Ge-codoped laser fibers for mitigating Stimulated Brillouin Scattering in high power fiber amplifiers

Rare-earth doped fibers for high power fiber amplifiers normally have a small refractive index difference between the core and inner cladding, but have a larger core diameter than conventional telecom fibers. We take advantage of this feature as well as the difference between the optical and acoustic waveguides and proposed several fiber designs to mitigate Stimulated Brillouin Scattering (SBS) to produce higher output powers. The numerical modeling showed that an increase in SBS threshold by 3-5 dB can be achieved using Ge-codopant while maintaining diffraction limited beam quality. The study also highlights the need to take into account the effects of minor refractive index profile variation in evaluating SBS performance.