Fig. 1. Trend of PS-FBG transmission slit bandwidth with coupling strength, where the inset shows the transmission spectra of PS-FBG

Fig. 2. Variation trend of DFB-FL slope efficiency with coupling coefficient and length of PS-FBG under different intracavity losses. (a) Variation with coupling coefficient; (b) variation with grating length

Fig. 3. Numerical simulation results of DFB-FL threshold gain coefficient and threshold coupling strength. (a) Threshold gain coefficient G_th versus coupling strength; (b) fundamental mode G_th value for different phase shifts; (c) threshold coupling strength κLth versus phase shift difference

Fig. 4. Amplitude of intracavity loss disturbance transfer function varies with PS-FBG coupling strength

Fig. 5. Schematic diagram of experimental device and measured PS-FBG and DFB-FL spectra. (a) DFB-FL and test system; (b) PS-FBG spectra; (c) DFB-FL output laser spectrum

Fig. 6. Measured linewidth of DFB-FL output laser. (a) Measured linewidth of DFB-FL output laser at different coupling strengths;

Fig. 7. Test results of DFB-FL pumping efficiency under different conditions. (a) At different grating lengths; (b) at different coupling coefficients

Fig. 8. Polarization state test of DFB-FL output laser. (a) Dual polarization state output; (b) single polarization state output; (c) PER test

Fig. 9. RIN test results of DFB-FL output laser at different coupling strengths

Fig. 10. Laser optical path system package structure diagram

Fig. 11. Packaged laser index test results. (a) PER; (b) linewidth; (c) RIN; (d) pump efficiency