Input / output coupling lattice and display including the same

Abstract

A head-mounted display system includes a waveguide configured to guide light from an optical projection system coupled within the waveguide, and a grating structure optically coupled to the waveguide and configured to couple light from the optical projection system into the waveguide. The grating structure is a grating layer having a plurality of ridges with a blaze profile in at least one cross-section, the blaze profile having an anti-blaze angle of 85° or less, and one or more additional layers on the grating layer, the additional layer including a first layer of material having a refractive index of 1.5 or less at the operating wavelength of the head-mounted display, the first layer being the outermost layer of the grating structure.

Description

Technical Field

[0001] (Cross - Reference to Related Applications) This application claims the benefit of priority of U.S. Patent Application No. 63 / 342,004, filed on May 13, 2022, and U.S. Patent Application No. 63 / 348,694, filed on Jun. 3, 2022, the contents of which are incorporated herein by reference.

[0002] The present disclosure relates to display systems, and more particularly, to input coupling gratings (ICGs) or output coupling gratings for augmented and virtual reality display systems and their combination use.

Background Art

[0003] Modern computing and display technologies have facilitated the development of systems for so - called “virtual reality” or “augmented reality” experiences, in which digitally reproduced images or portions thereof are presented to a user in a manner that appears or can be perceived as being real. Virtual reality, i.e., the “VR” scenario, typically involves the presentation of digital or virtual image information without transparency to other actual real - world visual inputs, and augmented reality, i.e., the “AR” scenario, typically involves the presentation of digital or virtual image information as an augmentation to the visualization of the actual world around the user. Mixed reality, i.e., the “MR” scenario, is a type of AR scenario and typically involves virtual objects integrated into and responsive to the natural world. For example, in an MR scenario, AR image content can be perceived as being blocked by or otherwise interacting with objects within the real world.

[0004] Referring to FIG. 1, an augmented reality scene 10 is depicted, and to the user of AR technology, a real-world park-like setting 20 featuring people, trees, buildings in the background, and a concrete platform 30 can be seen. In addition to these items, the user of AR technology also "sees" and perceives a robotic image 40 standing on the real-world platform 30 and "virtual content" such as a flying comic-like avatar character 50 that appears to be an anthropomorphic honeybee, but these elements 40, 50 do not exist in the real world. The human visual perception system is complex, and it is difficult to produce AR technology that promotes a comfortable, natural, and rich presentation of virtual image elements among other virtual or real-world image elements.

[0005] The systems and methods disclosed herein address various issues related to AR and VR technologies.

Summary of the Invention

Means for Solving the Problems

[0006] A grating structure suitable for an input coupling grating (ICG) for coupling light into an optical waveguide, an orthogonal pupil expander (OPE) for expanding an eyebox by separating internally coupled light into a plurality of parallel light beams, an exit pupil expander (EPE) for redirecting and externally coupling light out of the optical waveguide, and a combined pupil expander (CPE) for implementing both sides of the OPE and EPE is disclosed, which is substantially insensitive to polarization, has a low back reflectivity, and is described as enabling operation over a wide range of input angles. Such a grating structure can be used in an in-line alignment configuration, and the ICGs for a plurality of stacked optical waveguides are aligned along a common optical path. Such an ICG may be particularly useful for a head-mounted display using a micro LED (μLED) light projection system that can emit non-polarized light over a wide range of angles.

[0007] Examples of grating structures include asymmetric blazed (or "blaze") gratings that are either formed from a high refractive index material and / or coated with a high refractive index material (such as titanium dioxide, gallium phosphide, silicon carbide, and others). Such high refractive index layers can provide a relatively low optical loss rate to the grating structure. Due to the high refractive index film, the reflected light can become significant (e.g., > 10% for some angles of incidence), which can cause undesirable results in the virtual image, such as undesirable back-reflection coupling and afterimages, reduced contrast, etc. Reducing this back-reflection can lead to more light being diffracted and coupled in the correct order in TIR within the waveguide, and thus the benefits of reduced reflection can outweigh the advantages of light recycling that can occur from the reflection.

[0008] The grating structures described herein can have a low reflectivity with high diffraction efficiency in both the transverse electric (TE) and transverse magnetic (TM) polarization modes. Such optical performance can be used, for example, in projectors that use unpolarized light and ideally operate with reduced back-reflection from the grating structure into the lens of the projection system, such as a μLED projection system, to enable the overall eyepiece efficiency per watt of energy. Such grating structures can also utilize the use of high diffraction efficiency in the orthogonal polarization states using a grating structure that operates in the transmission mode where all colors (e.g., R, G, B) are guided within a single high refractive index active layer, and thus can function well for a single active layer architecture that enables the use of a μLED projection system.

[0009] The grating structures described herein can have high directivity, which can enable the propagation of light within an eyepiece that includes the grating structure in a controlled direction. For example, a blazed grating can concentrate the diffracted light in a specific direction determined by the geometry of the blazed grating more than what an unblazed grating can achieve.

[0010] Various aspects of the disclosed subject matter are summarized as follows.

[0011] Generally, in a first aspect, the present disclosure provides a head-mounted display system comprising a head-mountable frame, an optical projection system configured to output light and provide image content, a waveguide supported by the frame and configured to guide at least a portion of the light from the optical projection system coupled therein, and a grating structure optically coupled to the waveguide and configured to couple the light from the optical projection system into the waveguide. The grating structure includes a grating layer having a plurality of (e.g., parallel) ridges with a blaze profile in at least one cross-section, the blaze profile having an anti-blaze angle of 85° or less, and one or more additional layers on the grating layer, the one or more additional layers including a first layer of material having a refractive index of 1.5 or less at the operating wavelength of the head-mounted display, the first layer being the outermost layer of the grating structure.

[0012] Examples of head-mounted display systems can include one or more of the following features. For example, the blaze profile can have a blaze angle of 95° or greater. The ridge can have a profile shape selected from the group including trapezoidal, parallelogram, triangular, and stepped. The anti-blaze angle can be in the range of 1° to 89° (e.g., 5° to 85°, 20° to 60°, 45° to 75°, 50° to 60°, 60° to 70°, 70° to 80°). The ridge can have a height in the range of 10 nm to 1,000 nm (e.g., 50 nm to 500 nm, 100 nm to 400 nm, 200 nm to 400 nm, 250 nm to 350 nm). The grating can have a pitch in the range of 100 nm to 5,000 nm (e.g., 100 nm to 2,500 nm, 100 nm to 1,000 nm, 200 nm to 750 nm, 250 nm to 500 nm, 300 nm to 400 nm). The grating can have a duty cycle in the range of 5% to 95% (e.g., 10% to 75%, 20% to 50%, 30% to 40%). The first layer can have a thickness in the range of 5 nm to 500 nm (e.g., 10 nm to 400 nm, 20 nm to 300 nm, 50 nm to 250 nm, 100 nm to 200 nm, 130 nm to 170 nm).

[0013] In some implementations, one or more additional layers include a second layer between the first layer and the grating layer, and the second layer includes a second material having a refractive index greater than 1.5 (e.g., greater than 1.6 or greater, greater than 1.7 or greater, greater than 1.8 or greater, greater than 1.9 or greater) at the operating wavelength. The second layer can have a thickness in the range of 5 nm to 500 nm (e.g., 10 nm to 400 nm, 20 nm to 300 nm, 50 nm to 250 nm, 100 nm to 200 nm, 130 nm to 170 nm).

[0014] The grating layer can include a grating material having a refractive index of 1.5 or greater (e.g., greater than 1.6, greater than 1.7, greater than 1.8, greater than 1.9) at the operating wavelength. The grating material can include a crosslinked polymer (e.g., a thermally or UV crosslinked polymer). The grating material can include nanoparticles (e.g., TiO 2 or ZrO 2 nanoparticles).

[0015] The grating structure can be at least partially transmissive (e.g., highly transmissive or partially reflective) at the operating wavelength.

[0016] The grating structure can be configured to couple light into the waveguide at the operating wavelength corresponding to a plurality of different color pixels of the light projection system during operation.

[0017] The grating layer and the waveguide can be made of the same material. The material can include a polymer. The material can have a refractive index of 1.7 or greater (e.g., greater than 1.8, greater than 1.9, greater than 2.0, greater than 2.1). The material can be a composite material. The composite material can include nanoparticles.

[0018] The light from the light projection system can be non-polarized light.

[0019] The light projection system can include a micro-LED display, an LCoS display, or a laser beam scanner display.

[0020] A head-mounted display can include one or more additional waveguides and one or more additional grating structures, each associated with a corresponding one of the additional waveguides. Each grating structure of the waveguides can be arranged in an in-line configuration. At least one of the grating structures can be a reflective grating. The reflective grating can be the grating structure of the waveguide farthest from the light projection system (e.g., for recycling light).

[0021] At least some of the ridges can have a single-stage geometry. At least some of the ridges can have a multi-stage geometry.

[0022] Generally, in another aspect, the present disclosure features an article including a waveguide layer made of a waveguide material having a refractive index of 1.7 or greater at an operating wavelength, and a grating structure on a surface of the waveguide layer. The grating structure is a grating layer having a grating composed of a plurality of (e.g., parallel) ridges having a blazed profile in at least one cross-section, the blazed profile having an anti-blaze angle of 89° or less, a height in the range of 10 nm to 1,000 nm, and a duty cycle in the range of 5% to 95%, and one or more additional layers disposed on the grating layer, the one or more layers including a first layer of a material having a thickness in the range of 5 nm to 500 nm and a refractive index of 1.5 or less at the operating wavelength, the first layer being the outermost layer of the grating structure, and one or more additional layers.

[0023] The implementation of the article can include one or more features of the foregoing aspects of the previous disclosure.

[0024] Generally, in a further aspect, the present disclosure features a head-mounted display system including a head-mountable frame, a light projection system configured to output light and provide image content, a waveguide supported by the frame and configured to guide at least a portion of light from the light projection system coupled therein, and a grating structure optically coupled to the waveguide and configured to couple light guided by the waveguide out of the waveguide. The grating structure includes a grating layer having a plurality of (e.g., parallel) ridges with a blazed profile in at least one cross-section, the blazed profile having an anti-blaze angle of 89° or less, and one or more additional layers on the grating layer, the one or more additional layers including a first layer of material having a refractive index of 1.5 or less at the operating wavelength of the head-mounted display, the first layer being the outermost layer of the grating structure.

[0025] Implementations of the head-mounted display system can include one or more of the following features and / or other aspects of the features. For example, the grating structure can be part of an exit pupil expander (EPE) or a combined pupil expander (CPE). The grating structure can be part of an orthogonal pupil expander.

[0026] Generally, in another aspect, the present disclosure features a device including a waveguide configured to guide light at an operating wavelength, and a grating layer supported by the waveguide, the grating layer including a plurality of spaced ridges of grating material forming a grating having a blazed profile in at least one cross-section, each ridge having a blazed side and an anti-blazed side opposite the blazed side, the anti-blazed side having a concave cross-sectional shape, and one or more additional layers supported by the grating layer, the one or more additional layers including a first layer including a first material different from the grating material, the first material being located on and between the ridges.

[0027] Generally, in another aspect, the present disclosure includes a waveguide for guiding light at an operating wavelength, and a grating layer extending in a plane, the grating layer being supported by the waveguide and including a plurality of spaced ridges of grating material forming a grating having a blaze profile in at least one cross-section, each ridge having a blaze side and an anti-blaze side opposite the blaze side, the anti-blaze side having a non-linear shape in cross-section, the apex of the anti-blaze side being aligned in cross-section with the bottom point of the anti-blaze side in a direction normal to the plane of the grating layer, a grating layer, and one or more additional layers supported by the grating layer, the one or more additional layers including a first layer including a first material different from the grating material, the first material being located on and between the ridges, and the device including the one or more additional layers.

[0028] Generally, in another aspect, the present disclosure includes a waveguide for guiding light at an operating wavelength, a grating layer supported by the waveguide, the grating layer including a plurality of spaced ridges of grating material forming a grating having a blaze profile in at least one cross-section, each ridge having a blaze side and an anti-blaze side opposite the blaze side, a grating layer, and one or more additional layers supported by the grating layer, the one or more additional layers including a first layer including a first material different from the grating material, the first material being located on and between the ridges, and with respect to at least some of the ridges, the device including the one or more additional layers such that the ridge and the one or more additional layers form a void on the anti-blaze side of the ridge.

[0029] Implementations of the three devices in these aspects can include one or more of the following features and / or features of other aspects. For example, the concave cross-sectional shape of the anti-blaze side includes a curved portion. The anti-blaze side can include a curved portion.

[0030] The radius of curvature of the curved portion can be within the range of 20 nm to 500 nm.

[0031] In some embodiments, the concave cross-sectional shape on the anti-blaze side includes one or more line segments. The anti-blaze side can include one or more line segments. The first line segment can have a positive slope, the second line segment can have a negative slope, and the first line segment can be higher in the vertical direction than the second line segment. In some embodiments, at least two of the one or more line segments intersect at an obtuse angle. The length of at least one of the line segments can be within the range of 5 nm to 500 nm.

[0032] In some embodiments, at least one edge of one or more additional layers and the anti-blaze side define a void.

[0033] The refractive index of the first layer of one or more additional layers can be at least 1.5 at the operating wavelength.

[0034] One or more additional layers can include a second layer, and the refractive index of the second layer is at least 1.5 at the operating wavelength.

[0035] In some embodiments, one or more additional layers do not coat the anti-blaze side of each ridge.

[0036] Each ridge can have a blaze angle of 95° or greater. Each ridge can have an anti-blaze angle within the range of 1° to 89°. The ridge can have a height within the range of 10 nm to 1,000 nm. The grating can have a pitch within the range of 100 nm to 5,000 nm. The grating can have a duty cycle within the range of 5% to 95%.

[0037] The first layer can have a thickness in the range of 5 nm to 500 nm. The second layer can have a thickness in the range of 5 nm to 500 nm.

[0038] The grating material can include a cross-linked polymer. The grating material can include nanoparticles.

[0039] The grating structure can be at least partially transmissive at the operating wavelength.

[0040] The grating layer and the waveguide can be made of the same material.

[0041] In some embodiments, the material includes a polymer. The material can have a refractive index of 1.7 or greater. The material can be a synthetic material (e.g., including nanoparticles).

[0042] The device can include one or more additional waveguides and one or more additional grating structures, each associated with a corresponding one of the additional waveguides.

[0043] The respective grating structures of the waveguides can be arranged in an in-line configuration. At least one of the grating structures can be a reflective grating.

[0044] At least some of the ridges can include a blazed side with a single-stage geometry. At least some of the ridges can include a blazed side with a multi-stage geometry.

[0045] In a further aspect, the present disclosure features a head-mounted display (HMD) configured to be worn on a user's head, the HMD including a frame, a pair of optical elements supported by the frame such that each optical element of the pair of optical elements can be positioned in front of the user's eyes, a device as described in the foregoing aspect disposed on at least one of the optical elements of the pair of optical elements, and a projection system configured to project light into a waveguide of the device for display to the user's eyes.

[0046] Each optical element can include a distal and a proximal surface, the proximal surface being closer to the user's eye than the distal surface, and the grating of the device being disposed on the proximal surface.

[0047] Each optical element can include a distal and a proximal surface, the proximal surface being closer to the user's eye than the distal surface, and the grating of the device being disposed on the distal surface.

[0048] The grating structure can be configured to couple light into the waveguide at an operating wavelength corresponding to a plurality of different color pixels during operation.

[0049] The light from the light projection system can be polarized or non-polarized light.

[0050] The light projection system can include a micro-LED display, an LCoS display, or a laser beam scanner display.

[0051] The device can include one or more additional grating structures, and the grating structure furthest from the light projection system is a reflective grating.

[0052] Generally, in another aspect, the present disclosure includes depositing an etch stop layer on a substrate, depositing a grating material on the etch stop layer, depositing a blazed grating template on the grating material, using the blazed grating template to etch the grating material, thereby transferring the shape of the blazed grating template to the grating material to form a blazed grating, coating the blazed grating with an etch mask at a first non-zero angle with respect to the vertical direction so that the anti-blaze side of the grating remains uncoated, etching at a second non-zero angle with respect to the vertical direction with a sign opposite to the sign of the first non-zero angle, thereby removing an inner portion of the anti-blaze side, and stripping the etch mask from the blazed grating.

[0053] The implementation of the head-mounted display system can include one or more than one of the following features and / or features of other aspects. For example, the substrate is a waveguide.

[0054] The shape of the blazed grating template can extend vertically beyond the shape of the blazed grating.

[0055] The step of etching the grating material can be completed before the blazed grating template is fully used.

[0056] The method can include stripping the remaining portion of the blazed grating template from the grating material before coating the blazed grating with the etch mask.

[0057] The step of etching the grating material can include at least one of dry plasma etching, chemical etching, and wet chemical etching.

[0058] The first non-zero angle can be determined by the anti-blaze angle of the blazed grating. The absolute value of the first non-zero angle can be equal to at least the difference between the anti-blaze angle and 90°.

[0059] The anti-blaze side can include a concave curved portion. The anti-blaze side can include one or more line segments.

[0060] The method can further include coating the blazed grating with one or additional layers, where at least one of the one or more additional layers includes a material having a refractive index of at least 1.5 at the operating wavelength. Coating the blazed grating with one or additional layers can lead to the formation of a gap between at least one edge of the one or more additional layers and the anti-blaze side.

[0061] Generally, in another aspect, the present disclosure features a head-mounted display (HMD) including a waveguide for guiding light at an operating wavelength, a grating layer supported by the waveguide, the grating layer including a plurality of spaced ridges of grating material forming a grating having a blaze profile in at least one cross-section, each ridge having a blaze side and an anti-blaze side opposite the blaze side, the anti-blaze side having a concave cross-sectional shape, a first layer supported by the grating layer and including one or more additional layers, the one or more additional layers including a first material different from the grating material, the first material including the one or more additional layers located on and between the ridges.

[0062] The implementation of the head-mounted display system can include one or more of the following features and / or other aspect features. For example, the diffraction efficiency of the grating structure for non-polarized light incidence over a range of incident angles from -20° to +20° across a wavelength range of 400 nm to 700 nm can be 10% or more (e.g., 20% or more, 30% or more).

[0063] The retroreflection of the grating structure can be 30% or less for non-polarized light incidence over a range of incident angles from -20° to +20° across a wavelength range of 400 nm to 700 nm.

[0064] The HMD can include a projection system, and during operation, the grating structure receives non-polarized light or polarized light from the projection system.

[0065] The grating structure can be positioned to receive light from the projection system that travels through the waveguide before being internally coupled into the waveguide by the grating structure.

[0066] Other features and advantages will become apparent from the drawings, the following description, and the claims.

Brief Description of the Drawings

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[0100] Throughout the drawings, reference numbers may be reused to indicate correspondence between referenced elements. The drawings are provided to illustrate exemplary implementations described in this specification and are not intended to limit the scope of the present disclosure.

Best Mode for Carrying Out the Invention

[0101] (Detailed Description) An AR system can still display virtual content to a user or viewer while allowing the user to see the surrounding world. Preferably, this content is displayed on a head-mounted display as part of eyewear that projects, for example, image information onto the user's eyes. In addition, the display can also transmit light from the surrounding environment to the user's eyes, allowing a view of the surrounding environment. As used herein, it should be understood that a "head-mounted" or "head-mountable" display is a display that can be mounted on the head of a viewer or user.

[0102] In some AR systems, a virtual / augmented / composite display having a relatively high field of view (FOV) can improve the viewing experience. The FOV of a display depends on the angle of the light output by the waveguide of the eyepiece through which the image projected into the viewer's eye can be seen. For example, a waveguide having a relatively high refractive index of 1.7 or greater can provide a relatively high FOV. However, in order to efficiently couple light into a high refractive index waveguide, a diffractive optical coupling element should also correspondingly have a high refractive index. Among other advantages, for some displays for AR systems according to the implementations described herein to achieve this goal, they include waveguides containing materials with a relatively high refractive index (e.g., greater than 1.8, such as greater than or equal to 2.0) having individual diffraction gratings formed thereon with a correspondingly high refractive index, such as oxides based on Ti, Ta, or Li. For example, the diffraction grating may be formed directly on a Ti, Ta, or Li-based oxide waveguide by patterning a surface portion of the waveguide formed from a Ti, Ta, or Li-based oxide.

[0103] Some high refractive index diffractive optical coupling elements, such as internal or external coupling optical elements, have strong polarization dependence. For example, an internal coupling grating (ICG) for internally coupling light into a waveguide, where the diffractive optical coupling element includes a high refractive index material, can receive significantly more light of a given polarization than light of another polarization. Such an element can, for example, internally couple light with TM polarization into the waveguide at a rate of about three times that of light with TE polarization. Diffractive optical coupling elements with this type of polarization dependence can have reduced efficiency (due to the poor efficiency and overall blocking of one polarization), and can also create coherent artifacts and reduce the uniformity of the far-field image formed by the light coupled out of the birefringent waveguide. To obtain diffractive optical coupling elements that are insensitive to polarization or have at least reduced polarization sensitivity (e.g., coupling light with a certain efficiency that is relatively independent of polarization), some displays for AR systems according to various implementations described herein include waveguides with diffractive gratings formed using a blazed geometry. The diffractive grating may also be formed directly within the waveguide, which may include a high refractive index material (e.g., having a refractive index of at least 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, or up to 2.7 or any value within any range between these values). The diffractive grating may be formed, for example, by patterning a high refractive index material using a blazed geometry, such as in a Ti, Ta, or Li-based oxide like lithium niobate (LiNbO 3 ) or lithium tantalate (LiTaO 3 ), or in a high refractive index material such as zirconium dioxide (ZrO 2 ), titanium dioxide (TiO 2 ) or silicon carbide (SiC).

[0104] Reference is now made to the drawings, where like reference numerals refer to like parts throughout. Unless otherwise indicated, the drawings are schematic and are not necessarily drawn to scale.

[0105] FIG. 2 illustrates a conventional display system for simulating a three-dimensional image for a user. The eyes of the user are separated, and when looking at a real object in space, each eye has a slightly different view of the object and can form an image of the object at different locations on the retina of each eye. This can be referred to as binocular disparity and can be utilized by the human visual system to provide a perception of depth. The conventional display system simulates binocular disparity by presenting two distinct images 190, 200 with slightly different views of one identical virtual object for each of the eyes 210, 220, corresponding to the views of the virtual object that would be seen by each eye as if the virtual object were a real object at the desired depth. These images provide binocular cues that can be interpreted by the user's visual system to derive a perception of depth.

[0106] Continuing to refer to FIG. 2, the images 190, 200 are separated from the eyes 210, 220 by a distance 230 on the z-axis. The z-axis is parallel to the optical axis of the viewer in a state where the eye is fixated on an object at optical infinity directly in front of the viewer. The images 190, 200 are flat and at a fixed distance from the eyes 210, 220. Based on the slightly different views of the virtual object in the images presented to the eyes 210, 220 respectively, the eyes can necessarily rotate so that the images of the object come to corresponding points on the respective retinas of the eyes and a single binocular vision is maintained. This rotation can converge the respective lines of sight of the eyes 210, 220 onto a point in the space where the virtual object is perceived to exist. As a result, the provision of a three-dimensional image has conventionally involved being able to manipulate the convergence / divergence movement of the user's eyes 210, 220 and providing binocular cues that the human visual system interprets to provide a perception of depth.

[0107] However, generating realistic and comfortable perception of depth is difficult. It should be understood that light from objects at different distances from the eye has wavefronts with different amounts of divergence. FIGS. 3A-3C illustrate the relationship between distance and divergence of light rays. The distances between the object and the eye 210 are represented in the order of decreasing distances R1, R2, and R3. As shown in FIGS. 3A-3C, the light rays diverge more as the distance to the object decreases. Conversely, as the distance increases, the light rays become more collimated. In other words, it can be said that the light field produced by a point (an object or a part of an object) has a spherical wavefront curvature that is a function of the distance the point is away from the user's eye. The curvature increases as the distance between the object and the eye 210 decreases. Only the single eye 210 is illustrated in FIGS. 3A-3C and other figures herein for clarity of illustration, but the discussion regarding the eye 210 can be applied to both eyes 210 and 220 of the viewer.

[0108] Continuing to refer to FIGS. 3A-3C, light from an object that the viewer's eye is fixated on can have different degrees of wavefront divergence. Due to the different amounts of wavefront divergence, the light can be focused differently by the lens of the eye, which in turn can require the lens to take on different shapes to form a focused image on the retina of the eye. If a focused image is not formed on the retina, the resulting retinal blur acts as a cue for accommodation, causing a change in the shape of the lens of the eye until a focused image is formed on the retina. For example, the cue for accommodation induces relaxation or contraction of the ciliary muscle that surrounds the lens of the eye, thereby modulating the force applied to the zonular fibers that hold the lens, and thus changing the shape of the lens of the eye until the retinal blur of the fixated object is eliminated or minimized, thereby forming a focused image of the fixated object on the retina (e.g., the fovea) of the eye. The process by which the lens of the eye changes shape can be referred to as accommodation, and the shape of the lens of the eye required to form a focused image of a fixated object on the retina (e.g., the fovea) of the eye can be referred to as the accommodative state.

[0109] Referring now to FIG. 4A, the representation of the accommodation-convergence / divergence movement response of the human visual system is illustrated. Eye movements to fixate an object cause the eyes to receive light from the object, and the light forms an image on each of the retinas of the eyes. The presence of retinal blur in the image formed on the retina can provide a cue for accommodation, and the relative location of the image on the retina can provide a cue for convergence / divergence movement. The cue for accommodation causes accommodation to occur, causing the eye's lens to assume a particular accommodation state that forms a focused image of the object on the eye's retina (e.g., the fovea), respectively. On the other hand, the cue for convergence / divergence movement causes a convergence / divergence movement (rotation of the eye) such that the images formed on each retina of each eye are at corresponding retinal points that maintain single binocular vision. At these positions, it can be said that the eyes are in a particular convergence / divergence movement state. Continuing to refer to FIG. 4A, accommodation can be understood as the process by which the eye achieves a particular accommodation state, and convergence / divergence movement can be understood as the process by which the eye achieves a particular convergence / divergence movement state. As shown in FIG. 4A, the accommodation and convergence / divergence movement states of the eyes can change when the user fixates on another object. For example, the accommodated state can change when the user fixates on a new object at a different depth on the z-axis.

[0110] Without being limited by theory, it is believed that the viewer of an object can perceive the object as "three-dimensional" due to the combination of convergence / divergence movement and accommodation. As described above, the convergence / divergence movement of the two eyes relative to each other (e.g., the movement of the pupils towards or away from each other, the rotation of the eyes that converges the lines of sight of the eyes to fixate on an object) is closely associated with the accommodation of the eye's lens. Under normal conditions, a change in the shape of the eye's lens to change the focus from one object to another object at a different distance will automatically cause a corresponding change in the convergence / divergence movement to the same distance under a relationship known as the "accommodation-convergence / divergence reflex". Similarly, a change in convergence / divergence movement will induce a corresponding change in the shape of the lens under normal conditions.

[0111] Referring now to FIG. 4B, examples of different accommodation and convergence / divergence states of the eyes are illustrated. A pair of eyes 222a fixates on an object at optical infinity, while a pair of eyes 222b fixates on a point 221 that is less than optical infinity. It should be noted that the convergence / divergence states of each pair of eyes are different, with a pair of eyes 222a being directed straight ahead, while a pair of eyes 222 converge on point 221. The accommodation states of the eyes forming each pair of eyes 222a and 222b also differ, as represented by the different shapes of the lenses 210a, 220a.

[0112] Unfortunately, many users of conventional "3-D" display systems find such conventional systems uncomfortable or do not perceive any sense of depth, due to the mismatch between accommodation and convergence / divergence states in these displays. As described above, many stereoscopic or "3-D" display systems present a scene by providing slightly different images to each eye. Such systems are uncomfortable for many viewers because they simply provide different presentations of the scene, causing a change in the convergence / divergence state of the eyes, but without a corresponding change in the accommodation state of those eyes. Rather, the images are presented at a fixed distance from the eyes by the display such that the eyes view all the image information in a single accommodation state. Such an arrangement goes against the "accommodation-convergence / divergence reflex" by causing a change in the convergence / divergence state without a corresponding change in the accommodation state. This mismatch is thought to cause discomfort to the viewer. A display system that provides a better match between accommodation and convergence / divergence can create a more realistic and comfortable simulation of a three-dimensional image.

[0113] Although not limited by theory, the human eye is typically thought to be able to interpret a finite number of depth planes and provide depth perception. As a result, a highly realistic simulation of the perceived depth can be achieved by providing different presentations of images corresponding to each of these limited number of depth planes to the eye. In some implementations, the different presentations can provide both cues for convergence / divergence motion and corresponding cues for accommodation, thereby providing a physiologically correct accommodation-convergence / divergence match.

[0114] Continuing to refer to FIG. 4B, two depth planes 240 corresponding to different distances in space from eyes 210, 220 are illustrated. For a given depth plane 240, convergence / divergence motion cues may be provided by appropriately displaying images from different viewpoints for each of eyes 210, 220. Additionally, for a given depth plane 240, the light forming the images provided to each eye 210, 220 may have a wavefront divergence corresponding to a light field generated by a point at the distance of that depth plane 240.

[0115] In the illustrated implementation, the distance along the z-axis of depth plane 240 containing point 221 is 1 m. As used herein, the distance or depth along the z-axis may be measured using a zero point located at the exit pupil of the user's eye. Thus, a depth plane 240 located at a depth of 1 m corresponds to a distance 1 m away from the exit pupil of the user's eye on the optical axis of those eyes with the eyes directed towards optical infinity. As an approximation, the depth or distance along the z-axis is measured from the front of the user's eye to the display (e.g., from the surface of the waveguide), and a value related to the distance between the device and the exit pupil of the user's eye may be added. That value may be referred to as the pupil distance and corresponds to the distance between the exit pupil of the user's eye and the display worn by the user in front of the eye. In practice, the value for the pupil distance may generally be a normalized value used for all viewers. For example, the pupil distance may be assumed to be 20 mm, and the depth plane at a depth of 1 m may be at a distance of 980 mm in front of the display.

[0116] Referring now to FIGS. 4C and 4D, examples of matched vergence accommodation - convergence / divergence movement distances and mismatched vergence accommodation - convergence / divergence movement distances are illustrated, respectively. As shown in FIG. 4C, the display system may provide an image of a virtual object to each eye 210, 220. The image may cause the eyes 210, 220 to assume a convergence / divergence movement state in which the eyes converge on a point 15 on the depth plane 240. Additionally, the image may be formed by light having a wavefront curvature corresponding to the real object in the depth plane 240. As a result, the eyes 210, 220 assume an accommodation state in which the image is in focus on the retinas of those eyes. Thus, the user may perceive the virtual object as being at the point 15 on the depth plane 240.

[0117] It should be understood that the accommodation and convergence / divergence movement states of the eyes 210, 220 are each associated with a specific distance on the z - axis. For example, an object at a specific distance from the eyes 210, 220 causes those eyes to assume a specific accommodation state based on the distance of the object. The distance associated with a specific accommodation state may be referred to as the accommodation distance Ad. Similarly, there exists a specific vergence movement distance Vd associated with a specific convergence / divergence movement state or the eyes at a particular position relative to each other. When the accommodation distance and the vergence movement distance match, the relationship between accommodation and convergence / divergence movement can be said to be physiologically correct. This is considered to be the most comfortable scenario for the viewer.

[0118] However, in a stereoscopic display, the focusing distance and the vergence / accommodation movement distance may not always match. For example, as shown in FIG. 4D, the images displayed on eyes 210, 220 may be displayed with wavefront divergence corresponding to depth plane 240, and eyes 210, 220 may take a specific focusing state in which points 15a, 15b on that depth plane are in focus. However, the images displayed on eyes 210, 220 may provide a cue for vergence / accommodation movement that converges eyes 210, 220 on a point 15 that is not located on depth plane 240. As a result, in some implementations, the focusing distance corresponds to the distance from the exit pupils of eyes 210, 220 to depth plane 240, while the vergence / accommodation movement distance corresponds to a greater distance from the exit pupils of eyes 210, 220 to point 15. The focusing distance is different from the vergence / accommodation movement distance. As a result, there is a focusing-vergence / accommodation movement mismatch. Such a mismatch is considered undesirable and can cause discomfort to the user. It should be understood that the mismatch corresponds to a distance (e.g., Vd - Ad) and can be characterized using diopters.

[0119] It should be understood that in some implementations, reference points other than the exit pupils of eyes 210, 220 can also be used to determine the distance for determining the focusing-vergence / accommodation movement mismatch as long as the same reference point is used for both the focusing distance and the vergence / accommodation movement distance. For example, the distance can be measured from the cornea to the depth plane, from the retina to the depth plane, from the eyepiece (e.g., the waveguide of the display device) to the depth plane, etc.

[0120] Although not limited by theory, it is believed that a user can physiologically perceive vergence-accommodation mismatches of up to about 0.25 diopters, up to about 0.33 diopters, and up to about 0.5 diopters as being correct without the mismatch itself causing significant discomfort. In some implementations, the display systems disclosed herein (e.g., display system 250, FIG. 6) present an image to a viewer that has a vergence-accommodation mismatch of about 0.5 diopters or less. In some other implementations, the vergence-accommodation mismatch of the image provided by the display system is about 0.33 diopters or less. In still other implementations, the vergence-accommodation mismatch of the image provided by the display system is about 0.25 diopters or less, including about 0.1 diopters or less.

[0121] FIG. 5 illustrates a side view of an approach for simulating a three-dimensional image by correcting wavefront divergence. The display system includes a waveguide 270 configured to receive light rays 770 encoded with image information and output the light to the user's eye 210. The waveguide 270 may output an exit beam 650 with a defined amount of wavefront divergence corresponding to the wavefront divergence of the light field produced by a point on a desired depth plane 240. In some implementations, the same amount of wavefront divergence is provided for all objects presented on that depth plane. Additionally, it will be shown that the user's other eye may be provided with image information from a similar waveguide.

[0122] In some cases, a single waveguide may be configured to output light with a set amount of wavefront divergence corresponding to a single or limited number of depth planes, and / or the waveguide may be configured to output light within a limited range of wavelengths. As a result, in some implementations, multiple or stacked waveguides may be utilized to provide different amounts of wavefront divergence for different depth planes and / or to output light within different ranges of wavelengths. It should be understood that, as used herein, a depth plane may follow the contour of a flat or curved surface.

[0123] FIG. 6 illustrates an example of a stack of waveguides for outputting image information to a user. The display system 250 includes a stack or stacked waveguide assembly 260 of waveguides that can be utilized to provide three-dimensional perception to the eye / brain using a plurality of waveguides 270, 280, 290, 300, 310. It should be understood that the display system 250 may be considered a light field display in some implementations. Additionally, the waveguide assembly 260 may also be referred to as an eyepiece.

[0124] In some implementations, the display system 250 may be configured to provide a substantially continuous cue for convergence / divergence movement and a plurality of discrete cues for depth adjustment. The cue for convergence / divergence movement may be provided by displaying different images to each of the user's eyes, and the cue for depth adjustment may be provided by outputting light that forms an image with a selectable discrete amount of wavefront divergence. In other words, the display system 250 may be configured to output light with a variable level of wavefront divergence. In some implementations, each discrete level of wavefront divergence may correspond to a particular depth plane and may be provided by a particular one of the waveguides 270, 280, 290, 300, 310.

[0125] Continuing to refer to FIG. 6, waveguide assembly 260 may also include a plurality of features 320, 330, 340, 350 between the waveguides. In some implementations, features 320, 330, 340, 350 may be one or more lenses. Waveguides 270, 280, 290, 300, 310, and / or the plurality of lenses 320, 330, 340, 350 may be configured to transmit image information to the eye using various levels of wavefront curvature or ray divergence. Each waveguide level may be associated with a particular depth plane and may be configured to output image information corresponding to that depth plane. Image input devices 360, 370, 380, 390, 400 may function as light sources for the waveguides and may be utilized to input image information into waveguides 270, 280, 290, 300, 310, respectively, configured to disperse incident light across each individual waveguide for output toward eye 210 as described herein. Light exits from output surfaces 410, 420, 430, 440, 450 of image input devices 360, 370, 380, 390, 400 and is input into corresponding input surfaces 460, 470, 480, 490, 500 of waveguides 270, 280, 290, 300, 310. In some implementations, input surfaces 460, 470, 480, 490, 500 may each be an edge of the corresponding waveguide or a portion of the major surface of the corresponding waveguide (i.e., one of the waveguide surfaces directly facing the world 510 or the viewer's eye 210). In some implementations, a single beam of light (e.g., a collimated beam) may be input into each waveguide and output an entire field of cloned collimated beams directed toward eye 210 at a particular angle (and amount of divergence) corresponding to the depth plane associated with the particular waveguide. In some implementations, a single one of image input devices 360, 370, 380, 390, 400 may be associated with and input light into a plurality (e.g., three) of waveguides 270, 280, 290, 300, 310.

[0126] In some implementations, the image input devices 360, 370, 380, 390, 400 are individual displays that each produce image information for input into their respective waveguides 270, 280, 290, 300, 310. In some other implementations, the image input devices 360, 370, 380, 390, 400 are the output ends of a single multiplexed display that can send image information to each of the image input devices 360, 370, 380, 390, 400, for example, via one or more optical waveguides (such as an optical fiber cable). It should be understood that the image information provided by the image input devices 360, 370, 380, 390, 400 can include light of different wavelengths or colors (e.g., different primary colors as discussed herein).

[0127] In some implementations, the light input into the waveguides 270, 280, 290, 300, 310 is provided by an optical projector system 520 that includes an optical module 530 that can include a light emitter such as a light emitting diode (LED). The light from the optical module 530 can be directed via a beam splitter 550 to a light modulator 540, such as a spatial light modulator, and thereby modified. The light modulator 540 can be configured to vary the perceived intensity of the light input into the waveguides 270, 280, 290, 300, 310 and to encode the light with image information. Examples of spatial light modulators include liquid crystal displays (LCDs) including liquid crystal on silicon (LCOS) displays. The image input devices 360, 370, 380, 390, 400 are shown schematically and, in some implementations, these image input devices can represent different optical paths and locations within a common projection system that are configured to output light into the associated ones of the waveguides 270, 280, 290, 300, 310. In some implementations, the waveguides of the waveguide assembly 260 can function as ideal lenses while relaying the light input into the waveguides to the user's eye. In this concept, the object can be the spatial light modulator 540 and the image can be an image on a depth plane.

[0128] In some embodiments, the μLED display can be used within the optical projector system 520. The μLED display can emit non-polarized light over a wide range of angles. Thus, the μLED display can advantageously provide imaging with high efficiency over a wide field of view.

[0129] In some implementations, the display system 250 can be a scanning fiber display that includes one or more scanning fibers configured to project light into one or more waveguides 270, 280, 290, 300, 310 in various patterns (e.g., raster scan, spiral scan, Lissajous pattern, etc.) and ultimately into the viewer's eye 210. In some implementations, the illustrated image input devices 360, 370, 380, 390, 400 can schematically represent a single scanning fiber or a bundle of scanning fibers configured to input light into one or more waveguides 270, 280, 290, 300, 310. In some other implementations, the illustrated image input devices 360, 370, 380, 390, 400 can schematically represent a plurality of scanning fibers or a plurality of bundles of scanning fibers, each configured to input light into an associated one of the waveguides 270, 280, 290, 300, 310. It should be understood that one or more optical fibers can be configured to transmit light from the optical module 530 to one or more waveguides 270, 280, 290, 300, 310. One or more intervening optical structures can be provided between the scanning fiber or fibers and one or more waveguides 270, 280, 290, 300, 310 and can, for example, redirect light exiting the scanning fiber into one or more of the waveguides 270, 280, 290, 300, 310.

[0130] Controller 560 controls the operation of one or more of the stacked waveguide assemblies 260, including the operation of the image input devices 360, 370, 380, 390, 400, the optical module 530, and the optical modulator 540. In some implementations, controller 560 is part of the local processing and data module 140. Controller 560 includes programming (e.g., instructions in a non-transitory medium) that adjusts the timing and provision of image information to waveguides 270, 280, 290, 300, 310, for example, according to any of the various schemes disclosed herein. In some implementations, the controller may be a single integrated device or a distributed system connected by wired or wireless communication channels. Controller 560 may, in some implementations, be part of the local processing and data module 140 or the remote processing module 150 (FIG. 9D).

[0131] Continuing to refer to FIG. 6, the waveguides 270, 280, 290, 300, 310 may be configured to propagate light within each individual waveguide by total internal reflection (TIR). The waveguides 270, 280, 290, 300, 310 may each be planar, or have another shape (e.g., curved), with a major top surface and a bottom surface and an edge extending between their major top and bottom surfaces. In the illustrated configuration, the waveguides 270, 280, 290, 300, 310 each include external coupling optical elements 570, 580, 590, 600, 610 configured to extract light from the waveguide by redirecting the light propagating within each individual waveguide out of the waveguide and outputting the image information to the eye 210. The extracted light may also be referred to as external coupled light, and the external coupling optical elements may also be referred to as light extraction optical elements. The beam of extracted light may be output by the waveguide at the location where the light propagating within the waveguide impinges on the light extraction optical element. The external coupling optical elements 570, 580, 590, 600, 610 may be gratings, for example, including diffractive optical features as further discussed herein. For ease of explanation and clarity of the drawings, the external coupling optical elements 570, 580, 590, 600, 610 are shown disposed on the bottom major surface of the waveguides 270, 280, 290, 300, 310, but in some implementations, the external coupling optical elements 570, 580, 590, 600, 610 may be disposed on the top and / or bottom major surfaces, and / or directly within the volume of the waveguides 270, 280, 290, 300, 310, as further discussed herein. In some implementations, the external coupling optical elements 570, 580, 590, 600, 610 may be attached to a transparent substrate and formed within a layer of material forming the waveguides 270, 280, 290, 300, 310. In some other implementations, the waveguides 270, 280, 290, 300, 310 may be a monolithic piece of material, and the external coupling optical elements 570, 580, 590, 600, 610 may be formed on and / or within the surface of that piece of material.

[0132] Continuing to refer to FIG. 6, as discussed herein, each of the waveguides 270, 280, 290, 300, 310 is configured to output light and form an image corresponding to a particular depth plane. For example, the waveguide 270 closest to the eye may be configured to deliver collimated light (input into such waveguide 270) to the eye 210. The collimated light may represent an optically infinite focal plane. The next upper waveguide 280 may be configured to output collimated light that passes through a first lens 350 (e.g., a negative lens) before reaching the eye 210. Such a first lens 350 may be configured to create a slightly convex wavefront curvature such that the eye / brain interprets the light arising from the next upper waveguide 280 as arising from a first focal plane that is closer inwardly toward the eye 210 from the optically infinite. Similarly, the third upper waveguide 290 passes its output light through both the first and second lenses 350 and 340 before reaching the eye 210. The combined refractive power of the first and second lenses 350 and 340 may be configured to create another incremental amount of wavefront curvature such that the eye / brain interprets the light arising from the third upper waveguide 290 as arising from a second focal plane that is closer inwardly toward the person from the optically infinite than the light from the next upper waveguide 280 was.

[0133] The other waveguide layers 300, 310 and lenses 330, 320 are similarly configured, and the top waveguide 310 in the stack sends its output through all of the lenses between it and the eye for the converging focusing power that represents the focal plane closest to the person. When viewing / interpreting light originating from the world 510 on the other side of the stacked waveguide assembly 260, a compensating lens layer 620 may be disposed on top of the stack to compensate for the stack of lenses 320, 330, 340, 350. Such a configuration provides the same number of perceived focal planes as there are available waveguide / lens pairs. Both the external coupling optical elements of the waveguides and the focusing sides of the lenses may be static (i.e., not dynamic or electroactive). In some alternative implementations, one or both may be dynamic using electroactive features.

[0134] In some implementations, two or more of the waveguides 270, 280, 290, 300, 310 may have the same associated depth plane. For example, a plurality of waveguides 270, 280, 290, 300, 310 may be configured to output an image set at the same depth plane, or multiple subsets of waveguides 270, 280, 290, 300, 310 may be configured to output an image set at the same multiple depth planes, with one set per depth plane. This can provide the advantage of forming a tiled image to provide an extended field of view at those depth planes.

[0135] Continuing to refer to FIG. 6, the external coupling optical elements 570, 580, 590, 600, 610 may be configured to redirect light out of their respective waveguides for a particular depth plane associated with the waveguide and output this light with an appropriate amount of divergence or collimation. As a result, waveguides having different associated depth planes may have different configurations of the external coupling optical elements 570, 580, 590, 600, 610 that output light with different amounts of divergence depending on the associated depth plane. In some implementations, the external coupling optical elements 570, 580, 590, 600, 610 may be three-dimensional or surface features that are configured to output light at a particular angle. For example, the external coupling optical elements 570, 580, 590, 600, 610 may be volume holograms, surface holograms, and / or diffraction gratings. In some implementations, the features 320, 330, 340, 350 may not be lenses. Rather, they may simply be spacers (e.g., cladding layers and / or structures for forming voids).

[0136] In some implementations, the external coupling optical elements 570, 580, 590, 600, 610 are diffraction features or “diffractive optical elements” (also referred to herein as “DOEs”) that form a diffraction pattern. Preferably, the DOE has a sufficiently low diffraction efficiency such that only a portion of the light of the beam is deflected towards the eye 210 at each intersection of the DOE while the remainder continues to travel through the waveguide via TIR. The light carrying the image information is thus split into several associated output beams that exit the waveguide at various locations, resulting in a very uniform pattern of output emission towards the eye 210 with respect to this particular collimated beam that bounces within the waveguide.

[0137] In some implementations, one or more diffractive optical elements (DOEs) can be switchable between an “on” state where they actively diffract and an “off” state where they do not significantly diffract. For example, a switchable DOE may include a layer of polymer dispersed liquid crystals in which microdroplets contain a diffraction pattern within a host medium, and the refractive index of the microdroplets may be switched to substantially match that of the host material (in which case the pattern does not significantly diffract incident light), or the microdroplets may be switched to a refractive index that does not match that of the host medium (in which case the pattern actively diffracts incident light).

[0138] In some implementations, a camera assembly 630 (e.g., a digital camera including a visible light camera and an infrared light camera) may be provided to capture an image of the eye 210 and / or the tissue surrounding the eye 210, and for example, to detect user input and / or monitor the user's physiological state. As used herein, the camera may be any image capture device. In some implementations, the camera assembly 630 may include an image capture device and a light source (e.g., infrared light) that projects light onto the eye and then can be reflected by the eye and detected by the image capture device. In some implementations, the camera assembly 630 may be attached to the frame 80 (FIG. 9D) and may communicate electrically with a local processing and data module 140 and / or a remote processing module 150 that can process image information from the camera assembly 630. In some implementations, one camera assembly 630 may be utilized per eye to monitor each eye separately.

[0139] Referring now to FIG. 7, an example of an output beam output by a waveguide is shown. Although one waveguide is illustrated, it should be understood that other waveguides within the waveguide assembly 260 (FIG. 6) may function in a similar manner, and the waveguide assembly 260 includes a plurality of waveguides. Light 640 is input into the waveguide 270 at the input surface 460 of the waveguide 270 and propagates within the waveguide 270 by TIR. At the point where the light 640 impinges on the external coupling optical element 570, for example, a DOE, a portion of the light exits the waveguide as the output beam 650. The output beams 650 are illustrated as being substantially parallel, but as discussed herein, they may also be redirected to propagate to the eye 210 at an angle (e.g., to form a diverging output beam) depending on the depth plane associated with the waveguide 270. It should be understood that a waveguide with an external coupling optical element that externally couples light to form an image that appears to be set on a depth plane at a long distance (e.g., optical infinity) from the eye 210 may be shown. Other waveguides or other sets of external coupling optical elements may output a more diverging output beam pattern, which would require the eye 210 to focus at a closer distance and would be interpreted by the brain as light from a distance closer to the eye 210 than optical infinity.

[0140] In some implementations, a full-color image may be formed on each depth plane by overlaying the image on each of the primary colors, e.g., three or more primary colors. FIG. 8 illustrates an embodiment of a stacked waveguide assembly, and each depth plane includes an image formed using a plurality of different primary colors. The illustrated implementation shows depth planes 240a - 240f, although more or fewer depths may also be considered. Each depth plane may have three or more primary color images associated therewith, including a first image of a first color G, a second image of a second color R, and a third image of a third color B. Different depth planes are illustrated by different numbers associated with the diopter (dpt) following the letters G, R, and B. As a mere example, the numbers following each of these letters indicate the diopter (1 / m), i.e., the inverse distance of the depth plane from the viewer, and each box in the figure represents an individual primary color image. In some implementations, the exact placement of the depth planes for different primary colors may vary to account for differences in the focusing of light of different wavelengths by the eye. For example, the different primary color images for a given depth plane may be placed on depth planes corresponding to different distances from the user. Such an arrangement may increase visual acuity and user comfort and / or reduce chromatic aberration.

[0141] In some implementations, the light of each primary color may be output by a single dedicated waveguide, and as a result, each depth plane may have a plurality of waveguides associated therewith. In such implementations, each box in the figure, including those containing the letters G, R, or B, may be understood to represent an individual waveguide, and three waveguides may be provided for each depth plane, with three primary color images being provided for each depth plane. The waveguides associated with each depth plane are shown adjacent to each other in this figure for ease of explanation, but it should be understood that in a physical device, all of the waveguides may be arranged in a stack with one waveguide per level. In some other implementations, a plurality of primary colors may be output by the same waveguide, such that, for example, only a single waveguide may be provided for each depth plane.

[0142] Continuing to refer to FIG. 8, in some implementations, G is green, R is red, and B is blue. In some other implementations, other colors associated with other wavelengths of light, including magenta and cyan, may also be used in addition to or in place of one or more of red, green, or blue.

[0143] It should be understood that references throughout this disclosure to the color of a given light include light having one or more wavelengths within the range of wavelengths of light that are perceived by a viewer as being that given color. For example, red light may include light having one or more wavelengths within the range of about 620 - 780 nm, green light may include light having one or more wavelengths within the range of about 492 - 577 nm, and blue light may include light having one or more wavelengths within the range of about 435 - 493 nm.

[0144] In some implementations, the light module 530 (FIG. 6) may be configured to emit light having one or more wavelengths outside of the viewer's visual perception range, such as infrared and / or ultraviolet wavelengths. Additionally, the internal coupling, external coupling, and other light redirection structures of the waveguide of the display system 250 may be configured to direct and emit this light from the display towards the user's eye 210, for example, for imaging and / or user stimulation applications.

[0145] Referring now to FIG. 9A, in some implementations, light that impinges on a waveguide may need to be redirected to internally couple the light into the waveguide. An internal coupling optical element may be used to redirect and internally couple the light into its corresponding waveguide. FIG. 9A illustrates a cross-sectional side view of an example of a plurality of stacked waveguides or a set 660 of stacked waveguides, each including an internal coupling optical element. Each waveguide may be configured to output light of one or more different wavelengths or one or more different wavelength ranges. The set 660 of stacked waveguides may correspond to the waveguide assembly 260 (FIG. 6), and the illustrated waveguides of the set 660 of stacked waveguides may correspond to a portion of the plurality of waveguides 270, 280, 290, 300, 310, except that light from one or more of the image input devices 360, 370, 380, 390, 400 is input into the waveguide from a position that requires the light to be redirected for internal coupling.

[0146] The illustrated set 660 of stacked waveguides includes waveguides 670, 680, and 690. Each waveguide includes an associated internal coupling optical element (which may also be referred to as a light input area on the waveguide). For example, internal coupling optical element 700 is disposed on a major surface (e.g., the upper major surface) of waveguide 670, internal coupling optical element 710 is disposed on a major surface (e.g., the upper major surface) of waveguide 680, and internal coupling optical element 720 is disposed on a major surface (e.g., the upper major surface) of waveguide 690. In some implementations, one or more of internal coupling optical elements 700, 710, 720 may be disposed on the bottom major surface of the respective waveguides 670, 680, 690 (in particular, one or more of the internal coupling optical elements are reflective deflecting optical elements). As illustrated, internal coupling optical elements 700, 710, 720 may be disposed on the upper major surface (or the upper portion of the next lower waveguide) of their respective waveguides 670, 680, 690, and in particular, those internal coupling optical elements are transmissive deflecting optical elements. In some implementations, internal coupling optical elements 700, 710, 720 may be disposed within the bodies of the respective waveguides 670, 680, 690. In some implementations, as discussed herein, internal coupling optical elements 700, 710, 720 are wavelength selective such that they selectively redirect one or more wavelengths of light while transmitting other wavelengths of light. Although illustrated on one side or corner of their respective waveguides 670, 680, 690, it should be understood that in some implementations, internal coupling optical elements 700, 710, 720 may be disposed within other areas of their respective waveguides 670, 680, 690.

[0147] As shown, the internally coupled optical elements 700, 710, 720 may be laterally offset from each other. In some implementations, each internally coupled optical element may be offset so that its light is received without passing through another internally coupled optical element. For example, each of the internally coupled optical elements 700, 710, 720 may be configured to receive light from different image input devices 360, 370, 380, 390, and 400, as shown in FIG. 6, and may be separated (e.g., laterally spaced) from other internally coupled optical elements 700, 710, 720 so as to substantially not receive light from other ones of the internally coupled optical elements 700, 710, 720.

[0148] Each waveguide also includes an associated light dispersing element. For example, the light dispersing element 730 is disposed on a major surface (e.g., upper major surface) of the waveguide 670, the light dispersing element 740 is disposed on a major surface (e.g., upper major surface) of the waveguide 680, and the light dispersing element 750 is disposed on a major surface (e.g., upper major surface) of the waveguide 690. In some other implementations, the light dispersing elements 730, 740, 750 may each be disposed on a bottom major surface of the associated waveguides 670, 680, 690. In some other implementations, the light dispersing elements 730, 740, 750 may each be disposed on both upper and bottom major surfaces of the associated waveguides 670, 680, 690, or the light dispersing elements 730, 740, 750 may each be disposed on different ones of the upper and bottom major surfaces within different associated waveguides 670, 680, 690.

[0149] Waveguides 670, 680, 690 may be separated and isolated, for example, by a gas, liquid, and / or solid layer of material. For example, as shown, layer 760a may separate waveguides 670 and 680, and layer 760b may separate waveguides 680 and 690. In some implementations, layers 760a and 760b are formed from a low refractive index material (i.e., a material having a lower refractive index than the material forming the nearest of waveguides 670, 680, 690). Preferably, the refractive index of the material forming layers 760a, 760b is 0.05 or more, or 0.10 or less than the refractive index of the material forming waveguides 670, 680, 690. Advantageously, the lower refractive index layers 760a, 760b may function as cladding layers that facilitate total internal reflection (TIR) of light (e.g., TIR between the upper major surface and the lower major surface of each waveguide) through waveguides 670, 680, 690. In some implementations, layers 760a, 760b are formed from air. It should be understood that although not shown, the top and bottom of the illustrated set 660 of waveguides may include a nearest cladding layer.

[0150] Preferably, for ease of manufacturing and other considerations, the materials forming waveguides 670, 680, 690 are similar or identical, and the materials forming layers 760a, 760b are similar or identical. In some implementations, the materials forming waveguides 670, 680, 690 may be different between one or more waveguides, and / or the materials forming layers 760a, 760b may still be different while maintaining the various refractive index relationships described above.

[0151] Continuing to refer to FIG. 9A, light rays 770, 780, 790 are incident on the set 660 of waveguides. It should be understood that light rays 770, 780, 790 may be input into waveguides 670, 680, 690 by one or more image input devices 360, 370, 380, 390, 400 (FIG. 6).

[0152] In some implementations, the light rays 770, 780, 790 may have different properties, such as different wavelengths or different wavelength ranges, corresponding to different colors. The internal coupling optical elements 700, 710, 720 each deflect the incident light so that light propagates through an individual one of the waveguides 670, 680, 690 by TIR. In some implementations, the internal coupling optical elements 700, 710, 720 each selectively deflect one or more specific wavelengths of light while transmitting other wavelengths to the underlying waveguide and the associated internal coupling optical element.

[0153] For example, the internal coupling optical element 700 may be configured to deflect the light ray 770 having the first wavelength or wavelength range while transmitting the light rays 780 and 790 having different second and third wavelengths or wavelength ranges, respectively. The transmitted light ray 780 impinges on the internal coupling optical element 710 configured to deflect light of the second wavelength or wavelength range, thereby being deflected. The light ray 790 is deflected by the internal coupling optical element 720 configured to selectively deflect light of the third wavelength or wavelength range.

[0154] Continuing to refer to FIG. 9A, the deflected light rays 770, 780, 790 are deflected to propagate through the corresponding waveguides 670, 680, 690. That is, the internal coupling optical elements 700, 710, 720 of each waveguide deflect light into its corresponding waveguide 670, 680, 690 and internally couple the light into its corresponding waveguide. The light rays 770, 780, 790 are deflected at an angle that causes light to propagate through the individual waveguides 670, 680, 690 by TIR. The light rays 770, 780, 790 propagate through the individual waveguides 670, 680, 690 by TIR until they impinge on the corresponding light dispersion elements 730, 740, 750 of the waveguide.

[0155] Referring now to FIG. 9B, a perspective view of an embodiment of the plurality of stacked waveguides of FIG. 9A is illustrated. As described above, the internally coupled light rays 770, 780, 790 are each deflected by the internally coupled optical elements 700, 710, 720 and then each propagate by TIR within waveguides 670, 680, 690. The light rays 770, 780, 790 then each impinge on the light dispersion elements 730, 740, 750. The light dispersion elements 730, 740, 750 each deflect the light rays 770, 780, 790 so as to propagate towards the external coupling optical elements 800, 810, 820.

[0156] In some implementations, the light dispersing elements 730, 740, 750 are orthogonal pupil expanders (OPEs). In some implementations, the OPEs deflect or disperse light to the external coupling optical elements 800, 810, 820, and in some implementations, also increase the beam or spot size of the present light as it propagates to the external coupling optical elements. In some implementations, the light dispersing elements 730, 740, 750 may be omitted, and the internal coupling optical elements 700, 710, 720 may be configured to directly deflect light to the external coupling optical elements 800, 810, 820. For example, referring to FIG. 9A, the light dispersing elements 730, 740, 750 may each be replaced with the external coupling optical elements 800, 810, 820. In some implementations, the external coupling optical elements 800, 810, 820 are an exit pupil (EP) or an exit pupil expander (EPE) that directs light within the viewer's eye 210 (FIG. 7). It should be understood that the OPE may be configured to increase the size of the eyebox in at least one axis, and the EPE may increase the eyebox in an axis that intersects, e.g., is orthogonal to, the axis of the OPE. For example, each OPE may be configured to redirect a portion of the light impinging on the OPE to the EPE of the same waveguide while allowing the remaining portion of the light to continue to propagate along the waveguide. Again, in response to a collision with the OPE, another portion of the remaining light is redirected to the EPE, and the remaining portion of that portion continues to propagate further along the waveguide, etc. Similarly, in response to a collision with the EPE, a portion of the colliding light is directed out of the waveguide towards the user, and the remaining portion of that light continues to propagate through the waveguide until it impinges again on the EP, at which point another portion of the colliding light is directed out of the waveguide, etc. As a result, a single beam of internally coupled light is "replicated" each time a portion of that light is redirected by the OPE or EPE, thereby forming a beam field of cloned light as shown in FIG. 6. In some implementations, the OPE and / or EPE may be configured to modify the size of the beam of light.

[0157] Thus, referring to FIGS. 9A and 9B, in some implementations, the waveguide set 660 includes, for each primary color, waveguides 670, 680, 690, internal coupling optical elements 700, 710, 720, light dispersion elements (e.g., OPEs) 730, 740, 750, and external coupling optical elements (e.g., EPs) 800, 810, 820. The waveguides 670, 680, 690 may be stacked with a gap / cladding layer between each one. The internal coupling optical elements 700, 710, 720 redirect or deflect the incident light into their respective waveguides (using different internal coupling optical elements for receiving light of different wavelengths). The light then propagates at an angle that will result in TIR within the individual waveguides 670, 680, 690. In the illustrated embodiment, the ray 770 (e.g., blue light) is polarized by the first internal coupling optical element 700 in the manner described above, then bounces along the waveguide and interacts with the light dispersion element (e.g., OPE) 730, then the external coupling optical element (e.g., EP) 800. The rays 780 and 790 (e.g., green and red light, respectively) pass through the waveguide 670, and the ray 780 collides with the internal coupling optical element 710 and is thereby deflected. The ray 780 then bounces along the waveguide 680 via TIR and proceeds to its light dispersion element (e.g., OPE) 740, then the external coupling optical element (e.g., EP) 810. Finally, the ray 790 (e.g., red light) passes through the waveguide 690 and collides with the internal coupling optical element 720 of the waveguide 690. The internal coupling optical element 720 deflects the ray 790 such that the ray propagates by TIR to the light dispersion element (e.g., OPE) 750, then by TIR to the external coupling optical element (e.g., EP) 820. The external coupling optical element 820 then finally externally couples the ray 790 to the viewer, who also receives the light externally coupled from the other waveguides 670, 680.

[0158] FIG. 9C illustrates a top and bottom plan view of an embodiment of the plurality of stacked waveguides of FIGS. 9A and 9B. As shown, waveguides 670, 680, 690 may be vertically aligned with associated optical dispersion elements 730, 740, 750 and associated external coupling optical elements 800, 810, 820 of each waveguide. However, as discussed herein, internal coupling optical elements 700, 710, 720 are not vertically aligned. Rather, the internal coupling optical elements are non-overlapping (e.g., laterally separated as seen in the top and bottom views). As further discussed herein, this non-overlapping spatial arrangement facilitates the injection of light from different resources into different waveguides on a one-to-one basis, thereby enabling a particular light source to be uniquely coupled to a particular waveguide. In some implementations, an array including non-overlapping spatially separated internal coupling optical elements may be referred to as an offset pupil system, and the internal coupling optical elements within these arrays may correspond to sub-pupils.

[0159] Alternatively, in some implementations, two or more of the internal coupling optical elements can be in an in-line arrangement, in which they are vertically aligned. In such an arrangement, light for waveguides farther from the projection system preferably passes through the internal coupling optical elements for waveguides closer to the projection system with minimal scattering or diffraction.

[0160] The in-line configuration can advantageously reduce and simplify the size of the projector. Further, this can increase the field of view of the eyepiece, for example, by taking advantage of crosstalk and by coupling the same color to several waveguides. For example, green light can be coupled into the blue and red active layers. Since the pitch of each ICG can vary to provide improved (e.g., optimal) performance for a particular color, the allowable field of view can be increased.

[0161] In an inline configuration, except for the last layer in the optical path, the ICG should be either maximally partially reflective or otherwise transmissive to light having the operating wavelength of the subsequent layer in the waveguide stack. In either case, the efficiency can be low, unfortunately, unless the grating is etched into a high refractive index layer (e.g., 1.8 or above for a polymer-based layer) or a high refractive index coating is deposited or grown on the grating. However, this approach can increase back reflection into the projector lens, which can thus generate image artifacts such as image ghosting.

[0162] FIG. 9D illustrates an embodiment of a wearable display system 60 into which various waveguides and related systems disclosed herein may be integrated. In some implementations, the display system 60 is the display system 250 of FIG. 6, which schematically shows some parts of that display system 60 in more detail. For example, the waveguide assembly 260 of FIG. 6 may be part of the display 70.

[0163] Continuing to refer to FIG. 9D, the display system 60 includes a display 70 and various mechanical and electronic modules and systems to assist in the function of that display 70. The display 70 may be wearable by a display system user or user 90 and may be coupled to a frame 80 configured to position the display 70 in front of the eyes of the user 90. In some implementations, the display 70 may be regarded as an eyepiece. In some implementations, a speaker 100 is coupled to the frame 80 and configured to be positioned adjacent to the outer ear canal of the user 90 (in some implementations, another speaker, not shown, may optionally be positioned adjacent to the other outer ear canal of the user to provide stereo / formable sound control). The display system 60 may also include one or more microphones 110 or other devices and may detect sound. In some implementations, the microphone is configured to enable the user to provide an input or command (e.g., selection of an audio menu command, natural language question, etc.) to the display system 60 and / or to enable audio communication with other persons (e.g., other users of similar display systems). The microphone may further be configured as a peripheral sensor to collect audio data (e.g., sound from the user and / or the environment). In some implementations, the display system may also include a peripheral sensor 120a that is separate from the frame 80 and may be attached to the body of the user 90 (e.g., on the head, torso, limbs, etc. of the user 90). In some implementations, the peripheral sensor 120a may be configured to obtain data for characterizing the physiological state of the user 90. For example, the sensor 120a may be an electrode.

[0164] Continuing to refer to FIG. 9D, the display 70 is operably coupled to the local processing and data module 140 by a communication link 130, such as a wired conductor or wireless connectivity, which may be mounted in various configurations, such as fixedly attached to the frame 80, fixedly attached to a helmet or hat worn by the user, built into headphones, or removably attached to the user 90 in some other manner (e.g., in a backpack configuration, in a belt attachment configuration). Similarly, the sensor 120a may be operably coupled to the local processing and data module 140 by a communication link 120b, such as a wired conductor or wireless connectivity. The local processing and data module 140 may include digital memory, such as a hardware processor and non-volatile memory (e.g., flash memory or hard disk drive), both of which may be utilized to assist in the processing, caching, and storage of data. Optionally, the local processing and data module 140 may include one or more central processing units (CPUs), graphics processing units (GPUs), dedicated processing hardware, and the like. The data may include (a) data captured from sensors such as an image capture device (e.g., a camera), microphone, inertial measurement unit, accelerometer, compass, GPS unit, wireless device, gyroscope, and / or other sensors disclosed herein (e.g., operably coupled to the frame 80 or otherwise attachable to the user 90), and / or (b) optionally, data obtained and / or processed using the remote processing module 150 and / or remote data repository 160 (including data related to virtual content) for passage to the display 70 after processing or retrieval. The local processing and data module 140 may be operably coupled to the remote processing module 150 and the remote data repository 160 by communication links 170, 180 via a wired or wireless communication link or the like, such that these remote processing modules 150 and remote data repository 160 are operably coupled to each other and available as resources to the local processing and data module 140.In some implementations, the local processing and data module 140 may include one or more of an image capture device, a microphone, an inertial measurement unit, an accelerometer, a compass, a GPS unit, a wireless device, and / or a gyroscope. In some other implementations, one or more of these sensors may be attached to the frame 80 or may be a stand-alone structure that communicates with the local processing and data module 140 via a wired or wireless communication path.

[0165] Continuing to refer to FIG. 9D, in some implementations, the remote processing module 150 may include one or more processors configured to analyze and process data and / or image information, including, for example, one or more central processing units (CPUs), graphics processing units (GPUs), dedicated processing hardware, etc. In some implementations, the remote data repository 160 may include a digital data storage facility, which may be available through the Internet or other networking configurations in a “cloud” resource configuration. In some implementations, the remote data repository 160 may include one or more remote servers that provide information, for example, information for generating augmented reality content, to the local processing and data module 140 and / or the remote processing module 150. In some implementations, all data is stored and all calculations are performed in the local processing and data module, enabling fully autonomous use from the remote module. Optionally, an external system (e.g., one or more processors, one or more computer systems) including a CPU, GPU, etc. may perform at least a portion of the processing (e.g., generating image information, processing data) and provide information to and receive information from the local processing and data module 140, the remote processing module 150, and the remote data repository 160, for example, via a wireless or wired connection. Diffraction grating with reduced polarization sensitivity

[0166] Providing a high-quality immersive experience to users of waveguide-based display systems, such as various display systems configured for the virtual / augmented / composite display applications described above, depends, among other things, on various characteristics of optical coupling into and / or out of waveguides within the eyepieces of the display system. For example, a virtual / augmented / composite display having high internal and external coupling efficiencies can improve the viewing experience by increasing the brightness of the light directed towards the user's eye. As discussed above, internal coupling optical elements, such as internal coupling diffraction gratings, may be employed to couple light into the waveguide such that it is guided therein by total internal reflection. Similarly, external coupling optical elements, such as external coupling diffraction gratings, may be employed to couple light guided within the waveguide out of the waveguide by total internal reflection.

[0167] For example, referring to FIGS. 6 and 7, as described above, a display system according to various implementations described herein may include optical elements, such as internal coupling optical elements, external coupling optical elements, light dispersing elements, and / or a combined pupil expander-extractor (CPE), which may include diffraction gratings. As disclosed herein, the CPE may operate as both a light dispersing element that diffuses or disperses light within the waveguide, potentially increasing the beam size and / or the eyebox, and an external coupling optical element that couples light out of the waveguide.

[0168] For example, as described above with reference to FIG. 7, light 640 incident into waveguide 270 at input surface 460 of waveguide 270 propagates within waveguide 270 and is guided by total internal reflection (TIR). In various implementations, at the point where light 640 impinges on external coupling optical element 570, a portion of the light guided within the waveguide may exit the waveguide as output beam 650, e.g., as a beamlet. In some implementations, any of optical elements 570, 580, 590, 600, 610, which may include one or more than one of an internal coupling optical element, an external coupling optical element, a light distribution element, or a CPE, may be configured as a diffraction grating.

[0169] To achieve the desired characteristics of the internal coupling (or external coupling) of light into the waveguides 270, 280, 290, 300, 310, the optical elements 570, 580, 590, 600, 610 configured as diffraction gratings can be formed from a suitable material and have a suitable structure for controlling various optical properties, including diffraction properties such as diffraction efficiency as a function of polarization. Desirable diffraction properties that can be considered as possibilities include, among other properties, any one or more of the following, namely, spectral selectivity, angular selectivity, polarization selectivity (or non - selectivity), high spectral bandwidth, high diffraction efficiency, or wide field of view (FOV).

[0170] Some diffraction gratings have strong polarization dependence and thus can have a relatively reduced overall efficiency (due to the blocking of one polarization). Such diffraction gratings can also create coherent artifacts and reduce the uniformity of the far - field image. To provide a diffraction grating with reduced polarization sensitivity (e.g., coupling light with an efficiency relatively independent of polarization), some displays for AR systems according to the implementations described herein include waveguides with blazed diffraction gratings formed therein. The blazed grating may include diffraction features having, for example, a "sawtooth" shape. In some implementations, the blazed grating can achieve an improved grating diffraction efficiency for a given diffraction order, while the diffraction efficiency for other orders is reduced or minimized. As a result, more light may be directed to a particular given diffraction order in some implementations, as opposed to any of the other orders.

[0171] Figure 10A illustrates a partial cross-sectional view of a display device 1000, such as an eyepiece lens, including a waveguide 1004 and a blazed diffraction grating 1008 formed on a substrate, which is the waveguide 1004, according to some designs described herein. In the illustrated implementation, the blazed diffraction grating 1008 is formed within the substrate / waveguide 1004 (which is planar in this example). The surface of the substrate or waveguide 1004 has a surface topography that includes diffraction features that together form the diffraction grating 1008. The blazed diffraction grating 1008 is configured to diffract light having wavelengths within the visible spectrum such that light incident thereon is guided within the waveguide 1004 by TIR. The waveguide 1004 may be transparent and may form part of an eyepiece lens through which the user's eye can see. Such a waveguide 1004 and eyepiece lens may be included within a head-mounted display such as an augmented reality display. The waveguide 1004 may correspond to, for example, one of the waveguides 670, 680, 690 described above with respect to FIGS. 9A-9C. The blazed diffraction grating 1008 may correspond to, for example, one of the internal coupling optical elements 700, 710, 720 described above with respect to FIGS. 9A-9C. The blazed diffraction grating 1008, which is configured to internally couple light into the waveguide 1004, may be referred to herein as an internal coupling grating (ICG). The display device 1000 may additionally include an optical element 1012 that may correspond to, for example, a light dispersing element (e.g., one of the light dispersing elements 730, 740, 750 shown in FIGS. 9A-9C) or an external coupling optical element (e.g., one of the external coupling optical elements 800, 810, 820 shown in FIGS. 9A-9C).

[0172] During operation, an incident light beam 1016, such as from a light projection system that provides image content, for example visible light, is incident on a blazed diffraction grating 1008 at an incident angle α measured with respect to a plane normal 1002 that is normal or orthogonal to the surface or plane in which the blazed diffraction grating or the substrate / waveguide extends and / or the surface 1004S of the waveguide 1004, for example the major surface of the waveguide (shown in FIG. 10A as extending parallel to the y-x plane) on which the grating is formed. The blazed diffraction grating diffracts the incident light beam 1016 as a diffracted light beam 1024, at least partially, at a diffraction angle θ measured with respect to the plane normal 1002. When the diffracted light beam 1024 is diffracted at a diffraction angle θ that exceeds the critical angle θ for the occurrence of total internal reflection within the waveguide 1004 TIR the diffracted light beam 1024 propagates within the waveguide 1004 and is generally guided via total internal reflection (TIR) along a direction parallel to the x-axis and along the length of the waveguide. A portion of the light thus guided within the waveguide 1004 reaches one of the light dispersing elements 730, 740, 750 or one of the external coupling optical elements (800, 810, 820, FIGS. 9A-9C) and can be diffracted again, for example.

[0173] As described herein, as in the illustrated implementation, a light beam incident at an angle in the clockwise direction (i.e., to the right of the plane normal 1002) with respect to the plane normal 1002 is said to have a negative incident angle α (α < 0), while a light beam incident at an angle in the counterclockwise direction (i.e., to the left of the plane normal) with respect to the plane normal 1002 is said to have a positive incident angle α (α > 0).

[0174] As further described elsewhere in this specification, a suitable combination of the high refractive index material and / or the structure of the diffraction grating 1008 can result in a particular range (Δα) of the incident angle α, herein referred to as the acceptance angle or field of view (FOV). One range Δα can be described by a certain angular range spanning negative and / or positive values of α, outside of which the diffraction efficiency drops to 10%, more than 25%, more than 50%, or 75%, 80%, 90%, more than 95%, or any value within a range defined by any of these values, relative to the diffraction efficiency at α = 0 or in some other direction. In some implementations, it may be desirable to have a range Δα in which the diffraction efficiency is relatively high and constant, for example, a uniform intensity of the diffracted light is desired within Δα. Thus, in some implementations, the range Δα is associated with the angular bandwidth of the diffraction grating 1008 such that the incident light beam 1016 within the range Δα is efficiently diffracted by the diffraction grating 1008 at a diffraction angle θ with respect to the surface normal 1002 (e.g., in a direction parallel to the y - z plane), where θ is greater than TIR In some implementations, this range Δα can affect the field of view seen by the user. It should be understood that in various implementations, light can be directed onto the internal coupling grating (ICG) from both sides. For example, light can be directed through the substrate or waveguide 1004 and incident on a reflective internal coupling grating (ICG) 1008 such as that shown in FIG. 10A. The light can be coupled into the substrate or waveguide 1004 by the internal coupling diffraction grating 1008 such that the light undergoes the same effect, e.g., the light is guided within the substrate or waveguide by total internal reflection. As used herein, the range (Δα) of the incident angle α, referred to as the acceptance angle or field of view (FOV), can be affected by the refractive index of the substrate or waveguide material. In FIG. 10A, for example, a reduced angular range (Δα’) shows the effect of the refraction of the high refractive index material on the light incident on the internal coupling grating (ICG). However, the range of the angle (Δα) or FOV is larger.

[0175] FIG. 10B illustrates a cross-sectional view of an exemplary blazed transmission diffraction grating 1008. The diffraction grating 1008 includes grating features having peaks 1003 and grooves 1005. The blazed transmission diffraction grating 1008 includes a surface corresponding to the surface 1004S of a substrate or waveguide that has a “sawtooth” shaped pattern as viewed from the cross-section shown. The “sawtooth” to be patterned is first formed by tilting a portion 1007 of the surface 1004S. In the embodiment shown in FIG. 10B, the diffraction grating 1008 also includes a second (steeper) ramp portion 1009. In the embodiment shown, the first ramp portion 1007 has a shallower slope than the second ramp portion 1009, which has a steeper slope. The first ramp portion 1007 is also wider than the second ramp portion 1009 in this embodiment.

[0176] Peak 1003 has a height H corresponding to the vertical distance from the bottom of groove 1005 to the top of peak 1003. Thus, this value may be referred to herein as peak height and / or groove depth, grating height or grating depth, or the height of the diffraction characteristics of the diffraction grating. In some implementations, the height H of neighboring ridges may be different and may follow a gradient, for example. In the embodiment shown in FIG. 10B, the bottom of groove 1005 is formed by the intersection of the first and second inclined portions 1007, 1009 of two adjacent peaks 1003. The first inclined portion 1007 is on one of the adjacent peaks 1003, and the second inclined portion 1009 is on the other adjacent peak. Similarly, the top of peak 1003 is formed by the intersection of the first and second inclined portions 1007, 1009 at the top of peak 1003. However, other configurations are also possible. For example, the first and second inclined portions do not necessarily intersect, for example, when the bottom of groove 1005 has a flat base or the top of peak 1003 includes a flat region, as discussed below. The blazed diffraction grating 1008 may have a constant line spacing or pitch d in some implementations. This line spacing or pitch d may be a measure of the separation of the vertices of peaks 1003 within the diffraction grating 1008 having a shape similar to that shown in FIG. 10B, for example. Similarly, the line spacing or pitch d may be a measure of the separation of the deepest locations of adjacent grooves 1005. The line spacing or pitch d may be measured from other positions on the grating features.

[0177] The inclined surface can be inclined at an angle δ with respect to a plane parallel to the surface of the diffraction grating 1008 or the waveguide (for example, the surface 1004S of the waveguide that can extend beyond the grating or surface 1004S' of the waveguide facing the grating in FIG. 10A). This angle δ of the first (more gently inclined) inclined portion 1007 may be referred to herein as the blaze angle.

[0178] As shown in FIG. 10B, the blazed diffraction grating 1008 can include grating lines or features having an asymmetric shape, for example, asymmetrically shaped peaks 1003 and / or grooves 1005. For example, in the diffraction grating shown in FIG. 10B, the diffraction features include peaks 1003 and / or grooves 1005 having an asymmetric triangular cross-sectional shape. As discussed above, this asymmetric shape results in different slopes and / or widths of the first and second ramp portions 1007, 1009. However, other shapes are also conceivable.

[0179] In a design where the diffraction feature is asymmetric, for example, where the slope of the first ramp portion is more gentle while the slope of the second ramp portion is steeper, the diffraction feature can be formed from repeated ramps and steps. Such a structure can be referred to herein as an inclined stepped structure. In some implementations, the second portion may not be as steep as the ramp. For example, the second portion may be parallel to the surface normal 1002.

[0180] However, in other implementations of the "sawtooth" pattern, the peaks 1003 and / or grooves 1005 may be symmetric. For example, the first and second ramp portions 1007, 1009 may have the same slope and the same width.

[0181] The cross-sectional pattern shown in FIG. 10B can be referred to herein as a single-step geometry as compared to a multi-step structure, which is also conceivable herein.

[0182] Regardless of whether the diffraction feature is asymmetric or symmetric, in some implementations, a flat region or flat portion may be located on top of the peak 1003 as discussed below. A diffraction grating 1008 including a diffraction feature having a flat region or flat portion on top of the peak 1003 is shown, for example, in FIG. 11B.

[0183] FIG. 10B shows an incident light beam 1016 incident on a diffraction grating 1008 at an angle α with respect to a surface normal 1002. (As discussed above with respect to FIG. 10A, in other embodiments, light can pass through a substrate or waveguide 1004 and be incident on the diffraction grating 1008 from the other side.) As discussed above, the surface normal 1002 is normal or orthogonal to the extended surface of the blazed diffraction grating 1008 or the plane of the grating or waveguide and / or the surface 1004S of the waveguide 1004, e.g., the major surface or the opposing planar surface 1004S' of the waveguide on which the grating is formed. In FIG. 10B, the incident light beam 1016 incident on the diffraction grating 1008 is shown as being diffracted at an angle β with respect to the surface normal 1002.

[0184] When configured as an internal coupling optical element or an internal coupling diffraction grating, the diffraction grating 1008 can diffractively couple light incident in a substrate 1004, which can be a waveguide, as described above. The diffraction grating 1008 may optionally be configured as an external coupling optical element, and in such an implementation, it can similarly diffractively couple light from a substrate 1004, which can be a waveguide, as described above.

[0185] Referring to FIGS. 10A and 10B, in some implementations, the substrate 1004 includes a high refractive index material having a refractive index of at least 1.9. The refractive index can be, for example, at least 2.0, at least 2.1, at least 2.2, or at least 2.3, and can be 2.4, 2.5, 2.6, 2.7, 2.8 or less, or within any range formed by any of these values, or outside of these ranges. In some implementations, for example, the substrate includes a Ti, Ta, or Li-based oxide. In various embodiments disclosed herein, the diffraction features of the diffraction grating 1008 may be formed on the surface of the substrate 1004. The diffraction features may be formed in the substrate 1004, such as within a waveguide, or across the substrate 1004, such as across a waveguide, and optically communicate with the substrate 1004, for example, configured to couple light into or out of the substrate 1004, and may be formed in any of separate layers. In the illustrated embodiment, the diffraction features of the diffraction grating 1008, such as lines, are formed within the substrate 1004, such as on the surface of the substrate. The diffraction features may be etched into the substrate 1004, for example, including a high refractive index material such as a Ti, Ta, or Li-based oxide. The substrate may include, for example, lithium niobate, and the diffraction grating may be formed in the lithium niobate substrate by etching or patterning the surface of the substrate. Other materials having a high refractive index may also be used. For example, lithium oxides, such as lithium tantalate (LiTaO 3 ) and the like containing lithium, may be employed as the substrate. Silicon carbide (SiC) is another option for the substrate material. The embodiments are not so limited. In other embodiments, the diffraction features of the diffraction grating 1008 may be formed in a separate layer disposed across the substrate 1004, for example, physically contacting it. For example, zinc oxide (ZNO) with a thickness of less than 200 nm, silicon nitride (Si 3 N 4 ), zirconium dioxide (ZrO 2 ), titanium dioxide (TiO 2) A thin film coating such as silicon carbide (SiC) may be disposed over an existing high refractive index substrate. The thin film coating may be patterned to form diffraction features. However, in some implementations, diffraction features such as the lines of diffraction grating 1008 may be formed from a material different from that of the substrate. The substrate may include, for example, a Ti, Ta, or Li-based oxide (e.g., lithium niobate, LiNbO 3 , or lithium tantalate, LiTaO 3 ) and other high refractive index materials, but the diffraction features may be formed from different materials such as a coating of zinc oxide (ZNO), zirconium dioxide (ZrO 2 ), titanium dioxide (TiO 2 ), silicon carbide (SiC), or other materials described herein. In some implementations, other materials formed on the substrate may have a lower refractive index. In some cases, the substrate 1004 may include, for example, silica glass (e.g., doped silica glass), silicon oxynitride, transition metal oxides (e.g., hafnium oxide, tantalum oxide, zirconium dioxide, niobium oxide, aluminum oxide (e.g., sapphire)), plastics, polymers, or other materials based on, for example, a material having a suitable refractive index different from that of the Ti, Ta, or Li-based oxide features and substantially optically transparent to visible light, such as those described above (including amorphous high refractive index glass substrates).

[0186] However, as described above, in the various implementations described herein, both the diffraction grating 1008 and the substrate 1004 or waveguide include the same material, e.g., a Ti-, Ta-, or Li-based oxide. In some implementations, the diffraction grating 1008 is directly patterned into the substrate 1004 such that the diffraction grating 1008 and the substrate 1004 form a single piece or a monolithic structure. For example, the substrate 1004 includes a waveguide having a diffraction grating 1008 formed directly within the surface of the waveguide or substrate. In these implementations, the bulk Ti-, Ta-, or Li-based oxide material may be patterned on the surface 1004S to form the diffraction grating 1008, while the Ti-, Ta-, or Li-based oxide material below the diffraction grating 1008 may form the waveguide. Further, in some other implementations, the bulk or substrate 1004 and the surface 1004S patterned to form the diffraction grating 1008 include different Ti-, Ta-, or Li-based oxides. For example, the bulk Ti-, Ta-, or Li-based oxide material patterned in the surface region to form the diffraction grating 1008 may be formed from a first Ti-, Ta-, or Li-based oxide material, while the Ti-, Ta-, or Li-based oxide material below the diffraction grating 1008 that forms the substrate 1004 or substrate region may be formed from a second Ti-, Ta-, or Li-based oxide material different from the first Ti-, Ta-, or Li-based oxide material. As discussed above, in some other implementations, the diffraction grating 1008 includes different high refractive index materials such as zirconium dioxide (ZrO2), titanium dioxide (TiO2), silicon carbide (SiC), etc., and the material below the diffraction grating 1008 that forms the substrate 1004 or substrate region is LiTaO 3 , LiNbO 3 etc., and may be different from the first material coated as a thin film.

[0187] In the embodiments illustrated in FIGS. 10A and 10B, diffraction grating 1008 may include a plurality of blazed diffraction grating lines that extend in a first horizontal direction or y - direction and are periodically repeated in a second horizontal direction or x - direction. The diffraction grating lines can be, for example, straight and solid lines that extend in the y - direction. However, the implementation is not so limited. In some implementations, the diffraction grating lines can be, for example, intermittent lines in the y - direction. In some other implementations, the intermittent lines can form a plurality of pillars protruding from the surface of the grating substrate. In some implementations, at least some of the diffraction grating lines can have different widths in the x - direction.

[0188] In the illustrated embodiments, the diffraction grating lines of diffraction grating 1008 have a sawtooth profile with profiles, for example, asymmetric opposing side surfaces that form different angles with respect to the plane of the substrate. However, the implementation is not so limited, and in other implementations, the diffraction grating lines can have symmetric opposing side surfaces that form similar angles with respect to the plane of the substrate.

[0189] Referring to FIGS. 10A and 10B, according to various implementations, diffraction grating 1008 may have various dimensions. For example, the diffraction characteristics of diffraction grating 1008 may have a height (H) of 10 nm or from 40 nm to 150 nm or 200 nm, 50 nm to 110 nm, 60 nm to 100 nm, 70 nm to 90 nm, or about 80 nm, or a height within a range defined by any of these values, according to the implementation. This height may correspond to the height of peak 1003 and / or the depth of groove 1005. Such a height with a blazed geometry in a high - refractive - index material can provide the diffraction grating with reduced polarization sensitivity. However, other heights are also possible.

[0190] Diffraction grating 1008 may have a pitch of from 250 nm to 350 nm, 300 nm to 400 nm, 250 nm to 450 nm, or a pitch within any range defined by any of these values, according to various implementations. Other pitches are also possible.

[0191] In some implementations, the diffraction grating 1008 may have a blaze angle (slow tilt side) of about 10 to 70 degrees and an anti-blaze angle (steep tilt side) of 140 to 70 degrees, or any value within the range defined by these values. Values outside these ranges are also considered, as discussed below, and are possible.

[0192] Generally, either a single-stage or multi-stage geometry blazed diffraction grating is possible, and various techniques can be used to form the grating. In the embodiments shown in FIGS. 11A-11B, the grating can be formed by depositing a blazed photoresist and then etching and patterning the photoresist.

[0193] Exemplary methods of forming blazed gratings and examples of various blazed grating geometries are described in US Patent Application Publication No. US20210072437A1, entitled "Display device with diffraction grating having reduced polarization sensitivity", the entire content of which is incorporated herein by reference. The methods disclosed in this publication can be applied to the curved and faceted anti-blaze structures disclosed herein.

[0194] FIG. 11A illustrates the formation of a single - stage blazed grating 1106 in a substrate 1104, which can be a waveguide 1004 (FIG. 10A). A patternable material such as a photoresist 1102 is deposited on the substrate 1104 that is or can include a waveguide. The patternable material / photoresist 1102 is patterned to have the shape of a blazed grating. Forming the blazed geometry in the photoresist 1102 may, in some implementations, involve imprinting a pattern such as a single - stage "saw - tooth" pattern into the photoresist 1102 (e.g., depositing the photoresist on the substrate 1104 and then imprinting the blazed geometry). The photoresist 1102 may include a mask such as a hard mask. The patterned photoresist 1102 and the substrate 1104 are then etched to form the blazed pattern in the substrate 1104. Etching the photoresist 1102 and the substrate 1104 may involve, for example, dry plasma or chemical etching and / or wet chemical etching. In some implementations, the etching illustrated in FIG. 11A etches the material at a relatively constant rate such that the portion where the patterned photoresist was thickest results in a relatively small removal of material from the substrate, e.g., negligible or no removal, while the portion where the patterned photoresist was thinnest (or non - existent) results in a relatively large removal of material from the substrate or the deepest etching into the substrate.

[0195] FIG. 11B is a scanning electron micrograph of a blazed diffraction grating 1112, where the blazed grating pattern is formed in a photoresist substrate 1104, for example, by imprinting the photoresist with a patterned master. The shown diffraction grating 1112 has a single - stage blazed geometry.

[0196] In some implementations, the blazed grating for ICG has a steep anti-blaze angle. For example, referring to FIG. 12, a cross-sectional profile for one pitch length of such a grating is shown, in which the grating structure 1200 includes a grating layer consisting of ridges 1220 on a substrate 1210. A Cartesian coordinate system is provided for reference. The grating extends in the y-direction, the ridges 1220 extend in the z-direction from a bottom point portion, and both opposing inclined surfaces are angled with respect to the upper surface of the ridge 1220 and the substrate surface. Due to the inclination of the ridge, for most of the anti-blaze side, there is a non-zero horizontal distance between the anti-blaze side and a vertical line 1235 that intersects the apex 1237 of the ridge 1220. For example, the apex 1237 and the vertical line have the same value along the x-axis. The horizontal distance means the distance along the x-axis between two points having the same value along the z-axis.

[0197] Two additional coatings 1230 and 1240 are formed on the surface of the grating layer. Coatings 1230 and 1240 are formed on the upper surface of the ridge 1220 and in the valleys between adjacent ridges, but only one inclined surface of the ridge 1220 (in this case, the left side) is coated while the other inclined surface remains substantially uncoated. Coatings 1230 and 1240 can be formed using a directed deposition method (e.g., evaporation, angled deposition). The asymmetric coating of the two ridge inclined surfaces can result from directed deposition and resulting self-shadowing. The intrusion of coatings 1230 and 1240 into the overhang portion can occur depending on the deposition method.

[0198] The grating design shown in FIG. 12 can be characterized, among other things, by six geometric parameters and three materials. Depending on the illumination wavelength and the desired response, these parameters can vary within the following ranges.

Table 1

[0199] As depicted in FIG. 12, the anti-blaze angle refers to the acute angle between the right slope of the ridge 1220 and the bottom point surface. The anti-blaze angle can be in the range of 5° to 85° (e.g., 10° to 80°, 30° to 80°, 40° to 75°, 50° to 70°, 60° to 70°).

[0200] The blaze angle refers to the obtuse angle between the left slope of the ridge 1220 and the bottom point surface. With respect to the geometric shape depicted in FIG. 12, which is a parallelogram, this angle is the supplementary angle of the anti-blaze angle (i.e., 180° - blaze angle). This angle can be in the range of 95° to 160° (e.g., 100° or greater, 110° or greater, 120° or greater, less than 150°, less than 140°). However, other geometric shapes are also conceivable. For example, the blaze profile can be trapezoidal, and both the blaze and anti-blaze sides are positive slopes but have different absolute values. In other words, at least a part of the anti-blaze side can have a tangent with the same sign as the slope of the blazed side.

[0201] The height of the grating layer refers to the ridge dimension along the z-direction. The ridge 1220 can have a height in the range of 10 nm to 1,000 nm (e.g., 50 nm to 500 nm, 100 nm to 400 nm, 200 nm to 400 nm, 250 nm to 350 nm).

[0202] The pitch of the grating layer is the dimension along the x-direction between adjacent ridges or adjacent valleys. Generally, the pitch can be determined experimentally and / or through simulation, like other parameters regarding the grating structure 1200. The pitch can be adjusted according to the operating wavelength for the grating. Generally, the pitch is in the range of 100 nm to 5,000 nm (e.g., 100 nm to 2,500 nm, 100 nm to 1,000 nm, 200 nm to 750 nm, 250 nm to 500 nm, 300 nm to 400 nm).

[0203] The ridge has a width, which refers to the dimension along the x - direction. For the lattice structure 1200, the opposing slopes of the ridge 1220 through the illustrated cross - section are parallel, and thus the ridge thickness is constant with respect to the ridge through its height. However, in some implementations, it is also possible for the width to vary (e.g., narrow) from the bottom point to the top of the ridge. In an implementation where the width varies, the width can be determined at the mid - point of the height of the ridge.

[0204] The duty cycle refers to the ratio of the width to the pitch, expressed as a percentage. In an implementation, the lattice structure can have a duty cycle within the range of 5% - 95% (e.g., 10% - 75%, 20% - 50%, 30% - 40%).

[0205] The ridge has a height corresponding to the dimension of the ridge in the z - direction measured from its bottom point to its upper surface. The ridge can have a height within the range of 10 nm - 1,000 nm (e.g., 50 nm - 500 nm, 100 nm - 400 nm, 200 nm - 400 nm, 250 nm - 350 nm).

[0206] The thickness of a layer, e.g., coatings 1230 and 1240, refers to the dimension of the layer in the z - direction measured at the point where the surface supporting the layer is perpendicular to the z - direction. The first coating 1230 and / or the second layer can have a thickness within the range of 5 nm - 500 nm (e.g., 10 nm - 400 nm, 20 nm - 300 nm, 50 nm - 250 nm, 100 nm - 200 nm, 130 nm - 170 nm). Generally, the thicknesses of the first and second layers can be the same or different.

[0207] The bottoming material of the lattice structure (i.e., the substrate 1210 and the ridge 1220) can be a UV or thermally cross-linked polymer. The refractive index of the bottoming material can be in the range of 1.5 to 2.2 (e.g., up to 2.2, such as 1.6 or greater, 1.7 or greater, 1.8 or greater, 1.9 or greater, 2.1 or greater). A high refractive index (e.g., 1.8 or greater) can be achieved, for example, using a polymer composite material containing nanoparticles (e.g., high refractive index nanoparticles, such as TiO 2 nanoparticles and / or ZrO 2 nanoparticles).

[0208] Although not wishing to be bound by theory, a higher refractive index of the base-patterned material is thought to help make the diffraction efficiency relatively uniform over a larger angle. For example, the variation in the average TE and TM diffraction efficiencies can be + / - 15% or less of the absolute average diffraction efficiency (e.g., + / - 10% or less, + / - 8% or less, + / - 5% or less).

[0209] In some implementations, the first coating 1240 is made of a material having a high refractive index (e.g., 1.8 or greater). The first coating 1240 can be formed from a dielectric material including, but not limited to, titanium dioxide, gallium phosphide, and silicon carbide.

[0210] In one implementation, the second coating 1230 is made of a material having a low refractive index dielectric constant (e.g., 1.6 or less, 1.5 or less, 1.45 or less). The second coating can be formed from a dielectric material such as, for example, (but not limited to) silicon dioxide, magnesium fluoride, and calcium fluoride.

[0211] Generally, the grating layers of the grating structure 1200 and similar grating structures can be formed using the techniques described herein and in US 20210033867A1 and US 20210072437 (the entire contents of both are incorporated herein by reference).

[0212] The first coating 1230 can be formed using various physical vapor deposition techniques including, but not limited to, sputtering and electron beam deposition. The second coating 1240 can be formed by various physical vapor deposition techniques including, but not limited to, sputtering and electron beam deposition. Generally, the techniques used to form the coating 1230 can be the same as or different from the techniques used to form the coating 1240.

[0213] The optical performance of the exemplary grating structure as described in FIG. 12 above was simulated using rigorous coupled-wave analysis (RWCA) as follows. The parameter values for the grating structure were as follows. [Table 2]

[0214] For simulation purposes, an operating wavelength of 525 nm was used and the bottom material had a refractive index of 2.0.

[0215] Figures 13A - D include plots of diffraction efficiency and reflection coefficient, e.g., as a function of emission angle, which include the percentage of light impinging on a diffraction grating that is diffracted or reflected. Figure 13A shows the diffraction efficiency in the emission direction as a function of illumination angle for a simulated grating over a 55° field of view. The three curves correspond to TM - polarized light, TE - polarized light, and unpolarized light. An integrated average of about 52% diffraction efficiency was calculated. Generally, such gratings are thought to be able to provide an average diffraction efficiency of 50% or more for TE and TM - polarized light over a + / - 20° angle of incidence. Figure 13B shows the reflection efficiency as a function of illumination angle for a simulated grating for TM - polarized light, TE - polarized light, and unpolarized light. An integrated average of 0.93% reflection efficiency was calculated. Figures 13C and 13D correspond to the same plots shown in Figures 13A and 13B, simulated for the same structure except without a second layer. The diffraction efficiency is still high, e.g., an integrated average of 40.62%, but the back - reflection increases significantly, e.g., having an integrated average of 4.13%.

[0216] Additional experiments were performed to compare the measurements of fabricated samples similar to the results of the simulated grating structures. The results of these experiments are shown in Figures 14A - 14D. Specifically, Figures 14A and 14B show plots of diffraction efficiency as a function of angle of incidence over a range of angles of incidence for TM, TE, and unpolarized light. Figure 14A shows the simulated data while Figure 14B shows the measurements of fabricated samples for a subset of the simulated range for p - polarized (TM) and s - polarized (TE) light. Figures 14C and 14D show a schematic of the cross - sectional profile for this grating structure (Figure 14C) and an SEM of the cross - section of the fabricated sample (Figure 14D).

[0217] Figures 15A - 15C illustrate the effect of including a low - refractive - index layer as the top layer within the grating structure. Figure 15A shows SiO 2 with a coating of TiO2 A plot of diffraction efficiency as a function of the angle of incidence for an orthogonal polarization state for a lattice structure, e.g., an s-polarized and a p-polarized state. The SEM of the cross-sectional profile of the lattice structure is shown in the inset. FIG. 15B is SiO 2 A further layer of TiO 2 A plot of diffraction efficiency as a function of the angle of incidence for the same lattice structure except that a further layer of SiO is formed over the TiO layer. The average diffraction efficiency is shown together with the diffraction efficiency for both s and p polarizations. FIG. 15C shows, for example, in the solid and dotted lines respectively, a plot of reflectivity as a function of wavelength for the visible light spectrum for the lattice structure, for normal incident light, e.g., an emission angle of 0°, with and without an SiO 2 coating. The reflectivity is lower across substantially the entire visible spectrum range for the lattice with an additional SiO 2 coating.

[0218] Measurements from further examples are shown in FIGS. 16A - 16F. The three lines in FIGS. 16A, 16C, and 16E correspond to p-polarized light, s-polarized light, and the average of the other two lines. FIG. 16A is a plot of diffraction efficiency as a function of the angle of incidence for the lattice structure shown in the SEM in FIG. 16B, which consists of a high refractive index (n = 2.0) composite on a glass substrate (n = 1.78). The blaze angle, e.g., "Aa1", is about 53°, the pitch "V3" is about 383 nm, the height "H1" of the flat portion between the ridges is about 39 nm, the height "H2" of the ridge relative to the flat portion is about 181 nm, the width "V2" at the top of the ridge is about 119 nm, and the width at the bottom point of the ridge is about 186 nm. The height "H1" can have a thin resist layer thickness (RLT), e.g., less than 50 nm or less than 20 nm. FIG. 16C is a plot of diffraction efficiency as a function of the angle of incidence for the lattice structure shown in the SEM in FIG. 16D. The lattice structure in FIG. 16D is one in which the lattice layer is TiO 2It is made of a high refractive index composite material (n = 2.0 with respect to light at 530 nm) on a substrate (n = 2.0 with respect to light at 530 nm), coated with 2 (n = 1.45 at 530 nm). A further coating of TiO 2 coats the TiO 2 layer. It is a plot of the diffraction efficiency as a function of the angle of incidence for a grating structure shown in SEM in FIG. 16F, consisting of a high refractive index composite material (n = 2.0 with respect to light at 530 nm) on a substrate (n = 1.45 with respect to light at 530 nm) with a TiO 2 coating (n = 2.15 with respect to light at 530 nm). The coating has a stepped shape and is accompanied by a first level at a height "H3" of 37.65 nm with respect to the substrate and a second level at a height "H1" that is about 173 nm above the maximum height of the ridge. FIG. 16E shows glass, for example, SiO 2 The maximum width "H1" of the first TiO 2 coating is about 181 nm, and the maximum width "H2" of the second SiO

[0219] The foregoing embodiments are of a grating structure with ridges that are parallelogram-shaped, but more generally, other cross-sectional shapes are also conceivable as possibilities. For example, trapezoidal, triangular, and stepped shapes are also conceivable as possibilities. Furthermore, the shapes are described corresponding to parallelogram shapes with mathematical precision, but deviations from these shapes are inevitable due to manufacturing limitations and the like. Generally, as used herein, such ridges and other features are considered to have a particular shape if their design defines such a shape and / or the structure has such a shape within the capabilities of the process used to manufacture such a structure on a large scale.

[0220] ​​​​​​ For example, the ridges of the grating structure can have a shape that promotes the formation of material deposition between the ridges without coating the anti-blaze side of the ridges. Coating the anti-blaze side with a high refractive index coating and not coating the flat portions of the grating between the ridges can each reduce the diffraction efficiency. FIG. 17A shows an embodiment of a cross-sectional view of a blazed grating 1700 with a concave anti-blaze side, and the concave surface can be curved or polygonal, for example, non-linear. The blaze side 1704 of the ridge 1702 is linear, and the anti-blaze side 1706 of the ridge 702 is concave. Thus, only the portion of the grating that does not have a portion of the ridge blocking the path along the vertical direction will be coated during deposition. In FIG. 17A, for example, a vertical line 1710a along the normal direction to the flat portion of the grating between the ridges connects the apex 1712, for example, the uppermost apex of the anti-blaze side, and the bottom point 1714 of the anti-blaze side 1706, and for example, the bottom point 1714 is directly below the apex 1712. Along the anti-blaze side, for most of the anti-blaze side, there is a non-zero horizontal distance between the anti-blaze side and the vertical line 1710a. In other words, a part of the anti-blaze side 1706 can protrude from the lower portion of the anti-blaze side. The curved concave anti-blaze side can be characterized by an angle formed by a tangent 1701 near the bottom point of the ridge. The tangent 1701 can form an angle of 89° or less with the flat portion of the grating.

[0221] Thus, as a result of the anti-blaze side 1706 curving outwardly near the bottom of the ridge, the flat portion 1716 of the grating between the ridges can be more completely coated during vertical deposition without coating the anti-blaze side 1706 of the ridge as compared to the case where the anti-blaze side is simply an inclined line. Increasing the coating rate (coating within the trench) of a portion of the grating between the ridges with a high refractive index coating can increase the diffraction efficiency of the grating (e.g., by 20% or more, 30% or more, 50% or more, up to a maximum of 60%). Due to the concave shape of the anti-blaze side 1706, a uniform coating rate of the flat portion of the grating between the ridges can be achieved without significantly coating the anti-blaze side 1706, which can reduce the diffraction efficiency of the blazed grating 1700.

[0222] FIG. 17B shows a cross-sectional view of another embodiment of a blazed grating 1720 with a concave anti-blaze side. In some implementations, the apex 712 and the bottom point 714 do not necessarily have the same values along the horizontal direction, e.g., along the x-axis, but still achieve some of the benefits discussed above. For example, the first ridge 1702a has a concave anti-blaze side, and the apex 1712a and the bottom point 1714a have different values along the horizontal direction. For example, the apex 1712a is further to the right compared to the bottom point 1714a (using the perpendicular line 1710b normal to the flat portion of the grating between the ridges as a reference). As a result, during deposition, the portion 1722a of the anti-blaze side will be coated. However, this portion 1722a is less than the portion that would be coated if the anti-blaze side were simply the tangent line 1718a following the initial curvature of the anti-blaze side near the apex 1712a. Thus, the concave shape can reduce the amount of the anti-blaze side that will be coated even when the apex 1712a and the bottom point 1714a of the anti-blaze side are not perfectly aligned. In some cases, the amount of the unshielded portion (1722a) or the shielded portion (1722b) can be about 30% of the trench width.

[0223] As another example, the second ridge 1702b has a concave anti-blaze side, and the apex 1712b and the bottom point 1714b have different values along the horizontal direction. For example, the apex 1712b is further to the left compared to the bottom point 1714b (using the perpendicular line 1710c normal to the flat portion of the grating between the ridges as a reference). As a result, the portion 1722b of the substrate will not be coated during deposition. However, this portion 1722b is less than the portion that would not be coated during deposition compared to the case where the anti-blaze side was simply the tangent line 1718b that follows the initial curvature of the anti-blaze side near the apex 1712b. Thus, the concave shape can help increase the amount of the substrate that is coated during deposition even when the apex 1712a and the bottom point 1714a of the anti-blaze side are not exactly aligned.

[0224] Note that the tangent lines 1718a and 1718b each have a negative slope, similar to the blaze side. In other words, at least a portion of the anti-blaze side has a tangent line with the same sign as the slope of the blaze side.

[0225] In some implementations, the anti-blaze side has a constant radius of curvature. In some implementations, the radius of curvature varies along the anti-blaze side. The radius of curvature can be 20 nm or greater (e.g., less than 750 nm, less than 500 nm, less than 400 nm, etc., greater than 50 nm, greater than 100 nm, greater than 200 nm, greater than 300 nm, up to 1,000 nm maximum).

[0226] Figures 17A and 17B depict the concave shape of the anti-blaze side, but other shapes can also provide the benefits described above. For example, Figures 17C and 17D show cross-sectional views of other embodiments of the grating with a multi-faceted anti-blaze side. The anti-blaze side in Figure 17C has an angle, e.g., an obtuse angle θ 1It has the profiles of two lines 1711 and 1713 that are connected by. In other words, the anti-braze side includes a series of line segments. With respect to the reference horizontal line 1715a, the line 1711 extends at a negative angle θ 2 For example, it can have a negative slope and extend at a positive angle with respect to the reference horizontal line 1715b. The length of each line segment is generally equal to or less than the height of the grid divided by the sine of the braze angle.

[0227] In some implementations, the anti-braze side has profiles of three or more lines that are connected by different angles, for example, in FIG. 17D, θ 4 and θ 5 For example, it can have the profiles of lines 1717, 1719, and 1721. Similar to the embodiments with a tilted or concave anti-braze side, the polyhedral embodiments in FIGS. 17C and 17D also exhibit the following behavior, that is, along the anti-braze side, with respect to at least a part of the anti-braze side, there is a non-zero horizontal distance between the anti-braze side and the perpendicular line 1710d, for example, along the normal direction with respect to the flat part of the grid between the ridges.

[0228] Examples of obtuse angles are given in FIGS. 17C and 17D, but other angles are also conceivable. In that case, no part of the anti-braze side protrudes further than the perpendicular line 1710d determined by the apex, bottom point, or both of the anti-braze side. For example, no part of the anti-braze side extends beyond the perpendicular line in the -x direction. Both FIGS. 17C and 17D depict embodiments where the anti-braze side has one surface with a slope associated with the same sign as the slope of the braze side and another surface with a slope associated with the opposite sign to the slope of the braze side. This geometric arrangement reduces the amount of the anti-braze side that will be coated during deposition and enables at least some of the benefits described above regarding coating the flat part of the grid between the ridges.

[0229] In some implementations, there is a gap between where one ridge starts and where another ridge ends, e.g., the gap "g" depicted in FIG. 17C between where the blade side intersects the flat portion of the grating and where the nearby anti - blade side rises from the flat portion of the grating. In some implementations, as depicted in FIG. 17D, there is no gap between where one ridge starts and where another ridge ends. For example, the location where the nearby blade and anti - blade sides intersect there is at or above the height of the flat portion of the grating (along the z - axis).

[0230] FIG. 17E shows a cross - sectional view of an example of a blazed grating 1730 with a concave anti - blade side that is coated by two layers of coating. Each ridge 1722 is coated with a first layer 1724 and a second layer 1726. The description of the two coatings in FIG. 16F can be applied to the first and second layers 1724 and 1726. For example, due to the shape of the ridge with a flat top and an inclined blade side and the widths of the first and second layers 1724 and 1726, i.e., the first layer 1724 of the second ridge 1702d and the second layer 1726 of the first ridge, the edges and the anti - blade side of the first and second layers 1724 and 1726 on the first ridge 1702c define a void 1732. The presence of the void 1732 means that at least a portion of the anti - blade side is not coated. The void 1732 extends along the y - direction. In some implementations, generally, it is beneficial to reduce the volume of the void because it has a refractive index lower than that of the ridge and the coating, e.g., n≈1. Reducing the size of the area within the coated grating with a lower refractive index can improve the diffraction efficiency of the grating.

[0231] In some implementations, when only one coating is present on the diffraction grating, if the surface of the coating is not parallel to the blaze side, for example, has a more gentle negative slope, voids can be formed. In some implementations, such as when the surface of the coating is substantially parallel to the ridges and each other, voids are formed when at least two coatings are present.

[0232] The bottom of the second layer 1726 that coats the first ridge 1702c bounds the bottom point 1714c of the second ridge 1702d, which means that none of the gratings are exposed. However, other implementations are also conceivable.

[0233] FIG. 18 is a scanning electron microscope (SEM) image of a reentrant blazed grating with a deformed slope on the anti-blaze sidewall. The reentrant grating is generally located on the side opposite the light source of the waveguide and couples light into the waveguide after the light passes through the waveguide. The reentrant blazed grating features an anti-blaze side with a curved portion, and the radius of curvature at the top is greater than the radius of curvature at the bottom. From the left side to the right side of the grating, the slope of the blaze side (the right side of the ridge) gradually decreases. In practice, the geometry of the blazed grating can be determined using SEM analysis, which can include measurements between line segments that indicate areas of high contrast.

[0234] In some implementations, such as when the blazed grating is used as an OPE, EPE, or CPE, the blazed grating is located on the grating surface (e.g., ICGs 700, 710, and 720, OPEs 730, 740, and 750, and EPEs 800, 810, and 820), as shown in FIG. 9C for example.

[0235] Figures 19A - 19I are cross - sectional views depicting a processing process for a reentrant grating with a multi - faceted anti - blaze side. The process starts with a substrate 1901, e.g., silicon or silicon dioxide, as depicted in Figure 19A. Next, the substrate 1901 is coated with an etching stop layer 1903 as depicted in Figure 19B. The etching stop layer 1903 can be, for example, chromium (Cr) or aluminum oxide (Al 2 O 3 ), and can protect the substrate in later steps, including dry etching. Next, in Figure 19C, a layer that will become the grating, e.g., grating layer 1905, is imprinted on the etching stop layer 1903. The grating layer 1905 can be made from materials described previously in this disclosure, e.g., silicon dioxide.

[0236] Figure 19D depicts a blazed grating template 1907, which can be wet - etched silicon on top of the grating layer 1905. In some implementations, the template has a flat top that is thinner than the flat top of the final blazed grating. A template with a thin flat top can provide additional protection during the dry - etching step because the thinner top can be removed by lift - off instead of etching, providing an additional portion on the top that can be removed.

[0237] Figure 19E depicts a dry - etching step (indicated by the downward arrow), which transfers the shape of the blazed grating from the template to the grating layer 1905. During dry - etching, the upper corners of the blazed - grating shape are etched more rapidly than the rest of the shape. A portion of the blazed grating template 1907 remains after dry - etching. The remaining portion of the blazed grating can be peeled off after dry - etching as depicted in Figure 19F. Peeling instead of etching the remaining portion of the blazed grating template 1907 can ensure feature fidelity. For example, the shape of the grating layer 1905 will be similar to the shape of the blazed grating template 1907 except for the portion that remains after dry - etching.

[0238] In FIG. 19G, the etching mask 1909 is directionally coated at an angle (indicated by the inclined arrow). Coating at an angle is beneficial in that it prevents the flat top and the blazed side from blocking the path to the anti-blazed side, thus preventing the anti-blazed side from being coated. The angle of the coating can be determined by the anti-blaze angle θ AB and, for example, the angle between the coating direction and the perpendicular line can be equal to or less than 90° - θ AB or less. Since θ AB exceeds 90°, the angle of the coating can be negative. For example, in FIG. 19G, it is directed to the left. In other words, the absolute value of the angle between the coating direction and the perpendicular line can be at least the difference between 90° - θ AB and.

[0239] FIG. 19H depicts the dry etching of the anti-blazed side at an angle indicated by the inclined arrow using the plasma from the Faraday cage. Due to the shielding effect, the Faraday cage can deflect the ions in the plasma in a direction perpendicular to the furnace of the Faraday cage. As a result, the use of the Faraday cage can deflect the ions from the plasma in a certain direction and etch the anti-blazed side of the grating layer 1905. The etching mask 1909 protects the top and the blazed side of the grating layer 1905 during etching. As a result of the dry etching using the Faraday cage, the inner part of the anti-blazed side, for example, the area to the left of the dotted perpendicular line in FIG. 19H, can be removed.

[0240] FIG. 19I depicts the final grating structure after the etching mask 1909 is peeled off. Therefore, the grating layer 1905 after dry etching has a different shape compared to the blazed grating template 1907 before etching, for example, the upper layer is removed and has a multi-faceted anti-blazed side.

[0241] In some implementations, dry etching using a Faraday cage is repeated multiple times at different angles to achieve the desired profile on the anti-braze side. For example, FIGS. 19A-I show the production of the anti-braze side with two surfaces by dry etching at one angle using a Faraday cage. However, dry etching at different angles in additional passes can produce an anti-braze side with three or more surfaces. Depending on the duration of dry etching using the Faraday cage, a smooth curved anti-braze side can be achieved.

[0242] FIG. 20 is a flow diagram of a process 2000 for forming a blazed grating with a concave anti-braze side, where, for example, the cross-section of the anti-braze side is concave. A system such as that described in US 20210072437A1 (incorporated above by reference) can be used to perform at least some of the steps.

[0243] Process 2000 includes the step of providing a substrate (2002), for example, substrate 1901. The substrate can be a waveguide. In some implementations, substrate 1004 can include a material such as amorphous high refractive index glass, as discussed, for example, with reference to substrate 1004.

[0244] Process 2000 includes the step of depositing an etch stop layer, for example, etch stop layer 1903, on the substrate (2004). The etch stop layer can be, for example, chromium (Cr) or aluminum oxide (Al 2 O 3 ) and can protect the substrate in subsequent steps, including dry etching.

[0245] Process 2000 includes the step of depositing a grating material, for example, grating layer 1905, on the etch stop layer (2006). The grating material can be a patternable material such as photoresist.

[0246] Process 2000 includes depositing a blazed grating template, e.g., blazed grating template 1907, on a grating material (2008). In some implementations, the blazed grating template is wet-etched silicon.

[0247] In some implementations, the blazed grating template extends vertically beyond the final shape of the grating. For example, as in FIGS. 19D and 19E, the blazed grating template 1907 can have an upper portion that is thinner due to the bottom point portion of the template and has a triangular shape. The shape of the thinner portion at the top is not intended to be transferred to the grating layer 1905 and provides a buffer for the top of the grating during etching.

[0248] Process 2000 includes etching the grating material, thereby transferring the shape of the blazed grating template to the grating material to form a blazed grating (2010). The etching step can include dry plasma etching, chemical etching, wet chemical etching, or combinations thereof.

[0249] In some implementations, step 2010 is completed before the entire blazed grating template is etched, as in FIG. 19E. When there is a remaining portion of the blazed grating template, process 2000 can include a step of peeling off the remaining portion of the blazed grating template before proceeding to step 2012.

[0250] Process 2000 includes coating the blazed grating with an etching mask, e.g., etching mask 1909, at a first non-zero angle with respect to the vertical direction so that the anti-blaze side of the grating remains uncoated. For example, the non-zero angle can be the angle between the arrow and the vertical line in FIG. 19G.

[0251] Process 2000 includes a step (2014) of etching at a second non-zero angle with respect to the vertical direction and with a sign opposite to that of the first non-zero angle, thereby removing an internal portion on the anti-blaze side. In some implementations, the step of etching includes a step of dry etching the anti-blaze side using plasma from a Faraday cage. By removing the internal portion on the anti-blaze side, the anti-blaze side becomes concave. In some implementations, the profile of the anti-blaze side is curved, includes line segments, or both.

[0252] Process 2000 includes a step (2016) of peeling an etching mask from the blazed grating. As a result, the grating becomes a blazed grating with a concave anti-blaze side as depicted in FIG. 19I.

[0253] In some implementations, process 2000 can include additional steps, or some of the steps can be divided into multiple steps. For example, process 2000 can continue to coat the blazed grating with one or more additional layers of a high refractive index material. Depending on the geometry, the step of coating the blazed grating with one or more additional layers of a high refractive index material leads to the formation of a gap between an edge of one of the additional layers and the anti-blaze side. In some implementations, using a non-zero angle with respect to the vertical direction while coating the blazed grating with a high refractive index coating is unnecessary to avoid coating the anti-blaze side. Additionally, vertical deposition can substantially cover the flat portions between the ridges of the grating without an overhang on the anti-blaze side that blocks the flat portions of the diffraction grating between the ridges.

[0254] Other processing variations are also possible. For example, the embodiments discussed above feature either one or two layers coating the grating layer, but additional layers are also possible. For example, an additional layer can be included between the grating layer and the outermost low refractive index layer.

[0255] The foregoing example lattice structure is a one-dimensional lattice, but other implementations are also conceivable as possibilities. For example, in some implementations, the array of structures can also be arranged in two directions to form a two-dimensional (2D) array of diffraction features. The 2D array of diffraction features can include undulations in two directions. In some cases, the undulations can be periodic, while in other cases, the pitch of the undulations can vary in at least one direction. According to various embodiments described herein, the diffraction features have opposing sidewalls that are asymmetrically angled or tilted. According to various embodiments described herein, the diffraction features can be tapered.

[0256] In some implementations, the diffraction features can have opposing sidewalls that are substantially angled or tilted. In some implementations, the opposing sidewalls can be tilted in the same direction, while in other implementations, the opposing sidewalls can be tilted in opposing directions. In some other implementations, the diffraction features can have one of the opposing sidewalls that is substantially tilted, while having the other sidewall that is substantially perpendicular or orthogonal to the horizontal axis or tilted less than at least the other sidewall. In various embodiments of the 2D diffraction features described herein, the 2D diffraction features can be formed within or on the underlying substrate, which can be a waveguide as described above with respect to various embodiments of the 1D diffraction features. For example, the 2D diffraction features can be formed by etching into the underlying substrate or by patterning a separate layer formed thereon. Thus, the 2D diffraction features can be formed from the same or a different material as the material of the substrate, similar to those described above with respect to various 2D diffraction features. Other variations and configurations are also conceivable as possibilities.

[0257] Therefore, any of the structures or devices described herein, such as a lattice structure, may include a 1D lattice. Similarly, any of the structures or devices described herein, such as a lattice structure, may include a 2D lattice. Such a 2D lattice may be capable of diffusing light. These lattices may also include blazed lattices. Such blazed lattices may preferentially direct light in a certain direction. In some implementations, a 2D lattice (e.g., having one inclined surface on the diffraction feature) preferentially directs light in one direction, while in other implementations, a 2D lattice (e.g., having two inclined surfaces with different diffraction features) preferentially directs light in multiple directions. Similarly, any of the methods or processes described herein may be used for a 1D lattice. Similarly, any of the methods or processes described herein may be used for a 2D lattice. These lattices, being 1D or 2D, may be included within or on a substrate and / or waveguide, within an eyepiece, and possibly integrated into a head-mounted display, as disclosed herein. These lattices may be employed as input lattices (e.g., ICG), output lattices (EPE), light distribution lattices (OPE), or a combined light distribution / output lattice (e.g., CPE). Examples of output coupling lattices are shown, for example, in FIGS. 9C and 10A. Alternatively, or in addition, such lattices may be used within an orthogonal pupil expander (e.g., 730, 740, 750 in FIG. 9C). Such geometries may similarly be optimized for output couplers that are insensitive to polarization, improving the transparency of the display within the frontal region of the user's eye and reducing back reflection, which can be a problem with diffractive surface relief gratings when used as a wearable waveguide.

[0258] Other implementations are in the following claims.

Claims

1. A head-mounted display system, comprising: a head-mountable frame; a light projection system configured to output light and provide image content; a waveguide supported by the frame, the waveguide being configured to guide at least a portion of the light from the light projection system coupled into the waveguide; a grating structure optically coupled to the waveguide, the grating structure being configured to couple the light from the light projection system into the waveguide, the grating structure comprising: a grating layer comprising a plurality of ridges having a blaze profile in at least one cross-section, the blaze profile having an anti-blaze angle of 89° or less; one or more additional layers disposed on the grating layer, the one or more additional layers comprising a first layer of a material having a refractive index of 1.5 or less at the operating wavelength of the head-mounted display, the first layer being the outermost layer of the grating structure; a grating structure; a head-mounted display system.

2. The head-mounted display system according to claim 1, wherein the blaze profile has a blaze angle of 95° or more.

3. The head-mounted display system according to claim 1 or claim 2, wherein the ridge has a profile shape selected from the group consisting of a trapezoid, a parallelogram, a triangle, and a stepped shape.

4. The head-mounted display system according to any one of the preceding claims, wherein the anti-blaze angle is in the range of 1° to 89°.

5. The head-mounted display system according to any one of the preceding claims, wherein the ridge has a height in the range of 10 nm to 1,000 nm.

6. The head-mounted display according to any one of the preceding claims, wherein the grating has a pitch in the range of 100 nm to 5,000 nm.

7. The head-mounted display system according to any one of the preceding claims, wherein the grating has a duty cycle in the range of 5% to 95%.

8. The head-mounted display according to any one of the preceding claims, wherein the first layer has a thickness in the range of 5 nm to 500 nm.

9. The one or more additional layers include a second layer between the first layer and the grating layer, and the second layer includes a second material having a refractive index greater than 1.5 at the operating wavelength, for the head-mounted display according to any of the preceding claims.

10. The head-mounted display according to claim 9, wherein the second layer has a thickness in the range of 5 nm to 500 nm.

11. The head-mounted display according to any of the preceding claims, wherein the grating layer includes a grating material having a refractive index of 1.5 or greater at the operating wavelength.

12. The head-mounted display according to any of the preceding claims, wherein the grating material includes a crosslinked polymer.

13. The head-mounted display according to claim 12, wherein the grating material includes nanoparticles.

14. The head-mounted display according to any of the preceding claims, wherein the grating structure is at least partially transparent at the operating wavelength.

15. During operation, the grating structure is configured to couple light into the waveguide at an operating wavelength corresponding to a plurality of differently colored pixels of the light projection system, for the head-mounted display according to any of the preceding claims.

16. The head-mounted display according to any of the preceding claims, wherein the grating layer and the waveguide are made of the same material.

17. The head-mounted display according to claim 16, wherein the material includes a polymer.

18. The head-mounted display according to claim 16, wherein the material has a refractive index of 1.7 or greater.

19. The head-mounted display according to claim 16, wherein the material is a composite material.

20. The head-mounted display according to claim 19, wherein the composite material includes nanoparticles.

21. The head-mounted display according to any of the preceding claims, wherein the light from the light projection system is non-polarized light or polarized light.

22. The head-mounted display according to any of the preceding claims, wherein the light projection system includes a micro-LED display, an LCoS display, or a laser beam scanner display.

23. The head-mounted display system according to claim 1, further comprising a second grating structure located on the side of the waveguide opposite to the first grating structure, wherein the second grating structure is optically coupled to the waveguide and comprises a second grating layer comprising a plurality of ridges having a blazed profile in at least one cross-section, and the blazed profile has an anti-blaze angle of 89° or less.

24. The head-mounted display according to any of the preceding claims, further comprising one or more additional waveguides and one or more additional grating structures, each associated with a corresponding one of the additional waveguides.

25. The head-mounted display according to claim 24, wherein the grating structures of the waveguides are arranged in an in-line configuration.

26. The head-mounted display according to claim 25, wherein at least one of the grating structures is a reflective grating.

27. The head-mounted display according to claim 26, wherein the reflective grating is the grating structure of the waveguide farthest from the light projection system.

28. The head-mounted display according to any of the preceding claims, wherein at least some of the ridges have a single-stage geometry.

29. The head-mounted display according to any of the preceding claims, wherein at least some of the ridges have a multi-stage geometry.

30. An article, comprising a waveguide layer made of a waveguide material having a refractive index of 1.7 or greater at an operating wavelength, a grating structure disposed on a surface of the waveguide layer, the grating structure comprising a grating layer comprising a plurality of ridges having a blazed profile in at least one cross-section, the blazed profile having an anti-blaze angle of 85° or less, a height in the range of 10 nm to 1,000 nm, and a duty cycle in the range of 5% to 95%, and one or more additional layers disposed on the grating layer, the one or more layers comprising a first layer of a material having a thickness in the range of 5 nm to 500 nm and a refractive index of 1.5 or less at the operating wavelength, the first layer being the outermost layer of the grating structure, comprising a grating structure comprising an article.

31. A head-mounted display system, comprising: a head-mountable frame; an optical projection system configured to output light and provide image content; a waveguide supported by the frame, the waveguide being configured to guide at least a portion of the light from the optical projection system coupled therein; a grating structure optically coupled to the waveguide, the grating structure being configured to couple the light guided by the waveguide out of the waveguide, the grating structure comprising: a grating layer comprising a plurality of ridges having a blazed profile in at least one cross-section, the blazed profile having an anti-blaze angle of 89° or less; one or more additional layers disposed on the grating layer, the one or more additional layers comprising a first layer of a material having a refractive index of 1.5 or less at the operating wavelength of the head-mounted display, the first layer being the outermost layer of the grating structure; a grating structure; a head-mounted display system. **Claim 32** A device, comprising: a waveguide for guiding light at an operating wavelength; a grating layer supported by the waveguide, the grating layer comprising a plurality of spaced ridges of a grating material forming a grating having a blazed profile in at least one cross-section, each ridge having a blazed side and an anti-blazed side opposite the blazed side, the anti-blazed side having a concave cross-sectional shape; one or more additional layers supported by the grating layer, the one or more additional layers comprising a first layer comprising a first material different from the grating material, the first material being located on and between the ridges; a device. **Claim 33** A device, comprising: a waveguide for guiding light at an operating wavelength; A grating layer extending in a plane, the grating layer being supported by the waveguide and comprising a plurality of spaced ridges of grating material forming a grating having a blaze profile in at least one cross-section, each ridge having a blaze side and an anti-blaze side opposite the blaze side, the anti-blaze side having a non-linear shape in the cross-section, the apex of the anti-blaze side being aligned with the bottom point of the anti-blaze side in the cross-section in a direction normal to the plane of the grating layer, a grating layer; One or more additional layers supported by the grating layer, the one or more additional layers comprising a first layer comprising a first material different from the grating material, the first material being located on and between the ridges, one or more additional layers; A device comprising.

34. A device, A waveguide for guiding light at an operating wavelength, A grating layer supported by the waveguide, the grating layer comprising a plurality of spaced ridges of grating material forming a grating having a blaze profile in at least one cross-section, each ridge having a blaze side and an anti-blaze side opposite the blaze side, a grating layer; One or more additional layers supported by the grating layer, the one or more additional layers comprising a first layer comprising a first material different from the grating material, the first material being located on and between the ridges, one or more additional layers; Comprising, For at least some of the ridges, the ridge and the one or more additional layers form a void on the anti-blaze side of the ridge, a device.

35. The device according to claim 32, wherein the concave cross-sectional shape of the anti-blaze side comprises a curved portion.

35. The device according to claim 33 or 34, wherein the anti-blaze side comprises a curved portion.

36. The device according to claim 34 or 35, wherein the radius of curvature of the curved portion is in the range of 20 nm to 500 nm.

37. The device according to any one of claims 32 or 35, wherein the concave cross-sectional shape of the anti-blaze side comprises one or more line segments.

38. The anti-blaze side comprises one or more line segments, the device according to any one of claims 33, 34, and 36.

39. The first line segment has a positive slope, the second line segment has a negative slope, and the first line segment is higher in the vertical direction than the second line segment, the device according to claim 38 or 39.

40. At least two of the one or more line segments intersect at an obtuse angle, the device according to any one of claims 37 - 39.

41. The length of at least one of the line segments is in the range of 5 nm to 500 nm, the device according to any one of claims 37 - 40.

42. At least one edge of the one or more additional layers and the anti-blaze side define a void, the device according to any one of claims 32 and 33.

43. The refractive index of the first layer of the one or more additional layers is at least 1.5 at the operating wavelength, the device according to any one of claims 32 - 42.

44. The one or more additional layers comprise a second layer, and the refractive index of the second layer is at least 1.5 at the operating wavelength, the device according to any one of claims 32 - 43.

45. The one or more additional layers do not coat the anti-blaze side of each ridge, the device according to any one of claims 32 - 44.

46. Each ridge has a blaze angle of 95° or more, the device according to any one of claims 32 - 45.

47. Each ridge has an anti-blaze angle in the range of 1° to 89°, the device according to any one of claims 32 - 46.

48. The ridge has a height in the range of 10 nm to 1,000 nm, the device according to any one of claims 32 - 47.

49. The grating has a pitch in the range of 100 nm to 5,000 nm, the device according to any one of claims 32 - 48.

50. The grating has a duty cycle in the range of 5% to 95%, the device according to any one of claims 32 - 49.

51. The first layer has a thickness in the range of 5 nm to 500 nm, the device according to any one of claims 32 - 50.

52. The device according to claim 44, wherein the second layer has a thickness in the range of 5 nm to 500 nm.

53. The device according to any one of claims 32 - 52, wherein the grating material comprises a crosslinked polymer.

54. The device according to claim 53, wherein the grating material comprises nanoparticles.

55. The device according to any one of claims 32 - 54, wherein the grating structure is at least partially transmissive at the operating wavelength.

56. The device according to any one of claims 32 - 55, wherein the grating layer and the waveguide are made of the same material.

57. The device according to claim 56, wherein the material comprises a polymer.

58. The device according to claim 56, wherein the material has a refractive index of 1.7 or greater.

59. The device according to claim 56, wherein the material is a synthetic material.

60. The device according to claim 59, wherein the synthetic material comprises nanoparticles.

61. The device according to any one of claims 32 - 60, further comprising one or more additional waveguides and one or more additional grating structures, each associated with a corresponding one of the additional waveguides.

62. The device according to claim 61, wherein the grating structures of the waveguides are arranged in an in-line configuration.

63. The device according to claim 62, wherein at least one of the grating structures is a reflective grating.

64. The device according to any one of claims 32 - 62, wherein at least some of the ridges comprise a blazed side with a single-stage geometry.

65. The device according to any one of claims 32 - 63, wherein at least some of the ridges comprise a blazed side with a multi-stage geometry.

66. A head-mounted display (HMD) configured to be worn on a user's head, the HMD comprising: a frame; a pair of optical elements supported by the frame such that each optical element of the pair of optical elements can be positioned in front of the user's eye; a device according to any one of claims 32 - 65, the device being disposed on at least one of the optical elements of the pair of optical elements. A projection system, the projection system being configured to project light into an optical waveguide of the device for display to the user's eye, the projection system and An HMD comprising. **Claim 67** The HMD according to claim 66, wherein each optical element comprises a distal and a proximal surface, the proximal surface being closer to the user's eye than the distal surface, and the grating of the device being disposed on the proximal surface. **Claim 68** The HMD according to claim 66, wherein each optical element comprises a distal and a proximal surface, the proximal surface being closer to the user's eye than the distal surface, and the grating of the device being disposed on the distal surface. **Claim 69** The HMD according to any one of claims 66-68, wherein the grating structure is configured to couple light into the optical waveguide at operating wavelengths corresponding to pixels of a plurality of different colors during operation of the HMD. **Claim 70** The HMD according to any one of claims 66-69, wherein the light from the light projection system is non-polarized light. **Claim 71** The HMD according to any one of claims 66-70, wherein the light projection system comprises a micro-LED display, an LCoS display, or a laser beam scanner display. **Claim 72** The HMD according to any one of claims 66-71, wherein the device comprises one or more additional grating structures, and the grating structure furthest from the light projection system is a reflective grating. **Claim 73** A method, Depositing an etch stop layer on a substrate; Depositing a grating material on the etch stop layer; Depositing a blazed grating template on the grating material; Using the blazed grating template to etch the grating material, thereby transferring the shape of the blazed grating template to the grating material to form a blazed grating; Coating the blazed grating with an etching mask at a first non-zero angle with respect to the vertical direction so that the anti-blaze side of the grating remains uncoated; Etching at a second non-zero angle with respect to the vertical direction with a sign opposite to the sign of the first non-zero angle, thereby removing an inner portion of the anti-blaze side; Removing the etching mask from the blazed grating; A method comprising. **Claim 74** The method according to claim 73, wherein the substrate is a waveguide. **Claim 75** The method according to claim 73 or 74, wherein the shape of the blazed grating template extends vertically beyond the shape of the blazed grating. **Claim 76** The method according to any one of claims 73 - 75, wherein etching the grating material is completed before the blazed grating template is completely used. **Claim 77** The method according to claim 75, further comprising peeling the remaining portion of the blazed grating template from the grating material before coating the blazed grating with the etching mask. **Claim 78** The method according to any one of claims 73 - 77, wherein etching the grating material comprises at least one of dry plasma etching, chemical etching, and wet chemical etching. **Claim 79** The method according to any one of claims 73 - 78, wherein the first non - zero angle is determined by the anti - blaze angle of the blazed grating. **Claim 80** The method according to claim 79, wherein the absolute value of the first non - zero angle is at least equal to the difference between the anti - blaze angle and 90°. **Claim 81** The method according to any one of claims 73 - 80, wherein the anti - blaze side comprises a concave curved portion. **Claim 82** The method according to any one of claims 73 - 81, wherein the anti - blaze side comprises one or more line segments. **Claim 83** The method according to any one of claims 73 - 82, further comprising coating the blazed grating with one or additional layers, wherein at least one of the one or more additional layers comprises a material with a refractive index of at least 1.5 at the operating wavelength. **Claim 84** The method according to claim 83, wherein coating the blazed grating with one or additional layers leads to the formation of a gap between at least one edge of the one or more additional layers and the anti - blaze side. **Claim 85** A head - mounted display (HMD), a waveguide for guiding light at an operating wavelength, a grating structure, A grating layer supported by the waveguide, the grating layer comprising a plurality of spaced ridges of grating material forming a grating having a blaze profile in at least one cross-section, each ridge having a blaze side and an anti-blaze side opposite the blaze side, the anti-blaze side having a concave cross-sectional shape, the grating layer and One or more additional layers supported by the grating layer, the one or more additional layers comprising a first layer comprising a first material different from the grating material, the first material being located on and between the ridges, the one or more additional layers and Comprising, a grating structure Comprising, an HMD. **Claim 86** The diffraction efficiency of the grating structure for unpolarized light incidence over a range of incident angles from -20° to +20° across a wavelength range of 400 nm to 700 nm is 10% or more, the HMD according to claim 85. **Claim 87** The back reflection of the grating structure is 30% or less for unpolarized light incidence over a range of incident angles from -20° to +20° across a wavelength range of 400 nm to 700 nm, the HMD according to claim 85 or 86. **Claim 88** Further comprising a projection system, during operation, the grating structure receiving unpolarized or polarized light from the projection system, the HMD according to any of claims 85 - 87. **Claim 89** The grating structure is positioned to receive light from the projection system traveling through the waveguide before being internally coupled into the waveguide by the grating structure, the HMD according to claim 88.

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