New twist on encryption

A method of encrypting information in beams of light will provide complete protection against eavesdroppers and provide a massive increase in bandwidth for optical communication, according to researchers in Scotland.

Existing optical communication devices, Free-Space Optical (FSO) transmitters and decoders transmit data using the Spinning Angular Momentum (SAM) of single photons – the way individual particles spin on their own axes.

But the new system is the first to use both the SAM and Orbital Angular Momentum (OAM) of light particles – the way each particle, or photon, rotates around the beam’s axis – to encrypt and decode.

By encrypting data in the OAM, the transmitter effectively forms ‘twists’ of light. To decode the encryption, eavesdroppers would have to intercept the entire beam of light, and then ‘untwist’ it.

The device is the result of a collaboration between Glasgow and Strathclyde universities, who have created a prototype.

‘Because the full beam has to be decoded in its entirety, it would be virtually impossible to read the information from scattered light alone,’ said Glasgow’s Dr. Graham Gibson.

‘In other words, it wouldn’t mean anything if you only eavesdropped on a scattered segment. It needs to be all or nothing,’ said Gibson.

Measuring OAM yields much more data on the movement of photons, and so allows each particle to carry much more information.

Scientists have studied the OAM of photons for a decade, but this is the first device able to utilise this property of light to transmit coded information.

The researchers hope the breakthrough can be used in conjunction with other developments in quantum cryptography, such as Toshiba’s research into ‘uncrackable’ transmissions using the single photon method.

‘We believe [the Toshiba] single photon source can complement our technology, where information is encoded using different OAM states,’ said Gibson.

The prototype is on display at Glasgow University to generate feedback from businesses. The collaboration cost £200,000 and was funded by Scottish Enterprise’s Proof of Concepts allowance.