Comparison of different Raman amplification schemes in long-span fiber transmission systems with double Rayleigh backscattering

In this letter, three Raman amplification configurations, which are bidirectional pumping scheme, backward pumping with mid-way isolators, and Raman plus erbium-doped fiber amplifier hybrid amplification, respectively, are optimized and compared in long-span (> 120 km) transmission systems including the impacts of double Rayleigh backscattering (DRB). Numerical results show that a balanced bidirectional pumping scheme can achieve the best performance for most practical conditions at identical nonlinearity. However, hybrid amplification will be a better choice when DRB noise is overwhelming.