Waveguide with overlapping reflective facets

Abstract

The waveguide includes an output coupler implemented in the waveguide as a set of reflective facets arranged along a first direction. Each reflective facet is made by applying a reflective coating to a flat face of one or more substrates. Adjacent reflective facets in the set of reflective facets overlap each other along a first direction. For example, a front portion of one reflective facet of the set of reflective facets overlaps a tail portion of a reflective facet adjacent thereto.

Description

BACKGROUND OF THE INVENTION

[0001] In a glasses-type display, display light beams from an optical engine are initially coupled into a waveguide by an input coupler, which can be formed on one or more surfaces of the waveguide or disposed within the waveguide. Once the display light beams have been coupled into the waveguide, the input-coupled display light beams are typically "guided" through the waveguide by multiple instances of total internal reflection (TIR) to then be led out of the waveguide by an output coupler, which can also 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 which a virtual image generated by the optical engine can be viewed by a user of the glasses-type display. The waveguide may also include an exit pupil expander positioned between the input coupler and the output coupler to increase the size of the exit pupil within which the user can view the virtual image.

[0002] In some cases, one or more of the input coupler, the exit pupil expander, and the output coupler are implemented as a set of reflective facets in the waveguide. Conventional waveguides having reflective facets are often susceptible to degraded optical performance due to discontinuities in the virtual images delivered to the user. SUMMARY OF THE INVENTION

[0003] Various embodiments include waveguides having overlapping reflective facets that reduce or eliminate discontinuities in the virtual images delivered to a user of a glasses-type display.

[0004] In a first embodiment, a waveguide includes a plurality of reflective facets arranged in the waveguide along a first direction. For example, the plurality of reflective facets are arranged in a linear series to implement an output coupler of the waveguide. Adjacent reflective facets among the plurality of reflective facets overlap each other along the first direction.

[0005] In some aspects of the first embodiment, the waveguide includes two substrates. The first substrate of the two substrates includes a first plurality of flat surfaces, and the second substrate of the two substrates includes a second plurality of flat surfaces. In some aspects, the first plurality of flat surfaces and the second plurality of flat surfaces are at least partially coated (or fully coated) with a reflective coating, such as a metal layer coating or a dichroic layer coating. The first plurality of flat surfaces coated with the reflective coating are positioned to contact the second plurality of flat surfaces coated with the reflective coating. In this way, each of the plurality of reflective facets is formed at the interface between the first plurality of flat surfaces with the reflective coating and the second plurality of flat surfaces with 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 for bonding the first substrate to the second substrate. The adhesive material has a refractive index corresponding to the refractive indices of the materials of the first substrate and the second substrate. For example, the refractive index of the adhesive material matches the refractive indices 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 facets arranged successively in a first direction in the waveguide. The second plurality of reflective facets are adjacent to the plurality of reflective facets, and adjacent reflective facets in the second plurality of reflective facets 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 flat surfaces, and the fourth substrate includes a fourth plurality of flat surfaces. In some aspects, the third plurality of flat surfaces and the fourth plurality of flat surfaces are at least partially coated (or fully coated) with a second reflective coating. In some cases, the second reflective coating is different from the reflective coating on the first plurality of flat surfaces and the second plurality of flat surfaces. In some aspects, the third plurality of flat surfaces coated with the second reflective coating are positioned to contact the fourth plurality of flat surfaces coated with the second reflective coating. In this way, each of the reflective facets in the second plurality of reflective facets is formed at the interface between the third plurality of flat surfaces with the second reflective coating and the fourth plurality of flat surfaces with the second reflective coating. In some aspects, there is a gap between the third substrate and the fourth substrate, and this gap is filled with an adhesive material for bonding the third substrate to the fourth substrate. In some cases, the adhesive material includes a refractive index corresponding to the refractive indices of the materials of the third substrate and the fourth substrate. In some aspects, 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. Additionally, in some cases, there is an additional adhesive material layer for bonding the first substrate or the second substrate to the third substrate or the fourth substrate.

[0007] In a second embodiment, a waveguide includes a first plurality of reflective facets and a second plurality of reflective facets. The first plurality of reflective facets are arranged in the waveguide along a first direction, and adjacent reflective facets in the first plurality of reflective facets overlap each other along the first direction. The second plurality of reflective facets are arranged in the waveguide along the first direction, and adjacent reflective facets in the second plurality of reflective facets overlap each other along the first direction.

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

[0009] In a third embodiment, a method includes: reflecting light in an output coupling direction via a first reflective facet among a plurality of reflective facets at an output coupler of a waveguide, and reflecting light in the output coupling direction via a second reflective facet among the plurality of reflective facets at the output coupler, wherein a portion of the light reflected from the second reflective facet coincides with a portion of the light reflected from the first reflective facet. In some aspects of the third embodiment, the plurality of reflective facets are arranged in series in the waveguide along a first direction, and adjacent reflective facets among the plurality of reflective facets overlap each other along the first direction. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The present disclosure can be better understood by reference to the accompanying drawings, and numerous features and advantages of the present disclosure will be apparent to those skilled in the art. The same reference numerals are used in different drawings to indicate similar or identical items.

[0011] Figure 1 An example eyewear display according to some embodiments is shown.

[0012] Figure 2 An example projection system is shown having a filter between an optical engine of an eyewear display and an input coupler of a waveguide of the eyewear display as shown in Figure 1 the eyewear display.

[0013] Figure 3 An example plan view is shown illustrating the propagation of light in a waveguide of Figure 2 the projection system according to some embodiments.

[0014] Figure 4 An example of a conventional reflective facet configuration and problems associated with such a configuration are shown.

[0015] Figure 5Shows an example of a set of overlapping reflective facets to be implemented at one or more of an input coupler, an exit pupil expander, or an output coupler in a waveguide according to various embodiments.

[0016] Figures 6 to 8 Shows an example of an alternative embodiment of multiple sets of overlapping reflective facets to be implemented at one or more of an input coupler, an exit pupil expander, or an output coupler in a waveguide according to various embodiments.

[0017] Figure 9 Shows an example of a stack of multiple sets of overlapping reflective facets according to some embodiments.

[0018] Figure 10 Shows a method flow diagram for reflecting light via overlapping reflective facets according to some embodiments. Detailed Description

[0019] A reflective facet waveguide includes one or more sets of reflective facets for implementing one or more of an input coupler, an output coupler, or an exit pupil expander. Using the output coupler as an example, the output coupler is implemented as a set of reflective facets that receive light from the exit pupil expander and reflect the light out of the waveguide to the user. Typically, the set of reflective facets is made by applying a reflective coating to a series of flat surfaces on a molded plastic or polymer substrate. Ideally, each reflective facet has sharp corners at both sides and there are no gaps between adjacent reflective facets. However, in practice, due to molding process limitations, a conventionally molded plastic substrate has flat surfaces with rounded edges and a draft angle (i.e., a non-vertical angle) between the flat surfaces. These rounded edges and draft angles result in gaps between adjacent conventional reflective facets applied to the flat surfaces. The gaps between adjacent conventional reflective facets create gaps in the output-coupled light, which in turn create discontinuities in the virtual image delivered to the user. For example, if the virtual image is supposed to be a straight line, the gaps in the output-coupled light create "blips" in the line perceived by the user. Waveguides with overlapping reflective facets are described herein, which eliminate the aforementioned gaps in the light output-coupled to the user, thereby reducing or eliminating discontinuities in the virtual image perceived by the user. This improves the optical performance of the waveguide and the eyewear display incorporating such a waveguide.

[0020] For illustration, 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 set of reflective facets arranged along a first direction, i.e., the reflective facets in the set are arranged in succession along a common direction. In some embodiments, each reflective facet is made by applying a reflective coating to a flat surface of one or more substrates. Adjacent reflective facets in the set of reflective facets overlap each other along the first direction. For example, a front portion (also referred to as a "head") of one reflective facet in the set of reflective facets overlaps a tail portion (also referred to as a "root") of an adjacent reflective facet. In this way, the set of reflective facets eliminates gaps that can be caused by rounded edges and draft angles of one or more substrates. This reduces discontinuities in the light beam output-coupled from the waveguide, thereby improving the quality of the image generated by the output-coupled light beam.

[0021] For further illustration, in another embodiment, one or more of the input coupler, the exit pupil expander, and the output coupler are each implemented as two sets of reflective facets. A first set of reflective facets is arranged in succession along a first axis, and a second set of reflective facets is arranged in succession along a second axis, where the first axis is parallel to the second axis. The reflective facets of the first set are offset from the reflective facets of the second set such that when viewed from a perspective orthogonal to the first axis or the second axis, the reflective facets of the first set overlap the reflective facets of the second set. In this way, the light reflected from the two sets of reflective facets overlaps, thereby minimizing or eliminating any discontinuities in the light output-coupled to the user.

[0022] Figure 1 An example eyewear display 100 according to various embodiments is shown. The eyewear display 100 (also referred to as a wearable head-up display (WHUD), a head-mounted display (HMD), a near-eye display, etc.) has a support structure 102 that includes temple arms 104 that house a microdisplay projection system configured to project an image toward a user's eye such that the user perceives the projected image as being displayed in a field of view (FOV) region 106 of a display at one or both of lens elements 108, 110. In the depicted embodiment, the support structure 102 of the eyewear display 100 is configured to be worn on a user's head and has the general shape and appearance of an eyeglass frame (i.e., a "form factor"). The support structure 102 contains or otherwise includes various components for facilitating the projection of such images toward the user's eye, such as a light engine and a waveguide (e.g., as Figure 2shown). In some embodiments, the support structure 102 further includes various sensors, such as one or more front cameras, rear 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 Bluetooth™ interfaces, WiFi interfaces, etc. Further, in some embodiments, the support structure 102 includes one or more batteries or other portable power sources for supplying power to the electrical components of the eyewear display 100. In some embodiments, some or all of these components of the eyewear display 100 are fully or partially contained within the internal volume of the support structure 102, such as within the temple 104 in the region 112 of the support structure 102. It should be noted that although an example form factor is depicted, it should be understood that in other embodiments, the eyewear display 100 may have a shape and appearance different from that of the Figure 1 eyeglass frame depicted in

[0023] The eyewear display 100 uses one or both of the lens elements 108, 110 to provide an augmented reality (AR) or mixed reality (MR) display, in which the rendered graphical content can be superimposed on the real-world view perceived by the user through the lens elements 108, 110 or otherwise combined with the real-world view. In some embodiments, one or both of the lens elements 108, 110 function as an optical combiner that combines ambient light (also referred to as surrounding light) from outside the eyewear display 100 and light emitted from the light engine in the eyewear display 100. For example, the light used to form a perceivable image or series of images may be projected onto the user's eyes by the light engine of the eyewear display 100 via a series of optical elements, such as waveguides that are at least partially formed in the corresponding lens elements, one or more scanning mirrors, one or more optical relays, and / or one or more prisms. Thus, one or both of the lens elements 108, 110 include at least a portion of a waveguide that guides the display light received by the input coupler of the waveguide to the output coupler of the waveguide, and the output coupler outputs the display light toward the eyes of the user of the eyewear display 100. The display light is modulated and projected onto the user's eyes such that the user perceives the display light as an image in the FOV region 106. Additionally, in some embodiments, each of the lens elements 108, 110 is transparent enough to allow the user to see through the lens element to provide a field of view of the user's real-world environment, such that the image appears to be superimposed on at least a portion of the real-world environment.

[0024] In some embodiments, the light engine is any combination of a matrix-based projector, a scanning laser projector, or 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, for example, the light engine includes a plurality of laser diodes (e.g., red laser diodes, green laser diodes, and / or blue laser diodes) and at least one scanning mirror (e.g., two one-dimensional scanning mirrors that are microelectromechanical systems (MEMS)-based or piezo-based). 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, which when executed by the controller cause the controller to control the operation of the projector. In some embodiments, the controller controls the size and position of the scanning area of the light engine and is communicatively coupled to a processor (not shown) that generates the content to be displayed at the eyewear display 100. The light engine scans light over a variable area of the display system 100 that is designated as the FOV area 106. The size of the scanning area corresponds to the size of the FOV area 106, and the position of the scanning area corresponds to an area of one of the lens elements 108, 110 where the FOV area 106 is visible to the user. Generally, it is desirable for the display to have a wide FOV to accommodate the output coupling of light over a wide angular range. Herein, the range of different user eye positions from which the display can be seen is referred to as the eyebox of the eyewear display 100.

[0025] 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, and in other configurations, the waveguide includes a plurality of waveguide substrates (referred to as a waveguide stack) stacked on top of each other. In some cases, the waveguide includes one or more of an input coupler for input-coupling light from the light engine into the waveguide, an exit pupil expander for expanding the input-coupled light in one dimension within the waveguide, and an output coupler for output-coupling the display light to the eyebox of the eyewear display 100. In some cases, one or more of the input coupler, the exit pupil expander, and the output coupler are implemented as a corresponding set of reflective facets in the waveguide. For example, the output coupler is constituted by a set of reflective facets that receive light from the exit pupil expander and redirect the light out of the waveguide to the user via the FOV area 106. In some embodiments, the reflective facets overlap each other to minimize or eliminate gaps in the light output-coupled to the user. This reduces visual artifacts in the virtual image delivered to the user, thereby improving the optical performance of the eyewear display 100.

[0026] Figure 2FIG. showing a projection system 200 that projects an image onto a user's eye 216 according to various embodiments. It can be implemented in the Figure 1 The projection system 200 that can be implemented in the head-mounted display 100 in Figure 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 scanning mirror 204, a second scanning 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 one or more of the output couplers 214 are optically aligned with the user's eye 216. For example, one or more of the output couplers 214 substantially overlap with the FOV region 106 shown in

[0027] 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 lasers; and / or invisible lasers such as infrared lasers). In some embodiments, the light engine 202 is coupled to a controller or driver (not shown) that controls the emission timing of the light from the light sources of the light engine 202 (e.g., according to instructions received by the controller or driver from a computer processor coupled thereto) to modulate the light 218 to be perceived as an image when output to the retina of the user's eye 216. For example, during operation of the projection system 200, one or more beams of the display light 218 are output by the light sources of the light engine 202 and then guided into the waveguide 210 before being guided to the user's eye 216. The light engine 202 modulates the corresponding intensities of the light beams such that the combined light reflects a series of pixels of the image, where the specific intensity of each light beam at any given time point contributes to the amount of the corresponding color content and brightness in the pixel represented by the combined light at that time.

[0028] In some embodiments, the optical scanner 220 includes a first scanning mirror 204, a second scanning mirror 206, and an optical relay 208. In some embodiments, one or both of the scanning mirrors 204 and 206 are MEMS mirrors. For example, the scanning mirror 204 and the scanning mirror 206 are MEMS mirrors that are driven by corresponding actuation voltages to oscillate during the active operation of the laser projection system 200, thereby causing the scanning mirrors 204 and 206 to scan the laser 218. The oscillation of the scanning mirror 204 causes the light 218 output by the optical engine 202 to pass through the optical relay 208 and scan across the surface of the second scanning mirror 206. The second scanning mirror 206 scans the light 218 received from the scanning mirror 204 toward the input coupler 212 of the waveguide 210.

[0029] The waveguide 210 of the projection system 200 includes an input coupler 212 and an output coupler 214. As used herein, the term "waveguide" will be understood to mean a combiner that uses total internal reflection (TIR) or a combination of TIR, specialized filters, and / or reflective surfaces to transmit light from the input coupler to the output coupler. For example, for a display application, the light represents a collimated image, and the waveguide transmits and duplicates the collimated image to the eye. In general, the terms "input coupler" and "output coupler" will be understood to refer to any type of optical grating structure, including but not limited to a set of reflective facets, diffraction gratings, tilted gratings, blazed gratings, holographic plates, holographic optical elements (e.g., optical elements using one or more holographic plates), volume diffraction gratings, volume holographic plates, surface relief diffraction gratings, and / or surface relief holographic plates. In some embodiments, one or more of the input coupler 212, the exit pupil expander ( Figure 2 not shown in) and the output coupler 214 are implemented in the waveguide 210 by a corresponding set of reflective facets. In this example, the light 218 received at the input coupler 212 is propagated through the waveguide 210 using TIR to the output coupler 214. Then, the light 218 is output to the user's eye 216 via the output coupler 214.

[0030] Figure 3 is shown Figure 2 A plan view of an example of light propagation within the waveguide 210 of the projection system 200 is shown. As shown, the light is received via the input coupler 212, guided as light 320 into the exit pupil expander (EPE) 316, and then guided as light 322 to the output coupler 214 for output from the waveguide 212 towards the user's eye (e.g., the light is reflected by the output coupler 214 in the direction out of the page). In some embodiments, the exit pupil expander 316 expands one or more dimensions of the eye movement range of the head-mounted display including the laser projection system 200 (e.g., relative to the dimensions of the eye movement range of the head-mounted 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 includes a set of reflective facets. For example, at the input coupler 212, a first set of reflective facets 312 (one is labeled for clarity) receives light from an optical engine (such as from Figure 2 the optical engine 202 in, Figure 3The light emitted by (not shown in the figure) is reflected such that the light 320 is input-coupled into the waveguide 210. The second set of reflective facets 318 (one is marked for clarity) at the exit pupil expander 316 receives the input-coupled light 320 and reflects the light such that the light expands in the second direction 322 towards the output coupler 214. The third set of reflective facets 314 (one is marked for clarity) at the output coupler 214 reflects the light received from the exit pupil expander 316 such that the light is output-coupled from the waveguide 210. As further described herein, in some embodiments, the reflective facets overlap with other adjacent reflective facets in the corresponding set of reflective facets to eliminate gaps in the light reflected from the corresponding optical component (e.g., from the output coupler 214).

[0031] Figure 4 FIG. 400 shows a cross-sectional view of a set of conventional reflective facets 420 to 428 (not shown for clarity) in an exemplary waveguide and associated problems. For example, when implemented as an output coupler in the waveguide, the set of conventional reflective facets 420 to 428 receives light from the exit pupil expander in a first direction indicated by arrow 401 and redirects the light out of the waveguide to the user in a second direction indicated by arrow 403.

[0032] Generally, the substrate 402 is manufactured by a molding process and is made of at least partially transparent plastic or polymer material. The molded substrate 402 includes a plurality of flat surfaces 418 (one is labeled for clarity). The molded substrate 402 also includes a plurality of sub-flat surfaces 430 (one is labeled for clarity). The set of conventional reflective facets 420 to 428 is formed by applying a reflective coating to the plurality of flat surfaces 418. Ideally, the plurality of flat surfaces 418 of the substrate 402 have sharp corners, and the sub-flat surfaces are vertical such that there are no gaps between adjacent reflective facets in the reflective facets. In practice, a molded plastic substrate such as the substrate 402 does not meet this ideal shape and instead includes rounded ends 444 (one is labeled for clarity) and rounded roots 442 (one is labeled for clarity). In addition, the sub-flat surfaces 430 of a molded plastic substrate such as the substrate 402 are not vertical, and a draft angle 440 (one is labeled for clarity) is imparted between the root 442 of one conventional reflective facet 428 and the end 444 of an adjacent conventional reflective facet 426. The combination of the rounded edges (i.e., the roots 442 and the ends 442) and the draft angle 440 creates a gap between adjacent conventional reflective facets in the set of conventional reflective facets 420 to 428, which in turn creates a gap in the light reflected by the set of conventional reflective facets 420 to 428. For example, referring to the conventional reflective facets 422 and 424, there is a gap 452 between the light 450-1 reflected by the conventional facet 424 and the light 450-2 reflected by the conventional facet 422. These gaps 452 create discontinuities in the virtual image delivered to the user, thus resulting in reduced optical performance.

[0033] Figure 5 FIG. 500 shows an exemplary cross-sectional view of a set of overlapping reflective facets 520 to 528 to be implemented as an output coupler (not shown for clarity) of a waveguide according to various embodiments. In some embodiments, the set of overlapping reflective facets 520 to 528 is included in a waveguide (such as Figure 2 and Figure 3 the waveguide 210 in) to implement one or more of an input coupler, an exit pupil expander, or an output coupler. For example, if implemented as part of an output coupler (e.g., such as the output coupler 214 in the previous figures), the set of reflective facets 520 to 528 is positioned in the waveguide to receive light from the exit pupil expander in the direction indicated by the arrow 501 and reflect the light such that the light is redirected out of the waveguide in another direction (referred to as the "output coupling direction") indicated by the arrow 503. As shown, a series of reflective facets 520 to 528 (also referred to as a plurality of reflective facets) are arranged in succession (e.g., one after another) in the waveguide in the direction indicated by the arrow 503.

[0034] As shown in cross-sectional view 500, the set of reflective facets 520 - 528 includes an overlap region 530 (one is labeled for clarity) between adjacent reflective facets among the reflective facets 520 - 528. That is, the set of reflective facets 520 - 528 are positioned successively along a first direction (e.g., corresponding to arrow 501), and adjacent reflective facets in the set of reflective facets overlap each other along the first direction. In some embodiments, as shown, each of the reflective facets 520 - 528 is oriented parallel or substantially parallel to each other. For example, referring to reflective facets 526 and 528, the bottom (also referred to as the tail portion or root) of reflective facet 528 overlaps with the top (also referred to as the leading portion or head) of reflective facet 526 in the output coupling direction 503, as indicated by overlap region 530. That is, when viewed from a perspective in the direction of arrow 503, the coverage areas of reflective facet 526 and reflective facet 528 coincide with each other in the area indicated by overlap region 530. The overlap region 530 between adjacent reflective facets among the reflective facets 520 - 528 eliminates the aforementioned gaps of light generated by conventional reflective facets (e.g., as Figure 4 shown), thereby eliminating the discontinuities in the output-coupled light and improving the quality of the image delivered by the waveguide. In some embodiments, the overlap region 530 is up to about 500 µm, or in other embodiments up to about 250 µm. For example, in some configurations, the overlap region 530 is minimized (i.e., designed to be close to zero), because increasing the amount of overlap may also result in an increase in the thickness of the waveguide.

[0035] For illustration, in some embodiments, a plurality of overlapping reflective facets 520 to 528 are created by applying a reflective coating to a first plurality of flat surfaces 510-1, 512-1, 514-1, 516-1, 518-1 on a first substrate 502-1 and to a second plurality of flat surfaces 510-2, 512-2, 514-2, 516-2, 518-2 on a second substrate 502-2. Each of the first plurality of flat surfaces 510-1, 512-1, 514-1, 516-1, 518-1 is oriented parallel or substantially parallel to each other. In some embodiments, the reflective coating is a metal coating, a dichroic coating, a dielectric coating, a holographic coating, a partially reflective / transmissive coating, etc. In some embodiments, sub-reflective facets 536-1 (one is marked for clarity) on the first substrate 502-1 and sub-reflective facets 536-2 (one is marked for clarity) on the second substrate 502-2 are also at least partially covered with the reflective coating. The first substrate 502-1 and the second substrate 502-2 are positioned such that corresponding reflective facets among the plurality of reflective facets 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 there is an offset relative to the other substrate, such that a portion of the main facet on the first substrate 502-1 protrudes beyond the corresponding main facet on the second substrate 502-2, and a portion of the corresponding main facet on the second substrate 502-2 protrudes beyond the main facet on the first substrate 502-1. This offset creates an overlapping region 530 (one is marked for clarity) between adjacent reflective facets among the reflective facets 520 to 528. Additionally, this offset creates a gap 540 (one is marked for clarity) between a sub-flat surface 536-1 (one is marked for clarity) of the first substrate 502-1 and a sub-flat surface 536-2 (one is marked for clarity) of the second substrate 502-2. That is, for example, the sub-flat surface 536-2 of the second substrate 502-2 is not positioned flush with the sub-flat surface 536-1 of the first substrate 502-1 in order to create the 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 helps to fix the first substrate 502-1 to the second substrate 502-2. Additionally, the adhesive or polymer material has a refractive index that matches the refractive indices 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 polymeric material filling the gap 540 all have the same or substantially the same (e.g., within 5%) refractive index.

[0036] Figure 5 An additional cross-sectional view 550 of a set of overlapping reflective facets 520-528 that reflect light in the direction indicated by arrow 503 is also shown. As shown, the overlapping reflective facets 520-528 eliminate gaps in the light reflected from adjacent reflective facets of a conventional reflective facet configuration, such as Figure 4 the gap 452 shown in. By eliminating the gaps in the light reflected from adjacent reflective facets, a waveguide having overlapping reflective facets 520-528 (e.g., such as waveguide 210 in the previous figures) reduces discontinuities (i.e., gaps) in the output-coupled light. This improves the quality of the virtual image provided to the user.

[0037] In some embodiments, the first substrate 502-1 and the second substrate 502-2 are positioned to reduce the area of the overlapping region 530. In this way, the light reflected from the bottom portion of one reflective facet (e.g., from the bottom of reflective facet 522) that is blocked by the top portion of an adjacent reflective facet (e.g., from the top of reflective facet 520) is minimized. Figure 5 Five overlapping reflective facets 520-528 are shown. In other embodiments, the number of overlapping reflective facets is a number other than five.

[0038] In the above embodiments described with reference to Figure 5 a series of reflective facets are discussed as being flat. In other embodiments, the series of reflective facets is non-flat (i.e., curved). Additionally, in some embodiments, the top and bottom reflective surfaces of the reflective facets differ in terms of wavelength sensitivity, amount of reflection, polarization sensitivity, etc. Similarly, in some embodiments, wavelength sensitivity, amount of reflection, polarization sensitivity, etc. vary across the face of a given reflective facet.

[0039] Additionally, in Figure 5 some embodiments of the overlapping reflective facet configuration shown in, there can be a reduced brightness (at least to some extent) of the light reflected from the reflective facets in the overlapping region 530 compared to the light reflected from the non-overlapping regions. However, any such reduction in brightness in the overlapping region 530 (e.g., from 100% to 50%, or even from 100% to 25%) is still beneficial compared to the total drop in brightness (i.e., from 100% to 0%) caused by the gaps in the conventional configuration described in Figure 4 .

[0040] Figure 6 and Figure 7Shows examples of alternative embodiments of overlapping reflective facets to be implemented at one or more of an input coupler, an exit pupil expander, or an output coupler of a waveguide. In some aspects, Figure 6 and Figure 7 the alternative embodiments shown in facilitate film processing, which enables a thinner substrate with smaller reflective facets.

[0041] Figure 6 Shows an example cross-sectional view 600 of overlapping multiple sets of reflective facets. A first reflective coating film 604-1 is applied to a first substrate 602-1 and a second reflective coating film 604-2 is applied to a second substrate 602-2 to provide a first set of reflective facets 620-1, 622-1, 624-1, 626-1, 628-1 on the first substrate 602-1 and a second set of reflective facets 620-2, 622-2, 624-2, 626-2, 628-2 on the second substrate 602-2. The first set of reflective facets 620-1, 622-1, 624-1, 626-1, 628-1 and the second set of reflective facets 620-2, 622-2, 624-2, 626-2, 628-2 receive light coming from the direction indicated by arrow 601 and reflect the light towards the direction indicated by arrow 603. The second set of reflective facets 620-2, 622-2, 624-2, 626-2, 628-2 overlaps with the first set of reflective facets 620-1, 622-1, 624-1, 626-1, 628-1 and fills the gaps of the light reflected by the first set of reflective facets 620-1, 622-1, 624-1, 626-1, 628-1.

[0042] In some embodiments, the first reflective coating film 604-1 applied to the first substrate 602-1 is different from the second reflective coating film 604-2 applied to the second substrate 602-2. For example, the first reflective coating film 604-1 is a reflective film that reflects red light, and the second reflective coating film 604-2 is a dichroic film that transmits red light and reflects green light.

[0043] An adhesive film 608 is disposed 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 indices of the materials of the first substrate 602-1 and the second substrate 602-2. For example, the adhesive film 608 has a refractive index that is the same as (or substantially the same within a range of 5% or less) the refractive indices of the materials of the first substrate 602-1 and the second substrate 602-2.

[0044] Figure 7Shows an example cross-sectional view 700 of overlapping multiple sets of reflective facets. A first reflective coating film 704-1 is applied to a first substrate 702-1 and a second reflective coating film 704-2 is applied to a second substrate 702-2 to provide a first set of reflective facets 720-1, 722-1, 724-1, 726-1, 728-1 on the first substrate 702-1 and a second set of reflective facets 720-2, 722-2, 724-2, 726-2, 728-2 on the second substrate 702-2. The first set of reflective facets 720-1, 722-1, 724-1, 726-1, 728-1 and the second set of reflective facets 720-2, 722-2, 724-2, 726-2, 728-2 receive light from the direction indicated by arrow 701 and reflect the light in the direction indicated by arrow 703. The second set of reflective facets 720-2, 722-2, 724-2, 726-2, 728-2 overlaps with the first set of reflective facets 720-1, 722-1, 724-1, 726-1, 728-1 and fills the gaps of the light reflected by the first set of reflective facets 720-1, 722-1, 724-1, 726-1, 728-1.

[0045] In some embodiments, the first reflective coating film 704-1 applied to the first substrate 702-1 is different from the second reflective coating film 704-2 applied to the second substrate 702-2. For example, the first reflective coating film 704-1 is a reflective film that reflects red light, and the second reflective coating film 704-2 is a dichroic film that transmits red light and reflects green light.

[0046] An adhesive film 708 and an intermediate film 710 are disposed 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 have refractive indices that are the same (or substantially the same within a range of 5% or less) 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 materials 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 of the same material as the first substrate 702-1 and the second substrate 702-2.

[0047] Figure 8 Shows the one related to Figure 7 and Figure 8800 of an example cross-sectional view of an overlapping set of reflective facets corresponding to those overlapping reflective facets shown in FIG. 808 is also shown between the first substrate 802-1 and the second substrate 802-2. As shown, the second set of reflective facets 810-2, 812-2, 814-2, 818-2 (the label of the fourth reflective facet is omitted for clarity) of the second substrate 802-2 fills the gap in the light reflected from the first set of reflective facets 810-1, 812-1, 814-1, 816-1, 818-1 of the first substrate 802-1. For example, the reflective facet (not labeled for clarity) in the second set of reflective facets between facets 814-2 and 818-2 reflects light 822-2 to fill the gap between the light 822-1 reflected from the reflective facet 816-1 and the light 820-1 reflected from the reflective facet 818-1. As in the previous figures, light is received from the direction indicated by arrow 801 .

[0048] Figure 9 An example cross-sectional view 900 of a stack of multiple sets of overlapping reflective facets according to various embodiments is shown. For example, the stack includes each implementing Figure 5 A separate set of overlapping reflective facets is shown in Figure 9 as multiple layers 902-1, 902-2 of a separate set of overlapping reflective facets.

[0049] The first layer 902-1 includes a first substrate 904-1 and a second substrate 906-1 (eg, with respective Figure 5 2 and 502-2). As shown, the first group of overlapping reflective facets 910-1, 912-1, 914-1, 916-1, 918-1 are arranged adjacent to each other in a row along the first direction 901. Adjacent reflective facets in the first group of overlapping reflective facets 910-1, 912-1, 914-1, 916-1, 918-1 overlap each other along the first direction 901. The gap 920-1 created between the first substrate 904-1 and the second substrate 906-1 (one is marked for clarity) is filled with an adhesive or polymer material having a refractive index that matches the refractive index of the material of the first substrate 904-1 and the second substrate 906-1. Therefore, the first group of overlapping reflective facets 910-1, 912-1, 914-1, 916-1, 918-1 reflects light without gaps or discontinuities. In some embodiments, the first set of overlapping reflective facets 910-1, 912-1, 914-1, 916-1, 918-1 are made of a dichroic or other partially reflective material to reflect light in a first wavelength range (e.g., blue and green light) and transmit light in a second wavelength range (e.g., red light).

[0050] The second layer 902-2 includes a third substrate 904-2 and a fourth substrate 906-2 that implement a second set (also referred to as a second plurality) of overlapping reflective facets 910-2, 912-2, 914-1, 916-2, 918-2 (e.g., corresponding to the substrates 502-2 and 502-2 of Figure 5 respectively). As shown, the second set of overlapping reflective facets 910-2, 912-2, 914-2, 916-2, 918-2 are arranged adjacent to each other in a first direction 901 and are successively disposed below the first set of overlapping reflective facets 910-1, 912-1, 914-1, 916-1, 918-1. Adjacent reflective facets in the second set of overlapping reflective facets 910-2, 912-2, 914-2, 916-2, 918-2 overlap each other in the first direction 901. A gap 920-2 created between the third substrate 904-2 and the fourth substrate 906-2 (one is marked for clarity) is filled with an adhesive or polymeric material having a refractive index that matches the refractive indices of the materials of the third substrate 904-2 and the fourth substrate 906-2. Thus, the second set of overlapping reflective facets 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 facets 910-2, 912-2, 914-2, 916-2, 918-2 are made of dichroic or other partially reflective materials to reflect light in a second wavelength range (e.g., red light) transmitted by the first set of overlapping reflective facets 910-1, 912-1, 914-1, 916-1, 918-1. In this way, each set of reflective facets can be designed to reflect light in a specific wavelength range to increase the total amount of light reflected from the stack of multiple sets of overlapping reflective facets.

[0051] Figure 10 FIG. 1000 is a flow chart showing a method for reflecting light from a set of overlapping reflective facets according to various embodiments. For example, the set of overlapping reflective facets is implemented as an output coupler of a waveguide shown or described in one of the previous figures. At 1002, the method includes reflecting light in an output coupling direction via a first reflective facet in the set of overlapping reflective facets. For example, the output coupling direction is towards a user wearing a head-mounted display such as Figure 1 of the head-mounted display. At 1004, the method includes reflecting light in the output coupling direction via a second reflective facet that overlaps the first reflective facet.

[0052] In some embodiments, the techniques provided herein eliminate the gaps between reflective facets seen in conventional reflective faceted waveguides. Accordingly, the techniques provided herein provide a reflective faceted waveguide that delivers a more uniform and higher quality virtual image. In some embodiments, the techniques provided herein allow for shorter reflective facets to be molded in each substrate, thereby facilitating the processing of the corresponding substrate. Additionally, the techniques described herein allow for thinner substrates, thereby allowing multiple substrates to be stacked together (e.g., as Figure 9 shown) within an allowable form factor (e.g., within the thickness of a lens of an eyewear display).

[0053] Note that not all 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 additional activities may be performed, or that additional elements may be included, in addition to those described. Further still, the order in which activities are listed is not necessarily the order in which the activities are performed. Additionally, concepts have been described with reference to specific embodiments. However, one of ordinary skill in the art will understand that various modifications and changes can be made without departing from the scope of the present disclosure as set forth in the appended claims. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present disclosure.

[0054] Benefits, other advantages, and solutions to problems have been described above with respect to specific embodiments. However, the benefits, advantages, solutions to problems, and any feature that may cause any benefit, advantage, or solution to occur or become more pronounced should not be construed as a critical, required, or essential feature of any or all the claims. Moreover, the specific embodiments disclosed above are illustrative only, as the disclosed subject matter may be modified and practiced in different but equivalent manners obvious to those skilled in the art having the benefit of this disclosure. The details of the construction or design shown herein are not intended to be limiting other than as described in the appended claims. Thus, it is evident that the specific embodiments disclosed above may be altered or modified, and all such variations are considered to be within the scope of the disclosed subject matter. Accordingly, the protection sought herein is as set forth in the appended claims.

Claims

1. A waveguide, comprising: a plurality of reflective facets, the plurality of reflective facets being arranged in a first direction in the waveguide, wherein adjacent reflective facets among the plurality of reflective facets overlap each other along the first direction.

2. The waveguide according to claim 1, further comprising two substrates, a first substrate of the two substrates comprising a first plurality of flat surfaces, and a second substrate of the two substrates comprising a second plurality of flat surfaces.

3. The waveguide according to claim 2, further comprising a reflective coating on the first plurality of flat surfaces and on the second plurality of flat surfaces.

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

5. The waveguide according to claim 4, wherein, each reflective facet among the plurality of reflective facets is formed at an interface between the first plurality of flat surfaces having the reflective coating and the second plurality of flat surfaces having the reflective coating.

6. The waveguide according to claim 2, further comprising a gap between the first substrate and the second substrate, wherein the gap is filled with an adhesive material for bonding the first substrate to the second substrate.

7. The waveguide according to claim 6, wherein, the adhesive material comprises a refractive index corresponding to the refractive indices of the materials of the first substrate and the second substrate.

8. The waveguide according to claim 7, wherein, the refractive index of the adhesive material matches the refractive indices of the materials of the first substrate and the second substrate.

9. The waveguide according to claim 2, further comprising a second plurality of reflective facets arranged in series in the first direction in the waveguide, the second plurality of reflective facets being adjacent to the plurality of reflective facets, wherein adjacent reflective facets among the second plurality of reflective facets overlap each other along the first direction.

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

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

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

13. The waveguide according to claim 12, wherein, each reflective facet among the second plurality of reflective facets is formed at an interface between the third plurality of flat surfaces having the second reflective coating and the fourth plurality of flat surfaces having the second reflective coating.

14. The waveguide according to claim 10, further comprising a gap between the third substrate and the fourth substrate, wherein the gap between the third substrate and the fourth substrate is filled with an adhesive material for bonding the third substrate to the fourth substrate, and wherein the adhesive material for bonding the third substrate to the fourth substrate includes a refractive index corresponding to the refractive indices of the materials of the third substrate and the fourth substrate.

15. The waveguide according to claim 14, wherein, 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, and wherein an additional adhesive material layer bonds the first substrate or the second substrate to the third substrate or the fourth substrate.

16. A waveguide, comprising: a first plurality of reflective facets arranged in a first direction in the waveguide, wherein adjacent reflective facets in the first plurality of reflective facets overlap each other along the first direction; and a second plurality of reflective facets arranged in the first direction in the waveguide, wherein adjacent reflective facets in the second plurality of reflective facets overlap each other along the first direction.

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

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

19. A method, comprising: reflecting light in an output coupling direction via a first reflective facet among a plurality of reflective facets at an output coupler of a waveguide; and reflecting light in the output coupling direction via a second reflective facet among the plurality of reflective facets at the output coupler, wherein a part of the light reflected from the second reflective facet coincides with a part of the light reflected from the first reflective facet.

20. The method according to claim 19, wherein, the plurality of reflective facets are arranged successively in a first direction in the waveguide, and adjacent reflective facets in the plurality of reflective facets overlap each other along the first direction.

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