High-Accuracy BOTDR Based on Real-Time Envelope Accumulative and Frequency Response Convolution

Brillouin optical time domain reflectometer (BOTDR) suffers from issues such as poor signal-to-noise ratio (SNR) and low accuracy of Brillouin frequency shift (BFS) extraction. This article presents an optimized BOTDR with high measurement accuracy. A double-sideband modulation (DSM) local oscillator (LO) scheme is proposed to fully utilize both Stokes and anti-Stokes light in backward spontaneous Brillouin scattering (SpBS), resulting in an intensity improvement of 2.57x. Then, a real-time envelope accumulative is implemented using a field-programmable gate array (FPGA), and its processing speed is accelerated fourfold through a four-channel parallel computing architecture. A symmetric kernel (SK) function is realized using a frequency response convolution (FRC) method, which can reconstruct the measured Brillouin gain spectrum (BGS), thereby eliminating distortion caused by the system’s nonideal frequency response and reducing error in BFS extraction. Experimental results show the reconstructed BGS has a Lorentzian curve fitting (LCF) determination coefficient (R²) of 0.997 and an 11.4-dB SNR improvement. The absolute error of the BFS extracted from the reconstructed BGS is decreased from 4.138 to 1.271 MHz. A good linear relationship between temperature and BFS is obtained with a linear fitting coefficient R² of 0.99983, and a temperature coefficient of 1.17 MHz/°C. The temperature measurement uncertainty is reduced to 0.23 °C.