Another use of optical fiber - earthquake monitoring

The optical fiber sensing technology has developed rapidly since the 1970 s with the development of the optical fiber communication technology, with the light wave as the carrier, optical fiber as medium, perception and transmission of measured signal is a new type of sensing technology, As the carrier of the measured signal and the transmission medium of light wave, compared with other carriers and media,optical fiber has its unique advantages.Light wave is not afraid of electromagnetic interference and easy to receive a variety of light detectors, can be easily converted into photoelectric or lightning, matched with advanced modern electronics and computers.

The excellent characteristics of optical fiber make it widely used in many fields such as optical fiber communication, sensing, image transmission, light transmission lighting and energy signal transmission. It has become an emerging pillar industry in today's world, .In the past 50 years, optical fiber technology in optical fiber sensing, optical fiber image transmission, light transmission lighting, energy transmission and signal control, especially in optical fiber communication and other civil and military fields have obtained an important and large number of applications, especially in the field of information technology is showing more and more powerful vitality and broad application prospects.

In collaboration with Baoshan Wang and Huajian Yao from the School of Earth and Space Sciences, a team led by Yang Chen and Dongfeng Zhao from the Hefei National Research Center for Microscale Physical Sciences at the University of Science and Technology of China has successfully developed a distributed optical fiber Acoustic/Vibration sensing (DAS) system with independent intellectual property rights.The equipment can be used for seismic monitoring, geological disaster prediction, underground structure imaging, urban underground space detection and so on.

   Some regional and global earthquakes have been successfully detected, including a 2.3-magnitude earthquake that happened in Dingyuan, Anhui on June，4, a 2.7-magnitude earthquake that happened in Xuancheng, Anhui on July，22, a 6.6-magnitude earthquake that happened in the  on July,24  and a 5.8-magnitude earthquake that happened in Yilan county, Taiwan on August 5.

When the earthquake occurs and the seismic wave propagates to the optical fiber, and the optical fiber will be stretched or compressed due to the strain. Because of the elastic optical effect of coherent laser in the optical fiber medium, the amplitude and phase of Rayleigh scattering light will be changed. By receiving and demodulating the Rayleigh scattering light, the information of seismic wave can be received.

DAS technology uses the elastic optical effect of coherent laser in the fiber medium to perceive and transmit the vibration and acoustic signals of the outside world. It has the advantages of distribution, high integration, long distance transmission, strong anti-interference, and so on. Therefore, it provides a new technical approach for seismic monitoring and underground structure imaging.

Modern technology has applied optical fiber sensing technology to the manufacture of seismometers, which can effectively improve the detection range and sensitivity of seismometers, and this technology will be improved and optimized in the future development.