**Raman Amplification Optimization in Short-Reach High Data Rate Coherent Transmission Systems †**

**Mingming Tan 1,\*, Md Asif Iqbal 2, Tu T. Nguyen 1,3, Paweł Rosa 4, Lukasz Krzczanowicz 1,5, Ian. D. Phillips 1, Paul Harper 1 and Wladek Forysiak 1**


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† This manuscript is extension version of the conference paper: Tan, M.; Iqbal, M.A.; Krzczanowicz, L.; Phillips, I.D.; Harper, P.; Forysiak, W. Optimization of Raman Amplification Schemes for Single-Span High Data Rate Coherent Transmission Systems. In Proceedings of the CLEO: Science and Innovations 2021, San Jose, CA, USA, 9–14 May 2021.

**Abstract:** We compared the transmission performances of 600 Gbit/s PM-64QAM WDM signals over 75.6 km of single-mode fibre (SMF) using EDFA, discrete Raman, hybrid Raman/EDFA, and firstorder or second-order (dual-order) distributed Raman amplifiers. Our numerical simulations and experimental results showed that the simple first-order distributed Raman scheme with backward pumping delivered the best transmission performance among all the schemes, notably better than the expected second-order Raman scheme, which gave a flatter signal power variation along the fibre. Using the first-order backward Raman pumping scheme demonstrated a better balance between the ASE noise and fibre nonlinearity and gave an optimal transmission performance over a relatively short distance of 75 km SMF.

**Keywords:** Raman amplification; optical fibre communication
