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 first light guide formed from transparent material, said first light guide having a first pair of mutually-parallel surfaces and a second pair of mutually-parallel surfaces, said second pair of surfaces being orthogonal to said first pair of surfaces, said image projector being coupled to said first light guide so as to introduce the collimated image from said projector optical aperture into said first light guide so as to propagate within said first light guide by four-fold internal reflection at said first and second pairs of surfaces; and
(c) a light-guide optical element (LOE) formed from transparent material, said LOE comprising:
(i) a set of mutually-parallel major external surfaces, said major external surfaces extending across a first region and a second region,
(ii) a first set of planar, mutually-parallel, partially-reflecting surfaces, located in said first region of said LOE between said major external surfaces and having a first orientation non-parallel to said major external surfaces, and
(iii) a second set of planar, mutually-parallel, partially-reflecting surfaces, located in said second region of said LOE between said major external surfaces and having a second orientation obliquely angled to said major external surfaces,
wherein said first light guide includes a third set of internal mutually-parallel partially-reflecting surfaces deployed so as to progressively deflect said collimated image propagating within said first light guide so as to be introduced into said LOE and to propagate within said LOE by internal reflection at said major external surfaces towards said first set of partially-reflecting surfaces,
and wherein said first set of partially-reflecting surface are configured to progressively deflect said collimated image propagating within said LOE so as to propagate within said LOE by internal reflection at said major external surfaces towards said second set of partially-reflecting surfaces,
and wherein said second set of partially-reflecting surfaces are configured to progressively deflect said collimated image to as to couple said collimated image out of said LOE for viewing by the user.
2. The optical system of claim 1 , wherein said first pair of mutually parallel surfaces of said first light guide are parallel to said major external surfaces of said LOE.
3. The optical system of claim 1 , wherein both said first and second pairs of mutually parallel surfaces of said first light guide are non-parallel to said major external surfaces of said LOE, and wherein the collimated image deflected by said third set of partially-reflecting surfaces passes through a coupling prism before entering said LOE.
4. The optical system of claim 1 , wherein the collimated image deflected by said third set of partially-reflecting surfaces passes through an air gap before entering said LOE.
5. The optical system of claim 1 , wherein the collimated image deflected by said third set of partially-reflecting surfaces passes through an optical layer emulating an air gap before entering said LOE.
6. 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.
7. The optical system of claim 6 , wherein a last reflectivity of said first sequence of successively-increasing reflectivities is greater than 90%.
8. The optical system of claim 1 , wherein said first region and said second region are non-overlapping.
9. The optical system of claim 1 , wherein said image projector is coupled to said first light guide so as to introduce the collimated image from said projector optical aperture into said first light guide such that no ray of said collimated image is parallel to said first or second pairs of surfaces or to said third set of partially-reflecting surfaces, and wherein said collimated image propagates within said LOE such that no ray of said collimated image is parallel to said major external surface or to said first set of partially-reflecting surfaces.