Free-carrier induced soliton fission unveiled by in-situ measurements in nanophotonic

Solitons are localized waves formed by a balance of focusing and defocusing effects. These
nonlinear waves exist in diverse forms of matter yet exhibit similar properties including
stability, periodic recurrence and particle-like trajectories. One important property is soliton
fission, a process by which an energetic higher-order soliton breaks apart due to dispersive or
nonlinear perturbations. Here we demonstrate through both experiment and theory that
nonlinear photocarrier generation can induce soliton fission. Using near-field measurements,
we directly observe the nonlinear spatial and temporal evolution of optical pulses in situ in a nanophotonic semiconductor waveguide. We develop an analytic formalism describing the
free-carrier dispersion (FCD) perturbation and show the experiment exceeds the minimum
threshold by an order of magnitude. We confirm these observations with a numerical
nonlinear Schro¨dinger equation model. These results provide a fundamental explanation and
physical scaling of optical pulse evolution in free-carrier media and could enable improved
supercontinuum sources in gas based and integrated semiconductor waveguides.