Investigation and compensation of polarization-induced signal fading in an extrinsic fiber-based Fabry-Perot interferometric vibrometer

An extrinsic-type fiber Fabry-Perot interferometer is proposed and demonstrated for vibrometric applications. The sensor operates on the principle of a “virtual” pseudo-dual cavity generated within the sensing arm due to the introduction of an adapted polarization-controlling optics into the optical path of the sensing cavity. This configuration enables two sets of “quadrature phase-shifted” interference signals with a circular polarization state along the fiber to be obtained. Experimental results show the competency of this technique for solving directional ambiguity of the target movement, improving resolution in the displacement measurements and, more significantly, compensating the problem of polarization-induced signal fading (PIF) of the fundamental interference fringe. The fiber interferometer has been found capable of displacement measurements from approximately 0.2 μm to 87 μm with a λ/64 resolution. A reference sensor was used for comparison with output data from the interferometer where an average percentage displacement error of approximately 0.64% was subsequently obtained.