Model-Based Machine Learning for Joint Digital Backpropagation and PMD Compensation

TL;DR

This paper introduces a model-based machine learning method called LDBP-PMD for joint digital backpropagation and polarization-mode dispersion compensation in dual-polarization optical systems, achieving near-PMD-free performance without prior PMD knowledge.

Contribution

It proposes a novel, hardware-friendly, distributed PMD compensation approach using learned digital backpropagation, capable of adapting to changing PMD conditions without prior system knowledge.

Findings

Converges within 1% of peak dB performance after 428 iterations

Achieves only 0.30 dB SNR below PMD-free case

Successfully retrains after abrupt PMD changes

Abstract

In this paper, we propose a model-based machine-learning approach for dual-polarization systems by parameterizing the split-step Fourier method for the Manakov-PMD equation. The resulting method combines hardware-friendly time-domain nonlinearity mitigation via the recently proposed learned digital backpropagation (LDBP) with distributed compensation of polarization-mode dispersion (PMD). We refer to the resulting approach as LDBP-PMD. We train LDBP-PMD on multiple PMD realizations and show that it converges within 1% of its peak dB performance after 428 training iterations on average, yielding a peak effective signal-to-noise ratio of only 0.30 dB below the PMD-free case. Similar to state-of-the-art lumped PMD compensation algorithms in practical systems, our approach does not assume any knowledge about the particular PMD realization along the link, nor any knowledge about the total accumulated PMD. This is a significant improvement compared to prior work on distributed PMD compensation, where knowledge about the accumulated PMD is typically assumed. We also compare different parameterization choices in terms of performance, complexity, and convergence behavior. Lastly, we demonstrate that the learned models can be successfully retrained after an abrupt change of the PMD realization along the fiber.