Nov. 16, 2011 A team at Stanford's School of Engineering has demonstrated an ultrafast nanoscale light-emitting diode (LED) that is orders of magnitude lower in power consumption than today's laser-based systems and is able to transmit data at the very rapid rate of 10 billion bits per second. The researchers say it is a major step forward in providing a practical ultrafast, low-power light source for on-chip data transmission.
Stanford's Jelena Vuckovic, an associate professor of electrical engineering, and Gary Shambat, a doctoral candidate in electrical engineering, announced their device in a research paper in the journal Nature Communications.
Vuckovic had earlier this year produced a nanoscale laser that was similarly efficient and fast, but that device operated only at temperatures below 150 degrees Kelvin, about minus-190 degrees Fahrenheit, making it impractical for commercial use. The new device operates at room temperature and could, therefore, represent an important step toward next-generation computer chips.
"Low-power, electrically controlled light sources are vital for next-generation optical systems to meet the growing energy demands of the computer industry," said Vuckovic. "This moves us in that direction significantly."
The LED in question is a "single-mode LED," a special type of diode that emits light more or less at a single wavelength, similarly to a laser.
"Traditionally, engineers have thought only lasers can communicate at high data rates and ultralow power," said Shambat. "Our nanophotonic, single-mode LED can perform all the same tasks as lasers, but at much lower power."
Nanophotonics is key to the technology. In the heart of their device, the engineers have inserted little islands of the light-emitting material indium arsenide, which, when pulsed with electricity, produce light. These "quantum dots" are surrounded by photonic crystal -- an array of tiny holes etched in a semiconductor. The photonic crystal serves as a mirror that bounces the light toward the center of the device, confining it inside the LED and forcing it to resonate at a single frequency.
"In other words, it becomes single-mode," said Shambat.
"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," said Vuckovic.
The new device includes a bit of engineering ingenuity, too. Existing devices are actually two devices, a laser coupled with an external modulator. Both devices require electricity. Vuckovic's diode combines light transmission and modulation functions into one device, drastically reducing energy consumption.
In tech-speak, the new LED device transmits data, on average, at 0.25 femto-joules per bit of data. By comparison, today's typical "low" power laser device requires about 500 femto-joules to transmit the same bit.
"Our device is some 2,000 times more energy efficient than best devices in use today," said Vuckovic.
Stanford Professor James S. Harris, former PhD student Bryan Ellis and doctoral candidates Arka Majumdar, Jan Petykiewicz and Tomas Sarmiento also contributed to this research.
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