Robust atmospheric FSO communication receiver based on the coherent combination of spatial modes: an experimental evaluation

The experimental assessment of a novel all-optical FSO communication receive device based on a spatial mode demultiplexer and a photonic integrated coherent combiner, is reported. The device collects light from the spatial modes coupled into the input multimode fiber and coherently recombines these modes into an output single-mode fiber via a binary-tree integrated photonic circuit. It was evaluated in FSO transmission laboratory experiments featuring an atmospheric propagation channel emulator. The BER performance of a pre-amplified, OOK direct-detection receiver were measured at 10 Gbps, under various disturbance conditions and strengths. Efficient coupling into the receiver input was shown to be maintained resulting in almost constant BER. Low BER floors and limited detection sensitivity penalties were observed. The feasibility of the proposed FSO receiver is proven, together with its ability to provide higher collection efficiency and greater robustness to phase and intensity disturbances than standard SMF receivers.