Improvement of a polarisation optical fibre sensor for the detection of seismic vibration

Near acoustic frequencies from seismic activities can be observed by sensors with band pass higher than the 5-second period peak noise. By using a single mode fibre optic specially adjusted, a planar vibration travelling on surface can modify the optogeometrical properties of its material and enhanced a birefringence effect. This type of sensor already effective in acoustic frequencies is now adapted to seismic vibration. The high noise background at these frequencies disturbs greatly the measure and isolation by adjustment of spring and plates dimensions leads to interesting questions in regard of dynamic behaviour in this window. Currently, the sensor can detect small and local vibrations but cannot measure with good precision its velocity and acceleration value. In the first part of this paper, the basics of seismic vibration will be briefly exposes in coordination with the way the sensor works; a brief walkthrough of the fibre optic sensing behaviour will be exposed. The next part will display the different elements of the sensor and the choices that were made at this stage. Eventually, the behaviour of the sensor will be displayed along with the calibration method and the different errors that need to be corrected.