Generation of mode-locked thulium doped fluoride fiber laser using graphene-zinc oxide (G-ZnO) coated dual arc-shaped fiber

Abstract In this work, mode-locked laser generation at the S-band region was achieved using a graphene-zinc oxide (G-ZnO) coated dual arc-shaped fiber as a saturable absorber (SA) within a thulium-doped fluoride fiber (TDFF) ring cavity. Two-step polishing was implemented to fabricate a dual arc-shaped fiber, and a G-ZnO solution was then deposited on the dual arc region via the drop-casting method to form the SA. Mode-locked pulses were generated by incorporating the G-ZnO-based SA into the TDFF ring cavity, with the pulses having a central wavelength, 3 dB bandwidth and pulse duration of 1503.4 nm, 0.68 nm and 3.52 ps, respectively. At the maximum pump power of 202 mW, an average output power of 2.47 mW was obtained with a maximum pulse energy of 6.16 nJ and a peak power of 1.75 kW. At this pump power, the generated pulses have a frequency of 401.6 kHz with a signal-to-noise ratio (SNR) of 54 dB. The mode-locking threshold was at a pump power of 118 mW. The results obtained in this work indicate the potential of a new class of 2D composite materials which can be used as nonlinear optical devices.