Study Of Fiber Bragg Gratting Geophone

Geophone is one kind of the special sensors that could convert signal of mechanical vibration into signal of electrical and could be used in geophysical prospecting and measure of project-field. It is also a special precision instrument to incept and record seism. Its capability directly affects recording quality of seismic wave and explaining of seismic data. It is the most important part in seismic wave data collecting system.The traditional geophones have disadvantages of narrower bandwidth and dynamic range, lower accuracy 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 (FBG) has particular advantage such as:(1)the sensing information is coded in the wavelength that can construct sensing network easily; (2)wider bandwidth; (3)higher accuracy; (4)larger dynamic range; (5)resist to electromagnetic interefring.An optic seismic geophone is developed in this paper and a new measure to demodulation FBG based on DFB LD is first provided. The main content of this paper includes:(1) To get a comprehensive understanding of the newest development status of FBG sensor and establish the virtual significance of the subject.(2) 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 FBG are introduced, especially advantages and disadvantages of each method are analyzed and contrasted.(3) The structure and principle of the sensing probe of FBG geophone are introduced; the sensitivity characteristics of the sensing probe are analyzed in detail; the encapsulation of sensing probe is introduced.(4) A new demodulation scheme is given; the system of optical unit and the design method of electric circuits are given in detail, especially the temperature control syetem based on single chip.(5) Testing system is finished to examine the performance parameters of the FBG geophone and the performance of the system is analyzed. Following the workout, the sensor of the seismic geophone system is working normally under the vibration upto lOg m/s2. Sensitivity of the demodulation can reach 785mV/m/s2 and the resolution of lm/s2 is accessed. Besides, the futher working stresses of the seismic geophone system is prospected.