Hardware-Efficient Adaptive Equalization and Carrier Phase Recovery for 100-Gb/s/λ-Based Coherent WDM-PON Systems

We propose a 100-Gb/s/λ-based coherent wavelength division multiplexing passive optical network system with a hardware-efficient digital signal processing (DSP), which features a new adaptive equalization (AEQ) and carrier phase recovery (CPR). While a conventional AEQ consists of four finite impulse response (FIR) filters in a butterfly configuration, we propose to split the conventional AEQ into a 1-tap butterfly FIR filter and two nonbutterfly FIR filters to halve the number of long FIR filters, sacrificing compensation of differential group delay (DGD). To reduce the complexity of the CPR, we propose to replace the phase estimation of one of the two polarizations by the less computation-intensive estimation of the phase offset between the two polarizations, since the phase noises of the two polarizations are almost identical. With the proposed AEQ and CPR, the number of multiplications is reduced by 41% compared with more conventional cases. An 80-km downstream transmission experiment with 32 Gbaud dual-polarization quadrature phase-shift keying (DP-QPSK) signals and offline DSP showed that our proposed system achieved a loss budget of 40.7 dB capable of supporting 8 ONU splits over an 80-km single-mode fiber span. The tolerance to DGD is evaluated by numerical simulation, and the results revealed that the penalty from DGD was less than the margin obtained in the transmission experiment.