Three fiber designs for mitigating thermal mode instability in high-power fiber amplifiers

An improved fiber amplifier model for simulating thermal mode instability (TMI) in high-power fiber amplifiers is developed. The model is applied to reveal new physics regarding the thermal physics that is critical to the TMI process, which are not the glass volume or the cooling method, but rather the transit path length of the quantum-defect-defined thermal peak in the fiber amplifier. The new physics and model analysis are applied to create a set of design rules to guide the development of new fiber types specifically for intrinsically mitigating TMI. These rules and the improved model are applied to three new fiber concepts for mitigating TMI in high-power fiber amplifiers. All three fiber types are shown to substantially increase the TMI threshold, up to a factor of 2 in some cases. In addition, all three new fiber classes offer ways to simultaneously increase the core diameter and the TMI threshold.