Branching Interferometric Distributed Fiber Optic Vibration Sensor Insensitive to Dual-Fiber Phase-Shift Difference

The branching interferometric distributed fiber optic vibration sensor (IDFOVS) attracts attention for its capability to monitor regions with intricate geometries. However, the localization accuracy of existing branching IDFOVS will deteriorate if affected by dual-fiber phase-shift difference (DFPSD). This article introduces an improved branching IDFOVS with insensitivity to DFPSD. The insensitivity is achieved through a modified optical path configuration, wherein conjugated wavelength components (CWCs) traverse the two sensing fibers within a branch path in reverse sequences. The effect of DFPSD is eliminated by summing the demodulation signals of each CWC pair and the sum signals generated are employed to localize disturbances by time-delay estimation. The experimental results demonstrate that the localization errors are within ±40 m over a sensing fiber of 50 km. Furthermore, the superiority of the proposed sensor, attributed to its insensitivity to DFPSD, is confirmed through comparative analysis with a previously reported sensor. Given that the sensing optical cables utilized in engineering may not inherently have a low DFPSD level, the sensor proposed in this article has potential for practical application.