Dynamic displacement measurements with a dual-cavity fiber Fabry-Perot interferometer

An extrinsic fiber Fabry-Perot interferometric sensor is reported for use in vibrometric applications. The sensor operates on the principle of a "virtual" dual-cavity generated within the sensing arm due to the introduction of a birefringent element into the optical path of the sensing cavity. The resulting two sets of "phase-shifted" interference signals produced allowed non-ambiguous directional detection as well as improved resolution in displacement measurements. Experimental displacement data obtained using the fiber interferometer were found to be in good agreement with the reference sensor employed. The potential for overcoming polarization-induced signal fading is also qualitatively illustrated.