Research On Key Technologys Of Opto-mechatronic System Integration For Ocean Bottom Optical Fiber Seismometer

Earthquake is a common natural phenomenon.Seismic waves generated by earthquakes can not only bring destruction,but also help people understand the internal structure of the earth.Ocean area accounts for about two-thirds of the earth’s surface,covering most of the plate boundaries.Therefore,many earthquakes occur at the bottom of the ocean.The long term and high quality seismic observation in the ocean is an important part of global seismic observation.With the rapid development of optical fiber technology,optical fiber sensing technology has become a new method of earthquake monitoring.It has the advantages of high sensitivity,anti-electromagnetic interference,small size and so on.Using optical fiber as a direct sensing element changes the mechanical pick-up mode which relying on the principle of inertia,and the measurement frequency band is not limited by the resonance frequency of mechanical devices.The frequency bandwidth is improved.The method of optical interference is used to design the structure,so that the optical fiber seismometer has high sensitivity.Based on the optical fiber sensing unit,a long-term observable ocean bottom optical fiber seismometer is developed,and several key technologies of the ocean bottom optical fiber seismometer are researched.Including: 1)The structure and optical path design of the ocean bottom optical fiber seismometer,2)The research on the cabin structure of the ocean bottom optical fiber seismometer and the coupling model of seismometer and subsea medium,3)The research on the time synchronization and communication technology of the ocean bottom optical fiber seismometer,4)The research on environmental adaptability and application test method of ocean bottom optical fiber seismometer.The ocean bottom optical fiber seismometer is studied from the following four aspects.(1)According to the principle of optical fiber sensing for seismic measurement,the optical fiber sensing unit of the ocean bottom seismometer is constructed by combining the optical fiber Michelson interferometer and the disk structure.The influence of the light source on the performance of the optical fiber sensing unit is analyzed,and the selection of a longer wavelength optical fiber laser suppresses the thermal effect in the optical fiber to improve the resolution.(2)After the selecting of cabin materials,the design method of cabin structure is proposed,and the harmonic response of ocean bottom optical fiber seismometer is analyzed.The influence of ocean bottom optical fiber seismometer structure on vibration signal transmission is studied and the stress and temperature distribution of the cabin are analyzed.The coupling model of optical fiber seismometer and ocean bottom medium is studied and simulated.According to the simulation results,the coupling base of the optical fiber subsea seismometer is designed.(3)For ocean bottom seismic observation,the key technologies include energy supply,underwater network transmission and time synchronization technology,ocean bottom seismometer layout design and so on.Therefor,the integration of ocean bottom optical fiber seismometer system is studied.The power system,sensing unit,demodulation unit,time synchronization and communication system,attitude measurement unit,cabin environment monitoring unit and watertight coupling structure are integrated to form an ocean bottom seismometer suitable for the application of ocean bottom environment.Meanwhile,the relevant tests are carried out.The time synchronization accuracy is better than 10 μs and the communication bandwidth is 6 Mbit/s.(4)Environmental adaptability test and field test of ocean bottom optical fiber seismometer.The environmental adaptability testing method of ocean bottom optical fiber seismometer is studied.The environmental adaptability of ocean bottom optical fiber seismometer and the response ability of vibration frequency in water are tested.The application test method of ocean bottom optical fiber seismometer is studied through the experiment in seismic observation station and the application experiment in marine environment.The experimental results show that the performance of each functional module of the ocean bottom optical fiber seismometer meets the application requirements,which has good consistency with the traditional seismometer in the frequency range of 1-50 Hz,slightly worse in the frequency domain below 1 Hz.And especially,it has obvious advantages in the frequency domain above 50 Hz.