Underwater channel characteristics and wireless optical communications using a blue mode-locked semiconductor disk laser

An advanced light source at blue-green waveband is the key to improve the link-distance and communication performance of an underwater wireless optical communication (UWOC) system. This work presents the underwater channel characteristics and UWOC system using a blue semiconductor disk laser that passively mode-locked by a semiconductor saturable absorb mirror for the first time. The attenuation coefficients of the continuous-wave and mode-locked lasers under different concentrations of Maalox solution are studied, and the results indicate that the attenuation coefficients of the mode-locked laser are obviously lower than that of the continuous-wave laser. Then an UWOC system based on an acousto-optic modulator are constructed, and the water tank communication experiments are carried out by using quasi-cyclic low-density-parity-check coding and 64-pulse-position-modulation. Experimental results show that the bit error rates of the mode-locked laser are significantly lower than that of continuous-wave laser under the same Maalox solution concentration and same signal-noise-ratio. These results provide an attractive light source for practical long-distance UWOC.