Wide field-of-view angle linear retarder with an ultra-flat retardance response

We propose a universal method for optimal design of a wide field-of-view (FOV) angle linear retarder with an ultra-flat retardance response based on paired positive/negative birefringent plates. The mechanism and rules for the FOV effect compensation are revealed to determine the structure of the proposed retarder by introducing the partial derivative of refractive index with respect to the incident angle. A concrete example based on quartz/sapphire plates is designed and manufactured as a proof-of-concept of the proposed method. The maximum deviation in the retardance of the optimally designed quartz/sapphire wide FOV angle retarder over the concerned FOV angles (incidence: -20°-20°; azimuth: 0°-360°) is only 0.08°, which has been reduced by 3 orders of magnitude compared with the common quartz retarder.