the light guide plate, the light entering the light guide plate along the edge of the light guide plate. 17. The head-mounted display of claim 13, wherein the diffraction grating includes curved diffraction features having a feature spacing that decreases with increasing distance from the edge of the light guide plate, light being coupled into the light guide plate along the edge of the light guide plate. 18. The head-mounted display of claim 13, wherein the diffraction grating is configured such that light confined within the light guide plate diffracts and couples first-order diffracted light out of the light guide plate, and focuses the first-order diffracted light into the eye socket. 19. The head-mounted display of claim 13, further comprising a second light valve array oriented substantially parallel to the light guide plate and positioned such that light emanating from the first light valve array passes through the second light valve array. 20. The head-mounted display of claim 13, further comprising a pixelated contact lens configured to be worn on a viewer's eyes, wherein the pixelated contact lens comprises a plurality of individually operating pixels that control the amount of light entering the viewer's eyes when the viewer's eyes are in an eyeglass case.