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“We’re going to be communicating with terabits of information in the next decade,” says Mario Paniccia, an Intel fellow and director of the Photonics Technology Lab in Santa Clara, CA. A terabit of data is the capacity of roughly 35 DVDs. But today’s fastest telecommunications networks use chips that zip data around at 10 to 40 gigabits per second, and most networks use expensive, clunky components that are assembled piecemeal and achieve lesser speeds. “The ability to have an integrated chip that can transmit and receive a terabit is a compelling solution, and we’re still talking a chip the size of your fingernail,” says ­Paniccia, holding in his palm three silicon chips that could prove to be the heart of that solution–thumbnail-size squares that reflect light like mirrors.

Photonic technology, which uses light to transmit data, is the key to networks with terabit-per-second speeds. But silicon, a mainstay of the electronics industry, has been largely useless for photonics because of its poor optical properties. Photonics researchers have had to rely on exotic semiconductors such as indium phosphide, which emit light easily but are expensive and hard to work with. But in 2004, ­Paniccia’s group showed that silicon could be used to make a modulator that encodes data onto a light beam at one gigabit per second. (Telecom companies are beginning to use non-­silicon-based modulators that operate at 40 gigabits per second.) Then, in 2005, the Intel researchers bumped up the speed to 10 gigabits per second and built a surprisingly good all-­silicon laser (see “Intel’s Breakthrough,” July 2005).

Intel’s goal is to build a single silicon chip that integrates a laser, modulator, and detector, so it can emit light, encode it with data, and register incoming signals. Such a chip, says Paniccia, will affect several areas of technology. It could boost Internet bandwidth, because telecom networks would have access to more and cheaper integrated chips. It could enable new types of optical cables that transfer full-length movies from computers to iPhones or other mobile Internet devices in seconds. And computers themselves would speed up if the sluggish copper wiring that shuttles data between circuits on a microchip, and between the chip and the computer’s memory, were replaced with beams of light.

In building these new optical chips, Intel plans to piggyback on existing sili­con fabrication technology such as the litho­graphic systems used to pattern tiny transistors onto chips. Paniccia says that the ability to build photonic devices on large silicon wafers, using fine-tuned lithography to carve out features, could someday make photonic devices nearly as cheap and abundant as transistors. And if Intel has its way, integrated photonic chips that use ­silicon-­based components will be on the market within the next five years.

“The Intel group has essentially been debunking the myth that silicon isn’t good for photonics,” says Alan ­Willner, a professor of electrical engineering at the University of Southern California.

The Current Work
Researchers in Paniccia’s lab are spending a lot of time tweaking the designs of three key silicon-based devices. One, the silicon hybrid laser, was first demonstrated in September 2006. While the all-silicon laser announced in 2005 emits light at near-infrared wavelengths useful for medical applications, the hybrid laser operates in the infrared range used in telecommunications networks. It is this laser that Paniccia calls the “game changer” for telecom and consumer electronics applications.

To make their silicon laser produce light at the right wavelengths, the researchers needed to use a small amount of indium phosphide. The trick was to develop a glue that easily bonded the two materials together. At present, ­Paniccia’s team is trying out slight variations on the design to improve performance. For instance, to reduce power consumption, the researchers are changing the position of the metal contacts that supply electricity to the laser.

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Credit: Saul Bromberger and Sandra Hoover

Tagged: Computing

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