Accuracy evaluation of demodulation results of fiber Bragg grating sensors

Fiber Bragg grating (FBG) sensors are prone to spectral distortions in practical applications, which may cause large demodulation errors. There are many algorithms demodulating FBG spectra, but no approach is able to evaluate demodulation results under spectral distortions. To address this problem, four spectral indices are comparatively utilized to quantify distortions of spectra. Seven representative demodulation algorithms are adopted to analyze impacts of various simulated distorted spectra. Simulation results show that the side-mode suppression ratio (SMSR) of the spectrum is the most suitable spectral index for accuracy evaluation of demodulation results. In particular, when SMSR is larger than 6.3 dB, demodulation results will be accurate, and they are inaccurate when SMSR is smaller than 2.1 dB. The effectiveness of the proposed evaluation approach is validated with fatigue experiments of 9 FBG sensors.