Fast, Accurate, and Low-Disturbance Automatic Bias Control for Coherent Optical Transmitter Using Dither Vector Mapping Monitoring

A fast, accurate automatic bias control (ABC) scheme with low disturbance for optical IQ modulators is proposed by using the dither-vector-mapping monitoring (DVMM) technique. The proposed scheme solely necessitates vector length calculation via addition and subtraction operations and obviates the necessity of employing a direct digital synthesis (DDS) module, in contrast to conventional ABC schemes. By this means, the proposed scheme demonstrates reduced algorithmic complexity and a faster convergence rate, requiring only 0.3∼0.5 s to track and lock from a random bias point to a linear bias point, about 30 times faster than current commercial products. Moreover, unlike the commonly used single-tone dither signal (STDS), the PRBS-based dither signal in this scheme is broadband and has lower power spectral density and peak power at the same power level. Therefore, it not only induces lower nonlinear distortion in the transmitted signal but also has strong noise resistance, contributing to good control accuracy and robustness. The performance of DVMM-based ABC and STDS-based ABC is evaluated in 40/20 Gbaud 16/64 QAM coherent optical transmission systems, showing that DVMM can effectively reduce the bit error rate (BER) and has superior transmission performance.