Optical systems including light-guide optical elements with two-dimensional expansion
An optical system including a light-guide optical element (LOE) with first and second sets ( 204, 206 ) of mutually-parallel, partially-reflecting surfaces at different orientations. Both sets of partially-reflecting surfaces are located between parallel major external surfaces. A third set of at least partially-reflecting surfaces ( 202 ), deployed at the coupling-in region, receive image illumination injected from a projector ( 2 ) with an optical aperture having a first in-plane width and direct the image illumination via reflection of at least part of the image illumination at the third set of at least partially-reflective facets towards the first set of partially-reflective facets with an effective optical aperture having a second width larger than the first width.
1. An optical system for directing image illumination from an image projector towards a user for viewing, the optical system comprising:
(a) an image projector for projecting a collimated image having an angular field of view about an optical axis, said collimated image having a projector optical aperture;
(b) a light-guide optical element (LOE) formed from transparent material, said LOE comprising:
(i) a first region containing a first set of planar, mutually-parallel, partially-reflecting surfaces having a first orientation;
(ii) a second region containing a second set of planar, mutually-parallel, partially-reflecting surfaces having a second orientation non-parallel to said first orientation;
(iii) a set of mutually-parallel major external surfaces, said major external surfaces extending across said first and second regions such that both said first set of partially-reflecting surfaces and said second set of partially-reflecting surfaces are located between said major external surfaces; and
(iv) a coupling-in surface having a coupling-in optical aperture, said coupling-in surface being positioned such that a collimated image introduced via said coupling-in surface propagates within said LOE by internal reflection at said major external surfaces, is partially reflected by said first set of partially-reflecting surfaces to generate a deflected propagating image propagating within said LOE by internal reflection at said major external surfaces, and is partially reflected by said second set of partially-reflecting surfaces to generate a coupled-out image directed outwards from one of said major external surfaces towards the user,
wherein said coupling-in optical aperture has at least one dimension larger than a corresponding dimension of said projector optical aperture, and wherein said image projector is associated with said coupling-in surface via an aperture expanding arrangement comprising a third set of planar, mutually-parallel, at least partially-reflecting surfaces deployed between said image projector and said coupling-in surface, said aperture expanding arrangement expanding an effective optical aperture of said image projector by specular reflection at successive surfaces of said third set of partially-reflecting surfaces to fill said coupling-in optical aperture.
2. The optical system of claim 1 , wherein said coupling-in surface is obliquely angled relative to said major external surfaces.
3. The optical system of claim 2 , wherein said aperture expanding arrangement further comprises a pair of mutually-parallel external faces, said third set of partially-reflecting surface being located between said external faces, one of said external faces being deployed in facing relation to said coupling-in surface, with an air gap between said external face and said coupling-in surface.
4. The optical system of claim 1 , wherein said third set of at least partially-reflecting surfaces has a first sequence of successively-increasing reflectivities in an order in which the image illumination reaches them, and wherein said first set of partially-reflecting surfaces has a second sequence of successively-increasing reflectivities in an order in which the image illumination reaches them, said second sequence starting at a reflectivity smaller than a last reflectivity of said first sequence.
5. The optical system of claim 4 , wherein a last reflectivity of said first sequence of successively-increasing reflectivities is greater than 90%.
6. The optical system of claim 1 , wherein a majority of the image illumination arriving at said first set of partially-reflecting surfaces has undergone exactly one reflection from said third set of at least partially-reflecting surfaces.
7. The optical system of claim 1 , wherein a majority of the image illumination arriving at said first set of partially-reflecting surfaces has undergone two reflections from said third set of at least partially-reflecting surfaces.
8. The optical system of claim 1 , wherein said first region and said second region are non-overlapping.