Fiber-Optic Interferometric Horizontal Accelerometer for Seismic Signals Recording

A high-sensitivity fiber-optic interferometric horizontal accelerometer using passive phase demodulation is proposed and demonstrated. The principle of sensitivity improvement using multiturn optical fiber coil as a horizontal sensing element is described. A fiber-optic 3 × 3 splitter is used as a phase demodulator. The optical responsivity for the frequencies below the resonance was found to be equal 1770 rad/g. Accelerations as small as 0.16 μg at 55 Hz have been detected. The noise level of a fiber-optic accelerometer was compared with a piezoelectric accelerometer. The intrinsic noise level of the fiber-optic accelerometer is lower than that of the piezoelectric accelerometer and provides an opportunity to detect accelerations down to 5 × 10–8 g. Operating frequency band is 10 to 130 Hz.