Intracavity Tandemly-Pumped and Gain-Switched Tm-doped Fiber Laser at 1.7 μm

We propose and demonstrate a novel method to achieve pulsed operation of thulium-doped fiber lasers at 1.7 μm. In our design, the thulium-doped fiber laser cavity was embedded within the cavity of an erbium/ytterbium-codoped fiber laser operating at 1.5 μm. The thulium-doped fiber in the erbium/ytterbium-codoped fiber laser cavity served as a saturable absorber, forcing the 1.5 μm laser to operate in a passively Q-switched scheme. The 1.7 μm thulium-doped fiber laser was in-turn pumped by the Q-switched 1.5 μm laser and was gain-switched. This made the pulse duration of 1.7 μm emission much shorter than that of 1.5 μm emission. 1.02 W average output power at 1720 nm was obtained for 10 W of pump power at 976 nm. The pulse repetition frequency, pulse energy and pulse duration were 134 kHz, 7.6 μJ and 102 ns, respectively. A rate equation model was developed to examine the power- and temporal-behavior of the laser system. The calculated pulse duration and pulse repetition frequency matched well with the experimental results. Methods of further improving the laser performance are discussed based on insights gleaned from our modeling.