Modeling and Integration of Highly Parallel Optical Interconnects in Electronic Systems

• de examencommissie voor de geïnvesteerde tijd en opbouwende com-mentaar. the examination commission for their time and constructive comments. Dit werk werd ondersteund door het Fonds voor Wetenschappelijk Onderzoek – Vlaanderen, het Interconnect by Optics-project (IST-2000-28358) binnen het vijfde kaderprogramma voor onderzoek en technologische ontwikkeling van de Europese Gemeenschap, en het Belgian Photon Network (IAP V/18) van het Interuniversitaire Attractiepolen-programma van de Belgische Staat, Diensten van de Eerste Minister, Federaal Wetenschapsbeleid. Summary Optical interconnections inside the box? Electrical and optical interconnec-tions are the foremost resources for guided-wave digital communication. The length, throughput and application of an interconnection are decisive for the choice between the alternatives. Optical interconnect has been commercially introduced in the late 1970s for high-bandwidth multi-km telecommunications due to its vast power and bandwidth advantages: the attenuation is essentially bandwidth independent and much lower when compared to electrical interconnect. Since then, the increasing bandwidth demands of end user applications and the rise of smaller and cheaper optoelectronics has promoted ever smaller optical link lengths, presently down to a few meters. Electrical interconnect is the native interface of logic and memory primitives inside computational systems. Here, the limiting factor for system performance is often the interconnection latency. The light velocity encourages a spatially dense setup, whereas the time necessary to modulate a data packet on a link translates again into a bandwidth requisite. In a dense computational system, the cross-section available to an interconnec-tion is limited. The resistivity of even the best available conductors limits the electrically attainable bandwidth through a confined cross-section, given the distance and power budget. The transistor density of integrated circuits in complementary metal-oxide– semiconductor (CMOS) technology continues to rise. Although more calculations can be performed in the same space and time, the bandwidth and latency of electrical interconnections can hardly keep pace. Strongly connected distributed algorithms face an actual interconnect-related performance bottleneck. Parallel short-range optical interconnections can provide a solution to the bandwidth density problem. After all, on a system scale, the throughput of even tight optical interconnections is limited by the bandwidth of active components rather than the attenuation or dispersion of the optical path. The break-even distance beyond which optical interconnect can outperform electrical interconnect, with respect to bandwidth density at a similar power xii Summary budget, is presently estimated in the centimeter range. Surface-level optical chip access We focus on the optoelectronic very large scale integration (OE-VLSI) approach, which provides a …