Fully-Integrated Heterogeneous DML Transmitters For High-Performance Computing

Optical connectivity which has been widely deployed in today's datacenters and high-performance computing (HPC) systems is a disruptive technological revolution to IT industry in the new Millennium. In our journey to debut an Exascale supercomputer, a completely new computing concept, called memory-driven computing, was innovated recently. This new computing architecture brings challenges and opportunities for novel optical interconnect solutions. Here we first discuss our strategy to develop appropriate optical link solutions for different data traffic scenarios in memory-driven HPCs. Then we present detailed review on recent work to demonstrate fully photonics-electronics-integrated single- and multi-wavelength directly modulated laser (DML) transmitters on silicon for the first time. Compact heterogeneous microring lasers and laser arrays are fabricated as photonic engines to work with a customized complementary metal-oxide semiconductor (CMOS) driver circuit. Microring lasers based on conventional quantum well and new quantum dot lasing medium were compared in the experiment. Thermal shunt and MOS capacitor structures were integrated into the lasers for effective thermal management and energy-free tuning. It enables a controllable dense wavelength division multiplexing (DWDM) link architecture in HPC environment. An equivalent microring laser circuit model was constructed to allow photonics-electronics co-simulation. Equalization functionality in the CMOS driver circuit was proved to be critical to achieve up to 14 Gb/s direct modulation with 6 dB extinction ratio. Finally on-going and future work is discussed towards more robust, higher speed, and more energy efficient DML transmitters.