  Multimode optical fibres are enjoying a renewed attention, boosted by the
urgent need to overcome the current capacity crunch of single-mode fibre
systems and by recent advances in multimode complex nonlinear optics [1-13]. In
this work, we demonstrate that standard multimode fibres can be used as
ultrafast all-optical tool for transverse beam manipulation of high power laser
pulses. Our experimental data show that the Kerr effect in a graded-index
multimode fibre is the driving mechanism for overcoming speckle distortions,
leading to a somewhat counter-intuitive effect resulting in a spatially clean
output beam robust against fibre bending. Our observations demonstrate that
nonlinear beam reshaping into the fundamental mode of a multimode fibre can be
achieved even in the absence of a dissipative process such as stimulated
scattering (Raman or Brillouin) [14,15].
