Lightguide-based optical system for conveying an image
Specific management of configuration of overlap of facets reduces non-uniformity in an image outcoupled toward a nominal point of observation. A waveguide including at least two parallel surfaces, first, middle, and last partially reflecting facets are configured such that in a geometrical projection of the facets onto one of the surfaces the facets overlap, preferably with adjacent facets overlapping and non-adjacent facets starts and ends coinciding along at least a portion of the waveguide.
1. An optical system comprising:
(a) a light-guide optical element (LOE) formed from a transparent material and having a first major surface and a second major surface parallel to said first major surface;
(b) a coupling-in arrangement for coupling-in image light rays into the LOE so as to propagate within the LOE by internal reflection at said first and second major surfaces, a first set of image light rays reflected off said first major surface spanning a first range of propagation angles relative to said major surfaces and a second set of image light rays reflected off said second major surface spanning a second range of propagation angles, opposite to said first range of propagation angles, relative to said major surfaces;
(c) a plurality of mutually-parallel partially-reflecting internal surfaces deployed within the LOE and obliquely angled to said first major surface, said partially-reflecting internal surfaces being angled so that said image light rays within both said first and second ranges of propagation angles are incident on each of said partially-reflecting internal surfaces from the same side within a first angular range of incident angles and a second angular range of incident angles, respectively, said first angular range of incident angles being at a smaller inclination to a normal to the partially-reflecting surfaces than said second angular range of incident angles, said partially-reflecting internal surfaces being coated so as to be partially-reflecting for said first angular range of incident angles while being substantially transparent for said second angular range of incident angles.
2. The optical system of claim 1 , wherein image light rays reflected at said partially-reflecting internal surfaces form outcoupled rays directed outwards from said LOE, and wherein, for a majority of the outcoupled rays, a line along the direction of the outcoupled ray intersects at least two of said partially-reflecting internal surfaces.
3. The optical system of claim 1 , wherein a spacing between successive of said partially-reflecting internal surfaces is non-uniform.
4. The optical system of claim 1 , wherein a spacing between successive of said partially-reflecting internal surfaces increases monotonically.
5. The optical system of claim 1 , wherein a reflectivity of successive of said partially-reflecting internal surfaces increases along said LOE.
6. An optical system comprising:
(a) a light-guide optical element (LOE) formed from a transparent material and having a first major surface and a second major surface parallel to said first major surface;
(b) a coupling-in arrangement for coupling-in image light rays into the LOE so as to propagate within the LOE by internal reflection at said first and second major surfaces, a first set of image light rays reflected off said first major surface spanning a first range of propagation angles relative to said major surfaces and a second set of image light rays reflected off said second major surface spanning a second range of propagation angles, opposite to said first range of propagation angles, relative to said major surfaces;
(c) a plurality of mutually-parallel partially-reflecting internal surfaces deployed within the LOE and obliquely angled to said first major surface, each of said partially-reflecting internal surfaces being formed at an interface between a preceding portion of the LOE and a subsequent portion of the LOE, said partially-reflecting internal surfaces being angled so that said image light rays within both said first and second ranges of propagation angles are incident on each of said partially-reflecting internal surfaces from the preceding portion of the LOE within a first angular range of incident angles and a second angular range of incident angles, respectively, said first angular range of incident angles being at a smaller inclination to a normal to the partially-reflecting surfaces than said second angular range of incident angles, said partially-reflecting internal surfaces being coated so as to be partially-reflecting for said first angular range of incident angles while being substantially transparent for said second angular range of incident angles.