Key Technology Of The High-precision Demodulation For FBG Wavelength Information

Fiber Bragg gratings(FBG) are one type of developing fast passive fiber devices in recent years. FBG sensors have the characteristics of compact structure, easy to integrate and bury. Also they are modulated by wavelength and immune to electromagnetic interference and light intensity fluctuation. Multi-sensing like stress and temperature sensing are achieved by wavelength, time and space division multiplexing technologies. FBG sensors are mainly applied in the fields of electric power,medicine and chemical engineering ect. Nowadays the application research on FBG has gone into a popular field of optical sensing. The key technology of FBG sensing lies in how to measure the minute shift of Bragg reflecting wavelength precisely. And this is called demodulating of the coded wavelength signals.This paper has done a research on the key technology to improve the precision of demodulation system of FBG based on tunable fiber Fabry-Perot interferometer. Modern digital signal processing technique is applied in fiber grating sensing and the scheme of signal processing of wavelength demodulation and real time correction is optimized. The main research work is as follows:The theories and general situations correlative with FBG sensors are briefly introduced. And our wavelength demodulation system is presented. In order to get the accurate time of the output signal peak of the demodulation system, signal reconstructing arithmetics are presented to filter the noises. By analyzing the frequency spectrum of the output signal, we get the frequency range of noises and design a low-pass digital filter using Kaiser window. Because the low-pass digital filter can't filter the noise completely, local Gaussian fitting filter is designed according to the spectral reflective characteristics of FBG. Series and parallel correction methods are analyzed, and we choose and imprvove the parallel one. A multi-point FBG sensor demodulation system based on the tunable F-P interferometer is built. The piezoelectric driving voltage-wavelength function is built according to the 48 reference points using fast method. This system can calibrate the nonlinear problems of the micro-displacement driver and the structural errors of tunable F-P interferometer in real-time, that is to say, the measurement precision is improved.