Professional Engineering

Imagine switching on the light in your living room and simultaneously activating an ultra-high-speed broadband link. As the light illuminates the room it also bathes it in information. Uploading and downloading information from the internet happens in a flash.

Harald Haas, professor of mobile communications at the University of Edinburgh, is developing technology that can do exactly this. In the laboratory he and his team have produced what is said to be the world’s fastest realtime data transmission system. It can transmit and download streamed video at a rate of 130Mb/s using visible light. By comparison, the average domestic broadband connection in the UK works at 9Mb/s, according to the telecoms watchdog Ofcom. 

The technology, known as li-fi, uses LEDs as a source of light to transmit the data wirelessly. Haas says: “LEDs are electronic devices that are a little bit like a transistor and as a consequence they can be switched on and off very quickly.” The pattern of this flashing light can project the data in the form of 0s and 1s at very high speeds. The data is encoded in the light and transmitted from the light source.

He adds: “You are not really switching the light on and off, you are changing the intensity in a very subtle and specific way.” The light then hits a sensitive photosensor that decodes the data. It does this by creating an output current that varies in response to the changing intensity of light. The changes are so fast that they are invisible to the human eye.

Wireless data is normally transmitted by radio waves. But the radiofrequency spectrum has only a limited number of wavelengths, which are becoming increasingly congested as more and more commercial applications jostle for space. Radio bands are also heavily regulated by telecoms bodies and can be expensive. 

Haas explains that the radiofrequency spectrum available in the home is “very limited” and this restricts the rate at which data can be transmitted. And in places such as hotels where many wi-fi access points are installed, transmission rates fall and services are delayed if lots of people connect. Haas explains: “That effect is caused by interference. The radiofrequency signal goes through walls, so the signal from one room will interfere with that in another room.”

By contrast, light signals do not penetrate physical barriers or interfere with radio waves. The light spectrum is also unrestricted and is 10,000 times larger than the radiofrequency spectrum, so potentially providing space for the world’s growing bandwidth needs.Networking company Cisco says that the amount of data transmitted through wireless networks doubles every year. It predicts that by 2016 data traffic on the internet, managed IP and mobile systems will reach 1.3 zettabytes. 

Using li-fi would mean that each room would need an enabled light source. Haas explains: “Light bulbs are connected to the power line infrastructure so we don’t have to wire up these new access points. We just use the existing infrastructure to create a new wireless network that will be able to supply this increasing demand for wireless data traffic.” In the laboratory, Haas and his colleagues are now working towards achieving speeds of 1Gb/s. “We know this is feasible,” he says. 

His spin-out company Pure VLC is now working to commercialise the technology. It hopes to have its first product available for sale by the end of the year. Known as a “smart lighting development kit,” it will be capable of downloading and uploading data at speeds of between 15 and 50Mb/s. 

Dr Brian Sadler, a fellow of the US Army Research Laboratory, says that li-fi devices potentially represent a “pot of gold”. He adds that the technology is likely to be a “game changer” within its domain. “It scales up really well.”

He says that the ability to transmit data by light has been feasible for decades. The issues with commercialising the technology come down to the business model because the light can only carry data in the line of sight. “But there is a lot of commercial stuff on the drawing board,” he says.

Sadler is researching the possible applications of light communications in defence. He explains: “There is this inherent ability of light to be very confined from point A to point B, which makes it very difficult for anyone to mess with it in terms of interception. But you generally need line of sight and you need to be able to point and track.” As light beams cannot penetrate barriers, it is generally a supplementary technology that can be used in addition to radio.