Crystal waveguide and wearable device comprising same

Abstract

A head-mounted display system includes: a head-mounted display frame; a first eyepiece supported by the frame, the first eyepiece comprising a first substrate consisting of a crystalline transparent material having a crystal axis in a first orientation relative to the frame, the substrate having a first surface and a second surface opposite the first surface, the first eyepiece further includes a first coupling-in element having a grating located on the first surface, and a first coupling-out element having a grating located on the first surface and / or a grating located on the second surface; and a second eyepiece comprising a second substrate composed of a crystalline transparent material having a crystal axis in a second orientation different from the first orientation relative to the frame, a second coupling-in element on either surface of the second substrate, and a second coupling-out element on either surface of the second substrate.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims the benefit of priority of U.S. Provisional Patent Application Serial No. 63 / 433,335, filed on December 16, 2022, the content of which is incorporated herein by reference. Technical Field

[0003] The present disclosure relates to display systems, and more particularly, to augmented and virtual reality display systems and substrates for such display systems. Background Art

[0004] 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 way that appears to be real or can be perceived as real. Virtual reality or "VR" scenarios typically involve the presentation of digital or virtual image information in a situation that is opaque to other actual real - world visual inputs; augmented reality or "AR" scenarios typically involve the presentation of digital or virtual image information as an enhancement to the visualization of the user's surrounding real world. Mixed reality or "MR" scenarios are a type of AR scenario and typically involve virtual objects that are integrated into the natural world and respond to the natural world. For example, in an MR scenario, AR image content can be occluded by objects in the real world or be perceived as interacting with objects in the real world.

[0005] Reference Figure 1 , shows an augmented reality scenario 10, in which a user of AR technology sees a real - world park - like setting 20, which features people, trees, buildings in the background, and a concrete platform 30. In addition to these items, the user of AR technology also perceives that he "sees" "virtual content", such as a robotic statue 40 standing on the real - world concrete platform 30, and a flying cartoon - style avatar character 50, which appears to be an avatar of a bumblebee, even though these elements 40, 50 do not exist in the real world. Because the human visual perception system is complex, it is extremely challenging to develop AR technologies that facilitate the comfortable, natural, and rich presentation of virtual image elements among other virtual or real - world image elements.

[0006] The systems and methods disclosed herein address various challenges associated with AR and VR technologies. Summary of the Invention

[0007] In an augmented reality (AR) system, a substrate having a high refractive index can advantageously provide a large field of view (FOV). However, some materials having a high refractive index are optically anisotropic (also known as birefringent), e.g., the refractive index depends on the propagation direction of light relative to the optical axis of the material.

[0008] In an AR system, many factors can cause optical artifacts, such as unwanted optical effects. The occurrence of these optical artifacts depends on the refractive index of the material. Therefore, the orientation of any birefringent material in the system will affect the magnitude of the optical artifacts caused by birefringence. This disclosure contemplates apparatuses, systems, and methods for reducing the occurrence of optical artifacts that rely on the birefringence of crystalline materials having a high refractive index.

[0009] Aspects of the disclosed subject matter are summarized below.

[0010] Generally, in a first aspect, features of the present disclosure

[0011] Examples of a head-mounted display system may include one or more of the following features.

[0012] Other features and advantages will be apparent from the drawings, the following description, and the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 An augmented reality (AR) view seen by a user through an AR device is shown.

[0014] Figure 2 A conventional display system for simulating three-dimensional images for a user is shown.

[0015] Figure 3A 、 3B And 3C show the relationship between the radius of curvature and the focal radius.

[0016] Figure 4A A representation of the accommodation-vergence response of the human visual system is shown.

[0017] Figure 4B Examples of different accommodation states and vergence states of a user's pair of eyes are shown.

[0018] Figure 4C An example of a representation of a top view of a user viewing content via a display system is shown.

[0019] Figure 4D Another example of a representation of a top view of a user viewing content via a display system is shown.

[0020] Figure 5 Some aspects of a method for simulating three-dimensional images by varying wavefront divergence are shown.

[0021] Figure 6 An example of a waveguide stack for outputting image information to a user is shown.

[0022] Figure 7Shows an example of an outgoing beam output from a waveguide.

[0023] Figure 8 Shows an example of a stacked waveguide assembly, where each depth plane includes an image formed using multiple different component colors.

[0024] Figure 9A Shows a cross-sectional side view of an example of a set of stacked waveguides, each stacked waveguide including an optically coupled-in element.

[0025] Figure 9B Shows Figure 9A A perspective view of an example of multiple stacked waveguides.

[0026] Figure 9C Shows Figure 9A And 9B A top plan view of an example of multiple stacked waveguides.

[0027] Figure 9D Shows an example of a wearable display system.

[0028] Figure 10 Shows a head-mounted device having a frame that supports left and right side eyepieces.

[0029] Figure 11A Shows a pattern of points assigned to a substrate. Figure 11B Shows an uneven coating on a substrate surface.

[0030] Figure 12A 、 12B 、12C and 12D show schematic diagrams of a process for depositing a dielectric coating.

[0031] Figure 13 、 14A 、14B, 14C and 14D show a substrate surface having a dielectric coating.

[0032] Figure 15A And 15B Show the fields of view of eyepieces having LiTaO3 and LiNbO3 substrates, respectively.

[0033] Figure 16A And 16B Show the optical artifacts of the left and right side eyepieces of X- and Y-cut wafers, respectively.

[0034] Figure 16C And 16D Show the optical artifacts of the left and right side eyepieces of Z-cut wafers, respectively.

[0035] Figure 16E Shows a wafer having six eyepieces, where the crystal axis is oriented in a first direction. Figure 16F Shows the same asFigure 16E Optical artifacts associated with the six eyepieces of the wafer.

[0036] Figure 16G A wafer with six eyepieces is shown, where the crystal axis is oriented in a second direction different from the first direction. Figure 16H Shown is Figure 16G Optical artifacts associated with the six eyepieces of the wafer.

[0037] Figure 16I and 16J respectively show Figure 16E and 16G The wafers of, marked with the angle between the line between the coupling-in element and the coupling-out element and the optical axis of the substrate material in the wafer.

[0038] Figure 17 Light propagating in different directions and the k-space ellipses of different lithium niobate cuts are shown.

[0039] Figure 18A , 18B and 18C show the head-mounted device images corresponding to red light, green light, and blue light respectively.

[0040] Figure 19A and 19B respectively show X-cut wafers with left and right side eyepieces. Figure 19C is Figure 19A and 19B Schematic diagrams of the right and left eyepieces aligned for the head-mounted device in. Figure 19D , 19E , 19F and 19G are images captured by a camera located above the eyepiece coupling-out elements of the wafers in Figure 19A and 19B .

[0041] Figure 20A A Z-cut wafer with an eyepiece is shown. Figure 20B and 20C respectively are images generated using non-polarized light and polarized light with the eyepieces of the wafers of Figure 20A . Figure 20D , 20E and 20F are Figure 20A Optical artifacts of different orientations of the eyepieces of.

[0042] Figure 21A and 21B respectively show images of the outputs of the polarization-sensitive coupling-in element and the polarization-insensitive coupling-in element.

[0043] Figure 21C A polarization-insensitive coupling grating on the substrate is shown.

[0044] Figure 21D ,21E 21F, 21G, 21H, and 21I show red, green, and blue images generated using Figure 21C a polarization-insensitive coupling grating.

[0045] Figure 22A and 22B show a reflective and a transmissive coupling grating, respectively.

[0046] Figure 23A and 23B show an eyepiece with a non-uniform height distribution. Figure 23C and 23D are respectively Figure 23A and 23B plan views of the eyepiece.

[0047] Figure 23E , 23F and 23G respectively show the red, green, and blue eye box efficiencies of the eyepiece of FIG. 32A. Figure 23H , 23I and 23J respectively show Figure 23B the red, green, and blue eye box efficiencies of the eyepiece.

[0048] Figure 23K shows various multi-refractive index eyepieces.

[0049] Figure 24A shows a wafer with a thickness variation. Figure 24B shows Figure 24A the height grading of the wafer. Figure 24C shows Figure 24A a cross-sectional view of the wafer.

[0050] Figure 24D , 24E and 24F show wafers with different thickness variations. Figure 24G and 24H show images generated by the eyepieces within the wafers of Figure 24D , 24E and 24F.

[0051] Figure 25 shows eyepieces with a conductive coating, an absorptive adhesive, and both.

[0052] Throughout the drawings, reference numerals may be reused to indicate corresponding relationships between reference elements. The drawings are provided to illustrate example implementations described herein and are not intended to limit the scope of the disclosure. Detailed Description

[0053] An AR system can display virtual content to a user or viewer while still allowing the user to see the world around them. The content is preferably displayed on a head-mounted display, such as part of glasses, which projects image information onto the user's eyes. In addition, the display can also transmit light from the surrounding environment to the user's eyes to allow viewing of the surrounding environment. As used herein, it will be understood that a "head-mounted" or "head-worn" display is a display that can be mounted on the head of a viewer or user.

[0054] In some AR systems, a virtual / augmented / mixed display with a relatively high field of view (FOV) can enhance the viewing experience. The FOV of the display depends on the angle of the light output from the waveguide of the eyepiece through which the viewer sees the image projected onto his or her eyes. A waveguide with a relatively high refractive index (e.g., 1.8 or higher) can provide a relatively high FOV. However, in order to effectively couple light into a high refractive index waveguide, the diffractive optical coupling element should also have a corresponding high refractive index. To achieve this, among other advantages, according to the embodiments described herein, some displays for AR systems include a waveguide comprising a material with a relatively high refractive index (e.g., 1.8 or higher, such as 2.0 or higher) on which a corresponding diffractive grating with a high refractive index, such as lithium-based oxide, is formed. For example, by patterning a surface portion of the waveguide formed of lithium-based oxide, the diffractive grating can be formed directly on the lithium-based oxide waveguide.

[0055] Some high refractive index diffractive optical coupling elements, such as input or output optical elements, have strong polarization dependence. For example, an input coupling grating (ICG) for coupling light into a waveguide, where the diffractive optical coupling element includes a high refractive index material, can admit significantly more light of a particular polarization than of the other polarization. For example, such an element can couple light with TM polarization into the waveguide at a rate approximately three times that of light with TE polarization. Diffractive optical coupling elements with such polarization dependence may have reduced efficiency (due to low efficiency and general rejection of one polarization), and may also produce coherent artifacts and reduce the uniformity of the far-field image formed by light coupled out of a birefringent waveguide. To obtain diffractive optical coupling elements that are insensitive to polarization or at least have reduced polarization sensitivity (e.g., that couple light with relatively polarization-independent efficiency), according to various embodiments described herein, some displays for AR systems include waveguides having diffractive gratings formed with a blazed geometry. The diffractive grating can also be formed directly in the waveguide, which can 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 any of the foregoing values). For example, by patterning the high refractive index material with a blazed geometry, the diffractive grating can be formed in the high refractive index material, such as a lithium-based oxide like lithium niobate (LiNbO3) or lithium tantalate (LiTaO3), or such as zirconium dioxide (ZrO2), titanium dioxide (TiO2), silicon nitride Si3N4, or silicon carbide (SiC).

[0056] Reference will now be made to the accompanying drawings, in which like reference numerals always refer to like parts. Unless otherwise noted, the drawings are schematic and not necessarily drawn to scale.

[0057] Figure 2 A conventional display system for simulating three-dimensional images for a user is shown. The user's eyes are spaced apart, and when viewing a real object in space, each eye will have a slightly different view of the object, and an image of the object can be formed at different positions on the retina of each eye. This can be referred to as binocular parallax and can be used by the human visual system to provide a sense of depth. The conventional display system simulates binocular parallax by presenting two different images 190, 200 with slightly different views of the same virtual object (one image for each eye 210, 220), which correspond to the views of the virtual object that would be seen by each eye as a real object at the desired depth. These images provide binocular cues that the user's visual system can interpret to obtain a sense of depth.

[0058] Continue to refer to Figure 2, images 190, 200 are spaced apart from eyes 210, 220 by a distance 230 along the Z-axis. The Z-axis is parallel to the optical axis of the viewer who is looking at an object at optical infinity directly in front of the viewer. Images 190, 200 are flat and at a fixed distance from eyes 210, 220. Based on slightly different views of the virtual object in the images presented to eyes 210, 220 respectively, the eyes can rotate naturally so that the images of the object fall on corresponding points on the retina of each eye to maintain single binocular vision. This rotation can cause the lines of sight of each eye 210, 220 to converge on the spatial point where the virtual object is perceived to exist. Thus, providing 3D images generally involves providing binocular cues that can manipulate the vergence of the user's eyes 210, 220 and are interpreted by the human visual system to provide a sense of depth.

[0059] However, generating a realistic and comfortable sense of depth is challenging. It should be understood that light from objects at different distances from the eyes has wavefronts with different amounts of divergence. Figures 3A to 3C The relationship between distance and light divergence is shown. The distances between the object and eye 210 are represented in decreasing order of distance as R1, R2, and R3. As Figures 3A to 3C shown, as the distance to the object decreases, the light becomes more divergent. Conversely, as the distance increases, the light becomes more collimated. In other words, it can be said that the light field generated by a point (object or part of an object) has a spherical wavefront curvature that is a function of how far that point is from the user's eye. The curvature increases as the distance between the object and eye 210 decreases. Although only a single eye 210 is shown in Figures 3A to 3C and other figures in this document for clarity, the discussion regarding eye 210 applies to both eyes 210 and 220 of the viewer.

[0060] Continuing to refer to Figures 3A to 3C, light from an object being looked at by a viewer's eyes can have different degrees of wavefront divergence. Due to the different amounts of wavefront divergence, the light can be focused differently by the eye's lens, which in turn may require the lens to assume different shapes to form a focused image on the retina of the eye. In the case where a focused image is not formed on the retina, the resulting retinal blur serves as an accommodation cue that causes a change in the shape of the eye's lens until a focused image is formed on the retina. For example, the accommodation cue can trigger the relaxation or contraction of the ciliary muscles surrounding the eye's lens, thereby adjusting the force applied to the zonular ligaments that hold the lens, so that the shape of the eye's lens changes until the retinal blur of the object being looked at is eliminated or minimized, thereby forming a focused image of the object being looked at on the retina (e.g., the fovea) of the eye. The process by which the eye's lens changes shape can be referred to as accommodation, and the shape of the eye's lens required to form a focused image of the object being looked at on the retina (e.g., the fovea) of the eye can be referred to as the accommodative state.

[0061] Now referring to Figure 4A , a representation of the accommodation-vergence response of the human visual system is shown. The movement of the eyes to look at an object causes the eyes to receive light from the object, where the light forms an image on each retina of the eye. The presence of retinal blur in the image formed on the retina can provide an accommodation cue, and the relative position of the image on the retina can provide a vergence cue. The accommodation cue causes accommodation to occur, such that the eye's lens assumes a particular accommodative state that forms a focused image of the object on the retina (e.g., the fovea) of the eye, respectively. On the other hand, the vergence cue causes vergence movement (eye rotation) to occur so 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 have assumed a particular vergence state. Continuing to refer to Figure 4A , accommodation can be understood as the process by which the eyes achieve a particular accommodative state, and vergence can be understood as the process by which the eyes achieve a particular vergence state. As Figure 4A shown, if the user looks at another object, the accommodation and vergence states of the eyes can change. For example, if the user looks at a new object at a different depth on the z-axis, the accommodative state may change.

[0062] Without being limited by theory, it can be considered that a viewer of an object may perceive the object as "three-dimensional" due to the combination of convergence and accommodation. As described above, the convergence movement of the two eyes relative to each other (e.g., the eyes rotate so that the pupils move toward or away from each other to converge the lines of sight of the eyes to fixate on an object) is closely related to the accommodation of the eye lenses. Under normal circumstances, under the known "accommodation-convergence reflex" relationship, changing the shape of the eye lens to change the focus from one object to another object at a different distance will automatically cause a matching convergence change to the same distance. Similarly, under normal circumstances, a change in convergence will trigger a matching change in the shape of the lens.

[0063] Now referring to Figure 4B , an example of different accommodation states and convergence states of the eyes is shown. A pair of eyes 222a is fixated on an object at optical infinity, while a pair of eyes 222b is fixated on a point 221 less than optical infinity. It is noted that the convergence states of each pair of eyes are different, where a pair of eyes 222a looks straight ahead, while a pair of eyes 222 converges on the point 221. The accommodation states of the eyes forming each pair of eyes 222a and 222b are also different, as represented by the different shapes of the lenses 210a, 220a.

[0064] Unfortunately, many users of traditional "3D" display systems find that such traditional systems are uncomfortable or may not be able to perceive a sense of depth at all due to the mismatch between the accommodation and convergence states in these displays. As described above, many stereoscopic or "3D" display systems display a scene by providing slightly different images to each eye. Such systems are uncomfortable for many viewers because, among other things, such systems only provide different presentations of the scene and cause a change in the convergence state of the eyes, but the accommodation states of these eyes do not change correspondingly. Instead, the images are displayed by a display at a fixed distance from the eyes so that the eyes view all the image information in a single accommodation state. This arrangement violates the "accommodation-convergence reflex" by causing a change in the convergence state without a matching 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 can form a more realistic and comfortable three-dimensional image simulation.

[0065] Without being limited by theory, it can be considered that the human eye can generally interpret a limited number of depth planes to provide a sense of depth. Therefore, a highly believable perceived depth simulation can be achieved by providing different presentations of images corresponding to each of these limited number of depth planes to the eyes. In some embodiments, the different presentations can simultaneously provide convergence cues and matching accommodation cues, thereby providing a physiologically correct accommodation-convergence match.

[0066] Continuing to refer to Figure 4B, shows two depth planes 240, which correspond to different distances from the eyes 210, 220 in space. For a given depth plane 240, vergence cues can be provided by displaying appropriately different perspective images for each eye 210, 220. Additionally, for a given depth plane 240, the light forming the images provided to each eye 210, 220 can have a wavefront divergence corresponding to the light field generated by points at the distance of that depth plane 240.

[0067] In the illustrated implementation, the depth plane 240 containing the point 221 is at a distance of 1 meter along the Z-axis. As used herein, the distance or depth along the Z-axis can be measured with the zero point located at the exit pupil of the user's eye. Thus, the depth plane 240 at a depth of 1 meter corresponds to a distance of 1 meter from the exit pupil of the user's eye on the optical axis of the user's eye when the eye is pointed at optical infinity. As an approximation, the depth or distance along the Z-axis can be measured from a display in front of the user's eye (e.g., from the surface of the waveguide), plus the value of the distance between the device and the exit pupil of the user's eye. This value can be referred to as the eye relief 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 of the eye relief can be a standardized value common to all viewers. For example, it can be assumed that the eye relief is 20 mm, and the depth plane at a depth of 1 meter can be at a distance of 980 mm in front of the display.

[0068] Now refer to Figure 4C and 4D , which respectively show examples of a matched accommodation-vergence distance and a mismatched accommodation-vergence distance. As Figure 4C shown, the display system can provide images of a virtual object to each eye 210, 220. These images can cause the eyes 210, 220 to assume a vergence state in which the eyes converge at the point 15 on the depth plane 240. Additionally, the images can be formed by light having a wavefront curvature corresponding to a real object at that depth plane 240. As a result, the eyes 210, 220 assume an accommodation state in which the images are focused on the retinas of these eyes. Thus, the user can perceive the virtual object as being located at the point 15 on the depth plane 240.

[0069] It will be understood that each of the accommodation and vergence states of eyes 210, 220 is associated with a specific distance on the z-axis. For example, an object at a specific distance from eyes 210, 220 causes these 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 is a specific vergence distance Vd associated with the eyes or their positions relative to each other in a specific vergence state. When the accommodation distance and the vergence distance match, it can be said that the relationship between accommodation and vergence is physiologically correct. This is considered the most comfortable scenario for the viewer.

[0070] However, in a stereoscopic display, the accommodation distance and the vergence distance may not always match. For example, as Figure 4D shown, the images presented to eyes 210, 220 may be presented with wavefront divergence corresponding to depth plane 240, and eyes 210, 220 may assume a specific accommodation state in which points 15a, 15b on that depth plane are in focus. However, the images presented to eyes 210, 220 may provide vergence cues that cause eyes 210, 220 to converge at a point 15 that is not located on depth plane 240. As a result, in some embodiments, the accommodation distance corresponds to the distance from the exit pupils of eyes 210, 220 to depth plane 240, while the vergence distance corresponds to a greater distance from the exit pupils of eyes 210, 220 to point 15. The accommodation distance is different from the vergence distance. Thus, there is an accommodation-vergence mismatch. This mismatch is considered undesirable and may 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.

[0071] In some implementations, it will be understood that reference points other than the exit pupils of eyes 210, 220 can be used to determine the distances for determining the accommodation-vergence mismatch, provided that the same reference point is used for both the accommodation distance and the vergence distance. For example, the distance 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., can be measured.

[0072] Without being limited by theory, it can be considered that in cases where the accommodation-vergence mismatch itself does not cause significant discomfort, the user may still perceive accommodation-vergence mismatches of up to about 0.25 diopters, up to about 0.33 diopters, and up to about 0.5 diopters as being physiologically correct. In some embodiments, the display systems disclosed herein (e.g., Figure 6The display system 250) presents an image to a viewer with an accommodation-convergence mismatch of about 0.5 diopters or less. In some other embodiments, the accommodation-convergence mismatch of the image provided by the display system is about 0.33 diopters or less. In still other embodiments, the accommodation-convergence mismatch of the image provided by the display system is about 0.25 diopters or less, including about 0.1 diopters or less.

[0073] Figure 5 Shows some aspects of a method for simulating a three-dimensional image by varying 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 can output an outgoing beam 650 with a limited amount of wavefront divergence corresponding to the wavefront divergence of the light field generated by a point on the desired depth plane 240. In some embodiments, the same amount of wavefront divergence is provided for all objects presented on the depth plane. Additionally, it will be described that image information from a similar waveguide can be provided to the user's other eye.

[0074] In some cases, a single waveguide can be configured to output light with a set amount of wavefront divergence corresponding to a single depth plane or a limited number of depth planes, and / or the waveguide can be configured to output light within a limited wavelength range. Thus, in some embodiments, multiple waveguides or a waveguide stack can be utilized to provide different amounts of wavefront divergence for different depth planes and / or output light within different wavelength ranges. As used herein, it should be understood that a depth plane can be planar or can follow a curved surface profile.

[0075] Figure 6 Shows an example of a waveguide stack for outputting image information to a user. The display system 250 includes a waveguide stack or a stacked waveguide assembly 260 that can be used to provide a three-dimensional perception to the eye / brain using multiple waveguides 270, 280, 290, 300, 310. It should be understood that in some embodiments, the display system 250 can be considered a light field display. Additionally, the waveguide assembly 260 can also be referred to as an eyepiece.

[0076] In some embodiments, the display system 250 is configured to provide substantially continuous convergence cues and multiple discrete accommodation cues. The convergence cues can be provided by displaying different images to each eye of the user, and the accommodation cues can be provided by outputting light forming an image with a selectable discrete amount of wavefront divergence. In other words, the display system 250 can be configured to output light with a variable wavefront divergence level. In some embodiments, each discrete level of wavefront divergence corresponds to a specific depth plane and can be provided by a specific one of the waveguides 270, 280, 290, 300, 310.

[0077] Continuing to refer Figure 6 , the waveguide assembly 260 may further include a plurality of features 320, 330, 340, 350 between waveguides. In some embodiments, the features 320, 330, 340, 350 may be one or more lenses. The waveguides 270, 280, 290, 300, 310 and / or the plurality of lenses 320, 330, 340, 350 may be configured to send image information to the eye with various levels of wavefront curvature or light 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. The image injection devices 360, 370, 380, 390, 400 may serve as light sources for the waveguides and may be used to inject image information into the waveguides 270, 280, 290, 300, 310. As described herein, each waveguide may be configured to distribute incident light across each corresponding waveguide for output toward the eye 210. Light exits from the output surfaces 410, 420, 430, 440, 450 of the image injection devices 360, 370, 380, 390, 400 and is injected into the corresponding input surfaces 460, 470, 480, 490, 500 of the waveguides 270, 280, 290, 300, 310. In some embodiments, each of the input surfaces 460, 470, 480, 490, 500 may be an edge of the corresponding waveguide or may be 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 embodiments, a single light beam (e.g., a collimated light beam) may be injected into each waveguide to output the entire field of a cloned collimated light beam that is directed toward the eye 210 at a particular angle (and amount of divergence) corresponding to the depth plane associated with a particular waveguide. In some embodiments, a single image injection device among the image injection devices 360, 370, 380, 390, 400 may be associated with and inject light into a plurality (e.g., three) of the waveguides 270, 280, 290, 300, 310.

[0078] In some embodiments, the image injection devices 360, 370, 380, 390, 400 are discrete displays, each of which separately generates image information for injection into the corresponding waveguides 270, 280, 290, 300, 310. In some other embodiments, the image injection devices 360, 370, 380, 390, 400 are output terminals of a single multiplexed display. For example, the output terminals of the multiplexed display can pipe image information to each of the image injection devices 360, 370, 380, 390, 400 via one or more optical ducts such as fiber optic cables. It should be understood that the image information provided by the image injection devices 360, 370, 380, 390, 400 can include light of different wavelengths or colors (e.g., different component colors as discussed herein).

[0079] In some embodiments, the light injected into the waveguides 270, 280, 290, 300, 310 is provided by a light projector system 520 that includes a light module 530, which may include a light emitter such as a light-emitting diode (LED). The light from the light module 530 can be directed to a light modulator 540 (e.g., a spatial light modulator) via a beam splitter 550 and modified by the light modulator 540. The light modulator 540 can be configured to change the perceived intensity of the light injected into the waveguides 270, 280, 290, 300, 310 to encode the light with image information. Examples of spatial light modulators include liquid crystal displays (LCDs), which include liquid crystal on silicon (LCOS) displays. It should be understood that the image injection devices 360, 370, 380, 390, 400 are schematically shown, and in some embodiments, these image injection devices can represent different optical paths and positions in a common projection system that is configured to output light into the associated waveguides of the waveguides 270, 280, 290, 300, 310. In some embodiments, the waveguides in the waveguide assembly 260 can act as ideal lenses while relaying the light injected into the waveguides out to the user's eyes. In this concept, the object can be the spatial light modulator 540, and the image can be an image on a depth plane.

[0080] In some examples, a μLED display can be used in the light projector system 520. The μLED display can unpolarize light over a large angular range. Thus, the μLED display can advantageously provide an image efficiently over a wide field of view.

[0081] In some implementations, the display system 250 can be a scanned fiber optic display that includes one or more scanned optical fibers configured to project light into one or more waveguides 270, 280, 290, 300, 310 in various patterns (e.g., raster scan, helical scan, Lissajous pattern, etc.) and ultimately to the viewer's eye 210. In some embodiments, the illustrated image injection devices 360, 370, 380, 390, 400 may schematically represent a single scanned optical fiber or a bundle of scanned optical fibers configured to inject light into one or more of the waveguides 270, 280, 290, 300, 310. In some other embodiments, the illustrated image injection devices 360, 370, 380, 390, 400 may schematically represent multiple scanned optical fibers or multiple bundles of scanned optical fibers, each of the multiple scanned optical fibers or multiple bundles of scanned optical fibers being configured to inject 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 of the waveguides 270, 280, 290, 300, 310. It should be understood that one or more intermediate optical structures can be disposed between the one or more scanned optical fibers and the one or more waveguides 270, 280, 290, 300, 310 to, for example, redirect light exiting the scanned optical fibers into the one or more waveguides 270, 280, 290, 300, 310.

[0082] The controller 560 controls the operation of one or more of the stacked waveguide assemblies 260, including the operation of the image injection devices 360, 370, 380, 390, 400, the optical module 530, and the light modulator 540. In some embodiments, the controller 560 is part of the local processing and data module 140. The controller 560 includes programming (e.g., instructions in a non-transitory medium) that regulates the timing and provision of image information to the waveguides 270, 280, 290, 300, 310 according to any of the various schemes disclosed herein, for example. In some embodiments, the controller can be a single monolithic device or a distributed system connected via wired or wireless communication channels. In some embodiments, the controller 560 can be part of the local processing and data module 140 or the remote processing module 150 ( Figure 9D ).

[0083] Continuing reference Figure 6, waveguides 270, 280, 290, 300, 310 can be configured to propagate light within each respective waveguide by total internal reflection (TIR). Waveguides 270, 280, 290, 300, 310 can each be planar or have another shape (e.g., curved), having a top major surface and a bottom major surface and an edge extending between these top and bottom major surfaces. In the illustrated configuration, waveguides 270, 280, 290, 300, 310 can each include light extraction optical elements 570, 580, 590, 600, 610, which are configured to extract light from the waveguides by redirecting the light propagating inside the respective corresponding waveguides out of the waveguides to output image information to the eye 210. The extracted light can also be referred to as coupled-out light, and the light extraction optical elements can also be referred to as light extraction optical elements. The extracted light beam can be output from the waveguide at the location where the light propagating in the waveguide is incident on the light extraction optical element. As further discussed herein, the light extraction optical elements 570, 580, 590, 600, 610 can be, for example, gratings of diffractive optical features. Although shown as being disposed at the bottom major surface of waveguides 270, 280, 290, 300, 310, for ease of description and clarity of drawing, in some embodiments, as further discussed herein, the light extraction optical elements 570, 580, 590, 600, 610 can be disposed at the top and / or bottom major surfaces, and / or can be disposed directly within the volume of waveguides 270, 280, 290, 300, 310. In some embodiments, the light extraction optical elements 570, 580, 590, 600, 610 can be formed in a material layer attached to a transparent substrate to form waveguides 270, 280, 290, 300, 310. In some other embodiments, waveguides 270, 280, 290, 300, 310 can be a single-piece material, and the light extraction optical elements 570, 580, 590, 600, 610 can be formed on and / or within the surface of the piece of material.

[0084] Continue to refer to Figure 6, as discussed herein, each of waveguides 270, 280, 290, 300, 310 is configured to output light to form an image corresponding to a specific depth plane. For example, the waveguide 270 closest to the eye can be configured to deliver collimated light (which is injected into such a waveguide 270) to the eye 210. This collimated light can represent an optically infinite focal plane. The next upward waveguide 280 can be configured to emit collimated light that passes through a first lens 350 (e.g., a negative lens) before reaching the eye 210; such a first lens 350 can be configured to produce a slightly convex wavefront curvature such that the eye / brain interprets the light from this next upward waveguide 280 as coming from a first focal plane that is closer to the eye 210 inward from the optically infinite. Similarly, the third upward waveguide 290 has its output light pass through both the first lens 350 and the second lens 340 before reaching the eye 210; the combined optical power of the first lens 350 and the second lens 340 can be configured to produce another increment of wavefront curvature such that the eye / brain interprets the light from the third waveguide 290 as coming from a second focal plane that is closer to the person further inward from the optically infinite than the light from the next upward waveguide 280.

[0085] The other layers of waveguide layers 300, 310 and lenses 330, 320 are configured similarly, where the highest waveguide 310 in the stack sends its output through all the lenses between it and the eye to obtain the total optical power representing the focal plane closest to the person. To compensate for the stack of lenses 320, 330, 340, 350 when observing / interpreting light from the world 510 on the other side of the stacked waveguide assembly 260, a compensation lens layer 620 can be provided at the top of the stack to compensate for the total optical power of the stack of lenses 320, 330, 340, 350 below. This configuration provides as many perceived focal planes as there are available waveguide / lens pairs. Both the outcoupling optical elements of the waveguides and the focusing aspects of the lenses can be static (i.e., not dynamic or electroactive). In some alternative embodiments, one or both of them can be dynamic by using electroactive features.

[0086] In some embodiments, two or more of the waveguides 270, 280, 290, 300, 310 can have the same associated depth plane. For example, multiple waveguides 270, 280, 290, 300, 310 can be configured to output a set of images to the same depth plane, or multiple subsets of the waveguides 270, 280, 290, 300, 310 can be configured to output a set of images to the same multiple depth planes, one set of images per depth plane. This can provide an advantage for forming a stitched image to provide an extended field of view at those depth planes.

[0087] Continuing to refer to Figure 6, the output optical elements 570, 580, 590, 600, 610 can be configured to both redirect light out of their respective waveguides and output the light with an appropriate amount of divergence or collimation for a particular depth plane associated with the waveguide. As a result, waveguides with different associated depth planes can have differently configured output optical elements 570, 580, 590, 600, 610, and the differently configured output optical elements 570, 580, 590, 600, 610 output light with different amounts of divergence according to the associated depth plane. In some embodiments, the output optical elements 570, 580, 590, 600, 610 can be volume features or surface features that can be configured to output light at a particular angle. For example, the output optical elements 570, 580, 590, 600, 610 can be volume holograms, surface holograms, and / or diffraction gratings. In some embodiments, the features 320, 330, 340, 350 can not be lenses; rather, they can simply be spacers (e.g., cladding and / or structures for forming air gaps).

[0088] In some implementations, the output optical elements 570, 580, 590, 600, 610 are diffraction features that form a diffraction pattern, or “diffractive optical elements” (also referred to herein as “DOEs”). Preferably, the DOE has a low enough diffraction efficiency such that only a portion of the light beam is deflected towards the eye 210 with each intersection of the DOE, while the remainder continues through the waveguide via TIR. Thus, the light carrying the image information is split into multiple associated output beams that exit the waveguide from multiple locations such that a fairly uniform output pattern towards the eye 210 is formed for the particular collimated beam bouncing around within the waveguide.

[0089] In some embodiments, one or more DOEs can be switched between an “on” state in which they actively diffract and an “off” state in which they do not significantly diffract. For example, a switchable DOE can include a polymer dispersed liquid crystal layer, where the microdroplets include a diffraction pattern in a host medium, and the refractive index of the microdroplets can be switched to substantially match the refractive index of the host material (in which case the pattern does not significantly diffract incident light) or the microdroplets can be switched to a refractive index that is mismatched with the refractive index of the host medium (in which case the pattern actively diffracts incident light).

[0090] In some embodiments, a camera component 630 (e.g., a digital camera, including a visible light camera and an infrared light camera) can be provided to capture images of the eye 210 and / or the tissue around the eye 210 to, for example, detect user input and / or monitor the user's physiological state. As used herein, a camera can be any image capture device. In some embodiments, the camera component 630 can include an image capture device and a light source to project light (e.g., infrared light) onto the eye, and then the light can be reflected by the eye and detected by the image capture device. In some embodiments, the camera component 630 can be attached to the frame 80( Figure 9D ) and can be in electrical communication with the local processing and data module 140 and / or the remote processing module 150, which can process the image information from the camera component 630. In some embodiments, one camera component 630 can be used for each eye to monitor each eye separately.

[0091] Now referring to Figure 7 , an example of an outgoing light beam output by a waveguide is shown. One waveguide is shown, but it should be understood that in the case where the waveguide assembly 260 includes multiple waveguides, the other waveguides in the waveguide assembly 260( Figure 6 ) can function similarly. Light 640 is injected 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 is incident on the outcoupling optical element 570 (e.g., DOE), a portion of the light exits the waveguide as an outgoing light beam 650. The outgoing light beams 650 are shown as being substantially parallel, but as discussed herein, they can also be redirected to propagate at an angle (e.g., to form a diverging outgoing light beam) to the eye 210, the angle depending on the depth plane associated with the waveguide 270. It should be understood that substantially parallel outgoing light beams can indicate a waveguide having an outcoupling optical element that outcouples light to form an image that appears to be set on a depth plane at a long distance from the eye 210 (e.g., optical infinity). Other waveguides or other sets of outcoupling optical elements can output a more diverging outgoing light beam pattern, which will require the eye 210 to accommodate to a closer distance to focus the more diverging outgoing light beam pattern on the retina and will be interpreted by the brain as light from a distance closer to the eye 210 than optical infinity.

[0092] In some embodiments, a full-color image can be formed at each depth plane by superimposing images in each of the component colors (e.g., three or more component colors). Figure 8An example of a stacked waveguide assembly is shown, where each depth plane includes an image formed using multiple different component colors. The illustrated embodiment shows depth planes 240a - 240f, but more or fewer depths may also be contemplated. Each depth plane may have three or more component 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. For the diopters (dpt) following the letters G, R, and B, different depth planes are represented by different numbers in the figure. By way of example only, the numbers following each of these letters represent the diopter (1 / m), or the reciprocal of the distance of that depth plane from the viewer, and each box in the figure represents a separate component color image. In some embodiments, to account for differences in the eye's focusing of light of different wavelengths, the precise placement of the depth planes of different component colors may vary. For example, the different component color images of a given depth plane may be placed on depth planes corresponding to different distances from the user. Such an arrangement can increase visual acuity and user comfort, and / or can reduce chromatic aberration.

[0093] In some embodiments, the light of each component color may be output by a single dedicated waveguide, and thus, each depth plane may have multiple waveguides associated therewith. In such an embodiment, each box in the figure that includes the letter G, R, or B may be understood to represent a separate waveguide, and each depth plane may provide three waveguides, where each depth plane provides three component color images. Although, for ease of description, the waveguides associated with each depth plane are shown adjacent to each other in this figure, it should be understood that in a physical device, the waveguides may all be arranged in a stacked form with one waveguide per layer. In some other embodiments, multiple component colors may be output by the same waveguide, such that, for example, each depth plane may provide only a single waveguide.

[0094] Continuing to refer to Figure 8 , in some embodiments, G is green, R is red, and B is blue. In some other embodiments, in addition to red, green, or blue, other colors associated with light of other wavelengths (including magenta and cyan) may be used, or these other colors may replace one or more of red, green, or blue.

[0095] It will be understood that references to light of a given color throughout this disclosure will be understood to include light of one or more wavelengths within the wavelength range of light that is perceived by a viewer as having that given color. For example, red light may include light of one or more wavelengths in the range of approximately 620 - 780 nm, green light may include light of one or more wavelengths in the range of approximately 492 - 577 nm, and blue light may include light of one or more wavelengths in the range of approximately 435 - 493 nm.

[0096] In some implementations, the optical module 530( Figure 6 ) can be configured to emit light at one or more wavelengths outside the viewer's visual perception range, such as light at infrared and / or ultraviolet wavelengths. Additionally, the input, output, and other light redirecting structures of the waveguides of the display system 250 can be configured to direct this light and cause this light to exit the display and be directed towards the user's eyes 210, e.g., for imaging and / or user stimulation applications.

[0097] Now referring to Figure 9A , in some embodiments, it may be necessary to redirect light incident on a waveguide to couple the light into the waveguide. An input optical element can be used to redirect and couple the light into its corresponding waveguide. Figure 9A A cross-sectional side view of an example of a plurality of stacked waveguides or a set of stacked waveguides 660 is shown, each waveguide including an input optical element. The waveguides can be individually configured to output light at one or more different wavelengths, or light in one or more different wavelength ranges. It should be understood that the set of stacked waveguides 660 can correspond to the waveguide assembly 260( Figure 6 ), and the waveguides shown in the set of stacked waveguides 660 can correspond to a portion of the plurality of waveguides 270, 280, 290, 300, 310, except that light from one or more image injection devices 360, 370, 380, 390, 400 is injected into the waveguide at a location where the light needs to be redirected for coupling.

[0098] The stacked waveguide group 660 shown includes waveguides 670, 680, and 690. Each waveguide includes an associated coupling optical element (which may also be referred to as a light input region on the waveguide), wherein, for example, the coupling optical element 700 is disposed on a major surface (e.g., top major surface) of the waveguide 670, the coupling optical element 710 is disposed on a major surface (e.g., top major surface) of the waveguide 680, and the coupling optical element 720 is disposed on a major surface (e.g., top major surface) of the waveguide 690. In some embodiments, one or more of the coupling optical elements 700, 710, 720 may be disposed on the bottom major surface of the corresponding waveguide 670, 680, 690 (particularly in the case where one or more coupling optical elements are reflective deflection optical elements). As shown, the coupling optical elements 700, 710, 720 may be disposed on the top major surface (or the top of the next downstream waveguide) of their corresponding waveguides 670, 680, 690, particularly in the case where those coupling optical elements are transmissive deflection optical elements. In some embodiments, the coupling-in optical elements 700, 710, 720 can be disposed in the body of the respective waveguides 670, 680, 690. In some embodiments, as discussed herein, the coupling-in optical elements 700, 710, 720 are wavelength selective such that they selectively redirect light of one or more wavelengths while transmitting light of other wavelengths. Although shown on one side or corner of their respective waveguides 670, 680, 690, it should be understood that in some embodiments, the coupling-in optical elements 700, 710, 720 can be disposed in other areas of their respective waveguides 670, 680, 690.

[0099] As shown, the coupling optical elements 700, 710, 720 can be laterally offset from each other. In some embodiments, each coupling optical element can be offset so that the coupling optical element receives light without the light passing through another coupling optical element. For example, each coupling optical element 700, 710, 720 can be configured to be offset from the Figure 6 The different image injection devices 360, 370, 380, 390 and 400 shown receive light and can be separated from other coupling optical elements 700, 710, 720 (e.g., laterally spaced apart) so that the coupling optical element does not substantially receive light from other coupling optical elements in the coupling optical elements 700, 710, 720.

[0100] Each waveguide also includes an associated optical distribution element. For example, the optical distribution element 730 is disposed on the main surface (e.g., the top main surface) of the waveguide 670, the optical distribution element 740 is disposed on the main surface (e.g., the top main surface) of the waveguide 680, and the optical distribution element 750 is disposed on the main surface (e.g., the top main surface) of the waveguide 690. In some other embodiments, the optical distribution elements 730, 740, 750 may be respectively disposed on the bottom main surfaces of the associated waveguides 670, 680, 690. In some other embodiments, the optical distribution elements 730, 740, 750 may be respectively disposed on both the top main surface and the bottom main surface of the associated waveguides 670, 680, 690; or the optical distribution elements 730, 740, 750 may be respectively disposed on different main surfaces (either the top main surface or the bottom main surface) of different associated waveguides 670, 680, 690.

[0101] The waveguides 670, 680, 690 may be spaced apart and separated by, for example, layers of gas, liquid, and / or solid materials. For example, as shown in the figure, the layer 760a may separate the waveguides 670 and 680; the layer 760b may separate the waveguides 680 and 690. In some embodiments, the layers 760a and 760b are formed of a low refractive index material (i.e., the refractive index of the material in a given direction is lower than that of the material forming the adjacent waveguides among the waveguides 670, 680, 690). For example, the refractive index of the material forming the layers 760a, 760b in a given direction is 0.05 or more, or 0.10 less than the refractive index of the material forming the waveguides 670, 680, 690 in the given direction. The lower refractive index layers 760a, 760b can act as cladding layers, which are beneficial for total internal reflection (TIR) of light passing through the waveguides 670, 680, 690 (e.g., TIR between the top main surface and the bottom main surface of each waveguide). In some embodiments, the layers 760a, 760b are formed of air. Although not shown, it should be understood that the top and bottom of the shown waveguide set 660 may include adjacent cladding layers.

[0102] Preferably, for ease of fabrication and for other considerations, the materials forming the waveguides 670, 680, 690 are similar or the same, and the materials forming the layers 760a, 760b are similar or the same. In some embodiments, the materials forming the waveguides 670, 680, 690 may be different between one or more waveguides, and / or the materials forming the layers 760a, 760b may be different, while still maintaining the various refractive index relationships described above.

[0103] Continue to refer to Figure 9A, light rays 770, 780, 790 are incident on waveguide set 660. It should be understood that light rays 770, 780, 790 can be injected into waveguides 670, 680, 690 through one or more image injection devices 360, 370, 380, 390, 400( Figure 6 ).

[0104] In some embodiments, light rays 770, 780, 790 have different characteristics, e.g., different wavelengths or different wavelength ranges corresponding to different colors. Coupling optical elements 700, 710, 720 each deflect the incident light such that the light propagates through a respective one of waveguides 670, 680, 690 by TIR. In some embodiments, coupling optical elements 700, 710, 720 each selectively deflect light of one or more specific wavelengths while transmitting other wavelengths to the underlying waveguides and associated coupling optical elements.

[0105] For example, coupling optical element 700 can be configured to deflect light ray 770 having a first wavelength or first wavelength range while transmitting light rays 780 having a different second wavelength or second wavelength range and light ray 790 having a third wavelength or third wavelength range, respectively. The transmitted light ray 780 is incident on coupling optical element 710 and is deflected by coupling optical element 710, which is configured to deflect light of the second wavelength or second wavelength range. Light ray 790 is deflected by coupling optical element 720, which is configured to selectively deflect light of the third wavelength or third wavelength range.

[0106] Continuing to refer to Figure 9A , the deflected light rays 770, 780, 790 are deflected such that light rays 770, 780, 790 propagate through corresponding waveguides 670, 680, 690; that is, the coupling optical elements 700, 710, 720 of each waveguide deflect light into the corresponding waveguide 670, 680, 690 to couple the light into the corresponding waveguide. Light rays 770, 780, 790 are deflected at an angle that causes the light to propagate through respective waveguides 670, 680, 690 by TIR. Light rays 770, 780, 790 propagate through respective waveguides 670, 680, 690 by TIR until incident on corresponding light distribution elements 730, 740, 750 of the waveguides.

[0107] Now referring to Figure 9B , there is shown Figure 9APerspective view of an example of multiple stacked waveguides. As described above, the coupled-in light rays 770, 780, 790 are respectively deflected by the optical elements 700, 710, 720 and then propagate through TIR in the waveguides 670, 680, 690 respectively. Then, the light rays 770, 780, 790 are respectively incident on the light distribution elements 730, 740, 750. The light distribution elements 730, 740, 750 deflect the light rays 770, 780, 790 such that the light rays 770, 780, 790 respectively propagate towards the out-coupling optical elements 800, 810, 820.

[0108] In some embodiments, the light distribution elements 730, 740, 750 are orthogonal pupil expanders (OPEs). In some embodiments, the OPE deflects or distributes light to the out-coupling optical elements 800, 810, 820, and in some embodiments, the beam size or spot size of this light can also be increased as the light propagates to the out-coupling optical elements. In some embodiments, the light distribution elements 730, 740, 750 can be omitted, and the in-coupling optical elements 700, 710, 720 can be configured to deflect light directly to the out-coupling optical elements 800, 810, 820. For example. Refer Figure 9A , the light distribution elements 730, 740, 750 can be respectively replaced by the out-coupling optical elements 800, 810, 820. In some embodiments, the out-coupling optical elements 800, 810, 820 are exit pupils (EPs) or exit pupil expanders (EPEs) that direct light into the viewer's eye 210 ( Figure 7 ). It should be understood that the OPE can be configured to increase the size of the eye box on at least one axis, and the EPE can increase the eye box on an axis that intersects (e.g., is orthogonal to) the axis of the OPE. For example, each OPE can 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 propagating along the waveguide. When the remaining light is incident on the OPE again, 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, and so on. Similarly, when impinging on the EPE, a portion of the incident light is directed out of the waveguide towards the user, and the remaining portion of the light continues to propagate through the waveguide until it impinges on the EPE again, at which time another portion of the incident light is directed out of the waveguide, and so on. Thus, whenever a portion of a single beam of coupled-in light is redirected by the OPE or EPE, that light can be "copied", thereby forming a field of cloned light beams, as Figure 6 shown. In some embodiments, the OPE and / or EPE can be configured to modify the size of the light beam.

[0109] Thus, refer Figure 9A and 9B, in some embodiments, waveguide group 660 includes, for each component color: waveguides 670, 680, 690; optical coupling-in elements 700, 710, 720; light distribution elements (e.g., OPE) 730, 740, 750; and optical coupling-out elements (e.g., EPE) 800, 810, 820. Waveguides 670, 680, 690 can be stacked with an air gap / cladding between each waveguide. Optical coupling-in elements 700, 710, 720 redirect or deflect incident light (receiving light of different wavelengths through different optical coupling-in elements) into their waveguides. The light then propagates at an angle that will result in TIR within the corresponding waveguides 670, 680, 690. In the example shown, light ray 770 (e.g., blue light) is deflected by the first optical coupling-in element 700 in the previously described manner and then continues to bounce along the waveguide, interacting with the light distribution element (e.g., OPE) 730 and the optical coupling-out element (e.g., EPE) 800. Light rays 780 and 790 (e.g., green light and red light, respectively) will transmit through waveguide 670, where light ray 780 impinges on the optical coupling-in element 710 and is deflected by it. Then, light ray 780 bounces along waveguide 680 via TIR, proceeds to its light distribution element (e.g., OPE) 740, and then proceeds to the optical coupling-out element (e.g., EPE) 810. Finally, light ray 790 (e.g., red light) transmits through waveguide 690 and impinges on the optical light coupling-in element 720 of waveguide 690. The optical light coupling-in element 720 deflects light ray 790 such that the light ray propagates to the light distribution element (e.g., OPE) 750 via TIR and then to the optical coupling-out element (e.g., EPE) 820 via TIR. Then, the optical coupling-out element 820 finally couples out light ray 790 to the viewer, who also receives the coupled-out light from the other waveguides 670, 680.

[0110] Figure 9C shows a Figure 9A and 9B top plan view of an example of a plurality of stacked waveguides. As shown, waveguides 670, 680, 690 and the associated light distribution elements 730, 740, 750 and the associated optical coupling-out elements 800, 810, 820 of each waveguide can be vertically aligned. However, as discussed herein, the optical coupling-in elements 700, 710, 720 are not vertically aligned; rather, the optical coupling-in elements do not overlap (e.g., are laterally spaced apart when viewed in a top view). As further discussed herein, this non-overlapping spatial arrangement helps to inject light from different sources one-to-one into different waveguides, thereby allowing a particular light source to be uniquely coupled to a particular waveguide. In some embodiments, an arrangement including non-overlapping spatially separated optical coupling-in elements can be referred to as a shifted pupil system, and the optical coupling-in elements within these arrangements can correspond to sub-pupils.

[0111] Alternatively, in some embodiments, two or more coupled-in optical elements may be in an inline arrangement, in which they are vertically aligned. In such an arrangement, light for a waveguide farther from the projection system is transmitted through the coupled-in optical element for a waveguide closer to the projection system, preferably with minimal scattering or diffraction.

[0112] An inline configuration can advantageously reduce the size of the projector and simplify the projector. In addition, it also increases the field of view of the eyepiece, for example, by coupling light of the same color to multiple waveguides using crosstalk. For example, green light can be coupled into the active layers of blue and red. Since the pitch of each ICG can be different to provide improved (e.g., optimal) performance for a particular color, the allowable field of view can be increased.

[0113] In an inline configuration, except for the last layer in the optical path, the ICG should at most partially reflect or otherwise transmit light at the operating wavelength of the subsequent layer in the stack of waveguides. In each case, the efficiency will be very low unless a grating is etched in a high refractive index layer (e.g., 1.8 or higher for a polymer-based layer), or a high refractive index coating is deposited or grown on the grating. However, this method increases the back reflection into the projector lens, which may thus produce image artifacts such as image ghosts.

[0114] Figure 9D An example of a wearable display system 60 is shown into which various waveguides and related systems disclosed herein can be integrated. In some embodiments, the display system 60 is Figure 6 the display system 250, where Figure 6 some components of the display system 60 are shown schematically in more detail. For example, Figure 6 the waveguide assembly 260 can be part of the display 70.

[0115] Continuing to refer to Figure 9D, the display system 60 includes a display 70, as well as various mechanical and electronic modules and systems that support the functions of the display 70. The display 70 can be coupled to a frame 80 that is wearable by a user of the display system or user 90, and the frame 80 is configured to position the display 70 in front of the eyes of the user 90. In some embodiments, the display 70 can be considered to be glasses. In some embodiments, a speaker 100 is coupled to the frame 80 and is configured to be positioned adjacent to the ear canal of the user 90 (in some embodiments, another speaker (not shown) can optionally be positioned adjacent to the other ear canal of the user to provide stereo / surround sound control). The display system 60 can also include one or more microphones 110 or other devices to detect sound. In some embodiments, the microphone is configured to allow the user to provide input or commands to the display system 60 (e.g., selection of voice menu commands, natural language questions, etc.), and / or can allow audio communication with other people (e.g., other users of similar display systems). The microphone can further be configured as a peripheral sensor to collect audio data (e.g., sounds from the user and / or the environment). In some embodiments, the display system can also include a peripheral sensor 120a that can be separated from the frame 80 and attached to the body of the user 90 (e.g., on the head, torso, limbs, etc. of the user 90). In some embodiments, the peripheral sensor 120a can be configured to acquire data characterizing the physiological state of the user 90. For example, the sensor 120a can be an electrode.

[0116] Continuing reference Figure 9D, the display 70 is operably coupled to the local processing and data module 140 via a communication link 130 (such as, via a wired lead or a wireless connection). The local processing and data module 140 can be installed in various configurations, such as fixedly attached to the frame 80, fixedly attached to a helmet or hat worn by a user, embedded in a headset, or otherwise removably attached to the user 90 (e.g., in a backpack configuration, in a belt-coupled configuration). Similarly, the sensor 120a can be operably coupled to the local processing and data module 140 via a communication link 120b (e.g., a wired lead or a wireless connection). The local processing and data module 140 can include a hardware processor and a digital memory, such as a non-volatile memory (e.g., flash memory or a hard disk drive), both of which can be used to assist in the processing, caching, and storage of data. Optionally, the local processing and data module 140 can include one or more central processing units (CPUs), graphics processing units (GPUs), dedicated processing hardware, and the like. The data can include a) data captured from sensors (which can be, for example, operably coupled to the frame 80 or otherwise attached to the user 90), such as image capture devices (such as cameras), microphones, inertial measurement units, accelerometers, compasses, GPS units, radios, gyroscopes, and / or other sensors disclosed herein; and / or b) data obtained and / or processed using the remote processing module 150 and / or the remote data repository 160 (including data related to virtual content), which may be used to transmit to the display 70 after such processing or retrieval. The local processing and data module 140 can be operably coupled to the remote processing module 150 and the remote data repository 160 via communication links 170, 180 (such as via a wired or wireless communication link) such that the remote processing module 150 and the remote data repository 160 are operably coupled to each other and can be used as resources for the local processing and data module 140. In some embodiments, the local processing and data module 140 can include one or more of an image capture device, a microphone, an inertial measurement unit, an accelerometer, a compass, a GPS unit, a radio, and / or a gyroscope. In some other embodiments, one or more of these sensors can be attached to the frame 80 or can be independent structures that communicate with the local processing and data module 140 via a wired or wireless communication path.

[0117] Continuing to refer to Figure 9D, in some embodiments, the remote processing module 150 may include one or more processors configured to analyze and process data and / or image information, e.g., including one or more central processing units (CPUs), graphics processing units (GPUs), dedicated processing hardware, etc. In some embodiments, the remote data repository 160 may include a digital data storage facility that may be obtained via the Internet or other network configurations in a "cloud" resource configuration. In some embodiments, the remote data repository 160 may include one or more remote servers that provide information to the local processing and data module 140 and / or the remote processing module 150, e.g., information for generating augmented reality content. In some embodiments, all data is stored and all computations are performed in the local processing and data module, thus allowing for fully autonomous use from the remote module. Optionally, an external system (e.g., a system of one or more processors, one or more computers) 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, e.g., via a wireless or wired connection.

[0118] Diffraction grating with reduced polarization sensitivity

[0119] Providing a high-quality immersive experience to a user of a waveguide-based display system (such as various display systems configured for the above-described virtual / augmented / mixed display applications), among other things, depends on various characteristics of the light coupled into and / or out of the waveguide in the display system eyepiece. For example, a virtual / augmented / mixed display with high light coupling-in and coupling-out efficiency can enhance the viewing experience by increasing the brightness of the light guided to the user's eyes. As discussed above, an input coupling optical element (such as an input coupling diffraction grating) can be employed to couple light into the waveguide for guiding therein by total internal reflection. Similarly, an output coupling optical element (such as an output coupling diffraction grating) can also be employed to couple the light guided within the waveguide by total internal reflection out of the waveguide.

[0120] As described above, for example, refer to Figure 6 and 7 , a display system according to various embodiments described herein may include optical elements, e.g., an input coupling optical element, an output coupling optical element, a light distribution element, and / or a combined pupil expander-extractor (CPE) that may include a diffraction grating. As disclosed herein, the CPE can both disperse or distribute light within the waveguide as a light distribution element, thus possibly increasing the beam size and / or the eye box, and couple light out of the waveguide as an out-coupling optical element.

[0121] For example, as referred to above Figure 7As described above, the light 640 injected into the waveguide 270 at the input surface 460 of the waveguide 270 propagates and is guided within the waveguide 270 by total internal reflection (TIR). In various embodiments, at the point where the light 640 is incident on the outcoupling optical element 570, a portion of the light guided within the waveguide may exit the waveguide as an outgoing beam 650 (e.g., a small beam). In some embodiments, any of the optical elements 570, 580, 590, 600, 610 that may include one or more of an incoupling optical element, an outcoupling optical element, a light distribution element, or a CPE may be configured as a diffraction grating.

[0122] To achieve the desired characteristics for the incoupling (or outcoupling) of light into the waveguides 270, 280, 290, 300, 310, the optical elements 570, 580, 590, 600, 610 configured as diffraction gratings may be formed of a suitable material and have a suitable structure for controlling various optical characteristics, including diffraction characteristics, such as diffraction efficiency according to polarization variations. Among other characteristics, possible desired diffraction characteristics may include any one or more of the following: spectral selectivity, angular selectivity, polarization selectivity (or non - selectivity), high spectral bandwidth, high diffraction efficiency, or wide field of view (FOV).

[0123] Some diffraction gratings have strong polarization dependence and may thus have a relatively reduced overall efficiency (due to rejecting one polarization). Such diffraction gratings may also produce coherent artifacts and reduce the uniformity of the far - field image. To provide a diffraction grating with reduced polarization sensitivity (e.g., a diffraction grating that couples light with an efficiency relatively independent of polarization), some displays for AR systems according to embodiments described herein include waveguides having blazed diffraction gratings formed therein. For example, a blazed grating may include diffraction features having a "sawtooth" shape. In some embodiments, a blazed grating may achieve improved grating diffraction efficiency for a specific diffraction order while reducing or minimizing the diffraction efficiency for other orders. Thus, in some embodiments, more light may be guided to a specific given diffraction order relative to any other diffraction order.

[0124] Optical Artifact Management

[0125] Reference Figure 10 , the head - mounted device 1000 includes a frame 1002 and eyepieces 1004a and 1004b disposed within the frame 1002. The frame 1002 may be similar to Figure 9D the frame 80, and the eyepieces 1004a and 1004b may correspond to Figure 9A the stacked waveguide group 660 in Figure 6 or the waveguide assembly 260 in

[0126] The eyepieces 1004a and 1004b respectively include waveguide substrates 1010a and 1010b, and have an input coupling element 1006a and 1006b and an output coupling element 1008a and 1008b on the surfaces of the substrates 1010a and 1010b, respectively. The substrates 1010a and 1010b are made of a crystalline material with a relatively high refractive index (e.g., 2.0 or higher, 2.1 or higher, 2.2 or higher, 2.3 or higher, 2.4 or higher, 2.5 or higher, 2.6 or higher). The crystalline material can be transparent, e.g., transmitting at least 70%, 80%, or 90% of the visible light wavelength. Examples of such crystalline materials include lithium niobate (LNO or LiNbO3), lithium tantalate (LiTaO3), and silicon carbide (SiC). The crystalline material can be a birefringent material.

[0127] Generally, wafers formed of crystalline materials such as lithium niobate, lithium tantalate, and silicon carbide can have different crystal orientations depending on the crystal growth mode and the way of cutting the wafer from the crystal. For example, the wafers formed of the crystal can be X-cut, Y-cut, or Z-cut wafers. The coordinate system, e.g., the X, Y, Z axes (or the a, b, and c axes of the crystal), is determined according to the symmetry group of the Hermann-Maugin notation of the crystal. Cutting refers to the orientation of the wafer surface relative to the crystal axis. For example, in a Z-cut wafer, the polar Z axis is oriented perpendicular to the wafer surface.

[0128] As will be explained in more detail with reference Figure 16A -H, in this example, the substrates 1010a and 1010b are respectively from different wafers and are selected for the left and right sides of the head-mounted device 1000 to reduce the left and right image competition for the user. The substrates 1010a and 1010b can be cut along a specific orientation respectively and have a specific clock position to reduce optical artifacts. Orientations such as X, Y, or Z cuts define the orientation of the substrate surface normal relative to the optical axis. For example, in LNO, a Z-cut means that the surface normal of the cut crystal is parallel to the Z axis, e.g., the optical axis in LNO. An X or Y cut means that the surface normal of the crystal is perpendicular to the optical axis. In this example, the eyepieces 1004a and 1004b are X-cut, e.g., the out-of-page direction is along the X axis.

[0129] The surface charge and piezoelectric properties of the crystal change with cutting because the surface termination of the bond depends on the cutting. For example, due to the mirror charge displacement along the X axis, X-cut LNO tends not to exhibit piezoelectric properties. The non-polarity of the surface of X-cut LNO is beneficial in wet chemical processes (e.g., wet chemical cleaning, resin dispensing, and filling the liquid between the template (overlay) and the substrate before patterning).

[0130] However, Y-cut and Z-cut LNO exhibit surface charge and piezoelectric properties. For example, Z-cut LNO has positive surface charge due to ––Nb-O3-Li2 termination and negative surface charge due to O-Li termination. Generally, more -O terminations result in more positive surface charge, and more -Li terminations result in more negative surface charge.

[0131] The surface charge distribution on the substrate can be harmful during manufacturing and use. For example, since Z-cut LNO is polar, the surface of Z-cut LNO may undergo unwanted reactions during wet chemical cleaning and wetting processes, such as attaching to cleaners, imprints, and resins.

[0132] For example, Figure 11A and 11B shows how a polymer resist solution is unevenly distributed on a 41 ° -X-cut wafer, for example, the surface relief grating plane (the surface with patterned coupling-in and coupling-out element diffraction structures) has an angle of 41° relative to the X-axis, the surface normal, and the optical axis. Figure 11A shows a uniform pattern 1100 of droplets 1102 distributed on the LNO surface, and Figure d shows a non-uniform coating 1104 on the surface after the droplets 1102 have spread. For example, the coating in the light-colored area 1106 is thinner than that in the dark-colored area 1108, and the droplets have pre-infiltrated into the area 1110. Due to the non-uniform volume distribution, subsequent steps in substrate manufacturing and processing may be difficult.

[0133] Dielectric coatings can mitigate the negative effects stemming from surface charge. Referring to Figure 12A -D, in the first stages 1200 and 1201, a substrate 1204 to be patterned is prepared. A dielectric coating 1206 (such as TiO2) is provided on the substrate 1204 (e.g., LNO). Dielectric coatings, especially high refractive index coatings with a refractive index greater than 2.2, can prevent spurious effects on Y-cut and Z-cut LNO during the resin dispensing and filling processes of nanoimprint lithography. Additionally or alternatively, a dielectric coating with a lower refractive index (e.g., SiO2) can be provided on the LNO surface, for example, before the high refractive index coating, to prevent surface charge accumulation. The prepolymer imprint resin can be in the form of droplets 1210a or as a spin-coated coating 1210b on the layer 1208.

[0134] Layer 1208 promotes adhesion between post-patterning (e.g., template and mold demolding) of the prepolymer material and curing on the desired surface or substrate. In some embodiments, layer 1208 includes a crosslinked silane coupling agent. One end of these coupling agents contains an organic functional group and the other end contains a hydrolyzable group, forming a durable bond with different types of organic and inorganic materials. For example, acryloyl can be crosslinked into the patternable polymer material to form the desired optical pattern / shape. In some embodiments, a template or mold can be coated with a similar coating, where the acryloyl end is replaced by a fluorinated chain, which can reduce the surface energy, e.g., as a release point. Vapor deposition can be carried out at low pressure, where the coupling agent is delivered in vapor form, and an inert gas such as N2 can be used or not used, where there are activated -O and / or -OH groups on the surface of the material to be coated. The vapor coating process can deposit a single-layer thin film.

[0135] After stage 1201 or 1202, in the second stage 1202, the prepolymer imprint resin can be imprinted with the template 1214 to form the pattern 1216. In stage 1203, the template 1214 is removed. In some embodiments, a dielectric coating is located on one or both surfaces of the LNO.

[0136] In some embodiments, a dielectric coating can also be applied to an X-cut or any angled-cut wafer to improve total internal reflection of light with a longer wavelength (e.g., greater than 635 nm). For example, Figure 13 shows a 41° X-cut LNO imprinted with a TiO2 coating. Compared with Figure 11B the coating is more uniform, thus preventing problems related to the diffusion profile, such as variations in the residual layer thickness. As another example, Figure 14A -D shows the prepolymer resin dispensed above the LNO for two types of resins and two cuts. Figure 14A shows the surface 1400a with the first resin above the Y-cut LNO, Figure 14B shows the surface 1400b with the first resin above the Z-cut LNO, Figure 14C shows the surface 1400c with the second resin above the Z-cut LNO, Figure 14D shows the surface 1400d with the second resin above the Y-cut LNO. Generally, all surfaces 1400a - d exhibit more uniformity than those without a dielectric coating. Figure 11B

[0137] Although the examples so far have focused on lithium niobate substrates, the present disclosure is generally applicable to substrates composed of crystalline materials with a high refractive index and / or optical anisotropy, such as silicon carbide (SiC), e.g., n = 2.65, and LiTaO3. For example, Figure 15A and15B The fields of view (FOVs) 1500a and 1500b of LiTaO3 and LiNbO3 are shown respectively. Given the high refractive indices of LiTaO3 and LiNbO3, the FOVs are relatively large, e.g., greater than 50°. The FOVs 1500a and 1500b are generated using red light (e.g., 635 nm). In some embodiments, it is beneficial to use different materials for each of the red, green, and blue eyepieces because different crystals have different absorption profiles.

[0138] Reference Figure 16A -D, the coupling-in elements 1644 and 1611 and the coupling-out elements 1634 and 1601 are associated with the respective eyepieces. Cuts are selected, e.g., with respect to the crystal axes and / or clock positions of the substrate surfaces of the left and right side eyepieces of the frame, to reduce the occurrence of optical artifacts. In LNO, the X and Y axes are optically equivalent, and X- and Y-cut substrates tend to produce optical artifacts parallel to the Z axis.

[0139] For example, the X- or Y-cut substrate supporting the coupling-in element 1644 and the coupling-out element 1634 produces the optical artifact 1600a, and the X- or Y-cut substrate supporting the coupling-in element 1611 and the coupling-out element 1601 produces the optical artifact 1600b. Selecting a pair of coupling-in elements and coupling-out elements on the X- or Y-cut wafers of each of the left and right sides of the frame based on the clock position and the orientation of the coupling elements relative to the optical axis can result in the alignment of the optical artifacts.

[0140] As another example, Z-cut substrates tend to produce bullseye (e.g., annular or circular) optical artifacts. Shapes with circular symmetry do not change when rotated, e.g., when rotated about the Z axis, the optical artifacts 1600c and 1600d look the same. Therefore, the clock positions of the coupling-in elements and the coupling-out elements on the Z-cut substrate do not have to satisfy the same design rules as the X- or Y-cut substrates to align the optical artifacts.

[0141] Optical artifacts that cross each other rather than being parallel to each other can cause competition of the virtual images for the user. For example, when the head-mounted device 1000 displays an image to the user, if the optical artifacts are similar, the optical artifacts may be less obvious. However, if the optical artifacts cross each other, e.g., are significantly different for each eye, the user may feel blurry. For example, some users prefer overlapping spatial uniformity variations rather than non-overlapping spatial uniformity variations. Therefore, selecting paired eyepieces (e.g., substrates supporting optical elements) that align the optical artifacts can provide a better visual experience for the user.

[0142] Reference Figure 16E-H, the optical artifacts 1600a and 1600b respectively correspond to a pair of input elements and output elements from two wafers, and the two wafers are patterned differently. For example, the grating directions in the eyepiece are different with respect to the crystal axes 1691a and 1691b of each wafer. For example, wafer 1600e is X-cut, and the optical axis is along the first transverse direction. For example, the Z-axis is parallel to the vertical direction 1607a. Wafer 1600g is X-cut, and the optical axis is along the second transverse direction. For example, the Z-axis is parallel to the horizontal direction 1607b. In other words, although wafers 1600e and 1600g are made of the same material, the crystal axes of wafers 1600e and 1600g are different.

[0143] Wafer 1600e includes six pairs of input elements 1611, 1612, 1613, 1614, 1615, and 1616 and output elements 1601, 1602, 1603, 1604, 1605, and 1606 respectively at the first to sixth clock positions. Wafer 1600g includes six pairs of input elements 1641, 1642, 1643, 1644, 1645, and 1646 and output elements 1631, 1632, 1633, 1634, 1635, and 1636 respectively at the first to sixth clock positions.

[0144] The difference between wafers 1600e and 1600g is that for wafer 1600e, the directions of the light emitted from the input elements 1614 and 1611 to the output elements 1604 and 1601 are parallel to the optical axis, while in wafer 1600g, the directions of the light emitted from the input elements to the output elements are not parallel to the optical axis. Instead, the directions of the light emitted from the input elements 1644 and 1641 to the output elements 1634 and 1631 are perpendicular to the optical axis. For X- and Y-cut wafers, the optical artifacts tend to be parallel to the optical axis. Therefore, this difference between wafers 1600e and 1600g affects the appearance of the optical artifacts for each pair of input and output elements.

[0145] For example, the schematic diagram 1600f shows how the pairs of input and output elements correspond to the optical artifacts when viewed from the right and left. Based on the direction of the optical axis in wafer 1600e, the input element 1611 and the output element 1601 generate a vertical optical artifact 1621, the input element 1612 and the output element 1602 generate a positively inclined optical artifact 1622, the input element 1613 and the output element 1603 generate a negatively inclined optical artifact 1623, the input element 1614 and the output element 1604 generate a vertical optical artifact 1624, the input element 1615 and the output element 1605 generate a positively inclined optical artifact 2625, and the input element 1616 and the output element 1606 generate a negatively inclined optical artifact 1626.

[0146] By rotating 45°, each pair of the light-incoupling element and the light-outcoupling element can be located on the right or left side of the head-mounted device. For example, for the right side, it rotates clockwise, and for the left side, it rotates counterclockwise. As a result, the optical artifact 1621 can be either the right-side optical artifact or the left-side optical artifacts 1621a and 1621b. The same applies to the right-side optical artifacts and the left-side optical artifacts 1622a, 1622b, 1623a, 1623b, 1624a, 1624b, 1625a, 1625b, 1626a, and 1626b, and so on. A similar analysis also applies to the schematic diagram 1600h.

[0147] Based on the optical axis direction in the wafer 1600g, the light-incoupling element 1641 and the light-outcoupling element 1631 generate a horizontal optical artifact 1651, the light-incoupling element 1642 and the light-outcoupling element 1632 generate a negative-tilt optical artifact 1652, and the light-incoupling element 1643 and the light-outcoupling element 1633 generate a positive-tilt optical artifact 1653. The same applies to the optical artifacts 1654, 1655, and 1656, and so on. Similarly, by rotating 45°, the light-incoupling element and the light-outcoupling element can be located on the right or left side of the head-mounted device respectively, thereby generating the right-side optical artifacts and the left-side optical artifacts 1651a, 1651b, 1652a, 1652b, 1653a, 1653b, 1654a, 1654b, 1655a, 1655b, 1656a, and 1656b.

[0148] When the optical artifacts generated by the right side and the left side respectively are aligned, the optical artifacts are substantially parallel. Referring to the schematic diagram 1600f of the wafer 1600e, if the light-incoupling element 1611 and the light-outcoupling element 1601 at the first clock position are selected for the right side, neither the pair of the light-incoupling element and the light-outcoupling element will generate parallel optical artifacts. For example, the optical artifact 1621a is positively tilted, while the optical artifacts 1621b - 1626b are not positively tilted. However, the schematic diagram 1600h of the wafer 1600g includes positively tilted optical artifacts 1651b and 1654b on the left side.

[0149] Referring to Figure 10 、 16A and 16B, using the light-incoupling element 1611 and the light-outcoupling element 1601 on the right side and the light-incoupling element 1644 and the light-outcoupling element 1634 on the left side will generate parallel optical artifacts. For example, Figure 16A and 16B the optical artifacts 1600a and 1600b in Figure 16F and 16H match the optical artifacts 1621a and 1654b in

[0150] respectively. Therefore, pairs of the light-incoupling element and the light-outcoupling element can be selected for the right and left sides of the head-mounted device respectively to reduce the competition between the left and right images. Figure 16A and16B In an example, the pair of eyepieces formed by the input coupling elements and output coupling elements 1644 and 1634, and the input coupling elements and output coupling elements 1611 and 1601 may have different or the same crystal axes 1671a and 1671b, and still be able to manage the optical artifacts 1600a and 1600b. For example, the crystal axes 1671a and 1671b may respectively have an X-axis or a Y-axis located outside the page, as indicated by the "Y, X" and "X, Y" labels. In this example, changing the crystal axes to switch the X or Y points out of the page involves rotation about the Z-axis (optical axis), which does not change the optical properties of the uniaxial crystal.

[0151] Various other pairs can be made that produce parallel optical artifacts (e.g., optical artifacts 1622a and 1655b) on the right and left sides. In some cases, for example, when the optical artifacts are vertical or horizontal in the rotating right and left configurations, the pairs of input coupling elements and output coupling elements on the right and left sides can be from the same wafer, e.g., optical artifacts 1653a and 1655b.

[0152] In some embodiments, the optical artifacts of the X- and Y-cut wafers are asymmetric along the Z-axis. For example, referring to Figure 15A and 15B , the optical artifacts along the Z-axis fan out along the Z-axis. Thus, even if the optical artifacts are aligned, the shape (e.g., width) of the optical artifacts may be different. To avoid problems related to optical artifacts having different shapes along the Z-axis, the pairs of input coupling elements and output coupling elements on the right and left sides can be selected to have opposite clock positions, e.g., the input coupling elements and output coupling elements from clock position 1 are paired with the input coupling elements and output coupling elements from clock position 4, the input coupling elements and output coupling elements from clock position 2 are paired with the input coupling elements and output coupling elements from clock position 5, and the input coupling elements and output coupling elements from clock position 3 are paired with the input coupling elements and output coupling elements from clock position 6.

[0153] Although Figure 16A -H shows a wafer having six pairs of input coupling elements and output coupling elements (e.g., six clock positions), other embodiments are possible. For example, the wafer can include 2 to 20 eyepieces.

[0154] The design rules for selecting the right and left eyepieces determine the relationship between the substrate optical axis and the angle between the light emission directions from the input coupling element to the output coupling element of each eyepiece. Referring to Figure 16I and 16J , for each clock position in wafers 1600e and 1600g, the angle between the optical axis and the light direction is different.

[0155] For example, wafer 1600e includes the input coupling elements and output coupling elements shown in Figure 16E and wafer 1600g includes the input coupling elements and output coupling elements shown inFigure 16G The coupled-in element and the coupled-out element shown. In the wafer 1600e, the optical axis (parallel to the vertical direction 1607a) is represented by each vertical thin dashed line. In the wafer 1600g, the optical axis (parallel to the horizontal direction 1607b) is represented by each horizontal thin dashed line.

[0156] For each pair of the coupled-in element and the coupled-out element, the light emission direction (e.g., the shortest line connecting the coupled-in element and the coupled-out element) is represented by the thick dashed lines 1661, 1662, 1663, 1664, 1665, and 1666. In some embodiments, the shortest line connecting the coupled-in element and the coupled-out element is perpendicular to the grating within the coupled-in element or the coupled-out element. In Figure 16E and 16G the example of, each symbol of the coupled-in elements 1611 - 1616 and 1641 - 1646 includes a line indicating the direction parallel to the grating within the coupled-in element. For example, the symbol of the coupled-in element 1641 includes a horizontal line, indicating that the grating is perpendicular to the horizontal line, and the light emission direction (e.g., the line 1664) is a vertical line.

[0157] For each of the first to sixth clock positions, the angles between the optical axis and the light emission direction are represented by θ1, θ2, θ3, θ4, θ5, and θ6, respectively.

[0158] In this example, in the wafer 1600e, θ1 = 0°, θ2 = 60°, θ3 = 120°, θ4 = 0°, θ5 = 60°, θ6 = 120°. In the wafer 1600f, θ1 = 90°, θ2 = 150°, θ3 = 30°, θ4 = 90°, θ5 = 150°, θ6 = 30°. As previously described, the coupled-in element 1611 and the coupled-out element 1601 at the first clock position can be paired with the coupled-in element 1644 and the coupled-out element 1634 at the fourth clock position, as the right side and the left side respectively. The difference between θ1 of the wafer 1600e and θ4 of the wafer 1600f is 90°, resulting in the alignment of the optical artifacts 1621a and 1654b.

[0159] Generally, the left and right pairs can be selected by choosing angle pairs with a difference of approximately ±90°. In this example, the angle difference is 90° instead of 0° because the right eyepiece and the left eyepiece are rotated 45° in opposite directions respectively. For example, when placed in the frame 1002, each eyepiece is tilted 45°, so the light emission directions intersect at 90°. The paired eyepieces are tilted at different angles, and the angle difference will vary. As previously described, the sign of the difference affects whether the optical artifacts are symmetric about the optical axis. In this specification, when referring to a numerical range, "about" indicates that the value of the item is close to the numerical range, for example, within 1%, 5%, or 10%.

[0160] As light passes through the eyepiece, the origin of optical artifacts may change. In birefringent materials, optical artifacts appear to be somewhat regularly spaced and aligned along one or more optical axis directions. When the substrate has optical anisotropy, such as uniaxial or biaxial birefringence, the refractive index depends on the polarization of the light and the orientation of the light relative to the optical axis (or, in the case of biaxial materials, relative to both optical axes). Thus, optical artifacts appear as patterns caused by refractive indices that vary along different directions, because light corresponding to different points in the FOV may experience different refractive indices, for example, by reflecting different numbers of times in the substrate.

[0161] In uniaxial materials, there are two refractive indices that control light propagation, such as the ordinary refractive index n o and the extraordinary refractive index n i , which can be represented by a refractive index ellipsoid. In biaxial materials, there are three refractive indices that control light propagation, such as n α 、n β and n γ , can be represented by a refractive index sphere. The cross section of a refractive index ellipsoid or sphere is an ellipse whose major and minor semi-axes are equal to the two refractive indices of a wavefront propagating perpendicular to the cross section.

[0162] Uniaxial crystals have tetragonal or hexagonal symmetry, and biaxial crystals have orthorhombic, monoclinic, or triclinic symmetry. For example, SiC and LiNbO3 are both hexagonal crystals and are therefore uniaxial crystals, while LiTaO3 is an orthorhombic crystal and is therefore a biaxial crystal. In uniaxial crystals, the optical axis is defined as the c-axis using the Hermann-Maugin convention. In biaxial crystals, the relationship between the optical axis and the a, b, and c axes varies. For example, for orthorhombic LiTaO3, the optical axis can be parallel to any of the three a, b, or c axes. The optical axis is located between the regions where light experiences the maximum and minimum refractive indices n α and n γ In biaxial crystals, optical artifacts appear along both optical axes. For example, in the FOV of biaxial LiTaO3 Figure 15A In the image processing, optical artifacts appear along both the Z axis and the X / Y axis.

[0163] refer to Figure 17The shape of the k-space ring 1700 of a birefringent crystal varies depending on the direction of light propagation and the cut of the birefringent crystal. The inner radius is equal to the refractive index of the medium into which the light is incident, for example, an air refractive index of 1. The outer radius indicates how much light can be coupled into the substrate depending on the substrate refractive index (for example, the allowed angle of the incident light). Therefore, the k-space ring size corresponds to the field of view size. In optically isotropic materials, the k-space ring is a true ring, for example, the outer contour is a circle with a radius equal to the refractive index of the material. In optically anisotropic materials, the outer contour is an ellipse with the major and minor axes determined by the refractive indices along different directions.

[0164] Figure 17 K-space ellipses 1702a, 1702b, and 1702c for uniaxial LNO are shown. In LNO, the Z axis is the optical axis, and the X and Y axes are optically equivalent. Ellipse 1702a represents the k-space of light propagating perpendicular to the XY plane for a Z-cut wafer, ellipse 1702b represents the k-space of light propagating along the X or Y axis for an X or Y-cut wafer, and ellipse 1702c represents the k-space of light propagating along the Z axis for an X or Y-cut wafer. Ellipse 1702a is circular because all light propagating perpendicular to the XY plane experiences the same refractive index. Ellipses 1702b and 1702c have unequal semi-major and minor axes because light propagating along the X or Y axis experiences different refractive indices.

[0165] In LNO, light propagating along the Z axis is the only light that experiences the same refractive index regardless of polarization. Light propagating in other directions will experience different refractive indices depending on polarization. Incident light that does not propagate parallel to the optical axis couples in and propagates at different angles via TIR, resulting in different numbers of bounces along the substrate surface. Thus, non-uniformity is formed along the Z axis.

[0166] The refractive index also depends on the wavelength of light. In general, the larger the wavelength, the lower the refractive index. Therefore, depending on the wavelength of light, optical artifacts can be more or less noticeable depending on the spacing. Figure 18A -C, image 1800a corresponds to blue light, e.g., 355 nm, image 1800b corresponds to green light, e.g., 530 nm, and image 1800c corresponds to red light, e.g., 635 nm. Image 1800c corresponds to light with the longest wavelength and lowest refractive index of the three images, resulting in more noticeable optical artifacts. Each of images 1800a-c is produced by an LED reticle projector that emits light into an X-cut LNO waveguide having an outcoupling element (e.g., a polymer resin grating) corresponding to a combined pupil expander. The field of view of each of images 1800a-c is greater than 60°.

[0167] refer to Figure 19A and 19B, wafers 1900a and 1900b can be X-cut LNO wafers respectively. Wafers 1900a and 1900b each include a substrate, such as substrate 1905a or 1905b, on which an input coupling element, such as input coupling element 1906a or 1906b, and an output coupling element, such as a combined pupil expander (CPE) 1908a or 1908b, are disposed. In wafer 1900a, the light emission direction (e.g., the direction of the line connecting input coupling element 1906a and CPE 1908a) is along the Y-axis perpendicular to the optical axis.

[0168] Reference Figure 19C , a pair of eyepieces 1900c includes input coupling element 1906a and CPE 1908a, and each eyepiece is rotated by ±45°. Figure 19D And 19E Shows images 1900d and 1900e obtained when input coupling element 1906a and CPE 1908a are used for the left and right eyepieces respectively. Images 1900d and 1900e are captured by a camera located above CPE 1908a, and the light is p-polarized, e.g., transverse magnetic (TM) polarized.

[0169] In wafer 1900b, the light emission direction is along the Z-axis parallel to the optical axis. Reference Figure 19C , a pair of eyepieces 1900c can be composed of input coupling element 1906b and CPE 1908b, and each eyepiece is rotated by ±45°. Figure 19F And 19G Shows images 1900f and 1900g obtained when input coupling element 1906b and CPE 1908b are used for the left and right eyepieces respectively. Images 1900f and 1900g show optical artifacts only along the Z-axis. Images 1900f and 1900g are captured by a camera located above CPE 1908b, and the light is p-polarized, e.g., transverse magnetic (TM) polarized.

[0170] For Z-cut wafers, the severity of optical artifacts depends on the polarization of the incident light. For example, reference Figure 20A , wafer 2000a includes a Z-cut substrate 2005, on which an input coupling element 2006 and an output coupling element (e.g., CPE 2008) are disposed. Figure 20B And 20C Shows images 2000b and 2000c generated by the light propagating from input coupling element 2006 to CPE 2008. The light in image 2000b is unpolarized, while the light in image 2000c is TM polarized. Image 2000b is more uniform than image 2000c, which shows a more obvious bull's-eye pattern, indicating that using unpolarized light can reduce the optical artifacts of Z-cut wafers. In some embodiments, a light source such as a lithography system 520 can be configured to deliver unpolarized light to the input coupling element.

[0171] For a Z-cut wafer, due to the rotational symmetry of the target eye pattern, when the clockwise direction of the wafer 2000a changes with respect to the optical axis, for example, rotates in the X-Y plane, the shape of the optical artifacts is generally the same. Therefore, referring to Figures 20D - 20F , each of the optical artifacts 2000d, 2000f, and 2000g exists in the image 2000b.

[0172] Using a polarization-insensitive coupling element (e.g., an input grating (ICG)) can reduce the optical artifacts of the Z-cut wafer. Polarization insensitivity can be defined as the ratio of TM / TE (and vice versa, e.g., TE / TM) polarized light coupled above a specific field of view. For example, if the ICG has polarization insensitivity, equal amounts of TM and TE polarized light are coupled, resulting in a ratio of 1. For example, an ICG with polarization insensitivity in the range of 0.5 - 2.0 above a 10°, 20°, or 30° field of view is considered polarization-insensitive.

[0173] Referring to Figure 21A and 21B , images 2100a and 2100b respectively show the outputs of a polarization-sensitive ICG (e.g., ratio greater than 2) and a polarization-insensitive ICG (e.g., ratio between 0.5 and 1.5). Images 2100a and 2100b each have a 50° field of view and are generated using green (e.g., 530 nm) TM polarized light from an LED. Image 2100b is more uniform than image 2100a, indicating that using a polarization-insensitive ICG can reduce the optical artifacts of the Z-cut wafer.

[0174] As an example, Figure 21C the eyepiece 2100c of

[0175] varies according to the polarization of the coupled light. The eyepiece 2100c includes a Z-cut silicon carbide substrate 2102 with n = 2.65. The grating 2104 has a pitch that can be selected based on the light wavelength. For example, a pitch of 350 nm works well for blue light. The grating height can vary, e.g., graded at different rates. The ICG 2106 includes a blazed grating 2110 composed of a first material with a medium refractive index (e.g., n = 1.53), and this blazed grating has a silver (Ag) coating 2112. An anti-reflection coating 2114 with n = 1.3 is located on the side of the substrate 2102 opposite to the grating (e.g., grating 2104) and the ICG 2106. Figure 21D and 21EThe blue light outputs of unpolarized light and polarized light are shown respectively. FOV 2100d1 does not present circular fringes, while FOV 2100e1 presents circular fringes. This results in circular distortion in image 2100e2 compared to 2100d2, and circular distortion in 2100e3 compared to 2100d3. Figure 21F and 21G The green light outputs of unpolarized light and polarized light are shown respectively. FOV 2100f1 presents reduced circular fringes compared to FOV 2100e1. This results in stronger circular distortion in image 2100g2 than in 2100f2, and stronger circular distortion in 2100g3 than in 2100f3. Figure 21H and 21I The green light outputs of unpolarized light and polarized light are shown respectively. FOV 2100h1 presents reduced circular fringes compared to FOV 2100i1. This results in stronger circular distortion in image 2100i2 than in 2100h2, and stronger circular distortion in 2100i3 than in 2100h3.

[0176] The polarization-insensitive ICG can take various forms. For example, Figure 22A and 22B ICG 2200a and 2200b are shown respectively. ICG 2200a is a reflective ICG, in which ridge 2201a reflects the incident light before the incident light is coupled into substrate 2202a. ICG 2200b is a transmissive ICG, in which ridge 2201b transmits the incident light into substrate 2202b before the incident light is coupled into substrate 2202b.

[0177] Substrates 2202a and 2202b can be composed of high refractive index crystal waveguide materials (such as LNO) respectively. ICG 2200a and 2200b include multi-refractive index ridges. For example, the ridges are composed of two or more layers of materials with different refractive indices. For example, ICG2200a includes a first ridge 2201a composed of an imprinted material 2204 and a metal coating 2206; a second ridge 2201c composed of an imprinted material 2204, a metal coating 2206, and a high refractive index material intermediate coating 2208 located between the imprinted material 2204 and the metal coating 2206. The third ridge 2201d is composed of an imprinted material 2204 and a high refractive index material coating 2208, and the fourth ridge 2201e is composed of the same material as substrate 2202a and has a metal coating 2206. The first to third ridges 2201a-c are all disposed on a layer of imprinted material 2204 on substrate 2202a, and the fourth ridge is directly disposed on substrate 2202a. The first to fourth ridges 2201a-d have a blazed grating shape. For example, the sides of the ridges are inclined. In this example, each ridge has a trapezoidal shape.

[0178] The ICG 2200b includes first and second ridges 2201f and 2201b composed of an imprint material 2204 and a high refractive index material coating 2208, a third ridge 2201g composed of an imprint material and a low refractive index coating 2210 within a high refractive index material intermediate coating 2208 between the imprint material 2204 and the low refractive index coating 2210, and a fourth ridge 2201h composed of the same material as the substrate 2202b and the low refractive index coating 2210. The first to third ridges 2201f, 2201b, and 2201g are all disposed on a layer of the imprint material 2204 on the substrate 2202b, and the fourth ridge 2201h is directly disposed on the substrate 2202b. The first to fourth ridges 2201f, 2201b, 2201g, and 2201h have a blazed shape. The first ridge 2201f has a trapezoidal shape, and the second to fourth ridges 2201b, 2201g, and 2201h have a parallelogram shape.

[0179] The form of each ridge can determine the polarization sensitivity, for example, the coupling rate of TM and TE polarized light. For example, the ridges 2201a and 2201c equally couple TM and TE polarized light. The ridges 2201b and 2201d diffract TE and TM polarized light with approximately the same diffraction efficiency.

[0180] In some embodiments, a single eyepiece may include ICGs on both sides of the substrate, for example, reflective and transmissive ICGs.

[0181] In some embodiments, the high refractive index coating includes titanium oxide (TiO2), the refractive index of the low refractive index coating ranges from 1.3 to 1.45, the refractive index of the imprint material ranges from 1.5 to 2.0, and the metal coating includes aluminum and / or silver.

[0182] Other design considerations

[0183] The above design rules regarding optical artifact management can be combined with the following features. The coupling element and the decoupling element may include multi-refractive index features, for example, nano-scale patterns including two or more refractive indices.

[0184] Reference Figure 23A and 23B, the eyepieces 2300a and 2300b each include an ICG (e.g., ICG 2302a and 2302b) and a CPE (e.g., CPE 2304a and 2304b) respectively disposed on substrates 2306a and 2306b. The substrates 2306a and 2306b each have a non-uniform height distribution. For example, on each side of the substrate 2303a, the substrate 2306a includes a grating having a graded height in a first portion 2303a and a height elevated relative to the surface of the substrate 2306a in the first portion 2303a in a second portion 2303b, which is connected by a sloped region 2307a. Similarly, on each side of the substrate 2303b, the substrate 2306b includes a grating having a graded height in a first portion 2305a and a height elevated relative to the surface of the substrate 2306b in the first portion 2302a in a second portion 2305b, which is connected by a sloped region 2307b.

[0185] The ICG 2302a includes a top 2302a1 and a bottom 2302a2. The top 2302a1 includes a blazed grating, and the bottom 2302a2 includes a uniform imprinted material layer. The ICG 2302b includes a top 2302a1 and a bottom 2302b2. The top 2302a1 includes a blazed grating, and the bottom 2302b2 includes a uniform imprinted material layer. The top 2302a1 and the bottom 2302a2 are located on opposite sides of the substrate 2306a. The CPE 2304a includes a top 2304a1 and a bottom 2304a2, and the bottom has symmetric features on opposite sides of the substrate 2306a. The CPE 2304b includes a top 2304b1 and a bottom 2304b2, and the bottom has symmetric features on opposite sides of the substrate 2306b.

[0186] Due to the height distribution variations of the substrates 2306a and 2306b respectively and the height variations of the ridges in the CPE, the heights of the diffractive features on the substrates 2306a and 2306b also vary. For example, the height of the ICG 2308a along the vertical direction 2312 is greater than the height of the CPE 2304a.

[0187] Throughout the present disclosure, the coupling-in element may refer to an ICG, such as a 1D or 2D array, and the coupling-out element may refer to an EPE, an OPE, or a CPE, such as a 1D or 2D array. The diffractive features within the array may be asymmetric in order to provide a blazed grating. In some embodiments, the diffractive features have materials deposited thereon asymmetrically to provide a blazed grating.

[0188] Substrates 2306a and 2306b are X-cut respectively and are composed of a high refractive index material, for example, with a refractive index between 2.2 and 2.3. ICGs 2302a and 2302b and CPEs 2304a and 2304b include a medium refractive index material, for example, with a refractive index between 1.6 and 1.7. ICGs 2302a and 2302b respectively include a reflective coating 2308a or 2308b.

[0189] The patterns of CPEs 2304a and 2304b are different. For example, ridge 2310a includes a medium refractive index material disposed at a different horizontal level along the vertical direction 2312 from other ridges in CPE 2304a, and ridge 2310b does not include a medium refractive index material and is disposed at the same vertical level as other ridges in CPE 2304b.

[0190] Figure 23C and 23D Top views 2300c and 2300d of eyepieces 2300a and 2300b are shown.

[0191] The patterns of CPE and ICG affect the light output efficiency and uniformity. Refer to Figures 23E - 23J , images 2300e, 2300f, and 2300g respectively show the red light (e.g., 635 nm ± 30 nm), green light (e.g., 530 nm ± 30 nm), and blue light (e.g., 455 nm ± 30 nm) eye box efficiencies of eyepiece 2300a. Images 2300h, 2300i, and 2300j respectively show the red light, green light, and blue light eye box efficiencies of eyepiece 2300b. For eyepiece 2300a, the efficiency of red light is 4.8%, the efficiency of green light is 6.1%, and the efficiency of blue light is 2.7%. For eyepiece 2300b, the efficiency of red light is 3.5%, the efficiency of green light is 3.6%, and the efficiency of blue light is 1.1%. Therefore, eyepiece 2300a generally has a greater eye box efficiency than eyepiece 2300b.

[0192] Figure 23K Various features of eyepieces 2500a, 2500b, 2500c, 2500d, 2500e, 2500f, 2500g, 2500h, 2500i, 2500j, and 2500k are shown, for example, multi-refractive index thin film coatings, etched gratings, feathered thin film coatings, and embedded etched gratings. Each of eyepieces 2500a - 2500k has a different combination of elements and refractive indices and is marked with different patterns according to the refractive index.

[0193] For example, the eyepiece 2500a includes a high refractive index waveguide substrate 2512, such as LNO, which has a CPE 2514 and an ICG 2516 composed of an imprinted material having a refractive index, for example, between 1.5 and 2.0. Imprinted material layers 2515 are provided on each side of the substrate 2512 and are located between the substrate 2512 and each of the CPE 2514 and the ICG 2516.

[0194] Compared with the eyepiece 2500a, the eyepiece 2500b includes a high refractive index coating 2518 (e.g., TiO2) between the substrate 2512 and the underlying layer 2515. Compared with the eyepiece 2500b, the eyepiece 2500c includes a low refractive index coating 2520 (e.g., SiO2) between the substrate 2512 and the high refractive index coating 2518. Compared with the eyepiece 2500b, the eyepiece 2500d includes an upper high refractive index coating 2518 between the substrate 2512 and the top layer 2518. Compared with the eyepiece 2500d, the upper high refractive index coating 2518 and the layer 2515 slope downward toward the ICG 2516 in the eyepiece 2500e.

[0195] Compared with the eyepiece 2500a, the eyepiece 2500f does not include the imprinted layer 2515, and the ICG 2516 and the CPE 2514 are composed of the same material as the substrate 2512 (e.g., LNO). Compared with the eyepiece 2500a, there is no upper imprinted layer in the eyepiece 2500g, and the upper portions of the CPE 2514 and the ICG 2516 are composed of the same material as the substrate 2512. Portions of the substrate 2512 (e.g., the space between the ICG2516 and the CPE 2514 and the space between adjacent ridges of the CPE 2514) are exposed. Compared with the eyepiece 2500g, the upper portions of the CPE 2514 and the ICG 2516 in the eyepiece 2500h are composed of a high refractive index material rather than the same material as the substrate 2512. Compared with the eyepiece 2500f, the lower portions of the CPE 2514 and the ICG 2516 in the eyepiece 2500i are composed of an imprinted material, and there is an imprinted coating 2519 above the top of the CPE.

[0196] Compared with the eyepiece 2500e, the eyepiece 2500j does not include an imprint layer between the substrate 2512, the CPE 2514, and the ICG 2516. In addition, the lower and upper portions of the CPE 2514 respectively include a ridge 2521 composed only of a high refractive index coating and another ridge 2523 composed of both an imprint material and a high refractive index material. In addition, there is a high refractive index coating 2524 between the ICG 2516 and the ridge 2523 on the top of the substrate 2512, and there is a high refractive index coating 2525 on the lower surface of the substrate 2512 directly below the ICG 2516. The high refractive index coating 2525 and the lower portion of the CPE 2514 are separated by the space of the exposed area of the substrate 2525. Compared with the eyepiece 2500e, both sides of the eyepiece 2500k are immersed in the low refractive index material 2527. In some embodiments, only one side of the eyepiece 2500k is immersed in the low refractive index material 2527.

[0197] Throughout Figure 23K Among them, various coatings (e.g., high, medium, or low refractive index) coatings can be 500nm + / - 10nm or less. The coating (e.g., layer) can have a thickness between 100nm and 500nm.

[0198] As Figures 22A - 23K As shown in various examples in, the coupling-in element and the coupling-out element can be located on either side of the substrate. For example, the coupling-in element and the coupling-out element can be located on one side of the substrate, or the coupling-in element and the coupling-out element can be located on both sides of the substrate. The coupling-in element and the coupling-out element can be located on the same side or opposite sides of the substrate. In some embodiments, the coupling-in element is located on both sides of the substrate, and the coupling-out element is located on one side of the substrate. In some embodiments, the coupling-out element is located on both sides of the substrate, and the coupling-in element is located on one side of the substrate. Both the coupling-in element and the coupling-out element can include gratings located on one side of the substrate and / or gratings located on the opposite side of the substrate. In some embodiments, there is a substrate stack, and the coupling-in element and the coupling-out element can include gratings located on one side of the first substrate and / or gratings located on one side of the second substrate.

[0199] Throughout this disclosure, examples of coupling-in elements (e.g., ICG) and coupling-out elements (e.g., EPE, OPE, and CPE) supported by one or both surfaces of the substrate are described. If there is an intermediate layer, for example, in the eyepiece 2500c having a low refractive index coating 2520, a high refractive index coating 2518, and an imprint layer 2515, the substrate (e.g., crystal material) still supports the coupling-in element and the coupling-out element.

[0200] Changing the wafer thickness can have a positive impact on image uniformity. Refer to Figure 24A, the wafer 2400a includes six pairs of input elements 2404 and output elements 2402, which are evenly distributed around the center 2405 of the wafer 2400a. For example, they are equidistantly distributed around the center 2405 with an angular increment (in this example, 60°). For example, each input element 2404 is located at an equal distance from the center of the wafer 2400a along a different radial direction, and each radial direction has an equal angular displacement relative to the previous radial direction.

[0201] Figure 24A A plan view of the wafer 2400a is shown. Figure 24B A total thickness variation (TTV) diagram 2400b is shown. As indicated by the refractive index, the thickness varies from zero at the edge of the wafer 2400a to 500 nm at the center of the wafer 2400a. For example, the height generally decreases from the center towards the edge. In this example, the wafer 2400a is circular, and the height varies radially from the origin of the circle.

[0202] Along the plane 2406, the height starts to increase from 0 nm, reaches 500 nm at the center, and then drops back to 0 nm at the opposite end. Refer to Figure 24C , the cross-section 2400c is the cross-section of the wafer 2400a through the plane 2406. The substrate 2408 has a height distribution according to the thickness variation. In this example, the height distribution of the substrate 2408 is dome-shaped, for example, corresponding to a spherical surface or a part of a rotationally symmetric spherical surface. In the cross-section 2400c, two pairs of input elements 2404a and 2404b and output elements 2402a and 2402b can be seen. The input elements and output elements are conformally disposed on the substrate surface 2410 with height variation.

[0203] In this example, there are six pairs of input elements and output elements, which correspond to six eyepieces. For example, the contour 2407 marks the contour of one eyepiece of the wafer 2400a. As mentioned before, the height distribution varies along the radial direction 2409. In this example, the radial direction 2409 is parallel to the line connecting the input element 2404 and the output element 2402. In addition, the height distribution varies along a second direction 2411, for example, the tangential direction perpendicular to the radial direction. The variation of the height distribution along the radial direction is faster than that along the tangential direction. Although the contour 2407 and the eyepiece do not have circular symmetry, the eyepiece corresponds to a part of a rotationally symmetric object (for example, the wafer 2400a).

[0204] Although Figure 24BA rotationally symmetric TTV is shown, but other implementations are possible. For example, FIGS. 24-24F show the TTVs of three different wafers, each wafer including two or more pairs of coupled-in elements 2404 and coupled-out elements 2402. The height distribution in wafers 2400d, 2400e, and 2400f is a function of the radius and angular position because these three TTVs do not have exact circular symmetry. The contour line 2412 marks an incremental change in height of 50 nm.

[0205] Reference Figure 24G and 24H , images 2400g and 2400h include images output by the eyepieces of wafers 2400d-2400f. Image 2400g includes the image of the left eyepiece. The top row is the image generated by the eyepiece of wafer 2400d, the middle row is the image generated by the eyepiece of wafer 2400e, and the bottom row is the image generated by the eyepiece of wafer 2400f. The left column includes blue light images, the middle column includes green light images, and the right column includes red light images. The same organization applies to image 2400h. In this example, wafer 2400e produces a blue light image with an eyebox efficiency of 3.94%, a green light image with an eyebox efficiency of 5.85%, and a red light image with an eyebox efficiency of 3.64%. In this example, the field of view is greater than 65°, and the wafer is X-cut LNO.

[0206] The TTV can be further modulated with a high refractive index (e.g., n between 2.2 and 2.3) dielectric film coating (e.g., depositing TiO2 by vapor deposition above the substrate using a shadow mask). It is easier to fabricate using a coating to achieve the desired distribution (e.g., wedge shape) than a substrate with the desired distribution. In some embodiments, the total length across the coupled-in and coupled-out elements is 65 mm, e.g., in the range of 60-70 mm.

[0207] Additional design features can improve the image contrast by preventing light from deviating out of the eyepiece in an unwanted manner. In some embodiments, a conductive material (e.g., indium tin oxide (ITO)) is coated on the outer edge of the substrate. The conductive material can be connected to a metal frame inside the head-mounted device. Reference Figure 25 , the eyepiece 2500a can be processed in various ways. The schematic diagram 2502 of the eyepiece 2500a shows the coupled-in element 2506, the coupled-out element 2508, and the substrate 2505. The CPE close-up indicated by the dashed line shows various options 2504a, 2504b, 2504c, 2504d, 2504e, 2504f, 2504g, and 2504h of the CPE design. Options 2504a-f include different configurations of the substrate, patterning, high refractive index dielectrics (e.g., TiO2 or ZrO2), or conductive ITO coatings, conductive coatings (e.g., Al, Ag, Cu, or ITO), and absorbent adhesives for absorbing stray light.

[0208] The eyepiece 2500b includes a stack 2510 of substrates 2505 having a pattern 2509, forming a template around the coupling-in and coupling-out elements 2508. The eyepiece 2500c includes the pattern 2509 and an absorptive adhesive 2511 (e.g., carbon black, which can be conductive).

[0209] The eyepiece 2500d includes a coupling-in element 2506, a coupling-out element 2508, and a substrate 2505 coated with an absorptive adhesive 2511. Although one substrate 2505 in the eyepiece 2500d is shown, other implementations are possible. For example, the eyepiece 2522a includes two stacked substrates 2502 with an absorptive adhesive 2511 on the substrate edges, and each substrate has a corresponding coupling-in element 2506 and coupling-out element 2508. As another example, the eyepiece 2522b includes two stacked substrates 2505 with an absorptive adhesive 2511 on the substrate edges, where there are no coupling-in or coupling-out elements on the upper substrate 2505a. As another example, the eyepiece 2522c includes three stacked substrates 2502 with an absorptive adhesive 2511 on the substrate edges, where there are no coupling-in or coupling-out elements on the upper substrate 2505a or the lower substrate 2505b, and the middle substrate 2505c has coupling-out elements 2508 disposed on both sides of the substrate 2505c and a coupling-in element 2506 on the upper surface of the substrate 2505c.

[0210] For the components of the disclosed eyepieces, there are various material choices. The entire content of US20220128817A1, titled "Waveguides with High Refractive Index Materials and Methods of Making the Same," is incorporated herein by reference, which describes the use of waveguides with high refractive index materials (including LiNbO3 or LiTaO3) in an AR system, and the AR system is an example environment where the above technologies can be deployed.

[0211] The imprint material can be a patterned imprintable prepolymer material, including resin materials such as epoxy vinyl ester. The resin can include vinyl monomers (e.g., methyl methacrylate) and / or difunctional or trifunctional vinyl monomers (e.g., diacrylate, triacrylate, dimethacrylate, etc.), and there may or may not be aromatic molecules in the monomers. The prepolymer material can include monomers having one or more functional groups such as alkyl, carboxyl, carbonyl, hydroxyl, and / or alkoxy groups. Sulfur atoms and aromatic groups exhibiting polarizability can be incorporated into the acrylate component to increase the refractive index, e.g., the refractive index is between 1.5 and 1.75. In some embodiments, the prepolymer material can include cycloaliphatic epoxy resins, which can be cured using ultraviolet light and / or heat. Additionally, the prepolymer material can include ultraviolet cationic photoinitiators and co-reactants to facilitate effective ultraviolet curing under ambient conditions.

[0212] Incorporating inorganic nanoparticles (NPs) such as ZrO2 and TiO2 into a stampable resin polymer, or even adding them to an edge-bonding resin, can increase the refractive index to 2.1. For patterned optical features (e.g., gratings), a higher refractive index can improve the overall diffraction efficiency over a wider angle. For an edge-blackening adhesive, a higher refractive index can help the refractive index better match the edge surface of LiNbO3, e.g., reducing the mismatch to 1.7 from 1.5. The refractive index matching increases the likelihood of coupling in and eliminating stray light. The refractive indices of pure ZrO2 and TiO2 crystals are 2.2 and 2.4 - 2.6 at 532 nm. In the preparation of optical nanocomposites of acrylate monomers and inorganic nanoparticles, a particle size less than 10 nm helps avoid excessive Rayleigh scattering. Due to the high specific surface area, high polarity, and incompatibility with the cross-linked polymer matrix of ZrO2 NPs, ZrO2 NPs tend to aggregate in the polymer matrix. Surface modification of the NPs can be used to overcome this problem. In this technique, the hydrophilic surface of ZrO2 is modified to be compatible with organic matter, enabling the NPs to be uniformly mixed with the polymer. This modification can be carried out with capping agents containing silanes and carboxylic acids. One end of the capping agent binds to the ZrO2 surface, and the other end of the capping agent contains a functional group or a non-functional organic moiety that can participate in acrylate cross-linking. Examples of surface-modified sub-10 nm ZrO2 particles include those provided by Pixelligent Technologies TM and Cerion Advanced Materials TM These functionalized nanoparticles are typically sold as a homogeneous mixture uniformly suspended in a solvent and can be combined with other substrates to form a resist formulation with an increased refractive index and an inkjet-printable viscosity.

[0213] The prepolymer material can be patterned using a template (rigid or flexible overlay) having an inverse tone of optical-functional nanostructures (diffractive and sub-diffractive) in direct contact with the liquid prepolymer. The liquid prepolymer material can be dispensed onto the substrate or surface to be patterned using, for example, a drop-on-demand or continuous jetting device, slot coating, spin coating, knife coating, microgravure coating, screen printing, or spraying or atomization. The template is in contact with the liquid, and when the liquid fills the template features, the prepolymer with a diffractive pattern cross-links and patterns with the contacting template (e.g., in the case of imprint lithography, e.g., J-FIL TM , where the prepolymer material is dispensed by inkjet), including exposing the prepolymer to actinic radiation having a wavelength between 310 nm and 410 nm and an intensity between 0.1 J / cm 2 and 100 J / cm 2 . The method can also include heating the prepolymer to a temperature between 40 °C and 120 °C while exposing the prepolymer to actinic radiation.

[0214] To promote adhesion between post-patterning (demolding of templates / molds) of prepolymer materials and curing on the desired surface film coatings (such as TiO2, ZrO2, SiO2, etc.) above LiNbO3 or LiNbO3, a crosslinking silane coupling agent can be used. One end of the silane coupling agent contains an organic functional group, and the other end contains a hydrolyzable group, and forms a durable bond with different types of organic and inorganic materials. Examples of the organic functional group can be acryloyl, and acryloyl can be crosslinked into the patternable polymer material. A coating layer can be applied on the template or mold, where the acryloyl end is replaced by a fluorinated chain, which can reduce the surface energy and thus serve as a non-bonding release point. Vapor deposition can be carried out under low pressure, where the coupling agent is delivered in vapor form, and an inert gas such as N2 can be used or not used, where there are activated -O and / or -OH groups on the surface of the material to be coated. The vapor coating process can deposit a single-layer thin film with a thickness in the range of 0.5 nm - 0.7 nm or greater.

[0215] UV acrylate coatings and films tend to be inhibited by oxygen during ambient curing. During curing, oxygen reacts with acrylate radicals on the surface to produce inactive peroxide radicals. This reaction effectively blocks the chain reaction and results in a sticky and wet surface after UV irradiation. The viscosity of the material can be in the range of about 10 cPs to about 100,000 cPs to about 500,000 cPs. Suitable dyes and pigments include carbon black (size range 5 nm - 500 nm), rhodamine B, lemon yellow, chemical dyes from Yamada chemical Co., Ltd., SUNFAST pigments from SunChemical (e.g., green 36, blue, purple 23, etc.).

[0216] A dye or pigment is mixed with a solvent and then mixed with a UV-curable resin to obtain a color-absorbing resin. The solvent can be a volatile solvent such as alcohol (methanol, ethanol, butanol, etc.) or other less volatile organic solvents such as dimethyl sulfoxide (DMSO), propylene glycol monomethyl ether acetate (PGMEA), toluene, etc. The dye or pigment can be separated or concentrated (e.g., using centrifugal evaporation) to produce an optimal concentration with the crosslinked organic resin (e.g., a highly transparent UV-cured material). The optimal concentration of the dye or pigment can impart the desired optical properties to the absorption film, such as a higher concentration of color-absorbing dye or pigment and produce a film with lower reflectivity.

[0217] Compared with traditional waterborne and solventborne coatings, UV radiation-curable coatings and adhesives face more challenges in balancing the acceptable viscosity for a specific application, the target gloss, and the desired film properties such as scratch resistance, hardness, adhesion strength, etc. Due to solvent evaporation, traditional coatings begin to orient and "concentrate" the matting agents during the physical drying of the film. As the volatile compounds evaporate, the applied film begins to shrink. This shrinkage can vary between 30% and 60% of the wet film volume, depending on the volume solids content. In contrast, 100% UV coatings only shrink by about 10% during a rapid curing cycle, resulting in a significantly reduced packing density of the matting agents. Silica-based matting agents effectively reduce gloss by introducing surface roughness and wrinkling. Examples of silica matting agents include products from Evonik: Acematt HK 400 with a D50 particle size of 6.3 um; Acematt OK 607 with a D50 particle size of 4.4 um; Acemat OK 412 with a D50 particle size of 6.3 um; Acematt 3600 with a D50 particle size of 5.0 um.

[0218] Patterns in the cured polymeric material can also be used as masks and directly etched into a high-index or low-index substrate (inorganic or organic) or a high-index or low-index film (e.g., TiO2, SiO2, etc.) above the substrate and below the patterned and cured polymer. High-index or low-index inorganic thin films can also be deposited by physical vapor deposition (e.g., evaporation, sputtering) or chemical vapor deposition methods (low-pressure plasma-enhanced CVD, atmospheric PECVD, ALD) with refractive indices ranging from 1.38 to 2.6 (e.g., MgF2, SiO2, ZrO2, TiO2, etc.). An imprint polymer with a certain actin energy can be selected to provide an etching selectivity (etching of the target material / etching of the patterned polymer) with a refractive index in the range of 0.3 to 3.0. The curable prepolymer material (as described above) with a refractive index of 1.5 to 2.1 is used to further planarize the imprinted or etched pattern by, for example, using an on-demand inkjet or continuous jetting device, slot coating, spin coating, knife coating, microgravure coating, screen printing, spraying or atomization. For example, using an on-demand inkjet device, a uniform or varying volume can also be achieved, where different regions obtain different densities or droplet volumes. In some embodiments, a blank template can be used to planarize the surface. The blank template can consist of a laminate that needs to be adhered to the patterned substrate. The thickness variation of the refractive index of each individual layer can be in the range of 0 - 50 nm, 0 - 100 nm, <200 nm, <300 nm, <800 nm, or <1000 nm. The shape can be wedge-shaped, for example, thickest near the ICG and tapering away from the ICG or vice versa. Opposing wedge-shaped laminates can also be combined together to increase the uniformity and expandability of the light wavelengths in different diffraction pitch waveguides.

[0219] Although the inventive concepts disclosed include those defined in the appended claims, it should be understood that these inventive concepts can also be defined according to the following embodiments.

[0220] In addition to the embodiments of the appended claims and the above embodiments, the following numbered embodiments are also innovative.

[0221] Embodiment 1 is a head-mounted display, comprising: a head-mounted display frame; a first eyepiece supported by the frame, the first eyepiece including a first substrate composed of a crystal transparent material having a crystal axis in a first orientation relative to the frame, the substrate having a first surface and a second surface opposite the first surface, the first eyepiece further including a first coupling element having a grating located on the first surface, and a first decoupling element having a grating located on the first surface and / or a grating located on the second surface; and a second eyepiece including a second substrate composed of a crystal transparent material having a crystal axis in a second orientation different from the first orientation relative to the frame, a second coupling element located on either surface of the second substrate, and a second decoupling element located on either surface of the second substrate.

[0222] Embodiment 2 is the head-mounted display according to Embodiment 1, wherein, for the first orientation and the second orientation, a first crystal axis among the crystal axes is oriented perpendicular to the surface of the corresponding substrate, and a second crystal axis among the crystal axes is oriented within the plane of the substrate.

[0223] Embodiment 3 is the head-mounted display according to Embodiment 2, wherein the first crystal axis is the Z axis.

[0224] Embodiment 4 is the head-mounted display according to Embodiment 3, wherein the second crystal axis in the first orientation is perpendicular to the second crystal axis in the second orientation.

[0225] Embodiment 5 is the head-mounted display according to Embodiment 3, further comprising a light projection system configured to transmit unpolarized light to the first and second coupling elements.

[0226] Embodiment 6 is the head-mounted display according to Embodiment 2, wherein the first crystal axis is the X axis.

[0227] Embodiment 7 is the head-mounted display according to Embodiment 2, wherein the first crystal axis is the Y axis.

[0228] Embodiment 8 is the head-mounted display according to any one of Embodiments 1 to 7, wherein the optical axis of the crystal transparent material in the first eyepiece is parallel to the optical axis of the crystal transparent material in the second eyepiece.

[0229] Example 9 is a head-mounted display according to any one of Examples 1 to 8, wherein the thickness of the first substrate varies across the first substrate.

[0230] Example 10 is a head-mounted display according to Example 9, wherein the thickness of the first substrate at the edge of the substrate is less than the thickness of the first substrate away from the edge.

[0231] Example 11 is a head-mounted display according to any one of Examples 1 to 10, wherein, for the first and second eyepieces, the shortest line between the corresponding coupling-in element and the coupling-out element defines a respective first direction of the corresponding eyepiece, and, for the first substrate, a first crystal axis among the crystal axes is arranged parallel to the first direction, and for the second substrate, a second crystal axis among the crystal axes is arranged parallel to the first direction.

[0232] Example 12 is a head-mounted display according to any one of Examples 1 to 11, wherein the crystalline transparent material is selected from the group consisting of LiNbO3, SiC, and LiTaO3.

[0233] Example 13 is a head-mounted display according to any one of Examples 1 to 12, wherein the crystalline transparent material is a birefringent material.

[0234] Example 14 is a head-mounted display according to any one of Examples 1 to 13, wherein the first and second substrates are components of first and second waveguide stacks.

[0235] Example 15 is a head-mounted display according to any one of Examples 1 to 14, wherein the first and second eyepieces correspond to portions of first and second wafers, and a first orientation of a first optical axis relative to a first line is different from a second orientation of a second optical axis relative to a second line.

[0236] Example 16 is a head-mounted display according to any one of Examples 1 to 15, wherein at least one of the first and second coupling-in elements and the first and second coupling-out elements comprises a plurality of materials having different refractive indices.

[0237] Example 17 is a head-mounted display according to any one of Examples 1 to 16, wherein the first surface supports a first dielectric material layer extending above the first coupling-in element and the first coupling-out element, and the first dielectric material has a refractive index of 1.5 or less.

[0238] Example 18 is a head-mounted display according to Example 17, wherein the refractive index of the first dielectric material is in the range of 1.2 to 1.3.

[0239] Example 19 is the head-mounted display according to Example 17, wherein the refractive index of the first dielectric material is in the range of 1.2 to 1.3.

[0240] Example 20 is the head-mounted display according to any one of Examples 1 to 19, wherein the second surface supports a second dielectric material layer extending above the second coupling element and the second decoupling element, and the second dielectric material has a refractive index of 1.5 or less.

[0241] Example 21 is the head-mounted display according to any one of Examples 1 to 20, further comprising an adhesive layer located on an edge of at least one of the first and second eyepieces, the adhesive layer being configured to absorb visible light.

[0242] Example 22 is the head-mounted display according to any one of Examples 1 to 21, further comprising a material layer disposed above the coupling element and the decoupling element.

[0243] Example 23 is the head-mounted display according to Example 22, wherein the material layer comprises a polymeric resin.

[0244] Example 24 is the head-mounted display according to any one of Examples 1 to 23, wherein the coupling element and the decoupling element are spaced apart by a space, and the space includes an exposed area of a crystalline transparent material.

[0245] Example 25 is the head-mounted display according to any one of Examples 1 to 24, wherein at least one of the first and second coupling elements and the first and second decoupling elements are respectively etched into the surfaces of the first and second substrates.

[0246] Example 26 is an article, comprising: a wafer composed of a crystalline transparent material having a crystal axis in a first orientation with respect to the surface of the wafer, the thickness of the wafer varying across the surface of the wafer such that for a cross-sectional profile of the wafer, the thickness monotonically increases from an edge of the wafer to a maximum thickness position away from the edge; and a plurality of optical elements including gratings spaced apart from each other on the surface of the wafer, each grating corresponding to a portion of the wafer for partitioning into an eyepiece assembly of a head-mounted display, each portion having the same thickness profile.

[0247] Example 27 is the article according to Example 26, further comprising corresponding optical elements for each grating in a corresponding portion of the wafer.

[0248] Example 28 is an article according to Example 26 or 27, wherein the corresponding optical element is a combined pupil expander, an exit pupil expander, or an orthogonal pupil expander.

[0249] Example 29 is an article according to any one of Examples 26 to 28, wherein the difference between the maximum thickness and the minimum thickness is in the range of 1 to 500 nm.

[0250] Example 30 is an article according to any one of Examples 26 to 29, wherein the wafer is circular.

[0251] Example 31 is an article according to Example 30, wherein the thickness of the wafer follows the sector of the circular wafer.

[0252] Example 32 is an article according to Example 30 or 31, wherein the plurality of gratings are equidistantly spaced from the center of the circular wafer.

[0253] Example 33 is an eyepiece, comprising: a transparent crystal substrate composed of a material having a refractive index greater than 2.2, the substrate extending in a plane and having a thickness in a direction perpendicular to the plane, the thickness varying along a first direction in the plane and varying along a second direction in a plane substantially perpendicular to the second direction; a coupling element comprising a grating supported by a first surface of the substrate; and an optical element comprising a grating supported by the first surface and / or the second surface of the substrate opposite to the first surface.

[0254] Example 34 is an eyepiece according to Example 33, wherein the optical element is a combined pupil expander, an exit pupil expander, or an orthogonal pupil expander.

[0255] Example 35 is an eyepiece according to Example 33 or 34, wherein the eyepiece corresponds to a part of a spherical or rotationally symmetric aspherical surface.

[0256] Example 36 is an eyepiece according to any one of Examples 33 to 35, wherein the eyepiece is coated with an absorbent adhesive material.

[0257] Example 37 is an eyepiece according to any one of Examples 33 to 36, wherein the difference between the maximum thickness and the minimum thickness is in the range of 1 to 500 nm.

[0258] Example 38 is an eyepiece according to any one of Examples 33 to 37, wherein the total length in the plane spanning the coupling element and the optical element is in the range of 60 - 70 mm.

[0259] Embodiment 39 is the eyepiece according to any one of Embodiments 33 to 38, wherein the substrate is configured to guide light within the range of 455 nm + / - 30 nm.

[0260] Embodiment 40 is the eyepiece according to any one of Embodiments 33 to 38, wherein the substrate is configured to guide light within the range of 530 nm + / - 30 nm.

[0261] Other embodiments are in the following claims.

[0262] Embodiment 41 is the eyepiece according to any one of Embodiments 33 to 38, wherein the substrate is configured to guide light within the range of 635 nm + / - 30 nm.

[0263] Embodiment 42 is the eyepiece according to any one of Embodiments 33 to 41, wherein at least one of the coupling grating and the optical element comprises two or more materials having different refractive indices.

[0264] Although this specification contains many specific implementation details, these details should not be construed as limitations on the scope of the claimed subject matter itself, but rather as descriptions of features specific to particular embodiments of a particular invention. Certain features that are described in the context of separate embodiments in this specification can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented separately in multiple embodiments or in any suitable sub-combination. Additionally, although the features are described above as acting in certain combinations and even initially claimed as such, in some cases, one or more features from the claimed combination can be deleted from the combination, and the claims can cover sub-combinations or variations of the sub-combinations.

[0265] Similarly, although operations are described in a particular order in the figures and recited in the claims, this should not be understood in itself as requiring that the operations be performed in the particular order shown or in sequential order, or that all of the illustrated operations be performed to achieve the desired result. In some cases, multitasking and parallel processing may be advantageous. Additionally, the separation of various system modules and components in the above embodiments should not be understood as required in all embodiments, and it should be understood that the described program components and systems can generally be integrated in a single software product or packaged into multiple software products.

[0266] Specific embodiments of the subject matter have been described. Other embodiments are within the scope of the following claims. For example, the acts recited in the claims can be performed in a different order and still achieve the desired result. As one example, the processes described in the figures need not be in the particular order or sequence shown to achieve the desired result. In some cases, multitasking and parallel processing may be advantageous.

Claims

1. A head-mounted display, comprising: A head-mounted display frame; A first eyepiece supported by the frame, the first eyepiece including a first substrate composed of a crystalline transparent material having a crystal axis with a first orientation relative to the frame, the substrate having a first surface and a second surface opposite the first surface, the first eyepiece further including a first coupling-in element having a grating located on the first surface, and a first coupling-out element having a grating located on the first surface and / or a grating located on the second surface; And A second eyepiece including a second substrate composed of a crystalline transparent material having a crystal axis with a second orientation different from the first orientation relative to the frame, a second coupling-in element located on either surface of the second substrate, and a second coupling-out element located on either surface of the second substrate.

2. The head-mounted display according to claim 1, wherein, For the first orientation and the second orientation, a first crystal axis among the crystal axes is oriented perpendicular to the surface of the corresponding substrate, and a second crystal axis among the crystal axes is oriented within the plane of the substrate.

3. The head-mounted display according to claim 2, wherein, The first crystal axis is the Z axis.

4. The head-mounted display according to claim 3, wherein, The second crystal axis in the first orientation is perpendicular to the second crystal axis in the second orientation.

5. The head-mounted display according to claim 3, further comprising a light projection system configured to transmit unpolarized light to the first and second coupling-in elements.

6. The head-mounted display according to claim 2, wherein, The first crystal axis is the X axis.

7. The head-mounted display according to claim 2, wherein, The first crystal axis is the Y axis.

8. The head-mounted display according to claim 1, wherein, The optical axis of the crystalline transparent material in the first eyepiece is parallel to the optical axis of the crystalline transparent material in the second eyepiece.

9. The head-mounted display according to claim 1, wherein, The thickness of the first substrate varies across the first substrate.

10. The head-mounted display according to claim 9, wherein, The thickness of the first substrate at the edge of the substrate is less than the thickness of the first substrate away from the edge.

11. The head-mounted display according to claim 1, wherein, For the first and second eyepieces, the shortest line between the corresponding coupling-in element and the coupling-out element defines a respective first direction of the corresponding eyepiece, and for the first substrate, a first crystal axis among the crystal axes is arranged parallel to the first direction, and for the second substrate, a second crystal axis among the crystal axes is arranged parallel to the first direction.

12. The head-mounted display according to claim 1, wherein, The crystalline transparent material is selected from the group consisting of LiNbO3, SiC, and LiTaO3.

13. The head-mounted display according to claim 1, wherein, The crystalline transparent material is a birefringent material.

14. The head-mounted display according to claim 1, wherein, The first and second substrates are components of first and second waveguide stacks.

15. The head-mounted display according to claim 1, wherein, The first and second eyepieces correspond to portions of first and second wafers, and a first orientation of a first optical axis relative to a first line is different from a second orientation of a second optical axis relative to a second line.

16. The head-mounted display according to claim 1, wherein, At least one of the first and second coupling-in elements and the first and second coupling-out elements includes multiple materials having different refractive indices.

17. The head-mounted display according to claim 1, wherein, The first surface supports a first dielectric material layer extending above the first coupling-in element and the first coupling-out element, and the first dielectric material has a refractive index of 1.5 or less.

18. The head-mounted display according to claim 17, wherein, The refractive index of the first dielectric material is in the range of 1.2 to 1.

3.

19. The head-mounted display according to claim 17, wherein, The refractive index of the first dielectric material is in the range of 1.2 to 1.

3.

20. The head-mounted display according to claim 1, wherein, The second surface supports a second dielectric material layer extending over the second coupling-in element and the second coupling-out element, the second dielectric material having a refractive index of 1.5 or less.

21. The head-mounted display according to claim 1, further comprising an adhesive layer located on an edge of at least one of the first and second eyepieces, the adhesive layer being configured to absorb visible light.

22. The head-mounted display according to claim 1, further comprising a material layer disposed over the coupling-in element and the coupling-out element.

23. The head-mounted display according to claim 22, wherein, The material layer comprises a polymeric resin.

24. The head-mounted display according to claim 1, wherein, The coupling-in element and the coupling-out element are spaced apart by a space, and the space includes an exposed area of the crystalline transparent material.

25. The head-mounted display according to claim 1, wherein, At least one of the first and second coupling-in elements and the first and second coupling-out elements is etched into the surface of the first and second substrates, respectively.

26. An article, comprising: A wafer composed of a crystalline transparent material having a crystal axis in a first orientation relative to the surface of the wafer, the thickness of the wafer varying across the surface of the wafer such that for a cross-sectional profile of the wafer, the thickness monotonically increases from an edge of the wafer to a maximum thickness position away from the edge; And A plurality of optical elements including gratings spaced apart from each other on the surface of the wafer, each grating corresponding to a portion of the wafer for partitioning into an eyepiece assembly of a head-mounted display, each portion having the same thickness profile.

27. The article according to claim 26, further comprising corresponding optical elements for each grating in a corresponding portion of the wafer.

28. The article according to claim 26, wherein The corresponding optical element is a combined pupil expander, an exit pupil expander, or an orthogonal pupil expander.

29. The article according to claim 26, wherein, The difference between the maximum thickness and the minimum thickness is in the range of 1 to 500 nm.

30. The article according to claim 26, wherein, The wafer is circular.

31. The article according to claim 30, wherein The thickness of the wafer follows a sector of the circular wafer.

32. The article according to claim 30, wherein, The plurality of gratings are equidistantly spaced from the center of the circular wafer.

33. An eyepiece, comprising: A transparent crystal substrate composed of a material having a refractive index greater than 2.2, the substrate extending in a plane and having a thickness in a direction perpendicular to the plane, the thickness varying in a first direction in the plane and varying in a second direction in a plane substantially perpendicular to the second direction; A coupling-in element including a grating supported by a first surface of the substrate; And An optical element including a grating supported by the first surface and / or the second surface of the substrate opposite the first surface.

34. The eyepiece according to claim 33, wherein, The optical element is a combined pupil expander, an exit pupil expander, or an orthogonal pupil expander.

35. The eyepiece according to claim 33, wherein, The eyepiece corresponds to a portion of a spherical or rotationally symmetric aspherical surface.

36. The eyepiece according to claim 33, wherein, The eyepiece is coated with an absorptive adhesive material.

37. The eyepiece according to claim 33, wherein, The difference between the maximum thickness and the minimum thickness is in the range of 1 to 500 nm.

38. The eyepiece according to claim 33, wherein, The total length in the plane spanning the coupling-in element and the optical element is in the range of 60 - 70 mm.

39. The eyepiece according to claim 33, wherein, The substrate is configured to guide light in the range of 455 nm + / - 30 nm.

40. The eyepiece according to claim 33, wherein, The substrate is configured to guide light in the range of 530 nm + / - 30 nm.

41. The eyepiece according to claim 33, wherein The substrate is configured to guide light in the range of 635 nm + / - 30 nm.

42. The eyepiece according to claim 33, wherein, At least one of the input grating and the optical element includes two or more materials having different refractive indices.

Images