The Research On The Characteristics Of Optical Fiber Based On The Evanescent Field-effect

Non-destructive testing which faced on the biochemical risk environment has become theresearch hot spot. Optical fiber has been widely used in the detection of trace substances as ananti-electromagnetic interference and loss conductive material.This thesis is based on the Evanescent field-effect which on the surface of the opticalfiber, focusing on analysis of the optical properties and transmission characteristics of thetapered optical fiber, and based on this, designed a kind of double tapered fiber optic sensorwhich be used to trace substances detection, and made an preliminary research andexploration for its sensing properties. As the optical fiber is made of silicon material，it hasgood biocompatibility ,Inertia and Easy to functional (There is abundant hydroxyl groups, caneasily react with alcohols and silane coupling agent, to facilitate further combined with thetarget biomolecules).so we combined the surface modification technology with optical fiber sensingtechnology and try to detect which of the substances.The optical fiber probe which taper length were 20, 25, 30 mm were prepared byHydroxide flame fusion Rafah. A sensitivity analysis was made from both theoreticalcalculations and experimental tests, and come to a Conclusion that the optical fiber sensorwhich tapered length was 30mm has higher sensitivity and stronger evanescent field effect. Atlast, we improved the fiber cleaning and packaging process and made slides as theencapsulated devices which neither react with concentrated sulfuric acid nor produceimpurities, and complete the package under the action of air flow.The prepared fiber-optic sensor was used to the spectral measurements of water andalcohol solution，through the method that search the characteristic absorption peaks to achievematerial detection which has certain characteristics and the power absorption was reach to3-5dB.However, due to the broad spectral range, there was a peaks overlap phenomenon indifferent substances during the process of looking for the characteristic absorption peak. Forthis, we explored the fiber surface modification experiments and modified the silane coupling agent with polar and nonpolar specific functional groups to detect the substance which hascorresponding features. The experimental results show that the absorption peaks were moreobvious, more absorption and the absorption rate was improved about 1-2dB compared withthe unadorned and this fully proved that our experiment is feasible.After the qualitative substances detection, we also carried out a number of quantitativetests. As alcohol for example, the Spectra tests were carried which mixing ratio were 1:10,1:15, 1:20, 1:25 and 1:30with the water. The test results show that the absorption wasescaladed with alcohol concentration increased and the double tapered fiber sensor we madewas sensitized to the concentration of a substance can be used for the quantitative detection ofthe substance concentration.