Beam steering device

Abstract

A beam steering device uses a liquid crystal with an array of back electrodes. Voltages are applied to the array to cause a desired phase distribution across the array, the distribution being selected to steer a beam incident upon the array into a desired direction. Reflective elements are disposed to reflect light incident in the spaces between the electrodes to reduce losses and to smooth the transitions in phase between adjacent electrodes.

1 . A device for steering a beam of light, the device comprising an array of elements, said beam of light being incident upon said array of elements, each element having a reflective back electrode and a front electrode, the back and front electrodes being disposed respectively behind and in front of a liquid crystal layer, the back electrodes being spaced apart to define said array, and a reflective layer disposed behind the back electrodes to reflect light incident in the spaces between the back electrodes substantially in phase with the light reflected from the back electrodes.  
     
     
         2 . The device of  claim 1  wherein there is provided a single front electrode per element.  
     
     
         3 . The device of  claim 2  wherein the front electrode is common to the array of elements.  
     
     
         4 . The device of  claim 1 ,  2  or  3  having drive circuitry on a substrate, and a planarising layer disposed on said drive circuitry, wherein said back electrodes are disposed on said planarising layer, and respective wirings pass through said planarising layer from said back electrodes to said drive circuitry, and wherein a portion of said drive circuitry provides said reflective layer.  
     
     
         5 . The device of  claim 1 ,  2  or  3  having drive circuitry on a substrate, and a planarising layer disposed on said drive circuitry, wherein said back electrodes are disposed on said planarising layer, and respective wirings pass through said planarising layer from said back electrodes to said drive circuitry, and wherein said reflective layer is disposed within said planarising layer.  
     
     
         6 . The device of  claim 1 ,  2  or  3  having drive circuitry on a substrate, a first planarising layer disposed on said drive circuitry wherein said reflective layer is disposed on said first planarising layer, and a second planarising layer disposed on said circuitry layer and said first planarising layer wherein said back electrodes are disposed on said second planarising layer, wherein respective wirings pass through said planarising layers from said back electrodes to said drive circuitry.  
     
     
         7 . The device of any preceding claim having a further planarising layer disposed over said back electrodes.  
     
     
         8 . The device of any preceding claim having a wave plate disposed over said back electrodes.  
     
     
         9 . The device of any preceding claim wherein said reflective layer is composed of metal.  
     
     
         10 . The device of any preceding claim wherein said reflective layer extends only to substantially fill said spaces between said back electrodes.  
     
     
         11 . The device of any of claims  1 - 8  wherein said reflective layer extends beneath said back electrodes.  
     
     
         12 . The device of any of claims  1 - 8  wherein said reflective layer extends substantially level with said back electrodes.  
     
     
         13 . The device of any of claims  1 - 9  wherein said reflective layer extends only partway across said spaces.  
     
     
         14 . The device of any preceding claim further comprising circuitry for connecting at least a portion of said reflective layer to a selected potential.  
     
     
         15 . The device of any preceding claim, wherein each element has plural front electrodes.  
     
     
         16 . A method of steering light having a first direction to a desired second direction, the method comprising: 
 causing a beam of said light to be incident upon a reflective liquid crystal device;    selecting a desired spatial phase modulation characteristic for said liquid crystal device thereby to provide a deflection from said first direction to said second direction; and    providing a spatial distribution of phase levels across said liquid crystal device to at least approximate to said desired characteristic;    wherein the step of providing a spatial distribution of phase levels comprises driving said liquid crystal at sequential spaced driving locations to produce rising discrete phase levels; and    smoothing transitions in phase between said spaced driving locations by providing further locations between said spaced driving locations, and reflecting said light through said liquid crystal in said further locations.    
     
     
         17 . A method according to  claim 16 , wherein said step of driving said liquid crystal comprises providing electrodes at said discrete driving locations, and applying voltages to sequential electrodes to cause said rising phase levels due to the liquid crystal.  
     
     
         18 . A method according to  claim 17 , wherein said step of smoothing comprises providing spaces between the electrodes at said further locations and providing reflective elements in the spaces and behind the electrodes.  
     
     
         19 . A method according to  claim 16  wherein said electrodes are reflective whereby said liquid crystal device is reflective.  
     
     
         20 . A method according to  claim 17 , comprising providing a reflective layer disposed behind the electrodes whereby said liquid crystal device is reflective.  
     
     
         21 . A method according to  claim 19 , wherein the step of providing reflective elements comprises disposing the reflective elements at a distance behind said electrodes such that light reflected thereby leaves said liquid crystal device substantially in phase with light reflected by said electrodes.  
     
     
         22 . An optical routing switch comprising at least one beam steering device according to any of claims  1 - 15 .