Remote vibration sensor using fiber optic fused 2x2 coupler

A simple geometrical fiber optic vibration sensor is designed and demonstrated using fiber optic fused 2x2 coupler that utilizes the principle of reflection intensity modulation. The rational output is used to avoid the effects of source signal power fluctuations and fiber bending losses. The calibrated 1mm linear region of the displacement characteristic curve of the sensor having high sensitivity of 2.1 mV/mm (0.36 a.u. /mm) is considered for vibration measurement. The experimental results show that the sensor is capable to measure the frequency up to 3500 Hz with ~0.03µm resolution of vibration amplitude over a dynamic range of 0-1mm. The SNR of the rational output is also improved with respect to the sensing signal. In comparison with dual-fiber and bifurcated-bundle fiber, this sensor eliminates the dark region and front slope which facilitates the easy alignment. The simplicity of design, non-contact measurement, high degree of sensitivity, economical along with advantages of fiber optic sensors are attractive attributes of the designed sensor that lend to real time monitoring and embedded applications.