Researchers from the University of Illinois Urbana-Champaign and the University of Notre Dame have developed a gallium nitride micro-LED capable of achieving an optical modulation bandwidth of 2.75 gigahertz while consuming just 25 milliwatts of power. The device sets a new record for optical switching speed in quantum well LEDs and could help make data center communications faster and more energy efficient.
The team optimized the device to a diameter of just 5 micrometers, balancing its speed, size and energy consumption. The researchers believe the technology could offer an alternative to conventional wire connections and laser-based optical links, particularly for short-distance data transmission.
“Ninety percent of communications in data centers is short range, meaning less than 10 meters,” said Abdelghany Abouelnagga, a graduate student at Illinois Grainger Engineering and lead author of the study. “It is standard to use lasers for the kind of high-frequency communications needed in this context, but lasers are power hogs. If we want to manage energy use in data centers, we need to consider lower-power optical communications such as LEDs, and we show exactly how to do so.”
Why Data Centers Need More Efficient Optical Links
Data centers rely on rapid communication between servers and other computing components. To support increasingly demanding data transmission, they use optical communication links that transfer information through pulses of light.
Unlike conventional copper wires, optical links can transmit data at very high frequencies without significant signal loss. However, maintaining the speed and accuracy required for these connections has traditionally involved using lasers.
Although lasers provide the high-frequency performance needed for optical communication, they consume considerable amounts of electricity and generate substantial heat. This creates an energy-efficiency challenge for data centers, where large numbers of communication links operate continuously.
LEDs could provide a lower-power alternative, but their switching speeds have historically limited their suitability for high-frequency applications.
The new research demonstrates how carefully designed micro-LEDs could help address this limitation.
Researchers Identify the Optimal Micro-LED Size
To understand how device dimensions affect performance, the researchers systematically reduced the diameter of their micro-LEDs from 100 micrometers to 2 micrometers. They measured how optical modulation bandwidth and power consumption changed as the devices became smaller.
Optical modulation bandwidth indicates how quickly a light source can switch on and off while maintaining its brightness. This is an important measure of how effectively an LED can transmit rapidly changing data signals.
The team discovered that reducing the device size did not always improve performance. Instead, the 5-micrometer design provided the best balance between switching speed and power consumption.
“We systematically shrunk our micro-LEDs down from 100 micrometers to 2 micrometers in diameter, a level of deep scaling that has never been done before,” Abouelnagga said. “We found that, contrary to popular belief, smaller is not always better. Our work gives a development roadmap to systematically study the tradeoffs between size, bandwidth and power consumption, which shows that the best device is actually the 5-micrometer one.”
The researchers also modelled material imperfections and electrical properties that can produce parasitic effects and reduce device performance. This theoretical modelling, combined with experimental testing, helped them optimize the final design.
Low Power Consumption and Potential for Compact Data Arrays
The researchers say the device’s performance is particularly promising because it combines gigahertz-scale responsiveness with an electrical power consumption of only 25 milliwatts.
While certain nonstandard LED designs can operate at higher frequencies, they produce unstable light with low intensity. The researchers argue that their quantum well LED design is better suited to data center applications because it combines high optical bandwidth with useful optical power and low energy consumption.
“To put the speed and power efficiency in perspective, our micro-LED responds to electrical signals on a gigahertz scale, comparable to computer processors, but consumes just 25 milliwatts of electrical power,” Abouelnagga said. “Of course, processors and optical transmitters perform different functions, but the comparison illustrates how fast this tiny light source can respond with a small power budget. Its 5-micrometer diameter also opens the possibility of arranging many emitters into compact, two-dimensional arrays with each carrying a separate stream of data.”
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