Optical Fiber

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fibras optiocas

Transcript of Optical Fiber

  • Optical fiber

    A bundle of optical fibers

    Stealth Fiber Crew installing a 432-count fiber cable underneaththe streets of Midtown Manhattan, New York City

    An optical fiber (or optical fibre) is a flexible, trans-parent fiber made of extruded glass (silica) or plastic,slightly thicker than a human hair. It can function as awaveguide, or light pipe,[1] to transmit light between thetwo ends of the fiber.[2] The field of applied science and

    A TOSLINK fiber optic audio cable with red light being shone inone end transmits the light to the other end

    A wall-mount cabinet containing optical fiber interconnects. Theyellow cables are single mode fibers; the orange and aqua cablesare multi-mode fibers: 50/125 m OM2 and 50/125 m OM3fibers respectively.

    engineering concerned with the design and application ofoptical fibers is known as fiber optics.Optical fibers are widely used in fiber-optic communi-cations, where they permit transmission over longer dis-tances and at higher bandwidths (data rates) than wire ca-bles. Fibers are used instead of metal wires because sig-nals travel along them with less loss and are also immune



  • 2 1 HISTORY

    to electromagnetic interference. Fibers are also used forillumination, and are wrapped in bundles so that they maybe used to carry images, thus allowing viewing in confinedspaces. Specially designed fibers are used for a variety ofother applications, including sensors and fiber lasers.Optical fibers typically include a transparent core sur-rounded by a transparent cladding material with a lowerindex of refraction. Light is kept in the core by total inter-nal reflection. This causes the fiber to act as a waveguide.Fibers that support many propagation paths or transversemodes are called multi-mode fibers (MMF), while thosethat only support a single mode are called single-modefibers (SMF). Multi-mode fibers generally have a widercore diameter, and are used for short-distance communi-cation links and for applications where high power mustbe transmitted. Single-mode fibers are used for mostcommunication links longer than 1,000 meters (3,300 ft).Joining lengths of optical fiber is more complex than join-ing electrical wire or cable. The ends of the fibers must becarefully cleaved, and then carefully spliced together withthe cores perfectly aligned. A mechanical splice holdsthe ends of the fibers together mechanically, while fusionsplicing uses heat to fuse the ends of the fibers together.Special optical fiber connectors for temporary or semi-permanent connections are also available.

    1 History

    Guiding of light by refraction, the principle that makesfiber optics possible, was first demonstrated by DanielColladon and Jacques Babinet in Paris in the early 1840s.John Tyndall included a demonstration of it in his publiclectures in London, 12 years later.[3] Tyndall also wroteabout the property of total internal reflection in an intro-ductory book about the nature of light in 1870:

    When the light passes from air into wa-ter, the refracted ray is bent towards theperpendicular... When the ray passes from wa-ter to air it is bent from the perpendicular... Ifthe angle which the ray in water encloses withthe perpendicular to the surface be greater than48 degrees, the ray will not quit the water atall: it will be totally reflected at the surface....The angle which marks the limit where totalreflection begins is called the limiting angle ofthe medium. For water this angle is 4827', forflint glass it is 3841', while for diamond it is2342'.[4][5]

    Unpigmented human hairs have also been shown to act asan optical fiber.[6]

    Practical applications, such as close internal illuminationduring dentistry, appeared early in the twentieth century.Image transmission through tubes was demonstrated in-dependently by the radio experimenter Clarence Hansell

    Daniel Colladon first described this light fountain or light pipein an 1842 article titled On the reflections of a ray of light insidea parabolic liquid stream. This particular illustration comes froma later article by Colladon, in 1884.

    and the television pioneer John Logie Baird in the 1920s.The principle was first used for internal medical examina-tions by Heinrich Lamm in the following decade. Mod-ern optical fibers, where the glass fiber is coated with atransparent cladding to offer a more suitable refractiveindex, appeared later in the decade.[3] Development thenfocused on fiber bundles for image transmission. HaroldHopkins and Narinder Singh Kapany at Imperial Collegein London achieved low-loss light transmission througha 75 cm long bundle which combined several thousandfibers. Their article titled A flexible fibrescope, usingstatic scanning was published in the journal Nature in1954.[7][8] The first fiber optic semi-flexible gastroscopewas patented by Basil Hirschowitz, C. Wilbur Peters,and Lawrence E. Curtiss, researchers at the Universityof Michigan, in 1956. In the process of developing thegastroscope, Curtiss produced the first glass-clad fibers;previous optical fibers had relied on air or impractical oilsand waxes as the low-index cladding material.A variety of other image transmission applications soonfollowed.In 1880 Alexander Graham Bell and Sumner Tainter in-vented the Photophone at the Volta Laboratory in Wash-


  • 3

    ington, D.C., to transmit voice signals over an opticalbeam.[9] It was an advanced form of telecommunications,but subject to atmospheric interferences and impracticaluntil the secure transport of light that would be offeredby fiber-optical systems. In the late 19th and early 20thcenturies, light was guided through bent glass rods to illu-minate body cavities.[10] Jun-ichi Nishizawa, a Japanesescientist at Tohoku University, also proposed the useof optical fibers for communications in 1963, as statedin his book published in 2004 in India.[11] Nishizawainvented other technologies that contributed to the de-velopment of optical fiber communications, such as thegraded-index optical fiber as a channel for transmittinglight from semiconductor lasers.[12][13] The first workingfiber-optical data transmission system was demonstratedby German physicist Manfred Brner at Telefunken Re-search Labs in Ulm in 1965, which was followed by thefirst patent application for this technology in 1966.[14][15]Charles K. Kao and George A. Hockham of the Britishcompany Standard Telephones and Cables (STC) werethe first to promote the idea that the attenuation in opti-cal fibers could be reduced below 20 decibels per kilo-meter (dB/km), making fibers a practical communica-tion medium.[16] They proposed that the attenuation infibers available at the time was caused by impurities thatcould be removed, rather than by fundamental physicaleffects such as scattering. They correctly and systemati-cally theorized the light-loss properties for optical fiber,and pointed out the right m