First Demonstration of 1Gb/s PAM4 Signal Transmission Over A 130m Underwater Optical Wireless Communication Channel with Digital Equalization

We use a single-mode pigtailed 520 nm laser diode (LD) and an avalanche photo detector (APD) to construct an underwater optical wireless communication (UOWC) system. A 1 Gb/ $s$ PAM4 signal is experimentally generated and transmitted over a 130 m underwater optical wireless channel while the maximum emitted optical power is 7.2 mW. A linear digital post-equalizer is adopted to combat the inter-symbol interference (ISI). To further improve the system performance, the impact of direct current to drive the LD is discussed concerning about the signal-dependent shot noise and a nonlinear digital pre-equalizer is also employed to mitigate the nonlinearity in the turn-on region of LD. The experimental results show that the BER performance can be improved from 2.4E - 1 to 8E - 4 and the corresponding transmitted optical power can be reduced from 7.2 mW to 5.71 mW.