Fiber-optic temperature sensor using dual fabry-perot cavities filled with gas of different pressure

We present a fiber-optic temperature sensor based on dual Fabry-Perot cavities formed at the end of a multicore fiber and filled will with gas of differential pressure. Making use of the unique relationship of the refractive index of a gas to its pressure and absolute temperature, a theoretical model is developed to extract the absolute temperature from the differential shifts of the spectral fringes from the two cavities. The demodulation of the sensor is inherently insensitive to the strain applied on the sensor. In addition, the sensor has excellent stability due to the use of gas, which has stable optical properties even at elevated temperature, as the sensing element. Such a sensor was fabricated with dual cavities filled with air of a differential pressure of 1000 psi and the sensor is tested for measurement of absolute temperatures up to 900 K (627 °C). The sensor performance in terms of accuracy, resolution, cross-sensitivity to strain, and stability are studied.