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

Coherent crosstalk in wavelength-division-multiplexed (WDM) add/drop multiplexers and switches places severe limitations on the acceptable crosstalk suppression level. We propose and analyze a method of reducing the effects of coherent crosstalk in add-drop multiplexers by purposely introducing fiber 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" bits of the main signal instead of the "1" bits. For a 16-channel WDM system, this method reduces the device requirement for crosstalk suppression by /spl sim/10 dB for return-to-zero and /spl sim/5 dB for nonreturn-to-zero transmission.