Fiber Optic Sensor Based on Linear Sagnac Interferometer for Branch Localization

One of the challenges of distributed fiber optic sensors is to monitor objects that have multiple branches, such as pipelines or power grids. Existing sensors require multiple sensing systems to cover each branch, which increases the cost and complexity of the monitoring. We propose a fiber optic sensor based on linear Sagnac interferometer for branch localization for practical environments where branch paths exist. The system is based on a dual-wavelength single-core Sagnac interferometer, which can extend multiple branches in the sensing cable part. The phase difference signals caused by external disturbances are demodulated and go through different signal processing. By using time delay estimation and null frequency method, we can determine the exact location of the disturbance on the main or branch path. Moreover, we propose a new method to reduce interference with null frequencies of the spectrum by subtracting the phase difference signal at one wavelength from the other. We demonstrate the feasibility and performance of our proposed system through theoretical analysis and experimental results. Our proposed system offers a simple and effective solution for branch localization in distributed fiber optic sensing applications.