Influence of signal bandwidth on mode instability threshold of fiber amplifiers

TL;DR

This paper investigates how the bandwidth of the signal influences the mode instability threshold in fiber amplifiers by analyzing the impact of signal linewidth on stimulated thermal Rayleigh scattering gain.

Contribution

It introduces a theoretical framework linking signal linewidth to mode instability thresholds, including equations for various pulse types and chirp conditions.

Findings

Signal linewidth reduction decreases STRS gain

Coherence time shorter than mode walk-off reduces instability

Derived equations applicable to short pulses and chirped signals

Abstract

We show how signal linewidth affects the gain of stimulated thermal Rayleigh scattering (STRS) which is responsible for 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 modes LP$_{01}$ and LP$_{11}$. We derive equations for short pulses, linear chirps, and general periodic cases.