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Nanophotonics Reshapes Data Transmission

Photonics.com
Nov 2011
STANFORD, Calif., Nov. 15, 2011 — A new ultrafast nanoscale single-mode LED can transmit data at 10 billion bits per second and is thousands of times more energy-efficient than today’s laser-based systems. The new device operates at room temperature and could therefore represent an important step toward next-generation computer processors.


This chip carrier holds a chip with hundreds of the Stanford low-power LEDs at its center. (Image: Jan Petykiewicz, Stanford School of Engineering)


Earlier this year, Jelena Vuckovic, an associate professor of electrical engineering at Stanford University, produced a nanoscale laser that was similarly efficient and fast; however, that device operated only at temperatures below 150 K, about -190 ºF, making it impractical for commercial use.

“Low-power, electrically controlled light sources are vital for next-generation optical systems to meet the growing energy demands of the computer industry,” Vuckovic said. “This moves us in that direction significantly.”


This illustration shows how a single nanophotonic single-mode LED is constructed. (Image: Gary Shambat, Stanford School of Engineering)


The Stanford team used a single-mode LED for the device because it emits light more or less at a single wavelength, similar to a laser.

“Traditionally, engineers have thought only lasers can communicate at high data rates and ultralow power,” said Gary Shambat, a doctoral candidate in electrical engineering at Stanford. “Our nanophotonic, single-mode LED can perform all the same tasks as lasers, but at much lower power.”

In the heart of the LED device, the engineers inserted little islands of indium arsenide that produce light when pulsed with electricity. These islands are surrounded by photonic crystals, which serve as mirrors that bounce the light toward the center of the device, confining it inside the LED and forcing it to resonate at a single frequency.

“Without these nanophotonic ingredients — the quantum dots and the photonic crystal — it is impossible to make an LED efficient, single-mode and fast all at the same time,” Vuckovic said.


Members of the Vuckovic team in the lab from left to right: Arka Majumdar, Tomas Sarmiento, Jan Petykiewicz, Jelena Vuckovic and Gary Shambat (holding the chip carrier). (Image: Michal Bajcsy, Stanford School of Engineering)

What makes the new device drastically more energy-efficient is the fact that it combines light emission and modulation functions into a singular device, as opposed to existing methods that require a laser combined with an external modulator.

On average, the new LED device transmits data at 0.25 femtojoules per bit. By comparison, today’s typical low-power laser device requires about 500 femtojoules to transmit a single bit. Some technologies consume as much as one picojoule per bit. Vuckovic said the device is 2000 to 4000 times more energy-efficient than the best devices in use today.

The research was published in Nature Communications; Vuckovic is the study’s senior author, and Shambat is first author.

For more information, visit: www.stanford.edu  


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