Dual-Wavelength Passively Q-Switched Ytterbium-Doped Fiber Laser Based on Aluminum Oxide Nanoparticle Saturable Absorbers

We report on generation of a dual-wavelength, all-fiber, passively Q-switched ytterbium-doped fiber laser using aluminum oxide nanoparticle (Al_2O_3-NP) thin film. A thin film of Al_2O_3 was prepared by embedding Al_2O_3-NPs into a polyvinyl alcohol (PVA) as a host polymer, and then inserted between two fiber ferrules to act as a saturable absorber (SA). By incorporating the Al_2O_3-PVA SA into the laser cavity, a stable dual-wavelength pulse output centered at 1050 and 1060.7 nm is observed at threshold pump power of 80 mW. As the pump power is gradually increased from 80 to 300 mW, the repetition rate of the generated pulse increases from 16.23 to 59 kHz, while the pulse width decreases from 19 to 6 μs. To the best of our knowledge, this is the first demonstration for this type of SA operating in the 1 μm region.