Influence of source parameters and atmospheric turbulence on the polarization properties of partially coherent electromagnetic vortex beams.

Abstract

In this paper, we introduce a vortex class of a partially coherent source of Schell type with an electromagnetic Gaussian Schell-model vortex (EGSMV) beam, which is the product of the partially coherent EGSM beam passing through a spiral phase modulator. The analytical expressions for the degree of polarization (DoP) and orientation angle of polarization (OAoP) of the EGSMV beam propagating through atmospheric turbulence are derived. The expressions are used to analyze the influence of topological charge, wavelength, and atmospheric turbulence on the DoP and OAoP of the EGSMV beam, and we come to some new conclusions. The larger the topological charge is, the bigger the dark spot in the center of the partially coherent EGSMV beam, the more dispersed the DoP distribution, and the wider the OAoP distribution are; therefore, there is more information received by the detector when the partially coherent EGSMV beam propagates in atmospheric turbulence. The longer the wavelength is, the smaller the near-surface refractive index structure constant and the larger the inner scale are and the more concentrated the DoP distribution is, but the influence of the outer scale is negligible. The number of petals, which is the shape of the OAoP distribution, is equal to just twice the topological charge. These results provide a theoretical basis for better control of coherent detection in optical communication when the partially coherent EGSMV beam propagating through atmospheric turbulence is used as the local oscillator in a wireless optical communication system.