Variable-Focus Liquid-Crystal Fresnel Lens

Abstract

Liquid-crystal lens-cells shaped like a plano-convex Fresnel lens with homogeneous alignment are prepared. Their focal length can be varied from the value f _e for an extraordinary ray to nearly f _o for an ordinary ray by applying an electric field across the cell. The response and recovery times within several seconds are attained in the liquid-crystal lenses. More transparent (\gtrsim80%) variable-focus liquid-crystal lenses are achieved in the double-layered structure of two identical liquid-crystal Fresnel lenses with a mutually orthogonal optic axis.