BFS Extraction for Double-Peak Brillouin Gain Curve Based on Triangular Cross Correlation

In the engineering applications of distributed Brillouin optical fiber sensing systems, it is often encountered that the spatial resolution of the system is greater than the length of the event zone, resulting in the acquired Brillouin gain spectrum with double peaks. When the curve fitting method and the centroid method were used to extract the Brillouin frequency shift (BFS) of the double-peak gain curve, the physical quantities could not be measured accurately in the event zone. In this article, we propose to extract the BFS of the double-peak Brillouin gain curve using the cross correlation method, in which the triangular curve was used as the reference curve. We study the effects of the frequency sweep steps, full-width at half-maximum (FWHM) of the reference curve, and signal-to-noise ratio (SNR) on the BFS extraction using triangular cross correlation. The ability of the Lorentzian cross correlation and triangular cross correlation to extract the BFS of the double-peak gain curve was compared, and the results showed that the triangular cross correlation method can extract the BFS of the double-peak Brillouin gain curve more accurately. By extracting the BFS of the double-peak Brillouin gain spectrum acquired experimentally, it is shown that the triangular cross correlation method is more effective than the Lorentzian fitting method and the centroid method in extracting the double-peak BFS.