Fig. 1. Reflection spectrum of π-phase-shifted fiber gratings

Fig. 2. Diagram of overall encapsulation of grating. (a) Model of grating sensitisation package; (b) model of fibre grating after integral package

Fig. 3. Relationship between wavelength and temperature

Fig. 4. High-precision temperature sensing system based on swept-frequency laser

Fig. 5. Working principle of demodulation system. (a) Original signal; (b) signal after power compensation; (c) resampled signal; (d) center frequency of calibration grating

Fig. 6. Temperature measurement range result

Fig. 7. Temperature and central wavelength variation curves for grating No. 6

Fig. 8. Fitted result of temperature data within 3000 s ( inset is fitted residual within 60 s)