Experimental Demonstration and Practical Application of a Real-Time Full-Duplex Underwater Wireless Optical Communication Transceiver

With the development of the underwater Internet of Things (UIoTs), underwater wireless optical communication (UWOC), with characteristics of wide bandwidth, high transmission rate, and low time delay, has become a promising technology for high-speed underwater wireless communication. In this paper, the current status of real-time UWOC systems was reviewed in detail at first, and then a Gbps-level real-time full-duplex underwater wireless optical communication transceiver (RTFD-UWOCT) based on laser diodes (LDs) was proposed. Furthermore, the performance of the RTFD-UWOCT was validated through water tank experiments, swimming pool experiments, and sea trials. In a swimming pool with water attenuation coefficients being measured as 0.5311 dB/m (0.1233 m(-1)) at 455 nm and 0.4761 dB/m (0.1096 m(-1)) at 525 nm, respectively, we demonstrated a 30-m/1.2-Gbps full-duplex UWOC link. Moreover, a 35-m/1.0-Gbps uplink and a 40-m/1.0-Gbps downlink in the simplex operation mode were achieved. Afterward, to further explore the robustness of the RTFD-UWOCT to turbulence, a 20-m/1-Gbps full-duplex UWOC link was realized under bubble-induced turbulence generated by an air pump and bubble stones with an air flow rate of 8.5 L/min. Finally, considering the practicality and reliability, a sea trial was conducted at a depth of 10 m in Sun Bay, Sanya, China. A 5-m/0.25-Gbps real-time UWOC link in a real seawater channel was achieved with extremely high attenuation coefficients of 5.6794 dB/m (1.3077 m(-1)) at 455 nm and 6.0717 dB/m (1.3981 m(-1)) at 525 nm, respectively. Nevertheless, considering the link budget in a pure seawater channel, it is estimated that our proposed RTFD-UWOCT could achieve a 54.27-m/1.2-Gbps real-time full-duplex UWOC. The above results verified that the RTFD-UWOCT can achieve a full-duplex communication link in the short-to-medium range at Gbps levels, which is also expected to meet the high-speed communication needs of UIoTs in the future.