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Twisted Light Encryption

Or "Free Space Information Transfer Using Light Beams Carrying Orbital Angular Momentum" (see Gibson et al.)

Introduction

Researchers in optical communications in Glasgow (and some colleagues in Kiev) have recently proposed a new way to send information through space via laser beams. By using filters to twist the light, or more technically, to "change its angular momentum," and using the degrees and directions of twist as an "alphabet," in the way that binary digital communications use 1's and 0's, information can be transferred in the laser beam. Moreover, though the light beam is sent through open air, or even the vacuum of space, it is inherently encrypted, say the researchers, because an unintended observer would be at a point in space from which the beam is distorted relative to the intended receiver, and the states of angular momentum that the sender and receiver use to communicate would be effectively hidden.

Background

Gibson, Graham Johannes Courtial, and Miles J. Padgett, University of Glasgow; Mikhail Vasnetsov and Valeriy Pasko, Institute of Physics; Stephen M. Barnett and Sonja Franke-Arnold, University of Strathclyde. Free-space information transfer using light beams carrying orbital angular momentum. Optics Express. Vol 12, 5448-5456 (2004).
full text

See also: http://www.exn.ca/news/video/exn2004/11/02/exn20041102-optics.asx (Discovery Channel segment)

In normal light beams, or even lasers, photons move straight ahead. Information can be sent with light beams in typical binary fashion, either the light is on or off. This is essentially what happens in fiber-optic cables, or buidling to builing open-air laser transmission or "Free Space Optics" (FSO) - a small but growing market that hopes to become a rival to current wireless systems in downtowns, universities and industrial parks across the world. What Gibson, Courtial, Paglett and company have done in Glasgow is introduce filters that change the light's angular momentum, causing individual photons to move in distinct orbital paths through the beam as it moves forward. They have used 8 distinct filters, producing a base-8 "alphabet," which obviously can pack in more data than the simple on vs. off of a binary system. Moreover, an observer who isn't at the correct angle and correct distance to the sender will not see the same changes in angular momentum, or same intensities of those changes, as the intended receiver, creating a supposedly inherently secure system (as far as the signal in the air goes, in any case - any system is only as strong as its weakest point, ergo the point here is not ncesssarily to create an unhackable system, but an open-air system that is more secure than 802.xx).

Source: Gibson et al.
An overview of the Glasgow team's system, including a CCD image of the twisting effects on the light beam.

Current State

The Glasgow team's study was just that, so their system isn't ready for prime time. However, their efforts seem faily easy to reproduce given a few computers, a HeNe laser and the transmission/reception devices the team put together with telescopes, cameras (typical FSO equipment) and their light-bending filters.

Forecast

According to FreeSpaceOptics.org, which may be a little biased, futurists and investment capital types predict huge growth in the FSO market in the next two years. Given, lasers are pretty inefficient machines from a power-in/power-out standpoint, so putting one on every other rooftop in your downtown area could be a little bit of a drag. The cost of power, though, probably pales in comparison to digging up the ground to bury cables, or dealing with radio spectrum issues with current wireless technology. If someone can get a system like this on the shelves, they could stand to capture a good part of a growing niche market.