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 paper presents an optimized BOTDR with high measurement accuracy. A double-sideband modulation (DSM) local oscillator scheme is proposed to fully utilize both Stokes and anti-Stokes light in backward spontaneous Brillouin scattering (SpBS), resulting in an intensity improvement of 2.57 times. Then, a real-time envelope accumulative is implemented using a field-programmable gate array (FPGA), and its processing speed is accelerated 4-fold through a four-channel parallel computing architecture. A symmetric kernel 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 non-ideal 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 MHz 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.