8 Tb/s long haul transmission over low dispersion fibers using 100 Gb/s PDM-QPSK channels paired with coherent detection

100 Gb/s end-to-end broadband optical solutions are attractive to cope with the increasing demand for capacity. Polarization-division-multiplexed (PDM) quaternary-phase-shift-keying (QPSK) paired with coherent detection has been found to be promising for upgrading optical legacy systems based on 50 GHz wavelength slots thanks to its high spectral efficiency (2 bit/s/Hz) and its tolerance to linear effects. One of the major concerns for the deployment of such a solution is the transmission reach, mainly limited by nonlinear effects. This limitation can be exacerbated over non-zero dispersion shifted fiber (NZDSF) due to low local chromatic dispersion of the transmission fiber. The aim of this paper is first to report on the benefits brought by combining coherent detection techniques with advanced modulation formats as compared to conventional direct detection schemes for optical fiber communications. Digital signal processing paired with coherent detection is described to point out the efficiency of a coherent receiver to combat noise and to mitigate linear impairments. We then report on nonlinear tolerance of 100 Gb/s coherent PDM-QPSK through an 8 Tb/s transmission over a dispersion-managed link based on low dispersion fibers.

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