Distributed temperature sensors based on modified-cladding optical-fibers

The measurement of temperature along optical fibers using an optical time domain reflectometer (OTDR) is discussed. A review of optical principles used to design a distributed temperature measurement system is included. Mathematical expressions for the back-reflected power coefficient due to thermal disturbance at the modified-cladding section are provided. The theoretical analysis is based on geometrical optics and Fresnel reflection. The measurement method makes use of optical radar techniques to obtain the range information along a test fiber. A silicone rubber elastomer is chosen as a temperature sensitive modified-cladding material. For distributed modified-cladding sections, the relative transmission loss is measured. A sensitivity of - 0.0072 dB/°C at each sensing region was obtained on OTDR. A comparison between theory and experimental results is carried out. The theory is sufficient to predict the behavior of the modified-cladding section depending on temperature