links. We test the accuracy of our model in the context of ultradense wavelength-division-
multiplexing polarization-multiplexed quadrature phase-shift keying (PM-QPSK) systems, at
the Nyquist spectral efficiency limit. We show that the predicted system performance
matches simulation results very accurately over a broad range of system scenarios. A simple
closed-form analytical formula provides an effective tool for the quick and accurate …