This illustration shows how a single nanophotonic single-mode LED is constructed. Image: Gary Shambat, Stanford School of Engineering |
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 able to
transmit data at 10 billion bits per second. The researchers say it is a
major step forward in providing a practical ultrafast, low-power light
sources for on-chip computer data transmission.
Stanford’s
Jelena Vuckovic, an associate professor of electrical engineering and
the study’s senior author, and first author Gary Shambat, a doctoral
candidate in electrical engineering, announced their device in paper to
be published November 15 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 Kelvin, about -190 F, making them impractical for commercial use.
The new device operates at room temperature and could, therefore,
represent an important step toward next-generation computer processors.
“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.”
Single-mode light
The
LED in question is a “single-mode LED,” a special type of diode that
emits light more or less at a single wavelength, very similar 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 material indium arsenide, which,
when pulsed with electricity, produce light. These islands 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, the light becomes single-mode,” said Shambat.
This chip carrier holds a chip with hundreds of the Stanford low-power LEDs at its center. Image: Jan Petykiewicz, Stanford School of Engineering |
“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.
Engineering ingenuity
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 emission and modulation functions into one device that drastically
reduces energy consumption.
On
average, the new LED device transmits data 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 a single bit. Some
technologies consume as much as one pico-Joule per bit.
“Our device is 2,000 to 4,000 times more energy efficient than best devices in use today,” said Vuckovic.
Stanford
Professor James Harris, former PhD student Bryan Ellis, and doctoral
candidates Arka Majumdar, Jan Petykiewicz and Tomas Sarmiento also
contributed to this research.
