Research On The Signals Demodulation System Of Fiber Bragg Grating Geophone

Along with the development of seismic exploration, the demand of frequency, dynamic range, precision and resolution ration is increased. But the traditional geophone has disadvantages of narrower bandwidth, lower dynamic range and resolution, and can not meet the new needs of seismic exploration. As one of the most potential and successful optic passive device, fiber Bragg grating has particular advantage such as: (1)the sensing information is coded in the wavelength, can construct sensing network easily(2)higher accuracy(3)larger dynamic range(4)better immunity.In the sensing network based on fiber Bragg grating, the key to make FBG use more widely is to detect and process the tiny offset of center wavelength, i.e. to demodulate the wavelength signal of FBG. The acquisition and process of sensing signal of FBG mainly rely on some optical instruments such as OSA. But in practical engineering application, it has many disadvantages, how to develop a system of wavelength demodulation that has higher accuracy, larger dynamic and fit for engineering application has becoming one of the current heat research fields.The sustentation fund of this paper is open problem (2005-16)–"Research of fiber Bragg grating demodulation system based on Sagnac loop"supported by photoelectric information technology lab belongs to ministry of education. It is devoted to develop a distributed wavelength demodulation system that adapted to fiber Bragg grating geophone. The main content of this paper includes:1. FBG and the theory of sensing with FBG are introduced; the influence of temperature, strain and the cross sensitive of them are analyzed; the demodulation methods of fiber gratings are introduced, especially advantages and disadvantages of each method are analyzed and contrasted.2. The structure and principle of the sensing probe of FBG geophone are introduced; the sensitivity and frequency characteristics of the sensing probe are analyzed in detail; a simple performance test of sensing probe is made.3. Demodulation scheme is given from the function of demodulation system and design request; the system of optical unit and the design method of electric circuits are given in detail; experiment system is designed finally.4. Some experiments are set to test the demodulation method above, on the foundation of experimental results, the advantages and shortcomings are commentated, the use of this demodulation technique is been prospected.