Compound light-guide optical elements and method for manufacturing optical system comprising light-guide optical element

Abstract

An optical system for guiding image illumination injected at a coupling region toward a user for viewing includes a light-guide optical element (LOE) having a pair of parallel main outer surfaces. A first region of the LOE includes a first set of partially reflective surfaces oriented to redirect image illumination propagating within the LOE toward a second region of the LOE, the second region including a second set of partially reflective surfaces oriented to couple the image illumination toward the user. The first set of partially reflective surfaces extends across at least 95% of the thickness of the LOE, while the second set of partially reflective surfaces is contained within a sub-portion of the thickness spanning less than 95% of the thickness, such that the second set of partially reflective surfaces is excluded from one or both surface layers of the second region.

Description

[Technical Field]

[0001] The present invention relates to optical systems, and more particularly to optical systems including a light-guide optical element (LOE) for realizing optical aperture expansion. [Previous Technology]

[0002] This invention is a divisional application of Taiwan Patent Application No. 110118710, filed on September 2, 2021, entitled "Compound Light-Guide Optical Element". Compound Light-Guide Optical Elements (LOEs) or "two-dimensional extended waveguides" have been described in previous publications of Lumus Ltd. (Israel). Examples of such composite LOEs can be found, for example, in PCT (Patent Cooperation Treaty) Publication No. WO 2020 / 049542. Generally, these composite LOEs employ two regions, each of which is a block of parallel surfaces of transparent material used to support the propagation of light carrying a collimated image through internal reflection at a main surface, and includes a set of mutually parallel internal partially reflective surfaces or "facets" that progressively redirect a portion of the collimated image and achieve an expansion of the optical aperture. By combining two such elements with different facet orientations, a two-dimensional expansion of the optical aperture can be achieved within a single element, thereby expanding the input image from the image projector and outputting it toward the observer's eye over a larger area.

[0003] For ease of reference, the light guide optical element (LOE) region responsible for the first stage of the expansion within the composite element is referred to as the “first LOE” or “LOE1”, while the LOE region responsible for deflecting the image once toward the observer is referred to herein as the “second LOE” or “LOE2”. [Summary of the Invention]

[0004] The present invention is an optical system for guiding an image illumination injected at a coupling region toward a user for viewing.

[0005] According to the teachings of embodiments of the present invention, an optical system is provided for guiding an image illumination injected at a coupling region toward a user for viewing, the optical system comprising a light guide optical element (LOE) formed of a transparent material, the LOE comprising: (a) a first region comprising a first set of flat, mutually parallel partially reflective surfaces having a first orientation; (b) a second region comprising a second set of flat, mutually parallel partially reflective surfaces having a second orientation, the second orientation being non-parallel to the first orientation; and (c) a set of mutually parallel main outer surfaces extending across the first and second regions such that both the first set of partially reflective surfaces and the second set of partially reflective surfaces are located between the main outer surfaces. In the first set of partially reflective surfaces, the second set of partially reflective surfaces is angled to the main outer surface, such that a portion of the image illumination propagating from the first region to the second region within the LOE via internal reflection at the main outer surface is coupled out from the LOE toward the user, and wherein the first set of partially reflective surfaces is oriented such that a portion of the image illumination propagating within the LOE via internal reflection at the main outer surface from the coupled region is deflected toward the second region, wherein the LOE has a thickness between the main outer surfaces, and wherein the first set of partially reflective surfaces extends across at least 95% of the thickness, and the second set of partially reflective surfaces in the second region is contained within a sub-portion of the thickness spanning less than 95% of the thickness, such that the second set of partially reflective surfaces is excluded from at least one surface layer of the second region.

[0006] According to another feature of an embodiment of the present invention, the second set of partially reflective surfaces is excluded from the surface layer of the two main outer surfaces in the second region.

[0007] According to another feature of an embodiment of the present invention, the total thickness of at least one surface layer of the second region of the second set of partially reflective surfaces is between 6% and 33% of the thickness.

[0008] According to another feature of an embodiment of the invention, the spacing between adjacent surfaces of the second set of partial reflective surfaces in a direction parallel to the main outer surface is at least 1 mm, and wherein the total thickness of at least one surface layer excluding the second region of the second set of partial reflective surfaces is at least 10% of the thickness.

[0009] According to another feature of an embodiment of the invention, the first set of partially reflective surfaces extends across at least 96% of the thickness.

[0010] According to another feature of an embodiment of the invention, the first set of partially reflective surfaces extends across at least 98% of the thickness.

[0011] According to another feature of an embodiment of the invention, the first set of partially reflective surfaces extends across the entire thickness.

[0012] According to another feature of an embodiment of the present invention, the first orientation of the first set of partial reflective surfaces is orthogonal to the main outer surface.

Implementation Method

[0014] The present invention is an optical system for guiding an image illumination injected at a coupling region toward a user for viewing.

[0015] Certain embodiments of the present invention provide an optical system including a light guide optical element (LOE) for realizing optical aperture expansion for use in a head-up display and most preferably a near-eye display, which may be a virtual reality display or more preferably an augmented reality display.

[0016] Figures 1A and 1B schematically illustrate an exemplary implementation of a near-eye display (generally designated 10) in the form of a LOE 12 employing the teachings of an embodiment of the present invention. The near-eye display 10 employs a compact image projector (or “POD”) 14 optically coupled to inject an image into the LOE (interchangeably referred to as a “waveguide,” “substrate,” or “slab”) 12, within which image light is captured in one dimension by internal reflection at a set of mutually parallel, flat outer surfaces. Light is directed toward a set of partially reflective surfaces (interchangeably referred to as “facets”) parallel to each other and at an angle to the direction of image light propagation, wherein each successive facet deflects a portion of the image light in a deflection direction, which is also captured / guided within the substrate by reflection. This first set of facets is not shown separately in Figures 1A and 1B, but is located in a first region (designated 16) of the LOE. The partial reflection at the successive small planes achieves the first-dimensional optical aperture expansion.

[0017] In a first set of preferred but non-limiting examples of the invention, the aforementioned set of facets is orthogonal to the main outer surface of the substrate. In this case, both the injected image and its conjugate, which undergoes internal reflection as it propagates within the first region 16, are deflected and become a conjugate image propagating in the deflection direction. In an alternative set of preferred but non-limiting examples, the first set of partially reflective surfaces is angled relative to the main outer surface of the LOE. In the latter case, the injected image or its conjugate forms a desired deflected image propagating within the LOE, while other reflections can be minimized, for example, by employing an angle-selective coating on the facets, which makes the facets relatively transparent to the range of incident angles from which the image does not require reflection.

[0018] The first set of partially reflective surfaces deflects the image illumination from a first direction of propagation captured within the substrate by total internal reflection (TIR) ​​to a second direction of propagation also captured within the substrate by TIR.

[0019] The deflected image is then directed into a second substrate region 18, which may be implemented as adjacent different substrates or as a continuation of a single substrate, in which a coupling arrangement (typically another set of partially reflective facets) gradually couples a portion of the image directed toward the observer's eye located within an area defined as an eye-motion box (EMB), thereby achieving a second-dimensional optical aperture expansion. The overall device may be implemented separately for each eye and is preferably supported relative to the user's head, with each LOE 12 facing the user's corresponding eye. In a particularly preferred option as shown here, the support arrangement is implemented as an eyeglass frame having sides 20 for supporting the device relative to the user's ears. Other forms of support arrangements may also be used, including but not limited to headbands, face shields, or devices suspended on a helmet.

[0020] Reference is made herein to the X-axis and Y-axis, which extend horizontally (Fig. 1A) or vertically (Fig. 1B) in the general direction of extension of the first region of the LOE, and the Y-axis extends perpendicular to the X-axis, i.e., vertically in Fig. 1A and horizontally in Fig. 1B.

[0021] In very approximate terms, the first region 16 of the first LOE or LOE 12 can be considered to achieve aperture expansion in the X direction, while the second region 18 of the second LOE or LOE 12 achieves aperture expansion in the Y direction. The details of the angular expansion of the different parts of the field of view will be described more precisely below. It should be noted that the orientation shown in FIG1A can be considered a “top-down” implementation in which image illumination entering the main (second region) of the LOE enters from the top edge, while the orientation shown in FIG1B can be considered a “lateral injection” implementation in which the horizontal deployment is referred to here as the Y-axis. In the remaining figures, various features of certain embodiments of the invention will be shown in the context of a “top-down” orientation similar to FIG1A. However, it should be recognized that all these features are equally applicable to lateral injection implementations that also fall within the scope of the invention. In some cases, other intermediate orientations may also be applicable and, unless explicitly excluded, are also included within the scope of the invention.

[0022] The POD used with the apparatus of the present invention is preferably configured to generate a collimated image, that is, in the collimated image, the light of each image primitive is a parallel beam of light having an angular direction corresponding to the position of the primitive, extending to infinity. Therefore, the image illumination spans an angular range corresponding to a two-dimensional angular field of view.

[0023] Image projector 14 includes at least one light source typically deployed to illuminate a spatial light modulator, such as an LCOS wafer. The spatial light modulator modulates the projection intensity of each pixel of the image, thereby generating an image. Alternatively, the image projector may include a scanning arrangement typically implemented using fast scanning mirrors that scans the illumination from the laser light source across the image plane of the projector, while the intensity of the beam changes synchronously with the movement of each pixel, thereby projecting a desired intensity for each pixel. In both cases, collimating optics are configured to generate an output projected image collimated to infinity. Some or all of the above components are typically arranged on the surface of one or more polarizing beam splitter (PBS) cubes or other prism arrangements known in the art.

[0024] The optical coupling between the image projector 14 and the LOE 12 can be achieved by any suitable optical coupling, for example, via a coupling prism having an angled input surface, or via a reflective coupling device, via a side edge and / or one of the main outer surfaces of the LOE. Details of the coupling configuration are not important to the present invention and are shown herein as a non-limiting example, schematically as a wedge-shaped prism 15 applied to one of the main outer surfaces of the LOE.

[0025] It will be appreciated that the near-eye display 10 includes various additional components, typically including a controller 22 for actuating the image projector 14, which typically draws power from a small onboard battery (not shown) or some other suitable power source. It will be appreciated that the controller 22 includes all the necessary electronic components for driving the image projector, such as at least one processor or processing circuitry, all of which are as known in the art.

[0026] Turning now to Figures 2A and 2B, the optical characteristics of the near-eye display implementation are shown in more detail. Specifically, a more detailed view of a light-guide optical element (LOE) 12 formed of a transparent material is shown. LOE 12 includes: a first region 16, also referred to herein as "LOE1", which contains a first set of mutually parallel, flat, partially reflective surfaces 17 having a first orientation; and a second region 18, also referred to herein as "LOE2", which contains a second set of mutually parallel, flat, partially reflective surfaces 19 having a second orientation that is not parallel to the first orientation. A set of mutually parallel main outer surfaces 24 extends across the first region 16 and the second region 18, such that both the first set of partially reflective surfaces 17 and the second set of partially reflective surfaces 19 are located between the main outer surfaces 24. Most preferably, the set of main outer surfaces 24 is a pair of surfaces that are integrally continuous across the first region 16 and the second region 18, but options for decreasing or increasing the thickness between the first region 16 and the second region 18 also fall within the scope of the invention. The first region 16 and the second region 18 can be placed close together such that they contact each other at their boundary, which can be a straight boundary or some other form of boundary. Alternatively, depending on the specific application, one or more additional LOE regions may be present between the first region 16 and the second region 18 to provide various additional optical or mechanical functions. While the invention is not limited to any particular manufacturing technique, in some particularly preferred implementations, a particularly high-quality main outer surface is achieved by employing continuous outer plates, with the separately formed first region 16 and second region 18 sandwiched between these continuous outer plates to form a composite LOE structure. Considerations regarding this option and the thickness of these plates will be discussed further below.

[0027] The optical characteristics of the LOE can be understood by tracing the image illumination path in reverse. The second set of partially reflective surfaces 19 are angled to the main outer surface 24, such that a portion of the image illumination propagating from the first region 16 to the second region 18 within the LOE 12 via internal reflection at the main outer surface is coupled out of the LOE toward the eye-tracking box 26. The first set of partially reflective surfaces 17 is oriented such that a portion of the image illumination propagating from the coupling region (coupled prism 15) within the LOE 12 via internal reflection at the main outer surface is deflected toward the second region 18.

[0028] In Figure 2A, the angular spread of the projected image from the image projector 14 in one dimension is represented by an illumination cone extending from the POD aperture on the right side of the LOE toward the left side of the LOE. In the non-limiting example shown here, the central optical axis of the POD defines the propagation direction aligned with the X-axis within the LOE, and the angular spread (within the LOE) is approximately ±16°. (It should be noted that the angular FOV increases in air due to the change in refractive index.) A first set of partially reflective surfaces 17 is shown in the first region 16, and a second set of partially reflective surfaces 19 is shown in the second region 18.

[0029] The near-eye display is designed to provide the user's eye with a complete field of view of the projected image, located at a position within a permissible range of position specified by the "Eye-motion Box" (EMB) 26 (i.e., typically represented as a rectangular shape, spaced apart from the plane of the LOE from which the pupil will view the projected image). To reach the eye-motion box, light must be coupled from the second region 18 toward the EMB 26 via a second set of partially reflective surfaces 19. To provide a complete field of view, each point in the EMB must receive the entire angular range of the image from the LOE. A larger rectangle 28, indicating the field of view back from the EMB, is associated with illumination coupled from the LOE toward the EMB from rectangle 28.

[0030] Figure 2A shows the first end of the field of view, which corresponds to the lower left primitive of the projected image. A beam of light coupled into the LOE with a width corresponding to the optical aperture of the projector is shown propagating to the left and upward from the POD and being partially reflected from a series of partially reflective surfaces 17. As shown here, only a subset of the facets generates reflections useful for providing the corresponding primitive in the image viewed by the user, and only sub-regions of these facets contribute to the image of the primitive being observed. The relevant areas are shown in thick black lines, and the rays corresponding to the primitive in the redirected image, reflected from facet 17 and then coupled by facet 19 to the four corners of the EMB 26, are shown. Here, and throughout the specification, it will be noted that only the in-plane propagation direction of the light during propagation within the LOE is shown, but the light actually follows a zigzag path of repeated in-plane reflections from the two main outer surfaces, and the entire dimension of the image field of view is encoded by the tilt angle of the light relative to the main outer surfaces corresponding to the primitive position in the Y dimension. As an additional example, the deflection and elliptical rays seen at the top left corner of the EMB, corresponding to the top left end of the image, are illustrated with dashed lines.

[0031] Figure 2B shows the same structure as Figure 2A, but here the rays reaching the four corners of the EMB and corresponding to the lower right primitive of the field of view are shown, where the relevant areas of the relevant part of the reflective surface 17 are also indicated by thick lines.

[0032] It will be apparent that, by further tracing the corresponding ray paths of all fields (directions or primitives) of the image reaching all regions of the EMB, the envelope of all ray paths propagating within the LOE from the coupling region, deflected by one of the first set of partial reflective surfaces, and coupled out by one of the second set of partial reflective surfaces in the direction reaching the eye-tracking box can be plotted, and this envelope defines the “imaging region” of each facet 17, while the remaining portion of the facet 17 outside the envelope is the “non-imaging region,” wherein the “imaging region” is required to deflect the portion of the image illumination that contributes to the image reaching the EMB, and the “non-imaging region” does not contribute to the desired image. Optionally, the in-plane extension of the facet can be truncated to cover only the imaging region. This embodiment and other variant embodiments are discussed in detail in existing publications of Lums Ltd. (Israel), particularly in PCT Publication No. WO 2020 / 049542, PCT Publication No. WO 2020 / 152688, and PCT Application No. PCT / IL2020 / 051354 (both of which were not published before the priority date of this application and are not considered prior art). These other variant embodiments employ different imaging injection locations and geometries, non-uniform small-plane spacing, or the introduction of additional (e.g., a third) sets of partially reflective inner surfaces. These additional features can all be implemented in the context of this invention, but for the sake of brevity, they will not be described in detail here.

[0033] A particularly preferred feature of certain embodiments of the invention is that the first set of partially reflective surfaces 17 extends across at least 95% of the thickness of the LOE, while the second set of partially reflective surfaces 19 in the second region 18 is contained within a sub-portion spanning less than 95% of the thickness, such that the second set of partially reflective surfaces 19 is excluded from at least one surface layer of the second region 18. The advantages of this combination will now be presented.

[0034] In terms of terminology, the term "cover plate" is generally used herein to refer to any implementation of a layer of a certain depth adjacent to one or both of the main surfaces of the LOE, wherein a set of internal partially reflective surfaces of the LOE are excluded from the main surface of the LOE. One way to form such a layer is by attaching a sheet of transparent material—i.e., a physically distinct cover plate—to the LOE component. However, other manufacturing techniques are also possible, for example, by stacking plates in which a partially reflective coating is applied only to the area corresponding to the effective LOE layer, and by bonding the area adjacent to the main outer surface of the LOE with a refractive index-matching adhesive without a reflective coating. The term "cover plate" is used independently of the manufacturing technique to refer to a functional structure in which a surface layer without facets acts as a cover plate, regardless of how the layer is formed.

[0035] Referring to Figure 3, which shows the path of a single ray 30 (here, the principal ray corresponding to the center of the field of view of the image in the X dimension), as the ray traverses a portion of LOE1, the ray is redirected toward LOE2 by reflection at one of the first set of partially reflective surfaces 17 (ray 30'), and redirected and coupled out toward the viewer by reflection at one of the second set of partially reflective surfaces 19 (ray 30''). Figures 4A and 4B show the geometry of the second redirection / coupling with and without a panel on the LOE, while Figures 5A and 5B show the geometry of the first redirection.

[0036] In LOE2 (region 18) from which the image is coupled toward the viewer, a tilted plane is used. When the plane is tilted (e.g., at 25 degrees to the main outer surface), light can be reflected twice from the same plane, as shown in Figure 4A. This results in a non-uniform beam leaving the waveguide. A darker area is generated by the second reflection. Dark fringes then appear on the wavelet exit pupil. For the viewer, this will result in dark fringes on the far-field image.

[0037] Figure 4B illustrates how the double reflection can be avoided by adding a cover plate 32 to one or both outer surfaces of the waveguide, thereby effectively separating the facet from the outer surfaces of the waveguide. In this way, after being reflected once by the facet, the transmitted portion of the light will skip over or be below the facet and propagate directly to the next facet, resulting in enhanced image uniformity.

[0038] However, it has been found that the considerations for achieving image uniformity in LOE1 are significantly different from those in LOE2 regarding the use of the cover plate. Since the partially reflective surface used to redirect image illumination from one direction guided within the waveguide to another must be much steeper, and in some embodiments orthogonal to the main outer surface of the waveguide, light is not reflected twice by a single facet. In this case, optimal image uniformity is achieved by using a facet spanning the entire thickness of the substrate (Fig. 5A); however, it has been found that facets not reaching the surface allow some light to completely skip the facet (Fig. 5B), resulting in dark lines in the output image. Fig. 6A schematically illustrates the overall result of setting the cover plate on both the first region 16 and the second region 18 as a whole, in which the input aperture 34 of uniform illumination from the image projector propagates through the LOE and is coupled outwards towards the eye-tracking box (EMB) 26 as an image region 36 interrupted by dark lines 38 in the output. In contrast, the structure of Figure 6B uses a cover plate only on LOE2 18, while the small plane of the first region 16 of LOE1 extends to the main outer surface of the device. In this case, the input aperture 34, which provides uniform illumination from the image projector, preferably produces a relatively uniform image 36 perceived by the viewer.

[0039] Although the presence of a cover plate in the first region 16 of LOE1 adversely affects the output image quality, there may be practical considerations that favor the use of a cover plate on one or both main surfaces of the first region 16 of LOE1. For example, the absence of any glued joints extending to the outer surface makes it easier to achieve a high-quality, flat outer surface for the waveguide. The presence of a cover plate is acceptable if it is thin enough that any resulting image interruption does not interfere with the human eye (Fig. 6C). A thin cover plate will generate fine dark stripes at which the output image is missing. The spatial frequency and width of the dark stripes determine their visibility and impact on the image perceived by the human eye. To properly assess the severity of unfilled stripes for the human eye, the convolution of the human pupil on the wavelet exit pupil shows what cover plate thickness should be allowed. If the spatial frequency of the dark stripes is significantly higher than the diameter of the pupil, the variation will be inherently averaged by the eye. If the spatial frequency is low, the stripes are still acceptable if the stripes are narrow enough that the intensity averaged across the pupil size does not vary significantly.

[0040] In practice, the thickness of the cover plate (if present) used for the LOE1 region should range from 1 to 100 micrometers, most preferably less than 50 micrometers. As a proportion of the thickness of the LOE, the total thickness of the cover plate is preferably less than 5% of the thickness, preferably no more than 4% of the thickness, and most preferably no more than 2% of the thickness. This corresponds to the first set of partially reflective surfaces extending across at least 95% of the thickness, more preferably at least 96% of the thickness, and most preferably at least 98% of the thickness. The dark stripe problem can be improved by using a cover plate on only one side of the first region 16 of LOE1, as schematically shown in FIG6D.

[0041] Despite the possible advantages of using a cover plate, in some particularly preferred implementations of the invention, the first set of partially reflective surfaces 17 extends across the entire thickness of the first region 16 of LOE1, i.e., without a cover plate, as schematically shown in FIG6B.

[0042] Regarding LOE2 in the second region 18, as described above, the cover plate in this region helps reduce the non-uniformity of illumination, thereby improving the quality of the viewed image. Preferably, the second set of partially reflective surfaces 19 are excluded from the surface layers of the two main outer surfaces in the second region, meaning that both main surfaces have a "cover plate". The total thickness of the surface layer of the second region 18, excluding the second set of partially reflective surfaces 19, is preferably between 6% and 33% of the total thickness of LOE2.

[0043] Similarly, the degree of nonuniformity of illumination perceived by the human eye depends on the spatial frequency of the intensity variation, its dynamic range, and its width, which in turn determines the preferred thickness of the cover plate that will be effective in mitigating these variations. In the case of the coupled facet 19, the spatial frequency is directly obtained from the spacing between adjacent surfaces of the second set of partially reflective surfaces 19 in a direction parallel to the main outer surface. Figure 7 shows the preferred minimum cover plate thickness (the percentage of the total cover plate thickness to the total thickness of LOE2) for various facet densities, where facet density is defined here as the number of facets overlapping with the pupil diameter, which is here taken as approximately 3 mm. It can be seen that for high facet densities, a relatively thin cover plate is sufficient because the intensity variations are inherently averaged over the pupil region and are therefore less perceived by the viewer. As the facet spacing increases, the spatial frequency of the intensity variation decreases, and a thicker cover plate is required to compensate for these variations.

[0044] As a useful reference point, as shown by the horizontal dashed line in FIG7, when the spacing between adjacent surfaces of the second set of partial reflective surfaces 19 in a direction parallel to the main outer surface is at least 1 mm (corresponding to a density of 3 small planes per 3 mm pupil diameter), the total thickness of the surface layer excluding the second region of the second set of partial reflective surfaces is preferably at least 10% of the total thickness.

[0045] As will be apparent to those skilled in the art, the optical system according to the invention can be produced by various processes based on standard manufacturing techniques employed in the art. Each LOE region is typically formed by bonding together a stack of thin plates coated on one or both sides (typically all plates are coated on one side, or alternatively, plates are coated on both sides) to provide desired partial reflective properties at each interface. The partial reflective properties are typically provided by a multilayer dielectric coating, which, as is known in the art, can provide angle-selective reflectivity. These stacks are then sliced ​​at the desired angle to produce LOE portions / regions with correctly oriented internal partial reflective surfaces. Then, if necessary, a cover plate of appropriate thickness is added to each region, and the edge surfaces of the LOE portions are polished and then bonded together to form the final composite LOE.

[0046] Optionally, when a cover plate is to be placed on one or both main surfaces of LOE1, it may be advantageous to produce LOE2 with a cover plate having a local thickness corresponding to the desired final cover plate thickness minus the required cover plate thickness of LOE1. A single continuous cover plate can then be added during the assembly of the composite LOE, providing the total desired cover plate thickness of LOE1 and supplementing the cover plate thickness of LOE2 to achieve the desired thickness. This option is further illustrated below with reference to Figures 9A and 9B.

[0047] Alternatively, in some cases, it may be desirable to produce a stepped cover plate having a first portion with a first thickness suitable for LOE1 and a second portion with a (larger) second thickness suitable for LOE2. The step between the two portions can then be used as an alignment feature for assembling the two LOE portions.

[0048] Figures 8A and 8B schematically illustrate another option for manufacturing the composite LOE of the present invention. In this case, the stack of plates used to form LOE1 is cut to form blocks 80 with dimensions corresponding to multiple LOEs. A second block 82 is formed by combining multiple effective layers 84 of LOE2 (i.e., portions of the LOE containing partial reflective surfaces) that are bonded to an intermediate transparent plate 86. The first block 80 is then bonded to the second block 82 to form an intermediate working product 81, which, as shown in Figures 8A and 8B, can be sliced ​​along a slicing plane 88 and polished to produce multiple composite LOEs, wherein a portion of the thickness of the intermediate transparent plate 86 becomes a cover for the second LOE region 18 of each composite LOE.

[0049] The fabrication techniques of Figures 8A and 8B and their variations are discussed in more detail in a co-pending PCT application entitled “Method of Fabrication of Compound Light-Guide Optical Elements”, filed on the same day as this application, which claims priority to U.S. Provisional Patent Application No. 63 / 029,500, filed on May 24, 2020.

[0050] Similarly, if a cover plate is desired on the first LOE region 16, it may be advantageous to generate a composite LOE structure according to Figures 8A and 8B, wherein the cover plate 32a of the second region 18 is smaller than the desired thickness by an amount equal to the desired thickness of the first region 16, as shown in Figure 9A. Then, by adding a uniform thickness plate 32b bonded to the waveguide across the entire structure, the two cover plates can be made to achieve their desired total thickness, thereby producing the final structure shown in Figure 9B.

[0051] For example, the present invention may also include the following technical solutions: Solution 1. An optical system for guiding an image illumination injected at a coupling region toward a user for viewing, the optical system comprising a light guide optical element (LOE) formed of a transparent material, the LOE comprising: (a) a first region comprising a first set of flat, mutually parallel partially reflective surfaces having a first orientation; (b) a second region comprising a second set of flat, mutually parallel partially reflective surfaces having a second orientation, the second orientation being non-parallel to the first orientation; (c) a set of mutually parallel main outer surfaces extending across the first region and the second region, such that both the first set of partially reflective surfaces and the second set of partially reflective surfaces are located between the main outer surfaces. In this embodiment, the second set of partially reflective surfaces is angled to the main outer surface such that a portion of the image illumination propagating from the first region to the second region within the LOE via internal reflection at the main outer surface is coupled out from the LOE toward the user, and wherein the first set of partially reflective surfaces is oriented such that a portion of the image illumination propagating within the LOE via internal reflection at the main outer surface from the coupled region is deflected toward the second region, wherein the LOE has a thickness between the main outer surfaces, and wherein the first set of partially reflective surfaces extends across at least 95% of the thickness, and the second set of partially reflective surfaces in the second region is contained within a sub-portion of the thickness spanning less than 95% of the thickness, such that the second set of partially reflective surfaces is excluded from at least one surface layer of the second region. Embodiment 2. The optical system according to Embodiment 1, wherein the second set of partially reflective surfaces is excluded from the surface layers of the two main outer surfaces in the second region. Embodiment 3. The optical system according to Embodiment 1, wherein the total thickness of the at least one surface layer of the second region where the second set of partially reflective surfaces is excluded is between 6% and 33% of the thickness. Option 4. The optical system of Option 1, wherein the spacing between adjacent surfaces of the second set of partial reflective surfaces in a direction parallel to the main outer surface is at least 1 mm, and wherein the total thickness of the at least one surface layer excluding the second region of the second set of partial reflective surfaces is at least 10% of the thickness. Option 5. The optical system of Option 1, wherein the first set of partial reflective surfaces extends across at least 96% of the thickness. Option 6. The optical system of Option 1, wherein the first set of partial reflective surfaces extends across at least 98% of the thickness. Option 7. The optical system of Option 1, wherein the first set of partial reflective surfaces extends across the entire thickness. Option 8. The optical system of Option 1, wherein the first orientation of the first set of partial reflective surfaces is orthogonal to the main outer surface.

[0052] It should be recognized that the above description is intended to be used as an example only, and many other embodiments are possible within the scope of the invention as defined by the appended claims. [Simplified Explanation of the Diagram]

[0013] The invention is described herein by way of example only with reference to the accompanying drawings, in which: Figures 1A and 1B are schematic isometric views of an optical system implemented using a light-guiding optical element (LOE) constructed and operated according to the teachings of the invention, showing a top-down configuration and a side-injection configuration, respectively; Figures 2A and 2B are enlarged schematic isometric views of the LOE from Figure 1A or 1B, showing the ray paths of the two end fields of the image; Figure 3 is a schematic front view of the LOE of Figures 2A and 2B, showing the path of the main ray propagating through the LOE and undergoing a first redirection and a second redirection for coupling out from the LOE toward the viewer; Figures 4A and 4B are partial schematic cross-sectional views taken along line IV-IV in Figure 3, showing the ray paths of light propagating in a second region of the LOE and encountering internal partial reflective surfaces that cross or do not cross the thickness of the LOE; Figures 5A, 5B, and 5C are partial schematic cross-sectional views taken along line VV in Figure 3, showing the ray paths of light rays propagating in the first region of the LOE and encountering internal partially reflective surfaces that completely cross the thickness of the LOE, are spaced apart from the two main surfaces, or are spaced apart from only one main surface, respectively; Figure 6A is a schematic side view of the LOE of Figures 2A and 2B in an implementation where both the first and second regions of the LOE have surface layers from which the partially reflective inner surfaces are excluded, i.e., cover plates; Figure 6B is a view similar to Figure 6A in an implementation where only the second region of the LOE has a cover plate; Figure 6C is a view similar to Figure 6A where the second region of the LOE has a cover plate, and the first region of the LOE has a cover plate that is thinner than the cover plate of the second region; Figure 6D is a view similar to Figure 6C where only one side of the first region of the LOE has a cover plate; Figure 7 is a schematic graph showing the relationship between the spatial density of the partially reflective surfaces of the LOE and the preferred minimum thickness of the cover plate of the second region of the LOE. Figures 8A and 8B are respectively a side view and an isometric view of an intermediate work product during the manufacturing process of an LOE according to certain embodiments of the present invention; Figure 9A is a schematic side view showing a stage of the production process in which a thin cover is applied across the entire LOE, wherein a first region is initially formed without a cover, and a second region is formed with a cover having only a portion of the desired cover thickness; and Figure 9B is a schematic side view showing the structure obtained from the production process of Figure 9A.

Claims

1. An optical system for guiding an image illumination injected at a coupling region toward a user for viewing, the optical system comprising a light guide optical element (LOE) formed of a transparent material, the LOE comprising: a. A first region comprising a first set of flat, mutually parallel partial reflective surfaces having a first orientation; b. A second region comprising a second set of flat, mutually parallel partial reflective surfaces having a second orientation that is not parallel to the first orientation; c. A pair of parallel, flat primary outer surfaces extending across a first region and a second region, such that both a first set of partially reflective surfaces and a second set of partially reflective surfaces are located between the flat primary outer surfaces, wherein the first orientation of the first set of partially reflective surfaces is orthogonal to the flat primary outer surfaces, wherein the second set of partially reflective surfaces is at an angle to the flat primary outer surfaces, such that a portion of image illumination propagating from the first region to the second region within the LOE via internal reflections at the flat primary outer surfaces is coupled out from the LOE toward the user, and wherein the first set of partially reflective surfaces is oriented such that a portion of image illumination propagating within the LOE via internal reflections at the flat primary outer surfaces from the coupled region is deflected toward the second region, wherein the LOE has a thickness between the flat primary outer surfaces, and wherein the first set of partially reflective surfaces extends across at least 95% of the thickness, and the second set of partially reflective surfaces in the second region is contained within a sub-portion of the thickness spanning less than 95% of the thickness, such that the second set of partially reflective surfaces is excluded from at least one surface layer of the second region. Specifically, the second set of partially reflective surfaces is excluded from the surface layer of the two flat main outer surfaces in the second region.

2. The optical system as claimed in claim 1, wherein, The total thickness of the at least one surface layer excluding the second region of the second set of partially reflective surfaces is between 6% and 33% of the thickness.

3. The optical system as claimed in claim 1, wherein, The spacing between adjacent surfaces of the second set of partial reflective surfaces in a direction parallel to the flat main outer surface is at least 1 mm, and wherein the total thickness of the at least one surface layer excluding the second region of the second set of partial reflective surfaces is at least 10% of the thickness.

4. The optical system as claimed in claim 1, wherein, The first set of partially reflective surfaces extends across at least 96% of the thickness.

5. The optical system as claimed in claim 1, wherein, The first set of partially reflective surfaces extends across at least 98% of the thickness.

6. The optical system as claimed in claim 1, wherein, The first set of partially reflective surfaces extends across the entire thickness.

7. The optical system as claimed in claim 1, wherein, The first set of partially reflective surfaces are at an angle relative to the main outer surface.

8. An optical system for guiding an image illumination injected at a coupling region toward a user for viewing, the optical system comprising a light guide optical element (LOE) formed of a transparent material, the LOE comprising: a. A first region comprising a first set of flat, mutually parallel partially reflective surfaces having a first orientation, the first set of partially reflective surfaces being sandwiched between transparent cover plates of a first thickness; and b. a second region comprising a second set of flat, mutually parallel partially reflective surfaces having a second orientation that is not parallel to the first orientation, the second set of partially reflective surfaces being sandwiched between transparent cover plates of a second thickness greater than the first thickness, wherein the first set of cover plates and the second set of cover plates are portions of a pair of flat, mutually parallel main outer surfaces that extend continuously across the first region and the second region, and wherein the first set of partially reflective surfaces is oriented such that a portion of image illumination propagating within the LOE via internal reflections at the flat main outer surfaces from the coupling region is deflected toward the second region, and wherein the second set of partially reflective surfaces is at an angle to the flat main outer surfaces such that a portion of image illumination propagating within the LOE from the first region to the second region via internal reflections at the flat main outer surfaces is coupled out of the LOE toward the user.

9. The optical system as claimed in claim 8, wherein, The mutually parallel, flat main outer surfaces are provided by a continuous cover plate of the first thickness, the continuous cover plate extending continuously across the first region and the second region, wherein the second region further includes a lower cover plate having a thickness corresponding to the difference between the second thickness and the first thickness, the lower cover plate together with the continuous cover plate constituting the second thickness.

10. A method for manufacturing an optical system including a light-guide optical element (LOE), the method comprising the steps of: a) generating a first region of a first thickness containing a first set of flat, mutually parallel partially reflective surfaces having a first orientation, the first set of partially reflective surfaces extending across the entire first thickness; b) Generate a second region with a second thickness smaller than the first thickness, the second region containing a second set of flat, mutually parallel partially reflective surfaces with a second orientation that is not parallel to the first orientation, the second set of partially reflective surfaces extending across the entire second thickness; c) Applying a first pair of cover plates to the interior of the second region to form an element within the second region, the first pair of cover plates together having a combined thickness equal to the first thickness; and d) sandwiching the interior of the first region and the element within the second region together between a second set of cover plates, the second set of cover plates extending continuously across both the interior of the first region and the element within the second region to form the LOE.

11. The method as described in claim 10, wherein, The second set of partially reflective surfaces is at an angle relative to the main outer surface provided by the second set of cover plates.

12. The method as described in claim 11, wherein, The first set of partially reflective surfaces are at an angle relative to the main outer surface.

13. The method as described in claim 11, wherein, The first set of partially reflective surfaces is orthogonal to the main outer surface.

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