Sagnac interference-based broadband distributed vibration sensing system

The limitation of detection frequency of distributed optical fiber vibration sensing system (DVS) is affected by the pulse repetition frequency. In order to improve the frequency detection limitation, a broadband DVS fused with Sagnac interference is proposed. To avoid the wavelengths overlapping between the broadband light source of the Sagnac interference and narrow line-width light source of the DVS, the optical filters and optical isolators are used, which makes the optical paths of the two sensing systems have little common sections, excepting the sensing fiber. Experiments are shown that the proposed converged sensing system not only maintains the unique sensing characteristics of each subsystem, but also avoids the disturbance with each other, making the converged system capable of detecting high-frequency signals over long distances. In the sensing system, the vibration signal with frequency at 60kHz over 20km sensing fiber is been detected and located successfully.