Abstract: The crosstalk is an important limiting factor in optical wavelength division multiplexing (WDM) networks.The impact of coherent and incoherent crosstalk on an optical signal passing through a typical OADM architecture is studied.We give the analytical power penalty expressions for both fixed decision-threshold (FDT) and optimum decision-threshold(ODT).Through calculation,the coherent crosstalk is found to be the most important limitation in the OADM.Compared with FDT,ODT will tolerate more crosstalk contributions.On the other hand,the power penalty will be decreased when the number of dropping wavelength increases or the crosstalk value of DMUX decreases.The DMUX/MUX filters and ODT receiuer are used for less requirements of total crosstalk specification for components.The increase of the DMUX performance is the best way of suppressing crosstalk.

Key words: wavelength division multiplexing(WDM), optical add-drop multiplexer(OADM), coherent crosstalk, incoherent crosstalk, fixed decision-threshold(FDT), optimum decision-threshold(ODT).