Numerical insights into noise amplification of high-energy mid-infrared supercontinuum generation in normal dispersion multimode fibers

We report on the noise properties of high-energy mid-infrared supercontinuum (MIR-SC) generation in normal dispersion multimode fibers from the numerical perspective. Unlike previous investigations centered on single-mode MIR-SC, the intermodal energy transfer and nonlinear coupling effects can offer a promising strategy to enhance first-order phase coherence of certain wavelengths at specific fiber modes, even amidst the coherence degradation of overall multimode MIR-SC. Lumped processing techniques are employed here to demonstrate that the noise amplification in multi-modes is still primarily due to the stimulated Raman scattering (SRS) effect. This leads to the emergence of “incoherent cloud formation” and “incoherent optical wave breaking”, similar to those observed in single-mode fibers. Increasing the pump technical noise from 0.1 % to 1 % significantly shortens the lumped coherence length $L_C$ and exacerbates the influence of incoherent broadening dynamics competing with coherent dynamics, resulting in MIR-SC being a strong consistency in the collapse evolution of amplitude noise and phase coherence. To minimize this noise amplification and achieve high-energy low-noise MIR-SC in practical applications, it is essential to use short-pulse pumping with low amplitude noise, ensuring that $L_C$ ≫ $L_{\mathrm{OWB}}$ (where $L_{\mathrm{OWB}}$ denotes the optical wave breaking length).