Passive Q-switched fiber laser based on niSe₂ saturable absorber

Nickel diselenide (NiSe₂) microspheres were synthesized using a chemical vapor deposition (CVD) method, and their nonlinear optical properties were investigated. The prepared NiSe₂ exhibits good nonlinear characteristics, demonstrating a high modulation depth and a low saturation intensity. Then the NiSe₂ was used as a saturable absorber device and integrated into a 1.5 μm erbium-doped fiber laser to generate Q-switched pulse. By optimizing the cavity dispersion and adjusting the polarization state within the cavity, the single pulse tunable Q-switched pulse, Q-switched mode-locking pulse and quasi-mode-locked pulse based on NiSe₂ saturable absorber are realized. Among them, the signal-to-noise ratio of the quasi-mode-locked pulse is as high as 68 dB, which proves that the resulting pulse has high stability. The findings of this study suggest that NiSe₂ SA devices have the potential to be developed as highly efficient candidates for ultrafast photonics and can find extensive applications in nonlinear optical fields.