Novel in-service supervisory system using OTDR for long-haul WDM transmission link including cascaded in-line EDFAs

In this letter, we propose and demonstrate a novel optical supervisory syst em for long-haul wavelength-division-multiplexing (WDM) transmission link i ncluding cascaded erbium-doped fiber amplifiers (EDFAs). By employing a mod ified optical time domain reflectometry technique with a wavelength selecti ve bidirectional EDFA, it was possible to monitor the status of the WDM tra nsmission link and EDFA at in-service states with negligible power penalty. Proof of the concept with a 2.5 Gb/s x eight-channel WDM transmission syst em [single-mode fiber, 320 km] shows clear trace of the transmission line l oss/gain/reflection map with minimal signal power penalty of 0.3 dB.