Methods for fabricating light-guide optical elements

Abstract

Methods for fabricating light-guide optical elements (LOEs) are provided. The methods involve obtaining first and second optical structures, each with a set of mutually-parallel partially reflective surfaces. These structures are bonded together such that their reflective surfaces are non-parallel, forming a third optical structure. At least one of the first or second optical structure is cut along a specific line, prior to bonding or after bonding, and the third optical structure is sliced along parallel planes to create one or more LOEs. Each LOE features parallel major external surfaces and regions with mutually-parallel partially reflective surfaces from both original sets. The specific line can include a contoured section and / or a typically straight section. The contoured section defines a contoured profile of the LOE, and the typically straight section defines a coupling-in surface of the LOE.

Description

[0001] APPLICATION FOR PATENT

[0002] TITLE METHODS FOR FABRICATING LIGHT-GUIDE OPTICAL ELEMENTS

[0003] CROSS-REFERENCE TO RELATED APPLICATIONS

[0004] This application claims priority from US Provisional Patent Application No. 63 / 605,523, filed December 3, 2023, US Provisional Patent Application No. 63 / 621,608, filed January 17, 2024, and US Provisional Patent Application No. 63 / 671,419, filed July 15, 2024, all of the whose disclosure are incorporated by reference in its entirety herein.

[0005] TECHNICAL FIELD

[0006] The present disclosure relates to optical systems, and in particular, it concerns methods for fabricating light-guide optical elements (LOEs) that achieve optical aperture expansion. BACKGROUND OF THE INVENTION

[0007] Various types of display, such as near eye displays, require large aperture to cover the area where the observer’s (i.e., user’s, viewer’s) eye is located (commonly referred to as the eye-motion box - or EMB). In order to implement a compact device, the image that is to be projected into the observer’s eye is generated by a small optical image generator (projector) having a small optical aperture. Optical arrangements for displays may employ a light-guide optical element (LOE) to expand an input image in one or more dimensions. Where two-dimensional expansion is required, an LOE with two expansion regions may be used, where one region is configured to expand an image in one dimension, and the other region is configured to expand the image in the other dimension. Of particular relevance to the present disclosure are reflective LOE’s, where the LOE is implemented as a transparent block bounded by two parallel major external surfaces configured to support propagation of light therebetween via (total) internal reflection, and where the image expansion in each region is performed by a set of mutually-parallel partially-reflecting internal surfaces (or “facets”) located between the major external surfaces. A collimated image propagating within the LOE is progressively partially deflected by the set of facets in the first region towards the set of facets in the second region, and is further progressively partially deflected by the set of facets in the second region outwards towards an eye of an observer, thereby presenting an image to the observer.

[0008] SUMMARY OF THE INVENTION

[0009] The present disclosure provides methods for fabricating light-guide optical elements (LOEs). According to the teachings of an embodiment of the present disclosure, there is provided a method for fabricating one or more light-guide optical elements (LOEs). The method comprises: obtaining a first optical structure having a first set of mutually-parallel partially reflective surfaces; obtaining a second optical structure having a second set of mutually-parallel partially reflective surfaces; bonding together the first optical structure and the second optical structure such that the partially reflective surfaces of the first set are non-parallel to the partially reflective surfaces of the second set, to form a third optical structure; cutting at least one of the first optical structure or the second optical structure along a contour line; and slicing the third optical structure along at least two parallel cutting planes to form one or more LOEs, each of the one or more LOEs being contoured according to the contour line so that all of the one or more LOEs have the same contour shape.

[0010] Optionally, cutting along a contoured section of the contour line is performed prior to bonding together the first and second optical structures.

[0011] Optionally, cutting along the contour line is performed by cutting the third optical structure.

[0012] Optionally, the contour line includes a segment that intersects part of the first optical structure to define a boundary surface at the first optical structure, the boundary surface defining a coupling-in surface of each LOE of the one or more LOEs.

[0013] Optionally, the method further comprises: polishing the boundary surface.

[0014] Optionally, the segment is a substantially straight-line segment such that the boundary surface defined by the second section is a boundary plane.

[0015] Optionally, the method further comprises: for each of the one or more LOEs, bonding coupling-in optics to the coupling-in surface.

[0016] Optionally, the method further comprises: prior to slicing the third optical structure, attaching a blank at the boundary surface such that each of the one or more LOE has a part of the blank located at the coupling-in surface.

[0017] Optionally, the method further comprises: for each of the one or more LOE, polishing the pair of parallel major external surfaces; and removing the part of the blank located at the couplingin surface.

[0018] Optionally, the method further comprises: for each of the one or more LOE, optically coupling an image projector to the LOE in association with the coupling-in surface.

[0019] Optionally, for each of the one or more LOE the coupling-in surface is a planar surface that is obliquely inclined relative to the pair of parallel major external surfaces, and the method further comprises: for each of the one or more LOE, optically coupling an image projector with the LOE, the coupling being between an interface of the image projector and the planar surface, the interface is obliquely inclined relative to the pair of parallel major external surfaces.

[0020] Optionally, the first optical structure includes a reference surface, and the at least two parallel cutting planes are perpendicular to the reference surface.

[0021] Optionally, the third optical structure includes an intermediate optical structure between the first and second optical structures.

[0022] Optionally, the intermediate optical structure is optically inert.

[0023] Optionally, the intermediate optical structure includes one or more of an optical filter or a polarization management element.

[0024] Optionally, the intermediate optical structure has at least one partially reflective surface located between the partially reflective surfaces of the first and second sets and parallel to the at least two cutting planes.

[0025] Optionally, the first optical structure is formed from a staggered stack of parallel-faced plates that are bonded together at a plurality of interfaces, one face at each of the interfaces having a coating to provide partially-reflecting optical properties such that the interfaces form the first set of mutually-parallel partially reflective surfaces.

[0026] Optionally, obtaining the first optical structure includes: bonding together a plurality of parallel-faced plates at a plurality of interfaces so as to form a stack of plates, one face at each interface having a coating to provide partially-reflecting optical properties, and cutting the stack along a pair of cutting planes that intersect at least some of the interfaces of the plurality of interfaces.

[0027] Optionally, bonding together the plurality of parallel-faced plates includes: at each interface providing adhesive between the coating and an other face at the interface, for each interface the boundary surface is closer to the one face having the coating than to the adhesive.

[0028] Optionally, the second optical structure is formed as a staggered stack of parallel-faced plates that are bonded together at a plurality of interfaces, one face at each of the interfaces having a coating to provide partially-reflecting optical properties such that the interfaces form the second set of mutually-parallel partially reflective surfaces.

[0029] Optionally, obtaining the second optical structure includes: bonding together a plurality of parallel-faced plates at a plurality of interfaces so as to form a stack of plates, one face at each interface having a coating to provide partially-reflecting optical properties, and cutting the stack along a pair of cutting planes that intersect at least some of the interfaces of the plurality of interfaces. Optionally, bonding together the plurality of parallel-faced plates includes: at each interface providing adhesive between the coating and an other face at the interface, for each interface the first optical structure is closer to the one face having the coating than to the adhesive.

[0030] There is also provided according to the teachings of an embodiment of the present disclosure a method for fabricating one or more light-guide optical elements (LOEs). The method comprises: obtaining a first optical structure and a second optical structure, the first optical structure having a first set of mutually-parallel partially reflective surfaces, the second optical structure having a second set of mutually-parallel partially reflective surfaces; bonding together the first optical structure and the second optical structure, such that the partially reflective surfaces of the first set are non-parallel to the partially reflective surfaces of the second set, to form a third optical structure; cutting the first and second optical structures along a contour line; slicing the third optical structure along at least two parallel cutting planes to form one or more LOEs, each of the one or more LOEs being contoured according to the contour line so that all of the one or more LOEs have the same contour shape; and cutting each of the one or more LOEs along a substantially straight cutting line that intersects part of the first region to define a coupling-in surface of the LOE.

[0031] Optionally, cutting each of the one or more LOEs along the substantially straight cutting line is performed on a plurality of the LOEs that are held together using a single cut.

[0032] Optionally, the method further comprises: for each of the one or more LOEs, bonding coupling-in optics to the coupling-in surface.

[0033] There is also provided according to the teachings of an embodiment of the present disclosure a method for fabricating one or more light-guide optical element (LOE). The method comprises: obtaining a first optical structure having a first set of mutually-parallel partially reflective surfaces; obtaining a second optical structure having a second set of mutually-parallel partially reflective surfaces; bonding together the first optical structure and the second optical structure such that the partially reflective surfaces of the first set are non-parallel to the partially reflective surfaces of the second set, to form a third optical structure; cutting along a cutting line that includes a section that intersects part of the first optical structure to define a boundary surface at the first optical structure; attaching a blank at the boundary surface; and slicing the third optical structure along at least two parallel cutting planes to form one or more LOE, each of the one or more LOE having a coupling-in surface defined by the boundary surface and having a part of the blank located at the coupling-in surface.

[0034] Unless otherwise defined herein, all technical and / or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although methods and materials similar or equivalent to those described herein may be used in the practice or testing of embodiments of the invention, exemplary methods and / or materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and are not intended to be necessarily limiting.

[0035] BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Some embodiments of the present disclosure are herein described, by way of example only, with reference to the accompanying drawings. With specific reference to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of embodiments of the disclosure. In this regard, the description taken with the drawings makes apparent to those skilled in the art how embodiments of the disclosure may be practiced.

[0037] Attention is now directed to the drawings, where like reference numerals or characters indicate corresponding or like components. In the drawings:

[0038] FIGS. 1 A and IB are schematic isometric views of an optical system implemented using a light-guide optical element (LOE), constructed and operative according to the teachings of the present disclosure, illustrating a top-down and a side-injection configuration, respectively;

[0039] FIGS. 2A and 2B are enlarged schematic isometric views of an LOE from FIG. 1A or IB showing ray paths for two extreme fields of an image;

[0040] FIG. 3 is a schematic representation of stages of a method for fabricating one or more LOEs, including stages of slicing a combined stack of two stacks of bonded plates and then contouring each slice, according to an embodiment of the present disclosure;

[0041] FIG. 4 is a schematic representation of stages of a modified method for fabricating one or more LOEs, including stages of cutting a combined stack of two stacks of bonded plates to generate a boundary plane forming a coupling-in surface, according to an embodiment of the present disclosure;

[0042] FIG. 5 is a schematic representation additional stages of a method for fabricating one or more LOEs, including stages of polishing LOE major external surfaces and optically coupling image projecting optics to an LOE coupling-in surface, according to an embodiment of the present disclosure;

[0043] FIG. 6 is a schematic representation of stages of a modified method for fabricating one or more LOEs, including stages of temporarily attaching a blank at the boundary plane, contouring the combined stack, and slicing out one or more LOE from the combined stack, according to an embodiment of the present disclosure; FIG. 7 is a schematic isometric representation of an LOE sliced out from the combined stack of FIG. 6;

[0044] FIG. 8 is a schematic representation of additional stages of the method of FIG. 6, including stages of polishing LOE major external surfaces, removing the blank, and optically coupling image projecting optics to the LOE coupling-in surface, according to an embodiment of the present disclosure;

[0045] FIG. 9 is a schematic isometric representation of an LOE produced by the method of FIG. 8;

[0046] FIG. 10 is a schematic representation of stages of a modified method for fabricating one or more LOEs, including stages of contouring a combined stack of two stacks of bonded plates, slicing out one or more contoured LOE from the contoured combined stack, and cutting each LOE to generate a boundary plane forming a coupling-in surface, according to an embodiment of the present disclosure;

[0047] FIG. 11 is a schematic representation of stages a method for extracting a sub- stack of bonded plates from a stack of bonded plates;

[0048] FIGS. 12A and 12B are different schematic isometric views of a first staggered stack of bonded plates which can be used in methods for fabricating one or more LOEs according to embodiments of the present disclosure;

[0049] FIGS. 13A and 13B are different schematic isometric views of a second staggered stack of bonded plates which can be used in methods for fabricating one or more LOEs according to embodiments of the present disclosure;

[0050] FIG. 14 is a schematic representation of stages of a method for fabricating one or more LOEs, including stages extracting a sub-stack of plates from the staggered stack of FIGS. 12A and 12B, forming a combined stack from the sub-stack and the second staggered stack of FIGS. 13A and 13B, and contouring and slicing the combined stack to extract one or more LOE, according to an embodiment of the present disclosure;

[0051] FIGS. 15A - 15C are different schematic isometric views of an LOE produced by the method of FIG. 14;

[0052] FIG. 16 is a schematic representation of an additional stage of the method of FIG. 14, including a stage of optically coupling an image projector with the LOE, according to an embodiment of the present disclosure;

[0053] FIG. 17 is a schematic representation of stages of a conventional method for fabricating a one-dimensional LOE, includes stages of stacking and bonding plates coated with partially- reflecting coating; FIG. 18 is a schematic representation of a single plate of FIG. 17, showing the partially- reflecting coating at one of the faces of one of the plates;

[0054] FIG. 19 is a schematic representation of an LOE produced using the method of FIG. 17, illustrating light propagating through the LOE;

[0055] FIGS. 20 A and 20B are schematic representations of two of the plates of FIG. 17, showing magnified views of the interface between the two of the plates with different orderings of coating and adhesive, according to an embodiment of the present disclosure;

[0056] FIGS. 21 A and 2 IB are schematic representations corresponding to FIGS. 20A and 20B, respectively, illustrating light propagating through the plates and interacting with the coating and adhesive at the interface, according to an embodiment of the present disclosure;

[0057] FIG. 22 is a schematic representation of stages of a method for fabricating a onedimensional LOE, including stages of coating a plurality of plates all on the same side of the plates and applying adhesive on the opposite side of the plates, according to an embodiment of the present disclosure; and

[0058] FIG. 23 is a schematic representation of an LOE produced using the method of FIG. 17, illustrating illumination of the LOE from an illumination direction so that the illumination first impinges the coatings and not on the adhesive, according to an embodiment of the present disclosure.

[0059] DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0060] Embodiments of the present disclosure provide methods for fabricating LOEs.

[0061] The principles of the methods according to present disclosure may be better understood with reference to the drawings accompanying the description.

[0062] Before explaining at least one embodiment of the disclosure in detail, it is to be understood that the disclosure is not necessarily limited in its application to the details of construction and the arrangement of the components and / or methods set forth in the following description and / or illustrated in the drawings and / or the examples. The embodiments of the disclosure are capable of other embodiments or of being practiced or carried out in various ways. Initially, throughout this document, references are made to directions, such as, for example, left and right, top and bottom, upper and lower, front and back, and the like. These directional references are exemplary only, and are used only for ease of presentation and refer to the arbitrary orientations as illustrated in the drawings. The final optical devices may be deployed in any required orientation.

[0063] Certain embodiments of the present disclosure provide a method for fabricating a lightguide optical element (LOE) for achieving optical aperture expansion for the purpose of a head- up display, and most preferably a near-eye display, which may be a virtual reality display, or more preferably an augmented reality display. FIGS. 1 - 3 illustrate certain particularly preferred examples of optical arrangements and corresponding devices for which the fabrication methods of the present disclosure are particularly relevant, although the fabrication methods are not limited to such applications.

[0064] An exemplary implementation of a device in the form of a near-eye display, generally designated 200, employing an LOE 212 according to the teachings of an embodiment of the present disclosure, is illustrated schematically in FIGS. 1A and IB. The near-eye display 200 employs a compact image projector (or “POD”) 214 optically coupled with the LOE so as to provide an image to be injected into the LOE (interchangeably referred to as a “waveguide,” a “substrate” or a “slab”) 212 within which the image light is trapped by internal reflection at a set of mutually- parallel planar external surfaces. The light impinges a set of partially-reflecting surfaces (interchangeably referred to as “facets”) that are parallel to each other, and inclined obliquely to the direction of propagation of the image light, with each successive facet deflecting a proportion of the image light into a deflected direction, also trapped / guided by internal reflection within the substrate. This first set of facets are not illustrated individually in FIGS. 1A and IB, but are located in a first region of the LOE designated 216. This partial reflection at successive facets achieves a first dimension of optical aperture expansion.

[0065] In a first set of preferred but non-limiting examples of the present invention, the aforementioned set of facets are orthogonal to the major external surfaces of the substrate. In this case, both the injected image and its conjugate undergoing internal reflection as it propagates within region 216 are deflected and become conjugate images propagating in a deflected direction. In an alternative set of preferred but non-limiting examples, the first set of partially-reflecting surfaces are obliquely angled relative to the major external surfaces of the LOE. In the latter case, either the injected image or its conjugate forms the desired deflected image propagating within the LOE, while the other reflection may be minimized, for example, by employing angularly-selective coatings on the facets which render them relatively transparent to the range of incident angles presented by the image whose reflection is not needed.

[0066] The first set of partially-reflecting surfaces deflect the image illumination from a first direction of propagation trapped by total internal reflection (TIR) within the substrate to a second direction of propagation, also trapped by TIR within the substrate.

[0067] The deflected image illumination then passes into a second region of the LOE designated 218, which may be implemented as an adjacent distinct substrate or as a continuation of a single substrate, in which a coupling-out arrangement, implemented as a further set of partially reflective facets, progressively couples out a proportion of the image illumination towards the eye of an observer located within a region defined as the eye-motion box (EMB), thereby achieving a second dimension of optical aperture expansion. The overall device may be implemented separately for each eye, and is preferably supported relative to the head of a user with the each LOE 212 facing a corresponding eye of the user. In one particularly preferred option as illustrated here, a support arrangement is implemented as an eye glasses frame with sides 220 for supporting the device relative to ears of the user. Other forms of support arrangement may also be used, including but not limited to, head bands, visors or devices suspended from helmets.

[0068] Reference is made herein and in the drawings to an X axis (dimension) which extends horizontally (FIG. 1A) or vertically (FIG. IB), in the general extensional direction of the first LOE region 216, and a Y axis (dimension) which extends perpendicular thereto, i.e., vertically in FIG. 1A and horizontally in FIG. IB.

[0069] In very approximate terms, the first LOE region 216 (interchangeably referred to as the first LOE or first region of the LOE) may be considered to achieve aperture expansion in the X dimension (in the direction denoted by the X arrow in the drawings) while the second LOE region 218 (interchangeably referred to as the second LOE or second region of the LOE) achieves aperture expansion in the Y dimension (in the direction denoted by the Y arrow in the drawings). It should be noted that the orientation as illustrated in FIG. 1A may be regarded as a “top-down” implementation, where the image illumination entering the main (second region) of the LOE enters from the top edge, whereas the orientation illustrated in FIG. IB may be regarded as a “sideinjection” implementation, where the axis referred to here as the Y axis is deployed horizontally. In the remaining drawings, the various features of certain embodiments of the present invention will be illustrated in the context of a “top-down” orientation, similar to FIG. 1A. However, it should be appreciated that all of those features are equally applicable to side-injection implementations, which also fall within the scope of the invention. In certain cases, other intermediate orientations are also applicable, and are included within the scope of the present invention except where explicitly excluded.

[0070] The image projector 214 employed with the devices of the present disclosure is preferably configured to generate a collimated image, i.e., in which the light of each image pixel is a parallel beam, collimated to infinity, with an angular direction corresponding to the pixel position. The image illumination thus spans a range of angles corresponding to an angular field of view in two dimensions.

[0071] The image projector 214 includes at least one light source, typically deployed to illuminate a spatial light modulator, such as an LCOS chip. The spatial light modulator modulates the projected intensity of each pixel of the image, thereby generating an image. Alternatively, the image projector may include a scanning arrangement, typically implemented using a fast-scanning mirror, which scans illumination from a laser light source across an image plane of the projector while the intensity of the beam is varied synchronously with the motion on a pixel-by-pixel basis, thereby projecting a desired intensity for each pixel. In both cases, collimating optics are provided to generate an output projected image which is collimated to infinity. Some or all of the above components are typically arranged on surfaces of one or more polarizing beam-splitter (PBS) cube or other prism arrangement, as is well known in the art.

[0072] Optical coupling of the image projector 214 to the LOE 212 may be achieved by any suitable optical coupling-in configuration, such as for example via a coupling prism with an obliquely angled input surface, or via a reflective coupling arrangement, via a side edge and / or one of the major external surface of the LOE. For sake of illustrative purposes, the coupling-in configuration is schematically illustrated in FIGS. 2A and 2B as a wedge prism 215 applied to one of the major external surfaces of the LOE. However, the LOEs produced using the fabrication methods of the present disclosure may typically have a different type of coupling-in configuration, as will be described in further detail below.

[0073] It will be appreciated that the near-eye display 200 includes various additional components, typically including a controller 222 for actuating the image projector 214, typically employing electrical power from a small onboard battery (not shown) or some other suitable power source. It will be appreciated that the controller 222 includes all necessary electronic components such as at least one processor or processing circuitry to drive the image projector, all as is known in the art.

[0074] Turning now to FIGS. 2 A and 2B, the optical properties of an implementation of the near- eye display are illustrated in more detail. Specifically, there is shown a more detailed view of a light-guide optical element (LOE) 212 formed from transparent material, including a first region 216 containing a first optical coupling configuration implemented as a first set of planar, mutually- parallel, partially-reflecting surfaces 217 having a first orientation, and a second region 218 containing a second optical coupling configuration implemented as a set of planar, mutually- parallel, partially-reflecting surfaces 219 having a second orientation non-parallel to the first orientation. A set of mutually-parallel major external surfaces 224 extend across the first and second regions 216 and 218 such that both the first set of partially-reflecting surfaces 217 and the second set of partially-reflecting surfaces 219 are located between the major external surfaces 24. Most preferably, the set of major external surfaces 224 are a pair of surfaces which are each continuous across the entirety of first and second regions 216 and 218, although the option of having a set down or a step up in thickness between the regions 216 and 218 also falls within the scope of the present invention. Regions 216 and 218 may be immediately juxtaposed so that they meet at a boundary, which may be a straight boundary or some other form of boundary, or there may be one or more additional LOE region interposed between those regions, to provide various additional optical or mechanical function, depending upon the particular application. Although the present invention is not limited to any particular manufacturing technique, in certain particularly preferred implementations, particularly high quality major external surfaces are achieved by employing continuous external plates between which the separately formed regions 216 and 218 are sandwiched to form the compound LOE structure.

[0075] The optical properties of the LOE 212 may be understood by tracing the image illumination paths backwards. The second set of partially-reflecting surfaces 219 are at an oblique angle to the major external surfaces 224 so that a part of image illumination propagating within the LOE 212 by internal reflection at the major external surfaces from the first region 216 to the second region 218 is coupled out of the LOE towards an eye-motion box (EMB) 226. The first set of partially- reflecting surfaces 217 are oriented so as to be inclined obliquely to the direction of propagation of the image illumination so that a part of image illumination propagating within the LOE 212 by internal reflection at the major external surfaces from a coupling-in surface (the coupling-in configuration, in this non-limiting example case the coupling prism 215) is deflected towards the second region 218.

[0076] One dimension of the angular spread of the projected image from image projector 214 is represented in FIG. 2A by the cone of illumination spreading from the POD aperture on the right side of the LOE towards the left side of the LOE. In the non-limiting example illustrated here, the central optical axis of the image projector 214 defines a direction of propagation within the LOE aligned with the X axis, and the angular spread (within the LOE) is roughly ±16°. (It should be noted that the angular FOV becomes larger in air due to the change in refractive index.) The first set of partially-reflecting surfaces 217 are illustrated in first region 216, and the second set of partially-reflecting surfaces 219 are illustrated in second region 218.

[0077] The near-eye display is designed to provide a full field-of-view of the projected image to an eye of the user that is located at some position within the permitted range of positions designated by the EMB 226 (that is, a shape, typically represented as a rectangle, spaced away from the plane of the LOE from which the pupil of the eye will view the projected image). In order to reach the EMB 26, light must be coupled-out from the second region 218 by the second set of partially- reflecting surfaces 219 towards the EMB 226. In order to provide the full image field-of-view, each point in the EMB must receive the entire angular range of the image from the LOE. Tracing back the field-of-view from the EMB indicates a larger rectangle 228 from which relevant illumination is coupled-out of the LOE towards the EMB. FIG. 2A illustrates a first extremity of the field of view, corresponding to the bottom-left pixel of the projected image. A beam of a width corresponding to the optical aperture of the projector as coupled into the LOE is shown propagating leftwards and upwards from the POD and being partially reflected from a series of partially-reflecting surfaces 217. As illustrated here, only a subset of the facets generate reflections that are useful for providing the corresponding pixel in the image viewed by the user, and only a sub-region of those facets contributes to the observed image of this pixel. The relevant regions are illustrated by heavy black lines, and the rays corresponding to this pixel in the redirected image reflected from facets 217 and then coupled-out by facets 219 reaching the four corners of the EMB 26 are shown. Here and throughout the description, it will be noted that only the in-plane propagation directions of the rays are illustrated here during propagation within the LOE, but the rays actually follow a zigzag path of repeated internal reflection from the two major external surfaces, and one entire dimension of the image field of view is encoded by the angle of inclination of the rays relative to the major external surfaces, corresponding to the pixel position in the Y dimension. By way of one additional example, deflected and coupled-out rays corresponding to the top-left extremity of the image as viewed at the top-left corner of the EMB are shown in dash-dot lines.

[0078] FIG. 2B illustrates the same configuration as FIG. 2A, but here shows the rays corresponding to the bottom-right pixel of the field-of-view reaching the four corners of the EMB, again with the relevant regions of the relevant partially-reflecting surfaces 217 denoted by a heavy line.

[0079] Various methods for producing LOEs, such as the LOE illustrated schematically in FIGS. 2 A and 2B, have been proposed. Conventional methods typically rely on stacking and bonding transparent plates optically coated with at least partially reflective coating to form a stack, where the interfaces between the plates correspond to the LOE facets. The stack is then sliced at desired angles relative to the facets surfaces. The external surfaces of the LOE should be polished in order to produce LOEs of high optical quality. In addition, and as discussed above, certain preferred implementations provide LOEs in an eye glass form factor. In such implementations, it may be advantageous to shape the LOE to have an eye glass lens contour. It is a particular feature of certain embodiments of the present disclosure to provide methods of fabricating LOEs that, among other things, produce LOEs with parallel and smooth major external surfaces while at the same time having a shape according to a desired contour, which in a preferred but non-limiting implementation is the shape an eye glass lens.

[0080] Referring now to FIG. 3, there is schematically illustrated stages (steps) of a method (process) which may be used to fabricate one or more LOEs, according to embodiments of the present disclosure. As illustrated, a pair of optical structures (stacks) 4 and 6 are obtained. Each of the optical structures 4 and 6 has a set of mutually-parallel partially reflective surfaces (facets), designated 5 and 7, respectively. The optical structures 4 and 6 can be formed by stacking and bonding parallel-faced transparent plates optically coated with at least partially reflective coating to form respective stacks, and then slicing the stack at a desired angle relative to the plate faces, whereby the interfaces between the plates correspond to the facets 5 and 7.

[0081] In the illustrated embodiment, the optical structure 4 also has a pair of end elements 8 and 9, shown here as trapezoidal prisms, disposed at opposing ends of the stack (i.e., attached to the plates at the left-end and right-end of the stack). The trapezoidal prism shape can be obtained from the stack slicing process. Alternatively, one or both of the prisms 8 and 9 can be attached to the plates after slicing to form the optical structure 5. Each of the prisms 8 and 9 has a plurality of surfaces. The upper surface of the prism 8 is designated in the drawings as 10, and can be parallel to the facets 5. As will be discussed in subsequent sections of this document, the surface 10 can be used as a reference surface during subsequent slicing stages of the methods according to the present disclosure.

[0082] The optical structures 4 and 6 are combined to form a new (combined) optical structure (a “bonded stack of stacks”) 11. The combining is achieved via bonding, whereby the optical structures 4 and 6 are bonded together at an interface 3 between the two structures 4 and 6. The optical structures 4 and 6 are bonded together such that the facets 5 are non-parallel to the facets 7. The optical structures 4 and 6 may be aligned prior to bonding to achieve the desired non-parallel orientation between the sets of facets 5 and 7. The interface 3 may form the boundary between the two LOE regions (each containing a set of parallel facets) in the final LOE product.

[0083] Parenthetically, throughout this document, the term “bonded” or “bonding” should be understood to mean attached or attaching with adhesive, such as an optical cement or glue, or any other suitable adhesive. Bonding between two optical structures or elements may be direct bonding, where the two structures / elements are directly attached to each other via adhesive, or may be indirect bonding, where the two structures / elements are indirectly attached to each other, for example via one or more intermediate optical structures / elements glued between the two structures / elements. Examples of intermediate optical structures include, but are not limited to, a blank to provide a gap between faceted optical sections, an optical filter, a polarization management element such as a waveplate or depolarizer, and the like.

[0084] The optical structure 11 is then sliced along a plurality of parallel slicing (cutting) planes 14 that intersect the interface 3 to produce one or more slices (one such slice 12 is shown in the figure). In the figure, the slicing planes 14 are represented as a plurality of lines, with the direction of slicing shown as arrows to generate the slicing planes. In certain embodiments, the prism surface 10 may be used as a reference to define the orientation of the slicing planes 14. In a particularly preferred but non-limiting embodiment, the slicing planes 14 are perpendicular to the prism surface 10. Preferably the slicing planes 14 are also perpendicular to surface 15 of the optical structure 6, where the surface 15 is parallel to the facets 7. The parallel cutting planes 14 define the major external surfaces of the final LOE product.

[0085] Each slice 12 is then polished from both sides (front and back, i.e., the major external surfaces), and is then cut along a cutting line 16. The cutting line 16, also referred to as a contourline, has multiple sections (or segments), including a contoured section 18a. The contoured section 18a may intersect parts of both optical structures 4 and 6, and may have one or more curved sections or piecewise linear sections 15a (or a combination thereof) that intersect at least some of the facets 7 twice. Cutting along contoured section 18a generates contour 18b, which provides the slice 12 with its contour shape. In certain embodiments, the contoured section 18a intersects all of the facets 7 twice, whereas in other embodiments, the contoured section 18a intersects most of the facets 7 twice (most meaning all but a few, e.g., all but one, two, or three, of the facets 7, typically located at the bottom portion of the stack 6). In certain embodiments, the contoured section 18a intersects some of the facets 5, for example the first few facets 5 located closer to the end prism 8. In certain embodiments, the contoured section 18a intersects part of the end prism 8.

[0086] The cutting (contour) line 16 also includes another section (segment) 20a, which is preferably a straight-line segment, that intersects part of the optical structure 4 as a cutting plane. In certain embodiments, section 20a intersects only the optical structure 4 and does not intersect any part of the other optical structure 6. In certain embodiments, the section 20a intersects the end prism 9 and intersects with a small number (e.g., one, two, three, or four) of the facets 5 at the end of the stack closer to the end prism 9. In certain embodiments, the cutting plane formed by section 20a is obliquely angled relative to the interface 3 between the two optical structures 4 and 6.

[0087] Cutting the slice 12 along the section 20a generates (produces) a boundary surface 20b at the optical structure 5. This boundary surface serves to couple in image illumination from the image projector, and defines the coupling-in surface of the final LOE product. The boundary surface 20b should be of good optical quality, and may be polished after cutting along section 20a. In embodiments in which the section 20a is a straight-line segment, the boundary surface is a boundary plane (i.e., the coupling-in surface is a planar surface). In cases in which the section 20a is not a straight-line segment, polishing the boundary surface 20b may help to achieve flatness (planarity) of the boundary surface. The resultant contoured and polished LOE is designated in the FIG. 3 as 22. The LOE 22 is contoured (according to the contoured section 18a) and includes: a pair of parallel major external surfaces 224 (defined by a pair of adjacent cutting planes of the parallel cutting planes 14), a first region 216 having a first plurality of parallel facets 217 formed from part of the facets 5, a second region 218 having a second plurality of parallel facets 219 obliquely inclined relative to the LOE major external surfaces and formed from part of the facets 7, and a coupling-in surface (the boundary surface 20b). Image projecting (i.e., coupling-in optics, e.g., wedge prism) and / or an image projector may then be optically coupled with the LOE in association with the coupling-in surface (i.e., at the boundary surface 20b).

[0088] Although the embodiment described with reference to FIG. 3 can be used to produce LOEs of high performance, including LOEs with high degree of parallelism between the LOE major external surfaces, good optical quality of the coupling-in surface, and non-parallelism between the two sets of facets, the aforementioned embodiment may present certain drawbacks in terms of manufacturing efficiency. Specifically, since cutting along contour-line 16 is performed on the slice level (i.e., per slice), there is required a degree of repetition of contour cutting that is proportional to the number of LOEs being sliced out of the optical structure 11.

[0089] FIG. 4 schematically illustrates stages of a more efficient process which may be used to fabricate one or more LOEs, according to another embodiment of the present disclosure. The embodiment illustrated in FIG. 4 is a more efficient variant of the embodiment illustrated in FIG. 3. Here, the optical structure 11 is cut along a cutting (contour) line, which may include section / segment 20a’ (which is similar to section 20a in FIG. 3), to produce optical structure Ila. As a result, boundary surface 20b’ (which is similar to boundary surface 20b in FIG. 3) is generated on the optical structure Ila (combined stack) rather than individually per slice. The boundary surface 20b’ is then preferably polished to ensure optical quality and planarity (flatness), and the optical structure Ila is then sliced along planes 14 as described above. Consequently, after slicing, each slice already has a (preferably polished) boundary surface 20b (that is a part of the boundary surface 20b’), thereby saving the time of having to cut and polish each slice along cutting line section 20a as in FIG. 3.

[0090] It is noted that as in the previous embodiment, section 20a’ is preferably a straight-line segment that intersects part of the optical structure 4 as a cutting plane. In certain embodiments, section 20a’ intersects only the optical structure 4 and does not intersect any part of the other optical structure 6. In certain embodiments, the section 20a’ intersects the end prism 9 and intersects with a small number (e.g., one, two, three, or four) of the facets 5 at the end of the stack closer to the end prism 9. In certain embodiments, the cutting plane formed by section 20a’ is obliquely angled relative to the interface 3 between the two optical structures 4 and 6.

[0091] It is further noted that the contour line along which the optical structure 11 is cut may include a contoured section instead of, or in addition to, segment 20a’ . The contoured section may intersect parts of both optical structures 4 and 6, and may have multiple sections / segments including one or more curved sections or piecewise linear sections (similar to 18a) that intersect at least some (or most or all) of the facets 7 twice. Accordingly, by cutting the optical structure along the cutting line, a contoured optical structure can be produced. The optical structure can then be sliced along cutting planes 14 to produce a plurality of slices, where each slice is already contoured so that all of the slices have the same contour shape, which can include the shape of contoured section and / or the (preferably polished) boundary surface 20b. In such embodiments, it may be preferable that the contoured section 20a’ does not intersect the end prism 8, or intersects only a small portion of the end prism 8, so that surface 10 can be maintained on the optical structure 4 and used as a reference surface for the cutting planes 14.

[0092] It will be appreciated that variations of the embodiment described with reference to FIG. 4 are contemplated herein. In one variation, cutting along section 20a’ may be performed prior to bonding optical structures 4 and 6 together.

[0093] FIG. 5 schematically illustrates a top view of additional stages of methods of the present disclosure. The illustrated stages can be applied to each slice, for example the slices generated by slicing the optical structure 11 or Ila along pairs of parallel cutting planes 14. For illustrative purposes, the slice shown in FIG. 5 is a slice generated from the optical structure Ila of FIG. 4. As shown in FIG. 5, the slice 34 is polished at both the front 35 and back 36 sides of the slice 34 (as previously discussed). The polishing is represented in the figure as thick arrows 38. The boundary surface 20b (which is part of the boundary surface 20b’ of structure 11) is shown here at the (right) edge of the slice 34. Typically, the force applied to the slice during the polishing process is not uniform, and the non-uniform polishing force can lead to distortion of the slice, in particular distortion of the shape of the edge (ends) of the slice. Distorted edges, including an edge at which the boundary surface 20b is located, are shown in the figure as 46 (not shown to scale). At the distorted edges, the slice 34 may be thinner, or may be rounded (as shown). This edge distortion may lead to degradation in performance of the LOE, due to poor optical coupling between the LOE and image projecting optics 48 (i.e., coupling-in optics, e.g., prism, mirror, PBS, or other). FIG. 5 shows a polished slice (LOE) having a distorted edge 46 optically coupled (interfaced) with image projecting optics 48 at the distorted edge 46 (i.e., a distorted boundary surface 20b), for example via an adhesive layer (designated 49). Due to the edge distortion, part of the injected beam of image illumination (represented in the drawing as 50) from the projecting optics 48 will be coupled into the LOE (the coupled in illumination represented by rays 52) and propagate by internal reflection between the major external surfaces (front 35 and back 36 sides), but part of the beam 50 will also scatter (represented by rays 54), thereby degrading image quality. Consequently, the polishing process must be closely monitored and preferably performed against hard surfaces with low pressure to minimize distortion of the slices (and hence distortion of the LOE).

[0094] FIGS. 6 and 7 schematically illustrate stages of a process which may be used to fabricate one or more LOEs, according to another embodiment of the present disclosure. The embodiment illustrated in FIGS. 6 and 7 is a variant of the process illustrated in FIG. 4, and maintains the integrity of the boundary surface 20b without imposing strict polishing process constraints. As illustrated in FIG. 6, a blank 62 is provided and temporarily attached to the optical structure Ila (identical to the structure illustrated in FIG. 4) at boundary surface 20b’ to form a new optical structure 11b. The temporary attachment between the blank 62 and the optical structure Ila can be effectuated by a dissolvable adhesive, or any other suitable temporary adhesive.

[0095] The optical structure 11b can then be cut along a contoured section 18a’ that may intersect both constituent optical structures 4 and 6, and that may have multiple sections / segments including one or more curved sections or piecewise linear sections (similar to 18a) that intersect at least some (or most or all) of the facets 7 twice, to produce contoured optical structure 11c having contour 18b’. The contoured optical structure 11c can then be sliced along cutting planes 14 to produce a plurality of slices, where each slice is already contoured so that all of the slices have the same contour shape, and each slice includes a part of the blank 62 attached at the boundary surface 20b (i.e., located at the coupling-in surface). It is noted that in such embodiments, it may be preferable that the contoured section not intersect the end prism 8, or intersect only a small portion of the end prism 8, so that surface 10 can be maintained and used as a reference surface for the cutting planes 14.

[0096] FIG. 8 shows an isometric view of a slice 70 extracted from the optical structure 11c by cutting the optical structure 11c along two parallel cutting planes 14. The slice 70 is contoured according to the contoured section and includes: a pair of parallel major external surfaces (defined by a pair of adjacent cutting planes of the parallel cutting planes 14), a first region having a first plurality of parallel facets formed from part of the facets 5, a second region having a second plurality of parallel facets obliquely inclined relative to the LOE major external surfaces and formed from part of the facets 7, and a coupling-in surface (the boundary surface 20b) which can be part of the contour shape. Image projecting (i.e., coupling- in) optics and / or an image projector may then be optically coupled with the LOE in association with the coupling-in surface (i.e., at the boundary surface 20b).

[0097] FIG. 7 schematically illustrates (as a top view) additional stages of methods of the present disclosure that can be applied to each slice 70 that is extracted from the optical structure 11c. As before, the slice 70 is polished, where the thick arrows 38 represent polishing pressure. Also as before, the edges 72 and 73 of the slice 70 tend to be distorted as a result of the polishing process. However, in the present embodiment, the distorted edge 73 is not located at boundary surface 20b, but is rather a part of the blank 62, which insulates the boundary surface 20b from the polishing process. The blank 62 can then be removed from the slice 70 to produce LOE 22 having a preserved (i.e., flat and undistorted) boundary surface 20b. FIG. 9 shows an isometric view of the LOE 22, which is contoured (according to the contoured section) and includes: a pair of parallel major external surfaces (defined by a pair of adjacent cutting planes of the parallel cutting planes 14), a first region having a first plurality of parallel facets formed from part of the facets 5, a second region having a second plurality of parallel facets obliquely inclined relative to the LOE major external surfaces and formed from part of the facets 7, and a coupling-in surface (the boundary surface 20b) which can be part of the contour shape. Image projecting optics and / or an image projector may then be optically coupled with the LOE in association with the coupling-in surface (i.e., at the boundary surface 20b).

[0098] The removal of the blank 62 can be effectuated, for example, by dissolving the adhesive 64, for example, using heat, solvent, radiation, or any other suitable method that dissolves the adhesive 64 but preserves the integrity of other adhesives in the optical structure.

[0099] Consequently, the interface between projecting optics 48 and the LOE 22 (formed from the slice 70 after removal of the blank 62), for example using adhesive 49, is uniform, and thus the beam of illumination 50 is coupled into the LOE with minimal scattering (the coupled in illumination shown as ray 52), and propagates by internal reflection between the major external surfaces of the LOE.

[0100] It will be appreciated that many variations of the above-described embodiments are contemplated herein. In one variation, the contouring of the optical structure 11b may be performed on the individual optical structures 4 and 6 prior to bonding together. For example, each of the optical structures 4 and 6 may be individually contoured by cutting along appropriate contoured cutting sections that combine to resemble line 18a when the two optical structures 4 and 6 are in proper alignment, and then the contoured optical structures 4 and 6 may be bonded together. The same may be true for the optical structure 11 illustrated in FIG. 4. It is further appreciated that the attachment of the blank 62 to the boundary surface 20b’ may, in certain embodiments, be performed prior to bonding together the optical structures 4 and 6. In such embodiments, the optical structure 4 may be cut along the line (section / segment) 20a’ prior to bonding the two optical structures 4 and 6 together. In a further variation, an additional blank (similar to blank 62) may be attached to the other end prism 8, for example at the surface 10, for example in cases where integrity of the other edge 72 of the slice is desired.

[0101] Referring now to FIG. 10, there is schematically illustrated stages of a process which may be used to fabricate one or more LOEs, according to yet another embodiment of the present disclosure. Here, no dissolvable adhesive is needed, yet the method is significantly simplified compared to the method described with reference to FIGS. 6 - 9. The optical structure 11 (formed from bonded optical structures 4 and 6) is cut along cutting line 16’. The cutting line 16’ is generally similar to cutting line 16 in that it includes a contoured section 18a’ , which may have multiple sections / segments including one or more curved sections or piecewise linear sections, that intersect at least some of the facets 7 twice. However, in the present embodiment, the cutting line does not include the section (e.g., 20a’) that intersects the optical structure 4. Consequently, the boundary surface 20b’ is not generated as a result of cutting along cutting line 16’. The contoured optical structure (having contour 18b) is then sliced along parallel cutting planes (i.e., planes 14, similar as described above) to produce slices. A front view of one such slice 70 is illustrated in FIG. 10. The slice has contour 18b, generated as a result of the cutting of the structure 11 along contoured section 18a’. All other slices produced by cutting along planes 14 share the same contour as that of slice 70 (i.e., each slice has the same contour shape). The slice 70 can then be polished at the front and back sides (as previously described), and the slice 70 can be cut along section 20a to produce the boundary surface 20b. In certain embodiments, multiple slices can be grouped together in alignment (using, for example, mechanical fastening equipment) and a single cut along cutting line (segment) 20a can be made to simultaneously generate the boundary surface 20b for each slice. The slices can also be polished at the boundary surfaces 20b together as a group. Optionally, a blank can be attached at the boundary surface 20b of each slice prior to polishing using temporary adhesive. The blank can be removed after polishing, thereby maintaining integrity of the boundary surface 20b.

[0102] As mentioned above, the optical structures 4 and 6 from which the bonded stack 11 is formed can be produced from bonded stacks of parallel-faced coated plates. For example, FIG. 11 illustrates an exemplary stack 1 of bonded coated plates 13, where a shape designated 6a is cut out from the stack 1 to produce the optical structure 6, and the remaining volume of the stack 1 (designated 2) is scrap. In order to reduce (and in certain cases minimize) the amount of scrap when producing the base stacks (e.g., optical structures 4 and 6), a “shaped” stacking process may be performed. The following paragraphs describe certain embodiments of the present disclosure that utilize shaped-stacking.

[0103] Referring now to FIGS. 12A - 13B, there is illustrated different views of shaped stacks that can be used to form base stack that are equivalent to (yet different from) the optical structures 4 and 6. FIGS. 12A and 12B illustrate different views of an optical structure in the form of a staggered stack 102 of coated parallel-faced plates 104 that can be used to produce a further optical structure (designated 120 in FIG. 14), which is equivalent to, yet different from, the optical structure 4. The staggered placement of the plates 104 can be by groups of plates in steps 106, or may be a continuous stepped stack (not shown). The stack 102 is shown as being topped off (at the top and bottom) with a transparent plate 107 having a thickness of several times that of the other plates 104. In a preferred but non-limiting implementation, the shape of the stacked plates 104 may be a parallelogram (as illustrated in FIGS. 12A and 12B). The parallelogram shape of the plates may contribute to optimal material use (i.e., reduced scrap / waste). However, a rectangular shape may be used, but consequently more material will be lost as scrap.

[0104] The plates 104 are bonded together at a plurality of interfaces. One face (of one of the plates 104) at each of the interfaces has an at least partially reflective coating applied thereto, which provides partially-reflecting optical properties. As a result, the interfaces form the facets 5.

[0105] FIGS. 13A and 13B illustrate different views of an optical structure in the form of a staggered stack 108 of coated parallel-faced plates 110 which is equivalent to, yet different from, the optical structure 6. The stack 108 is shown as being topped off at the bottom with a transparent plate 109 having a thickness of several times that of the other plates 110. Here too the staggered placement of the plates 110 is by groups of plates in steps 112 (but a continuous stepped stack is also possible), and the stacked plates 110 have a parallelogram shape for optimal material use (however, a rectangular shape may be used). The plates 110 are bonded together at a plurality of interfaces. One face (of one of the plates 110) at each of the interfaces has an at least partially reflective coating applied thereto, which provides partially-reflecting optical properties. As a result, the interfaces form the facets 7.

[0106] FIG. 14 illustrates stages of a process which may be used to fabricate one or more LOEs with reduced (preferably minimal) scrap (i.e., waste), using the two stacks (optical structures) 102 and 108. As shown, the stack 102 is cut (sliced) along a pair of cutting planes (illustrated as lines 118) to generate a new optical structure 120. The cutting planes 118 are preferably, but not necessarily, parallel cutting planes. It is noted that the stack 102 may be sliced multiple times along multiple cutting planes 118 to generate multiple structures 120. The optical structure 120 is equivalent to the optical structure 4, with like reference numerals indicating like components. The optical structures 120 and 108 are bonded together at an interface 3 to form (produce) a new (combined) optical structure 122. The optical structure 122 may then be shaped, for example contoured, to produce contoured optical structure 123. The process of contouring is not shown in FIG. 14, but similar techniques as described above with reference to FIGS. 3, 4, 6, and 10 can be used to produce contoured optical structure 123. The contoured optical structure 123 can then be sliced along two or more parallel cutting planes 124 to extract one or more LOE 128 (which can then be polished at the front and back sides, i.e., major external surfaces). The cutting planes 124 are diagonal (oblique) to the plates 110 (facets 7) at a desired angle to effectuate the oblique angle of the facets in the second LOE region (the facets formed from facets 7) relative to the major external surfaces of the LOE 128. The slicing of the optical structure 123 along the cutting planes 124 thus results in one or more contoured LOEs (i.e., one or more LOEs contoured according to the contoured section) where all of the LOEs have the same contour shape and have a pair of parallel major external surfaces (defined by the cutting planes 124), a first region having a first plurality of parallel facets formed from part of the facets 5, a second region having a second plurality of parallel facets obliquely inclined relative to the LOE major external surfaces and formed from part of the facets 7, and a coupling-in surface (the boundary surface 20b) which can be part of the contour shape.

[0107] FIGS. 15A - 15C illustrate various views of the LOE 128 produced using the method of FIG. 14. As can be seen in FIGS. 15A - 15C, the edges 134a, 134b, and 136 (which is the boundary surface 20b) are slanted. The slant of edges 134a and 134b has no significant optical impact. The edge 136 (boundary surface 20b / coupling-in surface) is slanted such that the edge 136 is obliquely inclined relative to the major external surfaces of the LOE. According to certain embodiments, a cost-effective solution to the slant of edge 136 (20b), illustrated schematically in FIG. 16, is to have the interface 142 of the image projector 214 be slanted in a correspondingly configured fashion to the slant of the edge 136 (i.e., oblique to the LOE major external surfaces) such that the lower surface 150 of the projector 214 is parallel to the front (lower) major external surface 24 of the LOE 128, and more preferably such that the surface 150 forms an extension of the front major external surface 24.

[0108] It will be appreciated that although the embodiments described thus far have pertained to contouring and slicing optical structures to produce a plurality of slices so that all of the slices have the same contour shape, other embodiments are contemplated herein in which a subset, but not all, of the slices extracted from an optical structure have the same contour shape. For example, an optical structure may be cut according to a first contour and a first set of LOEs may be extracted from the contoured optical structure by slicing along parallel cutting planes. The slicing may be paused, and the optical structure may be further cut according to a second contour, and then the slicing may be resumed to extract a second set of LOEs from the re-contoured optical structure. As a result, the LOEs in the first set may have the same first contour shape, and the LOEs in the second set may have the same second contour shape which is different from the first contour shape. As one non-limiting illustrative example, consider the optical structure Ila illustrated in FIGS. 4 and 6, which is shown as having contour defined by the boundary surface 20b’. The optical structure Ila may be sliced along a plurality of cutting planes 14 to produce a first set of LOEs that have the same contour shape. The remaining part of the optical structure Ila may then be further contoured, for example by cutting along contoured section 18a’ , and then the re-contoured optical structure may be sliced along cutting planes 14 to produce a second set of LOEs that have the same contour shape as each other but different from the shape of the LOEs of the first set.

[0109] The embodiments of the fabrication methods described thus far can be considered to be part of a first aspect of the present disclosure, which generally includes stages of bonding optical structures, contouring optical structures, and slicing optical structures to extract one or more LOEs. A second aspect of the present disclosure relates to the construction of the base optical structures that have the embedded facets, in particular methods by which embedded facets are produced, specifically using parallel-faced plate stacking and bonding. This second aspect is thought to be of independent utility from the first aspect. Nevertheless, there may be particular advantages when using the second aspect in combination with the first aspect.

[0110] By way of introduction, and as discussed above, the partial reflectivity of the facets of the various optical structures described herein can be provided by application of an at least partially reflective to one of the faces stacked parallel-faced plates. For example, as described with reference to FIGS. 12A and 12B, parallel-faced plates 104 can be bonded together at a plurality of interfaces, where one face (of one of the plates 104) at each of the interfaces has an at least partially reflective coating applied thereto, which provides partially -reflecting optical properties so that the interfaces form the facets 5.

[0111] FIGS. 17 and 18 illustrate a conventional process of plate stacking to produce a conventional LOE (in this example, the LOE is a one-dimensional LOE in that it achieves only a single dimension of aperture expansion). As shown in FIG. 17, a plurality of parallel-faced plates 304 are stacked and bonded together at a plurality of interfaces 305 to form bonded stack (optical structure) 308. One face at each of the interfaces 305 has a coating to provide partially-reflecting optical properties such that the interfaces form a set of mutually-parallel partially reflective surfaces (facets). The stack 308 is then cut (sliced) along at least two parallel cutting planes 310 that are obliquely inclined relative to the faces of the plates 304 to produce one or more LOEs 312 having a pair of parallel major external surfaces 324 (defined by a pair of adjacent cutting planes of the at least two cutting planes 312) and a plurality of parallel facets 319 formed from the interfaces 305 (in particular, the partially-reflecting coating at the interfaces 305).

[0112] FIG. 18 shows the partially-reflecting coating 306 at one of the faces of the plates 304 in more detail. Practically, the coating 306 is smooth at the interface 303 with the face of the plate 304, but is less smooth (i.e., rougher) in the areas further way from the interface 303. In the figure, the roughness is not shown to scale, and is exaggerated for clarity.

[0113] FIG. 19 shows the propagation of a beam 316 of image illumination through the LOE 312 by (total) internal reflection between the major external surfaces 324. As the beam 316 propagates, it encounters the facets 319. Some of the reflections from the facets 319 are required for progressively deflecting the illumination (represented as rays 318) out of the LOE, but some of the reflections from the facets 319 need to be suppressed by proper coating design (the suppressed reflections are represented as dashed rays 320). The coating should also reflect and transmit the beam with minimal scattering.

[0114] FIGS. 20 A and 20B illustrate magnified views of one interface 305 between two of the plates from the stack 308 of FIG. 17. In FIGS. 20A and 20B, the two plates are designated 304a and 304b. The plates are bonded together using an adhesive. In FIGS. 20A and 20B, the adhesive, applied between the plates 304a and 304b, is designated 307. As a result, the coated plates bonded with adhesive form a sandwich arrangement. The partially reflective coating 306 is produced as layers of materials having different refractive indices. In order to minimize perturbation to the coating 306 and for optimal optical performance, the refractive index of the adhesive 307 is designed to be approximately equal to that of the plates 304. This adhesive 307 retains the shape of the coating on one side and is planar as the surface of the plate on the other side (i.e., the side at the interface 303 with the face of the plate). In FIG. 20A, the adhesive 307 is located between the plate 304b and the coating 306, and the coating 306 is located between the adhesive 307 and the plate 304a. In other words, the sequence of the sandwich arrangement, from left-to-right in FIG. 20A, is plate 304b, adhesive 307, coating 306, plate 304a. In FIG. 20B, the order of adhesive 307 and the coating 306 is switched so that the coating 306 is located between the plate 304b and the adhesive 307, and the adhesive 307 is located between the coating 306 and the plate 304a. In other words, the sequence of the sandwich arrangement, from left-to-right in FIG. 20B, is plate 304b, coating 306, adhesive 307, plate 304a.

[0115] FIGS. 21 A and 21B illustrate the effect of beam 316 impinging on the facet of FIGS. 20A and 20B, respectively. In FIG. 21A, the beam 316 impinges facet 319 from the adhesive side. In such a case the reflection is from the rough surface of the coating 306, therefore the reflected beam, designated 318a, is somewhat scattered. The transmitted beam, designated 320a, is only slightly dispersed because during transmission through slightly non-uniform refractive interface, and therefore the scattering is minimal.

[0116] In FIG. 2 IB, the beam 316 impinges first on the flat side of the coating 306 (coated on the plate 304b) so that the reflected beam 318b is from the flat plane and has reduced scattering. The transmitted beam 320b also has minimal scattering as described earlier.

[0117] Thus, in order to achieve reflection and transmission with reduced scattering, it is preferable to produce the LOE by coating each of the parallel-face plates on the same side, and then illuminating the LOE from that same side (i.e., the coated side) so that the illumination impinges the coating first. For example, the sandwich arrangement between each pair of adjacent plates can be first plate, adhesive, coating, second plate, and the LOE is illuminated from an illumination direction so that the illumination impinges the second plate first. As another example, the sandwich arrangement between each pair of adjacent plates can be first plate, coating, adhesive, second plate, and the LOE is illuminated from an illumination direction so that the illumination impinges the first plate first. FIG. 22 shows an example of an LOE formed from a set of six parallel-faced plates 304a, 304b, 304c, 304d, 304e, 304f, where the LOE has facets 319a, 319b, 319c, 319d, 319e, 319f formed from the interfaces between the six parallel-faced plates 304a, 304b, 304c, 304d, 304e, 304f. All of the plates 304a, 304b, 304c, 304d, 304e, 304f are coated on the same side (in the figure, the right side) with coating 306, and adhesive 307 is in contact with the opposite side (the left side) of the plates. Since the coating 306 is on the right side, the LOE should be illuminated with beam 316 from the left side of the constituent plates, so that the illumination first impinges the coatings and not on the adhesive, as illustrated in FIG. 23.

[0118] The embodiments of the second aspect of the disclosure can be used in combination with the embodiments of the first aspect of the disclosure. For example, the coating and adhesive can be applied between the various parallel-faced plates to form the optical structure having facets 5 so that at each interface between the parallel-faced plates, the adhesive is provided between the coating (at one face at the interface) and the other face at the interface so that for each interface, the boundary surface 20b is closer to the face having the coating than to the adhesive. This arrangement ensures that the illumination (injected via the boundary surface 20b) will encounter the coating (forming facets 5, 117) before the adhesive.

[0119] A similar procedure can be performed for the optical structure having facets 7. For example, the coating and adhesive can be applied between the various parallel-faced plates to form the optical structure having facets 7 so that at each interface between the parallel-faced plates, the adhesive is provided between the coating (at one face at the interface) and the other face at the interface so that for each interface, the optical structure 4 (and similarly the interface 3 between the two optical structures 4 and 6) is closer to the face having the coating than to the adhesive. This arrangement ensures that the illumination entering the second LOE region from the first LOE region (i.e., the illumination deflected into the second LOE region by the facets 117 formed from part of the facets 5), will encounter the coating (forming facets 7, 119) before the adhesive.

[0120] It will be noted that the production methods of the present invention are applicable to a wide range of LOE structures for different applications, and can be adapted to provide different parameters of the LOE. For example, although the methods disclosed herein have pertained to producing LOEs with two immediately adjacent regions each having a set of parallel facets (where the facets in the two sets are non-parallel to each other), the methods disclosed herein can be used to fabricate LOEs having one or more intermediate region between the two faceted LOE regions. Such LOEs can be fabricated by bonding one or more intermediate optical structures between the base optical structures (e.g., between optical structures 4 and 6). In one embodiment, the intermediate region is a blank, optically inert, region, that provides a gap between the two faceted regions. In another embodiment, the intermediate region includes an optical filter. In yet another embodiment, the intermediate region includes a polarization management element such as a waveplate or a depolarizer. In yet a further embodiment, the intermediate region can be a faceted region having a facet or one or more sets of parallel facets, for example an additional facet(s) parallel to the LOE major external surfaces and located in an intermediate region that is between the first and second LOE regions. One non-limiting example of an LOE having an additional facet(s) in an intermediate region that is between the first and second LOE regions is described in International Patent Application No. PCT / IL2022 / 050374. In embodiments for producing such LOEs, the optical structure from which the LOEs are sliced-out (e.g., optical structure 11, Ila, 11c 122, etc.) has an additional facet(s) (or set of parallel facets) located in a region between the facets of the base optical structures (e.g., facets 5 and 7 of optical structures 4 and 6, 108 and 120, etc.), and for example parallel to the slicing planes (e.g., cutting planes 14) such that the additional facet(s) of the final LOE product is parallel to the LOE major external surfaces. Inclusion of the additional facet(s) in the to-be-sliced optical structure can be effectuated in different ways. In one non-limiting example, the additional facet(s) can be included in the to-be-sliced optical structure by bonding one or more additional optical structure having said additional facet(s) between the base optical structures (e.g., optical structures 4 and 6, optical structures 108 and 120, etc.) such that the base optical structures are indirectly bonded together. As another non-limiting example, one or both of the base optical structures (e.g., optical structure 4 or 6) may include an additional faceted region, separate from the region containing facets 5 or 7, containing said additional facet(s).

[0121] The embodiments described herein have pertained to methods of fabricating LOEs by performing various processing stages on various optical structures. All of these optical structures can be considered to be intermediate work products of LOE fabrication processes.

[0122] The present document has detailed methods for producing (i.e., fabricating) LOEs according to various embodiments. These methods have included stages of slicing optical structures to produce (i.e., form, generate) slices, which may then be further processed to produce final LOE products. It will be appreciated, however, that within the context of the present document, each such generated “slice” is itself an LOE, albeit an LOE that may be an unfinished LOE product, for example due to the LOE being prior to one or more further processing stages. Such further processing stages can include, for example, polishing of the major external surfaces (for example in order to ensure high optical quality and / or high degree of parallelism), contouring (for example in order to resemble an eye glass lens shape), cutting (for example to produce the boundary surface, i.e., coupling-in region / surface), polishing of the boundary surface (for example to ensure high degree of planarity), and other fine-tuning stages.

[0123] It will be appreciated that the bonded optical structures described herein are aligned prior to the bonding stage, or in some cases during the bonding stage. The alignment of the various optical structures can be performed using any suitable optical alignment apparatus / device(s) / tool(s) that perform suitable optical alignment techniques / methods. Such suitable optical alignment apparatus / device(s) / tool(s) can include, for example, one or more computerized control device, one or more computerized processing device, one or more optical subsystem having, for example, one or more light source, one or more light detector / sensor (including optical sensors), one or more optical component (e.g., one or more lens, one or more folding optic, one or more prism, etc.), autocollimators, and the like. Details of non-limiting examples of suitable optical alignment apparatus / device(s) / tool(s) / method(s) that can be used for aligning the various optical structures described herein can be found in various publications by Lumus Ltd. (Israel), including, for example, International Patent Application No. PCT / IL2021 / 051377 and International Patent Application No. PCT / IL2021 / 051378.

[0124] The present disclosure has described various cutting and slicing stages in which optical structures are cut along cutting lines and / or planes in order to produce various other optical structures or optical products. In certain embodiments, as discussed above, some or all of the surfaces of these optical structures, including and in particular those surfaces that result from these cutting stages, can be polished to, for example, increase optical quality. In certain embodiments, polishing can be performed as part of, or subsequent to, these cutting stages, and prior to subsequent optical coupling (e.g., bonding) stages. In the above-described fabrication methods, the cutting or slicing of the various optical structures described herein can be performed by any suitable cutting apparatus / device / tool, as should be understood by those of ordinary skill in the art. The polishing of the faces and surfaces of the various optical structures described herein can be performed by any suitable polishing apparatus / device / tool, as should be understood by those of ordinary skill in the art.

[0125] The descriptions of the various embodiments of the present disclosure have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.

[0126] As used herein, the singular form, “a”, “an” and “the” include plural references unless the context clearly dictates otherwise.

[0127] The word “exemplary” is used herein to mean “serving as an example, instance or illustration”. Any embodiment described as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments and / or to exclude the incorporation of features from other embodiments.

[0128] It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination or as suitable in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.

[0129] Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A method for fabricating one or more light-guide optical elements (LOEs), the method comprising: obtaining a first optical structure having a first set of mutually-parallel partially reflective surfaces; obtaining a second optical structure having a second set of mutually-parallel partially reflective surfaces; bonding together the first optical structure and the second optical structure such that the partially reflective surfaces of the first set are non-parallel to the partially reflective surfaces of the second set, to form a third optical structure; cutting at least one of the first optical structure or the second optical structure along a contour line; and slicing the third optical structure along at least two parallel cutting planes to form one or more LOEs, each of the one or more LOEs being contoured according to the contour line so that all of the one or more LOEs have the same contour shape.

2. The method of claim 1, wherein cutting along a contoured section of the contour line is performed prior to bonding together the first and second optical structures.

3. The method of claim 1, wherein cutting along the contour line is performed by cutting the third optical structure.

4. The method of claim 1 , wherein the contour line includes a segment that intersects part of the first optical structure to define a boundary surface at the first optical structure, the boundary surface defining a coupling-in surface of each LOE of the one or more LOEs.

5. The method of claim 4, further comprising: polishing the boundary surface.

6. The method of claim 4, wherein the segment is a substantially straight-line segment such that the boundary surface defined by the second section is a boundary plane.

7. The method of claim 4, further comprising: for each of the one or more LOEs, bonding coupling-in optics to the coupling-in surface.

8. The method of claim 4, further comprising: prior to slicing the third optical structure, attaching a blank at the boundary surface such that each of the one or more LOE has a part of the blank located at the coupling-in surface.

9. The method of claim 8, further comprising: for each of the one or more LOE, polishing the pair of parallel major external surfaces; and removing the part of the blank located at the coupling-in surface.

10. The method of claim 4, further comprising: for each of the one or more LOE, optically coupling an image projector to the LOE in association with the coupling-in surface.

11. The method of claim 4, wherein for each of the one or more LOE the coupling-in surface is a planar surface that is obliquely inclined relative to the pair of parallel major external surfaces, and wherein the method further comprises: for each of the one or more LOE, optically coupling an image projector with the LOE, the coupling being between an interface of the image projector and the planar surface, wherein the interface is obliquely inclined relative to the pair of parallel major external surfaces.

12. The method of claim 1, wherein the first optical structure includes a reference surface, and wherein the at least two parallel cutting planes are perpendicular to the reference surface.

13. The method of claim 1, wherein the third optical structure includes an intermediate optical structure between the first and second optical structures.

14. The method of claim 13, wherein the intermediate optical structure is optically inert.

15. The method of claim 13, wherein the intermediate optical structure includes one or more of an optical filter or a polarization management element.

16. The method of claim 13, wherein the intermediate optical structure has at least one partially reflective surface located between the partially reflective surfaces of the first and second sets and parallel to the at least two cutting planes.

17. The method of claim 1, wherein the first optical structure is formed from a staggered stack of parallel-faced plates that are bonded together at a plurality of interfaces, one face at each of the interfaces having a coating to provide partially-reflecting optical properties such that the interfaces form the first set of mutually-parallel partially reflective surfaces.

18. The method of claim 1, wherein obtaining the first optical structure includes: bonding together a plurality of parallel-faced plates at a plurality of interfaces so as to form a stack of plates, one face at each interface having a coating to provide partially-reflecting optical properties, and cutting the stack along a pair of cutting planes that intersect at least some of the interfaces of the plurality of interfaces.

19. The method of claim 18, wherein bonding together the plurality of parallel-faced plates includes: at each interface providing adhesive between the coating and an other face at the interface, wherein for each interface the boundary surface is closer to the one face having the coating than to the adhesive.

20. The method of claim 1 , wherein the second optical structure is formed as a staggered stack of parallel-faced plates that are bonded together at a plurality of interfaces, one face at eachof the interfaces having a coating to provide partially-reflecting optical properties such that the interfaces form the second set of mutually-parallel partially reflective surfaces.

21. The method of claim 1, wherein obtaining the second optical structure includes: bonding together a plurality of parallel-faced plates at a plurality of interfaces so as to form a stack of plates, one face at each interface having a coating to provide partially-reflecting optical properties, and cutting the stack along a pair of cutting planes that intersect at least some of the interfaces of the plurality of interfaces.

22. The method of claim 21, wherein bonding together the plurality of parallel-faced plates includes: at each interface providing adhesive between the coating and an other face at the interface, wherein for each interface the first optical structure is closer to the one face having the coating than to the adhesive.

23. A method for fabricating one or more light-guide optical elements (LOEs), the method comprising: obtaining a first optical structure and a second optical structure, the first optical structure having a first set of mutually-parallel partially reflective surfaces, the second optical structure having a second set of mutually-parallel partially reflective surfaces; bonding together the first optical structure and the second optical structure, such that the partially reflective surfaces of the first set are non-parallel to the partially reflective surfaces of the second set, to form a third optical structure; cutting the first and second optical structures along a contour line; slicing the third optical structure along at least two parallel cutting planes to form one or more LOEs, each of the one or more LOEs being contoured according to the contour line so that all of the one or more LOEs have the same contour shape; and cutting each of the one or more LOEs along a substantially straight cutting line that intersects part of the first region to define a coupling-in surface of the LOE.

24. The method of claim 23, wherein cutting each of the one or more LOEs along the substantially straight cutting line is performed on a plurality of the LOEs that are held together using a single cut.

25. The method of claim 24, further comprising: for each of the one or more LOEs, bonding coupling-in optics to the coupling-in surface.

26. A method for fabricating one or more light-guide optical element (LOE), the method comprising:obtaining a first optical structure having a first set of mutually-parallel partially reflective surfaces; obtaining a second optical structure having a second set of mutually-parallel partially reflective surfaces; bonding together the first optical structure and the second optical structure such that the partially reflective surfaces of the first set are non-parallel to the partially reflective surfaces of the second set, to form a third optical structure; cutting along a cutting line that includes a section that intersects part of the first optical structure to define a boundary surface at the first optical structure; attaching a blank at the boundary surface; and slicing the third optical structure along at least two parallel cutting planes to form one or more LOE, each of the one or more LOE having a coupling-in surface defined by the boundary surface and having a part of the blank located at the coupling-in surface.

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