A phase compensational elliptical Fresnel zone plate for generating elliptical optical vortices

Abstract

A phase compensational elliptical Fresnel zone plate (PCEFZP) is proposed to control the light field in this paper. It compensates the optical path difference from PCEFZP to the major focal point to control the beam focus on the specified position. Besides, the PCEFZP and the spiral phase plate are combined to produce vortex beams. By changing different phase plates, three types of elliptical vortex beams (EVB) are generated. Simulation and experimental results show that there are obvious differences among the three beam fields: EVB of type B has the longest focal depth among them, in addition, when the topological charge increases, beam fields of type A and B can maintain a perfect elliptical shape, while the central null of the type C EVB field intensity splits into a different number of nulls and the number of nulls is equal to topological charge. These parameter-tunable vortex beams can find applications in different fields, such as particle manipulation and optical communication.