Optical system for two-dimensional image magnification that reduces glint and ghosting from waveguides.

Abstract

To direct image illumination introduced into the combined input area to the eye-motion box that the user will view. [Solution] The optical system employs a waveguide, which includes a first set of partial reflective surfaces ("facets") for continuously deflecting image illumination propagating from a coupled input region toward a second region, and a second set of facets in the second region for continuously coupled outputting the deflected image illumination toward the observer's eye. The first set of facets includes at least a first facet adjacent to the coupled input region, a third facet from the coupled input region, and a second facet located in an intermediate plane between the first and third facets. The second facet is located in a sub-region of the intermediate plane such that image illumination propagating from the coupled input region toward the third facet passes through the intermediate plane but not through the second facet.

Description

Technical Field

[0001] Field and Background of the Invention The present invention relates to an optical system, and more particularly to an optical system for two-dimensional magnification of an image to be displayed to a user from an image projector.

[0002] FIG. 1A shows a near-eye display optical engine including an image projector 200 that projects image light having an angular field through a transmissive coupling prism 202T and through a vertical aperture 203V into a waveguide 204. Light propagates in the waveguide while undergoing total internal reflection. A partially reflective plate 206 embedded in the waveguide reflects an image from the waveguide (dashed arrow) toward an observer having a center of the eyeball 208.

[0003] FIG. 1B shows another method of coupling into a waveguide by using a reflective coupling prism 202R having a mirror on its back surface.

[0004] FIG. 1C schematically shows a front view of a 2D aperture-expanding waveguide. Here, the image projector 200 introduces an image into the waveguide 204 through a coupling prism 202 and through a horizontal aperture 203L (203V also exists but is not visible from this orientation). Image rays 220A propagate horizontally in the waveguide while being reflected by total internal reflection (TIR) between waveguide surfaces. Here, two sets of facets are used. The set 206L expands the aperture horizontally by continuously reflecting the induced image in different induced directions 220B, while the facets 206V expand the aperture vertically by continuously coupling the image from an area 210 on the waveguide to the observer's eye.

Summary of the Invention

[0005] The present invention is an optical system for guiding image illumination introduced into a coupling input region to an eye motion box for a user to view.

[0006] According to the teaching of one embodiment of the present invention, an optical system is provided for guiding image illumination introduced into a coupled input region to an eye motion box for viewing by the user's eye. The optical system comprises a light guide optical element (LOE) formed from a transparent material. The LOE comprises (a) a first region having a first orientation, being planar, and including a first pair of mutually parallel partial reflective surfaces; (b) a second region having a second orientation nonparallel to the first orientation, being planar, and including a second pair of mutually parallel partial reflective surfaces; and (c) a pair of mutually parallel main outer surfaces, the main outer surfaces extending across the first and second regions such that both the first pair of partial reflective surfaces and the second pair of partial reflective surfaces are located between the main outer surfaces. The second set of partial reflective surfaces is oblique to the main outer surface, and the first set of partial reflective surfaces is oriented such that a portion of the image illumination propagating within the LOE by internal reflection from the main outer surface from the first region into the second region is coupled toward the eye-motion box, and a portion of the image illumination propagating within the LOE by internal reflection from the main outer surface of the coupled input region is deflected toward the second region. The first set of partial reflective surfaces includes a first partial reflective surface located proximal to the coupled input region so as to contribute to a first portion of the user's field of view when viewed with the eye-motion box, a third partial reflective surface located distal to the coupled input region so as to contribute to a third portion of the user's field of view when viewed with the eye-motion box, and a second partial reflective surface placed on an intermediate surface between the first and third partial reflective surfaces so as to contribute to a second portion of the user's field of view when viewed with the eye-motion box. The second partial reflective surface is positioned in a sub-region of the intermediate surface such that image illumination propagating from the combined input region to the third partial reflective surface and contributing to the third portion of the user's field of view when viewed through the eye motion box passes through the intermediate surface without passing through the second partial reflective surface.

[0007] According to further features of one embodiment of the present invention, the coupled input region comprises a coupled input prism having a first plane continuous with one of the main outer surfaces within the first region. The coupled input prism has a thickness dimension measured perpendicular to the main outer surface, which is greater than the thickness of the LOE.

[0008] According to further features of one embodiment of the present invention, the coupled input prism presents a coupled input surface and a transition line between the coupled input prisms as the LOE. The coupled input surface defines the optical aperture of the coupled input prism in a dimension parallel to the main outer surface, and the transition line defines the optical aperture of the coupled input prism in a dimension perpendicular to the main outer surface.

[0009] According to further features of one embodiment of the present invention, the first set of partial reflectors further comprises at least one partial reflector located within the volume of the coupled input prism.

[0010] According to the teaching of one embodiment of the present invention, an optical system is also provided for guiding image illumination introduced into a coupled input area to an eye motion box for viewing by the user's eye. The optical system comprises a light guide optical element (LOE) formed from a transparent material. The LOE comprises (a) a first region having a first orientation, being planar, and including a first pair of mutually parallel partial reflective surfaces; (b) a second region having a second orientation nonparallel to the first orientation, being planar, and including a second pair of mutually parallel partial reflective surfaces; and (c) a pair of mutually parallel main outer surfaces, the main outer surfaces extending across the first and second regions such that both the first pair of partial reflective surfaces and the second pair of partial reflective surfaces are located between the main outer surfaces. The second set of partial reflective surfaces is oblique to the main outer surface, and the first set of partial reflective surfaces is oriented such that a portion of the image illumination propagating within the LOE by internal reflection from the main outer surface from the first region into the second region is coupled toward the eye motion box, and a portion of the image illumination propagating within the LOE by internal reflection from the main outer surface of the coupled input region is deflected toward the second region. The coupled input region comprises a coupled input prism having a first plane continuous with one of the main outer surfaces within the first region. The coupled input prism has a thickness dimension measured perpendicular to the main outer surface, which is greater than the thickness of the LOE. The coupled input prism presents a coupled input surface and transition line between the coupled input prisms as the LOE. The coupled input surface defines the optical aperture of the coupled input prism in a dimension parallel to the main outer surface, and the transition line defines the optical aperture of the coupled input prism in a dimension perpendicular to the main outer surface.

[0011] According to further features of one embodiment of the present invention, the first set of partial reflectors further comprises at least one partial reflector located within the volume of the coupled input prism.

[0012] According to the teaching of embodiments of the present invention, an optical system is also provided for guiding image illumination introduced into a coupled input region to an eye motion box for viewing by the user's eye. The optical system comprises a light guide optical element (LOE) formed from a transparent material. The LOE comprises (a) a first region having a first orientation and including a first pair of planar, mutually parallel partial reflective surfaces; (b) a second region having a second orientation non-parallel to the first orientation and including a second pair of planar, mutually parallel partial reflective surfaces; and (c) a pair of mutually parallel main outer surfaces, the main outer surfaces extending across the first and second regions such that both the first pair of partial reflective surfaces and the second pair of partial reflective surfaces are located between the main outer surfaces. The second set of partial reflective surfaces is oblique to the main outer surface so that a portion of the image illumination propagating within the LOE by internal reflection from the first region to the second region is coupled toward the eye motion box, and the first set of partial reflective surfaces is oriented so that a portion of the image illumination propagating within the LOE by internal reflection from the main outer surface of the coupled input region is deflected toward the second region. The coupled input region comprises a coupled input prism having a first plane continuous with one of the main outer surfaces within the first region, the coupled input prism having a thickness dimension measured perpendicular to the main outer surface, which is greater than the thickness of the LOE. The first set of partial reflective surfaces further comprises at least one partial reflective surface located within the volume of the coupled input prism.

[0013] According to further features of one embodiment of the present invention, the coupled input prism presents a coupled input surface and a transition line between the coupled input prisms as the LOE. The coupled input surface defines the optical aperture of the coupled input prism in a dimension parallel to the main outer surface, and the transition line defines the optical aperture of the coupled input prism in a dimension perpendicular to the main outer surface.

[0014] According to further features of one embodiment of the present invention, the coupled input prism is bonded to the LOE at an edge surface. Alternatively, the coupled input prism is bonded to one of the main outer surfaces of the LOE. [Brief explanation of the drawing]

[0015] The invention is described herein only as an embodiment with reference to the accompanying drawings.

[0016] [Figure 1A] The schematic side view of a conventional near-eye waveguide display shows two geometric shapes for coupled input of image illumination into the waveguide (as described above). [Figure 1B] The schematic side view of a conventional near-eye waveguide display shows two geometric shapes for coupled input of image illumination into the waveguide (as described above). [Figure 1C] This is a front view of a conventional near-eye waveguide display (as described above), showing how the optical aperture of an image projector is expanded in two dimensions using a first and second set of partially reflective inner surfaces. [Figure 1D] This is a schematic isometric view of a waveguide similar to the waveguide in Figure 1C and corresponding to Figure 5A in Publication WO2020 / 049542A1. [Figure 2A] These are isometric, top, and side views, respectively, of the angular representation of image propagation through an optical system according to the teachings of the present invention. [Figure 2B] These are isometric, top, and side views, respectively, of the angular representation of image propagation through an optical system according to the teachings of the present invention. [Figure 2C] These are isometric, top, and side views, respectively, of the angular representation of image propagation through an optical system according to the teachings of the present invention. [Figure 3A] This is a schematic front view of a photoguide optical element (LOE or waveguide) constructed and operable according to the teachings of one aspect of the present invention, showing the propagation of image illumination from a coupled input region to a first set of partial reflective surfaces (facets) and from the first set of facets to a second set of facets. [Figure 3B]A figure similar to FIG. 3A showing the theoretical locus of facet positions necessary to provide a field of view (FOV) at a single viewpoint. [Figure 3C] A figure similar to FIG. 3B showing the locus of the corresponding set of facet positions for providing a FOV across the "eye motion box" (EMB) of the allowable viewing positions. [Figure 3D] A figure similar to FIG. 3A showing the facet positions and dimensions necessary to draw the locus shown in FIG. 3C. [Figure 3E] A figure similar to FIG. 3C, in which the locus is further increased according to the geometric requirements resulting from using a first set of facets angled obliquely. [Figure 3F] A schematic representation of the LOE of FIG. 3D, in which the facet-containing region is delimited by a corresponding polygon and the first set of facets is delimited by a concave polygon. [Figure 3G] A figure similar to FIG. 3F, in which the concave polygon containing the first set of facets is subdivided into a number of non-concave blocks or slices. [Figure 3H] A schematic isometric view showing how such blocks can be assembled to generate the structure of FIG. 3G in order to form a plurality of LOEs by slicing continuously. [Figure 4A] A figure similar to FIG. 3A showing exemplary dimensions of an implementation for generating a rectangular field of view having the angular dimensions as shown in FIG. 4B. [Figure 4B] A figure similar to FIG. 3A showing exemplary dimensions of an implementation for generating a rectangular field of view having the angular dimensions as shown in FIG. 4B. [Figure 4C] A figure similar to FIG. 3A showing exemplary dimensions of an implementation for generating a trapezoidal field of view having the angular dimensions as shown in FIG. 4D. [Figure 4D] A figure similar to FIG. 3A showing exemplary dimensions of an implementation for generating a trapezoidal field of view having the angular dimensions as shown in FIG. 4D. [Figure 5A]A view similar to FIG. 4A showing an image projector and a combined input prism for introducing image illumination into the LOE. [Figure 5B] A schematic isometric view of the combined input prism of FIG. 5A. [Figure 5C] A side view of the combined input prism of FIG. 5A showing the dimensions required for an exemplary implementation of the present invention. [Figure 5D] A modified example of an implementation of the present invention employing a combined input prism attached to the main outer surface of the LOE is shown. [Figure 6A] A schematic front view similar to FIG. 5A showing the use of an integrated laser scanning image projector integrated with a combined input prism. [Figure 6B] A schematic side view of an integrated laser scanning image projector integrated with the combined input prism of FIG. 6A. [Figure 7A] A schematic side view of a combined input arrangement employing an inclined reflector coupling arrangement and a combined input prism and also employing an external collimating optical element. [Figure 7B] A view similar to FIG. 7A in which an inclined reflector coupling arrangement and a combined input prism are combined and the size is reduced. [Figure 7C] A view similar to FIG. 7A employing a polarization beam splitter and integrating a reflective collimating optical element into the reflective combined input arrangement. [Figure 7D] A view similar to FIG. 7C but using an external collimating optical element. [Figure 8A] A view similar to FIG. 5A but in which the combined input prism is integrated with a part of the waveguide. [Figure 8B] A schematic isometric view of the combined input prism of FIG. 8A. [Figure 9A] A schematic side view of the combined input prism of FIG. 8A implemented as a combined input prism joined to the LOE at the edge surface of the LOE. [Figure 9B] A schematic isometric view of the combined input prism of FIG. 9A respectively showing the inclusion of full or partial reflection facets within the prism. [Figure 9C]Figure 9A is a schematic isometric view of the coupled input prism, showing the inclusion of full or partial reflection facets within the prism. [Figure 9D] This is a schematic side view of the coupled input prism shown in Figure 8A, which is implemented as a coupled input prism joined to one of the main outer surfaces of the LOE. [Figure 9E] Figure 9D is a schematic isometric view of the coupled input prism, showing the inclusion of full or partial reflection facets within the prism, respectively. [Figure 9F] Figure 9D is a schematic isometric view of the coupled input prism, showing the inclusion of full or partial reflection facets within the prism, respectively. [Figure 10A] This is a side view with an angled display similar to Figure 2C, showing two specific points within the field of view of the projected image. [Figure 10B] This is a sub-diagram similar to Figure 4A, showing the image light propagation paths corresponding to the two points in Figure 10A. [Figure 10C] This is a side view of the coupled input prism, showing the entry angles of these two field points and the corresponding desired positions of the first reflective facet where they should meet. [Figure 10D] This is a side view of the coupled input prism, showing the entry angles of these two field points and the corresponding desired positions of the first reflective facet where they should meet. [Figure 11A] These figures, similar to Figures 7A, 7C, and 7D, illustrate implementations of these geometric shapes having partial reflection facets within a coupled prism. [Figure 11B] These figures, similar to Figures 7A, 7C, and 7D, illustrate implementations of these geometric shapes having partial reflection facets within a coupled prism. [Figure 11C] These figures, similar to Figures 7A, 7C, and 7D, illustrate implementations of these geometric shapes having partial reflection facets within a coupled prism. [Figure 11D] This figure, similar to Figure 6B, shows an implementation of this geometric shape having a partial reflection facet within a coupled prism. [Figure 12]Figure 12A is a schematic isometric view of a series of plates having selectively arranged partial reflective coatings for assembly according to the manufacturing method of the present invention, where each coating follows the required pattern on different planes of the LOE in Figure 3D. Figure 12B is a schematic isometric view of a stack of hierarchical plates formed by joining the series of plates of Figure 12A together. Figure 12C is a schematic isometric view of a block formed by slicing the stack of Figure 12B along the indicated dashed lines. Figure 12D is a schematic isometric view of a portion of the LOE formed by slicing the block of Figure 12C along the indicated dashed lines. [Figure 13] This is a schematic side view of a coupling input configuration employing air gaps and mirror surfaces. [Figure 14A] These figures, similar to Figures 2A and 2C, show image propagation through the optical system in the case of a first set of obliquely oriented partial reflectors. [Figure 14B] These figures, similar to Figures 2A and 2C, show image propagation through the optical system in the case of a first set of obliquely oriented partial reflectors. [Figure 14C] This figure is similar to Figure 3F, for an optimized implementation of LOE for image propagation as described in Figures 14A and 14B. [Figure 15] This is a schematic side view of a side-coupled input configuration employing a beam splitter to fill the waveguide with the introduced image and its conjugate. [Figure 16A] This is a side view showing the angle of image propagation through a second region of the LOE according to a modified embodiment of the present invention, employing a second set of highly inclined partial reflective surfaces. [Figure 16B] This is a schematic side view of the second region of the LOE implemented according to the optical geometric shape of Figure 16A. [Figure 16C] This graph schematically shows the preferred angular dependence of the facet reflectivity for the implementation configuration of Figure 16B. [Figure 17A] This is a schematic isometric view of a plate with selectively deployed partial reflective coating, similar to the plate in Figure 12A. [Figure 17B] This is an enlarged schematic side view showing a coated area with a sharp edge. [Figure 17C] This is a schematic diagram showing how to generate a coating with a limit region where the thickness varies in steps, using a raised mask. [Figure 17D] This is a schematic diagram illustrating the deposition of a multilayer coating with a limiting region where the thickness varies in steps, using the principle shown in Figure 17C. [Figure 17E] This is a schematic diagram showing how a second raised mask is used to generate a complementary clear coating in areas not coated by the first process. [Figure 17F] This is a schematic side view showing the partial reflection region resulting from the coating process sequence described with reference to Figures 17D and 17E. [Modes for carrying out the invention]

[0017] The present invention is an optical system for guiding image illumination introduced into a coupled input region to an eye-motion box for user viewing.

[0018] As a preface, in the context of the type of near-eye display shown in Figure 1C, particularly advantageous geometric characteristics, specifically the minimization of the dimensions required for a given field of view at a given angle, can be provided by introducing image illumination into the waveguide at a “shallow angle.” This means that all of the image illumination is incident on only one side of both the first and second sets of facets. Typically, in shallow-angle configurations, at least a portion of each image is within about 15 degrees, more preferably about 10 degrees, from the plane of the outer surface of the waveguide. This shortens the light path from the image projector to the observer’s eye, and therefore also allows for a reduction in the size of the optical components for a given field of view at a given angle. The present invention relates to many embodiments that facilitate shallow-angle configurations of such displays, and presents specific design challenges, particularly with respect to coupled input configurations. However, it should be noted that the various embodiments of the present invention described herein are not limited to shallow-angle configurations and may be applicable to other configurations.

[0019] Figures 2A to 2C show the angular polarity representation of an image propagating through a waveguide according to the present invention. Figure 2A is an isometric view, Figure 2C is a side view, and Figure 2B is a top view (relative to Figure 2A) corresponding to the view from the front of the waveguide.

[0020] The waveguide has a total internal reflection (TIR) ​​boundary circle 228, and the coupled output shows that images within these circles are not TIR'd and escape the waveguide.

[0021] Image 220A1 is coupled within the waveguide and propagates forward and backward to 220A2 by TIR. These images propagate along a very shallow trajectory along the waveguide, where the shallowest part of the image is only 7 degrees from the waveguide plane (shown as angle 221 in Figure 2C). Facet 224 (equivalent to 206L in Figure 1C) in this implementation is perpendicular to the waveguide and therefore directly reflects images 220A1 and 220A2 to 220B1 and 220B2, respectively. Images 220B1 and 220B2 are coupled by TIR as they propagate through the waveguide. In the second part of the LOE, facet 226 (equivalent to 206V in Figure 1C) couples image 220B2 from the waveguide toward the observer into image 220C.

[0022] As one non-limiting example, the figures shown herein relate primarily to an image having an aspect ratio of 4:3 and a diagonal field of view of 70 degrees, introduced within a waveguide with a refractive index of 1.6. The design shown herein produces a complete image (including interpupillary distance, ocular radius, and margin) at the center of the eyeball 35 mm away from the waveguide. Adapting these implementations to different fields of view and aspect ratios can be readily carried out by those skilled in the art based on the description herein.

[0023] One aspect of the present invention relates to the optimal arrangement of partial reflective surfaces (or “facets”) in a first portion of a waveguide responsible for expanding an optical aperture in a first dimension. A prior patent application published as WO2020 / 049542A1 ("Publication '542") proposes selectively arranging facets within an envelope that encompasses the facets necessary to deliver image illumination to an eye-motion box on which an image is displayed.

[0024] An example of the resulting facet development is shown in Figure 5A of the published patent, which is reproduced here as Figure 1D. In the implementation embodiment, the optical system for guiding image illumination introduced into a coupled input area 15 for viewing by the user's eye to an eye motion box 26 employs a light guide optical element (LOE) 12 formed from a transparent material having a first region 16 having a first orientation, being planar, and including a first pair of mutually parallel partial reflective surfaces 17, and a second region 18 having a second orientation having a second orientation nonparallel to the first orientation, and including a second pair of mutually parallel partial reflective surfaces 19. A pair of mutually parallel main outer surfaces 24 extends across the first and second regions such that both the first and second pairs of partial reflective surfaces are located between the main outer surfaces. The second set of partial reflective surfaces 19 is angled with respect to the main outer surface 24 so that a portion of the image illumination propagating within the LOE from the first region to the second region due to internal reflection from the main outer surface is coupled outside the LOE from the combined output region 28 toward the eye motion box 26. The first set of partial reflective surfaces 17 is oriented so that a portion of the image illumination propagating within the LOE from the combined input region is deflected toward the second region due to internal reflection from the main outer surface.

[0025] According to the teachings in Publication 542, a specific portion of the first region 16 of the LOE outside the envelope of useful facets is implemented as an optical continuum (i.e., without partial reflection of the internal surface), thereby reducing unwanted "ghost" reflections. However, as shown in the drawings, within the convex polygonal envelope, the facets are implemented to fill the entire width of the convex polygon. As a result, a portion of the field of view reflected from facets located distal to the coupled input region reaches the facets that deliver a portion of that field of view to the eye motion box after passing through a long series of partially reflected facets.

[0026] According to one aspect of the present invention, the region of facets necessary to deliver a given field of view to the eye motion box is further refined to generate a concave polygon that defines the position of the necessary facets, thereby eliminating some intermediate facets that could unnecessarily attenuate the image illumination that is guided to provide a portion of the field reflected by the facets furthest from the combined input region.

[0027] Therefore, as shown in Figure 3D, the first set of partial reflective surfaces, here labeled 206L, includes a first partial reflective surface 17A located proximal to the coupled input region 240 so as to contribute to a first portion of the user's field of view (FOV) when viewed with the eye-motion box, a third partial reflective surface 17C located distal to the coupled input region so as to contribute to a third portion of the user's FOV when viewed with the eye-motion box, and a second partial reflective surface 17B located on an intermediate surface 22 between the first and third partial reflective surfaces so as to contribute to a second portion of the user's FOV when viewed with the eye-motion box. In the example shown in Figure 3D, facet 17A contributes to the right side of the FOV, facet 17C contributes to the left side of the FOV, and facet 17B contributes to the central region of the FOV. A particular feature of this embodiment of the present invention is that the second partial reflective surface 17B is located within a sub-region of the intermediate surface 22, thereby allowing image illumination propagating from the coupled input region to the third partial reflective surface (arrow 23) and contributing to the third portion of the user's field of view when viewed through the eye motion box to pass through the intermediate surface 22 without passing through the second partial reflective surface 17B.

[0028] In this context, the terms “proximal,” “distal,” and “intermediate” are used herein to indicate the relative position of a point or region of interest (in this case, the combined input region 240), and may refer to a facet that is relatively close (proximal), relatively far (distal), or “centralized” (intermediate) to the combined input region, and should be noted that they do not necessarily indicate the closest, farthest, or central facet according to any particular geometric definition.

[0029] Herein, a conceptual explanation is provided to facilitate a better understanding of the geometric optical element considerations related to preferred design parameters for a given implementation of this embodiment of the present invention. It should be noted that this explanation is for informational purposes only, and the usefulness of the claimed invention does not depend on the accuracy of any aspect of this explanation, and that effective and advantageous implementations of the claimed invention may alternatively be implemented by empirical methods.

[0030] Figure 3A shows front views of several selected beams of projected images with parameters corresponding to the exemplary FOV described above. Solid lines represent the beam of the image introduced horizontally into the waveguide, and dashed lines represent the beam propagating vertically after horizontal aperture expansion and reflection. Note that any example illustrating vertical expansion following horizontal expansion can be changed to horizontal expansion following vertical expansion without essentially changing the structure. This can be illustrated simply by rotating the above figure by 90 degrees.

[0031] All beams are transmitted from the inlet pupil of the coupled input region 240. The beams propagate through the waveguide until they are reflected by a pair of parallel-embedded reflectors (facets) 206L. The facets in this figure are assumed to be perpendicular to the outer surface of the waveguide. Thus, all lines (solid and subsequent dashed lines) represent different horizontal sections of the image field projected to the observer's eye. The vertical field of each section is illuminated by multiple overlapping beams (when viewed from the front) propagating at different angular inclinations (on the page) (such internal reflections are shown in the side view of Figure 1A) and reflected by the TIR (Those internal reflections are shown in the side view of Figure 1A).

[0032] To simplify the geometric analysis, we first assume that only the center 208 of the eyeball needs to be illuminated across the entire horizontal field. This can theoretically be achieved by arranging infinitely small horizontal factions 206L at positions nearly infinitely close to each other along a trajectory represented as 244A in Figure 3B. However, the movement of curve 244A is determined by the requirement to absorb the horizontal movement of the center of the eyeball (e.g., due to variations in interpupillary distance between users). Figure 3C schematically shows the curves for the three horizontal positions of the eyeball 208 as 244A, 244B, and 244C. The width of the facets needs to be widened to cover the required width of the eye motion box.

[0033] Other requirements include the following: ● A finite minimum distance exists between facets (i.e., they cannot approach each other infinitely). ● The size of the opening cannot be made excessively small. ● The facet must project a continuous reflection toward the vertically enlarged facet 206V.

[0034] Figure 3D shows a finite-sized facet 206L suitable for the above conditions. The length of the facets can be varied according to the spacing between the facets, as well as other optical parameters such as the refractive index, the size of the projected field, and the position of the image introduction 240.

[0035] When the horizontal expansion facet 206L is oblique to the main outer surface of the LOE, the image is introduced into the waveguide rotated with respect to the waveguide axis, and the image is rotated to the desired orientation by reflection from facet 206L. Thus, the curve for projection to the center of the eyeball 208 is as shown in Figure 3C, and further considering the required spread of the horizontal eye motion box, it becomes as shown in Figure 3E, showing further augmentation of curves 244A, 244B, and 244C. Thus, this requires a somewhat wider facet than the corresponding implementation embodiment having orthogonal facets for the first augmentation.

[0036] Certain advantages of this embodiment of the present invention can be better understood by referring to Figure 3F. The area of ​​the horizontally expanding facet is denoted by SL, the area of ​​the “recess” above it is SD, and the area of ​​the vertically expanding facet is SV. Due to the concave polygon of SL, light propagating horizontally from the inlet 240 propagates mainly within the transparent area SD and is then reflected downward within SL. Propagation in the transparent area reduces the loss of image illumination due to reflection in undesirable directions, thereby improving waveguide efficiency. Furthermore, there is no undesirable reflection of the view from SD by the facets, thereby substantially reducing glint and ghost images from the waveguide.

[0037] One possible method for manufacturing a horizontally enlarged section SL having a “recess” SD is shown in Figures 3G and 3H. The section containing SD and SL is subdivided into blocks, as indicated by the thick contour within the region 300 designated in Figure 3G. Figure 3H shows how this structure may be assembled from a transparent prism 302 having appropriate facet angles and three plates having appropriate facet angles (indicated by lines along the plates) that fit together with the corresponding surfaces of the prism 302 and with respect to each other to form the assembled structure as shown. This structure is combined with an additional transparent prism and a vertically enlarged section of LOE to produce the entire structure.

[0038] Optionally, the combined prism and plate may be sliced, or they may be initially mounted on a separate stack and sliced ​​together to generate waveguides in all sections.

[0039] The waveguide size described above is shown in Figure 4A, and the angular size of the image field is obtained as shown in Figure 4B. Note that the most horizontally spread beam 250 illuminates only the lower corner of the image, requiring a large waveguide area while contributing to only a small portion of the image. In certain applications, it may be acceptable, and even more advantageous, to provide a non-rectangular FOV, particularly a trapezoidal image field, as shown in Figure 4D. In this case, an image is shown with the same total area as in Figure 4B (shown by a dashed line in Figure 4D for comparison), but distributed as a trapezoid, with a wider field at the top than at the bottom. The LOE that produces this FOV is shown in Figure 4C, with corresponding dimensions, in which case the horizontal edge light beam 252 illuminates the entire field vertically (at different angles corresponding to the paper), and thus utilizes the LOE size much more efficiently. As a result, the waveguide size in Figure 4C is substantially smaller than the waveguide size in Figure 4A, as shown by the exemplary dimensions of the entire same FOV area. The following description illustrates further aspects of the invention in the non-limiting illustrative context of the configuration shown in Figure 4A, but it should be understood that configurations such as the one shown in Figure 4C can be implemented using the same principles.

[0040] A relatively large coupling prism 202 is required to introduce a shallow image into the waveguide. Figure 5A shows a waveguide with a horizontal inlet pupil 203L and a coupling prism 202M at a constant scale. An image projector 200 is schematically shown. Figure 5B is an isometric view of the coupling prism 202M with a vertical aperture 203T and a horizontal aperture 203L, both of which are coplanar to define a rectangular aperture. Figure 5C shows a side view of the coupling prism 202M, which requires a 14mm long coupling prism designed to couple light from all field angles into the waveguide for a 1.7mm thick waveguide. A portion of the beam 262 is reflected from the bottom of the prism and then enters the waveguide 204 through the pupil 203V. The height of the prism 202M above the waveguide is 6.4mm, which is acceptable for many applications. However, the size of the Projector 200, which requires image input via the Prism 202M, also occupies space and volume, making it unacceptable for many applications.

[0041] Prisms 202M (and others described herein) preferably have a bottom surface parallel to the waveguide surface for uniform reflection, while the top and side surfaces do not require specific optical properties, and their shapes may be other than those shown in these figures.

[0042] Figure 5D shows an alternative architecture where the coupled prism 202L is located above the waveguide and the inlet pupil is the prism surface 264. In this case, the prism and the required projector are larger than those in Figures 5A-5C, and this configuration is not optimal.

[0043] One option for reducing the overall dimensions of the combined configuration and image projector is shown in Figures 6A and 6B, which illustrate the integration of the image projector with the coupling prism. Although a scanning laser image projector is shown here as a non-limiting example, the same principle can be implemented by using an image projector based on another type of image generator, such as employing an LCOS (liquid crystal on silicon) spatial light modulator or a micro-LED image generator.

[0044] Figure 6A shows a coupled prism 202P mounted on waveguide 204. Figure 6B shows a side view of an integrated (embedded) image projector. Laser 270 directs a polarized beam onto a scanning mirror 272 that scans the intermediate image plane across a microlens array (MLA) or diffuser 274. The scanned light passes through the diffuser and is reflected from a polarizing beam splitter 276 to a collimating reflection lens 278 (combined with a quarter-wavelength plate). The reflected light passes through PBS 276 and enters the coupled prism 202P. Thus, this coupled prism also functions as part of PBS 276. Some of the light enters the waveguide directly, and some of it is reflected by the bottom surface 279 before entering the waveguide, thereby filling the waveguide aperture with both the image and its conjugate.

[0045] In this specification, where the arrangement of PBS is illustrated as sequentially reflecting and then transmitting light, or vice versa, it is understood that half-wavelength plates (for single transmission) or quarter-wavelength plates (for double transmission) are appropriately arranged to achieve the polarization rotation required for the function described. Polarization rotation elements are not mentioned in each case.

[0046] Alternative architectures for combining an image projector with a coupled prism are shown in Figures 7A–7D. Figure 7A shows how light from an image generator (not shown, but as before, may be a scanning laser, LCOS, or other) (the beams in the figure are from different field points and therefore not parallel) is parallelized by a refractive lens 280 and input to a prism section 282, where it is reflected by a mirror 284 into a prism section 202Q and waveguide 204. In this configuration, prism sections 282 and 202Q can be combined to form a single prism, as shown in Figure 7B. In this case, polarization of the light is not required.

[0047] The structure in Figure 7B employs a reflector architecture similar to that in Figure 7A, but with a smaller prism. Here, the length of the prism is on the order of 14 mm, similar to prism 202M in Figure 5C for similar output parameters. However, the height is only 3.2 mm, half that of 202M. As with all prisms described herein, the upper (non-reflective) surface of prism 283 is preferably absorptive. This is depicted here according to the upper beam 260 (defined in Figure 5C), although the upper surface may be taller and / or have other shapes, as it is not optically significant.

[0048] This prism may also have a coupling configuration that includes a low refractive index portion on its underside, equivalent to element 286 or 228, as described later with reference to Figures 7C and 7D. It can be attached to a PBS as an image projector using the interface.

[0049] Figure 7C shows the introduction of divergent polarization corresponding to the image (emitted from an MLA, scanning laser, LCOS, or other image generator) that passes through interface 286 and enters PBS section 290, and is reflected onto the reflective collimating lens 294 by PBS 292. The reflected collimated light enters the coupled prism 202Q and waveguide 204 through PBS 292. In this architecture, since some of the light is reflected by the lower sections of prisms 290 and 202Q, these surfaces need to have good image quality and be continuous. Interface 286 can be air, but it can also be a low refractive index medium (relative to prism 290), so TIR occurs for light reflected from 294.

[0050] Figure 7D is similar to Figure 7C, but shows an arrangement that includes an external optical element that collimates light (e.g., a refractive lens 296) and a flat reflector 298.

[0051] Referring now to Figures 8A and 8B, these illustrate an alternative configuration according to a further aspect of the present invention, in which the coupled prism is integrated with a portion of the waveguide, instead of being an enlargement as shown in Figure 5A. Figure 8A shows the coupled prism 202Y (dotted area) above the waveguide 204. Thus, the image generator 200 is located close to the waveguide and has a smaller size. Since all light rays propagating within the waveguide continue to emerge from point 240, the horizontal aperture 203L2 is located in the same place as in the previously described embodiment. However, the vertical aperture 203V is located here at the end of the prism, where the thicker portion of the prism intersects with the main outer surface defining the main portion of the LOE. Figure 8B shows the shape of the coupled prism in isometric view. The two apertures 203L2 and 203V2 have the same width as described above, but to separate their positions, the prism is vertically elongated at 203L2.

[0052] From Figure 8A, it is clear that some of the facets (represented herein as 206A and 206B) are located within the prism. Several possible implementations of these facets in prism 202Y are shown in Figures 9A–9F. For clarity, facets located within the main portion of the LOE are omitted here.

[0053] Figure 9A shows prism 202Y mounted on the edge of the waveguide, and Figure 9B shows the equilateral arrangement of facets within the prism. However, since the facets do not need to reflect light across the entire width of the prism (as seen in Figure 8A, which shows that the required width of facets 206A and 206B is limited), Figure 9C shows that the reflective areas (shaded areas) are only a portion of the corresponding planes within the prism.

[0054] Figure 9D shows an alternative configuration in which prism 202Y is formed by attaching a block of the corresponding shape to the top of waveguide 204 (facets of 204 are not shown). Figure 9E shows the same structure with facets provided across the entire cross-section of 202Y, exceeding the thickness of LOE, and Figure 9F shows the reflection region implemented only as a shaded area, corresponding to the optimal required area.

[0055] In certain cases, the aforementioned integrated image projector (Figures 6A-7D) can be combined with the LOE integrated coupled prism shown in Figures 8A-9F. Specific geometric considerations in such implementations are shown with reference to Figures 10A-10D.

[0056] Figure 10A shows a side view of the angular distribution equivalent to that in Figure 2C, but with markings for two field points associated with facets 206A (circle) and 206B (square). The same field points are shown in Figure 10B.

[0057] Figure 10C shows a side view of the waveguide overlap-coupled prism, where the shaded area represents the preferred position of the facet associated with 206A, and Figure 10D shows the preferred position of the facet of 206B. PBS292 is shown here for reference. It is clear that the preferred position of the facet in the overlap-coupled prism should be above the PBS plane. In implementations where the facet is in front of the PBS plane, distortion is introduced into the transmitted image.

[0058] Figures 11A–11D are side views showing the implementation of facets on a coupled prism incorporating projector optical elements. Figures 11A, 11B, and 11C show the integration of facet section 202T (marked as a shaded area) into a configuration that may be similar to those in Figures 7A, 7C, and 7D, respectively. The 3D representation remains the same as that described with reference to Figures 10A–10D.

[0059] Figure 11D corresponds to Figure 6B and shows that when the orientation of the PBS is reversed, the facet section 202T2 is optimally mounted only partially behind the PBS plane. Thus, the coupled prism extends slightly further outside the horizontal aperture plane 203L2 (shown in Figures 8A-8B).

[0060] Furthermore, the deployment of facet 202T2 as shown in Figure 11D is also suitable for configurations employing the waveguide architectures shown in Figures 4C and 4D.

[0061] Referring here to Figures 12A-12D and 3G-3H, as an alternative to the manufacturing process shown above, the facet patterns in Figure 3D or 3F may be manufactured based on stacking and slicing selectively coated plates. In this case, the plates are coated with a predetermined pattern as shown in Figure 12A, which shows a set of plates shown from the front 300F coated with a predetermined pattern 302F. These patterns have widths and positions according to the required coated facets shown in 112. These patterns are preferably generated by masking the uncoated portions of the waveguide during the coating process. Alternatively, to maintain a flat surface or to keep the phase of the transmitted light passing through 304 the same as the phase of the transmitted light passing through 302, an anti-reflective coating may be applied only to the other portions of the plate 304F.

[0062] Figure 12B shows a stack formed by joining partially coated plates together, with dashed lines indicating slice planes crossing the stack. Figure 12C shows one slice with side views of plate 300S and reflection pattern 302S. Another slice is made as indicated by the dashed lines in Figure 12C, producing the final upper section of Figure 12D, corresponding to the upper part of LOE in Figure 3D.

[0063] Please note that the order of the slices may be changed. Also, the diagrams in Figures 12A–12D are very schematic, and it should be understood that typically more plates are used.

[0064] By reducing the refractive index of the coupled prism 202M, the size of the prism can be reduced, thereby making the system more compact. Figure 13 shows an extreme example of this concept, where 202M is replaced by an air gap and a mirror 310 that is coplane with the lower waveguide surface 312. Light from the projection optics element 308 is guided to the vertical inlet 306 and input into the waveguide 204 and then into the mirror surface 310. Due to the lower refractive index of the air gap, the beam angle changes. As a result, the length of the mirror becomes shorter than the length of the prism 202M. The angle of the lower beam 262 is 11.5 degrees here, instead of the previous 7 degrees. As a result, the length of the mirror is 8.5 mm here, instead of 14 mm in Figure 5C. When the beam enters the waveguide, its angular distribution is as shown in Figure 5C. For mechanical mounting, the mirror can be superimposed on the waveguide.

[0065] A conceptually similar approach using low refractive index materials can be implemented using a low refractive index glass prism. When using a low refractive index glass prism, it is possible to compensate for some of the dispersion generated by the incident angle of the optical input surface 306.

[0066] In the embodiments described in detail above, the facet 206L employed for the first set of facets is perpendicular to the main outer surface of the LOE, as detailed in Figures 2A-2C. In an alternative set embodiment shown with reference to Figures 14A-14C, the first set of facets is implemented using oblique facet 336. Figure 14A shows an isometric view of such a system used to transmit shallow-angle images, and Figure 14B shows a partial side view corresponding to the angular view. Although this non-limiting example employs a trapezoidal FOV equivalent to the smallest image size shown in Figures 4C and 4D, it will be apparent that this structure can also be used for rectangular FOVs.

[0067] In this architecture, the initial horizontally propagated image 334A1 is coupled with 334A2 by TIR reflection. Only 334A2 is deflected toward a second region of LOE 334B1 by an oblique facet 336 positioned at an angle to the waveguide surface. Facet 336 is preferably coated with a multilayer dielectric coating, as known in the art, so as to be mostly transparent to the range of incident angles corresponding to image 334A1, while providing a desired degree of partial reflectivity to the range of incident angles corresponding to image 334A2 (as in all of the embodiments described above), so as to minimize energy loss and the formation of undesirable reflections. Image 334B1 is coupled to 334B1 by TIR as it propagates at a shallow angle along the second region of the waveguide. Image 334B2 is then coupled to 334C by facet 338 (shown only in Figure 14A) in a manner equivalent to facet 226 in Figures 2A-2C.

[0068] Figure 14C shows the waveguide footprint equivalent to that in Figure 4C, where the shaded region 340 is the optimal area for the first set of facets 336, and region 342 is the optimal area for the output coupling facet 338.

[0069] The various coupled input prism arrangements described above are configured to "fill" the waveguide with the image by coupled inputting both the image and its conjugate to the LOE. A particularly attractive alternative method for introducing shallow-angle images into the waveguide is to introduce the image directly into the waveguide, as shown in Figure 15. To fill the waveguide 370 with the introduced image and its conjugate, the waveguide 370 has a coupled region 372 having a partial reflector 374 along the center plane of the waveguide. The partial reflector 374 is most preferably implemented as a 50% reflector, which is unaffected by angle and preferably has chromatic aberration corrected, such as by having a partially silver surface.

[0070] In Figure 15, the three beams are shown, associated with the lowest point in the field, and therefore the shallowest beam of image illumination. The lower beam (solid arrow) enters the waveguide after passing through the collimating optical element 376 and the coupling prism 378. After one reflection, it is split into two beams via partial reflection by 374. The middle beam (dashed line) is split at the entrance, and the upper beam (dashed dot line) is split in half along the combiner 372. It is clear that after the beams are split (and thus the image illumination is split between the image and its conjugate), the waveguide is uniformly illuminated. Therefore, a uniform image can be expected after the light is coupled and output.

[0071] If the partial reflector 374 has a reflectivity of 50% and a transmittance of 50%, the waveguide is uniformly illuminated over a length equivalent to that shown in Figure 5C (14 mm in our embodiment). In this configuration, since the optical elements are almost adjacent to the entrance of the waveguide, the aperture of the illuminating optical element 376 is very small, reducing the thickness of the optical assembly.

[0072] Referring now to Figures 16A-16C, this illustrates an alternative scheme for combining and outputting images within the second region of the LOE toward an eye-motion box for viewing by the user's eyes. The angle display in Figure 16A is similar to that in Figure 2C, but in this case, the output combining facet 390 has a steeper angle. As a result, image 220B1 is combined and output to 220C (instead of 220B1 as in Figure 2C). In this configuration, image 220B can be higher and is not limited by the angle of facet 390.

[0073] Figure 16B schematically shows how such a configuration would look in real space. As the beam propagates downward (in this figure), it is partially reflected downward from the waveguide by the facets. In such a configuration, it is preferable to narrow the spacing between the facets to ensure a uniform image.

[0074] Figure 16C schematically shows the preferred reflectivity of the facets for such a configuration. Here, low reflectivity is desired at low incidence angles (near perpendicular), and high reflectivity is desired at high angles (for output coupling). Again, such properties can be easily achieved using a well-designed multilayer dielectric coating, as is well known in the art.

[0075] Referring here to Figures 17A-17F, in modifications of the preferred embodiments described herein, it is necessary to partially and selectively apply a reflective coating to only a portion of the plate, then assemble the plates in a stack, and further slice some or all of the LOE from the stack. Partial coating of facets, as shown in Figure 17A, can result in a scattering effect at the edges of the coating due to the physical discontinuity of the coating, as shown in the schematic cross-sectional view of Figure 17B. Furthermore, this mechanical discontinuity can cause mechanical stress in the plates when stacked (as in Figure 12B). Figures 17C-17F show a preferred manufacturing method according to one aspect of the present invention to overcome these limitations.

[0076] Figure 17C illustrates the principle of coating properties when the mask 394 is positioned close to the plate surface 300F but slightly separated from the surface. When coating (thick arrows) is performed, the plate is coated where there is no mask, but near the mask, a phenomenon occurs where the coating thickness is gradually reduced around the edge of the mask 396. Figure 17D schematically shows how this property can be used to generate a gradual reduction ("tail-off") of the coating pattern 302F around a desired area.

[0077] For thin coatings, this configuration of progressively thinning coatings may be sufficient. For thicker coatings, it may be advantageous to use a second mask over region 302F (Figure 17E), as shown in Figure 17F, to apply a complementary transparent coating 98 alongside the reflective area 302F. Note that the mask in Figure 17E is not typically the exact opposite of the mask in Figure 17D, as it is preferable to increase it around the boundary by an amount corresponding to the tailing-off area (which may be determined empirically).

[0078] It will be understood that the above description is intended to serve only as an example, and that many other embodiments are possible within the scope of the invention as defined in the appended claims.

Claims

1. An optical system for guiding image illumination introduced into a coupled input area to an eye motion box for viewing by the user's eyes, wherein the optical system comprises a light guide optical element (LOE) formed from a transparent material, and the LOE is (a) A first region having a first orientation, being planar, and including a first set of mutually parallel partial reflecting surfaces, (b) A second region having a second orientation nonparallel to the first orientation, and including a second set of mutually parallel partial reflecting surfaces in a plane, (c) A pair of main outer surfaces parallel to each other, the main outer surfaces extending across the first and second regions such that both the first pair of partial reflective surfaces and the second pair of partial reflective surfaces are located between the main outer surfaces, The second set of partial reflective surfaces is at an oblique angle to the main outer surface, and the first set of partial reflective surfaces is oriented such that a portion of the image illumination propagating within the LOE by internal reflection from the main outer surface from the first region into the second region is coupled toward the eye motion box from the LOE, An optical system comprising: a first set of partial reflective surfaces including: a first partial reflective surface located proximal to the coupled input region such as to contribute to a first portion of the user's field of view when viewed in the eye-motion box; a third partial reflective surface located distal to the coupled input region such as to contribute to a third portion of the user's field of view when viewed in the eye-motion box; and a second partial reflective surface located on an intermediate surface between the first and third partial reflective surfaces such as to contribute to a second portion of the user's field of view when viewed in the eye-motion box, wherein the second partial reflective surface is positioned in a sub-region of the intermediate surface such that image illumination propagating from the coupled input region to the third partial reflective surface and contributing to the third portion of the user's field of view when viewed in the eye-motion box passes through the intermediate surface but not through the second partial reflective surface.

2. The optical system according to claim 1, wherein the coupled input region comprises a coupled input prism having a first plane continuous with one of the main outer surfaces within the first region, and the coupled input prism has a thickness dimension measured perpendicular to the main outer surface, which is greater than the thickness of the LOE.

3. The optical system according to claim 2, wherein the coupled input prism provides a coupled input surface and a transition line between the coupled input prisms as the LOE, the coupled input surface defines the optical aperture of the coupled input prism in a dimension parallel to the main outer surface, and the transition line defines the optical aperture of the coupled input prism in a dimension perpendicular to the main outer surface.

4. The optical system according to claim 2, wherein the first set of partial reflectors further comprises at least one partial reflector located within the volume of the coupled input prism.

5. An optical system for guiding image illumination introduced into a coupled input area to an eye motion box for viewing by the user's eyes, wherein the optical system comprises a light guide optical element (LOE) formed from a transparent material, and the LOE is (a) A first region having a first orientation, being planar, and including a first set of mutually parallel partial reflecting surfaces, (b) A second region having a second orientation nonparallel to the first orientation, and including a second set of mutually parallel partial reflecting surfaces in a plane, (c) A pair of main outer surfaces parallel to each other, the main outer surfaces extending across the first and second regions such that both the first pair of partial reflective surfaces and the second pair of partial reflective surfaces are located between the main outer surfaces, The second set of partial reflective surfaces is at an oblique angle to the main outer surface, and the first set of partial reflective surfaces is oriented such that a portion of the image illumination propagating within the LOE by internal reflection from the main outer surface from the first region into the second region is coupled toward the eye motion box from the LOE, The coupled input region comprises a coupled input prism having a first plane continuous with one of the main outer surfaces within the first region, and the coupled input prism has a thickness dimension measured perpendicular to the main outer surface, which is greater than the thickness of the LOE. An optical system in which the coupled input prism presents a coupled input surface and a transition line between the coupled input prisms as the LOE, the coupled input surface defines the optical aperture of the coupled input prism in a dimension parallel to the main outer surface, and the transition line defines the optical aperture of the coupled input prism in a dimension perpendicular to the main outer surface.

6. The optical system according to claim 5, wherein the first set of partial reflectors further comprises at least one partial reflector located within the volume of the coupled input prism.

7. An optical system for guiding image illumination introduced into a coupled input area to an eye motion box for viewing by the user's eyes, wherein the optical system comprises a light guide optical element (LOE) formed from a transparent material, and the LOE is (a) A first region having a first orientation, being planar, and including a first set of mutually parallel partial reflecting surfaces, (b) A second region having a second orientation nonparallel to the first orientation, and including a second set of mutually parallel partial reflecting surfaces in a plane, (c) A pair of main outer surfaces parallel to each other, the main outer surfaces extending across the first and second regions such that both the first pair of partial reflective surfaces and the second pair of partial reflective surfaces are located between the main outer surfaces, The second set of partial reflective surfaces is at an oblique angle to the main outer surface, and the first set of partial reflective surfaces is oriented such that a portion of the image illumination propagating within the LOE by internal reflection from the main outer surface from the first region into the second region is coupled toward the eye motion box from the LOE, The coupled input region comprises a coupled input prism having a first plane continuous with one of the main outer surfaces within the first region, and the coupled input prism has a thickness dimension measured perpendicular to the main outer surface, which is greater than the thickness of the LOE. An optical system wherein the first set of partial reflectors further comprises at least one partial reflector located within the volume of the coupled input prism.

8. The optical system according to claim 7, wherein the coupled input prism presents a coupled input surface and a transition line between the coupled input prisms as the LOE, the coupled input surface defines the optical aperture of the coupled input prism in a dimension parallel to the main outer surface, and the transition line defines the optical aperture of the coupled input prism in a dimension perpendicular to the main outer surface.

9. The optical system according to any one of claims 2 to 8, wherein the coupled input prism is joined to the LOE at the edge surface of the LOE.

10. The optical system according to any one of claims 2 to 8, wherein the coupled input prism is bonded to one of the main outer surfaces of the LOE.

Images