Generation of vortex beams with nonuniform phase jumps in azimuthal locations

Abstract

The phase angle of the vortex beam along a closed loop centered on the optical singularity changes 2πℓ where ℓ is the number of phase jumps (PJs) from 0 to 2 and indicates the topological charge (TC) of the vortex beam. In this paper, generation and specification of a new type of vortex beams that their PJs are asymmetrically embedded in the phase pattern are reported. In contrast to Laguerre-Gaussian (LG) vortex beams, where PJs are equally spaced azimuthally around the optical singularity, the presented vortex beams have PJs embedded at arbitrary azimuthal angles. By designing a particular forked grating and displaying it on a spatial light modulator, this type of vortex beam is experimentally generated. As with conventional forked grating, the designed grating produces vortex beams with opposite orbital angular momentum (OAM) sign in the first diffraction order. By measuring the relative orientation of the intensity profile of these OAM beams in the first diffraction order, the position of the PJs on the wavefront of a vortex beam with ℓ =2 can be determined. This type of vortex beam could have potential applications in various fields of photonics, especially in optical communications based on optical vortices.