1.
Single-mode optical fiber
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In fiber-optic communication, a single-mode optical fiber is an optical fiber designed to carry light only directly down the fiber - the transverse mode. Modes are the solutions of the Helmholtz equation for waves, which is obtained by combining Maxwells equations. These modes define the way the wave travels through space, i. e. how the wave is distributed in space, waves can have the same mode but have different frequencies. Although the ray travels parallel to the length of the fiber, the 2009 Nobel Prize in Physics was awarded to Charles K. Kao for his theoretical work on the single-mode optical fiber. In September 1970, they announced they had made single-mode fibers with attenuation at the 633-nanometer helium-neon line below 20 dB/km, professor Huang Hongjia of the Chinese Academy of Sciences, developed coupling wave theory in the field of microwave theory. He led a team that successfully developed Single-mode optical fiber in 1980. Like multi-mode optical fibers, single mode fibers do exhibit modal dispersion resulting from multiple spatial modes, Single mode fibers are therefore better at retaining the fidelity of each light pulse over longer distances than multi-mode fibers. For these reasons, single-mode fibers can have a higher bandwidth than multi-mode fibers, equipment for single mode fiber is more expensive than equipment for multi-mode optical fiber, but the single mode fiber itself is usually cheaper in bulk. A typical single mode optical fiber has a diameter between 8 and 10.5 µm and a cladding diameter of 125 µm. Data rates are limited by polarization mode dispersion and chromatic dispersion, as of 2005, data rates of up to 10 gigabits per second were possible at distances of over 80 km with commercially available transceivers. By using optical amplifiers and dispersion-compensating devices, state-of-the-art DWDM optical systems can span thousands of kilometers at 10 Gbit/s, and several hundred kilometers at 40 Gbit/s. The solution of Maxwells equations for the lowest order bound mode will permit a pair of orthogonally polarized fields in the fiber, in step-index guides, single-mode operation occurs when the normalized frequency, V, is less than or equal to 2.405. For power-law profiles, single-mode operation occurs for a frequency, V, less than approximately 2.405 g +2 g. In practice, the orthogonal polarizations may not be associated with degenerate modes, oS1 and OS2 are standard single-mode optical fiber used with wavelengths 1310 nm and 1550 nm with a maximum attenuation of 1 dB/km and 0.4 dB/km. OS1 is defined in ISO/IEC11801, and OS2 is defined in ISO/IEC24702, Optical fiber connectors are used to join optical fibers where a connect/disconnect capability is required. The basic connector unit is a connector assembly, a connector assembly consists of an adapter and two connector plugs. However, the assembly and polishing operations involved can be performed in the field, Optical fiber connectors are used in telephone company central offices, at installations on customer premises, and in outside plant applications. Outside plant applications may involve locating connectors underground in subsurface enclosures that may be subject to flooding, on outdoor walls, or on utility poles
2.
Fiber-optic communication
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Fiber-optic communication is a method of transmitting information from one place to another by sending pulses of light through an optical fiber. The light forms a carrier wave that is modulated to carry information. Fiber is preferred over electrical cabling when high bandwidth, long distance, optical fiber is used by many telecommunications companies to transmit telephone signals, Internet communication, and cable television signals. Researchers at Bell Labs have reached speeds of over 100 petabit×kilometer per second using fiber-optic communication. First developed in the 1970s, fiber-optics have revolutionized the industry and have played a major role in the advent of the Information Age. Because of its advantages over electrical transmission, optical fibers have largely replaced copper wire communications in core networks in the developed world, due to much lower attenuation and interference, optical fiber has large advantages over existing copper wire in long-distance and high-demand applications. However, infrastructure development within cities was difficult and time-consuming. Since 2000, the prices for fiber-optic communications have dropped considerably, the price for rolling out fiber to the home has currently become more cost-effective than that of rolling out a copper based network. Prices have dropped to $850 per subscriber in the US and lower in countries like The Netherlands, since 1990, when optical-amplification systems became commercially available, the telecommunications industry has laid a vast network of intercity and transoceanic fiber communication lines. Bell considered it his most important invention, the device allowed for the transmission of sound on a beam of light. On June 3,1880, Bell conducted the worlds first wireless transmission between two buildings, some 213 meters apart. Due to its use of a transmission medium, the Photophone would not prove practical until advances in laser. The Photophones first practical use came in military communication systems many decades later, in 1954 Harold Hopkins and Narinder Singh Kapany showed that rolled fiber glass allowed light to be transmitted. Initially it was considered that the light can traverse in only straight medium, after a period of research starting from 1975, the first commercial fiber-optic communications system was developed, which operated at a wavelength around 0.8 µm and used GaAs semiconductor lasers. This first-generation system operated at a bit rate of 45 Mbit/s with repeater spacing of up to 10 km, soon on 22 April 1977, General Telephone and Electronics sent the first live telephone traffic through fiber optics at a 6 Mbit/s throughput in Long Beach, California. The second generation of fiber-optic communication was developed for use in the early 1980s, operated at 1.3 µm. In 1984, they had developed a fiber optic cable that would help further their progress toward making fiber optic cables that would circle the globe. Canadian service provider SaskTel had completed construction of what was then the world’s longest commercial fiberoptic network, by 1987, these systems were operating at bit rates of up to 1.7 Gb/s with repeater spacing up to 50 km
3.
Optical fiber
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An optical fiber or optical fibre is a flexible, transparent fiber made by drawing glass or plastic to a diameter slightly thicker than that of a human hair. Fibers are also used for illumination, and are wrapped in bundles so that they may be used to carry images, thus allowing viewing in confined spaces, as in the case of a fiberscope. Specially designed fibers are used for a variety of other applications, some of them being fiber optic sensors. Optical fibers typically include a transparent core surrounded by a transparent cladding material with an index of refraction. Light is kept in the core by the phenomenon of internal reflection which causes the fiber to act as a waveguide. Fibers that support many propagation paths or transverse modes are called multi-mode fibers, multi-mode fibers generally have a wider core diameter and are used for short-distance communication links and for applications where high power must be transmitted. Single-mode fibers are used for most communication links longer than 1,000 meters, being able to join optical fibers with low loss is important in fiber optic communication. This is more complex than joining electrical wire or cable and involves careful cleaving of the fibers, precise alignment of the cores. For applications that demand a permanent connection a fusion splice is common, in this technique, an electric arc is used to melt the ends of the fibers together. Another common technique is a splice, where the ends of the fibers are held in contact by mechanical force. Temporary or semi-permanent connections are made by means of specialized optical fiber connectors, the field of applied science and engineering concerned with the design and application of optical fibers is known as fiber optics. The term was coined by Indian physicist Narinder Singh Kapany who is acknowledged as the father of fiber optics. Guiding of light by refraction, the principle that makes fiber optics possible, was first demonstrated by Daniel Colladon, John Tyndall included a demonstration of it in his public lectures in London,12 years later. When the ray passes from water to air it is bent from the perpendicular. If the angle which the ray in water encloses with the perpendicular to the surface be greater than 48 degrees, the angle which marks the limit where total reflection begins is called the limiting angle of the medium. For water this angle is 48°27′, for flint glass it is 38°41′, unpigmented human hairs have also been shown to act as an optical fiber. 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 medical examinations by Heinrich Lamm in the following decade
4.
Helmholtz equation
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In mathematics, the Helmholtz equation, named for Hermann von Helmholtz, is the partial differential equation ∇2 A + k 2 A =0 where ∇2 is the Laplacian, k is the wavenumber, and A is the amplitude. The Helmholtz equation often arises in the study of problems involving partial differential equations in both space and time. The Helmholtz equation, which represents a time-independent form of the wave equation, for example, consider the wave equation u =0. Separation of variables begins by assuming that the function u is in fact separable. Substituting this form into the equation, and then simplifying, we obtain the following equation. Notice the expression on the left-hand side depends only on r, as a result, this equation is valid in the general case if and only if both sides of the equation are equal to a constant value. Rearranging the first equation, we obtain the Helmholtz equation, ∇2 A + k 2 A = A =0 and we now have Helmholtzs equation for the spatial variable r and a second-order ordinary differential equation in time. The solution in time will be a combination of sine and cosine functions, with angular frequency of ω. Alternatively, integral transforms, such as the Laplace or Fourier transform, are used to transform a hyperbolic PDE into a form of the Helmholtz equation. Because of its relationship to the equation, the Helmholtz equation arises in problems in such areas of physics as the study of electromagnetic radiation, seismology. The solution to the spatial Helmholtz equation A =0 can be obtained for simple geometries using separation of variables, the two-dimensional analogue of the vibrating string is the vibrating membrane, with the edges clamped to be motionless. The elliptical drumhead was studied by Émile Mathieu, leading to Mathieus differential equation, the solvable shapes all correspond to shapes whose dynamical billiard table is integrable, that is, not chaotic. When the motion on a billiard table is chaotic, then no closed form solutions to the Helmholtz equation are known. The study of systems is known as quantum chaos, as the Helmholtz equation. An interesting situation happens with a shape where about half of the solutions are integrable, a simple shape where this happens is with the regular hexagon. Another simple shape where this happens is with an L shape made by reflecting a square down, if the domain is a circle of radius a, then it is appropriate to introduce polar coordinates r and θ. The Helmholtz equation takes the form A r r +1 r A r +1 r 2 A θ θ + k 2 A =0 and we may impose the boundary condition that A vanish if r = a, thus A =0. The method of separation of variables leads to solutions of the form A = R Θ
5.
Maxwell's equations
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Maxwells equations are a set of partial differential equations that, together with the Lorentz force law, form the foundation of classical electromagnetism, classical optics, and electric circuits. They underpin all electric, optical and radio such as power generation, electric motors, wireless communication, cameras, televisions. Maxwells equations describe how electric and magnetic fields are generated by charges, currents, one important consequence of the equations is the demonstration of how fluctuating electric and magnetic fields can propagate at the speed of light. This electromagnetic radiation manifests itself in ways from radio waves to light. The equations have two major variants, the microscopic Maxwell equations have universal applicability but are unwieldy for common calculations. They relate the electric and magnetic fields to total charge and total current, including the complicated charges, the macroscopic Maxwell equations define two new auxiliary fields that describe the large-scale behaviour of matter without having to consider atomic scale details. However, their use requires experimentally determining parameters for a description of the electromagnetic response of materials. The term Maxwells equations is used for equivalent alternative formulations. The space-time formulations, are used in high energy and gravitational physics because they make the compatibility of the equations with special and general relativity manifest. In many situations, though, deviations from Maxwells equations are immeasurably small, exceptions include nonclassical light, photon-photon scattering, quantum optics, and many other phenomena related to photons or virtual photons. In the electric and magnetic field there are four equations. The two inhomogeneous equations describe how the fields vary in space due to sources, Gausss law describes how electric fields emanate from electric charges. Gausss law for magnetism describes magnetic fields as closed field lines not due to magnetic monopoles, the two homogeneous equations describe how the fields circulate around their respective sources. A separate law of nature, the Lorentz force law, describes how the electric and magnetic field act on charged particles, a version of this law was included in the original equations by Maxwell but, by convention, is no longer. The precise formulation of Maxwells equations depends on the definition of the quantities involved. Conventions differ with the systems, because various definitions and dimensions are changed by absorbing dimensionful factors like the speed of light c. This makes constants come out differently, the vector calculus formulation below has become standard. For formulations using tensor calculus or differential forms, see alternative formulations, for relativistically invariant formulations, see relativistic formulations
6.
Transverse mode
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A transverse mode of electromagnetic radiation is a particular electromagnetic field pattern of radiation measured in a plane perpendicular to the propagation direction of the beam. Transverse modes occur in waves and microwaves confined to a waveguide. Transverse modes occur because of conditions imposed on the wave by the waveguide. For this reason, the supported by a waveguide are quantized. The allowed modes can be found by solving Maxwells equations for the conditions of a given waveguide. Unguided electromagnetic waves in space, or in a bulk isotropic dielectric, can be described as a superposition of plane waves. However in any sort of waveguide where boundary conditions are imposed by a physical structure and these modes generally follow different propagation constants. When two or more modes have a propagation constant along the waveguide, then there is more than one modal decomposition possible in order to describe a wave with that propagation constant. Modes in waveguides can be classified as follows, Transverse electromagnetic modes. Transverse electric modes, no field in the direction of propagation. These are sometimes called H modes because there is only a field along the direction of propagation. Transverse magnetic modes, no field in the direction of propagation. These are sometimes called E modes because there is only a field along the direction of propagation. Hybrid modes, non-zero electric and magnetic fields in the direction of propagation, hollow metallic waveguides filled with a homogeneous, isotropic material support TE and TM modes but not the TEM mode. In coaxial cable energy is transported in the fundamental TEM mode. The TEM mode is usually assumed for most other electrical conductor line formats as well. In an optical fiber or other dielectric waveguide, modes are generally of the hybrid type, in circular waveguides, circular modes exist and here m is the number of full-wave patterns along the circumference and n is the number of half-wave patterns along the diameter. In a laser with cylindrical symmetry, the transverse mode patterns are described by a combination of a Gaussian beam profile with a Laguerre polynomial, the modes are denoted TEMpl where p and l are integers labeling the radial and angular mode orders, respectively
7.
Electromagnetic radiation
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In physics, electromagnetic radiation refers to the waves of the electromagnetic field, propagating through space carrying electromagnetic radiant energy. It includes radio waves, microwaves, infrared, light, ultraviolet, X-, classically, electromagnetic radiation consists of electromagnetic waves, which are synchronized oscillations of electric and magnetic fields that propagate at the speed of light through a vacuum. The oscillations of the two fields are perpendicular to other and perpendicular to the direction of energy and wave propagation. The wavefront of electromagnetic waves emitted from a point source is a sphere, the position of an electromagnetic wave within the electromagnetic spectrum can be characterized by either its frequency of oscillation or its wavelength. Electromagnetic waves are produced whenever charged particles are accelerated, and these waves can interact with other charged particles. EM waves carry energy, momentum and angular momentum away from their source particle, quanta of EM waves are called photons, whose rest mass is zero, but whose energy, or equivalent total mass, is not zero so they are still affected by gravity. Thus, EMR is sometimes referred to as the far field, in this language, the near field refers to EM fields near the charges and current that directly produced them, specifically, electromagnetic induction and electrostatic induction phenomena. In the quantum theory of electromagnetism, EMR consists of photons, quantum effects provide additional sources of EMR, such as the transition of electrons to lower energy levels in an atom and black-body radiation. The energy of a photon is quantized and is greater for photons of higher frequency. This relationship is given by Plancks equation E = hν, where E is the energy per photon, ν is the frequency of the photon, a single gamma ray photon, for example, might carry ~100,000 times the energy of a single photon of visible light. The effects of EMR upon chemical compounds and biological organisms depend both upon the power and its frequency. EMR of visible or lower frequencies is called non-ionizing radiation, because its photons do not individually have enough energy to ionize atoms or molecules, the effects of these radiations on chemical systems and living tissue are caused primarily by heating effects from the combined energy transfer of many photons. In contrast, high ultraviolet, X-rays and gamma rays are called ionizing radiation since individual photons of high frequency have enough energy to ionize molecules or break chemical bonds. These radiations have the ability to cause chemical reactions and damage living cells beyond that resulting from simple heating, Maxwell derived a wave form of the electric and magnetic equations, thus uncovering the wave-like nature of electric and magnetic fields and their symmetry. Because the speed of EM waves predicted by the wave equation coincided with the speed of light. Maxwell’s equations were confirmed by Heinrich Hertz through experiments with radio waves, according to Maxwells equations, a spatially varying electric field is always associated with a magnetic field that changes over time. Likewise, a varying magnetic field is associated with specific changes over time in the electric field. In an electromagnetic wave, the changes in the field are always accompanied by a wave in the magnetic field in one direction
8.
Nobel Prize in Physics
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The Nobel Prize in Physics is a yearly award given by the Royal Swedish Academy of Sciences for those who conferred the most outstanding contributions for mankind in the field of physics. The first Nobel Prize in Physics was awarded to German/Dutch physicist Wilhelm Röntgen in recognition of the services he has rendered by the discovery of the remarkable rays. This award is administered by the Nobel Foundation and widely regarded as the most prestigious award that a scientist can receive in physics and it is presented in Stockholm at an annual ceremony on December 10, the anniversary of Nobels death. Through 2016, a total of 203 individuals have been awarded the prize, only two women have won the Nobel Prize in Physics, Marie Curie in 1903, and Maria Goeppert Mayer in 1963. Though Nobel wrote several wills during his lifetime, the last one was written a year before he died and was signed at the Swedish-Norwegian Club in Paris on 27 November 1895. Nobel bequeathed 94% of his assets,31 million Swedish kronor, to establish. Due to the level of surrounding the will, it was not until April 26,1897 that it was approved by the Storting. The executors of his will were Ragnar Sohlman and Rudolf Lilljequist, the members of the Norwegian Nobel Committee who were to award the Peace Prize were appointed shortly after the will was approved. The prize-awarding organisations followed, the Karolinska Institutet on June 7, the Swedish Academy on June 9, the Nobel Foundation then reached an agreement on guidelines for how the Nobel Prize should be awarded. In 1900, the Nobel Foundations newly created statutes were promulgated by King Oscar II, according to Nobels will, The Royal Swedish Academy of sciences were to award the Prize in Physics. A maximum of three Nobel laureates and two different works may be selected for the Nobel Prize in Physics, compared with other Nobel Prizes, the nomination and selection process for the prize in Physics is long and rigorous. This is a key reason why it has grown in importance over the years to become the most important prize in Physics, the Nobel laureates are selected by the Nobel Committee for Physics, a Nobel Committee that consists of five members elected by The Royal Swedish Academy of Sciences. In the first stage begins in September, around 3,000 people – selected university professors, Nobel Laureates in Physics and Chemistry. The completed nomination forms arrive at the Nobel Committee no later than 31 January of the following year and these nominees are scrutinized and discussed by experts who narrow it to approximately fifteen names. The committee submits a report with recommendations on the candidates into the Academy. The Academy then makes the selection of the Laureates in Physics through a majority vote. The names of the nominees are never announced, and neither are they told that they have been considered for the prize. Nomination records are sealed for fifty years, while posthumous nominations are not permitted, awards can be made if the individual died in the months between the decision of the prize committee and the ceremony in December
9.
Charles K. Kao
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Kao holds multiple citizenship of Hong Kong, the United Kingdom and the United States. Charles Kao was born in Shanghai in 1933, and his home is in nearby Jinshan. He studied Chinese classics at home with his brother, under a tutor and he also studied English and French at an international school in Shanghai which was founded by a number of progressive Chinese educators including Cai Yuanpei. Kaos family moved to Hong Kong in 1948 where he completed his education at St. Josephs College in 1952. He did his studies in electrical engineering at Woolwich Polytechnic. It is there that Kao did his first groundbreaking work as an engineer and researcher working alongside George Hockham under the supervision of Alec Reeves. Kao joined The Chinese University of Hong Kong in 1970, to found the Department of Electronics, under his leadership, the School of Education and other new research institutes were established. He then went back to ITT Corporation in 1974 in the United States and worked in Roanoke, Virginia, first as Chief Scientist, in 1982, he became the first ITT Executive Scientist and was stationed mainly at the Advanced Technology Center in Connecticut. While there, he served as a professor and Fellow of Trumbull College at Yale University. In 1985, Kao spent one year in West Germany, at the SEL Research Centre, in 1986, Kao was the Corporate Director of Research at ITT. Kao was the Vice-Chancellor of the Chinese University of Hong Kong from 1987 to 1996, from 1993 to 1994, he was the President of ASAIHL. Kao then worked as the Chairman and CEO of Transtech Services Ltd. a telecommunication consultancy company in Hong Kong and he was the founder, Chairman and CEO of ITX Services Limited. From 2003 to January 30,2009, Kao was an Independent Non-executive Director, since 1991, Kao has been an Independent Non-Executive Director and a member of the Audit Committee of the Varitronix International Limited in Hong Kong. In 2000, Kao founded the Independent Schools Foundation Academy, which is located in Cyberport and he was its founding Chairman in 2000, and stepped down from the Board of the ISF in December 2008. Kao was the speaker at IEEE GLOBECOM2002 in Taipei. In 2003 Kao was named a Chair Professor by special appointment at the Electronics Institute of the College of Electrical Engineering and Computer Science, National Taiwan University. In 1996, Kao donated to Yale University, and the Charles Kao Fund Research Grants was established to support Yales studies, research, the fund currently is managed by Yale University Councils on East Asian and Southeast Asian Studies. Kao has been suffering from Alzheimers disease since early 2004 and has speech difficulty, Kaos father also suffered from the same disease
10.
Multi-mode optical fiber
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Multi-mode optical fiber is a type of optical fiber mostly used for communication over short distances, such as within a building or on a campus. Typical multi-mode links have data rates of 10 Mbit/s to 10 Gbit/s over link lengths of up to 600 meters, Multi-mode fiber has a fairly large core diameter that enables multiple light modes to be propagated and limits the maximum length of a transmission link due to modal dispersion. The equipment used for communications over multi-mode optical fiber is less expensive than that for optical fiber. Typical transmission speed and distance limits are 100 Mbit/s for distances up to 2 km,1 Gbit/s up to 1000 m, because of its high capacity and reliability, multi-mode optical fiber generally is used for backbone applications in buildings. An increasing number of users are taking the benefits of closer to the user by running fiber to the desktop or to the zone. Because of the core and also the possibility of large numerical aperture. However, compared to single-mode fibers, the multi-mode fiber bandwidth–distance product limit is lower, because multi-mode fiber has a larger core-size than single-mode fiber, it supports more than one propagation mode, hence it is limited by modal dispersion, while single mode is not. The LED light sources sometimes used with multi-mode fiber produce a range of wavelengths and this chromatic dispersion is another limit to the useful length for multi-mode fiber optic cable. In contrast, the used to drive single-mode fibers produce coherent light of a single wavelength. Due to the dispersion, multi-mode fiber has higher pulse spreading rates than single mode fiber. Single-mode fibers are used in high-precision scientific research because restricting the light to only one propagation mode allows it to be focused to an intense. Jacket color is used to distinguish multi-mode cables from single-mode ones. The standard TIA-598C recommends, for applications, the use of a yellow jacket for single-mode fiber. Some vendors use violet to distinguish higher performance OM4 communications fiber from other types, Multi-mode fibers are described by their core and cladding diameters. Thus,62. 5/125 µm multi-mode fiber has a size of 62.5 micrometres. The transition between the core and cladding can be sharp, which is called a profile, or a gradual transition. The two types have different dispersion characteristics and thus different effective propagation distance, Multi-mode fibers may be constructed with either graded or step-index profile. In addition, multi-mode fibers are described using a system of classification determined by the ISO11801 standard — OM1, OM2, OM4 was finalized in August 2009, and was published by the end of 2009 by the TIA
11.
Fiberscope
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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 early 1840s. Then in 1930, Heinrich Lamm, a German medical student and these discoveries led to the invention of endoscopes and fiberscopes. In the 1960s the endoscope was upgraded with glass fiber, a material that allowed light to transmit. While this provided users with the capability of real-time observation, it did not provide them with the ability to take photographs, in 1964 the fiberscope, the first gastro camera, was invented. It was the first time an endoscope had a camera that could take pictures and this innovation led to more careful observations, and more accurate diagnoses. Fiberscopes work by utilizing the science of fiber-optic bundles, which consist of numerous fiber-optic cables, fiber-optic cables are made of optically pure glass and are as thin as a human’s hair. When light travels from one medium to another it is refracted, if the light is traveling from a less dense medium to a dense medium it is refracted away from the normal. The opposite applies if the light is traveling from a medium to a less dense medium. In optic cables, light travels through the dense glass core by constantly reflecting from the less dense cladding and this happens because the surface of the core acts like a perfect mirror and the angle of the light is always larger than the critical angle. Eyepiece – Magnifies the image carried back by the imaging bundle so the eye can view it. Imaging bundle – Continuous strand of glass fibers that transmit the image to the eyepiece. Distal lens – The combination of lenses that take images. Fiberscope body – The control section that is designed to help aide one hand operation, insertion tube – Most of the length of the fiberscope, made to be durable and flexible. This protects the fiber bundle and the articulation cables. Bending section – The most flexible part of the fiberscope, it connects the insertion tube to the distal viewing section, distal section – Where the ending points of both the illumination and imaging fiber bundle are. Fiberscopes are used in the field as a tool to help doctors. This procedure is called an endoscopy, doctors use this when they suspect that a patient’s organ is infected, damaged, or cancerous. There are numerous types based on the area of the body being examined, although the fiberscope is mainly used for medical purposes, it is also used for other purposes
12.
Dispersion (optics)
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In optics, dispersion is the phenomenon in which the phase velocity of a wave depends on its frequency. Media having this property may be termed dispersive media. Sometimes the term chromatic dispersion is used for specificity, the most familiar example of dispersion is probably a rainbow, in which dispersion causes the spatial separation of a white light into components of different wavelengths. Most often, chromatic dispersion refers to material dispersion, that is. However, in a waveguide there is also the phenomenon of waveguide dispersion, more generally, waveguide dispersion can occur for waves propagating through any inhomogeneous structure, whether or not the waves are confined to some region. In a waveguide, both types of dispersion will generally be present, although they are not strictly additive, for example, in fiber optics the material and waveguide dispersion can effectively cancel each other out to produce a zero-dispersion wavelength, important for fast fiber-optic communication. Material dispersion can be a desirable or undesirable effect in optical applications, the dispersion of light by glass prisms is used to construct spectrometers and spectroradiometers. Holographic gratings are used, as they allow more accurate discrimination of wavelengths. However, in lenses, dispersion causes chromatic aberration, an effect that may degrade images in microscopes, telescopes. The phase velocity, v, of a wave in a uniform medium is given by v = c n where c is the speed of light in a vacuum. In general, the index is some function of the frequency f of the light, thus n = n, or alternatively. The wavelength dependence of a refractive index is usually quantified by its Abbe number or its coefficients in an empirical formula such as the Cauchy or Sellmeier equations. In particular, for materials, the susceptibility χ that appears in the Kramers–Kronig relations is the electric susceptibility χe = n2 −1. The most commonly seen consequence of dispersion in optics is the separation of light into a color spectrum by a prism. From Snells law it can be seen that the angle of refraction of light in a prism depends on the index of the prism material. For visible light, refraction indices n of most transparent materials decrease with increasing wavelength λ,1 < n < n < n, or alternatively, in this case, the medium is said to have normal dispersion. Whereas, if the index increases with increasing wavelength, the medium is said to have anomalous dispersion, at the interface of such a material with air or vacuum, Snells law predicts that light incident at an angle θ to the normal will be refracted at an angle arcsin. Thus, blue light, with a refractive index, will be bent more strongly than red light
13.
Optical amplifier
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An optical amplifier is a device that amplifies an optical signal directly, without the need to first convert it to an electrical signal. An optical amplifier may be thought of as a laser without an optical cavity, optical amplifiers are important in optical communication and laser physics. There are several different physical mechanisms that can be used to amplify a light signal, in doped fibre amplifiers and bulk lasers, stimulated emission in the amplifiers gain medium causes amplification of incoming light. In semiconductor optical amplifiers, electron-hole recombination occurs, in Raman amplifiers, Raman scattering of incoming light with phonons in the lattice of the gain medium produces photons coherent with the incoming photons. Almost any laser active gain medium can be pumped to produce gain for light at the wavelength of a made with the same material as its gain medium. Such amplifiers are used to produce high power laser systems. Special types such as amplifiers and chirped-pulse amplifiers are used to amplify ultrashort pulses. Doped fibre amplifiers are amplifiers that use a doped optical fibre as a gain medium to amplify an optical signal. They are related to fibre lasers, the signal to be amplified and a pump laser are multiplexed into the doped fibre, and the signal is amplified through interaction with the doping ions. An erbium-doped waveguide amplifier is an amplifier that uses a waveguide to boost an optical signal. Amplification is achieved by stimulated emission of photons from dopant ions in the doped fibre, the pump laser excites ions into a higher energy from where they can decay via stimulated emission of a photon at the signal wavelength back to a lower energy level. The excited ions can also decay spontaneously or even through nonradiative processes involving interactions with phonons of the glass matrix and these last two decay mechanisms compete with stimulated emission reducing the efficiency of light amplification. The amplification window of an amplifier is the range of optical wavelengths for which the amplifier yields a usable gain. The amplification window is determined by the properties of the dopant ions, the glass structure of the optical fibre. This broadening is both homogeneous and inhomogeneous, homogeneous broadening arises from the interactions with phonons of the glass, while inhomogeneous broadening is caused by differences in the glass sites where different ions are hosted. Different sites expose ions to different local fields, which shifts the energy levels via the Stark effect. In addition, the Stark effect also removes the degeneracy of states having the same total angular momentum. Thus, for example, the trivalent erbium ion has a state with J = 15/2
14.
Wavelength-division multiplexing
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This technique enables bidirectional communications over one strand of fiber, as well as multiplication of capacity. This is purely convention because wavelength and frequency communicate the same information, a WDM system uses a multiplexer at the transmitter to join the several signals together, and a demultiplexer at the receiver to split them apart. With the right type of fiber it is possible to have a device that does both simultaneously, and can function as an optical add-drop multiplexer, the optical filtering devices used have conventionally been etalons. As there are three different WDM types, whereof one is called WDM, we would use the notation xWDM when discussing the technology as such. The concept was first published in 1978, and by 1980 WDM systems were being realized in the laboratory, the first WDM systems combined only two signals. Modern systems can handle 160 signals and can expand a basic 100 Gbit/s system over a single fiber pair to over 16 Tbit/s. A system of 320 channels in also present WDM systems are popular with telecommunications companies because they allow them to expand the capacity of the network without laying more fiber. By using WDM and optical amplifiers, they can accommodate several generations of development in their optical infrastructure without having to overhaul the backbone network. Capacity of a link can be expanded simply by upgrading the multiplexers and demultiplexers at each end. This is often done by use of optical-to-electrical-to-optical translation at the edge of the transport network. Most WDM systems operate on single-mode fiber optical cables, which have a diameter of 9 µm. Certain forms of WDM can also be used in multi-mode fiber cables which have diameters of 50 or 62.5 µm. Early WDM systems were expensive and complicated to run, however, recent standardization and better understanding of the dynamics of WDM systems have made WDM less expensive to deploy. Optical receivers, in contrast to laser sources, tend to be wideband devices, therefore, the demultiplexer must provide the wavelength selectivity of the receiver in the WDM system. WDM systems are divided into three different wavelength patterns, normal, coarse and dense, normal WDM uses the two normal wavelengths 1310 and 1550 on one fiber. Coarse WDM provides up to 16 channels across multiple transmission windows of silica fibers, dense wavelength division multiplexing uses the C-Band transmission window but with denser channel spacing. Channel plans vary, but a typical DWDM system would use 40 channels at 100 GHz spacing or 80 channels with 50 GHz spacing, some technologies are capable of 12.5 GHz spacing. New amplification options enable the extension of the wavelengths to the L-band
15.
Telecommunication
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Telecommunication is the transmission of signs, signals, messages, writings, images and sounds or intelligence of any nature by wire, radio, optical or other electromagnetic systems. Telecommunication occurs when the exchange of information between communication participants includes the use of technology and it is transmitted either electrically over physical media, such as cables, or via electromagnetic radiation. Such transmission paths are divided into communication channels which afford the advantages of multiplexing. The term is used in its plural form, telecommunications. Early means of communicating over a distance included visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, other examples of pre-modern long-distance communication included audio messages such as coded drumbeats, lung-blown horns, and loud whistles. Zworykin, John Logie Baird and Philo Farnsworth, the word telecommunication is a compound of the Greek prefix tele, meaning distant, far off, or afar, and the Latin communicare, meaning to share. Its modern use is adapted from the French, because its use was recorded in 1904 by the French engineer. Communication was first used as an English word in the late 14th century, in the Middle Ages, chains of beacons were commonly used on hilltops as a means of relaying a signal. Beacon chains suffered the drawback that they could pass a single bit of information. One notable instance of their use was during the Spanish Armada, in 1792, Claude Chappe, a French engineer, built the first fixed visual telegraphy system between Lille and Paris. However semaphore suffered from the need for skilled operators and expensive towers at intervals of ten to thirty kilometres, as a result of competition from the electrical telegraph, the last commercial line was abandoned in 1880. Homing pigeons have occasionally used throughout history by different cultures. Pigeon post is thought to have Persians roots and was used by the Romans to aid their military, frontinus said that Julius Caesar used pigeons as messengers in his conquest of Gaul. The Greeks also conveyed the names of the victors at the Olympic Games to various cities using homing pigeons, in the early 19th century, the Dutch government used the system in Java and Sumatra. And in 1849, Paul Julius Reuter started a service to fly stock prices between Aachen and Brussels, a service that operated for a year until the gap in the telegraph link was closed. Sir Charles Wheatstone and Sir William Fothergill Cooke invented the telegraph in 1837. Also, the first commercial electrical telegraph is purported to have constructed by Wheatstone and Cooke. Both inventors viewed their device as an improvement to the electromagnetic telegraph not as a new device, samuel Morse independently developed a version of the electrical telegraph that he unsuccessfully demonstrated on 2 September 1837
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Power law
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For instance, considering the area of a square in terms of the length of its side, if the length is doubled, the area is multiplied by a factor of four. Few empirical distributions fit a power law for all their values, acoustic attenuation follows frequency power-laws within wide frequency bands for many complex media. Allometric scaling laws for relationships between biological variables are among the best known power-law functions in nature, one attribute of power laws is their scale invariance. Given a relation f = a x − k, scaling the argument x by a constant factor c causes only a proportionate scaling of the function itself and that is, f = a − k = c − k f ∝ f. That is, scaling by a constant c simply multiplies the original power-law relation by the constant c − k, thus, it follows that all power laws with a particular scaling exponent are equivalent up to constant factors, since each is simply a scaled version of the others. This behavior is what produces the linear relationship when logarithms are taken of both f and x, and the straight-line on the plot is often called the signature of a power law. With real data, such straightness is a necessary, but not sufficient, in fact, there are many ways to generate finite amounts of data that mimic this signature behavior, but, in their asymptotic limit, are not true power laws. Thus, accurately fitting and validating power-law models is an area of research in statistics. This can be seen in the thought experiment, imagine a room with your friends. Now imagine the worlds richest person entering the room, with an income of about 1 billion US$. What happens to the income in the room. Income is distributed according to a known as the Pareto distribution. On the one hand, this makes it incorrect to apply traditional statistics that are based on variance, on the other hand, this also allows for cost-efficient interventions. For example, given that car exhaust is distributed according to a power-law among cars it would be sufficient to eliminate those very few cars from the road to reduce total exhaust substantially. For instance, the behavior of water and CO2 at their boiling points fall in the universality class because they have identical critical exponents. In fact, almost all material phase transitions are described by a set of universality classes. Similar observations have made, though not as comprehensively, for various self-organized critical systems. Formally, this sharing of dynamics is referred to as universality, scientific interest in power-law relations stems partly from the ease with which certain general classes of mechanisms generate them
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ISO/IEC 11801
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It covers both balanced copper cabling and optical fibre cabling. The standard was designed for use within commercial premises that may consist of either a building or of multiple buildings on a campus. It was optimized for premises that span up to 3 km, up to 1 km2 office space, Class F features even stricter specifications for crosstalk and system noise than Class E. To achieve this, shielding has been added for individual wire pairs, besides the shield, the twisting of the pairs and number of turns per unit length increases RF shielding and protects from crosstalk. The Category 7 cable standard has been created to allow 10 Gigabit Ethernet over 100 m of copper cabling, the cable contains four twisted copper wire pairs, just like the earlier standards. Category 7 cable can be terminated either with 8P8C compatible GG45 electrical connectors which incorporate the 8P8C standard or with TERA connectors, when combined with GG-45 or TERA connectors, Category 7 cable is rated for transmission frequencies of up to 600 MHz. Category 7 is not recognized by the TIA/EIA, Class FA channels and Category 7A cables, introduced by ISO11801 Edition 2 Amendment 2, are defined at frequencies up to 1000 MHz, suitable for multiple applications including CATV. Each pair offers 1200 MHz of bandwidth, simulation results have shown that 40 Gigabit Ethernet may be possible at 50 meters and 100 Gigabit Ethernet at 15 meters. In 2007, researchers at Pennsylvania State University predicted that either 32 nm or 22 nm circuits would allow for 100 Gigabit Ethernet at 100 meters. Category 8 should be fully compatible with Category 6A and below. As of January 2014, draft versions of ISO/IEC TR 11801-99-1, the final specifications will depend on transceiver requirements to be defined by IEEE802. 3bq workforce. Annex E, Acronyms for balanced cables, provides a system to specify the exact construction for both unshielded and shielded balanced twisted pair cables, european standard EN50173, Information technology — Generic cabling systems
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Optical fiber cable
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An optical fiber cable, also known as fiber optic cable, is a cable containing one or more optical fibers that are used to carry light. The optical fiber elements are typically coated with plastic layers. Different types of cable are used for different applications, for long distance telecommunication. Optical fiber consists of a core and a layer, selected for total internal reflection due to the difference in the refractive index between the two. In practical fibers, the cladding is coated with a layer of acrylate polymer or polyimide. This coating protects the fiber from damage but does not contribute to its optical waveguide properties, individual coated fibers then have a tough resin buffer layer and/or core tube extruded around them to form the cable core. Several layers of protective sheathing, depending on the application, are added to form the cable, rigid fiber assemblies sometimes put light-absorbing 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, for indoor applications, the jacketed fiber is generally enclosed, with a bundle of flexible fibrous polymer strength members like aramid, in a lightweight plastic cover to form a simple cable. Each end of the cable may be terminated with an optical fiber connector to allow it to be easily connected and disconnected from transmitting and receiving equipment. For use in more environments, a much more robust cable construction is required. In loose-tube construction the fiber is laid helically into semi-rigid tubes and this protects the fiber from tension during laying and due to temperature changes. Loose-tube fiber may be dry block or gel-filled, dry block offers less protection to the fibers than gel-filled, but costs considerably less. Instead of a tube, the fiber may be embedded in a heavy polymer jacket. Tight buffer cables are offered for a variety of applications, Breakout cables normally contain a ripcord, two non-conductive dielectric strengthening members, an aramid yarn, and 3 mm buffer tubing with an additional layer of Kevlar surrounding each fiber. The ripcord is a cord of strong yarn that is situated under the jacket of the cable for jacket removal. Distribution cables have an overall Kevlar wrapping, a ripcord, and these fiber units are commonly bundled with additional steel strength members, again with a helical twist to allow for stretching. A critical concern in outdoor cabling is to protect the fiber from contamination by water and this is accomplished by use of solid barriers such as copper tubes, and water-repellent jelly or water-absorbing powder surrounding the fiber. Finally, the cable may be armored to protect it from environmental hazards, in September 2012, NTT Japan demonstrated a single fiber cable that was able to transfer 1 petabit per second over a distance of 50 kilometers
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Waveguide (optics)
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An optical waveguide is a physical structure that guides electromagnetic waves in the optical spectrum. Common types of optical waveguides include optical fiber and rectangular waveguides, optical waveguides are used as components in integrated optical circuits or as the transmission medium in local and long haul optical communication systems. Optical waveguides can be classified according to their geometry, mode structure, refractive index distribution, practical rectangular-geometry optical waveguides are most easily understood as variants of a theoretical dielectric slab waveguide, also called a planar waveguide. The slab waveguide consists of three layers of materials with different dielectric constants, extending infinitely in the parallel to their interfaces. Light may be confined in the layer by total internal reflection. This occurs only if the index of the middle layer is larger than that of the surrounding layers. Guided modes of a slab waveguide cannot be excited by light incident from the top or bottom interfaces, light must be injected with a lens from the side into the middle layer. Alternatively a coupling element may be used to couple light into the waveguide, the critical angle depends on the index of refraction of the materials, which may vary depending on the wavelength of the light. Such propagation will result in a mode only at a discrete set of angles where the reflected planewave does not destructively interfere with itself. This structure confines electromagnetic waves only in one direction, and therefore it has practical application. Structures that may be approximated as slab waveguides do, however, a strip waveguide is basically a strip of the layer confined between cladding layers. The simplest case is a waveguide, which is formed when the guiding layer of the slab waveguide is restricted in both transverse directions rather than just one. Rectangular waveguides are used in integrated circuits and in laser diodes. They are commonly used as the basis of optical components as Mach-Zehnder interferometers. The cavities of laser diodes are constructed as rectangular optical waveguides. Optical waveguides with rectangular geometry are produced by a variety of means, a rib waveguide is a waveguide in which the guiding layer basically consists of the slab with a strip superimposed onto it. Rib waveguides also provide confinement of the wave in two dimensions, optical waveguides typically maintain a constant cross-section along their direction of propagation. This is for example the case for strip and of rib waveguides, however, waveguides can also have periodic changes in their cross-section while still allowing lossless transmission of light via so-called Bloch modes
20.
General Services Administration
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The General Services Administration is an independent agency of the United States government, established in 1949 to help manage and support the basic functioning of federal agencies. GSA employs about 12,000 federal workers and has an operating budget of roughly $26.3 billion. GSA oversees $66 billion of procurement annually and it contributes to the management of about $500 billion in U. S. federal property, divided chiefly among 8,300 owned and leased buildings and a 210,000 vehicle motor pool. GSAs business lines include the Federal Acquisition Service, the Public Buildings Service, the GSA is member of the Procurement G6, an informal group leading the use of framework agreements and e-procurement instruments in public procurement. In 1947 President Harry Truman asked former President Herbert Hoover to lead what became known as the Hoover Commission to make recommendations to reorganize the operations of the federal government, one of the recommendations of the commission was the establishment of an Office of the General Services. This proposed office would combine the responsibilities of the following organizations, General Jess Larson, Administrator of the War Assets Administration, was named GSAs first Administrator. The first job awaiting Administrator Larson and the newly formed GSA was a renovation of the White House. The structure had fallen into such a state of disrepair by 1949 that one inspector of the time said the structure was standing “purely from habit. Everything, except the four walls without a roof, was stripped down. GSA completed the renovation in 1952, GSA headquarters, located at Eighteenth and F Streets, NW, was U. S. General Services Administration Building listed on the National Register of Historic Places in 1986 as Interior Department Offices, in 1960, GSA created the Federal Telecommunications System, a government-wide intercity telephone system. In 1970, the Nixon administration created the Consumer Product Information Coordinating Center, the Federal Buildings Fund was initiated in 1974, which allowed the GSA to issue rent bills to federal agencies. In 1972, the GSA established the Automated Data and Telecommunications Service, in 1973, the GSA created the Office of Federal Management Policy. GSA’s Office of Acquisition Policy centralized procurement policy in 1978, in 1984, GSA introduced the federal government to the use of charge cards, known as the GMA SmartPay system. The National Archives and Records Administration was spun off into an independent agency in 1985, the same year, the GSA began to provide governmentwide policy oversight and guidance for federal real property management as a result of an Executive Order signed by President Ronald Reagan. In 2003, the Federal Protective Service was moved to the Department of Homeland Security, in 2005, GSA reorganized to merge the Federal Supply Service and Federal Technology Service business lines into the Federal Acquisition Service. On April 3,2009, President Barack Obama nominated Martha N. Johnson to serve as the GSA Administrator, after a 9-month delay, the United States Senate confirmed her nomination on February 4,2010. In July 1991, GSA contractors began the excavation of what is now the Ted Weiss Federal Building in New York City, when initial excavation disturbed burials, destroying skeletons and artifacts, GSA sent archaeologists to excavate—but hid their findings from the public
This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C".
This article incorporates