Frequency-comb-based BOTDA sensors for high-spatial-resolution/long-distance sensing.

Frequency-comb-based Brillouin optical time-domain analysis (BOTDA) sensors were developed to achieve acquisition-time reduction and high-spatial-resolution/long-distance sensing simultaneously. We found that, for the standard frequency-comb-based BOTDA, the use of a double-sideband (DSB) pulse generates a series of pulse pairs that simultaneously propagate along the sensing fiber, leading to a nonlinear interaction between the two sidebands of each frequency comb pulse, and a significant splitting of the Brillouin gain spectrum (BGS). This problem prevents its application in high-spatial-resolution sensing due to the higher pulse power requirement. Thus, one of the sidebands of DSB pulse was proposed for greatly suppressing the BGS distortion. In combination with the phonon pre-excitation technique based on phase-shifted pulse, a sensor with a spatial-resolution approximately 60 cm along a fiber approximately 592 m in length was demonstrated. Furthermore, we explored the detailed performance of long-distance sensing by frequency- comb-based BOTDA. The use of a frequency comb for the probe wave can suppress the pulse distortion and non-local effect, which is helpful for extending the sensing distance. A spatial resolution of approximately 6 m along a sensing fiber approximately 74.2 km in length was successfully demonstrated.

BOTDA sensors enhanced using high-efficiency second-order distributed Brillouin amplification.

A novel approach for long-distance sensing through Brillouin optical time-domain analysis (BOTDA) assisted by second-order distributed Brillouin amplification (DBA) was proposed and experimentally demonstrated. To the best of our knowledge, this is the first BOTDA study that used second-order DBA. Compared with BOTDA assisted by first-order DBA, the proposed approach enhanced the signal-to-noise ratio of the Brillouin trace by ~3 dB for a range featuring minimum sensing intensity. Long-distance sensing with ~5 m spatial resolution and ± 1.6°C measurement uncertainty over ~99 km fiber was successfully realized by employing high-efficiency pumping using ~6 dBm second-order and ~1.5 dBm first-order pumps.