IM/DD Beyond Bandwidth Limitation for Data Center Optical Interconnects

Intensity modulation with direct detection (IM/DD) provides a low-cost solution for data center optical interconnects. To achieve higher data rate, Tomlinson–Harashima precoding (THP) is adopted to increase the operating symbol rate beyond the Nyquist rate defined by the system bandwidth. By applying THP, the signal is precoded by a feedback filter at the transmitter for the mitigation of the intersymbol interference caused by the faster-than-Nyquist signaling and the spectral power fading induced by the interaction of chromatic dispersion and direct detection. In this paper, high-performance THP-based IM/DD transmission is demonstrated, increasing the achievable data rate using a limited system bandwidth. In the experimental demonstration, we achieve a net bit rate of 185 Gb/s for up to 2-km fiber link, transmitting 74 GBd precoded eight-level pulse amplitude modulation (PAM-8) using an IM/DD system with 33 GHz brick-wall electrical bandwidth limitation.