WO2023101934A1

WO2023101934A1 - Waveguides for displays constructed from a combination of flat and curved surfaces

Info

Publication number: WO2023101934A1
Application number: PCT/US2022/051169
Authority: WO
Inventors: Daniel Adema; Timothy Paul Bodiya; Shreyas Potnis; Ido Raveh
Original assignee: Google Llc
Priority date: 2021-12-02
Filing date: 2022-11-29
Publication date: 2023-06-08

Abstract

A waveguide (208) includes a first section (502-1, 802-1) between an input coupler (218) and an exit pupil expander (222). The first section includes a non-flat configuration, such as an angled configuration or a curved configuration. The waveguide further includes a second section (502-2, 802-2) between the exit pupil expander and an output coupler (220). The second section includes a substantially flat configuration.

Description

WAVEGUIDES FOR DISPLAYS CONSTRUCTED FROM A COMBINATION OF FLAT AND CURVED SURFACES

BACKGROUND

[0001] In HMDs, light from an image source is coupled into a lightguide substrate, generally referred to as a waveguide, by an optical input coupling element, such as an incoupling grating (i.e., an “input coupler”), which can be formed on a surface, or multiple surfaces, of the substrate or disposed within the substrate. Once the light beams have been coupled into the waveguide, the light beams are “guided” through the substrate, typically by multiple instances of total internal reflection (TIR) or by a coated surface(s). The guided light beams are then directed out of the waveguide by an output optical coupling (i.e., an “output coupler”), which can also take the form of an optical grating. The output coupler directs the light at an eye relief distance from the waveguide, forming an exit pupil within which a virtual image generated by the image source can be viewed by a user of the display device. In many instances, an exit pupil expander, which can also take the form of an optical grating, is arranged in an intermediate stage between the input coupler and output coupler to receive light that is coupled into the waveguide by the input coupler, expand the light, and redirect the light towards the output coupler.

SUMMARY OF EMBODIMENTS

[0002] In accordance with one aspect, a waveguide includes a first section between an input coupler and an exit pupil expander. The first section includes a non-flat configuration. The waveguide further includes a second section between the exit pupil expander and an output coupler. The second section includes a substantially flat configuration.

[0003] In at least some embodiments, the non-flat configuration includes one of a curved configuration or an angled configuration. The non-flat configuration includes one of a curved configuration or an angled configuration. The angled configuration indicates that the first section includes a non-zero angle relative to at least one of the second section, the input coupler, the exit pupil expander, or the output coupler.

[0004] In at least some embodiments, the waveguide further includes a third section between the output coupler and an edge of the waveguide opposite the input coupler. The third section includes one of a flat configuration or a non-flat configuration. The non-flat configuration including one a curved configuration or an angled configuration. The angled configuration indicates that the third section includes a non-zero angle relative to at least one of the first section, the second section, the input coupler, the exit pupil expander, or the output coupler.

[0005] In at least some embodiments, the waveguide further includes a fourth section between the input coupler and an edge of the waveguide opposite the output coupler. The fourth section includes one of a flat configuration or a non-flat configuration. The non-flat configuration includes one of a curved configuration or an angled configuration. The angled configuration indicates that the fourth section includes a non-zero angle relative to at least one of the first section, the second section, the third section, the input coupler, the exit pupil expander, or the output coupler.

[0006] In at least some embodiments, the input coupler includes at least one of a onedimensional grating or a two-dimensional grating. The exit pupil expander and the output coupler, in at least some embodiments, are combined in a single grating.

[0007] In accordance with another aspect, a wearable head-mounted display system includes an image source to project light including an image, at least one lens element, and the waveguide according to one or more embodiments described herein.

[0008] In at least some embodiments, the input coupler includes at least one of a onedimensional grating or a two-dimensional grating. The exit pupil expander and the output coupler, in at least some embodiments, are combined in a single grating.

[0009] In accordance with a further aspect, a method includes forming a first section of a waveguide between an input coupler and an exit pupil expander. The first section including a non-flat configuration. The non-flat configuration including one of a curved configuration or an angled configuration, the angled configuration indicating that the first section comprises a non-zero angle relative to at least one of the second section, the input coupler, the exit pupil expander, or an output coupler. The method further includes forming a second section between the exit pupil expander and an output coupler. The second section includes a substantially flat configuration.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The present disclosure may be better understood, and its numerous features and advantages made apparent to those skilled in the art by referencing the accompanying drawings. The use of the same reference symbols in different drawings indicates similar or identical items. [0011] FIG. 1 shows an example display system with an integrated laser projection system in accordance with some embodiments.

[0012] FIG. 2 shows a block diagram of a laser projection system that projects laser light representing images onto the eye of a user via a display system, such as the display system of FIG. 1 , in accordance with some embodiments.

[0013] FIG. 3 shows an example of light propagation within a waveguide implementing a one-dimensional grating in accordance with some embodiments.

[0014] FIG. 4 shows an example of light propagation within a waveguide implementing a two-dimensional grating in accordance with some embodiments.

[0015] FIG. 5 shows the waveguide of FIG. 3 embedded in the lens element of a display system and comprising a plurality of sections configured in accordance with some embodiments.

[0016] FIG. 6 shows a top view of the waveguide embedded in the lens element of FIG. 5 based on a first waveguide configuration in accordance with some embodiments.

[0017] FIG. 7 shows a top view of the waveguide embedded in the lens element of FIG. 5 based on a second waveguide configuration in accordance with some embodiments.

[0018] FIG. 8 shows the waveguide of FIG. 4 embedded in lens element of a display system and comprising a plurality of sections configured in accordance with some embodiments.

[0019] FIG. 9 shows a top view of the waveguide embedded in the lens element of FIG. 8 based on a third waveguide configuration in accordance with some embodiments.

[0020] FIG. 10 shows a top view of the waveguide embedded in the lens element of FIG. 8 based on a fourth waveguide configuration in accordance with some embodiments.

[0021] FIG. 11 is a flow diagram illustrating an overall example method of forming a waveguide in accordance with some embodiments.

DETAILED DESCRIPTION

[0022] HMDs and other near-eye display devices have multiple practical and leisure applications, but the development and adoption of wearable electronic display devices have been limited by the optics, aesthetics, manufacturing process, thickness, field of view, and prescription lens limitations of the optical systems used to implement existing display devices. For example, many conventional examples of HMDs implement planar/flat waveguides in an attempt to achieve the maximum optical performance of the waveguide. However, embedding a planar waveguide into a curved lens typically results in a lens configuration that is very bulky and unnatural looking on a user's face when compared to the sleeker and more streamlined look of typical curved eyeglass and sunglass lenses. As such, curved waveguide architectures have been developed to, among other things, overcome the constraints placed on lens and frame design for HMDs by planar waveguides. Curved waveguides conform better to the curvature of a lens when compared to planar waveguides and allow for thinner lenses to be implemented within an HMD. However, the non-parallel or non-flat surfaces of a curved waveguide tend to propagate light at different angles, thereby reducing the optical performance of the waveguide. For example, the display information represented by the light can be deformed, and artifacts, such as ghosting, can be introduced into the displayed images.

[0023] Accordingly, described herein are example waveguide configurations/architectures that overcome the light deformation and artifact issues experienced by conventional curved waveguides. As described in greater detail below, a waveguide is embedded within a curved lens, such as an ophthalmic lens, of an HMD or other near-eye display device according to the waveguide configurations described herein. The waveguide includes an input coupler, an exit pupil expander, and an output coupler. In a first configuration, the waveguide comprises a plurality of planar/flat piecewise sections. As used herein, “planar” and “flat” sections refer to sections of the waveguide that are non-curved and straight. A first piecewise section of the waveguide is situated between the input coupler and the exit pupil expander and comprises an angled configuration. For example, the first piecewise section comprises a first sub-section and a second sub-section that are angled relative to each other. In another example, the first piecewise section comprises at least one section that is angled with respect to another piecewise section of the waveguide situated before the input coupler. Angling the first piecewise section of the waveguide allows the first piecewise section of the waveguide to better conform to the curvature of the lens and further allows the light rays to bend as a result of the light rays passing through two flat surfaces at different angles. A second piecewise section of the waveguide situated between the exit pupil expander and the output coupler comprises a flat configuration. Stated differently, the angle of the second piecewise section of the waveguide does not vary between the exit pupil expander and the output coupler. A third piecewise section of the waveguide situated after the output coupler comprises a flat or angled configuration. For example, the third piecewise section comprises a first sub-section and a second sub-section that are angled relative to each other. In another example, the third piecewise section comprises at least one section that is angled with respect to the second piecewise section. In yet another example, the third piecewise section comprises a flat configuration, so the angle along the third piecewise section does not vary. It should be understood that, in at least some embodiments, the first waveguide configuration comprises one or more piecewise sections situated before the input coupler that are flat or angled. It should be further understood that the first waveguide configuration can include additional piecewise sections, wherein one or more of the piecewise sections of the waveguide can include multiple sub-sections.

[0024] In a second configuration, the waveguide is comprised of a plurality of piecewise sections wherein one or more piecewise sections are curved, and at least one of the piecewise sections is flat. For example, a first piecewise section situated between the input coupler and the exit pupil expander comprises a curved configuration. Here, a “curved” configuration refers to a non-flat configuration that bends in a smooth continuous way without sharp angles compared to an “angled” configuration, which has two straight sections of the waveguide that meet at a common point. Similar to the first waveguide configuration, curving the first piecewise section of the waveguide allows the waveguide to better conform to the curvature of the lens and further allows the light rays to bend as they travel within the volume defined by the curved surface. In another example, the first piecewise section comprises at least one curved sub-section and at least one flat sub-section. The flat section or subsection, in at least some embodiments, is angled with respect to another piecewise section of the waveguide situated before the input coupler. Similar to the first waveguide configuration, a second piecewise section of the waveguide situated between the exit pupil expander and the output coupler comprises a flat configuration. Stated differently, the angle of the second piecewise section of the waveguide does not vary between the exit pupil expander and the output coupler. A third piecewise section of the waveguide situated after the output coupler comprises a curved, flat, or angled configuration. For example, the third piecewise section comprises a first sub-section and a second sub-section that are angled relative to each other. In another example, the third piecewise section comprises at least one section that is angled with respect to the second piecewise section. In yet another example, the third piecewise section comprises a flat configuration such that the angle along the third piecewise section does not vary. It should be understood that, in at least some embodiments, the second waveguide configuration comprises one or more sections situated before the input coupler that are curved, flat, or angled. It should be further understood that the second waveguide configuration can include additional piecewise sections, wherein one or more of the piecewise sections of the waveguide can include multiple sub-sections.

[0025] The first piecewise section of the waveguide is angled or curved in the first and second configurations, respectively, whereas the second piecewise section is flat because any deformation caused during light travel between the input coupler and the exit pupil expander is common to all outcoupling locations of the output coupler. Therefore, a common correction can be applied by the HMD to the display information for all exit pupils. In contrast, any deformations caused during light travel between the exit pupil expander and the output coupler are varied across outcoupling locations of the output coupler, and correction of the deformations is specific for each exit pupil. By implementing a second piecewise section between the exit pupil expander and the output coupler having a flat configuration, deformations in the light traveling in this waveguide area are reduced or eliminated. As such, the waveguide configurations described herein allow a waveguide to be embedded within a curved lens of an HMD with reduced thickness compared to conventional planar waveguides and with increased optical performance compared to conventional curved waveguides.

[0026] It should be noted that, although some embodiments of the present disclosure are described and illustrated with reference to a particular example near-eye display system in the form of a wearable head-mounted display, it will be appreciated that the apparatuses and techniques of the present disclosure are not limited to this particular example, but instead may be implemented in any of a variety of display systems using the guidelines provided herein.

[0027] FIG. 1 illustrates an example display system 100 capable of implementing one or more of the waveguide configurations described herein. It should be understood that the waveguide configurations of one or more embodiments are not limited to display system 100 of FIG. 1 and apply to other display systems. In at least some embodiments, the display system 100 comprises a support structure 102 that includes an arm 104, which houses a laser projection system configured to project images toward the eye of a user such that the user perceives the projected images as being displayed in a field of view (FOV) area 106 of a display at one or both of lens elements 108, 110. In the depicted embodiment, the display system 100 is a near-eye display system in the form of an HMD that includes the support structure 102 configured to be worn on the head of a user and has a general shape and appearance of an eyeglasses frame. The support structure 102 includes various components to facilitate the projection of such images toward the eye of the user, such as a laser projector, an optical scanner, and a waveguide. In at least some embodiments, the support structure 102 further includes various sensors, such as one or more front-facing cameras, rear-facing cameras, other light sensors, motion sensors, accelerometers, and the like. The support structure 102 further can include one or more radio frequency (RF) interfaces or other wireless interfaces, such as a Bluetooth(TM) interface, a Wireless Fidelity (WiFi) interface, and the like.

[0028] Further, in at least some embodiments, the support structure 102 includes one or more batteries or other portable power sources for supplying power to the electrical components of the display system 100. In at least some embodiments, some or all of these components of the display system 100 are fully or partially contained within an inner volume of support structure 102, such as within the arm 104 in region 112 of the support structure 102. It should be noted that while an example form factor is depicted, it will be appreciated that in other embodiments, the display system 100 may have a different shape and appearance from the eyeglasses frame depicted in FIG. 1 .

[0029] One or both of the lens elements 108, 110 are used by the display system 100 to provide an augmented reality (AR) or a mixed reality (MR) display in which rendered graphical content is superimposed over or otherwise provided in conjunction with a real-world view as perceived by the user through the lens elements 108, 110. For example, laser light used to form a perceptible image or series of images may be projected by a laser projector of the display system 100 onto the eye of the user via a series of optical elements, such as a waveguide formed at least partially in the corresponding lens element, one or more scan mirrors, and one or more optical relays. Thus, one or both of the lens elements 108, 110 include at least a portion of a waveguide that routes display light received by an input coupler, or multiple input couplers, of the waveguide to an output coupler of the waveguide, which outputs the display light toward an eye of a user of the display system 100. The display light is modulated and scanned onto the eye of the user such that the user perceives the display light as an image. In addition, each of the lens elements 108, 110 is sufficiently transparent to allow a user to see through the lens elements to provide a field of view of the user’s real-world environment such that the image appears superimposed over at least a portion of the real-world environment.

[0030] In at least some embodiments, the projector is a matrix-based projector, a digital light processing-based projector, a scanning laser projector, or any combination of a modulative light source such as a laser or one or more light-emitting diodes (LEDs) and a dynamic reflector mechanism such as one or more dynamic scanners or digital light processors. The projector, in at least some embodiments, includes multiple laser diodes (e.g., a red laser diode, a green laser diode, and a blue laser diode) and at least one scan mirror (e.g., two one-dimensional scan mirrors, which may be micro-electromechanical system (MEMS)-based or piezo-based). The projector is communicatively coupled to the controller and a non-transitory processor-readable storage medium or memory storing processor-executable instructions and other data that, when executed by the controller, cause the controller to control the operation of the projector. In at least some embodiments, the controller controls a scan area size and scan area location for the projector and is communicatively coupled to a processor (not shown) that generates content to be displayed at the display system 100. The projector scans light over a variable area, designated the FOV area 106, of the display system 100. The scan area size corresponds to the size of the FOV area 106, and the scan area location corresponds to a region of one of the lens elements 108, 110 at which the FOV area 106 is visible to the user. Generally, it is desirable for a display to have a wide FOV to accommodate the outcoupling of light across a wide range of angles. Herein, the range of different user eye positions that will be able to see the display is referred to as the eyebox of the display.

[0031] In some embodiments, the projector routes light via first and second scan mirrors, an optical relay disposed between the first and second scan mirrors, and a waveguide disposed at the output of the second scan mirror. A portion of an output coupler of the waveguide, in at least some embodiments, may overlap the FOV area 106. These aspects are described in greater detail below.

[0032] FIG. 2 illustrates a simplified block diagram of an image source in the form of a laser projection system 200 that projects images directly onto the eye 202 of a user via a waveguide 208. The laser projection system 200 includes an optical engine 204, an optical scanner 206, and a waveguide 208. In some embodiments, the laser projection system 200 is implemented in a display system, such as the display system 100 of FIG. 1 , or another display system. The optical engine 204 includes one or more laser light sources configured to generate and output laser light 210 (e.g., visible laser light such as red, blue, and green laser light and, in some embodiments, non-visible laser light such as infrared laser light). In some embodiments, the optical engine 204 is coupled to a driver or other controller (not shown), which controls the timing of emission of laser light from the laser light sources of the optical engine 204 (e.g., in accordance with instructions received by the controller or driver from a computer processor coupled thereto) to modulate the laser light 210 to be perceived as images when output to the retina of the eye 202 of the user. [0033] For example, during operation of the laser projection system 200, multiple laser light beams having respectively different wavelengths are output by the laser light sources of the optical engine 204, then combined via a beam combiner (not shown) before being directed to the eye 202 of the user. The optical engine 204 modulates the respective intensities of the laser light beams so that the combined laser light reflects a series of pixels of an image, with the particular intensity of each laser light beam at any given point in time contributing to the amount of corresponding color content and brightness in the pixel being represented by the combined laser light at that time.

[0034] While, in the present example, the optical engine 204 is shown to output a single beam of laser light 210 (which itself may be a combination of two or more beams of light having respectively different polarizations or wavelengths) toward the first scan mirror, in some embodiments, the optical engine 204 is configured to generate and output two or more laser light beams toward the first scan mirror, where the two or more laser light beams are angularly separated with respect to one another (i.e., they are “angularly separated laser light beams”). Two or more laser light beams are “angularly separated” when they propagate along respectively different non-parallel and non-perpendicular optical paths that are tilted (e.g., angularly offset) with respect to one another, with the angular separation of the optical paths, in some instances, causing the two or more laser light beams to converge to overlap one another along one or more dimensions (e.g., such overlap corresponding to a virtual aperture of a pupil plane).

[0035] The optical scanner 206 includes a first scan mirror 212, a second scan mirror 214, and an optical relay 216. One or both of the first and second scan mirrors 212, 214 of the optical scanner 206 are MEMS mirrors in some embodiments. For example, the first scan mirror 212 and the second scan mirror 214 are MEMS mirrors driver by respective actuation voltages to oscillate during active operation of the laser projection system 200, causing the first and second scan mirrors 212, 214 to scan the laser light 210. Oscillation of the first scan mirror 212 causes laser light 210 output by the optical engine 204 to be scanned through the optical relay 216 and across a surface of the second scan mirror 214. The second scan mirror 214 scans the laser light 210 received from the first scan mirror 212 toward an input coupler 218 of the waveguide 208. In some embodiments, the first scan mirror 212 oscillates or otherwise rotates around a first axis 219, such that the laser light 210 is scanned in only one dimension (i.e., in a line) across the surface of the second scan mirror 214. In some embodiments, the second scan mirror 214 oscillates or otherwise rotates around a second axis 221 . In some embodiments, the first axis 219 is skew with respect to the second axis 221.

[0036] The waveguide 208, in at least some embodiments, is implemented as part of an eyeglasses lens, such as the lens elements 108 or 110 (FIG. 1) of the display system 100 (FIG. 1) having an eyeglass form factor and employing the laser projection system 200. The term “waveguide,” as used herein, will be understood to mean a combiner using total internal reflection (TIR) or via a combination of TIR, specialized filters, and/or reflective surfaces to transfer light from an input coupler to an output coupler. In at least some display applications, the light, for example, is a collimated image, and the waveguide 208 transfers and replicates the collimated image to the eye 202. The waveguide 208, in at least some embodiments, is formed by a plurality of layers, such as a first substrate layer, a partition element layer, and a second substrate layer. Also, in at least some embodiments, the waveguide 208 is comprises of a plurality of sections, as described below.

[0037] The waveguide 208, in at least some embodiments, includes the input coupler (IC) 218 and the output coupler (OC) 220. In other embodiments, the waveguide 208 includes the input coupler 218, the output coupler (OC) 220, and an exit pupil expander (EPE) 222. In general, the terms “input coupler” and “output coupler” will be understood to refer to any type of optical grating structure, including, but not limited to, diffraction gratings, slanted gratings, blazed gratings, holograms, holographic optical elements (e.g., optical elements using one or more holograms), volume diffraction gratings, volume holograms, surface relief diffraction gratings, and/or surface relief holograms. In some embodiments, the input coupler includes one or more facets or reflective surfaces.

[0038] In at least some embodiments, a given input coupler or output coupler is configured as a transmissive grating (e.g., a transmissive diffraction grating or a transmissive holographic grating) that causes the input coupler or output coupler to transmit light and to apply designed optical function(s) to the light during the transmission. In some embodiments, a given input coupler or output coupler is a reflective grating (e.g., a reflective diffraction grating or a reflective holographic grating) that causes the input coupler or output coupler to reflect light and to apply designed optical function(s) to the light during the reflection. In the present example, the laser light 210 received at the input coupler 218 is relayed to the output coupler 220 via the waveguide 208 using TIR. The laser light 210 is then output to the eye 202 of a user via the output coupler 220. In at least some embodiments, the EPE 222 is implemented using a diffraction or other type of grating and is arranged in an intermediate stage between input coupler 218 and output coupler 220 to receive light that is coupled into waveguide 208 by the input coupler 218, expand the light, and redirect the light towards the output coupler 220. The output coupler 220 then couples the laser light out of waveguide 208 (e.g., toward the eye 202 of the user). In other embodiments, the EPE 222 is combined with the output coupler 220.

[0039] The input coupler 218, in at least some embodiments, has a substantially rectangular profile and is defined by a smaller dimension (i.e., width) and a larger orthogonal dimension (i.e., length). In at least some embodiments, the input coupler 218 is configured to receive the laser light 210 from, for example, the optical scanner 206 and direct the laser light 210 into the waveguide 208. For example, the optical relay 216 is a line-scan optical relay that receives the laser light 210 scanned in a first dimension by the first scan mirror 212 (e.g., the first dimension corresponding to the small dimension of the input coupler 218), routes the laser light 210 to the second scan mirror 214, and introduces a convergence to the laser light 210 in the first dimension. The second scan mirror 214 receives the converging laser light 210 and scans the laser light 210 in a second dimension, the second dimension corresponding to the long dimension of the input coupler 218 of the waveguide 208. The second scan mirror causes the laser light 210 to converge to a focal line along the second dimension. In some embodiments, the input coupler 218 is positioned at or near the focal line downstream from the second scan mirror 214 such that the second scan mirror 214 scans the laser light 210 as a line over the input coupler 218.

[0040] Although not shown in the example of FIG. 2, in some embodiments, additional optical components are included in any of the optical paths between the optical engine 204 and the first scan mirror 212, between the first scan mirror 212 and the optical relay 216, between the optical relay 216 and the second scan mirror 214, between the second scan mirror 214 and the input coupler 218, between the input coupler 218 and the output coupler 220, or between the output coupler 220 and the eye 202 (e.g., to shape the laser light for viewing by the eye 202 of the user).

[0041] FIG. 3 shows an example of light propagation within the waveguide 208 when onedimensional (1 D) gratings are implemented in accordance with some embodiments. As shown, light received via the input coupler 218 is directed into the exit pupil expander 222, and then routed to the output coupler 220 to be output (e.g., toward the eye 202 of the user). In some embodiments, EPE 222 expands one or more dimensions of the eyebox of a display system (e.g., the display system 100 of FIG. 1) that includes the laser projection system 200 (e.g., with respect to what the dimensions of the eyebox of the HMD would be without the EPE 222). In some embodiments, the input coupler 218 and the exit pupil expander 222 each include respective 1 D diffraction gratings (i.e., diffraction gratings that extend along one dimension), which diffract incident light in a particular direction depending on the angle of incidence of the incident light and the structural aspects of the diffraction gratings. It should be understood that FIG. 3 shows a substantially ideal case in which the input coupler 218 directs light straight down (with respect to the presently illustrated view), and the exit pupil expander 222 directs light to the right (with respect to the presently illustrated view) in a second direction that is perpendicular to the first direction. While not shown in the present example, it should be understood that, in some embodiments, the first direction in which the input coupler 218 directs light is slightly or substantially diagonal

[0042] In at least some embodiments, the EPE 222 and the output coupler 220 are separated into or onto separate sections of the waveguide 208. For example, the input coupler 218 and the EPE 222 are located in or on a first section, and the output coupler 220 is located in or on a second section, where a planar direction of the first section is substantially parallel to a planar direction of the second section. In some embodiments, the input coupler 218 and the EPE 222 are located in or on a first substrate, and the output coupler 220 is located in or on a second substrate, where the first substrate and the second substrate are arranged adjacent to one another in the manners described herein.

[0043] The waveguide 208, in at least some embodiments, includes multiple substrates with the EPE 222 located in or on a first substrate and the output coupler 220 located in or on a second substrate that is separate from and adjacent to the first substrate. In some embodiments, a partition element is placed between the first substrate and the second substrate. For example, the partition element is an airgap (or gas-filled gap), a low-index refractive material layer, a polarizing beam splitter layer, or any combination thereof. In at least some embodiments, the partition element includes additional elements or an opening to direct light from the first substrate to the second substrate.

[0001] FIG. 4 shows another example of light propagation within the waveguide 208 when two-dimensional gratings (2D) are implemented in accordance with some embodiments. As shown, light received via the input coupler 218 is routed to the output coupler 220 to be output (e.g., toward the eye 202 of the user). In the example shown in FIG. 4, an EPE 222 is not implemented by the waveguide 208 or is combined with the output coupler 220. If the EPE 222 is combined with the output coupler 220, the EPE 222 expands one or more dimensions of the eyebox of the display system as described above. In this example, the output coupler 220 includes a 2D diffraction grating(s) (i.e., a diffraction grating(s) that extends along two dimensions), which diffracts incident light in a particular direction depending on the angle of incidence of the incident light and the structural aspects of the diffraction gratings.

[0044] As described above, implementing entirely flat waveguides in curved lenses generally necessitates the use of thicker lenses, which is undesirable from a design and aesthetic perspective, and implementing entirely curved waveguides in curved lenses increases the likelihood of display information being deformed or artifacts being introduced into displayed images. As such, the waveguide 208 implements one or more configurations/architectures that overcome the design and aesthetic issues of entirely flat waveguides and the light deformation and artifact issues caused by conventional curved waveguides.

[0045] For example, FIG. 5 and FIG. 6 together show a first configuration 600 of the waveguide 208, and FIG. 5 and FIG. 7 together show a second configuration 700 of the waveguide 208. FIG. 5 is an eye-side view (or a real-world side view) of the lens element 108 (or 110), and FIG. 6 and FIG. 7 are top views of the lens element 108 (or 110). In each of the first configuration 600 and the second configuration 700, the waveguide 208 is embedded within a curved lens element, such as lens element 108 or 110 of FIG. 1 . The waveguide 208, in at least some embodiments, comprises a plurality of sections 502 (illustrated as sections 502-1 to 502-4). Herein, a “section” refers to a portion of the waveguide 208 comprising opposing surfaces that define a volume through which light travels within the waveguide 208. A first section 502-1 of the waveguide 208 is situated between the input coupler 218 and the EPE 222, a second section 502-2 of the waveguide 208 is situated between the EPE 222 and the output coupler 220, and a third section 502-3 of the waveguide 208 is situated after the output coupler 220, e.g., between the output coupler 220 and an edge 223-1 of the waveguide 208 opposite the input coupler 218. In at least some embodiments, a fourth section 502-4 of the waveguide 208 is situated before the input coupler 218, e.g., between the input coupler 218 and an edge 223-2 of the waveguide 208 opposite the output coupler 220. It should be further understood that the waveguide 208 can include additional sections other than those illustrated in FIG. 5 to FIG. 7. Also, one or more of the sections 502 of the waveguide 208 can include multiple sub-sections.

[0046] In the first configuration 600 shown in FIG. 6, each of the plurality of sections 502 of the waveguide 208 is a planar/flat piecewise section. Herein, “planar” and “flat” sections refer to sections of the waveguide 208 that are non-curved and straight. As such, the surfaces forming a planar/flat section 502 of the waveguide 208 define a straight (or substantially straight) volume within the waveguide 208 for light to travel. Herein, “straight” refers to being without a curve or bend, or extending uniformly in one direction. In at least some embodiments, the first section 502-1 of the waveguide 208 situated between the input coupler 218 and the EPE 222 comprises an angled configuration. The angled configuration indicates that the first section 502-1 comprises a non-zero angle relative to at least one of the second section 502-2, the input coupler 218, the output coupler 220, or the EPE 222. For example, in at least some embodiments, the first section 502-1 comprises multiple subsections 602 (illustrated as first sub-section 602-1 and second sub-section 602-2). In this example, the first sub-section 602-1 has a non-zero angle relative to the second section 502- 2 and also relative to a second sub-section 602-2. Alternatively, the first section 602-1 comprises at least one sub-section having a non-zero angle relative to the fourth section 502- 4 of the waveguide 208 situated before the input coupler 218. Angling the first section 502-1 of the waveguide 208 allows at least the first section 502-1 to better conform to the curvature of the lens element 108 and further allows the light rays traveling through the waveguide 208 to bend as a result of the light rays passing through two flat surfaces of the sub-sections 504 at different angles.

[0047] The second section 502-2 of the waveguide 208 situated between the EPE 222 and the output coupler 220 comprises a flat (or substantially flat) configuration as represented by the flat line 604 in FIG. 6. Stated differently, the angle of the second section 502-2 of the waveguide 208 does not vary (or minimally varies) between the EPE 222 and the output coupler 220. The third section 502-3 of the waveguide 208 situated after the output coupler 220 is a portion of the waveguide 208 that receives non-display light and comprises an angled configuration or a flat (or substantially flat) configuration. The angled configuration indicates that the third section 502-3 comprises a non-zero angle relative to at least one of the first section 502-1 , the second section 502-2, the input coupler 218, the output coupler 220, or the EPE 222. For example, as shown in FIG. 6, the third section 502-3 comprises multiple sub-sections 606 (illustrated as first sub-section 606-1 and second sub-section 606- 2). In this example, the second sub-section 606-2 has a non-zero angle relative to the second section 502-2 and also relative to the first sub-section 606-1 . In another example, the third section 502-3 comprises a single section that has a non-zero angle relative to the second section 502-2 of the waveguide 208. In yet another example, the third section 502-3 comprises a flat (or substantially flat) configuration such that the angle along the third section 502-3 does not vary. If the waveguide 208 includes the fourth section 502-4 situated before the input coupler 218, the fourth section 502-4 can be flat (or substantially flat) or angled. For example, the fourth section 502-4 can have a non-zero angle relative to at least one of the first section 502-1 , the second section 502-2, the third section 502-3, the input coupler 218, the output coupler 220, or the EPE 222.

[0048] In the second configuration 700 shown in FIG. 7, the plurality of sections 502 of the waveguide 208 comprises one or more piecewise sections that are curved and at least one piecewise section that is flat (or substantially flat). For example, the first section 502-1 situated between the input coupler 218 and the EPE 222 comprises a curved configuration, as represented by the curved line 702. Here, a “curved” configuration refers to a non-flat configuration that bends in a smooth continuous way without sharp angles compared to an “angled” configuration, which has two straight sections of the waveguide that meet at a common point. As such, the surfaces forming a curved section 502 of the waveguide 208 define a curved volume within the waveguide 208 for light to travel. Similar to angling the first section 502-1 in the first configuration 600, curving the first section 502-1 allows at least this section of the waveguide 208 to better conform to the curvature of the lens element 108 and further allows the light rays to bend as they travel within the volume defined by the curved surface. In another example, the first section 502-1 comprises at least one curved sub-section and at least one flat (or substantially flat) sub-section. The flat section or subsection, in at least some embodiments, is angled with respect to another section of the waveguide 208, such as the fourth section 502-4 situated before the input coupler 218 or the second section 502-2 situated between the EPE 222 and the output coupler 220. Similar to the first configuration 600, the second section 502-2 of the waveguide 208 situated between the EPE 222 and the output coupler 220 comprises a flat (or substantially flat) configuration 704 as represented by the flat line 704. Stated differently, the angle of the second section 502-2 of the waveguide does not (or minimally varies) vary between the EPE 222 and the output coupler 220. The third section 502-3 of the waveguide 208 situated after the output coupler 220 is a portion of the waveguide 208 that receives non-display light and comprises a curved configuration, as represented by the curved line 706. In other embodiments, the third section 502-3 comprises an angled or curved configuration. For example, the third section 502-3 comprises a first sub-section and a second sub-section that are angled relative to each other. In another example, the third section 502-3 comprises at least one section that is angled with respect to the second section 502-2. In yet another example, the third section 502-3 comprises a flat (or substantially flat) configuration such that the angle along the third section 502-3 does not vary. If the waveguide 208 includes the fourth section 502-4 situated before the input coupler 218, the fourth section 502-comprises one or more sections that are curved, flat (or substantially flat), or angled. [0049] In the examples illustrated in FIG. 5 to FIG. 7, the input coupler 218 implements a 1 D grating, and the EPE 222 is separate from the output coupler 220. However, as shown in FIG. 8 to FIG. 10, waveguide configurations similar to those described above with respect to FIG. 5 to FIG. 7 are also applicable to an input coupler 218 that implements a 2D grating or an EPE 222 combined with an output coupler 220. For example, FIG. 8 is a an eye-side view (or a real-world side view) of the lens element 108 (or 110) with an embedded waveguide 208 comprising an input coupler 218 that implements a 2D grating and further comprising a combined output coupler/EPE 820 (e.g., the output coupler 220 and the EPE 222 are combined in a single grating). Similar to the example described above with respect to FIG. 5, the waveguide 208 in FIG. 8 comprises a plurality of sections 802 (illustrated as sections 802-1 to 802-3). A first section 802-1 of the waveguide 208 is situated between the input coupler 218 and the combined output coupler/EPE 820, a second section 802-2 of the waveguide 208 comprises the combined output coupler/EPE 820 and the intermediate space therebetween, and a third section 802-3 of the waveguide 208 is situated after the combined output coupler/EPE 820, e.g., between the combined output coupler/EPE 820 and an edge 223-1 of the waveguide 208 opposite the input coupler 218. In at least some embodiments, a fourth section 802-4 of the waveguide 208 is situated before the input coupler 218, e.g., between the input coupler 218 and an edge 223-2 of the waveguide 208 opposite the combined output coupler/EPE 820.

[0050] FIG. 9 is a top view of the lens element 108 (or 110) illustrating a third configuration 900 of the waveguide 208, similar to the first configuration 600 described above with respect to FIG. 6. In the third configuration 900, each of the plurality of sections 802 of the waveguide 208 is a planar/flat piecewise section. In at least some embodiments, the first section 802-1 of the waveguide 208 situated between the input coupler 218 and the combined output coupler/EPE 820 comprises an angled configuration. The angled configuration indicates that the first section 802-1 comprises a non-zero angle relative to at least one of the second section 802-2, the input coupler 218, or the combined output coupler/EPE 820. For example, in at least some embodiments, the first section 802-1 comprises multiple sub-sections 802 (illustrated as first sub-section 802-1 and second subsection 802-2). In this example, the first sub-section 802-1 has a non-zero angle relative to the second section 802-2 and also relative to a second sub-section 802-2. Alternatively, the first section 802-1 comprises at least one sub-section having a non-zero angle relative to the fourth section 802-4 of the waveguide 208 situated before the input coupler 218. [0051] The second section 802-2 of the waveguide 208 comprising the combined output coupler/EPE 820 is flat (or substantially flat). For example, the intermediate space/volume of the waveguide 208 between the output coupler and EPE of the combined output coupler/EPE 820 is flat (or substantially flat). Therefore, similar to the first configuration 600 and second configuration 700, the light travels along a straight (or substantially straight) path between the output coupler and EPE of the combined output coupler/EPE 820.

[0052] The third section 802-3 of the waveguide 208 situated after the combined output coupler/EPE 820 is a portion of the waveguide 208 that receives non-display light and comprises an angled configuration or a flat (or substantially flat) configuration. The angled configuration indicates that the third section 802-3 comprises a non-zero angle relative to at least one of the first section 802-1 , the second section 802-2, the input coupler 218, or the combined output coupler/EPE 820. For example, as shown in FIG. 8, the third section 802-3 comprises multiple sub-sections 806 (illustrated as first sub-section 806-1 and second subsection 806-2). In this example, the second sub-section 806-2 has a non-zero angle relative to the second section 802-2 and also relative to the first sub-section 806-2. In another example, the third section 802-3 comprises a single section that has a non-zero angle relative to the second section 802-2 of the waveguide 208. In yet another example, the third section 802-3 comprises a flat (or substantially flat) configuration such that the angle along the third section 802-3 does not vary. If the waveguide 208 includes the fourth section 802-4 situated before the input coupler 218, the fourth section 802-4 can be flat (or substantially flat) or angled. For example, the fourth section 802-4 can have a non-zero angle relative to at least one of the first section 802-1 , the second section 802-2, the third section 802-3, the input coupler 218, or the combined output coupler/EPE 820.

[0053] FIG. 10 is a top view of the lens element 108 (or 110) illustrating a fourth configuration 1000 of the waveguide 208 similar to the second configuration 700 described above with respect to FIG. 7. In the fourth configuration 1000 shown in FIG. 10, the plurality of sections 802 of the waveguide 208 is comprised of one or more piecewise sections that are curved and at least one piecewise section that is flat (or substantially flat). For example, the first section 802-1 situated between the input coupler 218 and the combined output coupler/EPE 820 comprises a curved configuration, as represented by the curved line 1002. In another example, the first section 802-1 comprises at least one curved sub-section and at least one flat (or substantially flat) sub-section. The flat section or sub-section, in at least some embodiments, is angled with respect to another section of the waveguide 208, such as the fourth section 802-4 situated before the input coupler 218. The second section 802-2 of the waveguide 208 comprising the combined output coupler/EPE 820 is flat (or substantially flat), similar to the third configuration 900. Therefore, similar to the other configurations, the light travels along a straight (or substantially straight) path between the output coupler and EPE of the combined output coupler/EPE 820. The third section 802-3 of the waveguide 208 situated after the combined output coupler/EPE 820 is a portion of the waveguide 208 that receives non-display light and comprises a curved configuration, as represented by the curved line 906. In other embodiments, the third section 802-3 comprises an angled or curved configuration. For example, the third section 802-3 comprises a first sub-section and a second sub-section that are angled relative to each other. In another example, the third section 802-3 comprises at least one section that is angled with respect to the second section 802-2. In yet another example, the third section 802-3 comprises a flat (or substantially flat) configuration such that the angle along the third section 802-3 does not vary. If the waveguide 808 includes the fourth section 802-4 situated before the input coupler 218, the fourth section 802-comprises one or more sections that are curved, flat (or substantially flat), or angled.

[0054] The first section 502-1 of the waveguide 208 in the first and second configurations 600, 700 and the first section 802-1 of the waveguide 208 in the third and fourth configurations 900, 1000 are angled or curved instead of flat because any deformation caused during light travel between the input coupler 218 and the EPE 222 is common to all outcoupling locations of the output coupler 220. Therefore, a common correction can be applied by the display system 100 to the display information for all exit pupils. For example, one or more components of the optical system (e.g., the optical engine 204, the optical scanner 206, or both) situated ahead of the waveguide 208 can be configured with an opposite curvature effect so that the optical system and waveguide 208 curvatures (or angles) cancel each other out. In another example, the input signal to the display system 100 can be modified (e.g., the image can be warped) to compensate for the curvature of the first section 502-1 or 802-1 of the waveguide 208. Both of these methods can be combined, or other methods for compensating for the curvature of the first section 502-1 can be implemented as well. The second section 502-2 of the waveguide 208 in the first and second configurations 600, 700 and the second section 802-2 of the waveguide 208 in the third and fourth configurations 900, 1000 are flat (or substantially flat) because any deformations caused during light travel between the EPE 222 and the output coupler 220 are varied across the outcoupling locations of the output coupler 220 and correction of the deformations is specific for each exit pupil. As such, by implementing a flat (or substantially flat) section 502- 2 or 802-1 of the waveguide 208 between the EPE 222 and the output coupler 220, deformations in the light traveling in this area of the waveguide 208 are reduced or eliminated.

[0055] FIG. 11 illustrates, in flow chart form, an overview of one example method 1100 of forming a waveguide 208 in accordance with one or more embodiments. At block 1102, the first section 502-1 of the waveguide is formed between the input coupler 218 and the EPE 222. The first section 502-1 comprises a non-flat configuration, such as an angled or curved configuration. At block 1104, the second section 502-2 or 802-1 of the waveguide 208 is formed between the EPE 222 and the output coupler 220. The second section 502-2 or 802- 2 comprises a substantially flat configuration. At block 1106, the third section 502-3 or 802-3 is formed after the output coupler 220. The third section 502-3 or 802-3 comprises one of a flat, angled, or curved configuration. At block 1108, the fourth section 502-4 or 802-4 is formed before the input coupler 218. The fourth section 502-4 or 802-4 comprises one of a flat, angled, or curved configuration. It should be understood that the sequence of the operations performed in the method 1100 can be different from what is illustrated in FIG. 11 .

[0056] In some embodiments, certain aspects of the techniques described above may be implemented by one or more processors of a processing system executing software. The software comprises one or more sets of executable instructions stored or otherwise tangibly embodied on a non-transitory computer readable storage medium. The software can include the instructions and certain data that, when executed by the one or more processors, manipulate the one or more processors to perform one or more aspects of the techniques described above. The non-transitory computer readable storage medium can include, for example, a magnetic or optical disk storage device, solid state storage devices such as Flash memory, a cache, random access memory (RAM) or other non-volatile memory device or devices, and the like. The executable instructions stored on the non-transitory computer readable storage medium may be in source code, assembly language code, object code, or other instruction format that is interpreted or otherwise executable by one or more processors.

[0057] A computer readable storage medium may include any storage medium, or combination of storage media, accessible by a computer system during use to provide instructions and/or data to the computer system. Such storage media can include, but is not limited to, optical media (e.g., compact disc (CD), digital versatile disc (DVD), Blu-Ray disc), magnetic media (e.g., floppy disc , magnetic tape, or magnetic hard drive), volatile memory (e.g., random access memory (RAM) or cache), non-volatile memory (e.g., read-only memory (ROM) or Flash memory), or microelectromechanical systems (MEMS)-based storage media. The computer readable storage medium may be embedded in the computing system (e.g., system RAM or ROM), fixedly attached to the computing system (e.g., a magnetic hard drive), removably attached to the computing system (e.g., an optical disc or Universal Serial Bus (USB)-based Flash memory), or coupled to the computer system via a wired or wireless network (e.g., network accessible storage (NAS)).

[0058] Note that not all of the activities or elements described above in the general description are required, that a portion of a specific activity or device may not be required, and that one or more further activities may be performed, or elements included, in addition to those described. Still further, the order in which activities are listed are not necessarily the order in which they are performed. Also, the concepts have been described with reference to specific embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present disclosure as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present disclosure.

[0059] Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any feature(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature of any or all the claims. Moreover, the particular embodiments disclosed above are illustrative only, as the disclosed subject matter may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. No limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope of the disclosed subject matter. Accordingly, the protection sought herein is as set forth in the claims below.

Claims

WHAT IS CLAIMED IS:

1. A waveguide (208) comprising: a first section (502-1 , 802-1) between an input coupler (218) and an exit pupil expander (222), the first section comprising a non-flat configuration; and a second section (502-2, 802-2) between the exit pupil expander and an output coupler (220), the second section comprising a substantially flat configuration.

2. The waveguide of claim 1 , wherein the non-flat configuration comprises one of a curved configuration or an angled configuration, the angled configuration indicating that the first section comprises a non-zero angle relative to at least one of the second section, the input coupler, the exit pupil expander, or the output coupler.

3. The waveguide of any one of claims 1 or 2, further comprising: a third section (502-3, 802-3) between the output coupler and an edge (223-1) of the waveguide opposite the input coupler.

4. The waveguide of claim 3, wherein the third section comprises one of a flat configuration or a non-flat configuration.

5. The waveguide of claim 4, wherein the non-flat configuration comprises one a curved configuration or an angled configuration, the angled configuration indicating that the third section comprises a non-zero angle relative to at least one of the first section, the second section, the input coupler, the exit pupil expander, or the output coupler.

6. The waveguide of any one of claims 1 to 5, further comprising: a fourth section (502-4, 802-4) between the input coupler and an edge (223-2) of the waveguide opposite the output coupler.

7. The waveguide of claim 6, wherein the fourth section comprises one of a flat configuration or a non-flat configuration.

8. The waveguide of claim 7, wherein the non-flat configuration comprises one of a curved configuration or an angled configuration, the angled configuration indicating that the fourth section comprises a non-zero angle relative to at least one of the first section, the second section, the third section, the input coupler, the exit pupil expander, or the output coupler. waveguide of any one of claims 1 to 8, wherein the input coupler comprises a onedimensional grating. waveguide of any one of claims 1 to 8, wherein the input coupler comprises a two- dimensional grating. waveguide of any one of claims 1 to 10, wherein the exit pupil expander and the output coupler are combined in a single grating. earable head-mounted display system (100) comprising: an image source (200) to project light comprising an image; at least one lens element (108, 110); and the waveguide of any of claims 1 to 11 . ethod of fabricating the waveguide of any of claims 1 to 11 , the method comprising: forming a first section (502-1) of a waveguide between an input coupler (218) and an exit pupil expander (222), the first section comprising a non-flat configuration; and forming a second section (502-2) of the waveguide between the exit pupil expander and an output coupler (220), the second section comprising a substantially flat configuration. e method of claim 13, wherein the non-flat configuration comprises one of a curved configuration or an angled configuration, the angled configuration indicating that the first section comprises a non-zero angle relative to at least one of the second section, the input coupler, the exit pupil expander, or the output coupler. method of any one of claims 13 or 14, further comprising forming a third section

(502-3, 802-3) between the output coupler and an edge (223-1) of the waveguide opposite the input coupler.