Analysis of nonlinearity mitigation using phase-sensitive optical parametric amplifiers.

Benjamin Foo,Mikael Mazur,Peter A Andrekson,Magnus Karlsson,Kovendhan Vijayan

doi:10.1364/oe.27.031926

Abstract

Phase-sensitive optical parametric amplifiers (PSAs) can provide low-noise optical amplification while simultaneously mitigating nonlinear distortions caused by the Kerr effect. However, nonlinearity mitigation using PSAs is affected by link parameters, and imperfect link design results in residual nonlinear distortions. In this paper, we use first-order perturbation theory to describe these residual nonlinear distortions, and develop a way to mitigate them using a modified third-order Volterra nonlinear equalizer (VNLE) in the receiver. Using numerical simulations, we show that our proposed VNLE reduces the residual nonlinear distortions in links using in-line PSAs for several combinations of symbol rates and modulation formats, and can increase the maximum transmission distance by up to 80%. We also perform a proof-of-concept experiment and confirm that our modified VNLE can mitigate the residual nonlinear distortions on a 10-Gbaud 16QAM signal after transmission through a 10×80-km link with in-line PSAs.

Highlights

The transmission performance of modern long-haul optical communications systems is limited by additive white Gaussian noise (AWGN) from optical amplifiers and distortions caused by the nonlinear Kerr effect [1,2,3]
We considered the transmission of 10, 28, and 50-Gbaud single-polarization signals modulated with either quadrature-phase-shift keying (QPSK) or 16-ary quadrature amplitude modulation (16QAM)
In the signal/idler path, an optical processor (OP) ensured that the signal and idler were launched into the span with the same power, and an Erbium-doped fiber amplifiers (EDFAs) followed by a variable optical attenuator (VOA) controlled the signal launch power into the span (PIN)

Summary

Introduction

The transmission performance of modern long-haul optical communications systems is limited by additive white Gaussian noise (AWGN) from optical amplifiers and distortions caused by the nonlinear Kerr effect [1,2,3]. The optical fiber channel is nonlinear, and increasing the signal power causes systems to run into the limitation imposed by the Kerr effect [1]. The nonlinear Kerr effect is a change in the refractive index of the optical fiber that depends on the instantaneous power of the signal [5]. As this is a deterministic effect, distortions from the Kerr nonlinearity can be compensated with sufficient information about the link and the transmitted signal. This has led to the development of various nonlinearity compensation (NLC) techniques in both the digital [6,7,8,9], and optical [10,11,12] domains

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Conclusion