Today’s computer processors are strictly electronic devices, transmitting data by means of electrons traveling through copper wires. But this technology is relatively slow and produces heat. Now, researchers at Intel have developed an optical device that could play a key role in replacing electrons and copper wires with photons and beams of light. The team has demonstrated a record-breaking silicon modulator that can encode data at a rate of 30 gigabits per second–nearly as fast as many nonsilicon modulators currently used in fiber optics hardware.
A silicon modulator that can operate at these speeds, says Mario Paniccia, Intel research fellow and director of the Silicon Photonics Technology Lab, could make it possible to design faster computers that include photonic chips. In addition, Paniccia says, it could be part of an all-silicon photonic chip that might be used in fiber optic networks. Since silicon devices are easy to mass-produce and relatively inexpensive, the chips could replace more expensive network hardware, reducing the cost of bandwidth.
Historically, photonic devices such as modulators and lasers have been made of exotic, costly semiconductors such as indium phosphide. In 2004, however, Paniccia’s group showed that with clever engineering, they could make a silicon modulator operate at one gigabit per second. In 2005, they increased its speed to 10 gigabits per second and built a surprisingly good silicon laser (see “Intel’s Breakthrough”). Throughout 2006, the researchers tweaked their original design to make the silicon laser more efficient and easier to manufacture (see “Bringing Light to Silicon”).
“The Intel group has essentially been debunking the myth that silicon isn’t good for photonics,” says Alan Willner, professor of electrical engineering at the University of Southern California in Los Angeles. And while the silicon laser is important, he says, a fast modulator is crucial. Today’s state-of-the-art modulators work at 40 gigabits per second, and for silicon to compete as an optical material, it needs to operate at comparable speeds. Intel’s 30-gigabit-per-second silicon modulator is thus “a big deal,” he says.
At the heart of the silicon modulator design is a diode, similar to those found in electronics. Light enters a modulator from one end of the device and is split into two beams. Both beams pass through silicon diodes. When a voltage is applied to these diodes, they shift the phase, or position, of the light wave. This phase shift is what encodes data: depending on the phase of the light, it can represent a 1 or a 0.
The research, published this week in Optics Express, details the design and fabrication of a single 30-gigabit-per-second silicon modulator. By slightly altering the chemical makeup of the diodes, Paniccia expects to achieve the same rates as commercially available nonsilicon modulators. “We believe this design will be extendable to 40 gigabits per second in the future,” he says.
Paniccia expects that by 2010, silicon photonics modulators or lasers could be ready for commercialization in the fiber optics industry. But, he says, his team’s goal is to build an integrated photonic chip. “The really exciting part is that once you have these building blocks, you can integrate them together,” he says. “If you take 25 of those [silicon] lasers and direct them into an array of 25 modulators, then you have a terabit of information all on a piece of silicon the size of my fingernail.”