Heteronuclear soliton molecules with two frequencies

Bound states of optical solitons represent ideal candidates to investigate fundamental nonlinear wave interaction principles and have been shown to exhibit intriguing analogies to phenomena in quantum mechanics. Usually, such soliton molecules are created by a suitable balance of phase-related attraction and repulsion between two copropagating solitons with overlapping tails. However, there exists also another type of compound state, where strong binding forces result directly from the Kerr nonlinearity between solitons at different center frequencies. The physical mechanisms as well as the properties of these objects are quite different from those of usual soliton molecules, but are hardly known. Here we characterize and investigate these compound states in greater detail. We demonstrate unique propagation dynamics by investigating the robustness of the compound states under perturbations, such as third-order dispersion and the Raman effect. The constituents are individually affected by the perturbations, but the impact on the compound state is not a mere superimposition. One observes complex dynamics resulting from a strong entanglement between the subpulses. For example, in the case of the Raman effect both subpulses are subject to a cancellation of the self-frequency shift, although only one subpulse is approaching a zero-dispersion frequency. We extend the concept of the molecule states to three and more constituents by adopting appropriate propagation constants. These multicolor soliton molecules open up further perspectives for exploring the complex physics of photonic molecules, but also show great potential for application resulting from their robustness and the possibility to control their properties.

Automated summary

Bound states of optical solitons are ideal for studying nonlinear wave interaction principles and have similarities with phenomena in quantum mechanics. We investigate the properties of these compound states and demonstrate their unique propagation dynamics. These findings have implications for the study and application of photonic molecules.