Fig. 1. Schematic diagram of the basic structure of DFB laser

Fig. 2. Schematic diagram of sampling grating and simulation results of its transmission spectra

Fig. 3. Schematic diagram of FBG demodulation principle based on tunable DFB laser

Fig. 4. Schematic diagram of the MZI-based instantaneous-wavelength-variation measurement system of frequency-swept laser

Fig. 5. The relationship between the signal measured by MZI system and the reflection signal of reference FBG and the variation of laser wavelength with time in a single frequency-swept period

Fig. 6. Wavelength-swept spectra of laser measured by optical spectrum analyzer

Fig. 7. Schematic diagram of FBG temperature sensing system based on tunable REC-DFB laser

Fig. 8. FBG reflection spectra and FBG central wavelengths measured repeatedly at different temperatures

Fig. 9. FBG central wavelengths measured at different temperatures and their linear fitting relationship