Optical interconnects to silicon CMOS using densely-integrated optoelectronics

Silicon CMOS integrated circuits will continue improving at a rapid pace as feature sizes are reduced. While the physics governing the transistor favors this size reduction, the performance of the wires used for electrical interconnects does not significantly improve under this type of scaling. A new approach to signaling and clock distribution will be needed to take CMOS circuit performance beyond the limits imposed by electrical interconnects. Optical interconnects have the potential to circumvent these limitations, provided a number of technological issues can be addressed. This paper discusses the major problems with electrical interconnects, particularly those of low capacity, high power dissipation, and timing uncertainty. It is shown that an optical approach can potentially reduce or eliminate all of these problems. To fully realize such benefits, dense arrays of optoelectronics must be integrated with silicon circuits; current integration techniques and appropriate I/O devices are considered in detail. Finally, several experimentally-demonstrated systems are described, including such novel approaches as optical clock distribution, the use of ultrafast optical techniques, and wavelength-division multiplexing.