Switching of soliton rain, bunches, and NLP from a thulium/holmium co-doped fiber laser using NPR

• Investigated temporal and spectral features of multiple pulse regimes in a ML-THDFL using DPA and NPR. • Observed the coexistence of multisolitons (MS) and noise-like pulses (NLPs) under high pump power and anomalous dispersion. • Identified distinct behaviors and interactions among NLP, NLSP, soliton rain (SR), and soliton bunching (SB) regimes. • Showcased the ML-THDFL as a versatile platform for exploring nonlinear pulse dynamics in the Ho emission band. An experimental study on the switching between different multipulse regimes in a Thulium/Holmium-doped fiber (THDF) laser is reported by precise control of polarization controllers. Gaussian and square-shaped noise-like pulses (NLPs) and multiple solitons (MS), including soliton rains (SRs) and soliton bunches (SBs), are generated by the nonlinear polarization rotation technique (NPR) and by employing a double-pass amplifier (DPA) configuration. The study examines the role of polarization controllers and pump power in driving the transitions between these regimes, with a detailed analysis of their temporal and spectral characteristics under different pump powers. To the authors’ knowledge, this is the first demonstration of switching among SR, SB, conventional NLPs, and the coexistence of square-shaped NLP with MS within a hybrid cavity configuration that combines NPR and a DPA. The system operates with a tunable central wavelength ranging from 1984 to 1993 nm, employing a THDF as the gain medium. This investigation provides new insights into the transitions between various multi-pulse regimes and nonlinear dynamics in mode-locked fiber lasers operating near the 2-µm wavelength region.