Miniature All-Fiber High Temperature Sensor Based on Michelson Interferometer Formed with a Novel Core-Mismatching Fiber Joint

An miniature all-fiber high temperature sensor based on Michelson interferometer is experimentally demonstrated in common single-mode fiber. The sensor probe consists of a core-mismatching fiber joint (CMFJ) followed by a section of end-cleaved fiber. Generating of the CMFJ is due to fusion-splicing the prefusion-inducing micro-bend fiber end with a normal cleaved fiber end in axial alignment. Light coupled into the fiber cladding by the CMFJ is coupled back to the fiber core at the same point after being reflected by the cleaved fiber end-face, which then interferes with the reflected core propagating light. The dip wavelength in the reflected interferential spectrum presents a red shift in the temperature range of 50 °C to 600 °C. The maximum temperature sensitivity is 115.34 pm/°C at 550 °C, and the nonlinear correlation coefficient is 99.95%. The all-fiber temperature sensor owns the advantages of compactness, easy fabrication, low cost, and good repeatability, and has the ability to monitor temperature changes in different environments.