High modulation depth assisted by FeIn2S4 nanocrystals for ultrashort pulse generation in mode-locked erbium-doped fiber lasers

In this study, we demonstrated ultrashort pulse generation in an erbium-doped fiber laser (EDFL) operating at 1.5 μm using iron indium sulfide nanocrystals (FIS-NCs) as a potential saturable absorber (SA). The FIS-NCs-based SA was synthesized using the hydrothermal approach and was then characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HR-TEM). With FIC-NCs, the resulting SA exhibited excellent optical properties, with a modulation depth of 45.6 %, saturation intensity of 12.73 MW/cm², including non-saturable losses of 27.1 %. It was noticed that with the integration of FIS-NCs as SA inside the laser cavity, the EDFL exhibited the CW operation at the pump power of 24 mW that further transitioned into mode-locked operation at a low threshold of 54 mW. The measured experimental results revealed that the EDFL utilizing FIS-NCs based SA at pump power 242 mW yielded repetition rates of 20.6 MHz, central wavelength of 1533.68 nm, and pulse duration of 2.28 ps with a corresponding average output power of 4.25 mW. Besides, the stability of EDFL was assessed by measuring root-mean-square (RMS) power fluctuations (0.035 % over 3.5 h), and the numerical simulations were further carried out, which indicated a reasonable agreement with the experimental measurements. These findings demonstrate the potential of FIS-NCs as an effective SA in EDFLs, showing promising results for ultrafast pulse generation and mode-locking applications.