Electro-optic modulator bias point optimization by detecting its nonlinear behavior

In this paper, we present a study concerning the stabilization of an electrooptic modulator (EOM) by controlling its optical bias point. A digital proportional-integral-derivative (PID) controller using an auto-tuning algorithm has been developed with a PSOC microcontroller in order to keep the bias point at an optimal value. The evolution of the modulator characteristics can be followed through its nonlinear behavior by detecting the second harmonic of a low-frequency modulating signal. By such a bias point control of the EOM it is possible to compensate completely the effects of the modulator drift for duration of at least two hours.