Communication technologies like Bluetooth and Wi-Fi operate on invisible radio waves, but transmitting data on wavelengths we can see might turn out to be more efficient and secure. Researchers at King Abdullah University of Science and Technology (KAUST) have developed a nanocrystal that helps boost data speeds transmitted through a visible light LED up to 2 Gbps – while pleasantly lighting the room.
Only a fraction of the electromagnetic spectrum is visible to the human eye, and making use of those wavelengths could lead to faster, safer and more efficient wireless data systems. With so many wireless signals jostling for the attention of devices, certain frequencies can become clogged, and radio waves can interfere with sensitive equipment used for navigation or in hospitals. Visible-light communication (VLC) systems may help bypass those issues.
Currently, VLC devices are based on LEDs which use phosphorus to turn some of the blue light emitted by a diode into red and green. When combined, the red, blue and green form white light, comfortably lighting a room while providing a wireless signal. But this technique has its limits.
"VLC using white light generated in this way is limited to about one hundred million bits per second," says Boon Ooi, a KAUST Professor of Electrical Engineering, though a University of Virginia study reached 300 Mbps, and Siemens managed 500 Mbps. Pennsylvania State University has even hit 1.6 Gbps, albeit using invisible infrared light.
The KAUST researchers have achieved 2 Gbps using visible light, converting the colored light into white using nanocrystals instead of phosphorus. These crystals are eight nm long and made of cesium lead bromide, and when hit by a blue laser, emit green light. An incorporated nitride phosphor emits red light, and the three colors combine to form the white, room-illuminating light that's reportedly comparable to that of existing LEDs.
Data is transferred through a series of quick flashes, imperceivable to the human eye yet loud and clear to a receiving sensor. That's because in these nanocrystals, the optical processes operate on a time-scale of about seven nanoseconds, meaning the optical emission of the light operates at a frequency of 491 MHz. That in turn allows the data to be transmitted at 2 Gbps, although other research indicates VLC could go as fast as 10 Gbps.
"The rapid response is partly due to the size of the crystals," says Osman Bakr, Associate Professor at KAUST. "Spatial confinement makes it more likely that the electron will recombine with a hole and emit a photon."
The research was published in the journal ACS Photonics.