Research at the Li-Fi Centre at the University of Edinburgh

During the last decade, light emitting diodes (LEDs) have become an integral part of almost every electronic device used in everyday life. From household light bulbs to large-area screens, LEDs are everywhere. They come in all sizes and forms. Look at the electronic device that you are using to read this e-mail. It has at least one LED, not only as an integral part of the display, but also as an indicator light used to convey the status of the device functionality to the user.

In a 2014 publication, research at the Li-Fi Centre demonstrated the possibility of achieving data transmission at over 3 Gb/s using a single-color LED pixel [1] with a diameter of 50 micro mm – well within the size range of pixels on a typical hand-held device display. Small-sized LEDs are particularly suitable for communication as they offer significant improvements in terms of available modulation bandwidth when compared to typical commercially-available LEDs designed for illumination purposes. The significant reduction of the device size leads to a reduction of the innate junction capacitance and to an increase in the device current density. These features, in turn, lead to a reduced response time by the LED and to an increase in the available modulation bandwidth. At the same time, smaller LED sizes result in lower optical output power. As a consequence, the experiment presented in [1] was conducted at a short distance of about 5 cm. In addition, in that same publication, we made the case that the transmission distance can be increased and the precise alignment requirements in the system can be relaxed with the help of an avalanche photo diode (APD) at the receiver combined with appropriate optics.

Our recent experimental results have shown that the use of an APD and simple adequate optics can retain the high-speed capabilities of a microLED device at practical distances for indoor communication. Experimental results with off-line processing have revealed the capability of the link supporting a Gb/s transmission at the same distance. Furthermore, for more realistic indoor transmission distances of up to 3-4 metres, the large lens at the receiver frontend can be removed whilst still retaining the link capabilities of realising a Gb/s transmission.

These exciting new experimental results have demonstrated the enormous potential of microLEDs for realizing high-speed visible light communication (VLC) links at practical transmission distances. In future applications, such VLC-capable microLEDs can be integrated into smart device displays and indicator lights, turning them into powerful data transmission ports. Truly, we seem to be at a verge of VLC where every single pixel counts.

[1] D. Tsonev et. al., “A 3-Gb/s Single-LED OFDM-Based Wireless VLC Link Using a Gallium Nitride µLED”, IEEE Photonics Technology Letters, vol: 26, p. 637-640, 2014.

Dobroslav Tsonev 

Li-Fi Research Associate