Electrically and optically tunable Fresnel lens in a liquid crystal cell with a rewritable photoconductive layer

This work investigates an electrically and optically tunable Fresnel lens in a liquid crystal (LC) cell with an erasable and rewritable photoconductive layer. By using a Sagnac interferometer, a Fresnel-like pattern can be induced on the photoconductive polymer layer which results in conductive and nonconductive structures in bright and dark zones. This effect causes the mismatch of the LC refractive index between adjacent zones with external voltage, generating a LC Fresnel lens. The focal length of the proposed Fresnel lens can be easily tuned by varying the Fresnel pattern size, and the focusing efficiency can be optically and electrically controlled.