Frequency- and time-multiplexed high-precision BOTDR using a frequency-shifting loop

The Brillouin optical time domain reflectometer (BOTDR) has become a widely applied distributed sensing technique thanks to its unique advantages such as single-end access, simple system architecture and ease of implementation. However, with the development of BOTDR, its limitations, such as low system signal-to-noise ratio and limited maximum sensing distance, have become increasingly apparent. Traditional methods commonly adopt large number of averages to improve system accuracy, which leads to extended measurement time. In response to the above issues, we propose a high accuracy BOTDR based on a frequency-shifting loop. This technology employs frequency division multiplexing, which not only maintains spatial resolution but also enhances the system's measurement accuracy by a factor of &radic;<i>N</i> using N frequencies. Additionally, it maximizes the Local Oscillator (LO) power, thereby breaking the limitations imposed by Photoelectric Detector (PD) saturation. This method provides a new approach for multi-frequency BOTDR and contributes to the development of high-precision and long-distance sensing techniques.