Development of a Low Cost 3x3 Coupler Mach-Zehnder Interferometric Optical Fibre Vibration Sensor

In this paper, a low cost 3x3 coupler Mach-Zehnder interferometric optical fibre vibration sensor is proposed. Unlike traditional Mach-Zehnder interferometer with a strain free reference arm, two parallel optical fibres with different strain transfer sensitivity is adopted. With proper demodulation algorithm, the time rate of change of the strain can be computed from the light signal of the outputs of the 3×3 coupler. The proposed optical fibre vibration sensor is verified by experiment. The vibrating frequency spectrum of a 2-layer metal frame is measured by both the proposed optical fibre vibration sensor and MEMS-based accelerometer. It is found that the proposed vibration sensor is more sensitive unless it is located near zero strain region compared to MEMS-based accelerometer. Several proposed sensor can be easily multiplexed to minimise the overall cost.