Discussion of the direct detection Rx-power distribution as derived from intensity statistics and comparison with measurements

The intensity of a laser beam after propagation through turbulent media such as the atmosphere may follow different probability density functions (PDFs) depending on the fluctuation regime. For non-coherent receivers the aperture averaging effect reduces the power scintillation leading to a different PDF. Since the analytical approach of deriving the received power PDF knowing the joint-PDF of the intensity at more than just a few points becomes rapidly complex, we review here a much more simplified approach as well as a simulative approach. Both approaches are based on the results of scintillation theory. First, starting from the PDF of the intensity and its spatial correlation, aperture sub-areas can be defined over which the intensity is assumed equal and independent from other sub-areas' intensity. Under those conditions the power PDF is easily worked out. The validity of this method is evaluated according to the level of spatial correlation of the intensity. In a second method, intensity variables are sampled from the Rx-aperture and an approximation of the power PDF is obtained by generating multivariate correlated intensity values. Weak and strong fluctuation regimes are treated separately and the effects of different resolution of the input-intensity-field are discussed. In addition, this paper compares the predicted power characteristics to those deduced from experimental data where the intensity characteristics (PDF, spatial correlation) have been evaluated.