A pulsed 1720 nm Tm-doped fiber laser based on dual-cavity scheme

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 resulted in the pulse duration of 1.7 μm emission was 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.