Multiplexed optical fibre Fabry-Perot sensors for strain metrology

Abstract

This paper demonstrates the feasibility of multiplexing several optical fibre-based Fabry-Perot sensors in series for strain metrology. White-light interferometry was employed using the laser-referenced Michelson interferometer of a standard Fourier-transform spectrometer as a receiving (interrogating) interferometer. The primary aim was to demonstrate that at least six fibre Fabry-Perot transducer interferometers (sensors) can be multiplexed in series. A prerequisite for this sensor system is that each sensor has to have a unique optical cavity length within the multiplex. The resulting differing optical path differences at each fibre Fabry-Perot sensor give rise to sharp correlation features (side bursts) at unique positions in the time domain as observed in the interferogram. An optical cavity length change due to an axial strain perturbation is observed as a change in the position in the time domain of the side-burst feature associated with the optical fibre Fabry-Perot sensor. This paper demonstrates that multiplexed strain metrology in the quasi-static regime using optical fibre Fabry-Perot sensors is possible with a measurement range of typically 0-4000 microstrain and a strain resolution of better than 10 microstrain.