Effect of Linear Crosstalk of WDM Filters on Multilevel Modulation

The effect of the crosstalk of wavelength-division-multiplexing (WDM) optical filters on the performance of WDM transmission systems that use multilevel modulation formats are examined and it is found that the currently common specification of -30 dBm is not adequate when more than eight signal levels are used. Also, the systems using coherent detectors and those using direct detection receivers are compared