Long-Term and Real-Time High-Speed Underwater Wireless Optical Communications in Deep Sea

The seafloor observation network can perform all-weather, long-term, continuous, real-time, and in-situ observation of the ocean by combining various observation methods including cabled seafloor nodes and self-contained nodes, as well as mobile platforms, where reliable and long-term high-speed underwater wireless communication becomes an essential requirement. Recently, underwater wireless optical communication (UWOC) has emerged as a highly promising solution and is rapidly becoming a research hotspot for meeting this requirement. In this article, we demonstrate an experiment with the application of a high-speed UWOC system for the deep sea seafloor observation network. To the best of our knowledge this is the first long-term real-time deep-sea UWOC link with bitrate as high as 125 Mb/s. Between two nodes of 30 m distance and at a depth of 1650 m, two-way Ethernet UWOC links are achieved with 125 Mb/s direction-adjustable green light link and 6.25 Mb/s nonline-of-sight (NLOS) blue light link. High quality video transmission of 8K 30 FPS and 4K 120 FPS are achieved through a high-speed 125 Mb/s green light link, with 100 percent peak signal-to-noise ratio (PSNR) agreement, showing the capability of transmitting high-quality lossless videos. Our 30-day long-term measurement results show that the BER performance of both 125 Mb/s and 6.25 Mb/s links is lower than 10– ⁵ , proving the stability and reliability of this UWOC system at a depth of 1650 m. By measuring the light attenuation of a deep-sea water sample, the maximum transmission distance for the green and blue light links are estimated to be 117.7 and 128.3 m with geometry loss, which can be extended to 231.6 and 337.5 m without geometry loss. With the first long-term and real-time UWOC system in the deep sea, we believe this demonstration can provide valuable experience for further UWOC studies and converged ocean observation networking with cabled and cable-less observation platforms.