Full-field Real-Time Measurement of Ultrafast Soliton Fission

The real-time characterization of ultrafast dynamics is essential to the understanding of the underlying physics and in recent years there has been major interest into the measurement of complex instabilities. One important example of instability is associated with modulation instability, a key physical process underlying the emergence of localized structures such as the Peregrine soliton. It is only very recently that it has been possible to precisely characterize these dynamics in the laboratory with the development of real-time measurement techniques. All previous experimental studies have been made for the case of ideal modulation instability excited by a near continuous wave input but it is in fact much more common for modulation instability to develop under non-ideal conditions in a regime where the dynamics present mixed multiscale features of both nonlinear envelope evolution and modulation instability dynamics on the pulse envelope itself. Here, combining a broadband reference phase-stable field generated by self-phase modulation with Fourier-transform spectral interferometry (FTSI) [1] , [2] we characterize for the first time modulation instability dynamics of an ultrafast pulse leading to fission into its fundamental soliton constituents. Our experiments can characterize the associated complex field in real-time with 20 fs resolution, allowing to resolve the individual soliton structures emerging from the initial stage of modulation instability.