| With the outbreak of the new crown pneumonia epidemic,the use of ethanol on a global scale has greatly increased,which will inevitably lead to ethanol leakage and environmental pollution.As a volatile organic compound,there are many monitoring methods for ethanol gas,but there are few reports on the monitoring of ethanol or even trace ethanol in solution.As a porous metal-organic framework material,ZIF-8 has the advantages of hydrophobicity and structural stability,and can absorb trace amounts of ethanol in aqueous solutions.In this paper,a ZIF-8 film is grown on the surface of a new type of fiber-coreless fiber,and singlemode-nocore-singlemode(SNS)and coreless-singlemode-coreless are designed and prepared(Nocore-Singlemode-Nocore,NSN)Two optical fiber sensing structures,respectively,to study the sensing performance of these two optical fiber structures to trace ethanol in aqueous solution.The main research contents of this paper are as follows:1.Designed and prepared a ZIF-8-based optical fiber sensor,which includes a single-mode-coreless-single-mode fiber(SNS)structure constructed by fusion splicing single-mode fibers at both ends of a coreless fiber,and the original ZIF-8 nano-films of different thicknesses grown on the surface of coreless optical fibers by bit crystallization technology.When an optical signal is coupled from a single-mode fiber into a coreless fiber,it will excite a variety of higher-order modes and form multi-mode interference.The result of the interference is extremely sensitive to changes in the refractive index around the coreless fiber.Utilizing the porosity of the ZIF-8 material and the specific adsorption capacity for ethanol molecules,the refractive index of the ZIF-8 nano film after the adsorption of ethanol molecules will be changed due to the filling of the pores,which changes the multimode interference conditions in the coreless fiber.The transmission spectrum line is shifted to realize the detection of trace ethanol in the aqueous solution.The experimental results show that the200nm thickness ZIF-8 fiber optic sensor has the best sensing performance,and the minimum detection ethanol concentration can reach 1%(ethanol/water solution),and the sensitivity is 1.3 nm%–1,and has good response recovery characteristics.2.On the basis of the SNS optical fiber sensor,the structure is re-innovated,and a section of single-mode optical fiber is spliced in the middle of the coreless optical fiber to form an NSN optical fiber sensor.When the optical signal passes through the first section of coreless fiber,a high-order mode is excited.When it passes through the middle section of single-mode fiber,the excited high-order mode and the core fundamental mode are simultaneously transmitted in the cladding and the core,and the light of different modes propagates to the second section of coreless fiber,more order modes will be excited,and finally coupled to the output single-mode fiber.Because of the two phase differences produced by the two sections of coreless fiber,the light of different modes will interfere,and the interference spectrum will be obtained.Taking 200nm thick ZIF-8 film as the research object,two ZIF-8-based NSN fiber sensors were prepared:ZIF-8 film was grown only on the surface of the first section of coreless fiber and ZIF-8 film was grown on the surface of two sections of coreless fiber at the same time.The experimental results show that the optical fiber sensor with ZIF-8 thin film grown on the surface of two coreless fibers at the same time has a higher sensitivity,about 1.6nm%-1.The optical fiber sensor based on ZIF-8 has a simple structure and is easy to prepare,and has certain application prospects in the detection of trace organic molecules in water. |
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