Proof of concept for adaptive sequential optimization of free-space communication receivers

© 2020 Optical Society of America]. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modifications of the content of this paper are prohibited. In a downlink scenario, the performance of laser satellite communications is limited due to atmospheric turbu- lence, which causes fluctuations in the intensity and the phase of the received signal, leading to an increase in bit error probability. In principle, a single-aperture phase-compensated receiver, based on adaptive optics, can over- come atmospheric limitations by adaptive tracking and correction of atmospherically induced aberrations. However, under strong turbulence situations, the effectiveness of traditional adaptive optics systems is severely compromised. We have developed an alternative intensity-based technique that corrects the wavefront by iter- atively updating the phases of individual focal-plane speckles, which maximizes the power coupled into a single- mode fiber. Here, we present the proof of concept for this method. We show how this technique offers around 4 dB power gain with fewer than 60 power measurements under strong turbulence conditions. It delivers a good performance in different turbulent regimes, and it shows robustness against severe deterioration of the signal-to-noise ratio.