Passively Q-switched thulium-doped fiber laser based on oxygen vacancy MoO3-x saturable absorber

We reported on a passively Q-switched double-clad thulium-doped fiber laser by using oxygen vacancies (OVs) enriched with MoO3-x as a saturable absorber (SA). The MoO3-x was successfully embedded in polyvinyl alcohol and acted as the SA for a stable Q-switching operation in the 2 µm wavelength region. Stable Q-switched pulses were obtained at a central wavelength of ∼1992.1 nm with a maximum output power of ∼62.7 mW, maximum pulse energy of ∼1.63 µJ and a minimum pulse duration of ∼2 µs. The repetition rate of the pulses can be tuned from ∼15.5 kHz to ∼38.5 kHz with increasing the pump power. Our experiment was the first demonstrated use of MoO3-x as a SA for pulse laser generation, in which OVs were considered as the original reason for the optical saturable absorption. Moreover, it provides a novel idea for optical SA preparation by controlling the vacancy defects in such materials.