Distributed Dynamic Strain Measurement Based on Dual-Slope-Assisted Brillouin Optical Correlation Domain Analysis

In this paper, we propose and demonstrate a high-speed Brillouin optical correlation domain analysis (BOCDA) system by exploiting the slope of the Brillouin gain spectrum (BGS). In the slope-assisted (SA) scheme, the Brillouin frequency shift change is obtained by recording the Brillouin power variation. In this case, the time-consuming frequency sweeping process is avoided, leading to an ultrahigh measurement speed for Brillouin sensors. Here, this SA concept is adopted into the BOCDA system to improve its measurement speed. Moreover, in order to achieve pump-power-independent and fiber-loss-insensitive measurements, a dual-slope-assisted (DSA) scheme is implemented by measuring the ratio between readings taken from both slopes of the BGS. By employing this new technique, a repetition rate of 625 Hz as well as a centimeter-level spatial resolution is achieved, which is verified by measuring dynamic strains with frequencies up to 100 Hz. Meanwhile, by using the proposed system, distributed and dynamic tracking of mechanical wave propagating along the fiber under test is realized. Moreover, the limitations of DSA-BOCDA on measurement accuracy, spatial resolution, and measurement speed are also discussed in detail.