Raman-accelerated power depletion of the fundamental mode in a few-mode fiber in the visible spectral range

This study unravels the underlying physical mechanisms responsible for the power-dependent depletion of the fundamental mode in few-mode fibers. Utilizing a holographic mode decomposition technique, our experiments reveal an accelerated amplification of higher-order modes at the expense of the LP01 mode. This process modifies the initial modal fractions and ultimately yields an intensity-null profile from a superposition of degenerate modes. Notably, simulations indicate that purely Kerr-driven thermalization models fail to capture these effects. Instead, phase-insensitive intermodal Raman scattering acts as a crucial seed, with differential Raman gain modulating a Kerr–Raman instability that drives spatiotemporal energy dynamics, altering our understanding of spatial self-organization in high-power fiber systems.