  Recent remarkable progress in wave-front shaping has enabled control of light
propagation inside linear media to focus and image through scattering objects.
In particular, light propagation in multimode fibers comprises complex
intermodal interactions and rich spatiotemporal dynamics. Control of physical
phenomena in multimode fibers and its applications is in its infancy, opening
opportunities to take advantage of complex mode interactions. 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 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 show for the first time versatile spectrum manipulations including shifts,
suppression, and enhancement of Stokes and anti-Stokes peaks. These
demonstrations illustrate the power of wave-front shaping to control and
optimize nonlinear wave propagation.
