A wavelength division multiplexed, hereinafter referred to as WDM, optical system comprising: at least one trunk terminal configured to provide a WDM trunk input signal on a trunk path, said WDM trunk input signal occupying a plurality of trunk channels including at least one drop channel; at least one branch terminal (150,160) configured to provide a WDM branch input signal on a branch add path, said WDM branch input signal occupying a plurality of branch channels including at least one add channel, at least one of said branch channels being an unutilized channel loaded with a loading signal; at least one branching unit coupled to said trunk path and said branch add path for receiving said trunk input signal and said branch input signal and providing a trunk output signal on said trunk path and a branch output signal on a branch drop path, wherein said branching unit comprises means adapted to drop said at least one drop channel and add said at least one add channel to and from corresponding ones of said branch channels on said branch drop path and said branch add path respectively, said corresponding ones of said trunk channels and said branch channels having corresponding wavelengths, and wherein said branching unit comprises means adapted to remove said loading signal from said unutilized channel on said branch add path and to couple said loading signal on a corresponding unutilized channel on said branch drop path with said at least one drop channel to produce said WDM branch output signal, said corresponding unutilized channels having corresponding wavelengths; the system characterized by a variable optical attenuator, hereinafter referred to as VOA, configured to selectively adjust said at least one drop channel in response to a command signal before said branching unit couples said loading signal on said branch drop path with said at least one drop channel. at least one trunk terminal configured to provide a WDM trunk input signal on a trunk path, said WDM trunk input signal occupying a plurality of trunk channels including at least one drop channel; at least one branch terminal (150,160) configured to provide a WDM branch input signal on a branch add path, said WDM branch input signal occupying a plurality of branch channels including at least one add channel, at least one of said branch channels being an unutilized channel loaded with a loading signal; at least one branching unit coupled to said trunk path and said branch add path for receiving said trunk input signal and said branch input signal and providing a trunk output signal on said trunk path and a branch output signal on a branch drop path, wherein said branching unit comprises means adapted to drop said at least one drop channel and add said at least one add channel to and from corresponding ones of said branch channels on said branch drop path and said branch add path respectively, said corresponding ones of said trunk channels and said branch channels having corresponding wavelengths, and wherein said branching unit comprises means adapted to remove said loading signal from said unutilized channel on said branch add path and to couple said loading signal on a corresponding unutilized channel on said branch drop path with said at least one drop channel to produce said WDM branch output signal, said corresponding unutilized channels having corresponding wavelengths; the system characterized by a variable optical attenuator, hereinafter referred to as VOA, configured to selectively adjust said at least one drop channel in response to a command signal before said branching unit couples said loading signal on said branch drop path with said at least one drop channel.