A Photon-counting Optical Time-domain Reflectometry Based Optical Fiber Temperature Sensor System

With the rapid increase of large infrastructure facilities in China,temperature monitoring,as an important component of health monitoring of large infrastructure structures,has attracted more and more attention.By monitoring the temperature changes of large infrastructure,we can infer the impact of structural damage and deformation,which caused by temperature changes,on the reliability of the infrastructure.Furthermore,temperature monitoring,through which pipeline leaks,fires and other safety accidents can be effectively avoided,is also widely used in natural gas and oil pipeline health monitoring,real-time online monitoring of power loads and coal mine safety production monitoring.As one of the most promising technologies in optical fiber sensing technology,compared to traditional electrical sensing systems,optical fiber temperature sensing system has the advantages of corrosion resistance,no electromagnetic interference,low transmission loss,long-distance real-time online detection and working in flammable,explosive and other harsh environments.The common optical fiber temperature sensing system is based on the optical time-domain reflectometry(OTDR)to detect and analyze the backscattered light signal with temperature information,thus completing the real-time monitoring of the external temperature field.However,the traditional OTDR has the principle contradiction that it is difficult to improve the spatial resolution and dynamic range simultaneously.In this paper,we replaced the OTDR of traditional optical fiber temperature sensing system with a photon-counting optical time-domain reflectometry(PC-OTDR).By using the advantages that the single photon avalanche diode(SPAD)in PC-OTDR can detect Single photon with high sensitivity,the positioning accuracy,detection speed and measurement range of optical fiber temperature sensing system is improved.We also tested the performance of the self-designed photon-counting light reflectometry,which is built with a photon-counting module consisting of a silicon based single photon avalanche diode(Si-SPAD)and an active quenching and reset integrated circuits(AQR-IC).The experimental results show that PC-OTDR system achieving the OTDR trace of 20 m fiber-under-test within 0.2ms and 6km fiber-under-test within 20 s.The spatial resolution measured is 3.8cm and 60 cm respectively.Meanwhile,by means of fiber microstructure processing technology,a single-mode fiber(SMF)-capillary optical fiber(COF)-single-mode fiber(SMF)cascade structure fiber temperature probe is designed,we tested the temperature measurement performance of the optical fiber temperature sensing system composed of PC-OTDR and SMF-COF-SMF cascade structure.The experimental results show that the optical fiber temperature sensor can quickly respond to the region temperature from 20℃ to 220℃ while achieving high precision positioning.The innovation of this paper is listed as follows:(1).The self-designed photon-counting light reflectometry,which is built with a photon-counting module consisting of a silicon based single photon avalanche diode(Si-SPAD)and an active quenching and reset integrated circuits(AQR-IC),has characteristics of fast detection of "events",high positioning accuracy and high spatial resolution.(2).Based on the designed PC-OTDR,combined with fiber optic microstructure processing,an optical fiber temperature sensor with regional temperature measurement and high positioning accuracy is designed.