SBS mitigation with multi-tone amplification- a theoretical model

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.