Extrinsic fibre Fabry-Perot interferometer for vibration and displacement measurement: the benefit of polarization decomposition

摘要

We have successfully developed a new design of an extrinsic fibre Fabry-Perot interferometer (EFPI) sensor dedicated to the characterization of vibration and displacement of a target. This device, based on a low finesse Fabry-Perot cavity formed by the end of a 'sensing' optical fibre and the target, gives information on the direction of the motion without the use of an additional reference arm. The incoming light, emitted by a 1310 nm laser diode, is decomposed according to two orthogonal polarization orientation inside the cavity. The two resulting interference signals are then carried back by the same optical fibre and sent to two photodiodes via a coupler and a polarizing beam splitter. With a relatively simple signal processing, a precision of λ/4 is achieved for the measurement of the displacement, for which the direction is also extracted. In addition, one can determine the velocity of the motion, that have been successfully compared with a reference sensor. The use of a polarization maintaining fibre as sensing arm, not mandatory for monitored laboratory set-up, allows the use of this sensor principle even with external perturbation (temperature changes, mechanical stress,....).