Study On Demodulation Technology For Fiber Bragg Grating Seismic Detection

Geophone is the special sensor in the field of seism prospecting and project measuring, which can convert the vibration of the earth into the several kinds of signals(one of the most important is electronic signal). It is the most important part during collecting the seism prospecting data. It’s capability directly affects recording quality of seismic wave and explaining of seismic data. With the highly development of petroleum industry and electronic industry, the seismic exploration technology has remarkable developed. Thus, the demanding for precision and quality of seismic data collecting is much more urgent, as a result of geophone with high-resolution capability, high anti-jamming capability, high SNR, high-fidelity, high-definition and large dynamic range. In the vibration sensing filed, compare to the traditional probe, fiber grating sensor has some distinctive advantages, such as higher-accuracy, larger dynamic range, better immunity, the sensing information is coded in the wavelength, can construct sensing network easily.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. This dissertation is based on the edge filter demodulation technology, using the improved EDFS as the edge filter, and LabVIEW is selected to collect, dispose and display demodulation signals, realizing to demodulate seism signals.The contributions of this dissertation are:(1) FBG transmit theory model and the sensing theory are introduced:The principle of the FBG geophone is analyzed.(2)The advantages and disadvantages of several common demodulation methods are analyzed and contrasted. An edge filter demodulation method which uses EDFS as filter is selected. Optical and electronic constitution of the demodulation system is studied and designed, experiment system is established.(3)Dynamic vibration sensing experiment is set to test the experiment system, experimental results are analyzed, advantages and disadvantages of the demodulation method are summarized, and experimental errors are analyzed.(4)A demodulation method of measurement of vibration and temperature based on edge filter and matching grating is proposed.