Curvature and temperature sensor based on bulge-taper structures interferometer with embedded fiber Bragg grating

A sensor head consisting of an all single-mode fiber (SMF) in-line Mach–Zehnder interferometer (MZI) with an embedded fiber Bragg grating (FBG) is proposed and experimentally demonstrated for simultaneous measurement of curvature and temperature. It is fabricated by cascading two bulge-taper fusion structures in a section of SMF including an FBG. The MZI is sensitive to fiber bending and ambient temperature with a sensitivity of − 16.59  nm/m −1 in the range of 1.05 to 4.05  m −1 and 58  pm/°C in the range of 30°C to 100°C, respectively. However, the FBG is only sensitive to the latter with a sensitivity of 13  pm/°C . Simultaneous measurement of curvature and temperature is obtained and the cross-sensitivity issue can be solved. The experimental results show that the average relative error of the curvature is 0.38%, which is about 18 times better than that without temperature compensating. The average error of temperature is only 0.21°C.