Fe₃O₄ nanoparticles as the saturable absorber for a mode-locked fiber laser at 1558 nm

We demonstrated a mode-locked erbium doped fiber laser (EDFL) operating at 1558 nm by exploiting ferroferric-oxide nanoparticles (FONPs) as the saturable absorber (SA) material. FONPs, with an average diameter of ∼20 nm, were prepared by a thermal decomposition method, then mixed with sodium carboxymethylcelluose to form an FONP film. The FONP SA was fabricated through a sandwiched FONP film between two fiber connectors. By inserting the FONPs SA into an EDFL cavity pumped by a 980 nm laser diode, stable passive mode-locking was achieved with a threshold pump power of ∼120 mW. The obtained mode-locked laser had a central wavelength of ∼1558 nm, a spectral bandwidth of ∼0.8 nm, a pulse width of ∼4.35 ns, and a repetition rate of ∼37.32 MHz. Furthermore, a maximum average power of ∼17 mW was obtained for a pump power of 340 mW. To the best of our knowledge, this is the first time that it has been demonstrated that FONPs can be used for constructing mode-locked fiber lasers.