In-service OTDR-monitoring-supported fiber-Bragg-grating optical add-drop multiplexers

Two optical time-domain reflectometer (OTDR)-monitoring-supported fiber-Bragg-grating optical add-drop multiplexer (OADM) structures for in-service fault-location monitoring by using a conventional OTDR are demonstrated. Negligible system power penalty, due to the OTDR monitoring, of both structures in 10-Gb/s dense wavelength-division-multiplexing (DWDM) link is achieved. We find that the multiport-optical-circulator-based structure is superior to the wavelength-division-multiplexing structure to have compact structure, fewer components required, and potentially low cost. Such OADMs may find important applications in DWDM networks to implement a centralized automated in-service surveillance system to enhance system reliability.