An Extrinsic Fibre Optic Interferometer with Possible Signal Fading Compensation for Vibrometric Applications

We report and demonstrate the use of an extrinsic fibre-based Fabry-Perot interferometer (EFFPI) for vibrometric applications. Preliminary results were obtained for both displacement and velocity measurements of a vibrating target. The sensor operates on a "virtual" pseudo-double cavity within the single sensing arm of the EFFPI, generated due to the presence of a birefringent film introduced into the optical path of the lightwave. Two sets of "phase-shifted" interference signals are thus detected and lead to nonambiguous directional detection of the desired parameters as well as improved resolution in displacement measurements. A further advantage is the potential for overcoming polarisation-induced signal fading as encountered in many interferometric systems