Method for fabricating composite optical guide elements

Abstract

Further improvements to the manufacturing method of LOE are needed. [Solution] A method for fabricating a composite optical element (LOE) is provided. A bonded stack of a plurality of LOE precursors and a plurality of transparent spacer plates arranged alternately between them is bonded to a first optical block having a plurality of mutually parallel inclined inner surfaces. This block is connected to the stack such that the first plurality of partially reflective inner surfaces of the block are non-parallel to the inner surfaces of the LOE precursors. After bonding, a second optical element is formed. At least one composite LOE is sliced ​​out from the second optical block by cutting the second block through at least two consecutive spacer plates with the LOE precursors sandwiched between them.

Description

Technical Field

[0001] The present invention relates to a light guiding optical element (LOE), and more particularly, to a composite LOE for two-dimensional image magnification and a method for manufacturing the same.

Background Art

[0002] Composite LOEs or “two-dimensional magnifying light guides” have been described by Lumus Ltd. (Israel) in previous publications. Examples of such composite LOEs can be found, for example, in PCT Publication No. 2020 / 049542. Generally, these composite LOEs utilize two regions, each of which is a block having parallel surfaces of a transparent material for assisting the propagation of light that conveys a parallel image by internal reflection at the main surface, and includes a set of mutually parallel internal partially reflective surfaces, i.e., “facets”, that change the orientation of the parallel image while achieving an expansion of the optical aperture. By combining two such elements having different facet orientations, a two-dimensional expansion of the optical aperture can be achieved within a single element, thereby making it possible to expand an input image from an image projector and output it over a larger area towards the observer's eyes.

Summary of the Invention

[0003] According to one aspect of the present invention, a method for fabricating a composite optical element (LOE) is provided, comprising a bonded stack of a plurality of LOE precursors and a plurality of transparent spacer plates, wherein the stack has a first pair of parallel surfaces, and the stack has LOE precursors and transparent spacer plates arranged alternately along the length of the stack perpendicular to the pair of parallel surfaces, and each LOE precursor includes a main pair of parallel surfaces and a first plurality of mutually parallel partially reflective interior surfaces inclined with respect to the pair of parallel surfaces, and a first optical block having a second pair of parallel surfaces and a plurality of mutually parallel interior surfaces inclined with respect to the second pair of parallel surfaces. A method is provided comprising: providing a first block having an internal surface that is at least partially reflective, thereby including a second plurality of mutually parallel partially reflective internal surfaces; joining the first block to a stack such that one of the surfaces of the first block is connected to one of the surfaces of a stack, and the first plurality of partially reflective internal surfaces are non-parallel to the second plurality of partially reflective internal surfaces, thereby forming a second optical block; and slicing at least one composite LOE from the second block by cutting the second block through at least two consecutive spacer plates with an LOE precursor sandwiched between them.

[0004] According to some embodiments, each of the interior surfaces of the first block is partially coated with a partially reflective coating, and the interior surface includes multiple strips of reflective coating with gaps in between.

[0005] In some embodiments, the method includes polishing the surface of the stack to be joined to the first block before joining the stack to the first block, and / or polishing the surface of the first block to be joined to the stack before joining the first block to the stack.

[0006] According to some embodiments, the first block and the stack are aligned such that the first plurality of partially reflective interior surfaces and the second plurality of partially reflective interior surfaces are orthogonal to each other, before joining the first block to the stack.

[0007] According to some embodiments, the method includes polishing the outer surface of at least one composite LOE that has been cut out in the form of a slice parallel to the principal parallel plane of the LOE precursor.

[0008] According to some embodiments, each of the interior surfaces of the first block is partially coated with a partially reflective coating, and the interior surface includes multiple strips of reflective coating with gaps in between.

[0009] According to another aspect of the present invention, an optical structure is provided which is an intermediate working product of a composite LOE fabrication process, the optical structure comprising: a first region comprising a plurality of LOE precursors separated by a transparent spacer plate in between, each LOE precursor comprising a pair of main outer parallel planes and a first plurality of mutually parallel partially reflective inner planes inclined with respect to the pair of parallel planes; a second region comprising a second plurality of mutually parallel partially reflective inner planes non-parallel to the first plurality of partially reflective inner planes; and at least one inner plane separating the first region and the second region, the inner plane being perpendicular to the pair of parallel planes.

[0010] According to some embodiments, the optical structure is formed by joining a first optical block including a first region with a second optical block including a second region.

[0011] In some embodiments, the optical structure may include a third optical region between the first region and the second region. The third optical region may include one or more optical elements. The optical elements may be optically active or optically inactive. In some embodiments, at least one sub-region within the second region does not have any partially reflective interior surfaces, and / or each LOE precursor within the first region may include at least one sub-region that does not have any partially reflective interior surfaces. [Brief explanation of the drawing]

[0012] The invention is described herein only as an embodiment with reference to the accompanying drawings.

[0013] [Figure 1(a)] This shows one embodiment of a composite LOE based on prior art. [Figure 1(b)] This shows one embodiment of a composite LOE based on prior art. [Figure 2] Known methods for fabricating composite LOEs are shown. [Figure 3(a)] Another embodiment of the composite LOE is shown. [Figure 3(b)] Another embodiment of the composite LOE is shown. [Figure 4(a)] This shows a LOE with a given thickness d1. [Figure 4(b)] This shows a LOE with a given thickness d1. [Figure 5(a)] This shows a stack of bonded LOE precursors separated by a transparent plate of a given thickness d2. [Figure 5(b)] This shows a stack of bonded LOE precursors separated by a transparent plate of a given thickness d2. [Figure 6(a)] This shows a block of transparent plates. [Figure 6(b)] This shows a block of transparent plates. [Figure 6(c)] The method for forming the blocks shown in Figures 6(a) and 6(b) is illustrated. [Figure 7(a)]An optical structure formed by joining the blocks of FIGS. 6(a) to 6(b) to the stack of FIGS. 5(a) to 5(b) is shown. [Figure 7(b)] An optical structure formed by joining the blocks of FIGS. 6(a) to 6(b) to the stack of FIGS. 5(a) to 5(b) is shown. [Figure 7(c)] Slices taken from the blocks of FIGS. 7(a) to 7(b) are shown. [Figure 7(d)] Slices taken from the blocks of FIGS. 7(a) to 7(b) are shown. [Figure 8(a)] Alternative embodiments of the blocks of FIGS. 6(a) to 6(b) are shown. [Figure 8(b)] Alternative embodiments of the blocks of FIGS. 6(a) to 6(b) are shown. [Figure 9(a)] An optical structure formed by joining the blocks of FIGS. 8(a) to 8(b) to the stack of FIGS. 5(a) to 5(b) is shown. [Figure 9(b)] An optical structure formed by joining the blocks of FIGS. 8(a) to 8(b) to the stack of FIGS. 5(a) to 5(b) is shown. [Figure 10(a)] A composite LOE cut out from the optical structure of FIGS. 9(a) to 9(b) is shown. [Figure 10(b)] A composite LOE cut out from the optical structure of FIGS. 9(a) to 9(b) is shown. [Figure 11(a)] Another embodiment of block 16 is shown. [Figure 11(b)] Another embodiment of block 16 is shown. [Figure 12(a)] An optical structure formed by joining the blocks of FIGS. 11(a) to 11(b) to the stack of FIGS. 5(a) to 5(b) is shown. [Figure 12(b)] An optical structure formed by joining the blocks of FIGS. 11(a) to 11(b) to the stack of FIGS. 5(a) to 5(b) is shown. [Figure 12(c)] Slices taken from the optical structure of FIGS. 12(a) to (b) are shown. [Figure 12(d)] Slices taken from the optical structure of FIGS. 12(a) to (b) are shown. [Figure 13(a)] Another embodiment of block 16 is shown. [Figure 13(b)] Another embodiment of block 16 is shown. [Figure 13(c)] Figures 13(a) and 13(b) show slices extracted from the optical structure. [Figure 13(d)] Figures 13(a) and 13(b) show slices extracted from the optical structure. [Modes for carrying out the invention]

[0014] Figures 1(a) and 1(b) show an embodiment of a prior art composite LOE 100. The composite LOE 100 includes a first LOE 1 and a second LOE 2 joined together at an interface 102. LOE 1 includes a pair of principal parallel surfaces 101, 102 and a plurality of mutually parallel partially reflective interior surfaces ("facets") 4 inclined with respect to surfaces 101, 102. Reflectivity is provided via coatings on the interior surfaces before LOE 1 is formed. The reflectivity of each facet may be the same as or different from that of the others. Facets 4 are configured to guide an image from an external microprojector (not shown) toward LOE 2, while magnifying the image in one dimension (in this example, the x-dimension). LOE 1 includes a surface 103 perpendicular to surfaces 101, 102.

[0015] LOE2 also includes a pair of principal parallel planes 201 perpendicular to planes 101 and 102 of LOE1, and a plurality of mutually parallel partially reflective facets 5 inclined with respect to planes 201. In some embodiments, the spatial orientation of facets 5 relative to facets 4 may be orthogonal, as shown in Figures 1(a) to 1(b), but other orientations are possible depending on the design specifications for the specific application of the composite LOE. The reflectivity of facets 5 is provided via a coating on the internal surface before forming LOE2. The reflectivity of each facet may be the same as or different from that of the others. Facets 5 are configured to guide the image from LOE1 (magnified in one dimension here) to the observer, while magnifying it in a second dimension (z-dimension in this example).

[0016] The composite LOE100 further includes a transparent cover plate 3 on the surface of LOE100 in the XZ plane. The surfaces covered by plate 3 include surface 103 of LOE1 and surface 201 of LOE2. Therefore, these surfaces must be precisely aligned in order to attach plate 3.

[0017] Figures 2(a) to 2(c) show a known method for fabricating a composite LOE. Typically, LOE1 and LOE2 are fabricated separately and then joined together. Throughout this specification, the term “joining” should be understood to mean attaching them using an optical adhesive or adhesive. The joined LOE is then polished on its outer surface. Cover plates 3 are attached to this polished surface, and these cover plates are also typically polished. When using this fabrication method, the joining process of LOE1 to LOE2 must be performed with very high precision so that the surface 103 of LOE1 is coplanar with the corresponding surface 201 of LOE2. This method is prone to improper alignment, as shown in Figures 2(a) to 2(c).

[0018] To overcome the difficulties described above, the present invention discloses a novel method for fabricating a compound LOE. In addition to overcoming the problem of precise alignment between the bonding of LOE1 to LOE2, the process disclosed herein enables the fabrication of a novel embodiment of a compound LOE100 in which the transparent cover plate 3' is located only on the surface 201 of LOE2, as shown in Figures 3(a) to 3(b). This embodiment of the compound LOE is discussed in further detail in a concurrently pending PCT application, entitled “Compound Light-Guide Optical Elements,” filed on the same date as this application, which takes priority from U.S. Provisional Patent Application No. 63 / 029,496 filed on 24 May 2020.

[0019] Figures 4(a) and 4(b) show an LOE “precursor” 2’, which should be understood to represent an intermediate optical element in the manufacture of LOE2. The LOE precursor 2’ includes a pair of principal parallel outer surfaces 6 and a plurality of mutually parallel partially reflective inner surfaces (“facets”) 5 inclined with respect to the pair of parallel surfaces. The LOE precursor has a predetermined thickness between the surfaces 6, also referred to herein as d1. Known methods exist for manufacturing the LOE precursor, such as those described in PCT Publication No. 2016 / 103263.

[0020] Referring to Figures 5(a) to 5(b), after fabricating multiple LOE precursors, a stack 15 is formed by joining multiple LOE precursors having the same thickness d1 with multiple transparent spacer plates 7. The stack consists of LOE precursors and transparent spacer plates arranged alternately along the length (y dimension) of the stack. Each transparent plate has the same predetermined thickness, indicated herein as d2. The stack 15 has pairs of parallel surfaces 8a, 8b extending along the length of the stack perpendicular to the surface 6.

[0021] Referring to Figures 6(a) and 6(b), the optical block 16 having parallel surfaces 10a and 10b is formed from a plurality of joined transparent coated plates 17 (each plate is coated with a partially reflective coating), thereby forming a plurality of mutually parallel partially reflective internal surfaces 9, each inclined at a predetermined angle 11 (also called the "facet inclination angle") with respect to surface 10b.

[0022] Known methods exist for forming the optical block 16. For example, as shown in Figure 6(c), one method involves stacking and joining multiple coated plates 17 to obtain the block, and then cutting the stack along the dashed line shown in Figure 6(c). The surface 10b is then polished by polishing equipment 18 to achieve a desired facet inclination angle 11, which may vary according to the specific design specifications of the final composite LOE.

[0023] Referring here to Figures 7(a) and 7(b), block 16 is aligned and joined with stack 15 to form optical block 18. More specifically, surface 10b of block 16 is joined to surface 8a of stack 15. Either or both of surfaces 10b and 8a may be polished flat before joining. The specific alignment between block 16 and stack may vary according to the product design specifications. In embodiments corresponding to the composite LOE shown in Figures 3(a) and 3(b), the alignment between block 15 and block 16 can be understood as follows, referring to the coordinate system XYZ shown in Figures 7(a) and 7(b). Stack 15 and block 16 are aligned such that the surface 6 of the LOE precursor 2' is parallel to the plane XZ, the surface 8a of stack 15 is parallel to the plane XY, the facet 5 of the LOE precursor 2' is perpendicular to the plane YZ, the plate 17 of block 16 is perpendicular to the plane XZ, and the surface 10b of block 16 is parallel to the plane XY. After alignment, plate 17 is perpendicular to the surface 6 of the LOE precursor 2' in stack 15.

[0024] The aligned and joined structure is shown herein as an optical block 18 and is in fact an optical structure which is an intermediate working product of the composite LOE fabrication process. As shown in the figure, the block 18 includes a first region having a plurality of LOE precursors separated by transparent spacer plates between the LOE precursors, a second region having a plurality of mutually parallel partially reflective inner surfaces, and an inner surface separating the first region and the second region. In other embodiments, as will be further detailed below, the intermediate block 18 may include one or more additional sub-regions in the first and / or second regions. These sub-regions may include regions containing one or more optically active or optically inactive elements, in addition to regions without facets. These sub-regions can be added to the block 18 by adding one or more plates, some of which may contain optically active elements, to the block 16 before joining with the stack 15, as will be further detailed below with reference to Figures 11(a) to 13(d).

[0025] Block 18 is sliced ​​using a cutting device (not shown) through spacer plates 7 at predetermined intervals along the length (y-dimension) of stack 15 to form multiple composite LOE structures cut out in slices from block 18. The slice faces are shown as dashed lines 12 in Figures 7(a) to 7(b), with one slice shown in Figures 7(c) to 7(d). The composite LOEs cut out in slices from block 18 have a structure similar to the composite LOEs shown in Figures 3(a) to 3(b). It should be noted that after slicing, the spacer plates (more precisely, half of the spacer plates) provide a structure similar to the cover plate 3' in Figures 3(a) to 3(b), thereby eliminating the need to attach a separate cover plate 3'. Each of the sliced ​​composite LOE structures is then polished on its outer surface, which is made up of plates 7 and 17, to form a final composite LOE suitable for light guiding via internal reflection.

[0026] Optionally, additional transparent cover plates may be bonded to the final composite LOE on plates 17 and 17, and these cover plates may be polished (in this example, LOE1 will have a single cover plate and LOE2 will have a double cover plate).

[0027] As detailed above with reference to Figures 5(a) to 5(b), the transparent plate has a predetermined thickness d2. In some embodiments, the predetermined thickness d2 is determined according to the following formula. d² = 2t + 2p + s Here, t represents the desired difference in thickness between the cover plate of the first LOE and the cover plate of the second LOE, p represents the thickness of the material to be removed during grinding, and s represents the thickness of the cut, including tolerances for cutting positioning in the sawmill. It should be noted that if a cover plate is desired only for LOE2 and not for LOE1, t ​​simply represents the thickness of the cover plate of LOE2. Typical values ​​of t can range from 50 microns to 500 microns.

[0028] Figures 8(a) and 8(b) show an alternative embodiment of block 16, herein denoted as block 16'. In this embodiment, each transparent plate is partially coated with a partially reflective coating that is attached to each plate in strips with gaps between them. As described in U.S. Patent Publication 2018 / 0292599 to Lumus Ltd., each coating strip has the same predetermined thickness d3, and the gaps between the coating strips each have the same predetermined thickness d4. In this embodiment, d3 corresponds to the desired width of the reflective area of ​​LOE1 in the final composite LOE, and d4 is calculated according to the following formula: d4 = d1 + d2 - d3 Here, d1 and d2 are defined above.

[0029] Figures 9(a) to 9(b) show a block 16' aligned and joined to the stack 15 and cut along the plane 12, in a manner similar to that described above with reference to Figures 7(a) to 7(b). The extracted slices are shown in Figures 10(a) to 10(b). These slices may similarly be polished on the outer parallel surface to form the final composite LOE. It should be noted that the composite LOE formed by this embodiment includes a buffer between the partially reflective facets 4 of the LOE 1 and the outer surface 14, which is provided by the gap between the coating strips, achieving an effect similar to that of a transparent cover plate without requiring a physical cover plate.

[0030] It should be understood that the joined block 16' and stack 15 represent another embodiment of the intermediate optical structure block 18. Indeed, various other embodiments of block 16 (and therefore block 18) are possible to result in various composite LOEs having different structures with respect to LOE1, some of which are described below.

[0031] For example, in some embodiments, it may be desirable to have some of the facets 4 of LOE1 not extend throughout LOE1, thereby providing one or more facetless regions (i.e., regions without partially reflective interior surfaces) within LOE1, as shown in the following example.

[0032] Figures 11(a) and 11(b) show another embodiment of block 16, which is hereby referred to as block 19. Block 19 consists of block 16 (as in Figures 6(a) and 6(b)) with an additional plane-parallel transparent plate 20 bonded to the surface 10b of block 16. The outer surface 10b' of the plate 20 is polished parallel to the surface 10b.

[0033] Block 19 and stack 15 are aligned and joined together as shown in Figures 12(a)-(b) to form an intermediate optical block 21. Block 21 is then sliced ​​along a plane 12 parallel to the XZ plane. The resulting slice is shown in Figures 12(c)-(d). The slice consists of LOE1, LOE2, and an optically clean area 22 (also called an inert area) that has no reflective or semi-reflective surfaces. Alternatively, area 22 may contain one or more optical elements such as a partially reflective mixer or polarizer. In this case, the transparent plate 20 can be replaced with a plate incorporating the desired one or more optical elements (i.e., mixer, polarizer, etc.).

[0034] Figures 13(a) to 13(b) show another embodiment of block 16 in which more complex shapes of LOE1 can be manufactured by cutting block 16 and joining it with other optical plates and / or prisms. In Figures 13(a) to 13(b), block 16 is cut and polished along planes 31 and 32 and joined with a transparent plate 24 and triangular prisms 25 and 26. The polished surface 10b'' of plate 24 is parallel to the surface 10b of block 16. Block 16 with plate 24 and prisms 25 and 26 forms a new optical block 23 containing one or more facetless subregions within the block. In a similar manner to that shown in Figures 12(a) to 12(b), block 23 is aligned and joined with stack 15 to form a new intermediate structure. The intermediate structure is then sliced ​​along plane 12, resulting in the slices shown in Figures 13(c) to 13(d). Such slices have inert areas 27, 28, and 29 that do not have any reflective or semi-reflective surfaces.

[0035] In other embodiments (not shown), the LOE precursor of stack 15 may be modified to include one or more facetless regions within the LOE precursor, thereby resulting in a composite LOE in which LOE 2 includes one or more facetless (i.e., partially reflective inner) subregions.

[0036] It will be understood that the above description is intended to serve only as an example, and that many other embodiments are possible within the scope of the invention as defined in the appended claims.

Claims

1. A method for fabricating a composite optical element (LOE), To provide a bonded stack of multiple LOE precursors and multiple transparent spacer plates, wherein the stack has a first pair of parallel surfaces, and the stack includes LOE precursors and transparent spacer plates arranged alternately along the length of the stack perpendicular to the pair of parallel surfaces, and each LOE precursor includes a main pair of parallel surfaces and a first plurality of mutually parallel partially reflective interior surfaces inclined with respect to the pair of parallel surfaces, To provide a first optical block having a second pair of parallel surfaces and a plurality of mutually parallel internal surfaces inclined with respect to the second pair of parallel surfaces, wherein the internal surfaces are at least partially reflective, and thereby the first block includes a second plurality of mutually parallel partially reflective internal surfaces. The first block is joined to the stack such that one of the surfaces of the first block is connected to one of the surfaces of the stack, and the first plurality of partially reflective interior surfaces are non-parallel to the second plurality of partially reflective interior surfaces, thereby forming a second optical block. A method comprising cutting the second block through at least two consecutive spacer plates with LOE precursors sandwiched between them, thereby slicing at least one composite LOE from the second block.

2. The method according to claim 1, comprising polishing the surface of the stack that will be connected to the first block before joining the stack to the first block.

3. The method according to claim 1, comprising polishing the surface of the first block that will be connected to the stack before joining the first block to the stack.

4. The method according to claim 1, comprising aligning the first block and the stack such that the first plurality of partially reflective interior surfaces and the second plurality of partially reflective interior surfaces are orthogonal to each other, before joining the first block to the stack.

5. The method according to claim 1, further comprising polishing the outer surface of at least one composite LOE sliced ​​out parallel to the principal parallel plane of the LOE precursor.

6. The method according to claim 1, wherein each of the inner surfaces of the first block is partially coated with a partially reflective coating, and the inner surface comprises a plurality of strips of reflective coatings with gaps in between.

7. An optical structure which is an intermediate work product in the fabrication process of a composite LOE, wherein the optical structure is A first region comprising a plurality of LOE precursors separated by a transparent spacer plate, each LOE precursor comprising a pair of main outer parallel surfaces and a first plurality of mutually parallel partially reflective inner surfaces inclined with respect to the pair of parallel surfaces, A second region including a second plurality of mutually parallel partially reflective interior surfaces that are not parallel to the first plurality of partially reflective interior surfaces, An optical structure comprising at least one internal surface separating the first region and the second region, wherein the internal surface is perpendicular to the pair of parallel surfaces.

8. The optical structure according to claim 7, formed by joining a first optical block including the first region with a second optical block including the second region.

9. The optical structure according to claim 7, further comprising a third optical region between the first region and the second region.

10. The optical structure according to claim 9, wherein the third optical region includes one or more optical elements.

11. The optical structure according to claim 9, wherein the third optical region is optically inert.

12. The optical structure according to claim 7, wherein at least one sub-region within the second region does not have any partially reflective internal surfaces.

13. The optical structure according to claim 7, wherein each LOE precursor within the first region includes at least one sub-region that does not have any partially reflective internal surfaces.

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