Theoretical Reseach On The Lable-free Biosensor Characteristic Of The Microstructured Optical Fiber Grating

Recently, Label-free optical fiber biosensor has played an important role in thebiosensors research field for the advantages of very simple structure and highsensitivity. And with the excellence of natural microfluidic channels and flexiblestructure, the Microstructured Optic Fiber (MOF) is very suitable for the design ofbiosensors. Thus, the research of MOF biosensor has important theoretical andpractical significance.Based on the conclusion of fiber biosensor technology and status, this dissertationanalyzes the refractive index, biological film thickness and temperature sensingcharacteristics of the biosensor model of high birefringence microstructured opticalfiber grating and the grapefruit optical fiber grating theoretically. And a number ofexpeiments are designed to verify the refractive index and temperature characteristicsof grapefruit optical fiber Bragg grating and the long period grating. This work willprovide theoretical foundation and experiment reference for the MOF gratingbiosensors technology. The main contents of the paper are as follows:Firstly, the transmission characteristic of the high birefringence microstructuredfiber is analyzed with the finite-element method. Meanwhile, the propagation modesand mode field distribution are calculated comprehensively. Further more, the Bragggrating, the cascaded Bragg gratings and the chirped grating of the MOF are calculatedbased on the coupled mode method and the transfer matrix method, and the thereflection spectrums are simulated thoroughly.Secondly, the refractive index, the temperature and the biological film thicknessresponse sensitivity of the high birefringence MOF grating, the cascaded Bragggratings and the chirped grating is analyzed. A novel method for measuring thebiological film thickness by the mean of Bragg grating resonant wavelength differenceis studied. And then the relationship between the optic fiber parameters and thesensitivity of this biosensor’s refractive index and biological film thickness isinvestigated. And the simulation result will provide theoretical reference for the optimal design of the biosensor parameters.Thirdly, the reflection spectrum of grapefruit MOF Bragg grating and thetransmission spectrum of grapefruit MOF long period grating are analyzed with thetransfer matrix method. Moreover, the resonant wavelength variety laws areresearched respectively when filled into different refractive index or differentbiological film thickness. Also, considering the coefficient of thermal expansion andthermo-optic effect, the temperature sensitivity of the grapefruit MOF Bragg gratingand long period grating is got theoretically.Fourthly, the propagation characteristics of the cascaded grapefruit MOF longperiod grating and Bragg grating are analyzed thoroughly with the extenedtransmission matrix method. And the two reflection spectrums response characteristicswith different refractive index, biological film thickness and temperature of thecascaded MOF grating are investigated. Meanwhile, the different sensitivity responsesof the long period grating and Bragg grating on the biological film thickness andtemperature in the casecaded grating are analyzed thoroughly. The method andfeasibility of measuring the biological film thickness and temperature at the same timeis studied theoretically.At last, experiments are established to verify the refrective index and temperatureresponses of the grapefruit MOF Bragg grating and long period grating. And theexperiment results show the feasibility of the label-free microstructured fiber gratingbiosensor.The paper does a lot of theoretically analyzes and experiment work on thesensoring characteristics of the refractive index, and the work lays the foundation forthe further research and application of the label-free microstructured optical fibergrating biosensor.