Forward Transmission Distributed Fiber-Optic Sensing: A Short-Range Demonstration

The forward-transmission distributed fiber-optic sensing is a cutting-edge technology capable of detecting sounds and vibrations, along with their precise locations, across distances spanning hundreds of kilometers. While much of the existing research has focused on its long-range capabilities, where it offers significant benefits, little attention has been given to explore its performance at shorter ranges and its high-frequency response. Investigating these aspects can provide a more complete understanding of the technology and its comparative effectiveness against traditional methods at various sensing scales. In this work, a forward transmission distributed acoustic/vibration sensing system based on coherent detection using a $3\times 3$ coupler, arctangent phase demodulation method, and phase-spectrum time-delay method is theoretically simulated and experimentally demonstrated. In particular, the short-range performance of the system is studied when subject to multiple perturbations with short spacing intervals. The 5-kHz single-perturbation experimental results reveal a positioning accuracy of 2.4-m root-mean-square error (RMSE) and 0.5 m [standard deviation (STD)], which is comparable to conventional sensing technologies. The multipoint perturbation tests were performed perturbation events separated by 2 m, across a frequency range of 5–16 kHz. The findings indicate that the system can effectively and reliably identify the perturbation events, for example, located at 500 and 502 m, along a 1004-km-length sensing fiber.