4:1 Silicon Photonic Serializer for Data Center Interconnects Demonstrating 104 Gbaud OOK and PAM4 Transmission

With next-generation optical interconnects for data centers aiming for 0.8 Tb/s or 1.6 Tb/s, 100 Gbaud capable transmitters from a single-laser source will become indispensable. However, these lane rates would require bandwidths of 70 GHz or more, doubling the bandwidth requirements of the electrical and optical components with respect to the fastest current generation of optical interconnects running at 53 Gbaud pulse-amplitude modulation (PAM-4). In this paper, we propose an integrated 4:1 optical serializer topology to achieve 104 Gbaud On-Off Keying (OOK) and PAM-4 transmission using only quarter rate components at the transmitter. We show 104 (208) Gbit/s OOK (PAM4) transmission using four GeSi electro-absorption modulators (EAMs) over 1 km of single-mode fiber (SMF). For 104 Gbaud OOK, clearly open eyes are obtained, while for PAM-4 the performance is limited by the nonlinear E/O-transfer function of the EAM. However, adding pre-emphasis in the electrical driver or replacing the single EAM with our previously demonstrated optical DAC topology—consisting of two EAMs in parallel with a 90° phase difference between each—could substantially improve these results. Additionally, we discuss the possibility of a four channel transmitter (4 × 208 Gb/s) from a single mode locked laser, amounting to a 832 Gb/s rate based on the current demonstrator.