High-Temperature and High-Pressure Sensor Based on Sensitivity-Enhanced Suspended All-Optical Fiber Fabry—Pérot Interferometer for Downhole Oil Applications

This study aims to explore the temperature and pressure dual-parameter performance of the all-optical fiber suspended microstructure as well as the relationship between the pressure sensitivity (S_p) and wall thickness (t) of the capillary fiber. This expands on previous research that examines the relationship between the S_p and L₂/L₁ of the suspended microstructures. The sensor uses a wavelength tracking method, and its wavelength response to pressure changes can reach the S_p of 1495.71 pm/MPa. The temperature and pressure dual parametric performance of this type of sensor at 150 °C and 50 MPa was characterized under laboratory conditions. After one week of continuous high-temperature and high-pressure longterm testing, the maximum difference in S_p fluctuation was 2.28 pm/MPa, which accounted for ±0.25%F.S. of the S_p at the given temperature. Additionally, the pressure point exhibited a fluctuation of 10.07 MPa, accounting for 10.14%F.S. of the entire pressure range. Notably, the sensor continued to exhibit good stability and repeatability throughout the testing process. Analysis of a large amount of test data verified an inversely proportional relationship between the S_p of the sensor and the t of the capillary fiber. Increasing the t of the capillary fiber can improve the overall temperature and pressure resistance of the sensing microstructure; however, S_p will be lost to some extent. The high-temperature and high-pressure sensors are responsive, highly stable, repeatable, accurate, and sensitive for long-term monitoring of high temperatures and pressures.