Reduction of polarization-dependent loss in double-pass grating configurations

Abstract

Optical systems for routing light that reduce or eliminate polarization-dependent loss are provided. Such optical systems generally accommodate an optical element that has an intrinsic polarization-dependent loss and which is disposed to be encountered twice by the light being routed. In some instances, the optical element may be a dispersive element such as a diffraction grating or prism, but the invention has more general applicability. The optical system additionally includes both a reflective element and a wave plate assembly disposed to be encountered by the light between encounters with the dispersive element.

1 - 28 . (canceled) 
     
     
         29 . A method for reducing polarization-dependent loss in an optical system configured for routing light, the optical system including (1) an optical element having an intrinsic polarization-dependent loss and disposed to be encountered by the light at least twice, (2) a reflective element disposed to be encountered by the light between encounters with the optical element, and (3) a wave plate disposed to be encountered by the light between encounters with the optical element, the method comprising:
 determining an actual effect on polarization states of the light after propagation at least between encounters with the optical element, wherein the actual effect accounts for a material property of the reflective element;   determining a difference between the determined actual effect and a desired effect on polarization states of the light; and   calculating a characteristic of the wave plate based on the determined difference between the first and second effects.   
     
     
         30 . The method recited in  claim 29  wherein the characteristic comprises a retardance of the wave plate. 
     
     
         31 . The method recited in  claim 29  wherein the characteristic comprises an orientation of the wave plate. 
     
     
         32 . The method recited in  claim 29  wherein calculating the characteristic comprises calculating a plurality of characteristics. 
     
     
         33 . The method recited in  claim 29  wherein calculating the characteristic comprises locally minimizing a merit function defining the difference between the actual and desired effects. 
     
     
         34 . The method recited in  claim 29  wherein the reflective element includes an even number of reflective surfaces disposed to be encountered by the light. 
     
     
         35 . The method recited in  claim 29  wherein the reflective element includes an odd number of reflective surfaces disposed to be encountered by the light. 
     
     
         36 . The method recited in  claim 29  wherein the material property comprises an index of refraction. 
     
     
         37 . The method recited in  claim 29  wherein the material property comprises a complex index of refraction. 
     
     
         38 . An optical system for routing light, the optical system comprising:
 an optical element having an intrinsic polarization-dependent loss and disposed to be encountered by the light at least twice;   a reflective element disposed to be encountered by the light between encounters with the optical element, and   a wave plate disposed to be encountered by the light between encounters with the optical element, the wave plate having a characteristic that is calculated based on a difference between a first effect and a second effect, wherein:
 the first effect corresponds to an actual effect on polarization states of the light after propagation at least between encounters with the optical element, wherein the actual effect accounts for a material property of the reflective element, and 
 the second effect corresponds to a desired effect on polarization states of the light. 
   
     
     
         39 . The optical system recited in  claim 38  wherein the characteristic comprises a retardance of the wave plate. 
     
     
         40 . The optical system recited in  claim 38  wherein the characteristic comprises an orientation of the wave plate. 
     
     
         41 . The optical system recited in  claim 38  wherein the characteristic is calculated based on locally minimizing a merit function defining the difference between the first and second effects. 
     
     
         42 . The optical system recited in  claim 38  wherein the reflective element includes an even number of reflective surfaces disposed to be encountered by the light. 
     
     
         43 . The optical system recited in  claim 38  wherein the reflective element includes an odd number of reflective surfaces disposed to be encountered by the light. 
     
     
         44 . The optical system recited in  claim 38  wherein the material property comprises an index of refraction. 
     
     
         45 . The optical system recited in  claim 38  wherein the material property comprises a complex index of refraction. 
     
     
         46 . A method for reducing polarization-dependent loss in an optical system configured for routing light, the method comprising:
 determining an actual polarization transformation of the optical system based on at least one material property of a reflective element in the optical system;   constructing a merit function based on a difference between the actual polarization transformation and a desired polarization transformation associated with a wave plate in the optical system; and   determining a characteristic of the wave plate based on the merit function.   
     
     
         47 . The optical system recited in  claim 46  wherein determining the characteristic comprises locally minimizing the merit function. 
     
     
         48 . The method recited in  claim 46  wherein the characteristic comprises one of a retardance of the wave plate and an orientation of the wave plate.