A Q-switched fibre laser operating in the 2 mu m region based on nonlinear polarization rotation technique

We demonstrate a Q-switched fibre laser operating at 1949.0 nm, which is based on a nonlinear polarization rotation (NPR) technique. It uses a 2 m long commercial thulium-doped fibre and a 15 m long homemade thulium-ytterbium co-doped fibre as active media. They are pumped respectively by 800 nm single-mode and 905 nm multimode radiations. A stable Q-switched pulse train with the repetition rate 13.49 kHz and the pulse width 3.089 mu s is obtained when the 905 nm and 800 nm pump powers are fixed at 2.3 W and 110.4 mW, respectively. The maximum pulse energy, 11 nJ, is obtained at the 800 nm and 905 nm pump powers equal respectively to 110.4 mW and 2.5 W. To the best of our knowledge, this is the first reported Q-switched fibre laser using the NPR technique