Patent ID: 7174097

Claim:
A method of transmitting a plurality of signals having different wavelengths through a length of signal transmission cable which exhibits a Raman effect of transferring energy to longer-wavelength signals from shorter-wavelength signals as the signals travel through the length of signal transmission cable, comprising the steps of: a) providing a plurality of pump signals having wavelengths for providing energy for transfer to the plurality of signals traveling through the length of signal transmission cable; b) providing a selected-wavelength probe signal at a wavelength different from the wavelengths of the plurality of pump signals, the wavelength of the probe signal constituting a wavelength of a supervisory channel; c) transmitting the probe signal at the wavelength of the supervisory channel and the plurality of pump signals, one at a time, in turn, through the length of transmission cable; d) determining changes in power level of the probe signal resulting from the pump signals; e) setting power levels of the pump signals to provide a selected gain profile for the plurality of signals having different wavelengths, the power levels of the pump signals being determined in dependence on the changes in power level of the probe signal and in relation to differences in wavelengths among the probe signal, the pump signals and the plurality of signals having different wavelengths; and f) continuing to transmit the pump signals at a ratio of set power levels along with the plurality of signals having different wavelengths through the length of signal transmission cable.