Design rule of wavelength filter bandwidth and pulsewidth for ultimate spectral efficiency limited by crosstalk in DWDM systems

The relationship between the spectral efficiency and the crosstalk caused by the wavelength filter in DWDM systems was investigated. The bit rate and the wavelength channel spacing were optimally designed to minimize both the interchannel crosstalk and the intersymbol interference. We showed that the coherent crosstalk occurs at the frequency of about half of the channel spacing and it strongly deteriorates the total crosstalk.