FBG Multi-channel Demodulation Study Based On Matched FBG Linear Tuning

Fiber Bragg Grating(FBG) is a new fundamental fiber optic device that is expected to be of great applicative prospect in fiber communication, fiber sensing and other electro-optics processing fields. Nowadays the manufacturing and application research on FBG is turned into hot field in the world's fiber optics technology. As a sensor, FBG can be immune from light source disturbance and system loss by transforming sensing information into its reflecting wavelength shift, that is wavelength coding. Besides, FBG is of good reliance, immune from electromagnetic signals and corruption, and can be constructed as FBGs network by being put together on a single fiber so as to realize distributed sensing, which is an unexampled merit for FBG. The key point in FBG sensors lies in precise measurement of minute shift of Bragg reflecting wavelength, that is demodulating the coded signals of wavelength. Though it is can be achieved by Optical Spectrum Analyzer(OSA) with high resolution, OSA can not be applied into practical situation because of its huge-size and high-cost. So developing high-resolution and low-cost FBG demodulator is the key issue when it comes to FBG sensors industrializations.A new FBG demodulation scheme based on the use of tuning matching fiber grating to interrogate the sensing grating is proposed in this paper. To achieve the demodulation of temperature and strain sensing signals, matching FBG's wavelength is changed by computer controlled step motor. Then we creatively put forward a concept "multi-channel demodulation", by using multi-matching FBGs to interrogate the multi-channel sensing signals simultaneously. In this way, not only can Bragg wavelength shift be detected precisely, but multi-channel demodulation of FBG sensors have been resolved effectively, so the demodulation and measurement range of the distributed serial FBGs system have been broaden significantly and make the demands of multi-spot measurement in large sensing system. Because of its simple scheme,low-cost, and good reliance, this demodulation method is expected to be adopted in practical application in fiber sensing field.In this complicated research dealing with optics, mechanic and electrics, the contributions of this paper are:(1)Analyze the principle of fiber Bragg Grating, and investigate the temperature and strain sensing characteristic of FBG.(2)After analyzing the existed FBG demodulation method, according to problems confronted in practical fiber optical sensing application, a creative demodulation method has been put forward, that is, demodulating the sensing signals by wavelength-matched fiber grating tuning.especially extending this method to FBG multi-channel demodulation application.(3) Construct FBGs network to do multi-sensing demodulation experiment to detect the distributed temperature variables. Design and settle a set of optical and electrical device system, and programming parallel port muti-channel data collection and data processing software;(4)Process and analyze the experimental data, figure out the temperature characteristic curves and fix the exact value of each sensing FBGs in the network.(5) Based on the results of experiments, summarize the advantages and disadvantages of the demodulation scheme, and propose the improving method.