In a Wavelength Division Multiplexed (WDM) all-optical network having optical nodes linked together by optical fibers carrying communication channels of separate wave-lengths, a method is applied in order to extend the size of the all-optical network. According to the method, a model is set up for the all-optical network in which a wavelength graph containing vertices and edges represents the physical effects of the nodes and links. After identifying a set of demand, an objective function is calculated expressing the total routing cost and total signal power demand of the channels. The minimum of the objective function returns the signal powers for each channel to be tuned.