6.4 Tb/s (32×200 Gb/s) WDM direct-detection transmission with twin-SSB modulation and Kramers–Kronig receiver

We experimentally demonstrate 6.4 Tb/s wavelength division multiplexed (WDM) direct-detection transmission based on Nyquist twin-SSB modulation over 25 km SSMF with bit error rates (BERs) below the 20% hard-decision forward error correction (HD-FEC) threshold of 1.5 × 10−2. The two sidebands of each channel are separately detected using Kramers–Kronig receiver without MIMO equalization. We also carry out numerical simulations to evaluate the system robustness against I/Q amplitude imbalance, I/Q phase deviation and the extinction ratio of modulator, respectively. Furthermore, we show in simulation that the requirement of steep edge optical filter can be relaxed if multi-input–multi-output (MIMO) equalization between the two sidebands is used.