Design and Optimization of Two-Stage Bias Control for DD-MZM-Based Coherent Optical Modulation

This paper presents an optimized control framework for generating quadrature phase-shift keying (QPSK) optical signals using dual-drive Mach-Zehnder modulators (DD-MZMs). QPSK modulation in high-speed optical systems demands precise control of parameters like bias and peak-to-peak (P2P) voltages to ensure stable signal output and low bit error rates (BER). To address this, we introduce a two-stage automatic voltage control (TAVC) algorithm designed to track and optimize MZM and MZI bias voltages in real-time, even under environmental disturbances such as temperature fluctuations and device aging. Theoretical models are developed to quantify phase bias voltage jitter effects on BER, providing insights into selecting optimal P2P voltage offset values based on photodetector (PD) noise levels. Simulation results validate the proposed framework's effectiveness in achieving minimal BER and robust signal stability. This work contributes to advancing control methodologies for high-speed optical communications, paving the way for reliable QPSK signal generation in noise-prone environments.