Abstract: A multicore fiber-to-single core fiber adapting device, also referred a fan-in/fan-out (FIFO) device. More specifically, an optical fiber system comprising a multicore fiber, a tapered glass device that it is configured to connect a multicore fiber to a multiple single core fiber, and/or single mode fibers, advantageously having one or more protective layers to protect the tapered device. Associated methods of manufacture.

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.