Joint Polarization Tracking and Equalization in Real-Time Coherent Optical Receiver

We experimentally demonstrate a real-time polarization tracking and equalization method based on the state of polarization detection from the adaptive finite impulse response (FIR) filter coefficients in a polarization division multiplexed (PDM) coherent optical communication system. By calculating the variation of the polarization within a time interval, the polarization rotation speed can be evaluated. In a field-programmable gate array (FPGA), a feedback structure for polarization rotation speed detection and FIR coefficients update can be built up. In this feedback structure, the update coefficient of the filter will be adjusted to an optimal value with the change of detection result. The experimental results show that the establishment of this feedback structure improves the polarization tracking ability in the real-time coherent optical receiver.