Distributed Acoustic Sensor Using a Double Sagnac Interferometer Based on Wavelength Division Multiplexing
A. A. Zhirnov, T.V. Choban, Konstantin V. Stepanov, Kirill I. Koshelev, Anton O. Chernutsky, Alexey B. Pnev, Valeriy E. Karasik
Abstract
We demonstrated a fiber optic distributed acoustic sensor based on a double Sagnac interferometer, using two wavelengths separated by CWDM modules. A mathematical model of signal formation principle, based on a shift in two signals analysis, was described and substantiated mathematically. The dependence of the sensor sensitivity on a disturbance coordinate and frequency was found and simulated, and helped determine a low sensitivity zone length and provided sensor scheme optimization. A data processing algorithm without filtering, appropriate even in case of a high system noise level, was described. An experimental study of the distributed fiber optic sensor based on a Sagnac interferometer with two wavelengths divided countering loops was carried out. An accuracy of 24 m was achieved for 25.4 km SMF sensing fiber without phase unwrapping.