7 $,\times,$ 224 Gb/s/ch Nyquist-WDM Transmission Over 1600-km SMF-28 Using PDM-CSRZ-QPSK Modulation

We have transmitted a 7×224 Gb/s/ch Nyquist wavelength-division-multiplexed signal over a 1600-km conventional single-mode fiber (SMF-28) with 80 km per span and an erbium-doped fiber amplifier-only amplification. Each channel on the 50-GHz grid is modulated using polarization-division-multiplexed quadrature-phase-shift-keying at 56 Gbaud giving a record spectral efficiency of 4 b/s/Hz. Both the post filter and the Viterbi maximum likelihood sequence detection are introduced into digital signal processing, to suppress the undesired noise, linear crosstalk enhancement, and filtering effects. The bit error ratio of all channels after transmission over a 1600-km SMF-28 is smaller than the forward error correction limit of 3.8×10^-3.