Gain control in wavelength switched optical networks

A Raman module for amplifying a WDM signal with a dynamic spectrum traveling along a fiber span, comprising:

• a detecting unit for separating a fraction of said WDM signal, separating same into n sub-bands and providing a sub-band performance parameter for each said sub-band;
• a spectral gain estimating unit for determining an estimated vector gain Gainmeas based on said n sub-band performance parameters;
• and
• a Raman pump unit controlled with a gain GainRA evaluated based on said estimated vector gain Gainmeas for generating a pump signal and lunching same over said fiber span.

A method of determining the spectrum of a WDM signal with a dynamic spectrum, comprising:

• measuring n sub-band powers of said WDM signal at the output of a Raman module;
• determining the number of channels in each said sub-band;
• assuming a spectral distribution for said WDM signal, estimating an output power for each channel using a fiber gain model and calculating an estimated sub-band power for each said sub-band;
• comparing said measured sub-band powers with said estimated sub-band powers to obtain an error signal;
• and
• adjusting said spectral distribution to minimize said error signal.

A method for controlling the gain of an optical WDM signal with a dynamic spectrum, said WDM signal traveling along a fiber link between two switching nodes of an agile network, comprising:

• breaking said fiber link into gain controlled sections, and providing an optical amplifier at the egress side of each said section;
• providing a spectral gain estimating unit at each said optical amplifier for determining the actual spectral gain for each section;
• controlling a Raman pump at each said optical amplifier to adjust said actual spectral gain to a target gain,
• wherein said target gain is substantially equal for all said sections of said fiber link.