Abstract

Average power scaling with excellent beam quality out of fibers is currently limited by a threshold-like degradation of beam quality at a certain power level caused by dynamic energy transfer from the fundamental mode to higher order modes [1]. This effect is called mode instabilities (MI) and it is generally agreed that MI is caused by thermally induced index gratings, where the heating due to photo-darkening might play an important role [2]. Here we investigate MI for a reduced mode overlap (RMO) fiber design, promising very low photo-darkening properties [3]. The investigations are related to passive mitigation strategies regarding scaling of the mode field diameter, bending and seed excitation.

© 2015 IEEE