Dither-free Auto Bias Control Technique for In-service Optical IQ modulator Using Reference Pulsed Light

We propose a dither-free auto bias control technique for IQ modulators utilizing two pulsed reference lights. This technique does not dither the signal light after the startup sequence is complete. Therefore, no penalty is caused by the dithering during a transmission service. The bias conditions can be monitored by the built-in optical power monitor inside the IQ modulator, without using an external high-speed optical power monitor. Experimental results show that each bias voltage precisely and quickly converged to its optimal value despite bias drift due to temperature change. Measured Q-factor shows degradation of the 16QAM signal was negligible.