A novel fiber optic temperature monitoring sensor using hard-polymer-clad fiber and an optical time-domain reflectometer

Hard-polymer-clad fiber is a specific type of optical fiber, in which a hard polymer cladding made of fluoroacrylate acts as a protective coating for an inner silica core. An optical time-domain reflectometer is an optical loss measurement system that provides optical loss and event distance measurement in real time. This study proposes a novel fiber optic temperature monitoring sensor system using an economical optical time-domain reflectometer and hard-polymer-clad fiber. Sensor nodes were economically and quickly made by locally stripping hard-polymer-clad fiber clad through photothermal and photochemical processes using a continuous/pulse hybrid-mode laser. The core length exposed was easily controlled by adjusting the laser beam diameter, and the exposed core created a backscattering signal in the optical time-domain reflectometer attenuation trace. The backscattering peak was sensitive to the temperature variation. Since the elaborated hard-polymer-clad fiber temperature sensor was insensitive to strain applied to the sensor node and to temperature variation in the normal hard-polymer-clad fiber line, neither strain compensation nor isolation technique is required. These characteristics are important advantages for using as structure-integrated temperature sensors. The performance characteristics of the sensor nodes included an operating range of up to 120 °C, a resolution of 1.52 °C, a tensile strain resistance of 13%, and a temperature sensitivity of −0.01 dB/°C.