Mode instabilities: Physical origin and mitigation strategies

The phenomenon of mode instabilities has quickly become the most limiting effect for a further scaling of the average power of fiber laser systems. It is important to get a detailed understanding of its physical origin in order to develop efficient mitigation strategies. In this work we present an analysis of the different physical processes that give rise to mode instabilities and reveal that thermally-induced non-adiabatic waveguide changes play a key role. With this insight in the physical processes underlying mode instabilities a semi-analytic formula is obtained and several mitigation guidelines will be presented and discussed.