A network node (400) for use with a single-fiber bidirectional communication link comprises a filter (300). The filter (300) comprises at least four ports. A first port (301) is configured to communicate with the single-fiber in a west direction. A second port (303) is configured to communicate with the single-fiber in an east direction. A third port (305) is configured to add/drop in the west direction. A fourth port (307) is configured to add/drop in the east direction. The network node is configured to add a first wavelength (λA) to the west direction and the east direction, and configured to drop a second wavelength (λB) from the west direction and the east direction.