Abstract
The nonlinear interaction of copropagating optical solitons enables a large variety of intriguing bound-states of light. We here investigate the interaction dynamics of two initially superimposed fundamental solitons at distinctly different frequencies. Both pulses are located in distinct domains of anomalous dispersion, separated by an interjacent domain of normal dispersion, so that group velocity matching can be achieved despite a vast frequency gap. We demonstrate the existence of two regions with different dynamical behavior. For small velocity mismatch we observe a domain in which a single heteronuclear pulse compound is formed, which is distinct from the usual concept of soliton molecules. The binding mechanism is realized by the mutual cross phase modulation of the interacting pulses. For large velocity mismatch both pulses escape their mutual binding and move away from each other. The crossover phase between these two cases exhibits two localized states with different velocity, consisting of a strong trapping pulse and weak trapped pulse. We detail a simplified theoretical approach which accurately estimates the parameter range in which compound states are formed. This trapping-to-escape transition allows to study the limits of pulse-bonding as a fundamental phenomenon in nonlinear optics, opening up new perspectives for the all-optical manipulation of light by light.
Highlights
The nonlinear interaction of copropagating optical solitons enables a large variety of intriguing bound-states of light
An exact sech × tanh–shaped “dipole-soliton” solution was derived lately16. Besides such single-pulse solitary wave solutions, various types of molecule-like bound states have been reported that consist of multiple pulses. This includes bound states consisting of two identical optical pulses separated by a fixed time-delay, realized through dispersion engineering for a standard N SE17, bound solitons arising in models of coupled N SEs18–25, bound solitons copropagating in twin-core fibers subject to higher-order dispersion26, and dissipative optical soliton molecule generated in passively mode-locked fiber laser27,28
Despite the higher orders of dispersion featured by Eq [1], the results reported in Fig. 3e are in good qualitative agreement with the interaction dynamics of initially overlapping, group-velocity mismatched solitons in a model of two nonlinearly coupled N SEs56
Summary
The nonlinear interaction of copropagating optical solitons enables a large variety of intriguing bound-states of light. A different kind of molecule-like bound state was reported that forms a single complex, consisting of two subpulses with roughly similar amplitudes but distinctly different center frequencies29 Such compound states are enabled by a propagation constant that allows for group-velocity matched copropagation of pulses in Scientific Reports | (2021) 11:11190. We study the interaction dynamics of two initially superimposed fundamental solitons at distinctly different center frequencies in terms of a propagation constant for which the group velocity dispersion (GVD) has downward parabolic symmetry Such a profile allows to parametrically define pairs of center frequencies at which the local dispersion parameters have the same absolute values at any order. Building upon the interaction of a single soliton with a localized attractive potential in terms of a perturbed NSE, we derive a simplified theoretical approach that suggests an analogy to classical mechanics and allows to accurately estimate the parameter range wherein pulse compounds are formed
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