Research On Key Technologies Of Fiber Grating Sensors' Demodulation System

The fiber grating sensing system consists of four parts, Broadband Light-source, FBG/LPG based sensor, Signal demodulation section and Signal process section. This paper is mainly dealing with the research of the key technologies such as Signal demodulation techniques, temperature and strain's cross-sensitivity, and concentration sensing properties of LPGs. And one kind of low cost entire optical fiber grating sensing system is proposed.The creative achievements of the paper are described as follows:1.The sensing characteristics of FBG are analyzed, with the result of a linear relationship between the resonant wavelength of fiber bragg grating (FBG) and the temperature pressure of the environment. Meanwhile, the Temp-sensing experiment results which are in excellent agreement with the theoretical analysis are included in this paper.2. The temperature properties and strain properties of long period fiber gratings(LPGs) are investigated theoretically, together with the concentration sensing properties of LPGs. The research findings demonstrate that the temperature properties of LPFG base on the different order of cladding modes. When the mode order is higher, the LPG's resonant wavelength is more sensitive to the refractive index of the environment. The functional relation of the environment refractive index and its' s resonant wavelength shifts is found by the method of nonlinearity curve fitting. This finding is very valuable to the design of the LPGs concentration sensors.3.The physical mechanism of the temperature and strain's cross-sensitivity of fiber grating sensor are described systematically in this paper. Two novel fiber Bragg grating sensors, based on double-FBG sensor structure, are also addressed to resolve the cross-sensitivity problem. One kind of all-fiber structure sensing system is designed based on the long period of fiber grating as edge filter to interrogate the sensing signal of the FBG sensor. Strain and temperature can be measured by this system simultaneously. Besides there are many other advantages , such as all fiber design, low-cost, high-speed demodulation, high accuracy, and long stability, etc.