Fiber-Optic Temperature Sensor Using a Fabry–Pérot Cavity Filled With Gas of Variable Pressure

We report a high-temperature fiber-optic sensor based on measuring the spectral fringes of a Fabry–Pérot (FP) cavity on a microstructure fiber (MF) when the gas pressure in the cavity is varied through the holes in the MF. Theoretical analysis shows that the absolute temperature can be deduced from the slope of the spectral shift versus pressure curve, which requires no calibration and is insensitive to the FP cavity length variations. For demonstration, we fabricated a miniature sensor whose FP cavity is formed by sandwiching a fuse-silica tube between a side-hole MF and a solid-core fiber. Using the holes in the MF as gas channels, the pressure in the FP cavity is controlled. The sensor was tested for operation above 1000 °C. Strain-insensitive temperature measurement was demonstrated at ambient temperature for a strain range up to 3600 με.