Passively Q-switched erbium-doped fiber laser based on nickel ferrite (Ni-Fe2O4) nanoparticles’ saturable absorber: synthesis and experimental demonstration

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In this study, detailed experimental investigations of the passively Q-switched (PQS) erbium-doped fiber laser (EDFL) were reported based on nickel ferrite (Ni-Fe2O4) thin-film saturable absorber (SA). The Ni-Fe2O4 nanoparticles (NPs) were synthesized using a sol–gel autocombustion mechanism, and its thin film was prepared in polyvinyl alcohol (PVA) via the solution casting method. The crystallographic structure, surface morphology, and particle size of Ni-Fe2O4 NPs were characterized using the X-ray diffraction (XRD) technique, high-resolution transmission electron microscopy (HR-TEM), and scanning electron microscopy (SEM). The obtained findings indicate that the prepared Ni-Fe2O4 SA yielded a 12.6% modulation depth (ΔT), the saturation intensity (Isat) of 34.04MW/cm2, and nonsaturable losses (Tns) of 48.2%. The prepared SA upon integration within the laser cavity resulted in an emission wavelength of 1563.87 nm at an input pump power (Pin) of 104.6 mW. With increased Pin, a stable passively Q-switched pulse operation, initiated by incorporating a Ni-Fe2O4 thin film as an SA in the EDFL ring cavity, yielded a repetition rate (RR) ranges from 34.18 to 69.44 kHz, and pulse width (PW) varied from 10.94 to 4.74 µs upon tuning a Pin to 284 mW. Additionally, the pulse energy (PE), peak power, and average output power (Pavg) were 167.33 nJ, 35.30 mW, and 11. 62 mW, respectively. Finally, the stability of EDFLs with Ni-Fe2O4 SA was thoroughly examined by operating the SA continuously for 1 h at a Pin of 104.6 mW, which maintained a constant PW of 8.43±0.08µs and an RR of 43.89±0.10kHz. This study shows that ferrite composites serve as highly effective SAs in EDFLs, enabling stable and controllable generation of ultrashort pulses due to their high-damage threshold and nonlinear optical properties that are critical for a variety of uses in photonics.