So-called visible-light communication (VLC) combines information transmission with illumination. With a new nanocrystalline material that rapidly makes white light out of blue light it now demonstrates data speeds of up to 2 Gbps.
While Wi-Fi and Bluetooth are now well established technologies, there are several advantages gained by shortening the wavelength of the electromagnetic waves used for transmitting information.
So-called visible-light communication (VLC) makes use of parts of the electromagnetic spectrum that are unregulated and is potentially more energy-efficient. VCL also offers a way to combine information transmission with illumination and display technologies—for example, using ceiling lights to provide internet connections to laptops.
Many such VLC applications require light-emitting diodes (LEDs) that produce white light. These are
Electromagnetic spectrum. (Image: Wikimedia Commons).
usually fabricated by combining a diode that emits blue light with phosphorous that turns some of this radiation into red and green light. However, this conversion process is not fast enough to match the speed at which the LED can be switched on and off.
VLC using white light generated in this way is limited to about one hundred million bits per second. Instead, the researchers from the KAUST Functional Nanomaterials Laboratory use a nanocrystal-based converter that enables much higher data rates.
The team created nanocrystals of cesium lead bromide that were roughly eight nanometers in size using a simple and cost-effective solution-based method that incorporated a conventional nitride phosphor. When illuminated by a blue laser light, the nanocrystals emitted green light while the nitride emitted red light. Together, these combined to create a warm white light.
Visible-light communication with 2 Gbps
The researchers characterized the optical properties of their material using a technique known as femtosecond transient spectroscopy. They were able to show that the optical processes in cesium lead bromide nanocrystals occur on a time-scale of roughly seven nanoseconds. This meant they could modulate the optical emission at a frequency of 491 Megahertz, 40 times faster than is possible using phosphorus, and transmit data at a rate of two billion bits per second.
The rapid response is partly due to the size of the crystals. Spatial confinement makes it more likely that the electron will recombine with a hole and emit a photon. Importantly, the white light generated using their perovskite nanostructures was of a quality comparable to present LED technology.
The researchers believe that white light generated using semiconductor lasers will one day replace the LED white-light bulbs for energy-efficient lighting.
Developing efficient, optimized LED systems calls for the use of various technologies and combining them with one another. The SSL Forum 2016 will explain the current state of the art as well as the relationships and influences between the technologies used.