Symmetric Oscillating Soliton Molecules in Mode-Locked Fiber Lasers

The real-time dynamics of soliton molecules (bound solitons) have been extensively studied in mode-locked lasers by virtue of the emergence of fast detection techniques. Here, a new type of symmetric oscillating spectral evolution of soliton molecules was discovered in a figure-8 cavity. Different spectral components of soliton molecules have different evolutionary patterns. The long-wavelength and short-wavelength spectra have opposite oscillating phases with respect to the central wavelength. Numerical simulations corroborate experimental observations and reveal that this symmetric dynamic is caused by strong Kelly sidebands. This novel dynamic enriches our understanding of soliton molecules.