Patent ID: 8768165

Claim:
A method for Raman gain spectrum measurement of an optical WDM (wavelength division multiplex) signal implying a plurality of channels transmitted via an optical fiber, the method which comprises: at a transmitter side, generating an optical supervisory signal (OSS_TX); transmitting the supervisory signal (OSS_TX) together with the WDM signal via the optical fiber; determining a transmitter power level value (P CFLAT — TX /P TXT ) of a transmitted WDM signal (WMS_TX) and a transmitter power level value (P OSS — TX ) of the transmitted optical supervisory signal (OSS_TX); transmitting the transmitter power level values (P CFLAT — TX /P TXT ; P OSS — TX ); at a receiver side, measuring a receiver power level value (P RXT ) of a received WDM signal (WMS_RX) and a receiver power level value (P OSS — RX ) of a received supervisory signal (OSS_RX); characterized by the steps of: calculating a Raman amplification factor (κ) from transmitter power level values (P OSS — TX , P TXT ) and receiver power level values (P OSS — RX , P RXT ) based on wavelength dependent Raman gain coefficients g R (λ−λ RAP ) for each of said channels of said WDM signal and a wavelength dependent Raman gain coefficient g R (λ OSS −λ RAP ) of said supervisory signal, and calculating Raman gain values (G RAMAN (λ)) of the WDM channels (λ) based on said Raman amplification factor (κ) and said wavelength dependent Raman gain coefficient g R (λ−λ RAP ) of said channels, said wavelength dependent Raman gain coefficient g R (λ−λ RAP ) being a function of the difference between a channel wavelength λ and a Raman pump wavelength λ RAP .