Simultaneous dual-wavelength Q-switched fiber laser utilizing tungsten sulfide as saturable absorber

Dual-wavelength Q-switched Erbium-doped fiber laser (EDFL) was shown by using tungsten disulfide (WS2), which was deposited onto a micro-sphere resonator (MSR) as a saturable absorber (SA). WS2 functions to modulate the cavity loss for Q-switching while the dual-wavelength operation was realized due to MSR, which allows only two wavelengths to oscillate in the resonator. MSR with the sphere diameter of 200 mu m was fabricated at the tip of a standard single mode-fiber by employing a fiber fusion splicer machine. The SA was obtained by repeatedly dropping and drying of WS2 solution onto the MSR structure to form an active thin layer. The SA was incorporated into an EDFL cavity to realize a dual-wavelength Q-switched laser operating at 1554.0 nm and 1560.7 nm. The repetition rate of the pulse train is tunable from 72.4 kHz to 85.1 kHz as the pump power is increased from 104.6 mW to 145.8 mW. At 145.8 mW pump, the minimum pulse width and maximum pulse energy were obtained at 3.47 mu s and 131.4 nJ, respectively. The dual-wavelength Q-switched laser was stable and thus it is suitable for use in airborne Lidar, environmental sensing, and terahertz applications.