Patent ID: 8483559

Claim:
A wavelength division multiplexed (WDM) optical system comprising: a first trunk terminal coupled to a second trunk terminal through a trunk path, said first terminal being configured for transmitting a WDM signal on said trunk path; line monitoring equipment configured for generating a first monitoring signal having a first wavelength and a second monitoring signal having a second wavelength different from said first wavelength to be transmitted on said trunk path; a branch terminal coupled to said trunk path through a branch path and a branching configuration, said branching configuration configured to pass said first monitoring signal and at least one drop-channel of a WDM signal transmitted on said trunk path from said trunk path to said branch terminal and to insert said first monitoring signal and at least one add-channel from said branch terminal onto said trunk path, said branch path comprising at least one branch-drop fiber for carrying said first monitoring signal and said at least one drop-channel from said trunk path to said branch terminal and at least one branch-add fiber for carrying said first monitoring signal and said at least one add-channel from said branch terminal to said trunk path; said branching configuration configured to pass said second monitoring signal through said branching configuration and onto said trunk path without placing said second monitoring signal on said branch path; and a monitoring signal routing device disposed in said branch terminal, said monitoring signal routing device being configured to route said first monitoring signal from said at least one branch-drop fiber to said at least one branch-add fiber to thereby return said first monitoring signal to said trunk path.