Longitudinal mode dynamics in SOA-based random feedback fiber lasers

We experimentally demonstrate that single-mode operation of an SOA-based random fiber laser is only possible in pulsed regime at driving currents close to the threshold, whereas multimode regime dominates under higher SOA currents. Theoretical simulations support random frequency spacing of the laser modes to be due to residual stress on the optical fiber. Pulsed regime is shown to be due to randomly driven Q-switching induced by a scintillation effect in the Rayleigh backscattered light, which effectively translates as a time-varying cavity loss. Mode lifetimes of similar to 1 ms and narrow linewidths ranging from 4 to 7 kHz were experimentally observed. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement