Evolution of phase singularities of Laguerre–Gaussian Schell-model vortex beam

Abstract

In free space optical communication, the type and quality of the light source are very important. In this paper, we introduce a vortex class of partially coherent sources of Schell type with a Laguerre–Gaussian Schell-model vortex (LGSMV) beam, which is the product of the dark hollow Laguerre–Gaussian Schell-model beam (2013 Opt. Lett. 38 91) passing through a spiral phase modulator. We study the characteristics of the intensity distribution of the LGSMV beam in the far-field plane. The analytical expression of the cross-spectral density function of a LGSMV beam in the far-field plane is derived. We demonstrate an implicit rule that the number of phase singularities of an LGSMV beam is equal to the original topological charge, when the order p increases to a certain extent. This novel rule provides an effective method for detecting the topological charge of an LGSMV beam in applications such as free space optical communication and optical manipulation.