Field Demonstration of Turbulence-Resilient Self-Coherent Free-Space Optical Communications

We experimentally demonstrate a self-coherent free-space optical communications (FSOC) system based on the pilot-assisted scheme. By co-propagating the data-carrying beam with a continuous-wave pilot, the scheme reduces turbulence-induced losses in spatial coherence between the beams, which can adversely affect the performance of local oscillator (LO)-based coherent systems. The system utilizes a single free-space photodetector and self-coherent detection based on the Kramers-Kronig receiver to minimize receiver hardware complexity. Using an 800 m free-space link, we transmit a 10 Gbit/s 16-QAM single polarization signal over real atmospheric turbulence. Additionally, we present a method for simultaneous characterization of the atmospheric channel by recording image sequences of the received laser spot. Results demonstrate the robustness of the system in moderate turbulence, and serve as the first field demonstration of this approach over a real free-space link.