Hydrodynamic transverse condensation in multimode optical fibers

Spatiotemporal light beam dynamics in multimode opti- cal fibers (MMFs) has emerged as a fertile domain of scientific research in nonlinear optics and physics]. Intriguing spatiotemporal wave propagation phenomena such as multimode optical solitons, and parametric instabilities leading to ultra-wideband sideband series [3] have only been experimentally observed in MMFs over the last few years. Among these, we are interested to study here the phenomenon of spatial self-condensation or self-cleaning of multimode light beams in MMFs. It is well known that linear beam propagation in MMFs is affected by random mode coupling, which leads to highly irregular speckled intensity patterns at the fiber output, even when the fiber is excited with a high quality, diffraction-limited input beam