LED chips to take on lasers in computer transmission
The nanoscale devices which incorporate small islands of indium arsenide, are claimed to be ultrafast and a thousand times more energy efficient than laser-based devices.
A team at Stanford's School of Engineering has demonstrated an ultrafast nanoscale LED that it says 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.
Data device schematic of a single-mode LED nanophotonic. (Credit:Gary Shambat, Stanford School of Engineering)
Jelena Vuckovic, an associate professor of electrical engineering at Stanford and the study's senior author, and first author Gary Shambat, a doctoral candidate in electrical engineering, announced their device in paper published November 15 in the journal Nature Communications.
Vuckovic, had earlier this year produced a nanoscale laser that has a similarly efficiency and was very fast, but that particular device only operated at temperatures below 150 Kelvin, about 190 degrees below zero Fahrenheit, 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 Nanophotonic LED Chip Carrier which holds hundreds of the Stanford low-power LEDs at its centre (Credit:Jan Petykiewicz, Stanford School of Engineering)
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 centre 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.
"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.
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).(Credit:Michal Bajcsy, Stanford School of Engineering)
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 scientists say 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 2000 to 4000 times more energy efficient than best devices in use today" said Vuckovic.
Further details of this work have been published in the paper “Ultrafast direct modulation of a single-mode photonic crystal nanocavity light-emitting diode” by Shambat et al, Nature Communications, 2,
Article number: 539.