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An
optical fiber (or
fibre) is a glass or plastic fiber designed to guide light along its length.
Fiber optics is the overlap of applied science and
engineering concerned with such optical fibers. Optical fibers are widely used in
fiber-optic communication, which permits transmission over longer distances and at higher data rates than other forms of wired and wireless communications. Fibers are used instead of metal wires because signals propagate along them with less loss, and they are immune to electromagnetic interference. Optical fibers are also used to form
sensors, and in a variety of other applications.
In fibers with large core diameter, the confinement is based on total internal reflection. In smaller core diameter fibers, (widely used for most communication links longer than 200
meters) the fiber acts as a
waveguide. There are many different designs of optical fibers, including
graded-index fibers, step-index profiles which are characteristics of an optical fiber and different types of optical fiber as singlemode fibers (SMF) in which there are three kinds of fibers, non-dispersion shifted fibres (NDSF), nonzero dispersion-shifted fibers (NZDSF) and dispersion-shifted fibers (DSF), multimode fibers (MMF), birefringent polarization-maintaining optical fibers (PMF) and more recently
photonic crystal fibers (PCF), with the design and the wavelength of the light propagating in the fiber dictating whether or not it will be
multi-mode optical fiber or
single-mode optical fiber. Because of the mechanical properties of the more common glass optical fibers, special methods of splicing fibers and of connecting them to other equipment are needed. Manufacture of optical fibers is based on partially melting a chemically doped preform and pulling the flowing material on a draw tower. Fibers are built into different kinds of cables depending on how they will be used.
History
The light-guiding principle behind optical fibers was first demonstrated by Jean-Daniel Colladon and Jaques Babinet in the 1840s, with Irish inventor John Tyndall offering public displays using water-fountains ten years later.{{cite book | last =Bates
| first =Regis J
| authorlink =
| coauthors =
| title =Optical Switching and Networking Handbook
| publisher =McGraw-Hill
| date =2001
| location =New York
| pages =p10
| url =
| doi =
| id = ISBN 007137356X--> Practical applications, such as close internal illumination during dentistry, appeared early in the twentieth century. Image transmission through tubes was demonstrated independently by the radio experimenter [Clarence Hansell and the television pioneer [John Logie Baird in the 1920s. The principle was first used for internal medical examinations by [Heinrich Lamm in the following decade. In 1952 physicist [Narinder Singh Kapany conducted experiments that led to the invention of optical fiber, based on Tyndall's earlier studies; 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. Development then focused on fiber bundles for image transmission. The first fiber optic semi-flexible gastroscope was patented by [Basil Hirschowitz, C. Wilbur Peters, and Lawrence E. Curtiss, researchers at the [University of Michigan, in 1956. 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. A variety of other image transmission applications soon followed.
In 1965, Charles K. Kao and George A. Hockham of the British company
Standard Telephones and Cables were the first to suggest that attenuation of contemporary fibers was caused by impurities, which could be removed, rather than fundamental physical effects such as scattering. They speculated that optical fiber could be a practical medium for communication, if the
attenuation (electromagnetic radiation) could be reduced below 20 Decibel#Optics per kilometer (Hecht, 1999, p. 114).This attenuation level was first achieved in 1970, by researchers Robert D. Maurer, Donald Keck, Peter C. Schultz, and Frank Zimar working for American glass maker Corning Glass Works, now Corning Inc. They demonstrated a fiber with 17 dB optic attenuation per kilometer by Doping (semiconductors) silica glass with titanium. A few years later they produced a fiber with only 4 db/km using germanium oxide as the core dopant. Such low attenuations ushered in optical fiber telecommunications and enabled the Internet. Nowadays, attenuations in optical cables are far less than those in electrical copper cables, leading to long-haul fiber connections with repeater distances of 500 - 800 km.
The erbium-doped fiber amplifier, which reduced the cost of long-distance fiber systems by reducing or even in many cases eliminating the need for optical-electrical-optical repeaters, was co-developed by teams led by David Payne of the
University of Southampton, and
Emmanuel Desurvire at
Bell Laboratories in 1986. The more robust optical fiber commonly used today utilizes glass for both core and sheath and is therefore less prone to aging processes. It was invented by Gerhard Bernsee in 1973 by
Schott Glass in Germany.
In 1991, the emerging field of photonic crystals led to the development of Photonic-crystal fiber (
Science (2003), vol 299, page 358), which guides light by means of diffraction from a periodic structure, rather than total internal reflection. The first photonic crystal fibers became commercially available in 1996 . Photonic crystal fibers can be designed to carry higher power than conventional fiber, and their wavelength dependent properties can be manipulated to improve their performance in certain applications.
Applications
Optical fiber communication
Optical fiber can be used as a medium for telecommunication and Computer network because it is flexible and can be bundled as cables. It is especially advantageous for long-distance communications, because light propagates through the fiber with little attenuation compared to electrical cables. This allows long distances to be spanned with few Optical communications repeater. Additionally, the light signals propagating in the fiber can be modulated at rates as high as 40 Gigabit/s