Design Of Tapered Optical Fiber Sensor Based On Metal Organic Framework(MOF) Materials And Research On Trace Ethanol Detection

Ethanol is a flammable,volatile liquid that is dangerous to humans and organisms and is commonly used in food processing,medical,beverage and other industries.ZIF-8 is a typical MOF material,which has hydrophobicity,high porosity,selective adsorption and preconcentration of ethanol molecules.Coating the fiber with specific nanomaterials can further improve the efficiency of the sensor.The interaction between ZIF-8 coated on the fiber and ethanol molecules will lead to changes in the optical characteristics of the outside of the fiber,which makes the fiber sensor show remarkable sensing performance in the detection range and sensitivity of ethanol.Single mode and few mode fibers are prepared into tapered fibers.The main research of this paper is as follows:1.Design and fabrication of a single-mode tapered fiber sensor based on ZIF-8.The sensor is made by melting a single-mode fiber into a tapered fiber,and then growing ZIF-8 thin film on the tapered waist surface of the single-mode tapered fiber.When the optical signal is coupled from the single-mode fiber to the tapered fiber,HE₁₂ mode is excited from HE₁₁ mode.HE₁₂ mode will interfere with HE₁₁ mode in the tapered fiber,and also stimulate the evanescent field in the tapered waist region of the tapered fiber.The mode interference effect and evanescent field effect can excite the light field outside the waist region of the tapered fiber,causing the light field to directly interact with the ZIF-8 film,making the tapered fiber extremely sensitive to changes in the refractive index of the ZIF-8 film.ZIF-8 material has selective adsorption and pre concentration effects on ethanol molecules.When ethanol molecules are adsorbed on ZIF-8 film,the refractive index of the film will change due to the preconcentration effect.The change in refractive index of ZIF-8 thin film can change the mode interference conditions in the tapered fiber,causing the shift of the sensor transmission spectral line,which enables the detection of trace amounts of ethanol in solution.The experimental results show that the sensor with the film with a thickness of 200nm has the best sensing performance,with a minimum detection of up to 0.5%（ethanol/water solution）for trace amounts of ethanol.The sensitivity of the sensor is 1.77nm%^-1,and it has good response recovery characteristics and selective sensing.2.Design and fabrication of a less-mode tapered fiber sensor based on ZIF-8.Because there are more modes that can be supported for transmission in low mode fibers than in single mode fibers,low mode fibers can stimulate better mode interference and evanescent fields after being tapered.When the optical signal is coupled from the single-mode fiber to the low-mode tapered fiber,HE₁₂,HE₁₃ and other modes are excited by HE₁₁ mode.These modes have higher energy ratio and better interference effect.When these higher order modes are transmitted in the fiber cladding,the light field can be excited better in the taper waist region of tapered fiber.The higher the intensity of light field excited in the cone waist region,the better the sensing performance of the sensor.The experimental results show that the sensor with less mode taper fiber structure has higher sensitivity,about 2.13 nm%^-1.The fiber optic sensor based on ZIF-8 has a simple structure and is easy to prepare,which has certain application prospects in the detection of trace organic molecules.