In-service blind transceiver calibration for long-haul non-dispersion managed systems

In-service transceiver calibration is necessary for hot pluggable modules to achieve optimal component performance, especially for high baud rate and high order modulation systems. Here, two 4 x 2 complex-valued equalizers operating at twice symbol rates are designed before and after carrier phase recovery to compensate Rx and Tx imbalance, respectively. Transceiver gain imbalance, phase imbalance and skew could be derived from the converged two equalizers taps. The proposed scheme is evaluated in a 42 GBaud PDM-16QAM system through 900-km standard single-mode fiber transmission. The experimental results show that the accuracies of gain, phase and skew measurements are greater than 0.1 dB, 0.2 deg. and 0.1 ps for the receiver, 0.2 dB, 0.4 deg. and 0.6 ps for the transmitter.