Adjustable square optical vortices generated by modified square spiral zone plates

Abstract

A modified square spiral zone plate (MSSZP) is proposed to generate a square optical vortex with an adjustable shape and position. A radial modulation r 0 adjusts the shape of the two-arms-cross pattern for the square vortex. The vertical modulation a and horizontal modulation b make the central position of the square vortex move along the vertical and horizontal directions, respectively. The vertical or horizontal moving distance is linearly related to a or b , respectively. The slope of the corresponding fitting line is equal to 1/2. Based on the sum of topological charges of the MSSZP and spiral phase plate, the topological charge of the corresponding generated square vortex follows a modulo-4 transmutation rule, which is satisfied by setting the appropriate r 0 . The method of constructing the MSSZP is illustrated. It is proved in the simulations and experiments that the MSSZP has the adjustable square vortex. The proposed zone plate is applicable for optical image processing, infrared antennas, and laser alignment systems.