Chromatic dispersion calculation - Coherent optics

Hello everyone , In this article lets take a check on how do we calculate the chromatic dispersion in case where coherent optics is involved :-

D = (C * D * Baud rate^2 * L) / (2 * pi * S* lambda^2) where C is typically considered as 1 for SSMF (G.652) due to the single mode it can have ,

• D: Dispersion coefficient of the fiber (in ps/nm-km) which is typically 17ps/nm-km
• Baud rate: Baud rate of the signal (in symbols per second or bauds)
• L: Length of the fiber (in km)
• S: Spectral width of the signal (in Hz) which can be 50GHZ in case of fixed and can very in flex grid
• lambda: Operating Wavelength of the signal (in nm)

This equation calculates the chromatic dispersion caused by the wavelength-dependent variations in the refractive index of the fiber material.

Please note that Spectral width of QAM signal will be wider than that of a QPSK signal . As a result, the chromatic dispersion of the 8QAM signal will be higher than that of the QPSK signal