π -Phase-Shifted FBG for High-Resolution Static-Strain Measurement Based on Wavelet Threshold Denoising Algorithm

We propose a high-resolution static-strain sensor based on a π-phase-shifted Bragg grating (π-FBG) combined with a wavelet threshold denoising algorithm. The Pound-Drever-Hall (PDH) technique based on a narrow-linewidth fiber laser is used to interrogate the sensor. A reference FBG-based Fabry-Perot interferometer (FBG-FP) is used to compensate the temperature and laser source frequency fluctuation. As the reflect spectrums of π-FBG have a higher SNR than FBG-FP, the SNR of PDH signals from FBG-FP and π-FBG is increased from 18.1 to 35.6 dB. Wavelet threshold denoising algorithm is used to further improve the SNR of the PDH signals (about 8 dB). As a result, a static-strain resolution of 1.0 nε is obtained in the laboratory test.