Radio signals powered by light

A device that turns light in an optical fibre directly into radio signals could slash the cost of both wireless communication and broadband internet networks.

Developed by Microwave Photonics, it allows antennas to be fed from the light in an optical fibre without the need for electricity, by converting the light into radio signals. And the device also produces lower emissions of radiation than existing technology, easing safety fears.

Existing radio base stations need powerful amplifiers and electronics close to the antenna with mains power or batteries to broadcast and receive signals. But ‘Green Radio’ technology converts fibre optic light into signals to broadcast, then converts the signals back into light for two-way communications, said Peter Smyth, chief technology officer for Microwave Photonics.

The device, known as an optical wireless gateway, can be used in existing mobile communications and 3G networks, as well as wireless LANs and broadband internet, he said.

The signal-processing electronics needed can be up to 30km away from the antenna, meaning hundreds or even thousands of antennas could be connected across a city, with all the electronics on one site, said Smyth. ‘And because you are sending light down a fibre and turning it into a radio signal, you do not have to change anything in the base station to go from 2G to 3G, you simply alter a card in the central building.’ Light travels down an optical fibre until it reaches the gateway, or electro-optic absorption modulator. This turns the photons into an electric current, which is converted into a radio signal by the antenna. When it picks up phone signals, it changes the radio waves back into an electric current.

Each antenna would typically cover around 100m, which could be extended to around 500m by installing a cheap amplifier. Because of this small coverage area the devices also give off lower emissions, said Smyth.

The technology could also cut the cost of broadband internet, as the optical fibre cabling required would only need to be installed as far as each street, rather than into individual houses. ‘It would be a much cheaper way of rolling out broadband communications. Putting optical fibres into homes is extremely expensive, whereas this device would allow the fibre to be installed as far as the kerb, and the technology would take the signal the last 100m,’ he said.

The base stations can be sited in areas with no power, and no longer need costly housing to protect the expensive electronics equipment. ‘If you put all the processing power into one central hotel, it also means you can buy one big computer rather than lots of little ones, which is cheaper. A technician could be located at the site permanently to replace things when they go wrong, rather than having to go out to the individual base stations.’

Microwave Photonics is based within Brightstar, BTexact Technologies’ incubator, and is hoping to attract capital to help sell the technology to network operators.