6 $,\times,$ 128-Gb/s Nyquist-WDM PDM-16QAM Generation and Transmission Over 1200-km SMF-28 With SE of 7.47 b/s/Hz

The Nyquist wavelength-division multiplexing technique enable a solution to achieve high spectral efficiency in long-haul transmission system. Compare to polarization division multiplexing quadrature-phase-shift-keying, even high-level modulation scheme such as polarization division multiplexing 16-quadrature-amplitude-modulation is much more sensitive to intra-channel noise and inter-channel linear crosstalk caused by Nyquist wavelength-division multiplexing. We experimentally demonstrated the generation and transmission of the 6 × 128-Gb/s Nyquist wavelength-division multiplexing sixteen quadrature amplitude modulation signal over 1200-km single-mode fiber (SMF)-28 with Erbium-doped fiber amplifier only amplification with a net SE of 7.47 b/s/Hz, which is so far, to our knowledge, the highest SE for the signal with the bit rate above 100-Gb/s using the polarization-division multiplexing 16-quadrature-amplitude-modulation format. This experiment was successfully enabled by digital-signal-processing (DSP) pre-equalization of transmitter-side impairments and DSP post-equalization of the channel and receiver-side impairments. Nyquist-band is considered in the pre- equalization to enhance the tolerance of the polarization-division multiplexing 16-quadrature-amplitude-modulation to the aggressive spectral shaping. The bit error rate for each of the 6 channels is smaller than the limitation of the forward-error-correction limit of 3.8 ×10^-3 after 1200-km SMF-28 transmission.