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

In the present work, a theoretical analysis of the first-order of stimulatedBrillouin scattering (SBS) in a double-clad (DC) ytterbium (Yb)-doped silica fiber laserin unidirectional pumping mode is presented.An accurate simulation for calculating SBS nonlinearity is performed by considering thecoupled differential rate equations for pump, signal and Stokes powers, as well aspopulation inversion under the initial and boundary conditions in a typical all fiberbasedlaser with kW-range.In order to improve the laser operation and increase the laser efficiency, the dependenceof different parameters of the laser cavity such as active fiber length, fiber corediameter, dopant concentration, output mirror reflectivity at signal wavelength, as wellas the laser linewidth on the Brillouin threshold power has been studied.In addition, numerical analysis has been compared with the approximate analyticalsolution presented to emphasize the validity of modeling.As a result, the proposed laser design can generate up to 2.5 kW of output powerwithout the onset of SBS.