Study On The Information Processing Technology Of The Quasi-distributed Sensing System Based On Low-Bragg-reflective Fiber Grating

As distributed sensing technology based on FBG can extract distributed information inlarge measuring range and in various areas, it becomes the focus of distributed sensingresearch recently. Nowadays, there are new multiplexing schemes on FBG distributedsensing, such as time division multiplexing(TDM)、Frequency division multiplexing(FDM)、Code division multiple access(CDMA) and other multiplexing methods besides Wavelengthdivision multiplexing(WDM) scheme which is already common and mature. But thesemultiplexing methods more or less have their restriction. In order to improve the capacity ofthe FBG distributed sensing system, we propose a new multiplexing scheme based onlow-index Bragg reflective fiber gratings, which is proved to have large capacity, and highsensing precision in temperature measurement and strain measurement. The main jobs andachievements are listed as follows:Firstly, the analysis methods of FBG are introduced, including Coupled-wave theoryand Transfer-matrix method. The classification and manufacturing process of FBG is alsoelaborated. The production condition of low-reflective FBG is analyzed, its performance issimulated by MATLAB. The work of fabricating low-reflective FBGs is also finished.Secondly, the practical sensing system with large capacity using low-reflective FBGswritten in fiber is proposed, and its practical capacity is analyzed. A improved scheme isdesigned under high-loss situation.Thirdly, the detecting technique named Optical wavelength time-domain reflection(OTDR), which utilizes information of both time and wavelength to sense and thecorresponding dada processing algorithm are proposed. Experiments on this scheme are alsoinvestigated, which includes the distributed sensing work on temperature and strainmeasurement. A system involves9sensing units is proved to work.Lastly, the principle of low-coherent interference multiplexing and its theoreticalanalysis and application in the demodulation of distributed FBG sensing systems are alsodiscussed.