Research On The Demodulation For Optical Fiber Interferometer Sensors Applied In Monitoring The Submarine Earthquake

Tsunami is a disastrous natural disaster and it has a serious impact on health and safety of coastal residents,so the early warning is important to them.Recently,the optical fiber sensing technology constantly developed,because of the characteristic of small size,light quality,high accuracy,high corrosion resistance,immunity to electromagnetic interference of the interferometric fiber-optic sensors,it remained as a popular research projects of marine monitoring and warning.Submarine earthquakes and the fluctuation of water height will come with the tsunami,so it is important to achieve the measurement of vibration and pressure.The purpose of this paper is to design a kind of interferometric fiber-optic sensors to accomplish the function of vibration and pressure measurement,and to develop a demodulation algorithm with reliability and stability.First of all,the causes and disasters of the tsunami is illustrated,the development history,the conditions of interference,and the structure of the interferometric fiber-optic sensors is introduced by this paper.Secondly.the demodulation method for interferometric fiber-optic sensors,especially the phase generated carrier demodulation algorithm and the fringe counting algorithm are introduced,which are applied to the measurement of vibration and pressure.Besides,the phase generated carrier-differential and cross multiplying approach(PGC-DCM)and the phase generated carrier arctangent algorithm are analyzed,because of the shortcoming of the result easy interfered by light intensity and the small dynamic area,not only two kinds of methods for them are proposed.but also the simulation comparison is carried out to verify their authenticity.Moreover,a two directions and dual threshhold fringe counting method is proposed,and the demodulated accuracy of it is four times than before.Finally.a Michelson interference sensor system for vibration measurement and a Mach-Zehnder interference sensor system for pressure measurement are established.In low frequency measurement,the signal of 0.4 Hz can be measurement and the dynamic range is more than 100 d B.In pressure measurement,the pi/4 phase change,the 25 ? mm interference beam change,and the 1.1 cm liquid level change can be measured.