US Patent 7831144 Fast fault notifications of an optical network

A method and apparatus for fault notification in an optical network are described herein. In one embodiment, an exemplary process includes detecting at a node that at least a portion of a first unidirectional path of an optical circuit is down, where the first unidirectional path is originated from a first terminating node. In response to the detection, the node signals the first terminating node by removing at least a portion of light of a second unidirectional path in an opposite direction of the first unidirectional path of the optical circuit, to indicate a path between the node and the first terminating node is down. Other methods and apparatuses are also described.