Linear and Nonlinear Noise Characterisation of Dual Stage Broadband Discrete Raman Amplifiers

Md Asif Iqbal*, Mohammad A.Z. Al-Khateeb, Lukasz Krzczanowicz, Ian D. Phillips, Paul Harper, Wladek Forysiak

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


We characterise the linear and nonlinear noise of dual stage broadband discrete Raman amplifiers (DRAs) based on conventional Raman gain fibres. Also, we propose an optimised dual stage DRA setup that lowers the impact of nonlinear noise (generated in the amplifier) on the performance of a transmission link (with 100-km amplifier spacing). We numerically analyse the design of a backward pumped cascaded dual stage 100-nm DRA with high gain (∼20 dB) and high saturated output power (>23 dBm). We show that the noise figure (NF) of the dual stage DRA is mainly dominated by the first stage irrespective of the type of gain fibre chosen in the second stage, and we also demonstrate that optimising the length and the type of Raman gain fibre can have significant impact on the size of inter/intrasignal nonlinearities generated. Here, we report a theoretical model to calculate the nonlinear noise power generated in transmission spans with dual stage DRAs considering piecewise signal power evolution through the Raman gain fibres. The predicted signal-to-noise ratio (SNR) performances are calculated from the combined contributions from NF and nonlinear product power obtained using the proposed analytical model for transmission systems deployed with 100-km transmission span compensated by different dual stage DRAs. Finally, an optimised IDF 6 km-SMF 10 km dual stage configuration has been identified using the theoretical model, which allows maximum SNR of 14.6 dB at 1000 km for 1 THz Nyquist wavelength division multiplexed signal and maximum transmission reach of 3400 km at optimum launch power assuming 8.5 dB HD-FEC limit of the Nyquist PM-QPSK signal.

Original languageEnglish
Article number8723646
Pages (from-to)3679-3688
Number of pages10
JournalJournal of Lightwave Technology
Issue number14
Early online date28 May 2019
Publication statusPublished - 15 Jul 2019

Bibliographical note

© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.

This work was supported by the U.K. Engineering and Physical Sciences Research Council under Grants ToM3 (EP/M009092/1) and
PEACE (EP/L000091/1).


  • Nonlinear effects
  • optical amplifiers
  • optical fibre
  • optical fibre communication


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