Temperature and strain response of in-fiber air-cavity Fabry-Perot interferometer under extreme temperature condition

In this work, a simple fiber Fabry-Perot air-cavity interferometer (FPI) is formed by splicing a 246 mu m long hollow core silica tube (HCST) between two single mode fibers (SMFs). In the thermal characterization test, the FPI exhibits limited linear range up to 700 degrees C in the first cycle of isochronal annealing treatment from room temperature up to 1000 degrees C. However, after a series of repeated isochronal thermal annealing, the temperature response of the proposed FPI is extended further to 1000 degrees C with a good thermal repeatability. Meanwhile, the annealed FPI has linear axial strain sensitivities up to 1000 mu epsilon from room temperature up to 800 degrees C. The proposed fiber structure is a potential sensor for high-temperature or stress measurement in aeronautical or metallurgical fields.