Fig. 1. Transmission spectrum of FP-FBG

Fig. 2. Transmission spectra of FBG F-P when h changes. (a) 16 mm; (b) 10 mm; (c) 6 mm; (d) 2 mm

Fig. 3. Transmission spectra of FBG F-P when L_g changes. (a) 24 mm; (b) 18 mm; (c) 8 mm; (d) 4 mm

Fig. 4. Transmission spectra of FBG F-P when δn̅eff changes

Fig. 5. FBG reflection spectrum and transmission spectra of FP-FBGs

Fig. 6. Structural diagram of wavelength-switchable SLM TDFL

Fig. 7. Schematic of single longitudinal mode selection of fiber laser

Fig. 8. Laser output spectra of three center wavelengths. (a) 1941.48 nm; (b) 1941.57 nm; (c) 1941.65 nm

Fig. 9. Output spectra of 10 consecutive scans with 5 min interval. (a) 1941.48 nm; (b) 1941.57 nm; (c) 1941.65 nm

Fig. 10. Output power and center wavelength of TDFL change with time. (a) 1941.48 nm; (b) 1941.57 nm; (c) 1941.65 nm

Fig. 11. RF spectra of output laser. (a) Unregulated PC; (b) 1941.48 nm; (c) 1941.57 nm; (d) 1941.65 nm

Fig. 12. Output power of TDFL varying with pump power. (a) 1941.48 nm; (b) 1941.57 nm; (c) 1941.65 nm