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.

52 m/9 Gb/s PAM4 plastic optical fiber-underwater wireless laser transmission convergence with a laser beam reducer

A 52 m/9 Gb/s four-level pulse amplitude modulation（PAM4） plastic optical fiber（POF）-underwater wireless laser transmission（UWLT） convergence with a laser beam reducer is proposed. A 52 m/9 Gb/s PAM4 POFUWLT convergence is practically demonstrated with the application of a laser beam reducer to reduce the collimated beam diameter. A 50 m graded-index（GI）-POF is employed as an underwater extender to efficiently enhance the coverage of UWLT. The performances of PAM4 POF-UWLT convergence in view of bit error rate（BER） and eye diagrams improve with the decrease of the collimated beam diameter because of the small amount of light absorbed by clear ocean water. Competent BER and eye diagrams（three independent eye diagrams） are achieved over a 50 m GI-POF transmission with a 2 m clear ocean water link.