Study on the Impact of Nonlinearity and Noise on the Performance of High-Capacity Broadband Hybrid Raman-EDFA Amplified System

We experimentally demonstrated the transmission of 312 × 35 GBd DP-256QAM over 9 × 70 km spans using hybrid distributed Raman-EDFA (HRE) amplifiers with a continuous 91 nm gain bandwidth. A total throughput of 120 Tbit/s over 630 km is demonstrated, with anet achievable information rate after SD-FEC of 10.99 bit/symbol. An extensive, theoretical investigation of the noise contributions originating from amplifier, transceiver subsystem and fiber nonlinearity were carried out using the Gaussian noise model in the presence of inter-channel stimulated Raman scattering (ISRS GN model). The ISRS GN model accounts for arbitrary, wavelength dependent signal power profiles along fiber spans, which is vital for the modeling of ultra-wideband transmission, particularly for hybrid Raman-amplified links. The analysis serves to quantify the relative noise contributions and explain the performance achieved. It was found that, due to the low noise HRE amplifier and a transmission distance of 630 km, the noise originating from the transceiver sub-system imposed a penalty of 6 dB in SNR. For this system, the transceiver noise is, therefore, the main limitation to the system throughput.