Research On Key Technologies Of Broadband Ultra-sensitive Three-component Optical Fiber Seismic Observation

China is one of the countries with the most serious earthquake disasters,precautions against earthquake and relief of disaster is required for economy safety and people’s well-being.Seismometers can sense and record seismic waves,which are one of the most important measuring tools for understanding,studying and mastering the law of earthquakes.At present,the traditional seismometer can’t meet the needs of seismic monitoring and measurement development because of its performance has reached the limit.The optical fiber seismic observation technology is expected to develop as a new generation of seismic observation technology and instrument due to its great potential in the working frequency band,dynamic range,measurement resolution and its advantages in reliability and environmental adaptability..However,there are still many challenges in the low-frequency bandwidth and measurement resolution of optical fiber seismic observation technology.In this thesis,on the basis of the existing optical fiber seismic observation technology,the broadband ultra-sensitivity three-component optical fiber seismic observation method based on the interferometric optical fiber disk accelerometer is studied.In view of the shortcomings of optical fiber seismic observation in low-frequency working bandwidth and measurement resolution,a broadband ultra-high-sensitivity three-component optical fiber vibration measurement device is proposed and developed for seismic observation and monitoring.The research began in three aspects: ultralow frequency band noise limiting factor,temperature cross-sensitivity suppression,and sensitivity improvement.This thesis is carried out according to the ideas of ultralow frequency noise analysis on sensing optical path,optical path temperature cross-sensitivity suppression,quantitative design of high sensitivity sensor,sensor development and seismic observation verification.The main contents are as follows:(1)Aiming at the problem of unknown noise limiting factors and distribution rules in the the ultralow frequency band of the hundred-meter ultra-long fiber interferometer system,the related noise factors of the system are studied one by one through the combination of theory and experiment to determine the influence and characteristics of each noise factors.Afterward,the ultralow frequency noise of the hundred-meter ultra-long fiber interferometer system is analyzed,and the contribution of each noise factor to the overall noise spectrum is confirmed,so as to clarify the source and distribution of the ultralow frequency noise.It is confirmed that the 1Hz-1k Hz frequency band is mainly affected by the thermal noise of fiber,and the 10 m Hz-1Hz frequency band is mainly affected by the laser frequency noise,which lays a foundation for the improvement of the detection accuracy of the ultra-long fiber interferometer.(2)Aiming at the problem of temperature cross-sensitivity in optical fiber interferometry,a method of suppressing temperature cross-sensitivity in optical fiber interferometry based on polarization multiplexing is proposed.Based on the principle that the fast axis and slow axis of polarization maintaining fiber are sensitive to both temperature and parameters to be measured,a 2×2 response coefficient matrix is constructed to realize simultaneous measurement of two parameters.The simultaneous measurement error of strain and temperature of 2.43με and0.02°C is realized by using the dual cross-axis interference polarization maintaining fiber interferometer.The temperature stability of the fiber interferometer is improved and the temperature cross-sensitivity is suppressed.(3)Aiming at the problem of sensitivity improvement,a quantitative design method of sensor based on accurate finite element simulation analysis is proposed.The finite element simulation model is used to study the strain characteristics of the sensing fiber and its relationship with the sensitivity,and the strain distribution of the sensing fiber under the action of the disk and the correctness of the finite element model are verified by experiments.Then,based on the finite element simulation model,the material and size parameters of sensing structure are optimized,the measurement resolution is optimized with the noise analysis results,and the design method for improving the sensor performance is obtained.(4)Finally,the research results are applied to the design of high performance interferometric optical fiber disk accelerometer.The broadband ultra-sensitivity threecomponent optical fiber seismometer is developed.The performance test and field experiment show that its working bandwidth is 0.1Hz～200Hz,sensitivity ≥ 8000 rad/g,transverse crosstalk >40d B,dynamic range > 150 d B,measurement resolution ≤ NHNM,and the indicators meet the performance requirements set in the previous stage;The optical fiber seismometer can record seismic events of different magnitudes and distances in field experiments,and the detected waveform is consistent with that of the commercial seismometer,which verifies its performance and detection ability,and proves that the broadband ultra-sensitivity three-component optical fiber seismometer can be used for high-precision seismic observation.