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 ∼10 dB for return-to-zero and ∼5 dB for nonreturn-to-zero transmission.
- Add/drop multiplexer
- Coherent crosstalk
- Optical interference
- Wavelength division multiplexing