100 m full-duplex underwater wireless optical communication based on blue and green lasers and high sensitivity detectors

In this paper, in order to improve the practicability and performance of the underwater wireless optical communication (UWOC), we propose a full-duplex (FD) UWOC system based on blue–green wavelength division, which make full use of the low-loss transmission window of water. Narrowband optical filters corresponding to the blue and green wavelengths are employed to eliminate self-interference caused by the backscattering. Single-photon sensitivity photomultipliers (PMTs) are exploited to extend the communication range. The impairment introduced by limited bandwidth and nonlinearity of the devices is compensated by post equalizers. Finally, an FD UWOC system reaching a data rate up to 200-Mbps at a distance of 100 m is demonstrated in a standard swimming pool, which is competitive both in range and data rate among the reported explorations of FD UWOC system. By using a nonlinear equalizer based on the memory polynomial model, the data rates are enhanced by 60-Mbps and 140 Mbps for the blue and green links compared with hard decision, respectively. By measuring the minimum optical power at which the bit error ratio (BER) is lower than the forward error correction (FEC) threshold, and combining with the attenuation coefficient of water as well as the geometric loss caused by the beam divergence, we predict that the proposed FD UWOC system can achieve 200 Mbps over 120 m or 100 Mbps over 139 m underwater transmission. Finally, we analyze and estimate the performance of the FD UWOC system in practical seawater.