Reflective liquid crystal spatial light modulator

Abstract

An optical switch uses a polarisation insensitive spatial light modulator operating by a double pass through a liquid crystal cell. The switch includes two such modulators in a cross bar arrangement. Different embodiments employing techniques for reducing cross talk are described.

1 - 30 . (canceled)  
   
   
       31 . A reflective liquid crystal spatial light modulator comprising 
 a two dimensional array of a plurality of reflective pixel electrodes;    each reflective electrode defining a respective pixel,    the reflective liquid crystal spatial light modulator further comprising    a quarter wave plate disposed on the reflective electrodes,    a liquid crystal layer disposed over the quarter wave-plate, and    a transparent conductive layer over the liquid crystal layer, wherein the transparent conductive layer forms a common electrode plane to said array, the common electrode plane completely overlaying said plurality of the reflective electrodes.    
   
   
       32 . The reflective liquid crystal spatial light modulator of  claim 31 , wherein said liquid crystal layer is a nematic liquid crystal layer.  
   
   
       33 . The reflective liquid crystal spatial light modulator of  claim 31 , wherein said liquid crystal layer is a π-cell.  
   
   
       34 . An integrated spatial light modulator for light of a predetermined wavelength, the integrated spatial light modulator comprising: 
 a transparent common electrode,    a plurality of reflective electrodes,    a retardance layer having an optical retardance of an odd integer number of quarter-waves of said predetermined wavelength, the retardance layer being disposed on the plurality of reflective electrodes; and    a liquid crystal layer,    wherein the liquid crystal layer is disposed between the retardance layer and the transparent common electrode, wherein the liquid crystal layer is disposed and configured to provide out-of-plane tilt in response to voltage applied across the liquid crystal layer between the reflective electrodes and the transparent common electrode;    wherein the reflective electrodes are reflective pixel electrodes disposed in a regular two-dimensional array, and the transparent common electrode completely overlays said plurality of reflective electrodes.    
   
   
       35 . The integrated spatial light modulator of  claim 34 , wherein said liquid crystal layer is a nematic liquid crystal layer.  
   
   
       36 . The integrated spatial light modulator of  claim 34 , wherein said liquid crystal layer is a π-cell.  
   
   
       37 . The integrated spatial light modulator of  claim 34  further comprising voltage application circuitry for applying desired voltages across the liquid crystal layer whereby the liquid crystal layer has desired values of out of plane tilt; 
 the arrangement being such that application of voltage to each electrode causes a respective portion of the liquid crystal layer associated with a respective reflective pixel electrode to have a specific value of said out-of-plane tilt; and wherein    the voltage application circuitry is adapted to apply voltages to said two dimensional pixel array for two-dimensionally steering light incident upon said modulator.    
   
   
       38 . A method of routing a light beam incident on an array of phase modulating elements, the light beam having a first component polarized in a first direction and a second component polarized in a second direction orthogonal to the first, the method comprising: 
 a) providing an integrated spatial light modulator comprising a liquid crystal layer, a wave plate layer having an optical retardance of (2n+1) λ/4, a transparent conductive layer, and a reflector layer, the liquid crystal being responsive to a variation in a drive voltage to provide a variation in out-of-plane director angle tilt, the spatial light modulator having: 
 a two dimensional array of a plurality of pixels; and  
 an array of a plurality of reflective electrodes wherein each electrode is associated with a respective pixel of the integrated spatial light modulator and a respective portion of the liquid crystal layer to define a said phase modulating element whereby the spatial light modulator comprises a said array of phase modulating elements;  
 wherein the transparent conductive layer completely overlays said plurality of the reflective electrodes;  
   b) applying respective drive voltages to each said electrode whereby the portion of liquid crystal associated with the electrode has a respective specific value of director angle tilt;    c) applying said beam to the integrated spatial light modulator whereby the first and second components each pass through the liquid crystal layer and the wave plate layer, and are reflected at the reflector layer to again pass through the wave plate layer and liquid crystal layer to emerge with both components phase modulated by the same amount; and    d) controlling the drive voltages to vary a deflection direction of said light beam due to said array of phase modulating elements.    
   
   
       39 . An optical switch comprising an integrated spatial light modulator for light of a predetermined wavelength, the integrated spatial light modulator comprising: 
 a transparent conductive layer,    a plurality of reflective pixel electrodes, said reflective pixel electrodes being disposed in a regular two-dimensional array;    a retardance layer having an optical retardance of an odd integer number of quarter-waves of said predetermined wavelength, the retardance layer being disposed on the regular two-dimensional pixel array; and    a liquid crystal layer being disposed between the retardance layer and the transparent conductive layer, wherein the transparent conductive layer completely overlays said plurality of the reflective electrodes.    
   
   
       40 . The switch of  claim 39 , wherein said liquid crystal layer is a nematic crystal layer.  
   
   
       41 . The switch of  claim 40 , wherein said liquid crystal layer is a π-cell.