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Research On Modal Interference Sensor Based On Core-offset Splicing Of Single Mode Fiber

Posted on:2013-03-11Degree:MasterType:Thesis
Country:ChinaCandidate:M ZhouFull Text:PDF
GTID:2248330371499880Subject:Optics
Abstract/Summary:PDF Full Text Request
Optical fiber sensor has lots of advantages such as anti-electromagnetic interference, corrosion resistant ability, high sensitivity, small size, compact structure and large dynamic range, so the modal interferometer can be used in border security, large generating units, aircraft and space condition monitoring, bridge and dam safety monitoring and so on. Compared to traditional fiber sensor like Michelson and Mach-Zehnder interferometers which require more than two paths to achieve interference, the modal interferometer just need one fiber to achieve the interference of different modes, because of the different phase causing by the transmission velocities of different modes. For modal interference, the changes of external environment can make the effective refractive index different, which can cause the transmission modes change and recombine, and then the interference wave will shift. This shift can be detected by the Optical Spectrum Analyzer to measure the change of the environment parameters.This paper is research on the modal interferometric sensing mechanism based on the core offset splicing of single mode fiber. Two types of different structure of transmission and reflection interferometers are reported, and the research on temperature sensing and strain sensing of the two structures are also given; a hybrid interferometer based on modal interferometer and Sagnac loop is proposed, and this hybrid interferometer can effectively improve the output extinction ratio.The first chapter is a brief introduction of the development and the advantages of the fiber sensing technology. Then the classification of the fiber sensor is discussed and each category’s principle is also given. Besides, the development states of modal interferometer in the domestic and international are described. At last, the main contents and the innovations of this paper are introduced.In the second chapter, based on the electro-magnetic theory, the interference conditions of light wave are analyzed. Then according to Maxwell equations and the wave theory, the base principle of modal interferometer sensor is summarized. Using the simplified theory of the linear polarization mode, we analysis the mode fields based on single mode fiber core offset. These theories provide a solid foundation of the next chapters.A modal interferometer based on simple core-offset splicing of single mode fiber is mentioned in chapter3. The extinction ratio of interference spectrum can be controlled by setting the splicing mode and the parameters of Splicer. The transmission structure and reflective structure of this interferometer are researched, and their strain and temperature sensing characteristics are also analyzed.In chapter4, according to the Jones matrix of Sagnac interferometer which based on birefringence fiber, a hybrid structure which based on the core-offset splicing of single mode fiber and the Sagnac loop is proposed. The temperature sensing of this hybrid interferometer is measured and the effect of extinction ratio to our experiment is analyzed. In the experiment, the hybrid interferometer can significantly increase the extiction ratio by adjusting the polarizaiton state, and in some band, the increase in extinction ratio is up to10dB.
Keywords/Search Tags:Fiber sensing technology, modal interferometer, extinction ratio, single mode fiber, core-offset splicing
PDF Full Text Request
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