Suppression of stimulated Brillouin scattering in single-frequency multi-kilowatt fiber amplifiers

Abstract

Previous research has shown that temperature gradients along a fiber can broaden the Stimulated Brillouin Scattering (SBS) gain profile and thereby increase the SBS threshold. However, within practical temperature ranges this method has been limited to SBS thresholds of a few hundred Watts. It is also well known that strain gradients applied to a fiber can broaden the SBS resonance. To suppress the SBS threshold to kW levels in fiber amplifiers of length ~5 m requires broadening of the SBS resonance width to ~1 GHz, which can be achieved with a strain of 1 - 2%. Although tensile strain is generally limited by fiber failure to less than ~1%, compressive strain has been employed to the level of many percent in a number of applications in the tuning of fiber Bragg gratings. We demonstrate the effect of SBS gain broadening and suppression by strain gradients at high power (~ 190 W) for the first time to our knowledge, and explore scaling of this method to kW output levels.