Patent ID: 6697188
Filing Date: 2004-02-24
Classification: H04B,H04J

Abstract:
An add/drop multiplexer for a wavelength division multiplexed (WDM) optical communication system, comprising:a) dropping means for selectively diverting at least part of one or more radiation components present in WDM optical radiation received from the system; b) a radiation control unit for selectively controlling transmission of the radiation components of the WDM radiation; and c) adding means for adding additional radiation components to the radiation components output from the control unit, the radiation control unit being operable to selectively block the radiation components whose wavelengths are coincident with those of the additional radiation components added by the adding means, d) said radiation control unit including i) filtering means for partitioning the WDM radiation received into one or more radiation components corresponding to WDM communication channels of the system, ii) liquid crystal attenuating means for selectively transmitting or attenuating said one or more radiation components, iii) combining means for combining the one or more of the radiation components transmitted through the attenuating means to provide combined radiation, iv) monitoring means for measuring power present in said one or more of the radiation components included in the combined radiation and generating one or more corresponding radiation component power indicative signals, and v) controlling means for receiving said one or more power indicative signals from the monitoring means and selectively controlling attenuation provided by the attenuating means so that the radiation components included in the combined radiation have the same power to within a pre-selected error margin.