Light homogenization

Abstract

An optical reflective device for homogenizing light including a waveguide having a first and second waveguide surface and a partially reflective element is disclosed. The partially reflective element may be located between the first waveguide surface and the second waveguide surface. The partially reflective element may have a reflective axis parallel to a waveguide surface normal. The partially reflective element may be configured to reflect light incident on the partially reflective element at a first reflectivity for a first set of incidence angles and reflect light incident on the partially reflective element at a second reflectivity for a second set of incident angles.

What is claimed is: 
     
         1 . An electronic device comprising:
 a waveguide configured to propagate light via total internal reflection (TIR);   a first optical coupler configured to couple the light out of the waveguide;   a second optical coupler configured to redirect, towards the first optical coupler, the light propagating in the waveguide via TIR; and   a partial reflector on the waveguide.   
     
     
         2 . The electronic device of  claim 1 , wherein the waveguide comprises a first substrate layered on a second substrate, the first optical coupler comprising a diffractive grating in the first substrate. 
     
     
         3 . The electronic device of  claim 1 , wherein the diffractive grating comprises a volume hologram. 
     
     
         4 . The electronic device of  claim 3 , wherein the partial reflector is embedded in the first substrate. 
     
     
         5 . The electronic device of  claim 3 , wherein the partial reflector is layered between the first substrate and the second substrate. 
     
     
         6 . The electronic device of  claim 5 , wherein the waveguide comprises a third substrate, the first substrate being sandwiched between the second substrate and the third substrate. 
     
     
         7 . The electronic device of  claim 6 , further comprising:
 an additional partial reflector layered between the first substrate and the third substrate, wherein the additional partial reflector at least partially overlaps the partial reflector.   
     
     
         8 . The electronic device of  claim 1 , wherein the partial reflector is configured to reflect a first portion of the light and to transmit a second portion of the light. 
     
     
         9 . The electronic device of  claim 1 , wherein the partial reflector comprises a layer of metal. 
     
     
         10 . The electronic device of  claim 1 , wherein the partial reflector comprises a layer of dielectric. 
     
     
         11 . The electronic device of  claim 1 , wherein the partial reflector at least partially overlaps the second optical coupler. 
     
     
         12 . The electronic device of  claim 1 , wherein the partial reflector overlaps a portion of the waveguide between the first and second optical couplers. 
     
     
         13 . The electronic device of  claim 1 , further comprising a third optical coupler configured to couple the light into the waveguide. 
     
     
         14 . The electronic device of  claim 13 , wherein the partial reflector at least partially overlaps the third optical coupler. 
     
     
         15 . The electronic device of  claim 13 , wherein the partial reflector overlaps a portion of the waveguide between the second optical coupler and the third optical coupler. 
     
     
         16 . An electronic device comprising:
 a waveguide configured to propagate light via total internal reflection (TIR), wherein the waveguide has a first substrate, a second substrate, and a third substrate interposed between the first substrate and the second substrate;   a first optical coupler on the waveguide and configured to couple light into the waveguide;   a second optical coupler on the waveguide and configured to couple the light out of the waveguide; and   a partially reflective layer disposed in the third substrate, wherein the partially reflective layer is disposed separated from the first substrate by a first non-zero distance and is separated from the second substrate by a second non-zero distance.   
     
     
         17 . The electronic device of  claim 16 , wherein the first substrate has a first lateral surface that contacts the third substrate, the second substrate has a second lateral surface that contacts the third substrate, the second lateral surface extends parallel to the first lateral surface, and the partially reflective layer extends parallel to the first and second lateral surfaces. 
     
     
         18 . The electronic device of  claim 16 , wherein the second optical coupler comprises holograms in the third substrate. 
     
     
         19 . The electronic device of  claim 16 , further comprising:
 a third optical coupler on the waveguide and configured to redirect the light from the first optical coupler towards the third optical coupler.   
     
     
         20 . An electronic device comprising:
 a waveguide configured to propagate light via total internal reflection (TIR), wherein the waveguide has a first substrate and a second substrate layered onto the first substrate;   a first optical coupler on the waveguide and configured to couple light into the waveguide;   a second optical coupler on the waveguide and configured to couple the light out of the waveguide; and   a partially reflective layer between the first substrate and the second substrate, wherein the partially reflective layer directly contacts the first substrate, the partially reflective layer directly contacts the second substrate, the partially reflective layer is configured to transmit a first portion of the light, and the partially reflective layer is configured to reflect a second portion of the light.