Two polygon-like beams generated by a modified interfering vortex spiral zone plate

Abstract

A modified interfering vortex spiral zone plate (MIVSZP) is proposed to produce two polygon-like beams at the focal plane. A radial shift parameter t3 has influence on the shapes of two beams. When t3 has an appropriate value only, the MIVSZP has two polygon-like beams. With the increase of the inner phase modulation parameter t1, the rotation angle of the inner polygon-like beam increases firstly, then decreases and increases finally. When the outer phase modulation parameter t2 increases, the rotation angle of the inner polygon-like beam increases. However, t1 and t2 cannot make the outer polygon-like beam rotate. The topological charge p of the modified interfering vortex phase is equal to the number of sides of the polygon. In addition, for the arbitrary topological charge l of the spiral zone plate, the two polygon-like beams have the same topological charge equal to l. Moreover, it is proved in the simulations and experiments that the topological charges of two polygon-like beams can be identified by the number of fringes or spots generated by the interference binary phase transmittance. The method of constructing the MIVSZP is illustrated. The proposed zone plate is applicable to rotate particles located at different polygons simultaneously, and increase optical communication capacities.