Hypersensitive high-temperature gas pressure sensor with Vernier effect by two parallel Fabry-Perot interferometers

We demonstrate an optical fiber sensor produced by two parallel Fabry–Perot interferometers (FPIs) for simultaneous measurement of temperature and gas pressure under high temperature environments. Each FPI is manufactured by combining hollow silica tube (HST) and optical fiber. These two FPIs respectively form reference and sensing optical paths, which are connected by a 3-dB coupler to form the Vernier effect. A fiber Bragg grating (FBG) is introduced in sensing arm FPI to measure temperature. By optimizing the structure of the two FPIs, our sensor obtains relatively low temperature cross-sensitivity, and effectively improved the fringe contrast of the reflection spectrum by using multimode fiber (MMF). The temperature sensitivity of the sensor is 12.01 pm/°C within the range of 25–600 °C. The pressure sensitivity of the sensor is as high as 63.67 nm/MPa and 21.22 nm/MPa within the range of 0–0.7 MPa at 25 °C and at 600 °C respectively, which is approximately 15-times that of the open-cavity FPI. Its simple manufacturing method and relatively low temperature cross-sensitivity have potential application in high-temperature air pressure monitoring.