Novel SBS suppression scheme for high-power fiber amplifiers

A new scheme for suppression of Stimulated Brillouin Scattering (SBS) in high power fiber amplifiers is proposed where the fiber core diameter varies along the fiber length. The fiber has an ultra-large core diameter at most locations to suppress SBS, while at certain locations the core is relatively small to reduce bending sensitivity. A numerical model based on SBS rate equations is used to compare the SBS threshold of a uniform fiber to that of a fiber with variations in physical properties vs position. The model takes into account SBS gain dependence on temperature distributions as well as inhomogeneous spectral broadening due to NA variations. The modeling results show that the SBS threshold can be increased significantly when the seed power, fiber length, pump configuration, and fiber parameters are optimized. As a result, a single frequency fiber amplifier can generate up to 1 kW output power without the onset of SBS. Furthermore, the nonuniform fiber allows a high power amplifier to be packaged in a much more compact enclosure than an ultra-low NA fiber based amplifier.