  We demonstrate 32.5 Tbit/s 16QAM Nyquist WDM transmission over a total length
of 227 km of SMF-28 without optical dispersion compensation. A number of 325
optical carriers are derived from a single laser and encoded with
dual-polarization 16QAM data using sinc-shaped Nyquist pulses. As we use no
guard bands, the carriers have a spacing of 12.5 GHz equal to the Nyquist
bandwidth of the data. We achieve a high net spectral efficiency of 6.4
bit/s/Hz using a software-defined transmitter which generates the electrical
modulator drive signals in real-time.
