An underwater wireless optical communications (UWOC) system using different non-return to zero (NRZ) modulation schemes is proposed. Dual X- and Y-polarized Laguerre–Gaussian (LG) modes {LG[0,3], LG[1,3]} are realized at 10 Gbit/s data rate. It is found that the system using LG[1,3] offers 4.2 m range by using non-chirped NRZ modulation at −21.7 dBm receiver sensitivity and it can sustain 4.5 m distance with 1.7 mrad divergence, 0.1 dB transmitter and 0.5 dB receiver loss. Compared to existing UWOC systems, this design offers optimum performance with 8.2–9.5 µm photodiode (PD) width, −11.47 dB gain and −22.46 dBm signal and −79.10 dBm noise at receiver under clear and costal ocean scenarios.