Wednesday, 23 April 2014
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Microscopic LEDs could speed up wireless communication

Wireless communication that uses light instead of radio signals could become even faster thanks to new research using microscopic LED lights.

A UK team of researchers led by Strathclyde University has received funding to develop a visible light communication system that transmits data via the flickering of micron-sized LEDs — and hopes to reach speeds of up to 10Gb/sec per square metre of floor area.

Such ‘Li-Fi’ technology is seen as a potentially faster and cheaper alternative to traditional wireless systems that doesn’t take up space in the radio spectrum and could be used in places radio signals aren’t allowed, such as in parts of hospitals or on board aircraft.

The team at Strathclyde, led by Prof Martin Dawson, has shown that micron-sized LEDs made from gallium nitride can transmit data even quicker than conventional white LEDs because they can flicker on and off around 1,000 times faster.

The size of the LEDs also means 1,000 can fit into the same space as a single conventional bulb — allowing bandwidth to be increased by a total factor of one million over a similar area.

‘These white LEDs have a phosphorous layer that slows down the transmission speed because it has an afterglow even when it is switched off, and that slows down the switching capability,’ said Prof Harald Haas, who is leading the Edinburgh University researchers contributing to the project.

The phosphorus layer is used to create white light. ‘So instead of one large single LED, why don’t we take many small [coloured] LEDs with small capacitance each and mix the light in a way that you produce white light and we don’t need the phosphorous layer?’ Haas told The Engineer.

Larger LEDs also have a higher capacitance in order to create a brighter light, which again slows down the speed at which you can switch them on and off. Because the smaller LEDs are dimmer, however, they can only transmit signals over a shorter distance. But using multiple LEDs sending the same signal can compensate for this.

The researchers believe that visible light communication with micro-LEDs could transmit data even faster on printed circuit boards where optical-fibre waveguides could replace copper wires, with potential speeds of 100Gb/sec per millimetre for a linear LED array and perhaps as fast as 1Tb/s per square millimetre for a 2D LED array in the long-term.

The four-year project funded by the EPSRC will see the researchers develop the technology into a practical system, but also attempt to improve its underlying operation.

‘We may discover new principles that have an impact on achieving even higher data rates with lower complexity,’ said Haas. ‘So, for example, to achieve 10Gb/sec almost zero power covering tens of metres distance.

‘That would enable almost zero-energy wireless communication systems which, for example, would be important for self-powered sensor networks as well as machine-to-machine communications.’

As well as providing an alternative to wireless internet access, visible light communication could also be used to add data transmission to traditional light sources.

For example, it could create cars that communicate with each other via their headlights, or overhead lighting in shops that updates electronic tags attached to the stock.

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The Engineer April 2014 Online


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