Propagation of radial phase modulated vortex beams in atmospheric turbulence

Abstract

In practical free-space optical (FSO) communications, mitigating turbulence effects is crucial. This paper introduces radial phase modulation as a method to protect the signal's orbital angular momentum (OAM) in turbulent FSO. The results demonstrate that selecting appropriate modulation parameters can improve communication quality, particularly in stronger turbulence. However, a drawback is that radial phase modulation also increases crosstalk near the signal mode in strong turbulence. We further investigate the effects of radial phase modulation in two OAM multiplexing cases: mode broadcasting and intensity superposition. The results demonstrate that by employing radial phase modulation, both intensity and phase divergence, as well as beam wander, can be effectively reduced. In addition, the peaks in the OAM spectra enable easy identification of the signal modes. Moreover, even with a limited aperture in the detector, both channel capacity and transmission distance can be enhanced. These findings have potential applications in practical FSO communication in atmospheric turbulence.