Polarization crosstalk canceller for forward-pumping distributed Raman amplification

This paper proposes a novel polarization crosstalk canceller (PCC) based on receiver digital signal processing (DSP) in polarization di-vision multiplexed digital coherent transmission utilizing forward-pumping distributed Raman amplification (DRA). The PCC consists of 1-tap adaptive filters with a butterfly configuration controlled by the recursive least square algorithm. The PCC offsets the crosstalk between two polarization tributaries caused by the time-varying polarization fluctuation due to the relative inten-sity noise of the forward-pumping sources. The proposed PCC is applied to the long-haul dual-polarization QPSK transmission experiment with forward-pumping DRA, and confirmed to improve the transmission performance.