Nonlinear Noise of Low Transmission Penalty Dual-Stage Discrete Raman Amplifier

We experimentally characterize the linear and nonlinear performance of a >70 nm, dual-stage, 19.5 dB average net gain discrete Raman amplifier using different nonlinear fibres in the second stage. We propose an architecture built with a combination of IDF and SMF and compare its performance with amplifiers built with conventionally used nonlinear fibre types (IDF-IDF, IDF-DCF). The measured FWM product power shows the IDF-SMF architecture to generate less nonlinear interference when compared to other schemes. We test the amplifiers with
$5 \times 120$
Gb/s DP-QPSK WDM signals in a recirculating loop at 10 recirculations of 93.4 km SMF fibre, where the power sweep shows up to 2 dB optimum launch power difference, with the maximum
$Q^{2}$
factor varying by up to 1.6 dB. Using the optimum transmission point, we measure a
$Q^{2} = 8.8$
dB at 35 recirculations of 93.4 km transmission (3269 km) with the proposed IDF-SMF scheme, which is >460 km further than the other tested architectures. All characterized schemes performed similarly in the linear noise regime.