A method for establishing an embedded optical communication channel in an optical WDM transmission system, the optical WDM transmission system (1, 100) comprising a plurality of first channel transceivers at a first end of a bidirectional optical WDM transmission path, a plurality of second channel transceivers at a second end of the optical WDM transmission path and a central network device connected to the optical WDM transmission path, each first channel transceiver being configured to create and transmit a first optical channel signal (DS Chi), in a respective downstream channel, to the second end of the optical WDM transmission path and to receive a second optical channel signal (US Chi) created by a second channel transceiver and each second channel transceiver being configured to create and transmit a second optical channel signal (US Chi), in a respective upstream channel, to the first end of the optical WDM transmission path and to receive a first optical channel signal (DS Chi) created by a first channel transceiver, the method being characterized by the steps of: (a) creating, at the central network device, a broadband optical signal (S BR) having an optical spectrum which covers at least a group of neighboring or all optical upstream channels (US Chi) of the optical WDM transmission system (1, 100), the optical power of the broadband optical signal (S BR) being modulated according to a low-frequency modulation signal in such a way that there is no or no unacceptable spectral overlap of the low-frequency spectrum of the low-frequency modulation signal and any of the modulation spectra of the second optical channel signals (US Chi); (b) supplying the broadband optical signal (S BR), at a predefined position between the first and second end, to the optical WDM transmission path in the direction of the first end thereof; (c) transmitting the broadband optical signal (S BR) and the plurality of second optical channel signals (US CHi), if any, to an optical demultiplexer device, which is connected to the first end of the optical WDM transmission path and which optically filters and spatially separates the incoming optical signals according to optical channel bandwidths predefined for the optical WDM transmission system (1, 100); (d) transmitting, from the demultiplexer device to each of the plurality of channel transceivers, an optical signal consisting of a dedicated second optical channel signal, if any, and a filtered broadband optical signal; (e) receiving, at each first channel transceiver, the optical signal and creating a corresponding electrical receive signal comprising a second electrical channel signal corresponding to the dedicated second optical channel signal (US Chi) and an electrical signal corresponding to the filtered broadband optical signal (S BR); and (f) extracting, at each first channel transceiver, the electrical signal corresponding to the filtered broadband optical signal (S BR) from the electrical receive signal and detecting whether the electrical signal contains information intended for the respective first channel transceiver. (a) creating, at the central network device, a broadband optical signal (S BR) having an optical spectrum which covers at least a group of neighboring or all optical upstream channels (US Chi) of the optical WDM transmission system (1, 100), the optical power of the broadband optical signal (S BR) being modulated according to a low-frequency modulation signal in such a way that there is no or no unacceptable spectral overlap of the low-frequency spectrum of the low-frequency modulation signal and any of the modulation spectra of the second optical channel signals (US Chi); (b) supplying the broadband optical signal (S BR), at a predefined position between the first and second end, to the optical WDM transmission path in the direction of the first end thereof; (c) transmitting the broadband optical signal (S BR) and the plurality of second optical channel signals (US CHi), if any, to an optical demultiplexer device, which is connected to the first end of the optical WDM transmission path and which optically filters and spatially separates the incoming optical signals according to optical channel bandwidths predefined for the optical WDM transmission system (1, 100); (d) transmitting, from the demultiplexer device to each of the plurality of channel transceivers, an optical signal consisting of a dedicated second optical channel signal, if any, and a filtered broadband optical signal; (e) receiving, at each first channel transceiver, the optical signal and creating a corresponding electrical receive signal comprising a second electrical channel signal corresponding to the dedicated second optical channel signal (US Chi) and an electrical signal corresponding to the filtered broadband optical signal (S BR); and (f) extracting, at each first channel transceiver, the electrical signal corresponding to the filtered broadband optical signal (S BR) from the electrical receive signal and detecting whether the electrical signal contains information intended for the respective first channel transceiver.