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World’s Longest Laser Invented

Photonics.com
Feb 2006
BIRMINGHAM, England, Feb. 24, 2006 -- Researchers at Aston University in Birmingham, England, claim to have invented the world’s longest laser, which they transformed from an optical fiber 75 kilometers (about 47 miles) long. The team hopes the laser will improve long-distance transmissions across the world.

"The new laser is special because it can transmit light signals over such a long distance without any loss of power, so the signal that is being sent barely deteriorates," the university said in a statement.

When normal telephone conversations or data sent over the Internet are converted to light in order to travel through standard optical fibers, the signals lose around 5 percent of their power for every kilometer or mile they travel. The signals then have to be amplified to ensure that they reach their destination. But any time the signals get amplified, the background noise gets amplified too, until it gets so high the signals can no longer be understood.

Juan Diego Ania Castanon and his colleagues at Aston have used a process called the Raman effect -- a natural phenomenon that affects light passing through a material -- to transform a long optical fiber into an ultralong laser. Lasers inject light at each end, which makes some of the fiber’s atoms give out more energy and emit photons (particles of light) of a longer wavelength. These photons are reflected back into the fiber by special mirrors at each end of the optical link. The fiber then stores a stable, uniform amount of laser light that travels with the signals and strengthens them, enabling them to move across the fiber at full power without suffering any loss, thus removing the need to amplify the signals.

"The discovery is tremendously exciting, not only in the world of science, but in the world of telecommunications," said Ania-Castanon. "Lossless transmission of data has always been a dream goal in the world of communications. The development of a simple method to implement nearly ideal links between receiver and sender paves the way to important advances in long-distance telecommunications and opens exciting possibilities for research in other fields."

For more information, visit: www.aston.ac.uk



GLOSSARY
optical fiber
A thin filament of drawn or extruded glass or plastic having a central core and a cladding of lower index material to promote total internal reflection (TIR). It may be used singly to transmit pulsed optical signals (communications fiber) or in bundles to transmit light or images.  
raman effect
When light is transmitted through matter, part of the light is scattered in random directions. A small part of the scattered light has frequencies removed from the frequency of the incident beam by quantities equal to vibration frequencies of the material scattering system. This small part is called Raman scattering. If the initial beam is sufficiently intense and monochromatic, a threshold can be reached beyond which light at the Raman frequencies is amplified, builds up strongly, and...
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