Fiber Optic Temperature Sensor Using Dual Air- Filled Fabry-Perot Cavities With Variable Pressure

We present an approach for high temperature measurement using a pair of fiber-optic Fabry-Perot (FP) cavities filled with gas of identical but variable pressure. One of the FPs (reference FP) is placed in the cold zone with a known temperature. The temperature of the measuring FP can be deduced by the spectral fringe shift vs. pressure of the two FPs. This method does not require measurement of the pressure or the knowledge of the optical properties of the gas. The use of gas as the sensing material and the measurement mechanism also implies long-term stability and eliminates the cross-sensitivity to strain. We fabricated the sensors and tested them for measuring temperature up to 800 degrees C. The sensor shows good linearity in the range. Long-term test conducted at 800 degrees C exhibited the stability of the sensor with fluctuations of <= 0.3% over a duration exceeding 100 hours.