US Patent 7660526 Through channel loss prevention at a WDM node

At a WDM add/drop node of an optical fiber, an add/drop multiplexer system with opto-electric components in the through channel path has an optical switch connected in parallel with an add/drop multiplexer. Upon a power loss to the add/drop multiplexer, the optical switch bypasses the add/drop multiplexer so that WDM channel signals pass through the WDM add/drop node without interference from the unpowered add/drop multiplexer. Loss of through channels at the node is prevented. Upon a return of power, the optical switch reroutes the WDM signals on the optical fiber to the add/drop multiplexer but after the add/drop multiplexer is fully operational.