Adhesive-free bonding fiber optic Fabry–Perot pressure sensor based on oxy-hydrogen flame welding and spiral tube

In this paper, a fiber optic Fabry–Perot (F–P) cavity high pressure sensor used in oil wells is presented. An F–P cavity probe encapsulated by silica capillary was fabricated through oxy-hydrogen flame welding, and the F–P cavity was fully sealed with adhesive-free bonding. A spiral tube filled with silicone oil was chosen to prevent the probe from directly contacting with down-hole corrosion fluid and to transfer pressure. A fiber Bragg grating was linked with the F–P cavity probe to measure ambient temperature for the probe’s temperature compensation. The sensing pressure can be as high as 82 MPa with a sensitivity of 241 nm/MPa, a repeatability of 0.05% F.S.(full scale), a resolution of 0.0004 MPa with the temperature ranging from room temperature to 175 °C. Besides, the maximum fluctuation of the F–P cavity length can be as small as about 0.0072 MPa within 40 days at the pressure and temperature of 42 MPa and 130 °C. In addition, this kind of sensor has been used in Shengli Oil Field.