An Extrinsic Fiber Fabry-Perot Interferometer for Dynamic Displacement Measurement

This paper presents a fiber-based Fabry-Perot interferometer to determine dynamic displacement such as in vibration tracking of an oscillating target. This sensor exploits the dual-cavity principle in the sensing arm to achieve non-ambiguous directional displacement measurements and has a measurement range of ~120 mum for a sinusoidal excitation signal up to 125 Hz. By adopting a modified fringe counting technique to take into account all the appropriate points over the two sets of interference signals thereby generated due to target movement, a resolution of ~40 nm can be achieved. The results obtained from the fiber interferometric sensor employed to measure various displacement signals show good agreement with prediction.