Demonstration of 12.5 Mslot/s 32-PPM Underwater Wireless Optical Communication System with 0.34 Photons/Bit Receiver Sensitivity

High-capacity, long-distance underwater wireless optical communication (UWOC) technology is an important component in building fast, flexible underwater sensing networks. Underwater communication with light as a carrier has a large communication capacity, but channel loss induced by light attenuation and scattering largely limits the underwater wireless optical communication distance. To improve the communication distance, a low-power 450 nm blue continuous wave (CW) laser diode (LD)-based UWOC system was proposed and experimentally demonstrated. A communication link was designed and constructed with a BER of 3.6 × 10−3 in a total link loss of 80.72 dB in c = 0.51 m−1 water with a scintillation index (S.I.) equal to 0.02 by combining with 32-pulse-position modulation (32-PPM) at a bandwidth of 12.5 MHz and single photon counting reception techniques. The allowable underwater communication distance in Jerlov II (c = 0.528 m−1) water was estimated to be 35.64 m. The attenuation lengths were 18.82, which were equal at link distances of 855.36 m in Jerlov I (c = 0.022 m−1) water. A receiving sensitivity of 0.34 photons/bit was achieved. To our knowledge, this is the lowest receiving sensitivity ever reported under 0.1 dB of signal-to-noise ratio (SNR) in the field of UWOC.