Method for fabricating composite light-guiding optical element

Abstract

To meet the need for further improvement in a method for manufacturing a LOE.SOLUTION: A method for manufacturing a composite light guide optical element (a LOE) is provided. A bonded stack of a plurality of LOE precursors and a plurality of transparent spacer plates alternating therebetween is bonded to a first optical block having a plurality of mutually inclined interior surfaces in parallel. The block is coupled to the stack such that the first plurality of partially reflective interior surfaces of the block become non-parallel to the interior surface of the LOE precursor. After bonding, a second optical block is formed. By cutting the second block through at least two successive spacer plates between which the LOE precursor is sandwiched, at least one composite LOE is cut into slices from the second optical block.SELECTED DRAWING: Figure 7(a)

Description

[Technical Field]

[0001] The present invention relates to light-directing optical elements (LOEs), and more particularly to composite LOEs for two-dimensional image magnification and methods of making the same. [Background technology]

[0002] Compound LOEs or "two-dimensional magnification light guides" have been described by Lumus Ltd. (Israel) in prior publications. Examples of such compound LOEs can be found, for example, in PCT Publication No. 2020 / 049542. Generally, these compound LOEs utilize two regions, each of which is a block of transparent material with parallel surfaces to support the propagation of light that conveys a parallel image by internal reflection at its major surfaces, and includes a set of mutually parallel internal partially reflective surfaces or "facets" that redirect the parallel image while achieving an expanded optical aperture. Combining two such elements with different facet orientations allows for two-dimensional expansion of the optical aperture within a single element, thereby allowing an input image from an image projector to be magnified and output over a larger area toward the viewer's eye. Summary of the Invention

[0003] According to one aspect of the invention, a method of making a composite light-directing optical element (LOE) includes providing a bonded stack of a plurality of LOE precursors and a plurality of transparent spacer plates, the stack having a first pair of parallel surfaces, the stack having the LOE precursors and transparent spacer plates arranged alternately along the length of the stack perpendicular to the pair of parallel surfaces, each LOE precursor including a pair of primary parallel surfaces and a first plurality of mutually parallel partially reflective internal surfaces angled relative to the pair of parallel surfaces; and providing a first optical block having a second pair of parallel surfaces and a first plurality of mutually parallel internal surfaces angled relative to the second pair of parallel surfaces. The method includes providing a first block, wherein the internal surfaces are at least partially reflective, thereby including a second plurality of mutually parallel partially reflective internal surfaces; joining the first block 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 internal surfaces are non-parallel to the second plurality of partially reflective internal surfaces, thereby forming a second optical block; and cutting at least one composite LOE into slices from the second block by cutting the second block through at least two successive spacer plates with an LOE precursor sandwiched therebetween.

[0004] According to some embodiments, each interior surface of the first block is only partially coated with a partially reflective coating, the interior surfaces including a plurality of strips of the reflective coating with gaps therebetween.

[0005] According to some embodiments, the method includes polishing a surface of the stack that will be coupled to the first block before joining the stack to the first block, and / or polishing a surface of the first block that will be coupled to the stack before joining the first block to the stack.

[0006] According to some embodiments, prior to joining the first block to the stack, the method includes aligning the first block and the stack so that the first plurality of partially reflective internal surfaces and the second plurality of partially reflective internal surfaces are orthogonal.

[0007] According to some embodiments, the method includes polishing an exterior surface of at least one composite LOE cut into slices parallel to the major parallel planes of the LOE precursor.

[0008] According to some embodiments, each interior surface of the first block is only partially coated with a partially reflective coating, the interior surfaces including a plurality of strips of the reflective coating with gaps therebetween.

[0009] According to another aspect of the present invention, there is provided an optical structure that is an intermediate work product of a composite LOE fabrication process, the optical structure including: a first region including a plurality of LOE precursors separated by a transparent spacer plate therebetween, each LOE precursor including a pair of main external parallel faces and a first plurality of mutually parallel partially reflective internal faces that are inclined relative to the pair of parallel faces; a second region including a second plurality of mutually parallel partially reflective internal faces that are non-parallel to the first plurality of partially reflective internal faces; and at least one internal surface separating the first region from the second region, the internal surface being perpendicular to the pair of parallel faces.

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

[0011] According to 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 subregion in the second region may not have any partially reflective internal surfaces, and / or each LOE precursor in the first region may include at least one subregion that does not have any partially reflective internal surfaces. [Brief explanation of the drawings]

[0012] The invention is herein described, by way of example only, with reference to the accompanying drawings.

[0013] [Figure 1(a)] 1 illustrates one embodiment of a composite LOE according to the prior art. [Figure 1(b)] 1 illustrates one embodiment of a composite LOE according to the prior art. [Figure 2] 1 illustrates a known method for making a composite LOE. [Figure 3(a)] 10 illustrates another embodiment of a composite LOE. [Figure 3(b)] 10 illustrates another embodiment of a composite LOE. [Figure 4(a)] LOE with a given thickness d1 is shown. [Figure 4(b)] LOE with a given thickness d1 is shown. [Figure 5(a)] 1 shows a stack of bonded LOE precursors separated by a transparent plate of given thickness d2. [Figure 5(b)] 1 shows a stack of bonded LOE precursors separated by a transparent plate of given thickness d2. [Figure 6(a)] A block of transparent plates is shown. [Figure 6(b)] A block of transparent plates is shown. [Figure 6(c)] A method for forming the blocks of FIGS. 6(a) and 6(b) will be described. [Figure 7(a)]6(a)-6(b) show the optical structure formed by bonding the block of FIGS. 6(a)-6(b) to the stack of FIGS. 5(a)-5(b). [Figure 7(b)] 6(a)-6(b) show the optical structure formed by bonding the block of FIGS. 6(a)-6(b) to the stack of FIGS. 5(a)-5(b). [Figure 7(c)] 7(a)-7(b) show slices taken from the block. [Figure 7(d)] 7(a)-7(b) show slices taken from the block. [Figure 8(a)] 6(a)-6(b) show alternative embodiments of the blocks of FIG. 6(a)-(b). [Figure 8(b)] 6(a)-6(b) show alternative embodiments of the blocks of FIG. 6(a)-(b). [Figure 9(a)] 8(a)-8(b) show an optical structure formed by bonding the block of FIGS. 8(a)-8(b) with the stack of FIGS. 5(a)-5(b). [Figure 9(b)] 8(a)-8(b) show an optical structure formed by bonding the block of FIGS. 8(a)-8(b) with the stack of FIGS. 5(a)-5(b). [Figure 10(a)] 9(a)-9(b) show a composite LOE cut from the optical structure of FIG. 9(a)-FIG. 9(b). [Figure 10(b)] 9(a)-9(b) show a composite LOE cut from the optical structure of FIG. 9(a)-FIG. 9(b). [Figure 11(a)] 2 shows another embodiment of block 16. [Figure 11(b)] 2 shows another embodiment of block 16. [Figure 12(a)] 11(a)-11(b) show an optical structure formed by bonding the block of FIGS. 11(a)-11(b) with the stack of FIGS. 5(a)-5(b). [Figure 12(b)] 11(a)-11(b) show an optical structure formed by bonding the block of FIGS. 11(a)-11(b) with the stack of FIGS. 5(a)-5(b). [Figure 12(c)] 12(a)-(b) show slices taken from the optical structure of FIG. [Figure 12(d)] 12(a)-(b) show slices taken from the optical structure of FIG. [Figure 13(a)] 2 shows another embodiment of block 16. [Figure 13(b)] 2 shows another embodiment of block 16. [Figure 13(c)] 13(a)-(b) show slices taken from the optical structure of FIG. [Figure 13(d)] 13(a)-(b) show slices taken from the optical structure of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0014] 1(a)-1(b) show one embodiment of a composite LOE 100 according to the prior art. Composite LOE 100 includes a first LOE 1 and a second LOE 2 bonded together at interface 102. LOE 1 includes a pair of major parallel surfaces 101, 102 and a plurality of mutually parallel partially reflective internal surfaces ("facets") 4 that are angled relative to surfaces 101, 102. Reflectivity is provided via a coating on the internal surfaces prior to forming LOE 1. The reflectivity of each facet may be the same or different from the others. Facets 4 are configured to direct an image from an external microprojector (not shown) toward LOE 2 while magnifying the image in one dimension (the x-dimension in this example). LOE 1 includes surface 103 that is perpendicular to surfaces 101, 102.

[0015] LOE2 also includes a pair of major parallel surfaces 201 perpendicular to surfaces 101, 102 of LOE1 and a plurality of mutually parallel partially reflective facets 5 tilted relative to surfaces 201. In some embodiments, the spatial orientation of facets 5 relative to facets 4 may be orthogonal, as shown in FIGS. 1(a)-1(b), although other orientations are possible depending on the design specifications of a particular application for the composite LOE. The reflectivity of facets 5 is provided via a coating on the interior surfaces prior to forming LOE2. The reflectivity of each of the facets may be the same as or different from one another. Facets 5 are configured to direct an image from LOE1 (here magnified in one dimension) to a viewer while magnifying it in a second dimension (in this example, the z-dimension).

[0016] Composite LOE 100 further includes a transparent cover plate 3 on a surface of LOE 100 in the XZ plane. The surfaces covered by plate 3 include surface 103 of LOE 1 and surface 201 of LOE 2. Therefore, these surfaces must be precisely aligned in order to attach plate 3.

[0017] FIGS. 2(a)-2(c) illustrate a known method for fabricating composite LOEs. Typically, LOE1 and LOE2 are fabricated separately and then bonded together. It should be understood that throughout this specification, the term "bonding" refers to attaching using an optical adhesive or pressure-sensitive adhesive. The bonded LOEs are then polished on their exterior surfaces. Cover plates 3 are applied to the polished surfaces, and these cover plates are also typically then polished. When using this fabrication method, the bonding process of LOE1-LOE2 must be performed with great precision so that surface 103 of LOE1 is flush with the corresponding surface 201 of LOE2. This method is prone to improper alignment, as shown in FIGS. 2(a)-2(c).

[0018] To overcome the difficulties described above, the present invention discloses a new method for fabricating composite LOEs. In addition to overcoming the problem of precise alignment during bonding of LOE 1 to LOE 2, the process disclosed herein enables fabrication of a new embodiment of composite LOE 100 in which a transparent cover plate 3' is present only on surface 201 of LOE 2, as shown in Figures 3(a)-3(b). This embodiment of a composite LOE is discussed in further detail in a co-pending PCT application entitled "Compound Light-Guide Optical Elements," filed on the same day as this application, which takes priority from U.S. Provisional Patent Application No. 63 / 029,496, filed May 24, 2020.

[0019] 4(a)-4(b) show an LOE "precursor" 2', which should be understood to mean an intermediate optical element in the fabrication of an LOE 2. The LOE precursor 2' includes pairs of major parallel exterior surfaces 6 and a plurality of mutually parallel partially reflective interior surfaces ("facets") 5 that are angled relative to the pairs of parallel surfaces. The LOE precursor has a predetermined thickness between surfaces 6, also denoted herein as d1. Known methods exist for fabricating LOE precursors, such as those described in PCT Publication No. 2016 / 103263.

[0020] 5(a)-5(b), after fabricating multiple LOE precursors, a bonded stack 15 of multiple LOE precursors and multiple transparent spacer plates 7 having the same thickness d1 is formed. The stack is composed of LOE precursors and transparent spacer plates arranged alternately along the length of the stack (y dimension). Each transparent plate has the same predetermined thickness, denoted herein as d2. Stack 15 has a pair of parallel surfaces 8a, 8b extending along the length of the stack perpendicular to face 6.

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

[0022] There are known methods for forming the optical block 16. For example, as shown in FIG. 6(c), one method involves stacking and bonding multiple coated plates 17 and cutting the stack along the dashed lines shown in FIG. 6(c) to extract the block. Surface 10b is then polished by polishing equipment 18 to achieve the desired facet tilt angle 11, which can vary according to the particular design specifications of the final composite LOE.

[0023] 7(a)-7(b), block 16 is aligned with and bonded to stack 15, thereby forming optical block 18. More specifically, surface 10b of block 16 is bonded to surface 8a of stack 15. Either or both of surfaces 10b and 8a may be polished flat prior to bonding. The specific alignment between block 16 and the stack may vary according to product design specifications. In an embodiment corresponding to the composite LOE shown in FIGS. 3(a)-3(b), the alignment of block 15 and block 16 can be understood as follows, with reference to the coordinate system XYZ shown in FIGS. 7(a)-7(b). Stack 15 and block 16 are aligned so that face 6 of LOE precursor 2' is parallel to plane XZ, surface 8a of stack 15 is parallel to plane XY, facet 5 of LOE precursor 2' is perpendicular to plane YZ, plate 17 of block 16 is perpendicular to plane XZ, and surface 10b of block 16 is parallel to plane XY. After alignment, plate 17 is perpendicular to face 6 of LOE precursor 2' in stack 15.

[0024] The aligned and bonded structure, referred to herein as optical block 18, is actually an optical structure that is an intermediate work product of the composite LOE fabrication process. As shown, block 18 includes a first region having multiple LOE precursors separated by transparent spacer plates between the LOE precursors, a second region having multiple mutually parallel partially reflective internal surfaces, and an internal surface separating the first and second regions. In other embodiments, as described in further detail below, intermediate block 18 may include one or more additional subregions in the first and / or second regions. These subregions may include regions containing one or more optically active or optically inactive elements in addition to facet-free regions. These subregions can be added to block 18 by adding one or more plates, some of which may contain optically active elements, to block 16 before bonding with stack 15, as described in more detail below with reference to FIGS. 11(a)-13(d).

[0025] Block 18 is sliced ​​using a cutting device (not shown) through spacer plate 7 at predetermined intervals along the length (y dimension) of stack 15 to form multiple composite LOE structures sliced ​​from block 18. The planes of the slices are shown as dashed lines 12 in FIGS. 7(a)-7(b), and a single slice is shown in FIGS. 7(c)-7(d). The composite LOE sliced ​​from block 18 has a structure similar to the composite LOE shown in FIGS. 3(a)-3(b). It should be noted that after slicing, the spacer plate (more precisely, half a spacer plate) provides a structure similar to cover plate 3' in FIGS. 3(a)-3(b), thereby eliminating the need to attach a separate cover plate 3'. Each sliced ​​composite LOE structure is then polished at its outer surface, comprised of plates 7 and 17, to form the 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 the cover plates may be polished (in this example, LOE1 would have a single cover plate and LOE2 would have a double cover plate).

[0027] As described in detail above with reference to Figures 5(a)-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 where 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 material removed during grinding, and s represents the thickness of the cut, including tolerances for cut positioning in the sawmill. It should be noted that if a cover plate is desired only for LOE2 and not for LOE1, then t simply represents the thickness of the cover plate of LOE2. Typical values ​​for t can range from 50 microns to 500 microns.

[0028] 8(a)-8(b) illustrate an alternative embodiment of block 16, here designated block 16′. In this embodiment, each transparent plate is only partially coated with a partially reflective coating that is applied to each plate in strips with gaps between them. As described in U.S. Patent Publication No. 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 region of LOE1 in the final composite LOE, and d4 is calculated according to the following formula: d4=d1+d2-d3 where d1 and d2 are defined above.

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

[0030] It should be understood that bonded block 16' and stack 15 represent alternative embodiments of 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 relative to LOE 1, some of which are described below.

[0031] For example, in some embodiments, it may be desirable for some of the facets 4 of LOE1 to not extend entirely across LOE1, thereby providing one or more facet-less regions (i.e., without partially reflective internal surfaces) within LOE1, as shown in the example below.

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

[0033] Block 19 and stack 15 are aligned and bonded together as shown in FIGS. 12(a)-(b) to form intermediate optical block 21. Block 21 is then sliced ​​along plane 12 parallel to the XZ plane. The resulting single slice is shown in FIGS. 12(c)-(d). Such a slice consists of LOE 1, LOE 2, and an optically clean area 22 (also called an inactive area) that lacks any 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, transparent plate 20 can be replaced with a plate incorporating one or more desired optical elements (i.e., mixer, polarizer, etc.).

[0034] FIGS. 13(a)-13(b) show another embodiment of block 16, from which more complex shapes of LOE 1 can be fabricated by cutting block 16 and joining it with other optical plates and / or prisms. In FIGS. 13(a)-(b), block 16 is cut and polished along planes 31 and 32 and joined with transparent plate 24 and triangular prisms 25 and 26. The polished surface 10b'' of plate 24 is parallel to surface 10b of block 16. Block 16 with plate 24 and prisms 25 and 26 forms a new optical block 23, which includes one or more facet-less subregions within the block. In a manner similar to that shown in FIGS. 12(a)-(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 FIGS. 13(c)-(d). Such slices have inactive areas 27, 28 and 29 that do not have any reflective or semi-reflective surfaces.

[0035] In other embodiments (not shown), the LOE precursors 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 LOE2 includes one or more facetless subregions (i.e., no partially reflective internal surfaces).

[0036] 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 of making a composite light-directing optical element (LOE), comprising: obtaining a stack of a plurality of LOE precursors and a plurality of transparent spacer plates, the stack having a first pair of surfaces, the LOE precursors and the transparent spacer plates being arranged alternately in the stack along a length of the stack, each LOE precursor including a pair of major parallel faces and a first plurality of mutually parallel partially reflective internal faces that are inclined relative to the pair of major parallel faces; obtaining a first block having a second pair of surfaces and a second plurality of mutually parallel partially reflective interior faces; bonding the first block and the stack together, with one surface of a second pair of surfaces bonded to one surface of the first pair of surfaces, and with the first plurality of mutually parallel partially reflective interior surfaces becoming non-parallel to the second plurality of mutually parallel partially reflective interior surfaces, thereby forming a second block; and cutting at least one composite LOE into slices from the second block by cutting the second block through at least two successive spacer plates with the LOE precursor sandwiched therebetween.

2. 2. The method of claim 1, wherein the second plurality of mutually parallel partially reflective internal surfaces extend partially across the first block such that the first block includes a transparent region having no partially reflective internal surface of any of the second plurality of mutually parallel partially reflective internal surfaces.

3. The method of claim 2 , wherein the transparent area is an optically inactive area that does not have a reflective or semi-reflective surface.

4. A method for making a composite light-guiding optical element (LOE), comprising: obtaining a stack of a plurality of LOE precursors and a plurality of transparent spacer plates, the stack having a first pair of surfaces, the LOE precursors and the transparent spacer plates being arranged alternately in the stack along a length of the stack, each LOE precursor including a pair of major parallel faces and a first plurality of mutually parallel partially reflective internal faces that are inclined relative to the pair of major parallel faces; obtaining a first block having a second pair of surfaces and a second plurality of mutually parallel partially reflective interior faces; bonding the first block and the stack to a planar surface of the optical element such that the optical element is disposed between the first block and the stack, and the first plurality of mutually parallel partially reflective internal surfaces are non-parallel to the second plurality of mutually parallel partially reflective internal surfaces, thereby forming a second block; and cutting at least one composite LOE into slices from the second block by cutting the second block through at least two successive spacer plates with the LOE precursor sandwiched therebetween.

5. The method described in claim 4, wherein the optical element includes a partially reflective mixer.

6. The method of claim 4, wherein the optical element includes a polarizer.

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