Influence of seed power on mode instabilities in high power fiber amplifiers

TL;DR

This paper presents a theoretical study on how seed power influences mode instabilities in high power fiber amplifiers, considering gain saturation and photodarkening effects, supported by experimental validation.

Contribution

It introduces a semi-analytical model that explains the nonlinear dependence of mode instability thresholds on seed power, incorporating photodarkening effects.

Findings

Threshold behavior varies with seed power due to gain saturation and photodarkening.

Model predictions align well with experimental results.

Photodarkening significantly impacts mode instability thresholds.

Abstract

We use a semi-analytical model of stimulated thermal Rayleigh scattering to present theoretical study of seed power on mode instability with the presence of photodarkening. The behavior of mode instabilities as a function of seed power has been investigated. The nonlinear dependence of the threshold with lower seed powers is ascribed to the influence of gain saturation while the reduction behavior of the threshold with higher seed powers is put down to the effects of photodarkening, which agrees well with the experimental results.