Hillerkuss, D.; Schmogrow, R.; Koos, C.; Freude, W.; Leuthold, J. (Karlsruhe Institute of Technology (KIT), Institute of Photonics and Quantum Electronics (IPQ), and Institute of Microstructure Technology (IMT), Karlsruhe, Germany)
Spectral efficiency (SE) has become a key figure of merit in optical communication systems as a large SE allows an increase in data capacity on existing optical fiber links. Nyquist pulse shaping in coherent optical communications significantly enhances the SE. When using sinc-shaped Nyquist pulses, the bandwidth of the signal is limited to the Nyquist bandwidth, which is desirable in wavelength division multiplexed (WDM) systems. In this paper, we answer the three key questions when investigating communication systems with sinc-shaped Nyquist pulses: Can modern real-time digital signal processing perform Nyquist pulse shaping at the necessary speed? Does Nyquist pulse shaping offer potential for highest spectral efficiencies? And, does it work in a Nyquist WDM system? – The answer to all three questions is: Yes! Three experiments have been performed to support this claim: First, we demonstrate real-time generation of a 150 Gbit/s dual polarization 64QAM Signal. Second, we demonstrate 54 Gbit/s within an optical bandwidth of 3 GHz, which corresponds to a raw spectral efficiency of 18 bit/s/Hz, and last we show a 32.5 Tbit/s single laser Nyquist WDM transmission experiment with 325 optical carriers.