Strategic modal management for enhanced stimulated Raman scattering in optical fibers

Raman fiber lasers have attracted significant attention for their unique ability to generate high-power output at specific wavelengths. Theoretically, the quantum loss associated with the nonlinear Stokes frequency shift in Raman scattering is lower than that from energy level transitions in conventional ytterbium-doped lasers, suggesting that Raman lasers should achieve higher conversion efficiencies. However, in practice, the efficiency of high-power Raman lasers often fails to reach these theoretical limits, with power scaling being impeded by 2 nd order Raman effects. In this article, we delve into the dynamics of stimulated Raman scattering within few-mode fibers, offering an in-depth analysis of the underlying physical mechanisms from multiple perspectives. Our research combines theoretical analysis with experimental research, covering the frequency domain, spatial domain, and nonlinear behavior. The experimental findings indicate that strategically increasing the proportion of higher-order modes in the injected light can enhance the conversion efficiency of the Raman process and effectively suppress higher-order Raman and four-wave mixing nonlinear processes. This study provides profound theoretical insights and practical guidance, contributing significantly to the ongoing development and optimization of Raman laser technology.