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Abstract

An add/drop multiplexer (ADM) 100 includes an optical demultiplexer 200 and an optical multiplexer 300 that are connected in series. The optical multiplexer and the optical demultiplexer each include a number of corresponding passbands, which means that the central wavelengths of the multiplexer's passbands are approximately equal to the central wavelengths of the demultiplexer's passbands. The performance of the ADM is improved by making the edges of corresponding passbands complementary to each other. In one illustrative design, the transmission of the demultiplexer decreases at its passband edges as the wavelength moves away from its central wavelength, whereas the transmission of the multiplexer increases as the wavelength moves away from its central wavelength. The resultant cascaded passband of the pair is wider than the passband of the demultiplexer alone, thereby increasing the number of ADMs in a chain for the same performance. Not surprisingly, the advantages of the present invention are most evident in a wavelength-division-multiplexed system having many geographically separated locations 71-74 interconnected by an optical transmission path, and where selected channels of information need to be inserted or removed from the optical transmission path.

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First Claim