David A.B. Miller

 


Devices for Optical Interconnects to Chips

Abstract: This talk will summarize recent work in device requirements for optical interconnects, in novel device approaches using germanium quantum wells and nanophotonic and nanometallic structures, and in fundamental limits to optical components.

Power has become a dominant constraint in information processing, and will continue to be for the foreseeable future and beyond. Electrical wires operate at energies of ~ 1 pJ/bit or higher for off-chip interconnects and ~ a few 100 fJ/bit to ~ 1 pJ/bit for global on-chip interconnects. Optics can in principle solve such energy problems while simultaneously allowing higher densities of interconnects, especially for longer off-chip distances. For sufficient benefit, however, total system energy of < 100 fJ/bit will be required for optical interconnects, which implies optical output devices (lasers or modulators) that are efficient at ~ 10 fJ/bit transmitter energies, and optical receivers (photodetectors and associated circuitry) that can operate with < 1 fJ/bit of received energy. These are aggressive numbers for optoelectronics, but not unphysical. Quantum-confined Stark effect (QCSE) quantum well modulators are one possible transmitter approach that could scale to such low numbers. Recent work at Stanford on such modulators using germanium quantum wells on silicon substrates represent an interesting recent development for low energy devices compatible with silicon technology. We have also recently combined Ge with nanometallic antenna structures to make enhanced photodetectors in deeply subwavelength detector elements and to consider other nanometallic structures such as “two-conductor” optical nanometallic waveguides for photodetectors and light concentration. Nanometallic structures are very promising for concentrating light into deeply sub-wavelength optoelectronic devices with high speeds and low capacitances.

For interconnects it will also be important to make optical devices such as wavelength splitters very small. We have been able to model, design, and demonstrate superprism wavelength splitters, which potentially could enable dense wavelength splitters for optical interconnects and other applications. We have also examined fundamental limits to dispersive optical device performance devising a limit that has now also been applied to bound the performance of “slow light” devices. In summary, these and other approaches to novel optical and optoelectronic devices exploiting nanophotonics and quantum confinement are very promising for future applications such as optical interconnects.

Bio: David Miller received the B.Sc. degree from St Andrews University, and the Ph.D. degree from Heriot-Watt University, both in Physics. From 1981, he was with Bell Laboratories, first as a Member of Technical Staff and then, from 1987, as a Department Head. Since 1996 he has been a Professor of Electrical Engineering and, by Courtesy, of Applied Physics at Stanford and has served at a Director of several labs and centers. His research interests include nanophotonic and quantum-confined optoelectronic physics and devices, and fundamentals and applications of optics in information sensing, switching, and processing. He has published more than 230 scientific papers and holds 69 patents. He is the author of Quantum Mechanics for Scientists and Engineers (Cambridge, 2008).

He has served in various roles for the Optical Society of America (OSA) and the Institute of Electrical and Electronics Engineers (IEEE) Lasers and Electro-Optics Society (LEOS), being