Research On The Preparation And Refractive Index Sensing Characteristics Of Tapered Optical Fiber SPR Sensor

Surface plasmon resonance(SPR)is a physical phenomenon of surface plasma generated by coherent free electron oscillation on the metal surface when the incident light field at the metal and dielectric interface meets certain existence conditions.SPR sensosrs have excellent performance in detecting small changes of refractive index of metal surface medium.After decades of development,SPR sensors have been widely used in food safety,medical research,environmental detection and other fields.Among them,optical fiber SPR sensors have the advantages of small volume,low cost and simple structure.Meanwhile,tapered optical fiber is a common structure for generating evanescent wave and stimulating SPR effect,and it is more sensitive,compact and simple.In this dissertation,tapered structure is applied to polymer optical fiber and hollow core fiber with hetero-core structure respectively.The former greatly simplifies the preparation process of polymer optical fiber SPR sensor and has good sensitivity.The latter uses experimental results to propose a new method for measuring refractive index and obtains high sensitivity.The main work of this dissertation is as follows:A U-shape tapered polymer optical fiber based surface plasmon resonance sensors are fabricated and proposed for refractive index sensing.The tapered polymer optical fiber was fabricated by a heating and drawing method,and the U-shape tapered polymer optical fiber can be formed by a heat setting process.In this paper,the refractive index sensing properties of the straight tapered polymer optical fiber SPR sensor probe and the U-shape tapered polymer optical fiber SPR sensor probe were compared,and the effects of different taper ratio and Au film coating mode(horizontal coating and vertical coating)on the refractive index sensing properties of the U-shape tapered polymer optical fiber SPR sensor were studied.The experimental results show that the sensor has good linearity.For the U-shape tapered polymer optical fiber SPR sensor with a taper ratio of 6.7 and Au film coated in the vertical direction,the sensitivity can reach 1534.53 nm/RIU with refractive index range of1.335-1.41.An optical fiber SPR sensor based on multimode fiber-tapered hollow core fibermultimode fiber structure is proposed for refractive index sensing.The experimental results show that a multi-mode interference peak can be observed in addition to the SPR formant in the spectrum of high refractive index.With the increase of refractive index,the multi-mode interference peak appears blue shift,which is opposite to the SPR resonance peak.High sensitivity refractive index sensor can be obtained by monitoring the difference between two resonance peaks,which is a new method to measure refractive index.The refractive index sensing performance of the sensor probes with different taper ratios and different core diameters of hollow core fiber were studied.When the core diameter of the hollow core fiber is 30 μm,the taper ratio is 3.3 and the refractive index is 1.40,the sensitivity of SPR sensor probe based on the multimode fiber-tapered hollow core fiber-multimode fiber structure can reach 7592.25 nm/RIU.