Ricerc@Sapienza

Nonlinear mode coupling in multimode optical fibers leads to complex self-organization phenomena. These are associated with the emergence of extreme waves, in the form of stable nonlinear coherent attractors characterized by low-order transverse mode patterns. The periodic or quasi-periodic oscillations of the multimode beam intensity due to mode beating lead to light scattering into a series of spectral sidebands spanning multiple octaves.

We overview recent advances in the nonlinear optics of multimode optical fibers, including ultrabroadband sideband and supercontinuum generation, Kerr and Raman beam cleanup, modal modulation instabilities, four wave mixing, and second harmonic beam cleaning.

We experimentally study the interplay of Kerr and Raman beam cleanup in multimode air-silica microstructure optical fiber. The interplay of modal four-wave mixing and Raman scattering leads to high-brightness multimode supercontinuum

By controlling pump modes injected in the normal dispersion regime of few-mode graded index optical fiber, we investigated intermodal noise-seeded modulation instability and generation of highly-detuned cascaded intermodal four-wave mixing sidebands.

We overview recent experimental results of beam self-cleaning observed in various types of multimode fibers. We analyze the output spatial beam shapes and their connection with the refractive index profile of the fibers.