Extending the Sensing Distance of a Single-End Random-Access BOTDA for Dynamic Sensing

Long-range Brillouin optical time-domain analysis (BOTDA) requires a frequency scanning process and averaging to obtain Brillouin temporal traces to map the distributed Brillouin gain spectrum, which is highly time-consuming. Furthermore, the two-end accessibility of the BOTDA leads to a roundtrip wiring layout, which shortens the sensing distance to half of the fiber length. To overcome these issues, in this study, we proposed a single-end random-access BOTDA. Two pulses, namely, pump and probe pulses, were sequentially generated, one with constant frequency and the other with chirped modulation, between which a stimulated Brillouin scattering interaction occurred with a high signal-to-noise ratio; therefore, a frequency scanning process and averaging were not needed. The pump and probe pulses were sent into the sensing fiber at the near end, and only the probe was reflected by a narrow bandwidth filter placed at the far end. The proposed single-end BOTDA can randomly sense the interested position by adjusting the time delay between the pump and probe pulses. As a result, real-time dynamic acquisition up to 1 kHz can be achieved on any position along the 50-km-long fiber, and distributed measurements can be performed on the second level. In addition, the proposed sensor is immune to the nonlocal effect, demonstrating a higher sensing accuracy at the far end compared with that of a traditional BOTDA.