Sensing characteristics of integrated fiber Bragg grating sensors for high-temperature strain measurement

This study explored the response characteristics of fiber optic high-temperature strain sensors to axial strains under varying thermal conditions. The sensor assembly integrated a Type II fine-core pure silica fiber Bragg grating (FBG) with a Type I Ge-doped regenerative fiber Bragg grating (RFBG). The matrix's condition number was optimized by leveraging differential sensitivities to temperature and strain, combined with 2×2 matrix demodulation techniques, resulting in a substantial improvement in measurement accuracy. The sensor was found to exhibit good linearity and repeatability in strain response under conditions up to 550°C. Below 550°C, the temperature uncertainty was determined to be 5.49°C, and the strain uncertainty was 38.05 µɛ. However, the repeatability significantly decreased when the temperature exceeded 550°C, likely due to the viscoelastic behavior of the FBG at high temperatures. Therefore, for reliable measurements, it is recommended to use the high-temperature strain sensor for simultaneous strain and temperature monitoring in environments not exceeding 550°C.