SRS-Induced Spatial-Spectral Distortion and Its Mitigation Strategy in High-Power Fiber Amplifiers

Abstract

The spatial-spectral evolution properties of laser beam in the presence of stimulated Raman scattering (SRS) effect have been studied in large mode area (LMA) fiber. With the employment of long/short pass filters, spatial evolution of the signal and Raman light has been studied individually. After the onset of SRS, the simultaneous optimizing of signal light and degrading of Raman light was observed, which has been attributed to the SRS effect of multimode laser beams in LMA fiber. The spectral evolution characteristics indicated that the SRS effect in LMA fiber will trigger other nonlinear effects, mainly inter-modal four-wave-mixing effect and cross-phase-modulation induced modulation instability. Furthermore, the impacts of bending strategy and multimode LMA fiber on SRS-induced spatial-spectral distortion have also been studied, which shows that the SRS-induced mode distortion can be suppressed by increasing the fiber size while the bending strategy plays a limited role.