Reduction of coherent crosstalk in WDM add/drop multiplexing nodes by bit pattern misalignment

Coherent crosstalk in wavelength-division-multiplexed (WDM) add/drop multip lexers and switches places severe limitations on the acceptable crosstalk s uppression level. We propose and analyze a method of reducing the effects o f coherent crosstalk in add-drop multiplexers by purposely introducing fibe r delays on the order of bit times between different crosstalk paths. These delays decorrelate the bit pattern of the main signal with the interfering signals and place some of the crosstalk power in the "0" hits Of the main signal instead of the "1" bits. For a 16-channel WDM system, this method re duces the device requirement for crosstalk suppression by similar to 10 dB for return-to-zero and similar to 5 dB fur nonreturn-to-zero transmission.