Research Of The High Sensitivity Fiber Grating Sensing Demodulation System

With the increasing development of fiber grating manufacture and sensor technique, to develop fiber grating sensor apparatus with excellent quality, strong stability, high precision, low cost, and finally to realize the production of modularization, industrialization and with a large scale has become the focus of fiber grating sensor's research.This fiber grating sensor theory and technology are systematically researched in this paper. The research includes: the coupled mode theory; the fabricating technologies and categories of fiber grating; the sensing mechanism; the demodulation techniques; the theory and composing of filter demodulation; the design of long period fiber grating filter demodulation system; and the analysis of its accuracy.Firstly, the present situation and development of fiber and fiber grating sensor technique are reviewed. The coupled mode equations are built by means of expanding perfect waveguide modes. By using the coupled mode theory, the relationships between the reflective spectrum characteristics of fiber Bragg gratings and their structural parameters are studied. Moreover, the question about how to increase the sensors number of fiber Bragg grating is discussed, the narrowest bandwidth of fiber Bragg grating is analyzed in theory. Establishing mathematical models for strain and temperature sensing respectively, and the sensor with temperature model is built.The key technique of fiber grating sensor is the demodulation method. In this paper, the demodulating methods of fiber grating are discussed, several typical demodulation methods using optical filters are presented, and the advantages and disadvantages are analyzed. Based on the fiber grating sensor mechanism, the edge filter demodulation system with long period fiber grating is put forward. Then, introduced the sensing experiment system and data processing system. While elaborating on the composition of the system, explains principles and performance of the components in light road, aimed to detect weak optical signal, is then proposed. Finally, experiments with the sensing experiment system are described. The experiments indicated that LPG could be used effectively in sensing measurement of temperature.