Real-time transition dynamics of harmonic mode-locking states with spectral filtering effect in a hybrid mode-locked fiber laser

We experimentally investigated the transition dynamics between 2nd and 3rd harmonic mode-locking states using the dispersive Fourier transform technology in a hybrid mode-locked fiber laser. Keeping the pump power unchanged and adjusting polarization controller to change intracavity-loss-dependent gain profile and the spectral filtering effect, a set of soliton dynamics induced by soliton interaction are revealed before the soliton splitting. Solitons undergo similar oscillation behaviors during the reverse decay process of the harmonic mode-locking order until one of the solitons disappears. In these transient dynamics, a significant wavelength shift phenomenon could be observed in the transition process of harmonic orders. The numerical results further show that intracavity spectral filtering effects play key role in the harmonic order transition dynamics process, consistent with experimental results. It provides new insights into the evolution and dynamics behavior in harmonic mode-locked soliton order conversion and its potential applications.