Researchers Set New Record for Data Transmission Using LED Light

This novel technique makes white light out of blue light, allowing for data rates of up to 2 GB/s.

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Aug 14 2016, 4:52pm

Image: Flickr/Benjamin Linh VU

The Internet of Things is slated to have some 20 billion products online by 2020, which means that the radio spectrum used by these products to wirelessly transmit information is going to get increasingly crowded. As more internet connected devices demand a share of the radio spectrum, pressure has been put on the National Telecommunications and Information Administration to regulate more spectrum for devices to operate on.

In the meantime, researchers are experimenting with unregulated frequencies on the electromagnetic spectrum (like those in the visible and infrared light range) to develop novel ways of transmitting data wirelessly in an increasingly noisy world.

The latest development in this field is coming out of King Abdullah University of Science and Technology in Saudi Arabia, where researchers have successfully created a lightbulb capable of transmitting data over 20 times faster than previously existing LiFi devices.

Most methods of LiFi visible light communication (VLC) make use of lightbulbs that transmit wireless data using light emitting diodes (LEDs). LiFi is similar to WiFi, but rather than using lower frequencies that are closer to the radio spectrum, LiFi operates in the higher frequencies characteristic of visible, infrared, and ultraviolet light.

The electromagnetic spectrum. Image: Wikimedia Commons

The LED LiFi devices usually work by combining blue diodes with phosphorous which turns part of this radiation into red and green light, resulting in the white light desired for a bulb or display device.

"VLC using white light generated in this way is limited to about one hundred million bits per second," said Boon Ooi, a professor of electrical engineering at King Abdullah University of Science and Technology (KAUST).

The reason for this limit in the amount of data that can be transferred is that this process of generating white light is much slower than the rate at which an LED light can be turned on and off. The phosphors used in these devices are a photoluminescent material that are commonly found in LEDs, but their photoluminescent lifetime is relatively long once activated by a blue diode, thus limiting the device's bandwidth to about 12 megahertz (MHz).

The rate at which which the light can turn on and off is important because this is the method that the LED light uses to communicate. By turning on and off faster than the eye can see, the LED communicates in binary code with a receiver—the faster this transition happens the greater the bandwidth, which dictates how much information can be conveyed.

As detailed in their recent paper for ACS Photonics, the KAUST researchers improved upon this VLC model by using a nanocrystalline structure made of cesium lead bromide combined with a conventional nitride phosphor. When they would shine a blue laser at the nanocrystals, it would emit a green light while the nitride emitted red light—when the green and red lights were combined, they emit a soft white glow.

As the researchers discovered, the addition of this nanocrystalline structure decreased the photoluminescent lifetime of the phosphor from the order of microseconds characteristic of traditional LEDs down to just seven nanoseconds. This allowed for a bandwidth of nearly 500 megahertz and data transmission rates of up to two billion bits per second (2 Gbps), a 20-fold increase over other VLC technologies operating at around 100 million bits (100 Mbps).

For the sake of comparison, most WiFi systems you'll encounter today are operating at bit rates on the order of a few tens of Mbps.

Not only was this a dramatic improvement in data transmission rates, but the light emitted by the team's bulb was of a quality comparable to other LED lights and was actually more energy efficient.

"In this bandwidth hungry era, there will be a continuous push by consumers for VLC systems with higher bitrates," Ooi told Phys.org. "We believe that white light generated using semiconductor lasers will one day replace the LED white-light bulbs for energy-efficient lighting."