Fibre-amplifier-free coherent free-space FM optical communications with a >80-dB link budget enabled by photonic-crystal surface-emitting lasers

We demonstrate the first PCSEL-based coherent free-space optical communication. Utilizing the PCSEL's frequency chirp and coherent detection, we directly generate watt-class FM signals and achieve link budgets of 83 and 78 dB at gross rates of 0.5 and 1 Gbps, respectively, without fibre amplifiers.