Symbol-Rate Dependence of Dominant Nonlinearity and Reach in Coherent WDM Links

We provide simulations of the nonlinear threshold (NLT) versus per-channel symbol rate at a constant bandwidth efficiency for a 15-channel wavelength-division multiplexing long-haul coherent optical transmission over a 20 × 100 km single-mode fiber link, both dispersion-managed (DM) and dispersion-uncompensated (DU), with several popular polarization multiplexed modulation formats. We exploit the nonlinearity-decoupling method to estimate the NLT due to each individual nonlinear effect, and, thus, show how the dominant nonlinearity changes with symbol rate. Plots of the NLT normalized to the symbol rate also reveal the symbol rate achieving the longest distance. Assuming a signal-independent Gaussian nonlinear interference, we derive a new formula yielding the system reach based on knowledge of NLT measurements on a much shorter link. We finally provide reach simulations to verify the accuracy of the new reach formula for both DM and DU links.