Tunable Fe2+:ZnSe passively Q-switched Ho3+-doped ZBLAN fiber laser around 3 μm

We report a tunable passively Q-switched Ho3+-doped ZBLAN fiber laser at 3 mu m waveband using a Fe2+:ZnSe crystal as saturable absorber (SA) and a plane ruled grating in Littrow configuration as wavelength tuning element. Stable pulse trains with similar to 85 nm tuning range from 2919.1 nm to 3004.2 nm and spectrum bandwidths of similar to 1 nm were achieved for the Fe2+: ZnSe crystal with an initial transmission (IT) of 69%. Pulse duration increased from 1.23 mu s to 2.35 mu s and repetition rate decreased from 96.1 kHz to 43.56 kHz with the extension towards long wavelength direction. With the IT increasing to 79% and then 89%, though the available tuning range was slightly shortened, higher output power, pulse energy and slope efficiency were obtained with the slightly increased pulse duration and repetition rate. Maximum output power of 337 mW at a slope efficiency of 11.44% and pulse energy of 5.64 mu J were achieved at similar to 2970 nm and similar to 2991 nm, respectively. High signal noise ratio (SNR) of over 50 dB across the whole tuning range for the three ITs Fe2+:ZnSe crystals indicated the stable Q-switching. To our knowledge, this is the first reported wavelength tunable passively Q-switched ZBLAN fiber laser. (C) 2015 Optical Society of America