Azimuthal-segmented linear zone plate: 1D beam structurer and topological charge detector

Abstract

Unique linear structured light beams carrying fractional vortex dipoles in the shape of either a transverse elliptical beam or a transverse bottle-like beam are presented and studied. These beams are generated using a novel diffractive element produced by a given combination of two phase-shifted spiral linear zone plates with equal but opposite helicities. The impact of the topological charge upon the beams is surveyed and demonstrated to be that the size of the beams is quietly controlled by the charge. As an interesting application, we demonstrate that the element may be simply used to measure the topological charge of a vortex optical beam. On the other hand, when the element is illuminated by a vortex beam, the focused pattern is modulated so the number and direction of the modulated fringes easily reveal the sign and modulus of the topological charge. The experimental results verify that the simulation works well.