CC BY 4.0Jauregui Misas, CesarCesarJauregui MisasTu, YimingYimingTuKholaif, Sobhy E.Sobhy E.KholaifMöller, FriedrichFriedrichMöllerPalma Vega, GonzaloGonzaloPalma VegaHaarlammert, NicolettaNicolettaHaarlammertWalbaum, TillTillWalbaumSchreiber, ThomasThomasSchreiberLimpert, JensJensLimpert2026-01-192026-01-192026https://publica.fraunhofer.de/handle/publica/503599https://doi.org/10.24406/publica-710710.1016/j.yofte.2025.10449610.24406/publica-71072-s2.0-105023083932In this article we look at the newest developments in the understanding and mitigation of TMI in single-core fibers. This includes recent quantitative measurements that reveal the dependence of the TMI threshold on the modal content of the seed, systematic measurements on the dependence of the TMI threshold on the fiber core size, as well as the study of TMI in PM fibers including a novel passive mitigation strategy and the static modal energy transfer recently observed in these fibers.entrueFiber amplifierThermal effectsTransverse mode instabilityjournal article