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13 May 2010 Polarimetric single-mode fibre optic sensor for low level and low frequency vibration measurements
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Numerous approaches to seismic detection have been proposed. Usual methods to sense seismic vibrations use either accelerometers to measure the ground acceleration or geophones based on electro-dynamic actuator velocimeters. In this paper, we present the design and the development of a polarimetric transducer using a single-mode optical fiber for low level and low frequency vibration measurements such as those encountered in seismology. Polarimetric sensors can be optimized to have a reduced sensitivity to temperature. The mechanical part of our one-dimensional seismic sensor is based on a spring-mass device. A small section of the fiber is squeezed between a substrate connected to the ground and the sprung mass. The resulting force acts along a vertical direction onto a small section of the optical fiber. The elastooptic effect induces stress birefringence which varies temporally with the frequency of the applied force. We used a polarized and single-mode laser diode source to couple light in the fiber. The induced polarization modulation measured at the output of the fiber gives information of the seismic signals. The physical model of the developed inertial seismometer has been considered as a mass-and-spring system with viscous damping. Firstly, we expose the principle behind our optical fiber seismic sensor. Next, we computed the dynamic characteristics of the seismic sensor. Physical simulation results obtained using the analytical model are presented and discussed. Finally, we present experimental results measured with our seismic fiber sensor. Both model and experimental results demonstrate the potential of the sensor for low level and low frequency vibrations characterization.
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A. Lebrun, B. Serio, M. Guilhem, P. Pfeiffer, S. Lecler, and A. Chakari "Polarimetric single-mode fibre optic sensor for low level and low frequency vibration measurements", Proc. SPIE 7726, Optical Sensing and Detection, 77262A (13 May 2010);

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