Design And Optimization Of Distributed Fiber Temperature Sensor Based On Raman Scattering

Distributed fiber sensors have attracted much attention for decades with the development and maturity of fiber technology. In these systems, fiber plays the role of transmission channel and sensing medium. The environmental information such as temperature, strain, humidity could be detected by demodulating the change of characteristic parameters of light. Specially, the Raman distributed temperature sensor (RDTS) system is a kind of high-tech product, which combined optics, mechanics, electronics and weak signal detection technology. It could obtain the temperature information of thousands of points along the entire fiber simultaneously. Owing to their immunity to electromagnetic interference, the capability of handling much higher bandwidth, safety in hazardous conditions, RDTS system has found successful implementation in various application fields, such as power cable monitoring, leakage-detection of oil pipelines and health monitoring of dam.In this thesis, the RDTS system based on Raman scattering and optical time-domain reflectometry (OTDR) technique was designed, and the relative temperature tests were completed. Moreover, some theoretical analysis and optimization measures were proposed. The main contents and innovation are as follows:1. The Raman scattering theory was analyzed from traditional electromagnetic theory and quantum theory. And the influence factors on the calibrating area and reference temperature were simulated.2. The experiment system design was determined and technical characteristics of each device were introduced. Some methods were presented to improve the signal to noise ratio (SNR), including cumulative average method, wavelet transformation method, and Simplex coded method. The simulation results indicated the Simplex code was obviously more effective than averaging method in reducing noise level.3. Experiments about temperature measurements were completed. The temperature accuracy was±1℃and the spatial resolution was3m, which could satisfy the demands of common application.4. A dual-points temperature demodulating method was proposed to estimate the channels amplifications and system DC offsets. Moreover, a simple correction algorithm was proposed to compensate the fiber position error caused by wavelength dispersion. Temperature simulation results validated that the temperature distortion was corrected and the temperature accuracy was effectively improved.