SBS mitigation with multi-tone amplification: a theoretical model

Abstract

Two approaches to two-and three-tone seeding of high power ytterbium-doped fiber amplifiers are investigated using a symbolic and numerical code that solves a two point boundary problem consisting of a 12x12 system of nonlinear differential equations. Optimization of amplifier action is considered in relation to the two most dominant nonlinear effects: stimulated Brillouin scattering and four-wave mixing. One approach uses a large wavelength separation among the input seed beams, while in the other approach the seeds are separated by precisely twice the Brillouin shift. It is found that for both techniques significant increase in amplifier output can be obtained, although for the latter case a substantial amount of power is generated in the four-wave mixing sidebands.

Model of the Self-Q-Switching Instability of Passively Phased Fiber Laser Arrays

“…Since we believe to have established in this paper a causal connection between nonlinearity and a predicted Q-switching instability, we suggest that mitigation of the latter can to a large measure be accomplished by known means of mitigating other nonlinear effects. These include the use of shorter fiber lengths, the reduction of the effective amplifier length by means of counter pumping [33], the use of large mode area (LMA) fibers [34], and multi-tone amplification [35], or other means. Some of those methods would also reduce the magnitude of the coupling elements, nm S , such as by reduction of external path differences and nonlinearity of the amplifiers.…”