Impact of input FBG reflectivity and forward pump power on RIN transfer in ultralong Raman laser amplifiers

Relative intensity noise transfer from the pump to the signal in 2nd-order ultra-long Raman laser amplifiers for telecommunications is characterized numerically and experimentally. Our results showcase the need for careful adjustment of the front FBG reflectivity and the relative contribution of forward pump power, and their impact on performance. Finally, our analysis is verified through a 10 x 30 GBaud DP-QPSK transmission experiment, showing a large Q factor penalty associated with the combination of high forward pumping and high reflectivities.