Abstract
Optical connectivity, which has been widely deployed in today's datacenters and high-performance computing (HPC) systems, is a disruptive technological revolution to the 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 were 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 ultra low-energy tuning. It enables a controllable dense wavelength division multiplexing (DWDM) link architecture in an HPC environment. An equivalent microring laser circuit model was constructed to allow photonics-electronics co-simulation. Equalization functionality in the CMOS driver circuit proved to be critical to achieve up to 14 Gb/s direct modulation with 6 dB extinction ratio. Finally, the on-going and future work is discussed towards more robust, higher speed, and more energy efficient DML transmitters.
Highlights
F OR decades Moore’s Law guided exponential growth of computing capacity in silicon (Si) chips, and generated data was transported globally through long-haul fiber-optic networks
2.2 dB difference comes from waveguide loss and accumulated microring through port loss. −15 dBm sensitivity to achieve 10−12 bit error rate (BER) at 25 Gb/s was used for SiGe APD-based receiver, which is a low-end estimation as APD can be more sensitive at lower data rate [32]
Since typical 1 dB gain bandwidth for a multiple quantum well (MQW) diode laser structure is around 20 nm, such design can be scaled to 8 or more channels; Even more channels can fit into a single quantum dot (QD) structure as its wider gain bandwidth [58]
Summary
F OR decades Moore’s Law guided exponential growth of computing capacity in silicon (Si) chips, and generated data was transported globally through long-haul fiber-optic networks. They were the hardware backbone to enable today’s information era which demands a stronger bond between electronics and photonics as data growth is nearly doubled every two years. Memory-driven computing [2]–[4] was recently proposed and rises as a revolutionary concept to lift several fundamental constrains in traditional processor-concentric architecture. Electrical, optical and thermal characterizations are presented in details, followed by a laser circuit model developed from static and dynamic device performance This model provides electrical parameters for the design of customized CMOS driver with equalization functionality. Fabricated CMOS driver chip characterization and fully-integrated transmitter performance are presented
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