METHOD AND APPARATUS FOR ADDING/DROPPING OPTICAL CHANNELS

A filter topography is possible that can reduce the overall cost of a single Optical Add-Drop Multiplexer (OADM) or a series of OADMs that are within a network. The key is to have one of the wavelengths of a WDM signal being input to a filtering apparatus empty. The filtering apparatus can then with a reduced cost filter the received WDM signal such that a channel at a wavelength adjacent to the empty wavelength is removed and a channel is inserted at the previously empty wavelength. In one implementation of this topology within an OADM, a single filter can be used to perform both filtering operations due to the empty wavelength ensuring no corruption of the removed channel at the adjacent wavelength. In another implementation, the filtering operations are performed by two separate filters that each have asymmetrically reduced tolerances. In either case in which there is a reduced number of filters or reduced tolerances for those filters, a reduction in cost will be found.