The Impact of Transceiver Noise on Digital Nonlinearity Compensation

Daniel Semrau,Polina Bayvel,Lidia Galdino,Robert I Killey,Domanic Lavery

doi:10.1109/jlt.2017.2777452

Abstract

The efficiency of digital nonlinearity compensation (NLC) is analyzed in the presence of noise arising from amplified spontaneous emission noise (ASE) as well as from a non-ideal transceiver subsystem. Its impact on signal-to-noise ratio (SNR) and reach increase is studied with particular emphasis on split NLC, where the digital back-propagation algorithm is divided between transmitter and receiver. An analytical model is presented to compute the SNR's for non-ideal transmission systems with arbitrary split NLC configurations. When signal-signal nonlinearities are compensated, the performance limitation arises from residual signal-noise interactions. These interactions consist of nonlinear beating between the signal and co-propagating ASE and transceiver noise. While transceiver noise-signal beating is usually dominant for short transmission distances, ASE noise-signal beating is dominant for larger transmission distances. It is shown that both regimes behave differently with respect to the optimal NLC split ratio and their respective reach gains. Additionally, simple formulas for the prediction of the optimal NLC split ratio and the reach increase in those two regimes are reported. It is found that split NLC offers negligible gain with respect to conventional digital back-propagation (DBP) for distances less than 1000 km using standard single-mode fibers and a transceiver (back-to-back) SNR of 26 dB, when transmitter and receiver inject the same amount of noise. However, when transmitter and receiver inject an unequal amount of noise, reach gains of 56% on top of DBP are achievable by properly tailoring the split NLC algorithm. The theoretical findings are confirmed by numerical simulations.

Highlights

D IGITAL nonlinearity compensation (NLC) offers a great potential in overcoming the limit in optical communication systems imposed by fiber nonlinearity [1]–[3]
It was demonstrated that the gain of split NLC and the optimal split ratio are strongly dependent on whether TRX noise or amplified spontaneous emission noise (ASE) noise beating dominates
It was found that split NLC yields negligible gain compared to digital back-propagation (DBP) for distances below 800 km, when the transceiver noise is distributed between transmitter and receiver

Summary

INTRODUCTION

D IGITAL nonlinearity compensation (NLC) offers a great potential in overcoming the limit in optical communication systems imposed by fiber nonlinearity [1]–[3]. The performance difference between transmitter-side and receiver-side NLC lies only in the periodic arrangement of the optical amplifiers along the link [15] This is due to over/under-compensated ASE noise-signal interactions (hereafter “ASE noise beating”) that strongly depend on the specific location where each ASE noise contribution is introduced. Apart from transmitter and receiver-side NLC, an implementation has been proposed where the virtual link is divided between transmitter and receiver, which is referred to as split NLC or split DBP [15]–[17] This approach minimizes the residual ASE noise beating and yields at least 1.5 dB improvement in SNR compared to conventional DBP, assuming full-field compensation (NLC applied jointly to all channels) and the absence of transceiver noise. III): One where the transmitter and receiver introduce an equal amount of noise and another where an unequal amount of noise is introduced

ANALYTICAL MODEL

The impact of transceiver noise beating

Unequal transmitter and receiver noise contribution

CONCLUSION