Optical system

Abstract

Optical systems including an image surface, a stop surface, a partial reflector disposed between the image surface and the stop surface, a reflective polarizer disposed between the stop surface and the partial reflector, and a quarter wave retarder disposed between the reflective polarizer and the partial reflector are described. The reflective polarizer is convex along two orthogonal axes. The reflective polarizer may be a thermoformed multilayer reflective polarizer.

What is claimed is: 
     
         1 . An optical system, comprising:
 an image source;   an exit pupil;   a first optical stack disposed between the image source and the exit pupil and comprising:
 a first optical lens; 
 a partial reflector having an average optical reflectance of at least 30% in a pre-determined plurality of wavelengths; and 
   a second optical stack disposed between the first optical stack and the exit pupil and comprising:
 a second optical lens; 
 a reflective polarizer convex about orthogonal first and second axes; and 
 a first quarter wave retarder disposed between the reflective polarizer and the first optical stack, 
   wherein substantially any chief light ray having at least first and second wavelengths at least 150 nm apart in the pre-determined plurality of wavelengths and emitted by the image source and transmitted by the exit pupil has a color separation distance at the exit pupil of less than 1.5 percent of a field of view at the exit pupil.   
     
     
         2 . The optical system of  claim 1 , wherein the color separation distance at the exit pupil is less than 20 arc minutes. 
     
     
         3 . The optical system of  claim 1 , wherein the reflective polarizer has at least one first location having a radial distance, r1, from an optical axis passing through an apex of the reflective polarizer and a displacement, s, from a plane perpendicular to the optical axis at the apex, s/r1 being at least 0.2, and wherein for an area of the reflective polarizer defined by s1 and r1, a maximum variation of a transmission axis of the reflective polarizer is less than about 2 degrees. 
     
     
         4 . The optical system of  claim 1 , wherein the reflective polarizer comprises at least one layer that is substantially optically biaxial at at least one first location on the at least one layer away from an optical axis passing through an apex of the reflective polarizer and substantially optically uniaxial at at least one second location on the at least one layer away from the optical axis. 
     
     
         5 . The optical system of  claim 4 , wherein substantially any chief light ray that is emitted by the image source and that is transmitted through the exit pupil is incident on each of the reflective polarizer and the partial reflector with an angle of incidence less than about 25 degrees. 
     
     
         6 . An optical system, comprising:
 an image surface;   a stop surface;   a first optical stack disposed between the image surface and the stop surface and comprising:
 a first optical lens; 
 a partial reflector having an average optical reflectance of at least 30% in a desired plurality of wavelengths; and 
   a second optical stack disposed between the first optical stack and the stop surface and comprising:
 a second optical lens; 
 a thermoformed multilayer reflective polarizer rotationally symmetric about an optical axis passing through an apex of the thermoformed multilayer reflective polarizer and convex toward the image surface along orthogonal first and second axes orthogonal to the optical axis, the thermoformed multilayer reflective polarizer having at least one first location having a radial distance, r1, from the optical axis, and a displacement, s1, from a plane perpendicular to the optical axis at the apex, s1/r1 being at least 0.1; and 
   a first quarter wave retarder disposed between the reflective polarizer and the first optical stack.   
     
     
         7 . The optical system of  claim 6 , wherein an image source comprises the image surface and the stop surface is an exit pupil. 
     
     
         8 . The optical system of  claim 6 , wherein s1/r1 is in a range of 0.2 to 0.8. 
     
     
         9 . The optical system of  claim 6 , wherein for an area of the reflective polarizer defined by s1 and r1, a maximum variation of a transmission axis of the reflective polarizer is less than about 2 degrees. 
     
     
         10 . The optical system of  claim 6 , wherein the reflective polarizer comprises at least one layer that is substantially optically biaxial at at least one first location on the at least one layer away from the optical axis and substantially optically uniaxial at at least one second location on the at least one layer away from the optical axis. 
     
     
         11 . The optical system of  claim 10 , wherein substantially any chief light ray that passes through the image surface and the stop surface is incident on each of the first optical stack and the second optical stack with an angle of incidence less than about 25 degrees. 
     
     
         12 . The optical system of  claim 6 , wherein the thermoformed multilayer reflective polarizer is thermoformed APF. 
     
     
         13 . An optical system, comprising:
 an image source emitting an undistorted image;   an exit pupil;   a partial reflector having a first shape convex toward the image source along orthogonal first and second axes and having an average optical reflectance of at least 30% in a pre-determined plurality of wavelengths; and   a reflective polarizer having a different second shape convex toward the image source along the first and second axes, such that a distortion of the emitted undistorted image transmitted by the exit pupil is less than about 10%.   
     
     
         14 . The optical system of  claim 13  further comprising a first optical lens disposed between the image source and the exit pupil, and a second optical lens disposed between the first optical lens and the exit pupil, the partial reflector disposed on a surface of the first optical lens, the reflective polarizer disposed on a surface of the second optical lens. 
     
     
         15 . The optical system of  claim 13  further comprising a quarter wave retarder disposed between the partial reflector and the reflective polarizer. 
     
     
         16 . The optical system of  claim 13 , wherein the distortion of the emitted undistorted image transmitted by the exit pupil is less than about 5%. 
     
     
         17 . The optical system of  claim 13 , wherein the reflective polarizer has at least one first location having a radial distance, r1, from an optical axis passing through an apex of the reflective polarizer and a displacement, s1, from a plane perpendicular to the optical axis at the apex, s1/r1 being at least 0.2, and wherein for an area of the reflective polarizer defined by s1 and r1, a maximum variation of a transmission axis of the reflective polarizer is less than about 2 degrees. 
     
     
         18 . The optical system of  claim 13 , wherein the reflective polarizer comprises at least one layer that is substantially optically biaxial at at least one first location on the at least one layer away from an optical axis passing through an apex of the reflective polarizer and substantially optically uniaxial at at least one second location om the at least one layer away from the optical axis. 
     
     
         19 . The optical system of  claim 18 , wherein substantially any chief light ray that is emitted by the image source and that is transmitted through the exit pupil is incident on each of the reflective polarizer and the partial reflector with an angle of incidence less than about 25 degrees.