Optical solitons in multimode fibers: recent advances

Optical solitons in multimode fibers have been predicted 40 years ago and extensively investigated theoretically. Transmission experiments in nonlinear multimode fibers have gained renewed interest, motivated by their potential to extend the capacity of long-distance transmission systems; only in the last few years, new experiments have revealed unexpected properties of optical solitons propagating in graded-index and step-index multimode fibers, partially re-writing the existing theory. Here we provide an overview of the recent experimental, numerical and theoretical studies which revealed those new properties. It will be shown that multimode fiber solitons form with specific pulse width and energy dependent on the wavelength, and that they naturally evolve toward fundamental-mode Raman solitons. New soliton fission mechanisms, governed by the modal dispersion, will be explained. Possible applications in space-division multiplexed systems will be discussed. A recent thermodynamic approach to soliton condensation will be described.