DIRECT STATIC STRAIN-MEASUREMENT UTILIZING SIGNAL FADING AND SPECTRUMANALYSIS IN A FIBER OPTIC INTERFEROMETRIC SENSOR

An accurate linear method of static phase shift measurement in a fibre optic interferometric strain sensor, based on the concurrent utilizat ion of signal fading, photovoltage spectrum analysis and the arctangen t function, is presented. The static phase shift is superimposed on a controlled dynamic phase modulation derived from an optical phase modu lator in one arm of the interferometer. Good agreement is demonstrated between the phase shift obtained through experiment and that from the theoretical expression. This detection scheme has wide applications t o static and dynamic phase shift measurements in fibre optic interfero metric sensors, and to optical interferometry in general.