Abstract: A network is maintained functional in the presence of a wide range of faults, including physical fiber cuts, transmission impairments creating signal quality degradation, and failure of equipment modules, for example, transceivers, using a common control and backup channel, either alone or in combination with fiber loopback protection or wavelength loopback protection, or fiber loopback protection or wavelength loopback protection alone. Systems constructed according to the invention require only a single transceiver per wavelength at each node that accesses that wavelength. The invention is equally applicable to type 1 nodes, which drop and add a single, predetermined wavelength, and to type 2 nodes which have the capability to drop and add any subset of the wavelengths employed in the network.

Abstract: First and second optical fibers carry information modulated on an optical carrier. Information modulated on the carrier is to be recovered and transmitted at a first node along the first and second optical fibers. The first node includes apparatus for receiving and transmitting the information. The apparatus for receiving and transmitting the information includes a first receiver for demodulating the information modulated on the optical carrier and carried on the first optical fiber, a second receiver for demodulating the information modulated on the optical carrier and carried on the second optical fiber, a transmitter for modulating the information on the second optical fiber, and a splitter for splitting the optical carrier carried on the first optical fiber. The splitter is coupled to the first optical fiber and the first receiver. A portion of the optical carrier is coupled to the first receiver and another portion of the optical carrier continues on the first optical fiber.