A method and system for detecting optical signal degradation or loss within the optical domain of a fiber network. Optical cross-connect switches (OCCS) are provided at network nodes. Optical data traffic is conducted between nodes via a fiber link. The fiber link extends between respective ports of the optical cross-connect switches at each network node. Dedicated signals for detecting faults are introduced and removed within the optical domain of the fiber communication network. In one embodiment, transmitter/receiver units are coupled directly to the fiber link for broadcasting optical signals for fault detection. In another embodiment, transmitter/receiver units are coupled to the fiber link through one or more dedicated ports within optical cross-connect switches (OCCS) at network nodes. Optical signals for fault detection are then broadcast or switched through working and/or spare fibers. Distinctive optical fault detection signals are used when the signals are broadcast or switched over working fibers. Optical signal impairment or loss for a particular link or span is detected simply and quickly in the network optical domain. Rapid, accurate optical fault capability can be added to communication networks without requiring changes to existing light terminal elements and processing circuitry in the electrical domain.