Investigation of Nonlinear Effects in Multitone-Driven Narrow-Linewidth High-Power Amplifiers

In this paper, we investigate two approaches to multitone seeding of high-power ytterbium-doped amplifiers using a symbolic and numerical code that solves a two-point boundary problem. Optimization of amplifier action through wavelength separation and/or seed power ratios is considered in relation to the two most dominant nonlinear effects: stimulated Brillouin scattering (SBS) and four-wave mixing. One approach uses a large wavelength separation among the input signals, while the other approach entails that the wavelength separation is set to twice the Brillouin shift. Both techniques are shown to mitigate SBS effects, although for the latter case, four-wave mixing sidebands can carry a substantial amount of power.