WDM transport towards Terabits/s line rates - what will be gained?

Since per-channel data rates of 100 Gb/s have become available in commercial optical transport systems, research efforts are now targeted at the next step in high-speed channel rates, which likely will be in the 400 Gb/s and/or 1 Tb/s range. In this presentation, we investigate various optical transmission schemes and modulation formats which will enable this step while maintaining moderate requirements on electrical and optical component technology. Based on optical noise tolerance criteria and taking into account optical power limitations as well as non-linear fiber effects to a certain extent, multiple subcarriers modulated with dual-polarization quaternary phase-shift keying (DP-QPSK) will give a capacity-times-reach product comparable to 100-Gb/s channel rates. This is true for both 400 Gb/s and 1 Tb/s channel rates. However, the use of more advanced modulation formats, like polarization-switched (PS-) QPSK can improve this measure by 50%. For shorter reach applications like metro networks or data center connectivity, higher-order modulation formats can improve the spectral efficiency of the signals. These different applications are investigated, and technologies are proposed to achieve the next steps in high data-rate optical transmission.