Experimental demonstration of a frequency-domain Volterra series nonlinear equalizer in polarization-multiplexed transmission

Fernando P Guiomar,Jacklyn D Reis,Armando N Pinto,Gabriella Bosco,António L Teixeira,Andrea Carena

doi:10.1364/oe.21.000276

Abstract

Employing 100G polarization-multiplexed quaternary phase-shift keying (PM-QPSK) signals, we experimentally demonstrate a dual-polarization Volterra series nonlinear equalizer (VSNE) applied in frequency-domain, to mitigate intra-channel nonlinearities. The performance of the dual-polarization VSNE is assessed in both single-channel and in wavelength-division multiplexing (WDM) scenarios, providing direct comparisons with its single-polarization version and with the widely studied back-propagation split-step Fourier (SSF) approach. In single-channel transmission, the optimum power has been increased by about 1 dB, relatively to the single-polarization equalizers, and up to 3 dB over linear equalization, with a corresponding bit error rate (BER) reduction of up to 63% and 85%, respectively. Despite of the impact of inter-channel nonlinearities, we show that intra-channel nonlinear equalization is still able to provide approximately 1 dB improvement in the optimum power and a BER reduction of ~33%, considering a 66 GHz WDM grid. By means of simulation, we demonstrate that the performance of nonlinear equalization can be substantially enhanced if both optical and electrical filtering are optimized, enabling the VSNE technique to outperform its SSF counterpart at high input powers.

Highlights

Thanks to coherent detection, digital equalization of linear fibre impairments can nowadays be performed with negligible penalty
Recurring to experimental data, we have demonstrated the high performance of a dualpol Volterra series nonlinear equalizer (VSNE) in different propagation scenarios
The dual-pol VSNE has shown to attain the maximum accuracy of its split-step Fourier (SSF) counterpart

Summary

Introduction

Digital equalization of linear fibre impairments can nowadays be performed with negligible penalty. The ultimate limits of fibre capacity are set by nonlinearities and their interaction with noise. The development of efficient nonlinear compensation algorithms is of utmost importance. The issue of nonlinear compensation has been most commonly approached through digital backward propagation (DBP) employing split-step Fourier (SSF) methods 1. New algorithms based on Volterra series theory have been reported either in time 2 or frequency-domain 3. In 3, an intra-channel Volterra series nonlinear equalizer (VSNE) applied in frequency-domain has been proposed and assessed through numerical simulations. The VSNE algorithm can be beneficial for real-time implementation due to its parallel structure, while maintaining very high equalization performance even at 2 samples per symbol 3

Methods

Results

Conclusion