Nonlinear interference noise in 100-Gbit s^-1communication lines with the DP-QPSK modulation format

Abstract

The nonlinear interference noise power was measured experimentally as a function of the signal power and the length of the fibre coherent communication line, in which chromatic dispersion is not optically compensated. An expression was derived for the optimal signal power corresponding to a maximal excess of the measured optical signal-to-noise ratio (OSNR) over the OSNR required for conditionally error-free operation. The dependence of signal optimal power measured experimentally well agrees with the theoretical formula derived.