Theoretical Analysis of the Mode Distortion Induced by Stimulated Raman Scattering Effect in Large-Mode Area Passive Fibers

By employing the mode decomposition method to study the relative mode evolution characteristics during the stimulated Raman scattering (SRS) process, a numerical model of the core-pumped Raman effect in few-mode fibers has been proposed, which provides an accurate tool to reveal the underlying physical mechanism of SRS-induced mode distortion. Mode distortion induced by the SRS effect in large-mode area passive fibers has been investigated numerically. It reveals that the few-mode SRS effect can result in an irreversible power transfer from the signal fundamental mode (FM) to signal high order modes (HOMs), which is a static phenomenon, different from the SRS-induced transverse mode instability. To the best of our knowledge, it is the first time that the numerical results coincide with the experimental phenomenon. Simulation results also illustrate that the inter-mode wave-mixing effect among the signal FM and signal HOMs plays a key role in the signal power transfer. With the help of the numerical model, mitigation strategy by designing and using the Raman-gain-tailored fiber has also been proposed, which shows a clear advantage in suppressing SRS-induced mode distortion.