An optical transmission system comprising a first optical waveguide suitable for transmitting a first information signal, a second optical waveguide suitable for transmitting a second information signal, and input means for providing an electro magnetic radiation signal into said first waveguide, said signal being suitable for providing Raman amplification of the information signals, the system further comprising an optical coupling between said waveguides, arranged to transmit at least a portion of the Raman amplification signal from the first waveguide to the second whilst substantially blocking the transmission of the information signals between the waveguides.