At 1:51 PM 10/31/96, Michael Dillon wrote:
>I saw thsi in a USENET newsgroup. Any basis in fact?
>
>> I thought I read somewhere that someone had come up with a way to
>> "read" data going over a fiber link, by interference with a second laser
>> "perpendicular" to the fiber - does this ring any bells out there?
Well, it has been done...but with less than wonderful success. If you're
talking about conducting a covert intercept, good luck. First the cabling
and kevlar strain relief material that is extruded on most of these cables,
and the fiber outer jacket has to be removed without introducing microbends
in the glass cladding that surrounds the fiber core. Microbends are
submicron cracks in the sidewalls of the cladding around the core that
allows light to escape. Depending on the sensitivity of the receivers just
the loss of one comma's worth of light is enough to drop the db's below the
alarm threshold. Assuming that you can successfully beat that issue a
light source, usually a laser, operating at a close but differing
wavelength can be applied in such a manner as to "read" the modulated
lighwave in the core and "pull" a bitstream containing some data. But then
another problem arises. How to keep that laser from introducing additional
photonic energy into the fiber core without creating pseudo-random noise in
photo-detectors (receivers) on either end, thereby trashing the very signal
you're trying to capture? And it gets alot more complicated than that but
should do for now.
Can it be done? Theoretically yes. Given enough time, money and resoures
you can defeat most anything. But from a practical standpoint it's not a
useful exercise. For ten over ten years I was in the business of building
and installing secure optical fiber communication systems for the Defense
Department and I know of no system that has ever been successfully entered.
___________________________
Bob McKisson
Cypress Systems Corporation
P. O. Box 809
Virginia Beach, VA 23451
(757) 425-4195 Voice
(757) 425-4196 FAX
pelicans @
mindspring .
com
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