Diffraction gratings and manufacturing methods thereof

Abstract

Methods, devices, and systems for diffraction gratings and manufacturing methods thereof are provided. In one aspect, a method of fabricating one or more diffraction gratings includes: providing a waveguide that includes a glass substrate including one or more substances and a non-silica-based network former for the one or more substances, and a cover layer over the glass substrate, a refractive index of the cover layer being smaller than a refractive index of the glass substrate; providing a mask layer over the waveguide, the mask layer having a pattern corresponding to the one or more diffraction gratings, the pattern selectively exposing portions of the waveguide; and etching the exposed portions of the waveguide to define the one or more diffraction gratings.

Description

Attorney Docket No. 40589-0293WO1DIFFRACTION GRATINGS AND MANUFACTURING METHODS THEREOFTECHNICAL FIELD

[0001] This disclosure relates generally to micro / nanostructure fabrication, particularly to fabrication of diffraction gratings.BACKGROUND

[0002] Modem computing and display technologies have facilitated the development of systems for so called “virtual reality” or “augmented reality” experiences, in which digitally- reproduced images or portions thereof are presented to a user in a manner wherein they seem to be, or may be perceived as, real. A virtual reality, or “VR”, scenario typically involves the 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, an MR scenario may include AR image content that appears to be blocked by or is otherwise perceived to interact with objects in the real world.SUMMARY

[0003] The present disclosure describes methods, devices, systems and techniques for diffraction gratings and manufacturing methods of diffraction gratings, and applications of the diffraction gratings, e.g., in optical systems.

[0004] One aspect of the present disclosure features a method of fabricating one or more diffractive gratings, including: providing a waveguide that includes: a glass substrate comprising one or more substances and a non-silica-based network former for the one or more substances, and a cover layer over the glass substrate, a refractive index of the cover layer being smaller than a refractive index of the glass substrate; providing a mask layer over the waveguide, the mask layer having a pattern corresponding to the one or more diffractive gratings, the pattern selectively exposing portions of the waveguide; and etching the exposed portions of the waveguide to define the one or more diffractive gratings.

[0005] Another aspect of the present disclosure features a device including: a waveguide including a glass substrate, the glass substrate including one or more substances and a non-Attorney Docket No. 40589-0293WO1silica-based network former for the one or more substances, the waveguide defining a diffractive grating, the diffractive grating including: a plurality of first portions with a first refractive index; and a plurality of second portions with a second refractive index smaller than the first refractive index, each of the plurality of second portions being on a respective first portion of the plurality of first portions along a first direction, where a dimension of a second portion of the plurality of second portions along a second direction perpendicular to the first direction is greater than a dimension of a respective first portion of the plurality of first portions along the second direction.

[0006] A further aspect of the present disclosure features a device including: a light source configured to emit a light beam and a waveguide including a glass substrate. The glass substrate includes one or more substances and a non-silica-based network former for the one or more substances. The waveguide includes an incoupling diffractive optical element (DOE) and an outcoupling DOE, the incoupling DOE being configured to couple the light beam form the light source toward the outcoupling DOE. At least one of the incoupling DOE and the outcoupling DOE includes: a plurality of first portions with a first refractive index, the first portion including a top part, a bottom part, and a middle part between the top part and the bottom part along a first direction, a dimension of the middle part along a second direction perpendicular to the first direction being smaller than a dimension of the top part along the second direction; and a plurality of second portions with a second refractive index smaller than the first refractive index, each of the plurality of second portions being on the top part of a respective one of the plurality of first portions, where a dimension of a second portion of the plurality of second portions is greater than the dimension of the middle part of a corresponding first portion of the plurality of first portions.

[0007] The details of one or more disclosed implementations are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, the drawings and the claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 illustrates a user's view' of augmented reality (AR) through an AR device.

[0009] FIG. 2 illustrates an example of wearable display system.

[0010] FIG. 3 illustrates a conventional display system for simulating three-dimensional imagery' for a user.Attorney Docket No. 40589-0293WO1

[0011] FIG. 4 illustrates aspects of an approach for simulating three-dimensional imagery' using multiple depth planes.

[0012] FIGS. 5A-5C illustrate relationships between radius of curvature and focal radius,

[0013] FIG. 6 illustrates an example of a waveguide stack for outputting image information to a user.

[0014] FIG. 7 illustrates an example of exit beams outputted by a waveguide.

[0015] FIG. 8 illustrates an example of a stacked waveguide assembly in which each depth plane includes images formed using multiple different component colors.

[0016] FIG. 9A illustrates a cross-sectional side view' of an example of a set of stacked waveguides that each includes an incoupling optical element.

[0017] FIG. 9B illustrates a perspective view' of an example of the plurality of stacked waveguides of FIG. 9A.

[0018] FIG. 9C illustrates a top-down plan view of an example of the plurality of stacked waveguides of FIGS. 9A and 9B.

[0019] FIGS. 10A and 10B illustrate example diffraction gratings formed into a glass substrate used for a waveguide.

[0020] FIGS. 11A and 11B illustrate example diffraction gratings formed on a coating layer with high refractive index on top of a waveguide substrate.

[0021] FIGS. 12A through 12C illustrate cross-section view's of the example waveguide of FIG. 10A at various stages of a fabrication process.

[0022] FIGS. 13A through 13D illustrate cross-section views of the example waveguide of FIG. 11A at various stages of a fabrication process.

[0023] FIGS. 14A through 14D illustrate cross-section views of another example waveguide at various stages of a fabrication process.

[0024] FIG. 15 illustrates various example patterns of diffraction gratings.

[0025] FIG. 16 illustrates a flow-chart of an example process of a method of forming one or more diffraction gratings in a waveguide.

[0026] Like reference numbers and designations in the various drawings indicate like elements. It is also to be understood that the various exemplary implementations shown in the figures are merely illustrative representations and are not necessarily drawn to scale.DETAILED DESCRIPTION

[0027] VR and AR display systems may utilize high refractive index glass substrates as waveguides for providing image information in the form of light to a user. The high refractiveAttorney Docket No. 40589-0293WO1index of the substrates provides desirable optical properties, including allowing the output of light from the substrate at a wide range of angles and facilitating total internal reflection (TIR) of light within that substrate. It will be appreciated that optical elements may be provided on the surface of the substrate to, e.g., incouple light for TIR within the substrate and / or outcouple light to the user. As an example, these optical elements may take the form of diffractive gratings. It is to be noted that tire phrase “diffractive grating” can be used interchangeably with the phrase “diffraction grating” in the present disclosure.

[0028] The present disclosure describes methods, apparatus, and systems for micro / nanostructure fabrication, particularly for fabricating diffraction gratings, and applications of diffraction gratings, e.g., in optical systems. In some implementations, a method of fabricating one or more diffractive grating includes providing a waveguide that includes a glass substrate. The glass substrate has one or more substances and a non-silica-based network former for the one or more substances. The waveguide further includes a cover layer over the glass substrate, where a refractive index of the cover layer is smaller than a refractive index of the glass substrate. A mask layer is provided over the waveguide. The mask layer has a pattern corresponding to the one or more diffractive gratings. The pattern selectively exposes portions of the waveguide. The exposed portions of the waveguide is etched to define the one or more diffractive gratings. The glass substrate can be a non-silica-based glass substrate that is made of non-silica-based glass. The non-silica-based network former of the glass substrate can include at least one of Group 15 elements, e.g., phosphorous (P) or bismuth (Bi).

[0029] Implementations of the present disclosure can provide one or more of the following technical advantages and / or benefits. For example, high refractive index gratings are advantageous for their ability to create shorter structures. High refractive index gratings decrease the effective wavelength of light proportionally to the refractive index as the light travels through the gratings, allowing the grating period to be made smaller while still achieving the same diffraction efficiency. This also allows reduction or minimization of rainbow effects. In some implementations, etching directly into a substrate avoids cost from deposition steps for a high refractive index film. Additionally, having a monolithic substrate and grating reduces complications due to thin film interactions and reflections caused by refractive index mismatch. Further, the technologies described in the present disclosure utilize a non-silica-based network former (e.g., one or more of Group 15 elements) as a network former for a glass substrate, e.g., P or Bi. Compared to silica-based glass, P-based glass substrate can have a lower density (e.g., about 3.6 grams / cm3vs. about 5.0 grams / cm3) ■while providing a good refractive index (RI) (e.g., about 2.0), and P-based glass substrate can beAttorney Docket No. 40589-0293WO1etched easier during a fabrication process; Bi-based glass substrate has a greater transmittance (e.g., over 95% for a 10 mm internal pathlength at Blue wavelengths) and a higher RI (e.g., 2.1). Higher transmittance may allow more light to pass through without being absorbed, and lower density reduces the overall weight of the product, which is important in portable devices like AR glasses. In addition, the technologies enable the manufacture of a mushroom-shaped diffraction grating, which includes a low refractive index overhang / top (e.g., SiO2) above a high refractive index pillar / stem (e.g., high refractive index glass, TiO2, HfO2, Ta2O5, Nb2O5, Si3N4). This mushroom -shaped diffraction grating can allow high diffraction efficiency from the stem, along with anti -reflective properties from the top. In addition, in some implementations, directly etching gratings into high refractive index Phosphorous-based glasses can be advantageous as it may a) avoid the added cost, complexity, and potential yield fall out of the thin film deposition process, b) reduce the number of optical interfaces and ease the need to match the refractive index of the coating to that of tire substrate, and c) reduce uniformity artifacts stemming from thin film interference.

[0030] The technologies described in the present disclosure can be applied to fabrication of any suitable micro / nanostructures, e.g., grating, with any suitable materials, e.g., silicon, glass with any suitable type of network formers, polymer, or optical single crystals (e.g., LiNbO3, LiTaO3, SiC). For illustration purpose only, the following description is mainly directed to fabricating diffraction gratings in a waveguide that includes a glass substrate with a non-silica- based network former, e.g., one of Group 15 elements including P or Bi as a network former.

[0031] A number of implementations have been described, Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the technologies and devices described herein. Features shown in each of the implementations may be used independently or m combination with one another. Additional features and variations may be included in the implementations as well. Accordingly, other implementations are within the scope of the claims below.

[0032] Referring to FIG. 1, an augmented reality scene 1 is depicted, lire user of an AR technology sees a real-world park-like setting 1101 featuring people, trees, buildings in the background, and a concrete platform 1120. Tire user also perceives that he “sees”“virtual content” such as a robot statue 1111 standing upon the real-world platform 1120, and a flying cartoon-like avatar character 1130 which seems to be a personification of a bumble bee. These elements 1130, 1111 are “virtual” in that they do not exist in the real world. Because the human visual perception system is complex, it is challenging to produce AR technology that facilitatesAttorney Docket No. 40589-0293WO1a comfortable, natural-feeling, rich presentation of virtual image elements amongst other virtual or real -world imagery elements.

[0033] FIG. 2 illustrates an example of wearable display system 80 into which the etched high refractive index glass substrates may be incorporated. The display system 80 includes a display- 62, and various mechanical and electronic modules and systems to support the functioning of that display 62. The display 62 may be coupled to a frame 64, which is wearable by a display¬ system user or viewer 60 and which is configured to position the display 62 in front of the eyes of the user 60. The display 62 may be considered eyewear in some implementations. In some implementations, a speaker 66 is coupled to the frame 64 and positioned adjacent the ear canal of the user 60 (another speaker, not shown, may optionally be positioned adjacent the other ear canal of the user to provide for stereo / shapeable sound control). The display system may also include one or more microphones 67 or other devices to detect sound. In some implementations, the microphone is configured to allow the user to provide inputs or commands to the system 80 (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).

[0034] With continued reference to FIG. 2, the display 62 is operatively coupled by communications link 68, such as by a wired lead or wireless connectivity, to a local data processing module 70 which may be mounted in a variety of configurations, such as fixedly-attached to the frame 64, fixedly attached to a helmet or hat worn by the user, embedded in headphones, or otherwise removably attached to the user 60 (e.g., in a backpack-style configuration, in a belt-coupling style configuration). Tire local processing and data module 70 may comprise 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. The data include data a) captured from sensors (which may be, e.g., operatively coupled to the frame 64 or otherwise attached to the user 60), 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 72 and / or remote data repository 74 (including data relating to virtual content), possibly for passage to the display 62 after such processing or retrieval. The local processing and data module 70 may be operatively- coupled by communication links 76, 78, such as via a wired or wireless communication links, to the remote processing module 72 and remote data repository- 74 such that these remote modules 72, 74 are operatively coupled to each other and available asAttorney Docket No. 40589-0293WO1resources to the local processing and data module 70. In some implementations, the local processing and data module 70 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 64, or may be standalone structures that communicate with the local processing and data module 70 by wired or wireless communication pathways.

[0035] With continued reference to FIG. 2, in some implementations, the remote processing module 72 may compri se one or more processors configured to analyze and process data and / or image information. In some implementations, the remote data repository 74 may comprise a digital data storage facility, which may be available through the internet or other networking configuration in a “cloud” resource configuration. In some implementation, the remote data repository 74 may include one or more remote servers, which provide information, e.g., information for generating augmented reality content, to tire local processing and data module 70 and / or the remote processing module 72. 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.

[0036] With reference now to FIG. 3, the perception of an image as being “three-dimensional” or “3-D” may be achieved by providing slightly different presentations of the image to each eye of the viewer. FIG. 3 illustrates a conventional display system for simulating three- dimensional imagery for a user. Two distinct images 5, 7 — one for each eye 4, 6 — are outputted to the user. The images 5, 7 are spaced from the eyes 4, 6 by a distance 10 along an optical or z-axis parallel to the line of sight of the viewer. The images 5, 7 are flat and the eyes 4, 6 may focus on the images by assuming a single accommodated state. Such systems rely on the human visual system to combine tire images 5, 7 to provide a perception of depth and / or scale for the combined image.

[0037] It will be appreciated, however, that the human visual system is more complicated and providing a realistic perception of depth is more challenging. For example, many viewers of conventional “3-D” display systems find such systems to be uncomfortable or may not perceive a sense of depth at all. 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. Vergence movements (i.e., rotation of the eyes so that the pupils move toward or away from each other to converge the lines of sight of the eyes to fixate upon an object) of the two eyes relative to each other are closely associated with focusing (or “accommodation”) of the lenses and pupils of the eyes. Under normal conditions, changing the focus of the lensesAttorney Docket No. 40589-0293WO1of the eyes, or accommodating 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,” as well as pupil dilation or constriction. Likewise, a change in vergence will trigger a matching change in accommodation of lens shape and pupil size, under normal conditions. As noted herein, many stereoscopic or “3-D” display systems display a scene using slightly different presentations (and, so, slightly different images) to each eye such that a three-dimensional perspective is perceived by the human visual system. Such systems are uncomfortable for many viewers, however, since they, among other tilings, simply provide a different presentations of a scene, but with the eyes viewing all the image information at a single accommodated state, and work against the “accommodation-vergence reflex.” Display systems that provide a better match between accommodation and vergence may form more realistic and comfortable simulations of three-dimensional imagery.

[0038] FIG. 4 illustrates aspects of an approach for simulating three-dimensional imagery using multiple depth planes. With reference to FIG. 4, objects at various distances from eyes 4, 6 on the z-axis are accommodated by the eyes 4, 6 so that those objects are in focus. The eyes (4 and 6) assume particular accommodated states to bring into focus objects at different distances along the z-axis. Consequently, a particular accommodated state may be said to be associated with a particular one of depth planes 14, with has an associated focal distance, such that objects or parts of objects in a particular depth plane are in focus when the eye is in the accommodated state for that depth plane. In some implementations, three-dimensional imagery’ may be simulated by providing different presentations of an image for each of the eyes 4, 6, and also by providing different presentations of the image corresponding to each of the depth planes. While shown as being separate for clarity of illustration, it wall be appreciated that the fields of view of the eyes 4, 6 may overlap, for example, as distance along the z-axis increases. In addition, while shown as flat for ease of illustration, it will be appreciated that the contours of a depth plane may be curved in physical space, such that all features in a depth plane are in focus with the eye in a particular accommodated state.

[0039] The distance between an object and the eye 4 or 6 may also change the amount of divergence of light from that object, as viewed by that eye. FIGS. 5A-5C illustrates relationships between distance and the divergence of light rays. The distance between the object and the eye 4 is represented by, in order of decreasing distance, R1, R2, and R3. As shown in FIGS. 5A-5C, the light rays become more divergent as distance to the object decreases. As distance increases, the light rays become more collimated. Stated another way,Attorney Docket No. 40589-0293WO1it 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 4. Consequently, at different depth planes, the degree of divergence of light rays is also different, with the degree of divergence increasing with decreasing distance between depth planes and the viewer's eye 4. While only a single eye 4 is illustrated for clarity of illustration in FIGS.5 A-5C and other figures herein, it will be appreciated that the discussions regarding eye 4 may be applied to both eyes 4 and 6 of a viewer.

[0040] Without being limited by theory, it is believed that the human eye typically can 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 number of depth planes. The different presentations may be separately focused by the viewer's eyes, thereby helping to provide the user with depth cues based on the accommodation of the eye required to bring into focus different image features for the scene located on different depth plane and / or based on observing different image features on different depth planes being out of focus.

[0041] FIG. 6 illustrates an example of a waveguide stack for outputting image information to a user. A di splay system 1001 includes a stack of waveguides, or stacked waveguide assembly, 178 that may be utilized to provide three-dimensional perception to the eye / brain using a plurality of waveguides 182, 184, 186, 188, 190. In some implementations, the display system 1001 is the system 80 of FIG. 2, with FIG. 6 schematically showing some parts of that system 80 in greater detail. For example, the waveguide assembly 178 may be part of the display 62 of FIG. 2. It will be appreciated that the display system 1001 may be considered a light field display in some implementations.

[0042] With continued reference to FIG. 6, the waveguide assembly 178 may also include a plurality of features 198, 196, 194, 192 between the waveguides. In some implementations, the features 198, 196, 194, 192 may be one or more lenses. The waveguides 182, 184, 186, 188, 190 and / or the plurality of lenses 198, 196, 194, 192 may be configured to send image information to the eye with various levels of wavefront curvature or light ray divergence. Each waveguide level may be associated with a particular depth plane and may be configured to output image information corresponding to that depth plane. Image injection devices 200, 202, 204, 206, 208 may function as a source of light for the waveguides and may be utilized to inject image information into the waveguides 182, 184, 186, 188, 190, each of which may be configured, as described herein, to distribute incoming light across each respective waveguide,Attorney Docket No. 40589-0293WO1for output toward the eye 4. Light exits an output surface 300, 302, 304, 306, 308 of the image injection devices 200, 202, 204, 206, 208 and is injected into a corresponding input surface 382, 384, 386, 388, 390 of the waveguides 182, 184, 186, 188, 190. In some implementations, the each of the input surfaces 382, 384, 386, 388, 390 may be an edge of a corresponding waveguide, or may be part of a major surface of the corresponding waveguide (that is, one or both of the waveguide surfaces directly facing the world 144 or the viewers eye 4). 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 4 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 200, 202, 204, 206, 208 may be associated with and inject light into a plurality (e.g., three) of the waveguides 182, 184, 186, 188, 190.

[0043] In some implementations, the image injection devices 200, 202, 204, 206, 208 are discrete displays that each produce image information for injection into a corresponding waveguide 182, 184, 186, 188, 190, respectively. In some other implementations, the image injection devices 200, 202, 204, 206, 208 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 200, 202, 204, 206, 208. It will be appreciated that the image information provided by the image injection devices 200, 202, 204, 206, 208 may include light of different wavelengths, or colors (e.g., different component colors, as discussed herein).

[0044] In some implementations, the light injected into the waveguides 182, 184, 186, 188, 190 is provided by a light projector system 2000, which comprises a light module 2040, which may include a light emitter, such as a light emitting diode (LED), lire light from the light module 2040 may be directed to and modified by a light modulator 2030, e.g., a spatial light modulator, via a beam splitter 2050. The light modulator 2030 may be configured to change the perceived intensity of the light injected into the waveguides 182, 184, 186, 188, 190. Examples of spatial light modulators include liquid crystal displays (LCD) including a liquid cry stal on silicon (LCOS) displays.

[0045] In some implementations, the display system 1001 may be a scanning fiber display comprising 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 182, 184, 186, 188, 190 and ultimately to the eye 4 of the viewer. In some implementations, the illustrated image injection devices 200, 202, 204, 206, 208 may schematically represent a single scanningAttorney Docket No. 40589-0293WO1fiber or a bundles of scanning fibers configured to inject light into one or a plurality of the waveguides 182, 184, 186, 188, 190. In some other implementations, the illustrated image injection devices 200, 202, 204, 206, 208 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 182, 184, 186, 188, 190. It will be appreciated that the one or more optical fibers may be configured to transmit light from the light module 2040 to the one or more waveguides 182, 184, 186, 188, 190, 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 182, 184, 186, 188, 190 to, e.g., redirect light exiting the scanning fiber into the one or more waveguides 182, 184, 186, 188, 190,

[0046] A controller 210 controls the operation of one or more of the stacked waveguide assembly 178, including operation of the image injection devices 200, 202, 204, 206, 208, the light source 2040, and the light modulator 2030. In some implementations, the controller 210 is part of the local data processing module 70. The controller 210 includes programming (e.g., instructions in a non-transitory medium) that regulates the timing and provision of image information to the waveguides 182, 184, 186, 188, 190 according to, e.g., any of the 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 210 may be part of the processing modules 70 or 72 (FIG. 1) in some implementations.

[0047] With continued reference to FIG. 6, the waveguides 182, 184, 186, 188, 190 may be configured to propagate light within each respective waveguide by total internal reflection (TIR). The waveguides 182, 184, 186, 188, 190 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 the illustrated configuration, the waveguides 182, 184, 186, 188, 190 may each include outcoupling optical elements 282, 284, 286, 288, 290 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 4. Extracted light may also be referred to as outcoupled light and the outcoupling optical elements light may also be referred to light extracting optical elements. An extracted beam of light is outputted by the waveguide at locations at which the light propagating in the waveguide strikes a light extracting optical element. The outcoupling optical elements 282, 284, 286, 288, 290 may, for example, be diffraction gratings, including diffractive optical features, as discussed further herein. Wide illustrated disposed at the bottom major surfaces of the waveguides 182, 184, 186, 188, 190 forAttorney Docket No. 40589-0293WO1ease of description and drawing clarity, in some implementations, the outcoupling optical elements 282, 284, 286, 288, 290 may be disposed at the top and / or bottom major surfaces, and / or may be disposed directly in the volume of the waveguides 182, 184, 186, 188, 190, as discussed further herein. In some implementations, the outcoupling optical elements 282, 284, 286, 288, 290 may be formed in a layer of material that is attached to a transparent substrate to form the waveguides 182, 184, 186, 188, 190. In some other implementations, the waveguides 182, 184, 186, 188, 190 may be a monolithic piece of material and the outcoupling optical elements 282, 284, 286, 288, 290 may be formed on a surface and / or in the interior of that piece of material.

[0048] With continued reference to FIG. 6, as discussed herein, each waveguide 182, 184, 186, 188, 190 is configured to output light to form an image corresponding to a particular depth plane. For example, the waveguide 182 nearest the eye may be configured to deliver collimated light, as injected into such waveguide 182, to the eye 4. The collimated light may be representative of the optical infinity focal plane. The next waveguide up 184 may be configured to send out collimated light which passes through the first lens 192 (e.g., a negative lens) before it can reach the eye 4; such first lens 192 may be configured to create a slight convex wavefront curvature so that the eye / brain interprets light coming from that next waveguide up 184 as coming from a first focal plane closer inward toward the eye 4 from optical infinity. Similarly, the third up waveguide 186 passes its output light through both the first 192 and second 194 lenses before reaching the eye 4; the combined optical power of the first 192 and second 194 lenses may be configured to create another incremental amount of wavefront curvature so that the eye / brain interprets light coming from the third waveguide 186 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 184.

[0049] The other waveguide layers 188, 190 and lenses 196, 198 are similarly configured, with the highest waveguide 190 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 198, 196, 194, 192. when viewing / interpreting light coming from the world 144 on the other side of the stacked waveguide assembly 178, a compensating lens layer 180 may be disposed at the top of the stack to compensate for the aggregate power of the lens stack 198, 196, 194, 192 below. Such a configuration provides as many perceived focal planes as there are available waveguide / lens pairings. Both the outcoupling optical elements of the waveguides and the focusing aspects of the lenses may beAttorney Docket No. 40589-0293WO1static (i.e not dynamic or electro-active). In some alternative embodiments, either or both may be dynamic using electro-active features.

[0050] In some implementations, two or more of the waveguides 182, 184, 186, 188, 190 may have the same associated depth plane. For example, multiple waveguides 182, 184, 186, 188, 190 may be configured to output images set to the same depth plane, or multiple subsets of the waveguides 182, 184, 186, 188, 190 may be configured to output images set to the same plurality of depth planes, with one set for each depth plane. This can provide advantages for forming a tiled image to provide an expanded field of view at those depth planes.

[0051] With continued reference to FIG. 6, the outcoupling optical elements 282, 284, 286, 288, 290 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 outcoupling optical elements 282, 284, 286, 288, 290, which output light with a different amount of divergence depending on the associated depth plane. In some implementations, the light extracting optical elements 282, 284, 286, 288, 290 may be volumetric or surface features, which may be configured to output light at specific angles. For example, the light extracting optical elements 282, 284, 286, 288, 290 may be volume holograms, surface holograms, and / or diffraction gratings. In some implementations, the features 198, 196, 194, 192 may not be lenses; rather, they may simply be spacers (e.g., cladding layers and / or structures for forming air gaps).

[0052] In some implementations, the outcoupling optical elements 282, 284, 286, 288, 290 are diffractive features that form a diffraction pattern, or “diffractive optical element” (also referred to herein as a “DOE”). Preferably, the DOEs have a sufficiently low diffraction efficiency so that only a portion of the light of the beam is deflected away toward the eye 4 with each intersection of the DOE, while the rest continues to move through a waveguide via total internal reflection. 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 4 for this particular collimated beam bouncing around within a waveguide.

[0053] In some implementations, one or more DOEs 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 comprise a layer of polymer dispersed liquid crystal, in which microdroplets comprise 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 materialAttorney Docket No. 40589-0293WO1(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).

[0054] In some implementations, a camera assembly 500 (e.g., a digital camera, including visible light and infrared light cameras) may be provided to capture images of the eye 4 and / or tissue around the eye 4 to, e.g., detect user inputs. As used herein, a camera may be any image capture device. In some implementations, the camera assembly 500 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 500 may be attached to the frame 64 (FIG. 2) and may be in electrical communication with the processing modules 70 and / or 72, which may process image information from the camera assembly 500. In some implementations, one camera assembly 500 may be utilized for each eye, to separately monitor each eye.

[0055] With reference now to FIG. 7, an example of exit beams outputted by a waveguide is shown. One waveguide is illustrated, but it will be appreciated that other waveguides in the waveguide assembly 178 (FIG. 6) may function similarly, where the waveguide assembly 178 includes multiple waveguides. Light 400 is injected into the waveguide 182 at the input surface 382 of the waveguide 182 and propagates within the waveguide 182 by TIR. At points where the light 400 impinges on the DOE 282, a portion of the light exits the waveguide as exit beams 402. The exit beams 402 are illustrated as substantially parallel but, as discussed herein, they may also be redirected to propagate to the eye 4 at an angle (e.g,, forming divergent exit beams), depending on the depth plane associated with the waveguide 182. It will be appreciated that substantially parallel exit beams may be indicative of a waveguide with outcoupling optical elements that outcouple light to form images that appear to be set on a depth plane at a large distance (e.g., optical infinity) from the eye 4. Other waveguides or other sets of outcoupling optical elements may output an exit beam pattern that is more divergent, which would require the eye 4 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 4 than optical infinity..

[0056] 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 embodiment shows depth planes 14a-14f, although more or fewer depths are also contemplated. Each depth plane may have three component color images associated with it: a first image of a first color, G; aAttorney Docket No. 40589-0293WO1second image of a second color, R; and athird 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 the eye’s focusing of light of different wavelengths, the exact placement of the depth planes for different component colors may van’. 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.

[0057] In some implementations, light of each component color may be outputted by a single dedicated waveguide and, consequently, each depth plane may have multiple waveguides associated with it. In such embodiments, 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 m a stack with one waveguide per level. In some other implementations, multiple component colors may be outputted by the same waveguide, such that, e.g., only a single waveguide may be provided per depth plane.

[0058] 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.

[0059] 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 within 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.

[0060] With reference now to FIG. 9A, in some implementations, light impinging on a waveguide may need to be redirected to incouple that light into the waveguide. An incoupling optical element may be used to redirect and incouple the light into its corresponding waveguide. FIG. 9A illustrates a cross-sectional side view of an example of a plurality or set 1200 of stacked waveguides that each includes an incoupling optical element. The waveguides mayAttorney Docket No. 40589-0293WO1each 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 stack 1200 may correspond to the waveguide assembly 178 (FIG. 6) and the illustrated waveguides of the stack 1200 may correspond to part of the plurality of waveguides 182, 184, 186, 188, 190, except that light from one or more of the image injection devices 200, 202, 204, 206, 208 is injected into the waveguides from a position that requires light to be redirected for incoupling.

[0061] The illustrated set 1200 of stacked waveguides includes waveguides 1210, 12.20, and 1230. Each waveguide includes an associated incoupling optical element (which may also be referred to as a light input area on the waveguide), with, e.g., incoupling optical element 1212 disposed on a major surface (e.g., an upper major surface) of waveguide 1210, incoupling optical element 1222 disposed on a major surface (e.g., an upper major surface) of waveguide 1220, and incoupling optical element 1232 disposed on a major surface (e.g., an upper major surface) of waveguide 1230. In some implementations, one or more of the incoupling optical elements 1212, 1222, 1232 may be disposed on the bottom major surface of the respective waveguide 1210, 1220, 1230 (particularly where the one or more incoupling optical elements are reflective, deflecting optical elements). As illustrated, the incoupling optical elements 1212, 1222, 1232 may be disposed on the upper major surface of their respective waveguide 1210, 1220, 1230 (or the top of the next lower waveguide), particularly where those incoupling optical elements are transmissive, deflecting optical elements. In some implementations, the incoupling optical elements 1212, 1222, 1232 may be disposed in the body of the respective waveguide 1210, 1220, 1230. In some implementations, as discussed herein, the incoupling optical elements 1212, 1222, 1232 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 corner of their respective waveguide 1210, 1220, 1230, it will be appreciated that the incoupling optical elements 1212, 1222, 1232 may be disposed in other areas of their respective waveguide 1210, 1220, 1230 in some implementations.

[0062] As illustrated, the incoupling optical elements 1212, 1222, 1232 may be laterally offset from one another. In some implementations, each incoupling optical element may be offset such that it receives light without that light passing through another incoupling optical element. For example, each incoupling optical element 1212, 1222, 1232 may be configured to receive light from a different image injection device 1213, 1223, 1233 and may be separated (e.g., laterally spaced apart) from other incoupling optical elements 1212, 1222, 1232 such that it substantially does not receive light from the other ones of the incoupling optical elements 1212, 1222, 1232.Attorney Docket No. 40589-0293WO1

[0063] Each waveguide also includes associated light distributing elements, with, e.g., light distributing elements 1214 disposed on a major surface (e.g., a top major surface) of waveguide 1210, light distributing elements 1224 disposed on a major surface (e.g., a top major surface) of waveguide 1220, and light distributing elements 1234 disposed on a major surface (e.g., a top major surface) of waveguide 1230. In some other implementations, the light distributing elements 1214, 1224, 1234, may be disposed on a bottom major surface of associated waveguides 1210, 1220, 1230, respectively. In some other implementations, the light distributing elements 1214, 1224, 1234, may be disposed on both top and bottom major surface of associated waveguides 1210, 1220, 1230, respectively; or the light distributing elements 1214, 12.24, 1234, may be disposed on different ones of the top and bottom major surfaces in different associated -waveguides 1210, 1220, 1230, respectively.

[0064] The waveguides 1210, 1220, 1230 may be spaced apart and separated by, e.g., gas, liquid, and / or solid layers of material. For example, as illustrated, layer 1218a may separate waveguides 1210 and 1220; and layer 1218b may separate waveguides 12.20 and 12.30. In some implementations, the layers 1218a and 1218b 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 1210, 1220, 1230). Preferably, the refractive index of the material forming the layers 1218a, 1218b is 0.05 or more, or 0.10 or more less than the refractive index of the material forming the waveguides 1210, 1220, 1230. Advantageously, the lower refractive index layers 1218a, 1218b may function as cladding layers that facilitate total internal reflection (TIR) of light through the waveguides 1210, 1220, 1230 (e.g., TIR between the top and bottom major surfaces of each waveguide). In some implementations, the layers 1218a, 1218b are formed of air. While not illustrated, it will be appreciated that the top and bottom of the illustrated set 1200 of waveguides may include immediately neighboring cladding layers.

[0065] Preferably, for ease of manufacturing and other considerations, the material forming the waveguides 1210, 1220, 1230 are similar or the same, and the material forming the layers 1218a, 12.18b are similar or the same. In some implementations, the material forming the waveguides 1210, 1220, 12.30 may be different between one or more waveguides, and / or the material forming the layers 1218a, 1218b may be different while still holding to the various refractive index relationships noted above.

[0066] With continued reference to FIG. 9A, light rays 1240, 1242, 1244 are incident on the set 1200 of waveguides. It will be appreciated that the light rays 1240, 1242, 1244 may be injected into the waveguides 1210, 1220, 1230 by one or more image injection devices 200, 202, 204, 206, 208 (FIG. 6).Attorney Docket No. 40589-0293WO1

[0067] In some implementations, the light rays 1240, 1242, 1244 have different properties, e.g., different wavelengths or different ranges of wavelengths, which may correspond to different colors. The incoupling optical elements 1212, 1222, 1232 each deflect the incident light such that the light propagates through a respective one of the waveguides 1210, 1220, 1230 by TIR. In some implementations, the incoupling optical elements 1212, 1222, 1232 each selectively deflect one or more particular wavelengths of light, while transmitting other wavelengths to an underlying waveguide and associated incoupling optical element.

[0068] For example, incoupling optical element 1212 may be configured to deflect ray 1240, which has a first wavelength or range of wavelengths, while transmitting rays 1242 and 1244, which have different second and third wavelengths or ranges of wavelengths, respectively. The transmitted ray 1242 then impinges on and is deflected by the incoupling optical element 1222, which is configured to selectively deflect light of second wavelength or range of wavelengths. The ray 1244 is transmitted by the incoupling optical element 1222 and continues on to impinge on and be deflected by the incoupling optical element 1232, which is configured to selectively deflect light of third w avelength or range of wavelengths.

[0069] With continued reference to FIG. 9A, the deflected light rays 1240, 1242, 1244 are deflected so that they propagate through a corresponding waveguide 1210, 1220, 1230; that is, the incoupling optical elements 1212, 1222, 1232 of each waveguide deflects light into that corresponding waveguide 1210, 1220, 1230 to incouple light into that corresponding waveguide. The light rays 1240, 1242, 1244 are deflected at angles that cause the light to propagate through the respective waveguide 1210, 1220, 1230 by TIR, The light rays 1240, 1242, 1244 propagate through the respective waveguide 1210, 1220, 1230 by TIR until impinging on the waveguide's corresponding light distributing elements 1214, 1224, 1234.

[0070] 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 incoupled light rays 1240, 1242, 1244, are deflected by the incoupling optical elements 1212, 1222, 1232, respectively, and then propagate by TIR within the waveguides 1210, 1220, 1230, respectively. The light rays 1240, 1242, 1244 then impinge on the light distributing elements 1214, 12.24, 1234, respectively. The light distributing elements 1214, 1224, 1234 deflect the light rays 1240, 1242, 1244 so that they propagate towards the outcoupling optical elements 1250, 1252, 1254, respectively.

[0071] In some implementations, the light distributing elements 1214, 1224, 1234 are orthogonal pupil expanders (OPEs). In some implementations, the OPEs both deflect or distribute light to the outcoupling optical elements 1250, 1252, 1254 and also increase the beamAttorney Docket No. 40589-0293WO1or spot size of this light as it propagates to the outcoupling optical elements. In some implementations, e.g., where the beam size is already of a desired size, the light distributing elements 1214, 1224, 1234 may be omitted and the incoupling optical elements 1212, 1222, 1232 may be configured to deflect light directly to the outcoupling optical elements 1250, 1252, 1254. For example, with reference to FIG. 9A, the light distributing elements 1214, 1224, 1234 may be replaced with outcoupling optical elements 1250, 1252, 1254, respectively. In some implementations, the outcoupling optical elements 1250, 1252, 12.54 are exit pupils (EPs) or exit pupil expanders (EPEs) that direct light in a viewer's eye 4 (FIG. 7).

[0072] Accordingly, with reference to FIGS. 9A and 9B, in some implementations, the set 1200 of waveguides includes waveguides 1210, 1220, 1230; incoupling optical elements 1212, 1222, 1232; light distributing elements (e.g., OPEs) 1214, 1224, 1234; and outcoupling optical elements (e.g., EPs) 1250, 1252, 1254 for each component color. The waveguides 1210, 1220, 1230 may be stacked with an air gap / cladding layer between each one. The incoupling optical elements 1212, 1222, 1232 redirect, or deflect incident light (with different incoupling 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 1210, 1220, 1230. In the example shown, light ray 1240 (e.g., blue light) is deflected by the first incoupling optical element 1212, and then continues to bounce down the waveguide, interacting with the light distributing element (e.g., OPEs) 1214 and then the outcoupling optical element (e.g., EPs) 1250, in a manner described earlier. The light rays 12.42 and 1244 (e.g., green and red light, respectively) will pass through the waveguide 1210, with light ray 1242 impinging on and being deflected by incoupling optical element 1222. The light ray 1242 then bounces down the waveguide 1220 via TIR, proceeding on to its light distributing element (e.g., OPEs) 1224 and then the outcoupling optical element (e.g., EPs) 1252. Finally, light ray 1244 (e.g., red light) passes through the waveguide 1220 to impinge on the light incoupling optical elements 1232 of the waveguide 1230. Hie light incoupling optical elements 1232 deflect the light ray 1244 such that the light ray propagates to light distributing element (e.g., OPEs) 1234 by HR, and then to the outcoupling optical element (e.g., EPs) 1254 by TIR. The outcoupling optical element 1254 then finally outcouples the light ray 1244 to the viewer, who also receives the outcoupled light from the other waveguides 1210, 1220.

[0073] 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 1210, 1220, 1230, along with each waveguide's associated light distributing element 1214, 1224, 1234 and associated outcoupling optical element 1250, 1252, 1254, may be vertically aligned. However, asAttorney Docket No. 40589-0293WO1discussed herein, the incoupling optical elements 1212, 1222, 1232 are not vertically aligned; rather, the incoupling optical elements are preferably 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 incoupling optical elements may be referred to as a shifted pupil system, and the incoupling optical elements within these arrangements may correspond to sub pupils.

[0074] In some implementations, microscale and nanoscale features, such the various diffractive optical elements discussed herein, may be etched directly in a high refractive index glass substrate. For example, the glass substrate may be used as a waveguide and the plasma etching processes may be used to form the incoupling optical elements 1212, 1222, 1232, the light distributing elements 1214, 1224, 1234, and / or the outcoupling optical element 1250, 1252, 1254 of FIGS, 9A-9C directly in the substrate. In some implementations, microscale and nanoscale features, such the various diffractive optical elements discussed herein, may be etched in a high refractive index film that is formed on a glass substrate.

[0075] It will be appreciated that the term “high refractive index'’ is used herein to refer to materials, preferably optically transmissive materials such as glasses, that have a refractive index greater than or equal to 1.65. In some implementations, a high refractive index glass may have a refractive index of 1.65 or greater, 1.7 or greater, 1.75 or greater, or 1.8 or greater. In some implementations, the refractive index may be as noted above and also less than 4, less than 3, or less than 2.5.

[0076] FIGS. 10A-10B illustrate example diffraction gratings 1010 formed on a glass substrate 1002 of a waveguide 1000, according to one or more implementations of the present disclosure. The waveguide 1000 can be, e.g., waveguide 182, 184, 186, 188, or 190 of FIGS. 6 and 7, or waveguide 1210, 1220, or 1230 of FIGS. 9A-9C. The diffraction gratings 1010 can be, e.g., incoupling optical element 1212, 1222, or 1232 of FIGS. 9A-9C, outcoupling optical elements 282, 284, 286, 288, or 290 of FIGS. 6, 7, or outcoupling optical elements 1250, 1252, or 1254 of FIGS. 9B, 9C.

[0077] As illustrated in FIG. 10A, a waveguide 1000 includes a glass substrate 1002. In some implementations, the glass substrate includes one or more substances and a non-silica-based network former for the one or more substances. The glass substrate can be a non-silica-based glass substrate that is made of non-silica-based glass. The non-silica-based network former can include at least one of Group 15 elements, e.g., phosphorous (P) or bismuth (Bi). The at leastAttorney Docket No. 40589-0293WO1one of Group 15 elements can include nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), and / or moscovium (Mc). In some implementations, the glass substrate 1002 includes Phosphorous (P) or Bismuth (Bi) as a network former, which can be referred to as P-based glass substrate or Bi-based glass substrate in the present disclosure. In some implementations, the non -silica-based network former includes germanium (Ge), antimony (Sb), sulfur (S), selenium (Se), and / or tellurium (Te).0078] In some implementations, a mole percentage of the network former in the glass substrate 1002 is less than 50%. In some implementations, the one or more substances of the glass substrate 1002 include one or more of B2O3, Al2O3, ZrO2, Li2O, Na2O, K2O, MgO, CaO, SrO, BaO, ZnO, La2O3, Nb2O5, TiO2, HfO, and Sb2O3. The combination of one or more substances and their percentages can be adjusted based on the desired characteristics.

[0079] In some implementations, a refractive index of the glass substrate 1002 is in a range between 1.7 and 2.3. In some implementations, the glass substrate 1002 has a density between 2.5 gram / cm3and 7.5 gram / cm3. In some implementations, the glass substrate 1002 has a transmittance of over 90% for a 10 mm internal pathlength in the wavelength range of 440 nm to 700 nm. In some implementations, compared to the silica-based glass substrate, the P-based glass substrate has a lower density (e.g., about 3.6 grams / cm3) while providing a nearly equivalent refractive index (RI) (e.g., about 1.996 or 1.995 compared to 2.001 for silica-based glass substrate). In some implementations, compared to the Silica-based glass substrate, the Bi¬ based glass substrate has a greater transmittance (e.g., over 95% for a 10 mm internal pathlength) and a greater RI (e.g., 2.1-2.15). As noted above, a higher transmitance may allow more light to pass through without being absorbed, and a lower density reduces the overall weight of the product, which is important in portable devices like AR glasses. In some implementations, the glass substate has a transmittance of over 95% for a 10 mm internal pathlength in the visible wavelength range with a density smaller than or equal to 3 grams / cm3.0080] Tire waveguide 1000 defines a diffractive grating 1010. Tire diffractive grating 1010 includes a plurality of first portions 1012 with a first refractive index and a plurality of second portions 1014 with a second refractive index smaller than the first refractive index. Each second portion 1014 is stacked over a respective first portion 1012 along Z direction. Z direction can be the direction that is perpendicular to an extending direction (e.g., X direction) of the glass substrate 1002. The first portions 1012 can be formed in the glass substrate 1002. As noted above, the glass substrate 1002 can be P-based glass substrate or Bi-based glass substrate. In some implementations, the second portions 1014 include silicon dioxide (SiO2). In some implementations, the first refractive index of the glass substrate 1002 is in a range between 1.7Attorney Docket No. 40589-0293WO1and 2.3. In some implementations, the second refractive index of the second portions 1014 is smaller than 1.5. Without limiting to any particular theory, it is believed that the second portions 1014 with a lower refractive index can increase transmittance and reduce light reflection. In some implementations, the second portions 1014 include anti-reflection (AR) coating, which can be multiple layers and have a good etch selectivity with respect to the glass substrate 1002. It is to be understood that although each second portion 1014 in FIGS. 10A and JOB is shown as one layer, it can include multiple coatings of varying index (e.g, high to low, or low to high) going from top to bottom.0081 In some implementations, as illustrated in FIG. 10A, a dimension 1028 (e.g., width) of a second portion 1014 along X-direction is greater than a dimension 1024 (e.g., width) of a respective first portion 1012 along the same direction. In other words, a first portion 1012 has an undercut compared to the respective second portion 1014 by an undercut region 1016 below the respective second portion 1014.

[0082] In some implementations, each first portion 1012 includes a top part 1012a, a bottom part 1012c and a middle part 1012b between the top part 1012a and the bottom part 1012c along Y -direction. The second portion 1014 can be stacked over the top part 1012a of the first portion 1012. In some implementations, a dimension 1024 (e.g., width) of the middle part 1012b along X-direction is smaller than a dimension 1026 (e.g., width) of the top part 1012a and / or a dimension 1022 of the botom part 1012c along the same direction. As illustrated in FIG. I0A, tire first portion 1012 can have a ‘’neck” shape with a narrower middle part 1012b and wider top and bottom parts, 1012a, 1012c, In some implementations, the width 102.4 of the middle part 1012b ofthe first portion 1012 is smaller than the width 1028 of the second portion 1014 along X direction (e.g., a “mushroom” shape). In some implementations, as illustrated in FIG. 10A, tire width 1026 of the top part 1012a of tire first portion 1012 is smaller than the width 1028 ofthe second portion 1014.

[0083] As described below in reference to FIGS. 12A-12C, this “neck” shaped first portion 1012 can be formed during an etching process. For example, it can be formed by first punching through the glass substrate 1002 along Z direction by an anisotropic etching, followed by an isotropic etching to undercut the second portion 1014. Therefore, the shape of the diffraction grating 1010 illustrated in FIG. 10A can reflect the etching characteristics employed. In some implementations, e.g., in more ideal scenarios, the first portion 1012 of the diffraction grating 1010 has a straighter shape, as illustrated in FIG. 10B, where the top part 1012a, the middle part 1012b and the bottom part 1012c of the first portion 1012 can have substantially the same width along X direction.Attorney Docket No. 40589-0293WO1

[0084] In some implementations, a height 1032 of the diffraction grating 1010 along Y- direction is in a range between 5 nm and 500 nm. The height 1032 of the diffraction grating 1010 can be a sum of a height of the second portion 1014 and a height of the first portion 1012 along y direction,

[0085] FIGS. 11A-1 IB illustrate another example of diffraction gratings formed on a coating layer of a waveguide, according to one or more implementations of the present disclosure. The waveguide 1100 can be, e.g., waveguides 182, 184, 186, 188, or 190 of FIGS. 6 and 7, or waveguides 1210, 1220, or 1230 of FIGS. 9A-9C. The diffraction gratings 1110 can be, e.g., incoupling optical elements 1212, 1222, or 1232 of FIGS. 9A-9C, outcoupling optical elements 282, 284, 286, 2.88, or 290 of FIGS. 6, 7, or outcoupling optical elements 1250, 1252, or 12.54 of FIGS. 9B, 9C.

[0086] As shown in FIGS. 11A-11B, the waveguide 1100 includes a coating layer 1150 on a glass substrate 1102. The glass substrate 1102 can be, e.g., the glass substrate 1002 of FIGS.10A and 10B. In some implementations, the coating layer 1150 has a different material than the glass substrate 1102. For example, the coating layer 1150 can include, without limitation to, TiO2, Nb2O5, Ta2O5, HfO2, Si3N4, or SiC. The glass substrate 1102 can be P-based glass substrate or Bi-based glass substrate. In some implementations, the coating layer 1150 has better etch characteristics compared to the glass substrate 1102. For example, the coating layer 1150 can be more easily or more precisely etched (or patterned) during manufacturing process, e.g., a faster etch rate, a greater selectivity over mask and / or easier to form high aspect ratio trenches. The refractive index of the coating layer 1150 can be identical to or different from (e.g., greater or smaller than) that of the glass substrate 1102. In some implementations, the refractive index of the coating layer 1150 is greater than or equal to 2.0 at a wavelength of visible light.

[0087] FIGS. 11 A-l IB differ from FIGS. 10A-I0B in that the diffraction gratings 1110 are formed in the coating layer 1150 as opposed to in the glass substrate 1102. As shown in FIGS.11A and 11B, the diffraction grating 1110 includes a plurality of first portions 1112 and a plurality of second portions 1114, The plurality of first portions 1112 are over the glass substrate 1102. The second portion 1114 can be stacked over a top part 1112a of the respective first portion 1112 along y axis. The refractive index of the coating layer 1150 can be greater than a second refractive index of the second portion 1114. It is to be understood that although each second portion 1114 in FIGS. 11 A and 11 B is shown as one layer, it can include multiple coatings of varying index (e.g., high to low, or low to high) going from top to bottom.Attorney Docket No. 40589-0293WO1

[0088] Similar to the waveguide 1000 in FIGS. 10A and 1 OB, the diffraction gratings 1110 can have a “mushroom” shape. In some implementations, a dimension 1128 (e.g., width) of a second portion 1114 along X-direction is greater than a dimension 1124 (e.g., width) of a respective first portion 1112 along the same direction. In other words, a first portion 1112 has an undercut compared to the respective second portion 1114 by an undercut region 1116 below the second portion 1114.

[0089] In some implementations, as illustrated in FIG. 11 A, the first portions 1112 of the diffraction grating 1110 can have three parts: a top part 1112a, a middle part 1112b and a botom part 1112c. In some implementations, a dimension 1124 (e.g., width) of the 1112b along x-direction is smaller than a dimension 1126 (e.g., width) of the top part 1112a and / or a dimension 1122 of the bottom part 1112c along the same direction. As illustrated in FIG. 11 A, tlie first portion 1112 can have a “neck” shape with a narrower middle part 1112b and wider top and bottom parts 1112a, 1112c. In some implementations, the width 1124 of the middle part 1112b of the first portion 1112 is smaller than the width 1128 of the second portion 1 I 14 along x direction. In some implementations, as illustrated in FIG. HA, the width 1126 of the top part 1112a of the first portion 1112 is smaller than the width 1128 of the second portion 1114. In some implementations, the width of the first portion 1112. is defined by the width of the middle part 1112 b of the first portion 1112.

[0090] As described below in reference to FIGS. 13A-14D, this “neck” shaped first portion 1112 can come from an etching process. For example, it can be formed by first punching through the coating layer 1150 along y axis by an anisotropic etching, followed by an isotropic etching to remove a portion of the coating layer 1150 under the second portion 1114 (e.g., to undercut the second portion 1114).

[0091] Depending on the isotropic etching characteristics, the shapes of the first portions 1112. of the diffraction gratings 1110 can be different. In some implementations, as described below in reference to FIGS. 13A-13D, the isotropic etching step involves dry etching techniques, e.g., Fluorine Inductively Coupled Plasma Etching (ICP) and / or Reactive Ion Etching (RIE). With dry etching, as illustrated in FIG. 11A, openings 1306 between adjacent first portions 1112 of the diffraction gratings 1110 can have a barrel shape. For example, a spacing distance 1142 between middle parts 1112b of adjacent first portions 1112 of the diffraction gratings 1110 along X-direction can be smaller than a height 1144 of one of the adjacent first portions 1112. of the diffraction gratings 1110 along y-direction.

[0092] In some implementations, as described below in reference to FIGS. 14A-14D, the isotropic etching step can involve wet etching techniques, e.g., H2SO4. With wet etching, asAttorney Docket No. 40589-0293WO1illustrated below in FIG. 14D, openings 1406 between adjacent first portions 1112 of the diffraction gratings 1110 can have a light bulb shape. For example, a spacing distance 1142 between middle parts 1112b of adjacent first portions 1112 of the diffraction gratings 1110 along x-direction can be greater than a height 1144 of one of the adjacent first portions 1112 of the diffraction gratings 1110 along y-direction.

[0093] The shape of the diffraction gratings 1110 illustrated in FIG. HA can be reflective of the etching characteristics employed. In some implementations, e.g., in more ideal scenarios, the first portion 1112 of the diffraction grating 1110 can have a straighter shape. As illustrated in FIG. 1 IB, the top part 1112a, the middle part 1112b and the bottom part 1112c of the first portion 1112 can have substantially the same width along x-direction.0094] In some implementation, a height 1132 of the diffractive grating 1110 along Y-direction is in a range between 5 nm and 500 nrn. The height of the diffractive grating 1110 can be a sum of the a height of the second portion 1114 and a height of the first portion 1112 along Y-direction.

[0095] FIGS. 12 A-12C illustrate cross-section views of the waveguide lOOO ofFIGS. lOA and 10B at various stages of a fabrication process. As illustrated in FIG. 12A, a glass substrate 1002 is provided. The glass substrate 1002 can include one or more substances and a non-silica- based network former for the one or more substances. The glass substrate can be a non-silica- based glass substrate that is made of non-silica-based glass. The non-silica-based network former can include at least one of Group 15 elements, e.g.. Phosphorous (P) or Bismuth (Bi). For example, the glass substrate 1002 can be P-based glass substrate or Bi-based glass substrate. A cover layer 1215 can be formed on the glass substrate 1002. Tire cover layer 1215 can have a refractive index smaller than a refractive index of the glass substrate 1002. For example, the cover layer 1215 can be made of SiO2. In some implementations, the cover layer 1215 has a refractive index smaller than 1.5.

[0096] Tire cover layer 1215 can be patterned, and the pattern corresponds to the diffraction gratings 1010 to be formed at a later stage (e.g., FIG. 12C). Patterning the cover layer 1215 can include providing a mask layer over the cover layer 1215, where the mask layer has a pattern corresponding to the diffraction gratings 1010. The pattern of the mask layer can selectively expose portions of the cover layer 1215. An etching process can be performed to etch exposed portions of the cover layer 1215. The patterned cover layer 1215 can be, e.g., the second portions 1014 of FIGS. 10A and JOB. The etching process to pattern the cover layer 1215 can involve one or more dry etching and / or wet etching techniques, including, but not limited to, reactive ion etching (RIE), plasma etching, hydrofluoric acid (HF) etching, sputtering etching,Attorney Docket No. 40589-0293WO1KOH Etching (Potassium Hydroxide), TMAH Etching (Tetramethylammonium Hydroxide), Buffered Oxide Etchant (BOE), Piranha Solution (H2SO4 / H2O2), or any combination thereof.

[0097] In some implementations, tire cover layer 1215 is paterned together with an anisotropic etch that punches into the glass substrate 1002, as described below in reference to FIG. 12B. Therefore, the patterning process step illustrated in FIG. 12A can be optional.

[0098] As illustrated in FIG. 12B, an anisotropic etch can be performed to etch a trench 1253 into the glass substrate 1002 along Y -direction to form a first patern 1251. The first patern 1251 can include portions of the cover layer 1215 on corresponding portions of the glass substrate 1002. The anisotropic etch can include, but not limited to. Deep Reactive Ion etching (DRIE), Inductively Coupled Plasma (ICP) etching, KOH etching (Potassium Hydroxide Etching), SF6 plasma etching, or any combination thereof. In some cases, P-based glass substrate may be etched faster than Silica-based glass substrate.

[0099] As illustrated in FIG. 12C, an isotropic etch can be performed to undercut the cover layer 1215 (e.g., the second portions 1014 of FIGS. 10A and JOB) by partially removing the corresponding portions of the glass substrate 1002 under the portions of the cover layer 1215. For example, the undercut region 1016 can be formed under the cover layer 1215. In other words, the portions of the cover layer 1215 can overhang the corresponding portions of the glass substrate 1002 after the isotropic etch. The etching chemicals used for the isotropic etching can have a higher etching rate for the glass substrate 1002 (e.g., P-based glass substrate or Bi-based glass substrate) compared to the cover layer 1215 (e.g., SiO2). For example, the etching chemicals can include Ammonium hydroxide, Potassium hydroxide, H2SO4, Buffered Oxide Etch (BOE), hydrofluoric acid (HF), phosphoric acid (H3PO4), ammonium fluoride (NH4F), Piranha solution, or any combination thereof. In some implementations, after isotropic etching, a dimension 1028 (e.g., width) of a portion of the cover layer 1215 along x-direction is greater than a dimension 1024 (e.g., width) of a corresponding portion of the glass substrate 1002 along x-direction.[00100 [ In some implementations, a middle part 1012b of the first portions 1012 of the diffraction gratings 1010 is etched more during isotropic etch compared to the top part 1012a and the bottom part 1012c. Therefore, the first portions 1012 of the diffraction gratings 1010 can have a “neck” shape with narrower middle parts 1012b and wider top and bottom parts 1012a, 1012c. As described above in reference to FIG. 10B, m a more ideal scenarios, the first portions 1012 of the diffraction gratings 1010 can have a straight line shape.

[0101] FIGS. 13A-13D illustrate cross-section views of the example waveguide 1100 of FIG.11A at various stages of a fabrication process. As illustrated in FIG. 13A, a glass substrateAttorney Docket No. 40589-0293WO11102 is provided. The glass substrate 1102 can be, e.g., the glass substrate 1002 of FIGS. 10A- 10B and 12A-12C, or the glass substrate 1102 of FIGS. 11A and 1 IB. The glass substrate 1102 can include one or more substances and a network former for the one or more substances. The glass substrate can be a non-silica-based glass substrate that is made of non-silica-based glass. Hie non-silica-based network former can include at least one of Group 15 elements, e.g., Phosphorous (P) or Bismuth (Bi). For example, the glass substrate 1102 can be P-based glass substrate or Bi -based glass substrate.

[0102] A coating layer 1150 can be formed on the glass substrate 1102. The coating layer 1150 can have a refractive index greater than the refractive index of the glass substrate 1102, e.g,, to guide the light effectively through the waveguide 1100 without significant losses. In some implementations, the refractive index of the glass substrate 1102 is between 1.7 and 2.3, and the refractive index for the coating layer 1150 is greater than or equal to 2.0 at a wavelength of visible light. In some implementations, the refractive index for the coating layer 1150 is between 2.0 and 2.5. In some implementations, the coating layer 1150 includes TiO2, Nb2O5, Ta2O5, HfO2, Si3N4, or SiC.

[0103] A cover layer 1215 can be formed on the coating layer 1150. The cover layer 1215 can include a refractive index smaller than the refractive index of the coating layer 1150. For example, the cover layer 1215 can be made of SiO2. In some implementations, the cover layer 1215 has a refractive index smaller than 1.5.

[0104] A hard mask layer 1302 can be formed on the cover layer 1215. In some implementations, the hard mask layer includes Chromium (Cr) and / or Nickel (Ni) for protecting the underlying cover layer 1215 during subsequent dry' etch process depicted in FIG.13C.[00105 llie hard mask layer 1302, the cover layer 1215 and the coating layer 1150 can be patterned, and the pattern is corresponding to the diffractive gratings 1110, In some implementations, the patterning process involves nanoimprint lithography (NIL). The NIL techniques can involve (i) depositing a thin film 1304 (e.g., polymer or a resist) on the hard mask layer 1302, (ii) creating a mold or stamp (not shown) with pattern features corresponding to the diffractive gratings 1110, (iii) bringing the mold into contact with the thin film 1304 and (iv) applying pressure to the mold to transfer the pattern features of the mold onto the thin film 1304.

[0106] As illustrated in FIG, 13B, an anisotropic etch can be performed to punch through the hard mask layer 1302 and the cover layer 1215 and etch a trench 1352 into the coating layer 1150 along y direction to form a first pattern 1350. The first pattern 1350 can include portionsAttorney Docket No. 40589-0293WO1of the cover layer 1215 on corresponding portions of the coating layer 1150. Tire portions of the cover layer 1215 can be, e.g., the second portions 1114 of FIGS. HA and 11B. The anisotropic etch can include Chlorine (Cl)-based dry etching or wet etching for the hard mask layer with Cr, following by Fluorine (F)-based Reactive Ion Etching (RIE) for initial punching through the cover layer 1215 (e.g., SiCh) and into the coating layer 1150. In some implementations, the residual thin-film layer 1304 from NIL process is removed, e.g., by O2, Ar, and He gases, after the anisotropic etch.

[0107] As illustrated in FIG. 13C, an isotropic etching can be performed to further etch into the coating layer 1150. Hie isotropic etch can undercut the cover layer 1215 by partially removing the corresponding portions of the coating layer 1150 under the portions of the cover layer 1215. The etching chemicals utilized for the isotropic etching can have a higher etching rate for the coating layer 1150 compared to the cover layer 1215. In some implementations, dry etching techniques are used at this isotropic etching step. Hie dry etching can be a one step or a two-step process where using high ion-flux density in ICP along with high pressures can create barrel shaped openings, as illustrated in FIG. 13C. Without limiting to any particular theory, high ICP power may result in a more chemical -based etching process, as the higher ion density may lead to a greater concentration of reactive species that interact with the material being etched. Alternatively, or additionally, high pressure and lower RIE power can be utilized during dry etching, which may create etch environments with shorter mean free path for ions to constantly target the sidewall. As noted above, during this dry etching process, the hard mask layer 1302 (e.g., Cr) can protect the cover layer 1215 (e.g., SiCh) from being attacked.

[0108] As illustrated in FIG. 13D, the hard mask layer 1302 can be stripped. The patterned portions of the coating layer 1150 (e.g., the first portions 1112 of the diffraction gratings 1110 of FIG. 11 A) and the patterned cover layer 1215 (e.g., the second portions 1114 of the diffraction gratings 1110 of FIG. 11 A) can form one or more diffraction gratings 1110, The diffraction gratings 1110 can have a “mushroom” shape. For example, a dimension 1128 (e.g., width) of a portion of the cover layer 1215 along X-direction can be greater than a dimension 112.4 (e.g., width) of a corresponding portion of the coating layer 1150 along X-direction.

[0109] Referring back to FIG. 11 A, each of the portions of the coating layer 1150 includes a top part 1112a, a bottom part 1112c and a middle part 1112b between the top part 1112a and the bottom part 1112c along Y -direction. In some implementations, during the isotropic etching process, the middle part 1112b of the portions of tire coating layer 1150 can be etched more compared to the top part 1112a and the bottom part 1112c. Therefore, a dimension 1124 of theAttorney Docket No. 40589-0293WO1middle part 1112b along X-direction can be smaller than a dimension 1126 of the top part 1112a or a dimension 1122 of the bottom part 1112c along the same direction.

[0110] In some implementations, the isotropic drying etching process described in reference to FIG. 13C has a higher etch rate along the vertical direction (e.g., Z direction) compared to a lateral direction (e.g., X direction). Therefore, a barrel shaped opening 1306 can be formed between adjacent first portions 1112 of the diffraction gratings 1110. For example, a spacing distance 1142 between middle parts 1112b of adjacent first portions 1112 along X-direction can be smaller than a height 1144 of one of the adjacent first portions 1112 along Y- direction.

[0111] FIGS. 14A-14D illustrate cross-section views of another example waveguide 1400 at various stages of a fabrication process, according to one or more implementations of the present disclosure. Tire example waveguide 1400 differs from the waveguide 1100 of FIGS. 11 A-11B and 13A-13D primarily in that the shape of the openings 1406 between adjacent first portions 1112 of diffraction gratings 1110. It is to be noted that some of the fabrication processes to form the waveguide 1400 (e.g., the processes illustrated in FIGS. 14 A, 14B and 14D) are the same or substantially similar to those illustrated in FIGS. 13 A, 13B and 13D. Descriptions for these processes are omitted below. It is further to be noted that although FIGS. 14A-14C illustrate the use of the hard mask layer 1302, it can be optional in these process steps.

[0112] In contrast to the waveguide 1100 shown in FIG. 13D with a barrel-shaped opening 1306 (e.g., its lateral dimension being smaller than its vertical dimension), the waveguide 1400 illustrated in FIGS. 14C and 14D can have a light-bulb-shaped opening 1406, where its lateral dimension along x axis can be greater than its vertical dimension along y axis. Variations in the shapes of the openings between adjacent, first portions 1112 can result from different isotropic etching processes. For example, the barrel-shaped opening 1306 (e.g., as illustrated in FIG. 13D) can be formed by isotropic dry etching techniques, while the light-bulb-shaped opening 1406 (e.g,, as illustrated in FIGS. 14C and 14D) can be formed by isotropic wet etching techniques.

[0113] In some implementations, isotropic wet etching chemicals used in FIG. 14C include sulfuric acid (H2SO4) with or without peroxymonosulfuric acid, hydrogen peroxide, water, for example. These wet etch chemistry' may remove the coating layer 1150 (e.g., TiO2) without attacking the cover layer (e.g., SiO2). In some implementations, sputtered TiCh (e.g., refractive index n-2.35 at a wavelength of 530nm) has an etch removal rate of 1 nm / min when using H2SO4 85%, H2SO510%, H2O 5% and H2O2 1% at 70 °C. This rate can be higher with more concentration of H2SO4 and higher bath temperatures. Without limiting to any particular theory, wet etching can have more uniform etching in all directions (both vertically andAttorney Docket No. 40589-0293WO1laterally) compared to dry etching, allowing it to remove more materials under the cover layer 1215. In some implementations, as illustrated in FIG. 14D, a spacing distance 1142 between middle parts 1112b of adjacent first portions 1112 of the diffraction gratings 1110 along X-direction is greater than a height 1144 of one of the adjacent first portions 1112 of the diffraction gratings 1110 along Y-direction.

[0114] It is to be noted that two structures with different grating pattern density are illustrated in FIGS. 14B, 14C and 14D. Diagram (a) of FIGS. 14B-14D illustrates a lower pattern density for diffraction gratings 1110, while diagram (b) of FIGS. 14B-14D illustrates a higher pattern density. The process to form diffraction gratings 1110 for these two pattern densities can be substantially similar. In some implementations, a higher partem density has a greater aspect ratio of the openings 1406 (e.g., the ratio of the height 1144 to the width 1142 of the openings 1406), while a lower pattern density has a lower aspect ratio, as illustrated in diagram (a) and diagram (b) of FIG. 14D.

[0115] FIG. 15 illustrates various example paterns of diffraction gratings fabricated using the techniques implemented in the present disclosure. As illustrated in FIG. 15, in addition to the binary patterns as shown in FIGS. 10A-11B, the diffraction gratings 1500 can have various other patterns with high nano pattern feature fidelity based on a glass substrate as described herein, e.g,, a glass substrate including one or more substances and a non-silica-based network former for the one or more substances. The glass substrate can be e.g., the glass substrate 1002 of FIGS. 10A, 10B and 12A-12C, or the glass substrate 1102 of FIGS. 11A, 11B, 13A-13D and 14A-14D. The diffraction gratings 1500 can be formed using the process techniques described above in reference to FIGS. 12A-14D. As shown in FIG. 15, the diffraction gratings 1500 can have a pattern (or structure), including without limitation to, pillar structures 1502, discontinuous lines with varying angles and / or pitch 1504, mixed lines meta structure 1506 (also called morph in some cases), lines to pillars (e.g., with blended boundaries) 1508, multidirectional blaze sawtooth pillar 1510, blaze sawtooth 1512, pillars and holes (e.g., 1:1 hole to pillar) 1514, mixed holes and lines meta structure 1516, slanted pillar 1518, or slanted lines and / or sharkfin 1520. It is to be noted that examples shown in FIG. 15 are not intended to be construed in a limited sense. Other patterns for the diffraction gratings 1500 can also be formed.

[0116] FIG. 16 illustrates a flowchart of an example process 1600 to form one or more diffraction gratings in a waveguide. The diffraction gratings can be, e.g., incoupling optical elements 1212, 1222, 1232 of FIGS. 9A-9C, outcoupling optical elements 282, 284, 286, 288,Attorney Docket No. 40589-0293WO1diffraction gratings 1010 of FIGS. 10A, 10B and 12C, the diffraction gratings 1110 of FIGS.11A, 1 IB, 13D and 14D, or the diffraction gratings 1500 of FIG. 15. The waveguide can be, e.g., waveguides 182, 184, 186, 188, 190 of FIGS. 6 and 7, waveguides 1210, 1220, and 1230 of FIGS. 9A-9C, the waveguide 1000 of FIGS. 10A, 10B and 12C, or the waveguide 1100 of FIGS. 11A, 11B, 13D and 14D.00117] At step 1602, a waveguide is provided. The waveguide includes: a glass substrate including one or more substances and a non-silica-based network former for the one or more substances, and a cover layer over the glass substrate. A refractive index of the cover layer is smaller than a refractive index of the glass substrate. The glass substrate can be, e.g., the glass substrate 1002 of FIGS. 10A, 10B and 12A-12C, or the glass substrate 1102 of FIGS. HA, 1 IB, 13A-13D and 14A-14D. The glass substrate can be a non-silica-based glass substrate that is made of non-silica-based glass. The non-silica-based network former can include at least one of Group 15 elements. The cover layer can be, e.g., the second portions 1014 of FIGS. 10A and JOB, the second portions 1114 of FIGS. HA and 1 IB, or the cover layer 1215 of FIGS. 12A-14D. In some implementations, the non-silica-based network former includes germanium (Ge), antimony (Sb), sulfur (S), selenium (Se), and / or tellurium (Te).

[0118] At step 1604, a mask layer is provided over the waveguide, the mask layer having a pattern corresponding to the one or more diffractive gratings, the pattern selectively exposing portions of the waveguide. The mask layer can be, e.g., the thin film 1304 of FIG. I3A or 14A.

[0119] At step 1606, the exposed portions of the waveguide is etched to define the one or more diffractive gratings, e.g., as illustrated in FIGS. I2A-14D.

[0120] In some implementations, the at least one of Group 15 elements includes at least one of Phosphorus or Bismuth.

[0121] In some implementations, the cover layer includes silicon dioxide (SiO2).

[0122] In some implementations, the refractive index of the cover layer is smaller than 1.5. The refractive index of the glass substrate is greater than the refractive index of the cover layer.

[0123] In some implementations, etching the exposed portions of the waveguide to define the one or more diffractive gratings includes: anisotropically etching the exposed portions of the waveguide along a vertical direction to form a first pattern, the first pattern including portions of the cover layer on corresponding portions of the glass substrate; and isotropically etching the first pattern to partially cut the corresponding portions of the glass substrate under the portions of the cover layer, e.g., as described in reference to FIGS. 12B and 12C. The first pattern can be, e.g., the first pattern 1251 of FIG. 12C.Attorney Docket No. 40589-0293WO1

[0124] In some implementations, a dimension of a portion of the portions of the cover layer along a first direction is greater than a dimension of a corresponding portion of the portions of the glass substrate along the first direction. The dimension of the portion of the portions of the cover layer can be, e.g., the dimension 1028 of the second portions 1014 of FIGS. 10 A, 10B and 12C, the dimension 1128 of the second portions 1114 of FIGS. 11A, 11B, 13C and 14C. " Die dimension of the corresponding portion of the portions of the glass substrate can be, e.g., the dimension 1024 of the middle part 1012b of the first portions 1012 of FIGS. 10A, 10B and 12C.

[0125] In some implementations, each of the portions of the glass substrate includes a top part, a bottom part and a middle part between the top part and the bottom part along a second direction perpendicular to the first direction. A dimension of the middle part along the first direction is smaller than a dimension of the top part along the first direction. The dimension of tire corresponding portion of the portions of the glass substrate along the first direction is defined by the dimension of the middle part of the portion of the portions of the glass substrate. The top part can be, e.g., the top part 1012a of the first portion 1012 of FIGS. 10A, 10B and 12C. The middle part can be, e.g., the middle part 1012b of the first portion 1012 of FIGS.10A, 10B and 12C. The bottom part can be, e.g., the bottom part 1012c of the first portion 1012 of FIGS. 10A, 10B and 12C. The dimension of the middle part can be, e.g., the dimension 1024 ofthe middle part 1012b ofthe first portions 1012 of FIGS. 10A, 10B and 12C. Hie dimension of the top part can be, e.g., the dimension 1026 of the top part 1012a of the first portions 1012 of FIGS. 10A, 10B and 12C.

[0126] In some implementations, the waveguide includes a coating layer between the glass substrate and the cover layer. A refractive index of the coating layer is greater than the refractive index ofthe cover layer and the refractive index of tire glass substrate. The coating layer can be, e.g., the coating layer 1150 of FIGS. 11A, 11B and 13A-14D. In some implementations, the coating layer includes titanium dioxide (TiO2).

[0127] In some implementations, the refractive index of the coating layer is greater than the refractive index of the glass substrate.

[0128] In some implementations, etching the exposed portions of the waveguide to define the one or more diffractive gratings includes: anisotropically etching the exposed portions of the waveguide along a vertical direction to fonn a first pattern, tire first pattern including portions of the cover layer on corresponding portions of the coating layer; and isotropically etching the first pattern to partially cut the corresponding portions of the coating layer under the portions ofthe cover layer. The first pattern can be, e.g., the first pattern 1350 of FIGS. 13B and 14B.Attorney Docket No. 40589-0293WO1

[0129] In some implementations, a dimension of a portion of the portions of the cover layer along a first direction is greater than a dimension of a corresponding portion of the portions of the coating layer along the first direction. The dimension of the corresponding portion of the portions of the coating layer can be, e.g., the dimension 1124 of the middle part 1112b of the first portions 1112 of FIGS. 11 A, 11B and 13C.

[0130] In some implementations, each of the portions of the coating layer includes a top part, a bottom part and a middle part between the top part and the bottom part along a second direction perpendicular to the first direction. A dimension of the middle part along the first direction is smaller than a dimension of the top part along the first direction. The dimension of the corresponding portion of the portions of the coating layer along the first direction is defined by the dimension of the middle part of the portion of the portions of the coating layer. The top part can be, e.g., the top part 1112a of the first portion 1112 of FIGS. 11A and 1 IB. The middle part can be, e.g., the middle part 1112b of the first portion 1112 of FIGS. 11A and 11B. The bottom part can be, e.g., the bottom part 1112c of the first portion 1112 of FIGS. 11A and 11B. The dimension of the middle part can be, e.g., the dimension 1124 of the middle part 1112b of the first portions 1112 of FIGS. 11A, 1 IB and 13C. The dimension of the top part can be, e.g., the dimension 1126 of the top part 1112a of the first portions 1112 of FIGS. HA, 11B and 13C.

[0131] In some implementations, isotropically etching the first pattern to partially cut the corresponding portions of the coating layer under the portions of the cover layer includes wet etching. A spacing distance between middle parts of adjacent portions of the portions of the coating layer along the first direction is greater than a height of one of the adjacent portions of the portions of the coating layer along the second direction. The spacing distance can be, e.g., the width 1142 of FIGS. HA, 11B, I3D and 14D. The height can be, e.g., the height 1144 of FIGS. HA, 11B, 13D and 14D.

[0132] In some implementations, the method includes: providing a hard mask layer between the cover layer and the mask layer, the hard mask layer having the pattern corresponding to the one or more diffractive gratings. Isotropically etching the first pattern to partially cut the corresponding portions of the coating layer under the portions of the cover layer includes dry' etching. A spacing distance between middle parts of adjacent portions of the portions of the coating layer along the first direction is smaller than a height of one of the adjacent portions of the portions of the coating layer along the second direction. The hard mask layer can be, e.g., the hard mask layer 1302 of FIGS. 13A-13C and 14A-14C. In some implementations, the hard mask layer includes Chromium (Cr).Attorney Docket No. 40589-0293WO1

[0133] In some implementations, providing the mask layer over the waveguide includes: performing a nanoimprinting process to form the pattern on the mask layer corresponding to the one or more diffractive gratings, as described above in reference to FIG. 13A.

[0134] In some implementations, the refractive index of the glass substrate is in a range between 1.7 and 2.3.00135] In some implementations, tire glass substrate has a density between 2.5 gram / cm3and 7.5 gram / cm3.

[0136] In some implementations, the glass substrate has a transmittance greater than 90% for 10 mm internal pathlength at visible wavelengths (e.g., from 440 nm to 700 nm). In some implementations, the glass substrate has a transmittance greater than 93% for 10 mm internal pathlength at visible wavelengths (e.g., from 440 nm to 700 nm).

[0137] In some implementations, a mole percentage of the network former in the glass substrate is less than 50%.

[0138] In some implementations, the one or more substances of the glass substrate include one or more of B2O3, Al2O3, ZrO2, Li2O, Na2O, K2O, MgO, CaO, SrO, BaO, ZnO, La2O3, Nb2O5, TiO2, HfO, and Sb2O3

[0139] In the foregoing specification, various specific embodiments have been described. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention. The specification and drawings are, accordingly, to be regarded in an illustrative rather than restrictive sense.

[0140] Indeed, it will be appreciated that the systems and methods of the disclosure each have several innovative aspects, no single one of which is solely responsible or required for the desirable attributes disclosed herein. The various features and processes described above may be used independently of one another, or may be combined in various ways. All possible combinations and subcombinations are intended to fall within the scope of this disclosure.

[0141] Certain features that are described in this specification in the context of separate embodiments also may be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment also may 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 claimed as such, one or more features from a claimed combination may in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination. No single feature or group of features is necessary or indispensable to each and every embodiment.Attorney Docket No. 40589-0293WO1

[0142] It will be appreciated that conditional language used herein, such as, among others, “can, ’’“could, ’’“might, ’’“may, ”“e.g.,” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other implementations do not include, certain features, elements and / or steps. Thus, such conditional language is not generally intended to imply that features, elements and / or steps are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without author input or prompting, whether these features, elements and / or steps are included or are to be performed in any particular embodiment. The terms “comprising, ’’“including, ’’“having,” and the like are synonymous and are used inclusively, in an open-ended fashion, and do not exclude additional elements, features, acts, operations, and so forth. Also, the term “or” is used in its inclusive sense (and not in its exclusive sense) so that when used, for example, to connect a list of elements, the term “or” means one, some, or all of the elements in the list. In addition, the articles “a,”“an,” and “the” as used in this application and the appended claims are to be construed to mean “one or more” or “at least one” unless specified otherwise. Similarly, while operations may be depicted in the drawings in a particular order, it is to be recognized that such operations need not be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Further, the drawings may schematically depict one more example processes in the form of a flowchart. However, other operations that are not depicted may be incorporated in the example methods and processes that are schematically illustrated. For example, one or more additional operations may be performed before, after, simultaneously, or between any of the illustrated operations. Additionally, the operations may be rearranged or reordered in other implementations. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system 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 may generally be integrated together in a single software product or packaged into multiple software products. Additionally, other implementations are within the scope of the following claims. In some cases, the actions recited in the claims may be performed in a different order and still achieve desirable results.

[0143] The following numbered paragraphs are non-limiting examples of various embodiments of the present disclosure.

[0144] Paragraph 1. A method of fabricating one or more diffractive gratings, including: providing a waveguide including: a glass substrate comprising one or more substances and aAttorney Docket No. 40589-0293WO1non-silica-based network former for the one or more substances, and a cover layer over the glass substrate, a refractive index of the cover layer being smaller than a refractive index of the glass substrate; providing a mask layer over the waveguide, the mask layer having a pattern corresponding to the one or more diffractive gratings, the pattern selectively exposing portions of the waveguide; and etching the exposed portions of the waveguide to define the one or more diffractive gratings.

[0145] Paragraph 2. The method of paragraph 1, where the non-silica-based network former comprises at least one of Group 15 elements.00146] Paragraph 3. The method of paragraph 2, where the at least one of Group 15 elements comprises at least one of phosphorus (P) or bismuth (Bi).

[0147] Paragraph 4. The method of any one of paragraphs 1 to 3, where the refractive index of the cover layer is smaller than 1.5, and the refractive index of the glass substrate is greater than the refractive index of the cover layer.

[0148] Paragraph 5. The method of any one of paragraphs 1 to 4, where etching the exposed portions of the waveguide to define the one or more diffractive gratings includes: anisotropically etching the exposed portions of the waveguide along a vertical direction to form a first pattern, the first pattern including portions of the cover layer on corresponding portions of the glass substrate; and isotropically etching the first pattern to partially cut the corresponding portions of the glass substrate under the portions of the cover layer.

[0149] Paragraph 6. The method of paragraph 5, where a dimension of a portion of the portions of the cover layer along a first direction is greater than a dimension of a corresponding portion of the portions of the glass substrate along the first direction.

[0150] Paragraph 7. The method of paragraph 6, where each of the portions of the glass substrate includes a top part, a bottom part and a middle part between the top part and the bottom part along a second direction perpendicular to the first direction, and a dimension of the middle part along the first direction is smaller than a dimension of the top part along the first direction, and where the dimension of the corresponding portion of the portions of the glass substrate along the first direction is defined by the dimension of the middle part of the portion of the portions of the glass substrate.

[0151] Paragraph 8. The method of any one of paragraphs 1 to 7, where the waveguide includes a coating layer between the glass substrate and the cover layer, a refractive index of the coating layer being greater than the refractive index of the cover layer.

[0152] Paragraph 9. The method of paragraph 8, where etching the exposed portions of the waveguide to define the one or more diffractive gratings includes: anisotropically etching theAttorney Docket No. 40589-0293WO1exposed portions of the waveguide along a vertical direction to form a first pattern, the first pattern including portions of the cover layer on corresponding portions of the coating layer; and isotropically etching the first pattern to partially cut the corresponding portions of the coating layer under the portions of the cover layer.00153] Paragraph 10. The method of paragraph 9, where a dimension of a portion of the portions of the cover layer along a first direction is greater than a dimension of a corresponding portion of the portions of the coating layer along the first direction.

[0154] Paragraph 11. The method of paragraph 10, where each of the portions of the coating layer includes a top part, a bottom part, and a middle part between the top part and the bottom part along a second direction perpendicular to the first direction, and a dimension of the middle part along the first direction is smaller than a dimension of the top part along the first direction, and where the dimension of the corresponding portion of the portions of the coating layer along tire first direction is defined by the dimension of the middle part of the portion of the portions of the coating layer.

[0155] Paragraph 12. The method of paragraph 11, where isotropically etching the first pattern to partially cut the corresponding portions of the coating layer under the portions of the cover layer includes wet etching, and where a spacing distance between middle parts of adjacent portions of the portions of the coating layer along the first direction is greater than a height of one of the adjacent portions of the portions of the coating layer along the second direction.

[0156] Paragraph 13. The method of paragraph 11 or 12, including: providing a hard mask layer between the cover layer and the mask layer, the hard mask layer having the pattern corresponding to the one or more diffractive gratings, where isotropically etching the first pattern to partially cut the corresponding portions of the coating layer under the portions of the cover layer includes dry etching, and where a spacing distance between middle parts of adjacent portions of the portions of the coating layer along the first direction is smaller than a height, of one of the adjacent portions of the portions of the coating layer along the second direction.

[0157] Paragraph 14. The method of paragraph 13, where the hard mask layer includes at least one of chromium (Cr) or Nickel (Ni).

[0158] Paragraph 15. The method of any one of paragraphs 8 to 14, where the coating layer includes at least one of titanium dioxide (TiO2), niobium pentoxide (Nb2O5), tantalum pentoxide (Ta2O5), hafnium dioxide (HfO2), silicon nitride (Si3N4), or silicon carbide (SiC).

[0159] Paragraph 16. Tire method of any one of paragraphs 8 to 15, where a material of the coating layer is different from a material of the glass substrate.Attorney Docket No. 40589-0293WO1

[0160] Paragraph 17. The method of any one of paragraphs 1 to 16, where providing the mask layer over the waveguide includes: performing a nanoimprinting process to form the pattern on the mask layer corresponding to the one or more diffractive gratings.

[0161] Paragraph 18. Hie method of any one of paragraphs 1 to 17, where the refractive index of the glass substrate is in a range between 1.7 and 2.3.

[0162] Paragraph 19. The method of any one of paragraphs 1 to 18, where the glass substrate has a density between 2.5 gram / cm3and 7.5 gram / cm3.

[0163] Paragraph 20. The method of any one of paragraphs 1 to 19, where the glass substrate has a transmittance greater than 90% for 10 mm internal pathlength at a visible wavelength.

[0164] Paragraph 21. Hie method of any one of paragraphs 1 to 20, where a mole percentage of the non-silica-based network former in the glass substrate is less than 50%.

[0165] Paragraph 22. The method of any one of paragraphs 1 to 21, where the one or more substances of the glass substrate include one or more of B2O3, AI2O3, ZrO2, Li2O, Na2O, K2O, MgO, CaO, SrO, BaO, ZnO, La2O3, Nb2O5, TiO2, HfO, and Sb2O3

[0166] Paragraph 23. A device, including: a waveguide including a glass substrate, the glass substrate including one or more substances and a non-silica-based network former for the one or more substances, tire waveguide defining a diffractive grating, the diffractive grating including: a plurality of first portions with a first refractive index; and a plurality of second portions with a second refractive index smaller than the first refractive index, each of the plurality of second portions being on a respective first portion of the plurality of first portions along a first direction, where a dimension of a second portion of the plurality of second portions along a second direction perpendicular to the first direction is greater than a dimension of a respective first portion of the plurality of first portions along the second direction.

[0167] Paragraph 24. Hie device of paragraph 23, where each of the plurality of first portions includes a top part, a bottom part, and a middle part between the top part and the bottom part along the first direction, and a dimension of the middle part along the second direction is smaller than a dimension of the top part along the second direction, and where the dimension of the respective first portion of the plurality of first portions is defined by the dimension of the middle part of the respective first portion of the plurality of first portions.

[0168] Paragraph 25. The device of paragraph 23 or 24, where the non-silica-based network former includes at least one of Group 15 elements.

[0169] Paragraph 26. The device of paragraph 25, where the at least, one of Group 15 elements comprises at least one of phosphorus (P) or bismuth (Bi).Attorney Docket No. 40589-0293WO1

[0170] Paragraph 27. The device of any one of paragraphs 23 to 26. where the second refractive index is smaller than 1.5.

[0171] Paragraph 28. The device of any one of paragraphs 23 to 27, where the glass substrate includes the plurality of first portions.

[0172] Paragraph 29. The device of any one of paragraphs 23 to 28, where the waveguide includes a coating layer on the glass substrate, and the coating layer includes the plurality of first portions.

[0173] Paragraph 30. The device of paragraph 29, where a spacing distance between middle parts of adjacent first portions of the plurality of first portions along the second direction is greater than a height of one of the adjacent first portions of the plurality of first portions along the first direction.

[0174] Paragraph 31. The device of paragraph 29 or 30, where a spacing distance between middle parts of adj acent first portions of tire plurality of first portions along the second direction is smaller than a height of one of the adjacent first portions of the plurality of first, portions along the first direction.

[0175] Paragraph 32. The device of any one of paragraphs 23 to 31, where a height of the diffractive grating along the first direction is in a range between 5 nm to 500 nm.

[0176] Paragraph 33. The device of any one of paragraphs 23 to 32, where the glass substrate has a refractive index between 1.7 and 2.3.

[0177] Paragraph 34. The device of any one of paragraphs 23 to 33, where the glass substrate has a density between 2,5 gram / cm3and 7.5 gram / cm,

[0178] Paragraph 35. The device of any one of paragraphs 23 to 34, where the glass substrate has a transmittance greater than 90% for 10 mm internal pathlength at a visible wavelength.

[0179] Paragraph 36. The device of any one of paragraphs 23 to 35, where a mole percentage of the non-silica-based network former in the glass substrate is less than 50%.

[0180] Paragraph 37. Tire device of any one of paragraphs 23 to 36, where the one or more substances of the glass substrate include one or more of B2O3, AI2O3, ZrO2, Li2O, Na2O, K2O, MgO, CaO, SrO, BaO, ZnO, La2O3, Nb2O5, TiO2, HfO, and Sb2O3

[0181] Paragraph 38. The device of any one of paragraphs 23 to 37, where a pattern of the diffractive grating comprises at least one of a sawtooth blaze, a multi-step blaze, a slanted sharkfin, a meta structure, continuous lines, discontinuous lines, or isolated structures.

[0182] Paragraph 39. A device, including: a light source configured to emit a light beam; and a waveguide including a glass substrate, the glass substrate including one or more substances and a non-silica-based network former for the one or more substances, where the waveguideAttorney Docket No. 40589-0293WO1includes an incoupling diffractive optical element (DOE) and an outcoupling DOE, the incoupling DOE being configured to couple the light beam form the light source toward the outcoupling DOE, where at least one of the incoupling DOE and the outcoupling DOE includes: a plurality of first portions with a first refractive index, the first portion including a top part, a bottom part, and a middle part between the top part and the bottom part along a first direction, a dimension of the middle part along a second direction perpendicular to the first direction being smaller than a dimension of the top part along the second direction; and a plurality of second portions with a second refractive index smaller than the first refractive index, each of the plurality' of second portions being on the top part of a respective one of the plurality of first portions, where a dimension of a second portion of the plurality of second portions is greater than the dimension of the middle part of a corresponding first portion of the plurality of first portions.

[0183] Accordingly, the claims are not intended to be limited to the embodiments shown herein, but are to be accorded the widest scope consistent with this disclosure, the principles and the novel features disclosed herein.

Claims

Attorney Docket No. 40589-0293WO1CLAIMS1. A method of fabricating one or more diffractive gratings, the method comprising: providing a waveguide comprising:a glass substrate comprising one or more substances and a non-silica-based network former for the one or more substances, anda cover layer over the glass substrate, a refractive index of the cover layer beingsmaller than a refractive index of the glass substrate;providing a mask layer over the waveguide, the mask layer having a pattern corresponding to the one or more diffractive gratings, the pattern selectively exposing portions of the waveguide; andetching the exposed portions of the waveguide to define the one or more diffractive gratings.

2. The method of claim 1, wherein the non-silica-based network former comprises at least one of Group 15 elements.

3. The method of claim 2, wherein the at least one of Group 15 elements comprises at least one of phosphorus (P) or bismuth (Bi).

4. The method of claim 1, wherein the refractive index of the cover layer is smaller than 1.5, and the refractive index of the glass substrate is greater than the refractive index of the cover layer.

5. The method of claim 1, wherein etching the exposed portions of the waveguide to define the one or more diffractive gratings comprises:anisotropically etching the exposed portions of tire waveguide along a vertical direction to form a first pattern, the first pattern comprising portions of the cover layer on corresponding portions of the glass substrate; andisotropically etching the first pattern to partially cut the corresponding portions of the glass substrate under the portions of the cover layer.Attorney Docket No. 40589-0293WO16. The method of claim 5, wherein a dimension of a portion of the portions of the cover layer along a first direction is greater than a dimension of a corresponding portion of the portions of the glass substrate along the first direction.

7. The method of claim 6, wherein each of the portions of the glass substrate comprises a top part, a bottom part and a middle part between the top part and the bottom part along a second direction perpendicular to the first directi on, and a dimension of the middle part along the first direction is smaller than a dimension of the top part along the first direction, and wherein the dimension of the corresponding portion of the portions of the glass substrate along the first direction is defined by the dimension of the middle part of the portion of the portions of the glass substrate.

8. The method of claim 1, wherein the waveguide comprises a coating layer between the glass substrate and the cover layer, a refractive index of the coating layer being greater than the refractive index of the cover layer.

9. The method of claim 8, wherein etching the exposed portions of the waveguide to define the one or more diffractive gratings comprises:anisotropically etching the exposed portions of the waveguide along a vertical direction to form a first pattern, the first pattern comprising portions of the cover layer on corresponding portions of the coating layer; andisotropically etching the first pattern to partially cut the corresponding portions of the coating layer under the portions of the cover layer.

10. The method of claim 9, wherein a dimension of a portion of the portions of the cover layer along a first direction is greater than a dimension of a corresponding portion of the portions of the coating layer along the first direction.

11. The method of claim 10, wherein each of the portions of the coating layer comprises a top part, a bottom part, and a middle part between the top part and the bottom part along a second direction perpendicular to the first direction, and a dimension of the middle part along the first direction is smaller than a dimension of the top part along the first direction, andAttorney Docket No. 40589-0293WO1wherein the dimension of the corresponding portion of the portions of the coating layer along the first direction is defined by the dimension of the middle part of the portion of the portions of the coating layer.

12. The method of claim 11, wherein isotropically etching the first pattern to partially cut the corresponding portions of the coating layer under the portions of the cover layer comprises wet etching, andwherein a spacing distance between middle parts of adjacent portions of the portions of the coating layer along the first direction is greater than a height of one of the adjacent portions of the portions of the coating layer along the second direction.

13. The method of claim 11, comprising:providing a hard mask layer between the cover layer and the mask layer, the hard mask layer having the pattern corresponding to the one or more diffractive gratings, wherein isotropically etching the first pattern to partially cut the corresponding portions of the coating layer under the portions of the cover layer comprises dry etching, and wherein a spacing distance between middle parts of adjacent portions of the portions of the coating layer along the first direction is smaller than a height of one of the adjacent portions of the portions of the coating layer along the second direction.

14. The method of claim 13, wherein the hard mask layer comprises at least one of chromium (Cr) or Nickel (Ni).

15. The method of claim 8, wherein the coating layer comprises at least one of titanium dioxide (TiO₂), niobium pentoxide (Nb₂O₅), tantalum pentoxide (Ta₂O₅), hafnium dioxide (HfO₂), silicon nitride (Si₃N₄), or silicon carbide (SiC).

16. The method of claim 8, wherein a material of the coating layer is different from a material of the glass substrate.

17. The method of claim 1, wherein providing the mask layer over the waveguide comprises:performing a nanoimprinting process to form the pattern on the mask layer corresponding to the one or more diffractive gratings.Attorney Docket No. 40589-0293WO118. The method of claim 1, wherein the refractive index of the glass substrate is in a range between 1.7 and 2.3.

19. The method of claim 1, wherein the glass substrate has a density between 2.5 gram / cm3and 7.5 gram / cm3.

20. The method of claim 1, wherein the glass substrate has a transmittance greater than 90% for 10 mm internal pathlength at a visible wavelength.

21. The method of claim 1, wherein a mole percentage of the non-silica-based network former in the glass substrate is less than 50%.

22. The method of claim 1, wherein the one or more substances of the glass substrate comprise one or more of B2O3, AI2O3, Z1O2, L12O, Na2O, K2O, MgO, CaO, SrO, BaO, ZnO, La2O3, Nb2O5, TiO2, HfO2, and Sb2O3.

23. A device, comprising:a waveguide comprising a glass substrate, the glass substrate comprising one or more substances and a non-silica-based network former for the one or more substances, the waveguide defining a diffractive grating, the diffractive grating comprising:a plurali ty of first portions with a first refractive index; anda plurality of second portions with a second refractive index smaller than the firstrefractive index, each of the plurality of second portions being on a respective first portion of the plurality of first portions along a first direction,wherein a dimension of a second portion of the plurality of second portions alonga second direction perpendicular to the first direction is greater than a dimension of a respective first portion of the plurality of first portions along the second direction.

24. The device of claim 23, wherein each of the plurality of first portions comprises a top part, a bottom part and a middle part between the top part and the bottom part along the firstAttorney Docket No. 40589-0293WO1direction, and a dimension of the middle part along the second direction is smaller than a dimension of the top part along the second direction, andwherein the dimension of the respective first portion of the plurality’ of first portions is defined by the dimension of the middle part of the respective first portion of the plurality of first portions.

25. The device of claim 23, wherein the non-silica-based network former comprises at least one of Group 15 elements.

26. The device of claim 25, wherein the at least one of Group 15 elements comprises at least one of phosphorus (P) or bismuth (Bi).

27. The device of claim 23, wherein the second refractive index is smaller than 1.5.

28. The device of claim 23, wherein the glass substrate comprises the plurality of first portions.

29. The device of claim 23, wherein the waveguide comprises a coating layer on the glass substrate, the coating layer comprises the plurality of first portions.

30. The device of claim 29, wherein a spacing distance between middle parts of adjacent first portions of the plurality of first portions along the second direction is greater than a height of one of the adjacent first portions of the plurality of first portions along the first direction.

31. The device of claim 29, wherein a spacing distance between middle parts of adjacent first portions of the plurality of first portions along the second direction is smaller than a height of one of the adjacent first portions of the plurality of first portions along the first direction.

32. The device of claim 23, wherein a height of the diffractive grating along the first direction is in a range between 5 nm to 500 nm.Attorney Docket No. 40589-0293WO133. The device of claim 23, wherein the glass substrate has a refractive index between 1.7 and 2.3.

34. The device of claim 23, wherein the glass substrate has a density between 2.5 gram / cm3and 7.5 gram / cm3.

35. The device of claim 23, wherein the glass substrate has a transmittance greater than 90% for 10 mm internal pathlength at a visible wavelength.

36. The device of claim 23, wherein a mole percentage of the non-silica-based network former in the glass substrate is less than 50%.

37. The device of claim 23, wherein the one or more substances of the glass substrate comprise one or more of B2O3, AI2O3, Z1O2, L12O, Na2O, K2O, MgO, CaO, SrO, BaO, ZnO, La2O3, Nb2O5, TiO2, HfO2, and Sb2O3.

38. The device of claim 23, wherein a pattern of the diffractive grating comprises at least one of a sawtooth blaze, a multi-step blaze, a slanted sharkfin, a meta structure, continuous lines, discontinuous lines, or isolated structures.

39. A device, comprising:a light source configured to emit a light beam; anda waveguide comprising a glass substrate, the glass substrate comprising one or more substances and a non-silica-based network former for the one or more substances, wherein the waveguide comprises an incoupling diffractive optical element (DOE) and an outcoupling DOE, the incoupling DOE being configured to couple the light beam form the light source toward the outcoupling DOE,wherein at least one of the incoupling DOEs and the outcoupling DOE comprises: a plurality of first portions with a first refractive index, the first portion comprising a top part, a bottom part, and a middle part between the top part and the bottom part along a first direction, a dimension of the middle part along a second direction perpendicular to the first direction being smaller than a dimension of the top part along the second direction; andAttorney Docket No. 40589-0293WO1a plurality of second portions with a second refractive index smaller than the firstrefractive index, each of the plurality of second portions being on the top part of a respective one of the plurality of first portions,wherein a dimension of a second portion of the plurality of second portions is greater than the dimension of the middle part of a corresponding first portion of the plurality of first portions.

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