Connecting at the speed of light

Light has a clear advantage over electronics as the medium of ultrafast information transmission. Optical fibers are used extensively in long-distance telecommunications applications and are making a strong showing in local-area networks. Board-to-board interconnects for terrabit data rates are just over the horizon. These technologies will see their full potential only when active, all-optical switches and logic can be coupled to present-day passive technologies. The key ingredient of the new systems will be the availability of nonlinear optical materials that meet active device needs. In this paper, material performance is shown to depend intimately on quantum mechanics, which sets fundamental limits on the nonlinear-optical response. While today's materials are already good enough to make devices, an understanding of the underlying quantum mechanics of how a material interacts with light can lead to even better materials.