A team of researchers from the University of Illinois Urbana-Champaign (Grainger College of Engineering) and the University of Notre Dame has set a world record for optical switching speed for quantum-well light-emitting diodes. The gallium nitride-based device - a micro-LED - demonstrated an optical modulation bandwidth of 2.75 GHz at a power consumption of just 25 mW. The results were published in the journal IEEE Electron Device Letters.
Optical modulation bandwidth is a measure of how quickly an LED can turn on and off without losing brightness. The higher the value, the more data can be transmitted per unit of time. The new record was achieved through careful modeling and experiments: the scientists systematically reduced the size of the LEDs from 100 to 2 micrometers in diameter to find the optimal balance between speed, size and power consumption.
"We found that, contrary to popular belief, smaller is not always better," a press release quotes lead author Abdelgani Abouelnagga (a graduate student at the University of Illinois) as saying. "Our work provides a roadmap for studying the trade-offs between size, bandwidth and power consumption, and shows that the best device is an LED with a diameter of 5 micrometers."
In data centers, most communications are short links less than 10 meters long. Lasers are usually used for high-frequency transmission over such distances, but they consume a lot of energy and generate heat. LEDs could become a more energy-efficient alternative. However, until now their speed has lagged behind that of lasers. The new work demonstrates that a properly designed micro-LED can operate at gigahertz frequencies comparable to those of processors, at low power consumption.
The device is fabricated using standard quantum-well technology. Although other LED designs with higher frequency exist, they produce unstable light of low intensity. According to the researchers, their 5-micrometer design is better suited to data centers thanks to the combination of optical power, bandwidth and low power consumption. In addition, the small diameter makes it possible to assemble many emitters into compact two-dimensional arrays, each of which can transmit a separate data stream.
The study was carried out under the guidance of professors Can Bayram, Peter Dragic and Milton Feng of the University of Illinois and professor Patrick Fay of the University of Notre Dame. Zetai Liu and Jonathan Wright also participated in the work. The scientists emphasize that this is a laboratory result, and commercial implementation is still far off, but it charts a path toward faster and more energy-efficient optical communication links.