Raman Fibre Laser Based Amplification in Long-haul/ Unrepeatered Coherent Transmission Systems

The paper reviews recent advances of Raman fibre laser (RFL) based amplification techniques in long-haul/unrepeatered coherent transmission systems. Different aspects of theRFL based amplification have been characterised, including signal power distributions and relative intensity noise (RIN). Various RFL based amplifier designs were evaluated in long-haul coherent transmission systems. The results showed that Fabry-Perot fibre laser based amplifier with two fibre Bragg gratings (FBGs) gave significant Q factor penalty using symmetrical bidirectional pumping, as the RIN of the signal was increased dramatically. However, random distributed feedback fibre laser based amplifier with one FBG can mitigate the RIN of the signal, which enables the use of bidirectional second order pumping and therefore gives the best transmission performance up to 7915 km. Furthermore, using random DFB fibre laser based amplifier has been proven to be effective to combat nonlinear impairment. In addition, unrepeatered transmission over >350 km fibre length using RFL based amplification technique has been demonstrated experimentally using DP-QPSK WDM signals.