An all-fiber Fabry-Pérot pressure sensor based on an extended silica capillary for sensitivity enhancement

An all-fiber Fabry-Pérot interferometric pressure sensor based on an extended silica capillary is proposed and experimentally demonstrated for high-temperature pressure measurement. The proposed sensor is designed to enhance pressure sensitivity while suppressing pressure-temperature cross-sensitivity. In the proposed structure, pressure-induced axial deformation of the silica capillary is transferred to the Fabry-Pérot interferometric cavity, resulting in an enlarged cavity-length variation and, consequently, enhanced pressure response. Theoretical analysis and experimental results indicate that the pressure and temperature sensitivities can be regulated relatively independently by tailoring different structural parameters. Specifically, the pressure sensitivity is mainly determined by the effective capillary length L₂, whereas the temperature sensitivity is mainly affected by the FPI cavity length L_1. With L_2=9 mm, the sensor achieves a pressure sensitivity of -224.10 nm/MPa. When L_1=80 μm, the temperature sensitivity is 0.082 nm/℃, corresponding to a low pressure-temperature cross-sensitivity of 0.36 kPa/℃. The sensor exhibits a linear pressure response over 0 to 30 MPa at room temperature and maintains good linearity for pressure measurements from 0 to 3 MPa over a wide temperature range of 20 to 800 ℃. The proposed sensor provides a compact and effective approach for developing high-sensitivity, low-crosstalk fiber-optic pressure sensors for high-temperature and high-pressure applications.