Flexible IM/DD Beyond Bandwidth Limitation for Data Center Optical Interconnects
22 July 2019
The legacy intensity-modulation with direct-detection (IM/DD) provides a low-cost solution for the 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. Applying THP, the signal is precoded by a feedback filter at the transmitter for the mitigation of the inter-symbol interference (ISI) caused by the faster-than-Nyquist (FTN) signaling and the spectral power fading induced by the interaction of the chromatic dispersion (CD) and the direct detection. In this paper, THP based IM/DD transmission is demonstrated, delivering 185 Gb/s over 2 km and 155 Gb/s over 4 km with 33 GHz brick-wall electrical bandwidth limitation. In addition, due to a flexible trade-off between symbol rate and number of amplitude levels, the investigated system can achieve various BERs that are not achievable with conventional multilevel pulse amplitude modulation (PAM) formats under Nyquist condition, allowing a fine-grained adjustment of data rate according to the target performance.
