Mode-Locked Thulium-Doped Fiber Laser in Multi-wavelength Operation Regime

We demonstrate a tunable mode-locked thulium-doped fiber laser within a wide wavelength range 1880-1990 nm, in the regime of soliton mode-locking and multi-wavelength operation. The gain spectrum of the laser cavity is periodically modulated induced by the nonlinear polarization rotation (NPR) effect, which enables mode-locking at a number of selected wavelengths, individually and simultaneously. With Kelly sidebands in the soliton spectrum, we further extract a wavelength-dependent cavity net dispersion that may contribute to the knowledge of thulium-doped fiber laser systems as well as cavity dissipative soliton dynamics at the onset of mid-infrared range.