Extrinsic Fabry-Perot interferometric sensor using a polarization-switched phase interrogator

In this paper, a phase variation tracking method for the extrinsic Fabry-Perot interferometric (EFPI) voice sensing system is designed and experimentally demonstrated through a polarization-switched unit based on the combination of polarization-maintaining fiber Bragg grating (PMFBG). The measurements at two operation wavelengths are firstly achieved in one total-optical path, which eliminates the imbalance of optical power from the external disturbances, optical source fluctuation, different detecting response of photoelectric detector and different background noise. Two operation wavelengths reflected from a PMFBG for interference phase tracking are switched via an electro-optic modulator at a high switching speed of 10 kHz. Besides, an ellipse fitting-differential cross multiplication (EF-DCM) algorithm is proposed and illustrated for interrogating the variation of EFPI cavity gap length of the EFPI voice sensor effectively. Preliminary experimental results have proven that the polarization-switched system based on the EF-DCM algorithm could find potential applications in the fields of marine acoustic, medical science measurements, etc.