| The optical sensors based on multimode interference have got rapid development in thefield of sensors. The optical sensors possess their inherent advantages, including highsensitivity, easy fabrication, low cost and immunity to electromagnetic interference.The single-mode-multimode-single-mode (SMS) structure is a new type of multimodeinterference sensor that has been extensively researched by experts. Based on the analyses onthe theory and applications of the SMS structure, this assay had studied two kinds of opticalfiber sensors which are based on corrosive multimode fiber. The numerical simulation andexperiment have been analyzed. The followings are the main content:1) The development situation, basic principle and classification of optical fiber sensors, andthe application are depicted and the existing problems of optical fiber sensors areanalyzed. And then, the development and research progress of multimode interferencesensor and the SMS structure are described in detail.2) The theory of SMS structure is introduced. First, the multimode optical fiber evanescentwave theory is depicted; then the basic theory of step type multimode fiber is analyzed,which including the optical field, patterns, and the corrosion principle of multimode fiber;at last, the numerical simulation of the SMS structure and corrosion type of the SMSstructure are described respectively.3) The multimode interference principle and the structure of the traditional SMS sensingcharacteristic are analyzed, and then a refractive index sensor of corrosion type SMS isproposed. Two dips are selected as recorded points, because they have the sametemperature characteristics and different refractive sensitive features, which caneffectively eliminate the effects of temperature in the refractive index measurement. Theexperiment results showed the refractive index sensitivity coefficients of the two dips are183.03nm/RIU and80.969nm/RIU.4) A novel type of corrosion multimode interference sensor is proposed in the paper. In thetraditional SMS structure which is composed of small core diameter clad multimode, abig core diameter without clad multimode fiber is inserted to make up of SMMS structure.A variety of fiber core models will be inspired in the two pieces of multimode fibers, thusthey interference, using the different sensitivity to temperature and liquid level of thedifferent dips in the interference spectrum, the water temperature and liquid level aremeasured simultaneously. In addition, the experiments of the level of the water and saltwater have been carried on, respectively. The experiment results show that the sensitivityof the level of salt water is much higher than that of water, the highest sensitivitycoefficients of the level of salt water is-1.251nm/mm. |
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