WECLAIM:
1. An optical device comprising:
(a) a lightguide having:
(i) a first pair of external surfaces parallel to each other, and (ii) at least two sets of facets, each of said sets:
(A) including a plurality of partially reflecting facets parallel to each other,
and
(B) between said first pair of external surfaces, and
(b) wherein in each of said sets of facets, the respective facets are:
(i) at an oblique angle relative to said first pair of external surfaces, and (ii) non-parallel relative to another of said sets of facets.
2. The device of claim 1 wherein said lightguide includes exactly two of said sets of facets.
3. The device of claim 1 wherein said lightguide includes exactly three of said sets of facets.
4. The device of claim 1 wherein at least a first set of said sets of facets provides continuous coverage as viewed in a viewing direction over a respective deployment area of said first set of facets so at least a portion of the light in said viewing direction passes through at least one facet of at least two sets of facets within said lightguide.
5. The device of claim 1 wherein each of said sets of facets spans an area of coverage, said spanning being an area over which each of said sets of facets are deployed, and wherein said areas of coverage for two of said sets of facets are at least partially overlapping.
6. The device of claim 1 wherein said lightguide is a one-section lightguide including:

(a) a first set of said sets of facets, and
(b) a second set of said sets of facets,
wherein said first and second sets are overlapping in a same plane of a thickness dimension of said lightguide, said thickness dimension between said first pair of external surfaces.
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7. The device of claim 1 wherein
(a) said lightguide has a thickness dimension between said first pair of external surfaces,
(b) facets of a first of said sets of facets extend across said thickness dimension so as to span a first depth band from a first depth to a second depth, and
(c) facets of a second of said sets of facets extend across said thickness dimension so as to span a second depth band from a third depth to a fourth depth.

8. The device of claim 7 wherein said first depth band and said second depth band span overlapping depths.
9. The device of claim 7 wherein said first depth band and said second depth band span the same range of depths.
10. The device of claim 7 wherein said first depth band and said second depth band are non-overlapping.
11. The device of claim 1 wherein a section of facets is bounded by a boundary pair of surfaces parallel to, or coincident with, said first pair of external surfaces, said section containing at least one of said sets of facets.
12. The device of claim 11 wherein said lightguide is a single section lightguide including:
(a) a first section of said section of facets, said first section including two of said sets of
facets.
13. The device of claim 11 wherein said lightguide is a two-section lightguide including:
(a) a first section of said section of facets having a first boundary pair of surfaces, and
(b) a second section of said section of facets having a second boundary pair of surfaces, wherein one surface of said first boundary pair of surfaces is adjacent to one surface of said second boundary pair of surfaces and said first and second boundary pairs of surfaces are parallel.
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14. The device of claim 13 wherein said lightguide is a three-section lightguide further
including:
(a) a third section of said section of facets having a third boundary pair of surfaces,
wherein one surface of said third boundary pair of surfaces is adjacent to one surface
of either said first boundary pair of surfaces or said second boundary pair of surfaces,
and
wherein said third boundary pair of surfaces is parallel to said first and second
boundary pairs of surfaces.
15. The device of claim 11 wherein said lightguide includes:
(a) a first section of said section of facets having a first boundary pair of surfaces, and
(b) a second section of said section of facets having a second boundary pair of surfaces,
(c) wherein said first and second boundary pairs of surfaces are parallel; and
(d) at least one interface, each said interface:
(i) being at least partially between two sections, and (ii) parallel to said first pair of external surfaces,
(e) wherein said interface is at least one selected from the group consisting of:
(i) a partially reflecting surface,
(ii) a partially reflective optical coating,
(iii) a transition from a material of one of said sections to another material of
another of said sections, (iv) a polarization modifying coating, and (v) a flexible intermediate layer.
16. The device of claim 1 wherein a second of said sets of facets is configured to perform coupling-out of light from said lightguide, said second set of facets having a constant number of facets overlap in a line of sight toward a nominal point of observation of light coupling-out of said lightguide via one of said first pair of external surfaces.
17. The device of claim 1 further comprising:
(a) a coupling-in arrangement configured to guide light into said lightguide such that said light propagates via internal reflection of said first pair of external surfaces along the lightguide in a propagation direction with a first in-plane component, and
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(b) wherein in each of said sets of facets, the respective facets are orientated to deflect part of the light to be guided by internal reflection of said lightguide to propagate along said lightguide with a propagation direction with a second in-plane component non-parallel to said first in-plane component.
18. The device of claim 17 wherein said coupling-in arrangement is a second lightguide
including:
(a) a second pair of external surfaces parallel to each other, and
(b) a set of facets.

19. The device of claim 1 wherein in at least one of said sets of facets, a spacing between each of the partially reflecting facets is configured such that: Within a field of view of an image to be reflected by said one of said sets of facets, a distance over which a double reflection propagation step occurs along the lightguide does not match an exact multiple of said spacing.
20. The device of claim 1 wherein a first angle of said partially reflecting facets in a first set of said at least two sets of facets is different from a second angle of said partially reflecting facets in a second set of said at least two sets of facets, said angles being relative to said first pair of external surfaces.
21. The device of claim 1 wherein a first angle of said partially reflecting facets in a first set of said at least two sets of facets is substantially the same as a second angle of said partially reflecting facets in a second set of said at least two sets of facets, said angles being relative to said first pair of external surfaces and said first set is rotated relative to said second set.
22. The device of claim 1 further including:

(a) a light source (3200) providing input illumination (3202) into said lightguide (16), and
(b) an image modulator (3215) reflecting propagating light (3204) generated by said lightguide from said input illumination, said reflecting producing reflected image light (3206) that traverses said lightguide.
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23. A method of producing an optical device, the optical device comprising a lightguide (16)
having:
(i) at least two sets of facets (32, 36) between a first pair of external surfaces (22, 24),
(ii) said external surfaces (22, 24) parallel to each other,
(iii) each of said sets of facets (32, 36) including a plurality of partially reflecting facets
parallel to each other, and wherein in each of said sets of facets (32, 36), the respective facets are at an oblique angle relative to said first pair of external surfaces (22, 24), and non-parallel to another of said sets of facets (32, 36), the method comprising:
(a) providing a first array (52) of partially reflecting facets,
(b) providing a second array (56) of partially reflecting facets, and
(c) optically attaching said first array (52) and said second array (56) such that said facets of said first array (32) and said facets of said second array (36) are at an oblique angle relative to said first pair of external surfaces (22, 24), and non-parallel to each other.

24. The method of claim 23 wherein said optically attaching is performed by pressing together said first and second arrays with a flowable adhesive between said first and second arrays.
25. The method of claim 23 wherein a first angle of said partially reflecting facets in said first array is different from a second angle of said partially reflecting facets in said second array, said angles being relative to respective external surfaces of said arrays.
26. The method of claim 23 wherein a first angle of said partially reflecting facets in said first array is substantially the same as a second angle of said partially reflecting facets in said second array, said angles being relative to respective external surfaces of said arrays, and said first array is rotated relative to said second array prior to optically attaching said arrays.
27. A method of producing an optical device, the optical device comprising a lightguide (16) having:
(i) at least two sets of facets (32, 36) between a first pair of external surfaces (22, 24), (ii) said external surfaces (22, 24) parallel to each other,
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(iii) each of said sets of facets (32, 36) including a plurality of partially reflecting facets
parallel to each other, and wherein in each of said sets of facets (32, 36), the respective facets are at an oblique angle relative to said first pair of external surfaces (22, 24), and non-parallel to another of said sets of facets (32, 36), the method comprising:
(a) providing a plurality of transparent flat windows (50) having partially reflecting surfaces;
(b) optically attaching together said windows (50) so as to create a first stack (51),
(c) slicing said first stack (51) to create a plurality of first flat arrays (52), said slicing across a plurality of said windows (50) and at an oblique angle relative to at least two pairs of opposing sides of said first stack (70),
(d) optically attaching together a plurality of said first flat arrays (52) so as to create an array stack (70), and
(e) slicing said array stack (70) to create at least one said lightguide (71, 16), said slicing across a plurality of said first flat arrays (52) and at an oblique angle relative to at least two pairs of opposing sides of said array stack (70).

28. The method of claim 27 wherein said first flat arrays are polished and coated before being optically attached to create said array stack.
29. A method for expanding an optical aperture in two dimensions by providing an image as a light input to the optical device of claims 1.
Dated this 23 day of January 2020
~Digitally signed~
Arindam Paul
REG. NO: IN/PA-174
of De Penning & De Penning
Agent for the Applicants
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