An optical fiber (or fibre) is a glass or plastic fiber that carries light along its length. Glass in the common sense refers to a Hard, Brittle, transparent Solid, such as that used for Windows many Plastic is the general common term for a wide range of synthetic or semisynthetic organic solid materials suitable for the manufacture of industrial products Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700 Fiber optics is the overlap of applied science and engineering concerned with the design and application of optical fibers. For the song by 311, see Grassroots. Applied science is the application of knowledge from one or more natural scientific Engineering is the Discipline and Profession of applying technical and scientific Knowledge and Optical fibers are widely used in fiber-optic communication, which permits transmission over longer distances and at higher data rates than other forms of communications. Fiber-optic communication is a method of transmitting information from one place to another by sending Light through an Optical fiber. Fibers are used instead of metal wires because signals travel along them with less loss, and they are immune to electromagnetic interference. In Physics, attenuation (in some context also called extinction) is the gradual loss in intensity of any kind of Flux through a medium Optical fibers are also used to form sensors, and in a variety of other applications. A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument

Light is kept in the "core" of the optical fiber by total internal reflection. This causes the fiber to act as a waveguide. An optical waveguide is a physical structure that guides electromagnetic waves in the optical spectrum Fibers which support many propagation paths or transverse modes are called multimode fibers (MMF). Multi-mode optical fiber ( multimode fiber or MM fiber or fibre) is a type of Optical fiber mostly used for communication over shorter distances Fibers which support only a single mode are called singlemode fibers (SMF). In Fiber-optic communication, a single-mode optical fiber ( SMF) is an Optical fiber designed to carry only a single ray of light (mode Multimode fibers generally have a large-diameter core, and are used for short-distance communication links or for applications where high power must be transmitted. Singlemode fibers are used for most communication links longer than 200 meters.

Joining lengths of optical fiber is more complex than joining electrical wire or cable. The ends of the fibers must be carefully cleaved, and then spliced together either mechanically or by fusing them together with an electric arc. A cleave in an Optical fiber is a deliberate controlled break intended to create a perfectly flat endface perpendicular to the longitudinal axis of the fiber A mechanical splice is a junction of two or more Optical fibers that are aligned and held in place by a self-contained assembly (usually the size of a large carpenter's nail Fusion splicing is the act of joining two Optical fibers end-to-end using heat An electric arc is an Electrical breakdown of a gas which produces an ongoing plasma discharge, resulting from a current flowing through normally nonconductive Special connectors are used to make removable connections. An optical fiber connector terminates the end of an Optical fiber, and enables quicker connection and disconnection than splicing.

Contents 1 History 2 Applications 2.1 Optical fiber communication 2.2 Fiber optic sensors 2.3 Other uses of optical fibers 3 Principle of operation 3.1 Multimode fiber 3.2 Singlemode fiber 3.3 Special-purpose fiber 4 Manufacturing 4.1 Materials 4.2 Process 5 Practical issues 5.1 Optical fiber cables 5.2 Termination and splicing 5.3 Free-space coupling 5.4 Fiber fuse 6 See also 7 Notes 8 References 9 External links

History

Guiding of light by refraction, the principle that makes fiber optics possible, was first demonstrated by Daniel Colladon and Jacques Babinet in Paris in the 1840s, with Irish inventor John Tyndall offering public displays using water-fountains ten years later. Jean-Daniel Colladon (born on 15 December 1802 in Geneva and died on 30 June 1893) was a Swiss physicist Jacques Babinet ( March 5 1794 in Lusignan France &ndash October 21 1872 in Paris France) was a French physicist John Tyndall FRS ( August 2, 1820 &ndash December 4, 1893) was a prominent 19th century Irish Physicist. ^[1] 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. Clarence Weston Hansell was an American research Engineer who pioneered investigation into the biological effects of Ionized air John Logie Baird (August 13 1888 – June 14 1946 was a Scottish engineer and inventor of the world's first working television system 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. Narinder Singh Kapany is widely acknowledged as the father of Optical fiber. The refractive index (or index of Refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves is reduced inside the medium ^[1] Development then focused on fiber bundles for image transmission. The first fiber optic semi-flexible gastroscope was patented by Basil Hirschowitz, C. Basil Isaac Hirschowitz is an academic gastroenterologist from the University of Alabama at Birmingham (UAB best known in the field for having invented an improved Optical Wilbur Peters, and Lawrence E. Curtiss, researchers at the University of Michigan, in 1956. The University of Michigan Ann Arbor ( U of M, U-M, UM or simply Michigan) is a top-ranked Coeducational public research 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. The advent of ultrapure silicon for semiconductor devices made low-loss silica fiber practical.

In 1965, Charles K. Kao and George A. Charles Kuen Kao (高錕 Pinyin: Gāo Kūn born November 4, 1933) is a pioneer in the use of fiber optics in Telecommunications. 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. Standard Telephones and Cables Ltd (later STC plc) was a British Telephone, Telegraph, Radio, Telecommunications and related They speculated that optical fiber could be a practical medium for communication, if the attenuation could be reduced below 20 dB per kilometer. In Physics, attenuation (in some context also called extinction) is the gradual loss in intensity of any kind of Flux through a medium The decibel ( dB) is a logarithmic unit of measurement that expresses the magnitude of a physical quantity (usually power or intensity relative to ^[2] 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 silica glass with titanium. Dr Robert D Maurer (July 20 1924 -) is an American industrial Physicist noted for his leadership in the invention of Optical fiber. Peter C Schultz, PhD (born 3 December 1942) is co-inventor of the Fiber optics now used worldwide for telecommunications Corning Incorporated ( is an American manufacturer of Glass, Ceramics and related materials primarily for industrial and scientific applications In Semiconductor production doping is the process of intentionally introducing impurities into an extremely pure (also referred to as intrinsic) semiconductor to Fused quartz and fused silica are types of Glass containing primarily Silica in amorphous (non- Crystalline form Titanium (taɪˈteɪniəm is a Chemical element with the symbol Ti and Atomic number 22 A few years later they produced a fiber with only 4 dB/km using germanium oxide as the core dopant. Germanium dioxide, also called germanium oxide and germania, is an Inorganic compound, an Oxide of Germanium. 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. An optical amplifier is a device that amplifies an Optical signal directly without the need to first convert it to an electrical signal David Payne is the name of David L Payne (1836-1884 US soldier and pioneer "Father of Oklahoma" David N The University of Southampton is a university situated in the city of Southampton, on the south coast of England. Bell Laboratories (also known as Bell Labs and formerly known as AT&T Bell Laboratories and Bell Telephone Laboratories) is the Research organization 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. SCHOTT AG is a manufacturer of high-quality industrial Glass products such as fiber-optics and components used in Flat panel displays Schott [1]

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. Photonic crystals are periodic Optical (nanostructures that are designed to affect the motion of Photons in a similar way that periodicity of a Semiconductor Photonic-crystal fiber (PCF is a new class of Optical fiber based on the properties of Photonic crystals Because of its ability to confine light in hollow cores or The first photonic crystal fibers became commercially available in 1996. [2] 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

Main article: Fiber-optic communication

Optical fiber can be used as a medium for telecommunication and networking because it is flexible and can be bundled as cables. Fiber-optic communication is a method of transmitting information from one place to another by sending Light through an Optical fiber. A computer network is a group of interconnected Computers. Networks may be classified according to a wide variety of characteristics 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 repeaters. An optical communications repeater is used in a Fiber-optic communications system to regenerate an optical signal by converting it to an electrical signal processing that electrical Additionally, the light signals propagating in the fiber can be modulated at rates as high as 40 Gb/s ^[3], and each fiber can carry many independent channels, each by a different wavelength of light (wavelength-division multiplexing). A gigabit is a unit of information or computer storage abbreviated Gbit (or Gb) In Fiber-optic communications wavelength-division multiplexing ( WDM) is a technology which multiplexes multiple optical carrier signals on a Over short distances, such as networking within a building, fiber saves space in cable ducts because a single fiber can carry much more data than a single electrical cable. Fiber is also immune to electrical interference, which prevents cross-talk between signals in different cables and pickup of environmental noise. Also, wiretapping is more difficult compared to electrical connections, and there are concentric dual core fibers that are said to be tap-proof. Wiretap redirects here For the radio program see WireTap (radio program Telephone tapping (or wire tapping / wiretapping in Because they are non-electrical, fiber cables can bridge very high electrical potential differences and can be used in environments where explosive fumes are present, without danger of ignition.

Although fibers can be made out of transparent plastic, glass, or a combination of the two, the fibers used in long-distance telecommunications applications are always glass, because of the lower optical attenuation. Plastic optical fiber (POF (or fibre) is an Optical fiber which is made out of Plastic. Silica fiber or silicic acid fibres are produced from sodium silicate fibers in a dry spinning method the sodium silicate fibres are free of non-alkali metal compounds and have a mole In Telecommunications and Fiber optics, a plastic-clad silica fiber or polymer-clad silica fiber (PCS is an Optical fiber that has a Silica In Physics, attenuation (in some context also called extinction) is the gradual loss in intensity of any kind of Flux through a medium Both multi-mode and single-mode fibers are used in communications, with multi-mode fiber used mostly for short distances (up to 500 m), and single-mode fiber used for longer distance links. Because of the tighter tolerances required to couple light into and between single-mode fibers (core diameter about 10 micrometers), single-mode transmitters, receivers, amplifiers and other components are generally more expensive than multi-mode components.

Fiber optic sensors

Optical fibers can be used as sensors to measure strain, temperature, pressure and other parameters. The small size and the fact that no electrical power is needed at the remote location gives the fiber optic sensor an advantage over a conventional electrical sensor in certain applications.

Optical fibers are used as hydrophones for seismic or SONAR applications. A hydrophone (Greek "hydro" = "water" and "phone" = "sound" is a Microphone designed to be used underwater for recording or listening Sonar (which started as an Acronym for sound navigation and ranging) is a technique that uses Sound propagation (usually underwater to navigate Hydrophone systems with more than 100 sensors per fiber cable have been developed. Hydrophone sensor systems are used by the oil industry as well as a few countries' navies. Both bottom mounted hydrophone arrays and towed streamer systems are in use. The German company Sennheiser developed a microphone working with a laser and optical fibers^[4]. Sennheiser electronic GmbH & Co KG is a private German company that makes Microphones Headphones Telephony accessories and Avionics A laser microphone is a Surveillance device that uses a Laser beam to detect Sound Vibrations in a distant object A laser is a device that emits Light ( Electromagnetic radiation) through a process called Stimulated emission.

Optical fiber sensors for temperature and pressure have been developed for downhole measurement in oil wells. The fiber optic sensor is well suited for this environment as it is functioning at temperatures too high for semiconductor sensors (Distributed Temperature Sensing). Distributed temperature sensing systems ( DTS) are Optoelectronic devices which measure temperatures by means of Optical fibres functioning as linear

Another use of the optical fiber as a sensor is the optical gyroscope which is in use in the Boeing 767 and in some car models (for navigation purposes) and the use in Hydrogen microsensors. A fibre optic gyroscope (FOG is a Gyroscope that uses the Interference of light to detect mechanical rotation WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout A hydrogen microsensor is a Gas detector that detects the presence of Hydrogen.

Fiber-optic sensors have been developed to measure co-located temperature and strain simultaneously with very high accuracy^[5]. This is particularly useful when acquiring information from small complex structures.

Other uses of optical fibers

Fibers are widely used in illumination applications. They are used as light guides in medical and other applications where bright light needs to be shone on a target without a clear line-of-sight path. In some buildings, optical fibers are used to route sunlight from the roof to other parts of the building (see non-imaging optics). Non-imaging optics is the branch of Optics concerned with the optimal transfer of Light radiation between a source and a target Optical fiber illumination is also used for decorative applications, including signs, art, and artificial Christmas trees. Commercial signage identifies a business or similar entity assists in Wayfinding and attracts customers Art refers to a diverse range of Human activities creations and expressions that are appealing to the Senses or Emotions of a human individual A Christmas tree, Yule tree, holiday tree or Tannenbaum (fir tree is one of the most popular Traditions associated with the celebration Swarovski boutiques use optical fibers to illuminate their crystal showcases from many different angles while only employing one light source. Swarovski is the luxury Brand name for the range of precision-cut Lead crystal Glass and related products produced by companies owned by Optical fiber is an intrinsic part of the light-transmitting concrete building product, LiTraCon. LiTraCon ("light transmitting concrete" is a Translucent Concrete building material

Optical fiber is also used in imaging optics. A coherent bundle of fibers is used, sometimes along with lenses, for a long, thin imaging device called an endoscope, which is used to view objects through a small hole. Medical endoscopes are used for minimally invasive exploratory or surgical procedures (endoscopy). Endoscopy means looking inside and typically refers to looking inside the body for medical reasons using an instrument called an endoscope. Industrial endoscopes (see fiberscope or borescope) are used for inspecting anything hard to reach, such as jet engine interiors. A fiberscope is a flexible Fiber optic bundle with an eyepiece at one end and a lens at the other BorescopeApplicationpng|thumb|250px|right|Borescope in use with example of what you might see through the borescope

An optical fiber doped with certain rare-earth elements such as erbium can be used as the gain medium of a laser or optical amplifier. A dopant, also called doping agent and dope, is an impurity element added to a crystal or semiconductor lattice in low concentrations in order to alter the optical/electrical Rare earth elements and rare earth metals are according to IUPAC, the collection of seventeen Chemical elements in the Periodic table, namely Erbium (ˈɝbiəm is a Chemical element with the symbol Er and Atomic number 68 The active laser medium or gain medium is the source of optical Gain within a Laser. A fiber laser or fibre laser is a Laser in which the Active gain medium is an Optical fiber doped with Rare-earth elements such as An optical amplifier is a device that amplifies an Optical signal directly without the need to first convert it to an electrical signal Rare-earth doped optical fibers can be used to provide signal amplification by splicing a short section of doped fiber into a regular (undoped) optical fiber line. The doped fiber is optically pumped with a second laser wavelength that is coupled into the line in addition to the signal wave. Optical pumping is a process in which Light is used to raise (or "pump" Electrons from a lower Energy level in an Atom or Molecule Both wavelengths of light are transmitted through the doped fiber, which transfers energy from the second pump wavelength to the signal wave. The process that causes the amplification is stimulated emission. In Optics, stimulated emission is the process by which an electron perturbed by a Photon having the correct energy may drop to a lower Energy level resulting

Optical fibers doped with a wavelength shifter are used to collect scintillation light in physics experiments. A wavelength shifter is a photofluorescent material that absorbs higher Frequency Photons and emits lower frequency photons A scintillator is a substance that absorbs high-energy (ie Ionizing) electromagnetic or charged Particle radiation then in response fluoresces Physics (Greek Physis - φύσις in everyday terms is the Science of Matter and its motion.

Optical fiber can be used to supply a low level of power (around one watt) to electronics situated in a difficult electrical environment. Examples of this are electronics in high-powered antenna elements and measurement devices used in high voltage transmission equipment.

Optical fibers are also used in fiber optic gyroscopes, and other interferometry instruments. A fibre optic gyroscope (FOG is a Gyroscope that uses the Interference of light to detect mechanical rotation Interferometry is the technique of using the pattern of Interference created by the superposition of two or more Waves to diagnose the properties of

Principle of operation

An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis, by the process of total internal reflection. A dielectric is a nonconducting substance ie an insulator. The term was coined by William Whewell in response to a request from Michael Faraday. An optical waveguide is a physical structure that guides electromagnetic waves in the optical spectrum The fiber consists of a core surrounded by a cladding layer. To confine the optical signal in the core, the refractive index of the core must be greater than that of the cladding. The refractive index (or index of Refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves is reduced inside the medium The boundary between the core and cladding may either be abrupt, in step-index fiber, or gradual, in graded-index fiber. For an Optical fiber, a step-index profile is a Refractive index profile characterized by a uniform refractive index within the core and a sharp decrease In Fiber optics, a graded-index or gradient-index fiber is an Optical fiber whose core has a Refractive index that decreases with

Multimode fiber

Fiber with large (greater than 10 μm) core diameter may be analyzed by geometric optics. A micrometre ( American spelling: micrometer; symbol µm) is one millionth of a Metre, or equivalently one thousandth of a Millimetre Such fiber is called multimode fiber, from the electromagnetic analysis (see below). Multi-mode optical fiber ( multimode fiber or MM fiber or fibre) is a type of Optical fiber mostly used for communication over shorter distances In a step-index multimode fiber, rays of light are guided along the fiber core by total internal reflection. In Optics, a ray is an idealized narrow Beam of light. Rays are used to model the propagation of Light through an optical system by dividing the real light Rays that meet the core-cladding boundary at a high angle (measured relative to a line normal to the boundary), greater than the critical angle for this boundary, are completely reflected. The critical angle (minimum angle for total internal reflection) is determined by the difference in index of refraction between the core and cladding materials. Rays that meet the boundary at a low angle are refracted from the core into the cladding, and do not convey light and hence information along the fiber. The critical angle determines the acceptance angle of the fiber, often reported as a numerical aperture. In Optics, the numerical aperture ( NA) of an optical system is a Dimensionless number that characterizes the range of angles over which the system can accept A high numerical aperture allows light to propagate down the fiber in rays both close to the axis and at various angles, allowing efficient coupling of light into the fiber. However, this high numerical aperture increases the amount of dispersion as rays at different angles have different path lengths and therefore take different times to traverse the fiber. In Optics, dispersion is the phenomenon in which the Phase velocity of a wave depends on its frequency In Optics, optical path length (OPL is the product of the geometric length of the path light follows through the system and the Index of refraction of the medium A low numerical aperture may therefore be desirable.

In graded-index fiber, the index of refraction in the core decreases continuously between the axis and the cladding. This causes light rays to bend smoothly as they approach the cladding, rather than reflecting abruptly from the core-cladding boundary. The resulting curved paths reduce multi-path dispersion because high angle rays pass more through the lower-index periphery of the core, rather than the high-index center. The index profile is chosen to minimize the difference in axial propagation speeds of the various rays in the fiber. This ideal index profile is very close to a parabolic relationship between the index and the distance from the axis. In Mathematics, the parabola (pəˈræbələ from the Greek παραβολή) is a Conic section, the intersection of a right circular

Singlemode fiber

Fiber with a core diameter less than about ten times the wavelength of the propagating light cannot be modeled using geometric optics. In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency. Instead, it must be analyzed as an electromagnetic structure, by solution of Maxwell's equations as reduced to the electromagnetic wave equation. Electromagnetism is the Physics of the Electromagnetic field: a field which exerts a Force on particles that possess the property of In Classical electromagnetism, Maxwell's equations are a set of four Partial differential equations that describe the properties of the electric The electromagnetic wave equation is a second-order partial differential equation that describes the propagation of Electromagnetic waves through a medium The electromagnetic analysis may also be required to understand behaviors such as speckle that occur when coherent light propagates in multi-mode fiber. A speckle pattern is a random intensity pattern produced by the mutual Interference of a set of Wavefronts This phenomenon has been investigated by scientists In Physics, coherence is a property of waves that enables stationary (i As an optical waveguide, the fiber supports one or more confined transverse modes by which light can propagate along the fiber. Fiber supporting only one mode is called single-mode or mono-mode fiber. In Fiber-optic communication, a single-mode optical fiber ( SMF) is an Optical fiber designed to carry only a single ray of light (mode The behavior of larger-core multimode fiber can also be modeled using the wave equation, which shows that such fiber supports more than one mode of propagation (hence the name). The results of such modeling of multi-mode fiber approximately agree with the predictions of geometric optics, if the fiber core is large enough to support more than a few modes.

The waveguide analysis shows that the light energy in the fiber is not completely confined in the core. Instead, especially in single-mode fibers, a significant fraction of the energy in the bound mode travels in the cladding as an evanescent wave. An evanescent wave is a nearfield standing Wave exhibiting Exponential decay with distance

The most common type of single-mode fiber has a core diameter of 8 to 10 μm and is designed for use in the near infrared. Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of The mode structure depends on the wavelength of the light used, so that this fiber actually supports a small number of additional modes at visible wavelengths. Multi-mode fiber, by comparison, is manufactured with core diameters as small as 50 micrometres and as large as hundreds of micrometres.

Special-purpose fiber

Some special-purpose optical fiber is constructed with a non-cylindrical core and/or cladding layer, usually with an elliptical or rectangular cross-section. These include polarization-maintaining fiber and fiber designed to suppress whispering gallery mode propagation. In Fiber optics, polarization-maintaining optical fiber ( PMF or PM fiber) is Optical fiber in which the Polarization of linearly-polarized

Photonic crystal fiber is made with a regular pattern of index variation (often in the form of cylindrical holes that run along the length of the fiber). Photonic-crystal fiber (PCF is a new class of Optical fiber based on the properties of Photonic crystals Because of its ability to confine light in hollow cores or Such fiber uses diffraction effects instead of or in addition to total internal reflection, to confine light to the fiber's core. Diffraction is normally taken to refer to various phenomena which occur when a wave encounters an obstacle The properties of the fiber can be tailored to a wide variety of applications.

Manufacturing

Materials

Glass optical fibers are almost always made from silica, but some other materials, such as fluorozirconate, fluoroaluminate, and chalcogenide glasses, are used for longer-wavelength infrared applications. The Chemical compound silicon dioxide, also known as silica or silox (from the Latin " Silex " is an Oxide A chalcogenide glass (hard "ch" as in "chemistry" is a Glass containing one or more Chalcogenide element (Group VI in the Periodic Like other glasses, these glasses have a refractive index of about 1. 5. Typically the difference between core and cladding is less than one percent.

Plastic optical fibers (POF) are commonly step-index multimode fibers with a core diameter of 0. Plastic optical fiber (POF (or fibre) is an Optical fiber which is made out of Plastic. 5 mm or larger. POF typically have higher attenuation co-efficients than glass fibers, 1 dB/m or higher, and this high attenuation limits the range of POF-based systems.

Process

Standard optical fibers are made by first constructing a large-diameter preform, with a carefully controlled refractive index profile, and then pulling the preform to form the long, thin optical fiber. The preform is commonly made by three chemical vapor deposition methods: inside vapor deposition, outside vapor deposition, and vapor axial deposition. Chemical vapor deposition (CVD is a Chemical process used to produce high-purity high-performance solid materials ^[6]

With inside vapor deposition, a hollow glass tube approximately 40 cm in length known as a "preform" is placed horizontally and rotated slowly on a lathe, and gases such as silicon tetrachloride (SiCl₄) or germanium tetrachloride (GeCl₄) are injected with oxygen in the end of the tube. Silicon tetrachloride is the Chemical compound with the formula SiCl4 Germanium tetrachloride is a colourless liquid used as an intermediate in the production of purified germanium metal Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the The gases are then heated by means of an external hydrogen burner, bringing the temperature of the gas up to 1900 kelvins, where the tetrachlorides react with oxygen to produce silica or germania (germanium oxide) particles. The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic The Chemical compound silicon dioxide, also known as silica or silox (from the Latin " Silex " is an Oxide Germanium dioxide, also called germanium oxide and germania, is an Inorganic compound, an Oxide of Germanium. When the reaction conditions are chosen to allow this reaction to occur in the gas phase throughout the tube volume, in contrast to earlier techniques where the reaction occurred only on the glass surface, this technique is called modified chemical vapor deposition.

The oxide particles then agglomerate to form large particle chains, which subsequently deposit on the walls of the tube as soot. The deposition is due to the large difference in temperature between the gas core and the wall causing the gas to push the particles outwards (this is known as thermophoresis). Thermophoresis, also called thermodiffusion or Soret effect, is the effect of a temperature Gradient on multicomponent (or isotopic mixtures of particles The torch is then traversed up and down the length of the tube to deposit the material evenly. After the torch has reached the end of the tube, it is then brought back to the beginning of the tube and the deposited particles are then melted to form a solid layer. This process is repeated until a sufficient amount of material has been deposited. For each layer the composition can be modified by varying the gas composition, resulting in precise control of the finished fiber's optical properties.

In outside vapor deposition or vapor axial deposition, the glass is formed by flame hydrolysis, a reaction in which silicon tetrachloride and germanium tetrachloride are oxidized by reaction with water (H₂O) in an oxyhydrogen flame. In outside vapor deposition the glass is deposited onto a solid rod, which is removed before further processing. In vapor axial deposition, a short seed rod is used, and a porous preform, whose length is not limited by the size of the source rod, is built up on its end. The porous preform is consolidated into a transparent, solid preform by heating to about 1800 kelvins.

The preform, however constructed, is then placed in a device known as a drawing tower, where the preform tip is heated and the optic fiber is pulled out as a string. By measuring the resultant fiber width, the tension on the fiber can be controlled to maintain the fiber thickness.

Practical issues

Optical fiber cables

Main article: Optical fiber cable

In practical fibers, the cladding is usually coated with a tough resin buffer layer, which may be further surrounded by a jacket layer, usually plastic. An optical fiber cable is a Cable containing one or more Optical fibers The optical fiber elements are typically individually coated with plastic layers and contained Resin, not to be confused with Rosin, is a Hydrocarbon Secretion of many Plants particularly coniferous trees. In a fiber optic Cable, a buffer is one type of Component used to encapsulate one or more optical fibers for the purpose of providing such functions as These layers add strength to the fiber but do not contribute to its optical wave guide properties. Rigid fiber assemblies sometimes put light-absorbing ("dark") glass between the fibers, to prevent light that leaks out of one fiber from entering another. This reduces cross-talk between the fibers, or reduces flare in fiber bundle imaging applications. In Electronics, the term crosstalk ( XT) refers to any phenomenon by which a signal transmitted on one circuit or channel of a Transmission system Lens flare is the light scattered in lens systems through generally unwanted image formation mechanisms such as internal reflection and Scattering from ^[7][8]

Modern cables come in a wide variety of sheathings and armor, designed for applications such as direct burial in trenches, dual use as power lines [3], installation in conduit, lashing to aerial telephone poles, submarine installation, or insertion in paved streets. In recent years the cost of small fiber-count pole-mounted cables has greatly decreased due to the high Japanese and South Korean demand for fiber to the home (FTTH) installations.

Fiber cable can be very flexible, but traditional fiber's loss increases greatly if the fiber is bent with a radius smaller than around 30 mm. This creates a problem when the cable is bent around corners or wound around a spool, making FTTX installations more complicated. Fiber to the x ( FTTX) is a generic term for any network architecture that uses Optical fiber to replace all or part of the usual copper Local loop "Bendable fibers", targeted towards easier installation in home environments, have been standardized as ITU-T G. 657. This type of fiber can be bent with a radius as low as 7. 5 mm without adverse impact. Even more bendable fibers have been developed. ^[9] Bendable fiber may also be resistant to fiber hacking, in which the signal in a fiber is surreptitiously monitored by bending the fiber and detecting the leakage. ^[10]

Termination and splicing

Optical fibers are connected to terminal equipment by optical fiber connectors. An optical fiber connector terminates the end of an Optical fiber, and enables quicker connection and disconnection than splicing. These connectors are usually of a standard type such as FC, SC, ST, LC, or MTRJ.

Optical fibers may be connected to each other by connectors or by splicing, that is, joining two fibers together to form a continuous optical waveguide. The generally accepted splicing method is arc fusion splicing, which melts the fiber ends together with an electric arc. An electric arc is an Electrical breakdown of a gas which produces an ongoing plasma discharge, resulting from a current flowing through normally nonconductive For quicker fastening jobs, a "mechanical splice" is used.

Fusion splicing is done with a specialized instrument that typically operates as follows: The two cable ends are fastened inside a splice enclosure that will protect the splices, and the fiber ends are stripped of their protective polymer coating (as well as the more sturdy outer jacket, if present). The ends are cleaved (cut) with a precision cleaver to make them perpendicular, and are placed into special holders in the splicer. The splice is usually inspected via a magnified viewing screen to check the cleaves before and after the splice. The splicer uses small motors to align the end faces together, and emits a small spark between electrodes at the gap to burn off dust and moisture. Then the splicer generates a larger spark that raises the temperature above the melting point of the glass, fusing the ends together permanently. The melting point of a solid is the temperature range at which it changes state from solid to Liquid. The location and energy of the spark is carefully controlled so that the molten core and cladding don't mix, and this minimizes optical loss. A splice loss estimate is measured by the splicer, by directing light through the cladding on one side and measuring the light leaking from the cladding on the other side. A splice loss under 0. 1 dB is typical. The complexity of this process makes fiber splicing much more difficult than splicing copper wire.

Mechanical fiber splices are designed to be quicker and easier to install, but there is still the need for stripping, careful cleaning and precision cleaving. The fiber ends are aligned and held together by a precision-made sleeve, often using a clear index-matching gel that enhances the transmission of light across the joint. In Optics and Fiber optics, an index-matching material is a substance usually a liquid cement (adhesive or Gel, which has an Index of refraction Such joints typically have higher optical loss and are less robust than fusion splices, especially if the gel is used. All splicing techniques involve the use of an enclosure into which the splice is placed for protection afterward.

Fibers are terminated in connectors so that the fiber end is held at the end face precisely and securely. A fiber-optic connector is basically a rigid cylindrical barrel surrounded by a sleeve that holds the barrel in its mating socket. The mating mechanism can be "push and click", "turn and latch" ("bayonet"), or screw-in (threaded). A typical connector is installed by preparing the fiber end and inserting it into the rear of the connector body. Quick-set adhesive is usually used so the fiber is held securely, and a strain relief is secured to the rear. Once the adhesive has set, the fiber's end is polished to a mirror finish. Various polish profiles are used, depending on the type of fiber and the application. For singlemode fiber, the fiber ends are typically polished with a slight curvature, such that when the connectors are mated the fibers touch only at their cores. This is known as a "physical contact" (PC) polish. The curved surface may be polished at an angle, to make an "angled physical contact" (APC) connection. Such connections have higher loss than PC connections, but greatly reduced back reflection, because light that reflects from the angled surface leaks out of the fiber core; the resulting loss in signal strength is known as gap loss. Gap loss is a type of Signal strength loss that occurs in fiber optic transmission when the signal is transferred from one section of fiber or cable APC fiber ends have low back reflection even when disconnected.

Free-space coupling

It often becomes necessary to align an optical fiber with another optical fiber or an optical device such as a light-emitting diode, a laser diode, or an optoelectronic device such as a modulator. A laser diode is a Laser where the active medium is a Semiconductor similar to that found in a Light-emitting diode. Optoelectronics is the study and application of electronic devices that source detect and control Light, usually considered a sub-field of Photonics. In Telecommunications, modulation is the process of varying a periodic Waveform, i This can involve either carefully aligning the fiber and placing it in contact with the device to which it is to couple, or can use a lens to allow coupling over an air gap. A lens is an optical device with perfect or approximate Axial symmetry which transmits and refracts Light, converging or diverging In some cases the end of the fiber is polished into a curved form that is designed to allow it to act as a lens.

In a laboratory environment, the fiber end is usually aligned to the device or other fiber with a fiber launch system that uses a microscope objective lens to focus the light down to a fine point. An objective in Optics is the lens or Mirror in a Microscope, Telescope, camera or other optical instrument A precision translation stage (micro-positioning table) is used to move the lens, fiber, or device to allow the coupling efficiency to be optimized. A linear stage or translation stage is a component of a Motion system used to restrict an object to a single axis of motion

Fiber fuse

At high optical intensities, above 2 megawatts per square centimetre, when a fiber is subjected to a shock or is otherwise suddenly damaged, a fiber fuse can occur. The watt (symbol W) is the SI derived unit of power, equal to one Joule of energy per Second. The reflection from the damage vaporizes the fiber immediately before the break, and this new defect remains reflective so that the damage propagates back toward the transmitter at 1–3 meters per second. ^{[11],[12],[13]} The open fiber control system, which ensures laser eye safety in the event of a broken fiber, can also effectively halt propagation of the fiber fuse. In Telecommunication, Open fiber control is a protocol to ensure that a both ends of a Fiber optic cable are connected before Laser signals are Laser safety is the avoidance of Laser accidents especially those involving eye injuries ^[14] In situations, such as undersea cables, where high power levels might be used without the need for open fiber control, a "fiber fuse" protection device at the transmitter can break the circuit to prevent any damage.

See also

Notes

References

External links

• The Fiber Optic Association
• FOA color code for connectors
• Lennie Lightwave's Guide To Fiber Optics
• "Fibers", article in RP Photonics' Encyclopedia of Laser Physics and Technology
• How Fiber Optics are made In video
• "Fibre optic technologies", Mercury Communications Ltd, August 1992.
• "Photonics & the future of fibre", Mercury Communications Ltd, March 1993.
• "Fiber Optic Tutorial" Educational site from Arc Electronics

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