In this paper, we propose and demonstrate an ultrahigh-speed Brillouin optical correlation domain analysis (BOCDA) with a single-position sampling rate of 200 kS/s and a spatial resolution of 8 cm. The Brillouin gain spectrum (BGS) is obtained by using a data subtraction scheme rather than the conventional lock-in amplifier (LIA) detection configuration, thus removing the limitation of measurement speed imposed by the LIA. Meanwhile, a voltage controlled oscillator (VCO) is used to sweep the frequency interval between the pump and the probe rapidly. As a proof of concept, we implement measurements of various dynamic strains with frequencies up to 20 kHz at arbitrary position. Moreover, to implement high-speed distributed measurements of Brillouin frequency shift (BFS) along the whole fiber under test (FUT), we propose a novel measuring method which moves the correlation peak and sweeps the pump-probe frequency interval simultaneously. A repetition rate of 1 kHz is verified by measuring dynamic strains with frequencies up to 200 Hz, for distributed measurements performed with 200 points.

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We propose and experimentally demonstrate a novel method to enhance the performance of the Brillouin optical correlation domain analysis (BOCDA) by analyzing the shape characteristic of the measured Brillouin gain spectrum. We theoretically analyze and simulate the operation of BOCDA, and it is found that the Brillouin signal peak generated at the correlation peak shows a sharp Lorentzian shape with a large value of convexity, while the background noise structure stacked from other positions shows a smooth trapezoidal shape with a small value of convexity. By extracting the convexity of measured BGS, the signal part can be enhanced while the noise part is suppressed drastically, which leads to an enlarged strain/temperature measurement range and a narrowed spatial resolution for BOCDA. This concept is verified by both numerical simulation and experiments. By using this method, a >16-mε/800-• C strain/temperature measurement range and a fivefold-improved spatial resolution are achieved experimentally without extra hardware complexity.

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