Stimulated brillouin scattering in double-clad thulium-doped fiber amplifier

In this paper, the effect of Stimulated Brillouin Scattering(SBS) on the laser output performance in a 2 mu m thulium -doped fiber amplifier was analyzed theoretically. The optical mode distribution, the effective refractive index, the effective mode field area, and the normalized frequency of the double -clad thuliumdoped fiber at 793 nm pump wavelength and 1.9-2.1 mu m laser waveband were studied. The stimulated Brillouin scattering characteristics, including the Brillouin frequency shift and the Brillouin gain spectrum, in the double -clad thulium -doped fiber were numerically simulated in the laser waveband of 1.9-2.1 mu m. The influence of stimulated Brillouin scattering on the laser output performance of thulium -doped fiber amplifiers was investigated using the theoretical model of stimulated Brillouin scattering in gain fibers. In the DTDF-10/130 double -clad thulium -doped fiber, a continuous wave with power of 100 W and wavelength of 793 nm is used as a pump to amplify a continuous signal wave with wavelength of 2 mu m and power of 0.01 W. The maximum output powers of the signal wave are 25.27 W, 31.08 W and 34.06 W when the pump power filling factors are 0.01, 0.02 and 0.03, respectively. The corresponding optimal double -clad fiber lengths are 2.66 m, 2.02 m and 1.75 m. Additionally, the Stokes optical powers generated by the stimulated Brillouin scattering are 1.68 W, 1.39 W and 1.14 W, respectively. The results show that the double -clad fiber with large pump power filling factor in the thulium -doped fiber amplifier can effectively reduce the fiber length, thus to minimize the influence of stimulated Brillouin scattering on the output power of the signal laser. The numerical model can optimize the fiber length of the fiber amplifier, which is of great significance to improve experimental efficiency and reduce experimental costs.