Stimulated Brillouin Scattering Suppression With a Chirped Laser Seed: Comparison of Dynamical Model to Experimental Data

Abstract

A numerical model is developed to simulate stimulated Brillouin scattering (SBS) in high power single-mode fiber amplifiers. The time dependent model incorporates both laser and Stokes wave amplification and initiates the Brillouin scattering from thermal phonons. A frequency chirped laser is used as the seed to suppress SBS. Experiments with Yb-doped fiber amplifiers show good agreement with the modeling. Using experimentally determined parameters, the model is used to predict chirp requirements for multi-kilowatt amplifiers with tens of meters of delivery fiber. A comparison is made between a chirped seed source and random phase modulation for SBS suppression.

16 kW Yb fiber amplifier using chirped seed amplification for stimulated Brillouin scattering suppression

“…An intuitive explanation of the SBS suppression due to a chirped seed has been given in our previous work, and a numerical model has shown good agreement with experiment [16]. If the chirp is linear and the Brillouin gain gν is Lorentzian, the gain for every frequency component of the Stokes wave will follow a Lorentzian in space.…”

“…This will occur when 2βτ > Δν B . For a 25 m fiber, this effect will begin to occur for chirps β > 6.6 × 10 16 Hz∕s. The effect was large enough for us to notice at β 2.6 × 10 17 Hz∕s.…”

“…The model described previously [16] has been modified to include the effect of temperature on the speed of sound, which in turn affects the Brillouin frequency, bandwidth, and the strength of the thermal phonon "noise" from which the stimulated scattering grows. Changes in the Brillouin frequency are accompanied by changes in the acoustic wave vector, the acousto-optic coefficient, and the elasto-optic coefficient.…”

High power monolithic linearly polarized narrow linewidth single mode fiber laser at 1064 nm

“…The power scaling for the narrow linewidth fiber lasers is challenging due to the limitation primary from the stimulated Brillouin scattering (SBS). The SBS threshold significantly depends on the laser linewidth [1]. For the single frequency lasers, the linewidth is much narrower than the bandwidth (~50 MHz) of the Brillouin gain spectrum.…”

“…Up to 608 W single frequency fiber lasers were developed although some bulky optics were adopted in these lasers [2][3][4]. When the laser linewidth is broadened to GHz level, the SBS threshold will be enhanced significantly and the power scaling is easier accordingly [1]. Most recently, A. Flores et al demonstrated a 1.17 kW GHz-level-linewidth fiber amplifier [5].…”