Phase and Channel Estimation for High-Capacity Phase-Asynchronous Mode-Division Multiplexing Multiple-Input Multiple-Output Free-Space Optical Communications in Strong Turbulent Channels

In this paper, we propose a novel pilot-aided phase and channel estimation algorithm for coherent mode-division multiplexing multiple-input multiple-output free-space optical communication system. This algorithm enables the implementation of advanced multiple-input multiple-output decoders, leading to a significantly better bit error rate performance. This algorithm also supports phase-asynchronous light sources at each transmit and receive channel, significantly reducing the hardware requirements. Moreover, it has low computational complexity and Cramér-Rao lower bound approaching estimation performance. In our proof-of-concept experiment, we employed 10 decorrelated channels to achieve a record-high 689.2 Gbit/s/wavelength line rate in strong turbulence, verifying the feasibility of our phase and channel estimation algorithm.