Research On Demodulating The Reflected Signal Of Distributed Fiber Bragg Grating(FBG)

Optical fiber grating is a kind of optical fiber passive device, it has been developed quickly and widely used in recent years. It has great application prospective in optical fiber communication and optical sensor field and so on for it's many unique merits. Optical fiber grating sensors based on optical fiber grating technology have become the focus in sensors study field. Because of their intrinsic nature and inherent wavelength-encoded operation, fiber gratings are utilized as sensing elements in recent years. The most important advantage is that wavelength is an absolute parameter and thus does not depend on loss of the system or fluctuation of the source power. Most of today's demodulation techniques rely on optical filtering method, such as scanning fiber Fabry-Perot filters, WDM fiber couplers and Mach-Zehnder filters. The sensor net can be composed by using many optical fiber gratings. It can be applied in detecting many sensor points especially in intelligent and smart structure.In this dissertation, we mainly focus on the research and realiation of fiber Bragg grating networks, including the principles and experiments of sensing and demodulation techniques. the contents are listed as follows:1 Theory analysis of fiber Bragg gratings(FBG)are presented including the coupled-mode theory used in fiber grating, the propagation characteristics of light wave in FBG, the physics characteristics of FBG, optical fiber grating sensor mechanism. The developments and application of fiber grating sensors are presented.2 Studying the common method of FBG wavelength demodulation and wavelength demodulation technology of multiplexing network.3 Designing a kind of original and Parallel demodulation system which is based on the expression of transmission and reflectivity of Fabry-Perot interferometer, spatial division multiplexing transform as time division multiplexing, the wavelength displacement reflect from FBG can be demodulated.4 The way that demodulating alternate frequency of the reflective wave was proposed. Calibrate wavelength according to corresponding relation of scanning voltage and wavelength of transmitted light of F-P filter with high precision.