Abstract

Relative intensity noise (RIN) transfer from the pumps is one of the most important impairments in Raman fibre lasers, in particular when themselves need to be used for signal amplification. In recent times, randomly distributed feedback Raman fibre lasers without a cavity, in which Rayleigh backscattering provides the feedback [1], have become increasingly popular both in sensing and communications applications. In previous analysis of the RIN transfer in random lasers [2-3], we observed oscillations in the RIN transfer figure for frequencies higher than a well-known value. Here we show how, in some particular cases, these oscillations can lead to the maximum of RIN transfer occurring for a frequency different from zero, and indeed to maximum RIN transfer to be displaced towards high frequencies, in spite of the filtering effect associated to the faster averaging of pump oscillations at higher frequencies in counter-propagating Raman amplification. We theoretically analyse this potentially harmful situation in which the RIN transfer for low frequencies is lower than for an intermediate band. In order to observe this phenomenon, we consider a span of fibre pumped at 1365 nm from one end where two counter-propagating Stokes signals at 1455 nm are generated inside the fibre. We numerically obtain the RIN transfer for the signal co-propagating with the pump.

© 2015 IEEE