Cross Sensitivity Of Fiber Bragg Grating Sensing Technology Research

Fiber grating is a new type of optical passive device, because of its many unique advantages such as simple structure, better reliability, strong corrosion resistance, good resistance to electromagnetic interference, multiplexing capability, easy to create various forms of sensor networks and a large area of the multi-point measurement and so on. So fiber grating has extensive and good prospects in the sensing field. Cross-sensitivity of fiber grating sensor is a key problem that need to resolve in practical application.This thesis mainly focuses on theoretical analysis and computer simulation of the fiber Bragg grating cross-sensitivity mechanism,analysis of traditional cross-sensitive solutions and research of design optimization. The contents are listed as follows:Firstly, the development of fiber grating, classification and production methods of fiber grating and fiber grating sensor in the application are introduced. The significance of the subject is expounded on.Secondly, the fiber grating's basic theories are analyzed. According to the coupled mode theory, the basic principles and techniques of fiber grating sensor are researched and analyzed completely. Main contents include fiber grating sensing mechanism, fiber grating's temperature and strain sensing principles, demodulation and multiples technique.The cross-sensitivity of temperature and strain is an inherent problem of fiber grating, so fiber Bragg grating's cross-sensitivity causes are studied systematically. Usual cross-sensitive solutions are presented as well as the working principles of the various options are analyzed. A new equation with cross-sensitivity coefficient of Bragg gratings is described. The influences on the measurement results caused by the second-order temperature and strain sensitivities as swell as temperature-strain cross sensitivity are analyzed. In addition, according to the expressions of relative error about strain and temperature, the curves of strain relative error and temperature relative error are given. By analyzing the expressions and curves, a conclusion about the influence of cross-sensitivity is drawn. Based on fiber Bragg grating coupled mode, the simulation program is writed, and computer simulates the reflection spectrums of fiber Bragg grating under various external environments. Further in-depth research on cross-sensitivity is carried out.Finally, based on dual-wavelength matrix calculation's basic principle, a set of FBG sensing system based on cantilever is designed, which is used to overcome the cross sensitivity problem. Design ideas and system architecture are explained detailedly; moreover, the feasibility of the system is discussed. Computer also simulates the operation of the system. The advantages of system are presented which need only a light source, a demodulator and optical architecture is simple, so this system has good application prospects.