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 preemphasis 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. Manuscript received November 3, 2018; revised December 27, 2018 and January 29, 2019; accepted January 30, 2019. Date of publication February 4, 2019; date of current version March 27, 2019. This work was supported in part by SPOC (DNRF123). (Jochem Verbist and Michael Vanhoecke contributed equally to this work.) (Corresponding author: Michael Vanhoecke.) J. Verbist is with the IDLab and Photonics Research Group, Department of Information Technology, Ghent University—IMEC, Ghent 9052, Belgium, and also with BiFAST, Ghent 9000, Belgium (e-mail:,jochem.verbist@ugent.be). M. Vanhoecke, X. Yin, and J. Bauwelinck are with the IDLab, Department of Information Technology, Ghent University—IMEC, Ghent 9052, Belgium (e-mail:,michael.vanhoecke@ugent.be; xin.yin@ugent.be; johan.bauwelinck@ ugent.be). M. Lillieholm, M. Galili, and L. K. Oxenløwe are with the DTU Fotonik, Technical University of Denmark, Kongens Lyngby DK-2800, Denmark (e-mail:,madsl@fotonik.dtu.dk; mgal@fotonik.dtu.dk; lkox@fotonik.dtu.dk). S. A. Srinivasan, P. De Heyn, and J. Van Campenhout are with the IMEC, Leuven 3001, Belgium (e-mail:, ashwyn.srinivasan@imec.be; Peter.DeHeyn@ imec.be; joris.vancampenhout@imec.be). G. Roelkens is with the Photonics Research Group, Department of Information Technology, Ghent University—IMEC, Ghent 9052, Belgium (e-mail:, gunther.roelkens@ugent.be). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JLT.2019.2897401