Nanovation’s short-term interest is in delivering smaller, more efficient network devices, including simple switches (this spring the company introduced an initial line of such products), but down the road the company hopes integration will deliver more sophisticated and functional optical devices. “This is like the very early days of integrated circuits,” Bjorklund says. “The day after they invented the integrated circuit they didn’t go from individual transistors to the Pentium. That took thirty years. But there is a lot of value added by putting twenty or thirty transistors on one chip.”
Before Nanovation-or anyone else-can become the Intel of microphotonics, they must learn to tame the unruly photon. Electrons have proven useful because they have a charge and are therefore relatively easy to manipulate by, say, applying a voltage. That makes it possible to route electronic signals around microscopic integrated circuits; it also makes it possible to utilize electrons to manipulate and store information. It is these qualities that have made electrons so valuable in microelectronics and computing.
Photons, however, are much less malleable characters than electrons. They’re great for speeding information from one place to another over long distances, but it’s tough to control them. Try sending them around a sharp corner, for instance, and they scatter wildly.
Dreams of taming photons and using them in integrated optical circuits are not new. But recent research in industrial telecommunications labs, universities and at least a dozen startup companies is opening up ways to better invoke the required mastery over photons.
One key to this work could be the fabrication of smaller and more efficient waveguides that could be used to control the flow of photons in integrated optical circuits. To gain higher levels of functionality for optical circuits-and gain a higher level of control over photons-Nanovation and MIT, among others, are exploring waveguides fabricated in novel materials such as silicon-silica hybrids and indium phosphide. These materials confine light so strongly that beams with a wavelength of 1.5 micrometers-the standard for telecommunications-can be contained in waveguides about half a micrometer wide. These waveguides can also make tighter turns-about a thousand times tighter than the millimeter-scale bends achieved in earlier waveguides-without spilling their contents.
Photons confined in these tiny structures take on odd and potentially useful behaviors. For example, relatively small voltages can entice photons in the waveguide to jump between adjacent channels. And rings as small as 5 micrometers in diameter-about the width of a human hair-can pluck lightwaves of a given wavelength out of one waveguide and shoot them down another, providing a color-selective switch.
Such advances are opening up possibilities for integrated photonic chips. And that is boosting hopes for smarter optical switches that will better distribute the power of fiber optics. For instance, an optical chip could select one wavelength of high-bandwidth light off the fiber passing through your neighborhood and divert that data-rich wavelength to your home, where another optical chip would grab your phone calls, high-definition TV shows and Web browsing. This type of networking is already being explored in regional systems. Future microphotonics could bring it to the living room.
The promise inherent in integrated photonic circuits, however, extends beyond fiber-optic networks. In much the same way integrated optical devices could improve how data is transmitted in long-range communication systems, they could also facilitate the sharing of information in the microscopic realm where computers talk to themselves. For years physicists have been dreaming of computing that relied on photons, rather than electrons. That idea may or may not become a practical reality; while it has proven possible to use photonics for logic and memory functions, electronics remain much better at the job.
Still, photons may be the key to faster computer chips, which are suffering from their own form of electronic bottleneck. Increasingly, the speed of transistors and integrated chips are outpacing the metal wires and cables that connect them-the wires can’t carry data fast enough. “Whereas microphotonics is giving you complex optical circuits for communications, now it’s also required at the other end-the very localized end-to make the next generations of microprocessors,” says MIT’s Kimerling.