Research On SPR Sensor For Low Refractive Index Detection Based On Photonic Crystal Fiber

Surface Plasmon Resonance?SPR?sensing technology has attracted extensive attention from researchers in recent years,owing to its advantages of high sensitivity,fast response,and free-labeling detection.The introduction of photonic crystal fiber?PCF?in SPR sensors not only solves the problem of hard phase matching in traditional SPR structure,but also can achieve detection of substances like aerogel and sevoflurane through reasonable structural design,whose refractive index are far less than fibers.With the continuous development of biological and chemical technology,developing excellent-performance PCF-SPR sensors for low refractive index detection is of great significance for medical diagnosis,water pollution monitoring,gas sensing and other fields.In view of the existing problems of PCF-SPR low-refractive-index sensor,different PCF sensing structures are designed.Their sensing performance are studied by using the finite element method.The main research contents in this paper are as follows:?1?Based on the Maxwell equations,the excitation conditions of SPR are studied,and the basic principle of optical fiber SPR sensing is analyzed;The common numerical analysis methods of PCF are discussed,and the basic idea of solving PCF mode by finite element method is studied emphatically;The modulation methods and spectral analysis methods of SPR sensor are analyzed.?2?Based on a double-core D-type photonic crystal fiber,a surface plasmon resonance sensor for low refractive index detection between 1.12 and 1.37 is designed.The photonic crystal fiber in this sensor is composed of two kinds of air holes with different sizes around the central air hole.The effective refractive index of the core mode is reduced,by increasing the radii of the air holes on the left and right sides of the core,to realize the measurement of low refractive index.After polishing the fiber,the outermost large air hole directly contacts the substance to be measured for continuous real-time detection of refractive index based on metal external coating.Under optimized structural parameters,the maximum sensitivity of the sensor is 12000 nm/RIU and the resolution is 8.33×10^-6.?3?Based on a photonic crystal fiber with sector air rings,a surface plasmon resonance sensor for low refractive index detection between 1.0 and 1.27 is designed.The PCF consists of two layers of sector rings and a substrate,in which the number of air rings in the first layer is twice that in the second layer,to form a large leakage channel and improve the detection sensitivity of the sensor.The metal is coated on the outer surface of the cladding for the external sensing mechanism.The results show that the sensor is independent of polarization,with an average sensitivity of 5807 nm/RIU and a maximum resolution of 1.11×10^-5.