Using Eqns. (9)–(11), we computed the theoretical margin for the six cases of our experiments (SMF, MDF, or LAF with 32 or 28 GBaud channels). These computations appear as the solid lines in the margin plots; see Fig. 5. We observe excellent adherence of our data to the theoretical predictions. We also note that the margin calculations contain no free “fitting” parameters—the link characteristics were simply used within Eqns. (3)–(5). As expected, the margin curves exhibit a 1 dB/dB linear slope for low launch powers. As the launch power increases the nonlinear noise increases and the margin peaks, and then, decreases.