Terabit Faster-Than-Nyquist PDM 16-QAM WDM Transmission With a Net Spectral Efficiency of 7.96 b/s/Hz

In this paper, we experimentally demonstrate a 1.28 Tb/s faster-than-Nyquist (FTN) wavelength division multiplexing (WDM) system with polarization division multiplexed (PDM) 16-ary quadrature amplitude modulation (16-QAM) signal and coherent detection. Note that intersymbol interference (ISI) and intercarrier interference (ICI) are two major problems in FTN-WDM systems. In our experiment, we use a digital brick-wall filter at the transmitter to reduce the signal bandwidth and fit the FTN-WDM channel spacing. In doing so, the ICI can be mostly suppressed when aggregating the WDM channels. The aggressive filtering induced ISI is compensated based on duobinary signal processing at the receiver. Through numerical simulation, we evaluate the robustness of the receiver-side duobinary signal processing against bandwidth truncation ratio of the digital brick-wall filter, the ICI from neighboring channels, and laser phase noise. The FTN WDM transmission is based on five-channel 32 Gbaud PDM 16-QAM signal with 29 GHz channel spacing. The gross data capacity is 1.28 Tb/s (5 × 256 Gb/s). After 80 km standard single-mode fiber transmission, the bit-error rates of the five WDM channels are all below than 7% hard-decision forward error correction threshold of 4.5 × 10
^-3
. The net bit rate is 1.15 Tb/s and the net optical spectral efficiency achieves a record of 7.96 b/s/Hz for PDM 16-QAM format. To our best knowledge, our work is the first report of Terabit FTN-WDM system with high-order modulation of PDM 16-QAM signal.