The optical add/drop multiplexer (OADM) is an important device in modern optical networks. Optical filters in OADMs often introduce group-velocity dispersion (GVD) and/or slope of GVD, the accumulation of which could distort the signals significantly. A computer model is built for commercial filters, accounting for the filtering gain and dispersion characteristics. When the model is incorporated into a network simulator, the filter dispersion is found to severely limit the number of OADMs that

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... ay be cascaded when transmitting 40Gb/s WDM signals with a channel spacing of 100GHz. As such high spectral efficiency difficult to achieve, the next considerations would be to transmit 40Gb/s over 200GHz channel spacing, or 10Gb/s over 50GHz channel spacing. The dispersion problem is mitigated, but still an un-negligible factor of limitation. For a large OADM network size, low-dispersion filters should be used, or a proper dispersion compensator is needed to offset the filter dispersion.