Analysis of Steady-State Brillouin Nonlinearity in High-Power Fiber Lasers

In the present work, a theoretical analysis of the first-order of stimulated Brillouin scattering (SBS) in a double-clad (DC) ytterbium (Yb)-doped silica fiber laser in unidirectional pumping mode is presented. An accurate simulation for calculating SBS nonlinearity is performed by considering the coupled differential rate equations for pump, signal and Stokes powers, as well as population inversion under the initial and boundary conditions in a typical all fiberbased laser with kW-range. In order to improve the laser operation and increase the laser efficiency, the dependence of different parameters of the laser cavity such as active fiber length, fiber core diameter, dopant concentration, output mirror reflectivity at signal wavelength, as well as the laser linewidth on the Brillouin threshold power has been studied. In addition, numerical analysis has been compared with the approximate analytical solution presented to emphasize the validity of modeling. As a result, the proposed laser design can generate up to 2.5 kW of output power without the onset of SBS.