System and method for monitoring a branched optical communication system

1. 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.

2. The system of claim 1 wherein:

said branching configuration is configured to pass said first monitoring signal and at least one second terminal drop-channel transmitted on said trunk path by said second trunk terminal to said branch terminal and to insert said first monitoring signal and at least one second terminal add-channel from said branch terminal onto said trunk path;

said branch path comprises a first fiber pair and a second fiber pair, said first fiber pair comprising said at least one branch-drop fiber and said at least one branch-add fiber;

said second fiber pair comprising a second branch-drop fiber for carrying said first monitoring signal and said at least one second terminal drop-channel from said trunk path to said branch terminal and a second branch-add fiber for carrying said first monitoring signal and said at least one second terminal add-channel from said branch terminal to said trunk path; and

said monitoring signal routing device is configured to route said first monitoring signal from said at least one branch-drop fiber to said second branch-add fiber, and to route said first monitoring signal from said second branch-drop fiber to said at least one branch-add fiber.

3. The system of claim 2 , wherein said monitoring signal routing device comprises a first filter coupling said at least one branch-drop fiber to said second branch-add fiber, and a second filter coupling said second branch-drop fiber to said at least one branch-add fiber.

4. 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 said WDM signal 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, and to pass said first monitoring signal and at least one second terminal drop-channel transmitted on said trunk path by said second trunk terminal to said branch terminal and to insert said first monitoring signal and at least one second terminal add-channel from said branch terminal onto said trunk path;

said branch path comprising a first fiber pair and a second fiber pair, said first fiber pair comprising a first 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 a first 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 second fiber pair comprising a second branch-drop fiber for carrying said first monitoring signal and said at least one second terminal drop-channel from said trunk path to said branch terminal and a second branch-add fiber for carrying said first monitoring signal and said at least one second terminal add-channel from said branch terminal to said trunk path;

said branching configuration configured to pass said second monitoring signal through said branching configuration in a direction from said first trunk terminal to said second trunk terminal and in a direction from said second trunk terminal to said first trunk terminal 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 second branch-add fiber, and to route said first monitoring signal from said second branch-drop fiber to said at least one branch-add fiber.

5. The system of claim 4 , wherein said monitoring signal routing device comprises a first filter coupling said at least one branch-drop fiber to said second branch-add fiber, and a second filter coupling said second branch-drop fiber to said at least one branch-add fiber.

6. A method of monitoring a branched optical communication system including first and second trunk terminals coupled to a trunk path and a branch terminal coupled to the trunk path through a branching configuration and a branch path, the method comprising:

transmitting a first monitoring signal having a first wavelength from the first trunk terminal onto the trunk path;

passing said first monitoring signal onto a branch-drop fiber of the branch path, the branch-drop fiber configured to carry at least one drop-channel of a WDM signal from the trunk path to the branch terminal;

routing said first monitoring signal from said branch-drop fiber to a branch-add fiber within the branch terminal, said branch-add fiber being configured to carry at least one add-channel from the branch terminal to the trunk path;

transmitting a second monitoring signal having a second wavelength from the first trunk terminal onto the trunk path; and

passing said second monitoring signal through the branching configuration toward said second terminal without placing said second monitoring signal on said branch path.

7. The method of claim 6 , wherein said WDM signal is transmitted by said first trunk terminal and wherein said branch-drop fiber and said branch-add fiber form single fiber pair associated with the first trunk terminal, said branch-add fiber configured to carry said at least one add-channel from the branch terminal to the trunk path for transmission to said first trunk terminal.

8. The method of claim 6 , said method further comprising routing said first monitoring signal from said branch-drop fiber to said branch-add fiber within the branching configuration.

9. The method of claim 6 , wherein said WDM signal is transmitted by said first trunk terminal and wherein said branch-drop fiber and said branch-add fiber are associated with first and second fiber pairs, respectively, said branch-add fiber configured to carry said at least one add-channel from the branch terminal to the trunk path for transmission to the second trunk terminal.