Splitter and Combining Prism Arrangement

Abstract

The optical system may include a light input section, a light guide having first and second outer major surfaces parallel to each other for guiding light by internal reflection, a projector configured to project light corresponding to an image from an aperture, the light having a chief ray defining an optical axis of the projector and exiting the aperture with a field angle about the chief ray, and a prism disposed adjacent to the light input section and having an image input surface and a partially reflective surface parallel to the first and second outer major surfaces, the projector being associated with the image input surface and oriented such that the chief ray and at least a portion of the field angle about the chief ray are input through the image input surface and the partially reflective surface partially reflects and partially transmits some of the light rays corresponding to the field angle before entering the light guide.

Description

[Technical Field]

[0001] The present disclosure relates to the field of near-eye display optical systems, such as head-mounted displays, and more particularly to reducing the size of near-eye display optical systems by employing a splitter and combining prism arrangement. [Background technology]

[0002] Consumer demand for improved human-computer interfaces has led to increased interest in high-quality imaging head-mounted displays (HMDs) or near-eye displays (NEDs), commonly known as smart glasses. These devices can provide virtual reality (VR) or augmented reality (AR) experiences, enhancing the way users interact with digital content and their surroundings.

[0003] Consumers consistently demand better image quality, a more immersive experience, and greater comfort when using HMDs. Consumers expect displays with high resolution, vibrant colors, and minimal distortion to create a realistic and enjoyable viewing experience. Additionally, because users often wear these devices for extended periods of time, comfort is a crucial factor. Consumers desire lightweight, sleek designs that are less obtrusive to wear and more convenient in various scenarios. Smaller devices also offer improved portability, making them easier to carry and use in a variety of environments. Therefore, there is an increasing demand for smaller, more compact HMDs that offer higher performance.

[0004] A key element of a near-eye display system is the projector. In the context of HMDs and NEDs, the image projector is the device that generates the visual content delivered to the eye and projects it onto an intermediate medium (i.e., a light guide). The goal is to provide the user with the perception of an image or video, often with the illusion of depth or three-dimensionality. In the realm of HMDs and NEDs, the size of the image projector can be affected by the entrance pupil to the light guide. Ideally, for compactness and efficiency, both the projector and the entrance pupil of the light guide are small.

[0005] The technologies behind projectors for HMDs and NEDs include LED, OLED, liquid crystal on silicon (LCoS), etc. A projector technology gaining popularity involves laser projectors. Laser projectors in near-eye displays (NEDs) utilize a laser light source to generate and project images. Although these laser projectors offer several advantages, such as high brightness, wide color gamut, compactness, and low power consumption, there are also several challenges associated with the use of laser projectors, such as the susceptibility of laser projectors to generating coherent interference patterns. Summary of the Invention

[0006] In near-eye displays, the geometric relationship between the entrance pupil of the light guide and the size of the image projector is crucial. The size of the entrance pupil directly affects the size of the projector, and a smaller entrance pupil is desirable for a more compact projector. In conventional light guides, the pupil size is approximately twice the thickness of the light guide. This disclosure presents an improved optical system that provides a reduced pupil size by employing a splitter and combining prism arrangement.

[0007] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate various example systems, methods, etc., illustrating various example embodiments of aspects of the present invention. It will be understood that the boundaries of elements shown in the figures (e.g., boxes, groups of boxes, or other shapes) represent example boundaries. Those skilled in the art will understand that one element may be designed as multiple elements, and multiple elements may be designed as one element. An element shown as an internal component of another element may be implemented as an external component, and vice versa. Additionally, elements may not be drawn to scale. [Brief explanation of the drawings]

[0008] [Figure 1] 1 shows a schematic diagram of a typical optical system incorporating a splitter and combining prism arrangement. [Figure 2A] 2 shows a schematic diagram of the optical system of FIG. 1 showing different angles for the beam entering the optical system; [Figure 2B] 2 shows a schematic diagram of the optical system of FIG. 1 showing different angles for the beam entering the optical system; [Figure 2C] 2 shows a schematic diagram of the optical system of FIG. 1 showing different angles for the beam entering the optical system; [Figure 3] 1 shows a schematic diagram of a typical optical system incorporating a splitter and combining prism arrangement. [Figure 4] 1 illustrates an exemplary process for manufacturing an optical system. [Figure 5] 1 shows a schematic diagram of a typical optical system incorporating a splitter and combining prism arrangement. [Figure 6] 1 shows a schematic diagram of a typical optical system incorporating a splitter and combining prism arrangement. [Figure 7A] 1 shows a schematic diagram of a typical optical system incorporating a splitter and combining prism arrangement. [Figure 7B] 1 shows a schematic diagram of a typical optical system incorporating a splitter and combining prism arrangement. [Figure 7C] 1 shows a schematic diagram of a typical optical system incorporating a splitter and combining prism arrangement. [Figure 7D] 10A-10C show schematic alternative structures for various prisms and splitters as disclosed. [Figure 7E] 10A-10C show schematic alternative structures for various prisms and splitters as disclosed. [Figure 8] 1 shows a schematic diagram of a typical optical system incorporating two splitters and a combining prism. [Figure 9] 1 shows a schematic diagram of a typical optical system incorporating a combining prism with multiple built-in splitter surfaces. [Figure 10A] 1 shows a schematic diagram of a typical optical system incorporating a coupling prism and a splitter with built-in multiple splitting surfaces. [Figure 10B] 1 shows a schematic diagram of a typical optical system incorporating a coupling prism and a splitter with built-in multiple splitting surfaces. [Figure 11A] 1 shows a diagram of a typical optical system incorporating a splitter and combining prism arrangement. [Figure 11B] 1 shows a diagram of a typical optical system incorporating a splitter and combining prism arrangement. [Figure 11C] 1 shows a diagram of a typical optical system incorporating a splitter and combining prism arrangement. [Figure 12A] 1 shows a prior art optical system. [Figure 12B] 1 shows a prior art optical system. [Figure 12C] 1 shows a prior art optical system. [Figure 12D] 1 shows a prior art optical system. [Figure 13A] 1 shows a diagram of a typical optical system incorporating a splitter and combining prism configuration. [Figure 13B] 1 shows a diagram of a typical optical system incorporating a splitter and combining prism configuration. [Figure 13C]1 shows a diagram of a typical optical system incorporating a splitter and combining prism configuration. [Figure 13D] 1 shows a diagram of a typical optical system incorporating a splitter and combining prism configuration. DETAILED DESCRIPTION OF THE INVENTION

[0009] In near-eye displays, the geometric relationship between the entrance pupil of the light guide and the size of the image projector is crucial. The size of the entrance pupil directly affects the size of the projector, and a smaller entrance pupil is desirable for a more compact projector. In conventional light guides, the pupil size is approximately twice the thickness of the light guide. This disclosure presents an improved optical system that provides a reduced pupil size.

[0010] FIG. 1 shows a schematic diagram of a typical optical system 1 .

[0011] System 1 includes a light-directing optical element (LOE) 10, typically formed from a transparent material. LOE 10 has first and second parallel exterior major surfaces 11 a, 11 b for internally directing light by internal reflection. LOE 10 may also include a light input portion 11 c through which light enters LOE 10.

[0012] System 1 also includes a beamsplitter 17 disposed adjacent to optical input 11c of LOE 10. Beamsplitter 17 has a partially reflective surface 17a that is parallel to first and second outer major surfaces 11a, 11b of LOE 10. Beamsplitter 17 also has an in-coupling surface 17b through which light enters beamsplitter 17.

[0013] System 1 also includes projector 12, which projects light corresponding to an image (e.g., a collimated image) and has beam width 12a, which is the beam width of one collimated beam. Projector 12 may be, for example, a laser projector. Beam 12a defines the optical axis of projector 12 and has a chief ray 24 that corresponds to a point in the image. The projected light also has a field angle around chief ray 24 that corresponds to another point in the image. The system has aperture 17c. All collimated beams of the image traverse aperture 17c. Aperture 17c is both the exit aperture of the laser system and the entrance aperture to waveguide 10. Figure 2 below illustrates various angles of the field angle, all passing through aperture 17c. The size of projector 12 is not to scale.

[0014] System 1 also includes a coupling prism 15 having an image input surface 15a. Projector 12 projects light corresponding to an image that is input to prism 15 via image input surface 15a. The input beams (represented by the two extreme end beams 14a and 14b) impinge on image input surface 15a of prism 15. Chief ray 24 impinges on image input surface 15a perpendicularly, thereby minimizing aberrations. Light rays corresponding to the field angle similarly enter prism 15 via image input surface 15a. This light travels through prism 15 to input coupling surface 17b of beam splitter 17.

[0015] Partially reflective surface 17a of beam splitter 17 transmits a portion (e.g., 50%) of the light that strikes it and reflects a portion (e.g., 50%), as described, for example, in PCT International Phase Application Publication No. WO 2021 / 001841 A1. In this embodiment, partially reflective surface 17a is designed to have a length such that any ray of light at the shallowest angle of view that enters through in-coupling surface 17b strikes partially reflective surface 17a of beam splitter 17 only once before entering LOE 10 via light input section 11c to propagate within LOE 10 by internal reflection. Having beam splitter 17 effectively split the input light in half doubles the irradiance on LOE 10, thereby requiring smaller projection optics for light guide 10, reducing its size. Ideally, therefore, partially reflective surface 17a is long enough to allow every ray of light to strike partially reflective surface 17a. However, if the partially reflective surface 17a is too long, previously split rays may strike the partially reflective surface a second time and recombine, resulting in undesired interference. In system 1, rays split after initially striking surface 17a do not strike this surface a second time. In practice, the length of the partially reflective surface 17a of the beam splitter 17 is such that most of the rays in the field of view transmitted through the in-coupling surface 17b strike the partially reflective surface 17a only once before entering the LOE, so that they propagate through the LOE by internal reflection. Therefore, surface 17a acts as a splitter rather than a combiner. As a result, coherent light can be injected into the light guide without the risk of generating a coherent interference pattern.

[0016] System 1 may also include a light absorber 18 that trims excess light at one end of the range between 14a and 14b. Light absorber 18 is adjacent to face 17d of beamsplitter 17, opposite in-coupling face 17b. Trim position 20 (corresponding to the end of light absorber 18) is located directly opposite corner 16, which trims excess light at the other end of the range between 14a and 14b. Corner 16 and trim position 20 therefore provide symmetric trimming of the transmitted beam. In effect, an imaginary plane 17c is formed between corner 16 and position 20, defining the entrance pupil for LOE 10.

[0017] 2A, 2B, and 2C show schematic diagrams of optical system 1 illustrating different angles for a beam entering optical system 1 as it traverses surface 17c, the entrance aperture to waveguide 10. FIG. 2A illustrates the shallowest angle α for first and second major surfaces 11a, 11b, FIG. 2C illustrates the steepest angle γ for first and second major surfaces 11a, 11b, and FIG. 2B illustrates the angle β therebetween, where α<β<γ for first and second major surfaces 11a, 11b. From these illustrations, it is clear that the optimal length of partially reflective surface 17a is different for different viewing angles. In FIG. 2A, the length of partially reflective surface 17a is set to maximize beam splitting while minimizing interference for the shallowest angle represented by rays 14a, 14b. In Figure 2A, any overlap at 30a between the extreme edge rays 14a, 14b (i.e., at the edge of partially reflective surface 17a) is minimized. However, in Figures 2B and 2C, there is significant overlap between rays 34a, 34b and rays 44a, 44b (at 30b and 30c), which corresponds to an undesirable length of partially reflective surface 17a for these steeper-angled rays. In practice, the length of surface 17a is a compromise; if it is too long, some interference caused by recombination at 30b and 30c is expected. However, if the length of partially reflective surface 17a is set too short, some illumination non-uniformity caused by a lack of beam splitting is expected.

[0018] In determining the length of partially reflective surface 17a, a compromise may be made to maximize beam splitting to ensure uniform illumination while minimizing interference caused by recombination as much as possible. This is equivalent to optimizing for the shallowest angle of light, as shown in FIGS. 1 and 2A. With this goal in mind, it can be seen from FIG. 1 that an appropriate length L for partially reflective surface 17a may be approximately equal to half the total internal reflection round trip for ray 14b. Thus, length L of partially reflective surface 17a may be set approximately equal to the length L of LOE 10 over which light from ray 14b (i.e., the ray of light at the most oblique (i.e., shallowest) angle of view entering through in-coupling surface 17b farthest from the top surface of beamsplitter 17) travels once from first exterior major surface 11a to second exterior major surface 11b as it propagates through LOE 11 by internal reflection.

[0019] This set length L of the partially reflective surface 17a of the beam splitter 17 maximizes the illumination of the LOE 10 while minimizing interference patterns caused by light corresponding to a point in the image hitting the partially reflective surface 17a of the beam splitter 17 more than once before entering the LOE 10.

[0020] FIG. 3 shows a system 1a similar to system 1 of FIG. 1, except that a coupling prism 35 is positioned above a beam splitter 37, thereby achieving a simpler implementation of a larger projector 12 at the expense of the larger projector 12.

[0021] System 1a includes LOE 10 having parallel first and second outer major surfaces 11a, 11b for internally guiding light by internal reflection and a light input surface 11c through which light enters LOE 10. System 1a also includes a beamsplitter 37 disposed adjacent to light input 11c of LOE 10. Beamsplitter 37 has a partially reflective surface 37a that is parallel to LOE 10's first and second outer major surfaces 11a, 11b. Beamsplitter 37 also has an input coupling surface 37b through which light enters beamsplitter 37. System 1a also includes projector 12 that projects light corresponding to an image (e.g., a collimated image) and having beamwidth 12a. System 1a also includes a coupling prism 35 having an image input surface 35a.

[0022] Projector 12 projects light corresponding to an image that is injected into prism 35 via image injection surface 35a. The injected beams (represented by the two extreme end beams 14a and 14b) impinge on image injection surface 35a of prism 35. The light travels through prism 35 to input coupling surface 37b of beam splitter 37. Partially reflective surface 37a of beam splitter 37 transmits a portion (e.g., 50%) and reflects a portion (e.g., 50%) of the light that impinges on it.

[0023] In this embodiment, partially reflective surface 37a is designed to have a length such that any rays of light at the shallowest angle of view that enter through in-coupling surface 37b strike partially reflective surface 37a of beamsplitter 37 only once before entering LOE 10 via light input section 11c for propagation within LOE 10 by internal reflection. The length of partially reflective surface 37a of beamsplitter 37 is such that the majority of rays of light in the field that are transmitted through in-coupling surface 37b strike partially reflective surface 37a only once before entering LOE 10 for propagation within LOE 10 by internal reflection. Thus, surface 37a acts as a splitter rather than a combiner. As a result, coherent light can be injected into the light guide without the risk of generating coherent interference patterns.

[0024] System 1a may also include a light absorber 38 that trims excess light at one end of the range between 14a and 14b. Light absorber 38 is adjacent to face 37d of beam splitter 37, opposite in-coupling face 37b. Trim location 40 (corresponding to the end of light absorber 38) is located directly opposite corner 36, which trims excess light at the other end of the range between 14a and 14b. Corner 36 and trim location 40 thus provide symmetric trimming of the transmitted beam. In effect, an imaginary plane is formed between corner 36 and location 40, defining the entrance pupil (also referred to herein as the aperture) for LOE 10.

[0025] In the system 1 of Figure 1, the input coupling surface 17b is at an oblique angle to the first and second major surfaces 11a, 11b, whereas in the system 1a of Figure 3, the coupling surface 37b is parallel to the first and second major surfaces 11a, 11b.

[0026] 4 shows an exemplary process for manufacturing optical systems 1 and 1a. In step 40, plates are coated with a partial reflector and attached together in step 42 to form beamsplitter 17. The attached plates forming beamsplitter 17 may be attached to light guide 10 in step 44 and polished together to create a combined exterior facet. In step 46a, the corners of beamsplitter 17 may be polished and prism 15 may be attached onto the corners. Alternatively, in step 46b, prism 35 may be attached directly to the light guide surface (here 37 since the corners are not removed) of beamsplitter 17.

[0027] At this stage, an absorbing coating may be applied to form the light absorber 18 or 38 .

[0028] Further simplification of the beam splitting configuration may be achieved by implementing the partial reflector within the combining prism, rather than as a separate part or as part of the light guide 10. This is shown in Figures 5 and 6.

[0029] In system 1b of FIG. 5, partial reflector 57 is housed within prism 55, so that partial reflector 57 can be fabricated as a single element attached to light guide 10. In this configuration, light beam 12 enters through face 55a and illuminates directly onto aperture 12 between faces 56 and 70. Here, arrow 86 represents the direct beam (not split), so that a portion of the illumination has twice the intensity, while section 88 indicates an area where no light passes (missing light shown as dashed arrow 87 outside illuminator aperture 12). Therefore, illumination uniformity is reduced in this configuration. Nevertheless, in some applications, this non-uniformity may be acceptable.

[0030] A light absorber 58 may be disposed adjacent a second face 55b of the prism 55 opposite the input face 55a.

[0031] FIG. 6 shows configuration 1c, which is equivalent to FIG. 5, except that the illumination is at the bottom of the aperture and bottom surface 65b of prism 65 is reflective. Partial reflector 67 is housed within prism 65, so partial reflector 67 can be fabricated as a single element attached to light guide 10. In this configuration, light beam 12 enters through surface 65a and directly illuminates aperture 10 between surfaces 66 and 70. Here, arrow 86 represents the direct beam (not split), so a portion of the illumination will have twice the intensity, while section 88 indicates an area where no light passes (missing light). Therefore, illumination uniformity is reduced in this configuration. Nevertheless, in some applications, this non-uniformity may be acceptable.

[0032] FIG. 7A shows a further simplified configuration 1d in which the coupling configuration is limited to the width of LOE 10. Beams 14a, 14b enter optical system 1d through blank prism 50 with a perpendicular entrance face 51, which serves to minimize aberrations. The exit from prism 50 and the entrance to LOE 10 serve as entrance pupil 52. The projection optics can be designed with an exit aperture that overlaps this light guide entrance aperture 52. Aperture 52 is located very close to entrance face 51, thereby enabling a compact projection optics system. Stray light is trimmed away at the entrance by optional absorbing surfaces 54a, 54b. In the first section of LOE 10, the beams impinge once on partially reflective surface 37a, thus creating uniform illumination of LOE 10.

[0033] FIG. 7B shows two central beams 24a, 24b at different angles (field angles), with the dashed arrow 24a representing the shallowest one and the chained arrow 24b representing the steepest beam in the image. At least a portion of the steepest beam 24b strikes the partial reflector 37a twice. The extra length of the surface 37a is labeled 76. As a result, a portion of the field angle of the projected image may have an interference pattern when using coherent illumination. As described in FIG. 1, the length of 37a may be set shorter, partially compromising illumination uniformity at the field angle edges.

[0034] In system 1 of Figure 1, input coupling surface 17b is at an oblique angle to first and second major surfaces 11a, 11b, in system 1a of Figure 3, coupling surface 37b is parallel to first and second major surfaces 11a, 11b, and in system 1d of Figures 7A and 7B, coupling surface 52 is perpendicular to the first and second major surfaces.

[0035] Optional absorber 54a can be set so that its end does not cut off the steepest beam, as shown.

[0036] 7C shows an equivalent configuration 1e in which the transparent entrance prism is replaced with a reflecting prism 70 having a reflector 78. More optical components can be added (not shown) to suppress aberrations. The input coupling surface 52 is perpendicular to the first and second major surfaces. The reflective surface 78 may be attached to, coated on, or form part of the coupling prism 70 such that light 12 injected through the image input surface 70a is reflected by the reflective surface 78 towards the input coupling surface 52. In some embodiments, the reflective prism 70 may be larger than the width of the light guide 10.

[0037] For rectangular cross-section light guides, the transparent prism 50, the reflector 70, and all prisms described above can be tilted out of the plane of the drawing to launch the light in the proper orientation.

[0038] FIG. 7D shows a schematic front view of a rectangular light guide implementation in which splitter 37 is oriented laterally as described above.

[0039] 7E shows a further implementation of a vertical splitter 60 in addition to splitter 37. Vertical splitter 60 can be implemented in transparent prism 50 or in reflective prism 70. Alternatively, vertical splitter 60 can be implemented in various beam splitters 17, 37, etc., in the configurations described above.

[0040] Beamsplitters implemented with multiple partial reflectors can further improve system performance in terms of projector size, uniformity, and combining section size. Figures 8, 9, and 10 show systems incorporating multiple partial reflectors.

[0041] FIG. 8 shows a system 1f in which a beam splitter 97 includes two partial reflectors 97a, 97b that serve to reduce an input aperture 97c. In one embodiment, partial reflector 97a has a reflectivity of 33%, while partial reflector 97b has a reflectivity of 50%. In other embodiments, partial reflectors 97a, 97b may have reflectivities different from 33% and 50%, respectively. In the embodiment of FIG. 8, partial reflector 97a has the same length but is shifted to the left relative to partial reflector 97b. Here, the entrance pupil 97c is smaller than in the single partial reflector case, as described in FIG. 1.

[0042] The positioning and reflectivity of the partial reflectors 97a, 97b may be selected to ensure uniform illumination of the light guide 10 for a nominal illumination angle. The light absorbers 98a, 98b may serve to absorb stray light. The absorbers 98a, 98b may be implemented simultaneously, separately, or not at all.

[0043] Advantages of system 1f having reduced size aperture 97c may include the ability to use a smaller size prism 95 and / or a smaller size projector 12.

[0044] Figure 9 shows system 1g including a prism 105 with three partial reflectors 107a, 107b, and 107d housed therein to improve light uniformity in a simplified configuration equivalent to that of Figure 5. Light absorbers 108a, 108b, and 108c may be used to attenuate stray light. Various reflectivity values ​​may be defined for partial reflectors 107a, 107b, and 107d. In one embodiment, partial reflector 107a has a lower reflectivity than partial reflector 107d, and partial reflector 107b has a reflectivity between them.

[0045] In this configuration, an input aperture 107c can be defined. Reflections from partial reflectors 107a, 107b, 107d serve to shift the illumination to fill light guide 10. In this configuration, light beam 12 enters through prism 105 and illuminates directly onto aperture 107c.

[0046] In system 1g, the output illumination onto light guide 10 is more uniform compared to the illumination of the system shown in Figures 5 and 6. Here, all sections are uniformly illuminated. None of blank sections 88 and sections 86 are fully illuminated as shown in Figures 5 and 6.

[0047] FIG. 10A shows a system 1h including a beam splitter 117 with two partial reflectors 117a, 117b in a configuration similar to that of FIG. 7A. The additional beam split caused by the additional partial reflector 117b allows for a reduction in the length of the beam splitter 117 and the partial reflectors 117a, 117b compared to the configuration of FIG. 7A. The beams 14a, 14b enter the optical system 1h through a blank prism 50 with a perpendicular entrance face 51, which serves to minimize aberrations. The exit from the prism 50 and the entrance to the LOE 10 serve as an entrance pupil 52. The projection optics can be designed with an exit aperture that overlaps with this light guide entrance aperture 52. The aperture 52 is located very close to the entrance face 51, thereby enabling a compact projection optics system. Stray light is trimmed away at the entrance by optional absorbing surfaces 54a, 54b. The light beam hits the partial reflectors 107 a , 107 b once, thus creating a uniform illumination of the LOE 10 .

[0048] FIG. 10B shows schematically that beam splitter 117 may also include vertical partial reflectors 120a, 120b in addition to horizontal partial reflectors 117a, 117b.

[0049] 11A and 11B show an implementation of a single prism that acts as both a reflector and a single reflective beam splitter (primarily due to ergonomic considerations).

[0050] FIG. 11A graphically illustrates the reflectivity profile of a dielectric coating with minimum reflectivity at low angle 118 and 50% reflectivity at high angle 120. This coating is implemented as splitting surface 122 in system 1i, in the configuration shown in FIG. 11B. An impinging beam having width 12 (boundary labeled as a dashed arrow) enters prism 124 at a low angle (within range 118). A portion of beam 12 strikes splitting surface 122 and therefore passes through splitting surface 122 with minimal loss. This portion is reflected by section 126 of planar reflector 128 onto light guide 10 (large solid arrow). Light that does not pass through splitter 122 illuminates planar reflector 128 at section 130 to be reflected at the same angle. This light is labeled as a thick dashed arrow. The reflections (solid and dashed arrows) are identical and consecutive. Here, they are separated for clarity.

[0051] Illumination from section 126 strikes splitter 122 at high angle 120 and is therefore split as shown. Reflection from section 130 first reflects off the end of prism 124 (which may also be referred to as the face of light guide 10) before striking the end of splitting face 122 at high angle 120 and is therefore split in two as shown. By appropriate selection of the width of reflector 128 and the length of splitter 122, uniform and complete illumination of light guide 10 can be achieved. A single prism 124 containing splitter 122 and reflector 128 (which may be implemented with top and bottom reflectors, if desired, and followed by the outer face of light guide 10) allows for simple and low-cost manufacturing of the folding and splitting arrangement.

[0052] Figure 11C shows system 1j in which reflector 128 of Figure 11B is positioned anywhere along the same plane. Illumination 12 illuminates all of this reflector 128, resulting in a uniform output while only the relative widths of sections 126 and 130 change. In this figure, reflector 128 has been moved to its lowest position (optimal for reducing the size and ease of manufacturing of the optics), so that the illumination from section 126 is smaller than the illumination from section 130. This configuration may include more splitters, thereby allowing for a narrower input beam 12 and optics.

[0053] In a further embodiment, the two-dimensional light guide includes two sets of parallel planes that are perpendicular to each other. Coupling into these rectangular cross-section light guides is described in U.S. Pat. No. 10,564,417. Figures 12A-12D show various coupling configurations based on refractive and reflective optics, as disclosed in the '417 patent. The coupling arrangements include trimmed edges 16a and 16b. The beam splitting configurations described in Figures 1-11 of this disclosure can be combined to produce optimal coupling into such 2D light guides. The aperture can be reduced in one or two dimensions.

[0054] 13A, 13B, and 13C show side, top, and isometric views, respectively, of system 1k coupled to a 2D light guide based on combining a reflecting prism 134 in a configuration similar to that of FIG. 1. Light (beams 14a-d) enters prism 134 and is reflected by reflective surface 131a onto light guide 10. The entrance aperture is defined in one dimension by 16a and in the other by 16b. Partial reflector 17 allows for aperture reduction in the vertical direction (as described for FIG. 1), while also allowing prism 134 to include partial reflector 122 (with the profile of FIG. 11A), as described in FIG. 11B (or in FIG. 9, but here as a reflecting prism).

[0055] FIG. 13D shows a simplified configuration in which reflecting prism 134 is attached directly to light guide 10 without prism 15.

[0056] While beam splitting by crossing partial reflectors as shown in FIG. 10B is possible in all of the above configurations, the separation approach as described in FIG. 13 simplifies the manufacturing process by fabricating the splitter as a separate component.

[0057] The absorbers described in the above configurations can be replaced with prisms or other refractive components that combine the light from each system.

[0058] definition The following contains definitions of selected terms used herein. These definitions include various examples or forms of components that fall within the scope of the terms and that may be used in implementations. The examples are not intended to be limiting. Both singular and plural forms of terms are possible within the definitions.

[0059] An "operable connection," or a connection in which entities are "operably connected," is a connection in which signals, physical communications, or logical communications may be sent or received. Typically, an operable connection includes a physical interface, an electrical interface, or a data interface, but it should be noted that an operable connection may include different combinations of these or other types of connections sufficient to enable operable control. For example, two entities may be operably connected by being able to communicate signals to each other directly or through one or more intermediate entities, such as processors, operating systems, logic, software, or other entities. Logical or physical communication channels may be used to create an operable connection.

[0060] The terms "includes" or "including," to the extent that they are used in the detailed description or claims, when interpreted as a transitional clause in a claim, are intended to be inclusive in a manner similar to the term "comprising." Furthermore, to the extent that the term "or" is used in the detailed description or claims (e.g., A or B), it is intended to mean "A or B, or both." If the applicant intends to indicate "only A or B, but not both," the term "only A or B, but not both" is used. Thus, the use of the term "or" herein is inclusive, not exclusive. See Bryan A. Garner, A Dictionary of Modern Legal Usage 624 (2d. Ed. 1995).

[0061] Although exemplary systems, methods, etc. have been shown by way of description of examples, and while the examples have been described in considerable detail, it is not the applicant's intention to limit the scope to such details, or to be in any way limiting. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the systems, methods, etc. described herein. Additional advantages and modifications will be readily apparent to those skilled in the art. Therefore, the present invention is not limited to the specific details, representative devices, and illustrative examples shown and described. Therefore, the present application is intended to cover alterations, modifications, and variations that fall within the scope of the appended claims. Moreover, the foregoing description is not intended to limit the scope of the present invention. Rather, the scope of the present invention should be determined by the appended claims and their equivalents.

Claims

1. 1. An optical system comprising: a light-directing optical element (LOE) formed from a transparent material and having a light input portion and parallel first and second outer major surfaces for guiding light by internal reflection; a beam splitter disposed adjacent to the light input portion and having a partially reflective surface and an in-coupling surface parallel to the first outer major surface and the second outer major surface; a projector configured to project light corresponding to a collimated image from an aperture, the light having a chief ray defining an optical axis of the projector and exiting the aperture with a field angle about the chief ray; a coupling prism having an image input surface and adjacent to the in-coupling surface, the projector being associated with the image input surface and oriented such that the chief ray and at least a portion of the angle of view around the chief ray are input through the image input surface and travel to the in-coupling surface; an optical system, wherein a length dimension of the partially reflective surface of the beam splitter is such that any ray of light in the field angle that enters through the input coupling surface at the shallowest angle relative to the first and second major outer surfaces strikes the partially reflective surface of the beam splitter only once before entering the LOE, so that it propagates within the LOE by internal reflection.

2. 2. The optical system of claim 1, further comprising: a light absorber disposed adjacent a second surface of the beam splitter opposite the in-coupling surface, the end of the light absorber and an end of the in-coupling surface defining an entrance pupil within the LOE.

3. The in-coupling surface is at an oblique angle relative to the first and second major surfaces; parallel to the first major surface and the second major surface; and 10. The optical system of claim 1, wherein the first major surface is perpendicular to the first surface and the second major surface.

4. the in-coupling surface is perpendicular to the first principal surface and the second principal surface, and the optical system comprises:

10. The optical system of claim 1, further comprising a reflective surface attached to or forming part of the coupling prism such that light injected through the image injection surface is reflected by the reflective surface towards the input coupling surface.

5. 2. The optical system of claim 1, wherein the length dimension of the partially reflective surface of the beam splitter minimizes interference patterns caused by light corresponding to a point in the image hitting the partially reflective surface of the beam splitter more than once before entering the LOE.

6. The optical system of claim 1 , wherein the beam splitter includes a second partially reflective surface parallel to the first outer major surface and the second outer major surface.

7. 2. The optical system of claim 1, wherein the beam splitter includes a second partially reflective surface parallel to the first outer major surface and the second outer major surface, the second partially reflective surface being disposed closer to the LOE than the partially reflective surface.

8. The optical system of claim 1 , wherein the combining prism or the second combining prism incorporates one or more partially reflective surfaces perpendicular to the first and second outer major surfaces.

9. 1. An optical system comprising: a light-directing optical element (LOE) formed from a transparent material and having a light input portion and parallel first and second outer major surfaces for guiding light by internal reflection; a beam splitter disposed adjacent to the optical input portion and having a partially reflective surface parallel to the first and second outer major surfaces and an in-coupling surface on the input surface; a projector configured to project light corresponding to an image from an aperture, the light having a chief ray defining an optical axis of the projector and exiting the aperture with a field angle about the chief ray; a coupling prism adjacent to the in-coupling surface, the coupling prism having an image input surface angled obliquely relative to the first outer major surface and the second outer major surface, the projector being associated with the image input surface and oriented such that the chief light ray and at least a portion of the angle of view around the chief light ray are input through the image input surface; An optical system, wherein a length dimension of the partially reflective surface of the beam splitter is approximately equal to a length of the LOE through which light from a ray of light at the most oblique angle to the first and second major outer surfaces in the field angle that enters through the input coupling surface farthest from the input surface travels once from the first major outer surface to the second major outer surface when propagating within the LOE by internal reflection.

10. 10. The optical system of claim 9, comprising: an optical absorber disposed adjacent a second surface of the beam splitter opposite the input surface; an imaginary plane that is perpendicular to the first and second major surfaces and intersects an edge of the in-coupling surface; and a location on the second surface adjacent an edge of the optical absorber that corresponds to defining an entrance pupil to the LOE.

11. The in-coupling surface is at an oblique angle relative to the first major surface and the second major surface; parallel to the first major surface and the second major surface; and 10. The optical system of claim 9, wherein the first major surface is perpendicular to the second major surface.

12. the in-coupling surface is perpendicular to the first principal surface and the second principal surface, and the optical system comprises:

10. The optical system of claim 9, further comprising a reflective surface attached to or forming part of the coupling prism such that light injected through the image injection surface is reflected by the reflective surface towards the in-coupling surface.

13. 10. The optical system of claim 9, wherein the length dimension of the partially reflective surface of the beam splitter minimizes interference patterns caused by light corresponding to a point in the image hitting the partially reflective surface of the beam splitter more than once before entering the LOE.

14. The optical system of claim 9 , wherein the beam splitter includes a second partially reflective surface parallel to the first outer major surface and the second outer major surface.

15. 10. The optical system of claim 9, wherein the beam splitter includes a second partially reflective surface parallel to the first outer major surface and the second outer major surface, the second partially reflective surface being disposed closer to the LOE than the partially reflective surface.

16. The optical system of claim 9 , wherein the combining prism or the second combining prism incorporates one or more partially reflective surfaces perpendicular to the first and second outer major surfaces.

17. 1. An optical system comprising: a light-directing optical element (LOE) having a light input portion and parallel first and second outer major surfaces for guiding light by internal reflection; a beam splitter disposed adjacent to the light input portion and having a partially reflective surface and an in-coupling surface parallel to the first outer major surface and the second outer major surface; a laser projector configured to project light corresponding to an image from an aperture, the light having a chief ray defining an optical axis of the laser projector and exiting the aperture with a field angle about the chief ray; a coupling prism having an image input surface and adjacent to the in-coupling surface, the laser projector being associated with the image input surface and oriented such that the chief ray and at least a portion of the angle of view around the chief ray are input through the image input surface; An optical system, wherein the length dimension of the partially reflective surface of the beam splitter is such that most of the light rays within the field of view that are transmitted through the input coupling surface collide with the partially reflective surface of the beam splitter only once before entering the LOE, so that they propagate within the LOE by internal reflection.

18. 18. The optical system of claim 17, comprising an optical absorber disposed adjacent a second surface of the beam splitter opposite the input coupling surface, wherein an end of the optical absorber and a corner of the coupling prism adjacent the input coupling surface define an entrance pupil into the LOE.

19. The in-coupling surface is at an oblique angle relative to the first and second major surfaces; parallel to the first major surface and the second major surface; and 18. The optical system of claim 17, wherein the first major surface is perpendicular to the first major surface and the second major surface.

20. the in-coupling surface is perpendicular to the first principal surface and the second principal surface, and the optical system comprises:

18. The optical system of claim 17, further comprising a reflective surface attached to or forming part of the coupling prism such that light injected through the image injection surface is reflected by the reflective surface towards the in-coupling surface.

21. 18. The optical system of claim 17, wherein the length dimension of the partially reflective surface of the beam splitter minimizes interference patterns caused by light corresponding to a point in the image hitting the partially reflective surface of the beam splitter more than once before entering the LOE.

22. 18. The optical system of claim 17, wherein the beamsplitter has a second partially reflective surface perpendicular to the first outer major surface and the second outer major surface.

23. 18. The optical system of claim 17, wherein the beamsplitter includes a second partially reflective surface parallel to the first outer major surface and the second outer major surface.

24. 18. The optical system of claim 17, wherein the beam splitter includes a second partially reflective surface parallel to the first outer major surface and the second outer major surface, the second partially reflective surface being disposed closer to the LOE than the partially reflective surface.

25. 18. The optical system of claim 17, wherein the combining prism or the second combining prism incorporates one or more partially reflective surfaces perpendicular to the first and second outer major surfaces.

26. 20. The optical system of claim 17, comprising a second prism adjacent to the combining prism, the second prism incorporating one or more partially reflective surfaces perpendicular to the first and second outer major surfaces.

27. 1. An optical system comprising: a light-directing optical element (LOE) having a light input portion and parallel first and second outer major surfaces for guiding light by internal reflection; a projector configured to project light corresponding to an image from an aperture, the light having a chief ray defining an optical axis of the projector and exiting the aperture with a field angle about the chief ray; and a prism disposed adjacent to the light input section and having an image input surface and a partially reflective surface parallel to the first outer major surface and the second outer major surface, wherein the projector is associated with the image input surface and the prism is oriented such that the chief ray and at least a portion of the angle of view around the chief ray are input through the image input surface, and a portion of the light corresponding to the angle of view is partially reflected and partially transmitted by the partially reflective surface before entering the light emission element.

28. 28. The optical system of claim 27, comprising a light absorber disposed adjacent a base surface of the prism having an end adjacent the light input portion.

29. 28. The optical system of claim 27, wherein the prism has a reflective bottom surface, and the projector is configured such that a majority of light from a light beam injected through the image injection surface strikes the partially reflective surface only once.

30. 28. The optical system of claim 27, wherein a length dimension of the partially reflective surface minimizes interference patterns caused by light corresponding to a point in the image hitting the partially reflective surface more than once before entering the LOE.

31. 28. The optical system of claim 27, wherein the prism includes a second partially reflective surface parallel to the first outer major surface and the second outer major surface.

32. 28. The optical system of claim 27, wherein the prism includes second and third partially reflective surfaces parallel to the first and second outer major surfaces.

33. the partially reflective surface has applied thereon a dielectric coating having a different reflectivity for (a) light impinging on the partially reflective surface at a low angle and (b) light impinging on the partially reflective surface at a higher angle that is greater than the low angle; The system comprises:

28. The optical system of claim 27, comprising a reflective surface attached to or forming part of the combining prism and disposed relative to the partially reflective surface such that a portion of light injected through the image injection surface first passes through the partially reflective surface and is then reflected by the reflective surface towards the partially reflective surface, and a portion of light injected through the image injection surface does not first pass through the partially reflective surface but is reflected by the reflective surface towards the second outer major surface.

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