Waveguides with lower index grating and higher index coating

Abstract

A waveguide comprises a substrate composed of a substrate material, a grating on the substrate, and a high-index layer disposed on the grating. The grating is composed of a grating material and has a plurality of ridges. The high-index layer is composed of a high-index material having a refractive index of at least 1.9 at an operative wavelength. The refractive index of the high-index material exceeds a refractive index of the grating material. Forming a waveguide includes forming a grating on a surface of a substrate, and forming a high-index layer on the grating. The grating is composed of a grating material and has a plurality of ridges. The high-index layer is composed of a high-index material having a refractive index of 1.9 or more at an operative wavelength. The refractive index of the high-index material is greater than a refractive index of the grating material.

Description

[0001] Attorney Docket No. 40589-0383WO1 / ML-5024WO

[0002] WAVEGUIDES WITH LOWER INDEX GRATING AND HIGHER INDEX COATING

[0003] CLAIM OF PRIORITY

[0004]

[0001] This application claims priority under 35 USC §119(e) to U.S. Provisional Application No. 63 / 789,617, filed on April 16, 2025, the entire contents of which are hereby incorporated by reference herein.

[0005] TECHNICAL FIELD

[0006]

[0002] The present disclosure relates to display systems and, more particularly, to augmented and virtual reality display systems and grating structures for use therewith.

[0007] BACKGROUND

[0008]

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

[0009]

[0004] Referring to FIG. 1, an augmented reality scene 10 is depicted wherein a user of an AR technology sees a real-world park-like setting 20 featuring people, trees, buildings in the background, and a concrete platform 30. In addition to these items, the user of the AR technology also perceives that he “sees” “virtual content” such as a robot statue 40 standing upon the real -world platform 30, and a cartoon-like avatar character 50 flying by, which seems to be a personification of a bumble bee, even though these elements 40, 50 do not exist in the real world. Because the human visual perception system is complex, it is challenging to produce an AR technology that facilitates a comfortable, natural-feeling, rich presentation of virtual image elements among other virtual or real-world imagery elements.Attorney Docket No. 40589-0383WO1 / ML-5024WO

[0010]

[0005] Systems and methods disclosed herein address various challenges related to AR and VR technology.

[0011] SUMMARY

[0012]

[0006] In tire field of AR and VR technology, high-index substrates (e.g., having a refractive index of 1,65 or more or 1,7 or more) beneficially allow for a wider field-of-view (FoV). High-index gratings on a high-index substrate are especially beneficial for single-active layer eyepieces (e.g., eyepieces in which the red, green, and blue channels propagate within the same waveguide). For example, using a high-index grating for the orthogonal pupil expander (OPE) or the exit pupil expander (EPE) can increase tire efficiency of red light that is directed toward the eye of user, and other design parameters can increase the efficiency of blue light directed toward the user.

[0013]

[0007] Forming high-index gratings, however, can be expensive and difficult. Generally, forming gratings using resist materials having an index greater than 1.9 (e.g., 2) involves etching, which can increase cost and complexity of manufacturing. Forming slanted gratings through etching can be particularly expensive. The present disclosure describes methods, articles, and systems that avoid the difficulty and costs of etched diffraction gratings by including a lower-index diffraction grating covered by a higher-index coating. Simpler and less expensive methods, compared to etching, can be used to form the lower-index grating and the higher-index coating.

[0014]

[0008] Beyond reducing manufacturing cost and complexity, the grating structures of the present disclosure can provide improved optical characteristics. For example, by using a lower-index diffraction grating and a higher-index coating, the efficiencies of guiding red, green, and blue light to the eye of the user can be more similar compared to the efficiencies of gratings composed of a high-index material. The similarities of the efficiencies for each of the red, green, and blue channels lead to improved image uniformity in the display.

[0015]

[0009] Other features and advantages will be apparent from the drawings, the description, and the claims.Attorney Docket No. 40589-0383WO1 / ML-5024WO

[0016] BRIEF DESCRIPTION OF THE DRAWINGS

[0017]

[0010] FIG. 1 illustrates a user's view of augmented reality (AR) through an AR device.

[0011] FIG. 2 illustrates a conventional display system for simulating three-dimensional imagery for a user.

[0018]

[0012] FIGS. 3A, 3B, and 3C illustrate relationships between radius of curvature and focal radius.

[0019]

[0013] FIG. 4A illustrates a representation of the accommodation-vergence response of the human visual system. FIG. 4B illustrates examples of different accommodative states and vergence states of a pair of eyes of the user. FIG. 4C illustrates an example of a representation of a top-down view of a user viewing content via a display system. FIG. 4D illustrates another example of a representation of a top-down view of a user viewing content via a display system.

[0020]

[0014] FIG, 5 illustrates aspects of an approach for simulating three-dimensional imagery by modifying wavefront divergence.

[0021]

[0015] FIG. 6 illustrates an example of a waveguide stack for outputting image information to a user.

[0022]

[0016] FIG. 7 illustrates an example of exit beams output by a waveguide,

[0023]

[0017] FIG. 8 illustrates an example of a stacked waveguide assembly in which each depth plane includes images formed using multiple different component colors.

[0024]

[0018] FIG, 9A illustrates a cross-sectional side view of an example of a set of stacked waveguides that each includes an in-coupling optical element. FIG. 9B illustrates a perspective view of an example of the plurality of stacked waveguides of FIG. 9A. FIG. 9C illustrates a top-down plan view of an example of the plurality of stacked waveguides of FIGS. 9 A and 9B. FIG. 9D illustrates an example of a wearable display system,

[0025]

[0019] FIG. 10A depicts a cross-sectional view of an example of a waveguide including a low-index grating and a high-index layer, supported by a high-index substrate. FIGS. 10B and 10C depict cross-sectional views of examples of waveguides including a high-index grating and a low-index layer, supported by a high-index substrate.

[0026]

[0020] FIGS. 11A, 1 IB, and 11C depict cross-sections of examples of various geometries of waveguides with low-index gratings and high-index layers.

[0027]

[0021] FIGS. 12 A and 12B depict cross-sections of examples of waveguides with low-index gratings and high-index layers with different material choices.

[0028]

[0022] FIGS. 13A, 13B, 13C, and 13D depict cross-sections of examples of different waveguides. FIGS. 13E, 13F, 13G, and 13H depict plots of diffraction efficiencies, as aAttorney Docket No. 40589-0383WO1 / ML-5024WO

[0029] function of wavelength, of exit pupil expanders and orthogonal pupil expanders including the waveguides of FIGS. 13A, 13B, and 13C.

[0030]

[0023] FIGS. 14A, I4B, and 14C are plots depicting the intensity of light out-coupled from the waveguides described herein, for red, green, and blue light, respectively.

[0031]

[0024] FIG. 15 is a flowchart of an example of a process of making waveguides, as disclosed herein.

[0032]

[0025] FIG. 16A depicts an example of a waveguide including an antireflective layer. FIGS.

[0033] 16B and 16C depict an example of a waveguide including a diffraction grating formed of slanted ridges. FIG. 16D depicts an example of a waveguide including an in-coupling grating and an orthogonal pupil expander. FIGS. 16E and 16F depict examples of waveguides including low-index layers.

[0034]

[0026] FIG. 17 depicts an example of a waveguide with gratings on both a user side and a world side.

[0035]

[0027] FIGS. 18A, 18B, 18C, 18D, 18E, 18F, 18G, 18H, 18I, 18J, 18K, 18L, and 18M are scanning electron microscope (SEM) images of waveguides including a high-index substrate and a low-index grating.

[0036]

[0028] FIG. 19A depicts a waveguide in which a height of a high-index layer above each grating ridge in a grating is roughly uniform. FIG. 19B depicts a waveguide in which an upper surface of each grating ridge is pointed or rounded.

[0037]

[0029] The drawings are provided to illustrate example implementations described herein and are not intended to limit the scope of the disclosure.

[0038] DETAILED DESCRIPTION

[0039]

[0030] AR systems may display virtual content to a user, or viewer, while still allowing the user to see the w orld around them. Preferably, this content is displayed on a head-mounted display (e.g., as part of eyewear) that projects image information to the user's eyes. In addition, the display may also transmit light from the surrounding environment to the user's eyes, to allow a view' of that surrounding environment. As used herein, it will be appreciated that a ‘"head-mounted” or "‘head mountable” display is a display that may be mounted on the head of a viewer or user.

[0040]

[0031] In some AR systems, virtual / augmented / mixed display having a relatively high field of view (FOV) can enhance the view'ing experience. The FOV of the display depends on the angle of light output by waveguides of the eyepiece, through which the viewer sees images projected into his or her eye. A waveguide having a relatively high refractive index (e.g., 1.7Attorney Docket No. 40589-0383WO1 / ML-5024WO

[0041] or greater) can provide a relatively high FOV. However, to efficiently couple light into the high refractive index waveguide, the diffractive optical coupling elements should also have a correspondingly high refractive index. To achieve this goal, among other advantages, some displays for AR systems according to implementations described herein include a waveguide including a relatively high index (e.g., 1.8 or more, such as 2.0 or more) material, having formed thereon respective diffraction gratings with correspondingly high refractive index, such as Ti-,

[0042] Ta-, or Li-based oxide. For example, a diffraction grating may be formed directly on a Ti-, Ta-, or Li-based oxide waveguide by patterning a surface portion of the waveguide formed of a Ti-, Ta-, or Li -based oxide.

[0043]

[0032] Some high refractive index diffractive optical coupling elements such as in-coupling or out-coupling optical elements have strong polarization dependence. For example, incoupling gratings (ICGs) for in-coupling light into a waveguide where the diffractive optical coupling element includes high refractive index material may admit light of a given polarization significantly more than light of another polarization. Such elements may, for example, in-couple light with TM polarization into the waveguide at a rate approximately 3 times that of light with TE polarization. Diffractive optical coupling elements with this kind of polarization dependence may have reduced efficiency (due to tire poor efficiency and general rejection of one polarization) and may also create coherent artifacts and reduce the uniformity of a far field image formed by light coupled out of a birefringent waveguide. To obtain diffractive optical coupling elements that are polarization-insensitive or at least that have reduced polarization sensitivity (e.g., that couple light with an efficiency that is relatively independent of polarization), some displays for AR systems according to various implementations described herein include a waveguide with diffraction gratings formed with blazed geometries. The diffraction grating may also be formed directly in the waveguide, which may include high-index material (e.g., having an index of refraction 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 a value in any range between any of these values). A diffractive grating may, for example, be formed in high-index materials such as such as Ti-, Ta-, or Li-based oxide like lithium niobate (LiNbO₃) or lithium tantalate (LiTaO₃) or such as zirconium oxide (ZrO₂), titanium dioxide (TiO₂) or silicon carbide (SiC), for example, by patterning the high-index material with a blazed geometry’,

[0044]

[0033] FIG. 2 illustrates a conventional display system for simulating three-dimensional imagery for a user. A user's eyes are spaced apart, and when looking at a real object in space, each eye will have a slightly different view of the object and may form an image of the objectAttorney Docket No. 40589-0383WO1 / ML-5024WO

[0045] at different locations on the retina of each eye. This may be referred to as binocular disparity and may be utilized by the human visual system to provide a perception of depth.

[0046] Conventional display systems simulate binocular disparity by presenting two distinct images 190, 200 with slightly different views of the same virtual object -one for each eye 210, 220 — corresponding to the views of the virtual object that would be seen by each eye if the virtual object were a real object at a desired depth. These images provide binocular cues that the user's visual system may interpret to derive a perception of depth.

[0047]

[0034] With continued reference to FIG. 2, the images 190, 200 are spaced from the eyes 210, 220 by a distance 230 on a z-axis. The z-axis is parallel to the optical axis of the viewer with their eyes fixated on an object at optical infinity directly ahead of the viewer. The images 190, 200 are flat and at a fixed distance from the eyes 210, 220. Based on the slightly different views of a virtual object in the images presented to the eyes 210, 220, respectively, the eyes may naturally rotate such that an image of the object falls on corresponding points on the retinas of each of the eyes, to maintain single binocular vision. This rotation may cause the lines of sight of each of the eyes 210, 220 to converge onto a point in space at which the virtual object is perceived to be present. As a result, providing three-dimensional imagery conventionally involves providing binocular cues that may manipulate the vergence of the user's eyes 210, 220, and that the human visual system interprets to provide a perception of depth.

[0048]

[0035] Generating a realistic and comfortable perception of depth is challenging, however. It will be appreciated that light from objects at different distances from the eyes have wavefronts with different amounts of divergence. FIGS. 3A-3C illustrate relationships between distance and the divergence of light rays. The distance between the object and the eye 210 is represented by, in order of decreasing distance, Rl, R2, and R3. As shown in FIGS. 3A-3C, the light rays become more divergent as distance to the object decreases. Conversely, as distance increases, the light rays become more collimated. Stated another way, it may be said that the light field produced by a point (the object or a part of the object) has a spherical wavefront curvature, which is a function of how far away the point is from the eye of the user. The curvature increases with decreasing distance between the object and the eye 210. While only a single eye 210 is illustrated for clarity of illustration in FIGS. 3A-3C and other figures herein, the discussions regarding eye 210 may be applied to both eyes 210 and 220 of a viewer.

[0049]

[0036] With continued reference to FIGS. 3A-3C, light from an object that the viewer's eyes are fixated on may have different degrees of wavefront divergence. Due to the differentAttorney Docket No. 40589-0383WO1 / ML-5024WO

[0050] amounts of wavefront divergence, the light may be focused differently by the lens of the eye, which in turn may require the lens to assume different shapes to form a focused image on tire retina of the eye. Where a focused image is not formed on tire retina, the resulting retinal blur acts as a cue to accommodation that causes a change in the shape of the lens of the eye until a focused image is formed on the retina. For example, the cue to accommodation may trigger the ciliary muscles surrounding the lens of the eye to relax or contract, thereby modulating the force applied to the suspensory ligaments holding the lens, thus causing the shape of the lens of the eye to change until retinal blur of an object of fixation is eliminated or minimized, thereby forming a focused image of the object of fixation on the retina (e.g., fovea) of the eye. The process by which the lens of the eye changes shape may be referred to as accommodation, and the shape of the lens of the eye required to form a focused image of the object of fixation on the retina (e.g., fovea) of the eye may be referred to as an accommodative state,

[0051]

[0037] With reference now to FIG. 4 A, a representation of the accommodation-vergence response of the human visual system is illustrated. The movement of the eyes to fixate on an object causes the eyes to receive light from the object, with tire light forming an image on each of the retinas of the eyes. The presence of retinal blur in the image formed on the retina may provide a cue to accommodation, and the relative locations of the image on the retinas may provide a cue to vergence. The cue to accommodation causes accommodation to occur, resulting in the lenses of the eyes each assuming a particular accommodative state that forms a focused image of the object on the retina (e.g., fovea) of the eye. On the other hand, the cue to vergence causes vergence movements (rotation of the eyes) to occur such that the images formed on each retina of each eye are at corresponding retinal points that maintain single binocular vision. In these positions, the eyes may be said to have assumed a particular vergence state. With continued reference to FIG. 4A, accommodation may be understood to be the process by which the eye achieves a particular accommodative state, and vergence may be understood to be the process by which the eye achieves a particular vergence state. As indicated in FIG. 4A, the accommodative and vergence states of the eyes may change if the user fixates on another object. For example, the accommodated state may change if the user fixates on a new object at a different depth on the z-axis.

[0052]

[0038] Without being limited by theory’, it is believed that viewers of an object may perceive the object as being “three-dimensional” due to a combination of vergence and accommodation. As noted above, vergence movements (e.g., rotation of the eyes so that the pupils move toward or away from each other to converge the lines of sight of the eyes toAttorney Docket No. 40589-0383WO1 / ML-5024WO

[0053] fixate upon an object) of the two eyes relative to each other are closely associated w ith accommodation of the lenses of the eyes. Under normal conditions, changing the shapes of the lenses of the eyes to change focus from one object to another object at a different distance will automatically cause a matching change in vergence to the same distance, under a relationship known as the “accommodation-vergence reflex."’ Likewise, a change in vergence will trigger a matching change in lens shape under normal conditions,

[0054]

[0039] With reference now to FIG. 4B, examples of different accommodative and vergence states of the eyes are illustrated. The pair of eyes 222a is fixated on an object at optical infinity, while the pair eyes 222b are fixated on a point 221 at less than optical infinity. Notably, the vergence states of each pair of eyes is different, with the pair of eyes 222a directed straight ahead, while the pair of eyes 222b converge on the point 221. The accommodative 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,

[0055]

[0040] Undesirably, many users of conventional “3-D” display systems find such conventional systems to be uncomfortable or may not perceive a sense of depth at all due to a mismatch between accommodative and vergence states in these displays. As noted above, many stereoscopic or “3-D” display systems display a scene by providing slightly different images to each eye. Such systems are uncomfortable for many viewers, since they, among other things, simply provide different presentations of a scene and cause changes in the vergence states of the eyes, but without a corresponding change in the accommodative states of those eyes. Rather, the images are shown by a display at a fixed distance from the eyes, such that the eyes view' all the image information at a single accommodative state. Such an arrangement works against the “accommodation-vergence reflex” by causing changes in the vergence state without a matching change in the accommodative state. This mismatch is believed to cause viewer discomfort. Display systems that provide a better match between accommodation and vergence may form more realistic and comfortable simulations of three-dimensional imagery’,

[0056]

[0041] Without being limited by theory', it is believed that the human eye typically may interpret a finite number of depth planes to provide depth perception. Consequently, a highly believable simulation of perceived depth may be achieved by providing, to the eye, different presentations of an image corresponding to each of these limited numbers of depth planes. In some implementations, the different presentations may provide both cues to vergence and matching cues to accommodation, thereby providing physiologically correct accommodation-vergence matching.Attorney Docket No. 40589-0383WO1 / ML-5024WO

[0057]

[0042] With continued reference to FIG. 4B, two depth planes 240, corresponding to different distances in space from the eyes 210, 220, are illustrated. For a given depth plane 240, vergence cues may be provided by tire displaying of images of appropriately different perspectives for each eye 210, 220. In addition, for a given depth plane 240, light forming the images provided to each eye 210, 220 may have a wavefront divergence corresponding to a light field produced by a point at the distance of that depth plane 240.

[0058]

[0043] In the illustrated implementation, the distance, along the z-axis, of the depth plane 240 containing the point 221 is 1 meter (m). As used herein, distances or depths along the z-axis may be measured with a zero-point located at the exit pupils of the user's eyes. Thus, a depth plane 240 located at a depth of 1 m corresponds to a distance of 1 m away from the exit pupils of the user's eyes, on the optical axis of those eyes with the eyes directed towards optical infinity. As an approximation, the depth or distance along the z-axis may be measured from the display in front of the user's eyes (e.g,, from the surface of a waveguide), plus a value for the distance between the device and the exit pupils of the user's eyes. That value may be called 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 for the eye relief may be a normalized value used generally for all viewers. For example, the eye relief may be assumed to be 20 millimeters (mm) and a depth plane that is at a depth of 1 m may be at a distance of 980 mm in front of the display.

[0059]

[0044] With reference now to FIGS, 4C and 4D, examples of matched accommodation -vergence distances and mismatched accommodation-vergence distances are illustrated, respectively. As illustrated in FIG. 4C, the display system may provide images of a virtual object to each eye 210, 220. The images may cause the eyes 210, 220 to assume a vergence state in which the eyes converge on a point 15 on a depth plane 240, In addition, the images may be formed by a light having a wavefront curvature corresponding to real objects at that depth plane 240. As a result, the eyes 210, 220 assume an accommodative state in which the images are in focus on the retinas of those eyes. Tirus, the user may perceive the virtual object as being at the point 15 on the depth plane 240.

[0060]

[0045] It will be appreciated that each of the accommodative and vergence states of the eyes 210, 22.0 are associated with a particular distance on the z-axis. For example, an object at a particular distance from the eyes 210, 220 causes those eyes to assume particular accommodative states based upon the distances of the object. The distance associated with a particular accommodative state may be referred to as the accommodation distance, Ad.

[0061] Similarly, there are particular vergence distances, Vd, associated with the eyes in particularAttorney Docket No. 40589-0383WO1 / ML-5024WO

[0062] vergence states, or positions relative to one another. Where the accommodation distance and the vergence distance match, the relationship between accommodation and vergence may be said to be physiologically correct. This is considered to be the most comfortable scenario for a viewer.

[0063]

[0046] In stereoscopic displays, however, the accommodation distance and the vergence distance may not always match. For example, as illustrated in FIG, 4D, images displayed to the eyes 210, 220 may be displayed with wavefront divergence corresponding to depth plane 240, and the eyes 210, 220 may assume a particular accommodative state in which the points 15a, 15b on that depth plane are in focus. However, the images displayed to the eyes 210, 220 may provide cues for vergence that cause the eyes 210, 220 to converge on a point 15 that is not located on the depth plane 240. As a result, the accommodation distance corresponds to the distance from the exit pupils of the eyes 210, 220 to the depth plane 240, while the vergence distance corresponds to the larger distance from the exit pupils of the eyes 210, 220 to the point 15, in some implementations. The accommodation distance is different from the vergence distance. Consequently, there is an accommodation-vergence mismatch. Such a mismatch is considered undesirable and may cause discomfort in the user. It will be appreciated that the mismatch corresponds to distance (e.g,, Va-Aa) and may be characterized using diopters.

[0064]

[0047] In some implementations, it will be appreciated that a reference point other than exit pupils of the eyes 210, 220 may be utilized for determining distance for determining accommodation-vergence mismatch, so long as the same reference point is utilized for the accommodation distance and the vergence distance. For example, the distances could be measured from the cornea to the depth plane, from the retina to the depth plane, from the eyepiece (e.g., a waveguide of the display device) to the depth plane, and so on.

[0065]

[0048] Without being limited by theory, it is believed that users may still perceive accommodation-vergence mismatches of up to about 0.25 diopter, up to about 0.33 diopter, and up to about 0.5 diopter as being physiologically correct, without the mismatch itself causing significant discomfort. In some implementations, display systems disclosed herein (e.g., the display system 250, FIG. 6) present images to the viewer having accommodation-vergence mismatch of about 0.5 diopter or less. In some other implementations, tire accommodation-vergence mismatch of the images provided by the display system is about 0,33 diopter or less. In yet other implementations, the accommodation-vergence mismatch of the images provided by the display system is about 0.25 diopter or less, including about 0.1 diopter or less.Attorney Docket No. 40589-0383WO1 / ML-5024WO

[0066]

[0049] FIG. 5 illustrates aspects of an approach for simulating three-dimensional imagery by modifying wavefront divergence. The display system includes a waveguide 270 that is configured to receive light rays 770 that is encoded with image information, and to output that light to the user's eye 210. The waveguide 270 may output the exit beam 650 with a defined amount of wavefront divergence corresponding to the wavefront divergence of a light field produced by a point on a desired depth plane 240. In some implementations, the same amount of wavefront divergence is provided for all objects presented on that depth plane. In addition, it will be illustrated that the other eye of the user may be provided with image information from a similar waveguide.

[0067]

[0050] In some cases, a single waveguide may be configured to output light with a set amount of wavefront divergence corresponding to a single or limited number of depth planes and / or the waveguide may be configured to output light of a limited range of wavelengths. Consequently, in some implementations, a plurality or stack of waveguides may be utilized to provide different amounts of wavefront divergence for different depth planes and / or to output light of different ranges of wavelengths. As used herein, it will be appreciated at a depth plane may be planar or may follow the contours of a curved surface.

[0068]

[0051] FIG. 6 illustrates an example of a waveguide stack for outputting image information to a user. A display system 250 includes a stack of waveguides, or stacked waveguide assembly, 260 that may be utilized to provide three-dimensional perception to the eye / brain using a plurality of waveguides 270, 280, 290, 300, 310. It will be appreciated that the display system 250 may be considered a light field display in some implementations. In addition, the waveguide assembly 260 may also be referred to as an eyepiece.

[0069]

[0052] In some implementations, the display system 250 is configured to provide substantially continuous cues to vergence and multiple discrete cues to accommodation. The cues to vergence can be provided by displaying different images to each of the eyes of the user, and the cues to accommodation may be provided by outputting the light that forms the images with selectable discrete amounts of wavefront divergence. Stated another way, the display system 250 may be configured to output light with variable levels of wavefront divergence. In some implementations, each discrete level of wavefront divergence corresponds to a particular depth plane and may be provided by a particular one of the waveguides 270, 280, 290, 300, 310,

[0070]

[0053] With continued reference to FIG. 6, the waveguide assembly 260 may also include a plurality of features 320, 330, 340, 350 between the waveguides. In some implementations, the features 320, 330, 340, 350 may be one or more lenses. The waveguides 270, 280, 290,Attorney Docket No. 40589-0383WO1 / ML-5024WO

[0071] 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 can be configured to output image information corresponding to that depth plane. Image injection devices 360, 370, 380, 390, 400 may function as a source of light for the waveguides and may be utilized to inject image information into the waveguides 270, 280, 290, 300, 310, each of which may be configured, as described herein, to distribute incoming light across each respective waveguide, for output toward the eye 210. Light exits an output surface 410, 420, 430, 440, 450 of the image injection devices 360, 370, 380, 390, 400 and is injected into a corresponding input surface 460, 470, 480, 490, 500 of the waveguides 270, 280, 290, 300, 310. In some implementations, each of the input surfaces 460, 470, 480, 490, 500 may be an edge of a corresponding waveguide, or may be part of a major surface of the corresponding waveguide (that is, one of the waveguide surfaces directly facing the world 10 or the viewer's eye 210). In some implementations, a single beam of light (e.g., a collimated beam) may be injected into each waveguide to output an entire field of cloned collimated beams that are directed toward the eye 210 at particular angles (and amounts of divergence) corresponding to the depth plane associated with a particular waveguide. In some implementations, a single one of 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.

[0072]

[0054] In some implementations, the image injection devices 360, 370, 380, 390, 400 are discrete displays that each produce image information for injection into a corresponding waveguide 270, 280, 290, 300, 310, respectively. In some other implementations, the image injection devices 360, 370, 380, 390, 400 are the output ends of a single multiplexed display which may (e.g., pipe image information via one or more optical conduits, such as fiber optic cables) to each of the image injection devices 360, 370, 380, 390, 400. It will be appreciated that the image information provided by the image injection devices 360, 370, 380, 390, 400 may include light of different w avelengths, or colors (e.g., different component colors, as discussed herein).

[0073]

[0055] In some implementations, the light injected into the waveguides 270, 280, 290, 300, 310 is provided by a light projector system 520, which 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 may be directed to and modified by a light modulator 540 (e.g., a spatial light modulator) via a beam splitter 550. The light modulator 540 may be configured to change theAttorney Docket No. 40589-0383WO1 / ML-5024WO

[0074] 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 (LCD) including a liquid crystal on silicon (LCOS) displays. It will be appreciated that the image injection devices 360, 370, 380, 390, 400 are illustrated schematically and, in some implementations, these image injection devices may represent different light paths and locations in a common projection system configured to output light into associated ones of the waveguides 270, 280, 290, 300, 310. In some implementations, the waveguides of the waveguide assembly 260 may function as ideal lens while relaying light injected into the waveguides out to the user's eyes. In this conception, the object may be the spatial light modulator 540 and the image may be the image on the depth plane.

[0075]

[0056] In some examples, μLED displays can be used in light projector system 520. μLED displays can unpolarized light over a large range of angles. Accordingly, μLED displays can beneficially provide imagery over wide fields of view with high efficiency.

[0076]

[0057] In some implementations, the display system 250 may be a scanning fiber display including one or more scanning fibers configured to project light in various patterns (e.g., raster scan, spiral scan, Lissajous patterns, etc.) into one or more waveguides 270, 280, 290, 300, 310 and ultimately to the eye 210 of the viewer. In some implementations, the illustrated image injection devices 360, 370, 380, 390, 400 may schematically represent a single scanning fiber or a bundle of scanning fibers configured to inject light into one or a plurality of the waveguides 270, 280, 290, 300, 310, In some other implementations, the illustrated image injection devices 360, 370, 380, 390, 400 may schematically represent a plurality of scanning fibers or a plurality of bundles of scanning fibers, each of which are configured to inject light into an associated one of the waveguides 270, 280, 290, 300, 310. It will be appreciated that one or more optical fibers may be configured to transmit light from the light module 530 to the one or more waveguides 270, 280, 290, 300, 310. It will be appreciated that one or more intervening optical structures may be provided between the scanning fiber, or fibers, and the one or more waveguides 270, 280, 290, 300, 310 (e.g,, to redirect light exiting the scanning fiber into the one or more waveguides 270, 280, 290, 300, 310).

[0077]

[0058] A controller 560 controls the operation of one or more of the stacked waveguide assembly 260, including operation of the image injection devices 360, 370, 380, 390, 400, the light module 530, and the light modulator 540. In some implementations, 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 (e.g., any of theAttorney Docket No. 40589-0383WO1 / ML-5024WO

[0078] various schemes disclosed herein). In some implementations, the controller may be a single integral device, or a distributed system connected by wired or wireless communication channels. The controller 560 may be part of the local processing and data module 140 or remote processing module 150 (FIG. 9D) in some implementations.

[0079]

[0059] With continued reference to FIG. 6, the waveguides 270, 280, 290, 300, 310 may be configured to propagate light within each respective waveguide by total internal reflection (TIR). The waveguides 270, 280, 290, 300, 310 may each be planar or have another shape (e.g., curved), with major top and bottom surfaces and edges extending between those major top and bottom surfaces. In tire illustrated configuration, the waveguides 270, 280, 290, 300, 310 may each include out-coupling optical elements 570, 580, 590, 600, 610 that are configured to extract light out of a waveguide by redirecting the light, propagating within each respective waveguide, out of the waveguide to output image information to the eye 210. Extracted light may also be referred to as out-coupled light and the out-coupling optical elements light may also be referred to light extracting optical elements. An extracted beam of light may be output by the waveguide at locations at which the light propagating in the waveguide strikes a light extracting optical element. The out-coupling optical elements 570, 580, 590, 600, 610 may, for example, be gratings, including diffractive optical features, as discussed further herein. While illustrated disposed at the bottom major surfaces of the waveguides 270, 280, 290, 300, 310, for ease of description and drawing clarity, in some implementations, the out-coupling optical elements 570, 580, 590, 600, 610 may be disposed at the top and / or bottom major surfaces, and / or may be disposed directly in the volume of the waveguides 270, 280, 290, 300, 310, as discussed further herein. In some implementations, the out-coupling optical elements 570, 580, 590, 600, 610 may be formed in a layer of material that is attached to a transparent substrate to form the waveguides 270, 280, 290, 300, 310. In some other implementations, the waveguides 270, 280, 290, 300, 310 may be a monolithic piece of material and the out-coupling optical elements 570, 580, 590, 600, 610 may be formed on a surface and / or in the interior of that piece of material.

[0080]

[0060] With continued reference to FIG. 6, as discussed herein, each waveguide 270, 280, 290, 300, 310 is configured to output light to form an image corresponding to a particular depth plane. For example, the waveguide 270 nearest the eye may be configured to deliver collimated light (which was injected into such waveguide 270), to the eye 210. The collimated light may be representative of the optical infinity focal plane. Tire next waveguide up 280 may be configured to send out collimated light which passes through the first lens 350 (e.g., a negative lens) before it may reach the eye 210; such first lens 350 may be configuredAttorney Docket No. 40589-0383WO1 / ML-5024WO

[0081] to create a slight convex wavefront curvature so that the eye / brain interprets light coming from that next waveguide up 280 as coming from a first focal plane closer inward toward the eye 210 from optical infinity. Similarly, the third up -waveguide 290 passes its output light through both the first and second lenses 350 and 340 before reaching the eye 210; the combined optical power of the first and second lenses 350 and 340 may be configured to create another incremental amount of wavefront curvature so that the eye / brain interprets light coming from the third waveguide 290 as coming from a second focal plane that is even closer inward toward the person from optical infinity than was light from the next waveguide up 280.

[0082]

[0061] Tire other layers of waveguide 300, 310 and lenses 330, 320 are similarly configured, with the highest waveguide 310 in the stack sending its output through all of the lenses between it and the eye for an aggregate focal power representative of the closest focal plane to the person. To compensate for the stack of lenses 320, 330, 340, 350 when viewing / interpreting light coming from the world 510 on the other side of the stacked waveguide assembly 260, a compensating lens layer 620 may be disposed at the top of the stack to compensate for the aggregate power of the stack of lenses 320, 330, 340, 350 below. Such a configuration provides as many perceived focal planes as there are available waveguide / lens pairings. Both the out-coupling optical elements of the waveguides and the focusing aspects of the lenses may be static (i.e., not dynamic or electro-active). In some alternative implementations, either or both may be dynamic using electro-active features,

[0062] In some implementations, two or more of the waveguides 270, 280, 290, 300, 310 may have the same associated depth plane. For example, multiple waveguides 270, 280, 290, 300, 310 may be configured to output images set to the same depth plane, or multiple subsets of the waveguides 270, 280, 290, 300, 310 may be configured to output images set to the same plurality of depth planes, w ith one set for each depth plane. This may provide advantages for forming a tiled image to provide an expanded field of view at those depth planes.

[0083]

[0063] With continued reference to FIG. 6, the out-coupling optical elements 570, 580, 590, 600, 610 may be configured to both redirect light out of their respective waveguides and to output this light with the appropriate amount of divergence or collimation for a particular depth plane associated with the waveguide. As a result, waveguides having different associated depth planes may have different configurations of out-coupling optical elements 570, 580, 590, 600, 610, which output light with a different amount of divergence depending on the associated depth plane. In some implementations, the out-coupling optical elementsAttorney Docket No. 40589-0383WO1 / ML-5024WO

[0084] 570, 580, 590, 600, 610 may be volumetric or surface features, which may be configured to output light at specific angles. For example, the out-coupling optical elements 570, 580, 590, 600, 610 may be volume holograms, surface holograms, and / or diffraction gratings. In some implementations, the features 320, 330, 340, 350 may not be lenses; rather, they may simply be spacers (e.g., cladding layers and / or structures for forming airgaps).

[0085]

[0064] In some implementations, the out-coupling optical elements 570, 580, 590, 600, 610 are diffractive features that form a diffraction pattern, or “diffractive optical element” (also referred to herein as a “DOE”). Preferably, the DOE's have a sufficiently low diffraction efficiency so that only a portion of the light of the beam is deflected away toward the eye 210 with each intersection of the DOE, while the rest continues to move through a waveguide via TIR. The light carrying the image information is thus divided into a number of related exit beams that exit the waveguide at a multiplicity of locations, and the result is a fairly uniform pattern of exit emission toward the eye 210 for this particular collimated beam bouncing around within a waveguide.

[0086]

[0065] In some implementations, one or more DDEs may be switchable between “on” states in which they actively diffract, and “off” states in which they do not significantly diffract. For instance, a switchable DOE may include a layer of polymer dispersed liquid cry stal, in which microdroplets include a diffraction pattern in a host medium, and the refractive index of the microdroplets may be switched to substantially match the refractive index of the host material (in which case the pattern does not appreciably diffract incident light) or the microdroplet may be switched to an index that does not match that of the host medium (in which case the pattern actively diffracts incident light).

[0087]

[0066] In some implementations, a camera assembly 630 (e.g., a digital camera, including visible light and infrared light cameras) may be provided to capture images of the eye 210 and / or tissue around the eye 210 (e.g., to detect user inputs and / or to monitor the physiological state of the user). As used herein, a camera may be any image capture device. In some implementations, the camera assembly 630 may include an image capture device and a light source to project light (e.g., infrared light) to the eye, which may then be reflected by the eye and detected by the image capture device. In some implementations, the camera assembly 630 may be attached to the frame 80 (FIG. 9D) and may be in electrical communication with the local processing and data module 140 and / or remote processing module 150, which may process image information from the camera assembly 630. In some implementations, one camera assembly 630 may be utilized for each eye, to separately monitor each eye.Attorney Docket No. 40589-0383WO1 / ML-5024WO

[0088]

[0067] With reference now to FIG. 7, an example of exit beams output by a waveguide is shown. One waveguide is illustrated, but it will be appreciated that other waveguides in the waveguide assembly 260 (FIG. 6) may function similarly, where the waveguide assembly 260 includes multiple waveguides. Light 640 is injected into the waveguide 270 at the input surface 460 of the waveguide 270 and propagates w ithin the waveguide 270 by TIR. At points where the light 640 impinges on the out-coupling optical element 570 (e.g., a DOE) a portion of the light exits the waveguide as exit beams 650. The exit beams 650 are illustrated as substantially parallel but, as discussed herein, they may also be redirected to propagate to the eye 210 at an angle (e.g., forming divergent exit beams), depending on the depth plane associated with the waveguide 270. It will be appreciated that substantially parallel exit beams may be indicative of a w aveguide w ith out-coupling optical elements that out-couple light to form images that appear to be set on a depth plane at a large distance (e.g., optical infinity) from the eye 210. Other w aveguides or other sets of out-coupling optical elements may output an exit beam pattern that is more divergent, which would require the eye 210 to accommodate to a closer distance to bring it into focus on the retina and would be interpreted by the brain as light from a distance closer to the eye 210 than optical infinity.

[0089]

[0068] In some implementations, a full color image may be formed at each depth plane by overlaying images in each of the component colors (e.g., three or more component colors). FIG. 8 illustrates an example of a stacked waveguide assembly in which each depth plane includes images formed using multiple different component colors. The illustrated implementation shows depth planes 240a-240f, although more or fewur depths are also contemplated. Each depth plane may have three or more component color images associated with it, including: a first image of a first color, G; a second image of a second color, R; and a third image of a third color, B. Different depth planes are indicated in the figure by different numbers for diopters (dpt) following the letters G, R, and B. Just as examples, the numbers following each of these letters indicate diopters (1 / m), or inverse distance of the depth plane from a viewer, and each box in the figures represents an individual component color image. In some implementations, to account for differences in tire eye's focusing of light of different w avelengths, the exact placement of the depth planes for different component colors may vary. For example, different component color images for a given depth plane may be placed on depth planes corresponding to different distances from the user. Such an arrangement may increase visual acuity and user comfort and / or may decrease chromatic aberrations.

[0090]

[0069] In some implementations, light of each component color may be output by a single dedicated waveguide and, consequently, each depth plane may have multiple waveguidesAttorney Docket No. 40589-0383WO1 / ML-5024WO

[0091] associated with it. in such implementations, each box in the figures including the letters G, R, or B may be understood to represent an individual waveguide, and three waveguides may be provided per depth plane where three component color images are provided per depth plane. While the waveguides associated with each depth plane are shown adjacent to one another in this drawing for ease of description, it will be appreciated that, in a physical device, the waveguides may all be arranged in a stack with one waveguide per level. In some other implementations, multiple component colors may be output by the same waveguide, such that, for example, only a single waveguide may be provided per depth plane.

[0092]

[0070] With continued reference to FIG. 8, in some implementations, G is the color green, R is the color red, and B is the color blue. In some other implementations, other colors associated with other wavelengths of light, including magenta and cyan, may be used in addition to or may replace one or more of red, green, or blue.

[0093]

[0071] It will be appreciated that references to a given color of light throughout this disclosure will be understood to encompass light of one or more wavelengths w ithin a range of wavelengths of light that are perceived by a viewer as being of that given color. For example, red light may include light of one or more wavelengths in the range of about 620-780 nm, green light may include light of one or more wavelengths in the range of about 492-577 nm, and blue light may include light of one or more wavelengths in the range of about 435-493 nm.

[0094]

[0072] In some implementations, the light module 530 (FIG. 6) may be configured to emit light of one or more wavelengths outside the visual perception range of the view'er, for example, infrared and / or ultraviolet wavelengths. In addition, the in-coupling, out-coupling, and other light redirecting structures of the waveguides of tire display system 250 may be configured to direct and emit this light out of the display towards the user's eye 210 (e.g., for imaging and / or user stimulation applications).

[0095]

[0073] With reference now' to FIG. 9A, in some implementations, light impinging on a waveguide may need to be redirected to in-couple that light into the waveguide. An incoupling optical element may be used to redirect and in-couple the light into its corresponding waveguide. FIG. 9A illustrates a cross-sectional side view' of an example of a plurality or set 660 of stacked waveguides that each includes an in-coupling optical element. Tire waveguides may each be configured to output light of one or more different wavelengths, or one or more different ranges of wavelengths. It will be appreciated that the set 660 of stacked waveguides may correspond to the waveguide assembly 260 (FIG. 6) and the illustrated waveguides of tire set 660 of stacked waveguides may correspond to part of theAttorney Docket No. 40589-0383WO1 / ML-5024WO

[0096] plurality of waveguides 270, 280, 290, 300, 310, except that light from one or more of the image injection devices 360, 370, 380, 390, 400 is injected into the waveguides from a position that requires light to be redirected for in-coupling.

[0097]

[0074] The illustrated set 660 of stacked waveguides includes waveguides 670, 680, and 690. Each waveguide includes an associated in-coupling optical element (which may also be referred to as a light input area on the waveguide), with in-coupling optical element 700 disposed on a major surface (e.g., an upper major surface) of waveguide 670, in-coupling optical element 710 disposed on a major surface (e.g., an upper major surface) of waveguide 680, and in-coupling optical element 720 disposed on a major surface (e.g., an upper major surface) of waveguide 690. In some implementations, one or more of the in-coupling optical elements 700, 710, 720 may be disposed on the bottom major surface of the respective waveguide 670, 680, 690 (particularly where the one or more in-coupling optical elements are reflective, deflecting optical elements). As illustrated, the in-coupling optical elements 700, 710, 720 may be disposed on the upper major surface of their respective waveguide 670, 680, 690 (or the top of the next lower waveguide), particularly where those in-coupling optical elements are transmissive, deflecting optical elements. In some implementations, the in-coupling optical elements 700, 710, 720 may be disposed in the body of the respective waveguide 670, 680, 690. In some implementations, as discussed herein, the in-coupling optical elements 700, 710, 720 are wavelength selective, such that they selectively redirect one or more wavelengths of light, while transmitting other wavelengths of light. While illustrated on one side or comer of their respective waveguide 670, 680, 690, it will be appreciated that the in-coupling optical elements 700, 710, 720 may be disposed in other areas of their respective waveguide 670, 680, 690 in some implementations.

[0098]

[0075] As illustrated, the in-coupling optical elements 700, 710, 720 may be laterally offset from one another. In some implementations, each in-coupling optical element may be offset such that it receives light without that light passing through another in-coupling optical element. For example, each in-coupling optical element 700, 710, 720 may be configured to receive light from a different image injection device 360, 370, 380, 390, and 400 as shown in FIG. 6, and may be separated (e.g., laterally spaced apart) from other in-coupling optical elements 700, 710, 720 such that it substantially does not receive light from the other ones of the in-coupling optical elements 700, 710, 720.

[0099]

[0076] Each waveguide also includes associated light distributing elements (e.g., light distributing elements 730) disposed on a major surface (e.g., a top major surface) of waveguide 670, light distributing elements 740 disposed on a major surface (e.g., atop majorAttorney Docket No. 40589-0383WO1 / ML-5024WO

[0100] surface) of waveguide 680, and light distributing elements 750 disposed on a major surface (e.g., a top major surface) of waveguide 690. In some other implementations, the light distributing elements 730, 740, 750, may be disposed on a bottom major surface of associated waveguides 670, 680, 690, respectively. In some other implementations, the light distributing elements 730, 740, 750, may be disposed on both top and bottom major surface of associated waveguides 670, 680, 690, respectively; or the light distributing elements 730, 740, 750, may be disposed on different ones of the top and bottom major surfaces in different associated waveguides 670, 680, 690, respectively.

[0101]

[0077] The waveguides 670, 680, 690 may be spaced apart and separated by, for example, gas, liquid, and / or solid layers of material. For example, as illustrated, layer 760a may separate waveguides 670 and 680; and layer 760b may separate waveguides 680 and 690. In some implementations, the layers 760a and 760b are formed of low refractive index materials (that is, materials having a lower refractive index than the material forming the immediately adjacent one of waveguides 670, 680, 690). Preferably, the refractive index of the material forming the layers 760a, 760b is 0.05 or more, or 0.10 or less than the refractive index of the material forming the waveguides 670, 680, 690. Advantageously, the lower refractive index layers 760a, 760b may function as cladding layers that facilitate total internal reflection (TIR) of light through the waveguides 670, 680, 690 (e.g., TIR between the top and bottom major surfaces of each waveguide). In some implementations, the layers 760a, 760b are formed of air. While not i llustrated, it will be appreciated that the top and bottom of the illustrated set 660 of waveguides may include immediately neighboring cladding layers.

[0102]

[0078] Preferably, for ease of manufacturing and other considerations, the material forming the waveguides 670, 680, 690 are similar or tire same, and the material forming tire layers 760a, 760b are similar or the same. In some implementations, the material forming the waveguides 670, 680, 690 may be different between one or more waveguides, and / or the material forming the layers 760a, 760b may be different, while still holding to the various refractive index relationships noted above.

[0103]

[0079] With continued reference to FIG. 9A, light rays 770, 780, 790 are incident on the set 660 of waveguides. It will be appreciated that the light rays 770, 780, 790 may be injected into the waveguides 670, 680, 690 by one or more image injection devices 360, 370, 380, 390, 400 (FIG. 6).

[0104]

[0080] In some implementations, the light rays 770, 780, 790 have different properties (e.g., different wavelengths or different ranges of wavelengths), which may correspond to different colors. The in-coupling optical elements 700, 710, 720 each deflect the incident light suchAttorney Docket No. 40589-0383WO1 / ML-5024WO

[0105] that the light propagates through a respective one of the waveguides 670, 680, 690 by TIR. In some implementations, the in-coupling optical elements 700, 710, 720 each selectively deflect one or more particular wavelengths of light, while transmitting other wavelengths to an underlying waveguide and associated in-coupling optical element.

[0106]

[0081] For example, in-coupling optical element 700 may be configured to deflect light rays 770, which has a first wavelength or range of wavelengths, while transmitting light rays 780 and 790, which have different second and third wavelengths or ranges of wavelengths, respectively. The transmitted light rays 780 impinge on and are deflected by the in-coupling optical element 710, which is configured to deflect light of a second wavelength or range of wavelengths. The light ray 790 is deflected by the in-coupling optical element 720, which is configured to selectively deflect light of third wavelength or range of wavelengths.

[0107]

[0082] With continued reference to FIG. 9A, the deflected light rays 770, 780, 790 are deflected so that they propagate through a corresponding waveguide 670, 680, 690; that is, the in-coupling optical elements 700, 710, 720 of each waveguide deflects light into that corresponding waveguide 670, 680, 690 to in-couple light into that corresponding waveguide. The light rays 770, 780, 790 are deflected at angles that cause the light to propagate through the respective waveguide 670, 680, 690 by TIR. The light rays 770, 780, 790 propagate through the respective waveguide 670, 680, 690 by TIR until impinging on the waveguide's corresponding light distributing elements 730, 740, 750.

[0108]

[0083] With reference now to FIG. 9B, a perspective view of an example of the plurality of stacked waveguides of FIG. 9A is illustrated. As noted above, the in-coupled light rays 770, 780, 790, are deflected by the in-coupling optical elements 700, 710, 720, respectively, and then propagate by TIR within the waveguides 670, 680, 690, respectively. The light rays 770, 780, 790 then impinge on the light distributing elements 730, 740, 750, respectively. The light distributing elements 730, 740, 750 deflect the light rays 770, 780, 790 so that they propagate towards the out-coupling optical elements 800, 810, 820, respectively.

[0109]

[0084] In some implementations, the light distributing elements 730, 740, 750 are orthogonal pupil expanders (OPEs). In some implementations, the OPEs deflect or distribute light to the out-coupling optical elements 800, 810, 820 and, in some implementations, may also increase the beam or spot size of this light as it propagates to the out-coupling optical elements. In some implementations, the light distributing elements 730, 740, 750 may be omitted and the in-coupling optical elements 700, 710, 720 may be configured to deflect light directly to the out-coupling optical elements 800, 810, 820. For example, with reference to FIG. 9A, the light distributing elements 730, 740, 750 may be replaced with out-coupling optical elementsAttorney Docket No. 40589-0383WO1 / ML-5024WO

[0110] 800, 810, 820, respectively. In some implementations, the out-coupling optical elements 800, 810, 820 are exit pupils (EPs) or exit pupil expanders (EPEs) that direct light in a viewer's eye 210 (FIG. 7). It will be appreciated that the OPEs may be configured to increase the dimensions of the eye box in at least one axis and the EPEs may be to increase the eye box in an axis crossing (e.g., orthogonal to) the axis of the OPEs. For example, each OPE may be configured to redirect a portion of the light striking the OPE to an EPE of the same waveguide, while allowing the remaining portion of the light to continue to propagate down the waveguide. Upon impinging 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 down the waveguide, and so on. Similarly, upon striking the EPE, a portion of the impinging light is directed out of the waveguide towards the user, and a remaining portion of that light continues to propagate through the waveguide until it strikes the EP again, at which time another portion of the impinging light is directed out of the waveguide, and so on. Consequently, a single beam of in-coupled light may be “replicated” each time a portion of that light is redirected by an OPE or EPE, thereby forming a field of cloned beams of light, as shown in FIG. 6. In some implementations, the OPE and / or EPE may be configured to modify a size of the beams of light.

[0111]

[0085] Accordingly, with reference to FIGS. 9 A and 9B, in some implementations, the set 660 of waveguides includes waveguides 670, 680, 690; in-coupling optical elements 700, 710, 720; light distributing elements (e.g., OPEs) 730, 740, 750; and out-coupling optical elements (e.g., EPEs) 800, 810, 820 for each component color. The waveguides 670, 680, 690 may be stacked with an air gap / cladding layer between each one. The in-coupling optical elements 700, 710, 720 redirect or deflect incident light (with different in-coupling optical elements receiving light of different wavelengths) into its waveguide. The light then propagates at an angle which will result in TIR within the respective waveguide 670, 680, 690. In the example shown, light ray 770 (e.g., blue light) is deflected by the first in-coupling optical element 700, and then continues to bounce down the waveguide, interacting with the light distributing element (e.g., OPEs) 730 and then the out-coupling optical element 800 (e.g., EPEs), in a manner described earlier. The light rays 780 and 790 (e.g., green and red light, respectively) will pass through the waveguide 670, with light ray 780 impinging on and being deflected by in-coupling optical element 710. The light ray 780 then bounces down the waveguide 680 via TIR, proceeding on to its light distributing element (e.g., OPEs) 740 and then the out-coupling optical element (e.g., EPEs) 810. Finally, light ray 790 (e.g., red light) passes through the waveguide 690 to impinge on the light in-coupling optical elements 720 ofAttorney Docket No. 40589-0383WO1 / ML-5024WO

[0112] the waveguide 690. The light in-coupling optical elements 720 deflect the light ray 790 such that the light ray propagates to light distributing element (e.g., OPEs) 750 by TIR, and then to the out-coupling optical element (e.g., EPEs) 820 by TIR. The out-coupling optical element 820 then finally out-couples the light ray 790 to the viewer, who also receives the out- coupled light from the other waveguides 670, 680.

[0113]

[0086] FIG 9C illustrates a top-down plan view of an example of the plurality of stacked waveguides of FIGS. 9A and 9B. As illustrated, the waveguides 670, 680, 690, along with each waveguide's associated light distributing element 730, 740, 750 and associated out- coupling optical element 800, 810, 820, may be vertically aligned. However, as discussed herein, the in-coupling optical elements 700, 710, 720 are not vertically aligned; rather, the in-coupling optical elements are non-overlapping (e.g., laterally spaced apart as seen in the top-down view). As discussed further herein, this nonoverlapping spatial arrangement facilitates the injection of light from different resources into different waveguides on a one-to-one basis, thereby allowing a specific light source to be uniquely coupled to a specific waveguide. In some implementations, arrangements including nonoverlapping spatially- separated in-coupling optical elements may be referred to as a shifted pupil system, and the in-coupling optical elements within these arrangements may correspond to sub pupils.

[0114]

[0087] Alternatively, in certain implementations, two or more of the in-coupling optical elements can be in an inline arrangement, in which they are vertically aligned. In such arrangements, light for waveguides further from the projection system is transmitted through the in-coupling optical elements for waveguides closer to the projection system, preferably with minimal scattering or diffraction.

[0115]

[0088] Inline configurations can advantageously reduce the size of and simplify the projector. Moreover, it can increase the field of view of the eyepiece (e.g., by coupling of same color to several waveguides by making use of crosstalk). For example, green light can be coupled into blue and red active layers. Because the pitch of each ICG can be different to provide improved (e.g., optimal) performance for a specific color, the allowed field of view can be increased.

[0116]

[0089] In inline configurations, except for the last layer in the optical path, the ICGs should be either at most partially reflective or otherwise transmissive to light having operative wavelengths of subsequent layers in the waveguide stack. In either case, the efficiency can be undesirably low unless the gratings are etched in a high-index layer (e.g., 1.8 or more for polymer based layers), or a high-index coating is deposited or growth on the grating.Attorney Docket No. 40589-0383WO1 / ML-5024WO

[0117] However, this approach can increase the back reflection into the projector lens, which thus can generate image artifacts such as image ghosting.

[0118]

[0090] FIG. 9D illustrates an example of wearable display system 60 into which the various waveguides and related systems disclosed herein may be integrated. In some implementations, the display system 60 is the display system 250 of FIG. 6, with FIG. 6 schematically showing some parts of that display system 60 in greater detail. For example, the waveguide assembly 260 of FIG. 6 may be part of the display 70.

[0119]

[0091] With continued reference to FIG. 9D, the display system 60 includes a display 70, and various mechanical and electronic modules and systems to support the functioning of that display 70. The display 70 may be coupled to a frame 80, which is wearable by a display¬ system user or user 90 and which is configured to position the display 70 in front of the eyes of the user 90. The display 70 may be considered eyewear in some implementations. In some implementations, a speaker 99 is coupled to the frame 80 and configured to be positioned adjacent the ear canal of the user 90 (in some implementations, another speaker, not shown, may optionally be positioned adjacent the other ear canal of the user to provide stereo / shapeable sound control). The display system 60 may also include one or more microphones 110 or other devices to detect sound. In some implementations, the microphone is configured to allow the user to provide inputs or commands to the display system 60 (e.g., the selection of voice menu commands, natural language questions, etc.), and / or may allow audio communication with other persons (e.g,, with other users of similar display systems. The microphone may further be configured as a peripheral sensor to collect audio data (e.g., sounds from the user and / or environment). In some implementations, the display system may also include a peripheral sensor 120a, which may be separate from the frame 80 and attached to the body of the user 90 (e.g., on the head, torso, an extremity, etc, of the user 90), The peripheral sensor 120a may be configured to acquire data characterizing a physiological state of the user 90 in some implementations. For example, the sensor 120a may be an electrode.

[0120]

[0092] With continued reference to FIG. 9D, the display 70 is operatively coupled by communications link 130, such as by a wired lead or wireless connectivity, to a local processing and data module 140 which may be mounted in a variety of configurations, such as fixedly attached to the frame 80, fixedly attached to a helmet or hat worn by the user, embedded in headphones, or otherwise removably attached to the user 90 (e.g., in a backpack-style configuration, in a belt-coupling style configuration). Similarly, the sensor 120a may be operatively coupled by communications link 120b (e.g., a wired lead or wireless connectivity) to the local processing and data module 140. The local processing and dataAttorney Docket No. 40589-0383WO1 / ML-5024WO

[0121] module 140 may include a hardware processor, as well as digital memory, such as non¬ volatile memory (e.g., flash memory or hard disk drives), both of which may be utilized to assist in the processing, caching, and storage of data. Optionally, the local processing and data module 140 may include one or more central processing units (CPUs), graphics processing units (GPUs), dedicated processing hardware, and so on. The data may include data a) captured from sensors (which may be operatively 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, radio devices, gyros, and / or other sensors disclosed herein; and / or b) acquired and / or processed using remote processing module 150 and / or remote data repository 160 (including data relating to virtual content), possibly for passage to the display 70 after such processing or retrieval. The local processing and data module 140 may be operatively coupled by communication links 170, 180, such as via a wired or wireless communication link, to the remote processing module 150 and remote data repository 160 such that the remote processing module 150 and remote data repository 160 are operatively coupled to each other and available as resources to the local processing and data module 140. In some implementations, the local processing and data module 140 may include one or more of the image capture devices, microphones, inertial measurement units, accelerometers, compasses, GPS units, radio devices, and / or gyros. In some other implementations, one or more of these sensors may be attached to the frame 80 or may be standalone structures that communicate with the local processing and data module 140 by wired or wireless communication pathways.

[0122]

[0093] With continued reference to FIG. 9D, in some implementations, the remote processing module 150 may include one or more processors configured to analyze and process data and / or image information, for instance including one or more central processing units (CPUs), graphics processing units (GPUs), dedicated processing hardware, and so on. In some implementations, the remote data repository’ 160 may include a digital data storage facility, which may be available through the internet or other networking configuration in a “cloud” resource configuration. In some implementations, the remote data repository 160 may include one or more remote servers, which provide information (e.g., information for generating augmented reality’ content) to the local processing and data module 140 and / or the remote processing module 150. In some implementations, all data is stored, and all computations are performed in the local processing and data module, allowing fully autonomous use from a remote module. Optionally, an outside system (e.g., a system of oneAttorney Docket No. 40589-0383WO1 / ML-5024WO

[0123] or more processors, one or more computers) that includes CPUs, GPUs, and so on, may perform at least a portion of processing (e.g., generating image information, processing data) and provide information to, and receive information from, local processing and data module 140, remote processing module 150, and remote data repository 160, for instance via wireless or wired connections.

[0124]

[0094] Providing a high quality immersive experience to a user of waveguide-based display systems such as various display systems configured for virtual / augmented / mixed display applications described supra, depends at least in part on, among other things, various characteristics of the light coupling into and / or out of the waveguides in the eyepiece of the display systems. For example, a virtual / augmented / mixed display having high light incoupling and out-coupling efficiencies can enhance the viewing experience by increasing brightness of the light directed to the users eye. As discussed above, in-coupling optical elements such as in-coupling diffraction gratings may be employed to couple light into the waveguides to be guided therein by total internal reflection. Similarly, out-coupling optical elements such as out-coupling diffraction gratings may be employed to couple light guided within the waveguides by total internal reflection out of the waveguides.

[0125]

[0095] As described supra, for example, in reference to FIGS, 6 and 7, display systems according to various implementations described herein may include optical elements (e.g., in¬ coupling optical elements, out-coupling optical elements, light distributing elements, and / or combined pupil expander-extractors (CPEs)) that may include diffraction gratings. As disclosed herein, a CPE may operate both as a light distributing element spreading or distributing light within the waveguide, possibly increasing beam size and / or the eye box, as well as an out-coupling optical element coupling light out of the waveguide.

[0126]

[0096] For example, as described above in reference to FIG. 7, light 640 that is 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 (T1R). In various implementations, at points where the light 640 impinges on the out-coupling optical element 570, a portion of the light guided within the waveguide may exit the waveguide as an exit beam 650 (e.g., beamlets). In some implementations, any of the optical elements 570, 580, 590, 600, 610, which may include one or more of an in-coupling optical element, an out-coupling optical element, a light distribution element or a CPE, can be configured as a diffraction grating,

[0097] To achieve desirable characteristics of in-coupling of light into (or out-coupling of light from) the waveguides 270, 280, 290, 300, 310, the optical elements 570, 580, 590, 600, 610 configured as diffraction gratings can be formed of a suitable material and have aAttorney Docket No. 40589-0383WO1 / ML-5024WO

[0127] suitable structure for controlling various optical properties, including diffraction properties such as diffraction efficiency as a function of polarization. Possible desirable diffraction properties may include, among other properties, any one or more of the following: spectral selectivity, angular selectivity, polarization selectivity (or non-selectivity), high spectral bandwidth, high diffraction efficiencies or a wide field of view (FOV).

[0128]

[0098] Some diffraction gratings have strong polarization dependence and thus may have relatively diminished overall efficiency (due to the rejection of one polarization). Such diffraction gratings may also create coherent artifacts and reduce the uniformity of a far field image. To provide diffraction gratings that have reduced polarization sensitivity (e.g., that couple light with an efficiency that is relatively independent of polarization), some displays for AR systems according to implementation described herein include a waveguide with blazed diffraction gratings formed therein, The blazed grating may, for example, include diffractive features having a “saw tooth” shape. In some implementations, a blazed grating may achieve enhanced grating diffraction efficiency for a given diffraction order, while the diffraction efficiency for the other orders is reduced or minimized. As a result, more light may be directed into the particular given diffractive order as opposed to any of the other orders in some implementations.

[0129]

[0099] The waveguides discussed above can be designed to provide uniform image brightness. With reference to FIG. 10A, a waveguide 1000 includes a substrate 1002, a diffraction grating 1004 supported by the substrate 1002, and a high-index layer 1006 on the grating 1004. Waveguide 1000 can correspond to the waveguides disclosed above (e.g., waveguides 270, 280, 290, 300, or 310).

[0130]

[0100] In this example, the high-index layer 1006 directly contacts the grating 1004 and conforms to structures in the grating. As opposed to conventional waveguides with high-index substrates (e.g., waveguides 1001a and 1001b as depicted in FIGS. 10B and 10C, respectively), the diffraction grating 1004 has a lower index of refraction (n) than that of the high-index layer 1006.

[0131]

[0101] For example, the grating 1004 is composed of a grating material with an index of refraction in a range of 1.3 to 1.8 at an operative wavelength range of the waveguide (e.g., 620-780 nm, 492-577 nm, or 435-493 nm), and tire high-index layer 1006 is composed of a high-index material (e.g., having an index of refraction of 1.9 or higher at the operative wavelength range of the -waveguide, such as TiO₂). In some implementations, the operative wavelength range is a range within the visible spectrum (e.g., between 380 and 750 nm), such as red, green, blue, and cyan light. In contrast, gratings 1004a and 1004b are composed of aAttorney Docket No. 40589-0383WO1 / ML-5024WO

[0132] grating material having an index of refraction that is greater than 2, and high-index layers 1006a and 1006b are composed of a material having an index of refraction from 1.2 to 2.0. In all of these examples, the substrate 1002 is a high-index material (e.g., glass with the refractive index n = 2).

[0133]

[0102] Generally, when tire high-index layer conformally covers at least a portion of the grating, the high-index layer forms a diffraction grating, as well. A surface of this high-index layer in contact with the grating has an inverse shape to that of the grating. This inverse shape can also be referred to as a "‘reverse tone” or “opposite tone.”

[0134]

[0103] By using a grating 1004 with a relatively low index together with a high-index layer 1006 with a relatively high index, the waveguide 1000 can be manufactured at relatively low costs and with less process complexity and can provide improved optical characteristics. For example, forming high-index gratings (e.g., diffraction gratings with n > 2) generally involves etching, which can be expensive and time-consuming, since etching can be a vacuum-based process. Further, plasma-assisted deposition of the grating material before etching can expose the substrate to damagingly high temperatures. On the other hand, lower- index gratings (e.g., 1.3 < n < 1.8) can be formed using other methods, such as nanoimprinting, casting, nano-scale printing, or lithography, which are generally less expensive and simpler than etching.

[0135]

[0104] Compared to using a high-index grating on a high-index substrate, using the disclosed waveguides can improve image quality by reducing the difference between efficiencies of red and blue light directed to a user. In general, blue light is diffracted out of waveguides more quickly than red light is due to the wavelength dependence of the index of refraction. For example, due to the difference in the angle at which blue and red light are refracted into the waveguide, blue light will complete more bounces as it travels by total internal reflection along the waveguide. At each bounce, some of the light will diffract out of the waveguide in an undesired direction, thereby reducing the efficiency of directing blue light to the user.

[0136]

[0105] In waveguides using high-index gratings for displays using visible light, another factor reducing the amount of blue light reaching tire user is that high-index materials tend to have higher diffraction efficiencies for lower wavelengths, in the disclosed waveguides, however, using a low-index diffraction grating leads to higher diffraction efficiencies for red light instead of blue light. Therefore, although the amount of red light reaching the user is slightly reduced, the amounts of red and blue light are more similar, leading to enhanced image uniformity. In these examples, because the wavelength of the green light is betweenAttorney Docket No. 40589-0383WO1 / ML-5024WO

[0137] those of red and blue light, these two effects are somewhat averaged out for green light. The diffraction efficiencies will be discussed more in relation to FIGS. 13A-13H.

[0138]

[0106] With reference to FIGS. 11A, 11B, and 11C, the structure of the grating and high- index layer can vary. The material choices of substrate 1102, grating 1104, and a high-index layer 1106 can be similar as those for substrate 1002, grating 1004, and high-index layer 1006, respectively.

[0139]

[0107] As a first example depicted in FIG. 11 A, waveguide 1100a includes a grating 1104a composed of a grating material and including multiple ridges 1008a. The high-index layer 1106a covers (e.g., completely covers or encases) the ridges 1008a, as well as the regions 1110 between adjacent (e.g., directly adjacent) ridges. These regions 1110 have a nonzero residual layer thickness (RLT) (e.g., the grating material extends between and connects adjacent ridges 1008a). In this example, the ridges 1008a all have the same height (as measured along a vertical direction perpendicular to a propagation direction of light within the waveguide), and the height of the high-index layer 1106a varies. For example, the height of the high-index layer 1106a follows a staircase shape (e.g., three planar regions with different heights, increasing along the propagation direction). In some implementations, one or more of the height, width, and slant angle of the ridges vary’ along the propagation direction.

[0140]

[0108] As another example depicted in FIG. 1 IB, waveguide 1100b includes grating 1104b including multiple ridges 1108b with varying height. The height of the ridges 1108b generally decreases along the propagation direction, while the height of the high-index layer 1106b generally increases along the propagation direction. In waveguide 1100c, as depicted in FIG. 11C, the grating 1104c includes multiple ridges 1108c with decreasing height along the propagation direction, as well as decreasing height of the high-index layer 1106c along the propagation direction.

[0141]

[0109] In some implementations, the high-index layer has a planar upper surface. For example, FIG, 12A depicts a waveguide 1200a including substrate 1202a, grating 1204a, and high-index layer 1206a with a planar upper surface 1212. In this example, the substrate 1202a can be a glass having an index of 2.0, the grating 1204a can have an index in a range of 1.5 to 1.6, and the high-index layer 1206a can have an index of about 2.2. In other examples, the substrate material can include a crystalline material, such as LiNbO₃ or SiC,

[0142]

[0110] The index mismatch between the grating and the substrate can influence the desired range for the RLT of the grating. Generally, lower RLTs are desirable (e.g., less than 500 nm), since light propagating via total internal reflection (TIR) in the waveguide has weakerAttorney Docket No. 40589-0383WO1 / ML-5024WO

[0143] interactions with the grating when tlie RLT is high. When there is a large index mismatch between the grating and the substrate, this effect is heightened, so ultrathin RLTs (e.g., less than 30 nm) are desirable. For example, since the difference between the refractive index of the high-index material and the refractive index of the substrate material is high (e.g., greater than 0.1, such as 0.3), the RLT of the grating 1204a can be 5 nm to 20 nm.

[0144]

[0111] In another example, the RLT range can differ. FIG. 12B depicts waveguide 1200b including a substrate 1202b, a grating 1204b, and a high-index layer 1206b. The substrate 1202b can be a polymer substrate with an index in a range of 1.7 to 1.8, the grating 1204b can have an index in a range of 1.5 to 1.71, and the high-index layer 1206b can have an index of the range of 2.0 to 2.2. Thus, in this example, the index mismatch between the grating 1204b and the substrate 1202b can be small (e.g., less than 0.1, or as low as zero), so the RLT range can be higher compared to that for grating 1204a, without adverse effects.

[0145]

[0112] FIGS. 13A and 13B depict waveguides 1300a and 1300b, respectively, both of which include a high-index substrate (e.g., n = 1.75) with high-index gratings of different heights. For example, the height of the diffraction grating in waveguide 1300a is 30 nm, and in waveguide 1300b the height is 100 nm. Both of the gratings are covered by a low-index layer (e.g., n = 1.1).

[0146]

[0113] In contrast, FIGS. 13C and 13D depict waveguides 1300c and 1300d, respectively, which include a high-index substrate (e.g., n = 1.75) with low-index gratings (e.g., n = 1.53) of different heights. Tire height of the grating in waveguide 1300c is 80 nm, and the height of the grating in waveguide 1300d is 105 nm. The gratings in waveguides 1300c and 1300d are covered by a high-index layer (e.g., n = 2.0).

[0147]

[0114] As depicted in FIGS. 13E - 13H, the wavelength dependence of the diffraction efficiency follows different trends depending on whether the diffraction grating has a higher or low er index compared to the layer on top of the grating. For example, FIG. 13E depicts a plot 1300e of the diffraction efficiency for an exit pupil expander (EPE) including the waveguide of 1300a, waveguide 1300b, and other waveguides with gratings of different heights. Each waveguide with a different grating height is depicted by a different line style. FIG. 13F depicts a plot 1300f of the diffraction efficiency for an orthogonal pupil expander (OPE) including the waveguide of 1300a, waveguide 1300b, and other waveguides w ith gratings of different heights,

[0148]

[0115] Generally, for both FIGS. 13E and 13F, as the wavelength of light increases, the diffraction efficiency of the grating decreases, meaning that blue light has a higher diffraction efficiency than red light, so blue light will diffract out of the waveguide at a higher rate.Attorney Docket No. 40589-0383WO1 / ML-5024WO

[0149]

[0116] On the other hand, FIGS. 13G and 13H depict the opposite trend. FIG. 13G depicts a plot 1300g of the diffraction efficiency for an EPE including the waveguide of 1300c, waveguide 1300d, and other waveguides with gratings of different heights. FIG. 1311 depicts a plot 1300h of the diffraction efficiency for an OPE including the waveguide of 1300c, waveguide 1300d, and other waveguides with gratings of different heights. Betw een 460 nm and 625 nm, as the wavelength of light increases, the diffraction efficiency also increases. This means that red light has a higher diffraction efficiency than blue light, which can counterbalance the reduction in blue light due to the higher number of bounces blue light undergoes as it propagates via TIR in the waveguide.

[0150]

[0117] Due to the diffraction efficiencies of red and blue light (and green light, since its wavelength is between red and blue light) being more similar, image uniformity in displays generated using the disclosed waveguides is high. For example, FIGS. 14A, 14B, and 14C depict plots 1400a, 1400b, and 1400c of the intensity of out-coupled light for each of red, green, and blue light, respectively. This out-coupled light is the image light for the user, so each of plots 1400a, 1400b, and 1400c represent the intensity of light in 14° by 14° samples of a 20° squared field of view (FO V) for the user.

[0151]

[0118] Although there is some variation in intensity across the field of view for each of the red, green, blue, and composite plots, this variation is less than that of field of views produced using high-index gratings. For example, the average brightness can be represented by a parameter N with units of Nits / lumen, and the red channel, and Nred = 2858 Nits / lumen, Ngreen = 2985 Nits / lumen, and Nbiue = 26112 Nits / lumen. Additionally, user-side efficiency (diffraction efficiency in direction of the user) and world-side efficiency (diffraction efficiency in direction of the world) for an eyebox about 12mm by 10mm are represented by parameters PU and PW. For the red channel, PUred = 2,04% and PWred = 2.09%, For the green channel, PUgreen = 2.13% and PWgreen = 1.77%. For the blue channel, PUbiue = 1.86% and PWbiue = 1.34%.

[0152]

[0119] FIG, 15 is a flow diagram of a process 1500 for making a waveguide. For example, the process 1500 can be used to manufacture the waveguides discussed herein.

[0153]

[0120] Process 1500 includes providing a substrate (e.g., substrate 1002). In some implementations, the substrate is a high-index substrate 1510 (e.g., 1.7 < n < 2.7).

[0154]

[0121] Process 1500 includes forming a grating (e.g., grating 1004) on a surface of the substrate (1520). For example, forming the grating can include depositing an imprint resist or polymer casting resin. The grating includes a plurality of ridges (e.g., ridges 1108) and isAttorney Docket No. 40589-0383WO1 / ML-5024WO

[0155] composed of a grating material. The grating material can have a relatively low index (e.g., 1.3 <n < 1.8).

[0156]

[0122] In some implementations, forming the grating comprises nanoimprinting, casting, molding, stamping, nano-scale printing, lift-off patterning, electron-beam lithography, or photo-lithography.

[0157]

[0123] In some implementations, the grating is formed such that the RLT of the grating is ultrathin (e.g., in a range from 5 nm to 30 nm). For example, the RLT can be less than 30 nm, less than 20 nm, or less than 15 nm. This can be accomplished through various methods, such as ink-jetting resist, where tire drop size of the resist is 10 pL or less (e.g., 1 pL).

[0158] Additionally, the imprint resist surface tension in viscosity can be selected for ideal wetting, and the resist drop pattern can be selected to account for differences in density.

[0159]

[0124] Process 1500 includes forming a high-index layer (e.g., high-index layer 1008) on the grating (1530). The high-index layer is composed of a high-index material having a refractive index of 1.9 or more at an operative wavelength of the waveguide and exceeds the refractive index of the grating material. For example, forming the high-index layer can include depositing a Ti sol-gel. The high-index layer can include TiCh, Ta2O5, or HfCh.

[0160]

[0125] In some implementations, forming the high-index layer includes one of spin-coating, full area or selective area atomization (e.g., spray coating, drop-on-demand ink-jetting, screen printing, or gravure coating). Spin-coating can include depositing a thin film of resist material with constant thickness. Drop-on-demand type ink-jetting or selective area spray coating can include depositing a desired volume of material to obtain a desired thickness. Forming the high-index layer can include planarizing the high-index material.

[0161]

[0126] In some implementations, before forming the high-index layer, the grating material between adjacent ridges of the grating is removed, such that the RLT of the grating is zero,

[0127] In some implementations, the process 1500 can include additional steps, fewer steps, or some of the steps can be divided into multiple steps. For example, and with reference to FIG, 16, process 1500 can include, after forming the high-index layer 1606, forming an antireflective layer 1614 for light at the operative wavelength of the waveguide 1600. In some implementations, forming the antireflective layer includes spin coating, spray coating, drop-on-demand ink-jetting, screen printing, or gravure coating, lire antireflective layer 1614 can reduce back -reflection and boost transmission, increasing the amount of light that reaches a user’s eye.

[0162]

[0128] In some implementations, forming the grating includes forming a slanted grating. With reference to FIG. 16B, a grating 1604 can be formed using a slanted imprint. BeingAttorney Docket No. 40589-0383WO1 / ML-5024WO

[0163] “slanted” refers a non-normal angle 0 (90° > 0 > 90°) between an edge 1615 of a ridge, when viewed in cross-section, and an upper surface 1617 of the substrate 1602.

[0164]

[0129] Optionally, the waveguide 1600 can include a thin coating 1621 conformally coating the grating 1604. Tire thin coating 1621 can reduce, inhibit, or prevent geometrical distortion of the grating shape during harsh processing conditions (e.g., high temperatures) without comprising optical performance, such as the diffraction efficiencies toward the user. A thin coating can refer to a coating that is 10 nm or less (e.g., 5 nm). Thin coating 1621 can include, for example, SiO?..

[0165]

[0130] With reference to FIG. 16C, forming tire high-index layer 1606 results in forming a layer having a slanted grating (e.g., an inverse tone of the grating 1604), In this example, the substrate 1602 has an index of a range of 1.6 to 2.7, the grating 1604 has an index in a range of 1.3 to 1.8, and tire high-index layer 1606 has an index greater than 1.9.

[0166]

[0131] In contrast to forming slanted gratings through etching (e.g., angle ion milling), forming slanted gratings using nanoimprinting (e.g., filling and separation), can be carried out linearly along the propagation direction, which avoids feature shearing, improves yield, and increases imprinting longevity without template reclaim.

[0167]

[0132] Generally, the shapes of the ridges can vary (e.g., have a binary, slanted, or blazed shape when viewed in cross-section). In some implementations, the ridges form a meta¬ structure or are anti-reflective, sub-diffractive optical elements. Since the ridges are an additive feature on the substrate, the ridges protrude from the surface of the substrate,

[0168]

[0133] In some implementations, forming the grating can include forming an in-coupling grating, an orthogonal pupil expander, an exit pupil expander, a combined pupil expander, or a combination thereof. With reference to FIG. 16D, a waveguide 1600d includes a substrate 1602 supporting a grating including an in-coupling grating (ICG) 1603 and an orthogonal pupil expander (OPE) 1605. A high-index layer 1606d covers the ICG 1603, and OPE 1605 has a planar upper surface 1613.

[0169]

[0134] In some implementations, the process 1500 can further include forming a low-index layer on the high-index layer. With reference to FIG. 16E, a waveguide 1600e includes a substrate 1602 supporting a grating including an ICG 1603 and an OPE 1605. A high-index layer 1606e partially covers the ICG 1603 and OPE 1605, such that tire upper portions of the grating are exposed. Then, after the high-index layer is formed, a low-index material (e.g., 1.2 < n < 1.6) is deposited on the high-index layer and exposed portions of tire grating.

[0170]

[0135] In some implementations, the process 1500 can further include forming a low-index layer on the grating before forming the high-index layer. With reference to FIG. 16F, aAttorney Docket No. 40589-0383WO1 / ML-5024WO

[0171] waveguide 1600f includes a substrate 1602 supporting a grating including an ICG 1603 and an OPE 1605. Before forming the high-index layer 1606f. a low-index layer 1609b is formed on regions of the grating between adjacent ridges. Then, a high-index layer is formed, covering exposed portions of the ICG 1603 and OPE 1605. Next, another low-index layer 1609c is deposited on the high-index layer.

[0172]

[0136] Both of the waveguides 1600e and 1600f include multi-variable index stacks, the indices of w'hich can be selected to control how quickly or slowly light is extracted out of the waveguide and out-coupled to a user’s eye.

[0173]

[0137] The gratings and high-index layer, as well as other components, as described herein can be part of an in-coupling grating (ICG), an out-coupling grating, a light spreading element (e.g., an orthogonal pupil expander (OPE), an exit pupil expander (EPE), a combined pupil expander (CPE), or a light recycler). Additionally, each of these types of optical elements can be disposed on either or both of a world side or user side of the substrate, A “world side” of the substrate refers to the surface of the substrate that is farthest from a face of a user w hen worn by the user. A “user side” of the substrate refers to the surface of the substrate that is closest to the face of the user when worn by the user. Generally, the world and user sides are opposite each other and approximately parallel to each other. In some implementations, any of the ICG, OPE, EPE, CPE, or other mentioned optical elements can be configured to in-couple and out-couple visible and infrared light.

[0174]

[0138] With reference to FIG. 17, a waveguide 1700 includes substrate 1702, gratings 1704a and 1704b including respective ridges 1708a and 1708b, high-index layers 1706a and 1706b, and antireflective layer 1710.

[0175]

[0139] In this example, grating 1704a is an ICG and disposed on a user side of the substrate, and grating 1704b is either an OPE or an EPE and disposed on a world side of the substrate. Each of tire ridges 1708a and 1708b are slanted relative to a normal of the substrate 1702 and are completely covered by respective high-index layers 1706a and 1706b. High-index layer 1706a is further covered by an antireflective layer 1710, which also covers exposed portions of the lower surface 1702a of the substrate and has a parallelogram shape when viewed in cross-section.

[0176]

[0140] The substrate 1702 can have an index in a range of 1.71 to 1.75; the gratings 1704a and 1704b can have an index of about 1.53; the high-index layer can have an index of about 2.0, and the antireflective layer 1710 can have an index of about 1.4 and be about 100 nm thick.Attorney Docket No. 40589-0383WO1 / ML-5024WO

[0177]

[0141] FIGS. 18A-18M are scanning electron microscope (SEM) images of various fabricated waveguides including a diffraction grating with a relatively low-index on a substrate with a relatively high index. FIG. 18A shows two-dimensional pillars. FIG. 18B shows gratings with changing orientations (e.g., multiple gratings with different propagation directions). FIG. 18C shows a meta bi-grating structure (e.g., a grating structure formed by more than one grating). More information on meta gratings can be found in WO 2023 / 220480, which is hereby incorporated by reference for its disclosure related to meta¬ gratings. FIG. 18D shows an eyepiece including a pillar grating adjacent to a line grating. FIGS. 18E and 18F show three-dimensional sawtooth gratings. FIG. 18G shows another sawtooth grating. FIG. 1811 shows a grating including two-dimensional holes (e.g., recesses in the grating material). FIG. 181 shows a grating including three-dimensional holes. FIG. 18J shows a slanted, two-dimensional pillar structure. FIG. 18K shows a slanted, sharpened structure.

[0178]

[0142] FIGS. 18L and 18M show a “reverse tone construction” with TiCh nanoparticle loaded spin-on resist, which has a refractive index of about 2.0 at 530 nm. The high-index material can be planarized using spin-coating over a preexisting slanted imprint pattern (shown with the line 18001). In addition to the nanoparticle-containing resist, the high-index top-coating layer can also be fabricated using a sol-gel process. Titanium alkoxide precursors, such as Ti(0R)4, or mixed alkoxides Ti(0R)x(0R’)4x(X ranging from 0.1 to 4), can undergo controlled hydrolysis and stabilization to formulate a spin-on solution. This solution can be applied as an overcoat on the imprinted resist and, upon thermal curing, form a condensed high-index TiOz layer, resulting in a reverse-tone structure. The TiOz sol-gel approach eliminates the need for nanoparticles, reducing scattering and enhancing optical performance.

[0179]

[0143] FIG. 19A depicts a waveguide 1900a including a substrate 1902a, a grating formed by grating ridges 1904a and 1904b, a higher-index layer 1906a (having an index of refraction greater than that of the grating ridges), and an additional layer 1908. Each of grating ridges 1904a has the same height Hi (as measured along the vertical direction) and width Wi (as measured along the propagation direction). Adjacent grating ridges 1904a are spaced apart by a pitch Pi, making the duty cycle Di equal to Wi / Pi. Similarly, each of grating ridges 1904b has the same height H2 (as measured along the vertical direction) and width W2 (as measured along the propagation direction). Adjacent grating ridges 1904b are spaced apart by a pitch P2, making the duty cycle D2 equal to W2 / P2. In this example, grating ridges 1904a and 1904b have the same duty cycle Dw ) and form factor (e.g., trapezoidal).Attorney Docket No. 40589-0383WO1 / ML-5024WO

[0180]

[0144] The heights (and widths) of the grating ridges 1904a and 1904b, however, are different. As a result, if tire higher-index layer 1906a were formed to have a constant height that was great enough to fill the regions between all adjacent ridges (e.g., have a height greater than Hi), the height of the higher-index layer 1906a above grating ridges 1904b would be greater than height of the higher-index layer 1906a above grating ridges 1904a. Having a different amount of the higher-index layer 1906a above grating ridges 1904a versus 1904b would lead to uneven light distribution and extraction.

[0181]

[0145] To avoid this drawback, the higher-index layer 1906a in waveguide 1900a varies in height. Between adjacent grating ridges 1904a, the height of the higher-index layer 1906a is approximately Hi. Between adjacent grating ridges 1904b, the height of the higher-index layer 1906a is approximately lb. Between adjacent grating ridges 1904a and 1904b, the height of the higher-index layer 1906a is slightly less than Hz. The difference in height between 1906a and Hi can vary from 0 nm to 10 nm. The difference in height between 1906a and Hi can vary from 0 nm to 1 Onm. The difference in height between Hi and H2 can vary up to 100 nm. Tire duty cycle of the gratings keeps 1906a levels similar when compared to 1904a and 1904b, even if 1904a and 1904b can have a much larger delta. Above each grating ridge 1904a and 1904b, the height of the higher-index layer 1906a is relatively small (e.g., on the order of nanometers). As a result, the height of the higher-index layer 1906a above each of the grating ridges is about the same.

[0182]

[0146] While the height of additional layer 1908 is not exactly uniform, the height H3 of additional layer 1908 above each grating ridge 1904a and 1904b is approximately the same. The additional layer 1908 can be at least one of the following: an anti -reflective layer, provide hermetic sealing, improve material stability, or be a hard coat layer.

[0183]

[0147] In some implementations, avoiding the portions of the higher-index layer located above grating ridges having a flat upper surface can be beneficial. For example, portions of the higher-index layer located above grating ridges having a flat upper surface can lead to the higher-index layer acting as a top residual layer and absorbing light that would otherwise be coupled into the grating. Further, if the thickness of the flat, higher-index layer exceeds 20 nanometers, the higher-index layer can negatively impact light spreading and light extraction.

[0184]

[0148] To avoid this drawback, waveguide 1900b includes a variety of grating ridges, each of which has an uppermost surface that is pointed or rounded. The waveguide 1900b includes a substrate 1902b, a grating formed by the grating ridges 1904c-1904h, and a higher-index layer 1906b. Grating ridge 1904c has an irregular triangle shape, grating ridge 1904d has an isosceles triangle shape, grating ridge 1904e has an irregular pentagon shape (e.g., a “house”Attorney Docket No. 40589-0383WO1 / ML-5024WO

[0185] shape) and grating ridge 1904f has an irregular polygon shape (e.g., the shape of a quadrilateral next to an irregular pentagon). Accordingly, each of grating ridges 1904c, 1904d, 1904e, and 1904fhas a point (e.g., points 1910c, 191 Od, 1910e, and 1910f) at the uppermost part of the uppermost surface (the surface furthest away from the substrate 1902a along the vertical direction). As a result, the higher-index layer 1906b above each of the grating ridges 1904c- 1904f is not a flat layer. In other words, the contact surface between the higher-index layer 1906b and the uppermost surface of an individual grating is formed by multiple intersecting planes.

[0186]

[0149] Grating ridge 1904g has a dome shape (e.g., a semicircle on top of a quadrilateral) and grating ridge 1904h has an irregular shape (e.g., a quadrilateral next to a dome). The uppermost surface (the surface farthest away from the substrate 1902b along the vertical direction) of each of grating ridges 1904g and 1904h is curved. As a result, the higher-index layer 1906b above each of the grating ridges 1904g and 1904h is not a flat layer. In other words, the contact surface between tire higher-index layer 1906b and the uppermost surface of an individual grating is curved.

[0187] EMBODIMENTS

[0188]

[0150] Although the disclosed inventive concepts include those defined in the attached claims, it should be understood that the inventive concepts can also be defined in accordance with the following embodiments.

[0189]

[0151] In addition to the embodiments of the attached claims and the embodiments described above, the following numbered embodiments are also innovative.

[0190]

[0152] Embodiment 1 is a waveguide comprising: a substrate composed of a substrate material; a grating on the substrate, wherein the grating is composed of a grating material and comprises a plurality of ridges; and a high-index layer disposed on the grating, wherein the high-index layer is composed of a high-index material having a refractive index of at least 1.9 at an operative wavelength, and the refractive index of the high-index material exceeds a refractive index of the grating material,

[0191]

[0153] Embodiment 2 is the waveguide of embodiment 1, wherein the refractive index of the grating material is between 1.3 and 1.8 at the operative wavelength.

[0192]

[0154] Embodiment 3 is the waveguide of embodiment 1 or embodiment 2, wherein a residual layer thickness (RLT) of the grating material between adjacent ridges of the plurality of ridges is less than 500 nm.

[0193]

[0155] Embodiment 4 is the waveguide of embodiment 3, wherein the RLT is between 5 nm and 20 nm.Attorney Docket No. 40589-0383WO1 / ML-5024WO

[0194]

[0156] Embodiment 5 is the waveguide of embodiment 3 or embodiment 4, wherein a difference between the refractive index of the high-index material and the refractive index of the substrate material is at least 0,1 at the operative wavelength.

[0195]

[0157] Embodiment 6 is the waveguide of embodiment 5, wherein the difference between the refractive index of the high-index material and the refractive index of the substrate material is at least 0.3 at the operative wavelength.

[0196]

[0158] Embodiment 7 is the waveguide of any one of embodiments 3 through 6, wherein the substrate material comprises glass.

[0197]

[0159] Embodiment 8 is the waveguide of embodiment 7, wherein the refractive index of the glass is 1.65 or more.

[0198]

[0160] Embodiment 9 is the waveguide of any one of embodiments 3 through 6, wherein the substrate material comprises a crystalline material.

[0199]

[0161] Embodiment 10 is the waveguide embodiment 9, wherein the crystalline material is LiNbOs or SiC.

[0200]

[0162] Embodiment 11 is the waveguide of embodiment 1 or embodiment 2, wherein a residual layer thickness (RLT) of the grating material between adjacent ridges of the plurality of ridges is at least 40 nm.

[0201]

[0163] Embodiment 12 is the waveguide of embodiment 11, wherein a difference between the refractive index of the high-index material and the refractive index of the substrate material is 0.1 or less at the operative wavelength.

[0202]

[0164] Embodiment 13 is the waveguide of embodiment 8, embodiment 11 or embodiment 12, wherein the substrate material comprises a polymer.

[0203]

[0165] Embodiment 14 is the waveguide of any one of embodiments 1 through 13, wherein the substrate is configured to in-couple and propagate red, green, and blue light from a light projector.

[0204]

[0166] Embodiment 15 is the waveguide of any one of embodiments 1 through 14, wherein each ridge of the plurality' of ridges has a binary shape, a slanted shape, or a blazed shape.

[0205]

[0167] Embodiment 16 is the waveguide of any one of embodiments 1 through 15, wherein the plurality of ridges is on a first surface of the substrate, and further comprising an additional plurality of ridges on a second surface of the substrate, wherein the first surface is opposite the second surface.

[0206]

[0168] Embodiment 17 is the waveguide of any one of embodiments 1 through 16, wherein the plurality of ridges of the waveguide is disposed on a single surface the substrate.Attorney Docket No. 40589-0383WO1 / ML-5024WO

[0207]

[0169] Embodiment 18 is the waveguide of embodiment 17, wherein the single surface is a user side of the substrate.

[0208]

[0170] Embodiment 19 is the waveguide of embodiment 17, wherein the single surface is a world side of the substrate.

[0209]

[0171] Embodiment 20 is the waveguide of any one of embodiments 1 through 19, wherein the plurality of ridges comprises protrusions on a surface of the substrate.

[0210]

[0172] Embodiment 21 is the waveguide of any one of embodiments 1 through 20, wherein the grating comprises a meta-structure.

[0211]

[0173] Embodiment 22 is the waveguide of any one of embodiments 1 through 21, wherein a parameter of the grating is graded along a propagation direction of light within the waveguide.

[0212]

[0174] Embodiment 23 is the waveguide of any one of embodiments 1 through 22, wherein the parameter is a height of the plurality of ridges measured along a direction parallel to a normal of a surface of the substrate, a width of the plurality of ridges measured along a direction perpendicular to a normal of the surface of the substrate, or an angle of slanting between the surface of the substrate and a side of a ridge of the plurality of ridges.

[0213]

[0175] Embodiment 24 is the waveguide of any one of embodiments 1 through 23, wherein the grating is configured to function as an in-coupling grating, an out-coupling grating, an orthogonal pupil expander, an exit pupil expander, a combined pupil expander, or a light recycler,

[0214]

[0176] Embodiment 25 is the waveguide of any one of embodiments 1 through 24, wherein the plurality of the ridges are sub-diffractive optical elements that are anti-reflective at the operative wavelength.

[0215]

[0177] Embodiment 26 is the waveguide of any one of embodiments 1 through 25, further comprising an antireflective layer disposed on the high-index layer.

[0216]

[0178] Embodiment 27 is the waveguide of any one of embodiments 1 through 26, wherein a height of ridges of the plurality of ridges, measured along a direction parallel to a normal of a surface of the substrate, varies along a propagation direction of light within the substrate.

[0217]

[0179] Embodiment 28 is the waveguide of any one of embodiments 1 through 27, wherein a height of the high-index layer, measured along a direction parallel to a normal of a surface of the substrate, varies along a propagation direction of light within the substrate.

[0218]

[0180] Embodiment 29 is the waveguide of any one of embodiments 1 through 28, wherein an outer surface of the high-index layer is planarized.Attorney Docket No. 40589-0383WO1 / ML-5024WO

[0219]

[0181] Embodiment 30 is the waveguide of any one of embodiments 1 through 14 or 16 through 29, wherein each ridge of the plurality of ridges is slanted relative to the surface of the substrate

[0220]

[0182] Embodiment 31 is the waveguide of any one of embodiments 1 through 30, further comprising a low-index layer comprising a low-index material, the low-index layer disposed between the high-index layer and the grating, wherein the refractive index of the grating material exceeds the refractive index of the low-index material.

[0221]

[0183] Embodiment 32 is the waveguide of any one of embodiments 1 through 30, further comprising a low-index layer comprising a low-index material, wherein the low -index layer is disposed on the high-index layer and composed of a low-index material, wherein the low-index layer is an uppermost layer of the waveguide relative to the substrate, and the refractive index of the grating material exceeds the refractive index of the low-index material.

[0222]

[0184] Embodiment 33 is the waveguide of any one of embodiments 1 through 32, wherein the high-index layer is in direct contact with the grating.

[0223]

[0185] Embodiment 34 is the waveguide of any one of embodiments 1 through 33, wherein a height of the high-index layer as measured along a direction parallel to a normal of a surface of the substrate the plurality of ridges varies.

[0224]

[0186] Embodiment 35 is the waveguide of any one of embodiments 1 through 32 or 34, comprising a thin-film coating on the grating and between the grating and tlie high-index layer,

[0225]

[0187] Embodiment 36 is the waveguide of any one of embodiments 1 through 35, wherein the grating is configured to in-couple visible light, infrared light, or both.

[0226]

[0188] Embodiment 37 is the waveguide of any one of embodiments 1 through 36, wherein a height of portions of the high-index layer above each ridge of the plurality of ridges is uniform.

[0227]

[0189] Embodiment 38 is the waveguide of any one of embodiments 1 through 37, wherein an uppermost surface of at least one ridge of the plurality of ridges is pointed or rounded.

[0228]

[0190] Embodiment 39 is a method comprising: forming a grating on a surface of a substrate, w herein the grating is composed of a grating material and comprises a plurality of ridges and; and forming a high-index layer on tlie grating, w herein the high-index layer is composed of a high-index material having a refractive index of 1.9 or more at an operative wavelength, wherein the refractive index of the high-index material is greater than a refractive index of tlie grating material.Attorney Docket No. 40589-0383WO1 / ML-5024WO

[0229]

[0191] Embodiment 40 is the method of embodiment 39, wherein forming the grating comprises nanoimprinting, casting, molding, stamping, nano-scale printing, lift-off patterning, electron-beam lithography, or photo-lithography.

[0230]

[0192] Embodiment 41 is the method embodiments 39 or embodiment 40, wherein forming the high-index layer comprises one of spin-coating, full area or selective area atomization.

[0231]

[0193] Embodiment 42 is the method of any one of embodiments 39 through 41, further comprising, before forming the high-index layer, removing the grating material on the substrate between adjacent ridges of the plurality of ridges.

[0232]

[0194] Embodiment 43 is the method of embodiment 42, wherein a residual layer thickness (RLT) of the grating is zero.

[0233]

[0195] Embodiment 44 is the method of any one of embodiments 39 through 43, further comprising forming an antireflective layer on the high-index layer.

[0234]

[0196] Embodiment 45 is the method of embodiment 44, wherein depositing the antireflective layer comprises spin coating, spray coating, drop-on-demand ink-jetting, screen printing, or gravure coating.

[0235]

[0197] Embodiment 46 is the method of any one of embodiments 39 through 45, wherein forming the grating comprises ink jetting resist, wherein a drop size of the resist is 10 pL or less.

[0236]

[0198] Embodiment 47 is the method of any one of embodiments 39 through 46, further comprising, before forming the high-index layer, depositing a low-index material between adjacent ridges of the plurality of ridges, wherein the refractive index of the grating material exceeds the refractive index of the low-index material.

[0237]

[0199] Embodiment 48 is the method of any one of embodiments 39 through 47, further comprising, after forming the high-index layer, depositing a low-index material on the high-index layer, wherein the refractive index of the grating material exceeds the refractive index of the low-index material.

[0238]

[0200] Embodiment 49 is the method of any one of embodiments 39 through 48, wherein the substrate is composed of a substrate material having a refractive index of at least 1.65 at the operative wavelength.

[0239]

[0201] Embodiment 50 is the method of any one of embodiments 39 through 49, wherein form ing the grating compri ses forming at least one of an input coupling grating, an orthogonal pupil expander, an exit pupil expander, a combined pupil expander, or a light recycler.Attorney Docket No. 40589-0383WO1 / ML-5024WO

[0240]

[0202] Embodiment 51 is a system comprising: a head-mountable frame; a light projection system configured to output light to provide image content; a waveguide supported by the head-mountable frame, the waveguide configured to couple at least a portion of the light from the light projection system into the waveguide; a grating on the waveguide, wherein the grating is composed of a grating material and comprises a plurality of ridges; and a high- index layer disposed on the grating, wherein the high-index layer is composed of a high-index material having a refractive index of at least 1.9 at an operative wavelength, and the refractive index of the high-index material exceeds the refractive index of the grating material.

[0241]

[0203] Embodiment 52 is a system comprising: a head-mountable frame; a light projection system configured to output light to provide image content; and the waveguide of any one of embodiments 1 through 38.

[0242]

[0204] While this specification contains many specific implementation details, these should not be construed as limitations on the scope of what is being claimed, which is defined by the claims themselves, but rather as descriptions of features that may be specific to particular embodiments of particular inventions. Certain features that are described in this specification in the context of separate embodiments 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 in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially be claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claim may be directed to a subcombination or variation of a subcombination.

[0243]

[0205] Similarly, while operations are depicted in the drawings and recited in the claims in a particular order, this by itself should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system modules and components in the embodiments described above should not be understood as requiring such separation in all embodiments, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products.

[0244]

[0206] Particular embodiments of the subject matter have been described. Other embodiments are within the scope of the following claims. For example, the actions recited inAttorney Docket No. 40589-0383WO1 / ML-5024WO

[0245] the claims can be performed in a different order and still achieve desirable results. As one example, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results. In some cases, multitasking and parallel processing may be advantageous.

Claims

Attorney Docket No. 40589-0383WO1 / ML-5024WOWhat is claimed is:

1. A waveguide comprising:a substrate composed of a substrate material;a grating on the substrate, wherein the grating is composed of a grating material and comprises a plurality of ridges; anda high-index layer disposed on the grating, wherein the high-index layer is composed of a high-index material having a refractive index of at least 1.9 at an operative wavelength, and the refractive index of the high-index material exceeds a refractive index of the grating material.

2. The waveguide of claim 1, wherein the refractive index of the grating material is between 1.3 and 1.8 at the operative wavelength.

3. The waveguide of claim 1, wherein a residual layer thickness (RLT) of the grating material between adjacent ridges of the plurality of ridges is less than 500 nm.

4. The waveguide of claim 3, wherein the RLT is between 5 nm and 20 nm.

5. The waveguide of claim 3, wherein a difference between the refractive index of the high-index material and the refractive index of the substrate material is at least 0.1 at the operative wavelength.

6. The waveguide of claim 5, wherein the difference between the refractive index of the high-index material and the refractive index of the substrate material is at least 0.3 at the operative wavelength.

7. The waveguide of claim 3, wherein the substrate material comprises glass.

8. The waveguide of claim 7, wherein the refractive index of the glass is 1.65 or more.

9. The waveguide of claim 8, wherein a substrate material comprises a polymer10. The waveguide of claim 3, wherein the substrate material comprises a crystalline material.Attorney Docket No. 40589-0383WO1 / ML-5024WO11. The waveguide of claim 10, wherein the crystalline material is LiNbO3 or SiC.

12. The waveguide of claim 1, wherein a residual layer thickness (RLT) of the grating material between adjacent ridges of the plurality of ridges is at least 40 nm.

13. The waveguide of claim 11, wherein a difference between the refractive index of the high-index material and the refractive index of the substrate material is 0.1 or less at the operative wavelength.

14. The waveguide of claim 1, wherein the substrate is configured to in-couple and propagate red, green, and blue light from a light projector.

15. The waveguide of claim 1, wherein each ride of the plurality of ridges has a binary’ shape, a slanted shape, or a blazed shape.

16. The waveguide of claim 1, wherein the plurality of ridges is on a first surface of the substrate, and further comprising an additional plurality of ridges on a second surface of the substrate, wherein the first surface is opposite the second surface.

17. The waveguide of claim 1, wherein the plurality of ridges of the waveguide is on a single surface the substrate.

18. The waveguide of claim 17, wherein the single surface is a user side of the substrate.

19. The waveguide of claim 17, wherein the single surface is a world side of the substrate.

20. The waveguide of claim 1, wherein the plurality of ridges comprises protrusions on a surface of the substrate.

21. The waveguide of claim 1, wherein the grating comprises a meta-structure.

22. The waveguide of claim 1, wherein a parameter of the grating is graded along a propagation direction of light within the waveguide.

23. The waveguide of claim 22, wherein the parameter is height of the plurality of ridges measured along a direction parallel to a normal of a surface of the substrate, a width of theAttorney Docket No. 40589-0383WO1 / ML-5024WOplurality of ridges measured along a direction perpendicular to a normal of the surface of the substrate, or an angle of slanting between the surface of the substrate and a side of a ridge of the plurality of ridges.

24. The waveguide of claim 1, wherein the grating is configured to function as an in-coupling grating, an out-coupling grating, an orthogonal pupil expander, an exit pupil expander, a combined pupil expander, or a light recycler.

25. The waveguide of claim 1, wherein a dimension of the ridges of the plurality of the ridges is less than the operative wavelength of light, and the plurality of the ridges is anti-reflective at the operative wavelength.

26. The waveguide of claim 1, further comprising an antireflective layer on the high- index layer.

27. The waveguide of claim 1, wherein a height of ridges of the plurality of ridges, measured along a direction parallel to a normal of a surface of the substrate, varies along a propagation direction of light within the substrate.

28. The waveguide of claim 1, wherein a height of the high-index layer, measured along a direction parallel to a normal of a surface of the substrate, varies along a propagation direction of the substrate.

29. The waveguide of claim 1, wherein an outer surface of the high-index layer is planarized.

30. The waveguide of claim 1, wherein each ridge of the plurality of ridges is slanted relative to a surface of the substrate.

31. The waveguide of claim 1, further comprising a low-index layer between the high-index layer and the grating, wherein the low-index layer is composed of a low-index material, wherein the refractive index of the grating material exceeds the refractive index of the low-index material.

32. The waveguide of claim 1, further comprising a low-index layer composed of a low- index material, wherein the low-index layer is on the high-index layer, wherein the low-Attorney Docket No. 40589-0383WO1 / ML-5024WOindex layer is an outermost layer of the waveguide relative to the substrate, and the refractive index of the substrate material exceeds the refractive index of the low -index material.

33. The waveguide of claim 1, wherein the high-index layer is in direct contact with the grating.

34. The waveguide of claim 1, wherein a height of the high-index layer as measured along a direction parallel to a normal of a surface of the substrate the plurality of ridges varies.

35. The waveguide of claim 1, further comprising a thin-film coating on the grating and between the grating and the high-index layer.

36. The waveguide of claim 1, wherein the grating is configured to in-couple visible light, infrared light, or both.

37. The waveguide of claim 1, wherein a height of portions of the high-index layer above each ridge of the plurality of ridges is uniform.

38. The waveguide of claim 1, wherein an uppermost surface of at least one ridge of the plurality of ridges is pointed or rounded.

39. A method comprising:forming a grating on a surface of a substrate, wherein the grating is composed of a grating material and comprises a plurality of ridges; andforming a high-index layer on the grating, wherein the high-index layer is composed of a high-index material having a refractive index of 1.9 or more at an operative wavelength, wherein the refractive index of the high-index material is greater than a refractive index of the grating material.

40. The method of claim 39, wherein forming the grating comprises nanoimprinting, casting, molding, stamping, nano-scale printing, lift-off patterning, electron-beam lithography, or photo-lithography.

41. The method of claim 39, wherein forming the high-index layer comprises spin-coating or full area or selective area atomization.Attorney Docket No. 40589-0383WO1 / ML-5024WO42. The method of claim 39, further comprising, before forming the high-index layer, removing the grating material on the substrate between adjacent ridges of the plurality of ridges.

43. The method of claim 42, wherein a residual layer thickness (RLT) of the grating is zero.

44. The method of claim 39, further comprising forming an antireflective layer on the high-index layer.

45. The method of claim 44, wherein forming the antireflective layer comprises spin coating, spray coating, drop-on-demand ink-jetting, screen printing, or gravure coating.

46. The method of claim 39, wherein forming the grating comprises ink jetting resist, wherein a drop size of the resist is 10 pL or less.

47. The method of claim 39, further comprising, before forming the high-index layer, disposing a low-index material between adjacent ridges of the plurality of ridges, wherein the refractive index of the grating material exceeds the refractive index of the low-index material.

48. The method of claim 39, further comprising, after forming the high-index layer, disposing a low-index material on the high-index layer, wherein the refractive index of the grating material exceeds the refractive index of the low-index material.

49. The method of claim 39, wherein the substrate is composed of a substrate material having a refractive index of at least 1.65 at the operative wavelength.

50. The method of claim 39, wherein forming the grating comprises forming at least one of an input coupling grating, an orthogonal pupil expander, an exit pupil expander, a combined pupil expander, or a light recycler.

51. A head-mounted display system comprising:a head-mountable frame;a light projection system configured to output light to provide image content;Attorney Docket No. 40589-0383WO1 / ML-5024WOa waveguide supported by the head-mountable frame, the waveguide configured to couple at least a portion of the light from the light projection system into the waveguide; a grating on the waveguide, wherein the grating is composed of a grating material and comprises a plurality of ridges; anda high-index layer disposed on the grating, wherein the high-index layer is composed of a high-index material having a refractive index of at least 1.9 at an operative wavelength, and the refractive index of the high-index material exceeds the refractive index of the grating material.

Images