Reflective waveguide with seamless geometry

Abstract

A waveguide includes an input coupler, an exit pupil expander comprising a first prism array, an output coupler includes a second prism array, and a seamless transition at an interface between the first prism array and the second prism array. The seamless transition includes at least one prism geometric parameter having a value for each pair of corresponding prisms of the first prism array and the second prism array is matched or varied across the interface.

Description

REFLECTIVE WAVEGUIDE WITH SEAMLESS GEOMETRYBACKGROUND

[0001] A reflective waveguide is an optical component that typically incorporates semi-reflective mirrors positioned to modulate light transmission through partial reflection. This configuration manipulates the light path to expand the exit pupil, which determines the size of the eyebox (the area within which the user can view the entire image). By adjusting the orientation and properties of these mirrors, it is possible to expand the pupil in specific directions (i.e., horizontally, vertically, or both) according to the desired field of view. This expansion allows for a wide viewing angle and an increased eyebox, making the technology adaptable for various applications in compact optical systems such as augmented reality (AR) wearable display devices, mixed reality (MR) wearable display devices, heads-up displays (HUDs), and the like.SUMMARY OF EMBODIMENTS

[0002] In accordance with one aspect, a reflective waveguide includes an input coupler configured to couple input display light into the waveguide, an exit pupil expander comprising a first prism array, and an output coupler comprising a second prism array. The reflective waveguide further includes a seamless transition at an interface between the first prism array and the second prism array, and the seamless transition comprising at least one prism geometric parameter having a value for each pair of corresponding prisms of the first prism array and the second prism array is matched or varied across the interface.

[0003] In at least some embodiments, the at least one prism geometric parameter includes one or more of prism heights, polar angles of front surfaces of prisms, or polar angles of back surfaces of prisms.

[0004] In at least some embodiments, the value of the at least one prism geometric parameter is constant for each pair of corresponding prisms across the interface.

[0005] In at least some alternative embodiments, the value of the at least one prism geometric parameter varies among pairs of corresponding prisms across the interface.

[0006] In at least some embodiments, the at least one prism geometric parameter includes prism heights, wherein prism heights of corresponding prisms in the first prism array and the second prism array at the seamless transition satisfy the condition Hb = Hc, where Hb represents the height of a prism in the first prism array, and He represents the height of a corresponding prism in the second prism array.

[0007] In at least some embodiments, the at least one prism geometric parameter includes polar angles of front surfaces of corresponding prisms, wherein polar angles of front surfaces of corresponding prisms in the first prism array and the second prism array at the seamless transition satisfy the condition tan(ab) * sin(0b) = tan(ac) * sin(9c), where ab and acare the polar angles of the front surfaces of corresponding prisms in the first prism array and the second prism array, respectively, and 9b and 9c are angles relative to a seam between the first prism array and the second prism array.

[0008] In at least some embodiments, the at least one prism geometric parameter comprises polar angles of back surfaces of prisms, wherein polar angles of back surfaces of corresponding prisms in the first prism array and the second prism array at the seamless transition satisfy the condition tan(|3b) I sin(9b) = tan(pc) I sin(9c), where Pb and pcare the polar angles of the back surfaces of corresponding prisms in the first prism array and the second prism array, respectively, and 9b and 9Care angles relative to a seam between the first prism array and the second prism array.

[0009] In at least some embodiments, the seamless transition comprises an uncoated region between the first prism array and the second prism array.

[0010] In at least some embodiments, the uncoated region is immediately adjacent to the interface between the first prism array and the second prism array.

[0011] In at least some embodiments, prisms in the second prism array include curved prism surfaces configured to introduce optical power to the outcoupled display light.

[0012] In at least some embodiments, the seamless transition includes a curved interface configured to accommodate curved prism surfaces in the second prism array.

[0013] In at least some embodiments, the curved interface is defined by a polynomial curve.

[0014] In at least some embodiments, polynomial coefficients of the polynomial curve defining the curved interface are configured to maintain geometric continuity between prisms of the first prism array and prisms of the second prism array.

[0015] In at least some embodiments, the prisms of the first prism array and the second prism array include polymer prisms.

[0016] In at least some embodiments, the polymer prisms are fabricated by injection molding or casting processes.

[0017] In accordance with another aspect, a wearable head-mounted display system includes the waveguide described above and herein, an image source configured to project display light comprising images into the waveguide, and at least one lens element. The waveguide guides the display light from the image source through the input coupler, exit pupil expander, and output coupler, providing an immersive augmented reality or mixed reality viewing experience for a user.

[0018] In accordance with yet another aspect, a method of operating the wearable head-mounted display system described above and herein includes projecting the light from the image source to the waveguide, transmitting the projected light along the waveguide, and outputting at least a portion of the transmitted light in the direction of an eye of a user of the wearable head-mounted display system.BRIEF DESCRIPTION OF THE DRAWINGS

[0019] 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.

[0020] FIG. 1 is a schematic of a portion of a reflective waveguide in accordance with some embodiments.

[0021] FIG. 2 is a schematic of a portion of a reflective waveguide having additional adhesive between the exit pupil expander and output coupler prism arrays.

[0022] FIG. 3 is a cross-sectional view of a reflective waveguide having a seamless transition between the exit pupil expander and output coupler in accordance with some embodiments.

[0023] FIG. 4 is a cross-section view of the prism structure of FIG. 3 in accordance with some embodiments.

[0024] FIG. 5 is a more detailed view of the reflective waveguide of FIG. 3 in accordance with some embodiments.

[0025] FIG. 6 is a magnified view of a portion of reflective waveguide in FIG. 5 in accordance with some embodiments.

[0026] FIG. 7 is a schematic illustrating an example reflective waveguide configuration having curved prism surfaces with a discontinuity at an interface between prism arrays caused by prism curvature.

[0027] FIG. 8 is a magnified view of a portion of reflective waveguide of FIG. 7.

[0028] FIG. 9 is a schematic illustrating an example reflective waveguide configuration having curved prism surfaces with an intentionally curved, seamless interface in accordance with some embodiments.

[0029] FIG. 10 is a magnified view of a portion of reflective waveguide in FIG. 9 in accordance with some embodiments.

[0030] FIG. 11 is a block diagram of a near-eye display (NED) system in accordance with some embodiments.

[0031] FIG. 12 is a diagram illustrating a light projection system with an optical scanner that includes an optical relay disposed between two scan mirrors in accordance with some embodiments.DETAILED DESCRIPTION

[0032] A reflective waveguide is a type of waveguide combiner commonly employed in immersive technology applications, such as augmented reality (AR), mixed reality (MR), and other head-mounted display systems. In these applications, pupil expansion is typically achieved by employing semi-reflective mirrors or prism arrays configured within the waveguide structure to control the propagation and direction of light. The use of semi-reflective mirrors allows selective transmission and reflection of incident light, facilitating precise manipulation of the optical path and enabling controlled pupil expansion in either one-dimensional (1 D) or two-dimensional (2D) directions.

[0033] Waveguides featuring 1 D pupil expansion typically expand the pupil in a single direction (e.g., horizontally), whereas waveguides designed for 2D pupil expansion extend the image in two orthogonal directions (e.g., horizontally and vertically), resulting in a larger and more versatile viewing region. Reflective waveguides can be fabricated using various materials, notably glass or polymer substrates, each presenting distinct advantages and challenges. Glass substrates offer excellent optical properties but generally require complex and costly manufacturing processes. Polymer-based reflective waveguides, while providing benefits in terms of weight reduction, flexibility, and cost-efficiency, pose significant fabrication challenges, particularly for implementing precise geometries for seamless transitions and optimal optical performance.

[0034] An illustrative example of a polymer-based reflective waveguide is depicted in FIG. 1 . In this example, FIG. 1 depicts a schematic 100 of an example architecture for a reflective waveguide 102, specifically a bottom half or portion of a polymer reflective waveguide. The reflective waveguide 102 includes two prism arrays 104(illustrated as prism array 104-1 and prism array 104-2) defining an exit pupil expander (EPE) 106 and an output coupler (OC) 108, respectively. The prism array 104 are coated with a partially reflective coating, such as a thin film multilayer dielectric coating. After completing the coating process, the bottom portion is bonded with the opposite part (e.g., the top half or portion), forming a flat waveguide that guides light 110 from an image source (e.g., a projector) via total internal reflection (TIR). As the light 110 from the image source passes through a coated prism array 104, such as the EPE 106, the light 110 experiences partial reflection and is gradually directed towards the OC 108. Similarly, as the light 110 travels through the OC 108, the light 110 gradually outcouples towards the eye, forming the eyebox.

[0035] Although polymer-based reflective waveguides offer benefits such as weight reduction, flexibility, and cost-efficiency, extending reflective waveguide technology into polymer substrates introduces notable fabrication challenges. Currently, polymer-based reflective waveguides are predominantly limited to 1 D pupil expansion architectures due to constraints inherent in polymer fabrication processes, which consequently limit eyebox size. While two-dimensional (2D) reflective waveguides are desirable for their potential in advanced optical systems, such architectures have typically been restricted to glass substrates because of the complexity and precision required. The processes involved in fabricating 2D reflective waveguides from glass are intricate and expensive, thus limiting broader commercial adoption.

[0036] Polymer reflective waveguides (PRWs) are typically manufactured using processes such as injection molding or casting, both of which rely heavily on high- resolution molds commonly produced through diamond-turning machining (DTM). These manufacturing methods impose stringent constraints on waveguide designs, especially with regard to overall footprint, precise prism angles, and control of adhesive layers between prism arrays. FIG. 2 illustrates an example of a PRW structure 200 highlighting such a limitation, where additional adhesive 212 is required between the prism arrays 204 (illustrated as prism arrays 204-1 and 204-2) defining the EPE 206 and the OC 208, respectively. The presence of adhesive 212, while structurally necessary in conventional polymer waveguides, significantly degrades optical performance by reducing clarity, contrast, and overall efficiency of the waveguide. This example underscores the ongoing technical challenges inadvancing the configuration and production of high-quality 2D polymer-based reflective waveguides.

[0037] Accordingly, described herein are example waveguide configurations implementing a seamless geometry between the EPE and the OC. Unlike conventional polymer-based reflective waveguides, such as the configuration illustrated in FIG. 2 that requires additional adhesive layers between prism arrays, the disclosed seamless transition between the EPE and the OC ensures that no vertical sidewalls exist in the molded part. This approach eliminates or reduces the necessity of draft angles in the transition region between the EPE and OC, providing several significant manufacturing and optical performance advantages. For instance, mold complexity is substantially reduced by removing the need for multiple mold inserts, streamlining the fabrication process, and lowering associated manufacturing costs. Additionally, the absence of draft angles minimizes mechanical interference between the top and bottom waveguide parts, enhancing reliability and ease of assembly during bonding. Furthermore, the elimination of glue layers associated with conventional drafted surfaces improves optical clarity, increases the Modulation Transfer Function (MTF), and significantly reduces optical artifacts such as halos. The seamless transition also results in a compact and more efficient design by eliminating uncoated gaps between the EPE and OC, thereby effectively reducing the overall footprint of the waveguide.

[0038] Additionally, in some embodiments, the waveguide is configured to introduce optical power to the outcoupled light, projecting an image focused at a predetermined virtual image distance (e.g., 2 meters), rather than an image focused at infinity as found in conventional waveguides. To achieve this optical power, the surfaces of the OC mirrors are curved in both polar and azimuthal directions. However, curvature in the azimuthal direction may introduce complexity to the seamless transition between the EPE and OC. To address this, the seam itself is configured as a curved feature, with the curvature defined through polynomial parameterization. Polynomial coefficients describing the curvature of the seam are optimized to minimize any discontinuity between adjacent EPE and OC prisms, ensuring an effective seamless transition even with the presence of curved OC mirror surfaces.

[0039] FIG. 3 shows an example configuration 300 of a waveguide 302 having a seamless transition region 314 positioned between prism arrays 304 (illustrated as prism arrays 304-1 and 304-2) defining the EPE 306 and the OC 308, respectively, together with angle and dimensional definitions utilized to characterize and achieve seamless conditions. FIG. 4 provides a detailed view of the prism structures in FIG. 3 from multiple cross-sectional perspectives (noted as sections b and c). The seamless transition (interface) 314 in FIG. 3 represents the boundary along which the EPE 306 and OC 308 prism arrays 304 interface, configured to avoid discontinuities that could negatively impact optical performance.

[0040] Angle ab c401 in FIG. 4 represents the polar angle of the front side surfaces of the individual prisms taken along these cross-sectional directions. Similarly, angle (3b c403 represents the polar angle of the backside surfaces of the prisms along the same cross-sectional directions. Both of these angles (a and [3) are used for determining the optical properties of the prisms, including reflection efficiency, directionality, and consistency in pupil expansion.

[0041] Additionally, dimension Hb c405 is defined as the prism height measured perpendicularly from the waveguide base substrate along cross-sections b and c. Precise control and matching of the prism heights, together with careful alignment of their polar angles, help achieve the seamless transition across the interface 314 and ensuring optimal optical performance. Ensuring seamless geometry means that for corresponding prisms on either side of the interface 314, these angles and heights are matched to avoid structural discontinuities, eliminate unnecessary adhesive layers, and maintain superior optical quality.

[0042] Further, in embodiments where optical power is imparted to the outcoupled light, additional configurations may be employed. For instance, as illustrated in FIG.9 and FIG. 10 (both described later), the curvature of the OC 908 prism surfaces (particularly in the azimuthal direction) is accommodated by forming an intentionally curved seam 916 between the EPE 906 and OC 908 prism arrays 904. This curved seam 916 can be mathematically described by a polynomial function, where the polynomial coefficients are optimized to minimize discontinuities between adjacent prisms. By implementing such a precisely-defined curved seamless geometry,manufacturability is further enhanced, optical clarity is improved, and polymer-based reflective waveguides become even more effective in demanding optical applications, including augmented and mixed reality displays.

[0043] FIG. 5 and FIG. 6 together show a more detailed view 500 of the waveguide 302, emphasizing the seamless transition region. In this illustrated example, the waveguide 302 includes prism arrays 304 (illustrated as prism arrays 304-1 and 304- 2) defining the EPE 306 and OC 308. The waveguide 302, in this example, is configured with geometrical parameters to enable a seamless transition between the EPE 306 and OC 308 arrays prism arrays 304 at the EPE / OC seam 516.

[0044] In the context of the waveguide 302, the seam 516 refers to the interface or boundary region between adjacent prism arrays defining the EPE 306 and the OC 308. More specifically, the seam 516 represents the boundary line or surface along which optical elements, such as prisms, transition from the EPE prism array 304-1 to the OC prism array 304-2. A seamless transition at the seam 516 refers to a continuous geometric interface across which prism geometric parameters (e.g., prism heights, polar angles of prism front surfaces, and polar angles of prism back surfaces) are precisely matched or smoothly varied without abrupt discontinuities. Such a seamless transition effectively eliminates or significantly reduces optical discontinuities, mechanical misalignments, gaps, or sudden changes in refractive or reflective properties, thereby preserving optical integrity and minimizing visual artifacts across the boundary between the EPE and OC prism arrays 304.

[0045] This seamless transition minimizes optical artifacts, enhances optical clarity, and simplifies manufacturing. To achieve this seamless geometry, specific geometric conditions controlled and satisfied for each corresponding pair of prisms at the seam 516. For example, the following conditions, in at least some embodiments, are consistently applied:1 .) The heights of corresponding prisms in the EPE 306 and OC 308 prism arrays 304 are matched= Hc), thereby eliminating vertical discontinuities that could degrade optical performance;2.) The polar angles of the front sides of corresponding prisms in the EPE 306 and OC 308 arrays 304 are equal, governed by the condition tan(ab) * sin(0b) = tan(ac) * sin(6c). This matching of polar angles ensures optical continuity across the seam 516, avoiding aberrations in the transmitted image; and3.) Similarly, the polar angles of the back sides of corresponding prisms in the EPE 306 and OC 308 prism arrays 304 are equal, governed by the condition tan( ?b) / sin(0b) = tan( / ?c) / sin(0c). Maintaining equal backside angles further preserves the optical integrity across the seam 516.

[0046] In at least some embodiments, prism heights vary between the prisms within the EPE 306 and OC 308 prism arrays 304. In these cases, the above-listed conditions are applied to each individual prism pair (e.g., an EPE prism and a corresponding OC prism) at the seam 516. Moreover, in some implementations, these seamless conditions are satisfied only within a short, deliberately uncoated region immediately adjacent to the seam 516. Outside of this region, either prism heights, angles, or both may transition gradually or abruptly to different values selected to optimize overall optical performance, accommodating specific optical design objectives, such as enhancing image clarity, brightness, and uniformity across the waveguide’s viewing region.

[0047] In the previously described embodiments of FIG. 3 to FIG. 6, the seamless transition conditions at the interface between the EPE and OC arrays 304 were primarily described in terms of straight prism surfaces. However, in advanced optical systems such as those aiming to project images focused at finite virtual image distances (VID), additional optical power is employed by introducing curvature to the prism surfaces. Such curved surfaces present unique challenges for achieving and maintaining the previously-described seamless conditions.

[0048] FIG. 7 and 8 together illustrate an example of a waveguide 502 configured to project an output image focused at a finite virtual image distance, for example, approximately 2 meters, rather than at infinity as in other waveguide configurations. In this example, the waveguide 702 includes prism arrays 704 (illustrated as prism arrays 704-1 and 704-2) defining the EPE 706 and OC 708, respectively. To impartoptical power, the surfaces of the prisms in the OC 708 prism array 704-1 are curved along both polar and azimuthal directions. The curved arrow 718 highlights an exaggerated curvature along the azimuthal direction of the prisms in the OC 708 prism array 704-1 , depicting the significant curvature introduced to provide the configured optical focusing power.

[0049] As illustrated in the zoomed-in inset portion 707 of FIG. 8, the curvature of the prisms in the OC 708 prism array 704-1 can lead to a violation of the previously established seamless transition conditions at the interface between the EPE 706 and OC 708 prism arrays 704. For example, the prism curvature along the azimuthal direction disrupts the continuity of prism angles and heights, introducing potential optical discontinuities or mechanical misalignments that negatively affect optical performance. The dashed circle 709 in inset 707 highlights an example gap or discontinuity at the seam 716 caused by this prism curvature. Thus, while the incorporation of optical power through curved prism surfaces provides benefits in terms of focusing capability, it also introduces challenges in maintaining the integrity and advantages of a seamless geometry between adjacent prism arrays 704.

[0050] As illustrated in FIG. 9 and FIG. 10, to effectively address these challenges, one or more embodiments incorporate an intentionally curved seam between the EPE and OC prism arrays. This curved seam enables seamless geometry conditions to be preserved despite the presence of curved OC prism surfaces. The curved seam is mathematically defined by a polynomial curve having coefficients carefully optimized to maintain geometric continuity. Such optimization substantially reduces or eliminates discontinuities between corresponding prisms, thereby preserving the critical optical integrity across the seam.

[0051] For example, FIG. 9 and FIG. 10 together illustrates a waveguide configuration 902 incorporating an intentionally curved seam 916 positioned between prism arrays 904 (illustrated as prism arrays 904-1 and 904-2), which define the exit pupil expander (EPE) 906 and output coupler (OC) 908, respectively. For clarity, the curved seam 916 is depicted in FIG. 9 as a continuous bold line. In this example, the OC prism array 908 includes curved prisms, and a corresponding intentionally curved seam 916 separates the OC 908 prism array from the adjacent EPE 906 prism array. The curved seam 916, exaggerated for clarity, is mathematically defined throughpolynomial parameterization. In at least some embodiments, polynomial coefficients describing the shape of the seam 916 are computationally optimized to ensure continuity of prism angles and heights, thereby preserving optical integrity across the seam. In direct contrast to the gap or discontinuity shown in FIG. 7, the zoomed-in inset portion 1007 illustrates that this optimized curved seam 916 effectively maintains a truly seamless transition between the prism arrays 904. Thus, by carefully shaping and optimizing the seam 616, the waveguide configuration 902 preserves seamless conditions even with significant azimuthal curvature introduced by the OC 908 prisms 904-1. The curved polynomial seam approach accordingly resolves the previously identified optical and mechanical challenges, enabling the integration of optical power into polymer-based reflective waveguides while preserving seamless geometry and optimal optical performance.

[0052] Thus, the reflective waveguide techniques and architectures described herein enhance optical performance and manufacturing efficiency by employing seamless geometric transitions between prism arrays. By precisely matching or continuously varying prism geometric parameters at interfaces between prism arrays, the disclosed implementations substantially eliminate optical discontinuities, reduce visual artifacts, and simplify manufacturing processes. Consequently, these advancements enable compact, optically superior, and cost-efficient waveguide systems suitable for diverse immersive applications, including augmented reality and mixed reality wearable displays.

[0053] FIG. 11 illustrates an example near-eye display (NED) system 1100 for implementing a reflective waveguide, such as the reflective waveguide 302 of FIG. 3 to FIG. 6 or the reflective waveguide 902 of FIG. 9 and FIG. 10, having the seamless geometry described. In the illustrated implementation, the NED system 1100 utilizes an eyeglasses form factor. However, the NED system 1100 is not limited to this form factor and, thus, may have a different shape and appearance from the eyeglasses frame depicted in FIG. 11. The NED system 1100 includes a support structure 1120 (e.g., a support frame) to mount to a head of a user and that includes an arm 1122 that houses an image source, such as light projection system, including a microdisplay (e.g., micro-light emitting diode (LED) display) or other light engine, configured to project display light representative of images or imagery toward the eyeof a user, such that the user perceives the projected display light as a sequence of images displayed in a field of view (FOV) area 1124 at one or both of lens elements 1126, 1128 supported by the support structure 1120. In at least some embodiments, the support structure 1120 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 1120, in at least some embodiments, further includes one or more radio frequency (RF) interfaces or other wireless interfaces, such as a Bluetooth (TM) interface, a Wi-Fi interface, and the like.

[0054] The support structure 1120, in at least some embodiments, further includes one or more batteries or other portable power sources for supplying power to the electrical components of the NED system 1100. In at least some embodiments, some or all of these components of the NED system 1100 are fully or partially contained within an inner volume of support structure 1120, such as within the arm 1122 in region 1130 of the support structure 1120. In the illustrated implementation, the NED system 1100 utilizes an eyeglasses form factor. However, the NED system 1100 is not limited to this form factor and, thus, may have a different shape and appearance from the eyeglasses frame depicted in FIG. 11 .

[0055] One or both of the lens elements 1126, 1128 are used by the NED system 1100 to provide an immersive display in which rendered graphical content can be superimposed over or otherwise provided in conjunction with a real-world view as perceived by the user through the lens elements 1126, 1128. For example, laser light or other display light is used to form a perceptible image or series of images projected onto the user’s eye via one or more optical elements, including a waveguide, formed at least partially in the corresponding lens element. One or both of the lens elements 1126, 1128 thus include at least a portion of a waveguide that routes display light received by an IC (not shown in FIG. 11 ) of the waveguide to an OC (not shown in FIG. 11) of the waveguide, which outputs the display light toward an eye of a user of the NED system 1100. Additionally, the waveguide employs an EPE (not shown in FIG. 11) in the light path between the IC and OC or in combination with the OC to increase the dimensions of the display exit pupil. Each of the lens elements 1126, 1128 is sufficiently transparent to allow a user to see through the lenselements 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.

[0056] FIG. 12 depicts a cross-section view of an implementation of a display system 1200 (e.g., a near-eye display system or a wearable head-mounted display system) partially included in a lens element, such as lens element 1126, of an AR eyewear display system, such as NED system 1100, which in some embodiments includes a waveguide 1202, such as the waveguide 302 described above with respect to FIG. 3 to FIG. 6 or the waveguide 902 described above with respect to FIG. 9 and FIG. 10. The waveguide 1202 implements the seamless geometry as described above with respect to any one of FIG. 3 to FIG. 6, FIG. 9, or FIG. 10. Note that for illustration purposes, at least some dimensions in the Z-direction are exaggerated for improved visibility of the represented aspects.

[0057] The waveguide 1202 includes one or more mirror arrays, such as an IC 1232, an EPE 1206, and an OC 1208. The term “waveguide”, as used herein, will be understood to mean a combiner using one or more of total internal reflection (TIR), specialized filters, and / or reflective surfaces to transfer light from an input coupler (such as the IC 1232) to an output coupler (such as the OC 1208). In some display applications, the light is a collimated image, and the waveguide transfers and replicates the collimated image to the eye. In general, an input coupler and output coupler each includes, for example, one or more optical grating structures, including, but not limited to, reflective gratings, diffraction 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 at least 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. One or more of the input coupler 1232, the EPE 1206, or the OC 1208 are configured as described above with respect to FIG. 3 to FIG. 6, FIG. 9, or FIG. 10. Also, one or more of the input coupler 1232, the EPE 1206, or the OC 1208 are fabricated as part of the waveguide 1202 or are fabricated separately from the waveguide 1202 and then bonded thereto.

[0058] In the present example, the IC 1232 receives the display light 1210 and relays this light 1210 to the output coupler 1208 via the waveguide 1202 using TIR. For example, the IC 1232 directs the display light 1210 into the waveguide 1202. The ERE 1206 is arranged in an intermediate stage between IC 1232 and the OC 1208 to receive light that is coupled into waveguide 1202 by the IC 1232, expand the light, and redirect the light towards the OC 1208, where the OC 1208 then couples the light out of waveguide 1202 (e.g., toward the eye 1234 of the user). As described above, in some embodiments, the waveguide 1202 is implemented as part of an eyeglass lens, such as the lens 1126 or lens 1128 (FIG. 11 ) of the display system 1200 having an eyeglass form factor and employing the display system 1200.

[0059] In this example implementation, the waveguide 1202 implements facets as part of the ERE 1206, facets as part of the OC 1208, and facets as part of the IC 1232. The facets for these different components or regions are implemented toward the eye-facing side 1236 or the world-facing side 1238 of the waveguide 1202. Thus, under this approach, display light 1210 emitted or projected from a light source 1240 is incoupled to the waveguide 1202 via the IC 1232 and propagated (through total internal reflection in this example) toward the EPE 1206, whereupon the facets of the EPE 1206 reflect the incident display light for exit pupil expansion purposes, and the resulting light is propagated to the facets of the OC 1208, which output the display light toward a user’s eye 1234.

[0060] In at least some embodiments, operation of the display system 1200 includes, for example, projecting light from the image source 1240 into the waveguide 1202 through the input coupler 1232. The projected light is transmitted along the waveguide 1202 by total internal reflection and reflections from the prism arrays. At least a portion of the transmitted light is outputted in the direction of the user’s eye 1234 through the output coupler 1208. In this manner, the waveguide 1202 provides an optical path that enables images generated by the image source 1240 to be perceived by the user when worn as part of the head-mounted display system.

[0061] 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 storagemedium. 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.

[0062] 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)).

[0063] 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 anillustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present disclosure.

[0064] 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, comprising: an input coupler; an exit pupil expander comprising a first prism array; an output coupler comprising a second prism array; and a seamless transition at an interface between the first prism array and the second prism array, the seamless transition comprising at least one prism geometric parameter having a value for each pair of corresponding prisms of the first prism array and the second prism array that is matched or varied across the interface.

2. The waveguide of claim 1 , wherein the at least one prism geometric parameter comprise one or more of prism heights, polar angles of front surfaces of prisms, or polar angles of back surfaces of prisms.

3. The waveguide of any one of claims 1 or 2, wherein the value of the at least one prism geometric parameter is constant for each pair of corresponding prisms across the interface.

4. The waveguide of any one of claims 1 or 2, wherein the value of the at least one prism geometric parameter varies among pairs of corresponding prisms across the interface.

5. The waveguide of any one of claims 2 to 4, wherein the at least one prism geometric parameter comprises prism heights, and wherein prism heights of corresponding prisms in the first prism array and the second prism array at the seamless transition satisfy Hb = He, where Hb represents a height of a prism in the first prism array, and Hc, represents a height of a corresponding prism in the second prism array.

6. The waveguide of any one or claims 2 to 5, wherein the at least one prism geometric parameter comprises polar angles of front surfaces of prisms, and wherein polar angles of front surfaces of corresponding prisms in the firstprism array and the second prism array at the seamless transition satisfy tan(ab) * sin(6b) = tan(ac) * sin(0c), where ab and acare the polar angles of the front surfaces of corresponding prisms in the first prism array and the second prism array, respectively, and 0b and 0Care angles relative to a seam between the first prism array and the second prism array.

7. The waveguide of any one of claims 2 to 6 wherein the at least one prism geometric parameter comprises polar angles of back surfaces of prisms, and wherein polar angles of back surfaces of corresponding prisms in the first prism array and the second prism array at the seamless transition satisfy tan(Pb) I sin(0b) = tan(pc) I sin(0c), where Pb and pcare the polar angles of the back surfaces of corresponding prisms in the first prism array and the second prism array, respectively, and 0b and 0Care angles relative to a seam between the first prism array and the second prism array.

8. The waveguide of any one of claims 1 to 7, wherein the seamless transition comprises an uncoated region between the first prism array and the second prism array.

9. The waveguide of claim 8, wherein the uncoated region is immediately adjacent to the interface.

10. The waveguide of any one of claims 1 to 9, wherein the second prism array comprises prisms having curved prism surfaces.11 . The waveguide of claim 10, wherein the seamless transition comprises a curved interface.

12. The waveguide of claim 11 , wherein the curved interface is defined by a polynomial curve.

13. The waveguide of claim 12, wherein polynomial coefficients of the polynomial curve are configured to maintain geometric continuity between prisms of the first prism array and prisms of the second prism array.

14. The waveguide of any one of claims 1 to 13, wherein prisms of the first prism array and prisms of the second prism array comprise polymer prisms.

15. A wearable head-mounted display system comprising: the waveguide of any of claims 1 to 14; an image source to project light comprising an image; and at least one lens element.

16. A method of operating the wearable head-mounted display system of claim 15, the method comprising: projecting the light from the image source to the waveguide; transmitting the projected light along the waveguide; and outputting at least a portion of the transmitted light in the direction of an eye of a user of the wearable head-mounted display system.

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