Research On Temperature Sensor System Based On Weak Reflection Fiber Gratings Combined With WDM And OTDR

Currently, the quasi-distributed sensors based on Bragg grating has become one of the hot spots at home and abroad because of its many advantages, such as high precision, good stability, easy to detect, and so on. In order to improve the multiplex capacity of Bragg grating in sensor array, this paper proposes a new distributed temperature sensing network based on weak reflection Bragg grating. The system which combined WDM with OTDR has the advantages of vast multiplex capacity and real-time detection. In addition, in order to realize the intensive serial multiplexed grating and high-speed demodulation, a tunable multiple wavelength light source is developed which is used as the driving light source of the system. Main research work is as follows:Firstly, the development history and the main species of the optical fiber grating are introduced. the coupled-mode theory of optical fiber grating and principle of Bragg grating are expounded. This paper decides the research direction of weak reflection Bragg grating and discusses the common demodulation methods and the multiplex capacity of weak reflection Bragg grating.Secondly, a new weak reflection Bragg grating sensor array that combines with WDM and OTDR is presented. It uses WDM to improve the multiplex capacity of Bragg grating, and takes advantage of OTDR to detect every weak grating in real-time. Meanwhile, a multiple wavelength light source is developed by the characteristics of the system, which shortens the period of systematic detection, and enhances the ability of real-time.Thirdly, the data from high-speed data acquisition card is processed by the algorithm of getting rid of noise by averaging and overlaying the signals in time domain and Guass fitting algorithm by Lab VIEW. Then the center wave length of weak reflection Bragg grating is demodulated, and the user interface is programmed according to it.At last, the distributed temperature sensor network of weak reflection Bragg grating is set up, and then detects temperature in real-time. The results of the experiment show that, the system can detect9weak gratings on line in real-time. And it can detect the temperature in high accuracy. In addition, it is stable, reliable, and scalable to meet the needs of practical engineering survey.