Recent progress in controlling light propagation in multimode fibers in the linear regime, opened new opportunities for multimode fiber endoscopy. However, nonlinear light propagation in multimode fibers comprises complex intermodal interactions and rich spatiotemporal dynamics. In this work, we demonstrate a wave-front shaping approach for controlling nonlinear phenomena in multimode fibers. Using a spatial light modulator at the fiber’s input and a genetic algorithm optimization, we control a highly nonlinear stimulated Raman scattering cascade and its interplay with four wave mixing via a flexible implicit control on the superposition of modes that are coupled into the fiber. We demonstrate versatile spectrum manipulations that could be used to generate a multi-wavelength, tunable source. The wavefront shaping control allows spectral shifting and modal tuning. A theoretical analysis of modal phase matching in graded index multi-mode fibers is presented and we suggest potential bio-imaging applications.
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