Demodulation of Composite Spectral Signals of FBG-EFPI Based High-Temperature-High-Pressure Sensors

This paper presents an FBG-EFPI composite sensor, combining Fiber Bragg Gratings (FBG) and Extrinsic Fabry-Pérot Interferometers (EFPI) for simultaneous temperature and pressure monitoring. High-precision measurements are achieved using power-weighted algorithms and automatic Q initial point setting demodulation techniques. Within the temperature range from <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$35^{\circ}\mathrm{C}$</tex> to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$640^{\circ}\mathrm{C}$</tex>, the temperature sensitivity of the FBG central wavelength is <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$12.8\ \text{pm}/^{\circ}\mathrm{C}$</tex>, with a temperature measurement accuracy of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.16^{\circ}\mathrm{C}$</tex>. In the pressure range from 0 to 15 MPa, the pressure sensitivity of the FP cavity is 36.33 nm/MPa, achieving a pressure measurement accuracy of 0.275 MPa. The composite sensor demonstrates potential for temperature and pressure monitoring in high-temperature and high-pressure environments.