Photorefractive phase zone plates

Abstract

Zone plate is a type of important element widely used in modern optical instrumentation. In this paper we propose and realize a new method to fabricate phase zone pate in LiNbO 3 :Fe crystal. After the photo-excitation, migration and retrap of free charges in LiNbO 3 :Fe crystal, an axially symmetrical variation of refractive index is recorded in the crystal, an axially symmetrical variation of refractive index is recorded in the crystal. By this way, we get a phase zone plate. We can adjust the focal length of the phase zone plate by changing the imaging condition of the Fresnel zone plate, which will cause the variation of the radii of image of the zone plate in the crystal in our experiment, we use Fresnel zone plates we get can reach to as high as 21 percent. The phase zone plate can have long life-time after thermally fixed. Our method is very simple and can be widely used in optical information process and integrated optics.