| CPC G02B 6/0031 (2013.01) [G02B 6/0016 (2013.01); G02B 6/002 (2013.01); G02B 27/283 (2013.01)] | 17 Claims |

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1. An optical device comprising:
a lightguide for guiding light corresponding to a collimated image, the lightguide comprising a first external face and a second external face parallel to the first external face, the lightguide having a first section and a second section, the first section comprising a first set of partially reflecting facets parallel to each other and disposed between the first and second external faces, and the second section comprising a second set of partially reflecting facets parallel to each other and disposed between the first and second external faces;
the first section reflects the guided light propagating in a first guided direction in the lightguide to propagate in a second guided direction in the lightguide, the second section reflects the guided light propagating in the second guided direction in the lightguide to out of the lightguide;
each of the facets in the first set of partially reflecting facets and in the second set of partially reflecting facets reflects light at incidence angles between 55 and 85 degrees from the normal to the surface of the facet; and
in the first set of partially reflecting facets the respective partially reflecting facets are at a first angle which is oblique relative to the first and second external faces, and in the second set of partially reflecting facets the respective partially reflecting facets are at a second angle which is oblique relative to the first and second external faces;
wherein the surface of each of the facets in the first set and the second set has a facet coating providing angularly dependent reflectivity such that the image reflectivity at incidence angles between 55 and 85 degrees from the normal to the surface increases as the angle of incidence increases from 55 to 85 degrees from the normal to the surface.
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