Tu2I.2.pdf OFC 2019 © OSA 2019 104 Gbaud OOK and PAM-4 Transmission over 1km of SMF using a Silicon Photonics Transmitter with Quarter-Rate Electronics Jochem Verbist 1,2 , Mads Lillieholm 3 , Joris Van Kerrebrouck 1 , Srinivasan Ashwyn Srinivasan 4 , Peter De Heyn 4 , Joris Van Campenhout 4 , Michael Galili 3 , Leif K. Oxenløwe 3 , Xin Yin 1 , Johan Bauwelinck 1 , Gunther Roelkens 2 (1) IDLab, INTEC, Ghent University – imec, 9052 Ghent, Belgium (Jochem.Verbist@ugent.be) (2) Photonics Research Group, INTEC, Ghent University – imec, 9052 Ghent, Belgium (3) DTU Fotonik, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark (4) imec, 3001 Leuven, Belgium Abstract: We present a silicon photonics transmitter using four GeSi EAMs driven at 26 Gbaud with 1.2Vpp to realize the fastest reported single-wavelength PAM-4 transmission on silicon at 208 Gb/s over 1km of SMF. OCIS codes: (250.7360) Waveguide modulators, (250.5300) Photonic Integrated Circuits, (200.4650) Optical Interconnects 1. Introduction With the increasing bandwidth requirements for data center interconnects (DCI) the new generation DCIs will upgrade the existing 100 Gb/s links to 400 Gb/s, using either 8×26 Gbaud or 4×53 Gbaud PAM-4 depending on the fiber span as described by the IEEE 400GBASE standards. However, with these transceivers finding their way to the data center market in the coming years, research and discussion have started to shift towards the implementation of the next- generation transceivers at 800 Gb/s or even 1.6 Tb/s [1]. A 200 Gb/s/λ per lane scheme would provide an elegant upgrade towards these 0.8 TbE and 1.6 TbE interconnects, maintaining a low channel count. However, doubling the baudrate to 100 Gbaud would require a significant increase in the performance of the optical and electrical components, requiring bandwidths of 70 GHz or more. One possibility therefore is to abandon the intensity-modulated direct-detection (IMDD) links in favor of spectrally efficient coherent links. But data centers have been hesitant to make this shift, as these metro and long-haul devices still consume significantly more power than their comparable IMDD counterparts. Hence, it will be challenging to meet the extremely compact form factor requirements. Best in class coherent modules currently require ~20W for a 200 Gb/s PM-16-QAM link using a 4x10.7 cm CFP2-DCO transceiver module. The additional power consumption of the coherent DSP and the large form factor make IMDD links still the preferred solution for these next-generation intra-data center links. Recently, a transmitter capable of 204 Gb/s on-off keying (OOK) has been achieved using InP platforms for both the optics and electronics using offline DSP [2]. On silicon, the highest reported intensity modulated transmission with a single PD has been limited to 168 Gb/s PAM-4 using a large multi-electrode (>5 mm) traveling-wave Mach- Zehnder modulator (MZM) driven with 3.8 and 5 Vpp in combination with extensive TX-side DSP [3], making it less suited for DCI applications. Over the last two decades, optical serializers (used in optical time division multiplexing or OTDM schemes) have attracted much research as they can generate very high data rate optical transmissions with limited bandwidth (BW) electronics. However, the need for long integrated optical delays as well as the absence of a practical and low-cost Fig. 1: Operation principle of the optical serializer and modulator: a pulsed light source at 26 GHz with a 25% duty cycle (~9.6 ps pulse width) is split into four streams using three 1×2 MMIs. Each stream is modulated by a GeSi EAM driven with 26 Gbaud NRZ (or PAM4), delayed with 0,1,2 or 3 symbols periods using spiral waveguides and combined again using three 2x1 MMIs, producing 104 Gbaud OOK (or PAM-4).