Patent ID: 6915075

Claim:
An optical WDM network comprising at least two nodes interconnected by a bidirectional optical link, at least one of the nodes comprising at least two pairs of ordinary optical transmitters and ordinary optical receivers, each pair including an ordinary optical transmitter receiving electrical signals and converting the received electrical signals to issued first optical signals and an ordinary optical receiver receiving optical signals and converting them to electrical signals, ordinary transponders, each ordinary transponder receiving the issued first optical signals from only one of the ordinary optical transmitters of the pairs and converting the received signals to issued second optical signals of a well defined wavelength band, the wavelength bands of the second optical signals issued by different ones of the ordinary transponders being separate from each other, a first optical multiplexer or combiner connected to receive the second optical signals issued by the ordinary transponders of the at least one node, the first optical multiplexer or combiner combining the second optical signals to issue a combined optical signal on an optical fiber included in the bidirectional link interconnecting the at least one node and another node, a spare transponder connected to receive, for a failure of an ordinary transponder of the at least one node, the first optical signals, which are to be received by the ordinary transponder, and to convert the received first optical signals to issued third optical signals of a well defined wavelength band separate from the wavelength bands of the second optical signals issued by the ordinary transponders in the at least one node, the spare transponder connected to the first optical multiplexer or combiner of the at least one node to provide the third optical signals to the first optical multiplexer or combiner which combines the third optical signals issued by the spare transponder of the at least one node with the second optical signals issued by the ordinary transponders of the at least one node to issue a combined optical signal on the optical fiber, and wherein said at least one of the nodes further comprises first optical switches, each first optical switch having an input and a first output and a second output, the input of the first optical switch connected to one of the ordinary optical transmitters of the at least one node and the first output connected to that ordinary transponder which is connected to receive the first optical signals issued by said one of the ordinary optical transmitters of the at least one node to forward optical signals received on the input of the first optical switch to that ordinary transponder, and the second output connected to the spare transponder to forward optical signals received on the input of the first optical switch to the spare transponder, depending on a position of the first optical switch.