Mid-Infrared Q-Switched and Mode-Locked Fiber Lasers at 2.87 μm Based on Carbon Nanotube

We report Q-switching and mode-locking operations in a Ho³⁺/Pr³⁺ co-doped ZBLAN fiber laser at 3-μm mid-infrared waveband using a single-walled carbon nanotube saturable absorber (SWCNT-SA). The SWCNTs were produced by catalytic chemical vapor deposition method and then deposited on the surface of a flat gold-coated mirror to form the SWCNT-SA. The modulation depth and saturation intensity of the SWCNT-SA are 16.5% and 1.66 MW/cm², respectively. Stable Q-switched laser pulses operating at 2865.6 nm were obtained at a launched pump power of 530.6 mW. The resulting pulses have a measured repetition rate and pulse width of 178.6 kHz and 1.21 μs, respectively. The maximum pulse energy is calculated to be 0.36 μJ. By slightly adjusting the position of the SWCNT-SA, stable continuous-wave mode-locked pulses at 2865.2 nm were also achieved. Our work demonstrates that SWCNTs are promising SAs for 3-μm midinfrared pulsed lasers.