Fiber Optic Seismic Signal Demodulation Techniques

With the consumption and the dependence on energy, exploration of more and deeper oil and natural gas has become a necessity. Seismic exploration is the most mature and effective of the Earth exploration methods, and the requirements of prospecting tools and exploration methods also be increased due to more difficult with the exploration. With its advantages of optical fiber sensing technology is interested by a growing number of researchers, and tried to apply into seismic exploration. In this thesis, we try to establish a set of optical interrogation system utilized to detect seismic waves. Beginning from the theory of optical fiber sensing technology and the characteristics of seismic waves, studying a variety of the developed optical fiber interrogation method, we adopt the edge filter interrogation according to the advantages and disadvantages of various methods. Interrogation system design, including optical design, circuit design and software design, focus on research based on long period fiber grating interrogation system and based on two-order polarization maintaining fiber Sagnac ring laser interrogation system, and test experimentally. The main works of this paper are as follows:First, study the fiber optic sensing technology, and introduce fiber Bragg grating sensor theoretical principles and characteristics; study the characteristics of seismic waves, and learn the geophones have been developed at home and abroad, and describe the application of seismic technology and seismic wave detection. Then systematically study of optical fiber sensing systems, including fiber optic light source, cantilever beam of uniform strength sensor; description of the developed optical signal interrogation method, and by comparing the advantages and disadvantages of each methods, the edge filter was chosen for vibration detection.Secondly, a seismic signal interrogation technology based on the linear edge of the long-period fiber grating was proposed and experimentally demonstrated. Starting from the analysis of the basic principles, the optical design, circuit design and simulation and software modulation design were described. The system selected the LPFG wavelength range from 1550.35nm to 1553.14nm, which slope efficiency is 1.692dBm/nm, i.e. the of the wavelength sensitivity of power detection. And the adjusted coefficient of determination is 0.99896. Building comprehensive experimental system, the static measurement accuracy of the interrogation system is 1.13pm/mV, dynamic range is 50-60dB, and the resolution is 0.025 pm/(?).Finally, according to the shortcomings of using LPFG, an optimization technology based on two-order polarization maintaining fiber Sagnac loop fiber laser vibration detection system is proposed and experimentally demonstrated. In this system, beginning from the principle of polarization maintaining fiber Sagnac loop and the principle of laser mode selection proceeding, the feasibility and scientific design were discussed, and the interrogation circuit design was optimized, and in the last place numerical simulation and experiments was taken. By numerical simulation and experimental measurement, it is known that two-order polarization maintaining fiber Sagnac loop filter was good linearity edge, and were distributed in each band comb. With the polarization controller, the corresponding period from L1 to L1+L2 can be achieved. The detection system consisted by the laser can meet the real-time seismic detection technology parameters requirement as follows:38.2μW/nm of the sensitivity,0.9996 of linearity,40～70dB ofthe dynamic range.