Optimization of DP-M-QAM Transmitter Using Cooperative Coevolutionary Genetic Algorithm

We present a method for joint optimization of transmitter in-phase, quadrature and interpolarization time skew, amplitude mismatch, and bias voltages. The method is based on a cooperative coevolutionary genetic algorithm with fitness functions extracted from a directly detected reference quadrature amplitude modulation (QAM) signal generated at the transmitter. As a calibration method, it is able to find the values that will statically generate the best possible constellation. To the extent of the simulation investigations conducted, the algorithm is capable to calibrate time skews, bias voltages, IQ phase imbalances, and relative amplitude imbalances with standard deviation of residual error as low as 0.24 ps, 0.019 V, 0.56°, and 0.003, respectively, for a dual-polarization IQ modulator with V_π = 4 V and a 16-QAM reference signal operating at 16 GBd. An experimental demonstration is also reported.