Mitigation of Fiber Nonlinearity Using a Digital Coherent Receiver

TLDR

Coherent detection with receiver‑based DSP has recently enabled mitigation of fiber nonlinear effects. The study investigates the performance benefits of a backpropagation algorithm for PDM‑QPSK and PDM‑QAM16. Receiver performance is characterized using a digital backpropagation algorithm with varying nonlinear step size to determine an upper bound on intrachannel nonlinear suppression in a single‑channel system. The study finds that optimal step sizes are 160 km for PDM‑QPSK and 80 km for PDM‑QAM16, and that optimal launch power increases by 2 dB and 2.5 dB respectively, yielding Q‑factor gains of 1.6 dB and 1 dB, underscoring the benefit of nonlinear compensation for higher‑order modulation.

Abstract

Coherent detection with receiver-based DSP has recently enabled the mitigation of fiber nonlinear effects. We investigate the performance benefits available from the backpropagation algorithm for polarization division multiplexed quadrature amplitude phase-shift keying (PDM-QPSK) and 16-state quadrature amplitude modulation (PDM-QAM16). The performance of the receiver using a digital backpropagation algorithm with varying nonlinear step size is characterized to determine an upper bound on the suppression of intrachannel nonlinearities in a single-channel system. The results show that for the system under investigation PDM-QPSK and PDM-QAM16 have maximum step sizes for optimal performance of 160 and 80 km, respectively. Whilst the optimal launch power is increased by 2 and 2.5 dB for PDM-QPSK and PDM-QAM16, respectively, the Q-factor is correspondingly increased by 1.6 and 1 dB, highlighting the importance of studying nonlinear compensation for higher level modulation formats.