Study on stimulated Raman scattering in fiber amplifier employing tapered Yb3+doped fiber

Tapered fiber is expected to effectively suppress nonlinear effects while ensuring excellent beam quality, and may achieve higher power output by breaking through the power limit of ordinary uniform size fiber. Base on the rate equations and the proposed three types of tapered fibers, a nonlinear theoretical model including spectrum, power and stimulated Raman scattering (SRS) is established. Using this model, the SRS characteristics of the three tapered fiber amplifiers are numerically simulated in the condition of keeping same total absorption coefficient of different fibers guaranteed. The simulation results show that the type I fiber has the worst suppression effect on SRS, and the convex type III fiber has the best suppression effect on SRS. When using the backward pumping method, the convex type II fiber can reach almost consistent suppression effect of the convex type III fiber. Theoretical studies show that the use of tapered ytterbium-doped fiber to build fiber amplifiers has a certain suppression effect on SRS in fiber amplifiers, and provides a reference for the selection of fibers in high-power fiber amplifiers.