Ultra-long Brillouin optical time-domain analyzer based on distortion compensating pulse and hybrid lumped-distributed amplification

A Brillouin optical time-domain analysis (BOTDA) scheme based on hybrid amplification, consisting of distributed Raman amplification and lumped amplification provided by remotely pumped Erbium-doped fibers, is proposed and thorougly studied, enabling longest sensing distance among existing repeaterless techniques. First, criteria for optimizing the optical powers entering the sensing fiber are defined. Then, the walk-off effect in the forward distributed Raman amplification and associated self-phase modulation are pointed out and analyzed to describe the BOTDA pulse distortion and its impact on the balanced detection used for relative intensity noise mitigation. A compensating pulse approach is proposed to mitigate signal distortion, guaranteeing the safe use of balanced detection in an ultra-long BOTDA sensor. The combination of all approaches mentioned above is validated in two types of fiber loop configurations, with 150 km and 200 km real remoteness, both constituting record-high sensing performance in each case.