Recovered HCN Absorption Spectrum-Based FBG Demodulation Method Covering the Whole C-Band for Temperature Changing Environment

Calibration by hydrogen cyanide (HCN) absorption spectrum can make the fiber Bragg grating (FBG) demodulation system immune to environment temperature changes. The transmittance function of Fabry-Perot (F-P) filter will result in the distortion of the HCN absorption peaks. A demodulation scheme based on deconvolution is proposed to eliminate the impact of the F-P filter. A recovered HCN absorption spectrum with deeper, narrower and more symmetrical absorption peaks is obtained for the Bragg wavelength calibration. It is proved experimentally that this method can reduce the standard deviation of demodulated FBG wavelengths by at least 45.9% at a constant temperature, and 42.9% in the environment of varying temperature from 10 °C to 60 °C. Compared with the method of Bragg wavelength calibration based on the original HCN absorption spectrum, the spectral bandwidth that can be accurately demodulated is also expanded to the whole C-band.