A Q-switched, 1.89 µm fiber laser using an Fe₃O₄-based saturable absorber

The potential of Fe₃O₄ nanoparticles as a base material for saturable absorbers (SAs) that can operate in the 2 μm-wavelength regime, was investigated. An SA was fabricated on a sandwich-structured fiber-ferrule platform through the deposition of an Fe₃O₄ mixture with polyvinyl alcohol (PVA) onto the end surface of the fiber ferrule. Using the prepared Fe₃O₄/PVA-composite-based SA within a Tm-Ho codoped fiber laser, stable Q-switched pulses were readily produced at 1894 nm. The temporal characteristics of the output pulses were investigated as a function of the pump power, and the maximum energy of the output pulses was 322 nJ. The temporal width of the output pulses was measured as 2.6 µs at the maximum pulse-repetition rate of 37.2 kHz. The output performance of the passively Q-switched Tm-Ho-codoped fiber laser in this work was compared with those of recently demonstrated, passively Q-switched Tm-doped fiber lasers for which the other types of saturable-absorption materials.