Secure and covert communication by light

June 2004 IT infrastructure

An advance in the science of quantum optics by collaborating teams from the universities of Glasgow and Strathclyde will offer new encryption possibilities for security agencies that will limit eavesdropping and offer sophisticated covert communication techniques. The group is also investigating a related ability to increase the amount of information that can be carried by beams of light.

Collaborating under a strategic alliance between the two universities - known as the Synergy Programme - and with projects funded through the Scottish Enterprise's Proof of Concept Fund and the Engineering & Physical Sciences Research Council, the teams' approach uses a strange property of light called orbital angular momentum.

Photons - single particles of light - have long been known to spin but they can also twist. This movement is known as their orbital angular momentum (OAM). Light beams carrying this OAM can be transmitted to receivers where the information can then be decoded - the 'twists' need to be untwisted to decipher the full message.

A useful feature of the team's new method is that it can more effectively reveal when any attempt has been made to intercept the message because such eavesdropping activity would 'break' the beam. Steve Barnett from Strathclyde University says, "Sometimes it can be just as important to know if someone is trying to listen to your communications, so an effective method to detect intervention would be important to security agencies."

Miles Padgett, of Glasgow University, adds, "Because the full beam has to be decoded in its entirety, it would be virtually impossible to read the information from scattered light alone. In other words, it would not mean anything if you only 'eavesdropped' into a scattered segment of it. It needs to be all or nothing."

The practical application of the theory is being put to the test at Glasgow with a demonstrator unit designed by Dr Graham Gibson of the collaborative optics team.

He explains, "I envisage that the ongoing development of this system will be very much guided by the feedback that we will get from potential market sectors, particularly the security sector. We need to identify what matters most to them and maximise the technology's capabilities in these key areas."

The demonstrator unit has already proved an associated feature of orbital angular momentum - the ability to increase the communication bandwidth of free space optics systems. It is now allowing the related security features to be developed and evaluated.

For more information contact Don Whiteford, University of Glasgow, 0944 141 330 2728,,

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