Spatiotemporal Soliton Attractor in Multimode Graded-index Fibers

There is recently a considerable interest in nonlinear optical effects in multimode fibers (MMFs). Here we present the experimental evidence, supported by numerical simulations, that an initially excited multimode femtosecond soliton initially composed by few low-order transverse modes of a graded-index (GRIN) MMF irreversibly decays into a singlemode soliton carried by the fundamental mode of the MMF. Once formed, the singlemode soliton propagates stably over fiber lengths of up to 1 km, which corresponds to a record transmission distance, in a MMF, of 4600 modal dispersion distances, and 5600 chromatic dispersion lengths. This effect is of particular importance for technological applications, since it reveals that nonlinearity can counteract the effects of modal dispersion and random mode coupling, and enables a stable transport of high-spatial-quality beams over long distances by means of large area (when compared to singlemode fibers) MMFs. As a side aspect, our results invalidate theoretical predictions based on variational approaches, since the beam shape substantially evolves along the fiber, in such a way that the initial beam profile is not maintained [1] - [3] .