Tunable S-band mode-locked thulium-doped fluoride fiber laser using nickel phosphorus trisulfide (NiPS3) saturable absorber

Nickel Phosphate Trisulfide (NiPS3) prepared using the LPE technique was used as a saturable absorber (SA) in a thulium-doped fluoride fiber laser for the generation of mode-locked pulses. The polishing method was used to prepare the arc-shaped fiber before the NiPS3 solution was drop-casted onto it to form the SA device. The SA exhibited nonlinear optical properties, with modulation depth and saturation intensity of 29.44 % and 0.547 kW/cm2 respectively. Insertion of the SA in the TDFF cavity produced mode-locked pulses with central wavelength and 3-dB bandwidth of 1505 nm and 0.68 nm respectively, with a pulse width of 3.56 ps. The mode-locking operation also has a repetition rate of 582 kHz and an SNR of about 58 dB at a pump power of 280 mW. The maximum average output power measured was 2.4 mW at maximum pump power, with maximum pulse energy and peak power at 4.12 nJ and 1.16 kW respectively. Due to the optical interaction between NiPS3 and the evanescent wave in this arrangement, a larger damage threshold can be achieved, enabling the laser performance to operate at higher output power. Tunability was achieved by simultaneous adjustment of extinction and wavelength knob on the tunable Mach-Zehnder Filter (TMZF). The shape of spectra remained unchanged and continued exhibiting Kelly’s sidebands throughout the tunability range of about 2 nm. These results provide the first demonstration of tunable mode-locked pulses in the S-band region. •Performance of NiPS3 as a saturable absorber was investigated.•Generation of mode-locked in Thulium-doped fluoride fiber laser at 1505 nm.•NiPS3 exhibits a modulation depth of 29.44 % at 1550 nm•The pulse width generated was 3.56 ps with a peak power of 1.16 kW.•Tunability range of ∼2 nm with center wavelength between 1504.0.0 nm and 1506.5 nm