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Notice;
| In 1987 CPH claimed that
the speed of light deppends to external force and it is not
constant. Pleese see:
Definition, Principle and Explanation of CPH Theory [PDF] |
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A team of researchers
from the Ecole Polytechnique Fédérale de Lausanne (EPFL) has
successfully demonstrated, for the first time, that it is possible
to control the speed of light – both slowing it down and speeding
it up – in an optical fiber, using off-the-shelf instrumentation
in normal environmental conditions. Their results, to be published
in the August 22 issue of Applied Physics Letters, could have
implications that range from optical computing to the fiber-optic
telecommunications industry.
On the screen, a small pulse shifts back
and forth – just a little bit. But this seemingly unremarkable
phenomenon could have profound technological consequences. It
represents the success of Luc Thévenaz and his fellow
researchers in the Nanophotonics and Metrology laboratory at
EPFL in controlling the speed of light in a simple optical
fiber. They were able not only to slow light down by a factor of
three from its well – established speed c of 300 million
meters per second in a vacuum, but they've also accomplished the
considerable feat of speeding it up – making light go faster
than the speed of light.
This is not the first time that scientists
have tweaked the speed of a light signal. Even light passing
through a window or water is slowed down a fraction as it
travels through the medium. In fact, in the right conditions,
scientists have been able to slow light down to the speed of a
bicycle, or even stop it altogether. In 2003, a group from the
University of Rochester made an important advance by slowing
down a light signal in a room-temperature solid.
But all these methods depend on special media such as cold gases
or crystalline solids, and they only work at certain
well-defined wavelengths. With the publication of their new
method, the EPFL team, made up of Luc Thévenaz, Miguel Gonzaléz
Herraez and Kwang-Yong Song, has raised the bar higher still.
Their all-optical technique to slow light works in off-the-shelf
optical fibers, without requiring costly experimental set-ups or
special media. They can easily tune the speed of the light
signal, thus achieving a wide range of delays.
“This has the enormous advantage of being
a simple, inexpensive procedure that works at any wavelength,
notably at wavelengths used in telecommunications," explains
Thévenaz.
The telecommunications industry transmits
vast quantities of data via fiber optics. Light signals race
down the information superhighway at about 186,000 miles per
second. But information cannot be processed at this speed,
because with current technology light signals cannot be stored,
routed or processed without first being transformed into
electrical signals, which work much more slowly. If the light
signal could be controlled by light, it would be possible to
route and process optical data without the costly electrical
conversion, opening up the possibility of processing information
at the speed of light.
This is exactly what the EPFL team has
demonstrated. Using their Stimulated Brillouin Scattering (SBS)
method, the group was able to slow a light signal down by a factor
of 3.6, creating a sort of temporary"optical memory." They were
also able to create extreme conditions in which the light signal
travelled faster than 300 million meters a second. And even though
this seems to violate all sorts of cherished physical assumptions,
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