Toward Optimizing Partial Spatially Coherent Beams for Free Space Laser Communications

摘要

A performance metric is proposed as a general measure for optimizing the transverse coherence length l_c of a partial spatially coherent beam for a given communication scenario. The expression is essentially the mean intensity minus the standard deviation of the intensity and we seek to maximize this quantity. It is preliminarily verified by the probability of fade with log-normal distribution model under the weak turbulence condition. We also examine it as a function of l_c using wave optics simulations and compared these results with the relationships predicted by analytic theory under weak to medium-strong turbulence conditions. Our results verify there exists a unique coherence length that can optimize the receiver beam quality. After calculating the probability of fades of the optimal partially coherent beam and the fully coherent beam and comparing them with the wave optics simulation results, good agreement was observed.