Optical fiber connector
An optical fiber connector terminates the end of an optical fiber, enables quicker connection and disconnection than splicing. The connectors mechanically align the cores of fibers so light can pass. Better connectors lose little light due to reflection or misalignment of the fibers. In all, about 100 different types of fiber optic connectors have been introduced to the market. Optical fiber connectors are used to join optical fibers where a connect/disconnect capability is required. Due to the polishing and tuning procedures that may be incorporated into optical connector manufacturing, connectors are assembled onto optical fiber in a supplier's manufacturing facility. However, the assembly and polishing operations involved can be performed in the field, for example, to terminate long runs at a patch panel. Optical fiber connectors are used in telephone exchanges, for customer premises wiring, in outside plant applications to connect equipment and cables, or to cross-connect cables. Most optical fiber connectors are spring-loaded, so the fiber faces are pressed together when the connectors are mated.
The resulting glass-to-glass or plastic-to-plastic contact eliminates signal losses that would be caused by an air gap between the joined fibers. Performance of optical fiber connectors can be quantified by insertion return loss. Measurements of these parameters are now defined in IEC standard 61753-1; the standard gives five grades for insertion loss from A to D, M for multimode. The other parameter is return loss, with grades from 1 to 5. A variety of optical fiber connectors are available, but SC and LC connectors are the most common types of connectors on the market. Typical connectors are rated for 500–1,000 mating cycles; the main differences among types of connectors are methods of mechanical coupling. Organizations will standardize on one kind of connector, depending on what equipment they use. In many data center applications and multi-fiber connectors have replaced larger, older styles, allowing more fiber ports per unit of rack space. Outside plant applications may require connectors be located underground, or on outdoor walls or utility poles.
In such settings, protective enclosures are used, fall into two broad categories: hermetic and free-breathing. Hermetic cases prevent entry of moisture and air but, lacking ventilation, can become hot if exposed to sunlight or other sources of heat. Free-breathing enclosures, on the other hand, allow ventilation, but can admit moisture and airborne contaminants. Selection of the correct housing depends on the cable and connector type, the location, environmental factors. Many types of optical connector have been developed at different times, for different purposes. Many of them are summarized in the tables below. Modern connectors use a "physical contact" polish on the fiber and ferrule end; this is a convex surface with the apex of the curve centered on the fiber, so that when the connectors are mated the fiber cores come into direct contact with one another. Some manufacturers have several grades of polish quality, for example a regular FC connector may be designated "FC/PC", while "FC/SPC" and "FC/UPC" may denote "super" and "ultra" polish qualities, respectively.
Higher grades of polish give less insertion lower back reflection. Many connectors are available with the fiber end face polished at an angle to prevent light that reflects from the interface from traveling back up the fiber; because of the angle, the reflected light does not stay in the fiber core but instead leaks out into the cladding. Angle-polished connectors should only be mated to other angle-polished connectors; the APC angle is 8 degrees, however, SC/APC exists as 9 degrees in some countries. Mating to a non-angle polished connector causes high insertion loss. Angle-polished connectors have higher insertion loss than good quality straight physical contact ones. "Ultra" quality connectors may achieve comparable back reflection to an angled connector when connected, but an angled connection maintains low back reflection when the output end of the fiber is disconnected. Angle-polished connections are distinguished visibly by the use of a green strain relief boot, or a green connector body.
The parts are identified by adding "/APC" to the name. For example, an angled FC connector may be designated FC/APC, or FCA. Non-angled versions may be denoted FC/PC or with specialized designations such as FC/UPC or FCU to denote an "ultra" quality polish on the fiber end face. Two different versions of FC/APC exist: FC/APC-N and FC/APC-R. An FC/APC-N connector key will not fit into a FC/APC-R adapter key slot. SMA 906 features a "step" in the ferrule. SMA 905 is available as a keyed connector, used e.g. for special spectrometer applications. LC connectors are sometimes called "Little Connectors". MT-RJ connectors look like a miniature RJ-45 connector. ST connectors refer to having a "straight tip", as the sides of the ceramic tip are parallel—as opposed to the predecessor bi-conic connector which aligned as two nesting ice cream cones would. Other mnemonics include "Set and Twist", "Stab and Twist", "Single Twist", referring to how it is inserted, they are known as "Square Top" due to the flat end face.
SC connectors, being square, have a mnemonic of "Square Connector", which some people believe to be the correct name, rath
An optical fiber is a flexible, transparent fiber made by drawing glass or plastic to a diameter thicker than that of a human hair. Optical fibers are used most as a means to transmit light between the two ends of the fiber and find wide usage in fiber-optic communications, where they permit transmission over longer distances and at higher bandwidths than electrical cables. Fibers are used instead of metal wires. Fibers are used for illumination and imaging, are wrapped in bundles so they may be used to carry light into, or images out of 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 and fiber lasers. Optical fibers include a core surrounded by a transparent cladding material with a lower index of refraction. Light is kept in the core by the phenomenon of total 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, while those that support a single mode are called single-mode fibers.
Multi-mode fibers 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 fiber cores, the coupling of these aligned 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 mechanical 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, 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 and Jacques Babinet in Paris in the early 1840s. John Tyndall included a demonstration of it in his public lectures in London, 12 years later. Tyndall wrote about the property of total internal reflection in an introductory book about the nature of light in 1870:When the light passes from air into water, the refracted ray is bent towards the perpendicular... 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 ray will not quit the water at all: it will be reflected at the surface.... 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′, while for diamond it is 23°42′.
In the late 19th and early 20th centuries, light was guided through bent glass rods to illuminate body cavities. 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. In the 1930s, Heinrich Lamm showed that one could transmit images through a bundle of unclad optical fibers and used it for internal medical examinations, but his work was forgotten. In 1953, Dutch scientist Bram van Heel first demonstrated image transmission through bundles of optical fibers with a transparent cladding; that same year, Harold Hopkins and Narinder Singh Kapany at Imperial College in London succeeded in making image-transmitting bundles with over 10,000 fibers, subsequently achieved image transmission through a 75 cm long bundle which combined several thousand fibers. Their article titled "A flexible fibrescope, using static scanning" was published in the journal Nature in 1954.
The first practical fiber optic semi-flexible gastroscope was patented by Basil Hirschowitz, C. Wilbur Peters, Lawrence E. Curtiss, researchers at the University of Michigan, in 1956. In the process of developing the gastroscope, Curtiss produced the first glass-clad fibers. A variety of other image transmission applications soon followed. Kapany coined the term fiber optics, wrote a 1960 article in Scientific American that introduced the topic to a wide audience, wrote the first book about the new field; the first working fiber-optical data transmission system was demonstrated by German physicist Manfred Börner at Telefunken Research Labs in Ulm in 1965, followed by the first patent application for this technology in 1966. NASA used fiber optics in the television cameras. At the time, the use in the cameras was classified confidential, employees handling the cameras had to be supervised by someone with an appropriate security clearance. Charles K. Kao and George A. Hockham of the British company Standard Telephones and Cables were the first, in 1965, to promote the idea that the attenuation in optical fibers could be reduced below 20 decibels per kilometer, making fibers a practical communication medium.
They proposed th
In telecommunications, transmission is the process of sending and propagating an analogue or digital information signal over a physical point-to-point or point-to-multipoint transmission medium, either wired, optical fiber or wireless. One example of transmission is the sending of a signal with limited duration, for example a block or packet of data, a phone call, or an email. Transmission technologies and schemes refer to physical layer protocol duties such as modulation, line coding, error control, bit synchronization and multiplexing, but the term may involve higher-layer protocol duties, for example, digitizing an analog message signal, data compression. Transmission of a digital message, or of a digitized analog signal, is known as digital communication
A laser diode, injection laser diode, or diode laser is a semiconductor device similar to a light-emitting diode in which the laser beam is created at the diode's junction. Laser diodes can directly convert electrical energy into light. Driven by voltage, the doped p-n-transition allows for recombination of an electron with a hole. Due to the drop of the electron from a higher energy level to a lower one, radiation, in the form of an emitted photon is generated; this is spontaneous emission. Stimulated emission can be produced when the process is continued and further generate light with the same phase and wavelength; the choice of the semiconductor material determines the wavelength of the emitted beam, which in today's laser diodes range from infra-red to the UV spectrum. Laser diodes are the most common type of lasers produced, with a wide range of uses that include fiber optic communications, barcode readers, laser pointers, CD/DVD/Blu-ray disc reading/recording, laser printing, laser scanning and light beam illumination.
A laser diode is electrically a PIN diode. The active region of the laser diode is in the intrinsic region, the carriers are pumped into that region from the N and P regions respectively. While initial diode laser research was conducted on simple P-N diodes, all modern lasers use the double-hetero-structure implementation, where the carriers and the photons are confined in order to maximize their chances for recombination and light generation. Unlike a regular diode, the goal for a laser diode is to recombine all carriers in the I region, produce light. Thus, laser diodes are fabricated using direct band-gap semiconductors; the laser diode epitaxial structure is grown using one of the crystal growth techniques starting from an N doped substrate, growing the I doped active layer, followed by the P doped cladding, a contact layer. The active layer most consists of quantum wells, which provide lower threshold current and higher efficiency. Laser diodes form a subset of the larger classification of semiconductor p-n junction diodes.
Forward electrical bias across the laser diode causes the two species of charge carrier – holes and electrons – to be "injected" from opposite sides of the p-n junction into the depletion region. Holes are injected from the p-doped, electrons from the n-doped, semiconductor. Due to the use of charge injection in powering most diode lasers, this class of lasers is sometimes termed "injection lasers," or "injection laser diode"; as diode lasers are semiconductor devices, they may be classified as semiconductor lasers. Either designation distinguishes diode lasers from solid-state lasers. Another method of powering some diode lasers is the use of optical pumping. Optically pumped semiconductor lasers use a III-V semiconductor chip as the gain medium, another laser as the pump source. OPSL offer several advantages over ILDs in wavelength selection and lack of interference from internal electrode structures. A further advantage of OPSLs is invariance of the beam parameters - divergence and pointing - as pump power is varied over a 10:1 output power ratio.
When an electron and a hole are present in the same region, they may recombine or "annihilate" producing a spontaneous emission — i.e. the electron may re-occupy the energy state of the hole, emitting a photon with energy equal to the difference between the electron's original state and hole's state. Spontaneous emission below the lasing threshold produces similar properties to an LED. Spontaneous emission is necessary to initiate laser oscillation, but it is one among several sources of inefficiency once the laser is oscillating; the difference between the photon-emitting semiconductor laser and a conventional phonon-emitting semiconductor junction diode lies in the type of semiconductor used, one whose physical and atomic structure confers the possibility for photon emission. These photon-emitting semiconductors are the so-called "direct bandgap" semiconductors; the properties of silicon and germanium, which are single-element semiconductors, have bandgaps that do not align in the way needed to allow photon emission and are not considered "direct."
Other materials, the so-called compound semiconductors, have identical crystalline structures as silicon or germanium but use alternating arrangements of two different atomic species in a checkerboard-like pattern to break the symmetry. The transition between the materials in the alternating pattern creates the critical "direct bandgap" property. Gallium arsenide, indium phosphide, gallium antimonide, gallium nitride are all examples of compound semiconductor materials that can be used to create junction diodes that emit light. In the absence of stimulated emission conditions and holes may coexist in proximity to one another, without recombining, for a certain time, termed the "upper-state lifetime" or "recombination time", before they recombine. A nearby photon with energy equal to the recombination energy can cause recombination by stimulated emission; this generates another photon of the same frequency and phase, travelling in the same direction as the first photon. This means that stimulated emission will cause gain in an optical wave (of the correct wavele
An electronic component is any basic discrete device or physical entity in an electronic system used to affect electrons or their associated fields. Electronic components are industrial products, available in a singular form and are not to be confused with electrical elements, which are conceptual abstractions representing idealized electronic components. Electronic components leads; these leads connect to create an electronic circuit with a particular function. Basic electronic components may be packaged discretely, as arrays or networks of like components, or integrated inside of packages such as semiconductor integrated circuits, hybrid integrated circuits, or thick film devices; the following list of electronic components focuses on the discrete version of these components, treating such packages as components in their own right. Components can be classified as active, or electromechanic; the strict physics definition treats passive components as ones that cannot supply energy themselves, whereas a battery would be seen as an active component since it acts as a source of energy.
However, electronic engineers who perform circuit analysis use a more restrictive definition of passivity. When only concerned with the energy of signals, it is convenient to ignore the so-called DC circuit and pretend that the power supplying components such as transistors or integrated circuits is absent, though it may in reality be supplied by the DC circuit; the analysis only concerns the AC circuit, an abstraction that ignores DC voltages and currents present in the real-life circuit. This fiction, for instance, lets us view an oscillator as "producing energy" though in reality the oscillator consumes more energy from a DC power supply, which we have chosen to ignore. Under that restriction, we define the terms as used in circuit analysis as: Active components rely on a source of energy and can inject power into a circuit, though this is not part of the definition. Active components include amplifying components such as transistors, triode vacuum tubes, tunnel diodes. Passive components can't introduce net energy into the circuit.
They can't rely on a source of power, except for what is available from the circuit they are connected to. As a consequence they can't amplify, although they may increase current. Passive components include two-terminal components such as resistors, capacitors and transformers. Electromechanical components can carry out electrical operations by using moving parts or by using electrical connectionsMost passive components with more than two terminals can be described in terms of two-port parameters that satisfy the principle of reciprocity—though there are rare exceptions. In contrast, active components lack that property. Conduct electricity in one direction, among more specific behaviors. Diode, diode bridge Schottky diode – super fast diode with lower forward voltage drop Zener diode – passes current in reverse direction to provide a constant voltage reference Transient voltage suppression diode, unipolar or bipolar – used to absorb high-voltage spikes Varicap, tuning diode, variable capacitance diode – a diode whose AC capacitance varies according to the DC voltage applied.
Light-emitting diode – a diode that emits light Photodiode – passes current in proportion to incident light Avalanche photodiode – photodiode with internal gain Solar Cell, photovoltaic cell, PV array or panel – produces power from light DIAC, Trigger Diode, SIDAC) – used to trigger an SCR Constant-current diode Peltier cooler – a semiconductor heat pump Tunnel diode - fast diode based on quantum mechanical tunneling Transistors were considered the invention of the twentieth century that changed electronic circuits forever. A transistor is a semiconductor device used to amplify and switch electronic signals and electrical power. Transistors Bipolar junction transistor – NPN or PNP Photo transistor – amplified photodetector Darlington transistor – NPN or PNP Photo Darlington – amplified photodetector Sziklai pair Field-effect transistor JFET – N-CHANNEL or P-CHANNEL MOSFET – N-CHANNEL or P-CHANNEL MESFET HEMT Thyristors Silicon-controlled rectifier – passes current only after triggered by a sufficient control voltage on its gate TRIAC – bidirectional SCR Unijunction transistor Programmable Unijunction transistor SIT SITh Composite transistors IGBT Digital electronics Analog Hall effect sensor – senses a magnetic field Current sensor – senses a current through it Opto-electronics Opto-isolator, opto-coupler, photo-coupler – photodiode, BJT, JFET, SCR, TRIAC, zero-crossing TRIAC, open collector IC, CMOS IC, solid state relay Slotted optical switch, opto switch, optical switch LED display – seven-segment display, sixteen-segment display, dot-matrix display Current: Filament lamp Vacuum fluorescent display Cathode ray tube (monochro
In physics, attenuation or, in some contexts, extinction is the gradual loss of flux intensity through a medium. For instance, dark glasses attenuate sunlight, lead attenuates X-rays, water and air attenuate both light and sound at variable attenuation rates. Hearing protectors help reduce acoustic flux from flowing into the ears; this phenomenon is measured in decibels. In electrical engineering and telecommunications, attenuation affects the propagation of waves and signals in electrical circuits, in optical fibers, in air. Electrical attenuators and optical attenuators are manufactured components in this field. In many cases, attenuation is an exponential function of the path length through the medium. In chemical spectroscopy, this is known as the Beer–Lambert law. In engineering, attenuation is measured in units of decibels per unit length of medium and is represented by the attenuation coefficient of the medium in question. Attenuation occurs in earthquakes. One area of research in which attenuation plays a prominent role, is in ultrasound physics.
Attenuation in ultrasound is the reduction in amplitude of the ultrasound beam as a function of distance through the imaging medium. Accounting for attenuation effects in ultrasound is important because a reduced signal amplitude can affect the quality of the image produced. By knowing the attenuation that an ultrasound beam experiences traveling through a medium, one can adjust the input signal amplitude to compensate for any loss of energy at the desired imaging depth. Ultrasound attenuation measurement in heterogeneous systems, like emulsions or colloids, yields information on particle size distribution. There is an ISO standard on this technique. Ultrasound attenuation can be used for extensional rheology measurement. There are acoustic rheometers that employ Stokes' law for measuring extensional viscosity and volume viscosity. Wave equations which take acoustic attenuation into account can be written on a fractional derivative form, see the article on acoustic attenuation or e.g. the survey paper.
Attenuation coefficients are used to quantify different media according to how the transmitted ultrasound amplitude decreases as a function of frequency. The attenuation coefficient can be used to determine total attenuation in dB in the medium using the following formula: Attenuation = α ⋅ ℓ ⋅ f Attenuation is linearly dependent on the medium length and attenuation coefficient, –approximately– on the frequency of the incident ultrasound beam for biological tissue. Attenuation coefficients vary for different media. In biomedical ultrasound imaging however, biological materials and water are the most used media; the attenuation coefficients of common biological materials at a frequency of 1 MHz are listed below: There are two general ways of acoustic energy losses: absorption and scattering, for instance light scattering. Ultrasound propagation through homogeneous media is associated only with absorption and can be characterized with absorption coefficient only. Propagation through heterogeneous media requires taking into account scattering.
Fractional derivative wave equations can be applied for modeling of lossy acoustical wave propagation, see acoustic attenuation and Ref. Main article: Electromagnetic absorption by waterShortwave radiation emitted from the sun have wavelengths in the visible spectrum of light that range from 360 nm to 750 nm; when the sun's radiation reaches the sea-surface, the shortwave radiation is attenuated by the water, the intensity of light decreases exponentially with water depth. The intensity of light at depth can be calculated using the Beer-Lambert Law. In clear open waters, visible light is absorbed at the longest wavelengths first. Thus, red and yellow wavelengths are absorbed at higher water depths, blue and violet wavelengths reach the deepest in the water column; because the blue and violet wavelengths are absorbed last compared to the other wavelengths, open ocean waters appear deep-blue to the eye. In near-shore waters, sea water contains more phytoplankton than the clear central ocean waters.
Chlorophyll-a pigments in the phytoplankton absorb light, the plants themselves scatter light, making coastal waters less clear than open waters. Chlorophyll-a absorbs light most in the shortest wavelengths of the visible spectrum. In near-shore waters where there are high concentrations of phytoplankton, the green wavelength reaches the deepest in the water column and the color of water to an observer appears green-blue or green; the energy with which an earthquake affects a location depends on the running distance. The attenuation in the signal of ground motion intensity plays an important role in the assessment of possible strong groundshaking. A seismic wave loses energy; this phenomenon is tied into the dispersion of the seismic energy with the distance. There are two types of dissipated energy: geometric dispersion caused by distribution of the seismic energy to greater volumes dispersion as heat called intrinsic attenuation or anelastic attenuat
The decibel is a unit of measurement used to express the ratio of one value of a power or field quantity to another on a logarithmic scale, the logarithmic quantity being called the power level or field level, respectively. It can be used to express a change in an absolute value. In the latter case, it expresses the ratio of a value to a fixed reference value. For example, if the reference value is 1 volt the suffix is "V", if the reference value is one milliwatt the suffix is "m". Two different scales are used when expressing a ratio in decibels, depending on the nature of the quantities: power and field; when expressing a power ratio, the number of decibels is ten times its logarithm to base 10. That is, a change in power by a factor of 10 corresponds to a 10 dB change in level; when expressing field quantities, a change in amplitude by a factor of 10 corresponds to a 20 dB change in level. The decibel scales differ by a factor of two so that the related power and field levels change by the same number of decibels in, for example, resistive loads.
The definition of the decibel is based on the measurement of power in telephony of the early 20th century in the Bell System in the United States. One decibel is one tenth of one bel, named in honor of Alexander Graham Bell. Today, the decibel is used for a wide variety of measurements in science and engineering, most prominently in acoustics and control theory. In electronics, the gains of amplifiers, attenuation of signals, signal-to-noise ratios are expressed in decibels. In the International System of Quantities, the decibel is defined as a unit of measurement for quantities of type level or level difference, which are defined as the logarithm of the ratio of power- or field-type quantities; the decibel originates from methods used to quantify signal loss in telegraph and telephone circuits. The unit for loss was Miles of Standard Cable. 1 MSC corresponded to the loss of power over a 1 mile length of standard telephone cable at a frequency of 5000 radians per second, matched the smallest attenuation detectable to the average listener.
The standard telephone cable implied was "a cable having uniformly distributed resistance of 88 Ohms per loop-mile and uniformly distributed shunt capacitance of 0.054 microfarads per mile". In 1924, Bell Telephone Laboratories received favorable response to a new unit definition among members of the International Advisory Committee on Long Distance Telephony in Europe and replaced the MSC with the Transmission Unit. 1 TU was defined such that the number of TUs was ten times the base-10 logarithm of the ratio of measured power to a reference power. The definition was conveniently chosen such that 1 TU approximated 1 MSC. In 1928, the Bell system renamed the TU into the decibel, being one tenth of a newly defined unit for the base-10 logarithm of the power ratio, it was named the bel, in honor of the telecommunications pioneer Alexander Graham Bell. The bel is used, as the decibel was the proposed working unit; the naming and early definition of the decibel is described in the NBS Standard's Yearbook of 1931: Since the earliest days of the telephone, the need for a unit in which to measure the transmission efficiency of telephone facilities has been recognized.
The introduction of cable in 1896 afforded a stable basis for a convenient unit and the "mile of standard" cable came into general use shortly thereafter. This unit was employed up to 1923 when a new unit was adopted as being more suitable for modern telephone work; the new transmission unit is used among the foreign telephone organizations and it was termed the "decibel" at the suggestion of the International Advisory Committee on Long Distance Telephony. The decibel may be defined by the statement that two amounts of power differ by 1 decibel when they are in the ratio of 100.1 and any two amounts of power differ by N decibels when they are in the ratio of 10N. The number of transmission units expressing the ratio of any two powers is therefore ten times the common logarithm of that ratio; this method of designating the gain or loss of power in telephone circuits permits direct addition or subtraction of the units expressing the efficiency of different parts of the circuit... In 1954, J. W. Horton argued that the use of the decibel as a unit for quantities other than transmission loss led to confusion, suggested the name'logit' for "standard magnitudes which combine by addition".
In April 2003, the International Committee for Weights and Measures considered a recommendation for the inclusion of the decibel in the International System of Units, but decided against the proposal. However, the decibel is recognized by other international bodies such as the International Electrotechnical Commission and International Organization for Standardization; the IEC permits the use of the decibel with field quantities as well as power and this recommendation is followed by many national standards bodies, such as NIST, which justifies the use of the decibel for voltage ratios. The term field quantity is deprecated by ISO 80000-1. In spite of their widespread use, suffixes are not recognized by the IEC or ISO. ISO 80000-3 describes definitions for units of space and time; the decibel for use in acoustics is defined in ISO 80000-8. The major difference from the article below is that for acoustics the decibel has no