Dual-Cavity Fabry–Perot Interferometric Sensors for the Simultaneous Measurement of High Temperature and High Pressure

A fiber-optic hybrid sensor based on dual-cavity Fabry-Perot interferometers is proposed and demonstrated for the simultaneous measurement of high temperature and high pressure. The proposed sensor is fabricated by fusion splicing of two single-mode fibers (SMFs), a hollow core fiber (HCF), and a coreless fiber (CF), forming a four-section structure of leading SMF-SMF-HCF-CF. A micro-hole is fabricated at the end of the leading SMF using a femtosecond laser, forming an air gap between two SMFs. The CF is thinned and roughened by the femtosecond laser to form a diaphragm. The SMF-based cavity is used as the temperature sensor and the HCF-based cavity as the pressure sensor. Lengths of two cavities are interrogated simultaneously by using the fast Fourier transform-based white-light interferometry. Experimental results show that the proposed sensor exhibits a temperature sensitivity of 19.8 nm/°C and a pressure sensitivity of ~98 nm/MPa, within the temperature range of 20 °C-800 °C and the pressure range of 0-10 MPa. The maximum measurement errors of temperature and pressure are 5 °C and 0.2 MPa, respectively. As far as we know, it is the first time to detect the temperature of 800 °C and the pressure of 10 MPa simultaneously.