Patent ID: 7016610

Claim:
A method for dropping a drop channel from a wavelength division multiplexed (WDM) signal including one or more express WDM channels of equal power using a beam separator and controlling the power of an add channel of an optical add-drop multiplexer (OADM) used to add the add channel to the WDM signal, the method comprising: comparing the power P add of the add channel with the power P drop of the drop channel; and attenuating the power P add to match the attenuated power P express of the express WDM channels, according to the equation P express =P add −L +10 log(1 −y %)− L 4 where L is an attenuation introduced to P add and controlled by a variable optical attenuator, L 4 is an insertion loss introduced to P add by a beam combiner when the add channel is added to the WDM signal by the beam combiner, y % is a preset portion of P add tapped by a first tap, and P express is determined by P express =P inp −L 2 −L 3 , where P inp is the power of each express WDM channel prior to entrance to the OADM, and L 2 and L 3 are the insertion losses introduced to each express WDM channel when each express WDM channel passes through the beam separator and the beam combiner, respectively.