High repetition rate gain-switched Ho-doped fiber laser at 2.103 μm pumped by h-shaped mode-locked Tm-doped fiber laser at 1.985 μm

We present a MHz level high repetition rate gain-switched Ho-doped fiber laser at 2.103 mu m using a h-shaped mode-locked Tm-doped fiber laser as the pump, for the first time. A NPR mode-locked Tm-doped ring cavity was designed as the seed, which could generate h-shaped pulses at 1.985 mu m with a fundamental repetition rate of 1.435 MHz. It had a pump-dependent ns scale pulse duration with an almost unchanged peak amplitude. Then its output power and pulse energy were significantly scaled to 3.92W and 2.71 mu J. respectively based on a one-stage Tm-doped fiber based amplifier. After that, the amplified pulses were fed to a linear cavity Ho-doped fiber laser formed by a HR FBG and a perpendicularly cleaved fiber end. resulting in stable gain-switched pulses at 2.103 mu m with a repetition rate of 1.435 MHz, which marks the record of gain-switched fiber lasers in this spectral region. At this repetition rate, the maximum output power of 1.13 W and pulse energy of 0.79 mu J were achieved at a high slope efficiency of 75.4% with respect to its absorbed pump power, giving the shortest pulse duration of 10.8 ns. The results indicated that the h-shaped pulses were an alternative choice for high repetition rate gain-switching in an all-fiber configuration. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement