Distributed vibration measurement based on a coherent multi-slope-assisted BOTDA with a large dynamic range.

We propose a novel technique to enhance the dynamic range of a coherent slope-assisted Brillouin optical time domain analysis. A multi-tone probe and a reference wave are launched into the fiber under test (FUT); after interacting with the pump pulse, the Brillouin gain, as well as the Brillouin phase shift of each tone, can be demodulated simultaneously. In light of this, the strain information can be determined by the Brillouin phase-gain ratio of each tone. In the experiment, a three-tone probe with a 60 MHz interval is used; effective measurement frequency span larger than 180 MHz is verified in a ∼2  km single-mode fiber with 2.5 m spatial resolution and 1.5 kHz sampling rate to strain. A vibration signal with 41 Hz frequency and 2546 με amplitude is successfully demodulated.