Experimental validation of a statistical model of mode-diverse reception in coherent free-space optical communications

In this work, we present a statistical model for the turbulent atmospheric channel, which we study using the Monte Carlo method: With the help of the symmetric split-step method, we simulate the effect of the turbulent channel on the complex amplitude of a beam of light before considering the coupling to different single- and multi-mode fibers. Repeating these steps for numerous numerical realizations of the channel yields statistics on the coupling loss observed when detecting different numbers of modes at the FSO receiver. To verify the predictions of this channel model in the lab, we use off-axis digital holography to capture the complex amplitudes of light after traversing a turbulent atmosphere emulated in an optical turbulence generator (OTG). Investigating the coupling loss statistics obtained from these captures for the same fibers shows that the experimental data on the coupling loss reductions agrees with the predictions of our statistical model.