Interconnection between multiple chips has been becoming a serious system-level limitation for many years. A traditional solution to this has been system-in-package packaging in which multiple chips are stacked or otherwise connected in close physical proximity within the same package - a good example of this is the packaging of cache memory die along with the processor in the same package. In recent years however, the problem has become very acute as the intra-chip bandwidth has increased orders of magnitude faster than inter-chip bandwidth. This has led to the search for even better inter-chip communications technologies, including optical links to replace traditional electrical links.
This article gives readers an introduction to the use of silicon photonics for solving interconnection problems on future chips and systems. A review of current system requirements and the limitations of existing technologies helps the casual reader understand where the future of system integration needs to go. The authors make the case for an optical interposer as the most efficient way to cope with the problems of a purely electronic system. They then describe their own work in silicon photonic systems and the results of early prototyping activity are explained, with an example of data transmission at 12.5Gb/s at a bandwidth denity of 6.6Tb/s/cm2, which is an astonishing number for a chip.
The interesting aspect of the article is that it takes a high level view of chip to chip interconnection, and does a good job of making the case for a convergence of photonic and electronic components as being an optimal point for solving many system interconnection problems. Some information about the fabrication process for onchip optical components are also provided to help the reader understand how this is actually going to work. Finally, the authors propose a surface mount approach that will allow systems engineers without specialized photonics training to use these components. Overall, the article provides a useful introduction as well as catchup to the state of the art in photonic interconnects.