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Abstract

A Raman module comprises a detecting unit for measuring the output power of a WDM signal traveling along a fiber section, and a spectral gain estimating unit for determining an estimated vector gain Gain.sub.meas based on the output power alone. The Raman pump signal is controlled with a gain Gain.sub.RA evaluated based on the estimated gain Gain.sub.meas so that all channels have a similar gain. The spectral gain estimating unit comprises a fiber gain model and an input signal adjust unit. The model receives the output power, assumes a predicted input power for each channel and provides a corresponding estimated output power for each channel. The input signal adjust unit adjusts the predicted input power based on an error signal provided by the model. The gain is then calculated from the predicted input powers and the estimated output powers. The detecting unit demultiplexes a fraction of the WDM signal into n sub-band and detects sub-band optical power P.sub.B1, . . . P.sub.Bn. Any change in the spectrum of the WDM signal is detected as a power decrease or increase by the detectors, and the model re-distributes the power variation over the predicted launch spectrum accordingly. For n>1, power re-distribution affects only the sub-band(s) with the added/dropped/failed channel(s).

First Claim