Simulation of narrow generation in a Raman fiber laser with random distributed feedback

Numerical simulation of generation of a random fiber laser proves that a model, considering only major physical effects, is capable of reproducing the characteristic line spectrum consisting of narrow localized spectral modes near the generation threshold. Lifetime of narrow spectral modes is shown to amount to tens of full cavity pass times or 1 ms by order of magnitude, that well corresponds to experimental observations. It was ascertained that addition of technical noise by implementation of a random phase of backscattered wave does not change the generation regime significantly. Possibility of narrow generation well above the threshold is demonstrated in case of negligible nonlinear effects. Essential role of Rayleigh backscattering in its formation is emphasized by comparison with corresponding ideal fiber amplifier with no feedback, characterized under the same conditions by smooth spectrum.