Optical system including a light-guide optical device with two-dimension extension

Abstract

To provide an optical system including a light-guide optical element (LOE) for achieving optical aperture expansion.SOLUTION: An optical system including a light-guide optical element (LOE) comprising a first set of mutually parallel partially reflective surfaces and a second set of mutually parallel partially reflective surfaces in a different orientation than the first set. Both sets of partially reflective surfaces are located between the sets of mutually parallel major external surfaces. Image illumination introduced at the coupling-in position propagates along the LOE, is redirected by the first set of partially reflective surfaces towards the second set of partially reflective surfaces, and is coupled out at the second set of partially reflective surfaces towards the user's eye. The first set of partially reflective surfaces are implemented as partial surfaces located where needed to fill the eye motion box with the required image.SELECTED DRAWING: Figure 2E

Description

[Technical Field]

[0001] The present invention relates to optical systems, and more particularly to optical systems that include a light directing optical element (LOE) for achieving optical aperture expansion.

[0002] Many near-eye display systems include a transparent light-guiding optical element (LOE) or "waveguide" placed in front of a user's eye, which transmits an image by internal reflection within the LOE and then couples the image out toward the user's eye by a suitable output coupling mechanism. The output coupling mechanism can be based on embedded partial reflectors or "facets," or can utilize diffractive patterns. While the following description primarily refers to facet-based coupling-out arrays, it should be understood that various features of the present invention are also applicable to diffractive arrays. Summary of the Invention

[0003] The present invention is an optical system.

[0004] In accordance with the teachings of embodiments of the present invention, an optical system is provided for directing image illumination injected at a coupling-in region to an eye-motion box for viewing by a user's eyes, the optical system including a light-directing optical element (LOE) formed of a transparent material, the LOE including: (a) a first region including a first set of planar, mutually parallel partially reflective surfaces having a first orientation; (b) a second region including a second set of planar, mutually parallel partially reflective surfaces having a second orientation non-parallel to the first orientation; and (c) a set of mutually parallel major exterior surfaces extending across the first and second regions such that the first set of partially reflective surfaces and the second set of partially reflective surfaces are both located between the major exterior surfaces, wherein the second set of partially reflective surfaces transmits light within the LOE from the first region to a second region by internal reflection at the major exterior surfaces. the LOE is at an oblique angle to the major exterior surface such that a portion of the image illumination propagating into the second region is coupled out of the LOE toward the eye motion box, and wherein the first set of partially reflective surfaces is oriented within the LOE such that internal reflection at the major exterior surface causes a portion of the image illumination propagating from the coupling-in region to be refracted toward the second region, and wherein each of the partially reflective surfaces of the first set of partially reflective surfaces includes a partially reflective coating at a joining plane between two plates forming part of the LOE, and wherein the partially reflective coating is located on a first portion of the joining plane and at least one of the partially reflective surfaces has a second portion of the joining plane that is joined to form an optical continuum between the two plates.

[0005] According to a further feature of an embodiment of the present invention, an envelope of ray paths propagating within the LOE from the coupling-in region, refracted by one of the first set of partially reflective surfaces, and coupled out by one of the second set of partially reflective surfaces toward reaching the eye motion box defines an image region of one of the first set of partially reflective surfaces, and wherein an area of ​​the one of the first set of partially reflective surfaces located outside of that envelope defines a non-image region of one of the first set of partially reflective surfaces, wherein a majority of the non-image region couples to form an optical continuum between the two plates.

[0006] According to further features of embodiments of the present invention, the first set of partially reflective surfaces have non-uniform spacing such that the spacing between adjacent partially reflective surfaces closer to the coupling-in region is smaller than the spacing between adjacent partially reflective surfaces further from the coupling-in region.

[0007] According to further features of embodiments of the present invention, the optical system further includes an image projector for projecting a collimated image having a field of view angle about an optical axis, the image projector being optically coupled to the LOE to introduce the collimated image into the LOE at a coupling-in region as a propagation image that propagates within the LOE by internal reflection at the major external surfaces, the propagation image being partially reflected by a first set of partially reflective surfaces to generate a refracted propagation image that propagates within the LOE by internal reflection at the major external surfaces, the refracted propagation image being partially reflected by a second set of partially reflective surfaces to generate a coupling-out image that is directed outward from one of the major external surfaces toward the eye motion box, the optical axis of the coupling-out image being tilted with respect to a normal to the major external surfaces having a non-zero component of tilt along an elongation direction in the plane of the second set of partially reflective surfaces.

[0008] According to a further feature of an embodiment of the present invention, the device is configured to project an image onto the eye motion box with major axes including an X-axis corresponding to a first horizontal or vertical axis of the projected image and a Y-axis corresponding to the other axis of the projected image, and wherein the second set of partially reflective surfaces have an elongation direction parallel to the major exterior surface, the elongation direction having an angular offset with respect to the X-axis.

[0009] According to further features of embodiments of the present invention, the optical system is configured to project an image onto the eye motion box with major axes including an X-axis corresponding to a first horizontal or vertical axis of the projected image and a Y-axis corresponding to the other axis of the projected image, and the optical system further includes an image projector for projecting a collimated image having a field of view angle about the optical axis, the image projector being optically coupled to the LOE to introduce the collimated image into the LOE at a coupling-in region as a propagating image that propagates within the LOE by internal reflection at a major external surface, and an in-plane component of the optical axis of the propagating image is inclined toward a boundary of the second region with respect to the X-axis.

[0010] According to a further feature of an embodiment of the present invention, an in-plane component at one end of the field of view of the propagated image is substantially parallel to the X-axis.

[0011] According to further features of embodiments of the present invention, the optical system is configured to project an image onto the eye motion box with major axes including an X-axis corresponding to a first horizontal or vertical axis of the projected image and a Y-axis corresponding to the other axis of the projected image, and the optical system further includes an image projector for projecting a collimated image having a field of view angle about the optical axis, the image projector being optically coupled to the LOE to introduce the collimated image into the LOE at the coupling-in region as a propagation image that propagates within the LOE by internal reflection at the major external surfaces, the propagation image being partially reflected by the first set of partially reflective surfaces to generate a refracted propagation image that propagates within the LOE by internal reflection at the major external surfaces, and the in-plane component of the optical axis of the refracted propagation image is tilted with respect to the Y-axis.

[0012] According to the teachings of an embodiment of the present invention, there is provided an optical system for projecting an image injected at a coupling-in region for viewing by a user's eyes at an eye motion box, the image being viewed along major axes including an X-axis corresponding to a horizontal or vertical axis of the projected image and a Y-axis corresponding to an axis of the projected image perpendicular to the X-axis, the optical system including a light-directing optical element (LOE) formed of a transparent material, the LOE including: (a) a first region including a first set of planar, mutually parallel partially reflective surfaces having a first orientation; (b) a second region including a second set of planar, mutually parallel partially reflective surfaces having a second orientation non-parallel to the first orientation; and (c) a set of mutually parallel major exterior surfaces, the major exterior surfaces being separated by a first set of partially reflective surfaces and a second set of partially reflective surfaces. a set of major exterior surfaces extending across the first and second regions such that a second set of surfaces are both located between the major exterior surfaces, wherein the second set of partially reflective surfaces are at an oblique angle to the major exterior surfaces such that a portion of image illumination propagating within the LOE from the first region to the second region by internal reflection at the major exterior surfaces is coupled out of the LOE toward the eye motion box, and wherein the first set of partially reflective surfaces are oriented such that a portion of image illumination propagating within the LOE from the coupling-in region is refracted toward the second region by internal reflection at the major exterior surfaces, and wherein the second set of partially reflective surfaces has an elongation direction parallel to the major exterior surfaces, the elongation direction having an angular offset with respect to the X-axis.

[0013] According to the teachings of an embodiment of the present invention, there is provided an optical system for projecting an image injected at a coupling-in region for viewing by a user's eyes at an eye motion box, the image being viewed along major axes including an X-axis corresponding to a horizontal or vertical axis of the projected image and a Y-axis corresponding to an axis of the projected image perpendicular to the X-axis, the optical system including a light-directing optical element (LOE) formed of a transparent material, the LOE including: (a) a first region including a first set of planar, mutually parallel partially reflective surfaces having a first orientation; (b) a second region including a second set of planar, mutually parallel partially reflective surfaces having a second orientation non-parallel to the first orientation; and (c) a set of mutually parallel major exterior surfaces extending across the first and second regions such that the first set of partially reflective surfaces and the second set of partially reflective surfaces are both located between the major exterior surfaces; wherein the second set of partially reflective surfaces is at an oblique angle with respect to the major exterior surface such that a portion of image illumination propagating within the LOE from the first region to the second region by internal reflection at the major exterior surface is coupled out of the LOE toward the eye motion box, and wherein the first set of partially reflective surfaces is oriented such that a portion of image illumination propagating within the LOE from the coupling-in region is refracted toward the second region by internal reflection at the major exterior surface, and the optical system further includes an image projector for projecting a collimated image having a field of view angle about an optical axis, the image projector being optically coupled to the LOE to introduce the collimated image into the LOE at the coupling-in region as a propagation image propagating within the LOE by internal reflection at the major exterior surface, and an in-plane component of the optical axis of the propagation image being tilted toward the boundary of the second region with respect to the X-axis.

[0014] According to a further feature of an embodiment of the present invention, an in-plane component at one end of the field of view of the propagated image is substantially parallel to the X-axis.

[0015] According to the teachings of an embodiment of the present invention, there is provided an optical system for projecting an image injected at a coupling-in region for viewing by a user's eyes at an eye motion box, the image being viewed along major axes including an X-axis corresponding to a horizontal or vertical axis of the projected image and a Y-axis corresponding to an axis of the projected image perpendicular to the X-axis, the optical system including a light-directing optical element (LOE) formed of a transparent material, the LOE including: (a) a first region including a first set of planar, mutually parallel partially reflective surfaces having a first orientation; (b) a second region including a second set of planar, mutually parallel partially reflective surfaces having a second orientation non-parallel to the first orientation; and (c) a set of mutually parallel major exterior surfaces extending across the first and second regions such that the first set of partially reflective surfaces and the second set of partially reflective surfaces are both located between the major exterior surfaces, wherein the second set of partially reflective surfaces are located within the LOE and are parallel to the major exterior surfaces. the first set of partially reflective surfaces is at an oblique angle with respect to the major exterior surfaces such that a portion of the image illumination propagating from the first region to the second region is coupled out of the LOE toward the eye motion box by internal reflection at the major exterior surfaces, and wherein the first set of partially reflective surfaces is oriented within the LOE such that a portion of the image illumination propagating from the coupling-in region is refracted toward the second region by internal reflection at the major exterior surfaces; the optical system further includes an image projector for projecting a collimated image having a field of view about an optical axis, the image projector being optically coupled to the LOE to introduce the collimated image into the LOE at the coupling-in region as a propagation image that propagates within the LOE by internal reflection at the major exterior surfaces, the propagation image being partially reflected by the first set of partially reflective surfaces and propagating within the LOE by internal reflection at the major exterior surfaces to generate a refracted propagation image, the in-plane component of the optical axis of the refracted propagation image being tilted with respect to the Y-axis.

[0016] According to further features of the present invention, the i-motion box is bounded by at least one straight line parallel to the X-axis.

[0017] According to a further feature of an embodiment of the present invention, the projected image is a rectangular image having edges parallel to the X and Y axes.

[0018] According to a further feature of an embodiment of the present invention, there is also provided a support arrangement configured to support the LOE against a user's head in an orientation relative to the user's eyes such that one of the major exterior surfaces faces the user's eyes and the X axis is oriented horizontally.

[0019] According to further features in embodiments of the present invention, the first region and the second region are separated by a boundary extending parallel to the X-axis.

[0020] In accordance with the teachings of embodiments of the present invention, an optical system is provided for directing image illumination injected at a coupling-in region to an eye motion box for viewing by a user's eyes, the optical system including a light-directing optical element (LOE) formed of a transparent material, the LOE including: (a) a first region including a first set of planar, mutually parallel partially reflective surfaces having a first orientation; (b) a second region including a second set of planar, mutually parallel partially reflective surfaces having a second orientation non-parallel to the first orientation; and (c) a set of mutually parallel major exterior surfaces extending across the first and second regions such that the first set of partially reflective surfaces and the second set of partially reflective surfaces are both located between the major exterior surfaces. a set of surfaces, wherein the second set of partially reflective surfaces is at an oblique angle to the main exterior surface such that a portion of image illumination propagating within the LOE from the first region to the second region by internal reflection at the main exterior surface is coupled out of the LOE toward the eye motion box, and wherein the first set of partially reflective surfaces is oriented such that a portion of image illumination propagating within the LOE from the coupling-in region is refracted toward the second region by internal reflection at the main exterior surface, and wherein the first set of partially reflective surfaces have non-uniform spacing such that the spacing between adjacent partially reflective surfaces near the coupling-in region is smaller than the spacing between adjacent partially reflective surfaces farther from the coupling-in region.

[0021] According to the teachings of embodiments of the present invention, an optical system is provided for directing image illumination injected at a coupling-in region to an eye motion box for viewing by a user's eyes, the optical system including a light-directing optical element (LOE) formed of a transparent material, the LOE including: (a) a first region including a first set of planar, mutually parallel partially reflective surfaces having a first orientation; (b) a second region including a second set of planar, mutually parallel partially reflective surfaces having a second orientation that is non-parallel to the first orientation; and (c) mutually parallel primary and secondary reflective surfaces. a set of exterior surfaces extending across the first and second regions such that a first set of partially reflective surfaces and a second set of partially reflective surfaces are both located between the major exterior surfaces, wherein the second set of partially reflective surfaces are at an oblique angle to the major exterior surfaces such that a portion of image illumination propagating within the LOE from the first region to the second region by internal reflection at the major exterior surfaces is coupled out of the LOE toward the eye motion box; and The first set of reflective surfaces are oriented within the LOE such that a portion of the image illumination propagating from the coupling-in region is refracted toward the second region by internal reflection at the major external surfaces, and the optical system further includes an image projector for projecting a collimated image having a field of view angle about an optical axis, the image projector being optically coupled to the LOE to introduce the collimated image into the LOE at the coupling-in region as a propagation image that propagates within the LOE by internal reflection at the major external surfaces, the propagation image being partially reflected by the first set of partially reflective surfaces to generate a refracted propagation image that propagates within the LOE by internal reflection at the major external surfaces, and the refracted propagation image being partially reflected by the second set of partially reflective surfaces to generate a coupling-out image that is directed outward from one of the major external surfaces toward the eye motion box, the optical axis of the coupling-out image being tilted with respect to a normal to the major external surfaces having a non-zero component of tilt along an elongation direction in the plane of the second set of partially reflective surfaces. [Brief explanation of the drawings]

[0022] The invention is herein described, by way of example only, with reference to the accompanying drawings. [Figure 1A] 1A-1C are schematic isometric views of optical systems implemented using light-directing optical elements (LOEs), constructed and operative in accordance with the teachings of the present invention, illustrating top-down injection and side-injection configurations, respectively; [Figure 1B] 1A-1C are schematic isometric views of optical systems implemented using light-directing optical elements (LOEs), constructed and operative in accordance with the teachings of the present invention, illustrating top-down injection and side-injection configurations, respectively; [Figure 2A] an enlarged schematic isometric view of the LOE from Figure 1A or Figure 1B showing the ray paths for the two extreme fields of the image; [Figure 2B] an enlarged schematic isometric view of the LOE from Figure 1A or Figure 1B showing the ray paths for the two extreme fields of the image; [Figure 2C] 1A and 1B , which is an overview of the combination of the fields in Fig. 1A and 1B with additional fields to define the entire range of partially reflecting surfaces required to form a complete image in the eye motion box; [Figure 2D] An alternative implementation of Figure 2C in which partially reflective surfaces are selectively implemented; [Figure 2E] FIG. 2D is a view similar to FIG. 2D illustrating variable spacing between partially reflective surfaces; [Figure 2F] FIG. 2B is a view similar to FIG. 2E illustrating the areas of the LOE that can be trimmed; [Figure 3A] FIG. 2E is a diagram similar to FIG. 2E illustrating potential ray paths for ghost formation when a partially reflective surface is present and when it is not present outside the required profile of the partially reflective surface; [Figure 3B] FIG. 2E is a diagram similar to FIG. 2E illustrating potential ray paths for ghost formation when a partially reflective surface is present and when it is not present outside the required profile of the partially reflective surface; [Figure 4A] 1A or 1B , showing the ray paths for the two extreme fields; [Figure 4B] FIG. 4B is a view similar to FIG. 4A showing a partial depiction of partially reflective surfaces with variable spacing between the partially reflective surfaces; [Figure 4C] A view similar to Figure 4B showing some of the partially reflecting surfaces required at the extremes of the field; [Figure 5A] FIG. 4C is an enlarged schematic isometric view of an LOE including a first region similar to that of FIG. 4C , implemented according to the principles illustrated above in connection with FIG. 2E ; [Figure 5B] FIG. 5B is a view similar to FIG. 5A illustrating the area of ​​the LOE that can be cropped; [Figure 6A] Schematic isometric views similar to Figures 2A-2F illustrating the effect of various angular offset parameters; [Figure 6B] Schematic isometric views similar to Figures 2A-2F illustrating the effect of various angular offset parameters; [Figure 6C] Schematic isometric views similar to Figures 2A-2F illustrating the effect of various angular offset parameters; [Figure 6D] Schematic isometric views similar to Figures 2A-2F illustrating the effect of various angular offset parameters; [Figure 7] FIG. 1 is a schematic plan view of a near-eye display illustrating the angular offsets required for face curve correction and convergence correction in accordance with an aspect of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] Certain embodiments of the present invention provide an optical system including a light-directing optical element (LOE) for achieving optical aperture expansion for the purpose of a head-up display, which may be a virtual reality display, or more preferably an augmented reality display, and most preferably a near-eye display.

[0024] An exemplary implementation of a device in the form of a near-eye display, generally designated (10), utilizing an LOE (12) according to the teachings of embodiments of the present invention is illustrated schematically in FIGS. 1A and 1B. The near-eye display (10) utilizes 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 illumination is captured in one dimension by internal reflection at a set of mutually parallel, planar exterior surfaces. Light impinges on a set of partially reflective surfaces (interchangeably referred to as "facets") that are parallel to each other and obliquely tilted relative to the direction of propagation of the image light, with each successive facet refracting a portion of the image light in a refractive direction for further capture / direction by internal reflection within the substrate. This first set of facets, not separately illustrated in FIGS. 1A and 1B, is located in a first region of the LOE, designated (16). This partial reflection at successive facets achieves the first dimension of optical aperture expansion.

[0025] In a first set of preferred, but non-limiting examples of the present invention, the aforementioned set of facets is orthogonal to the major exterior surfaces of the substrate. In this case, both the injected image and its conjugate, which undergoes internal reflection as it propagates within region (16), are refracted and become conjugate images propagating in the direction of refraction. In another preferred, but non-limiting example, the first set of partially reflective surfaces is angled obliquely relative to the major exterior surfaces of the LOE. In the latter case, either the injected image or its conjugate forms the desired refracted image that propagates within the LOE, while reflection of the other is minimized, for example, by utilizing an angle-selective coating on the facet that renders the facet relatively transparent up to the range of incidence angles exhibited by the image that does not need to be reflected.

[0026] The first set of partially reflective surfaces refracts the image illumination from a first direction of propagation captured by total internal reflection (TIR) ​​within the substrate to a second direction of propagation also captured by TIR within the substrate.

[0027] The refractive image illumination then proceeds to a second substrate region (18), which may be implemented as an adjacent, separate substrate or as a continuation of a single substrate, where a coupling-out array (either a further set of partially reflective facets or a diffractive optical element) progressively couples out a portion of the image illumination toward the observer's eyes, located within an area defined as the eye motion box (EMB), thereby achieving a second dimension of optical aperture expansion. The entire device may be implemented separately for each eye and is preferably supported against the user's head, with each LOE (12) facing the user's corresponding eye. In one particularly preferred option, as illustrated herein, the support arrangement is implemented as an eyeglass frame with sides (20) for supporting the device against the user's ears. Other forms of support arrangements can also be used, including, but not limited to, a headband, a visor, or a device suspended from a helmet.

[0028] In the drawings and claims herein, reference is made to an X-axis and a Y-axis, with the X-axis extending horizontally (FIG. 1A) or vertically (FIG. 1B) in the general elongation direction of the first region of the LOE, and the Y-axis extending perpendicular to the X-axis, i.e., vertically in FIG. 1A and horizontally in FIG. 1B.

[0029] Very roughly speaking, 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), can be considered to achieve aperture expansion in the Y direction. Details of the angular spread through which various portions of the field of view propagate will be discussed in more detail below. Note that the orientation illustrated in FIG. 1A can be considered a “top-down” implementation, in which image illumination entering the main (second region) LOE enters from the top, while the orientation illustrated in FIG. 1B can be considered a “side-injection” implementation, in which the axis referred to herein as the Y axis is positioned horizontally. In the remaining figures, various features of certain embodiments of the present invention will be illustrated in terms of a “top-down” orientation similar to FIG. 1A. However, it should be understood that all of these features are equally applicable to side-injection implementations, which are also within the scope of the present invention. Other intermediate orientations may be applicable in some cases and are included within the scope of the present invention, except where expressly excluded.

[0030] PODs utilized with the devices of the present invention are preferably configured to produce collimated images, i.e., where the light for each image pixel is an infinitely collimated beam parallel to the angular direction corresponding to the pixel position, so that the image illumination spans a range of angles corresponding to the two-dimensional field of view.

[0031] The image projector (14) typically includes at least one light source arranged to illuminate a spatial light modulator, such as an LCOS chip. The spatial light modulator modulates the projected intensity of each pixel of the image, thereby generating the image. Alternatively, the image projector may include a scanning arrangement, typically implemented using a high-speed scanning mirror, which scans illumination from a laser light source across the projector's image plane while the beam's intensity varies synchronously with pixel-based motion, thereby projecting the desired intensity onto each pixel. In either case, collimating optics are provided to generate an infinitely collimated output projected image. 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 arrays, as known in the art.

[0032] Optical coupling of the image projector 14 to the LOE 12 can be achieved by any suitable optical coupling, for example, via a coupling prism with an obliquely angled input surface, or via a reflective coupling arrangement, through a side edge and / or one of the major exterior surfaces of the LOE. The details of the coupling-in configuration are not important to the invention and are shown schematically herein as a non-limiting example of a wedge prism 15 applied to one of the major exterior surfaces of the LOE.

[0033] It will be understood that the near-eye display 10 includes various additional components, including a controller 22 that generally operates the image projector 14, typically using power from a small on-board battery (not shown) or any other suitable power source. It will be understood that the controller 22 includes all necessary electrical components, such as at least one processor or processing circuitry, for driving the image projector, as known in the art.

[0034] 2A-2F, the optical characteristics of a near-eye display implementation are shown in more detail. Specifically, a more detailed view of a light-directing optical element (LOE) (12) formed of a transparent material is shown, where the LOE includes a first region (16) including a first set of planar, mutually parallel, partially reflective surfaces (17) having a first orientation, and a second region including a second set of planar, mutually parallel, partially reflective surfaces (19) having a second orientation that is non-parallel to the first orientation. A set of mutually parallel major exterior 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 major exterior surfaces (24). Most preferably, the set of major exterior surfaces 24 is a pair of surfaces that are contiguous throughout the first and second regions 16, 18, respectively, although options for reducing or increasing the thickness between the first and second regions 16, 18 are also within the scope of the present invention. The first and second regions 16, 18 may be directly juxtaposed, meeting at a boundary that may be a straight line or some other form of boundary, or one or more additional LOE regions may be interposed between them to provide various additional optical or mechanical functions depending on the particular application. While the present invention is not limited to any particular production technique, in certain preferred implementations, particularly high-quality major exterior surfaces are achieved by utilizing a continuous exterior plate that sandwiches the separately formed first and second regions 16, 18 to form a composite LOE structure.

[0035] The optical properties of the LOE can be understood by tracing back the image illumination path. The second set of partially reflective surfaces (19) is angled obliquely relative to the major exterior surface (24) so ​​that internal reflections at the major exterior surface couple a portion of the image illumination propagating within the LOE (12) from the first region (16) to the second region (18) out of the LOE toward the eye motion box (26). The first set of partially reflective surfaces (17) is oriented so that internal reflections at the major exterior surface refract a portion of the image illumination propagating within the LOE (12) from the coupling-in region (coupling prism (15)) toward the second region (18).

[0036] The one-dimensional angular spread of the projected image from the image projector (14) is represented in Figure 2A by the cone of illumination extending from the POD aperture on the right side of the LOE toward the left side of the LOE. In the non-limiting example described herein, the central optical axis of the POD defines a direction of propagation within the LOE aligned with the X-axis, and the angular spread (within the LOE) is approximately ±16°. (Note that the angular FOV becomes larger due to the change in refractive index.) A first set of partially reflective surfaces (17) is illustrated in the first region (16), and a second set of partially reflective surfaces (19) is illustrated in the second region (18).

[0037] Near-eye displays are designed to provide a complete field of view of the projected image to a user's eye located within a permissible range of positions specified by the "eye motion box" (EMB) (26) (i.e., a shape generally depicted as a rectangle, spaced from the plane of the LOE, from which the eye's pupil will view the projected image). To reach the eye motion box, light must be coupled out from the second region (18) toward the EMB (26) by a second set of partially reflective surfaces (19). To provide a complete image field, each point on the EMB must receive the entire angular range of the image from the LOE. Tracing back the field of view from the EMB reveals a larger rectangle (28) from which relevant illumination is coupled out toward the EMB.

[0038] Figure 2A shows the first end of the field of view, corresponding to the bottom-left pixel of the projected image. A beam of width corresponding to the projector's optical aperture when coupled into the LOE is shown propagating leftward and upward from the POD and partially reflected from a series of partially reflective surfaces (17). As explained herein, only a subset of the facets produce reflections useful for providing the corresponding pixel in the image viewed by the user, and only a subregion of those facets contributes to the observed image of this pixel. The relevant region is illustrated by a thick black line, and the rays corresponding to this pixel in the redirected image are shown reflected from facet (17) and coupled out by facet (19) to reach the four corners of the EMB (26). Note that throughout this specification and discussion, only the in-plane propagation direction of the ray is described herein in propagation within the LOE, but the ray actually follows a zigzag path of successive internal reflections from the two major exterior surfaces, and the entire one dimension of the image field is encoded by the angle of inclination of the ray with respect to the major exterior surfaces, which corresponds to the pixel position in the Y dimension. By way of an additional example, the refracted and coupled-out ray, corresponding to the upper left extremity of the image when viewed at the upper left corner of the EMB, is shown in dash-dotted lines.

[0039] FIG. 2B illustrates the same configuration as FIG. 2A, but now shows rays corresponding to the bottom right pixel of the field of view arriving at the four corners of the EMB, with the relevant areas of the associated partially reflective surfaces (17) again indicated by bold lines.

[0040] By further tracing the corresponding ray paths for all fields (directions or pixels) of the image that reach all regions of the EMB, it is possible to map out the range of all ray paths that propagate within the LOE, are refracted by one of the first set of partially reflective surfaces, and are coupled out by one of the second set of partially reflective surfaces in a direction that reaches the eye motion box. This range then defines the "image area" of each facet (17) needed to refract the portion of the image illumination that contributes to the image reaching the EMB, while the rest of the facet (17) outside the range is the "non-image area" that does not contribute to the required image. A simplified outline of this range, corresponding to all the "image areas" of the facets (17), is shown in bold in Figure 2C.

[0041] According to one particularly preferred set of implementations of the present invention, the facets (17) are implemented as "partial facets" such that the partially reflective properties exist only within a subregion of the cross-sectional area of ​​the region (16) that includes the "image area" of each facet plane, and preferably exclude at least a majority of the "non-image area" for some or all of the facets. Such an implementation is illustrated schematically in FIG. 2D. The active (partially reflective) area of ​​the facets preferably extends slightly beyond the minimum necessary to satisfy the geometric requirements for EMB image projection to avoid anomalies that may be caused by defects at the coating edges, and in some cases the facets may be extended further in the refracted image direction, with additional considerations related to integer number overlaps between facets, to achieve improved image uniformity. According to one particularly preferred implementation, the distance of the furthest partially reflective facet encountered along a line from the coupling location gradually increases with increasing angle clockwise, as shown, and becomes farther from the boundary with the second region (18) over most of the angular range of the image projected from the projector (14).

[0042] When the first region (16) is formed from a stack of coated plates and then cut at an appropriate angle (as described in PCT Patent Publication No. WO2007054928A1 and as known in the art), selective spatial placement of the partially reflective surface can be advantageously achieved by forming the stack of plates with a partially reflective coating located on a first portion of the joining plane between two plates, while a second portion of the joining plane is glued (typically with an index-matched adhesive and without a coating) to form an optical continuum between the two plates. Selective application of the partially reflective coating is generally achieved by applying an appropriate masking layer prior to the coating process and removing the masking layer at the end of the coating process.

[0043] According to an alternative production technique, a stack of full-area coated plates can be formed and then cut into the shape required for the faceted volume (e.g., corresponding to the faceted area shown in FIG. 2D). The required configuration of the LOE is then completed by optically coupling this irregular block containing the partially reflective facets with a complementary block of index-matched flat glass.

[0044] Figure 2E is similar to Figure 2D, but the first set of partially reflective surfaces (17) has non-uniform spacing between the planes of the surfaces such that the spacing between adjacent partially reflective surfaces near the coupling-in region is smaller than the spacing between adjacent partially reflective surfaces farther from the coupling-in region. This variable spacing is often preferable to increase the uniformity of the projected image, as explained further below.

[0045] The optical axis is not actually parallel to the X axis, but lies in the XZ plane, and the Z-component into the page is chosen so that the entire angular range of the depth dimension of the FOV undergoes total internal reflection at the major external substrate surface. For simplicity of presentation, the graphical depictions and descriptions herein will only concern the component in the plane (XY) of the ray propagation direction, referred to herein as the "in-plane component" or "component parallel to the major external surface of the LOE."

[0046] Note that the ray direction at the top of the field of view corresponds to the left side of the field of view reaching the observer's eye, while the ray direction at the bottom corresponds to the right side of the field of view. Note also that some reflections on the left side of the field of view will be reflected from facets near the right side of the LOE in a direction that does not reach the EMB and will therefore be lost. Similarly, some rays from the right side of the field of view will be reflected from facets near the left of the LOE and refracted in a direction that does not reach the EMB and will therefore be lost. Certain embodiments of the present invention take advantage of these observations to reduce the dimensions (and therefore volume and weight) of the first LOE (or LOE region).

[0047] In particular, Figure 2F illustrates, by shading, various regions of Figure 2E that are available for truncation, which do not contribute to the image reaching the EMB and therefore do not interfere with the image projection to the user's eyes. Note that the optical aperture for image injection from the image projector is in the lower half of the first region (16) of the LOE (12) because the portion of the image corresponding to downwardly angled rays, as shown, corresponds to the right side of the image field, which does not need to be reflected from facets closer to the left portion of the first region (16). This allows for a relatively compact implementation of the first region (16) of the LOE (12). Specifically, the extent of the LOE below the POD optical axis is selected so that rays from the POD aperture corresponding to the rightmost pixel of the field of view reach facets that refract them toward the entire region of the EMB, but facets are shortened in regions where such angles can no longer reach the EMB. Reducing the height of the first region (16) also causes a reduction in the X dimension, because reducing the LOE height brings the facets closer to the EMB, thus reducing the X dimension required to cover the desired range of FOV angles. Note that the terms “trimmed” and “truncated” here and elsewhere in this document are used to refer to a shape or dimension of the final product that is reduced relative to a theoretical starting point, such as the implementation of FIG. 2A, as a reference point. This terminology does not involve physically cutting material or implementing any other production techniques. It is not necessarily assumed that the LOE will be truncated exactly along the boundaries of the regions shown; rather, these regions provide design flexibility, allowing the LOE to terminate with any outer contour deemed aesthetically pleasing and / or mechanically compatible with additional details of the desired application.

[0048] It should be noted that the use of partial facets, as described above with reference to Figures 2D-2F, provides one or more of a number of advantages, including that the transfer of an image from a facet further from the coupling-in region does not have to pass through as many additional facets before reaching the second LOE region. Additional advantages are illustrated herein with reference to Figures 3A and 3B.

[0049] Specifically, Figure 3A illustrates a region of the facet labeled 17' outside the range of facet area necessary to transfer the projected image to the EMB (24). (This facet would typically be one of many, but is shown in isolation here to more easily explain its significance.) Figure 3A illustrates the ray path for a downwardly directed image ray that originates at the image projector and passes directly through the partially reflective surface. This ray travels (propagating by total internal reflection) into the second region (18), where it strikes one of a second set of partially reflective surfaces (19), and, as shown, is partially reflected, generating an unwanted "ghost" reflection that propagates upward back into the first region (16). The angle of this ray may be reflected from the extension of facet 17' in a direction toward the EMB (24), which may create a visible ghost that interferes with the viewed image.

[0050] Figure 3B, in contrast, illustrates what happens to the same ghost ray if the facets are placed only in a reduced area at or near the area needed to form the output image. In this case, the ray reflected from surface (19) and redirected back up into first region (16) does not encounter any partially reflective surfaces as it propagates through the first region of the LOE. As a result, the ray continues until it reaches the outer edge of the LOE, where it is absorbed or scattered, preferably by a suitably prepared nonreflective surface.

[0051] In the example of Figures 2A-2F, the dimension of the first LOE region (16) above the optical axis of the POD (14) cannot be significantly reduced because the leftmost region of the FOV must be reflected from the leftmost facet of the LOE. Figures 4A-5B show an alternative approach, in accordance with a further feature of certain particularly preferred implementations of the present invention, that allows for further reduction in the dimension of the first LOE region (16).

[0052] Specifically, in the arrangement of FIG. 4A , the POD and / or coupling-in prism are rotated so that the central optical axis of the image projection is angled downward across the first LOE region (16) at an angle most preferably selected so that the extreme left edge of the FOV is projected approximately parallel to the X-axis. In this case, the POD coupling-in is preferably at or near the extreme top edge (typically the upper third) of the first LOE region (16). The required dimensions of the LOE below the POD aperture are determined by geometric considerations similar to those described with reference to FIGS. 2A-2F : all image rays must encounter facets that are appropriately positioned and angled to deliver the corresponding region of the projected FOV to the entire EMB. The rightmost rays are inclined at a steeper angle in this case, and the facet angles are adjusted accordingly, but the overall Y dimension of the first LOE is further reduced.

[0053] In some cases, and as particularly highlighted by the steeper angle illustrated on the right side of the field in FIG. 4A , the geometric requirements for “filling” the EMB require significantly different facet spacing between the right and left sides of the field. Thus, in the example illustrated in FIG. 4A , for the coupled-in optical aperture width shown, the left field is effectively filled by one side of the pixel beam reflected from one facet, while the other side of that beam is reflected from an adjacent facet. On the right side of the field, however, uniform facet spacing as illustrated results in a “black line” (shown here as a wide black line) within which image illumination is no longer present. If facet spacing were to be uniformly reduced, this would lead to the opposite problem of a bright stripe near the left side of the field. To address this issue, variable facet spacing is preferred, as illustrated by the partial set of facets shown in FIG. 4B , and the corresponding geometric constructs show how the facet spacing can be appropriately adjusted to “fill” the EMB for each extreme of the field. The facet spacing preferably varies gradually (although not necessarily continuously or linearly) across the LOE region (16).

[0054] As described above with reference to Figures 2A-2E, it is possible to identify the various facet regions necessary to provide partial reflection to fill the EMB image for each field (pixel) of the image, as illustrated for the two extreme fields in Figure 4C. Here again, by defining an "area" to include all areas of all facets necessary to provide the output image in the eye motion box (26), it is possible to implement a first region (16) of the LOE (12) with selectively positioned partially reflective surfaces whose extent varies across the first region in a manner completely similar in structure and function to that described above with reference to Figures 2D and 2E. A corresponding implementation of the overall optical system in this case is illustrated in Figure 5A. Figure 5B illustrates various additional regions of the first and second LOEs that do not contribute to image transfer and can be further trimmed as shown, depending on the needs of each particular application.

[0055] Thus, by positioning the image projector (14) with the image projector's in-plane component of the optical axis of the propagated image tilted toward the boundary of the second region (18) relative to the X-axis, and most preferably by ensuring that one extreme in-plane component of the propagated image's field of view is substantially parallel to the X-axis, further compactness of the overall configuration can be achieved compared to the configurations of Figures 2A-2F. In all other respects, the structure, functionality, and range of options for implementing the apparatus of Figures 4A-5B are as described above with reference to Figures 2A-3B.

[0056] In addition to tilting the optical axis of the image projector as illustrated in Figures 4A-5B, many other angular parameters may be used to achieve various adjustments to the properties of the optical system, various examples of which will now be illustrated with reference to Figures 6A-6D and 7.

[0057] First, referring to Figures 6A and 6B, which illustrate the geometric principles underlying the adjustment of the eye-motion box position across the width dimension of the second region of the LOE (12). In Figure 6A, an arrangement equivalent to Figures 2A-2F is shown, with the ray path corresponding to the central ray of the image as viewed from the center of the eye-motion box. This allows for the positioning of the center of the EMB.

[0058] FIG. 6B illustrates the effect of implementing a second region (18) of the LOE (12) with a facet (19) that is angularly offset with respect to the X-axis. In this case, the light rays forming the center of the field are shifted with the center of the eye-motion box, resulting in a horizontal displacement of the eye-motion box, which is useful when asymmetric placement of the EMB with respect to the LOE is required. In this context, the "elongation" of a facet is interpreted as the line of the facet intersecting a plane parallel to the major exterior surface of the LOE. An equivalent definition is the line of intersection between the plane containing the partially reflective surface and the major exterior surface. This line is referred to herein as the elongation of the facet parallel to the major exterior surface, or the "in-plane" elongation. The range of the "angular offset" with respect to the X-axis in this context depends on the range of horizontal offset required, but in some preferred cases, the range may be between 5 and 25 degrees, although both smaller and larger angular offsets are possible.

[0059] 6C and 6D, which illustrate further forms of adjustment that allow correction for “facial curvature” and / or convergence angle, as shown in FIG. 7. Specifically, FIG. 7 schematically illustrates a plan view of a near-eye display in which the LOEs are positioned at an angle relative to each other and can be worn with a “wraparound” frame shaped to (somewhat) follow the side-to-side curvature of the face. To achieve stereoscopic vision in such a configuration, correction for facial curvature is required so that the images are presented centered along parallel lines in space (the dashed-dotted lines in FIG. 7), offset horizontally relative to the normal to the LOEs. Additionally or alternatively, in various applications, particularly but not limited to indoor use, it is desirable to provide a convergence angle between the two displays so that objects viewed with both eyes appear to be positioned in a desired direction from the user through the displays. This correction also requires a refraction with a horizontal (X-axis) component from the normal to the LOE plane.

[0060] To achieve this correction, the image projector (14) and the first set of partially reflective surfaces (17) are oriented such that a propagation image coupled into the LOE from the image projector (14) is refracted by the facets (17) to produce a refracted propagation image that propagates with an in-plane component of its optical axis tilted relative to the Y-axis. As a result of this offset, after coupling out by the facets (19), the optical axis of the coupled-out image is refracted in the horizontal plane, i.e., tilted with a non-zero component of tilt relative to the normal to the major exterior surface along the elongation direction in the plane of the second set of partially reflective surfaces, as shown in FIG. 6D.

[0061] Although these adjustments have been presented as independent adjustments, the various parameters of the projector optical axis tilt, the facet angle of the first LOE region, and the facet angle of the second LOE region are interrelated, and a variation in one of these parameters requires a corresponding adjustment in the other parameters to ensure transfer of the entire field of view, and these adjustments may result in a rotation of the injected image about its central axis, which can be directly corrected by rotating the projector and / or coupling arrangement as schematically illustrated in FIG. 6D.

[0062] 1B, all of the above principles can also be applied to a "sideway" configuration, in which an image is injected from a POD located vertically outside the viewing area for coupling into the user's eyes and spread vertically by a first set of facets and then horizontally by a second set of facets. It should be understood that all of the above configurations and variations are also applicable to side-injection configurations.

[0063] Throughout the above description, reference is made to the X-axis and Y-axis as indicated, where the X-axis corresponds to the first dimension of optical aperture extension, either horizontal or vertical, and the Y-axis is the other major axis corresponding to the second dimension of extension. In this context, X and Y may be defined relative to the orientation of the device when worn on a user's head in an orientation generally defined by a support arrangement, such as the aforementioned eyeglass frames of FIGS. 1A and 1B. Other terms that generally appear with the definition of the X-axis include: (a) at least one straight line that delimits the eye motion box, which may be used to define a direction parallel to the X-axis; (b) the edges of the rectangular projected image are generally parallel to the X-axis and Y-axis; and (c) the boundary between the first region (16) and the second region (18) generally extends parallel to the X-axis.

[0064] It will be understood that the above description is intended to serve as an example only, and that many other embodiments are possible within the scope of the invention as defined in the appended claims.

Claims

1. 1. An optical system for directing image illumination injected at a coupling-in region to an eye motion box for viewing by a user's eye, the optical system including a light-directing optical element (LOE) formed of a transparent material, the LOE comprising: (a) a first region including a first set of planar, mutually parallel partially reflective surfaces having a first orientation; (b) a second region including a second set of planar, mutually parallel partially reflective surfaces having a second orientation non-parallel to the first orientation; (c) a set of mutually parallel major exterior surfaces that extend across the first region and the second region such that the first set of partially reflective surfaces and the second set of partially reflective surfaces are both located between the major exterior surfaces; wherein the second set of partially reflective surfaces is at an oblique angle with respect to the major exterior surfaces such that a portion of image illumination propagating within the LOE from the first region to the second region by internal reflection at the major exterior surfaces is coupled out of the LOE towards an eye motion box, and wherein the first set of partially reflective surfaces is oriented such that a portion of image illumination propagating within the LOE from the coupling-in region is refracted towards the second region by internal reflection at the major exterior surfaces; wherein each of the partially reflective surfaces of the first set of partially reflective surfaces includes a partially reflective coating at a junction plane between two plates forming part of the LOE, and wherein the partially reflective coating is located on a first portion of the junction plane and at least one of the partially reflective surfaces has a second portion of the junction plane that is coupled to form an optical continuum between the two plates.

2. 2. The optical system of claim 1, wherein a range of ray paths propagating within the LOE from a coupling-in region, refracted by one of the first set of partially reflective surfaces, and coupled out by one of the second set of partially reflective surfaces toward reaching an eye motion box defines an image region of the one of the first set of partially reflective surfaces, and wherein a region of the one of the first set of partially reflective surfaces located outside the range defines a non-image region of the one of the first set of partially reflective surfaces, and wherein a majority of the non-image regions combine to form an optical continuum between the two plates.

3. 2. The optical system of claim 1, wherein the first set of partially reflective surfaces has a non-uniform spacing such that the spacing between adjacent partially reflective surfaces near the coupling-in region is smaller than the spacing between adjacent partially reflective surfaces farther from the coupling-in region.

4. 2. The optical system of claim 1, further comprising: an image projector for projecting a collimated image having a field of view about an optical axis; the image projector is optically coupled to the LOE to introduce the collimated image into the LOE at the coupling-in region as a propagation image that propagates within the LOE by internal reflection at the major exterior surfaces; the propagation image is partially reflected by the first set of partially reflective surfaces to produce a refracted propagation image that propagates within the LOE by internal reflection at the major exterior surfaces; and the refracted propagation image is partially reflected by the second set of partially reflective surfaces to produce a coupling-out image that is directed outward from one of the major exterior surfaces toward an eye motion box, the optical axis of the coupling-out image being tilted with respect to a normal to the major exterior surfaces having a non-zero component of tilt along an elongation direction in the plane of the second set of partially reflective surfaces.

5. 2. The optical system of claim 1, wherein the optical system is configured to project an image onto an eye motion box with major axes including an X-axis corresponding to a first horizontal or vertical axis of the projected image and a Y-axis corresponding to the other axis of the projected image, and wherein the second set of partially reflective surfaces has an elongation direction parallel to the major exterior surface, the elongation direction having an angular offset with respect to the X-axis.

6. 2. The optical system of claim 1, wherein the optical system is configured to project an image onto an eye motion box with major axes including an X-axis corresponding to a first horizontal or vertical axis of the projected image and a Y-axis corresponding to the other axis of the projected image, the optical system further comprising an image projector for projecting a collimated image having a field of view angle about the optical axis, the image projector being optically coupled to the LOE to introduce the collimated image into the LOE at the coupling-in region as a propagation image that propagates within the LOE by internal reflection at the major external surface, and wherein an in-plane component of the optical axis of the propagation image is tilted toward a boundary of the second region with respect to the X-axis.

7. The optical system of claim 6 , wherein an in-plane component at one end of the field of view of the propagated image is substantially parallel to an X-axis.

8. 2. The optical system of claim 1, wherein the optical system is configured to project an image onto an eye motion box with major axes including an X-axis corresponding to a first horizontal or vertical axis of the projected image and a Y-axis corresponding to the other axis of the projected image, the optical system further comprising an image projector for projecting a collimated image having a field of view angle about the optical axis, the image projector being optically coupled to the LOE at the coupling-in region to introduce the collimated image into the LOE as a propagation image that propagates within the LOE by internal reflection at the major external surfaces, the propagation image being partially reflected by the first set of partially reflective surfaces to generate a refracted propagation image that propagates within the LOE by internal reflection at the major external surfaces, and an in-plane component of the optical axis of the refracted propagation image being tilted with respect to the Y-axis.

9. An optical system for projecting an image injected at a coupling-in region for viewing by a user's eyes at an eye motion box, the image being viewed with major axes including an X-axis corresponding to a horizontal or vertical axis of the projected image and a Y-axis corresponding to an axis of the projected image perpendicular to the X-axis, the optical system including a light-guiding optical element (LOE) formed of a transparent material, the LOE comprising: (a) a first region including a first set of planar, mutually parallel partially reflective surfaces having a first orientation; (b) a second region including a second set of planar, mutually parallel partially reflective surfaces having a second orientation non-parallel to the first orientation; (c) a set of mutually parallel major exterior surfaces that extend across the first region and the second region such that the first set of partially reflective surfaces and the second set of partially reflective surfaces are both located between the major exterior surfaces; wherein the second set of partially reflective surfaces is at an oblique angle with respect to the major exterior surfaces such that a portion of image illumination propagating within the LOE from the first region to the second region by internal reflection at the major exterior surfaces is coupled out of the LOE towards an eye motion box, and wherein the first set of partially reflective surfaces is oriented such that a portion of image illumination propagating within the LOE from the coupling-in region is refracted towards the second region by internal reflection at the major exterior surfaces; and wherein the second set of partially reflective surfaces has an elongation direction parallel to the major exterior surface, the elongation direction having an angular offset with respect to the X-axis.

10. An optical system for projecting an image injected at a coupling-in region for viewing by a user's eyes at an eye motion box, the image being viewed with major axes including an X-axis corresponding to a horizontal or vertical axis of the projected image and a Y-axis corresponding to an axis of the projected image perpendicular to the X-axis, the optical system including a light-guiding optical element (LOE) formed of a transparent material, the LOE comprising: (a) a first region including a first set of planar, mutually parallel partially reflective surfaces having a first orientation; (b) a second region including a second set of planar, mutually parallel partially reflective surfaces having a second orientation non-parallel to the first orientation; (c) a set of mutually parallel major exterior surfaces that extend across the first region and the second region such that the first set of partially reflective surfaces and the second set of partially reflective surfaces are both located between the major exterior surfaces; wherein the second set of partially reflective surfaces is at an oblique angle with respect to the major exterior surfaces such that a portion of image illumination propagating within the LOE from the first region to the second region by internal reflection at the major exterior surfaces is coupled out of the LOE towards an eye motion box, and wherein the first set of partially reflective surfaces is oriented such that a portion of image illumination propagating within the LOE from the coupling-in region is refracted towards the second region by internal reflection at the major exterior surfaces; the optical system further includes an image projector for projecting a collimated image having a field of view angle about an optical axis, the image projector being optically coupled to the LOE to introduce the collimated image into the LOE at the coupling-in region as a propagation image that propagates within the LOE by internal reflection at the major exterior surface, an in-plane component of the optical axis of the propagation image being tilted toward a boundary of the second region with respect to an X-axis.

11. The optical system of claim 10 , wherein an in-plane component at one end of the field of view of the propagated image is substantially parallel to an X-axis.

12. An optical system for projecting an image injected at a coupling-in region for viewing by a user's eyes at an eye motion box, the image being viewed with major axes including an X-axis corresponding to a horizontal or vertical axis of the projected image and a Y-axis corresponding to an axis of the projected image perpendicular to the X-axis, the optical system including a light-guiding optical element (LOE) formed of a transparent material, the LOE comprising: (a) a first region including a first set of planar, mutually parallel partially reflective surfaces having a first orientation; (b) a second region including a second set of planar, mutually parallel partially reflective surfaces having a second orientation non-parallel to the first orientation; (c) a set of mutually parallel major exterior surfaces that extend across the first region and the second region such that the first set of partially reflective surfaces and the second set of partially reflective surfaces are both located between the major exterior surfaces; wherein the second set of partially reflective surfaces is at an oblique angle with respect to the major exterior surfaces such that a portion of image illumination propagating within the LOE from the first region to the second region by internal reflection at the major exterior surfaces is coupled out of the LOE towards an eye motion box, and wherein the first set of partially reflective surfaces is oriented such that a portion of image illumination propagating within the LOE from the coupling-in region is refracted towards the second region by internal reflection at the major exterior surfaces; The optical system further includes an image projector for projecting a collimated image having a field of view angle about an optical axis, the image projector being optically coupled to the LOE to introduce the collimated image into the LOE at the coupling-in region as a propagation image that propagates within the LOE by internal reflection at the major external surfaces, the propagation image being partially reflected by the first set of partially reflective surfaces to generate a refracted propagation image that propagates within the LOE by internal reflection at the major external surfaces, an in-plane component of the optical axis of the refracted propagation image being tilted with respect to the Y-axis.

13. 13. The optical system according to claim 5, wherein the eye motion box is bounded by at least one straight line parallel to the X axis.

14. 13. The optical system of claim 5, wherein the projected image is a rectangular image having edges parallel to the X and Y axes.

15. 13. The optical system of claim 5, further comprising a support arrangement configured to support the LOE against a user's head in an orientation relative to the user's eyes such that one of the major exterior surfaces faces the user's eyes and the X-axis is oriented horizontally.

16. 13. The optical system of claim 5, wherein the first region and the second region are separated by a boundary extending parallel to the X-axis.

17. 1. An optical system for directing image illumination injected at a coupling-in region to an eye motion box for viewing by a user's eye, the optical system including a light-directing optical element (LOE) formed of a transparent material, the LOE comprising: (a) a first region including a first set of planar, mutually parallel partially reflective surfaces having a first orientation; (b) a second region including a second set of planar, mutually parallel partially reflective surfaces having a second orientation non-parallel to the first orientation; (c) a set of mutually parallel major exterior surfaces that extend across the first region and the second region such that the first set of partially reflective surfaces and the second set of partially reflective surfaces are both located between the major exterior surfaces; wherein the second set of partially reflective surfaces is at an oblique angle with respect to the major exterior surfaces such that a portion of image illumination propagating within the LOE from the first region to the second region by internal reflection at the major exterior surfaces is coupled out of the LOE towards an eye motion box, and wherein the first set of partially reflective surfaces is oriented such that a portion of image illumination propagating within the LOE from the coupling-in region is refracted towards the second region by internal reflection at the major exterior surfaces; and wherein the first set of partially reflective surfaces have non-uniform spacing such that a spacing between adjacent partially reflective surfaces near the coupling-in region is smaller than a spacing between adjacent partially reflective surfaces farther from the coupling-in region.

18. 1. An optical system for directing image illumination injected at a coupling-in region to an eye motion box for viewing by a user's eye, the optical system including a light-directing optical element (LOE) formed of a transparent material, the LOE comprising: (a) a first region including a first set of planar, mutually parallel partially reflective surfaces having a first orientation; (b) a second region including a second set of planar, mutually parallel partially reflective surfaces having a second orientation non-parallel to the first orientation; (c) a set of mutually parallel major exterior surfaces that extend across the first region and the second region such that the first set of partially reflective surfaces and the second set of partially reflective surfaces are both located between the major exterior surfaces; wherein the second set of partially reflective surfaces is at an oblique angle with respect to the major exterior surfaces such that a portion of image illumination propagating within the LOE from the first region to the second region by internal reflection at the major exterior surfaces is coupled out of the LOE towards an eye motion box, and wherein the first set of partially reflective surfaces is oriented such that a portion of image illumination propagating within the LOE from the coupling-in region is refracted towards the second region by internal reflection at the major exterior surfaces; The optical system further includes an image projector for projecting a collimated image having a field of view angle about an optical axis, the image projector being optically coupled to the LOE to introduce the collimated image into the LOE at the coupling-in region as a propagation image that propagates within the LOE by internal reflection at the major exterior surfaces, the propagation image being partially reflected by the first set of partially reflective surfaces to generate a refracted propagation image that propagates within the LOE by internal reflection at the major exterior surfaces, the refracted propagation image being partially reflected by the second set of partially reflective surfaces to generate a coupling-out image that is directed outward from one of the major exterior surfaces toward an eye motion box, the optical axis of the coupling-out image being tilted with respect to a normal to the major exterior surfaces having a non-zero component of tilt along an elongation direction in the plane of the second set of partially reflective surfaces.

Images