Generation of a vortex and helix with square arrays with high-efficiency by the use of a 2D binary phase mask

Abstract

In this paper, we designed a binary phase mask (PM) with specific phase modulation characteristic and analyzed the spatial spectrum of the beam passing through the PM. In the case where the difference of phase modulation between two lattices of the binary PM is not equal to π, we found the spatial spectrum has the central spot (direct current component, DC component) except for the central eight strong symmetrical spots and many outer weak symmetrical spots. Based on the multiple-beam interference, the propagation-invariant vortex with a square array can be realized by interference of the eight plane waves with the same wave vectors along the optical axis from the central eight symmetrical spots via the modulated phase values of the central eight symmetric spots. The vortex arrays have two kinds of vortex with an opposite topological charge of l=±1. The helix can be formed with a square array by the interference of the vortex array and the plane wave along the optical axis from the DC component. The helix with outstanding helical intensity distributions have two screw directions, which coincide with the phase distribution of the optical vortex with the square array. The energy efficiency of this method can reach more than 80%. The simulation results demonstrate the feasibility of this method.