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Investigation On The Key Technologies And Implementation Of White Light Interferometric Distributed Optical Fiber Vibration Sensing

Posted on:2015-04-17Degree:MasterType:Thesis
Country:ChinaCandidate:H WangFull Text:PDF
GTID:2308330452455934Subject:Optical Engineering
Abstract/Summary:PDF Full Text Request
With the fiber properties of transmitting as well as sensing, distributed optical fibervibration sensing technology (DOFVS) could monitor strain and vibration signal aroundevery point along the fiber link. Such DOFVS system could realize a long distance vibrationmonitoring without any blind spot. DOFVS is particularly suited to regional security, oil andgas pipeline leak monitoring, structural health monitoring and communication link securitydefense and other fields. This thesis takes the in-line Sagnac interferometer as the researchobject to explore the sensing principle and locating method of the white light interferometricDOFVS.Firstly, we analyzed the basic theories of the white light interferometric DOFVS,including the stress and strain effect of the fiber, structures and characteristics of the basicinterferometric DOFVS. The sensing principle and extended structure of DOFVS based onSagnac interferometer were studied emphatically.Secondly, the sensing scheme and key technologies of the DOFVS based on in-lineSagnac interferometer were researched. We analyzed the phase modulation and locatingmethods in cases of single and multiple frequency vibration source, respectively. Theinfluence of3×3coupler and delay line fiber, and the differential-integral phasedemodulation algorithm were considered.Thirdly, the improved locating algorithm for the white light interferometric DOFVSwas proposed. Based on analyzing the drawbacks of the traditional locating method bysearching null-frequencies directly, we introduced the principle and procedure of the2-FFT(the twice-fast Fourier transform) locating algorithm. Moreover, the multi-point vibrationlocating ability of2-FFT locating algorithm was discussed in theory.Finally, the experiment on the white light interferometric DOFVS using2-FFT locatingalgorithm was investigated. Compared with the traditional locating method by searchingnull-frequencies directly, the experimental results of multiple groups of single vibrationshowed that the2-FFT locating algorithm could greatly improve the locating stability, andachieve an accuracy of less than100m along the41km length fiber link. The multi-pointlocating ability of the2-FFT locating algorithm was also verified when multiple vibrationsources were applied on the sensing fiber simultaneously. The white light interferometric distributed optical fiber vibration sensing system basedon2-FFT locating algorithm has the advantages of long distance, high locating accuracy andmulti-positions locating simultaneously ability. The system could be used in perimetersecurity, communication lines and pipeline damage behavior warning and other fields. Thetechnology is of great research value and social benefits.
Keywords/Search Tags:Distributed optical fiber vibration sensing, Sagnac interferometer, Vibration monitoring, Phase demodulation, Locating algorithm, Fast Fourier transformation
PDF Full Text Request
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