WO2024162971A1

WO2024162971A1 - Stray light control in multi-waveguide combiners

Info

Publication number: WO2024162971A1
Application number: PCT/US2023/012330
Authority: WO
Inventors: Thomas HOEKMAN
Original assignee: Google Llc
Priority date: 2023-02-03
Filing date: 2023-02-03
Publication date: 2024-08-08

Abstract

A waveguide combiner (200) includes a first waveguide (204-1), a second waveguide (204-2), and a diffraction grating (218). The first waveguide and the second waveguide are disposed in a stacked configuration, with the diffraction grating disposed between the first waveguide and the second waveguide. The diffraction grating is configured to prevent light beams (216-1, 216-2) having wavelengths within a first range of wavelengths from being coupled into the second waveguide, and transmit, to the second waveguide, light beams (216-3) having wavelengths within a second range of wavelengths different from the first range of wavelengths.

Description

STRAY LIGHT CONTROL IN MULTI-WAVEGUIDE COMBINERS

BACKGROUND

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

SUMMARY OF EMBODIMENTS

[0002] In accordance with one aspect, a waveguide combiner includes a first waveguide and a second waveguide disposed in a stacked configuration. A diffraction grating is disposed between the first waveguide and the second waveguide. The diffraction grating is configured to prevent light beams having wavelengths within a first range of wavelengths from being coupled into the second waveguide. The diffraction grating is further configured to transmit, to the second waveguide, light beams having wavelengths within a second range of wavelengths different from the first range of wavelengths.

[0003] In at least some embodiments, the first waveguide is configured to propagate light beams having wavelengths within the first range of wavelengths and the second waveguide is configured to propagate light beams having wavelengths within the second range of wavelengths. [0004] In at least some embodiments, the first waveguide comprises a first input coupling element and a first output coupling element, and the second waveguide comprises a second input coupling element and a second output coupling element.

[0005] In at least some embodiments, the first input coupling element and the second input coupling element at least partially overlap.

[0006] In at least some embodiments, the diffraction grating is configured to prevent the light beams having wavelengths within the first range of wavelengths from being coupled into the second waveguide by redirecting the light beams to at least one of a portion of the first waveguide comprising a light trap or a portion of the second waveguide comprising a light trap.

[0007] In at least some embodiments, the diffraction grating is configured to prevent the light beams having wavelengths within the first range of wavelengths from being coupled into the second waveguide by redirecting the light beams to an absorptive path in the first waveguide.

[0008] In at least some embodiments, the diffraction grating is configured to prevent the light beams having wavelengths within the first range of wavelengths from being coupled into the second waveguide by redirecting the light beams in at least one of a +1 or a -1 diffraction order.

[0009] In at least some embodiments, at least one of the first waveguide and the diffraction grating are separated by a first air gap or the second waveguide and the diffraction grating are separated by a second air gap; wherein the diffraction grating is bonded to at least one of the first waveguide or the second waveguide.

[0010] In at least some embodiments, the waveguide combiner further includes at least one of a first layer or a second layer, wherein the first layer is disposed on the first waveguide and the diffraction grating is disposed on first layer, and wherein the second layer is disposed on the second waveguide and the diffraction grating is disposed on the second layer.

[0011] In at least some embodiments, the at least one of the first layer or the second layer comprises a low refractive index material; wherein the diffraction grating is disposed on a first surface of the first waveguide that is facing the second waveguide and opposite a second surface of the first waveguide comprising a first input coupling element, or is disposed on a first surface of the second waveguide that is facing the first waveguide and opposite a second surface of the second waveguide comprising a second input coupling element.

[0012] In accordance with another aspect, a wearable head-mounted display system includes an image source to project light including an image, at least one lens element, and the waveguide according to one or more embodiments described herein.

[0013] In accordance with another aspect, a method of controlling stray light beams in a waveguide combiner having at least a first waveguide and a second waveguide in a stacked configuration includes receiving, at a first input coupling element of the first waveguide, a first light beam having a first wavelength and a second light beam having a second wavelength different from the first wavelength. The first input coupling element couples the first light beam into the first waveguide. The second light beam passes through the first waveguide without being coupled into the first waveguide. A diffraction grating disposed between the first waveguide and the second waveguide redirects a portion of the first light beam that passed through the first waveguide such that the portion of the first light beam is prevented from being coupled into the second waveguide. The diffraction grating transmits the second light beam to the second waveguide. A second input coupling element of the second waveguide couples the second light beam into the second waveguide.

[0014] In at least some embodiments, redirecting the portion of the first light beam includes redirecting the portion of the first light beam to at least one of a portion of the first waveguide comprising a light trap, a portion of the second waveguide comprising a light trap, or an absorptive path within the first waveguide.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present disclosure may be better understood, and its numerous features and advantages made apparent to those skilled in the art by referencing the accompanying drawings. The use of the same reference symbols in different drawings indicates similar or identical items.

[0016] FIG. 1 shows an example of a multi-waveguide combiner incoupling stray light beams into one of the waveguides.

[0017] FIG. 2 shows a configuration of a multi-waveguide combiner including a diffraction grating for controlling stray light beams in accordance with some embodiments. [0018] FIG. 3 shows the multi-waveguide combiner of FIG. 2 redirecting stray light beams such that the stray light beams are not coupled into one of the waveguides of the multiwaveguide combiner in accordance with some embodiments.

[0019] FIG. 4 shows a configuration of the multi-waveguide combiner of FIG. 2 in which one or more of the waveguides include a light trap in accordance with some embodiments.

[0020] FIG. 5 shows a k-space diagram for the multi-waveguide combiner of FIG. 2 in accordance with some embodiments.

[0021] FIG. 6 shows a configuration of the multi-waveguide combiner of FIG. 2 in which the diffraction grating is bonded to one of the waveguides in accordance with some embodiments.

[0022] FIG. 7 shows a configuration of the multi-waveguide combiner of FIG. 2 in which the diffraction grating is bonded to another one of the waveguides for in accordance with some embodiments.

[0023] FIG. 8 shows a configuration of the multi-waveguide combiner of FIG. 2 in which the diffraction grating is bonded to both waveguides in accordance with some embodiments.

[0024] FIG. 9 shows a k-space diagram for the multi-waveguide combiner of FIG. 2 when the diffraction grating is part of the incoupling element of at least one of the waveguides in accordance with some embodiments.

[0025] FIG. 10 shows a flow diagram illustrating an example method of controlling stray light beams in a multi-waveguide combiner in accordance with some embodiments.

[0026] FIG. 11 shows an example display system with an integrated laser projection system in accordance with some embodiments.

DETAILED DESCRIPTION

[0027] NED devices typically implement a waveguide combiner to guide light beams along one or more paths. The guided light beams are then directed out of the waveguide combiner by an output coupler to form an exit pupil within which a virtual image generated by an image source can be viewed by a user of the NED device. In some designs, the waveguide combiner implements multiple waveguides to increase the field-of-view (FOV), improve color uniformity, and raise the optical efficiency. For example, because the grating vector magnitude in phase space is proportional to wavelength, if a waveguide were to support multiple color channels (e.g., blue + green), then the maximum supported FOV is smaller than if each color channel had a dedicated waveguide. This is because the entire field must fit in the TIR region of k-space for the waveguide. Also, the wavelength dependence of the incoupling grating diffraction angle results in different bounce frequencies for different color channels if they share a waveguide. As such, shorter wavelengths (e.g., blue and green wavelengths) will decay more rapidly than longer wavelengths (e.g., red wavelengths), thereby affecting color uniformity. Accordingly, optimal (or at least improved) color uniformity can be achieved by having a separate waveguide for each color, or at least reducing the number of color channels supported by any given waveguide. For example a waveguide combiner can implement a waveguide stack including separate red, green, blue (RGB) waveguides, a waveguide stack including a blue/green waveguide and a separate red waveguide, or the like.

[0028] In designs implementing a waveguide combiner comprised of multiple waveguides, it is beneficial from a form factor and light engine design standpoint, to have the incouplers of the various waveguides at least partially overlap each other along the optical axis. However, this configuration introduces risks of crosstalk between the waveguides and stray light paths caused by interactions between diffracted orders of the gratings, which can result in free space light paths that reach the eyebox. For example, FIG. 1 shows a multi-waveguide combiner 100 comprising a plurality of waveguides 102 including a first waveguide 102-1 and a second waveguide 102-2 in a stacked configuration. In this example, the first waveguide 102-1 is a blue (B) I green (G) waveguide and the second waveguide 102-2 is a red (R) waveguide. Each of the waveguides includes an input coupling element (also referred to as an in-coupling grating 104 or an incoupler (IC) 104), such as IC 104-1 and IC 104-2. As shown in FIG. 1 , a light beam(s) 106 having a wavelength, such as a blue or green wavelength, that is intended for the first waveguide 102-1 has also been coupled into the second waveguide 102-2 resulting in an undesirable ray path(s) 108 in the second waveguide 102-2. These undesirable ray paths 108 can adversely affect the image quality of the display. For example, ghost images or bright “lightsabers” can show up in the field of view. Also, a particularly high power stray light path can create an eye safety issue.

[0029] Conventional methods for mitigating stray light light/ray paths in a multi-waveguide combiner include adding a color filter between the ICs, adding a reflective filter between the ICs, or offsetting the ICs so that they are not collinear. However, lithography of a color filter adds complexity and introduces a new process that needs to be tuned and monitored. Also, placing a color filter directly on the waveguide can cause absorption in the nominal ray paths, thereby compromising the efficiency of the waveguide. If the color filter is placed on a separate film, the added thickness between the two waveguides increases mechanical complexity and system volume. Adding a reflective filter between the ICs creates issues similar to those described above with respect to the color filter in addition to having the added risk of reflected light paths going back into the light engine, which can create ghost images or other unwanted artifacts. Offsetting the ICs so that they are not collinear increases the complexity of the light engine system since a different exit pupil is needed for each color/waveguide, and also drastically increases the system volume. Also, if the ICs are reduced in size, the efficiency of the waveguides decreases.

[0030] Accordingly, described herein are example waveguide combiner configurations/architectures that mitigate stray light paths and cross-talk between the waveguides of the combiner without negatively affecting the efficiency of the combiner or increasing the complexity of the combiner. For example, in at least some embodiments, a waveguide combiner includes a first waveguide and a second waveguide in a stacked configuration. The first waveguide is configured to guide light beams having wavelengths within a first range of wavelengths, such as blue light wavelengths and green light wavelengths, and the second waveguide is configured to guide light beams having a wavelengths within a second range of wavelengths, such as red light wavelengths, that are different from the first range of wavelengths. Each of the waveguides includes an IC and one or more output coupling elements (also referred to herein as outcoupling gratings or outcouplers (OCs)). In at least some embodiments, the ICs at least partially overlap each other.

[0031] The waveguide combiner also includes a diffraction grating situated between the first waveguide and the second waveguide. In at least some embodiments, the diffraction grating has relatively high spatial frequency to redirect the unwanted light beams (i.e., unwanted portions of the light spectrum) into a light trap/dump of the first waveguide having absorptive material, redirect the unwanted light beams to an absorptive light path of the first waveguide, or a combination thereof such that the unwanted light beams are not coupled into the second waveguide. For example, if the first waveguide is a blue/green waveguide and the second waveguide is a red waveguide, the diffraction grating is configured to redirect blue light beams and green light beams such that they are not coupled into the red waveguide. In at least some embodiments, the absorptive material is situated at an end or edge of the first waveguide.

[0032] In at least some embodiments, the diffraction grating is a binary grating, a slanted grating, a blazed grating, a holographic grating, or the like. The diffraction grating can be implemented by the waveguide combiner in various configurations. For example, in at least some embodiments, the diffraction grating is bonded to the first waveguide at a surface that is facing the second waveguide, is bonded to the second waveguide at a surface that is facing the first waveguide, or is bonded to both the first waveguide and the second waveguide. In at least some of these embodiments, a layer having, for example, a low-k index is bonded to the waveguide and the diffraction grating is bonded or formed on the low-k index layer. In at least some embodiments, if the diffraction grating is bonded to one of the first waveguide or the second waveguide, the waveguide combiner includes an air gap between the diffraction grating and the waveguide that is not bonded to the diffraction grating. Alternatively, an air gap exists between the diffraction grating and the first waveguide and between the diffraction grating and the second waveguide. In other embodiments, the diffraction grating is imprinted directly onto the first waveguide or the second waveguide. In further embodiments, the deflection functions described herein are incorporated into the IC of the first waveguide or the IC of the second waveguide instead of implementing a separate diffraction grating.

[0033] FIG. 2 illustrates an example waveguide combiner 200 configured to mitigate/control stray light paths and cross-talk between waveguides. In the example shown in FIG. 2, the waveguide combiner 200 is a dual waveguide combiner comprising two waveguides 202 (illustrated as a first waveguide 202-1 and a second waveguide 202-2). However, techniques and configurations described herein can also be applied to waveguide combiners implementing more than two waveguides. The term “waveguide” as used herein, will be understood to mean a combiner using total internal reflection (TIR) or via a combination of TIR, specialized filters, and/or reflective surfaces to transfer light from an input coupler to an output coupler. In at least some display applications, the light, for example, is a collimated image, and each waveguide 202 transfers and replicates at least a portion of the collimated image to an eye of a user. The waveguides 202, in at least some embodiments, are each formed by a plurality of layers, such as a first substrate layer, a partition element layer, and a second substrate layer.

[0034] Each of the first waveguide 202-1 and the second waveguide 202-2 includes an IC 204 (illustrated as first IC 204-1 and second IC 204-2) disposed approximate to, for example, a first end 210 (illustrated as first end 210-1 and first end 210-2) of the waveguide 102. In at least some embodiments, the first IC 204-1 and the second IC 204-2 at least partially overlap each other. Each of the first waveguide 202-1 and the second waveguide 202-2 also includes an output coupler (OC) 212 (illustrated as OC 212-1 and OC 212-2) disposed approximate to, for example, a second end 214 (illustrated as second end 214-1 and second end 214-2) of the waveguide 102. The second end 214, in at least some embodiments, is opposite the first end 210. In other embodiments, each waveguide 202 also includes an exit pupil expander (EPE), which is not shown for brevity. In general, the terms “input coupler” and “output coupler” will be understood to refer to any type of optical grating structure, including, but not limited to, diffraction gratings, slanted gratings, blazed gratings, holograms, holographic optical elements (e.g., optical elements using one or more holograms), volume diffraction gratings, volume holograms, surface relief diffraction gratings, and/or surface relief holograms. In at least some embodiments, an IC 204, an OC 212 includes, or both include one or more facets or reflective surfaces.

[0035] A given IC 204 or OC 212, in at least some embodiments, is configured as a transmissive grating (e.g., a transmissive diffraction grating or a transmissive holographic grating) that causes the IC 204 or OC 212 to transmit light and to apply designed optical function(s) to the light during the transmission. In some embodiments, a given IC 204 or OC 212 is a reflective grating (e.g., a reflective diffraction grating or a reflective holographic grating) that causes the IC 204 or OC 212 to reflect light and to apply designed optical function(s) to the light during the reflection. In the present example, the light emitted from a light source is received at the IC 204 and relayed to the OC 212 via the waveguide 202 using TIR. The light is then output to the eye of a user via the OC 212. If a waveguide 202 includes an EPE, the EPE is implemented using a diffraction or other type of grating and is arranged in an intermediate stage between IC 204 and the OC 212 to receive light that is coupled into waveguide 202 by the input coupler 204, expand the light, and redirect the light towards the OC 212. The OC 212 then couples the light out of waveguide 202 (e.g., toward the eye of the user). In other embodiments, the EPE is combined with the OC 212.

[0036] In at least some embodiments, the IC 204-1 of the first waveguide 202-1 receives light beams 216 (illustrated as beam 216-1 , light beam 216-2, and light beam 216-3) emitted directly from a light source, such as a laser projection system, or receives light beams 216 emitted from a light source and reflected by another component, such as a scan mirror. The IC 204-2 of the second waveguide 202-2 receives one or more of the light beams 216 that pass through the first waveguide 202-1 . For example, in at least some embodiments, the first wave waveguide 202-1 is configured to guide light beams 216-1 and 216-2 having wavelengths within a first rage of wavelengths, such as blue light wavelengths and green light wavelengths, and the second waveguide 202-2 is configured to guide light beams 216-3 having wavelengths within a second range of wavelengths, such as red light wavelengths, that are different from the first range of wavelengths. As such, the first waveguide 202-1 is configured such that light beams 216-3 having wavelengths within the second range of wavelengths pass through the first waveguide 202-1 .

[0037] In some instances, a light beam(s) 216 having a wavelength, such as a blue or green wavelength, that is intended for the first waveguide 202-1 may be coupled into the second waveguide 202-2 resulting in an undesirable ray path(s) in the second waveguide 102-2, as described above with respect to FIG. 1. As such, the waveguide combiner 200 includes at least one diffraction grating 218 (also referred to herein as diffractive angular filter 218) situated between the first waveguide 202-1 and the second waveguide 202-2. In at least some embodiments, the first waveguide 202-1 includes a first major surface 220 and the second waveguide 202-2 includes a second major surface 222 facing the first major surface 220. The diffraction grating 218, in at least some embodiments, is disposed between the first major surface 220 and the second major surface 222. The diffraction grating 218 mitigates crosstalk between the waveguides 202 and stray light paths in the second waveguide 202-2. For example, FIG. 3 shows that at least a portion of the light beams 216-1 and 216-2, which are intended for and coupled into the first waveguide 202-1 , passes through the first waveguide 202-1 towards the second waveguide 202-2. However, instead of being coupled into the second waveguide 202-2, these unwanted portions of the light beams 216-1 and 216-2 are redirected by the diffraction grating 218. In the example shown in FIG. 3, the diffraction grating 218 redirects the portions of light beams 216-1 and 216-2 into an absorptive light path of the first waveguide 202-1 , an absorptive light path of the second waveguide 202-1 , or a combination thereof. Alternatively, or in addition, the diffraction grating 218 redirects the unwanted portions of the light beams 216-1 and 216-2 to a light trap/dump 402 (illustrated as light trap 402-1 and light trap 402-2) of the first waveguide 202-1 , the second waveguide 202-2, or a combination thereof, as shown in FIG. 4. In at least some embodiments, each light trap 402 is situated at the first end 210 of the respective waveguide 202 and includes a light absorbing material. In the examples shown in FIG. 3 and FIG. 4, the diffraction grating 218 is redirecting the unwanted portions of the light beams 216-1 and 216-2 in the -1 order direction. However, depending on the configuration of the diffraction grating 218, the unwanted portions of the light beams 216-1 and 216-2 may also be redirected in the +1 order direction. For example, a binary diffraction grating redirects the unwanted portions of the light beams 216-1 and 216-2 in both the -1 and +1 order directions, whereas a blazed, slanted, or holographic diffraction grating can be configured to redirect the unwanted portions of the light beams 216-1 and 216-2 only in one of the -1 order direction or +1 order direction. [0038] In at least some embodiments, the diffraction grating 218 is a binary grating, a nonbinary grating, a holographic grating, a blazed grating, a slanted grating, or the like. The diffraction grating 218 comprises a set of diffraction features. In at least some embodiments, the set of diffraction features 224 are separated by a set of grooves which have a low relief compared to the high relief of the set of diffraction features 224. Each diffraction feature 224 comprises a grating pitch (period) , a grating line width, a grating height, and a grating space width. The fill factor (duty cycle) of the diffraction grating 218 is defined as the ratio between the grating line width and the pitch. In at least some embodiments, the set of diffraction features 224 comprises a material having a first refractive index and the air (or other material) between each diffraction feature 224 has a second refractive index. The grating line pitch comprises the distance between one edge of a given diffraction feature 224 and the same edge of the immediately adjacent diffraction feature 224. In at least some embodiments, the grating period is constant throughout the diffraction grating 218 or varies across the diffraction grating 218. The grating line width comprises the fraction of the surface of the diffraction grating 218 made up of diffraction features 224. When the grating line width is wide, there are very narrow grooves between each diffraction feature 224, and when the grating line width is narrow, there are wide grooves between each diffraction feature 224. In at least some embodiments, the grating height comprises the height of the diffraction features 224. The diffraction grating 218, in at least some embodiments, is configured with a period and orientation such that the diffraction grating vector is normal to the nominal IC grating vector of the first IC 204-1 , the second IC 204-2, or both. In other embodiments, the diffraction grating 218 is configured with a period and orientation such that the diffraction grating vector is not normal to the IC 204 k-vectors.

[0039] The diffraction grating 218, in at least some embodiments, is configured with a relatively high spatial frequency (e.g., less than the wavelength to be filtered) to redirect and prevent unwanted light beams 216 from being coupled into the second waveguide 202-2, and is configured with a large enough k-vector to allow wanted light beams 216 to be coupled into the second waveguide 202-2. In one configuration, the period of the diffraction grating 218 can be less than Wt /Ns, where Wt is the transmitted wavelength, Ns is the refractive index of the diffraction grating 218 material and the period is greater than the wavelength to filter out. FIG. 2 to FIG. 4 show an example in which the spatial frequency of the diffraction grating 218 is such that blue light beams 216-1 and green light beams 216-2 are redirected and prevented from being coupled into the second waveguide 202-2 but the k-vector of the diffraction grating 218 is large enough to prevent deflection of red light beams 216-3 so that they are coupled into the second waveguide 202-2. In at least some embodiments, the diffraction grating 218 is configured according to: — > 1.0 (EQ. 1), de fl where A,. is the wavelength (e.g., red wavelength) of the light beam 216 and A_defi is the pitch of the diffraction grating 218. In value larger than 1.0, in at least some embodiments, is substituted into EQ. 1 to manage the light beams having wavelengths within the second range of wavelengths (e.g., red light wavelengths) that are not at normal incidence (off-axis field points).

[0040] FIG. 5 shows a k-space diagram 500 for the configuration of the waveguide combiner 200 illustrated in FIG. 2 to FIG. 4. In this example, the k-space diagram 500 is a two-dimensional (2D) diagram illustrating only the k_x and k_y dimensions. In general, the k- space diagram 500 is useful for, among other things, visualizing TIR within a waveguide combiner, and represents the projected angle of a light beam 216 scaled by the refractive index of the waveguide combiner 200. For example, the inner circle 502 represents the refractive index of the waveguide combiner environment (e.g., air) and the outer circle 504 represents the refractive index of the waveguide combiner 200. In this example, the waveguide combiner 200 has a higher refractive index (e.g., 2) than its environment (e.g., 1) so the outer circle 504 is larger than the inner circle 502 in the diagram 500. In FIG. 2 to FIG. 4, the light beams 216 are coming in normal onto the waveguide combiner 200. Therefore, each light beam 216 is represented by a point 508 (illustrated as point 508-1 to point 508-3) at the origin 506 in the k-space diagram 500 of FIG. 5. The diffraction grating 218 has a different magnitude for each of the light beams 216 corresponding to a different color (e.g., red, green, and blue). Since the deflection imparted on a light beam 216 is dependent on its wavelength, a red light beam (e.g., the third light beam 216-3) is deflected more than a blue light beam and a green light beam (e.g., the first light beam 216-1 and the second light beam 216-2). As described above, the diffraction grating 218, in at least some embodiments, is designed such that a light beam 216-3 of a specified wavelength (e.g., red wavelength) is not diffracted by the diffraction grating 218 and is coupled into the second waveguide 202-2, whereas light beams 216-1 and 216-2 of other wavelengths (e.g., blue and green wavelengths) are diffracted by the diffraction grating 218 and prevented from being coupled into the second waveguide 202-2. This configuration of the waveguide combiner 200 is represented in the k-space diagram 500 by point 508-1 and point 508-2, which represent the first light beam 216-1 and the second light beam 216-2, respectively, lying within the first circle 502, and point 508-3, which represents the third light beam 216-3, lying within the second circle 504. In other words, the k-space diagram 500 shows that the red diffracted order cannot exist in air because point 508-3 lies within the second circle 504 (also referred to herein as “outer circle 504”), and further shows that the blue and green diffracted orders can exist in air because points 508-1 and 508-2 lie within the first circle 502 (also referred to herein as “inner circle 502”).

[0041] In the configuration of the waveguide combiner 200 illustrated in FIG. 2 to FIG. 4, the diffraction grating 218 is imprinted or fabricated on a material/substrate and situated between waveguides 202 with an air gap 226 (illustrated as air gap 226-1 and air gap 226-2) separating the waveguides 202 and the diffraction grating 218. For example, a first air gap 226-1 exists between the interface of the first waveguide 202-1 and the diffraction grating 218, and a second air gap 226-2 between the interface of the second waveguide 202-2 and the diffraction grating 218. The air gap 226 ensures that the diffraction order(s) for the wavelengths that are intended to be coupled into the second waveguide 202-2 do not exist. Stated differently, the air gap 226, in this configuration, ensures the that only the unwanted wavelengths (e.g., blue and green) are deflected by the diffraction grating 218 and not the wavelengths (e.g., red) intended to be coupled into the second waveguide 202-2. However, in at least some embodiments, the diffraction grating 218 is bonded to the second waveguide 202-2, the first waveguide 202-1 , or both the first waveguide 202-1 and the second waveguide 202-2, as shown in FIG. 6 to FIG. 8.

[0042] For example, FIG. 6 shows a configuration of the waveguide combiner 200 in which the diffraction grating 218 is bonded to the second waveguide 202-2. In this example, an air gap 226-2 exists between the interface of the first waveguide 202-1 and the diffraction grating 218. A layer 602 including a material with a low refractive index (e.g., a non-porous dielectric material, a low refractive index aerogel, a low refractive index polymer, and the like) is situated between the interface of the second waveguide 202-2 and the diffraction grating 218. The layer 602 is optically bonded to the second waveguide 202-2 at, for example, the second major surface 222, and the diffraction grating 218 is imprinted or fabricated on the layer 602. FIG. 7 shows a configuration of the waveguide combiner 200 in which the diffraction grating 218 is bonded to the first waveguide 201-2. In this example, an air gap 226-1 exists between the interface of the second waveguide 202-2 and the diffraction grating 218. A layer 702 including a material with a low refractive index is situated between the interface of the first waveguide 202-1 and the diffraction grating 218. The layer 702 is optically bonded to the first waveguide 202-1 at, for example, the first major surface 220, and the diffraction grating 218 is imprinted or fabricated on the layer 702. FIG. 8 shows a configuration of the waveguide combiner 200 in which the diffraction grating 218 is bonded to both the first waveguide 202-1 and the second waveguide 202-2. In this example, a layer 802, 804 including a material with a low refractive index is situated between the interface of the first waveguide 202-1 and the diffraction grating 218, and between the interface of the second waveguide 202-2 and the diffraction grating 218. Each layer 802, 804 is optically bonded to their waveguide 202 at, for example, the respective major surfaces 220, 224 and the diffraction grating 218 is imprinted or fabricated on each layer 804. In at least some embodiments, microsphere spacers to optically isolate the diffraction grating 218 from the waveguides 204. The microsphere spacers, in at least some embodiments, are disposed between the waveguides 204 and the layers 802, 804 comprising the low refractive index materials.

[0043] In other embodiments, the diffraction grating 218 is imprinted or fabricated directly onto or as part of the first waveguide 202-1 , the second waveguide 202-2, or both. If the diffraction grating 218 is part of the either of the waveguides 202, the diffraction grating 218 can be configured such that diffracted orders do not exist for m = +1 orders of the IC 204. In at least some embodiments, the deflection function can be incorporated into at least one of the ICs 204. For example, the IC 204 can have a two-grating configuration, which has an incoupling and a deflecting spatial frequency. Also, if the diffraction grating 218 is imprinted/fabricated directly onto one of the waveguides 204, the diffraction grating 218 is configured such that the grating 218 does not interact with the guided modes coupled into the waveguide 202 onto which the diffraction grating 218 is imprinted. An example of this in k- space for a single wavelength is illustrated in the k-space diagram 900 of FIG. 9.

[0044] In the example shown in FIG. 9, the inner/first circle 902 represents the refractive index of the waveguide combiner environment (e.g., air) and the outer/second circle 904 represents the refractive index of the waveguide combiner 200. In this example, the waveguide combiner 200 has a higher refractive index (e.g., 2) than its environment (e.g., 1) so the outer circle 904 is larger than the inner circle 902 in the diagram 900. The k-space diagram 900 shows that the diffraction grating 218 is operating in the vertical direction. For example, the vertical lines 906 (illustrated as line 906-1 to line 906-4) represent the +1 and -1 diffractive orders and the horizontal line 908 represents the IC 204 diffraction grating vector (k-vector), which brings the light beams 216 into the waveguide 202. Since the diffraction grating 218 is operating in the vertical direction, if the light beam 216 is in air or is coming in normal to the surface of the diffraction grating 218, the diffraction grating performs as described above with respect to at least FIG. 2 to FIG. 4. The diffraction order exists since the light beam 216 is inside the first circle 902 and the second circle 904. However, once the light beam 216 has been initially diffracted by the IC 204, that same grating vector no longer exists, it is outside of second circle 904. As such, the diffraction grating 218 operates on light beams that are coming in normal to the surface of the IC 204 (e.g., the first direction of propagation) and does not operate on any of the guided light once a light beam 216 is coupled into the waveguide 202. Therefore, the diffraction grating 218 can be placed on the surface of the first waveguide 202-1 or the second waveguide 202-2 without interfering with guided light within the waveguides 202. This allows for a reduced number of processing steps or a simpler integration with the waveguides 202 compared to other configurations.

[0045] FIG. 10 illustrates, in flow chart form, an overview of one example method of configuring a waveguide combiner 200 comprising multiple waveguides 202 and preventing unwanted light beams from being coupled into at least one of the waveguides 202. At block 1002, a first waveguide 202-1 is disposed over a second waveguide 202-2 in a stacked configuration. Alternatively, the first waveguide 202-1 can be positioned first and the second waveguide 202-2 can be disposed under the first waveguide 202-1 . The first waveguide 202- 1 includes a first IC 204-1 and a first OC 212-1 , and the second waveguide 202-2 includes a second IC 204-2 and a second OC 212-2. At block 1004, a diffraction grating 218 is disposed between the first waveguide 202-1 and the second waveguide 202-2. The diffraction grating 218 can be positioned after the waveguides 202 are disposed in the stacked configuration or after either of the first waveguide 202-1 or the second waveguide 202-2 has been positioned. The diffraction grating 218 is configured to redirect/diffract light beams 216 having wavelengths within a first range of wavelengths and transmit (without diffraction) light beams 216 having wavelengths within a second range of wavelengths different from the first range of wavelengths.

[0046] At block 1006, the first IC 204-1 receives a first light beam(s) 216, such as light beam 216-1 , having a wavelength within the first range of wavelengths and receives a second light beam(s) 216, such as light beam 216-3, having a wavelength within the second range of wavelengths. At block 1008, the first IC 204-1 couples the first light beam 216 into and for propagation by the first waveguide 202-1 . The first OC 212-1 outputs the first light beam 216. The second light beam 216 passes through the first waveguide 202-1 without being coupled into the first waveguide 202-1 . At block 1010, the diffraction grating 218 redirects any portions of the first light beam 216 that have passed through the first waveguide 202-1 such that these portions of the first light beam 216 are prevented from being coupled into the second waveguide 202-2. At block 1012, the diffraction grating 218 receives and transmits the second light beam 216 to the second waveguide 202-2. At block 1014, the second IC 204-2 couples the second light beam 216 into and for propagation by the second waveguide 202-2. The second OC 212-2 outputs the second light beam 216-2. [0047] FIG. 11 illustrates an example display system 1100 capable of implementing one or more of the waveguide combiner configurations described herein. It should be noted that, although the apparatuses and techniques described herein are not limited to this particular example, but instead may be implemented in any of a variety of display systems using the guidelines provided herein. In at least some embodiments, the display system 1100 comprises a support structure 1102 that includes an arm 1104, which houses an image source, such as laser projection system, configured to project images toward the eye of a user such that the user perceives the projected images as being displayed in a field of view (FOV) area 1106 of a display at one or both of lens elements 1108, 1110. In the depicted embodiment, the display system 1100 is a near-eye display system that includes the support structure 1102 configured to be worn on the head of a user and has a general shape and appearance of an eyeglasses frame. The support structure 1102 includes various components to facilitate the projection of such images toward the eye of the user, such as a laser projector, an optical scanner, and a waveguide combiner, such as the waveguide combiner 200 described above with respect to FIG. 1 to FIG. 9. In at least some embodiments, the support structure 1102 further includes various sensors, such as one or more front-facing cameras, rear-facing cameras, other light sensors, motion sensors, accelerometers, and the like. The support structure 1102 further can include one or more radio frequency (RF) interfaces or other wireless interfaces, such as a Bluetooth(TM) interface, a Wireless Fidelity (WiFi) interface, and the like.

[0048] Further, in at least some embodiments, the support structure 1102 includes one or more batteries or other portable power sources for supplying power to the electrical components of the display system 1100. In at least some embodiments, some or all of these components of the display system 1100 are fully or partially contained within an inner volume of support structure 1102, such as within the arm 1104 in region 1112 of the support structure 1102. It should be noted that while an example form factor is depicted, it will be appreciated that in other embodiments, the display system 1100 may have a different shape and appearance from the eyeglasses frame depicted in FIG. 11 .

[0049] One or both of the lens elements 1108, 1110 are used by the display system 1100 to provide an augmented reality (AR) or a mixed reality (MR) display in which rendered graphical content is superimposed over or otherwise provided in conjunction with a real-world view as perceived by the user through the lens elements 1108, 1110. For example, laser light used to form a perceptible image or series of images may be projected by a laser projector of the display system 1100 onto the eye of the user via a series of optical elements, such as a waveguide (e.g., the waveguide combiner 200) formed at least partially in the corresponding lens element, one or more scan mirrors, and one or more optical relays. Thus, one or both of the lens elements 1108, 1110 include at least a portion of a waveguide that routes display light received by an input coupler, or multiple input couplers, of the waveguide to an output coupler of the waveguide, which outputs the display light toward an eye of a user of the display system 1100. The display light is modulated and scanned onto the eye of the user such that the user perceives the display light as an image. In addition, each of the lens elements 1108, 1110 is sufficiently transparent to allow a user to see through the lens elements to provide a field of view of the user’s real-world environment such that the image appears superimposed over at least a portion of the real-world environment.

[0050] In at least some embodiments, the projector is a matrix-based projector, a digital light processing-based projector, a scanning laser projector, or any combination of a modulative light source such as a laser or one or more light-emitting diodes (LEDs) and a dynamic reflector mechanism such as one or more dynamic scanners or digital light processors. The projector, in at least some embodiments, includes multiple laser diodes (e.g., a red laser diode, a green laser diode, and a blue laser diode) and at least one scan mirror (e.g., two one-dimensional scan mirrors, which may be micro-electromechanical system (MEMS)-based or piezo-based). The projector is communicatively coupled to the controller and a non-transitory processor-readable storage medium or memory storing processor-executable instructions and other data that, when executed by the controller, cause the controller to control the operation of the projector. In at least some embodiments, the controller controls a scan area size and scan area location for the projector and is communicatively coupled to a processor (not shown) that generates content to be displayed at the display system 1100. The projector scans light over a variable area, designated the FOV area 1106, of the display system 1100. The scan area size corresponds to the size of the FOV area 1106, and the scan area location corresponds to a region of one of the lens elements 1108, 1110 at which the FOV area 1106 is visible to the user. Generally, it is desirable for a display to have a wide FOV to accommodate the outcoupling of light across a wide range of angles. Herein, the range of different user eye positions that will be able to see the display is referred to as the eyebox of the display.

[0051] Note that not all of the activities or elements described above in the general description are required, that a portion of a specific activity or device may not be required, and that one or more further activities may be performed, or elements included, in addition to those described. Still further, the order in which activities are listed are not necessarily the order in which they are performed. Also, the concepts have been described with reference to specific embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present disclosure as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present disclosure.

[0052] Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any feature(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature of any or all the claims. Moreover, the particular embodiments disclosed above are illustrative only, as the disclosed subject matter may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. No limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope of the disclosed subject matter. Accordingly, the protection sought herein is as set forth in the claims below.

Claims

WHAT IS CLAIMED IS:

1 . A waveguide combiner (200) comprising: a first waveguide (202-1) and a second waveguide (202-2) disposed in a stacked configuration; and a diffraction grating (218) disposed between the first waveguide and the second waveguide, wherein the diffraction grating is configured to prevent light beams (216-1 , 216-2) having wavelengths within a first range of wavelengths from being coupled into the second waveguide, and transmit, to the second waveguide, light beams (216-3) having wavelengths within a second range of wavelengths different from the first range of wavelengths.

2. The waveguide combiner of claim 1 , wherein the first waveguide is configured to propagate light beams having wavelengths within the first range of wavelengths and the second waveguide is configured to propagate light beams having wavelengths within the second range of wavelengths.

3. The waveguide combiner of any one of claims 1 or 2, wherein the first waveguide comprises a first input coupling element (204-1) and a first output coupling element (212-1), and the second waveguide comprises a second input coupling element (204- 2) and a second output coupling element (212-2).

4. The waveguide combiner of claim 3, wherein the first input coupling element and the second input coupling element at least partially overlap.

5. The waveguide combiner of any one of claims 1 to 4, wherein the diffraction grating is configured to prevent the light beams having wavelengths within the first range of wavelengths from being coupled into the second waveguide by redirecting the light beams to at least one of a portion of the first waveguide comprising a light trap (402- 1) or a portion of the second waveguide comprising a light trap (402-2).

6. The waveguide combiner of any one of claims 1 to 4, wherein the diffraction grating is configured to prevent the light beams having wavelengths within the first range of wavelengths from being coupled into the second waveguide by redirecting the light beams to an absorptive path in the first waveguide.

7. The waveguide combiner of any one of claims 1 to 6, wherein the diffraction grating is configured to prevent the light beams having wavelengths within the first range of wavelengths from being coupled into the second waveguide by redirecting the light beams in at least one of a +1 or a -1 diffraction order.

8. The waveguide combiner of any one of claims 1 to 7, wherein at least one of the first waveguide and the diffraction grating are separated by a first air gap (226-1) or the second waveguide and the diffraction grating are separated by a second air gap (226- 2).

9. The waveguide combiner of any one of claims 1 to 7, wherein the diffraction grating is bonded to at least one of the first waveguide or the second waveguide.

10. The waveguide combiner of any one of claims 1 to 7, further comprising at least one of a first layer or a second layer, wherein the first layer is disposed on the first waveguide and the diffraction grating is disposed on first layer, and wherein the second layer is disposed on the second waveguide and the diffraction grating is disposed on the second layer.

11 . The waveguide combiner of claim 10, wherein the at least one of the first layer or the second layer comprises a low refractive index material.

12. The waveguide combiner of claim 1 , wherein the diffraction grating is disposed on a first surface of the first waveguide that is facing the second waveguide and opposite a second surface of the first waveguide comprising a first input coupling element (204- 1), or is disposed on a first surface of the second waveguide that is facing the first waveguide and opposite a second surface of the second waveguide comprising a second input coupling element (204-2).

13. A wearable head-mounted display (1100) system comprising: an image source to project light comprising an image; at least one lens element (1108, 1110); and the waveguide combiner (200) of any of claims 1 to 12.

14. A method of controlling stray light beams in a waveguide combiner (200) having at least a first waveguide (202-1) and a second waveguide (202-2) in a stacked configuration, the method comprising: receiving, at a first input coupling element (202-4) of the first waveguide (202-1), a first light beam (216-1) having a first wavelength and a second light beam (216-3) having a second wavelength different from the first wavelength; coupling, by the first input coupling element, the first light beam into the first waveguide, wherein the second light beam passes through the first waveguide without being coupled into the first waveguide; redirecting, by a diffraction grating (218) disposed between the first waveguide and the second waveguide, a portion of the first light beam that passed through the first waveguide such that the portion of the first light beam is prevented from being coupled into the second waveguide; transmitting, by the diffraction grating, the second light beam to the second waveguide; and coupling, by a second input coupling element (204-2) of the second waveguide, the second light beam into the second waveguide.

15. The method of claim 14, wherein redirecting the portion of the first light beam comprises redirecting the portion of the first light beam to at least one of: a portion of the first waveguide comprising a light trap (402-1); a portion of the second waveguide comprising a light trap (402-2); or an absorptive path within the first waveguide.