Influence of signal bandwidth on mode instability thresholds of fiber amplifiers

摘要

We show how signal bandwidth affects the gain of stimulated thermal Rayleigh scattering (STRS) which is responsible for a transverse mode instability in fiber amplifiers. The gain is reduced if the coherence time of the signal is less than the group-velocity-induced walk off between the two interacting modes, usually LP_(01) and LP_(11). We derive expressions for the bandwidth required to suppress gain for short pulses, for periodically chirped continuous waves, and for general periodically modulated cases.