Research On Sensing Characteristics Of Photonic Crystal Fiber Based On Selective Filling Air Holes

Different from traditional electrical sensing technology,optical fiber sensing technol-ogy has the characteristics of anti-electromagnetic interference,lightweight,high sensitivi-ty,and wide detection range,playing an important role in the fields of medicine,aerospace,environmental monitoring,and high-speed telecommunications.Photonic crystal fiber（PCF）has become a research hotspot in the fields of fiber communication and sensing due to its excellent optical control characteristics and flexible structure design.In addition,the optical properties of optical functional materials can be changed under external action（sound,heat,electricity,magnetism,force,or light）.By filling the air holes with different materials,polishing the side of the optical fiber,and applying twisting to the PCF,high sensitivity sensing measurements with different functions can be realized,which greatly expands the application field of the PCF.In this thesis,three different PCF sensing models based on selective filling are designed and studied by the Finite Element Method（FEM）based on the coupled-mode theory.The major research works of thesis are as follows:（1）A dual-parameter sensing structure based on chiral PCF selective filling is pro-posed.The twist and temperature sensing can be realized by using the unique helical structure of chiral PCF and selectively filling the air hole with thermosensitive material toluene.The simulation results show that the average temperature sensitivity of the struc-ture is 10.68 nm/℃,and the twist sensitivity is 7.17×10^-5 mm²/rad.The excellent sensing performance of this structure makes it have great application prospects in the fields of manufacturing industry,civil engineering,and temperature early warning.（2）A flat-plate PCF structure based on liquid crystal（LC）selectively filled is pro-posed.The structure is realized by selectively filling the air hole with LC and coating the two flat surfaces with metal films,respectively.When the metal films are used as the elec-trode,the structure can be used as a filter and voltage sensor.The simulation results show that as a filter,the applied saturation voltage can be reduced from 2900 to 650 V.As a voltage sensor,the voltage sensitivity is increased from 0.025 to 0.117 nm/V.In addition,the metal films can also excite surface plasma resonance（SPR）.Because the SPR is sensi-tive to ambient refractive index changes,the structure can also be used as an ambient re-fractive index measuring instrument,with refractive index sensitivity up to 2700 nm/RIU.（3）A multi-parameter sensing structure based on selective filling D-shaped PCF is proposed.The D-shaped surface of the PCF is coated with a metal film to excite the SPR.Based on the relationship between the SPR wavelength and the external refractive index,the measurement of the refractive index of the external environment is realized.In addition,magnetic fluid（MF）,toluene,and LC are filled in the different air holes of the D-shaped PCF.Based on the principle of optical waveguide coupling and mutual antagonism,the sensing of the magnetic field,temperature,and voltage can be realized simultaneously.This structure can not only realize the simultaneous sensing of multiple parameters but also obtain very high sensitivity.The simulation results show that the average refractive index,magnetic field,temperature,and voltage sensitivity can reach 4600 nm/RIU,1.375 nm/Oe,15.143 nm/℃,and 0.971 nm/V,respectively.The excellent sensing performance of the structure makes it have a broad application prospect in the field of optical sensing.