Patent ID: 8396361

Claim:
Method for protecting a passive optical transmission network comprising an optical line terminal ( 5 ) that is connected to at least one remote node ( 15 ) to which a plurality of network termination nodes ( 3 ) are linked, (a) wherein bidirectional optical signal transmission can be established between each network termination node ( 3 ) and the optical line terminal ( 5 ), and (b) wherein the connection between the optical line terminal ( 5 ) and the one or more remote nodes ( 15 ) is realized by means of a first bidirectional optical transmission route by which means an optical wavelength-multiplexed signal is transmitted in the downstream direction from the optical line terminal ( 5 ) to the one or more remote nodes ( 15 ) and in the upstream direction from the one or more remote nodes ( 15 ) to the optical line terminal ( 5 ), characterized in that (c) a second bidirectional optical transmission route is provided between the optical line terminal ( 5 ) and the one or more remote nodes ( 15 ), (d) in the one or more remote nodes ( 15 ), the wavelength-multiplexed signal is fed in the upstream direction by means of a passive optical splitter unit ( 17 , 170 ) both to the first optical transmission route and to the second optical transmission route, (e) in the optical line terminal ( 5 ), in the case of the detection of a fault state that suggests a negative influence on the first or second optical transmission route, it is switched over to the other corresponding optical transmission route by means of an optical switch unit ( 23 ) for transmitting the wavelength-multiplexed signal in the downstream direction and/or for receiving the wavelength-multiplexed signal in the upstream direction, and (f) in the at least one remote node ( 15 ), the wavelength-multiplexed signal which is fed to the at least one remote node in the downstream direction either through the first or the second transmission route is output by means of the passive optical splitter unit ( 17 ) at an output port of the passive optical splitter unit or by means of an additional passive optical splitter unit ( 172 ) at an output of the additional passive optical splitter unit for a subsequent demultiplexing process.