Method for producing a light-guiding optical element

Abstract

A method for producing light-directing optical elements (LOEs) (16, 18, 56, 58), each having a set of mutually parallel partially reflective surfaces (17) positioned between and oriented non-parallel to a pair of major exterior surfaces, and at least one region (30a, 30b, 30c) without a partially reflective surface. The method includes bonding parallel opposing plates (4) together at interfaces to form a stack (42) of plates having a partially reflective coating therebetween. The stack is cut and polished to form interfaces (48, 48a, 48b) that intersect the interfaces, and blocks (50, 50a, 50b) of transparent material are bonded to the stack. The resulting precursor structure (52, 52') is sliced ​​along parallel planes to form slices, each including a portion of the stack and a portion of the block for the active region of the LOE.

Description

[Technical Field]

[0001] The present invention relates to displays, and in particular to a method for producing light-directing optical elements. [Background technology]

[0002] Various types of displays, such as near-eye displays, may employ light-guiding optical elements (LOEs) to magnify an input image in one or more dimensions. When two-dimensional magnification is required, two LOEs may be used, including a first LOE configured to magnify the image in one dimension and a second LOE configured to magnify the image in the other dimension. Of particular relevance to the present invention are reflective LOEs, in which at least one of the first and second LOEs is implemented as a transparent block bounded by two parallel major exterior surfaces configured to support the propagation of light rays therebetween via total internal reflection (TIR), and having a set of mutually parallel partially reflective interior surfaces (or "facets") located between and non-parallel to the major exterior surfaces. A collimated image propagating within the LOE is progressively partially deflected by the facets of the first set of facets toward the facets of the second set, and by the facets of the second set outward toward the viewer's eyes, thereby presenting the image to the viewer. Summary of the Invention

[0003] The present invention is a method for producing a light-directing optical element.

[0004] In accordance with the teachings of one embodiment of the present invention, there is provided a method for producing light-directing optical elements (LOEs), each LOE having a pair of mutually parallel major exterior surfaces for directing image illumination propagating within the LOE by internal reflection at the major exterior surfaces, each LOE further having an active region with a set of mutually parallel partially reflective surfaces positioned between and oriented non-parallel to the major exterior surfaces, and at least one secondary region, at least one of the partially reflective surfaces terminating at a boundary between the active region and the secondary region, the method comprising: (a) stacking a plurality of parallel opposing plates together at a plurality of interfaces to form a stack of plates; A method is provided that includes the steps of: (a) forming a stack of plates at a surface of the stack of plates, wherein one surface at each of the interfaces has a coating to provide partially reflective optical properties; (b) cutting and polishing the stack of plates to form an interface that intersects at least one of the interfaces; (c) bonding a block of transparent material to the stack at the interface to form a precursor structure; and (d) slicing the precursor structure along multiple parallel planes to form multiple slices, each slice including a portion of the stack to provide an active region of the LOE and a portion of a block to provide a secondary region of the LOE.

[0005] According to a further feature of an embodiment of the present invention, the interface is cut along a plane oriented obliquely relative to the plane of the interface.

[0006] According to a further feature of an embodiment of the present invention, the block of transparent material is index matched to the plurality of plates.

[0007] According to a further feature of an embodiment of the invention, the block of transparent material is a block of optically continuous material.

[0008] According to a further feature of an embodiment of the present invention, the block of transparent material is a continuous homogeneous block.

[0009] According to a further feature of an embodiment of the present invention, prior to slicing, the precursor structure is cut along at least one edge plane, a portion of which defines an edge of each LOE after slicing.

[0010] According to a further feature of an embodiment of the present invention, the plurality of parallel planes are perpendicular to the interface.

[0011] According to a further feature of an embodiment of the present invention, the plurality of parallel planes are angled obliquely relative to the interface.

[0012] According to a further feature of an embodiment of the present invention, the active region of the LOE is edged and the boundary is non-parallel to the edge, such that the length of the partially reflective surface in a direction parallel to the major exterior surface gradually decreases from partially reflective surface to partially reflective surface along at least one-quarter of the set of partially reflective surfaces.

[0013] According to a further feature of an embodiment of the present invention, the coating is configured to provide a sequentially varying reflectivity for a series of interfaces.

[0014] According to a further feature of an embodiment of the invention, the plates have different thicknesses such that the interfaces are non-uniformly spaced.

[0015] According to a further feature of an embodiment of the present invention, the method further includes the steps of: (a) cutting and polishing the stack of plates to form an additional interface that intersects at least one of the interfaces, the additional interface being non-coplanar with the interface; and (b) bonding an additional block of transparent material to the stack at the interface to form a precursor structure, wherein the slicing is performed such that each slice additionally includes a portion of the additional block.

[0016] In accordance with the teachings of one embodiment of the present invention, there is provided an intermediate work product sliceable along multiple parallel planes to form multiple light-directing optical elements (LOEs), each LOE having a pair of mutually parallel major exterior surfaces for guiding image illumination propagating within the LOE by internal reflection at the major exterior surfaces, each LOE further having an active region with a set of mutually parallel partially reflective surfaces located between and oriented non-parallel to the major exterior surfaces, and at least one secondary region, at least one of the partially reflective surfaces terminating at a boundary between the active region and the secondary region, the intermediate work product comprising: (a) a stack formed from multiple parallel opposing plates bonded to each other at multiple interfaces, one face at each of the interfaces having a coating that provides partially reflective optical properties, the stack being cut and polished at an interface intersecting at least one of the interfaces; and (b) a block of transparent material bonded to the stack at the interface.

[0017] According to a further feature of an embodiment of the present invention, the interface is oriented obliquely relative to the plane of the interface.

[0018] According to a further feature of an embodiment of the present invention, the block of transparent material is index matched to the plurality of plates.

[0019] According to a further feature of an embodiment of the invention, the block of transparent material is a block of optically continuous material.

[0020] According to a further feature of an embodiment of the present invention, the block of transparent material is a continuous homogeneous block.

[0021] According to a further feature of an embodiment of the present invention, the coating is configured to provide a sequentially varying reflectivity for a series of interfaces.

[0022] According to a further feature of an embodiment of the invention, the plates have different thicknesses such that the interfaces are non-uniformly spaced. [Brief explanation of the drawings]

[0023] The invention is herein described, by way of example only, with reference to the accompanying drawings. [Figure 1A-1B] 1A-1C are schematic isometric views of an optical system implemented using a light-directing optical element (LOE), constructed and operative in accordance with the teachings of the present invention, showing a top-down configuration and a side-looking configuration, respectively; [Figure 2A-2B] FIG. 1C is an enlarged schematic isometric view of the LOE of FIG. 1A or FIG. 1B showing the optical paths for the two extreme regions of the image. [Figure 2C] 1A and 1B in combination with additional areas to define the overall envelope of partially reflective surfaces required to form a complete image in the eye movement box. [Figure 2D] 2D is an alternative implementation of FIG. 2C in which partially reflective surfaces are selectively implemented. [Figure 3] 2E is an enlarged schematic isometric view of an alternative implementation of an LOE similar to that of FIG. 2D, in which the image projector is employed at a different position and with a different optical axis orientation. [Figure 4] 1 is a schematic isometric view of steps in a method for producing multiple LOEs by slicing a stack of plates. [Figure 5] 10 is a flowchart of a method for producing modified multiple LOEs having areas where partially reflective surfaces are excluded. [Figure 6] 6 is a schematic isometric representation of steps in a method for producing multiple LOEs by slicing a stack of plates according to the modified production method of FIG. 5. [Figures 7A-7B] 7A and 7B are enlarged schematic isometric views of two LOEs produced by the method of FIGS. 5 and 6, respectively, having one and two regions without a partially reflective surface. [Figure 8] The LOE in Figure 7B is a schematic isometric representation of the sliced ​​precursor structure. [Figure 9]7C is a schematic isometric view of a two-dimensional magnified LOE having a first LOE region corresponding to the LOE of FIG. 7B and a second LOE region implemented with an area without a partially reflective surface. [Figure 10A] 1 is a schematic isometric view of an alternative precursor structure produced according to an embodiment of the method of the present invention. [Figure 10B] FIG. 10B is a side view of the precursor structure of FIG. 10A showing the cut surface along which the precursor structure is cut to produce the modified precursor structure. [Figures 10C-10D] 10B are side and isometric views, respectively, of the modified precursor structure after cutting along the cross-sectional plane of FIG. 10B. [Figure 10E] Several LOEs obtained by slicing the precursor structure of Figure 10D are shown.

[0024] DESCRIPTION OF THE PREFERRED EMBODIMENT Certain embodiments of the present invention provide methods for manufacturing light-directing optical elements (LOEs) to achieve optical aperture expansion for the purposes of heads-up displays, most preferably near-eye displays, which may be virtual reality displays or, more preferably, augmented reality displays. Figures 1A-3 show certain particularly preferred examples of optical configurations and corresponding devices to which the inventive manufacturing methods are particularly relevant, although the manufacturing methods are not limited to such applications.

[0025] An exemplary implementation of a device in the form of a near-eye display, generally designated 10, employing an LOE 12 according to the teachings of one embodiment of the present invention is shown schematically in FIGS. 1A and 1B. Near-eye display 10 employs a compact image projector 14 optically coupled (often referred to in the art as a "POD") to inject an image into LOE 12, where image light is captured in one dimension by internal reflection at a set of mutually parallel, planar external surfaces (interchangeably referred to as a "waveguide," "substrate," or "slab"). Light impinges on a set of partially reflective surfaces (interchangeably referred to as "facets") parallel to one another and obliquely tilted relative to the propagation direction of the image light, with each successive facet deflecting a percentage of the image light that is also trapped / guided by internal reflection within the substrate in a deflected direction. This first set of facets, not individually shown in FIGS. 1A and 1B, is located in a first region of the LOE, designated 16. This partial reflection at successive facets achieves optical aperture expansion in the first dimension.

[0026] In a first set of preferred, but non-limiting, embodiments of the present invention, the facets of said set are orthogonal to the major exterior surface of the substrate. In this case, both the injected image and its conjugate, which undergoes internal reflection as it propagates within region 16, are polarized, resulting in a conjugate image propagating in the direction of polarization. In an alternative set of preferred, but non-limiting, embodiments, the partially reflective surfaces of the first set are angled obliquely relative to the major exterior surface of the LOE. In the latter case, either the injected image or its conjugate forms the desired polarized image propagating within the LOE, while other reflections can be minimized, for example, by employing angle-selective coatings on the facets that make them relatively transparent for the range of incident angles represented by images for which reflection is not desired.

[0027] The first set of partially reflective surfaces deflects the image illumination from a first direction of propagation that is captured within the substrate by total internal reflection (TIR) ​​to a second direction of propagation that is also captured within the substrate by TIR.

[0028] The deflected image illumination then enters a second substrate region 18, which may be implemented as an adjacent, distinct substrate or as a continuation of a single substrate, in which a coupling-out arrangement (either a further set of partially reflective facets or diffractive optical elements) progressively couples out a proportion of the image illumination toward an observer's eye located within an area defined as the eye movement box (EMB), thereby achieving a second dimension of optical aperture expansion. The entire device may be implemented separately for each eye and is preferably supported against the user's head, with each LOE 12 facing the user's corresponding eye. In one particularly preferred option as shown here, the support arrangement is implemented as an eyeglass frame having sides 20 for supporting the device against the user's ears. Other forms of support arrangements may also be used, including, but not limited to, a headband, a sun visor, or a device suspended from a helmet.

[0029] In the drawings and claims herein, reference is made to an X-axis extending horizontally (FIG. 1A) or vertically (FIG. 1B) in the general direction of extension of the first region of the LOE, and a Y-axis extending perpendicular thereto, i.e., vertically in FIG. 1A and horizontally in FIG. 1B.

[0030] Very broadly speaking, the first LOE, or first region 16 of LOE 12, can be considered to achieve aperture expansion in the X direction, while the second LOE, or second region 18 of LOE 12, achieves aperture expansion in the Y direction. The details of the angular spread through which different portions of the field of view propagate are discussed more precisely below. Note that an orientation such as that shown in FIG. 1A can be considered a “top-down” implementation, in which image illumination entering the main portion (second region) of the LOE enters from the top edge, while the orientation shown in FIG. 1B can be considered a “side-looking” implementation, in which an axis, referred to herein as the Y axis, is horizontally extended. In the remaining figures, various features of certain embodiments of the present invention are shown in the context of a “top-down” orientation similar to FIG. 1A. However, it should be understood that all of these features are equally applicable to side-looking implementations, which are also within the scope of the invention. In certain cases, other intermediate orientations are also applicable and, unless expressly excluded, are included within the scope of the present invention.

[0031] The PODs employed in the devices of the present invention are preferably configured to produce collimated images, i.e., images in which the light for each image pixel is a parallel beam collimated to infinity with the angular direction corresponding to the pixel location, and the image illumination therefore spans an angular range corresponding to the two-dimensional field of view angle.

[0032] The image projector 14 typically includes at least one light source arranged to illuminate a spatial light modulator, such as an LCOS chip. The spatial light modulator modulates the projected intensity of each pixel of the image, thereby generating the image. Alternatively, the image projector may include a scanning configuration, typically implemented using a high-speed scanning mirror, in which illumination from a laser light source is scanned across the projector's image plane while the beam intensity is varied pixel-by-pixel in synchronization with the movement, thereby projecting the desired intensity at each pixel. In either case, collimating optics are provided to generate an output projected image that is collimated to infinity. Some or all of the above components are typically disposed on the surface of one or more polarizing beam splitter (PBS) cubes or other prism configurations, as is well known in the art.

[0033] Optical coupling of image projector 14 to LOE 12 may be achieved by any suitable optical coupling, such as via a coupling prism with an obliquely angled input face or via a reflective coupling arrangement, via a side edge and / or one of the major exterior surfaces of the LOE. The details of the coupling input arrangement are not important to the invention and are shown here schematically as a non-limiting example wedge prism 15 applied to one of the major exterior surfaces of the LOE.

[0034] It will be understood that near-eye display 10 includes various additional components, including a controller 22 for operating image projector 14, typically employing power from a small on-board battery (not shown) or some other suitable power source. It will be understood that controller 22 includes all necessary electronic components, such as at least one processor or processing circuitry, for driving the image projector, all as is well known in the art.

[0035] 2A-2F, the optical characteristics of one implementation of a near-eye display are shown in more detail. Specifically, a more detailed view of a light-directing optical element (LOE) 12 formed from a transparent material is shown, including a first region 16 including a first set of planar, mutually parallel partially reflective surfaces 17 having a first orientation, and a second region 18 including a second set of planar, mutually parallel partially reflective surfaces 19 having a second orientation that is non-parallel to the first orientation. A set of mutually parallel major exterior surfaces 24 extends across first and second regions 16 and 18 such that both the first set of partially reflective surfaces 17 and the second set of partially reflective surfaces 19 are located between major exterior surfaces 24. Most preferably, set of major exterior surfaces 24 is a pair of surfaces that are each continuous throughout first and second regions 16 and 18, although the option of having a setdown or increase in thickness between regions 16 and 18 is also within the scope of the present invention. Regions 16 and 18 may be directly juxtaposed so as to meet at a boundary, which may be a straight boundary or some other shape, or there may be one or more additional LOE regions interposed between them to provide various additional optical or mechanical functions, depending on the particular application. In certain particularly preferred implementations, a particularly high quality main exterior surface is achieved by employing a continuous exterior plate between separately formed regions 16 and 18 to form a composite LOE structure.

[0036] The optical properties of the LOE can be understood by tracing the image illumination path backward. The second set of partially reflective surfaces 19 are at an oblique angle to the main exterior surface 24 so that a portion of the image illumination propagating within LOE 12 from first region 16 into second region 18 due to internal reflection at the main exterior surface is coupled out of the LOE toward eye movement box 26. The first set of partially reflective surfaces 17 are oriented so that a portion of the image illumination propagating within LOE 12 from the coupling input region (coupling prism 15) is deflected toward second region 18 due to internal reflection at the main exterior surface.

[0037] One dimension of the angular spread of the projected image from image projector 14 is represented in FIG. 2A by the cone of illumination extending from the POD opening on the right side of the LOE toward the left side of the LOE. In the non-limiting example shown here, the central optical axis of the POD defines a propagation direction within the LOE aligned with the X-axis, and the angular spread (within the LOE) is approximately ±16°. (Note that the FOV angle is larger in air due to changes in refractive index.) A first set of partially reflective surfaces 17 is shown in first region 16, and a second set of partially reflective surfaces 19 is shown in second region 18.

[0038] The near-eye display is designed to provide a full field of view of the projected image to a user's eye, positioned within a range of permitted positions specified by an "eye movement box" (EMB) 26 (i.e., a shape, typically represented as a rectangle, away from the plane of the LOE where the eye's pupil will see the projected image). To reach the eye movement box, light must be coupled out from the second region 18 toward the EMB 26 by a second set of partially reflective surfaces 19. To provide the full image field, each point within the EMB must receive a full angular range of images from the LOE. Tracing back the field of view from the EMB suggests a larger rectangle 28 into which the relevant illumination is coupled out from the LOE toward the EMB.

[0039] FIG. 2A shows the first end of the field of view, corresponding to the bottom-left pixel of the projected image. A beam of width corresponding to the projector's optical aperture when coupled into the LOE is shown propagating upward and left from the POD and being partially reflected from a series of partially reflective surfaces 17. As shown here, only a subset of the facets produce reflections useful for providing the corresponding pixel in the image viewed by the user, and only a subregion of those facets contributes to the observed image of this pixel. The relevant region is indicated by a thick black line, showing the light rays corresponding to this pixel in the redirected image reflected from facet 17 and then coupled out by facet 19 to reach the four corners of the EMB 26. Here, and throughout the description, only the in-plane propagation direction of the ray is shown, here during propagation within the LOE, but it should be noted that the ray actually follows a zigzag path of repeated internal reflections from the two major exterior surfaces, and the overall image field in one dimension is encoded by the angle of inclination of the ray with respect to the major exterior surfaces, which corresponds to the pixel location in the Y dimension. As an additional example, the deflected and combined out ray is shown in dashed lines, corresponding to the upper left extremity of the image, as seen in the upper left corner of the EMB.

[0040] FIG. 2B shows the same configuration as FIG. 2A, but now shows rays corresponding to the pixel in the bottom right of the field of view reaching the four corners of the EMB, and again the relevant areas of the associated partially reflective surfaces 17 are shown in bold.

[0041] By additionally tracing the corresponding ray paths for every region (direction or pixel) of the image that reaches every region of the EMB, it is possible to map the envelope of all ray paths that propagate from the combined input region, through the LOE, are deflected by one of the first set of partially reflective surfaces, and are combined out by one of the second set of partially reflective surfaces in the direction that reaches the eye movement box. It will be clear that this envelope defines the "imaging region" of each facet 17 required to deflect the portion of the image illumination that contributes to the image reaching the EMB, while the remainder of the facets 17 outside the envelope are "non-imaging regions" that do not contribute to the required image. A simplified outline of this envelope, corresponding to the "imaging regions" of all facets 17, is shown in bold in Figure 2C.

[0042] It has been found that the portions of the facets within the "non-image area" can, in certain cases, adversely affect image quality, for example, by supporting unintended multiple reflection light paths, resulting in ghost images of the input image illumination and / or extraneous radiation from ambient light sources. To minimize such effects, according to certain particularly preferred implementations of the present invention, facets 17 are preferably implemented as "partial facets" such that the partially reflective properties exist only within a subregion of the cross-sectional area of ​​region 16 that includes the "image area" of each facet plane, and preferably exclude at least a large portion of the "non-image area" for some or all of the facets. Such an implementation is shown schematically in FIG. 2D. The active (partially reflective) area of ​​the facet preferably extends slightly beyond the minimum necessary to accomplish the geometric requirements of EMB image projection. According to certain particularly preferred implementations, the distance of the furthest partially reflective facet encountered along the line from the coupling input location gradually increases, increasing in angle clockwise as shown, away from the boundary with second region 18 over most of the angular range of the image projected from projector 14. This leaves one or more regions, labeled herein as 30a, 30b, and 30c, within region 16 that are preferably implemented without partially reflective facets.

[0043] 2A-2D, the optical axis of projector 14 is shown as being parallel to the X-axis. It should be understood that the optical axis is not actually parallel to the X-axis, but rather lies in the XZ plane, and the Z component within the page is selected so that the entire angular range in the depth dimension of the FOV undergoes total internal reflection at the main substrate surface. For ease of presentation, the graphical representations and descriptions herein relate only to the in-plane (XY) component of the ray propagation direction, referred to herein as the "in-plane component" or "component parallel to the main exterior surface of the LOE."

[0044] 3 shows a similar implementation in which the optical axis of the projector is rotated to align one side of the field of view with the top edge of region 16. In this case, there are two regions, labeled 30a and 30b, which are preferably implemented without partially reflective facets.

[0045] FIG. 4 illustrates a typical production method for fabricating the LOE region 16 or 18 shown in FIGS. 2A-2C. The method involves first stacking and bonding multiple transparent plates 40, each optically coated with at least a partially reflective coating, to form a stack 42. The interfaces between the plates correspond to the facets of the LOE. The stack is typically finished (top and / or bottom) with transparent plates several times thicker than the other plates. The stack is cut into slices 44 at a desired angle relative to the facet surfaces. Each slice is then shaped (e.g., by cutting and / or grinding, followed by polishing) to form parallel exterior surfaces, with the facets oriented at a specific, predetermined angle relative to the exterior surface based on the desired LOE configuration 46. In other words, the LOE is formed from slices from a stack of parallel coated glass sheets, with the angle and orientation of the partially reflective surfaces determined by the slicing angle and the orientation of the subsequent cuts.

[0046] The above manufacturing process is efficient in that a single plate stack can be used to produce multiple similar LOEs through the slicing, cutting, and polishing steps described above. The use of thick end plates in the stack allows for the creation of transparent glass regions before the first facet and / or after the last facet, but only at the boundaries parallel to the facets. However, this approach does not directly create non-active regions, such as regions 30a, 30b, and 30c in Figures 2D and 3, because these regions intersect with the stacked and bonded transparent plates that form faceted region 17.

[0047] Therefore, to produce a waveguide as described in Figure 2D or Figure 3, or other similar waveguides with partial facets, additional steps are required beyond the manufacturing method described above with reference to Figure 4.

[0048] According to one particularly preferred aspect of the present invention, there is provided a method for producing light-directing optical elements (LOEs), each LOE having a pair of mutually parallel major exterior surfaces for directing image illumination propagating within the LOE by internal reflection at the major exterior surfaces, an active region having a set of mutually parallel partially reflective surfaces positioned between and oriented non-parallel to the major exterior surfaces, and at least one secondary region, at least one of the partially reflective surfaces terminating at a boundary between the active region and the secondary region. The method, as shown in the block diagram of Figure 5 and illustrated schematically in Figure 6, comprises at least the following steps: (a) bonding a plurality of parallel opposing plates 40 together at a plurality of interfaces to form a stack of plates 42, one surface at each of the interfaces having a coating to provide partially reflective optical properties (step 32); (b) cutting and polishing the stack of plates to form an interface 48 that intersects at least one of the interfaces (step 34); (c) bonding a block 50 of transparent material to the stack 42 at the interface 48 to form a precursor structure 52 (step 36); and (d) slicing the precursor structure 52 along multiple parallel planes to form multiple slices 54, each slice including a portion of the stack 42 for providing the active region of the LOE and a portion of the block 50 for providing the secondary region of the LOE.

[0049] In the embodiment shown in FIG. 6, a final LOE 56 is cut from each slice 54 as shown, thereby forming an LOE 56 having at least one region 30a in which the facets of this set are excluded.

[0050] Preferably, block 50 is formed from a transparent material that is index-matched to the multiple plates so that the boundaries between faceted and non-faceted regions do not create significant optical aberrations. For the same reason, attachment of block 50 to stack 42 may be preferred with an index-matching optical adhesive. Block 50 itself is preferably a block of optically continuous material, meaning that block 50 has no internal features that would cause significant optical aberrations, scattering, or deflection of light. Most preferably, block 50 is implemented as a continuous, homogenous block of transparent material, typically glass.

[0051] The orientation and location of interface 48 is selected according to the desired boundary location in the final LOE structure. In most cases, the orientation is a plane oriented obliquely relative to the plane of the interface. This is shown diagrammatically in Figure 6 as an angle α (greater than 90°).

[0052] While the method of Figures 5 and 6 presents steps for fabricating an LOE having a single inactive region 30a, as shown in Figure 7A, it is easily adapted to form two or more inactive regions in which set facets are excluded by repeating steps 34 and 36 to form additional interfaces and adding additional transparent blocks to the precursor structure before slicing. Figure 7B shows a further example of an LOE 56 having two inactive regions 30a and 30b, and Figure 8 shows several such LOEs 56 sliced ​​from a corresponding precursor structure 52, with each slice including a region of the stack and a region of both blocks.

[0053] While this specification primarily illustrates an example of first-dimensional optical aperture expansion, in which facets are responsible for deflecting image light propagation by the LOE from a first guided direction to a second guided direction, the same principles are applicable to LOEs employed for second (or any other) stage of optical aperture expansion. By way of example, FIG. 9 illustrates an optical configuration including a first LOE 56, as shown in FIG. 7B, for performing first-dimensional optical aperture expansion and a second LOE 58 for performing second-dimensional optical aperture expansion and coupling out image illumination toward the observer's eye. In this case, coupling-out facets 60 (shown schematically and excessively far apart for ease of understanding) are limited to the active region of LOE 58 and excluded from non-active region 62, where facets are not necessary to direct any portion of the image to any portion of the EMB. The facets terminate at interface 61. Again, the non-active area 62 is preferably produced along with the rest of the LOE by slicing a precursor assembly (not shown) comprising a transparent block bonded to a stack of coated plates, all as disclosed above with reference to Figures 5 and 6.

[0054] 10A-10E illustrate a further embodiment of the method of the present invention that is generally similar to the previous embodiment. In this case, precursor structure 52 (FIG. 10A) is formed by attaching first block 50a at first interface 48a and second block 50b at second interface 48b to stack 42. In this case, cutting second interface 48b also involves cutting a portion of first block 50a. FIG. 10B is a side view illustrating cut lines 64 along which the precursor structure is preferably cut prior to slicing. This cut preferably defines one or more edge planes, portions of which will define the edges of each LOE after slicing. The resulting preformed precursor structure 52′ is shown in FIGS. 10C and 10D. Subsequent slicing of precursor structure 52′ along the slicing plane (dashed line 66 in FIG. 10D) typically results in a near-final LOE structure 58 that requires only final polishing and any other steps necessary for assembling the LOEs as part of an overall optical design.

[0055] It should be noted that the production method of the present invention is applicable to a wide range of LOE structures for different applications and can be adapted to provide different LOE parameters. For example, in certain implementations, the parallel slice planes are oriented perpendicular to the stack interfaces, resulting in partially reflective surfaces that are orthogonal to the LOE's major exterior surfaces. For other applications, the parallel slice planes are angled obliquely relative to the interfaces, thereby producing an LOE with partially reflective surfaces that are oblique to the LOE's major exterior surfaces.

[0056] The methods of the present invention may also be implemented with a series of partially reflective surfaces implementing various additional features, all according to the requirements of a particular optical configuration. Examples include, but are not limited to, variable facet spacing, where the plates have different thicknesses from one another so that the interfaces are non-uniformly spaced, and variable reflectivity, where the coating is configured to provide sequentially varying reflectivity for a series of interfaces.

[0057] Obviously, depending on the desired geometry of the final optical device, the non-active regions of the LOEs may extend along a greater or lesser proportion of the facet area. According to certain particularly preferred implementations, the interfaces are non-parallel to the edges of the LOEs such that the lengths of the partially reflective surfaces in a direction parallel to the major exterior surfaces decrease gradually from partially reflective surface to partially reflective surface along at least one-quarter of the sets of partially reflective surfaces.

[0058] As discussed above in the context of Figure 1B, the two-dimensional optical magnification embodiments shown herein in a "top-down" context are all equally applicable to a "lateral" configuration in which an image is injected from a POD located laterally outside the viewing area and expanded vertically by a first set of facets and then horizontally by a second set of facets for coupling into the user's eye. It should be understood that all of the above configurations and variations are also applicable to side-looking configurations.

[0059] Throughout the above description, reference is made to X and Y axes as shown, where the X axis is either horizontal or vertical and corresponds to optical aperture expansion in a first dimension, and the Y axis is the other major axis corresponding to expansion in a second dimension. In this context, X and Y can be defined with respect to the orientation of the device when worn on a user's head, typically in an orientation defined by a support structure such as the eyeglass frames of FIGS. 1A and 1B described above. Other terms typically consistent with that X-axis definition include: (a) at least one straight line that delimits an eye movement box, which can be used to define a direction parallel to the X-axis; (b) the edges of a rectangular projected image are typically parallel to the X and Y axes; and (c) the boundary between first region 16 and second region 18 typically extends parallel to the X-axis.

[0060] It will be understood that the above description is intended to serve as an example only, and that many other embodiments are possible within the scope of the invention as defined in the appended claims.

Claims

1. 1. A method for producing light-directing optical elements (LOEs), each said LOE having a pair of mutually parallel major exterior surfaces for directing image illumination propagating within said LOE by internal reflection at said major exterior surfaces, each LOE further having an active region comprising a set of mutually parallel partially reflective surfaces located between and oriented non-parallel to said major exterior surfaces, and at least one secondary non-active region, selected as a region where said partially reflective surfaces are not required to direct any portion of an image to any portion of an eye movement box (EMB), and at least one of said partially reflective surfaces terminates at a boundary between said active region and said secondary non-active region, said method comprising: (a) bonding a plurality of parallel opposing plates together at a plurality of interfaces to form a stack of plates, one surface at each of the plurality of interfaces having a coating to provide partially reflective optical properties; (b) selecting an orientation and location of an interface according to a desired boundary location in the LOE; (c) cutting and polishing the stack of plates to form the interface in the stack, the interface intersecting at least one of a plurality of plates included in the stack and the plurality of interfaces; (d) bonding a block of transparent material to the stack at the interface to form a precursor structure; (e) slicing the precursor structure along a plurality of parallel planes to form a plurality of slices, each slice including a portion of the stack for providing the active region of the LOE and a portion of the block for providing the secondary inactive region of the LOE.

2. The method of claim 1 , wherein the boundary surface is cut along a plane oriented obliquely relative to a plane of the plurality of interfaces.

3. The method of claim 1 , wherein the block of transparent material is index-matched to the plurality of plates.

4. The method of claim 1 , wherein the block of transparent material is a block of optically continuous material.

5. The method of claim 1 , wherein the block of transparent material is a continuous, uniform block.

6. 10. The method of claim 1, further comprising, prior to the slicing, cutting the precursor structure along at least one edge plane, a portion of which defines an edge of each LOE after the slicing.

7. The method of claim 1 , wherein the parallel planes are perpendicular to the interfaces.

8. The method of claim 1 , wherein the parallel planes are angled obliquely relative to the interfaces.

9. 2. The method of claim 1, further comprising forming an edge in the active region of the LOE, the boundary being non-parallel to the edge such that a length of the partially reflective surface in a direction parallel to the major exterior surface gradually decreases from partially reflective surface to partially reflective surface along at least one-quarter of the set of partially reflective surfaces.

10. The method of claim 1 , wherein the coating is configured to provide a sequentially varying reflectivity for a series of the interfaces.

11. The method of claim 1 , wherein the plates have different thicknesses such that the interfaces are non-uniformly spaced.

12. (a) cutting and polishing the stack of plates to form an additional interface surface that intersects at least one of the plurality of interface surfaces, the additional interface surface being non-coplanar with the interface surface; (b) bonding an additional block of transparent material to the stack at the interface to form the precursor structure; The method of claim 1 , wherein the slicing is performed such that each slice additionally includes a portion of the additional block.

13. an intermediate work product sliceable along a plurality of parallel planes to form a plurality of light-directing optical elements (LOEs), each LOE having a pair of mutually parallel major exterior surfaces for directing image illumination propagating within the LOE by internal reflection at the major exterior surfaces, each LOE further having an active region comprising a set of mutually parallel partially reflective surfaces located between and oriented non-parallel to the major exterior surfaces, and at least one secondary non-active region, the secondary non-active region selected as a region where the partially reflective surfaces are not required to direct any portion of an image to any portion of an eye movement box (EMB), and only a portion of the partially reflective surfaces terminate at a boundary between the active region and the secondary non-active region; The intermediate work products are: (a) a stack formed from a plurality of parallel opposing plates bonded together at a plurality of interfaces, one surface at each of the plurality of interfaces having a coating that provides partially reflective optical properties, the stack being cut and polished at an interface that intersects the plates included in the stack and at least one of the plurality of interfaces, the interface being on a different plane than the pair of mutually parallel major exterior surfaces; (b) a block of transparent material bonded to said stack at said interface.

14. 14. The intermediate work product of claim 13, wherein the boundary surfaces are oriented obliquely relative to a plane of the plurality of interface surfaces.

15. The intermediate work product of claim 13 , wherein the block of transparent material is index-matched to the plurality of plates.

16. 14. The intermediate work product of claim 13, wherein the block of transparent material is a block of optically continuous material.

17. 14. The intermediate work product of claim 13, wherein the block of transparent material is a continuous homogenous block.

18. 14. The intermediate work product of claim 13, wherein the coating is configured to provide a sequentially varying reflectivity for a series of the plurality of interfaces.

19. 14. The intermediate work product of claim 13, wherein the plates have different thicknesses such that the interfaces are non-uniformly spaced.

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