Ricerc@Sapienza

We overview complex spatio-temporal propagation phenomena in nonlinear multimode optical fibers (MMFs) [1]. In the
anomalous dispersion regime, longitudinal periodic intensity oscillations of optical multimode solitons [2] lead to controlled
generation of ultra-wideband dispersive wave sidebands [3,4]. Whereas in the normal dispersion, sideband series from the
visible till the mid-infrared (MIR) are generated from parametric instability of continuous waves [5,6]. Before the onset of
temporal instabilities however, the Kerr effects leads to intriguing effect of spatial beam self-cleaning towards a well-defined
and robust bell-shaped transverse profile in graded-index (GRIN) MMFs [7]. The interplay with Raman scattering generates
spectrally flat, spatially single-mode supercontinua extending from the visible till the MIR from GRIN MMFs [8]. A
temporally resolved analysis reveals that significant (tenfold) temporal compression is achieved in the spectral sidebands [8].
Spatial Kerr self-cleaning was observed with increased efficiency in active, ytterbium doped MMF with a step-index profile
[9]. When optically poling a GRIN MMF, mutual self-cleaning of pump and second-harmonic beams was obtained [10].