Comparison of the use of first and second-order Raman amplification to assist a phase-sensitive optical time domain reflectometer in distributed vibration sensing over 125 km

1. Martins, H.F.
2. Martin-Lopez, S.
3. Filograno, M.L.
4. Corredera, P.
5. Frazão, O.
6. Gonzalez-Herraez, M.