Experimental and numerical study of different mode-locking techniques in holmium fiber laser with a ring cavity

Experimental and numerical study has been performed for three techniques of mode-locking in all-fiber Holmium laser. We have compared the fundamental repetition rate pulsed generation for mode-locking based on: nonlinear polarization evolution, polymer-free single-walled carbon nanotubes, and hybrid mode-locking. Experimental and numerical simulation results demonstrated the shortest pulse duration and maximum spectrum width for mode-locking based on the nonlinear polarization evolution: 1.3 ps, 4.2 nm and 1.3 ps, 4.1 nm, respectively. The self-starting mode in this case can vary depending on external conditions in the experiment. In Ho-doped fiber laser with polymer-free single-walled carbon nanotubes mode-locking, the small modulation depth of saturable absorption leads to a long time period of stationary single-pulse lasing development (about 10⁴ cavity roundtrips in simulation, and ≈5 s in the experiment). Both experimental and numerical studies have indicated that a Ho-doped fiber laser with hybrid mode-locking provides optimal generation, enabling self-starting and a relatively fast transition to stable single-pulse lasing (less than 1.5 × 10³ cavity roundtrips in simulation, and ≈3 s in experiment). This study presents the first employment of polymer-free single-walled carbon nanotubes for hybrid mode-locking in a Ho-doped fiber laser.