Active transverse mode instability mitigation for high power fiber amplifiers apparatus, methods, and applications

Abstract

Apparatus and methods for mitigating transverse mode instabilities (TMI) in high power fiber amplifiers that does not depend on active feedback loops. The apparatus and method involve the modulation of the amplitude and/or phase of selected spatial mode components of an input signal beam to increase the TMI threshold of the amplifier. Once the desired modal adjustments are made, the beam is input to a mode multiplexer whereupon an optimized output beam can be input to the active fiber of the amplifier system. By increasing the TMI threshold of the amplifier, the amplifier can be operated at higher power before TMI sets in. A control stage of the fiber amplifier system includes (a) a (seed) beam splitting section; (b) an amplitude and phase control component; and (c) a mode multiplexer that maps multiple individual signal beams to different fiber modes.