Comparative modeling of phase spiral and conventional zone plates

Abstract

In this paper, a comparative modeling of optical vortices focusing by a zone plate and a spiral zone plate is presented. The FullWAVE software package based on a finite difference time domain method was used for the numerical study. It has been demonstrated that a binary zone plate and a spiral binary zone plate with a topological charge m = 3 form a different intensity distribution in their focal planes for an incident Gaussian beam with linear polarization. For correct comparison, a topological charge m = 3 was embedded into launch field for an ordinary zone plate. The spiral binary zone plate produced the intensity distribution with three peaks, which formed a ring while their propagation in a free space. The conventional zone plate produced ring-shape intensity pattern with two maxima in a vertical axis directly in the focus.