Nonlinear Transmission Performance of Higher-Order Modulation Formats

We investigate the dependence of nonlinear penalties on symbol-rate in wavelength-division-multiplex (WDM)-transmission systems while maintaining a fixed spectral efficiency for several polarization-division-multiplexed (PDM) modulation formats. Transmission performance is found to be improved by up to 1.6 dB for lower symbol rates over the range 3.5-56 GBd for the case of WDM transmission.