Visible Light Communication
Visible light communication (VLC) is a broad term which covers the transmission of data, over free space or fibre, using light sources emitting at visible wavelengths. These light sources may be LEDs, laser diodes or any other visible emitter.
One implementation of VLC has been dubbed “Li-Fi”. This envisages using white-emitting LEDs for both lighting and data transmission , with  data transmission rates in excess of up to 1.1 Gbit/s having been demonstrated .
Polymer Optical Fibre (POF)
Another application concerns data transmission over polymer optical fibre (POF). POF is increasingly used to carry data over short distances, for example, within homes, cars or data acquisition from sensors. There is a an absorption loss minimum in POF around the blue-green region of the spectrum, so high-speed transmitters at these wavelengths are of particular interest.
Over the last few years, we've demonstrated that our micro-LED devices can meet the requirements for high-speed visible-emitting light sources for VLC.
A key advantage of micro-LEDs is their very high electrical-to-optical (E-O) modulation bandwidths, which can be in excess of 400 MHz. This represents the highest reported values for blue or green-emitting GaN LEDs , devices which are particularly suitable for use with POF. These high bandwidths have been attributed to their inherently small capacitance and their ability to be driven at high current densities compared to their larger “broad area” counterparts.
Error-free data transmission using on-off keying (OOK) has been demonstrated using blue and green-emitting micro-LEDs at bit rates of up to 1.1 Gbit/s . As of October 2012 our group is part of the four year £4.5 million EPSRC-funded “Ultra-parallel visible light communications” (UP-VLC) project. During the course of this project we will aim to demonstrate data transmission at higher bit rates using more complex modulation schemes. Further details about UP-VLC are available an EPSRC online podcast, involving Professor Martin Dawson (University of Strathclyde) and Professor Harald Haas (University of Edinburgh).
Our micro-LED devices are also suitable for “Li-Fi”. Micro-LEDs can be used to generate white light by integrating the devices with suitable colour-converting materials. By using novel materials, this can be achieved whilst maintaining the high-speed modulation characteristics of the devices, and even allow the emission properties of the hybrid devices to be modified. More details on these hybrid devices for VLC can be found here.
 H. Elgala et al., "Indoor broadcasting via white LEDs and OFDM", IEEE Transactions on Consumer Electronics, vol. 55, no. 3, pp. 1127–1134 (2009).
 F. Wu et al., “1.1-Gb/s White-LED-Based Visible Light Communication Employing Carrier-Less Amplitude and Phase Modulation”, IEEE Photonics Technology Letters, vol. 24, no. 19, pp. 1730-1732 (2012).
 J. J. D. McKendry et al., “Visible-Light Communications Using a CMOS-Controlled Micro-Light-Emitting-Diode Array,” Journal of Lightwave Technology, vol. 30, no. 1, pp. 61–67, 2012.
 J. J. D. McKendry et al., “High-Speed Visible Light Communications Using Individual Pixels in a Micro Light-Emitting Diode Array,” IEEE Photonics Technology Letters, IEEE, vol. 22, no. 18, pp. 1346–1348, 2010.