A Logarithmic Detection Scheme in BOTDR With Low-Bandwidth Requests

This paper presents a logarithmic detection scheme for reducing the bandwidth of the data acquisition (DAQ) in a Brillouin optical time domain reflectometer (BOTDR). From the analysis of signal features in frequency-scanning BOTDR, the reduction effect of the proposed detection scheme on the bandwidth of DAQ is investigated theoretically. We implement the scheme and evaluate its influence on the performance of BOTDR over a ~10-km sensing fiber by employing a digitalizer with bandwidth of only 50 MHz. The experimental results show that the spatial resolution of 1.02 m is achieved even though the bandwidth of DAQ is only 50 MHz. At 100-m end of sensing fiber, the root-mean-square error (RMSE) of Brillouin frequency shift (BFS) is 0.67 MHz corresponding to the strain error of 13.4 $\mu \varepsilon $ and temperature error of 0.66°C. As a comparison, the BFS is likewise acquired by a 200-MHz-bandwidth digitalizer, the RMSE of which is 0.66 MHz corresponding to the strain error of $13.2~\mu \varepsilon $ and temperature error of 0.65°C, nearly consistent with the former. It is confirmed that the logarithmic detection scheme can be used in BOTDR for reducing bandwidth request of DAQ meanwhile without excessive deterioration of spatial resolution or measurement accuracy.