Prism-based ghost suppression for lightguide near-eye displays

Abstract

A near-eye display (10) includes a lightguide optical element (LOE) (12) with opposed major surfaces (12a, 12b), an image projector (14), a first region (16) having partially reflective surfaces (26, 27), and a second region (18) with an out-coupling arrangement (28). To suppress ghosts from single reflections at a facet or interface (25), an elongated light-deflecting structure (261, 271, 251) is provided on the first major surface (12a) adjacent thereto. The structure is configured so that a reverse-traced unguided ray from an eye-motion box (102) that would otherwise impinge the facet / interface is deflected so it does not impinge. A corrective light-deflecting structure (262, 272, 252) on the second major surface (12b) may counter-deflect rays to reduce impact on the peripheral vision. The light-deflecting structures provide beam steering without optical power and may be implemented as prisms or as diffractive / metasurface or volume-holographic elements, formed as discrete strips or portions of a continuous film.

Description

[0001] Prism-Based Ghost Suppression for Lightguide Near-Eye Displays

[0002] FIELD AND BACKGROUND OF THE INVENTION

[0003] The present invention relates to near-eye and head-mounted display systems that employ a lightguide optical element (LOE) to guide image light by total internal reflection. More particularly, it concerns suppression of ghost images produced by light from external sources that, after entering the LOE, follow a path including a single reflection at internal partially reflective surfaces of a first region of the LOE and / or at an interface between first and second regions of the LOE.

[0004] Waveguide -based near-eye displays commonly employ an LOE having opposed major surfaces that confine and convey image light by total internal reflection (TIR). In representative architectures, a first region of the LOE includes a set of mutually-parallel internal partially reflective surfaces (sometimes referred to herein, for brevity, as “facets”) that progressively redirect the guided image light from a first guided propagation direction to a second guided propagation direction. A second region of the LOE then out-couples the guided image light toward locations from which the image is intended to be viewed, referred to as an eye-motion box (EMB), while a support structure fixes the LOE’s position relative to the user’s head, thereby defining the geometry of the EMB relative to the LOE.

[0005] In practical use, bright external illumination, e.g., sunlight or overhead lighting, can give rise to objectionable ghost images within the user’s field of view. A particularly troublesome mechanism occurs when external light enters the LOE through a major surface, undergoes a single reflection at one of the internal partially reflective surfaces of the first region (which surfaces are typically steep relative to the major surfaces), and then exits the LOE toward the EMB. A similar single-bounce path can originate at a plane of connection between the first and second regions of the LOE, for example where an optical element such as a retarder is disposed at that interface. These ghosts may be especially prominent for above-horizontal, forward-field illumination and can degrade image contrast and user comfort in see-through applications.

[0006] SUMMARY OF THE INVENTION

[0007] The present invention is a display apparatus with suppression of real-world ghost images.

[0008] According to the teachings of an embodiment of the present invention there is provided, a display apparatus for displaying an image to a user, the display apparatus comprising: (a) a lightguide optical element (LOE) having first and second mutually parallel major surfaces for guiding light by internal reflection at the major surfaces; (b) an image projector optically coupled to the LOE so as to introduce into the LOE image light corresponding to a collimated image to propagate within the LOE in a first guided propagation direction by internal reflection at the major surfaces; and (c) a support structure configured to support the LOE relative to the user’s head with the first major surface in facing relation to an eye of the user located within an eye-motion box (EMB) relative to the LOE, wherein the LOE comprises: (i) a first region including a first set of mutually-parallel internal partially reflective surfaces configured to progressively redirect the image light propagating in the first guided propagation direction to propagate in a second guided propagation direction, and (ii) a second region including an out-coupling arrangement configured to progressively couple out the image light propagating in the second guided propagation direction through the first major surface toward the EMB, and wherein, for at least one of the internal partially reflective surfaces of the first set, an elongated light-deflecting structure is disposed on the first major surface and extends along at least part of a length of the internal partially reflective surface adjacent to a line of intersection between a plane containing the internal partially reflective surface and the first major surface, the light-deflecting structure being configured such that, for at least one location within the EMB , a reverse-traced unguided ray path emanating from that location that, in the absence of the light-deflecting structure, would have entered the first major surface and impinged upon the internal partially reflective surface is deflected at the light-deflecting structure so that it does not impinge on the internal partially reflective surface.

[0009] According to a further feature of an embodiment of the present invention, there is also provided a corrective light-deflecting structure disposed on the second major surface in opposing relation to the light-deflecting structure, the corrective light-deflecting structure being configured to counter-deflect external- scene rays that traverse the LOE toward the EMB so as to reduce an angular deviation of the external-scene rays introduced by the light-deflecting structure.

[0010] According to a further feature of an embodiment of the present invention, the lightdeflecting structure is configured such that substantially all reverse-traced unguided ray paths emanating from a central location within the EMB that, in the absence of the light-deflecting structure, would have entered the first major surface and impinged upon the internal partially reflective surface are deflected at the light-deflecting structure so that they do not impinge on the internal partially reflective surface.

[0011] According to a further feature of an embodiment of the present invention, the lightdeflecting structure is configured such that substantially all reverse-traced unguided ray paths emanating from an entirety of the EMB that, in the absence of the light-deflecting structure, would have entered the first major surface and impinged upon the internal partially reflective surface are deflected at the light-deflecting structure so that they do not impinge on the internal partially reflective surface.

[0012] According to a further feature of an embodiment of the present invention, elongated lightdeflecting structures are provided along a plurality of the internal partially reflective surfaces of the first set. According to a further feature of an embodiment of the present invention, different ones of the elongated light-deflecting structures have different widths and / or refractive deflection powers selected in accordance with facet position relative to the EMB and LOE thickness.

[0013] According to a further feature of an embodiment of the present invention, the elongated light-deflecting structures for successive facets are integrated into a continuous film attached to the first major surface.

[0014] According to a further feature of an embodiment of the present invention, the elongated light-deflecting structures are provided along a majority of the internal partially reflective surfaces of the first set.

[0015] According to a further feature of an embodiment of the present invention, at least one elongated light-deflecting structure extends on one or both sides of the line of intersection along the first major surface.

[0016] According to a further feature of an embodiment of the present invention, at least one elongated light-deflecting structure is integrally formed on a surface of an external lens that is in facing relation with the first major surface.

[0017] According to a further feature of an embodiment of the present invention, there is also provided an additional elongated light-deflecting structure disposed on the first major surface and extending along at least part of a length of an interface between the first and second regions, adjacent to a line of intersection between a plane containing the interface and the first major surface.

[0018] According to a further feature of an embodiment of the present invention, the additional elongated light-deflecting structure is configured to impart a position-invariant angular deflection without optical power.

[0019] According to a further feature of an embodiment of the present invention, each elongated light-deflecting structure comprises a wedge prism having a direction of elongation extending parallel to the line of intersection.

[0020] According to a further feature of an embodiment of the present invention, the wedge prism has a rear surface provided with a light- absorbing coating.

[0021] According to a further feature of an embodiment of the present invention, the wedge prism has a rear surface provided with a light- scattering texture.

[0022] There is also provided according to the teachings of an embodiment of the present invention, a display apparatus for displaying an image to a user, the display apparatus comprising: (a) a lightguide optical element (LOE) having first and second mutually parallel major surfaces for guiding light by internal reflection at the major surfaces; (b) an image projector optically coupled to the LOE so as to introduce into the LOE image light corresponding to a collimated image to propagate within the LOE in a first guided propagation direction by internal reflection at the major surfaces; and (c) a support structure configured to support the LOE relative to the user’s head with the first major surface in facing relation to an eye of the user located within an eyemotion box (EMB) relative to the LOE, wherein the LOE comprises: (i) a first region including a reflective or diffractive arrangement configured to progressively redirect the image light propagating in the first guided propagation direction to propagate in a second guided propagation direction, (ii) a second region including an out-coupling arrangement configured to progressively couple out the image light propagating in the second guided propagation direction through the first major surface toward the EMB, (iii) an interface between the first region and the second region, and (iv) an elongated light-deflecting structure disposed on the first major surface extending along at least part of a length of the interface adjacent to a line of intersection between a plane containing the interface and the first major surface, the light-deflecting structure being configured such that, for at least one location within the EMB, a reverse-traced unguided ray path emanating from that location that, in the absence of the light-deflecting structure, would have entered the first major surface and impinged upon the interface is deflected at the light-deflecting structure so that it does not impinge on the interface.

[0023] According to a further feature of an embodiment of the present invention, there is also provided a corrective light-deflecting structure disposed on the second major surface in opposing relation to the light-deflecting structure, the corrective light-deflecting structure being configured to counter-deflect external- scene rays that traverse the LOE toward the EMB so as to reduce an angular deviation of such rays introduced by the light-deflecting structure.

[0024] According to a further feature of an embodiment of the present invention, the interface includes an optical element configured to modify a polarization state of light propagating within the LOE.

[0025] According to a further feature of an embodiment of the present invention, the elongated light-deflecting structure comprises a refractive prism.

[0026] There is also provided according to the teachings of an embodiment of the present invention, a display apparatus for displaying an image to a user, the display apparatus comprising: (a) a lightguide optical element (LOE) having first and second mutually parallel major surfaces for guiding light by internal reflection at the major surfaces; (b) an image projector optically coupled to the LOE so as to introduce into the LOE image light corresponding to a collimated image to propagate within the LOE in a first guided propagation direction by internal reflection at the major surfaces; and (c) a support structure configured to support the LOE relative to an eye of the user located within an eye-motion box (EMB) relative to the LOE; wherein the LOE comprises: (i) a first region including a first set of mutually-parallel internal partially reflective surfaces configured to progressively redirect the image light propagating in the first guided propagation direction to propagate in a second guided propagation direction, and (ii) a second region including an out-coupling arrangement configured to progressively couple out the image light propagating in the second guided propagation direction toward the EMB; and wherein a first prismatic array is disposed on the first major surface and a second prismatic array is disposed on the second major surface, each prismatic array being provided at least in zones located adjacent to a plurality of the internal partially reflective surfaces of the first set, each zone extending along at least part of a length of a corresponding one of the internal partially reflective surfaces and comprising one or more elongate prisms having ridges elongated in a direction substantially parallel to the length of the internal partially reflective surfaces, the first and second prismatic arrays being arranged to change directions of external-scene light passing into and through the LOE to reduce world-ghost reflections from the internal partially reflective surfaces reaching the EMB, the second prismatic array being configured to at least partially compensate for a direction-turning effect introduced by the first prismatic array.

[0027] BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein:

[0029] FIGS. 1 A and IB are schematic isometric views of an optical system including two displays each implemented using a lightguide optical element (LOE), constructed and operative according to the teachings of an embodiment of the present invention, illustrating a top-down and a sideinjection configuration, respectively.

[0030] FIG. 2 is a schematic of the LOE showing an image-ray path propagating by internal reflection, reflecting at an internal partially reflective surface (or “facet”) in a first region, passing an interface between regions, and entering a second region for out-coupling.

[0031] FIG. 3 is the schematic of FIG. 2 with an external- source ray path illustrated, showing a single-reflection ghost path toward the EMB.

[0032] FIG. 4A is an extracted detail of FIG. 3 isolating a first-region facet and the associated ghost-producing ray path.

[0033] FIG. 4B is a sectional view in a plane perpendicular to the LOE major surfaces and a plane containing the first-region facet, with the ghost-forming ray path of FIG. 4A projected onto that plane.

[0034] FIG. 5 is analogous to FIG. 3, illustrating a ghost path from a lower-quadrant external source.

[0035] FIG. 6A is an extracted detail of FIG. 5 isolating the surface and ray path. FIG. 6B is sectional view in a plane perpendicular to the LOE major surfaces and a plane containing the first-region facet, with the ghost-forming ray path of FIG. 6A projected onto that plane.

[0036] FIG. 7 is analogous to FIGS. 3 and 5, illustrating a ghost path reflecting from an interface between first and second regions.

[0037] FIG. 8A is a schematic cross-sectional view analogous to FIG. 4B, illustrating an embodiment of the present invention with a prism structure on the first major surface adjacent to an internal partially reflective surface together with a corrective prism structure on the second major surface in opposing relation, and showing representative reverse-traced and external-source rays.

[0038] FIG. 8B is a schematic cross-sectional view analogous to FIG. 6B, illustrating an embodiment of the present invention with a prism structure on the first major surface adjacent to an internal partially reflective surface together with a corrective prism structure on the second major surface in opposing relation, and showing representative reverse-traced and external-source rays for the lower-incident facet case.

[0039] FIG. 8C is a schematic plan view looking down along a plane of an interface between the first and second regions of the LOE, illustrating an embodiment of the present invention that addresses the ghost- forming mechanism of FIG. 7 by providing prism structures along the interface on the first and second major surfaces in opposing relation, and showing representative reverse- traced and external- source rays.

[0040] FIG. 9A is a schematic cross-sectional view similar to FIG. 4B, showing a bundle of reverse-traced rays from the eye in the absence of prisms (illustrating ghost-forming paths).

[0041] FIG. 9B is a schematic cross-sectional view, similar to FIG. 9A, illustrating an embodiment of the present invention in which the bundle of potentially ghost-forming reverse-traced rays are deflected by a prism on the first major surface, but without a prism on the second major surface, and illustrating an exceptional ray incident on a prism step.

[0042] FIG. 9C is a schematic cross-sectional view similar to FIG. 9A, illustrating an embodiment of the present invention in which the bundle of potentially ghost-forming reverse-traced rays are deflected by prisms on both major surfaces and illustrating an additional exceptional ray that bypasses the first-surface prism and is refracted by the second-surface prism.

[0043] FIG. 10 is a schematic cross-sectional view showing multiple internal partially reflective surfaces at different positions within the first region and illustrating how prism parameters and ray behaviors vary with angle of incidence; in each case, reverse-traced rays are shown, with the central rays refracted by the prisms to propagate within the lightguide substantially parallel to the plane containing the corresponding facet, and with exit ray directions restored by the corrective prism structure.

[0044] FIG. 11 A is a schematic cross-sectional view illustrating variation of incident angles across the eye-motion box, showing reverse-traced rays from lower, central, and upper locations; the central and lower rays achieve ghost elimination while the upper ray is refracted to a direction close to parallel to the internal partially reflective surface, yielding limited residual susceptibility.

[0045] FIG. 1 IB is a schematic cross-sectional view illustrating a configuration in which prism parameters are selected so that reverse-traced rays from upper and lower extremities of the eyemotion box are refracted to directions that eliminate ghost formation across the entire eye-motion box, with exit angles correspondingly compensated by the corrective prism structure.

[0046] FIG. 12 is a schematic system-level view analogous to FIG. 2, illustrating a representative embodiment in which prism structures are provided adjacent to multiple internal partially reflective surfaces of the first region and along the interface, on both major surfaces of the lightguide.

[0047] FIGS. 13 A and 13B are schematic side and top views, respectively, of a lightguide optical element with a push-and-pull external lens pair, showing prisms formed on inward-facing surfaces of the lenses adjacent to internal partially reflective surfaces and along the interface, representing an implementation in which the prisms are integrated with external optics.

[0048] DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0049] According to certain preferred embodiments of the present invention, there is provided a near-eye display apparatus 10 that includes a lightguide optical element 12 having opposed major surfaces 12a, 12b that guide image light by total internal reflection. An image projector assembly 14 is optically coupled to the lightguide so as to introduce image light corresponding to a collimated image that propagates within the lightguide in a first guided propagation direction by internal reflection at the major surfaces. A support structure 20 positions the lightguide relative to the user’ s head so that a viewer’ s eye 100 is located within an eye-motion box 102 defined spatially in relation to the lightguide.

[0050] The lightguide includes a first region 16 that includes an image redirection arrangement that progressively redirects the image light from the first direction to a second direction while expanding the optical aperture of the image in a first dimension. In representative implementations, the image redirection arrangement of the first region includes a set of mutually parallel internal partially reflective surfaces, labeled 26 or 27 according to criteria which will be detailed below. These surfaces progressively redirect the guided image light from the first guided propagation direction to a second guided propagation direction. The lightguide further includes a second region 18 with an out-coupling arrangement, which may include internally reflective out-coupling surfaces 28 or a diffractive out-coupler, that progressively couples out the guided image light toward the eye-motion box.

[0051] Displays of this type sometimes suffer from real-world ghost images. One class of real- world ghost images that is of particular concern can arise from external illumination entering the LOE 12 through a major surface and following a light path passing through the LOE that includes a single reflection at an internal partially reflective surface of the first region 16 or at an interface 25 between the first region 16 and the second region 18, and then exiting toward the eye-motion box 102. Such paths are common for bright overhead or off-axis sources, and they are distinct from any stray light originating within the image projector assembly 14.

[0052] According to particularly preferred embodiments of the present invention, suppression of the above single-reflection ghost paths is achieved by providing, on the first major surface, elongated light-deflecting prism structures positioned adjacent to internal partially reflective surfaces of the first region and / or adjacent to the interface between the first and second regions. Each prism structure extends along at least part of the length of the corresponding internal surface and is configured such that, for at least one location within the eye-motion box (EMB), at least one reverse-traced unguided ray that would otherwise enter through the first major surface and impinge the corresponding internal partially reflective surface or the interface is redirected (e.g., deflected by refraction at the prism structure) so that it does not impinge thereon. In certain embodiments, a corrective prism structure is provided on the second major surface in opposing relation to the lightdeflecting prism structure to counter-deflect external- scene rays traversing the LOE, thereby reducing impact on the user’s peripheral view. The prism structures may be provided along a plurality or majority of the internal partially reflective surfaces of the first region, may have differing widths and refractive powers tailored to local geometry and LOE thickness, and may be implemented as discrete strips or as portions of a continuous prism film extending over an expanded area of the first major surface.

[0053] The following terms are used for clarity in the detailed description. They are intended to be consistent with the claims and figures.

[0054] • Lightguide optical element (LOE, 12): a waveguide structure with opposed major surfaces (12a, 12b) configured to guide image light by total internal reflection.

[0055] • Internal partially reflective surface: one or more internal surfaces within the LOE that exhibit partial reflectance, typically dependent on angle of incidence and / or polarization, used to redirect light propagating within the LOE. Depending on the angle of these surfaces, the redirection may be toward a second direction of guided propagation within the LOE or toward out-coupling to direct image light to the viewer’ s eye. • Interface (25): a plane of connection between the first region and the second region. The interface can include an optical element such as a retarder. For the drawings and description, the interface is referenced as 25 without separately numbering the optical element.

[0056] • Structures on opposite major surfaces are in opposing relation when their orthogonal projections onto a reference plane parallel to the major surfaces overlap, at least partially, preferably over a majority of their areas, and most preferably, fully overlap.

[0057] • Eye-motion box (EMB, 102): locations from which the projected image is intended to be viewed, defined spatially in relation to the LOE.

[0058] • As used herein, a reverse-traced unguided ray path is a light path traced from a point in the EMB into the LOE (by optical reciprocity) that (i) enters through a major surface of the LOE, and (ii) is not confined by total internal reflection between the major surfaces before reaching an internal partially reflective surface or an interface.

[0059] • As used herein, substantially all reverse-traced unguided ray paths refers to all reverse- traced unguided ray paths which pass through the primary optical surfaces of the relevant components but excludes exceptional subsets of such rays that circumvent the primary optical surfaces. Examples of such exceptional subsets include rays that are incident on surfaces such as step surfaces of a prism structure or other chamfers, fillets or the like, rather than on its refracting facets. Such rays may in some cases be associated with a negligible contribution to formation of real-world ghost images. In other cases, where such contributions are potentially disturbing to the user, additional ghost suppression features may be employed to suppress ghost generation by such exceptional ray paths, as will be addressed below.

[0060] • Line of intersection: the line defined by the intersection of a plane containing an internal partially reflective surface, or the interface, with a major surface of the LOE. The length of an internal partially reflective surface or interface refers to the dimension of the surface as measured along the line of intersection.

[0061] • Substantially an entire length: at least ninety percent of the length of the corresponding internal partially reflective surface along the relevant line of intersection.

[0062] • Majority: when referring to a collection of elements, more than one half in number of the elements in that collection; when referring to a continuous quantity, more than one half of the magnitude of that quantity, for example, a majority of a length.

[0063] • Light-deflecting structure: an elongate feature disposed on a major surface of the LOE and used to deflect (i.e., change the direction of) a light ray entering or exiting the LOE relative to the path that would be followed by the ray undergoing refraction at the LOE surface in the absence of the light-deflecting structure. The type of deflection referred to here is a deflection without optical power, i.e., resulting neither in convergence or divergence of rays incident on the structure. This property can also be referred to as being “position-invariant” in that, over a relevant area, the extent of the ray deflection does not vary as a function of the position at which it is incident. Throughout this description, the light-deflecting structures will be illustrated in a particularly preferred but non-limiting example as refractive wedge prism structures. It should be noted however that the invention applies equally to implementations employing other technologies for light deflection, preferably without optical power. Examples include, but are not limited to, two- dimensional diffractive optical elements such as a surface-relief diffractive optical element, a metasurface array of subwavelength elements, and a volume holographic grating.

[0064] • Width and thickness: width refers to the in-plane dimension of a light-deflecting structure (e.g., prism) measured along the major surface and perpendicular to the line of intersection; thickness refers to the dimension of a light-deflecting structure perpendicular to the major surfaces, the same axis as the thickness of the LOE.

[0065] • Opacity: one minus transmittance across a visible spectral band, optionally averaged over polarization (for example, opacity of at least ninety percent).

[0066] • External light source: any light source outside the LOE that emits light which can enter the LOE and follow a path that includes a single reflection at an internal partially reflective surface or at the interface.

[0067] FIGS. 1A and IB are schematic isometric views of an optical system including two displays, each implemented using a lightguide optical element (LOE), constructed and operative according to an embodiment disclosed herein, illustrating a top-down configuration and a sideinjection configuration, respectively.

[0068] A near-eye display 10 employs a compact image projector assembly 14 integrated so as to inject an image into a lightguide optical element (LOE, also referred to as a waveguide, a substrate or a slab) 12 within which the image light is trapped by internal reflection at a pair of mutually parallel major external surfaces. The LOE 12 typically includes an arrangement for expanding the optical aperture of the injected image in one or two dimensions, and for coupling out the image illumination toward the eye of an observer. In representative implementations, these functions are based on internal partially reflecting surfaces or on diffractive optical elements.

[0069] In one non-limiting set of implementations, the light injected into LOE 12 by image projector assembly 14 impinges on a set of partially reflecting surfaces that are parallel to each other and inclined obliquely to a direction of propagation of the image light. Each successive surface deflects a proportion of the image light into a deflected direction that remains guided by internal reflection within the substrate. These surfaces, which are not illustrated individually in FIGS. 1A and IB, are located in a first region 16. This partial reflection at successive surfaces progressively redirects the direction of guided propagation while expanding the optical aperture in a first dimension. The redirected image illumination then passes into a second region 18, which may be implemented as an adjacent distinct substrate or as a continuation of a single substrate, in which a coupling-out arrangement, either a further set of partially reflective surfaces or a diffractive optical element, progressively couples out a proportion of the image illumination toward an eye located within an eye-motion box 102, thereby achieving a second dimension of optical aperture expansion.

[0070] The overall device may be implemented separately for each eye, and is preferably supported relative to the head of a user with each LOE 12 facing a corresponding eye 100. A support arrangement 20 may be implemented as an eyeglass frame with sides for supporting the device relative to the user’s ears. Other forms of support arrangement may also be used, including head bands, visors, or devices suspended from helmets.

[0071] Reference is made to an X axis which extends in the general extensional direction of the first region of the LOE, and to a Y axis which extends perpendicular thereto. In FIG. 1A the X axis is horizontal and the Y axis is vertical. In FIG. IB the X axis is vertical and the Y axis is horizontal. In approximate terms, the first region 16 may be considered to achieve aperture expansion in the X direction while the second region 18 achieves aperture expansion in the Y direction. For simplicity of presentation in subsequent drawings, the invention will be exemplified in the context of an LOE with orientation similar to FIG. IB, with the understanding that the same principles apply to aperture-expansion lightguides with other orientations or designs.

[0072] The image injected into the lightguides is preferably a collimated image, in which light of each image pixel is a parallel beam, collimated to infinity, with an angular direction corresponding to pixel position so that the image illumination spans an angular field of view in two dimensions. The near-eye display 10 may include additional components such as a controller 22 for actuating image projector 14, powered by an onboard battery or another suitable power source. The projector technology and coupling approach are not limiting, and additional options are described later in the detailed description.

[0073] FIG. 2 is a schematic illustration of LOE 12 corresponding to the side-injection arrangement of FIG. IB illustrating a typical ray path 31 followed by image light. Image light from projector 14 enters the LOE 12, is guided by internal reflection between major surfaces 12a, 12b, and impinges on an internal partially reflective surface in the first region 16 (illustrated as 26) which progressively redirects the guided image light from a first guided propagation direction to a second guided propagation direction. The redirected image light passes through an interface 25 and into the second region 18, where an out-coupling arrangement, for example reflective out- coupling surfaces 28 or a diffractive out-coupler, directs the image light toward the viewer’ s eye 100 located within the EMB designated by rectangle 102.

[0074] The internal structures of LOE 12 may give rise to various real-world ghost images that are addressed by various aspects of the present invention. For clarity in the following figures, reference will be made to three groups of real-world ghost paths:

[0075] 1. Upper-incident facet ghosts: external light entering a major surface of the LOE 12, following a path that includes a single reflection at an internal partially reflective surface in the first region 16, then exiting toward the EMB 102 from above-horizontal or upperforward directions. In the drawings these first-region surfaces are labeled 26.

[0076] 2. Lower-incident facet ghosts: analogous single-reflection paths arising from below- horizontal incidence, involving first-region surfaces labeled 27.

[0077] 3. Interface ghosts: paths including reflection at an interface 25 between the first region 16 and the second region 18.

[0078] These groups of ghost image ray paths will be illustrated below as they occur in the absence of the ghost-suppressing features of the present invention, and then, a preferred deployment of prism-based ghost suppression features for each will be described.

[0079] Turning now to FIG. 3, this presents the same schematic view as FIG. 2 but shows an external-source ghost path. Light from an external source incident in certain particular directions enters the LOE 12 through a major surface (somewhat bent by refraction, not shown here), and follows a path that includes a single reflection at an internal partially reflective surface in the first region 16 (labeled 26 in this upper-incident case). The reflected light then exits the LOE toward the EMB 102, generating a real-world ghost. This view establishes the geometry of the upperincident facet ghost family.

[0080] FIG. 4A isolates the elements of FIG. 3 that participate in the ghost path. A single internal partially reflective surface 26 of the first region 16 is shown together with the incident external light and the resulting single-reflection path toward the EMB 102. The surrounding portions of the LOE 12 are omitted for clarity.

[0081] FIG. 4B shows a sectional view through FIG. 3 taken in a sectional view in a plane perpendicular to the LOE major surfaces and to the plane containing the first-region facet, with the ghost-forming path of FIG. 4A projected onto that plane. The external source is depicted to the left. A representative ray enters through the left major surface of the LOE 12, impinges on an upper side of the internal partially reflective surface 26 (drawn horizontally in this view), and reflects upward and to the right to exit the LOE toward the eye 100 and the EMB 102. This sectional representation makes the single-reflection path of the upper-incident facet ghost explicit. Turning now to FIG. 5, this view is analogous to FIG. 3 but illustrates a lower-incident facet ghost. Light from an external source in a lower quadrant enters the LOE 12 through a major surface (somewhat bent by refraction, not shown here), and follows a path that includes a single reflection at an internal partially reflective surface in the first region 16 (labeled 27 for this lower- incident case). The reflected light then exits the LOE toward the EMB 102, establishing the geometry of the lower-incident facet ghost family.

[0082] FIG. 6A isolates the elements of FIG. 5 that participate in the ghost path. A single internal partially reflective surface 27 of the first region 16 is shown together with the incident external light and the resulting single-reflection path toward the EMB 102. Surrounding portions of the LOE 12 are omitted for clarity.

[0083] FIG. 6B shows a sectional view through FIG. 5 taken in a sectional view in a plane perpendicular to the LOE major surfaces and to the plane containing the first-region facet, with the ghost-forming path of FIG. 6A projected onto that plane. The external source is depicted to the left. A representative ray enters through the left major surface of the LOE 12, impinges on a lower side of the internal partially reflective surface 27 (drawn horizontally in this view), and reflects downwards and to the right to exit the LOE toward EMB 102. This sectional representation makes the single-reflection path of the lower-incident facet ghost explicit.

[0084] Turning now to FIG. 7, this view is analogous to FIGS. 3 and 5 but illustrates an interface ghost. Light from an external source above the LOE enters through a major surface 12b (somewhat bent by refraction, not shown here), and follows a path that includes a single reflection at the interface 25 between the first region 16 and the second region 18, after which the light exits the LOE toward the EMB 102. This establishes the geometry of the interface-reflection ghost family.

[0085] FIG. 8A illustrates an embodiment for the upper-incident facet ghost family, i.e., the ghost scenario of FIG. 4B. A light-deflecting structure 261 is formed on the first major surface 12a adjacent to an internal partially reflective surface 26 of the first region 16, and a corrective lightdeflecting structure 262 is formed on the second major surface 12b in opposing relation to the prism structure 261. Here and throughout the drawings, the various light-deflecting structures are exemplified as prism structures, typically elongated wedge prisms, oriented to extend parallel to the corresponding internal surface of the LOE. Other alternative implementation options will be discussed below.

[0086] A representative reverse-traced unguided ray from a location within the eye-motion box 102, depicted as a dashed ray, that would, absent the prism structure, enter through the first major surface 12a and impinge the internal partially reflective surface 26, is refracted at the prism structure 261 so that within the lightguide optical element 12 it propagates without impinging on the internal partially reflective surface 26. After traversing the lightguide optical element 12, the ray is refracted at the corrective prism structure 262 so that the exit direction is closer to that which would have been observed without the prism structure 261, thereby reducing impact on the user’s peripheral view. A representative external-source ray from an external light source 50, shown as a solid ray, follows a modified path in the presence of the prisms and does not produce a ghost at the eye-motion box 102. The suppression mechanism derives from the fact that reverse-traced unguided rays from the eye-motion box 102 do not reach the internal partially reflective surface 26 which, by symmetry, excludes the possibility of externally-originating rays following such a path. In other words, if the eye cannot “see” the facet, reflection of an unguided ray at that facet cannot give rise to a ghost ray path reaching the eye.

[0087] FIG. 8B illustrates a corresponding embodiment that addresses the lower-incident facet ghost scenario of FIG. 6B. A light-deflecting structure 271 (e.g., a prism structure) is formed on the first major surface 12a adjacent to an internal partially reflective surface 27 of the first region 16, and a corrective light-deflecting structure 272 (e.g., a prism structure) is formed on the second major surface 12b in opposing relation to the prism structure 271. Representative reverse-traced unguided rays that would otherwise impinge the internal partially reflective surface 27 are refracted at the prism structure 271 so that they do not impinge the internal partially reflective surface 27, and are thereafter refracted at the corrective prism structure 272 on exit to reduce change in external- scene angles. A representative external-source ray from the external light source 50 is shown for context.

[0088] FIG. 8C illustrates in top view an embodiment for addressing the interface-reflection ghosts of FIG. 7. A light-deflecting structure 251 (e.g., a prism structure) is formed on the first major surface 12a adjacent to the interface 25 between the first region 16 and the second region 18, and a corrective light-deflecting structure 252 (e.g., a prism structure) is formed on the second major surface 12b in opposing relation to the prism structure 251. A representative reverse-traced unguided ray that would, absent the prism structure, impinge the interface 25, is refracted at the prism structure 251 so that it does not impinge the interface 25, and is thereafter refracted at the corrective prism structure 252 on exit. A representative external- source ray from the external light source 50 is shown for context. It should be noted that the disclosed structures for reducing real- world ghost reflections from interface 25 constitute a free-standing aspect of the present invention which may be used to advantage in near-eye displays independent of the lightguide technology used in first and second regions 16 and 18, including in displays employing diffractive lightguide technology.

[0089] FIGS. 8A-8C illustrate the underlying principle of various preferred implementations of the present invention. Further aspects of the geometrical optics of these solutions and variants thereof will be discussed further with reference to FIGS. 9A-1 IB. FIG. 9A shows again the “reference case” of ghost-generating geometry equivalent to FIG. 4B (and by analogy, also other ghost-generating geometries), but in this case illustrated with reference to a bundle of reverse-traced unguided rays shown emanating from the eye 100 toward the internal partially reflective surface 26. The uppermost and lowermost rays, shown as solid rays, enter the lightguide optical element 12 above and below the internal partially reflective surface 26, are refracted at the first major surface 12a, traverse above or below the internal partially reflective surface 26, and are refracted out at the second major surface 12b to continue along their original directions. Three intermediate rays, shown as dashed rays, enter the first major surface 12a, are refracted to directions that impinge upon different locations across the internal partially reflective surface 26, are reflected, and exit through the second major surface 12b toward the eye-motion box 102, thereby illustrating ghost-forming paths, i.e., paths that, if they become aligned during use with an external source of illumination, may generate a disturbing reflection reaching the user’s eye. It is these ray paths (or their equivalents in the other ghost-generating scenarios) which are modified by the present invention.

[0090] FIG. 9B shows the bundle of FIG. 9A with a prism structure 261 formed on the first major surface 12a and no prism on the second major surface 12b. The uppermost and lowermost rays, shown as solid rays, again pass above and below the internal partially reflective surface 26. The three intermediate rays that in FIG. 9A impinged on the internal partially reflective surface 26 are here refracted at the prism structure 261 so that they pass through the lightguide optical element 12 substantially parallel to the plane containing the internal partially reflective surface 26, thereby avoiding reflection at facet 26. Without a corrective prism structure on the second major surface 12b, these rays exit with little angular deviation (e.g., approximately perpendicular to the second major surface 12b), which may perturb the user’s peripheral real- world view. An exceptional reverse-traced unguided ray, shown as a dotted ray, strikes a step of the prism structure 261. No continuation of this dotted ray is shown. Such exceptional rays are addressed by supplemental ghost-suppression features described below.

[0091] FIG. 9C depicts a preferred variant of FIG. 9B in which a corrective prism structure 262 is formed on the second major surface 12b in opposing relation to the prism structure 261. As before, the uppermost and lowermost rays, shown as solid rays, pass above and below the internal partially reflective surface 26. The three intermediate rays are refracted at the prism structure 261 to propagate within the lightguide optical element 12 substantially parallel to the plane containing the internal partially reflective surface 26, and are then refracted at the corrective prism structure 262 on exit so as to return to paths generally parallel to their original directions. This corrective deflection reduces disruption of the user’s peripheral view. The exceptional dotted ray incident on a step of the prism structure 261 is shown, together with an additional exceptional ray, shown as a dash-dot ray, that enters just above the prism structure 261 and is refracted at the corrective prism structure 262 to a steeper downward angle on exit. Such a path is typically of minimal significance for facets in planes closer to the EMB due to near-complete overlap between the prisms along the line of view. For the facets furthest from the eye, the exceptional ray path is typically directed downwards, rendering it non-problematic in most usage scenarios.

[0092] In the above solutions, the light-deflecting structures on the first major surface 12a are identified as the primary mechanism for ghost suppression according to the teachings of the present invention, since it is these structures which can reduce or prevent “visibility” of the facet from the EMB and thus suppress ghost ray paths. Nevertheless, in certain practical cases, deployment of light-deflecting structures on the second major surface 12b, i.e., on the side further from the eye, may also be used to achieve ghost suppression. Such a solution is particularly suitable for cases applications in which a particular range of incident angles is known to generate problematic ghost images, and the introduction of the light-deflecting structures on surface 12b allows redirection of rays from that range of incident angles in an alternative direction that does not reach the EMB. All such solutions also fall within the scope of the present invention.

[0093] FIG. 10 illustrates how prism parameters and ray behavior vary with angle of incidence as a function of internal partially reflective surface position within the first region 16. A set of four internal partially reflective surfaces is shown. The lowest internal partially reflective surface corresponds to the geometry of FIG. 9C. The next higher internal partially reflective surface shows a similar combination of reverse-traced rays, but with smaller incident angles (closer to orthogonal). The internal partially reflective surface above that shows even smaller incident angles. In each case, five rays are illustrated. The uppermost and lowermost rays, shown as solid rays, pass above and below the internal partially reflective surface, respectively, and their paths differ only in angle of incidence driven by position. The three intermediate rays are refracted at the prism structure 261 and at the corrective prism structure 262 as described for FIG. 9C, so that within the lightguide optical element 12 they propagate substantially parallel to the plane containing the corresponding internal partially reflective surface and exit with directions restored by the corrective prism structure 262. The top internal partially reflective surface illustrates a case of an underside-reflection ghost path, labeled as internal partially reflective surface 27, with a prism structure 271 on the first major surface 12a and a corrective prism structure 272 on the second major surface 12b, inverted in position relative to the lower cases, again at relatively small incident angles.

[0094] Although the cases of facets 26 with suppression of top-side reflected ghosts and facets 27 with suppression of bottom-side reflected ghosts have been illustrated here as distinct cases, certain facets may lie in a plane which bisects the EMB, and may be subject to top-side reflection ghosts from the upper region of the EMB and bottom-side reflection ghosts from the lower region of the EMB. In such cases, the relevant facets may advantageously be provided with light-deflecting structures along both the upper side and the lower side of the line of intersection for these facets with the major surfaces of the LOE.

[0095] FIG. 11 A illustrates variation of incident angles across the eye-motion box 102 for a single internal partially reflective surface 26. Three reverse-traced rays are shown from lower, central, and upper locations within the eye-motion box 102. The central ray is refracted at the prism structure 261 to propagate within the lightguide optical element 12 substantially parallel to the plane containing the internal partially reflective surface 26. The ray from the lower location, having a smaller incident angle, is refracted at the prism structure 261 to a direction slightly upward relative to the plane containing the internal partially reflective surface 26. The ray from the upper location is refracted at the prism structure 261 to a direction slightly downward within the thickness of the lightguide optical element 12. All three rays are shown exiting through the corrective prism structure 262 with directions generally corresponding to their entrance directions. This case achieves ghost elimination for the central and lower locations and near-parallel redirection for the upper location, leaving only a limited residual susceptibility that certain reverse-traced rays from the upper part of the EMB 102 might undergo reflection at near-glancing incidence at facet 26. Even such rays are unlikely to generate problematic ghost paths since the change of direction through reflection of a near-glancing incidence ray is small, and prism structure 262 will then deflect the ray path downwards in a direction that may be similar to reverse-traced rays from the lower part of the EMB.

[0096] FIG. 11B illustrates a configuration in which prism parameters are selected for more complete suppression across the eye-motion box 102. Two reverse-traced rays are shown from upper and lower extremities. The ray from the upper extremity is refracted at the prism structure 261 to propagate within the lightguide optical element 12 substantially parallel to the plane containing the internal partially reflective surface 26. The ray from the lower extremity is refracted at the prism structure 261 to a direction slightly diverging from the plane containing the internal partially reflective surface 26 so that it does not impinge the internal partially reflective surface 26. Both rays are then refracted at the corrective prism structure 262 to exit with directions corresponding to their entrance directions. The result is elimination of ghost formation across the entire eye-motion box 102 for the depicted geometry.

[0097] FIG. 12 provides a schematic system-level view analogous to FIG. 2, illustrating an embodiment in which light-deflecting structures are provided adjacent to multiple internal partially reflective surfaces of the first region 16 and along the interface 25, on both major surfaces of the lightguide optical element 12. For each internal partially reflective surface 26 or 27, a light- deflecting structure, such as a prism 261, 271 of the type described above, is provided on the first major surface 12a, with a corresponding corrective light-deflecting structure (e.g., prism 262, 272) on the second major surface 12b, and analogous structures 251, 252 are provided along the interface 25. This figure illustrates one representative configuration in which the prism-based ghost-suppression approach is deployed comprehensively across the first region 16 and the interface 25. It should be understood that the deployment may in fact be selective, along only a part of one or more facets that is determined to be likely to generate ghost ray paths and / or along only selected facets that are determined to be likely to generate ghost ray paths.

[0098] FIGS. 13 A and 13B illustrate an implementation in which prisms are integrated with a push-and-pull external lens pair. A concave external lens 110 is adhered to the first major surface 12a and a convex external lens 111 is adhered to the second major surface 12b. Prism structures 261 and 262 are formed as triangular grooves on the inward-facing flat surfaces of the external lenses 110, 111, respectively, adjacent to the internal partially reflective surfaces of the first region 16 as best seen in FIG. 13A. A prism structure 251 and a corrective prism structure 252 are formed as a triangular groove along the interface 25 on the inward-facing flat surfaces of the external lenses 110, 111, respectively, as best seen in FIG. 13B. Depending on the attachment technique used, the grooves may be air-filled or may be filled with a material (e.g., adhesive) having a different refractive index (e.g., lower) than the external lenses. In both views, the prisms are shown as integrated with the external optics, providing the same refractive deflection effect as when formed directly on the major surfaces of the lightguide optical element 12 and allowing the corrective prism structures to be placed in opposing relation to the corresponding prism structures. Implementation options

[0099] The present invention has been illustrated above with the light-deflecting structures implemented as refractive wedge prisms. It should be noted however that some or all of the lightdeflecting structures may be implemented using alternative light-deflecting structures, which may be two-dimensional diffractive optical elements, metasurface arrays or volume holographic gratings.

[0100] Thus, in some embodiments, the light-deflecting structure is implemented as a surfacerelief diffraction grating (e.g., blazed or multi-level), patterned in or on a film or directly on a major surface. The grating vector is oriented substantially parallel to the length of the corresponding internal partially reflective surface and, for each facet position, the grating implements a substantially constant phase gradient, producing the position-invariant angular deflection described herein without introducing appreciable optical power.

[0101] According to a further option, the light-deflecting structure is implemented as a metasurface array of sub-wavelength elements that imposes a phase gradient oriented along the length of the corresponding internal partially reflective surface, thereby steering incident rays by a substantially position-invariant angular offset in the cross-sectional plane.

[0102] According to a further option, the light-deflecting structure is implemented as a volume holographic grating recorded in photopolymer or glass, configured to steer rays by Bragg diffraction with near-constant angular offset across the required region of the LOE surface adjacent to each facet.

[0103] In the case of refractive prisms, the prism structures may be realized as discrete wedges or as micro-prismatic features deployed directly on a major surface of the lightguide optical element 12, or as features carried by a prism film. As used herein, a prismatic array denotes a series of elongate prism structures provided along multiple internal partially reflective surfaces, and a prism film denotes any continuous element that includes and interconnects elements of a prismatic array. The prism structures may be provided in localized zones adjacent to selected internal partially reflective surfaces or along selected portions of the interface 25. According to the prism film option, the prism structures may be formed as part of a continuous film deployable on the LOE surface which exhibits localized prism relief only where needed and has parallel outer faces elsewhere to remain optically neutral. Alternatively, the prism structures may be formed as continuous elements that generates deflection of light on entry and exit from the LOE even in regions between the internal surfaces that are not required for ghost suppression. Since the deflection is cancelled out by the complementary deflection film on the second major surface of the LOE, the overall impact on the peripheral vision is typically small. Optionally, the deflective power (e.g., prism wedge angle) can vary progressively across the deflection film to parallel the differing geometrical requirements for ghost suppression discussed with reference to FIG. 10.

[0104] Suitable fabrication techniques according to the various implementation options discussed above are well-known in the art and will be clear to a person having ordinary skill. Suitable techniques may include UV-curable replication, roll-to-roll embossing, injection or compression molding, laser ablation, grayscale lithography, diamond turning, and photolithographic etch of glass or polymer. A bonding layer may be used to adhere the light-deflecting structures, films or lenses to the LOE. The bonding layer may advantageously use a refractive index that is lower than that of the LOE material to maintain TIR within the LOE. Alternatively, multilayer dielectric coatings may be used to provide angularly- selective reflectivity that mimics TIR properties, thereby allowing greater flexibility in the choice of materials and their optical properties, and thereby also allowing use of index-matched adhesives and prism, to reduce Fresnel reflections. Anti-reflection coatings and environmental over-coats may be used on exposed faces.

[0105] As described with reference to FIGS. 9B and 9C, “exceptional reverse-traced rays” can occur that intersect step surfaces or chamfers of a prism structure rather than refracting at the intended prism facet. The “step surface” is also referred to herein as the “rear surface” of the wedge prism, i.e., the surface opposite the wedge angle that is not intended to serve an optical function in ray deflection. Such exceptional rays are excluded from the “substantially all reverse-traced unguided ray paths” terminology defined above. Where suppression of such rays is desirable, one or more of the following options may be implemented:

[0106] 1. Absorbing: a light-absorbing treatment may be provided to the rear surfaces of the prism structure.

[0107] 2. Scattering: textured diffusing properties may be provided to the rear surfaces of the prism structure.

[0108] 3. Light-path rejection: the orientation of the rear surface, the refractive index of the prism material and the refractive index of any bonding layer may be chosen to define reverse- traced ray paths from the EMB which are deflected towards non-problematic directions. For example, by use of a prism material with higher refractive index than an adhesive used for the bonding layer, exceptional reverse-traced rays from the EMB entering the rear surface of the wedge prism may undergo TIR within the prism and fail to enter the LOE, thus being redirected downwards via the major facet of the prism and back towards the user’s feet. This defines a ray path unlikely to generate a real- world ghost.

[0109] Similar measures may be applied whether the prism structures are formed directly on a major surface of the lightguide optical element 12 or on inward-facing surfaces of external lenses 110, 111.

[0110] The specific design considerations for each implementation will be clear to a person of ordinary skill in the art based on geometrical considerations of the intended device design and by employing straightforward principles of optical design. For example, the angular deflection occurring at a wedge prism with small apex angle is estimated readily by applying Snell’s law, as is known in the art. Similarly, the width of the zone adjacent to each facet over which the lightdeflecting structure should be deployed is defined by the LOE thickness, the incident angle from the EMB and the refractive index of the LOE material, as will be clear to one ordinarily skilled in the art. This geometry is typically a function of the EMB size, the eye relief (distance from the EMB to the lightguide), and the off-axis distance of each facet from the optical axis of the viewer. By way of example only, eye relief may be about 20-25 mm, the first-region surfaces may be located about 20-30 mm off an optical axis, and the eye-motion box may be about 10 mm by 10 mm, although all of these values may vary from implementation to implementation. For a representative LOE thickness on the order of 1-2 millimeters and a spacing between adjacent internal partially reflective surfaces in the range of about 1-3 millimeters, the relevant zone may be in the range of 150-600 microns along each facet, varying from facet to facet. The light- deflecting structures do not necessarily need to intercept all reverse-traced rays that could reach the facet, with partial coverage often being sufficient to attenuate potential ghosts to acceptable levels.

[0111] For embodiments employing a corrective prism structure 262, 272, 252, the prism structure on the second major surface 12b is preferably in opposing relation to the prism structure on the first major surface 12a. Ridge elongation for the prism structures is substantially parallel to the length of the corresponding internal partially reflective surface or the interface 25, as defined above. Misalignment tolerances may be specified as a parallelism tolerance of ridge direction to facet length and as a lateral registration tolerance in opposing relation, for example within tens of microns across the prism length, without limiting the invention.

[0112] As used herein, prism structure and corrective prism structure refer to refractive structures unless explicitly stated otherwise. The terms deflect, deflected, and deflection are used interchangeably with direction-turning in the context of refractive change of ray direction at a prism structure or a corrective prism structure. A zone adjacent to an internal partially reflective surface or to the interface 25 denotes a region on a major surface of the lightguide optical element 12 that extends along at least part of the length of the corresponding surface, as seen in FIGS. SA- 12.

[0113] It will be appreciated that the above descriptions are intended only to serve as examples, and that many other embodiments are possible within the scope of the present invention as defined in the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A display apparatus for displaying an image to a user, the display apparatus comprising:(a) a lightguide optical element (LOE) having first and second mutually parallel major surfaces for guiding light by internal reflection at said major surfaces;(b) an image projector optically coupled to said LOE so as to introduce into said LOE image light corresponding to a collimated image to propagate within said LOE in a first guided propagation direction by internal reflection at said major surfaces; and(c) a support structure configured to support said LOE relative to the user’s head with said first major surface in facing relation to an eye of the user located within an eye- motion box (EMB) relative to said LOE, wherein said LOE comprises:(i) a first region including a first set of mutually-parallel internal partially reflective surfaces configured to progressively redirect the image light propagating in the first guided propagation direction to propagate in a second guided propagation direction, and(ii) a second region including an out-coupling arrangement configured to progressively couple out the image light propagating in the second guided propagation direction through said first major surface toward the EMB, and wherein, for at least one of said internal partially reflective surfaces of said first set, an elongated light-deflecting structure is disposed on said first major surface and extends along at least part of a length of said internal partially reflective surface adjacent to a line of intersection between a plane containing said internal partially reflective surface and said first major surface, said light-deflecting structure being configured such that, for at least one location within the EMB, a reverse-traced unguided ray path emanating from that location that, in the absence of said lightdeflecting structure, would have entered said first major surface and impinged upon said internal partially reflective surface is deflected at said light-deflecting structure so that it does not impinge on said internal partially reflective surface.

2. The apparatus of claim 1, further comprising a corrective light-deflecting structure disposed on said second major surface in opposing relation to said light-deflecting structure, said corrective light-deflecting structure being configured to counter-deflect external-scene rays that traverse said LOE toward the EMB so as to reduce an angular deviation of the external-scene rays introduced by said light-deflecting structure.

3. The apparatus of claim 1, wherein said light-deflecting structure is configured such that substantially all reverse-traced unguided ray paths emanating from a central location within theEMB that, in the absence of said light-deflecting structure, would have entered said first major surface and impinged upon said internal partially reflective surface are deflected at said lightdeflecting structure so that they do not impinge on said internal partially reflective surface.

4. The apparatus of claim 1, wherein said light-deflecting structure is configured such that substantially all reverse-traced unguided ray paths emanating from an entirety of the EMB that, in the absence of said light-deflecting structure, would have entered said first major surface and impinged upon said internal partially reflective surface are deflected at said light-deflecting structure so that they do not impinge on said internal partially reflective surface.

5. The apparatus of claim 1, wherein elongated light-deflecting structures are provided along a plurality of said internal partially reflective surfaces of said first set.

6. The apparatus of claim 5, wherein different ones of said elongated light-deflecting structures have different widths and / or angular deflection powers selected in accordance with facet position relative to the EMB and LOE thickness.

7. The apparatus of claim 5, wherein said elongated light-deflecting structures for successive facets are integrated into a continuous film attached to said first major surface.

8. The apparatus of claim 1, wherein elongated light-deflecting structures are provided along a majority of said internal partially reflective surfaces of said first set.

9. The apparatus of claim 1, wherein at least one elongated light-deflecting structure extends on one or both sides of the line of intersection along said first major surface.

10. The apparatus of claim 1, wherein at least one elongated light-deflecting structure is integrally formed on a surface of an external lens that is in facing relation with said first major surface.

11. The apparatus of claim 1, further comprising an additional elongated light-deflecting structure disposed on said first major surface and extending along at least part of a length of an interface between said first and second regions, adjacent to a line of intersection between a plane containing said interface and said first major surface.

12. The apparatus of claim 1, wherein said additional elongated light-deflecting structure is configured to impart a position-invariant angular deflection without optical power.

13. The apparatus of claim 1, wherein each elongated light-deflecting structure comprises a wedge prism having a direction of elongation extending parallel to said line of intersection.

14. The apparatus of claim 13, wherein said wedge prism has a rear surface provided with a light-absorbing coating.

15. The apparatus of claim 13, wherein said wedge prism has a rear surface provided with a light-scattering texture.

16. A display apparatus for displaying an image to a user, the display apparatus comprising:(a) a lightguide optical element (LOE) having first and second mutually parallel major surfaces for guiding light by internal reflection at said major surfaces;(b) an image projector optically coupled to said LOE so as to introduce into said LOE image light corresponding to a collimated image to propagate within said LOE in a first guided propagation direction by internal reflection at said major surfaces; and(c) a support structure configured to support said LOE relative to the user’s head with said first major surface in facing relation to an eye of the user located within an eyemotion box (EMB) relative to said LOE, wherein said LOE comprises:(i) a first region including a reflective or diffractive arrangement configured to progressively redirect the image light propagating in the first guided propagation direction to propagate in a second guided propagation direction,(ii) a second region including an out-coupling arrangement configured to progressively couple out the image light propagating in the second guided propagation direction through said first major surface toward the EMB,(iii) an interface between said first region and said second region, and(iv) an elongated light-deflecting structure disposed on said first major surface extending along at least part of a length of said interface adjacent to a line of intersection between a plane containing said interface and said first major surface, said light-deflecting structure being configured such that, for at least one location within the EMB, a reverse-traced unguided ray path emanating from that location that, in the absence of said lightdeflecting structure, would have entered said first major surface and impinged upon said interface is deflected at said light-deflecting structure so that it does not impinge on said interface.

17. The apparatus of claim 16, further comprising a corrective light-deflecting structure disposed on said second major surface in opposing relation to said light-deflecting structure, said corrective light-deflecting structure being configured to counter-deflect external-scene rays that traverse said LOE toward the EMB so as to reduce an angular deviation of such rays introduced by said light-deflecting structure.

18. The apparatus of claim 16, wherein said interface includes an optical element configured to modify a polarization state of light propagating within said LOE.

19. The apparatus of claim 16, wherein said elongated light-deflecting structure comprises a refractive prism.

20. A display apparatus for displaying an image to a user, the display apparatus comprising:(a) a lightguide optical element (LOE) having first and second mutually parallel major surfaces for guiding light by internal reflection at the major surfaces;(b) an image projector optically coupled to the LOE so as to introduce into the LOE image light corresponding to a collimated image to propagate within the LOE in a first guided propagation direction by internal reflection at the major surfaces; and(c) a support structure configured to support the LOE relative to an eye of the user located within an eye-motion box (EMB) relative to the LOE; wherein the LOE comprises:(i) a first region including a first set of mutually-parallel internal partially reflective surfaces configured to progressively redirect the image light propagating in the first guided propagation direction to propagate in a second guided propagation direction, and(ii) a second region including an out-coupling arrangement configured to progressively couple out the image light propagating in the second guided propagation direction toward the EMB ; and wherein a first prismatic array is disposed on the first major surface and a second prismatic array is disposed on the second major surface, each prismatic array being provided at least in zones located adjacent to a plurality of the internal partially reflective surfaces of the first set, each said zone extending along at least part of a length of a corresponding one of the internal partially reflective surfaces and comprising one or more elongate prisms having ridges elongated in a direction substantially parallel to the length of the internal partially reflective surfaces, the first and second prismatic arrays being arranged to change directions of external- scene light passing into and through the LOE to reduce world-ghost reflections from the internal partially reflective surfaces reaching the EMB, said second prismatic array being configured to at least partially compensate for a direction-turning effect introduced by said first prismatic array.

Images