Interferometric Distributed Fiber Optic Vibration Sensor With Branching Sensing Optical Path Based on Time Delay Estimation for Disturbance Localization

In this article, an interferometric distributed fiber optic vibration sensor (IDFOVS) with branching sensing optical path is proposed. The sensing optical path of this sensor could consist of a main path and several branch paths. The branch paths are connected by the main path flexibly. Therefore, compared with traditional IDFOVSs with linear or cirular shape of sensing optical path, the proposed sensor is more suitable for monitoring areas with branches. The sensor is based on linear Sagnac fiber optic interferometer. With novel design of the branch path, disturbances can be localized based on time delay estimation (TDE), which would be conducted twice. In the first time of TDE, the disturbed branch path or the disturbance occurring on the main path is localized and in the second time, the disturbance location on the branch path is obtained. The localization performance of the proposed sensor is verified experimentally. For disturbances occurring on the main path and the branch path, the location errors are less than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 30 m and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 65 m respectively with the total sensing optical fiber length of 50 km and the branch path length of 20 km. The phase shift difference between two fibers in an optical cable is verified and its passive effect on the precision of localizing disturbances occurring on the branch path is analyzed. In addition, by comparing with a sensor proposed previously, the performance superiority of the sensor proposed in this article is demonstrated.