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Study On Refractive Index Measurement System Based On The Theory Of LPG

Posted on:2004-12-18Degree:MasterType:Thesis
Country:ChinaCandidate:L WangFull Text:PDF
GTID:2168360122480876Subject:Detection Technology and Automation
Abstract/Summary:PDF Full Text Request
Based on the analysis of long-period fiber gratings'(LPGs) research state and the problems of refractive index measurement, the theory of LPG was in detail analyzed and studied in this dissertation. Firstly, the mathematical model of LPG was established. Secondly, the refractive index measure system based on LPG was designed. Lastly, the feasibility and the influencing factor probably appeared were analyzed and researched through experiments.The eigen equation of fundamental mode and the cladding mode in weak optical fiber was derived using an accurate three-layer geometry model and solved the propagation constants and effective refractive index of fundamental mode and the first twenty cladding mode. Based on the previous work, the cladding modes' sensitivity to the surrounding media's refractive index was studied and the fittest cladding mode for refractive index measure was selected. From coupled mode theory, the mathematical model of LPG was established.LPGs' transmitted spectrum property with various length, period, coupled intensity and index change were researched in the light of the established mathematical model, and the relation between Full Width Half Maximum (FWHM) and parameter of grating was derived. Besides, the spectrum property of the phase shift LPG with different phase shift in different position and parallel or cascade LPG were also analyzed and studied. The fiber grating's parameter and combination fit for refractivity measure were selected.On the basis of the theoretical analysis and research, the refractivity measurement system was designed, which was based on cascade LPG and phase generated carrier technique. The feasibility of system was in detail demonstrated.Last, the refractive index measurement system based on LPG designed in this paper was research in the experiments. Including the analysis of the working principle and characteristic of the main devices in the measurementsystem. At the end of the dissertation, the testing result was given and the influencing factor such as temperature, strain, bend and so on were analyzed too. And it was found that bend is the main influence and it must be strictly avoid during the process of measuring.
Keywords/Search Tags:Long-period fiber grating, Coupled mode theory, Spectrum, Refractive index, Phase generated carrier technique
PDF Full Text Request
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