5×240 Gb/s WDM Direct Detection Transmission over 80 km with a Spectral Efficiency of 5.25 bits/s/Hz

With the exponential growth of the data traffic, dense wavelength-division-multiplexing (DWDM) is required for future data center interconnect (DCI) applications with increasing demand for spectral efficiency (SE). In this paper, we experimentally demonstrate a single-polarization WDM direct detection (DD) transmission over 80 km with a record SE of 5.25 bits/s/Hz. This has been achieved by transmitting 5 single-side-band (SSB) channels, which were modulated with 256 QAM format at 30 Gbaud, on 35-GHz grid in the C-band. At the receiver, each channel was detected using only one photodiode (PD) and effective digital signal processing algorithms were applied to remove the signal-signal beat interference (SSBI) resulting from the PD