Full-duplex underwater wireless optical communication with reflective modulation and coherent detection

We propose and experimentally demonstrate a full-duplex underwater wireless optical communication (UWOC) system with reflective modulation and coherent detection. A single 532 nm laser is used as the light source for both downlink and uplink data transmission. A highly sensitive silicon photomultiplier (SiPM) is used for the signal detection in the downlink with intensity modulation-direct detection (IM-DD), while the reflecting uplink signal is received using a dedicated time-division coherent detection (TDCD) scheme. We further apply digital signal processing (DSP) methods to mitigate uplink and downlink signal degradations caused by the imperfect characteristics of devices. The bit error rate (BER) performance of uplink and downlink data transmission with DSP is comprehensively investigated at different received power levels and data rates. The full-duplex data transmission performance of the proposed system is experimentally tested and analyzed. Results show that the full-duplex system with downlink/uplink data rates of 1 Gbps/0.2 Mbps and 1 Gbps/1.2 Mbps can achieve BERs lower than the forward error correction (FEC) limit at maximum channel attenuations of 43.7 dB and 6.49 dB, and the corresponding estimated maximum overall transmission distances in the pure sea water are 77.3 m and 26.7 m, respectively.