Fabry-Perot temperature sensor for quasi-distributed measurement utilizing OTDR

This paper presents a quasi-distributed Fabry-Perot fiber optic temperature sensor array using Optical Time Domain Reflectometry (OTDR) technique. The F-P sensor was made by two face to face single-mode optical fibers and their surfaces have been polished. Due to the low reflectivity of the fiber surfaces, the sensor was described as low Fresnel FPI. The working principle was analyzed using two-beam optical interference approximation. To measure the temperature, a certain temperature sensitive material was filled in the cavity. The slight changes of the reflective intensity which induced by the refractive index of the material was caught by OTDR. The length of the cavity was obtained by monitor the interference spectrum which is used for the setting of the sensor static characteristics within the quasi-linear range. Based on our design, a three point sensor array were fabricated and characterized. The experimental results show that with the temperature increasing from -30°C to 80°C, the reflectivity increased in a good linear manner. The sensitivity was approximate 0.074 dB/ °C. For the low transmission loss, more sensors can be integrated.