Fig. 1. Structure diagram of GIMF-SMF-GIMF

Fig. 2. Power-dependent transmission curves of GSG structure

Fig. 3. Schematic diagram of fiber laser

Fig. 4. Output power versus pump power

Fig. 5. Pulse output characteristics insingle wavelength mode-locked state. (a) Spectrum of single wavelength mode-locked at 1558.6 nm; (b) radio frequency spectrum with a fundamental frequency of 8.5 MHz; (c) pulse trains; (d) autocorrelation trace

Fig. 6. Spectra of single wavelength-tuning mode-locked fiber laser

Fig. 7. Switching between single and dual wavelengths. (a)(b) Spectra of 1556.2 nm and 1531.6 nm mode-locked states; (c) spectra of 1556.2‒1531.6 nm dual-wavelength mode-locked states; (d) pulse sequences during dual-wavelength mode-locked operation

Fig. 8. Tuning spectra of SMF lengths of 4 cm and 5 cm. (a) Tuning range length is 9.5 nm when SMF length is 4 cm; (b) tuning range length is 9 nm when SMF length is 5 cm

Fig. 9. Stability test of fiber laser