Design And Application Research Of Optical Fiber Evanescent Wave Chemical Sensor

Among many types of chemical sensors, fiber optic chemicalsensors have attracted much attention due to their advantages in small size,high sensitivity, and immunity to electromagnetic interference, and remoteoperation capability.In this dissertation, the principle of the proposed sensorsbased on evanescent wave are analyzed. Then the numerical analysis of lightdistribution and spectral reflectance of intrinsic type, taper type and Bragggrating type fiber structure is discussed. Design experiment sensor formeasurement base on the simulation above, and research the sensingcharacteristics of optical fiber sensor based on evanescent wave in threeaspects: theory, simulation and experimental.The main work of this thesis is as follows:1. The optical fiber modes theory related to evanescent wave sensor isdiscussed theoretically, such as finite difference beam propagation method(FD-BPM) and Coupled-mode theory (CMT). Moreover, the formula of thealgorithm expressions is derivable from the modes theory of optical fiber,starting from the expression, and the process steps of the algorithms andsimulation diagrams are presented, which lay a theoretical foundation forsubsequent sensor simulation analysis.2. The basic theoretical knowledge of evanescent wave theory of opticalfiber sensor is introduced and carried on detailed, through theoreticalderivation, the formula of sensitivity of evanescent wave optical fiber sensoris achieved, according to the formula, the optical fiber sensor are sensitive tothe structural parameters of the fiber in the sensing region and the externalenvironment parameters, to predict the optical fiber sensor based onevanescent wave potential application in the field of chemical sensing.Through the analysis of simulation results, achieving sensing characteristics,provide a reference for subsequent experiment sensor design.3. The refractive index of NaCl liquids is measured by intrinsic typefiber structure based on evanescent wave as an example for experiment research. Experiment optical fiber sensing region is etched by HFsolution.and fiber corrosion rate is measured by the method of experiment.Experiment explore the same sensing length of different diameter and thesame sensing diameter of different length of fiber Influence on refractiveindex sensing sensitivity, the results show that the sensor diameter is smaller,the longer the length of sensing, the smaller of the normalized output power,the higher of the refractive index sensitivity, which consistent with the resultsof numerical simulation.