Method for manufacturing substrate guiding elements for compact head-mounted display systems

Abstract

A method for manufacturing an optical device having a light-transmitting substrate having at least two main surfaces, edges, and an output coupling output reflection element carried by the substrate, thereby forming a substrate that allows light waves to pass through the substrate between the two main surfaces, the method comprising: (a) attaching a plurality of plates of selected thickness to each other, each of the plurality of plates having at least two parallel main surfaces and two edges, the plurality of plates being arranged in an unrestricted first periodic stack (175), the first periodic stack having the main surfaces parallel to the plates. (a) the stack at least two surfaces (104U, 104D) and edges (105R, 105L); (b) slicing the stack to form a plurality of slices (178) defining slice lines (107), wherein the stack is oriented such that for most of the stacks, the slice lines pass through at least two edges of the plate; (c) grinding or polishing the slices to form a substrate having two main surfaces and coupled output reflective elements, wherein the main surfaces are parallel to each other and not parallel to the coupled output reflective elements; and (d) cutting the substrate to the final size.

Description

Technical Field

[0001] The present invention relates to a substrate-based optical waveguide device, and more particularly to a device comprising a reflective surface supported by a light-transmitting substrate, and a method for manufacturing such an optical device.

[0002] This invention can be advantageously implemented in a wide range of imaging applications, such as head-mounted displays, head-up displays, cellular phones, compact displays, and 3D displays. Background Technology

[0003] One important application of compact optics is head-mounted displays (HMDs), where the optical module acts as both an imaging lens and a combiner, in which a two-dimensional display is imaged to infinity and reflected into the viewer's eye. The display can be indirectly obtained directly from any spatial light modulator (SLM) via relay lenses or fiber bundles, such as cathode ray tubes (CRTs), liquid crystal displays (LCDs), organic light-emitting diode arrays (OLEDs), scanning sources, and similar devices. The display comprises an array of elements (pixels) imaged to infinity by collimating lenses and transmitted to the viewer's eye by means of reflective or partially reflective surfaces, which act as combiners for both non-perspective and perspective applications. Typically, conventional free-space optical modules are used for these purposes. As the desired field of view (FOV) of the system increases, these conventional optical modules become larger, heavier, and bulkier, and therefore impractical even for medium-performance devices. This is a major drawback of all types of displays, but especially a major drawback of HMDs, where the system should be as light and compact as possible.

[0004] The need for compactness has led to several different complex optical solutions. On the one hand, all of these solutions are still not compact enough for most practical applications, and on the other hand, they have significant shortcomings in terms of manufacturability, price, and performance.

[0005] The teachings contained in Publications WO2017 / 141239, WO2017 / 141240, WO2017 / 141242, WO2019 / 077601, WO2020 / 157747 and IL 276466 are incorporated herein by reference. Summary of the Invention

[0006] This invention helps to provide compact substrates for HMDs and other applications. It allows for a relatively wide field of view (FOV) and a relatively large eye movement frame (EMB) value. The resulting optical system provides large, high-quality images that also accommodate significant eye movements. The optical system according to the invention is particularly advantageous because it is significantly more compact than prior art implementations and can be easily integrated, even into specially constructed optical systems.

[0007] Therefore, a broad objective of the present invention is to mitigate the disadvantages of prior art compact optical display devices according to specific needs, and to provide other optical components and systems with improved performance, and to provide a method for manufacturing such optical devices.

[0008] According to the present invention, a method for manufacturing an optical device having a light-transmitting substrate having at least two main surfaces, edges, and an output coupling output reflective element carried by the substrate, thereby forming a substrate that allows light waves to pass through the substrate between the two main surfaces, the method comprising: a. attaching a plurality of plates of selected thickness to each other, each plate having at least two parallel main surfaces and two edges, the plurality of plates being arranged in an unrestricted first periodic stack having at least two surfaces and edges parallel to the main surfaces of the plates; b. slicing the stack to form a plurality of slices defining slicing lines, wherein the stack is oriented such that for most of the stacked plates, the slicing lines pass through at least two edges of the plates; c. grinding or polishing the slices to form a substrate having two main surfaces and a coupled output reflective element, wherein the main surfaces are parallel to each other and not parallel to the coupled output reflective element; and d. cutting the substrate to a final size. Attached Figure Description

[0009] The invention will be described with reference to the following illustrative drawings and certain preferred embodiments, so that the invention can be more fully understood.

[0010] Referring specifically to the accompanying drawings, it is emphasized that the details shown are by way of example only and are intended to illustrate preferred embodiments of the invention only, and are presented to provide what is considered the most useful and readily understood description of the principles and concepts of the invention. In this regard, no further structural details of the invention are attempted to be shown, except for those details necessary for a basic understanding of the invention. The description taken in conjunction with the accompanying drawings is intended to guide those skilled in the art on how the various forms of the invention can be practiced.

[0011] In the attached diagram:

[0012] Figure 1 is a side view of an exemplary light-transmitting substrate of the prior art;

[0013] Figure 2 is a side view of another exemplary light-transmitting substrate of the prior art;

[0014] Figures 3A and 3B illustrate the desired reflectivity and transmittance characteristics of a selectively reflective surface in an exemplary transparent substrate for two incident angle ranges in the prior art.

[0015] Figure 4 The figure illustrates the reflectivity curves of an exemplary dielectric coating as a function of the incident angle.

[0016] Figures 5A, 5B, and 5C illustrate cross-sectional views of a prior art transparent substrate having coupling-in and coupling-out surfaces and partial reflection redirection elements.

[0017] Figures 6a-6e are illustrations of prior art methods for manufacturing transparent substrates;

[0018] Figures 7a-7e are illustrations of prior art methods for manufacturing redirection elements;

[0019] Figures 8a-8e are illustrations of another method for manufacturing redirection elements;

[0020] Figures 9a-9g are illustrations of a method for manufacturing a plurality of transparent substrates according to the present invention;

[0021] Figures 10a-10g are illustrations of another method for manufacturing a plurality of transparent substrates according to the present invention;

[0022] Figures 11a-11g are illustrations of a method for manufacturing a plurality of redirection elements according to the present invention;

[0023] Figure 12e -12h is a diagram illustrating another method for manufacturing a plurality of redirection elements according to the present invention;

[0024] Figures 13A, 13B, and 13C are schematic cross-sectional views of prior art substrate guiding embodiments having a single coupled output element, an intermediate prism, a redirection element, and an input aperture significantly smaller than the output aperture.

[0025] Figure 14 This is a schematic cross-sectional view of a substrate guiding embodiment according to the present invention, having a single coupled output element, an intermediate prism, and an extended redirection element;

[0026] Figure 15 This is another schematic cross-sectional view of a substrate guiding embodiment according to the present invention, having a single coupling output element, an intermediate prism, and an extended redirection element;

[0027] Figure 16A and 16B This is yet another schematic cross-sectional view of a substrate guiding embodiment according to the present invention, having a single coupling output element, an intermediate prism, and an extended redirection element; and

[0028] Figure 17 This is a schematic cross-sectional view of a substrate guiding embodiment according to the present invention, having a blank transparent plate, a coupling prism, and an extended redirection element. Detailed Implementation

[0029] Figure 1 illustrates a cross-sectional view of a prior art light-transmitting substrate, wherein a first reflective surface 16 is illuminated by collimated light waves 12 emitted from a display source 4 and collimated by a lens 6 located between the source 4 and the substrate 20 of the device. The reflective surface 16 reflects the incident light from the source 4, such that the light waves are trapped within the planar substrate 20 by total internal reflection. After several reflections from the main surfaces 26, 27 of the substrate 20, the trapped light waves reach a partial reflective element 22, which couples the light outward from the substrate to the viewer's eye 24 located within the output pupil 25. Here, the input aperture 17 of the substrate 20 is defined as the aperture through which the input light waves enter the substrate, and the output aperture 18 of the substrate is defined as the aperture through which the trapped light waves leave the substrate. In the case of the substrate shown in Figure 1, both the input and output apertures coincide with the lower surface 26. However, other configurations are also contemplated, in which the input and image light waves from the displacement source 4 are located on opposite sides of the substrate, or on one of the edges of the substrate. As shown, the effective areas of the input aperture and output aperture, which are approximated by the projections of the coupled input element 16 and the coupled output element 22 onto the main surface 26, are similar to each other.

[0030] In an HMD system, the entire area requiring an EMB is illuminated by all light waves emitted from the display source so that the viewer's eye can simultaneously see the entire field of view (FOV) of the projected image. Consequently, the system's output aperture must be correspondingly expanded. On the other hand, the optical module needs to be lightweight and compact. Since the lateral range of the collimating lens 6 is determined by the lateral dimension of the substrate's input aperture, it is desirable that the input aperture be as small as possible. In systems such as those shown in Figure 1, where the lateral dimensions of the input aperture are similar to those of the output aperture, there is an inherent contradiction between these two requirements. Most systems based on this optical architecture suffer from the problems of a small EMB, a small achievable FOV, and a large and bulky imaging module.

[0031] Figure 2 illustrates an embodiment that at least partially solves this problem, wherein the element coupling the output light wave from the substrate is an array of partially reflective surfaces 22a, 22b, etc. The output aperture of this configuration can be expanded by increasing the number of partially reflective surfaces embedded within the substrate 20. Therefore, optical modules with small input apertures and large output apertures can be designed and constructed. As can be seen, the captured light reaches the reflective surface from two different directions 28, 30. In this particular embodiment, the captured light reaches the partially reflective surface 22a from one of these directions 28 after an even number of reflections from the main surfaces 26 and 27 of the substrate, wherein the angle of incidence between the captured light and the normal to the reflective surface is β. ref .

[0032] The captured light reaches the partially reflective surface 22b from the second direction 30 after an odd number of reflections from substrate surfaces 26 and 27, wherein the angle of incidence between the captured light and the normal to the reflective surface is β. ref' .

[0033] As further illustrated in Figure 2, for each reflective surface, each ray first arrives at the surface from direction 30, with some rays then striking the surface again from direction 28. To prevent unwanted reflections and ghosting, it is important that the reflectivity is negligible for rays striking the surface from the second direction 28.

[0034] A solution to this requirement was previously proposed in the aforementioned publication, which utilizes the angle sensitivity of the thin-film coating. If one angle is significantly smaller than the other, the desired distinction between the two incident directions can be achieved. A coating with very low reflectivity at high incident angles and high reflectivity at low incident angles can be provided. This property can be used to prevent unwanted reflections and ghosting by eliminating reflectivity in one of these two directions.

[0035] Referring now specifically to Figures 3A and 3B, these figures illustrate the desired reflection behavior of a portion of the reflective surface 34. When β... ref When the off-axis ray 32 (Fig. 3A) is partially reflected and coupled outward from the substrate 20, it is at a relative angle β' to the reflecting surface 34. ref The off-axis light ray 36 (Fig. 3B) is transmitted through the reflective surface 34 without any obvious reflection.

[0036] Figure 4The figure illustrates the reflectivity curves of a typical partially reflective surface of this particular system for S-polarized light with a wavelength λ = 550 nm, based on the angle of incidence. For full-color displays, all other wavelengths in the relevant visible spectrum should exhibit similar reflectivity curves, typically between 430 nm and 660 nm for most display sources. Two significant regions are present in the figure: between 65° and 85°, where reflectivity is very low; and between 10° and 40°, where reflectivity increases monotonically with increasing angle of incidence. (See Figure 3 and...) Figure 4 As can be seen, the required reflective behavior of the partially reflective surface 22 in the embodiment shown in Figure 2 is not conventional. Furthermore, in order to maintain low reflectivity in higher angle regions, the reflectivity in lower angle regions cannot exceed 20%-30%. Additionally, to achieve uniform brightness across the entire field of view (FOV), the reflectivity of the partially reflective surface is required to gradually increase towards the edge of the substrate. Therefore, the maximum achievable efficiency is relatively low and typically cannot exceed 10%.

[0037] Figures 5A and 5B illustrate embodiments for overcoming the aforementioned problems. Instead of using a single element (22 in Figure 2, or 50 in Figure 5) that performs the dual function of coupling light waves outward from the substrate 20 and directing the light waves into the user's eye 24, the required function is divided into two distinct elements; that is, an element embedded within the substrate couples light waves outward from the substrate, while a second conventional partial reflective element located outside the substrate redirects the light waves into the viewer's eye. As shown in Figure 5A, two rays 63 (dashed lines) from a planar light wave emitted from the display source and collimated by a lens (not shown) are directed relative to the main surfaces 70 and 72 of the substrate at an α angle. in (0) The incident light enters the light-transparent substrate 64, which has two parallel main surfaces 70 and 72, through the input aperture 86. The light then illuminates a reflective surface 65, which forms an angle α with the main surfaces of the substrate. sur1 The reflective surface 65 reflects the incident light rays, causing them to be trapped within the planar substrate 64 by total internal reflection from the main surface. To distinguish the various "propagation orders" of the trapped light waves, the superscript (i) will denote order i. The input light wave incident on the substrate at zero order is indicated by the superscript (0). After each reflection from the coupled input reflective surface, the order of the trapped light ray increases from (i) to (i+1). The off-axis angle α between the trapped light ray and the normals of the main surfaces 70 and 72 is... in (1) for:

[0038]

[0039] After several reflections from the surface of the substrate, the captured light reaches the second flat reflective surface 67, which couples the light outward from the substrate. It is assumed that surface 67 is inclined at the same angle relative to the main surface and the first surface 65, that is, surfaces 65 and 67 are parallel and α... sur2 =α sur1 Then the angle α between the coupled output ray and the normal to the substrate plane is... out for:

[0040]

[0041] Therefore, the coupled output light beam is tilted relative to the substrate at the same angle as the incident light beam. So far, the behavior of the coupled input light wave is similar to that shown in Figure 1. However, Figure 5A illustrates a different behavior, where the light beam 63 has an α... in (0) Two rays 68 (dashed line) with the same angle of incidence strike the right side of the reflective surface 65. After two reflections from surface 65, the light wave is coupled within the substrate 64 via total internal reflection, and the off-axis angle of the trapped light within the substrate is now:

[0042]

[0043] After several reflections from the main surface of the substrate, the captured light reaches the second reflective surface 67. Light 68 is reflected twice from the coupling output surface 67. Then, this light travels at the same off-axis angle α as the other two rays 63. out Coupled out from the substrate, the two rays 63 are reflected only once from surfaces 65 and 67, and this off-axis angle is also the same incident input angle for all four rays on the principal plane of the substrate. Although all four rays are incident at the same off-axis angle and coupled outward from the substrate, there are substantial differences between them: the two rays 68 incident on the right side of the reflective surface 65 are closer to the right edge 66 of the substrate 64, are reflected twice from surfaces 65 and 67, and are coupled out from the substrate at the left side of surface 67, which is closer to the opposite left edge 69 of the substrate. On the other hand, the two rays 63 incident on the left side of the reflective surface 65 are closer to the center of the substrate 64, are reflected once from surfaces 65 and 67, and are coupled out from the substrate at the right side of surface 67, which is closer to the center of the substrate.

[0044] As further illustrated in Figures 5A and 5B, the tilt angle α of the image can be adjusted by adding a partially reflective surface 79. out This part of the reflective surface 79 is α redThe angle is tilted relative to the surface 72 of the substrate. As shown, the image is reflected and rotated so that it is again substantially normal to the main surface of the substrate, passes through the substrate, and reaches the viewer's eye 24 through the output aperture 89 of the substrate. To minimize distortion and chromatic aberration, it is preferable to embed surface 79 in the redirection prism 80 and complete the shape of the substrate 64 with a second prism 82, both of which are made of the same material, which does not need to be similar to the material of prism 80. To minimize the thickness of the system, as shown in FIG. 5B, a single reflective surface 79 can be replaced by an array of parallel partially reflective surfaces 79a, 79b, etc., where the number of partially reflective surfaces can be determined according to the needs of the system. Another method to redirect the coupled output light wave to the viewer's eye is to use a flat meta-surface with a subwavelength-scale pattern structure.

[0045] Figures 6a-6e illustrate a prior art method for manufacturing a main transparent substrate 64. As shown in the side view in the xz plane, multiple transparent plates 141 coated with a suitable optical coating 142 (step (a)) (if desired) are bonded together using a suitable optical adhesive to create a stacked form 143 (step (b)). Several segments 144 (step (c)) are then cut from the stacked form by cutting, ground, and polished to produce the desired substrate 146 (step (d)). As shown in the top view in the xy plane, several elements 148 can be cut from each slice 146 (step (e)). Figures 6a-6e illustrate a method for manufacturing a substrate having only two reflective surfaces 65 and 67. For other embodiments, such as a redirecting element 80, where a large number of reflective surfaces are embedded within the substrate, a large number of plates should be added to the manufacturing process.

[0046] As shown in Figures 7a-7e, which illustrate a side view of the xz plane, multiple identical partial reflective plates 150 coated with a suitable beam-splitting coating (step (a)) are bonded together between two transparent plates 152, 154 using a suitable optical adhesive to create a stacked configuration 156 (step (b)). Typically, the number of plates 150 is the same as the number of partial reflective surfaces in the redirection element 80. Several segments 158 are then cut from the stacked configuration (step (c)). The final dimensions of the redirection element are set by a cutting step (d), grinding, and polishing to produce the desired substrate 162 (step (e)). Figure 7 illustrates a method of manufacturing a redirection element having four partial reflective elements 79. However, for systems with large output apertures and thin redirection elements 80, a much larger number of partial reflective surfaces 79 need to be embedded in the element 80.

[0047] Figures 8a-8fAn alternative method for manufacturing the redirection element 80 is illustrated. As shown in the side view in the xz plane, multiple identical partial reflective plates 164 coated with a suitable beam-splitting coating (step (a)) are bonded together using a suitable optical adhesive to produce a stacked form 166 (step (b)). Multiple identical stacked pieces 166i (i = a, b, c...) are bonded together in a staggered arrangement between two transparent plates 167, 168 using a suitable optical adhesive to produce a stacked form 170 (step (c)). Typically, the number of plates 164 in the stacked piece 170 is the same as the number of partial reflective surfaces in the redirection element 80. Several segments 171 are then cut from the stacked form (step (d)). The final dimensions of the redirection element are set by cutting step (d), grinding, and polishing to produce the desired substrate 172 (step (e)).

[0048] In Figures 6a-6e to Figures 8a-8f In all the embodiments shown, the number of stackable plates is limited by the number of reflective surfaces in the final element. In Figures 6a-6e, the number of stacked plates is n+1, while in Figures 7a-7e to... Figures 8a-8f Here, n+2 is the number of reflective surfaces in the final element. This limitation on the number of stacked plates restricts the number of elements produced from a single stack. Typically, due to this limitation, conventional slicing devices, usually found in wire saws, can accommodate stacks much larger than achievable. As a result, Figures 6a-6e to Figures 8a-8f The total output of the manufacturing method shown is significantly limited.

[0049] To increase the throughput of the manufacturing process, the stacked components of the substrates need to be arranged in a periodic and unrestricted structure. That is, the structure should not be limited by the number of reflective surfaces in the substrate, but rather determined by the overall capacity of the slicing apparatus. The structure of the stacked components should also generally be periodic to allow the lines of the slicing apparatus to be evenly distributed.

[0050] Figures 9a-9g illustrate an improved method for manufacturing the main transparent substrate 64. As shown in the side view in the xz plane, a plurality of transparent plates 174, having at least two edges 101 and two main parallel surfaces 102 and coated with a suitable optical coating (step (a)) (if desired), are bonded together using a suitable optical adhesive to form a stacked configuration 175 having two main flat sides 105R, 105L (step (b)). Depending on the capacity of the slicing apparatus, the stacked configuration 175 may contain any number of plates 174. Optionally, two prisms 176a and 176b may be bonded to the lower main surface and upper main surface 104 of the stacked configuration 175 to simplify the positioning of the stacked configuration within the slicing apparatus. Several segments 178 (shaded lines, step (c)) are then cut from the stacked configuration. Individual slices 179 (dashed lines) containing the internal structure of the substrate 64 (Figures 5A-5C) may be cut from each plate 174 (step (d)). The final dimensions of the substrate are set by cutting at 180 (step (e)), grinding, and polishing to form the desired lateral dimensions of substrate 182 (step (f)). As shown in the top view in the xy plane, several elements 183 can be cut from each slice 179 (step (g)). Dashed lines indicate the cut contours, while dotted lines indicate the intersections of the inclined coupling input surface 65 and coupling output surface 67 with the main surfaces 70 and 72 of substrate 64. In the specific example shown here, eight plates are bonded together to form a stack 175. Thus, the number of plates forming this stack is significantly greater than the number of reflective coupling output surfaces 67, which is only one. Obviously, many more plates can be stacked together to form stack 175. To simplify the positioning of the stack within the slicing apparatus, the outer surfaces 177a, 177b of the prisms 176a, 176b (Fig. 9b) placed next to the surface of the apparatus should be at an angle α relative to the main surface of plate 174. sur1 tilt.

[0051] There are some significant differences between the prior art overlay methods shown in Figures 6 and 7 and the proposed method shown in Figure 9:

[0052] 1. In the prior art methods shown in Figures 6 and 7, the plates are arranged in an interlaced structure to increase the throughput of the process. In the method proposed in Figure 9, in addition to the two main surfaces 104U, 104L, the edges 101 of the plate 174 are aligned together to form at least two main flat sides 105R, 105L.

[0053] 2. In the proposed method shown in Figure 9, the stack is oriented such that the slice line 107 passes through the stack between its two main sides 105R, 105L. In prior art methods, the slice line either crosses diagonally from the upper left edge of the stack to the lower right edge (Figure 6), or crosses its main surface (Figure 7).

[0054] 3. In the proposed method shown in Figure 9, the stack 175 is oriented such that the slice line 107 passes through at least two edges 101 of all stacked plates 174. There may be configurations where the slice line 107 will only pass through one edge, typically in the two outermost plates. However, for most plates, both opposite edges are crossed by the slice line. In the prior art method shown in Figure 6, the slice line only crosses the left edge of the upper plate and the right edge of the lower plate, but not the edges of the intermediate plates. In the prior art method shown in Figure 7, the slice line only crosses the main surface of the stack and does not cross the edges of the plates at all.

[0055] 4. To maintain the periodic structure of the stacked components 175, the distance between two adjacent slice lines 107 is constant and proportional to the thickness of the plate 174. In prior art methods, there is no such relationship between these two parameters.

[0056] 5. As shown in Figure 9, for all stacked plates 174, the slice line 107 crosses the plate edge 101 at essentially the same location 108.

[0057] In the manufacturing method shown in Figures 9a-9g, the stack 175 can completely occupy the slicing apparatus along the z and y dimensions. However, the throughput of this manufacturing method can be further increased by expanding the stack along the x-axis. Figures 10a-10g illustrate another method for manufacturing the main transparent substrate 64. As shown in the side view in the xz plane, a plurality of transparent plates 184 coated with a suitable optical coating (step (a)) (if desired) are bonded together using a suitable optical adhesive to achieve a stack form 185 (step (b)). Each plate 184 is much longer along the x-axis than the plate 174 (Figure 9a). Depending on the capacity of the slicing apparatus, the stack 185 can contain any number of plates 184. Optionally, two prisms 186a and 186b can be bonded to the edge of the stack 185 to simplify the positioning of the stack 185 within the slicing apparatus. Several segments 188 are then cut from the stack form (step (c)). A single slice 189 containing the internal structure of at least two substrates 64 can be cut from each plate 184 (Figure 10d) (step (10d)). The final dimensions of the substrates are set by cutting at 190 (step (e)), grinding, and polishing to form the desired substrate 192 (step (f)). As shown in the top view of Figure 10(e) in the xy plane, a plurality of elements 193 can be cut from each slice 189 (step (g)). Unlike the method shown in Figures 9a-9g, in which a one-dimensional array along the y-axis of the elements 183 can be cut from each slice 179, a two-dimensional array along the x and y axes of the elements 193 can be cut from each slice 189.

[0058] Figures 11a-11g illustrate an improved method for manufacturing the repositioning element 80 (Figures 5A-5C). As shown in the side view in the xz plane, multiple transparent plates, including a staggered arrangement of 2n+1 plates comprising n+1 double-coated plates 195 and n uncoated plates 196 (step (a)), are bonded together using a suitable optical adhesive to produce an initial stack 197 (step (b)), each interface plane 199 between two adjacent plates containing one and only one partially reflective surface. The initial stack 197 is bonded to a blank plate 198 (Figure 11c) to achieve an intermediate stack 200 (step (c)). Multiple identical intermediate stacks 200i (i = a, b, c...) are bonded together in a staggered arrangement to form an inclusive stack 202 (step (d)). Depending on the capacity of the slicing apparatus, the inclusive stack 202 may contain any number of intermediate stacks 200. Optionally, the two prisms 205a and 205b (FIG. 11e) may be bonded to the edge of the containment stack 202 to simplify the positioning of the stack within the slicing apparatus. Several segments 204 are then cut from the containment stack (step (e)). Individual slices 207a and 207b containing the internal structure of the redirection element 80 can be cut from each segment 204. The exact portion for each segment of the element 80 is determined by the relative position of the slice within the containment stack 202. In segment 207a above cut line 206, the element 80 (FIG. 5a-5c) is composed of portions 198b, 197b, and 198c, while in segment 207b below cut line 206, the element 80 is composed of portions 198c, 197c, and 198d. The final dimensions of the redirection element are set by cutting 208 (step (f)), grinding, and polishing to form the desired substrate 210 (step (g)). In the specific example shown here, each intermediate stack 200 includes 2n+1 thin plates 195, 196 and 2n+2 partially reflective surfaces, which is the number of partially reflective surfaces 79 in the redirecting element 80. Assuming each enclosing stack 202 contains m intermediate stacks 200, the total number of plates 195, 196 in the enclosing stack is m·(2n+1). Therefore, the number of plates forming the enclosing stack is significantly greater than the number of partially reflective surfaces 79 in the redirecting element 80.

[0059] Figure 12e-12h illustrates a modified method for manufacturing the redirection element 80, wherein the dimensions of each initial stack 211 and plate 212 along the x-axis are significantly longer than those of the initial stack 197 and plate 198 in Figures 11a-11g. Here, step ad (not shown in this figure) is similar to step ad in Figures 11(a)-11(d). Several segments 214 are then cut from the enclosing stack form 218 (step (e)). Individual slices 217a, 217b containing the internal structure of at least two redirection elements 80 can be cut from each segment 214. The exact portion for each segment of the element 80 is determined by the relative position of the slice within the enclosing stack 218. In segment 217a above cut line 216, element 80 is composed of portions 212a, 211a, 212b, 211b, and 212c, while in segment 217b below cut line 216, element 80 is composed of portions 212b, 211b, 212c, 211c, and 212d. The final dimensions of the redirection element are set by cutting 219 (step (f)), grinding, and polishing to produce the desired substrate 220 (step (g)). As shown in the top view in the xy plane, a two-dimensional array of elements 222 along the x and y axes can be cut from each slice 214 (step (h)). Dashed lines indicate the cutting contours, while dotted lines indicate the intersections of the edge-branching surface 79 (Figs. 5A-5C) with the main surface of the redirection element 80. Each final redirection element 222 includes an ineffective segment 226 and an effective segment 228, the effective segment 228 containing 2n+2 partially reflective surfaces 79i (i = 1...2n+2), which redirect the coupled output light waves to the viewer's eye.

[0060] The exact cut position 219 of the redirection element 80 is not critical, as long as the effective segment 228 redirects the coupled output light wave from the coupling output element to the entire area of ​​the output aperture 89 (Figures 5A-5C). Furthermore, the boundary 229 between segments 226 and 228 is typically set at the intersection of the edge light reflected from the coupling output element 67 and the lower surface 70 of the substrate. However, there exist systems, as shown, in which the exact position of the cut position 229 is critical, and in which the effective segment 228 may extend beyond the aforementioned limitations.

[0061] Figure 13A illustrates a prior art tracing of three light waves from EMB 100 toward the input pupil 86' of substrate 64. As shown, the left edge light wave 307L, the central light wave 307M, and the right edge light wave 307R pass through the input pupil 86' and illuminate the lower surface 72 of substrate 64. These light waves enter the substrate and are coupled through the input surface 65. Since the incident angle of the input light waves is quite small and an AR coating is applied to surface 65, the reflectivity of the light waves from this surface is negligible. The light waves leaving substrate 64 enter the intermediate prism 314 through the lower surface 316 of the upper surface 70 of the substrate, are reflected from the reflective surface 318, and are emitted at an α... in (0) The input angle re-enters the substrate 64 through the input aperture 86. The light wave now illuminates the coupling input surface 65, thus having α in (0) +α Sur1 The incident angle is higher than the critical angle and coupled within the substrate. Light wave 307L (dashed line) illuminates the right-side portion of surface 65 and is trapped within the substrate, thus having an off-axis angle α after three reflections from surface 65. in (3) And after three reflections from surface 67, the light wave is coupled out from the substrate, wherein the third reflection, which couples the light wave outward from the substrate, is located on the left side of surface 67. The light wave 307M (dotted line) strikes the central portion of surface 65 and is trapped within the substrate, thus having an off-axis angle α after two reflections from surface 65. in (2) And after two reflections from surface 67, the light wave is coupled out from the substrate, wherein the second reflection, which couples the light wave outward from the substrate, is located at the central portion of surface 67. Light wave 307R (dotted line) irradiates the left portion of surface 65 and is trapped within the substrate, thus having an off-axis angle α after one reflection from surface 65. in (1) The light wave is coupled out from the substrate after a single reflection from the right side of surface 67. The coupled output light wave is partially reflected by redirection element 80, re-enters the substrate, passes through coupling output surface 67, exits the substrate through output aperture 89, and illuminates EMB 100.

[0062] As illustrated and explained in Figures 13A-13D of Published WO2020 / 157747, the lateral region of the input pupil 86' is significantly smaller than the lateral region of the output aperture 89. Nevertheless, for systems with a wide FOV, it is sometimes necessary to expand the output aperture even further without increasing the input pupil. In the embodiment shown in Figures 13A-13C, the right edge 79R of the effective segment of element 80 is set by tracing the right edge ray 307R from the right edge 67R of the coupled output element 67 to the lower surface 70. The right edge 89R of the output aperture 89 is set by tracing this ray to the upper surface 72. Subsequently, the range S of the output aperture 89 of the substrate... out Subject to the following relationship:

[0063] S out <d·cot(α) Sur1 (4)

[0064] Where d is the thickness of the substrate, and therefore, the right-hand side of equation (4) is the projection of the coupled output element 67 onto the main surfaces 70, 72 of the substrate 64. As a result, the effective segment and the output aperture are significantly smaller than this projection. It can be deduced from equation (4) that the output aperture and therefore the EMB will be reduced by α. sur1 This can be expanded. In this case, the available field of view (FOV) of the coupled light wave will also decrease. The output aperture can also be increased by increasing the substrate thickness, but the input aperture will also increase accordingly. Additionally, the substrate is generally required to be as thin as possible.

[0065] In the embodiment shown in FIG13A, light waves 307R, 307M and 307L are coupled after being reflected once, twice and three times from surface 65, and propagate within substrate 64 with first, second and third propagation orders respectively.

[0066] Figure 14 The illustration shows a method of increasing the output aperture 89 without modifying the structure of the substrate 64 by also utilizing at least a portion of the zero-order of the introduced light wave. As shown, k more partially reflective surfaces 79i (i = j+1, ..., j+k) have been added to the redirection element 80. Rays 307Rn (solid lines) parallel to the light wave 307R are directed at α... in (0) The maximum input angle (max) enters the substrate 64 through the input aperture 86. Light rays illuminate the lower surface 72 to the left of the intersection line 65L between surfaces 65 and 72. As a result, light ray 307Rn is not reflected by surface 65. However, for systems with a wide FOV, α... in (0) (max) can be higher than the critical angle, and therefore, it propagates within the substrate 64 via total internal reflection coupling, thus having zero-order α. in(0) (max). The light enters the redirection element 80 without being reflected by surface 67, is partially reflected by the redirection surface 79j+k, and re-enters the substrate. The light ray 307Rn now does not pass through the coupling output surface 65. It leaves the substrate at point 89Rn, which is located to the right of the edges 89R and 67R of the output aperture 89 and the coupling output element 67, respectively. The light ray illuminates the plane of the EMB 100 at point 100Rn, which is located to the right of the previous right edge 100R of the EMB 100. As a result, the constraint given in equation (4) is no longer valid. The effective segment of the redirection element 80 and the output aperture 89 are significantly larger than the projection of the coupling output element 67 onto the main surfaces 70 and 72. As shown, the output aperture 89 has been significantly extended by the distance between the two intersection points 89R and 89Rn. Furthermore, the EMB has been extended by the same range, namely the distance between 100R (the previous edge of the EMB) and 100Rn.

[0067] As shown, the EMB 100 has been significantly increased by using at least a portion of the coupled light wave with zero propagation order and by increasing the effective segment of the redirection element. For the example shown on page 19, lines 1-10 of publication WO2020 / 157747, the EMB has been extended by more than 5 mm. Alternatively, the output aperture can be kept within the same range, and alternatively, the substrate thickness d can be reduced, the exit pupil distance of the system can be increased, or the tilt angle α of the coupled input element 65 can be increased. Sur1 This is to expand the system's field of view (FOV). Generally, the exact values ​​for output aperture, substrate thickness, and FOV will be set according to the specific requirements of the system.

[0068] like Figure 14 As shown, the effective segment of the redirection element 80 has been extended by adding k additional partial reflective surfaces 79i (i = j+1, ..., j+k). However, this extension is not infinite. These additional surfaces reflect not only the edge light wave 309R, but also the light waves located at α. in (0) (max)-δ and α in (0) The continuous spectrum of light waves within the spectral range between (max) and (max). For example... Figure 15 As shown, the ray 320, which is traced backward by the EMB, is reflected by the partially reflective surface 79j+1 and has α in (0)The zero-order propagation direction of (max)-δ couples within the substrate. The light beam strikes the upper surface 72 just to the right of the right edge 67R of the coupled output surface 79. It continues to propagate at the same angle and strikes the lower surface 70 at point 322. Crucially, the light beam will not re-enter element 80. Otherwise, the light would be partially reflected again, and the image would be distorted. As a result, the redirection element 80 cannot be effective at point 322, and the active supplement is limited to k elements 79i (i = j+1,...,j+k). Therefore, the range Δ of this supplement is limited to:

[0069]

[0070] Furthermore, the interface surface 323 between the substrate 64 and the element 80 at point 322 must be totally internally reflected for zero-order propagating light waves. On the other hand, as shown, the reflected ray 307Rn enters the substrate 64 at point 321, located to the left of point 322. Therefore, the interface surface at this point should be transmissive for zero-order propagating light waves. Subsequently, a discontinuity should exist in the interface surface between points 321 and 322.

[0071] Figure 16A The diagram illustrates one possible method for achieving the required discontinuity. As shown, element 80 has been cut between points 321 and 322. Therefore, the interface at point 322 is located between substrate 64 and air. The critical angle at this point is much smaller than before, and all zero-order light waves are totally internally reflected from the lower surface 72 as required. As a result, the cut lines 208 and 219 shown accordingly in Figures 11(f) and 12(g) should be located between the calculated points 321 and 322. The main problem with the proposed method is that it is unsuitable for systems in which external elements are bonded to the outer surfaces 70, 72 of the substrate. These external elements could be ophthalmic lenses or protective layers. In this case, the bonding process would eliminate the glass-air interface at the exposed portion of surface 72 and terminate the total internal reflection of zero-order propagating light waves within the substrate.

[0072] Figure 16BThe diagram illustrates an alternative method. As shown, the redirecting element 80 is cut into two segments 324 and 325 at the line located between points 321 and 322. These two portions are bonded together to the substrate 64 at the lower surface 70, but using two different optical adhesives. The effective segment 324 is bonded using an optical adhesive that is transparent to the zero-order angle for coupled input light waves and totally internally reflects first-order propagating waves. The ineffective segment 325 is bonded adjacent to segment 324 to surface 72 using an optical adhesive that reflects zero-order propagating light waves, thereby defining a new interface surface 326. Typically, there is no lower limit to the refractive index of such adhesives. For the example given above, the optical adhesives Norland NOA-148 and Norland NOA-140, with refractive indices of 1.48 and 1.40 respectively, are good candidates for interface surfaces 323 and 326.

[0073] exist Figure 15 In the embodiment shown in -16, most of the light rays are coupled into and out of the substrate 64 via reflection from the coupling input surface 65 and the coupling output surface 67. Light waves 307R, 307M, and 307L are reflected once, twice, and three times respectively from surfaces 65 and 67. Other light rays 307Rn and 320 are coupled into and out of the substrate without interaction with these surfaces and are coupled within the substrate with a zero-order propagation order. However, there are systems in which only the zero-order propagation order is preferably used. For example... Figure 17 As shown, substrate 330 is a simple blank transparent plate without an internal reflective surface. Light waves 331R, 331M, and 331L are reflected from the reflective surface 332 of the folded prism 333 and directly coupled into the substrate. Light waves are reflected from the upper surface 72 and the interface surface 326. When they strike the interface surface 323, they enter the effective segment 324 of element 80 and are partially reflected from surface 79i. The light waves pass through substrate 330 and reach EMB 100. Typically, Figure 17 The embodiments shown are suitable for systems with limited FOV and small EMB, but their simple structure makes them suitable for inexpensive niches.

[0074] It will be apparent to those skilled in the art that the invention is not limited to the details of the embodiments illustrated above, and that the invention may be practiced in other specific forms without departing from its spirit or essential attributes. Therefore, the present embodiments are to be considered illustrative rather than restrictive in all respects, the scope of the invention is indicated by the appended claims rather than by the foregoing description, and thus all variations falling within the meaning and scope of equivalents of the claims are intended to be included therein.

Claims

1. A method for manufacturing an optical device having a light wave transmissive substrate with at least two main surfaces, an edge and a coupling-out reflective element carried by the substrate, wherein, The main surfaces are parallel to each other but not parallel to the coupled output reflective element, thereby forming a substrate that allows light waves to pass through the substrate between the two main surfaces, the method comprising: a. Attaching a plurality of plates of selected thickness to each other, each of the plurality of plates including two parallel main surfaces and two lateral edges, the plurality of plates being arranged as a first periodic stack; b. Slice the first periodic stack to form a plurality of slices defining slice lines, wherein the first periodic stack is oriented such that, for most stacks, the slice lines pass through at least two lateral edges of the stack. c. Grinding or polishing the slice to form a substrate having two main surfaces and the coupled output reflective element; and d. Cut the substrate to the final size.

2. The method according to claim 1, wherein, The coupled output reflective element includes at least one reflective surface that is tilted at a first angle relative to the main surface of the substrate.

3. The method according to claim 2, wherein, The first periodic stack is sliced ​​in a slicing device, and the slicing device contains a certain number of stacked plates.

4. The method according to claim 2, wherein, The number of stacked plates in the first periodic stack is greater than the number of reflective surfaces in the substrate.

5. The method according to claim 1, wherein, At least a two-dimensional array of at least four substrates cut from a single slice.

6. The method of claim 2, further comprising at least one prism having at least a first surface and a second surface, wherein, The first surface is bonded to the edge of the first periodic stack.

7. The method according to claim 6, wherein, The second surface is inclined at a second angle relative to the first surface, the second angle being similar to the first angle.

8. The method of claim 2, further comprising manufacturing a redirection element having two main surfaces and a plurality of partially reflective surfaces parallel to and not parallel to the main surfaces of the redirection element, for redirecting coupled output light waves from the substrate to the viewer's eye: e. Attaching a plurality of plates having two sides to each other, the plurality of plates being arranged as a second periodic stack having at least two edges; f. Cut the second periodic stack to form a slice; g. Grinding or polishing the slices to form a repositioning element; h. Cut the redirecting element to the final size; as well as i. Attach the redirecting element to one of the main surfaces of the substrate.

9. The method according to claim 8, wherein, At least a portion of the stacked plates in the second periodic stack is uncoated, and at least another portion of the stacked plates in the second periodic stack is coated on both sides with a partially reflective coating.

10. The method according to claim 9, wherein, In the second periodic stack, uncoated and double-coated stacked plates are arranged in an alternating configuration to form an interface plane between two adjacent stacked plates.

11. The method according to claim 10, wherein, Each interface plane contains a separate partial reflective surface.

12. The method according to claim 8, wherein, The redirection element includes an ineffective segment and an effective segment. The effective segment contains multiple partial reflective surfaces that redirect the coupled output light wave into the viewer's eye. The effective segment is larger than the projection of the coupled output reflective element onto the main surface of the substrate.

13. The method according to claim 12, wherein, The inactive and active sections are bonded to the main surface of the substrate using two different optical adhesives.

14. The method according to claim 8, wherein, At least a portion of the coupled light wave is redirected to the viewer's eye and is not reflected by the coupled output reflective element.

15. The method according to claim 8, wherein, Multiple identical second periodic stacked pieces are bonded together in a staggered arrangement to form an enclosing stacked piece.

16. The method of claim 2, further comprising a coupling input reflective surface embedded in the substrate and inclined at a third angle relative to the main surface of the substrate, the third angle being similar to the first angle.

17. The method according to claim 1, wherein, At least two edges of the stacked plate are aligned together to form at least two main flat sides of the first periodic stack.

18. The method according to claim 17, wherein, The first periodic stack is oriented such that the slice line passes through the first periodic stack between the two main flat sides.

19. The method according to claim 1, wherein, Two adjacent slice lines are separated by a constant distance and are proportional to the thickness of the stacked plate.

20. The method according to claim 1, wherein, For all of the aforementioned stacked plates, the slice line crosses the edge of the stacked plate at the same location.

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