Arbitrary Bias Point Control Technique for Optical IQ Modulator Based on Dither-Correlation Detection

A novel automatic bias control (ABC) method which could lock an optical IQ modulator at arbitrary bias points is proposed and experimentally demonstrated for the first time. In the proposed method, the sequences and parameters of the used dither signals and the switch of the applied bias voltages are specially designed to minimize the influence of the power coupling between three MZMs in optical IQ modulator and the nonideal extinction ratios. By this way, precise electro-optical characteristic parameters of these three MZMs can be obtained by calculating the relevancy of the produced dither signals and the optical output signal. Based on these obtained parameters, any-bias-locking operation could be achieved via a feedback control loop. The accuracy and stability of the proposed ABC scheme are experimentally verified by using 1 GHz sine signals and 6 Gbaud single-carrier QPSK signals, and the accuracy of the proposed ABC algorithm is about 0.4° due to the limit of DAC resolution. Moreover, thanks to this ABC scheme, a simple and stable 29.2 GHz millimeter wave generation with SNR of 30 dB by optical frequency quadrupling technique could be realized without any optical or electrical filter.