Waveguides with overlapping reflecting surfaces

Abstract

The waveguide includes an output coupler implemented within the waveguide as a group of reflective surfaces arranged along a first direction. Each reflective surface is created by applying a reflective coating to a planar surface of one or more substrates. Adjacent reflective surfaces in the group overlap each other along the first direction. For example, a front portion of one reflective surface in the group overlaps a rear portion of an adjacent reflective surface.

Description

[Background technology]

[0001] In an eyewear display, display light beams from a light engine are first coupled into a waveguide by an input coupler formed on one or more surfaces of the waveguide or disposed within the waveguide. After the display light beams are coupled into the waveguide, the input-coupled display light beams are "guided" through the waveguide, typically by multiple total internal reflections (TIR), and then directed out of the waveguide by an output coupler, which may be formed on or within the waveguide. The output-coupled display light beams overlap at an eye relief distance from the waveguide to form an exit pupil. Within this exit pupil, a virtual image generated by the light engine can be viewed by a user of the eyewear display. The waveguide may also include an exit pupil expander positioned between the input and output couplers to expand the size of the exit pupil through which the user can view the virtual image.

[0002] In some cases, one or more of the input coupler, exit pupil expander, and output coupler are implemented within the waveguide as reflective surfaces. Conventional waveguides with reflective surfaces are prone to poor optical performance due to discontinuities in the virtual image transmitted to the user. Summary of the Invention

[0003] Various embodiments include a waveguide with overlapping reflective surfaces that reduce or eliminate discontinuities in the virtual image transmitted to a user of the eyewear display.

[0004] In a first embodiment, the waveguide includes a plurality of reflective surfaces arranged along a first direction within the waveguide. For example, the reflective surfaces are arranged consecutively in a linear fashion to realize an output coupler of the waveguide. Adjacent reflective surfaces of the reflective surfaces overlap each other along the first direction.

[0005] In some aspects of the first embodiment, the waveguide includes two substrates. A first substrate of the two substrates includes a first plurality of planar surfaces, and a second substrate of the two substrates includes a second plurality of planar surfaces. In some aspects, the first plurality of planar surfaces and the second plurality of planar surfaces are at least partially (or completely) coated with a reflective coating, such as a metal layer coating or a dichroic layer coating. The first plurality of planar surfaces coated with the reflective coating are positioned to contact the second plurality of planar surfaces coated with the reflective coating. In this manner, each of the plurality of reflective surfaces is formed at the interface between the first plurality of planar surfaces having the reflective coating and the second plurality of planar surfaces having the reflective coating. In some cases, the waveguide includes a gap between the first substrate and the second substrate, and the gap is filled with an adhesive material to bond the first substrate to the second substrate. The adhesive material has a refractive index corresponding to the refractive index of the materials of the first substrate and the second substrate. For example, the refractive index of the adhesive material matches the refractive index of the materials of the first substrate and the second substrate.

[0006] In some aspects of the first embodiment, the waveguide includes a second plurality of reflective surfaces arranged consecutively along a first direction within the waveguide. The second plurality of reflective surfaces are adjacent to the plurality of reflective surfaces, and adjacent reflective surfaces of the second plurality of reflective surfaces overlap each other along the first direction. In some aspects, the waveguide includes a third substrate and a fourth substrate. The third substrate includes a third plurality of planar surfaces, and the fourth substrate includes a fourth plurality of planar surfaces. In some aspects, the third plurality of planar surfaces and the fourth plurality of planar surfaces are at least partially coated (or completely coated) with a second reflective coating. In some cases, the second reflective coating is different from the reflective coatings on the first plurality of planar surfaces and the second plurality of planar surfaces. In some aspects, the third plurality of planar surfaces coated with the second reflective coating are positioned to contact the fourth plurality of planar surfaces coated with the second reflective coating. In this manner, each of the second plurality of reflective surfaces is formed at the interface between a third plurality of planar surfaces having the second reflective coating and a fourth plurality of planar surfaces having the second reflective coating. In some embodiments, there is a gap between the third substrate and the fourth substrate, and the gap is filled with an adhesive material to bond the third substrate to the fourth substrate. In some embodiments, the adhesive material has a refractive index corresponding to the refractive index of the materials of the third and fourth substrates. In some embodiments, the adhesive material for bonding the third substrate to the fourth substrate is the same material as the adhesive material for bonding the first substrate to the second substrate. Furthermore, in some cases, there is an additional layer of adhesive material bonding the first substrate or the second substrate to the third substrate or the fourth substrate.

[0007] In a second embodiment, the waveguide includes a first plurality of reflective surfaces and a second plurality of reflective surfaces, the first plurality of reflective surfaces being arranged along a first direction within the waveguide, and adjacent reflective surfaces of the first plurality of reflective surfaces overlapping each other along the first direction, and the second plurality of reflective surfaces being arranged along the first direction within the waveguide, and adjacent reflective surfaces of the second plurality of reflective surfaces overlapping each other along the first direction.

[0008] In some aspects of the second embodiment, the first plurality of reflective surfaces are configured to reflect light in a first wavelength region and transmit light in a second wavelength region, hi some aspects, the second plurality of reflective surfaces are configured to reflect light in the second wavelength region, and light reflected from the second plurality of reflective surfaces passes through the first plurality of reflective surfaces.

[0009] In a third embodiment, a method includes reflecting light in an out-coupling direction via a first reflective surface of a plurality of reflective surfaces at an output coupler of the waveguide, and reflecting light in the out-coupling direction via a second reflective surface of the plurality of reflective surfaces at the output coupler, where a portion of the light reflected from the second reflective surface overlaps with a portion of the light reflected from the first reflective surface. In some aspects of the third embodiment, the plurality of reflective surfaces are arranged consecutively along a first direction within the waveguide, and adjacent reflective surfaces of the plurality of reflective surfaces overlap each other along the first direction.

[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, in which: The use of the same reference symbols in different drawings indicates similar or identical items. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 illustrates an exemplary eyewear display, according to some embodiments. [Figure 2] FIG. 2 illustrates an exemplary projection system in which an optical filter is positioned between the optical engine and the input coupler of the eyewear display waveguide, as shown in FIG. 1, in accordance with some embodiments. [Figure 3] 3A and 3B are plan views illustrating examples of light propagation within a waveguide of the projection system of FIG. 2, according to some embodiments. [Figure 4] 1A-1C illustrate examples of conventional reflective surface configurations and problems associated with such configurations. [Figure 5]1A-1C illustrate examples of overlapping reflective surfaces that implement one or more of an input coupler, an exit pupil expander, or an output coupler in a waveguide, according to various embodiments. [Figure 6] 10A-10C illustrate alternative examples of overlapping reflective surfaces that implement one or more of the input coupler, exit pupil expander, or output coupler in a waveguide, according to various embodiments. [Figure 7] 10A-10C illustrate alternative examples of overlapping reflective surfaces that implement one or more of the input coupler, exit pupil expander, or output coupler in a waveguide, according to various embodiments. [Figure 8] 10A-10C illustrate alternative examples of overlapping reflective surfaces that implement one or more of the input coupler, exit pupil expander, or output coupler in a waveguide, according to various embodiments. [Figure 9] 1A-1C illustrate examples of stacks of multiple groups of overlapping reflective surfaces, according to some embodiments. [Figure 10] FIG. 1 illustrates a flowchart of a method for reflecting light by overlapping reflective surfaces, according to some embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0012] A reflective surface waveguide includes one or more reflective surfaces to implement one or more of an input coupler, an output coupler, or an exit pupil expander. Taking the output coupler as an example, the output coupler is realized as a reflective surface that receives light from the exit pupil expander and reflects the light from the light guide toward a user. Typically, reflective surfaces are created by applying a reflective coating to continuous flat surfaces on a molded plastic or polymer substrate. Ideally, each reflective surface has sharp edges on both edges and no gaps between adjacent reflective surfaces. However, in reality, conventional molded plastic substrates have rounded edges and draft angles (i.e., non-perpendicular angles) between the flat surfaces due to the molding process constraints. These rounded edges and draft angles result in gaps between adjacent conventional reflective surfaces on the flat surfaces. The gaps between adjacent conventional reflective surfaces result in gaps in the out-coupled light, which in turn results in discontinuities in the virtual image transmitted to the user. For example, if the virtual image is assumed to be a straight line, gaps in the outcoupled light create "blips" in the line perceived by the user. Described herein are waveguides with overlapping reflective surfaces. These waveguides eliminate these gaps in the light that is outcoupled to the user, thereby reducing or eliminating the discontinuities in the virtual image perceived by the user. This improves the optical performance of the waveguides and eyewear displays incorporating such waveguides.

[0013] For example, in some embodiments, the waveguide includes optical components such as an input coupler, an exit pupil expander, and an output coupler. One or more of these optical components are implemented in the waveguide as a group of reflective surfaces arranged along a first direction, i.e., the reflective surfaces in the group are arranged consecutively along a common direction. In some embodiments, each reflective surface is created by applying a reflective coating to the planar surface of one or more substrates. Adjacent reflective surfaces in the group overlap each other along the first direction. For example, the front portion (also called the "tip") of one reflective surface in the group overlaps the rear portion (also called the "base") of the adjacent reflective surface. In this way, the group of reflective surfaces eliminates gaps that may result from rounded edges and draft angles of one or more substrates. This reduces discontinuities in the light beam outcoupled by the waveguide, thereby improving the quality of the image produced by the outcoupled light beam.

[0014] To further illustrate, in another embodiment, one or more of the input coupler, the exit pupil expander, and the output coupler are each implemented as two groups of reflective surfaces. The first group of reflective surfaces is arranged consecutively along a first axis, and the second group of reflective surfaces is arranged consecutively along a second axis, where the first axis is parallel to the second axis. The first group of reflective surfaces is offset relative to the second group of reflective surfaces such that the first group of reflective surfaces overlaps the second group of reflective surfaces when viewed perpendicular to the first axis or the second axis. In this manner, light reflected from the two groups of reflective surfaces overlaps, thereby minimizing or eliminating discontinuities in the light coupled out to the user.

[0015] FIG. 1 illustrates an exemplary eyewear display 100 according to various embodiments. The eyewear display 100 (also referred to as a wearable head-up display (WHUD), head-mounted display (HMD), near-eye display, etc.) has a support structure 102 including an arm 104 housing a microdisplay projection system configured to project images toward a user's eyes, such that the user perceives the projected images as displayed in a display field of view (FOV) area 106 on one or both of lens elements 108, 110. In the illustrated embodiment, the support structure 102 of the eyewear display 100 is configured to be worn on the user's head and has the general shape and appearance (i.e., form factor) of an eyeglass frame. The support structure 102 incorporates or otherwise comprises various components to facilitate projecting such images toward the user's eyes, such as a light engine and a waveguide (as illustrated in FIG. 2 ). In 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, etc. The support structure 102 may further include one or more radio frequency (RF) interfaces or other wireless interfaces, such as a Bluetooth interface, a WiFi interface, etc. Additionally, in some embodiments, the support structure 102 includes one or more batteries or other portable power sources for powering the electrical components of the eyewear display 100. In some embodiments, some or all of these components of the eyewear display 100 are housed completely or partially within the interior space of the support structure 102, such as within the arms 104 in region 112 of the support structure 102. It should be noted that while an exemplary form factor is shown, in other embodiments, the eyewear display 100 may have a different shape and appearance than the eyeglass frames shown in FIG. 1 .

[0016] One or both of the lens elements 108, 110 may be used by the eyewear display 100 to provide an augmented reality (AR) or mixed reality (MR) display in which rendered graphical content is overlaid on or provided in conjunction with a real-world view perceived by a user through the lens elements 108, 110. In some embodiments, one or both of the lens elements 108, 110 function as a light combiner that combines ambient light (also referred to as ambient light) from outside the eyewear display 100 with light emitted from a light engine of the eyewear display 100. For example, light used to form a recognizable image or series of images may be projected by the light engine of the eyewear display 100 to the user's eye via a series of optical elements, such as a waveguide, one or more scanning mirrors, one or more optical relays, and / or one or more prisms, formed at least partially in the corresponding lens element. Thus, one or both of lens elements 108, 110 include at least a portion of a waveguide that transmits display light received by an input coupler of the waveguide to an output coupler of the waveguide, which outputs the display light toward the eye of a user of eyewear display 100. The display light is modulated and projected to the user's eye such that the user perceives the display light as an image within FOV area 106. Additionally, in some embodiments, each of lens elements 108, 110 is sufficiently transparent to allow the user to see through the lens element, thereby providing a view of the user's real-world environment, such that the image appears superimposed on at least a portion of the real-world environment.

[0017] In some embodiments, the light engine is a matrix-based projector, a scanning laser projector, or any combination of a modulated light source, such as a laser or one or more LEDs, and a dynamic reflector mechanism, such as one or more dynamic scanners or digital light processors. In some embodiments, the light engine includes, for example, multiple laser diodes (e.g., red, green, and / or blue laser diodes) and at least one scan mirror (e.g., two one-dimensional scan mirrors that are microelectromechanical systems (MEMS)-based or piezoelectric). The light engine is communicatively coupled to a controller and a non-transitory processor-readable storage medium or memory that stores processor-executable instructions and other data that, when executed by the controller, cause the controller to control the operation of the projector. In some embodiments, the controller is communicatively coupled to a processor (not shown) that controls the scan area size and scan area position of the light engine and generates the content displayed on the eyewear display 100. The light engine scans light over a variable area of ​​the display system 100, designated by the FOV area 106. The scan area size corresponds to the size of the FOV area 106, and the scan area position corresponds to the area of ​​one of the lens elements 108, 110 where the FOV area 106 is visible to the user. It is generally desirable for the display to have a wide FOV to accommodate light output coupling over a wide range of angles. The range of varying user eye positions from which the display can be viewed is referred to herein as the eyebox of the eyewear display 100.

[0018] As previously mentioned, the waveguide is integrated into one or both of the lens elements 108, 110. In some configurations, the waveguide includes a single waveguide substrate, while in other configurations, the waveguide includes multiple waveguide substrates stacked on top of each other (referred to as a waveguide stack). The waveguide optionally includes one or more of an input coupler that couples light from a light engine into the waveguide, an exit pupil expander that expands the coupled light in one dimension into the waveguide, and an output coupler that couples display light into the eyebox of the eyewear display 100. In some cases, one or more of the input coupler, exit pupil expander, and output coupler are implemented within the waveguide as corresponding reflective surfaces. For example, the output coupler is made of reflective surfaces that receive light from the exit pupil expander and redirect the light from the waveguide through the FOV region 106 to the user. In some embodiments, the reflective surfaces overlap each other to minimize or eliminate gaps in the light that is coupled out to the user. This reduces visual artifacts in the virtual image conveyed to the user, thereby improving the optical performance of the eyewear display 100.

[0019] 2 shows a diagram of a projection system 200 for projecting an image to a user's eye 216, according to various embodiments. The projection system 200, which can be implemented in the eyewear display 100 shown in FIG. 1, includes one or more of a light engine 202, an optical scanner 220, and / or a waveguide 210. In this example, the optical scanner 220 includes a first scan mirror 204, a second scan mirror 206, and an optical relay 208. The waveguide 210 includes one or more input couplers 212 and one or more output couplers 214, where the one or more output couplers 214 are positioned to be optically aligned with the user's eye 216. For example, the one or more output couplers 214 substantially overlap with the FOV region 106 shown in FIG. 1.

[0020] The light engine 202 includes one or more light sources configured to generate and output light 218 (e.g., visible light, such as red, blue, and green laser light, and / or non-visible laser light, such as infrared laser light). In some embodiments, the light engine 202 is coupled to a controller or driver (not shown) that controls the timing of light emission from the light sources of the light engine 202 (i.e., according to instructions received by the controller or driver from a computer processor coupled thereto) and modulates the light 218 to be perceived as an image when output to the retina of a user's eye 216. For example, during operation of the projection system 200, one or more display light beams 218 are output from the light source(s) of the light engine 202, then directed into the waveguide 210, and ultimately to the user's eye 216. The light engine 202 modulates the intensity of each of the light beams such that the combined light reflects off a series of pixels of an image, with the particular intensity of each light beam at any given time contributing to the corresponding color content and amount of brightness of the pixel as represented by the light combined at that time.

[0021] In some embodiments, optical scanner 220 includes first scan mirror 204, second scan mirror 206, and optical relay 208. In some embodiments, one or both of scan mirrors 204 and 206 are MEMS mirrors. For example, scan mirror 204 and scan mirror 206 are MEMS mirrors that, when driven by respective actuation voltages, oscillate during active operation of laser projection system 200, causing scan mirrors 204 and 206 to scan laser light 218. Oscillating scan mirror 204 causes light 218 output by optical engine 202 to be scanned across the surface of second scan mirror 206 through optical relay 208. Second scan mirror 206 scans light 218 received from scan mirror 204 toward input coupler 212 of waveguide 210.

[0022] The waveguide 210 of the projection system 200 includes an input coupler 212 and an output coupler 214. As used herein, the term "waveguide" should be understood to mean a combiner that transmits light from an input coupler to an output coupler using total internal reflection (TIR) ​​or a combination of TIR, special filters, and / or reflective surfaces. In a display application, for example, the light represents a collimated image, and the waveguide transmits and replicates the collimated image to the eye. In general, the terms "input coupler" and "output coupler" should be understood to refer to any type of optical grating structure, including, but not limited to, reflective surfaces, diffraction gratings, tilted gratings, blazed gratings, holograms, holographic optical elements (e.g., optical elements that use one or more holograms), volume diffraction gratings, volume holograms, surface-relief diffraction gratings, and / or surface-relief holograms. In some embodiments, one or more of the input coupler 212, the exit pupil expander (not shown in FIG. 2), and the output coupler 214 are implemented within the waveguide 210 by corresponding reflective surfaces. In this example, light 218 received at the input coupler 212 is propagated through the waveguide 210 to the output coupler 214 using TIR. The laser light 218 is then output through the output coupler 214 to the user's eye 216.

[0023] 3 illustrates, in plan view, an example of light propagation within the waveguide 210 of the projection system 200 of FIG. 2. As shown, light is received via the input coupler 212 and directed to the exit pupil expander (EPE) 316 as light 320, and then directed to the output coupler 214 as light 322, where it is output from the waveguide 212 toward the user's eye (e.g., the light is reflected by the output coupler 214 toward the outside of the drawing). In some embodiments, the exit pupil expander 316 expands one or more dimensions of the eyebox of an eyewear display that includes the laser projection system 200 (e.g., relative to the dimensions of the eyebox of the eyewear display without the exit pupil expander 316). In some embodiments, at least one of the input coupler 212, the exit pupil expander 316, and the output coupler 214 each include a group of reflective surfaces. For example, at input coupler 212, a first set of reflective surfaces 312 (labeled one for clarity) receives light emitted from a light engine (such as from light engine 202 in FIG. 2 , not shown in FIG. 3 ) and reflects the light so that light 320 is coupled into waveguide 210. A second set of reflective surfaces 318 (labeled one for clarity) at exit pupil expander 316 receives the coupled light 320 and reflects it so that it is expanded in a second direction 322 toward output coupler 214. A third set of reflective surfaces 314 (labeled one for clarity) at output coupler 214 reflects the light received from exit pupil expander 316 so that light is coupled out of waveguide 210. As described further herein, in some embodiments, the reflective surfaces overlap with other adjacent reflective surfaces in a corresponding group of reflective surfaces to eliminate gaps in the light reflected from the respective optical component (e.g., from output coupler 214).

[0024] 4 shows a cross-sectional view 400 illustrating a conventional group of reflective surfaces 420-428 within a waveguide (not shown for clarity) and the associated problems. For example, when implemented within the waveguide as an output coupler, the conventional group of reflective surfaces 420-428 receives light from an exit pupil expander coming from a first direction indicated by arrow 401 and redirects the light out of the waveguide towards a user in a second direction indicated by arrow 403.

[0025] Typically, substrate 402 is fabricated by a molding process and is made from a plastic or polymer material that is at least partially transparent. Molded substrate 402 includes a plurality of planar surfaces 418 (one labeled for clarity). Molded substrate 402 also includes a plurality of secondary planar surfaces 430 (one labeled for clarity). Conventional reflective surfaces 420-428 are formed by applying a reflective coating to the planar surfaces 418. Because the planar surfaces 418 of substrate 402 have acute angles and the secondary planar surfaces are perpendicular, ideally there would be no gaps between adjacent reflective surfaces. In practice, molded plastic substrates such as substrate 402 do not meet this ideal shape and instead include a rounded tip 444 (one labeled for clarity) and a rounded base 442 (one labeled for clarity). Additionally, the quadratic planes 430 of a molded plastic substrate, such as substrate 402, are not perpendicular, resulting in a draft angle 440 (labeled one for clarity) between the base 442 of one conventional reflective surface 428 and the tip 444 of an adjacent conventional reflective surface 426. The combination of the rounded edges and the draft angle 440 (i.e., base 442 and tip 442) creates gaps between adjacent conventional reflective surfaces 420-428, which in turn creates gaps in the light reflected by conventional reflective surfaces 420-428. For example, with reference to conventional reflective surfaces 422 and 424, a gap 452 exists between light 450-1 reflected by conventional surface 424 and light 450-2 reflected by conventional surface 422. These gaps 452 degrade optical performance by creating discontinuities in the virtual image conveyed to the user.

[0026] FIG. 5 illustrates an exemplary cross-sectional view 500 of overlapping reflective surfaces 520-528 implemented as an output coupler of a waveguide (not shown for clarity), according to various embodiments. In some embodiments, the overlapping reflective surfaces 520-528 are included in a waveguide (such as waveguide 210 in FIGS. 2 and 3) to implement one or more of an input coupler, an exit pupil expander, or an output coupler. For example, when implemented as part of an output coupler (such as output coupler 214 in the previous figures), the reflective surfaces 520-528 are positioned within the waveguide to receive light from the exit pupil expander coming from the direction indicated by arrow 501 and redirect the light from the waveguide to another direction indicated by arrow 503 (referred to as the "output coupling direction"). As illustrated, the successive reflective surfaces 520-528 (also referred to as multiple reflective surfaces) are arranged successively (e.g., sequentially) along the direction indicated by arrow 503 within the waveguide.

[0027] As shown in cross-sectional view 500, reflective surfaces 520-528 include overlapping regions 530 (labeled one for clarity) between adjacent ones of reflective surfaces 520-528. That is, reflective surfaces 520-528 are positioned consecutively along a first direction (e.g., corresponding to arrow 501), with adjacent reflective surfaces of the reflective surfaces overlapping one another along the first direction. In some embodiments, as shown, each of reflective surfaces 520-528 is oriented to be parallel or substantially parallel to one another. For example, with reference to reflective surfaces 526 and 528, the bottom (also referred to as the back end or base) of reflective surface 528 overlaps with the top (also referred to as the front end or tip) of reflective surface 526 in the out-coupling direction 503, as illustrated by overlapping region 530. That is, when viewed in the direction of arrow 503, the footprint of reflective surface 526 and the footprint of reflective surface 528 overlap one another over an area indicated by overlap region 530. The overlap region 530 between adjacent ones of reflective surfaces 520-528 eliminates the aforementioned light gaps caused by conventional reflective surfaces (e.g., as shown in FIG. 4), thereby eliminating discontinuities in the outcoupled light and improving the quality of the image transmitted by the waveguide. In some embodiments, overlap region 530 is up to about 500 μm, or in other embodiments, up to about 250 μm. For example, in some configurations, overlap region 530 is minimized (i.e., designed to approach zero) because increasing the amount of overlap can increase the thickness of the waveguide.

[0028] By way of example, in some embodiments, the multiple overlapping reflective surfaces 520-528 are fabricated by applying a reflective coating to a first plurality of planar surfaces 510-1, 512-1, 514-1, 516-1, 518-1 on the first substrate 502-1 and a second plurality of planar surfaces 510-2, 512-2, 514-2, 516-2, 518-2 on the second substrate 502-2. Each of the first plurality of planar surfaces 510-1, 512-1, 514-1, 516-1, 518-1 is oriented parallel or substantially parallel to one another. In some embodiments, the reflective coating is a metallic coating, a dichroic coating, a dielectric coating, a holographic coating, a partially reflective / transmissive coating, or the like. In some embodiments, the secondary reflective surfaces 536-1 (labeled one for clarity) on the first substrate 502-1 and the secondary reflective surfaces 536-2 (labeled one for clarity) on the second substrate 502-2 are also at least partially covered with a reflective coating. The first substrate 502-1 and the second substrate 502-2 are positioned such that corresponding ones of the reflective surfaces coated with the reflective coating face each other. For example, the first substrate 502-1 is positioned such that one of the first plurality of flat surfaces 518-1 coated with the reflective coating contacts one of the second plurality of flat surfaces 518-2 coated with the reflective coating of the second substrate 502-2. As shown, the first substrate 502-1 and the second substrate 502-2 are positioned such that an offset exists relative to each other, such that a portion of a major surface on the first substrate 502-1 protrudes beyond the corresponding major surface on the second substrate 502-2, and a portion of a corresponding major surface on the second substrate 502-2 protrudes beyond the major surface on the first substrate 502-1. This offset creates overlap regions 530 (labeled one for clarity) between adjacent ones of the reflective surfaces 520-528. Furthermore, this offset creates a gap 540 (labeled one for clarity) between the secondary planar surface 536-1 (labeled one for clarity) of the first substrate 502-1 and the secondary planar surface 536-2 (labeled one for clarity) of the second substrate 502-2.That is, for example, the secondary surface 536-2 of the second substrate 502-2 is not positioned flush with the secondary surface 536-1 of the first substrate 502-1, resulting in a gap 540 between the first substrate 502-1 and the second substrate 502-2. In some embodiments, the gap 540 is filled with an adhesive or polymer material. The adhesive or polymer material serves to secure the first substrate 502-1 to the second substrate 502-2. Furthermore, the adhesive or polymer material has a refractive index that matches the refractive index of the materials forming the first substrate 502-1 and the second substrate 502-2. For example, in some embodiments, the first substrate 502-1, the second substrate 502-2, and the adhesive or polymer material filling the gap 540 all have the same refractive index, or substantially the same (e.g., within 5%).

[0029] 5 also shows an additional cross-sectional view 550 of overlapping reflective surfaces 520-528 reflecting light in the direction indicated by arrow 503. As shown, the overlapping reflective surfaces 520-528 eliminate gaps in light reflected from adjacent reflective surfaces in conventional reflective surface configurations, such as gap 452 shown in FIG. 4. By eliminating gaps in light reflected from adjacent reflective surfaces, a waveguide with overlapping reflective surfaces 520-528 (such as waveguide 210 in the previous figures) reduces discontinuities (i.e., gaps) in the light that is coupled out, thereby improving the quality of the virtual image presented to the user.

[0030] In some embodiments, the first substrate 502-1 and the second substrate 502-2 are positioned to reduce the area of ​​the overlap region 530. In this way, light reflected from the bottom of one reflective surface (e.g., from the bottom of reflective surface 522) being blocked by the top of an adjacent reflective surface (e.g., from the top of reflective surface 520) is minimized. Figure 5 shows five overlapping reflective surfaces 520-528. In other embodiments, the number of overlapping reflective surfaces is a number other than five.

[0031] The above embodiment illustrated in Figure 5 describes the continuous reflective surface as being planar. In other embodiments, the continuous reflective surface is non-planar (i.e., curved). Furthermore, in some embodiments, the reflective surface at the top and bottom of the reflective surface varies in wavelength sensitivity, reflectivity, polarization sensitivity, etc. Similarly, in some embodiments, the wavelength sensitivity, reflectivity, polarization sensitivity, etc. varies across the surface of a particular reflective surface.

[0032] 5, there may be a reduction (at least to some extent) in the brightness of light reflected from the reflective surfaces in the overlapping regions 530 compared to light reflected from non-overlapping regions. However, any reduction in brightness in the overlapping regions 530 (e.g., from 100% to 50%, or even from 100% to 25%) is still advantageous compared to the complete reduction in brightness (i.e., from 100% to 0%) caused by the gap in the conventional configuration described in FIG.

[0033] 6 and 7 illustrate alternative examples of overlapping reflective surfaces on which one or more of the waveguide input coupler, exit pupil expander, or output coupler are implemented, according to various embodiments. In some aspects, the alternative embodiments shown in FIGS. 6 and 7 facilitate film processing to achieve thinner substrates and smaller reflective surfaces.

[0034] 6 shows an example cross-sectional view 600 of overlapping reflective surfaces. A first reflective coating 604-1 is applied to a first substrate 602-1, and a second reflective coating 604-2 is applied to a second substrate 602-2 to form a first reflective surface group 620-1, 622-1, 624-1, 626-1, 628-1 on the first substrate 602-1, and a second reflective surface group 620-2, 622-2, 624-2, 626-2, 628-2 on the second substrate 602-2. The first group of reflective surfaces 620-1, 622-1, 624-1, 626-1, 628-1 and the second group of reflective surfaces 620-2, 622-2, 624-2, 626-2, 628-2 receive light from the direction indicated by arrow 601 and reflect it towards the direction indicated by arrow 603. The second group of reflective surfaces 620-2, 622-2, 624-2, 626-2, 628-2 overlap with the first group of reflective surfaces 620-1, 622-1, 624-1, 626-1, 628-1 and fill in the gaps in the light reflected by the first group of reflective surfaces 620-1, 622-1, 624-1, 626-1, 628-1.

[0035] In some embodiments, the first reflective coating 604-1 applied to the first substrate 602-1 is different from the second reflective coating 604-2 applied to the second substrate 602-2. For example, the first reflective coating 604-1 is a reflective coating that reflects red light, and the second reflective coating 604-2 is a dichroic coating that transmits red light and reflects green light.

[0036] An adhesive film 608 is provided between the first reflective coating film 604-1 and the second reflective coating film 604-2. In some embodiments, the adhesive film 608 has a refractive index that matches the refractive index of the material of the first substrate 602-1 and the second substrate 602-2. For example, the adhesive film 608 has the same refractive index (or substantially the same within 5%) as the refractive index of the material of the first substrate 602-1 and the second substrate 602-2.

[0037] 7 shows an example cross-sectional view 700 of overlapping reflective surfaces. A first reflective coating 704-1 is applied to a first substrate 702-1, and a second reflective coating 704-2 is applied to a second substrate 702-2, forming a first reflective surface group 720-1, 722-1, 724-1, 726-1, 728-1 on the first substrate 702-1, and a second reflective surface group 720-2, 722-2, 724-2, 726-2, 728-2 on the second substrate 702-2. The first group of reflective surfaces 720-1, 722-1, 724-1, 726-1, 728-1 and the second group of reflective surfaces 720-2, 722-2, 724-2, 726-2, 728-2 receive light from the direction indicated by arrow 701 and reflect it towards the direction indicated by arrow 703. The second group of reflective surfaces 720-2, 722-2, 724-2, 726-2, 728-2 overlap with the first group of reflective surfaces 720-1, 722-1, 724-1, 726-1, 728-1 and fill in the gaps in the light reflected by the first group of reflective surfaces 720-1, 722-1, 724-1, 726-1, 728-1.

[0038] In some embodiments, the first reflective coating 704-1 applied to the first substrate 702-1 is different from the second reflective coating 704-2 applied to the second substrate 702-2. For example, the first reflective coating 704-1 is a reflective coating that reflects red light, and the second reflective coating 704-2 is a dichroic coating that transmits red light and reflects green light.

[0039] An adhesive film 708 and an intermediate film 710 are provided between the first reflective coating film 704-1 and the second reflective coating film 704-2. In some embodiments, the adhesive film 708 and the intermediate film 710 have refractive indices that match the refractive indices of the materials of the first substrate 702-1 and the second substrate 702-2. For example, the adhesive film 708 and the intermediate film 710 are the same (or substantially the same within 5%) as the refractive indices of the materials of the first substrate 702-1 and the second substrate 702-2. For example, the adhesive film 708 and the intermediate film 710 include a material such as polycarbonate, polymethyl methacrylate (PMMA, or acrylic), etc. In some embodiments, the intermediate film 710 minimizes the thickness of the adhesive film 708. For example, the intermediate film 710 is made from the same material as the first substrate 702-1 and the second substrate 702-2.

[0040] Figure 8 shows a cross-sectional view 800 illustrating an example of overlapping reflective surfaces corresponding to those shown in Figures 7 and 8. An adhesive film 808 is also shown between the first substrate 802-1 and the second substrate 802-2. As shown, the second reflective surfaces 810-2, 812-2, 814-2, 818-2 (the label of the fourth reflective surface has been omitted for clarity) of the second substrate 802-2 fill the gaps in light reflected from the first reflective surfaces 810-1, 812-1, 814-1, 816-1, 818-1 of the first substrate 802-1. For example, a reflective surface (not labeled for clarity) in the second group of reflective surfaces between surface 814-2 and surface 818-2 reflects light 822-2 to fill the gap between light 822-1 reflected from reflective surface 816-1 and light 820-1 reflected from reflective surface 818-1. As with the previous figures, light is received from the direction indicated by arrow 801.

[0041] 9 illustrates an exemplary cross-sectional view 900 of a stack of overlapping reflective surfaces, according to various embodiments. For example, the stack may include multiple layers 902-1, 902-2, each implementing a separate overlapping reflective surface, such as the overlapping reflective surfaces illustrated in FIG.

[0042] The first layer 902-1 includes a first substrate 904-1 and a second substrate 906-1 (e.g., corresponding to substrates 502-1 and 502-2, respectively, in FIG. 5 ) on which a first (also referred to as a first plurality) of overlapping reflective surfaces 910-1, 912-1, 914-1, 916-1, 918-1 are mounted. As shown, the first overlapping reflective surfaces 910-1, 912-1, 914-1, 916-1, 918-1 are arranged adjacent to and consecutively with one another along the first direction 901. Adjacent ones of the first overlapping reflective surfaces 910-1, 912-1, 914-1, 916-1, 918-1 overlap each other along the first direction 901. The resulting gap 920-1 (labeled one for clarity) between the first substrate 904-1 and the second substrate 906-1 is filled with an adhesive or polymer material having a refractive index that matches the refractive index of the materials of the first substrate 904-1 and the second substrate 906-1. Thus, the first set of overlapping reflective surfaces 910-1, 912-1, 914-1, 916-1, 918-1 reflect light without gaps or discontinuities. In some embodiments, the first set of overlapping reflective surfaces 910-1, 912-1, 914-1, 916-1, 918-1 are made of a dichroic or other partially reflective material that reflects light in a first wavelength region (e.g., blue and green light) and transmits light in a second wavelength region (e.g., red light).

[0043] The second layer 902-2 includes a third substrate 904-2 and a fourth substrate 906-2 (e.g., corresponding to substrates 502-1 and 502-2, respectively, in FIG. 5 ) that implement a second (also referred to as a second plurality) of overlapping reflective surfaces 910-2, 912-2, 914-2, 916-2, 918-2. As shown, the second sets of overlapping reflective surfaces 910-2, 912-2, 914-2, 916-2, 918-2 are adjacent to and consecutively disposed along the first direction 901 below the first sets of overlapping reflective surfaces 910-1, 912-1, 914-1, 916-1, 918-1. Adjacent ones of the second set of overlapping reflective surfaces 910-2, 912-2, 914-2, 916-2, 918-2 overlap one another along the first direction 901. Gaps 920-2 (labeled one for clarity) resulting between the third substrate 904-2 and the fourth substrate 906-2 are filled with an adhesive or polymer material having a refractive index that matches the refractive index of the materials of the third substrate 904-2 and the fourth substrate 906-2. Thus, the second set of overlapping reflective surfaces 910-2, 912-2, 914-2, 916-2, 918-2 reflect light without gaps or discontinuities. In some embodiments, the second set of overlapping reflective surfaces 910-2, 912-2, 914-2, 916-2, 918-2 is made from a dichroic or other partially reflective material that reflects light in a second wavelength range (e.g., red light) that was transmitted through the first set of overlapping reflective surfaces 910-1, 912-1, 914-1, 916-1, 918-1. In this manner, each set of reflective surfaces can be designed to reflect light in a specific wavelength range to increase the total amount of light reflected from the stack of multiple overlapping reflective surfaces.

[0044] 10 shows a flowchart 1000 illustrating a method for reflecting light from overlapping reflective surfaces according to various embodiments. For example, the overlapping reflective surfaces may be implemented as a waveguide output coupler as shown or described in one of the previous figures. The method includes reflecting light in an out-coupling direction via a first reflective surface in the overlapping reflective surfaces (1002). For example, the out-coupling direction is toward a user wearing an eyewear display, such as the eyewear display of FIG. 1. The method includes reflecting light in the out-coupling direction via a second reflective surface that overlaps the first reflective surface (1004).

[0045] In some embodiments, the techniques provided herein eliminate the gaps between reflective surfaces found in conventional reflective surface waveguides. Thus, the techniques provided herein provide reflective surface waveguides that transmit more uniform, higher-quality virtual images. In some embodiments, the techniques provided herein enable molding shorter reflective surfaces within each substrate to facilitate processing of the corresponding substrate. Furthermore, the techniques described herein enable thinner substrates, thereby enabling multiple substrates to be stacked together (e.g., as illustrated in FIG. 9 ) within an acceptable form factor (e.g., within the thickness of an eyewear display lens).

[0046] It should be noted that not all of the operations or elements described above in the general description are required, some of the specific operations or devices may not be required, and one or more additional operations may be performed or elements may be included in addition to those described. Furthermore, the order in which activities are listed is not necessarily the order in which they are performed. Also, concepts have been described with reference to specific embodiments. However, those skilled in the art will recognize 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 drawings should be regarded in an illustrative rather than a restrictive sense, and all such variations are intended to be within the scope of the present disclosure.

[0047] Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, and solutions to problems, as well as any feature or features that may cause or make more pronounced any benefit, advantage, or solution, should not be construed as critical, necessary, or essential features of any or all claims. Moreover, the specific embodiments disclosed above are exemplary only, as the disclosed inventive subject matter may be modified and practiced in different but equivalent manners that will be 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 set forth in the claims below. It is therefore apparent that the particular embodiments disclosed above may be altered or modified, and that all such variations are considered within the scope of the disclosed inventive subject matter. Accordingly, the protection sought herein is as set forth in the claims below.

Claims

1. A waveguide, a plurality of reflective surfaces arranged along a first direction in the waveguide; Adjacent reflecting surfaces of the plurality of reflecting surfaces overlap each other along the first direction.

2. 10. The waveguide of claim 1, further comprising two substrates, a first of the two substrates comprising a first plurality of planar surfaces and a second of the two substrates comprising a second plurality of planar surfaces.

3. The waveguide of claim 2 further comprising a reflective coating on the first plurality of planar surfaces and on the second plurality of planar surfaces.

4. 4. The waveguide of claim 3, wherein the first plurality of planar surfaces coated with the reflective coating are positioned to contact the second plurality of planar surfaces coated with the reflective coating.

5. 5. The waveguide of claim 4, wherein each of the plurality of reflective surfaces is formed at an interface between the first plurality of planar surfaces having the reflective coating and the second plurality of planar surfaces having the reflective coating.

6. 3. The waveguide of claim 2, further comprising a gap between the first substrate and the second substrate, the gap being filled with an adhesive material for adhering the first substrate to the second substrate.

7. 7. The waveguide of claim 6, wherein the adhesive material has a refractive index that corresponds to the refractive index of the materials of the first and second substrates.

8. 8. The waveguide of claim 7, wherein the refractive index of the adhesive material matches the refractive index of the materials of the first and second substrates.

9. 3. The waveguide of claim 2, further comprising a second plurality of reflective surfaces arranged consecutively along the first direction within the waveguide, the second plurality of reflective surfaces being adjacent to the plurality of reflective surfaces, and adjacent reflective surfaces of the second plurality of reflective surfaces overlapping each other along the first direction.

10. 10. The waveguide of claim 9, further comprising a third substrate and a fourth substrate, the third substrate comprising a third plurality of planar surfaces and the fourth substrate comprising a fourth plurality of planar surfaces.

11. 11. The waveguide of claim 10, further comprising a second reflective coating on the third and fourth plurality of planes, the second reflective coating being different from the reflective coatings on the first and second plurality of planes.

12. 12. The waveguide of claim 11, wherein the third plurality of planar surfaces coated with the second reflective coating are positioned to contact the fourth plurality of planar surfaces coated with the second reflective coating.

13. 13. The waveguide of claim 12, wherein each of the second plurality of reflective surfaces is formed at an interface between the third plurality of planar surfaces having the second reflective coating and the fourth plurality of planar surfaces having the second reflective coating.

14. 11. The waveguide of claim 10, further comprising a gap between the third substrate and the fourth substrate, the gap between the third substrate and the fourth substrate being filled with an adhesive material for adhering the third substrate to the fourth substrate, the adhesive material for adhering the third substrate to the fourth substrate having a refractive index corresponding to the refractive index of materials of the third substrate and the fourth substrate.

15. 15. The waveguide of claim 14, wherein an adhesive material for bonding the third substrate to the fourth substrate is the same material as the adhesive material for bonding the first substrate to the second substrate, and an additional layer of adhesive material bonds the first substrate or the second substrate to the third substrate or the fourth substrate.

16. A waveguide, a first plurality of reflective surfaces arranged in the waveguide along a first direction, adjacent reflective surfaces of the first plurality of reflective surfaces overlapping each other along the first direction, and the waveguide further comprises: a second plurality of reflective surfaces arranged within the waveguide along the first direction, adjacent reflective surfaces of the second plurality of reflective surfaces overlapping each other along the first direction.

17. 17. The waveguide of claim 16, wherein the first plurality of reflective surfaces are configured to reflect light in a first wavelength range and transmit light in a second wavelength range.

18. 20. The waveguide of claim 17, wherein the second plurality of reflective surfaces are configured to reflect light in the second wavelength region, and light reflected from the second plurality of reflective surfaces passes through the first plurality of reflective surfaces.

19. 1. A method comprising: reflecting the light in an out-coupling direction via a first reflective surface of a plurality of reflective surfaces at an output coupler of the waveguide; and reflecting light in the output coupling direction via a second reflective surface of the plurality of reflective surfaces at the output coupler, wherein a portion of the light reflected from the second reflective surface overlaps with a portion of the light reflected from the first reflective surface.

20. 20. The method of claim 19, wherein the plurality of reflective surfaces are arranged consecutively along a first direction within the waveguide, and adjacent reflective surfaces of the plurality of reflective surfaces overlap each other along the first direction.

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