50 Gb/s PAM4 underwater wireless optical communication systems across the water–air–water interface [Invited]

A 50 Gb/s four-level pulse amplitude modulation(PAM4)underwater wireless optical communication(UWOC)system across the water-air-water interface is demonstrated in practice.In practical scenarios,laser beam misalignment due to oceanic turbulence degrades performance in UWOC systems.With the adoption of a reflective spatial light modulator(SLM)with an electrical controller,not only can the laser be arbitrarily adjusted to attain a water-air-water scenario,but oceanic engineering problems can also be resolved to establish a reliable UWOC link.Brilliant bit error rate performance and clear PAM4 eye diagrams are attained by adopting a Keplerian beam expander and a reflective SLM with an electrical controller.This proposed PAM4 UWOC system presents a feasible state that outperforms existing UWOC systems due to its feature providing a high-speed water-air-water link.