Research On The Optical Fiber Grating Sensors And Its Application In Rock Engineering

The fiber grating, as a new photo electronic device, enters the commercialization and integration along with the ripening technology for fabricating fiber gratings. the researches of the application of fiber grating sensors have obtained more and more attentions. Fiber grating has many advantages such as electromagnetism isolation , high sensitivity, wavelength code, etc. fiber grating is one of the most promising and representative passive optical fiber devices. It greatly extends applied realms of optical fiber technology. thus, the studies on theory and application of fiber gratings become very important.The main content of this paper is following:1. Starting from the Maxwell-field equations, we deduce the wave-propagation equations, and analyze the characteristics of guided modes in optical fiber. Based on these, we derive the coupled-mode equations. Using the coupled mode theory, we analyze fiber Bragg grating of a constant refractive index modulation and period, found the coupled-mode equations, Furthermore, the relationships between the spectrum characteristics of fiber Bragg gratings and their structural parameters (grating length, coupled coefficient, etc.) are studied.2.The mechanism and solutions of the cross- sensitivity of FBG sensors is analyzed in a systemic way in this chapter. On these bases, proposes a new method. And the error for simultaneous measurement temperature and strain is given detailed analysis and digital simulation.3.Studying the application of FBG in in rock engineering. By experiments we testify that The cross- sensitivity have to be taken into account . And The encapsulated FBG as temperature sensor is good for temperation compensate .The elimination of cross- sensitivity not only are easy to measure stress/temperature in the same time but protect FBG to adopt to work in the odious environment.