Novel automatic bias voltage control for travelling-wave electrode optical modulators

A novel method to control the bias voltage of LiNbO₃ travelling-wave electrode Mach-Zehnder modulators for multigigabit per second NRZ signals is proposed. This method uses the difference in modulator bandwidth for copropagating and counterpropagating signals against the travelling modulation field. This method successfully controls a modulator without distorting the output optical waveform.