US Patent 7327423 Retardation compensator for a liquid crystal-on-silicon imager

Phase retardation compensation can be achieved in liquid crystal-on-silicon imagers by stress freezing a photoelastic medium. As a result, a simple, one-piece compensator for the residual birefringence of the imagers may be provided in some cases. The stress may be frozen by subjecting a photoelastic material to a desired stress and temperature regime, resulting in a material which exhibits birefringence due to a stress level which is fixed or frozen at the molecular level within the material.