Patent ID: 7580085

Claim:
An optical device comprising an input polarizer ( 4 ) for passing light having a first polarization direction ( 11 ), a polarization modifying element ( 5 ) for receiving light of the first polarization direction from the input polarizer ( 4 ), and an output polarizer ( 7 ) for analysing light from the polarization modifying element ( 5 ), the polarization modifying element ( 5 ) comprising polarization directions of at least first and second sets of regions ( 8 , 9 ) asymmetric with respect to the first polarization direction, each region ( 8 ) of the first set changing the polarization of light from the input polarizer ( 4 ) to a second polarization direction different from the first polarization direction and each region ( 9 ) of the second set supplying light of a third polarization direction different from the second polarization direction to output a non-uniform wavefront, wherein the output polarizer ( 7 ) cooperates with the polarization modifying element ( 5 ) such that each first light path through each region ( 8 ) of the first set and the output polarizer ( 7 ) has substantially the same attenuation and phase change to light from the input polarizer ( 4 ) as each second light path through each region ( 9 ) of the second set and the output polarizer ( 7 ) to output a uniform wavefront, the output polarizer ( 7 ) is arranged to transmit only the slow axis component of light from the first and second sets of regions ( 8 , 9 ), and the polarization modifying element ( 5 ) comprises a patterned retarder, and wherein the output polarizer ( 7 ) is arranged to transmit equal proportions of slow and fast axis components of light from each of the first and second sets of regions ( 8 , 9 ).