Research On Photonic Crystal Fiber Sensor Based On Surface Plasmon Resonance

In modern industrial production,medicine,environmental monitoring,military,and many other fields,sensor is an indispensable component.Optical fiber sensors have many unique advantages,such as high sensitivity,real-time response,high accuracy,and long service life,etc.Photonic Crystal Fiber（PCF）sensor based on Surface Plasmon Resonance（SPR）is a new type of optical fiber sensor,which utilizes the transmission characteristics of guiding light to analyze and detect parameters from external environment.Compared with traditional fiber optic sensors,PCF sensors have the characteristics of higher sensitivity,wider measurement range,and label-free measurement.Aiming at the shortages of the existed PCF-SPR sensors,we design and analyze improved PCF structures in this thesis,and give an outlook to the future development.Starting from the history of PCF and SPR,we analyze the conduction mechanism of PCF,and introduce the SPR effect and its sensing principle.We review recent research of PCF-SPR sensors.The advantages and disadvantages of the existed designs are introduced.We then summarize the basic principles and analysis steps of the PCF numerical analysis method,the Finite element method（FEM）.The analysis method,index,and optimization of the detecting characteristics are introduced.A fan-shaped PCF refractive index（RI）sensor based on SPR is designed.When the analyte RI varies between 1.336–1.396,the sensor achieves the maximum wavelength sensitivity of 10,500 nm/RIU.The best amplitude sensitivity reaches 144.43 RIU^-1.An ideal figure of merit（FOM）of 73.32 RIU^-1 is obtained.The proposed sensor adopts a new plasma material of ITO,which reduces the manufacturing cost.The eightfold Penrose arrangement of air holes can not only increase the stability of the structure,but significantly improve the coupling between core mode and surface plasmon polarization（SPP）mode.In addition,the proposed sensor shows a single steep resonance peak.High sensitivity in RI detecting is obtained.In order to realize the simultaneous and independent detection of RI and temperature,a flat PCF temperature-RI sensor based on SPR is designed.A simple experimental configuration method is demonstrated.The key parameters are further optimized.The optimized structure shows that an excellent wavelength sensitivity of 17,000 nm/RIU is accomplished in the RI range from 1.32 to 1.41.The best amplitude sensitivity can be up to 354.39 RIU^-1.The best value of FOM is 216.74 RIU^-1.A maximum wavelength sensitivity of-5 nm/℃ is achieved in the temperature range of-30–40℃.The proposed sensor shows an ideal resolution of 5.88×10^-6 RIU and 0.02℃ for RI and temperature detection,respectively.Tolerance analysis of the sensor is carried out.Test results show that the sensor has good repeatability and stability.The sensing channel of temperature and RI is separated in x-and y-polarization,respectively,to diminish the detection crossover,and to avoid complex matrix calculation.In addition,manufacturing process of the sensor is also investigated and designed.The flat polishing area of the gold layer is adopted to reduce the manufacturing difficulty.The large thermos-optical coefficient of toluene improves the temperature sensitivity.The sensor shows better temperature sensitivity than most temperature-RI PCF sensors.Besides,the sensor obtains more superb wavelength sensitivity for RI sensing.A PCF-SPR sensor for simultaneous measurement of magnetic field and temperature is proposed.By designing the arrangement of air holes,the birefringence of the PCF is improved.Coupling between the y-polarization core mode and SPP mode is directionally excited.Two air holes are selectively coated with Au layer and Au/TiO₂ bimetallic layer to separate of the resonance peaks.Neither the magnetic field detection peak nor the temperature detection peak is affected by the change of another parameter.When magnetic field varies from 50 Oe to 170 Oe,the maximum spectral sensitivity obtained is 0.125 nm/Oe.When temperature is in the range of 24.3–64.3℃,the best sensitivity can reach-2.5 nm/℃.Sensing resolution of magnetic field and temperature is 0.8 Oe and 0.04℃,respectively.In conclusion,with the characteristics of improved sensing performance,non-cross multi-parameter detection,good manufacturing repeatability and stability,it can be anticipated that the proposed PCF-SPR sensors could be widely used in the fields of biomedicine,environmental monitoring,and chemical analysis,etc.