Research On SPR Sensing Mechanism Based On Novel Terahertz Fiber

Terahertz（THz）wave has unique and excellent characteristics,such as low photon energy and strong penetrability,due to its special position between infrared and microwave.It is expected that many substances have special spectral responses in THz range.Surface Plasmon Resonance（SPR）fiber optic sensors have important applications in the fields of biomedicine and chemistry due to their excellent properties such as high sensitivity,remote monitoring,label-free,and non-destructive properties.However,in the actual test environment,changes in ambient temperature and reactions between non-target molecules can affect the accuracy of detection.The above problems can be solved by introducing a reference test object using multi-channel sensing technology.And it can also meet the needs of multi-parameter,multi-channel,self-reference measurement of analytes.Therefore,it is of great value to develop SPR multi-channel sensors in the terahertz band.In this way,a terahertz dual-channel fiber optic sensor based on the SPR effect is designed,which can realize multi-channel measurement and self-reference measurement functions in the terahertz band,and provides a new solution for the design of SPR fiber optic sensors in the terahertz band.The design method and optical properties of new terahertz optical fibers are studied.Terahertz photonic crystal fibers with hexagonal lattice air holes,honeycomb air holes and octagonal air holes structures are designed.The finite element method was used to model the above-mentioned photonic crystal fibers.We discussed the design method of the core structure,the diameter of the core air hole,the influence of the substrate material on the transmission characteristics of the fiber,and analyzed the optimal structure of the terahertz SPR fiber sensor.The results show that the hexagonal dense photonic crystal fiber with higher porosity is more favorable to achieve the phase matching condition,and Zeonex’s material properties and transmission properties are more suitable for the substrate material of the fiber.The above work lays the foundation for the design of a dual-channel terahertz fiber SPR sensor in the following.For the dual-channel optical fiber SPR sensor based Zeonex,two semicircular large air hole channels are used to achieve multi-channel measurement in terahertz region.The SPR effect can be excited by coating the ferroelectric polyvinylidene fluoride（PVDF）layer on the inner surfaces of the channels.The influence of the porosity and the thickness of the PVDF layer on the sensing characteristics is discussed,and the measurement range of the THz SPR fiber and the possibility of dual-channel measurement are analyzed.Analysis shows that the THz fiber optic sensor has a refractive index range of 1.000 to 1.030,and can achieve dual-channel measurement.By introducing a dielectric layer into the sensing channel,multi-channel crosstalk is overcome and the independence of dual-channel sensing is improved.The optimization of the effect of multi-channel measurement under different structural parameters is studied,and the resonance wavelength can be easily tuned to the desired value by adjusting the structural parameters.The dual-channel sensing characteristics of the fiber were studied.The proposed optical fiber sensor has a sensitivity of 1100μm/RIU and a resolution of 2.4×10^-4 RIU.The designed dual-channel terahertz fiber SPR sensor has high sensitivity and can realize multi-channel measurement and self-reference measurement in the terahertz band,which is a good demonstration of extending the multi-channel SPR fiber optic sensor in the visible and near-infrared bands to terahertz.The band method has broad application prospects in the fields of biomedicine,food safety and environmental monitoring.