Research On Structure Design And Sensing Characteristics Of Photonic Crystal Fiber SPR Sensor

Photonic crystal fiber surface plasmon resonance(SPR)sensor has the advantages of high sensitivity,real-time detection and label-free,and has shown great potential in the fields of chemistry and biology.High performance photonic crystal fiber SPR sensor has become a research hot topic in the field of refractive index sensing.In order to improve the performance of photonic crystal fiber SPR sensor(sensitivity,detection limit,etc.),this paper designs different structures of photonic crystal fiber SPR sensor from the perspective of structure design for photonic crystal fiber,material selection and microstructure design of sensitive layer.Ag-TiO₂ composite micro gratings is used as the sensitive layer,and the sensing performance of the sensor is studied by full vector finite element method.The main research contents are as follows:1.In order to improve the sensitivity of photonic crystal fiber SPR sensor,Ag-TiO₂composite micro gratings sensitive layer is designed on the inner wall of annular microfluidic channel on both sides of photonic crystal fiber,and a groove type photonic crystal fiber SPR sensor is proposed.Full vector finite element method is used to study the influence of the structural parameters of the groove photonic crystal fiber and the microstructure parameters of the sensitive layer on the sensing performance,and the structural parameters are optimized.The simulation results show that when the thickness of Ag film is 45 nm,the thickness of TiO₂film is 15 nm,the number of single channel micro gratings is 40,and the spacing angle is 0.6°,the average wavelength sensitivity of sensor is 6329 nm/RIU in the refractive index range of1.330-1.360,which is 1700 nm/RIU higher than that without micro gratings,and 550 nm/RIU higher than that without TiO₂ sensitive materials.The maximum wavelength sensitivity is10600 nm/RIU in the refractive index range of 1.350-1.355.2.Although the sensitivity of grooved photonic crystal fiber SPR sensor is improved,the filling of the liquid and cleaning of the channel to be detected in the internal channel increase the detection difficulty.Therefore,a D-type photonic crystal fiber SPR sensor based on Ag-TiO₂ micro gratings is proposed.In the sensor,the photonic crystal fiber is polished on one side,and the sensitive layer is designed on the polishing plane,and the outer side is used as the liquid detection channel.The full vector finite element method is used to optimize the structure parameters of D-type photonic crystal fiber and the microstructure parameters of sensitive layer.The results show that when the thickness of Ag film is 40 nm,the thickness of TiO₂ film is 10 nm,the number of Ag-TiO₂ micro gratings is 20,and the spacing is 20 nm,in the refractive index range of 1.33-1.40,the maximum amplitude sensitivity of 2245 RIU^-1 and the maximum figure of merit of 480 RIU^-1 for the sensor are obtained.3.In order to improve the efficiency and accuracy of analyte refractive index detection,based on the D-type photonic crystal fiber SPR sensor,a double side polished D-type photonic crystal fiber SPR sensor is proposed.Taking advantage of the characteristics of the dual channels structure,the two channels are filled with liquid at the same time,and the full vector finite element method is used for numerical simulation to optimize the structural parameters of the sensor.The results show that when the thickness of Ag film is 40 nm,the thickness of TiO₂ film is 10 nm,the number of micro gratings in one side liquid channel is 50,and the spacing is 30 nm,the maximum wavelength sensitivity of the two channels is 14000 nm/RIU in the refractive index range of 1.33-1.40.It is proved that the sensor can detect the analyte in two channels at the same time,and it can not only be used to reduce the time cost of cleaning the detection channel and checking the symmetry of the two channels,but also can be used to determine whether the refractive index of the liquid in two channels is the same,and improve the detection efficiency and accuracy.