Computing structures and optical interconnect: friends or foes?

Optical interconnect is claimed to have signi ̄cant advantages over electrical interconnect due to the superior physical properties of photon propagation over electron propagation. These advantages translate to the well-known fundamentally di®erent bandwidth/distance/cross-section relationships of optical interconnects as compared to their electrical counterparts. Despite the validity of these basic results, too naive or straightforward an application of optical interconnects in electrical systems may not bring about the expected performance gains. In fact, the scienti ̄c literature contains several examples of proposed applications of optical interconnect where the real, quanti ̄able bene ̄ts are at best doubtful. Often, these examples are only intended to demonstrate the feasibility of a technological approach, not its great potential at the systems or application level. Typical °aws one encounters are (i) addressing the wrong problem: one tries to introduce optical interconnect at a location where the electrical interconnect is not the limiting factor; (ii) failing to realize the di®erences between interconnect and communications; and (iii) singling out one property of optical interconnect, while disregarding less bene ̄cial properties such as latency, area, power dissipation or optical pathway cost. Capitalizing on the intrinsic potential of optical interconnects in electrical systems requires a holistic approach, that should address the real issues in future electronic systems. To assess the true bene ̄ts of replacing an electrical interconnect by an optical one, it is imperative to take the systems context in which the interconnect is to be used into account. By means of examples taken from the computing area, we shall illustrate the profound impact of this context. We then propose a possible parameter space that is intended to capture part of the relevant context information at the link level, thus providing a badly required common domain of discourse for systems designers and optical component designers.