Pupil expansion

Abstract

A device including a waveguide having a first waveguide surface and a second waveguide surface parallel to the first waveguide surface is disclosed. The device may include a first volume holographic light coupling element disposed between the first waveguide surface and the second waveguide surface. The first volume holographic light coupling element may be structured to reflect at least a portion of incident light as reflected light. Incident light for which the first volume holographic light coupling element is structured to reflect may have a first angle of incidence within a total internal reflection (TIR) range with respect a first axis corresponding to a surface normal of the waveguide. Incident light for which the first volume holographic light coupling element is structured to reflect may have a second angle of incidence with respect to a second axis different from the first axis.

What is claimed is: 
     
         1 . A display system comprising:
 a waveguide having a first waveguide surface and a second waveguide surface parallel to the first waveguide surface, the waveguide being configured to propagate image light via total internal reflection;   a cross coupler disposed between the first waveguide surface and the second waveguide surface, wherein the cross coupler comprises a partially reflective louver mirror configured to reflect the image light; and   an output coupler disposed between the first waveguide surface and the second waveguide surface, wherein the output coupler is configured to couple, out of the waveguide and towards an eye box, the image light reflected by the partially reflective louver mirror.   
     
     
         2 . The display system of  claim 1 , wherein the output coupler comprises volume holograms. 
     
     
         3 . The display system of  claim 2 , wherein the waveguide comprises:
 a media layer between the first waveguide surface and the second waveguide surface, wherein the volume holograms and the partially reflective louver mirror are disposed within the media layer.   
     
     
         4 . The display system of  claim 2 , wherein the at least one of the volume holograms has a first reflective axis offset from a surface normal of the first waveguide surface. 
     
     
         5 . The display system of  claim 4 , wherein the partially reflective louver mirror has a second reflective axis that is different from the first reflective axis. 
     
     
         6 . The display system of  claim 1 , wherein the partially reflective louver mirror has a reflective axis that is offset from a surface normal of the first waveguide surface. 
     
     
         7 . The display system of  claim 6 , wherein the partially reflective louver mirror is configured to perform pupil expansion on the image light. 
     
     
         8 . The display system of  claim 1 , wherein the image light is incident upon the cross coupler at an incident angle within a total internal reflection range (TIR) of the waveguide and wherein the image light is reflected by the cross coupler at an output angle within the TIR range of the waveguide. 
     
     
         9 . The display system of  claim 1 , further comprising an input coupling prism mounted to the first waveguide surface and configured to couple the image light into the waveguide. 
     
     
         10 . A display comprising:
 a waveguide having a first waveguide surface and a second waveguide surface opposite the first waveguide surface, the waveguide being configured to propagate image light via total internal reflection;   a cross coupler disposed between the first waveguide surface and the second waveguide surface, wherein the cross coupler is configured to perform pupil expansion on the image light; and   an output coupler disposed between the first waveguide surface and the second waveguide surface, wherein the output coupler is configured to couple, out of the waveguide and towards an eye box, the image light that has been pupil-expanded by the cross coupler.   
     
     
         11 . The display of  claim 10 , wherein the output coupler comprises a first set of volume holograms. 
     
     
         12 . The display of  claim 11 , wherein the cross coupler comprises a second set of volume holograms. 
     
     
         13 . The display of  claim 10 , wherein the cross coupler comprises a louver mirror. 
     
     
         14 . The display of  claim 13 , wherein the output coupler comprises a set of volume holograms. 
     
     
         15 . The display of  claim 10 , wherein the cross coupler has a reflective axis that is offset with respect to a surface normal of the first waveguide surface. 
     
     
         16 . A head mounted display device comprising:
 a waveguide configured to propagate image light via total internal reflection;   an input coupler configured to couple the image light into the waveguide;   an output coupler on the waveguide and configured to couple the image light out of the waveguide and towards an eye box; and   a cross coupler on the waveguide and configured to redirect, towards the output coupler, the image light coupled into the waveguide by the input coupler.   
     
     
         17 . The head mounted display device of  claim 16 , wherein the cross coupler is configured to receive the image light in a first direction and is configured to reflect the image light in a second direction perpendicular to the first direction, the output coupler being configured to reflect the image light in a third direction perpendicular to the first direction and perpendicular to the second direction. 
     
     
         18 . The head mounted display device of  claim 16 , wherein the cross coupler is configured to perform pupil expansion on the image light. 
     
     
         19 . The head mounted display device of  claim 16 , wherein the output coupler comprises a set of volume holograms having a reflective axis offset from a surface normal of the first waveguide surface. 
     
     
         20 . The head mounted display device of  claim 16 , wherein the input coupler comprises an input coupling prism.