Beyond 400 Gb/s Direct Detection over 80km for Data Center Interconnect Applications

Due to the growing demand for cloud services with high availability, high connection speed and low latency, distributed data-centers have emerged as a key architecture for future optical networks. This architecture relies on power and cost-efficient solutions for 400 Gb/s client interfaces over distances up to 80 km which can be densely wavelength-division multiplexed (WDM) in the C-band. Recently, single side band (SSB) direct detection (DD) has been considered as an attractive transmission scheme for achieving data rates beyond 100 Gb/s per channel due to its capability of electronic dispersion compensation. However, as SSB DD schemes utilize only a single polarization for data transmission, achieving 400 Gb/s per channel requires a baudrate beyond 80 Gbaud, which might reduce the effectiveness of the commonly used signal-signal beat interference (SSBI) cancellation techniques such as iterative SSBI cancellation or Kramers-Kronig algorithm due to the imperfection of Tx drivers, modulator and Rx front-end. In this paper, through effective Tx calibration and Rx DSP, we have achieved for the first time a net data rate per channel above 400 Gb/s with a 64 QAM signal at 85 Gbaud using a single photodetector (PD) at the receiver. In addition, a WDM transmission consisting of 5 channels at 100 GHz spacing was successfully conducted. This result indicates that SSB DD is an effective transmission technique for high capacity data center interconnect (DCI) applications.