Investigation on WDM Nonlinear Impairments Arising From the Insertion of 100-Gb/s Coherent PDM-QPSK Over Legacy Optical Networks

In the perspective of smooth capacity upgrades of legacy systems, we experimentally investigate the performance of one 100-Gb/s coherent polarization-division-multiplexed quaternary-phase-shift-keying (PDM-QPSK) channel inserted in a 10-Gb/s ultra-long-haul (ULH) wavelength-division-multiplexing system relying on nonzero dispersion-shifted fibers. The impact of copropagating 10-Gb/s nonreturn-to-zero (NRZ) channels operating ULH distances onto the operational power range of the inserted 100-Gb/s coherent PDM-QPSK channel is analyzed. Moreover, the performance penalties brought by copropagating 10-Gb/s NRZ channels onto 100-Gb/s PDM-QPSK data are also analyzed depending on the number of channels in the multiplex and on the introduction of guardbands between both type of channels.