Spiral spectrum of the phase singularity beam in the source plane and atmospheric turbulence

Abstract

The phase singularity beam has a unique wavefront phase structure—a screw dislocation (optical vortex) or edge dislocation—which is closely related to the orbital angular momentum (OAM). Screw dislocation refers to the phase change of integer multiples of 2π around a point, while edge dislocation refers to the existing π phase shift along a curve in the wavefront phase distribution. In this study, we derived the OAM detection probability expression and mode probability density expression of the phase singularity beam propagating through atmospheric turbulence. These expressions were used to examine the spiral spectrum and the OAM mode probability density of the phase singularity beam. It was determined that the phase singularity beam carrying a noncanonical optical vortex or an edge dislocation has more than one OAM state, whereas the phase singularity beam carrying a canonical optical vortex has only one OAM state. In atmospheric turbulence transmission, atmospheric disturbances will cause crosstalk between OAM states. The larger is the detection probability of the OAM state at the source plane, the closer is the maximum value of the OAM mode probability density throughout the transmission process to the beam center. The conclusions obtained have important applications in optical communications.