Suppressing stimulated Raman scattering by adopting a composite cavity in a narrow linewidth fiber oscillator

The master oscillator power amplifier structure has been widely employed to realize high-power and narrow-linewidth output in fiber lasers. However, the stimulated Raman scattering (SRS) effect would appear in high-power operation and even become an important limitation on further power scaling, especially when the seed lasers are based on a fiber Bragg grating (FBG) pair. In order to improve SRS suppressing ability, a composite cavity structure was demonstrated by employing an additional wide-bandwidth low-reflectivity FBG outside the conventional oscillator. After passing through a piece of 50 m SMF-28e fiber, thanks to the improved temporal stability of the composite oscillator, the proportion of Raman Stokes light dropped dramatically compared with the proportion in a conventional fiber oscillator. This composite cavity design could provide a simple and compact approach for SRS suppression in a high-power narrow-linewidth fiber laser system.