Monday, August 17, 2009

Optical fiber
An optical fiber (or fibre) is a glass or plastic fiber that carries light along its length. Fiber optics is the overlap of applied science and engineering concerned with the design and application of optical fibers. Specially designed fibers are used for a variety of other applications, including sensors and fiber lasers.


Single-mode fibers are used for most communication links longer than 550 metres (1,800 ft).
In 1952, physicist Narinder Singh Kapany conducted experiments that led to the invention of optical fiber. Modern optical fibers, where the glass fiber is coated with a transparent cladding to offer a more suitable refractive index, appeared later in the decade.[1]In the process of developing the gastroscope, Curtiss produced the first glass-clad fibers; previous optical fibers had relied on air or impractical oils and waxes as the low-index cladding material. Jun-ichi Nishizawa, a Japanese scientist at Tohoku University, was the first to propose the use of optical fibers for communications in 1963.[4][5] Nishizawa invented the graded-index optical fiber in 1964 as a channel for transmitting light from semiconductor lasers over long distances with low loss.[6]
In 1981, General Electric produced fused quartz ingots that could be drawn into fiber optic strands 25 miles (40 km) long.[8]
Attenuations in modern optical cables are far less than those in electrical copper cables, leading to long-haul fiber connections with repeater distances of 70–150 kilometres (43–93 mi). The first photonic crystal fibers became commercially available in 2000.[11]

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