Differential Slope-Assisted BOCDA Based on Multicore Fiber for High Sensitivity Radial Vibration Measurement

We proposed and demonstrated a novel differential slope-assisted Brillouin optical correlation domain analysis (BOCDA) sensor based on a multicore fiber (MCF) for radial vibration measurement. Thanks to the bending-sensitivity of Brillouin frequency shift (BFS) in off-center cores in the MCF, by fixing the probe frequency around the mid-slope point of Brillouin gain spectrum (BGS) of the pump light, the BFS changes induced by radial vibration on the sensing fiber can be monitored through differential detection between the output probe powers of two symmetrical outer cores of the MCF. This scheme avoids the time-consuming process of frequency scanning and also removes the bandwidth limitation of the lock-in amplifier (LIA) in a conventional BOCDA with the help of the injection-locking technique. In addition, the proposed differential detection structure between two symmetrical outer cores improves the signal-to-noise ratio and sensitivity of the sensing system. For proof of concept, a 12-Hz radial vibration measurement is demonstrated with 8.7-cm spatial resolution. The proposed scheme paves the way to enable high spatial resolution and high sensitivity vibration detection using a freely placed sensing fiber with the BOCDA technique.