A Fiber-Optic Displacement Sensor Using the Spectral Demodulation Method

This paper reports a fiber-optic displacement sensor based on a Michelson interferometer using the spectral demodulation method. The displacement information is sensed through the length variation of the sensing fiber following the deformation of the measured object. By deploying the relaxed reference arm along the sensing arm, the optical path difference variation introduced by temperature can be eliminated. A spectral demodulation method is employed to obtain the displacement from the interference spectrum by using the fast Fourier transform and the Buneman frequency estimation. The experimental results show that the proposed displacement sensor has a high resolution of 90 nm over a long span of 15.7 m and a large displacement measurement range of 7.5 mm. The theoretical displacement measurement range of the proposed sensor can he up to 10 cm. The proposed displacement sensor will be very useful and promising in large-scale civil infrastructure monitoring applications.