Fig. 1. Preparation of NbTe₂ nanosheets

Fig. 2. Characterization of NbTe₂ nanosheets. (a) SEM image at 300 nm scale; (b) SEM image at 1 µm scale; (c) Raman optical spectrum; (d) XRD image; (e) AFM image

Fig. 3. Schematic diagram of the Z-scan experimental setup

Fig. 4. Closed-aperture Z-scan curves under different optical intensities. (a) 4.25 GW/cm²; (b) 5.95 GW/cm²; (c) 7.65 GW/cm²; (d) 9.35 GW/cm²; (e) 11.05 GW/cm²; (f) Nonlinear refractive index n₂ versus optical intensity

Fig. 5. Tapered fiber. (a) The manufacturing process of tapered fiber; (b) Microscopic image of the tapered region

Fig. 6. Experimental setup diagram of high-repetition-rate fiber laser based on DFWM

Fig. 7. Structural diagram of MZI

Fig. 8. The transmission curves at the output port of the MZI. (a) FSR is 0.64 nm; (b) FSR is 1 nm

Fig. 9. MZI test results. (a) Spectrum of the ASE broadband light source; (b) MZI transmission curve at 95 ps; (c) MZI transmission curve at 100 ps; (d) Corresponding relationship between different scales of the OTDL and the FSR

Fig. 10. DFWM mode-locking principle

Fig. 11. DFWM experimental results. (a) Spectrum when the FSR is 0.64 nm; (b) Autocorrelation trace; (c) Spectrum when the FSR is 1 nm; (d) Autocorrelation trace

Fig. 12. Evolution results. (a) The evolutionary process of the spectrum over time; (b) The evolutionary process of the output power over time