Holmium oxide thin film as a saturable absorber for generating Q-switched and mode-locked erbium-doped fiber lasers

We demonstrated a new type of transition metal oxide (TMO) material, Holmium oxide (Ho₂O₃) polymer film SA for compact passively Q-switched and mode-locked erbium-doped fiber laser (EDFL) generations. The film SA has a thickness of ~40 µm and modulation depth of ~45%. It was fabricated by embedding Ho₂O₃ nanoparticles into PVA polymer solution. The Q-switched laser operated stably at a center wavelength of 1563 nm within a pump power range of 45–97 mW. The maximum Q-switching pulse repetition rate and the narrowest attainable pulse width were 115.8 kHz and 0.64 µs, respectively; while, the maximum pulse energy was obtained as 129.36 nJ. On the other hand, the mode-locked EDFL emerged stably within a pump power range of 62–180 mW at a center wavelength of 1565.4 nm. The repetition rate was 17.1 MHz, while the pulse width was 650 fs. Additionally, the maximum output power was measured as 9.01 mW; while, the corresponding maximum pulse energy was obtained as 0.524 nJ. This Ho₂O₃ film SA offers simplicity and reliability in the design of compact and portable fiber pulsed laser generators particularly in the 1.55-µm regime.