The realization of an energy-efficient optical link would have an obvious impact in reducing the energy consumption of data centers, which have been recognized as the most rapidly growing consumers of global energy. One promising approach to solve this issue is to utilize optical rather than electrical signals to send and receive data, which can theoretically lead to much higher speed and lower power consumption. However, difficulties in integrating high-performance optical components onto silicon electronics have been hindering practical application of optical links to chip-scale data communications. Here, we propose an innovative yet feasible optical link architecture consisting of nanoscale transmitters and receivers on a silicon platform. Relating the fascination of optoelectronics to its impact on carbon footprint of data centers will be the foundation of a new education and community involvement platform. Already, the PI participates in several activities to broaden the impact of laboratory research to society including direct relationships with high-schools, on-campus teacher training and helping to organize UCLA students for community involvement. In this case, the PI will (a) incorporate the findings of the proposed research into the UCLA curriculum (b) train and mentor high-school students through summer internships and student exchange programs, (c) form a targeted effort aimed at increasing community knowledge and participation through a high-school technology roadshow and campus visitations to create excitement for innovations in high-speed, energy-efficient optical links.
The research objective of this proposal is to develop nanophotonic optical links based on compact, energy-efficient, and directly integrated lasers and photodetectors as transmitters and receivers on silicon-on-insulator via selective-area epitaxy of III-V nanopillars. The proposed design is fundamentally different from other interconnects with externally bonded lasers, as both transmitters and receivers are monolithically aligned and simultaneously integrated on conventional silicon waveguides. The proposed optical links include electrically-driven nanopillar array lasers and single nanopillar photodetectors, which are engineered to achieve an energy-to-data ratio of <10 fJ/bit. For lasers, a one-dimensional photonic crystal cavity consisting of an array of nanopillars can achieve a high cavity quality factor of 19,000 and waveguide coupling efficiency of 60 % with a footprint of only 7.7 × 0.2 µm2. Purcell enhancement from an ultra-small and high-Q cavity as well as an introduction of three-dimensional diffusion barriers from InGaAs/InP nanopillar heterostructures results in an internal quantum efficiency of 93 %. For detectors, nanopillar photodiodes combined with plasmonic field enhancement achieved by metal nanoslot couplers realize the efficiency far beyond the diffraction limit, resulting in a dark current of 1 pA at 10 V, a bandwidth of 3.4 GHz, and a noise-equivalent power of 1.5 × 10-13 W/Hz1/2. The total power consumption is expected to be 6.3 fJ/bit assuming that these transceivers are linked by 3 cm-long waveguide, which is more than an order of magnitude reduced power consumption compared with the state-of-the-art optical interconnects. The proposed electrically injected nanoresonators and plasmonic light manipulation architectures on silicon not only enable ultra-compact and energy-efficient optical links, but also pave the way toward quantum computing, all-optical switching and memories, single-photon sources, and bio- and chemical sensors.
