Temporal characteristics of gain-switched thulium-doped fiber laser near threshold

The temporal output characteristics of an all-fiber gain-switched thulium-doped fiber laser near threshold are investigated experimentally and numerically. The pulse repetition rate and pulse energy of the 1550 nm pump source are found to be two important parameters that affect the laser performance. Adjusting these two parameters, three different output working states, namely no lasing state, unstable state, and steady state, are observed experimentally. Particularly, in the unstable state relatively stable output pulse trains with repetition rate trisecting (PRR 1/3) and halving (PRR 1/2) with respect to the pump source are found. The experimental results together with corresponding numerical simulation afford a deep insight into the related lasing mechanisms.