Crystal fiber goes distance
Technology Research News
Telecommunications is all about sending
pulses of light quickly and efficiently.
Research efforts aimed at reducing the power needed to send light
signals over long stretches of optical fiber focused on making fiber lines
from photonic crystal, an artificial, patterned structure consisting of
a mix of materials or a material and air. Photonic crystal fiber is usually
constructed by forming patterns of holes along the length of a fiber.
The challenge is making photonic crystal fiber structures that
are consistent enough to efficiently channel light over useful distances.
Researchers from Corning Inc. have constructed photonic crystal
fiber that promises to carry light signals more efficiently than the fiber
lines in current use, and could prove cheaper as well.
The material could eventually be used in efficient telecommunications
lines, guides for high-power laser beams, and very sensitive light detectors,
said Karl Koch, a manager and project leader at Corning.
Photonic crystals work on the principle of refraction, or the
bending of light as it passes from one material to another. Refraction,
which is responsible for the bent drinking straw illusion, can be used
to block specific wavelengths of light.
The researchers' photonic crystal fiber keeps light confined to
a hollow core that is about five times narrower than a human hair. "The
fiber cross-section is an air core of about 15 microns in diameter surrounded
by a web-like structure of glass and air," said Koch. A micron is one
thousandth of a millimeter.
In contrast, today's fiber lines are made from solid glass or
plastic surrounded by a reflective coating. Researchers are developing
hollow fibers because light travels through air or a vacuum more efficiently
than through glass or plastic.
Light travels through the core of the Corning researchers' material
just as it travels through the middle of hollow fiber-optic lines. But
photonic crystal is better than a reflective coating at keeping light
from scattering or being absorbed, which keeps signals stronger over longer
distances, according to Koch.
The trick to producing the more efficient fiber is keeping the
holey structure consistent throughout the length of the fiber, said Koch.
The researchers' prototype is 100 meters long.
The researchers' prototype is 100 times more efficient at carrying
the 1,500-nanometer-wavelength light widely used in telecommunications
than previous photonic crystal prototypes, said Koch. "We have demonstrated
a 100 times improvement in the loss rate from roughly 1,000 decibels per
kilometer to 13 decibels per kilometer," he said.
Decibels per kilometer is a measure of the weakening of a signal
over distance. Existing commercial fibers range from about 0.5 to 3.5
decibels per kilometer. The researchers are ultimately aiming to reduce
losses to below 0.2 decibels per kilometer, according to Koch.
The researchers are also working to ensure that the photonic crystal
fiber does not effect light signal properties like polarization.
Electromagnetic energy like light consists of an electric field
and a magnetic field. The electric field of unpolarized light vibrates
in all directions in a plane perpendicular to the light wave. The electric
field of polarized light, however, vibrates in only one direction. Polarization
is used to filter light signals, represent data in quantum communications,
and make measurements in scientific experiments.
The material costs of the new fiber are cheaper than those of
existing fiber lines, according to Koch. The cost of manufacturing the
new fiber could prove higher however, he added.
The fiber could be ready for practical use for short-haul applications
within two years; it will be more than five years before the technology
will be ready for long-haul, low-loss applications, said Koch.
Koch's research colleagues were Charlene M. Smith, Natesan Venkataraman,
Michael T. Gallagher, Dirk Müller, James A. West, Nicholas F. Borrelli
and Douglas C. Allan. The work appeared in the August 7, 2003 issue of
Nature. The research was funded by Corning.
Timeline: 2 years, > 5 years
TRN Categories: Optical Computing, Optoelectronics and Photonics;Telecommunications
Story Type: News
Related Elements: Technical paper, "Low-Loss, Hollow-Core
Silica/Air Photonic Bandgap Fibre," Nature, August 7, 2003.
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