Average capacity and ABER for perfect optical vortex system in weakly to strongly turbulent oceans

Based on the modified Rytov method, the reception probability spectrum, average bit error rate (ABER), and average channel capacity of the perfect optical vortex (POV) optical system using quadrantal amplitude modulation (QAM) are derived by introducing the mutual coherence function of POV in weak to strong turbulent seawater. The relationship between eddy topological charge, seawater turbulence characteristic parameters, optical system performance parameters, reception probability spectrum the bit error rate, and the average capacity of the POV optical system is numerically analyzed. The following important results are obtained: in long-distance turbulent seawater, the conclusion that the radius of bright ring POV remains almost constant in short-distance standing water and running water is still valid. 4-QAM is more suitable for signal modulation of the POV system in moderate to strong turbulent seawater. The increase of the vortex ring will lead to the increase of the crosstalk degree between vortex modes and the bit error rate of the POV system. Medium to strong turbulence changes the properties that the transmission ability of POV vortex signal mode in non-turbulent media is independent of the topological charge of the vortex. The transmission performance of vortex signals of the POV optical system can be improved by choosing a smaller half-beamwidth of signal, a higher ring radius to the half-beamwidth ratio of the signal, a lower topological charge of vortex mode, a longer signal wavelength, and higher SNR of the optical system.