Reversible pairwise switching of soliton states in a hybrid mode-locked Erbium-doped fiber laser

Reliable and controllable state-switching capabilities are essential for the development of programmable and reconfigurable ultrafast laser sources. While conventional dual-state switching with various mode-locking mechanisms has been reported, the accessibility of multiple state-switching within a single cavity and the corresponding transient dynamics remain unexplored. Here, we investigate the state-switching characteristics of an Erbium-doped fiber laser using a hybrid scheme combining nonlinear polarization rotation (NPR) with a carbon nanotube saturable absorber (CNT-SA). We show that the hybrid scheme supports reversible switching among the third harmonic mode-locking, fundamental soliton, and bound states with high reproducibility. Real-time spectral characterizations confirm that the CNT-SA suppresses the intrinsic instability of the NPR counterpart during state transitions, as reflected in the extension of breathing oscillations. We experimentally demonstrate that the hybrid scheme effectively supports generation of multiple soliton states and mitigates the instabilities during the transition process, establishing a reversible pairwise state-switching platform for laser dynamics studies and intelligent laser source applications.