Reflection suppression in near-eye display devices

Abstract

To provide a near-eye display device having various features for suppressing a ghost image of a bright object.SOLUTION: A near-eye display device includes a light-guide optical element (LOE) (10) having first and second major outer surfaces (11A, 11B). The first and second major outer surfaces are planar and parallel to each other. The image projector (2) introduces the image-corresponding LOE illumination. As a result, illumination propagates within the LOE by internal reflection at the major outer surfaces. The outward coupling arrangement couples the illumination outward of the LEE toward the viewer's eye. The outward coupling arrangement may be a set of mutually parallel partially reflective surfaces (12A) deployed at an oblique angle within the LOE. Intervening baffles oriented to avoid reduced peripheral vision include various non-anti-reflective coatings and various polarizing filters.SELECTED DRAWING: FIG. 2A

Description

[Technical Field]

[0001] The present invention relates to near eye displays, and more particularly to near eye displays with various features to suppress ghost images of bright objects.

[0002] Many near-eye display systems include a transparent light-guiding optical element (LOE) or "light guide" placed in front of the user's eye. Such near-eye display devices transmit an image within the LOE by internal reflection and then couple the image to the user's eye via an appropriate out-coupling mechanism. The out-coupling mechanism may be based on embedded partial reflectors or "facets," or may use diffractive patterns. While the following description primarily refers to facet-based out-coupling configurations, it should be recognized that various features of the present invention are also applicable to diffractive configurations. When applied to diffractive configurations, the direction of facet extension referred to herein can be taken to refer to the orientation of the elements of a diffraction grating.

[0003] The light guides and facets are at least partially transparent, allowing light from the environment (scenery) to pass through them, giving the user a direct view of the real world. Some of the scene light rays are reflected by the facets and reach the eye at various angles, thereby creating unwanted "ghost" images (reflections) of the real world. Summary of the Invention

[0004] The present invention is a near-eye display device.

[0005] In accordance with the teachings of an embodiment of the present invention, a near-eye display device for projecting an image to an eye of an observer is provided, the near-eye display device including: (a) a light-guiding optical element (LOE) having first and second major outer surfaces, the first and second outer surfaces being planar, parallel to one another, and having edges; (b) a support structure configured to support the LOE against a head of an observer by the second major outer surface in a facing relationship with the eye of the observer; and (c) an image projector for projecting illumination corresponding to an image, the image projector optically coupled to the LOE to introduce illumination into the LOE, and a near-eye display device comprising: (a) an image projector, whereby illumination is spread within the LOE by internal reflection at the first and second outer major surfaces; (d) an outward coupling arrangement deployed to couple illumination outward from the LOE toward an eye of an observer; and (e) a light-blocking baffle extending along a major portion of one of the edges of the LOE and protruding from the plane of the second outer major surface, thereby blocking radiation incident from a range of glancing angles from reaching at least a portion of the second outer major surface and projecting it in a direction toward the eye of the observer at an acute angle with the second outer major surface.

[0006] According to still further features in embodiments of the present invention, the light blocking baffle protrudes in a direction towards the center of the viewer's eyeball.

[0007] According to a further feature of this embodiment of the present invention, the outcoupling arrangement includes a plurality of mutually parallel, partially reflective surfaces extending within the interior of the LOE at an oblique angle relative to the first exterior major surface.

[0008] According to further features of embodiments of the present invention, the baffle and deployment of the partially reflective surfaces precludes light paths from entering one of the first and second exterior major surfaces and reaching the observer's eye after reflecting once from one of the partially reflective surfaces.

[0009] According to further features of embodiments of the present invention, the partially reflective surface has an extension direction parallel to the second outer major surface, and the baffle extends along a major portion of one of the edges essentially parallel to the extension direction of the partially reflective surface.

[0010] According to a further feature of an embodiment of the present invention, the light blocking baffle is mechanically supported by attachment to the LOE.

[0011] According to a further feature of an embodiment of the present invention, the light blocking baffle is mechanically supported by attachment to a support structure.

[0012] In accordance with the teachings of one embodiment of the present invention, a near-eye display device for projecting an image to an eye of an observer is provided, the near-eye display device comprising: (a) an LOE (light-guiding optical element) having first and second major outer surfaces, the LOE being planar and parallel to one another; (b) a support structure configured to support the LOE against the observer's head with the second major outer surface in a relationship facing the observer's eye; (c) an image projector for projecting illumination corresponding to an image, the image projector being optically coupled to the LOE to introduce the illumination into the LOE, such that the illumination spreads within the LOE by internal reflection at the first and second major outer surfaces; and (d) an outcoupling arrangement for coupling the illumination out of the LOE toward the observer's eye, the first major outer surface being coated with a multi-layer coating configured to provide anti-reflection properties for visible light incident at an angle of incidence less than 40 degrees and to provide high reflectivity for at least a first polarization of visible light incident at an angle of incidence greater than 70 degrees.

[0013] According to further features of embodiments of the present invention, the second exterior major surface is coated with a multi-layer coating configured to provide anti-reflective properties for visible light incident at angles of incidence less than 40 degrees and to provide low reflectivity for a second polarization orthogonal to the first polarization incident at angles of incidence between 70 degrees and 85 degrees.

[0014] In accordance with the teachings of one embodiment of the present invention, a near-eye display device for projecting an image to an observer's eye is provided, the near-eye display device including: (a) a light-guiding optical element (LOE) having first and second major outer surfaces, the LOE being planar and parallel to one another; (b) a support structure configured to support the LOE against the observer's head by the second major outer surface in a relationship facing the observer's eye; (c) an image projector for projecting illumination corresponding to an image, the image projector optically coupled to the LOE to introduce illumination into the LOE, such that the illumination spreads within the LOE by internal reflection at the first and second major outer surfaces; (d) an outward coupling structure deployed to couple illumination outward from the LOE toward the observer's eye; and (e) a microlouver layer associated with the first major outer surface of the LOE, the microlouver layer blocking incident light at an incidence angle greater than 70 degrees from at least one direction entering the LOE.

[0015] According to a further feature of an embodiment of the present invention, the microlouver layer includes a one-dimensional array of microlouvers having an elongation direction, the microlouver layer extending in an essentially horizontal elongation direction.

[0016] According to a further feature of an embodiment of the present invention, the microlouver layer includes two arrays of microlouvers having essentially perpendicular directions of extension.

[0017] In accordance with the teachings of one embodiment of the present invention, there is provided a near-eye display device for projecting an image to an eye of an observer, the near-eye display device comprising: (a) a light-directing optical element (LOE) having first and second major outer surfaces, the LOE being planar and parallel to one another; (b) a support structure configured to support the LOE against an observer's head by the second major outer surface in a facing relationship with the observer's eyes; (c) an image projector for projecting illumination corresponding to an image, the image projector optically coupled to the LOE to introduce illumination into the LOE such that the illumination spreads within the LOE by internal reflection at the first and second major outer surfaces; (d) an outcoupling arrangement for coupling illumination out of the LOE toward the observer's eyes, the outcoupling arrangement defining at least one high-angle polarization-dependent optical path that enters one of the first and second major outer surfaces at an angle of incidence greater than 60 degrees and exits the LOE toward the observer's eyes, the polarization-dependent optical path having an orientation supported by polarization; and (e) a polarizing filter deployed to prevent external light traveling along a polarization-dependent optical path having a supported orientation from reaching the observer's eyes.

[0018] According to a further feature of an embodiment of the present invention, a polarizing filter is deployed to filter light entering the first exterior major surface.

[0019] According to a further feature of an embodiment of the present invention, a polarizing filter is deployed to filter light exiting the second outer major surface toward the viewer's eye.

[0020] According to a further feature of an embodiment of the present invention, illumination outside the LOE directed to the observer's eye is essentially polarized with the image polarization, and a polarizing filter is deployed to block light having a polarization perpendicular to the image polarization.

[0021] According to a further feature of an embodiment of the present invention, there is further provided a second polarizing filter deployed to filter light entering the first outer major surface, the first polarizing filter and the second polarizing filter being aligned so as to transmit light of the same polarization.

[0022] According to a further feature of an embodiment of the present invention, there is further provided a horizontal polarizing shade element for filtering light from at least one direction along an optical path between the observer and the LOE, wherein a polarization axis of the horizontal polarizing shade element has an angle that intersects with a polarization axis of the polarizing filter.

[0023] According to a further feature of embodiments of the present invention, there is further provided a horizontally polarizing shade element for filtering light from at least one direction along an optical path between the observer and the LOE.

[0024] According to a further feature of this embodiment of the present invention, the outcoupling arrangement includes a plurality of mutually parallel, partially reflective surfaces extending within the interior of the LOE at an oblique angle relative to the first exterior major surface. [Brief explanation of the drawings]

[0025] The present invention has been described, by way of example only, with reference to the accompanying drawings, in which: [Figure 1A] FIG. 1A is a schematic side view of an observer using a near-eye display device constructed and operative in accordance with the teachings of the present invention, illustrating various ambient light sources that may cause reflections to be suppressed. [Figure 1B] FIG. 1B is a schematic plan view of an observer using a near-eye display device constructed and operative in accordance with the teachings of the present invention and illustrating various ambient light sources that may cause reflections to be suppressed. [Figure 2A] FIG. 2A is an enlarged schematic side view of the near-eye display of FIG. 1A, illustrating the ray paths for the image illumination and for typical "ghost" light paths from ambient light sources. [Figure 2B] FIG. 2B is an angled diagram illustrating the ray paths for the image path and the angular relationships between various components of the ghost path of FIG. 2A. [Figure 2C] FIG. 2C is an angled diagram illustrating the ray paths for the image path and the angular relationships between various components of the ghost path of FIG. 2A. [Figure 3A]FIG. 3A is an enlarged schematic side view of the light-guiding optical element from the near-eye display device of FIG. 1A, illustrating an alternative set of typical "ghost" light paths from an ambient light source behind the light-guiding optical element. [Figure 3B] FIG. 3B is an angle diagram illustrating the angular relationships between various components of the ray path for the ghost path of FIG. 3A. [Figure 3C] FIG. 3C is an enlarged schematic side view of a variation of the light-directing optical element from the near-eye display device of FIG. 1A. [Figure 4] FIG. 4 is a schematic plan view illustrating the extent of an observer's ocular field of view through the near-eye display device of FIG. 1A. [Figure 5] FIG. 5 is a schematic plan view illustrating the extent of an observer's ocular field of view through the near-eye display device of FIG. 1A. [Figure 6] FIG. 6 is a diagram similar to FIG. 4 illustrating the range of angles at which an ambient ray from the rear of a light-guiding optical element can reach the observer's eye after a single reflection at an internal facet of the light-guiding optical element. [Figure 7] FIG. 7 is a view similar to FIG. 6 illustrating a variation in which the area containing the internal facets is restricted to suppress certain ghost light paths from reaching the viewer's eye. [Figure 8A] FIG. 8A is a view similar to FIG. 7 illustrating the use of an obstruction baffle according to a further aspect of an embodiment of the present invention to block ghost-specific light paths from reaching the observer's eye, shown with typical light paths. [Figure 8B] FIG. 8B is a view similar to FIG. 7 illustrating the use of an obstruction baffle according to a further aspect of an embodiment of the present invention, shown without typical ray paths, to block ghost light paths from reaching the observer's eye. [Figure 8C] FIG. 8C is a view similar to FIG. 8A illustrating a variation of a binocular near-eye display device according to an embodiment of the present invention using two non-coplanar light-guiding optical elements deployed at an angle between 10-30 degrees to better match the curvature of the face between the light-guiding optical elements and demonstrate the effect of the corresponding tilt on the baffle geometry. [Figure 9A] FIG. 9A is a graph illustrating reflectivity as a function of angle of incidence for an exemplary partially reflective (faceted) coating in accordance with an embodiment of the present invention. [Figure 9B] FIG. 9B is a corresponding graph of reflectance versus unmodified Fresnel reflection. [Figure 10A] FIG. 10A is a schematic side view similar to FIG. 1A illustrating a variation using an external polarizing filter. [Figure 10B] FIG. 10B is a diagram similar to FIG. 10A illustrating a variation using an internal polarizing filter. [Figure 10C] FIG. 10C is a plan view of a variation with a horizontal polarizing filter without a horizontal polarizing filter. [Figure 10D] FIG. 10D is a plan view of a variation similar to FIG. 10B with a horizontal polarizing filter. [Figure 10E] FIG. 10E is a diagram similar to FIG. 10A illustrating a variation that uses both internal and external polarizing filters. [Figure 11] FIG. 11 is a schematic plan view of a variation of the present invention illustrating typical angles of incidence of light rays from an ambient light source compared to the ocular field of view of a scene viewed directly by an observer. [Figure 12] FIG. 12 is a graph illustrating the reflectivity characteristics of a preferred anti-reflective coating corresponding to the angle of incidence on a surface of a light-directing optical element in accordance with aspects of an embodiment of the present invention. [Figure 13] FIG. 13 is a schematic diagram of a microlouver film for use in an embodiment of a near-eye display device according to a further aspect of an embodiment of the present invention. [Figure 14A] FIG. 14A is a schematic diagram of eye position relative to facet position for various embodiments of a near-eye display device using a light-directing optical element that includes two separate sets of partially reflective surfaces at different orientations. [Figure 14B] FIG. 14B is a schematic diagram of eye position relative to facet position for various embodiments of a near-eye display device using a light-directing optical element that includes two separate sets of partially reflective surfaces at different orientations. [Figure 14C] FIG. 14C is a schematic diagram of eye position relative to facet position for various embodiments of a near-eye display device using a light-directing optical element that includes two separate sets of partially reflective surfaces at different orientations. [Figure 15A] FIG. 15A is a schematic diagram of a further embodiment of a near-eye display device using a light-guiding optical element that includes two separate sets of partially reflective surfaces at different orientations, with the principal reflective polarization vectors for both sets of facets similarly aligned. [Figure 15B] FIG. 15B is a schematic diagram of a polarizing filter orientation suitable for use with the light-directing optical element of FIG. 15A. [Figure 16A] FIG. 16A is a partial schematic diagram of a near-eye display device based on the light-guiding optical element of FIG. 14A. [Figure 16B] FIG. 16B is a schematic plan view of the near-eye display of FIG. 16A implemented as a binocular display with non-uniform polarizing filters. [Figure 16C] FIG. 16C is a graph illustrating the reflectivity corresponding to the angle of incidence on the partially reflective surface of the light-directing optical element for the embodiment of FIGS. 16A and 16B. DETAILED DESCRIPTION OF THE INVENTION

[0026] The present invention is a near-eye display device.

[0027] The principles and operation of a near-eye display device according to the present invention may be better understood with reference to the drawings and the accompanying description.

[0028] Introduction and classification of "ghost images" To fully understand the various aspects of the present invention, it is important to distinguish between the various directions from which incident light reaching a light-directing optical element (LOE) can create "ghosts" that can potentially annoy the viewer's eyes.

[0029] By way of introduction, FIG. 1A schematically illustrates a viewer looking through a near-eye display. In general terms, the near-eye display includes a light-guiding optical element (LOE) or "light guide" 10 having first and second major outer surfaces 11A and 11B, which are planar or parallel to one another and typically have edges that are not optically active. An image projector 2 is optically coupled to LOE 10 to introduce illumination corresponding to an image into LOE 10 such that illumination propagates within the LOE by internal reflection at major outer surfaces 11A and 11B. Optical coupling of image projector 2 to LOE 10 can be achieved via a coupling prism with an input surface at an oblique angle, or via a reflective coupling configuration, one of the LOE's side edges and / or major outer surfaces.

[0030] Examples of suitable image projectors (or "PODs"), such as those comprising illumination sources, spatial light modulators, e.g., LCOS chips, and collimating optics, typically all disposed on the surface of one or more PBS cubes or other prism configurations, are well known in the art. Similarly, suitable internal coupling configurations for coupling images into the LOE through the use of internal coupling reflectors or appropriately angled coupling prisms are well known in the art. The coupling between the image projector and the LOE can be direct, or can be via an additional gap widening configuration to widen the gap across which the image is introduced onto the face of the LOE. For simplicity of presentation, neither the projector nor the internal coupling configuration will be discussed further herein. Also, their combination is represented herein only schematically.

[0031] The near-eye display device includes an outcoupling configuration deployed to couple illumination from the LOE toward the observer's eye for viewing. The outcoupling configuration is illustrated here as a plurality of mutually parallel partially reflective surfaces (or "facets") 12A deployed within LOE 10 at oblique angles relative to major exterior surfaces 11A and 11B. As discussed further below, the facets typically have angle-dependent coatings that provide high transmittance at certain angles and partial reflection at other angles. Various implementations of LOEs including such facets are commercially available from Lums LT (Israel). While the description herein primarily refers to facet-based outcoupling configurations, those skilled in the art will recognize that various aspects of the present invention are also applicable to alternative outcoupling configurations, such as outcoupling configurations based on diffractive optical elements.

[0032] The near-eye display device of the present invention is typically a head-mounted display and preferably includes a support structure configured to support LOE 10 against the observer's head with second major outer surface 11B in opposing relationship with the observer's eyes. The support structure is shown schematically in FIG. 1B as an eyeglass frame structure including sides 15 for supporting a display relative to the observer's ears. This is but one of many options, including further headband-mounted structures and helmet-related displays. The details of the support structure are not per se critical to the present invention and will not be described in detail herein.

[0033] As illustrated schematically in FIG. 1A, projector 2 injects light corresponding to a desired image (black arrow) into the light guide, where it is coupled out of the light guide toward the observer's eye. Light from objects 4 in the scene passes through the light guide (dashed-dotted line) to the observer, albeit with somewhat less specific intensity. The various potential directions of incidence of extraneous external light are labeled with two-letter symbols indicating direction and two-letter codes in reference number 6: upward, downward, or side (U, D, or S, respectively) and front or rear (F or B, respectively). The side direction is more clearly illustrated in the plan view of FIG. 1B.

[0034] FIG. 2A is an enlarged schematic view showing projector 2, light guide 10, and selected interior surfaces angled 13 relative to the major parallel exterior surfaces forming the front and back surfaces of the light guide. In the typical configuration illustrated herein, the projector resides at the top (as in FIG. 1A). The facets, in this case typically horizontally extending partial reflectors, though not necessarily horizontal, couple light out from the light guide toward the viewer's eye. In this example, only one light beam of the image is shown for clarity of presentation; in reality, the angular extent of the image, typically aimed at infinity, is projected along the light guide and coupled out toward the eye. To facilitate illustration of the reflection paths, the facet spacing is shown as unequal, but is typically not uniform.

[0035] The image-guided light is represented here by rays 14A and 16A reflecting from the outer surface of the light guide. Ray 16A strikes one of the facets and is partially reflected as ray 18A toward the viewer. FIG. 2B shows the corresponding ray directions at angular intervals, with 12B corresponding to the angle of the plane of facet 12A and the double arrow representing the vector in this plane (perpendicular to the applicable plane when the diffractive element performs outcoupling). Vectors 14B, 16B, and 18B represent the directions of rays 14A, 16A, and 18A, respectively. The dashed corners in FIGS. 2B and 2C represent the TIR angles of the outer surface of light guide 10; i.e., rays such as 18B; rays falling within the illustrated angular range will escape the light guide, while ray directions outside that range will be internally reflected.

[0036] Any light guide and output coupling architecture inherently has various unwanted mechanisms of reflection from the scene. Ray 20 originates from source 6UF (a source in front of the user and in the normal field of view of the real world as observed through the light guide, typically a sunlight or overhead lighting scenario) and refracts within the light guide as ray 22A. This ray is shown in angular intervals in Figure 2c as vector 22B. Most of this ray will pass through the light guide and refract outside the light guide as ray 20A, which is outside the normal field of view but does not disturb the observer. However, a portion of ray 22A may reflect from one of facets 12A (plane 12B) as ray 24A (vector 24B). This ray is reflected by the outer surface of the LOE as ray 26A (vector 26B) and is reflected again by one of facets 12A as ray 28A (vector 28B). Vector 28B is approximately the same as vector 14B. Therefore, the rays will continue to radiate toward the observer's eye in the same manner as 14A (14B). This is shown as rays 30A (equivalent to 16A) and 32A (equivalent to 18A).

[0037] Another possible mechanism for producing the disturbing ghost illumination is the partial reflection of ray 22A from the back surface 11B of the LOE and subsequent partial reflection of that ray from facet 12A, thereby producing output ray 23A.

[0038] FIG. 3A describes the optical path of a "single reflection" from source 102 in real space in the case of side injection of an image into the light guide, with the facet extension direction nearly vertical. This source is similar to source 6SB in FIG. 1B. FIG. 3B describes the same process at an angular interval. Light from the source refracts into the light guide as ray 106A (vector 106B) and is reflected and refracted back into the light guide by facet 104A (plane 104B) as ray 112A (vector 112B). This process involves only one reflection by a facet, as opposed to other types of reflection paths that involve multiple facet reflections. Therefore, this single, identical side reflection can be particularly bright in some cases. As illustrated by comparing rays 110A and 112A with rays 106A and 108A, the reflection angle becomes larger when the scene source shines at a further angle from grazing incidence.

[0039] The geometric characteristics of the light guide and its position relative to the eye determine the angular distribution of reflections reaching the eye. Figures 4 and 5 show plan views of an observer's head. The relative positioning of the light guide and the user's eye is determined by a support structure, such as an eyeglass frame support structure or some other head-mounted support structure, but is omitted here for simplicity of presentation. In this embodiment, the light guide 10 is configured with images introduced and illuminated from the side, as evident from the solid arrows and facet angles. The facets in this embodiment are referred to as "vertical facets."

[0040] Although the pupil can move within a range of specific positions and orientations, the central ray from the central region intersects the center of the eyeball 101 toward the fovea in all directions of viewing as shown in Figures 4 and 5. The specific range of angles that are of interest to the observer is called angle 100. An equivalent angle exists vertically. For clarity, other considerations for magnifying angle 100 are not included in the description, such as IPD or eye-box tolerance.

[0041] Geometric suppression of rear ghosting According to a first aspect of an embodiment of the present invention illustrated in Figures 8A-8C, the near-eye display device is provided with a light-blocking baffle (130L, 130R) extending along a majority of one of the edges of the LOE and projecting from the second outer major surface, thereby blocking incident radiation from a range of glancing angles from reaching at least a portion of said second outer major surface, the baffle projecting in a direction toward the observer's eye forming an acute angle with the second outer major surface, most preferably in a direction toward the center of the observer's eyeball. This ensures that the baffle has minimal impact on the observer's peripheral vision, leaving the observer with the impression of unlimited field of view.

[0042] The baffles preferably extend along edges of the LOE substantially parallel to the extension of the partially reflective facets parallel to the major surfaces. By geometric definition, the extension of the facets parallel to the major surfaces can be defined as the line of intersection between the plane in which one of the partially reflective faces lies and the plane of the first exterior major surface. As used herein, "substantially parallel" refers to directions that are parallel or within about 20 degrees of each other.

[0043] According to a first option, the light-blocking baffles 130L, 130R are mechanically supported by coupling to the LOE 10. Alternatively, the light-blocking baffles are mechanically supported by coupling to a support structure (not shown in the figures).

[0044] The preferred geometric conditions for implementing the baffle are as follows: As explained above, Figures 3A-3C show the angular dependence of light rays, which undergo a single reflection depending on the angle of incidence of the illumination at the back side of the light guide (3A, 3B) or a single reflection from the front side. Figure 6 illustrates the meaning of this angular dependence in a plan view of a near-eye display device deployed above the observer's head. Light guide 10 reflects scene rays from light guide point 121R toward the center of eyeball 101, namely, ray 122 from point 123R and grazing ray 124 from point 125R.

[0045] According to certain embodiments of the present invention, the last facet (i.e., furthest from the image projector) is positioned so that reflections from critical angle rays resulting from grazing incident rays from the scene (124R or L) can no longer reach the eye center 101, indicated by 125 in Figure 7. The facets of the right (or left) eye light guide end at the point where ray 124R (L) reflects onto the eye center 101. It is clear from Figure 6 that no other ray can reflect onto 101 because there are no facets to reflect light there.

[0046] While the above approach may be effective in avoiding bright ghosts of single reflections from ambient lighting on the back side in some scenarios, the geometric constraints on the location of the "last facet" may not provide a sufficient angular field of view for some applications. According to a further aspect of the invention, after identifying the required angular field of view using the geometric relationships illustrated in Figure 6 (e.g., extending to location 123R illustrated in Figure 6), a limited range of angles can be identified (e.g., from ray 124 through the angle of ray 122). This limited range of angles is necessary to avoid single reflection ghosts from reaching the viewer's central vision from the location requiring the output facet.

[0047] Light-blocking baffles 130L and 130R implemented according to these principles are typically relatively small and extend generally rearward from the periphery of the optical arrangement, with significantly reduced obstruction of the observer's peripheral vision compared to full-edge blocking arrangements. In certain particularly preferred embodiments, the baffles are implemented to extend from the periphery of the optical arrangement generally toward the eyes, and in some cases, coordinate with certain features on the projector and / or frame, resulting in little or no impact on the observer's peripheral vision.

[0048] FIG. 8A shows an example of a light-blocking baffle. Baffles 130R and 130L are shown here as horizontal surfaces positioned at the edges of the light guide and oriented toward 101, as indicated by the dashed-dotted lines. For a predetermined virtual FOV, the length of faceted light guide 10 is defined 123R(L). A back-reflected light path is defined, and the baffle 130R(L) length is set to block this path for the light ray reflected by the last facet, as shown in FIG. 8B. Tilted light guides can further utilize this scatter blocking, as shown in FIG. 8C. In addition to aesthetically matching the user's "facial curve," such a tilted light guide further relaxes the dimensional requirements of the baffle by allowing a given length of baffle to create a longer "shadow" across the back of the light guide.

[0049] Thus, most preferably, the deployment of baffles 130L, 130R and the partially reflective surfaces penetrates one of the first and second major exterior surfaces and prevents light from reaching the observer's eye after receiving a single reflection from one of the partially reflective surfaces.

[0050] High incidence angle ray rejection A further aspect of an embodiment of the present invention, useful both alone and in combination with other aspects described herein, relates to an approach for treating incident light rays approaching first (outer) major exterior surface 11A of LOE 10 at high angles of incidence.

[0051] 2A, it is noted that many of the problematic reflections of real-world light sources are initiated by incident rays at high angles, as illustrated schematically herein as ray 20. If such rays could be excluded from entering the LOE, this would obviously avoid incident radiation that produces troublesome reflections towards the observer's eye.

[0052] Appropriate coating of the exterior facets of light guide 10 can thus reduce scene reflections as shown in Figures 11 and 12. Angle 100 represents the range of angles over which an observer views their surroundings through light guide 10.

[0053] A preferred embodiment of the reflectivity of the first (outer) angled surface of a light guide with an anti-reflective coating is shown in FIG. 12. Angular range 166 represents angle 100. In this range, the transmittance of the light guide will be at its maximum. Light rays from the scene outside of range 100 originate from the front surface 168 or back surface 120 (limited by facet reflectance, facets, or obstructing the viewer's face). The angular range of these rays is shown as 170 in FIG. 10B. According to one aspect of the invention, the anti-reflective coating of the light guide is modified to have high reflectivity at 170 and high transmittance at 166. (High reflectivity at high angles is a well-known technique for AR coatings designed for normal light incidence.) This significantly reduces the scene illumination entering the light guide at high angles and reflecting off the internal facets above the eye.

[0054] Thus, according to one example of this aspect of the present invention, the first (outer) major exterior surface 11A is coated with a multilayer coating configured to provide anti-reflective properties for visible light at angles of incidence less than 40 degrees and high reflectivity for at least a first polarization of visible light at angles of incidence greater than 70 degrees. Depending on the particular requirements for the direct view of the viewer's field of view through the LOE and the direction from which problematic ambient lighting tends to be incident, it may be preferable to provide anti-reflective properties for angles up to 50 degrees and / or high reflectivity for angles greater than about 60 degrees. However, the closer these limits are approached, the more demanding the coating requirements become, to the point where they become impractical or prohibitively complex to implement. In this context, "anti-reflective properties" preferably refers to a reflectivity of less than 5%, and most preferably less than 3%. "High reflectivity" in this context refers to a reflectivity greater than 70%, preferably greater than 80%, more preferably at least 90%, and in some particularly preferred cases at least 95%.

[0055] When considering the range of angles at which external illumination can be incident, it may be difficult to achieve the desired rejection of high angles of incidence (small grazing angles) for the entire FOV and the entire visible spectrum. Therefore, in particularly preferred embodiments of the present invention, this reflectivity enhancement is optimized only for S-polarized light at high angles of incidence. As described below, an alternative solution is provided for reducing the visibility of ghosts from P-polarized illumination from external sources.

[0056] According to the above approach, with particular reference to refracted ray 22A in FIG. 2A , the remaining light from incident ray 20 will be refracted at or transmitted through the front major surface of the light guide and will be substantially p-polarized by the exterior surface coating. Some ghost reflection paths involve subsequent reflection of ray 22A at the substrate's second (rear) exterior major surface 11B to generate ghost ray 23A. However, due to refraction at interfaces away from the major surface normal, any portion of this light that transmits through rear major surface 11B will continue on a steeply downward path 20A that is substantially parallel to the direction of transmission of ambient light 20 that penetrates the front major surface of the LOE and will not interfere with the eyes of a wearer of a near-eye display device. Therefore, it has been proposed to coat the back surface of the LOE with an anti-reflective coating to increase the transmission of high-angle incident rays. It is more feasible to achieve an anti-reflective coating that is effective for P-polarized light at all angles. As a result, this second embodiment of the present invention complements the first embodiment in that most of the P-polarized ghost illumination can be transmitted at the rear surface 11B, while most of the incident external ghost illumination with S-polarization can be filtered out by external reflection at the front surface 11A. The result is that the overall ghost illumination following the path illustrated in Figure 2 is significantly reduced compared to existing LOEs.

[0057] Thus, in accordance with this aspect of the invention, the second outer major surface 11B is advantageously coated with a multi-layer coating configured to provide anti-reflective properties for visible light incident at angles of incidence less than 40 degrees, and low reflectivity for a second polarization of visible light perpendicular to the first polarization incident at angles of incidence between 70 degrees and at least about 85 degrees (preferably close to 90 degrees).

[0058] Regarding alternative optical paths that generate ghost 32A, and referring again to FIG. 2, the ghost may be formed by residual ambient light that enters the LOE and then reflects off the partially reflective facets of the light guide (e.g., from ray 22A to ray 24A, or from ray 26A to ray 28A) over a relatively limited range of angles that is typically different from the range of angles (and polarization orientation) over which the display signal spans. Therefore, it has been proposed to modify the design of the partially reflective surface coating to reduce reflectivity within one or both of these particular ranges of angles. Specifically, a facet coating that reduces reflection for high-angle rays would tend to minimize the amount of light that penetrates the waveguide mode (i.e., reflection from rays 22A to 24A), thus reducing the intensity of ghost 32A.

[0059] Modified microlouver film As an alternative or additional embodiment of the above aspect of the invention, rejection of high-angle incident light can be achieved using a louver film deployed in front of the exterior surface of the LOE and configured to block incident light from high angles, providing high transmission of light from exterior scenes beyond the desired field of view. Microlouver films are known and commonly used as "privacy films" to limit the visibility of computer display devices to a desired range of viewing angles. An example of such a film is commercially available from 3M Company under the designation Advanced Light Control Film (ALCF).

[0060] The structure of such a film is illustrated schematically in Figure 13, where the inner layer of the film comprises an array of opaque (or highly attenuated) microlouvers 300 supported on a transparent substrate 302, which defines the geometric limits of the angle at which incident light can pass through the film. Commercially available privacy films typically contain a one-dimensional array of microlouvers, i.e., the louvers all extend in the same direction. In this case, the film preferably deploys against the LOE, resulting in the louvers extending horizontally, thereby blocking high-angle external light sources coming from above. Alternatively, a two-dimensional array of microlouver structures can be used, with microlouvers extending in two perpendicular directions (typically stacked on top of each other in two separate layers of the film structure) to provide rejection of high-angle external light sources from all sides.

[0061] It is typically desirable not to apply the light control film directly to the LOE surface to avoid affecting the optical properties of the LOE due to internal reflection from the major surface. Optionally, a suitable structure may be provided to ensure that an air gap is maintained adjacent to the LOE. Alternatively, the light control film may be supported on a separate optical element (such as a lens) spaced slightly from the LOE. Alternatively, a buffer or "isolation" layer with a sufficiently low effective refractive index may be provided to preserve the optical properties of the LOE. Examples of suitable materials for such layers include commercially available aerogels and various other materials used for similar purposes. According to a further alternative embodiment, an angle-selective reflective coating, typically implemented using a multilayer dielectric coating, may be provided, allowing high transmittance at small angles while simulating TIR for an appropriate range of angles for an image extending inside the LOE. This option also allows for the direct optical attachment of a microlouver film to the coated surface of the LOE without impairing the optical properties of the LOE. Parenthetically, all of the aforementioned options that apply to supporting a microlouver film against the LOE without affecting its optical properties are equally applicable. Polarizing filters associated with one or both surfaces of the LOE are referred to herein.

[0062] In a particularly preferred embodiment, microlouver layer 300 is associated with first outer major surface 11A of LOE 10 and blocks at least light incident at an angle of incidence greater than 70 degrees from at least one direction from entering the LOE. When a microlouver layer 300 having a one-dimensional array of microlouvers is used, the microlouver layer preferably extends in a generally horizontal direction of extension. Alternatively, a microlouver layer having two arrays of microlouvers with generally vertical directions of extension may be used.

[0063] Polarization Filtering The design of the coatings on the facets has a significant effect on the reflection filter. Figure 9A shows the angular reflectivity of typical coatings used on facets 12A and 40A. In most cases, as is inherent in the more basic Fresnel reflection properties (Figure 9B), the reflectivity is polarization dependent (or "polarization sensitive") as shown.

[0064] Arrow 150 indicates the angle corresponding to reflections 26A(B) through 28A(B). For this coating, at this angle of incidence, P-polarized light is reflected more than S-polarized light. Arrow 154 indicates the angled reflections 22A(B) through 24A(B) with low reflectivity and no polarization selectivity. In alternative embodiments used for specific LOE facets, 155 and 152 represent reflection angles with a clearly predominant S-polarized light. According to aspects of an embodiment of the present invention, specific selection of facet slope angles and / or coating contours can be used to take advantage of the polarization-dependent properties of real-world reflection suppression as described herein.

[0065] Because the dominant polarization (such as 6UF or 6DF) of the reflection can be controlled in a predetermined manner (e.g., by an appropriate anti-reflective coating as described above, or by the properties of the facets themselves), ghost reflection attenuation is advantageously achieved by the use of a polarizing filter or "polarizer" 160U in front of the light guide as shown in FIG. 10A. Any suitable type of polarizer can be used; most preferably, a structural (or "Cartesian") polarizer, typically an absorptive polarizer, is used. This polarizer will reduce unpolarized light from the scene 4 by up to 50% (which may in many cases be necessary or desirable anyway), but will more likely reduce the polarized upper front reflection 6UF or lower front reflection 6DF. The polarizer orientation should preferably be set relative to the orientation of the facet reflection (perpendicular or horizontal to the facets, depending on S or P blocking).

[0066] In some cases, the LOE and outcoupling configuration define at least one high-incidence-angle polarization-dependent optical path that is incident on one of the first and second major exterior surfaces at an incidence angle greater than 60 degrees and exits the LOE toward the observer's eye, the polarization-dependent optical path having an orientation that benefits from polarization. The polarizing filter is then advantageously deployed to prevent external light traveling along the polarization-dependent optical path with an orientation that benefits from polarization from reaching the observer's eye. In the above example of FIG. 10A, polarizing filter 160U is deployed outward to filter light that enters first (outer) major exterior surface 11A.

[0067] One example of an embodiment of the present invention is a light guide with a facet coating designed to produce a reflection of a real-world ghost image with polarization perpendicular to the polarization of the outcoupled projected image. In this case, a polarizer can be placed on the inside facing the observer, as shown by 160I in FIGS. 10B and 10C, and a polarizing filter deployed to filter light exiting the second outer major surface toward the observer's eye. This configuration can also prevent reflections projected toward the eye, which also originate at the rear of the light guide (e.g., 6SB) and pass through the polarizer twice, as evident in FIG. 10C. However, this arrangement should only be used if the virtual image projected by projector 2 illuminates the eye with minimal attenuation or distortion by this polarizer. In other words, the image illumination outcoupled from the LOE toward the observer's eye is polarized substantially with the image polarization, and polarizing filter 160I is deployed to block light with polarization perpendicular to the image polarization.

[0068] In each case where a polarizer is used, the orientation of the polarizer is dictated by the facet structure (e.g., by at least 20 degrees, or by at least 30 degrees, and in certain cases by 60 to 120 degrees), and is oriented so as to reduce polarization of real-world ghost illumination potentially reflected by the facets, and not be significantly reflected by at least one of the set of facets at that particular angle of incidence by ghosts passing through the light path. This often results in a polarization orientation that is angularly offset from the normal polarized sunglasses deployment, which transmits P-polarized light and rejects S-polarized light from the horizontal plane.

[0069] Figure 10D shows the implementation of side polarizer 160S on the system side. This way the polarizer works is much the same as polarizer 160U, which blocks polarized light that is side-reflected from the light guide (6SB). Preferably, the side polarizer is implemented with front polarizer 160U or 160I. Therefore, the background intensity visibility is the same from the front or the periphery (side).

[0070] When 160I is used in conjunction with 160S (as shown in FIG. 10D), the orientation of 160S is preferably perpendicular to 160I (i.e., crossed polarization axes, such as one vertical and one horizontal), resulting in complete blocking of all side reflections while maintaining peripheral visibility.

[0071] In some light guide and facet architectures, the virtual introduced image impacts the eye with linear polarization. In such cases, a polarizer can be used closer to the eye (as shown in 10B), with the result that some of the ghost reflections are filtered. However, in addition to this, some of the background reflections are reflected with the same polarization after further polarization rotation in the light guide. Because this polarization rotation does not occur in the direct background ray 4, introducing a second polarizer 232 (FIG. 10E) with the same orientation as 230 would have no additional effect on the direct ray 4 but would introduce additional attenuation in the reflections 6UF and 6DF.

[0072] Variation for LOE with two sets of facets Particular embodiments of LOEs according to the present invention use two distinct, non-parallel sets of partially reflective surfaces to achieve optical aperture expansion in two dimensions within the LOE. Many of the features described above for eliminating or reducing (collectively "suppressing") unwanted reflections of real-world illumination (ghosting) are equally applicable to 2D-extended LOEs. In some of these applications, various additional considerations are addressed below with respect to Figures 14A-16C.

[0073] In FIG. 14A, facets 64A are positioned in front of the eye to reflect a guided image to the eye. Facets 68A are used for optical aperture expansion by reflection from one guided image direction to a different guided image direction within the light guide and are not coupled to the eye. This can be achieved by positioning these facets away from the relevant field of view, eliminating the visibility of their direct reflections. FIG. 14A shows a configuration in which facets 68A are positioned lower than the center of the eye. Further overlap reduction is possible via non-overlapping architectures such as those shown in FIGS. 14B and 14C, where the eye looks through only one type of facet.

[0074] Figure 15A shows two overlapping sets of facets. The polarization architecture shown in Figures 10A-10E can be applied to both sets of facets simultaneously. Polarizer efficiency is improved by manipulating the reflection from both polarizations to be close to parallel by configuring one to be P-polarized and the other to be S-polarized, as shown in Figure 15A by 200A and 202A. Figure 15B shows the overlay of the polarization orientations (200B and 202B) and the polarization orientation preferred to reject the combined polarization.

[0075] Alternatively, the polarizer can be set perpendicular (or parallel) to the facet that produces the primary reflection.

[0076] FIG. 16A shows a light guide with two sets of facets: an angled set of facets 220 is used for vertical aperture expansion of the incoming image, and a vertical set of facets 222 is used for horizontal expansion. The facets 220 can be angled relative to the exterior facets of the light guide. In this case, a single facet reflection will typically be from behind, as described in FIG. 6. However, if the facets 220 are perpendicular (or approaching perpendicular) to the exterior surface of the light guide, a single reflection may occur from the front of the light guide, as illustrated by the arrow in FIG. 16B.

[0077] Figure 16C shows the reflectivity of a typical facet coating (the reflectivity is as described by 3C, since it has nearly or exactly perpendicular facets), with the coating having a typical reflection angle 224 and the angle 226 of the front single reflection (Figure 16B). It is clear that the back reflection will tend to be at a near-perpendicular angle 224, where the dielectric coating has low differentiation between polarizations, whereas the front reflection angle 226 will have high differentiation. Therefore, according to an embodiment of the present invention, a polarizer 228 is placed in front of a light guide that would otherwise have a significant single front reflection, to filter the polarization.

[0078] Some coatings also have inherent polarization selectivity at perpendicular angles, such as wire grids or birefringent dielectrics (by 3M). In this case, a side polarizer (160S in Figure 10D) can be used advantageously to achieve effective return loss.

[0079] Polarizer 228 can be designed to have different orientations in front of 220 and in front of 222, because different orientations of the facets produce reflections with different polarizations. Optionally, a nonlinear polarizer that gradually transitions between the two desired polarization orientations can be used to avoid a sharp boundary.

[0080] The reflection can begin with repeated reflections from one or more sets of facets. For example, in Figure 12A, the reflection can have some linear polarization after reflection from facet 68A, and can be changed to an arbitrary polarization after reflection from facet 64A. In this case, the specific polarization of the reflection should be calculated, and a nonlinear polarization can be used in conjunction with a light guide. This may include a waveplate or other birefringent material with a linear polarizer.

[0081] The optical properties of the reflections striking the eye may vary across the light guide. Therefore, the methodology described above can be used non-uniformly across the light guide to achieve total reflection suppression across the observer's field of view. This may include (but is not limited to): *Variable polarizer *Variable wave plate *Variable coating of parallel and non-parallel facets *Tunable coating on the outer surface of the light guide to vary transmission and polarization

[0082] In all the above descriptions, a top-down configuration is equivalent to a side-on configuration, and a vertical facet is equivalent to a horizontal facet. In other words, the configurations are generally interchangeable; it is possible to rotate the system by 90 degrees. This includes baffles, coatings, and polarization.

[0083] It will be appreciated that the above description is intended to be given by way of example only, and that many other embodiments are possible within the scope of the invention as defined in the appended claims.

Claims

1. 1. A near-eye display device for projecting an image onto an observer's eye, comprising: The near-eye display device includes: (a) a light-directing optical element (LOE) having first and second outer major surfaces that are planar and parallel to one another and have edges; (b) a support arrangement configured to support the LOE against a head of an observer by the second outer major surface in opposing relationship with an eye of the observer; (c) an image projector for projecting illumination corresponding to an image, the image projector optically coupled to the LOE to introduce illumination into the LOE such that illumination propagates within the LOE by internal reflection at the first and second exterior major surfaces; and (d) an outcoupling arrangement deployed to couple illumination out of the LOE toward an observer's eye; (e) a light blocking baffle extending along a majority of one of the edges of the LOE and projecting out of the plane of the second outer major surface such that incident light rays from a range of grazing angles do not reach at least a portion of the second outer major surface, the baffle projecting in a direction toward an observer's eye and forming an acute angle with the second outer major surface; A near-eye display device comprising:

2. 10. The near-eye display device of claim 1, wherein the light-blocking baffle protrudes in a direction toward the center of the viewer's eyeball.

3. 10. The near-eye display device of claim 1, wherein the outcoupling arrangement includes a plurality of parallel, partially reflective surfaces deployed within the LOE at an oblique angle relative to the first outer major surface.

4. 4. The near-eye display device of claim 3, further comprising: excluding ray paths from reaching the observer's eye after penetrating the first and second exterior major surfaces and receiving said reflection from one of the partially reflective surfaces.

5. the partially reflective surface has an extension direction parallel to an extension direction of the second outer major surface; The near-eye display device of claim 3 , wherein the baffle extends along a majority of one of the edges substantially parallel to an extension direction of the partially reflective surface.

6. The near-eye display of claim 1 , wherein the light-blocking baffle is mechanically supported by attachment to the LOE.

7. The near-eye display device of claim 1 , wherein the light blocking baffle is mechanically supported by attachment to the support structure.

8. 1. A near-eye display device for projecting an image onto an observer's eye, comprising: The near-eye display device comprises: (a) a light-directing optical element (LOE) having first and second planar, parallel outer major surfaces; (b) a support arrangement configured to support the LOE against a head of an observer by the second outer major surface in opposing relationship with an eye of the observer; (c) an image projector for projecting illumination corresponding to an image, the image projector optically coupled to the LOE to introduce illumination into the LOE such that it propagates internally through internal reflection at the first and second exterior major surfaces; and (d) an outcoupling deployed to couple illumination out of the LOE toward an eye of an observer, the outcoupling having a first outer major surface coated with a multilayer coating configured to provide anti-reflective properties for visible light incident at angles of incidence less than 40 degrees and to provide high reflectivity for at least a first polarization of visible light incident at angles of incidence greater than at least 70 degrees; A near-eye display device comprising:

9. 9. The near-eye display device of claim 8, wherein the second major outer surface is coated with a multi-layer coating configured to provide anti-reflection properties for visible light incident at an angle of incidence less than 40 degrees and to provide low reflectivity for a second polarization of visible light perpendicular to the first polarization and incident at an angle of incidence between 70 degrees and 85 degrees.

10. 1. A near-eye display device for projecting an image onto an observer's eye, comprising: The near-eye display device comprises: (a) a light-directing optical element (LOE) having first and second planar, parallel outer major surfaces; (b) a support arrangement configured to support the LOE against a head of an observer by the second outer major surface in opposing relationship with an eye of the observer; (c) an image projector for projecting illumination corresponding to an image, the image projector optically coupled to the LOE to introduce illumination into the LOE such that it propagates within the LOE by internal reflection at the first and second outer major surfaces; and (d) an outcoupling arrangement deployed to couple illumination out of the LOE toward an observer's eye; (e) a microlouver layer associated with the first outer major surface of the LOE, the microlouver layer blocking light incident at an angle of incidence greater than 70 degrees from at least one direction from entering the LOE; A near-eye display device comprising:

11. The near-eye display device of claim 10 , wherein the microlouver layer includes a one-dimensional array of microlouvers having an extension direction, the microlouver layer deployed with the extension direction substantially horizontal.

12. The near-eye display device of claim 10 , wherein the microlouver layer includes two arrays of microlouvers having substantially perpendicular extension directions.

13. 1. A near-eye display device for projecting an image onto an observer's eye, comprising: The near-eye display device comprises: (a) a light-directing optical element (LOE) having first and second planar, parallel outer major surfaces; (b) a support arrangement configured to support the LOE against a head of an observer by the second outer major surface in opposing relationship with an eye of the observer; (c) an image projector for projecting illumination corresponding to an image, comprising: an image projector optically coupled to the LOE to introduce illumination into the LOE such that it propagates within the LOE by internal reflection at the first and second outer major surfaces; (d) an outcoupling configuration deployed to couple illumination out of the LOE toward the observer's eye, the LOE and the outcoupling configuration defining at least one high incidence angle polarization-dependent light path incident on one of the first and second outer major surfaces at an incidence angle greater than 60 degrees and exiting the LOE toward the observer's eye, the polarization-dependent light path preferably having a polarization orientation; and (e) a polarizing filter deployed to prevent external light traveling along a polarization-dependent optical path due to said polarization-beneficial orientation from reaching the observer's eye; A near-eye display device comprising:

14. 14. The near-eye display of claim 13, wherein the polarizing filter deploys to filter light that penetrates the first exterior major surface.

15. 14. The near-eye display of claim 13, wherein the polarizing filter deploys to filter light exiting the second exterior major surface toward an observer's eye.

16. 16. The near-eye display device of claim 15, wherein illumination outward from the LOE directed toward an observer is substantially polarized by an image polarization, and the polarizing filter is deployed to block light having a polarization perpendicular to the image polarization.

17. 16. The near-eye display device of claim 15, further comprising a second polarizing filter deployed to filter light entering the first outer major surface, the first polarizing filter and the second polarizing filter being aligned to transmit light of the same polarization.

18. 16. The near-eye display device of claim 15, further comprising a horizontal polarizing shade element for filtering light from at least one direction along a path between an observer's eye and the LOE, the polarization axis of the horizontal polarizing shade element being at a crossed angle relative to the polarization axis of the polarizing filter.

19. 14. The near-eye display device of claim 13, further comprising a horizontally polarizing shade element for filtering light from at least one direction along a path between an observer's eye and the LOE.

20. 20. The near-eye display device of claim 8, wherein the outcoupling arrangement comprises a plurality of parallel, partially reflective surfaces deployed within the LOE at an oblique angle relative to the first outer major surface.

Images