Image light guide with flexible substrate

Abstract

An image light guide for transmitting a virtual image includes a waveguide, an incoupling diffractive optical element operable to direct an image-bearing light beam into the waveguide, and an outcoupling diffractive optical element operable to direct the image-bearing light beam from the waveguide to an eyebox, the waveguide being configured to bend about one or more points thereof.

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE This disclosure relates to image light guides, and more particularly to image light guides that utilize flexible substrate materials and protective polymer coatings that enable the substrate materials to bend and damage resistant. [Background technology]

[0002] Head-mounted displays (HMDs) and virtual image near-eye display systems are being developed for a variety of applications, including military, commercial, industrial, firefighting, and entertainment. In many of these applications, it is valuable to create a virtual image that can be visually overlaid with a real-world image within the user's field of view. To direct the virtual image toward the viewer's pupil and enable this overlay function, an optical image light guide transmits image-bearing light to the viewer within a small space.

[0003] While conventional image light guide configurations have significantly reduced the volume, weight, and overall cost of near-eye display optical systems, further improvements are needed, especially in terms of safety. As virtual image near-eye display systems become smaller, usage is expected to increase dramatically, increasing the likelihood of operators becoming involved in dangerous situations. Therefore, eye safety is a major concern. While the rigidity of glass substrates in image light guides is desirable for stability, such substrates can be brittle and inflexible. The present disclosure provides a virtual near-eye display system with a flexible waveguide. Summary of the Invention

[0004] The present disclosure provides a wearable display device including an optical module that supports a display device adjacent to a viewer's head. In a first exemplary embodiment, a projector disposed within the optical module generates angularly related beams of image-bearing light that are projected along an optical path. An image light guide is coupled to a front portion of the optical module in the optical path of the image-bearing light beam. The image light guide includes a waveguide formed from a transparent optical material, an incoupling diffractive optical element formed in the waveguide and positioned to direct the image-bearing light beam into the waveguide, and an outcoupling diffractive optical element positioned to direct the image-bearing light beam out of the waveguide. The outcoupling diffractive optical element is positioned to expand the image-bearing light beam in at least one dimension to form a virtual image within the viewer's eyebox.

[0005] In an exemplary embodiment, the waveguide is formed of a thermo-chemically processed flexible material and protrudes from the optical module. The protruding portion of the flexible substrate not coupled to the optical module is operable to bend from 0 to 20 degrees or more along its length. In one embodiment, the waveguide system includes a protective layer to prevent damage and enhance debris containment of the waveguide. [Brief explanation of the drawings]

[0006] The accompanying drawings, which are incorporated as part of the specification, illustrate embodiments of the presently disclosed subject matter and illustrate selected principles and teachings of the present disclosure. However, the drawings do not depict every possible implementation of the presently disclosed subject matter, and are not intended to limit the scope of the present disclosure in any way.

[0007] [Figure 1] FIG. 2 is a schematic perspective view of an image light guide of a near-eye display system.

[0008] [Figure 2]FIG. 1 is a top view of a right-eye near-eye display system according to an exemplary embodiment of the disclosed subject matter.

[0009] [Figure 3] FIG. 1 is a top view of a left-eye near-eye display system according to an exemplary embodiment of the disclosed subject matter.

[0010] [Figure 4] FIG. 3 is a front view of the near-eye display system of FIG. 2.

[0011] [Figure 5] FIG. 3 is a perspective view of the near-eye display system of FIG. 2, showing the electronic module omitted.

[0012] [Figure 6A] FIG. 6 is a top view of the near-eye display system of FIG. 5.

[0013] [Figure 6B] FIG. 6B is a top view of the near-eye display system of FIG. 6A, showing the waveguide in a deflected state.

[0014] [Figure 6C] FIG. 6B is a top view of the near-eye display system of FIG. 6A, showing the waveguide in a deflected state.

[0015] [Figure 7A] 1 is a schematic diagram illustrating a simplified cross section of an image light guide according to an exemplary embodiment of the disclosed subject matter.

[0016] [Figure 7B] 7B is a schematic diagram showing a simplified cross section of the image light guide of FIG. 7A including a protective layer.

[0017] [Figure 8A] 1 is a schematic diagram illustrating a simplified cross section of a stacked waveguide system according to an exemplary embodiment of the disclosed subject matter.

[0018] [Figure 8B] 8B is a schematic diagram showing a simplified cross section of a portion of the stacked waveguide system of FIG. 8A. FIG.

[0019] [Figure 8C] 1 is a schematic diagram illustrating a simplified cross section of a near-eye display according to an exemplary embodiment of the disclosed subject matter.

[0020] [Figure 8D] FIG. 8D is a schematic diagram showing a simplified cross section of the near-eye display of FIG. 8C, showing the stacked waveguide system in a flexed state.

[0021] [Figure 9A] FIG. 1 is a schematic diagram showing a simplified cross section of a surface relief grating fixed to a substrate.

[0022] [Figure 9B] FIG. 1 is a schematic diagram showing a simplified cross section of a surface relief grating fixed to a deflected substrate.

[0023] [Figure 10] 1 is a schematic diagram illustrating a simplified cross section of a surface relief grating according to an exemplary embodiment of the disclosed subject matter.

[0024] [Figure 11A] FIG. 10 is a schematic diagram illustrating a simplified cross section of a surface relief grating according to another exemplary embodiment of the disclosed subject matter.

[0025] [Figure 11B] FIG. 11B is a schematic diagram showing a simplified cross section of the surface relief grating of FIG. 11A, shown in a deflected state. Detailed Description

[0026] It is to be understood that the present invention may assume various alternative arrangements and sequences of steps, except where expressly specified. It is also to be understood that the specific assemblies and systems illustrated in the drawings and described in the specification are merely exemplary embodiments of the inventive concepts defined herein. Accordingly, specific dimensions, orientations, or other physical characteristics relating to the disclosed embodiments are not to be considered limiting, unless expressly stated. Furthermore, like elements in the various embodiments described herein are referred to by like reference numerals.

[0027] In this specification, unless otherwise specified, terms such as "first," "second," etc. do not necessarily indicate an order or priority relationship, but are used merely to more clearly distinguish one element or set of elements from another element or set of elements.

[0028] As used herein, the terms "viewer," "operator," "observer," and "user" are considered equivalent and refer to a person or system viewing an image through a device having an image light guide.

[0029] As used herein, the term "set" refers to a non-empty set, as the concept of a set of elements or members is commonly understood in elementary mathematics. The term "subset," unless otherwise specified, refers to a non-empty proper subset, i.e., a subset of a larger set having one or more elements. In the case of a set S, a subset may include the complete set S. However, a "proper subset" of set S is strictly contained in set S and excludes at least one element of set S.

[0030] As used herein, the terms "coupled," "coupler," or "coupling" in the optical context refer to a coupling that transmits light from one optical medium or device to another.

[0031] As used herein, the term "exemplary" means "example" and does not imply a preferred or ideal embodiment.

[0032] As used herein, "beam expansion" refers to replicating a beam through multiple encounters with an optical element to provide exit pupil expansion in one or more directions. Similarly, "expanding a beam or portion of a beam" refers to replicating a beam through multiple encounters with an optical element to provide exit pupil expansion in one or more directions.

[0033] HMDs are being developed for a variety of applications, including military, commercial, industrial, firefighting, and entertainment. HMDs are operable to form virtual color images that can be visually superimposed on real-world images within the HMD user's field of view. An optically transparent parallel-plate waveguide, also known as a planar waveguide, transmits image-bearing light generated by a polychromatic or monochrome projector system to the HMD user. The planar waveguide transmits the image-bearing light through a narrow space and directs the image toward the HMD user's pupil, allowing the virtual image to be superimposed on real-world images within the HMD user's field of view.

[0034] In such conventional image light guides, a collimated, relative-angle-encoded light beam from a polychromatic or monochromatic image source is optically coupled into an optically transparent planar waveguide by an input coupling optical element, such as an incoupling diffractive optical element. This input coupling optical element is provided on or formed on the surface of the parallel-plate planar waveguide, or is disposed within the waveguide. Such a diffractive optical element can be formed as, but is not limited to, a diffraction grating or a holographic optical element. For example, the diffraction grating can be formed as a surface-relief grating. After propagating along the planar waveguide, the diffracted color image-bearing light is directed out of the planar waveguide by a similar output optical element, such as an outcoupling diffractive optical element. This output optical element is configured to provide pupil expansion along one or more dimensions of the eyebox E. Additionally, one or more intermediate optical elements, such as a diffraction grating, also known as a rotation grating, may be optically disposed along the waveguide between the input and output optical elements to provide pupil expansion in one or more dimensions of the virtual image. The image-bearing light output from the parallel-plate planar waveguide provides the viewer with an enlarged eyebox.

[0035] Optical systems such as HMDs can provide virtual images. In contrast to methods that form real images, the virtual image is not formed on a display surface. That is, no image is formed on a display surface if it were placed at the perceived location of the virtual image. Virtual image display has many inherent advantages over augmented reality displays. For example, the apparent size of the virtual image is not limited by the size or position of the display surface. Furthermore, the source object of the virtual image can be small. For example, a magnifying glass provides a virtual image of an object. Compared to systems that project real images, a more realistic viewing experience can be provided by forming a virtual image that appears at some distance. Providing a virtual image eliminates the need to compensate for screen artifacts, which is required when projecting a real image.

[0036] The perspective view of FIG. 1 shows an image light guide 20 configured to expand an eyebox 74 in two dimensions, i.e., along both the x-axis and y-axis of the intended image. To achieve beam expansion in the second dimension, an incoupling diffractive optical element IDO having a grating vector k0 is oriented to diffract a portion of the image-bearing light WG toward an intermediate optical element TO having a grating vector kl. The intermediate optical element TO is oriented to diffract a portion of the image-bearing light WG in a reflective mode toward the outcoupling diffractive optical element ODO. Only a portion of the image-bearing light WG is diffracted upon multiple encounters with the intermediate diffractive optical element TO, thereby laterally expanding the eyebox E via angularly related beam copies of the image-bearing light WG toward the outcoupling diffractive optical element ODO. The intermediate optical element TO may alternatively include a reflective mirror array as disclosed in U.S. Patent Application Publication No. 2021 / 0215941 A1, the contents of which are incorporated herein by reference. The intermediate optical element TO redirects the image-bearing light WG toward the outcoupling diffractive optical element ODO, where it is expanded in a second dimension, longitudinally of the eyebox E, via angularly related beam copies of the image-bearing light WG before exiting the planar waveguide 22 as image-bearing light WO. Grating vectors, such as grating vectors k0, k1, and k2, extend in a direction perpendicular to the diffractive features (e.g., grooves, lines, or rulings) of the diffractive optical element and have a magnitude that is the reciprocal of the period or pitch d (i.e., the center-to-center distance between grooves) of the diffractive optical elements IDO, TO, and ODO. The incoupling diffractive optical element IDO, the intermediate grating TO, and the outcoupling diffractive optical element ODO may have different periods or pitches d.

[0037] As shown in FIG. 1, the incoupling diffractive optical element IDO receives incident image-bearing light WI. This image-bearing light WI includes a set of angularly related beams corresponding to individual pixels or equivalent locations in an image generated by an image source 25. The image source 25 is operable to generate a gamut of angularly encoded beams for generating a virtual image and can be, but is not limited to, a physical display with focusing optics, a beam scanner for more directly setting the beam angles, or a one-dimensional physical display used in conjunction with a scanner. The image light guide 20 outputs a set of angularly related beams expanded in two dimensions of the eyebox by having the image-bearing light WG encounter both the intermediate diffraction grating TO and the outcoupling diffractive optical element ODO multiple times in different directions. For a given orientation of the planar waveguide 22, the intermediate optical element TO provides an exit pupil expansion in the y-axis direction, and the outcoupling diffractive optical element ODO provides a similar exit pupil expansion in the x-axis direction. The reflectivity properties and respective periods d of the incoupling diffractive optical element IDO, the outcoupling diffractive optical element ODO, and the intermediate optical element TO, along with the orientation of their respective grating vectors, provide exit pupil expansion in two dimensions while maintaining the intended relationship between angularly related beams of image-bearing light WI that emerge from the image light guide 20 as image-bearing light WO.

[0038] The image-bearing light WI incident on the image light guide 20 is encoded by the incoupling diffractive optical element IDO into a different set of angularly related beams, but the information necessary to reconstruct the image is maintained by the systematic effects of the incoupling diffractive optical element IDO. The intermediate optical element TO, located intermediately between the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO, is typically positioned so as not to cause significant changes to the encoding of the image-bearing light WG. The outcoupling diffractive optical element ODO is typically configured symmetrically with respect to the incoupling diffractive optical element IDO. For example, it contains diffractive features with the same period. Similarly, the period of the intermediate optical element TO also typically matches the common period of the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO. As shown in FIG. 1, the grating vector k1 of the intermediate optical element TO is shown oriented at 45 degrees relative to the other grating vectors K0 and K2 (all grating vectors are assumed to be unoriented). However, in one embodiment, the grating vector k1 of the intermediate optical element TO may be oriented at 60 degrees relative to the grating vector k0 of the incoupling diffractive optical element IDO and the grating vector k2 of the outcoupling diffractive optical element ODO. In this case, the image-bearing light WG is rotated by 120 degrees. By orienting the grating vector k1 of the intermediate optical element TO at 60 degrees relative to the grating vector k0 of the incoupling diffractive optical element IDO and the grating vector k2 of the outcoupling diffractive optical element ODO, the grating vectors k0 and K1 are also positioned at a 60-degree angle relative to each other. Based on the magnitudes of the grating vectors due to the common pitch of the intermediate optical element TO, the incoupling diffractive optical element IDO, and the outcoupling diffractive optical element ODO, the three grating vectors k0, k1, and k2 form an equilateral triangle and sum to zero magnitude. This avoids asymmetric effects that may introduce undesirable aberrations, such as chromatic dispersion.

[0039] The image-bearing light WI diffracted within the planar waveguide 22 is effectively encoded by the incoupling optical element, whether the incoupling optical element is a grating, hologram, prism, mirror, or other mechanism. The reflection, refraction, and / or diffraction of light occurring at the input requires corresponding decoding at the output to recreate the virtual image presented to the viewer. The intermediate optical element TO, located optically intermediate between the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO, is typically designed and oriented so as not to cause any changes to the encoded light. The outcoupling diffractive optical element ODO decodes the image-bearing light WG into its original or desired form of expanded, angularly related beams to fill the eyebox 74. In a broad sense, regardless of whether any symmetry is maintained between the rotating optical element TO, the incoupling diffractive optical element IDO, and the outcoupling diffractive optical element ODO, or whether changes occur along the planar waveguide 22 in the encoding of the angularly associated beams of the image-bearing light WI, the intermediate optical element TO, the incoupling diffractive optical element IDO, and the outcoupling diffractive optical element ODO are associated such that the image-bearing light WO output from the planar waveguide 22 retains the original or desired form of the image-bearing light WI to generate the intended virtual image.

[0040] The letter "R" represents the orientation of the virtual image as seen by a viewer whose eye is in the eyebox E. As shown, the orientation of the letter "R" in the represented virtual image matches the orientation of the letter "R" encoded by the image-bearing light WI. A change in the rotation or angular orientation of the incident image-bearing light WI about the z-axis relative to the xy plane causes a corresponding symmetric change in the rotation or angular orientation of the output light from the outcoupling diffractive optical element (ODO). From the perspective of image orientation, the intermediate optical element TO functions as a kind of optical relay, providing an expansion of the exit pupil along one axis (e.g., the y-axis). The outcoupling diffractive optical element ODO further expands the exit pupil along another axis (e.g., the x-axis) while maintaining the original orientation of the virtual image encoded by the image-bearing light WI. In one embodiment, if the intermediate optical element TO is a diffraction grating, the intermediate optical element TO is a tilted grating or a square grating, or alternatively, a blazed grating, and is disposed on the front surface 12 or the rear surface 15 of the planar waveguide 22.

[0041] In the following, optical path components, spacing, and constraints are described with reference to the observer's right eye 34R shown in Figure 2. The same characteristics and constraints can be selectively applied to the left eye, with comparable (parallel) components and corresponding changes in component location, as shown in Figure 3. Additionally, certain embodiments of the present disclosure contemplate providing optical path components to both the left and right eyes simultaneously. Thus, an HMD includes both monocular and binocular optical imaging devices.

[0042] As shown in FIG. 2 , in one embodiment, near-eye display system 12 includes electronics module 14, optical module 16 electrically connected and coupled to electronics module 14, and planar waveguide 18 coupled to optical module 16. In one embodiment, mount 54 is configured to mechanically secure planar waveguide 18 to optical module 16. Optical module 16 is operable to transmit image-bearing light to eye 34R via planar waveguide 18. In one embodiment, optical module 16 includes a projector operable to generate a full range of angularly encoded image-bearing light beams. In one embodiment, the projector is a color-field sequential projector system operable to pulse image-bearing light in red, green, and blue wavelength ranges to a digital light modulator / micromirror array (“DLP”) or liquid crystal on silicon (“LCOS”) display.

[0043] In one embodiment, near-eye display system 12 houses an integrated camera 70. Camera 70 may include a camera flash and / or light source 71, as shown in FIGS.

[0044] As shown in Figures 4 and 5, the planar waveguide 18 protrudes from the waveguide mount 54 at a ratio of 1.5:1 or greater along its x-axis. The waveguide mount 54 connects less than 50% of the periphery of the planar waveguide 18. In this embodiment, the majority of the planar waveguide 18 is suspended in front of the eye 34R. In one embodiment, the optical module 16 is detachable from the electronics module 14.

[0045] 6A, in one embodiment, the planar waveguide 18 has a deflection angle of zero degrees (0°) when not subjected to a physical stressor. In other words, in its rest state, the planar waveguide 18 does not include any curvature about the x-axis, y-axis, or z-axis. In its rest state orientation, the planar waveguide 18 includes a longitudinal axis 40.

[0046] As described further below, the planar waveguide 18 can be constructed from one or more substrates, including one or more flexible materials, forming a substrate system. The substrate system of the planar waveguide 18 can include, but is not limited to, materials such as polymer coatings, treated glass, and polyester films. Such films include materials of a class equal to or exceeding the tensile elasticity of Melinex® 339, Coming® Willow Glass Substrates, and PLEXIGLAS® Optical 0Z024. Referring now to FIGS. 6A, 6B, and 6C, the properties of these substrate materials, including the substrate, polymer coating layer, treated glass layer, adhesive deposit, and the like, allow the planar waveguide 18 to bend along the x-axis and z-axis before breaking. In one embodiment, the planar waveguide 18 can bend along the y-axis before breaking. In yet another embodiment, the planar waveguide 18 can bend along the z-axis before breaking. In yet another embodiment, the planar waveguide 18 can bend along more than one axis. For example, the planar waveguide 18 can be bent (eg, by twisting in multiple directions) to form a bend with a rotation angle.

[0047] Referring to FIG. 7A, in one embodiment, the planar waveguide 18 includes a substrate S. The substrate S includes an alkali-containing glass material compound that has been strengthened through a thermochemical process. In the thermochemical process, the substrate S is immersed in a molten salt bath at a temperature range below the melting point of the glass material compound, and ion exchange occurs during this process. Sodium ions diffuse from the substrate S into the molten salt bath and are replaced with potassium ions. This ion exchange causes surface compression of the glass material compound of the substrate S, reducing the likelihood of spallation. The compressed glass material compound of the substrate S is then suspended one or more times in an immersion tank (a heated steel tank) containing molten salt to further increase surface hardness.

[0048] 7A is a schematic diagram showing a simplified cross section of a planar waveguide 18 including a substrate S having substantially parallel surfaces 13, 15. In one embodiment, a coating 28 is disposed on substrate surface 15. In one embodiment, surface 15 is positioned proximate one of the wearer's eyes 34R, 34L (see FIGS. 2 and 3 ) during use, and surface 13 is positioned opposite surface 15. In another embodiment, coating 28 is disposed on substrate surface 13. In yet another embodiment, coating 28 is disposed on both sides 13, 15 of substrate S. In one embodiment, an incoupling diffractive optical element IDO and / or an outcoupling diffractive optical element ODO is disposed on the substrate coating 28.

[0049] For example, the substrate coating 28 may comprise a transparent polymeric material operable to transmit incident image-bearing light WI. Surface adhesion is maximized when the polymer deposition reacts with the substrate surface 13, 15 to present the greatest number of accessible sites with the appropriate surface energy. To promote adhesion between the substrate coating 28 and the substrate S, the substrate S may be treated with an adhesion promoter 32. This adhesion promoter 32 may include, but is not limited to, a hydrophobic silane-based layer (single or multiple layers), UV exposure, heat treatment, or other all-encompassing methods.

[0050] 6B and 6C, the substrate S, the substrate coating 28, and additional processing layers, if any, form a substrate system for the waveguide 18. This substrate system is operable to bend, for example, along the x-axis (i.e., in the z-direction) to form a bending arc 44 of between zero and twenty degrees (0°-20°) without delamination. For example, as shown in FIG. 6C, the waveguide 18 can be bent along the x-axis to a bending arc 44 of approximately twenty degrees (20°) without delamination. In another embodiment, the substrate system for the waveguide 18 may bend along its axis up to approximately ten degrees (10°) without delamination. In yet another embodiment, the substrate system for the waveguide 18 may bend along its axis from zero to five degrees (0°-5°) without delamination. In another embodiment, the substrate system for the waveguide 18 may bend along its axis from zero to fifteen degrees (0°-15°) without delamination. In one embodiment, the waveguide 18 can include a range of deflection along multiple axes without delamination, such as by twisting or applying forces along multiple directions, where the waveguide 18 can deflect between zero and twenty degrees (0°-20°) along each axis.

[0051] The allowable deflection of the substrate coating 28 or additional processing layers without damage may exceed twenty degrees (20°). "Acceptable deflection" and "deflection arc shape" refer to the amount of deflection of the substrate system of the waveguide 18 that allows the waveguide 18 to operate to return to an undeflected position after deflection without damage or delamination.

[0052] In one embodiment, one or more protective layers may be provided on the substrate S or between multiple substrates (see FIG. 8A). That is, in one embodiment, a waveguide 18 with one or more protective layers provided on the substrate S has a deflection range as described above. In another embodiment, a stacked set of planar waveguides 50 has a deflection range along one or more axes as described above.

[0053] 7A and 7B, the incoupling diffractive optical element IDO may be a transmissive diffraction grating disposed on an inner parallel surface 15 of the substrate S. However, the incoupling diffractive optical element IDO may instead be a volume hologram or other holographic diffractive element, or any other type of diffractive optical element operable to couple the image-bearing light WI into the waveguide 18. The incoupling diffractive optical element IDO may be disposed on an outer parallel surface 13 or an inner parallel surface 15 of the substrate S, and may be transmissive or reflective depending on the direction in which the image-bearing light WI approaches the substrate S.

[0054] When used as part of a virtual display system, the incoupling diffractive optical element IDO couples image-bearing light WI from a real image source into the substrate S of the planar waveguide 18. The real image or image dimension is first transformed into an array of angularly related overlapping beams. In this transformation, various pixel locations within the image are encoded for presentation to the incoupling diffractive optical element IDO. The image-bearing light WI is diffracted by the incoupling diffractive optical element IDO, which redirects at least a portion of the image-bearing light WI into the planar waveguide 18 as image-bearing light WG, which then propagates along the planar waveguide 18 by total internal reflection (TIR). Due to the boundaries established by TIR, the angularly related beams are diffracted to a more condensed extent, but the image-bearing light WG maintains the image information in its encoded form. The outcoupling diffractive optical element ODO receives the encoded image-bearing light WG and diffracts at least a portion of the image-bearing light WG out of the planar waveguide 18 as image-bearing light WO toward the intended location of the observer's eye. In general, the outcoupling diffractive optical element ODO is designed symmetrically with the incoupling diffractive optical element IDO to restore the original angular relationship of the image-bearing light WI between angularly related beams of the output image-bearing light WO. However, to increase the one-way overlap between the angularly related beams within the eyebox E where the virtual image is viewed, the outcoupling diffractive optical element ODO is configured to encounter the image-bearing light WG multiple times and diffract only a portion of the image-bearing light WG at each encounter. The multiple encounters along the length of the outcoupling optical element in the propagation direction have the effect of expanding the one-way overlap of the image-bearing light beams within the eyebox E. The expanded eyebox E reduces sensitivity to the eye position of the viewer viewing the virtual image.

[0055] The outcoupling diffractive optical element ODO is shown as a transmissive diffraction grating located on the inner surface 15 of the substrate S. However, like the incoupling diffractive optical element IDO, the outcoupling diffractive optical element ODO can be located on the outer surface 13 or the inner surface 15 of the substrate S, or both, and can be transmissive or reflective depending on the direction in which the image-bearing light WG exits the substrate S.

[0056] FIG. 7B shows an air gap 72 with a thickness of 0.1 mm or varying depending on the embodiment. The air gap 72 allows TIR to proceed efficiently within the substrate S. The air gap 72 interfaces with (bounds) the substrate S and / or coating 28 along both the outer surface 13 and the inner surface 15. In one embodiment, the air gap 72 may be a transparent material with a refractive index similar to that of air. Transparent materials include, but are not limited to, mesoporous aerogels made of silica, silica nanorods, organic polymers, and the like. In another embodiment, as shown in FIG. 8B, the air gap 72 contains air or a gaseous fluid maintained by a low-shrinkage, low-durometer material 73 operable to bend with the waveguide 18 assembly.

[0057] As shown in Figure 8A, an air gap 72 may exist between the substrates S1, S2 of the waveguide stack 50. In one embodiment, the waveguide stack 50 includes two or more waveguides 18. In one embodiment, as shown in Figure 8B, the air gap 72 is maintained by a low-shrinkage, low-durometer material 73 disposed around the periphery of the system and operable to provide for independent movement of the substrates S1, S2. In one embodiment, the low-durometer material 73 can act as a seal around the periphery of the substrates S1, S2 against the ingress of environmental contaminants between the substrates S1, S2.

[0058] 7B, first and second protective layers 68, 70 may be bonded to the substrate S, covering the substrate coating 28 and the air gap 72. In one embodiment, the protective layers 68, 70 comprise a completely transparent polymer, allowing the image-bearing light WI, WO to pass through and exit the substrate S without significantly affecting the function of the waveguide 18.

[0059] The protective layers 68, 70 function to enhance containment of potential spallation of the substrate S when the substrate S is subjected to an impact or excessive stress. For example, the polymer layers 68, 70 function to at least partially contain some of the spallation debris from the substrate S. As shown in FIG. 8A , a first protective layer 68 and a second protective layer 70 can surround the outer surface of each of the waveguides 18 in the stacked set 50 of planar waveguides. In one embodiment, three or more planar waveguides 18 having the same or different substrates can be stacked and protected as described above.

[0060] For diffractive optical elements formed as diffraction gratings, increasing the depth of the grating increases the diffraction efficiency. However, increasing the diffraction efficiency of an outcoupling grating can reduce the image-bearing light WO emitted from the outer regions of the grating. Furthermore, in embodiments including multiple input gratings, mixing of light beams within the waveguide, i.e., crosstalk, can occur. To compensate for these issues, in the example shown in FIG. 8A, two planar waveguides 18, each with a substrate S1 and S2, can be laminated together by a bonding process known to those skilled in the art.

[0061] The upper planar-parallel surface 15a of the planar waveguide substrate S1 is coated with a substrate coating 28. Similarly, the upper planar-parallel surface 15a of the planar waveguide substrate S2 is coated with a substrate coating 28. In one embodiment, the incoupling diffractive features of the first and second substrates S1, S2 affect the image-bearing light WI in different ways. For example, the incoupling diffractive features of the substrates S1, S2 diffract only a specific spectrum of the image-bearing light WI into the respective substrates S1, S2 and propagate via TIR to the respective outcoupling diffractive optical element ODO.

[0062] 8C, in one embodiment, near-eye display system 12 includes a stacked waveguide system 126 mounted in optical module housing 100. Stacked waveguide system 126 includes a first substrate S1 having an incoupling diffractive optical element ID01 and an outcoupling diffractive optical element OD01, and a second substrate S2 having an incoupling diffractive optical element ID02 and an outcoupling diffractive optical element OD02. In one embodiment, one or both of substrates S1, S2 includes an intermediate optical element. Projector 110 is disposed within housing 100 and is operable to emit angularly encoded image-bearing light.

[0063] In one embodiment, the stacked waveguide system 126 is secured within the housing 100 by distal waveguide fasteners 106 and proximal waveguide fasteners 104. Plate 112 is positioned within the housing 100 adjacent to the second substrate S2 and is operable to provide structural rigidity to the waveguide system 126 disposed within the housing 100. Plate 112 is operable to mitigate damage to the projector 110 when the stacked waveguide system 126 is bent. In one embodiment, additional plates 114, 116 are positioned adjacent to the first substrate S1 and the projector 100 and are operable to provide additional structural support to the stacked waveguide system 126. In one embodiment, plates 112, 114, 116 are used to provide rigidity to the portion of the stacked waveguide system 126 located within the housing 100. In one embodiment, plates 112, 114, 116 are mechanically secured to the stacked waveguide system 126.

[0064] Qualification testing and user handling patterns indicate that the most common failure point of stacked waveguide system 126 occurs less than one centimeter from the connection point with housing 100. In one embodiment, stacked waveguide system 126 includes a resilient flexure portion 128 and a substantially rigid portion 140. As shown in FIG. 8D , flexure portion 128 creates a resilient region operable to bend when a force is applied to stacked waveguide system 126, for example, in the z-axis direction. In one embodiment, flexure portion 128 may be mechanically programmed to fail under stress and / or stress that causes substrates S1, S2 to bend beyond a bend point (e.g., 20 degrees).

[0065] To reduce breakage and maintain dimensional stability of the substantially rigid portion 140, an abrasion-resistant hard coating 130 can be applied to the first and second substrates S1, S2. In one embodiment, the hard coating 130 encases the first and second substrates S1, S2 of the rigid portion 140, surrounding the tips of the substrates S1, S2. The hard coating 130 can be composed of any number of hard, transparent polymers, such as Allytics, polymethylpentene, or polycarbonate. In one embodiment, the hard coating 130 can be applied over the protective layers 68, 70 shown in FIG. 8A.

[0066] To further promote the structural integrity of the stacked waveguide system 126, the first substrate S1 and the second substrate S2 may be separated by a gasket 73, a bead of adhesive, or other low durometer material. This material can operate to help provide space for the air gap 72, thereby allowing independent movement of the first and second substrates S1, S2 along the x-axis when bent. In one embodiment, to avoid damage to the hard coating 130 when bent, the substrate flexure channel 136 provides a cleft in the inner wall of the hard coating 130, allowing independent displacement of the planar waveguide substrate S1 and the planar waveguide substrate S2 when bent.

[0067] In embodiments where the diffractive optical element is not located in a region of the substrate that is rigidly held by, for example, a coating or backing / plate, the diffractive optical element may be damaged when the waveguide / laminated waveguide system is bent. FIG. 9A shows an array of tilted face relief grating features 170 formed in a coating 178 on a planar surface 172 of a substrate S in an undeflected state. The grating features 170 are spaced apart by a distance represented by spacing e. FIG. 9B shows deflection of the substrate S. This deflection risks contact of the delicate grating microstructures at the optical grating impact points 176, thereby damaging the functionality of the waveguide system.

[0068] As shown in FIG. 10, in one embodiment, the grating features 170 have an expanded grating feature spacing f to compensate for bowing of the substrate S.

[0069] As shown in FIG. 11A , in another embodiment, the grating features 170 are separated into individual (discrete) sections (or grating strips 180) by a grating strip spacing h. Each grating strip 180 includes multiple grating features 170. The limited total surface contact between each grating strip 180 and the substrate surface 172 reduces the required deflection of the coating 178, thereby reducing the risk of delaminating the coating 178 from the substrate S. Each grating strip 180 is separated by a grating strip spacing h. The grating strip spacing h can be achieved by, but is not limited to, gluing the individual grating strips 180 to the substrate S or by separating the grating strips 180 with microlaser ablation. FIG. 11B shows the coating 178 in a deflected state. The grating features 170 of the separated grating strips 180 do not contact each other.

[0070] In an exemplary embodiment, a wearable display device includes an electronics module operable to mount an optical module adjacent to a viewer's head, a projector disposed within the optical module operable to generate an image-bearing light beam, and a waveguide coupled to the optical module. The waveguide includes a substrate formed of a transparent optical material and having a first surface and an opposing second surface, an incoupling optical element operable to direct the image-bearing light beam into the waveguide, and an outcoupling optical element operable to direct the image-bearing light beam from the waveguide into an eyebox to form a virtual image within the eyebox. The virtual image appears at a distance within the viewer's field of view. The waveguide includes a first end and a second end, the first end coupled to the optical module and the second end operable to flex (bend) relative to the first end.

[0071] In one embodiment, the optical module surrounds less than 50 percent of the periphery of the waveguide.

[0072] In one embodiment, a first polymer layer is bonded to a first surface of the waveguide, and at least one of an incoupling diffractive optical element and an outcoupling diffractive optical element is disposed in the first polymer layer.

[0073] In one embodiment, the second end of the waveguide can be displaced at a 20 degree angle relative to the first end of the waveguide, and the first polymer layer can flex without delaminating from the waveguide.

[0074] In one embodiment, the waveguide further comprises an adhesion promoter on a first surface of the waveguide, the first polymer layer being adhered to the adhesion promoter. In one embodiment, the waveguide further comprises a second polymer layer disposed over the first polymer layer, the second polymer layer operable to contain at least a portion of the waveguide debris resulting from sharding.

[0075] In one embodiment, the waveguide comprises an alkali compound, and the second end of the waveguide is operable to flex (bend) at least 0 to 20 degrees relative to the first end of the waveguide without breaking.

[0076] In one embodiment, the waveguide is a first waveguide, a second waveguide is coupled to the first waveguide, and an air gap is disposed between the first and second waveguides. In one embodiment, a low durometer material is disposed between the first and second waveguides, the low durometer material at least partially defining the air gap and operable to deflect with the first and second waveguides.

[0077] While various embodiments have been described in detail, it should be understood that they are presented by way of example and not limitation. It will be apparent to those skilled in the art that the disclosed subject matter can be embodied in other specific forms, variations, and modifications without departing from the scope, spirit, or essential characteristics thereof. The above-described embodiments are therefore to be considered in all respects as illustrative and not restrictive. The scope of the invention is indicated by the appended claims, and all changes that come within the meaning and range of equivalents thereof are intended to be embraced therein.

Claims

1. 1. An image light guide for transmitting a virtual image, comprising: a waveguide including a glass substrate having a first surface and a second surface opposite the first surface, and a coating coupled to the first surface of the substrate; an incoupling diffractive optical element formed in the coating and operable to direct an image-bearing light beam into the waveguide; an outcoupling diffractive optical element formed in the coating and operable to direct the image-bearing light beam from the waveguide to an eyebox; the waveguide comprises a first portion and a second portion, the second portion operable to deflect at an angle of up to at least 5 degrees relative to the first portion, and the coating operable to deflect with the substrate.

2. The image light guide of claim 1 , wherein an optical module surrounds less than 50 percent of the periphery of the waveguide.

3. The image light guide of claim 1 , wherein the coating comprises a polymer layer, the polymer layer operable to flex without delaminating from the substrate of the waveguide.

4. The image light guide of claim 3 further comprising an adhesion promoter disposed on the first surface, the polymer layer being adhered to the adhesion promoter.

5. The image light guide of claim 1 , wherein the waveguide comprises an alkali compound.

6. 10. The image light guide of claim 1, wherein the waveguide is a first waveguide, a second waveguide is coupled to the first waveguide, an air gap is disposed between the first waveguide and the second waveguide, and a second portion of the second waveguide is operable to flex relative to a first portion of the second waveguide.

7. 7. The image light guide of claim 6, further comprising a material disposed between the first waveguide and the second waveguide, the material at least partially defining the gap and operable to flex with the first waveguide and the second waveguide.

8. The image light guide of claim 1 , wherein the outcoupling diffractive optical element comprises a plurality of sections of diffractive features with gaps disposed between each section of the diffractive features.

9. 7. The image light guide of claim 6, wherein at least one of the first portion of the first waveguide and the first portion of the second waveguide is at least partially disposed within an optical module including an image-bearing light source, and the first portion is coupled to the optical module by a first fastener and a second fastener.

10. 10. The image light guide of claim 9, further comprising a plate coupled to the first waveguide or the second waveguide between the first fastener and the second fastener, the plate operable to provide rigidity to the first portion of the first waveguide and / or the first portion of the second waveguide.

11. further comprising a hard coating positioned around the second portion of the first waveguide and the second waveguide, the hard coating operable to inhibit flexure of the second portion; 10. The image light guide of claim 9, further comprising a third portion of the first and second waveguides located between the first and second portions, the third portion being operable to bend.

12. 1. A method of manufacturing a flexible image light guide, comprising: providing a substrate having a first surface and a second surface opposite the first surface; subjecting the substrate to an ion diffusion process; coating the first surface of the substrate with a polymeric material to form a polymeric coating; molding at least one of an incoupling diffractive optical element and an outcoupling diffractive optical element into the polymer coating; wherein the substrate comprises a first portion and a second portion, the second portion operable to deflect by at least 20 degrees relative to the first portion.

13. The method of claim 12 further comprising subjecting the substrate to a heat treatment after the ion diffusion process.

14. 13. The method of claim 12, wherein the ion diffusion process comprises immersing the substrate in a first molten salt bath at a first temperature range, thereby compressing material at the first and second surfaces of the substrate.

15. The image light guide of claim 1 , wherein the substrate comprises a treated glass material.

16. The image light guide of claim 3 , wherein the second portion is operable to flex relative to the first portion along multiple axes without delaminating the polymer layer.

17. An image light guide for transmitting a virtual image, comprising: a waveguide including a glass substrate having a first surface and a second surface opposite the first surface, and a coating coupled to the first surface of the substrate; an incoupling diffractive optical element formed in the coating and operable to direct an image-bearing light beam into the waveguide; an outcoupling diffractive optical element formed in the coating and operable to direct the image-bearing light beam from the waveguide to an eyebox; the waveguide comprises a first portion and a second portion, the second portion operable to deflect by at least 10 degrees relative to the first portion, and the coating operable to deflect with the substrate.

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