A Fiber-Optic Interferometric Tri-Component Geophone for Ocean Floor Seismic Monitoring

Abstract

For the implementation of an all fiber observation network for submarine seismic monitoring, a tri-component geophone based on Michelson interferometry is proposed and tested. A compliant cylinder-based sensor head is analyzed with finite element method and tested. The operation frequency ranges from 2 Hz to 150 Hz for acceleration detection, employing a phase generated carrier demodulation scheme, with a responsivity above 50 dB re rad/g for the whole frequency range. The transverse suppression ratio is about 30 dB. The system noise at low frequency originated mainly from the 1/f fluctuation, with an average system noise level −123.55 $\mathrm{dB}\mathrm{re}\mathrm{rad}/\sqrt{\mathrm{Hz}}$ ranging from 0 Hz to 500 Hz. The minimum detectable acceleration is about 2 $\mathrm{ng}/\sqrt{\mathrm{Hz}}$ , and the dynamic range is above 116 dB.