Phase Difference Measurement of the Target Signals of Sensing Elements in the Push-Pull Fiber Optic Interferometric Acoustic and Vibration Sensors

In this paper we consider a fiber-optic interferometric push-pull sensor containing 4 spirals of a single-mode optical fiber. Experimental determination of the phase difference of the target acoustic and vibrational signals is performed independently for each of the spirals. The sensor was placed into acoustic chamber, each of the sensor sensitive elements was connected to the interrogation system in an optical time domain multiplexing (TDM) scheme, and the phase difference of the target signals between 4 sensitive elements was determined. Additionally, similar measurements were performed when connecting the sensor to a vibrating test bench. The experimental results turned out to be close to theoretical values; under the influence of the target acoustic signal, the external and internal plates had counter-phase signals.