Structural Design And Characteristics Of D-Type PCF-SPR Refractive Index Sensor

PCF-SPR sensors are the result of combining a flexible structure of Photonic Crystal Fiber（PCF）with Surface Plasmon Resonance（SPR）technology.These sensors exhibit excellent sensing characteristics for refractive index changes in the surrounding environment and can be used as refractive index sensors,while the D-type structure simplifies the coating process and enhances the sensing performance compared to the conventional PCF structure.In this paper,three D-type PCF-SPR refractive index sensors are designed,and the influence of the structural parameters of optical fiber on the sensing performance is investigated in depth using loss spectrum analysis,and the sensing structure is optimized,and the spectral sensitivity and refractive index detection range of the sensors are further analyzed.（1）A D-type PCF-SPR sensor with gold film coating is proposed.The D-type structure and the single-layer coating of the gold film simplify the coating process,and two sizes of air holes exist inside the cladding.After optimizing the parameters in the geometric structure by the loss spectrum analysis method and the control variable method,the refractive index range of this D-type PCF-SPR sensor is 1.25-1.37,which can achieve low refractive index detection,the maximum wavelength sensitivity is 3000 nm/RIU,and the best detection resolution is 3.34×10^-5RIU.（2）A gold-coated D-type PCF-SPR sensor based on a circular groove is designed.A circular notch is introduced at the D-type platform as a microfluidic channel to reduce the use of detection samples and is suitable for the detection of scarce analytes to be measured.This D-type PCF-SPR sensor can achieve low refractive index and wide range detection in the refractive index range from 1.23 to 1.36 with the best resolution of 5.56×10^-6RIU,the maximum amplitude sensitivity of 258.26 RIU^-1,and the maximum wavelength sensitivity of 18000 nm/RIU by the finite element analysis method and the loss spectrum analysis method.（3）An ITO film-coated D-type PCF-SPR sensor with rectangular notch is designed.The introduction of the rectangular notch not only serves as a microfluidic channel to carry the analyte to be measured,but also allows for a more flexible design of this model structure.At the same time,the ITO film has a lower cost compared to the gold film and has excellent electrical conductivity,light transmission and oxidation resistance.The D-type PCF-SPR sensor achieves an ultra-wide range of refractive index detection from 1.00 to 1.38,while the best detection resolution of 1.38×10^-6RIU can be obtained,and the maximum wavelength sensitivity reaches 72,500 nm/RIU,which is significantly better than the same type of PCF-SPR sensors on the market.