PCF-Based Fabry–Pérot Interferometric Sensor for Strain Measurement at High Temperatures

We report a simple and robust all-fiber in-line Fabry-Pérot interferometer (FPI) with an air bubble cavity, which is fabricated by directly splicing a multimode photonic crystal fiber (MPCF) to a conventional single-mode fiber with a commercialized fusion splicer. The air microbubble inserted between the two fibers has two smooth glass-air interfaces separated by a distance
L
as two reflective mirrors of the FPI. Due to the big air holes in the cladding of MPCF and its large numerical aperture, this device has higher signal-to-noise ratio and fringe contrast than that of the FPI based on hollow-core photonic crystal fiber. Experimental results show that the FPI can be used to measure strain in the range of 0 ~ 1850 με at high temperatures of up to 750°C. Therefore, such an FPI sensor may find important applications in the aeronautics or metallurgy areas.