Crystal fiber goes distance
By
Eric Smalley,
Technology Research NewsTelecommunications 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
Funding: Corporate
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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November 5/12, 2003
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