2.8 μm passively Q-switched mode-locked fiber laser using TiCN as saturable absorber

A 2.8 μm passively Q-switched mode-locked erbium-doped fluoride fiber laser based on material saturable absorption is reported in this paper. By depositing TiCN particles directly onto the cavity mirror as the saturable absorber and using the vertical cleaved end of the fluoride fiber as an output coupler, the 2.8 μm pulsed fiber lasing with a low laser threshold and a compact cavity structure is realized. When the pump power reaches 330 mW, the Q-switched mode-locked pulses begin to appear. With the increase of pump power, the repetition frequency of Q-switched pulse envelope increases from 14.34 to 32.57 kHz, and the pulse width decreases from 10.51 to 5.40 μs. Under the pump power of 650 mW, the maximum average output power of 25.83 mW is obtained, and the slope efficiency is about 7.2%.