Fig. 1. Schematic of multi-beam interference in F-P etalon

Fig. 2. Diagram of experimental device for wavelength monitoring by F-P etalon

Fig. 3. Direct modulation performance test of DFB laser: The relationship between wavelength and temperature/current

Fig. 4. Intensity of reflected and transmitted light during current scanning

Fig. 5. Light intensity ratio of interference signals (The wavelength corresponding to the black dashed lines are in the "dead zone" of the θ₁ signal and the "effective zone" of the θ₂ signal)

Fig. 6. Wavelength shift in 30 min

Fig. 7. Reflected light intensity, transmitted light intensity and light intensity ratio change with wavelength scanning

Fig. 8. Linear relationship between the results of F-P system measurements and the reference wavemeter measurements, and its regular residual

Fig. 9. Wavelength monitoring results of F-P system output within 10 min

Fig. 10. Fluctuations of wavelength at different scanning voltages