175km phase-sensitive OTDR with hybrid distributed amplification

A phase-sensitive optical time-domain reflectometry with 175km sensing range is demonstrated using the combination of co-pumping 2nd-order Raman amplification based on random fiber lasing, counter-pumping 1st-order Raman amplification, and counter-pumping Brillouin amplification. With elaborate arrangements, each pumping scheme is responsible for the signal amplification in one particular segment of the all three. To the best of our knowledge, this is the first time that distributed vibration sensing is performed over such a long distance without inserting repeaters. The novel hybrid amplification scheme demonstrated in this work can also be incorporated in other fiber-optic sensing systems for extension of sensing distance.