20 dB SNR enhancement in phase-sensitive OTDR using pulse stretching and recompression - Pastor-Graells, J.; Romero Cortés, L.; Martins, H.F.; Fernández-Ruiz, M.R.; Azaña, J.; Martin-Lopez, S.; Gonzalez-Herraez, M. (Proceedings of SPIE - The International Society for Optical Engineering, 2017)