Effects of system pointing error and turbulence media anisotropy on the propagation of a perfect Laguerre-Gaussian vortex beam

Abstract

We investigate the influences of the system pointing errors, oceanic turbulence, and transceiver parameters on the perfect Laguerre-Gaussian(PLG) in an optical propagation system with M-order quadrature amplitude modulation(M-QAM). The model of the ABER for turbulent seawater propagation systems with pointing errors is created in Rytov approximation. The evolution of ABER under different modulation order M of QAM, signal-to-noise ratio (SNR) of the transceiver systems, and turbulent parameters of seawater shows with the increase of system pointing errors, there is a pointing error value corresponding to the conversion of modulation mode from 4-QAM to256-QAM of the system with the lowest ABER, and this conversion point is related to the aperture value of the transceiver of the system. The propagation systems with high-order modulation QAM and large-aperture optical transceivers have higher tolerance of system pointing error than those of low-order modulation QAM and small-aperture transceivers. The pointing error tolerance of the system with low PLG's radial order, low OAM topological charge, and high SNR of transceiver is larger than that of the system with high PLG's radial order, high OAM topological charge, low SNR of transceiver system. The PLG vortex has a better tolerance to pointing errors than the Bessel Gaussian beam.