Improved underwater wireless optical communication using a passively mode-locked VECSEL

Abstract

This paper presents improved underwater wireless optical communication (UWOC) based on a 490 nm passively mode-locked vertical-external-cavity surface-emitting laser (VECSEL) with the repetition rate of 1.46 GHz and the pulse width of 2.25 ps. After conducting a comprehensive evaluation of the performance characteristics of quasi-cyclic low-density parity-check (QC-LDPC) coding and pulse-position modulation (PPM) in relation to bit-error-rate (BER) and communication capacity across different signal-to-noise ratios (SNRs), a passively mode-locked VECSEL based UWOC system is designed and experimentally performed. The UWOC system employs the QC-LDPC encoding technique and PPM modulation scheme that are most suitable for the system. Compared with the case without QC-LDPC, the minimum received optical power with coding is improved by 3.5 dBm, and the SNR with coding is improved by 0.4 dB under condition of 256-PPM and forward error correction (FEC) threshold of 3.8×10−3. Meanwhile, compared with the UWOC system using a continuous-wave (CW) VECSEL as the light source, the attenuation coefficient of the UWOC system based on the mode-locked VECSEL is decreased by 0.04 m-1, and the BER of the mode-locked VECSEL based UWOC system is decreased by 0.3 dB.