Folded 2d expansion optical waveguide

Abstract

The optical waveguide includes a first waveguide and a second waveguide that are facing each other (e.g., they are parallel or have an acute angle between them). The first waveguide has an aperture configured to receive an input beam. The first waveguide also has a first set of facets configured to receive the input beam and at least partially reflect the input beam as first beams. The first waveguide further has a coupling-out element configured to receive the first beams and reflect the first beams out of the first waveguide. The second waveguide has a coupling-in element configured to receive the first beams and reflect the first beams towards a second set of facets of the second waveguide that are configured to at least partially reflect the first beams as second beams and couple the second beams out of the second waveguide.

Description

FOLDED 2D EXPANSION OPTICAL WAVEGUIDECROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 547,696, filed on November 8, 2023. The entire disclosure of U.S. Provisional Application No. 63 / 547,696 is incorporated herein by this reference.BACKGROUND

[0002] Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.

[0003] The present disclosure relates in general to systems and methods of presenting information to a user, more particularly, to optical systems and near eye displays for presenting information to a user.

[0004] In a near eye display, a very wide field of view (FoV) may be implemented through the use of two light-guide elements (e.g. one for each of two expansion dimensions). Often, the light-guide elements are positioned end-to-end; however, such an end-to-end arrangement may be bulky in the context of a head mounted display unit such as a smart glasses or virtual reality system.SUMMARY

[0005] An optical waveguide with folded 2D expansion is described herein. The optical waveguide includes a first waveguide and a second waveguide. The first waveguide has a pair of first major surfaces that are parallel and an aperture disposed on one of the first major surfaces that is configured to receive an input beam. The first waveguide also has a first set of facets disposed between the first major surfaces along a first axis that are configured to receive the input beam and at least partially reflect the input beam as first beams. The first waveguide further has a coupling-out element configured to receive the first beams and reflect the first beams out of the first waveguide. The second waveguide has a pair of second major surfaces that are parallel, with at least one of the second major surfaces facing towards at least one of the first major surfaces. The second waveguide also has a coupling-in elementconfigured to receive the first beams and reflect the first beams towards a second set of facets of the second waveguide. The second set of facets are disposed between the second major surfaces along a second axis and configured to receive the second beams and at least partially reflect the first beams as second beams and couple the second beams out of the second waveguide.

[0006] An apparatus is also described herein. The apparatus includes the optical waveguide discussed above and a projector configured to produce the input beam.

[0007] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description. In the drawings, like reference numbers indicate identical or functionally similar elements.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 illustrates an example of a system including an optical waveguide with folded 2D expansion, in accordance with various examples of the present disclosure.

[0009] FIG. 2 illustrates an example of an optical waveguide with folded 2D expansion, in accordance with various examples of the present disclosure.

[0010] FIG. 3 illustrates an example perspective view of a first light-guide optical element of the optical waveguide of FIG. 2, in accordance with various examples of the present disclosure.

[0011] FIG. 4 illustrates a side view of the optical waveguide of FIG. 2, in accordance with various examples of the present disclosure.

[0012] FIG. 5 illustrates an example perspective view of a second light-guide optical element of the optical waveguide of FIG. 2, in accordance with various examples of the present disclosure.

[0013] FIG. 6 illustrates a front view of the optical waveguide of FIG. 2, in accordance with various examples of the present disclosure.

[0014] FIG. 7 illustrates another example of an optical waveguide with folded 2D expansion, in accordance with various examples of the present disclosure.

[0015] FIG. 8 illustrates another example of an optical waveguide with folded 2D expansion, in accordance with various examples of the present disclosure

[0016] FIG. 9 illustrates another example of an optical waveguide with folded 2D expansion, in accordance with various examples of the present disclosure.DETAILED DESCRIPTION

[0017] In the following description, numerous specific details are set forth, such as particular structures, components, materials, dimensions, processing steps and techniques, in order to provide an understanding of the various embodiments of the present application. However, it will be appreciated by one of ordinary skill in the art that the various embodiments of the present application may be practiced without these specific details. In other instances, well- known structures or processing steps have not been described in detail in order to avoid obscuring the present application.

[0018] To be described in more detail below, a wearable device, such as a near eye display and / or smart glasses, can be implemented by a system and method described in accordance with the present disclosure. The system can efficiently provide high quality optical information to a user in various applications.

[0019] FIG. 1 illustrates a block diagram of an example of an optical system 100 containing a folded optical waveguide. Optical system 100 may include two or more devices or components. Optical system 100 may be implemented generally as a hybrid system including various electronic, optical, and electro-optical elements. To be described in more detail below, optical system 100 may include a wearable device 102, such as one or more near eye displays or smart glasses, which may be worn on or about the head of a user to convey optical information to one or more eyes of a user.

[0020] Wearable device 102 may include a controller 104 with a memory 106 where controller 104 may be configured to send and receive electrical signals to various other elements in optical system 100, to execute program instructions stored in memory 106 in order to process and provide information, to operate wearable device 102, and to interact with other systems outside wearable device 102, for example. Controller 104 may include a microcontroller, a processor, various discrete components, programmable logic devices, and / or various interface circuits that may access memory 106 which may be removable, replaceable, programmable, and reprogrammable to update instructions to controller 104.

[0021] Wearable device 102 may also include a power management module 108 having a battery 110, where power management module 108 may be configured to charge, discharge,and monitor power usage for battery 110. Various elements of wearable device 102 may receive power from battery 110, including controller 104, one or more image projector(s) 112 (e.g., a projecting optical device, or POD), a graphics engine 114 having one or more digital images 116, and an image capture device 115, for example.

[0022] Each of the image projector(s) 112 may be configured to produce a collimated image beam based on the digital image(s) 116. The collimated image beam may be an illuminated representation of the digital image having an image field which is a two-dimensional representation of the digital image based on either a single graphical image (e.g., a static image) or a sequence of graphical images (e.g., a moving image). The collimated image beam may be collimated to infinity.

[0023] Wearable device 102 may also include light-guide optical elements 118 (e.g., LOEs, also defined as waveguides WGs) comprising transparent materials configured to receive and propagate light, where light may enter into and exit from various external and internal surfaces of light-guide optical elements 118. For example, the transparent materials comprising light-guide optical elements 118 may include optical glass or other suitable material that is transformed into complex optical structures using a process that may include coating, stacking, slicing, polishing, and shaping the transparent materials. The process may include the addition of partially reflective or fully reflective materials such as mirror coatings, for example. Similarly, the process may also include the addition of partially opaque or fully opaque materials such as light covers to block light, for example.

[0024] Graphics engine 114 may be coupled to image projector(s) 112 and light-guide optical element(s) 118. Graphics engine 114 may be configured to directly operate image projector(s) 112 under the direction of the controller 104. For example, graphics engine 114 may provide graphics processing for the digital image before projection of an illuminated representation of the digital image by image projector(s) 112.

[0025] Image capture device 115 may comprise a video camera or other electrical component that is configured to capture at least a portion of an external environment around a user. Graphics engine 114 may be coupled to image capture device 115 and may utilize video or image inputs or other data obtained by image capture device 115 to generate the digital images, e.g., where the device operates in a mode that utilizes the surrounding external environment.

[0026] Wearable device 102 may also include a frame 120 (e.g., a structure) for supporting and retaining one or more elements in wearable device 102. For example, with reference also to FIGS. 2-5, frame 120 may support and retain an image projector 112 in position next to a first light-guide optical element (e.g., light-guide optical element 118a). Similarly, frame 120 may support a second light-guide optical element (e.g., light-guide optical element 118b) in position next to light-guide optical element 118a and separated by a gap 119, e.g., an air gap or a gap filled with an adhesive or another material. In this manner, frame 120 may support and retain an image projector 112 and multiple light-guide optical elements 118 on or about the head of a user. References are made herein regarding the orientation of various elements relative to each other. Such references may also include reference to various elements of wearable device 102 when supported by frame 120 or in reference to a coordinate system (e.g., X, Y, Z axes).

[0027] Optical system 100 may also include a host computer 122 that may include a processor 124 configured to read and execute operations based on instructions 126 stored in a computer-readable medium 128. Instructions 126 may include at least some instructions provided to controller 104 and stored in memory 106. Host computer 122 may communicate with one or more elements of wearable device 102 over a signal and power bus 130. In this manner, host computer 122 may provide power to charge battery 110, provide instructions to and receive status from controller 104 and various other elements of wearable device 102, to provide digital image data to graphics engine 114 and to receive and process video or image data captured by image capture device 115.

[0028] FIGS. 2-6 illustrate an example of a folded optical waveguide 200 (hereinafter “waveguide” 200) with an image projector 112 mounted thereto for reference. Waveguide 200 comprises two light-guide optical elements 118, e.g., light-guide optical element 118a and light-guide optical element 118b. The light-guide optical element 118a and light-guide optical element 118b are considered folded because they have two major surfaces that face each other. In other words, the light-guide optical element 118a is disposed parallel or at an acute angle to the light-guide optical element 118b. A line-of-sight of a user generally goes through both the light-guide optical element 118a and the light-guide optical element 118b in a sequential manner.

[0029] Light-guide optical elements 118a and 118b may be optically independent via their respective major surfaces except through a coupling-out element 208 and a coupling-inelement 210 that are together configured to direct light beams from light-guide optical element 118a to light-guide optical element 118b. A three-dimensional cartesian coordinate system (e.g., X, Y, and Z axes) is illustrated. The same coordinate system is used throughout for clarity. The coordinate system used may vary (e.g., axes and directions) without departing from the scope of this disclosure.

[0030] An input beam from image projector 112 enters light-guide optical element 118a of waveguide 200 through an aperture 202. In the illustrated example, aperture 202 is disposed on a major surface (e.g., one of two major surfaces) of light-guide optical element 118a. In some implementations, aperture 202 may be disposed on other surfaces or objects (e.g., a coupling-in prism). The input beam may also or alternatively be guided by a mirror 304 (FIGS. 7-9) within light-guide optical element 118a or by a coupling prism attached to lightguide optical element 118a. If a coupling prism is implemented, aperture 202 may be disposed on the coupling prism.

[0031] The input beam propagates via total internal reflection (TIR) between the major surfaces of the waveguide 200 towards a first set of facets 204 of light-guide optical element 118a. First set of facets 204 may be perpendicular or oblique to external surfaces of the waveguide 200 and are configured to at least partially reflect the input beam towards a second set of facets 206 of light-guide optical element 118b via a coupling-out element 208 and a coupling-in element 210, e.g., coupling mirrors, prisms or other elements that may be used to direct or reflect the light beam from light-guide optical element 118a into light-guide optical element 118b. In some embodiments, light-guide optical element 118a may comprise coupling-out element 208 and light-guide optical element 118b may comprise coupling-in element 210. In other embodiments, one or both of coupling-out element 208 and couplingin element 210 may be separate components from their respective light-guide optical elements 118. In some embodiments, coupling-out element 208 and coupling-in element 210 may together comprise a separate component that may be attached to the ends of light-guide optical element 118a and light-guide optical element 118b to facilitate directing the propagating beams from light-guide optical element 118a to light-guide optical element 118b.

[0032] The light beams reflected by first set of facets 204 propagate via TIR between the major surfaces between first set of facets 204 and coupling-out element 208 which then directs the light beams towards coupling-in element 210. Coupling-in element 210 directs the beams towards second set of facets 206. Second set of facets 206 may be oblique to theexternal surfaces of the waveguide 200 and are configured to at least partially reflect the beams out of waveguide 200, e.g., towards an eye box 132 (FIG. 6). In order to generate a uniform image, a cross-section of waveguide 200 may be fully illuminated.

[0033] The input beam generally propagates along light-guide optical element 118a, from a coupling-in element (e.g., mirror or prism) towards first set of facets 204 (it may reflect via TIR in multiple directions but generally progresses toward first set of facets 204). When it is partially reflected by first set of facets 204, the input beam becomes first beams that also generally propagate along light-guide optical element 118a towards coupling-out element 208 or a prism (they may reflect via TIR in multiple directions but generally progress toward coupling-out element 208 or prism). When they are directed by coupling-out element 208 or prism (e.g., a reflection or other adjustment to the beam direction), the first beams generally propagate towards coupling-in element 210. When they are directed by coupling-in element 210 (e.g., a reflection or other adjustment to the beam direction), the first beams generally propagate along light-guide optical element 118b towards second set of facets 206 (they may reflect via TIR in multiple directions but generally progress toward second set of facets 206). When they are partially reflected by second set of facets 206 the first beams become second beams. The second beams generally propagate along light-guide optical element 118b and out of light-guide optical element 118b (e.g., out of the waveguide 200 in a direction away from or opposite to the adjacent major surface of light-guide optical element 118a). The propagation directions may differ angularly from the axes without departing from the scope of this disclosure.

[0034] As used herein, each set or group of facets may include a plurality of planar, mutually parallel and partially reflecting optical elements (e.g., facets) spaced apart from each other. Hence, each of the facets of a respective group may be parallel to each other and disposed at the same perpendicular or oblique angle. Also, the facets described herein may include an angularly selective coating and may be controlled to have multiple states (e.g., on / off) or to change a level of reflectivity and / or transmissivity of each facet or a cooperative collection of facets in a structure.

[0035] Light-guide optical elements 118a and 118b may be joined together, for example, by an adhesive or other material. The joining may create a gap 119 between light-guide optical elements 118a and 118b, e.g., an air gap in some embodiments. In some embodiments, the gap 119 may comprise a material 404 (FIG. 9) that is configured to inhibit light transferbetween light-guide optical elements 118a and 118b except via coupling-out element 208 and coupling-in element 210. In some embodiments, the gap 119 may alternatively have a low transmissivity or material 404 may comprise a low transmissivity. A material 406 (FIG. 9), e.g., a light inhibiting layer or coating, may also or alternatively be added to an outer surface of light-guide optical element 118a, e.g., to inhibit light intrusion into waveguide 200 from an external environment. In some embodiments, material 404 and material 406 may comprise opaque materials.

[0036] While light-guide optical elements 118a and 118b are shown in FIGS. 2-5 as having similar or the same surface areas for their major surfaces for the purposes of clarity, they may, in some embodiments, have different surface areas of their major surface. For example, FIG. 6 illustrates a front view of waveguide 200, e.g., as would be seen from the perspective of a user, where the surface areas of the major surfaces of light-guide optical elements 118a and 118b are different. In some embodiments, for example, the major surfaces of light-guide optical element 118a may have a larger surface area than the major surfaces of light-guide optical element 118b as shown in FIG. 6. In other embodiments, the major surfaces of lightguide optical element 118a may have a smaller surface area than the major surfaces of lightguide optical element 118b. In other embodiments, the major surfaces of light-guide optical element 118a may have the same surface area as the major surfaces of light-guide optical element 118b.

[0037] The surface areas of the major surfaces of light-guide optical elements 118a and 118b may reflect a working surface area. Differences in the working surface areas of light-guide optical elements 118a and 118b may alternatively be defined by the locations of facets 204 and 206.

[0038] FIG. 7 illustrates a folded optical waveguide 300 (hereinafter “waveguide” 300) with an image projector 112 mounted thereto and a user eye for reference. Waveguide 300 comprises similar components to waveguide 200, thus similar numbers are used where applicable.

[0039] As seen in FIG. 7, waveguide 300 comprises a prism 302 disposed in the gap 119 between light-guide optical element 118a and light-guide optical element 118b, e.g., proximate the coupling-out element 208 and the coupling-in element 210. For example, prism 302 may comprise a material that is configured to correct or compensate for the dispersion induced by the material of the waveguide to direct the light beam from coupling-out element 208 to coupling-in element 210. In some embodiments, coupling-out element 208 may alternatively be utilized in conjunction with (or as a part of) prism 302 to direct light beams toward coupling-in element 210. Prism 302 may comprise a material selected to correct or compensate for the dispersion of the waveguide and may comprise a wedge, a block comprising two or more materials or prisms, or in any other manner. In an embodiment, the use of two prisms may enable the light-guide optical elements 118a and 118b to be parallel instead of at an acute angle to each other even, e.g., as shown in FIG. 4.

[0040] In some embodiments, gap 119 in waveguide 300 may be available for installation of additional components of optical system 100, e.g., other electronic components, processors, etc., enabling a further compactness to the design. Furthermore, the image projector 112 may be installed within the gap 119 and the aperture 202 disposed on an inside major surface of the light-guide optical element 118a.

[0041] FIG. 8 illustrates a folded optical waveguide 400 (hereinafter “waveguide” 400) with an image projector 112 mounted thereto and a user eye for reference. Waveguide 400 comprises similar components to waveguide 300 (and waveguide 200), thus similar numbers are used where applicable.

[0042] As seen in FIG. 8, waveguide 400 comprises prism 302 disposed in gap 119 between light-guide optical element 118a and light-guide optical element 118b, e.g., proximate coupling-in element 210. For example, prism 302 may comprise a material that is configured to correct or compensate for the dispersion induced by the material of the waveguide to direct the light beam from light-guide optical element 118a to coupling-in element 210. Compared to the embodiment of FIG. 7, in the embodiment of FIG. 8, coupling-out element 208 is not included and instead, prism 302 is utilized to direct the light beams that are internally reflecting within light-guide optical element 118a toward coupling-in element 210. To do so, prism 302 may be bonded or attached to light-guide optical element 118a and light-guide optical element 118b with an index-match adhesive or other material with a high enough index to let the beams propagating through the light-guide optical element 118a escape from TIR and traverse through prism 302. Prism 302 may also have a refractive index high enough to let the rays escape from TIR. Prism 302 may comprise a material selected to correct or compensate for the dispersion of the waveguide and may comprise a wedge, a block comprising two or more materials or prisms, or in any other manner. In an embodiment, the use of two prisms may enable the light-guide optical elements 118a and118b to be parallel instead of at an acute angle to each other without the use of a coupling-out element 208, e.g., as shown in FIG. 4.

[0043] In some embodiments, gap 119 in waveguide 400 may be available for installation of additional components of optical system 100, e.g., other electronic components, processors, etc., enabling a further compactness to the design. Furthermore, the image projector 112 may be installed within the gap 119 and the aperture 202 disposed on an inside major surface of the light-guide optical element 118a.

[0044] FIG. 9 illustrates a folded optical waveguide 500 (hereinafter “waveguide” 500) with an image projector 112 mounted thereto and a user eye for reference. Waveguide 500 comprises similar components to waveguide 200, thus similar numbers are used where applicable. Waveguide 500 illustrates a number of optional components or elements that may be implemented within the respective light-guide optical elements 118.

[0045] For example, waveguide 500 may include one or more homogenizer(s) 212 within light-guide optical elements 118 along the optical path between first set of facets 204 and second set of facets 206. In some implementations, the homogenizer(s) 212 may be disposed in a same area as first set of facets 204 or second set of facets 206 (e.g., instead of between them). As shown in FIG. 9, for example, a homogenizer 212 may be disposed within each of light-guide optical elements 118a and 118b. In other embodiments, one of light-guide optical element 118a or 118b may comprise a homogenizer while the other does not comprise a homogenizer. In other embodiments, multiple homogenizers may be utilized in the same light-guide optical element 118.

[0046] The homogenizer(s) 212 may be any type of light homogenizer configured to provide improved illumination uniformity. For example, the homogenizer(s) 212 may comprise a partial plane reflector as a semi-reflective surface, a partially transmissive surface, or film (e.g., partially reflective dielectric coating) added within either (or both) light-guide optical element 118. The homogenizer (s) 212 may effectively fill gaps in illumination within the waveguide 200 by partially splitting beams traversing through waveguide 500.

[0047] Waveguide 500 may also include material 404, material 406, or both to inhibit light from traveling through waveguide 200 from the external environment and / or between the light-guide optical elements 118a and 118b. For example, material 404 and / or material 406 may be a polarizer or any optical film (e.g., waveplate, color filter, etc.).

[0048] Waveguide 500 may comprise an optical element 408 disposed between coupling-out element 208 and coupling-in element 210. Optical element 408 may comprise, for example, a polarizer, a lens, prism, full waveplate, half waveplate, quarter waveplate, a color filter, or other optical elements or any combination thereof, that may be utilized to adjust a property of the light beam, block or inhibit a portion of the light beam from coming therethrough, etc.

[0049] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “includes”, "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. Further, the terms up, upper, down, lower, above, below, left, right, forward, rearward, and the like are intended to be understood in the context of the representations described and illustrated above so that a wearable device may have such an orientation in reference to the frame or to various elements as supported by the frame or as illustrated in the drawing figures.

[0050] The corresponding structures, materials, acts, and equivalents of all means or step plus function elements, if any, in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The various embodiments were chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.Examples

[0051] Example 1: An optical waveguide comprising: a first waveguide comprising: a pair of first major surfaces that are parallel; an aperture disposed on one of the first major surfacesand configured to receive an input beam; a first set of facets disposed between the first major surfaces along a first axis and configured to receive the input beam and at least partially reflect the input beam as first beams; and a coupling-out element configured to receive the first beams and reflect the first beams out of the first waveguide; and a second waveguide comprising: a pair of second major surfaces that are parallel, with at least one of the second major surfaces facing towards at least one of the first major surfaces; a coupling-in element configured to receive the first beams and reflect the first beams towards a second set of facets; and the second set of facets disposed between the second major surfaces along a second axis and configured to: receive the second beams and at least partially reflect the first beams as second beams; and couple the second beams out of the second waveguide.

[0052] Example 2: The optical waveguide of example 1, wherein the first waveguide and the second waveguide are parallel to one another.

[0053] Example 3: The optical waveguide of example 1, wherein the first waveguide is disposed at an acute angle to the second waveguide.

[0054] Example 4: The optical waveguide of any preceding example, wherein a gap is formed between the first waveguide and the second waveguide.

[0055] Example 5: The optical waveguide of example 4, further comprising a material disposed within the gap and configured to inhibit a transmission of light between the first waveguide and the second waveguide.

[0056] Example 6: The optical waveguide of example 4, further comprising a prism disposed within the gap and configured to couple the first beams between the first waveguide and the second waveguide.

[0057] Example 7: The optical waveguide of example 6, wherein the prism is attached to an end portion of the first waveguide and an end portion of the second waveguide.

[0058] Example 8: The optical waveguide of example 4, further comprising a polarizer, a lens, prism, a full waveplate, a half waveplate, or a quarter waveplate disposed within the gap-

[0059] Example 9: The optical waveguide of any preceding example, wherein the coupling- out element comprises a first mirror and the coupling-in element comprises a second mirror.

[0060] Example 10: The optical waveguide of any preceding example, wherein: the coupling- out element is arranged at a first end portion of the first waveguide and the coupling-in element is arranged at a second end portion of the second waveguide; and the first endportion and the second end portion are disposed adjacent to each other.

[0061] Example 11: The optical waveguide of any preceding example, further comprising a material disposed adjacent to one of the first major surfaces that is away from the second waveguide and configured to inhibit light from an external environment from entering the first waveguide.

[0062] Example 12: The optical waveguide of example 11, wherein the material comprises an opaque material.

[0063] Example 13: The optical waveguide of any preceding example, wherein the waveguide is configured such that a line-of-sight of a user goes sequentially through the second waveguide and the first waveguide.

[0064] Example 14: The optical waveguide of any preceding example, wherein a surface area of at least one of the first major surfaces is greater than a surface area of at least one of the second major surfaces.

[0065] Example 15: An apparatus comprising: a projector configured to produce the input beam; and the optical waveguide of any preceding example.

Claims

CLAIMSWhat is claimed is:

1. An optical waveguide comprising: a first waveguide comprising: a pair of first major surfaces that are parallel; an aperture disposed on one of the first major surfaces and configured to receive an input beam; a first set of facets disposed between the first major surfaces along a first axis and configured to receive the input beam and at least partially reflect the input beam as first beams; and a coupling-out element configured to receive the first beams and reflect the first beams out of the first waveguide; and a second waveguide comprising: a pair of second major surfaces that are parallel, with at least one of the second major surfaces facing towards at least one of the first major surfaces; a coupling-in element configured to receive the first beams and reflect the first beams towards a second set of facets; and the second set of facets disposed between the second major surfaces along a second axis and configured to: receive the first beams and at least partially reflect the first beams as second beams; and couple the second beams out of the second waveguide.

2. The optical waveguide of claim 1, wherein the first waveguide and the second waveguide are parallel to one another.

3. The optical waveguide of claim 1, wherein the first waveguide is disposed at an acute angle to the second waveguide.

4. The optical waveguide of claim 1, wherein a gap is formed between the first waveguideand the second waveguide.

5. The optical waveguide of claim 4, further comprising a material disposed within the gap and configured to inhibit a transmission of light between the first waveguide and the second waveguide.

6. The optical waveguide of claim 4, further comprising a prism disposed within the gap and configured to couple the first beams between the first waveguide and the second waveguide.

7. The optical waveguide of claim 6, wherein the prism is attached to an end portion of the first waveguide and an end portion of the second waveguide.

8. The optical waveguide of claim 4, further comprising a polarizer, a lens, prism, a full waveplate, a half waveplate, or a quarter waveplate disposed within the gap proximate the coupling-in element and the coupling-out element.

9. The optical waveguide of claim 1, wherein the coupling-out element comprises a first mirror and the coupling-in element comprises a second mirror.

10. The optical waveguide of claim 1, wherein: the coupling-out element is arranged at a first end portion of the first waveguide and the coupling-in element is arranged at a second end portion of the second waveguide; and the first end portion and the second end portion are disposed adjacent to each other.

11. The optical waveguide of claim 1, further comprising a material disposed adjacent to one of the first major surfaces that is away from the second waveguide and configured to inhibit light from an external environment from entering the first waveguide.

12. The optical waveguide of claim 11, wherein the material comprises an opaque material.

13. The optical waveguide of claim 1, wherein the waveguide is configured such that a line- of-sight of a user goes sequentially through the second waveguide and the first waveguide.

14. The optical waveguide of claim 1, wherein a surface area of at least one of the first major surfaces is greater than a surface area of at least one of the second major surfaces.

15. An apparatus comprising: a projector configured to produce the input beam; and the optical waveguide of claim 1.

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