Optical system comprising a light-guiding optical element having a two-dimensional extension

Abstract

An optical system includes an image redirection arrangement having at least two reflectors to direct a collimated image from an image projector to propagate in a first direction and a second direction within a light-guiding optical element (LOE), whereupon the collimated image is reflected by a corresponding first set of partially reflective inner surfaces and a second set of partially reflective inner surfaces toward an outcoupling optical arrangement. A portion of a field of view (FOV) adjacent to the right side of the collimated image propagating in the first direction intersects a plane of one of the sets of partially reflective inner surfaces or a plane parallel to the main outer surface, thereby forming a self-overlap of a portion of the collimated image in a field of view region that does not reach a user's eye.

Description

Technical Field

[0001] The present invention relates to optical systems, and in particular, the present invention relates to optical systems including a light-guide optical element (LOE) for achieving optical aperture expansion. Background Art

[0002] Many near-eye display systems include a transparent light-guiding optical element (LOE) or "waveguide" placed in front of the user's eye, which transmits an image within the LOE by internal reflection, and then couples the image out toward the user's eye through a suitable output coupling mechanism. The output coupling mechanism can be based on embedded partial reflectors or "facets", or a diffractive element can be employed. The following description will mainly refer to the facet-based outcoupling arrangement.

[0003] Various LOE configurations for achieving two-dimensional expansion of the optical aperture of an image projector are disclosed in U.S. Patent No. 10,551,544 and PCT Patent Application Publication No. WO 2020 / 049542 A1, which are commonly assigned with the present application. In these examples, a first set of partially reflective facets progressively reflects an image injected into the LOE to redirect the image from a first direction to a second direction while achieving a first dimension of aperture expansion, and a second set of partially reflective facets progressively couple out the redirected image while achieving a second dimension of aperture expansion.

[0004] When implementing such a configuration with a large field of view, the range of angles that can be used is limited at one end by the requirement that all rays of an image propagating within the LOE must be incident on a major surface of the LOE at an angle of incidence greater than the critical angle. At the other end, if the angular field of the image within the LOE intersects the central plane of the LOE, some of the rays of the image overlap as rays of a conjugate image (i.e., in the same direction), causing corruption of that portion of the image. Additional restrictions are imposed on the planes of partially reflecting surfaces ("facets") within the LOE, because any portion of the image field that intersects the plane of the facets is corrupted by reflections off adjacent areas of the image. These considerations complicate the design of LOEs for two-dimensional aperture expansion and impose restrictions on the angular field of images that can be displayed. Summary of the invention

[0005] The present invention is an optical system for directing image illumination to an eye box for viewing by a user's eye.

[0006] According to the teachings of an embodiment of the present invention, an optical system for guiding an image to an eye box for viewing by an eye of a user is provided, the optical system comprising: (a) an image projector, which projects illumination corresponding to a collimated image, the collimated image having an angular field of view from left to right and from top to bottom and a principal ray at the center of the field of view representing a propagation direction; (b) a light-guiding optical element (LOE), which is formed of a transparent material and has a first principal outer surface and a second principal outer surface parallel to each other; (c) an image redirection arrangement, which comprises at least a first reflector and a second reflector, the first reflector being arranged to redirect a portion of the illumination in a first direction within the LOE so that the collimated image propagates in the first direction by internal reflection within the LOE, and the second reflector being arranged to redirect a portion of the illumination in a second direction within the LOE so that the collimated image propagates in the second direction by internal reflection within the LOE; and (d) an outcoupling optical arrangement associated with the LOE and configured to cause the collimated image to propagate in the second direction by internal reflection within the LOE. Illumination propagating within the LOE is deflected outwardly toward the eye box; and (e) multiple groups of partially reflective inner surfaces within the LOE, the multiple groups of partially reflective inner surfaces comprising a first group of mutually parallel partially reflective inner surfaces and a second group of mutually parallel partially reflective inner surfaces, the first group of mutually parallel partially reflective inner surfaces being arranged to redirect illumination propagating in a first direction toward a coupling-out optical arrangement, the second group of mutually parallel partially reflective inner surfaces being arranged not parallel to the first group of partially reflective inner surfaces, for redirecting illumination propagating in a second direction toward the coupling-out optical arrangement, wherein a portion of the illumination redirected in the first direction and redirected by the first group of partially reflective inner surfaces provides at least a left side of the field of view to the eye box, and wherein a portion of the field of view adjacent to the right side of the collimated image propagating in the first direction intersects with a plane of one of the multiple groups of partially reflective inner surfaces or a plane parallel to the main outer surface, thereby forming a self-overlap of a portion of the collimated image in an area of ​​the field of view that does not reach the eye box.

[0007] According to another feature of an embodiment of the invention, a portion of the illumination redirected in a second direction and redirected by a second set of partially reflective inner surfaces provides at least a right side of the field of view to the eye box, and wherein a portion of the field of view adjacent to a left side of the collimated image propagating in the second direction intersects a plane of one of the multiple sets of partially reflective inner surfaces or a plane parallel to the main outer surface, thereby forming a self-overlap of a portion of the collimated image in an area of ​​the field of view that does not reach the eye box.

[0008] According to another feature of embodiments of the invention, the image redirection arrangement comprises a reflecting prism, which is external to the LOE, the reflecting prism providing the first reflector and the second reflector.

[0009] According to another feature of an embodiment of the invention, the first reflector is a reflective surface inside the LOE and parallel to the first set of partially reflective interior surfaces, and the second reflector is a reflective surface inside the LOE and parallel to the second set of partially reflective interior surfaces.

[0010] According to another feature of an embodiment of the invention, the first set of partially reflective interior surfaces and the second set of partially reflective interior surfaces are in an overlapping relationship in at least one region of the LOE.

[0011] According to another feature of an embodiment of the present invention, the first set of partially reflective interior surfaces and the second set of partially reflective interior surfaces are each at an oblique angle to the major exterior surface of the LOE.

[0012] According to another feature of an embodiment of the invention, a portion of the field of view adjacent to the right side of the collimated image propagating in the first direction intersects a plane of the second set of partially reflective inner surfaces.

[0013] According to another feature of an embodiment of the invention, a portion of the field of view adjacent to the right side of the collimated image propagating in the first direction intersects a plane parallel to the major outer surface.

[0014] According to another feature of an embodiment of the present invention, the coupling-out optical arrangement includes a third group of mutually parallel partially reflective inner surfaces, wherein the third group of mutually parallel partially reflective inner surfaces are not parallel to the first group of partially reflective inner surfaces and the second group of partially reflective inner surfaces, and the third group of mutually parallel partially reflective inner surfaces form an oblique angle with the main outer surface of the LOE. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention is herein described, by way of example only, with reference to the accompanying drawings, in which:

[0016] Figure 1A and Figure 1B are schematic isometric views of an optical system implemented using a light-guiding optical element (LOE) constructed and operative in accordance with the teachings of the first aspect of the present invention, showing top-down and side-injection configurations, respectively;

[0017] Figure 2A is a schematic isometric view showing a field of view (FOV) of an image viewed by a user's eyes;

[0018] Figure 2B is a schematic top view showing the area where the left and right ends of the FOV are provided to the LOE of the eye motion box (EMB);

[0019] Figure 2C is similar to Figure 2B, additionally showing the end of the field of view projected from the region of the LOE that does not reach the EMB, and thus allowing this end to be damaged according to aspects of the present invention;

[0020] Figure 3A is a schematic representation of a sequence of angles in space showing a sequence of reflections for providing alternative light paths to the right (top of the figure) and left (bottom of the figure) of the field of view;

[0021] 3B(1) and 3B(2) are schematic top views of high-quality and damaged portions of a projected image from the right and left sides of a LOE, respectively, where only the high-quality portion of the projected image reaches the EMB;

[0022] Figure 3C and Figure 3D They are respectively shown in the physical space Figure 3A A series of schematic front and side views of the optical path;

[0023] Figure 3E and Figure 3F yes Figure 3A A three-dimensional angular representation of the reflection sequence shown in Figure 3E includes arrows showing the sequence of reflections, and Figure 3F Indicate the damaged areas of each image;

[0024] Figure 4A and Figure 4B is an alternative embodiment of the present invention similar to Figure 3E and Figure 3F Three-dimensional angle representation of ;

[0025] Figure 5A and Figure 5B is another alternative embodiment of the present invention similar to Figure 3E and Figure 3F Three-dimensional angle representation of ;

[0026] Figures 6 to 8 are schematic diagrams of respective components and overall assembly structures of three alternative implementations of LOEs according to the teachings of embodiments of the present invention;

[0027] Fig. 9 is a graph showing the angular dependence of the reflectivity of a partially reflective interior surface (facet) for an implementation of the present invention, and also showing the angular ranges of various images propagating within the LOE;

[0028] Fig.10 yes Figures 1A to 8 A schematic front view of an implementation of LOE of , showing center-down injection of the coupled-in image;

[0029] Fig.11A is similar to Fig.10 A view showing an implementation method in which the coupled image is vertically injected;

[0030] Fig. 11B and Fig. 11C is along Fig.11A Schematic cross-sectional view taken along line XI-XI of , showing a first implementation and a second implementation of an image redirection arrangement for coupling in projection images in two directions;

[0031] Fig. 12A is similar to Fig.10 A view showing an implementation method of upward injection coupling into the image;

[0032] Fig. 12B and Fig. 12C is along Fig. 12A A schematic cross-sectional view taken along line XII-XII of , showing a first implementation and a second implementation for coupling in a projection image in an upward direction;

[0033] Fig.13A is a schematic angular representation of another implementation of the present invention employing a first set of partially reflective interior surfaces and a second set of partially reflective interior surfaces perpendicular to the major exterior surface of the LOE; and

[0034] Fig. 13B is with Fig.13A A schematic front view of a LOE corresponding to an embodiment of the present invention. DETAILED DESCRIPTION

[0035] The present invention is an optical system for directing image illumination to an eye box for viewing by a user's eye.

[0036] The principles and operation of an optical system according to the present invention may be better understood with reference to the drawings and accompanying description.

[0037] By way of introduction, certain aspects of the invention relate to an optical system for directing image illumination via a light guide optical element (LOE) to an eye box (EMB) for viewing by a user's eye. The optical system provides optical aperture expansion for the purpose of a heads-up display and most preferably a near-eye display, which may be a virtual reality display or more preferably an augmented reality display. Preferably, the optical system provides a two-stage expansion of the input optical aperture, and wherein the first expansion is achieved using two different sets of mutually parallel partially reflective surfaces ("facets"), each set of partially reflective surfaces presenting a different (non-identical but preferably overlapping) portion of the overall field of view (FOV) to the eye.

[0038] In a typical but non-limiting embodiment ( Figure 1A and Figure 1B), the optical system employs a single image projector ("POD") that provides image illumination to two sets of facets integrated into the LOE. In summary, Figure 1A and Figure 1B An optical system for directing image illumination injected into at least one incoupling region to an eye box for viewing by an eye of a user is shown. The optical system includes a light guide optical element (LOE) 112 formed of a transparent material and including a first region 116 comprising a first set of planar mutually parallel partially reflective surfaces ("facets") having a first orientation and a second set of planar mutually parallel partially reflective surfaces ("facets") having a second orientation that is non-parallel to the first orientation. (The facets are in the Figure 1A and Figure 1B ) The LOE also includes a second region 118 that includes a third set of planar mutually parallel partially reflective surfaces (or "facets", also referred to as "outcoupling surfaces") having a third orientation that is non-parallel to each of the first orientation and the second orientation. The LOE is bounded by a set of mutually parallel major exterior surfaces extending across the first region and the second region such that the first set of partially reflective surfaces, the second set of partially reflective surfaces, and the third set of partially reflective surfaces are all located between the major exterior surfaces.

[0039] The third set of partially reflective surfaces is angled with the primary outer surface such that a portion of the image illumination that propagates from the first region into the second region by internal reflection at the primary outer surface within the LOE is coupled out of the LOE toward the eye box for viewing by the user's eye. Alternatively, in lieu of the third set of facets, a diffractive optical element may be used in the second region 118 for gradually coupling out the image illumination toward the eye box. Similarly, a diffractive optical element may be used to couple image illumination from the projector 114 into the LOE for propagation within the first region 116 by internal reflection.

[0040] Each partially reflective surface of the first and second sets of partially reflective surfaces is oriented such that a portion of image illumination from at least one in-coupling region propagating within the LOE by internal reflection at the major exterior surface is deflected toward the second region.

[0041] Most preferably, each of the first and second sets of facets is responsible for aperture expansion of a different portion of the overall field of view. Specifically, preferably, the first set of partially reflective surfaces deflects a first portion of the field of view of an image toward the second region, and the second set of partially reflective surfaces deflects a second portion of the field of view of an image toward the second region, the first and second portions of the field of view combining to provide a continuous combined field of view that is larger than each of the first and second portions of the FOV. Preferably, the two portions of the FOV correspond roughly to two sides (left and right or top and bottom, but arbitrarily referred to as "left" and "right" hereinafter) of the overall FOV, but with sufficient overlap with the central region to ensure complete and continuous coverage of the central field across the eye box, which corresponds to an acceptable range of positions of the pupil of the viewer for whom the display is designed.

[0042] An exemplary embodiment of the present invention takes the form of a near-eye display, generally designated 110, that employs a LOE 112. A compact image projector (or "POD") 114 is optically coupled to inject an image into the LOE 112 (interchangeably referred to as a "waveguide," "substrate," or "slab") within which image light is captured in one dimension by internal reflection at a planar major outer surface. The light impinges upon a first set of partially reflective surfaces and a second set of partially reflective surfaces (interchangeably referred to as "facets"), wherein each set of facets is tilted relative to a direction of propagation of the image light, wherein each successive facet deflects a portion of the image light into a deflection direction that is also captured / guided within the substrate by internal reflection. These first set of facets and the second set of facets are not disposed in a manner that is consistent with the embodiment of the present invention. Figure 1A and Figure 1B 1 and 12. The partial reflections at the successive facets are shown separately in FIG. 1 and are instead located in a first region of the LOE designated 116. This partial reflection at the successive facets enables optical aperture expansion in a first dimension.

[0043] The first set of partially reflective surfaces and the second set of partially reflective surfaces located in region 116 deflect image illumination from a first propagation direction captured within the substrate by total internal reflection (TIR) ​​to a second propagation direction also captured within the substrate by TIR. This partial reflection at successive facets enables optical aperture expansion in a first dimension.

[0044] The deflected image illumination then enters a second substrate region 118, which may be implemented as adjacent distinct substrates or as a continuation of a single substrate, in which an outcoupling optical device (another set of partially reflective facets or diffractive optical elements) progressively couples a portion of the image illumination out toward the eye of an observer located within an area defined as an eye movement box (EMB), thereby achieving an optical aperture expansion in a second dimension. The entire device may be implemented separately for each eye, and preferably the entire device is supported relative to the user's head, with each LOE 112 facing a respective eye of the user. In a particularly preferred option as shown here, the support arrangement is implemented as an eyeglass frame having a side 120 for supporting the device relative to the user's ear. Other forms of support arrangements may also be used, including but not limited to headbands, goggles, or devices suspended from a helmet.

[0045] Reference is made herein to an X-axis and a Y-axis, wherein the X-axis is horizontal along the general extension direction of the first region of the LOE ( Figure 1A ) or vertical ( Figure 1B ) extends, and the Y axis extends perpendicular to the X axis, that is, Figure 1A Extends vertically in Figure 1B Medium horizontal extension.

[0046] In very similar terms, the first region 116 of the LOE 112 can be considered to achieve an aperture expansion in the X direction, while the second LOE or the second region 118 of the LOE 112 achieves an aperture expansion in the Y direction. The details of the expansion in the angular directions in which different portions of the field of view propagate will be described in more detail below. It should be noted that, as Figure 1A The orientation shown in can be viewed as a "top-down" implementation, in which the image illumination entering the primary (second region) of the LOE enters from the top edge, while Figure 1B The orientation shown in can be considered as a "lateral injection" implementation in which the axis referred to here as the Y axis is arranged horizontally. In the remaining figures, in an arrangement similar to Figure 1A Various features of certain embodiments of the present invention are shown in the context of a "top-down" orientation. However, it should be understood that all of these features are equally applicable to lateral injection implementations, which also fall within the scope of the present invention. In some cases, other intermediate orientations may also be applicable and are also included in the scope of the present invention unless expressly excluded. For simplicity and clarity of presentation, the two sides of the display image provided by the different first and second groups of facets are referred to below as "left" and "right" corresponding to the ends in the X direction, but as mentioned above, "left" and "right" do not necessarily correspond to the horizontal spacing in the final arrangement orientation of the device.

[0047] In a first set of preferred but non-limiting examples of the present invention, the aforementioned first set of facets and the second set of facets are orthogonal to the main outer surface of the substrate. In this case, the injected image and its conjugate that undergoes internal reflection when propagating within the region 116 are both deflected and become conjugate images propagating along the deflection direction. In an alternative set of preferred but non-limiting examples, the first set of partially reflective surfaces and the second set of partially reflective surfaces are at an oblique angle relative to the main outer surface of the LOE. In the latter case, the injected image or its conjugate forms the desired deflected image propagating within the LOE, while the other reflection can be minimized, for example, by employing an angle selective coating on the facet, wherein the angle selective coating makes it relatively transparent to the range of incident angles presented by the image that does not require its reflection.

[0048] Preferably, the POD employed by the apparatus of the present invention is configured to generate a collimated image, i.e., a parallel beam in which the light of each image pixel is collimated to infinity in an angular direction corresponding to the pixel position. Thus, the image illumination spans an angular range corresponding to a two-dimensional angular field of view. Figure 2A This angular field of view is schematically represented in , where the user's eyes view the field of view, in this case a rectangle extending from the left side "L" to the right side "R", and from the upper edge "T" to the lower edge "B". A representative propagation direction is considered to be the central direction corresponding to the chief ray "C".

[0049] The image projector 114 includes at least one light source, which is typically arranged to illuminate a spatial light modulator such as an LCOS chip. The spatial light modulator modulates the projection intensity of each pixel of the image, thereby generating an image. Alternatively, the image projector may include a scanning arrangement, which is typically implemented using one or more fast scanning mirrors, which scan the illumination from the laser light source across the image plane of the projector, while the intensity of the beam changes synchronously pixel by pixel with the movement, thereby projecting the desired intensity for each pixel. In both cases, collimating optics are provided to generate an output projection image that is collimated to infinity. Some or all of the above components are typically arranged on the surface of one or more polarizing beam splitters (PBS) cubes or other prism arrangements known in the art.

[0050] The optical coupling of the image projector 114 to the LOE 112 can be achieved by any suitable optical coupling, for example, via a coupling prism having an angled input surface, or via a reflective coupling arrangement, via a side edge and / or one of the major outer surfaces of the LOE. Alternatively, a diffractive optical element (DOE) can be used to couple the image into the substrate. Except for the details of the coupling configuration specified in certain examples below, the details of the coupling configuration are generally not critical to the present invention and are shown here only schematically.

[0051] It should be understood that the near-eye display 110 includes various additional components, typically including a controller 122 for actuating the image projector 114, typically using power from a small onboard battery (not shown) or some other suitable power source. It should be understood that the controller 122 includes all necessary electronic components, such as at least one processor or processing circuitry, to drive the image projector, all of which are well known in the art.

[0052] Now refer to Figure 2B 4, note that the right end of the projected image reaching EMB 4 originates from the region of LOE 2 indicated as "A", while the left end of the projected image reaching EMB 4 originates from the region of LOE "B". The EMB designates the range of eye positions required for the optical system to provide a full FOV image. Aspects of the present invention take advantage of this observation: allowing Figure 2C The projected image in the areas marked as 6 in FIG. 1 is partially damaged, the projected image in these areas does not reach EMB 4 and therefore does not affect the quality of the image viewed by the user.

[0053] Therefore, according to one aspect of the present invention, the manner in which the image from the projector 114 is redirected toward the first group of partially reflective surfaces and / or the second group of partially reflective surfaces is of particular importance. Specifically, according to this aspect of the present invention, the optical system also includes an image redirection arrangement, the image redirection arrangement including at least a first reflector and at least a second reflector, the first reflector being arranged to redirect a portion of the image illumination along a first direction within the LOE so that the collimated image propagates within the LOE by internal reflection along the first direction toward the first group of partially reflective internal surfaces, and at least the second reflector being arranged to redirect a portion of the illumination along a second direction within the LOE so that the collimated image propagates within the LOE by internal reflection along the second direction toward the second group of partially reflective internal surfaces. A portion of the field of view adjacent to the right side of the collimated image propagating along the first direction intersects with a plane of one of the groups of partially reflective internal surfaces or a plane parallel to the main outer surface, thereby forming a self-overlap of a portion of the collimated image. However, since the first group of partially reflective surfaces provides the left side of the image to the eye box, the self-overlap corrupts the image in the field of view area that does not reach the eye box.

[0054] Preferably, the opposite arrangement is used on the right side of the field of view. Specifically, preferably, a portion of the field of view adjacent to the left side of the collimated image propagating in the second direction intersects with a plane of one of the sets of partially reflective inner surfaces or a plane parallel to the main outer surface, thereby forming a self-overlap of a portion of the collimated image. However, since the second set of partially reflective surfaces provides the right side of the image to the eye box, this self-overlap corrupts the image in the area of ​​the field of view that does not reach the eye box. Specific examples of redirection arrangements and their corresponding effects on certain areas of the image that do not reach the eye box are presented below.

[0055] Now turn to FIG. 3A to FIG. 3D , these figures schematically illustrate two-dimensional aperture expansion for a large FOV according to a non-limiting example of the present invention. Figure 3A shows the process in angle space, while FIG. 3B(1) to FIG. 3D The equivalent process in real space is shown.

[0056] Figure 3A The representation of is based on a two-dimensional straight-line representation of angular space, in which spherical coordinates are depicted in Cartesian coordinates. This representation introduces various distortions, and displacements along different axes are not commutative (as is the property of rotations about different axes). However, it has been found that this form of diagram simplifies the description and provides a useful tool for system design. The circles represent the critical angles of the major outer surfaces of the waveguide (the boundaries of total internal reflection (TIR)). Therefore, the points outside the circle represent the angular direction of the beam that will be reflected by TIR, while the points inside the circle represent the beam that will pass through the face and transmit out of the waveguide. Circle 9 represents the critical angles of the front and back sides of the waveguide. The "distance" between the centers of the circles is 180 degrees.

[0057] These figures show 4 consecutive stages of image illumination by the optical system after successive reflections. The initial state after the injection of the rectangular image 14 into the waveguide is shown at stage 10. Since the image 14 is outside the circle 9, its rays are guided by TIR as it propagates along the waveguide by internal reflection at the major surfaces of the waveguide (hence the representation of the two coupled rectangles 14 and 14'). This propagation of the image Figure 3C 10 are represented as arrows in the real space depiction of the waveguide 16 shown in stage 10. Throughout this document, the real space propagation direction is shown with reference to the in-plane component of the propagation direction parallel to the major surface of the substrate. It should be understood that the arrows represent propagation by internal reflection from the front and back surfaces of the waveguide, and generally indicate the in-plane component of the chief ray of the image.

[0058] As the image propagates in the waveguide, it encounters the first and second reflectors of the redirecting optical arrangement, depicted in angular space as dash-dot lines 18A and 18B, respectively. These facets cause the image to change direction in angular space, as indicated by rectangles 15A and 15B, each of which generates its own conjugate image 15A′ and conjugate image 15B′ by internal reflection at the major outer surface of the LOE. In real space ( Figure 3C In stage 11), the redirected image propagation direction is represented by arrow “A” and arrow “B” for lateral propagation.

[0059] In this non-limiting example, the first reflector is a reflective surface inside the LOE and parallel to the first set of partially reflective interior surfaces, and the second reflector is a reflective surface inside the LOE and parallel to the second set of partially reflective interior surfaces. Figures 6 to 8 Specific examples of how such a structure may be implemented are described.

[0060] It is evident that facet plane 18A intersects one of the images 15A′ at region 20. This portion of the image is therefore itself reflected, rendering that segment of the image unusable. This unusable segment is shadowed within the rectangular image. A similar process occurs in the image redirected by facet 18B, where image 15B′ intersects the facet and causes damaged region 20. While in many cases multilayer dielectric coatings used to achieve partially reflective surfaces are designed to have low reflectivity at large angles of incidence, the reflectivity at grazing incidence is always high, and therefore such coatings cannot prevent damage to images that intersect the plane of the facets.

[0061] The deflected image is redirected to image 14 and image 14′ by further reflection in the first set of facets and the second set of facets. Since all the directed images are coupled to each other, the unusable segment due to facet 18A is reproduced to all four images, namely image 14, image 14′, image 15A and image 15A′, and the same is true for the unusable segment generated by facet 18B. However, image 15A propagating on one side of the LOE has an opposite unusable segment compared to image 15B, as shown in stage 12, which shows the coupling out of image 14′ by the coupling out facet 22 to generate coupled-out image 16A and coupled-out image 16B. The top view (Figures 3B(1) and 3B(2)) shows how each sub-image (A and B) illuminates the eye box 4 with the unimpaired portion of its corresponding image, while the unusable portion of image 6 is projected in a direction outside the eye box and is therefore not visible to the user.

[0062] Figure 3E and Figure 3F The three-dimensional angle representation shows Figure 3A Here, the planes of facets 18 and 22 are shown as circles. Figure 3E Shows Figure 3A The same image shown in Figure 3F The unusable portion is shown generated as 20A1 and 20A2 folded over each other around facet 18, and the combined unusable portion propagates as 20B, 20C, 20D and couples out as 20E.

[0063] Figure 4A and Figure 4B A different angular architecture according to an implementation of the invention is shown (in the non-limiting example of an image with a 4:3 form factor (ratio) and a 70 degree diagonal). Here, however, the facet angle intersects the image angular distribution twice, at 20A and at 20D. The two unusable portions overlap, and thus the final result is equivalent to the above referenced FIG. 3A to FIG. 3D Describe the results.

[0064] Figure 5A and Figure 5B The case where image 15 and image 15' (the image deflected from facet 18 and its conjugate) partially overlap, thereby generating an unusable portion 20. This corresponds to the case where a portion of the field of view adjacent to the right (or left) side of the collimated image propagating in the first (or second) direction intersects a plane parallel to the main external surface. This causes part of the image to fold back on itself. As in the previous example, this unusable portion illuminates only an area 6 ( Figure 2B ), while the eye box 4 is illuminated by parts A and B of the image having undisturbed areas.

[0065] Figure 6 , Figure 7 and Figure 8 Various configurations of waveguides and corresponding components are described. Dimensions are schematic for clarity of presentation. The actual dimensions of each component are geometrically determined by the optical path required to reach the eye box.

[0066] exist Figure 6 In the embodiment of the present invention, the waveguide 31 is formed of four separate parts: a beam splitting part 30, which is composed of two overlapping parts 30A and part 30B having facets tilted in different orientations. The orientations of the facets do not have to be oppositely or symmetrically tilted, and therefore, the redirected image illumination from the first reflector (18A) and the second reflector (18B) does not need to be in exactly opposite directions, and other considerations such as waveguide tilt relative to the output image or different trimming of the two images can be taken into account.

[0067] To improve the image uniformity, partial reflectors (PR) may be introduced between the overlapping portions parallel to the plane of the main outer surface of the waveguide.

[0068] Here, preferably, the lateral portion 32 has a facet parallel to the portion 30A, and the portion 34 has a facet parallel to the portion 30B, to perform image reflection towards the second portion 36 of the LOE. Figure 3A As shown in stage 13 of Figure 3B, part 36 is attached as a continuation to couple light out toward the user's eyes. In this example, all parts are attached side by side, with parts 30, 32 and 34 together forming Figure 1A or Figure 1B 116 , and portion 36 corresponds to the second waveguide portion 118 .

[0069] Figure 7 Another alternative implementation is shown in which waveguide 50 is assembled from portion 52 overlying portion 54 to provide a first waveguide portion 116 that implements the redirection optical arrangement and the beam splitting operation of the first set of partially reflective surfaces and the second set of partially reflective surfaces. Figure 1A or Figure 1B The portion 36 of the second waveguide portion 118 is placed continuously to couple out the image. Here, the partial reflector (PR) can also be implemented as a coating between the overlapping parts (here, the lower part 52 is shown attached to the upper part 54 in an opposing relationship). Figure 6 and Figure 7 In both cases, the component can optionally be sandwiched between continuous glass cover plates to help achieve a high quality flat outer surface of the waveguide.

[0070] Figure 8Another option is shown, according to which all the parts (part 62, part 64 and part 66) are placed one on top of the other to assemble the waveguide 60. As shown, each part includes a set of facets that are implemented at least in the relevant area of ​​the waveguide and optionally extend across the entire dimension of the waveguide. Partial reflectors can be implemented at one or both interfaces to enhance image uniformity.

[0071] Implementing a dielectric coating that provides the required partial reflective properties for a large angular spectrum and all colors can be challenging. In principle, a standard software package for designing a multilayer dielectric coating can provide the required reflectivity variation as a function of angle, and will generate a corresponding coating design. However, the more specific the requirements, the more complex and expensive the coating becomes, and / or more compromises may have to be made for the desired performance. The present invention helps with this aspect of the design, because angles corresponding to image regions that will be damaged anyway or will not contribute to the image visible from the EMB anyway do not need to meet the reflectivity requirements required for the rest of the image.

[0072] For example, Fig. 9 The angular reflectivity 18A of a typical implementation of the multilayer dielectric coating of the facet 18 of the implementation of Fig. 5 is shown. The angular spectrum of the nominal image 14 is described as line 14N here, and the angular spectrum of image 15 is described as 15N here. The folding of image 15 on itself can be represented as a partial overlap of 14N on 15N here, and the overlap angle range is 20N (representing 20). Because range 20N does not include high-quality images that will reach the eye box, this area can be ignored (i.e., no constraints are imposed) during coating design. Therefore, the actual range of reflectivity and transmittance required by the coating of facet 18A is actually shorter, which corresponds to line 14F and line 15F. This greatly facilitates the design of suitable coatings.

[0073] This process of shortening the dynamic spectrum applies to all other configurations shown, making the implementation of faceted coatings for large FOVs more practical.

[0074] In the examples discussed so far, image illumination from the image projector 114 is coupled into the first region 116 of the LOE before reaching the first and second reflectors of the image redirection arrangement, and these reflectors are integrated with the first set of partially reflective surfaces and the second set of partially reflective internal surfaces. Coupling in this case can be achieved by any conventional arrangement known in the art, such as a coupling prism with an inclined surface, a coupling reflector, or a diffractive optical element. Fig.10The power distribution along the waveguide for this family of solutions is schematically shown. The full input intensity of the image illumination is injected into the waveguide downward (in the arbitrary direction shown) as image 14. A portion of the light is coupled in the side directions 15A and 15B. This light is in turn coupled into the second waveguide portion as light 70. Some of the injected light 14 continues as light 71 without being reflected at the facets. This light is typically of relatively high intensity and will therefore produce non-uniformities in the projected image. This can be achieved by injecting a plurality of light beams into the waveguide in segments 30, 52, 54, 62 and 64 ( Figures 6 to 8 ) to mitigate this non-uniformity by achieving high reflectivity at some or all of the facets.

[0075] Fig.11A An alternative optical configuration is presented, wherein the first and second reflectors of the image redirection arrangement are part of an incoupling arrangement for coupling light from an image projector (not shown) into the waveguide. In this case, Fig.11A As shown by the circle 14 in FIG. 1 , preferably, the image 14 from the image projector is injected perpendicular to the major surface of the LOE. Fig. 11B and Fig. 11C Two non-limiting examples of implementations of image redirection arrangements are shown in .

[0076] exist Fig. 11B , projector 114 has an exit pupil on reflecting prism 78. The light from projector 114 is split by prism 78 into two beams: beam 15A and beam 15B, with beam 15A coupled into one side of the waveguide and beam 15B coupled into the other side. In this configuration, there is no Fig.10 The beam 71 is similar to the high intensity center beam.

[0077] Fig. 11C An alternative implementation is shown in which facet plates 80A and 80B are similar to Figure 6 30A and 30B of the waveguide but are attached to the outside of the waveguide. As described above, the facets in these two parts deflect the light into the sideward propagating images 15A and 15B. No high intensity central beam is generated here either.

[0078] The two images, image 15A and image 15B, are injected into the waveguide after being reflected by the facets of prism 78 or the facets of plates 80A and 80B. Preferably, during this injection, they are also trimmed by the edge 79 of the coupling arrangement. This trimming is most important for shallow beams. However, in particular for Figure 5A and Figure 5BWith an optical architecture of the type shown, these shallowest beams generally correspond to regions 20 that do not contribute in any case to the portion of the image that reaches the EMB, so they can also be trimmed at the incoupling stage without loss of performance. This allows the aperture of the image projector 114 and the width of the reflectors 78 and 80 of the image redirection arrangement to be smaller than would theoretically be required to transmit all of the image field in both directions. This enables the use of a smaller projector 114 and more concentrated energy.

[0079] exist FIG. 12A to FIG. 12C Another set of options is schematically shown in FIG. 1 . In this case, the high intensity input image beam 14 is deflected "upwards", i.e. away from the second region of the LOE where outcoupling occurs. This also avoids Fig.10 The formation of inhomogeneities discussed in the beam 71. Fig. 12A The resulting geometry is shown schematically in . Fig. 12B and Fig. 12C Two specific non-limiting example solutions for coupling the input image upwards are schematically shown. Fig. 12B In the case of Fig. 12C In , the incoupling prism provides a reflective surface for similarly coupling in an image from a projector (not shown). In both cases, the first and second reflectors of the image redirection arrangement are implemented here as internal reflectors within the waveguide.

[0080] Finally, refer to Fig.13A and Fig. 13B , the principle of the present invention can also be applied to the case of small facets perpendicular to the main outer surface of the substrate. Fig.13A An example of a vertical facet 90A (equivalent to the tilted facet 18) in angular space is shown, where for clarity the projection is polar as viewed along the direction of propagation of the output image 16. The injected image 15 is folded onto the image 14 by the vertical facet 90A. The overlap of the image 14 and the image 15 generates the ghost image portion 20. Fig. 13B The propagation of the same beam in real space is shown.Here, 90B is a vertical facet with equal but opposite inclination to facet 90A.

[0081] All of the above principles can also be applied to a "sideways" configuration, where an image is injected from a POD that is laterally located outside the viewing area and is spread vertically by a first set of facets and then spread horizontally by a second set of facets to couple into the user's eye. It should be understood that all of the above configurations and variations also apply to the sideways injection configuration.

[0082] Throughout the above description, reference is made to an X-axis and a Y-axis as shown, wherein the X-axis is horizontal or vertical and corresponds to a first dimension of optical aperture expansion, and the Y-axis is another principal axis corresponding to a second dimension of expansion. In this context, the orientation of the device when the device is mounted on the head of a user may be determined by a support device (e.g., the above-mentioned Figure 1A and Figure 1B The X and Y axes are defined by the orientation defined by the eyeglass frame. Other terms that are generally consistent with the definition of the X-axis include: (a) at least one straight line bounding the eye box can be used to define a direction parallel to the X-axis; (b) the edges of the rectangular projected image are generally parallel to the X-axis and the Y-axis; and (c) the border between the first area 16 and the second area 18 generally extends parallel to the X-axis.

[0083] It should be understood that the above description is intended to be exemplary only and that many other embodiments are possible within the scope of the invention as defined by the appended claims.

Claims

1. An optical system for directing an image to an eye box for viewing by a user, the optical system comprising: an image projector that projects illumination corresponding to a collimated image having an angular field of view from left to right and from top to bottom, and a chief ray at a center of the field of view representing a propagation direction; a light guide optical element LOE, the light guide optical element being formed of a transparent material and having a first main outer surface and a second main outer surface parallel to each other; an image redirection arrangement, the image redirection arrangement comprising at least a first reflector and at least a second reflector, the at least first reflector being arranged to: redirect part of the illumination along a first direction within the LOE such that the collimated image propagates along the first direction within the LOE by internal reflection, the at least second reflector being arranged to: redirect part of the illumination along a second direction within the LOE such that the collimated image propagates along the second direction within the LOE by internal reflection; an outcoupling optical arrangement associated with the LOE and configured to deflect illumination propagating within the LOE outwardly toward the eye box; as well as a plurality of groups of partially reflective internal surfaces within the LOE, the plurality of groups of partially reflective internal surfaces comprising a first group of mutually parallel partially reflective internal surfaces and a second group of mutually parallel partially reflective internal surfaces, the first group of mutually parallel partially reflective internal surfaces being arranged to redirect the illumination propagating along the first direction toward the out-coupling optical arrangement, the second group of mutually parallel partially reflective internal surfaces being arranged non-parallel to the first group of partially reflective internal surfaces to redirect the illumination propagating along the second direction toward the out-coupling optical arrangement, wherein the outcoupling optical arrangement comprises a third group of mutually parallel partially reflective inner surfaces, the third group of mutually parallel partially reflective inner surfaces are not parallel to the first group of mutually parallel partially reflective inner surfaces and the second group of mutually parallel partially reflective inner surfaces, and the third group of mutually parallel partially reflective inner surfaces are at an oblique angle to the main outer surface of the LOE, The mutually parallel first group of partially reflective inner surfaces, the mutually parallel second group of partially reflective inner surfaces and the mutually parallel third group of partially reflective inner surfaces are all located between the first main outer surface and the second main outer surface. wherein the portion of the illumination redirected in the first direction and redirected by the first set of partially reflective interior surfaces provides at least a left side of the field of view to the eye box, and wherein a portion of the field of view adjacent a right side of the collimated image propagating in the first direction intersects a plane of one of the plurality of sets of partially reflective interior surfaces or a plane parallel to the major exterior surface, thereby forming a self-overlap of a portion of the collimated image in a region of the field of view that does not reach the eye box; and wherein the first set of partially reflective interior surfaces and the second set of partially reflective interior surfaces are in an overlapping relationship in at least one region of the LOE, and Wherein, a partial reflector implemented as a coating is arranged between overlapping portions of the first group of partially reflective inner surfaces and the second group of partially reflective inner surfaces in the overlapping relationship.

2. The optical system according to claim 1, wherein: The portion of the illumination redirected in the second direction and redirected by the second set of partially reflective inner surfaces provides at least a right side of the field of view to the eye box, and wherein a portion of the field of view adjacent to a left side of the collimated image propagating in the second direction intersects a plane of one of the multiple sets of partially reflective inner surfaces or a plane parallel to the main outer surface, thereby forming a self-overlap of a portion of the collimated image in an area of ​​the field of view that does not reach the eye box.

3. The optical system according to claim 1, wherein: The image redirection arrangement comprises a reflecting prism, which is external to the LOE, the reflecting prism providing the first reflector and the second reflector.

4. The optical system according to claim 1, wherein: The first reflector is a reflective surface inside the LOE and parallel to the first set of partially reflective interior surfaces, and the second reflector is a reflective surface inside the LOE and parallel to the second set of partially reflective interior surfaces.

5. The optical system according to claim 1, wherein: The first set of partially reflective interior surfaces and the second set of partially reflective interior surfaces are each at an oblique angle to the major exterior surface of the LOE.

6. The optical system according to claim 1, wherein: A portion of the field of view adjacent to the right side of the collimated image propagating in the first direction intersects a plane of the second set of partially reflective interior surfaces.

7. The optical system according to claim 1, wherein: A portion of the field of view adjacent to the right side of the collimated image propagating in the first direction intersects the plane parallel to the major outer surface.

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