High-Sensitivity Fiber-Optic Fabry–Perot Interferometer Temperature Sensor

A novel structure of a fiber-optic Fabry–Perot interferometric (FFPI) temperature sensor is presented in this paper. The design of the sensor is analyzed and evaluated by the finite-difference time-domain (FDTD) method. Then, the proposed sensor is fabricated using a conventional single-mode fiber (SMF). A gold (Au) layer and a nickel (Ni) layer are sputtered and electroplated on the surface of the SMF, respectively. As a Fabry–Perot (FP) cavity, a micro-punch-hole is machined by focused ion beam (FIB) milling. Here, the structure of the FP cavity can be considered a pair of bimetallic strips. On the basis of the sharp difference in thermal expansion coefficient between the fused silica and the metallic materials, the temperature sensitivity of the proposed sensor was determined to be over 70 pm/°C in the 0 to +60 °C range. The standard deviation of temperature is less than 0.15 °C in 1 h.