Hiding in the noise and chaos

[InfoSec News <isn () c4i org>]

http://www.eurekalert.org/pub_releases/2002-08/oonr-hit081202.php

[Raw press releases are rare for ISN, unless its something really 
interesting, like this one.  - WK]


Public release date: 12-Aug-2002

Contact: Gail S. Cleere
cleereg () onr navy mil
703-696-4987
Office of Naval Research 

Communicating with light polarization

A new and novel way of communicating over fiber optics is being
developed by physicists supported by the Office of Naval Research.  
Rather than using the amplitude and frequency of electromagnetic
waves, they're using the polarization of the wave to carry the signal.  
Such a method offers a novel and elegant method of secure
communication over fiber optic lines.

Electromagnetic waves, like light and radio waves, have amplitude
(wave height), frequency (how often the wave crests each second), and
polarization (the plane in which the wave moves). Changes in amplitude
and frequency have long been used to carry information (AM radio uses
changes in the amplitude of radio waves; FM radio uses changes in
their frequency), but polarization has not been so thoroughly
explored.

ONR-supported physicists Gregory VanWiggeren (Georgia Tech) and
Rajarshi Roy (University of Maryland) have demonstrated an ingenious
method to communicate through fiber optics by using dynamically
fluctuating states of light polarization. Unlike previous methods, the
state of the light's polarization is not directly used to encode data.  
Instead the message (encoded as binary data of the sort used by
digital systems) modulates a special kind of laser light. Van Wiggeren
and Roy used an erbium-doped fiber ring laser. The erbium amplifies
the optical signal, and the ring laser transmits the message. In a
ring laser the coherent laser light moves in a ring-shaped path, but
the light can also be split from the ring to be transmitted through a
fiber optic cable.

The nonlinearities of the optic fiber produce dynamical chaotic
variations in the polarization, and the signal is input as a
modulation of this naturally occurring chaos. The signal can be kept
small relative to the background light amplitude. The light beam is
then split, with part of it going through a communications channel to
a receiver. The receiver breaks the transmitted signal into two parts.  
One of these is delayed by about 239 nanoseconds, the time it takes
the signal to circulate once around the ring laser. The light received
directly is compared, by measuring polarizations, to the time delayed
light. Then the chaotic variations are subtracted, which leaves only
the signal behind. Variations in stress and temperature on the
communications would be equally subtracted out.

"This is quite a clever method, which hides the signal in noise," says
ONR science officer Mike Shlesinger, who oversees the research. "It
provides a definite advantage over direct encoding of polarization,
leaving an eavesdropper only chaotic static, and no means to extract
the signal."

###

For more information on the technology, or to interview Mike
Shlesinger and his researchers, please contact John Petrik or Gail
Cleere at 703-696-5031, or email petrikj () onr navy mil or
cleereg () onr navy mil



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