Fig. 1. Structure diagram of FLM

Fig. 2. Variation curves of P_t and P_r with K

Fig. 3. Variation curves of η (|E₁|²/|E₃|²) with K

Fig. 4. Structure diagram of three-ring mechanical polarization controller (PC)

Fig. 5. Structure diagram of EDFL based on FLM

Fig. 6. Structure diagram of EDFL based on HR-FBG

Fig. 7. Comparison of FLM and HR-FBG structures. (a) Relationship between output power and pump power; (b) dual-wavelength laser output spectra

Fig. 8. Comparison of same and different LR-FBG reflectivities. (a) Relationship between output power and pump power; (b) dual-wavelength laser output spectra; (c) stability of output power

Fig. 9. Comparison of different wavelength intervals based on HR-FBG structure. (a) Relationship between output power and pump power; (b) dual-wavelength laser output spectra; (c) EDF amplified spontaneous emission spectrum

Fig. 10. Stabilities of laser output spectra (left) and center wavelengths (right) at different wavelength intervals. (a) Δλ=4 nm; (b) Δλ=8 nm; (c) Δλ=12 nm

Fig. 11. Stabilities of laser output power and 3 dB bandwidth at different wavelength intervals. (a) Δλ=4 nm; (b) Δλ=8 nm; (c) Δλ=12 nm