Fast Brillouin Optical Time-Domain Reflectometry Based on the Frequency-Agile Technique

A fast Brillouin optical time-domain reflectometry (BOTDR) for dynamic strain measurement is proposed and experimentally demonstrated based on the frequency-agile technique. Employing the band-pass filter and envelope detection, the spontaneous Brillouin gain spectrum can be online demodulated in the time domain for a truly distributed, one-end-access and dynamic strain measurement. A strain sampling rate of 62.5 Hz is achieved for the proposed sensor over 172 m single-mode fiber with 100 sweeping frequencies and 64 times of averaging. In the experiment, the vibration frequencies of 6.82 Hz and 14.77 Hz have been measured with 2 m spatial resolution and 4000 mu epsilon dynamic range. The measurement accuracy is calculated to be +/- 30 mu epsilon by the standard deviation of the static fiber Brillouin frequency shift. Furthermore, the performance on the strain sampling rate and measurement accuracy is investigated with different averaging times. It should be noted that the upgraded schemes for the frequency-agile based Brillouin optical time-domain analysis can be also introduced into the proposed fast BOTDR.