Mode-locked thulium/holmium co-doped fiber laser using WTe2-covered tapered fiber

Abstract

In this work, a WTe2 coated tapered fiber was used as a saturable absorber (SA) to induce mode-locking in a thulium/holmium doped fiber (THDF) laser through evanescent field interaction. The WTe2 was drop-casted onto the tapered fiber to form an SA which had a modulation depth of 18.08%, saturation intensity of 0.14 MW/cm2, and non-saturable absorption of 81.92%. Mode-locked pulses were obtained at a wavelength of 1909.81 nm with a pulse width of 1.77 ps, and a 3 dB bandwidth of 2.2 nm. It has a signal-to-noise ratio of 52 dB and a repetition rate of 11.54 MHz at a pump power of 436.4 mW. The maximum output power, pulse energy, and peak power obtained were 3.51 mW, 303.9 pJ, and 0.17 kW respectively. The use of evanescent field coupling in the tapered fiber with the WTe2 nanoparticles allows the realization of high-power mode-locking applications.