High power pump and signal combiner for backward pumping structure with two different fused fiber bundle designs by means of pretapered pump fibers.

Abstract

We report on two high power backward (6 + 1) × 1 pump and signal combiners with different optical designs based on end-pumping technique, each achieving more than 95% coupling ratio of signal light, 98% coupling ratio of pump light, and a total pump power of 2.95kW. Both designs solve the problem of non-uniform arrangement in asymmetric fiber bundles by the pretreatment of the pump fibers and signal fiber. Asymmetric fiber bundle in backward pump and signal combiners means the pump input fibers and signal output fiber have different cladding diameters. Two 3D simulation models were built to calculate the parameters of the fused fiber bundles for matching the mode field diameter between the signal input and the output fibers. Both optical designs of backward combiners were developed based on the beam propagation method and confirmed by experimental results.