Structural Design And Analysis Of SPR Type Photonic Crystal Fiber Refractive Index Sensor

In the field of sensors with remarkable information throughput,fiber optic sensing is highly regarded.Photonic crystal fiber（PCF）exhibits good sensing performance and has derived multiple sensor structure types based on different sensing principles.Among them,the combination of surface plasmon resonance（SPR）technology and PCF technology has shown good results in material concentration detection in solutions and gases.This study designs three PCF-SPR sensing structure models with different structures based on SPR sensing principles and the international research status of PCF-SPR sensors.Finite element method simulations are used to model and optimize the sensing structures and study their sensing performance.This study focuses on:（1）Introducing an H-type PCF-SPR refractive index sensor.Detailed sensor structure design process is described from the perspective of micro-structure design.After obtaining the optimal structure parameters,the relationship between the loss and refractive index of the proposed H-type sensing structure is analyzed.The wavelength sensitivity（WS）can reach 8,620 nm/RIU,with a resolution of 1.1×10^-5 RIU and a refractive index detection range of 1.35-1.40.（2）Introducing a double-side polished D-type PCF-SPR refractive index sensor.The sensor’s coupling mode is analyzed based on the fiber’s coupling characteristics.The thickness of the sensitive layer,polishing depth,and air hole parameters are analyzed.The analysis of the sensing characteristics is performed based on the optimal structure parameters of the sensor,and the research results show that the maximum WS of this sensor is 13,270 nm/RIU,with a corresponding wavelength resolution of 7.54×10^-6 RIU and a refractive index detection range of 1.19-1.40.（3）Introducing a deep-etched micro-opening high-sensitivity double-core symmetrical side-polished improved D-shaped PCF-SPR refractive index sensor.After optimizing the geometric parameters of the sensor,the impact of the deep-etched micro-opening structure on the sensor performance is analyzed.The simulation results show that the addition of deeply etched micro-opening structures significantly improves the sensing performance,enhances sensor sensitivity,and reduces the transmission loss from fiber core leakage to the cladding.Finally,the maximum WS of this sensing structure is 24,600 nm/RIU,corresponding to a wavelength resolution of 4.07×10^-6 RIU,refractive index detection range 1.26-1.41.Compared with the second sensing structure,it has higher sensitivity,but the refractive index detection range is reduced.The scenarios for the application of PCF-SPR refractive index sensors are then introduced,and the specific sensing system model used in this study is presented.