Fiber-optic communication is a method of transmitting information from one place to another by sending light through an optical fiber. Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700 An optical fiber (or fibre) is a Glass or Plastic fiber that carries Light along its length The light forms an electromagnetic carrier wave that is modulated to carry information. Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. In Telecommunications, a carrier wave, or carrier is a Waveform (usually Sinusoidal) that is modulated (modified with an input signal In Telecommunications, modulation is the process of varying a periodic Waveform, i First developed in the 1970s, fiber-optic communication systems have revolutionized the telecommunications industry and played a major role in the advent of the Information Age. Information Age is a term that has been used to refer to the present era Because of its advantages over electrical transmission, the use of optical fiber has largely replaced copper wire communications in core networks in the developed world. Fiber-optic communication is a method of transmitting information from one place to another by sending Light through an Optical fiber. A core network (or network core is the central part of a telecom network that provides various services to customers who are connected by the Access network.
The process of communicating using fiber-optics involves the following basic steps: Creating the optical signal using a transmitter, relaying the signal along the fiber, ensuring that the signal does not become too distorted or weak, and receiving the optical signal and converting it into an electrical signal.
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Applications
Optical fiber is used by many telecommunications companies to transmit telephone signals, Internet communication, and cable television signals. An optical fiber (or fibre) is a Glass or Plastic fiber that carries Light along its length Due to much lower attenuation and interference, optical fiber has large advantages over existing copper wire in long-distance and high-demand applications. In Physics, attenuation (in some context also called extinction) is the gradual loss in intensity of any kind of Flux through a medium In physics interference is the addition ( superposition) of two or more Waves that result in a new wave pattern However, infrastructure development within cities was relatively difficult and time-consuming, and fiber-optic systems were complex and expensive to install and operate. Due to these difficulties, fiber-optic communication systems have primarily been installed in long-distance applications, where they can be used to their full transmission capacity, offsetting the increased cost. Since the year 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, where digging costs are low.
Since 1990, when optical-amplification systems became commercially available, the telecommunications industry has laid a vast network of intercity and transoceanic fiber communication lines. An optical amplifier is a device that amplifies an Optical signal directly without the need to first convert it to an electrical signal By 2002, an intercontinental network of 250,000 km of submarine communications cable with a capacity of 2. A submarine communications cable is a cable laid beneath the sea to carry Telecommunications between countries 56 Tb/s was completed, and although specific network capacities are privileged information, telecommunications investment reports indicate that network capacity has increased dramatically since 2002. A terabit is a unit of Information or Computer storage, abbreviated Tbit (or Tb)
History
The need for reliable long-distance communication systems has existed since antiquity. Over time, the sophistication of these systems has gradually improved, from smoke signals to telegraphs and finally to the first coaxial cable, put into service in 1940. The smoke signal is one of the oldest forms of communication in recorded history The electrical telegraph is a telegraph that uses electric signals The electromagnetic telegraph is a device for human-to-human transmission Coaxial cable is a cable consisting of an inner conductor surrounded by a tubular insulating layer typically made from a flexible material with a high Dielectric constant, all As these communication systems improved, certain fundamental limitations presented themselves. Electrical systems were limited by their small repeater spacing (the distance a signal can propagate before attenuation requires the signal to be amplified), and the bit rate of microwave systems was limited by their carrier frequency. 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 In Physics, attenuation (in some context also called extinction) is the gradual loss in intensity of any kind of Flux through a medium Microwaves are electromagnetic waves with Wavelengths ranging from 1 mm to 1 m or frequencies between 0 In the second half of the twentieth century, it was realized that an optical carrier of information would have a significant advantage over the existing electrical and microwave carrier signals.
In 1966 Kao and Hockham proposed optical fibres at STC Laboratories (STL), Harlow, when they showed that the losses of 1000 db/km in existing glass (compared to 5-10 db/km in coaxial cable) was due to contaminants, which could potentially be removed. Harlow is a New town and local government district in Essex, England. [1]
The development of lasers in the 1960s solved the first problem of a light source, further development of high-quality optical fiber was needed as a solution to the second. A laser is a device that emits Light ( Electromagnetic radiation) through a process called Stimulated emission. Optical fiber was finally developed in 1970 by Corning Glass Works with attenuation low enough for communication purposes (about 20dB/km), and at the same time GaAs semiconductor lasers were developed that were compact and therefore suitable for fiber-optic communication systems. Corning Incorporated ( is an American manufacturer of Glass, Ceramics and related materials primarily for industrial and scientific applications The decibel ( dB) is a logarithmic unit of measurement that expresses the magnitude of a physical quantity (usually power or intensity relative to The kilometre ( American spelling: kilometer) symbol km is a unit of Length in the Metric system, equal to one thousand A laser diode is a Laser where the active medium is a Semiconductor similar to that found in a Light-emitting diode.
After a period of intensive research from 1975 to 1980, the first commercial fiber-optic communication 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.
On 22 April, 1977, General Telephone and Electronics sent the first live telephone traffic through fiber optics, at 6 Mbit/s, in Long Beach, California.
The second generation of fiber-optic communication was developed for commercial use in the early 1980s, operated at 1. 3 µm, and used InGaAsP semiconductor lasers. Although these systems were initially limited by dispersion, in 1981 the single-mode fiber was revealed to greatly improve system performance. In Fiber-optic communication, a single-mode optical fiber ( SMF) is an Optical fiber designed to carry only a single ray of light (mode By 1987, these systems were operating at bit rates of up to 1. 7 Gb/s with repeater spacing up to 50 km. A gigabit is a unit of information or computer storage abbreviated Gbit (or Gb)
The first transatlantic telephone cable to use optical fiber was TAT-8, based on Desurvire optimized laser amplification technology. A transatlantic telephone cable is a Submarine communications cable that carries telephone traffic under the Atlantic Ocean. TAT-8 was the 8th Transatlantic telephone cable,initially carrying 40000 telephone circuits (simultaneous calls between USA, England and France It went into operation in 1988.
TAT-8 was developed as the first undersea fiber optic link between the United States and Europe. TAT-8 is more than 3,000 nautical miles (5,600 km) in length and was the first transatlantic cable to use optical fibers. It was designed to handle a mix of information. When inaugurated, it had an estimated lifetime in excess of 20 years. TAT-8 was the first of a new class of cables, even though it had already been used in long-distance land and short-distance undersea operations. Its installation was preceded by extensive deep-water experiments and trials conducted in the early 1980s to demonstrate the project's feasibility.
Third-generation fiber-optic systems operated at 1. 55 µm and had loss of about 0. 2 dB/km. They achieved this despite earlier difficulties with pulse-spreading at that wavelength using conventional InGaAsP semiconductor lasers. In Optics, dispersion is the phenomenon in which the Phase velocity of a wave depends on its frequency Scientists overcame this difficulty by using dispersion-shifted fibers designed to have minimal dispersion at 1. Dispersion-shifted fiber ( DSF) specified in ITU-T G653 is a type of Single-mode optical fiber with a core-clad index profile tailored to shift the Zero-dispersion 55 µm or by limiting the laser spectrum to a single longitudinal mode. A longitudinal mode of a Resonant cavity is a particular Standing wave pattern formed by Waves confined in the cavity These developments eventually allowed 3rd generation systems to operate commercially at 2. 5 Gbit/s with repeater spacing in excess of 100 km.
The fourth generation of fiber-optic communication systems used optical amplification to reduce the need for repeaters and wavelength-division multiplexing to increase fiber capacity. An optical amplifier is a device that amplifies an Optical signal directly without the need to first convert it to an electrical signal In Fiber-optic communications wavelength-division multiplexing ( WDM) is a technology which multiplexes multiple optical carrier signals on a In Electrical engineering, Computer science and Information theory, channel capacity is the tightest upper bound on the amount of Information These two improvements caused a revolution that resulted in the doubling of system capacity every 6 months starting in 1992 until a bit rate of 10 Tb/s was reached by 2001. A terabit is a unit of Information or Computer storage, abbreviated Tbit (or Tb) Recently, bit-rates of up to 14 Tbit/s have been reached over a single 160 km line using optical amplifiers.
The focus of development for the fifth generation of fiber-optic communications is on extending the wavelength range over which a WDM system can operate. The conventional wavelength window, known as the C band, covers the wavelength range 1. 53-1. 57 µm, and the new dry fiber has a low-loss window promising an extension of that range to 1. 30 to 1. 65 µm. Other developments include the concept of "optical solitons, " pulses that preserve their shape by counteracting the effects of dispersion with the nonlinear effects of the fiber by using pulses of a specific shape. In Optics, the term soliton is used to refer to any Optical field that does not change during propagation because of a delicate balance between nonlinear Nonlinear optics (NLO is the branch of Optics that describes the behaviour of Light in nonlinear media, that is media in which the dielectric polarization
In the late 1990s through 2000, the fiber optic communication industry became associated with the dot-com bubble. The " dot-com bubble " (or sometimes the " IT bubble " was a speculative bubble covering roughly 1995–2001 (with a climax on March 10 Industry promoters, and research companies such as KMI and RHK predicted vast increases in demand for communications bandwidth due to increased use of the Internet, and commercialization of various bandwidth-intensive consumer services, such as video on demand. The Internet is a global system of interconnected Computer networks Video on demand ( VOD) or Audio video on demand ( AVOD) systems allow users to select and watch/listen Internet protocol data traffic was said to be increasing exponentially, and at a faster rate than integrated circuit complexity had increased under Moore's Law. The Internet Protocol ( IP) is a protocol used for communicating data across a Packet-switched Internetwork using the Internet Protocol Moore's law describes an important trend in the History of computer hardware. From the bust of the dot-com bubble through 2006, however, the main trend in the industry has been consolidation of firms and offshoring of manufacturing to reduce costs. Consolidation or amalgamation is the act of merging many things into one Offshore may refer to oil and Natural gas production at sea see Oil platform.
Technology
Modern fiber-optic communication systems generally include an optical transmitter to convert an electrical signal into an optical signal to send into the optical fiber, a cable containing bundles of multiple optical fibers that is routed through underground conduits and buildings, multiple kinds of amplifiers, and an optical receiver to recover the signal as an electrical signal. The information transmitted is typically digital information generated by computers, telephone systems, and cable television companies. Digital communications refers to the transmission of a sequence of Digital messages (a Bit stream) or a digitized analog signal Digital telephony is the use of digital electronics in the provision of digital Telephone services and systems
Transmitters
The most commonly-used optical transmitters are semiconductor devices such as light-emitting diodes (LEDs) and laser diodes. A laser diode is a Laser where the active medium is a Semiconductor similar to that found in a Light-emitting diode. The difference between LEDs and laser diodes is that LEDs produce incoherent light, while laser diodes produce coherent light. In Physics, coherence is a property of waves that enables stationary (i In Physics, coherence is a property of waves that enables stationary (i For use in optical communications, semiconductor optical transmitters must be designed to be compact, efficient, and reliable, while operating in an optimal wavelength range, and directly modulated at high frequencies.
In its simplest form, an LED is a forward-biased p-n junction, emitting light through spontaneous emission, a phenomenon referred to as electroluminescence. A p-n junction is a junction formed by combining P-type and N-type Semiconductors together in very close contact Spontaneous emission is the process by which a light source such as an Atom, Molecule, Nanocrystal or nucleus in an Excited state Electroluminescence (EL is an Optical phenomenon and Electrical phenomenon in which a material emits light in response to an Electric current passed through The emitted light is incoherent with a relatively wide spectral width of 30-60 nm. LED light transmission is also inefficient, with only about 1 % of input power, or about 100 microwatts, eventually converted into «launched power» which has been coupled into the optical fiber. However, due to their relatively simple design, LEDs are very useful for low-cost applications.
Communications LEDs are most commonly made from gallium arsenide phosphide (GaAsP) or gallium arsenide (GaAs). Gallium arsenide phosphide () is a Semiconductor material, an alloy of Gallium arsenide and Gallium phosphide. Gallium arsenide ( GaAs) is a compound of two elements Gallium and Arsenic. Because GaAsP LEDs operate at a longer wavelength than GaAs LEDs (1. 3 micrometers vs. 0. 81-0. 87 micrometers), their output spectrum is wider by a factor of about 1. 7. The large spectrum width of LEDs causes higher fiber dispersion, considerably limiting their bit rate-distance product (a common measure of usefulness). LEDs are suitable primarily for local-area-network applications with bit rates of 10-100 Mbit/s and transmission distances of a few kilometers. LEDs have also been developed that use several quantum wells to emit light at different wavelengths over a broad spectrum, and are currently in use for local-area WDM networks. A quantum well is a Potential well that confines particles which were originally free to move in three dimensions to two dimensions forcing them to occupy a planar region In Fiber-optic communications wavelength-division multiplexing ( WDM) is a technology which multiplexes multiple optical carrier signals on a
A semiconductor laser emits light through stimulated emission rather than spontaneous emission, which results in high output power (~100 mW) as well as other benefits related to the nature of coherent light. 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 The output of a laser is relatively directional, allowing high coupling efficiency (~50 %) into single-mode fiber. The narrow spectral width also allows for high bit rates since it reduces the effect of chromatic dispersion. In Optics, dispersion is the phenomenon in which the Phase velocity of a wave depends on its frequency Furthermore, semiconductor lasers can be modulated directly at high frequencies because of short recombination time. In the Solid state physics of Semiconductors carrier generation and recombination are processes by which mobile Electrons and Electron holes
Laser diodes are often directly modulated, that is the light output is controlled by a current applied directly to the device. In Telecommunications, modulation is the process of varying a periodic Waveform, i For very high data rates or very long distance links, a laser source may be operated continuous wave, and the light modulated by an external device such as an electroabsorption modulator or Mach-Zehnder interferometer. A continuous wave or continuous waveform ( CW) is an Electromagnetic wave of constant Amplitude and Frequency; and in Mathematical The Mach-Zehnder interferometer (named after physicists Ludwig Mach (son of Ernst Mach) and Ludwig Zehnder) is a device used to determine the phase shift External modulation increases the achievable link distance by eliminating laser chirp, which broadens the linewidth of directly-modulated lasers, increasing the chromatic dispersion in the fiber. A chirp is a signal in which the Frequency increases ('up-chirp' or decreases ('down-chirp' with time The spectral linewidth characterizes the width of a Spectral line, such as in the electromagnetic emission spectrum of an atom or the Frequency spectrum
Fiber
Optical fiber consists of a core, cladding, and a protective outer coating, which guides light along the core by total internal reflection. An optical fiber (or fibre) is a Glass or Plastic fiber that carries Light along its length The core, and the lower-refractive-index cladding, are typically made of high-quality silica glass, though they can both be made of plastic as well. 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 Chemical compound silicon dioxide, also known as silica or silox (from the Latin " Silex " is an Oxide An optical fiber can break if bent too sharply. Due to the microscopic precision required to align the fiber cores, connecting two optical fibers, whether done by fusion splicing or mechanical splicing, requires special skills and interconnection technology. [2].
Two main categories of optical fiber used in fiber optic communications are multi-mode optical fiber and single-mode optical fiber. 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 Fiber-optic communication, a single-mode optical fiber ( SMF) is an Optical fiber designed to carry only a single ray of light (mode Multimode fiber has a larger core (≥ 50 micrometres), allowing less precise, cheaper transmitters and receivers to connect to it as well as cheaper connectors. A micrometre ( American spelling: micrometer; symbol µm) is one millionth of a Metre, or equivalently one thousandth of a Millimetre However, multi-mode fiber introduces multimode distortion which often limits the bandwidth and length of the link. Modal dispersion is a distortion mechanism occurring in Multimode fibers and other Waveguides in which the signal is spread in time because the propagation Furthermore, because of its higher dopant content, multimode fiber is usually more expensive and exhibits higher attenuation. 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 Single-mode fiber’s smaller core (<10 micrometres) necessitates more expensive components and interconnection methods, but allows much longer, higher-performance links.
In order to package fiber into a commercially-viable product, it is protectively-coated, typically by using ultraviolet (UV) light-cured acrylate polymers, terminated with optical fiber connectors, and assembled into a cable. An acrylate polymer belongs to a group of Polymers which could be referred to as plastics generally An optical fiber connector terminates the end of an Optical fiber, and enables quicker connection and disconnection than splicing. A cable is one or more Wires or Optical fibers bound together typically in a common protective jacket or sheath It can then be laid in the ground, run through a building or deployed aerially in a manner similar to copper cable. Once deployed, such cables require substantially less maintenance than copper cable. [1]
Amplifiers
The transmission distance of a fiber-optic communication system has traditionally been limited primarily by fiber attenuation and second by fiber distortion. An optical amplifier is a device that amplifies an Optical signal directly without the need to first convert it to an electrical signal The solution to this has been to use opto-electronic repeaters. These repeaters first convert the signal to an electrical signal then use a transmitter to send the signal again at a higher intensity. Because of their high complexity, especially with modern wavelength-division multiplexed signals, and the fact that they had to be installed about once every 20 km, the cost for these repeaters was very high.
An alternative approach is to use an optical amplifier, which amplifies the optical signal directly without having to convert the signal into the electrical domain. Made by doping a length of fiber with the rare-earth mineral erbium, and pumping it with light from a laser with a shorter wavelength than the communications signal (typically 980 nm), amplifiers have largely replaced repeaters in new installations. In Semiconductor production doping is the process of intentionally introducing impurities into an extremely pure (also referred to as intrinsic) semiconductor to Erbium (ˈɝbiəm is a Chemical element with the symbol Er and Atomic number 68 Laser pumping is the act of energy transfer from an external source into the Gain medium of a Laser. A laser is a device that emits Light ( Electromagnetic radiation) through a process called Stimulated emission. A nanometre ( American spelling: nanometer, symbol nm) ( Greek: νάνος nanos dwarf; μετρώ metrό count) is a
Receivers
The main component of an optical receiver is a photodetector that converts light into electricity through the photoelectric effect. Photosensors or photodetectors are Sensors of Light or other Electromagnetic energy Introduction When a Metallic surface is exposed to Electromagnetic radiation above a certain threshold Frequency, the light is absorbed and Electrons The photodetector is typically a semiconductor-based photodiode, such as a p-n photodiode, a p-i-n photodiode, or an avalanche photodiode. A photodiode is a type of Photodetector capable of converting Light into either current or Voltage, depending upon the mode of operation Metal-semiconductor-metal (MSM) photodetectors are also used due to their suitability for circuit integration in regenerators and wavelength-division multiplexers. Microchipsjpg|right|thumb|200px|Microchips ( EPROM memory with a transparent window showing the integrated circuit inside
The optical-electrical converters are typically coupled with a transimpedance amplifier and limiting amplifier to produce a digital signal in the electrical domain from the incoming optical signal, which may be attenuated and distorted by passing through the channel. Three kinds of devices are used in Electronics: generators (having only outputs Converters (having inputs and outputs Further signal processing such as clock recovery from data (CDR) by a phase-locked loop may also be applied before the data is passed on. A phase-locked loop or phase lock loop (PLL is a Control system that generates a signal that has a fixed relation to the phase of a "reference"
Wavelength-division multiplexing
Wavelength-division multiplexing (WDM) is the practice of dividing the wavelength capacity of an optical fiber into multiple channels in order to send more than one signal over the same fiber. In Fiber-optic communications wavelength-division multiplexing ( WDM) is a technology which multiplexes multiple optical carrier signals on a This requires a wavelength division multiplexer in the transmitting equipment and a wavelength division demultiplexer (essentially a spectrometer) in the receiving equipment. In Electronics, a multiplexer or mux ( occasionally the term muldex is also found for a combination multiplexer-demultiplexer A spectrometer is an Optical instrument used to measure properties of Light over a specific portion of the Electromagnetic spectrum, typically used Arrayed waveguide gratings are commonly used for multiplexing and demultiplexing in WDM. Arrayed waveguide gratings (AWG are commonly used as optical (demultiplexers in wavelength division multiplexed (WDM systems Using WDM technology now commercially available, the bandwidth of a fiber can be divided into as many as 80 channels to support a combined bit rate into the range of terabits per second. A terabit is a unit of Information or Computer storage, abbreviated Tbit (or Tb)
Bandwidth-distance product
Because the effect of dispersion increases with the length of the fiber, a fiber transmission system is often characterized by its bandwidth-distance product, often expressed in units of MHz×km. The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. This value is a product of bandwidth and distance because there is a trade off between the bandwidth of the signal and the distance it can be carried. For example, a common multimode fiber with bandwidth-distance product of 500 MHz×km could carry a 500 MHz signal for 1 km or a 1000 MHz signal for 0. 5 km.
Through a combination of advances in dispersion management, wavelength-division multiplexing, and optical amplifiers, modern-day optical fibers can carry information at around 14 Terabits per second over 160 kilometers of fiber [3]. In Fiber-optic communications wavelength-division multiplexing ( WDM) is a technology which multiplexes multiple optical carrier signals on a Engineers are always looking at current limitations in order to improve fiber-optic communication, and several of these restrictions are currently being researched:
Dispersion
For modern glass optical fiber, the maximum transmission distance is limited not by attenuation but by dispersion, or spreading of optical pulses as they travel along the fiber. In Physics, attenuation (in some context also called extinction) is the gradual loss in intensity of any kind of Flux through a medium In Optics, dispersion is the phenomenon in which the Phase velocity of a wave depends on its frequency Dispersion in optical fibers is caused by a variety of factors. Intermodal dispersion, caused by the different axial speeds of different transverse modes, limits the performance of multi-mode fiber. Multi-mode optical fiber ( multimode fiber or MM fiber or fibre) is a type of Optical fiber mostly used for communication over shorter distances Because single-mode fiber supports only one transverse mode, intermodal dispersion is eliminated.
In single-mode fiber performance is primarily limited by chromatic dispersion (also called group velocity dispersion), which occurs because the index of the glass varies slightly depending on the wavelength of the light, and light from real optical transmitters necessarily has nonzero spectral width (due to modulation). In Optics, dispersion is the phenomenon in which the Phase velocity of a wave depends on its frequency In Optics, dispersion is the phenomenon in which the Phase velocity of a wave depends on its frequency Polarization mode dispersion, another source of limitation, occurs because although the single-mode fiber can sustain only one transverse mode, it can carry this mode with two different polarizations, and slight imperfections or distortions in a fiber can alter the propagation velocities for the two polarizations. Polarization mode dispersion (PMD is a form of Modal dispersion where two different Polarizations of light in a waveguide which normally travel at the same speed This phenomenon is called fiber birefringence and can be counteracted by polarization-maintaining optical fiber. Birefringence, or double refraction, is the decomposition of a ray of Light into two rays (the ordinary ray and the extraordinary ray In Fiber optics, polarization-maintaining optical fiber ( PMF or PM fiber) is Optical fiber in which the Polarization of linearly-polarized Dispersion limits the bandwidth of the fiber because the spreading optical pulse limits the rate that pulses can follow one another on the fiber and still be distinguishable at the receiver.
Some dispersion, notably chromatic dispersion, can be removed by a 'dispersion compensator'. This works by using a specially prepared length of fiber that has the opposite dispersion to that induced by the transmission fiber, and this sharpens the pulse so that it can be correctly decoded by the electronics.
Attenuation
Fiber attenuation, which necessitates the use of amplification systems, is caused by a combination of material absorption, Rayleigh scattering, Mie scattering, and connection losses. In Physics, attenuation (in some context also called extinction) is the gradual loss in intensity of any kind of Flux through a medium In Physics, absorption of electromagnetic radiation is the process by which the Energy of a Photon is taken up by matter typically the electrons of an Rayleigh scattering (named after Lord Rayleigh) is the elastic Scattering of Light or other electromagnetic radiation by particles much smaller Mie theory, also called Lorenz-Mie theory or Lorenz-Mie-Debye theory, is a complete analytical solution of Maxwell's equations for the Scattering Although material absorption for pure silica is only around 0. 03 dB/km (modern fiber has attenuation around 0. 3 dB/km), impurities in the original optical fibers caused attenuation of about 1000 dB/km. Other forms of attenuation are caused by physical stresses to the fiber, microscopic fluctuations in density, and imperfect splicing techniques.
Transmission windows
Each of the effects that contributes to attenuation and dispersion depends on the optical wavelength, however wavelength bands exist where these effects are weakest, making these bands, or windows, most favorable for transmission. These windows have been standardized, and the current bands defined are the following: [4]
| Band | Description | Wavelength Range |
|---|---|---|
| O band | original | 1260 to 1360 nm |
| E band | extended | 1360 to 1460 nm |
| S band | short wavelengths | 1460 to 1530 nm |
| C band | conventional ("erbium window") | 1530 to 1565 nm |
| L band | long wavelengths | 1565 to 1625 nm |
| U band | ultralong wavelengths | 1625 to 1675 nm |
Note that this table shows that current technology has managed to bridge the second and third windows- originally the windows were disjoint.
Historically, the first window used was from 800-900 nm; however losses are high in this region and because of that, this is mostly used for short-distance communications. The second window is around 1300 nm, and has much lower losses. The region has zero dispersion. The third window is around 1500nm, and is the most widely used. This region has the lowest attenuation losses and hence it achieves the longest range. However it has some dispersion, and dispersion compensators are used to remove this.
Regeneration
When a communications link must span a larger distance than existing fiber-optic technology is capable of, the signal must be regenerated at intermediate points in the link by 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 Repeaters add substantial cost to a communication system, and so system designers attempt to minimize their use.
Recent advances in fiber and optical communications technology have reduced signal degradation so far that regeneration of the optical signal is only needed over distances of hundreds of kilometers. This has greatly reduced the cost of optical networking, particularly over undersea spans where the cost and reliability of repeaters is one of the key factors determining the performance of the whole cable system. The main advances contributing to these performance improvements are dispersion management, which seeks to balance the effects of dispersion against non-linearity; and solitons, which use nonlinear effects in the fiber to enable dispersion-free propagation over long distances. In Optics, the term soliton is used to refer to any Optical field that does not change during propagation because of a delicate balance between nonlinear
Last mile
Although fiber-optic systems excel in high-bandwidth applications, optical fiber has been slow to achieve its goal of fiber to the premises or to solve the last mile problem. The last Mile is the final leg of delivering connectivity from a communications provider to a customer The last Mile is the final leg of delivering connectivity from a communications provider to a customer However, as bandwidth demand increases, more and more progress towards this goal can be observed. In Japan, for instance, fiber-optic systems are beginning to replace wire-based DSL as a broadband Internet source. South Korea’s KT also provides a service called FTTH (Fiber To The Home), which provides 100 percent fiber-optic connections to the subscriber’s home. Verizon, a US based telecom company, provides a service called FiOS which offers TV, high-speed internet, and telephone communications on a 100 percent fiber-optic network to a junction box mounted in a subscriber’s home. Verizon FiOS, sometimes simply FiOS which stands for " Fi ber O ptic S ervice", is an Internet telephone and TV service that is presently
Comparison with electrical transmission
The choice between optical fiber and electrical (or copper) transmission for a particular system is made based on a number of trade-offs. Copper (ˈkɒpɚ is a Chemical element with the symbol Cu (cuprum and Atomic number 29 Optical fiber is generally chosen for systems requiring higher bandwidth or spanning longer distances than electrical cabling can accommodate. The main benefits of fiber are its exceptionally low loss, allowing long distances between amplifiers or repeaters; and its inherently high data-carrying capacity, such that thousands of electrical links would be required to replace a single high bandwidth fiber. Another benefit of fiber is that even when run alongside each other for long distances, fiber cables experience effectively no crosstalk, in contrast to some types of electrical transmission lines. In Electronics, the term crosstalk ( XT) refers to any phenomenon by which a signal transmitted on one circuit or channel of a Transmission system A transmission line is the material medium or structure that forms all or part of a path from one place to another for directing the transmission of energy
In short distance and relatively low bandwidth applications, electrical transmission is often preferred because of its
- Lower material cost, where large quantities are not required.
- Lower cost of transmitters and receivers.
- Ease of splicing. The Western Union or Lineman splice was developed during the introduction of the Telegraph to mechanically terminate aerial conductors that were subject to loading
- Capability to carry electrical power as well as signals. Electric power is defined as the rate at which Electrical energy is transferred by an Electric circuit.
- Ease of operating transducers in linear mode. The word linear comes from the Latin word linearis, which means created by lines.
Because of these benefits of electrical transmission, optical communication is not common in short box-to-box, backplane, or chip-to-chip applications; however, optical systems on those scales have been demonstrated in the laboratory. A backplane (or "backplane system" is a circuit board (usually a Printed circuit board) that connects several connectors in parallel to each other so
In certain situations fiber may be used even for short distance or low bandwidth applications, due to other important features:
- Immunity to electromagnetic interference, including nuclear electromagnetic pulses (although fiber can be damaged by alpha and beta radiation). The term electromagnetic pulse ( EMP) has the following meanings Electromagnetic radiation from an Explosion (especially a Nuclear Alpha particles (named after and denoted by the first letter in the Greek alphabet, α consist of two Protons and two Neutrons bound together into a Beta particles are high-energy high-speed Electrons or Positrons emitted by certain types of Radioactive nuclei such as Potassium -40
- High electrical resistance, making it safe to use near high-voltage equipment or between areas with different earth potentials. Electrical resistance is a ratio of the degree to which an object opposes an Electric current through it measured in Ohms Its reciprocal quantity is
- Lighter weight, important, for example, in aircraft.
- No sparks, important in flammable or explosive gas environments.
- Not electromagnetically radiating, and difficult to tap without disrupting the signal, important in high-security environments.
- Much smaller cable size — important where pathway is limited, such as networking an existing building, where smaller channels can be drilled.
Governing standards
In order for various manufacturers to be able to develop components that function compatibly in fiber optic communication systems, a number of standards have been developed. The International Telecommunications Union publishes several standards related to the characteristics and performance of fibers themselves, including
- ITU-T G. 651, «Characteristics of a 50/125 µm multimode graded index optical fibre cable»
- ITU-T G. 652, «Characteristics of a single-mode optical fibre cable»
Other standards, produced by a variety of standards organizations, specify performance criteria for fiber, transmitters, and receivers to be used together in conforming systems. A standards organization, standards body, standards development organization or SDO is any entity whose primary activities are developing coordinating Some of these standards are the following:
- 10 gigabit Ethernet
- FDDI
- Fibre Channel
- Gigabit Ethernet
- HIPPI
- Synchronous Digital Hierarchy
- Synchronous Optical Networking
TOSLINK is the most common format for digital audio cable using plastic optical fiber to connect digital sources to digital receivers. Fiber distributed data interface ( FDDI) provides a standard for Data transmission in a Local area network Fibre Channel, or FC, is a Gigabit -speed network technology primarily used for Storage networking. Gigabit Ethernet (GbE or 1 GigE is a term describing various technologies for transmitting Ethernet frames at a rate of a gigabit per second, as defined by the HIPPI ( HIgh Performance Parallel Interface) is a Computer bus for the attachment of high speed storage devices to Supercomputers It was popular in the late Synchronous optical networking (SONET and Synchronous Digital Hierarchy (SDH are two closely related Multiplexing protocols for transferring multiple Synchronous optical networking (SONET and Synchronous Digital Hierarchy (SDH are two closely related Multiplexing protocols for transferring multiple TOSLINK or Optical Cable is a standardized Optical fiber connection system Digital audio uses Digital signals for Sound reproduction. This includes analog-to-digital conversion, digital-to-analog conversion, storage Plastic optical fiber (POF (or fibre) is an Optical fiber which is made out of Plastic. This article is about a radio receiver for other uses see Radio (disambiguation.
See also
References
- Encyclopedia of Laser Physics and Technology
- Fiber-Optic Technologies by Vivek Alwayn
- Agrawal, Govind P. Optical communication is any form of Telecommunication that uses Light as the transmission medium Information theory is a branch of Applied mathematics and Electrical engineering involving the quantification of Information. Verizon FiOS, sometimes simply FiOS which stands for " Fi ber O ptic S ervice", is an Internet telephone and TV service that is presently In Fiber-optic communications dark fiber or unlit fiber (or fibre refers to unused fibers, available for use (2002). Fiber-optic communication systems. New York: John Wiley & Sons. John Wiley & Sons Inc, also referred to as Wiley, is a global Publishing company that markets its products to professionals and consumers students and instructors ISBN 0-471-21571-6.
Notes
- ^ University of Birmingham - Fibre Optic Materials
- ^ Alwayn, Vivek (2004-04-23). "MMIV" redirects here For the Modest Mouse album see " Baron von Bullshit Rides Again " Events 215 BC - A temple is built on the Capitoline Hill dedicated to Venus Erycina to commemorate the Roman defeat at Splicing. Fiber-Optic Technologies. Cisco Systems. Retrieved on 2006-12-31. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 406 – Vandals, Alans and Suebians cross the Rhine, beginning an invasion of Gallia.
- ^ NTT (2006-09-29). Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 522 BC - Darius I of Persia kills the Magian usurper Gaumâta securing his hold as king of the Persian Empire. "14 Tbit/s over a single optical fiber: successful demonstration of world's largest capacity". Press release. A news release, media release, press release or press statement is a written or recorded Communication directed at members of the News Retrieved on 2006-12-31. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 406 – Vandals, Alans and Suebians cross the Rhine, beginning an invasion of Gallia.
- ^ Encyclopedia of Laser Physics and Technology
External links
- How Fiber-optics work (Howstuffworks.com)
- The Laser and Fiber-optic Revolution
- Fiber Optics, from Hyperphysics at Georgia State University
- "Understanding Optical Communications" An IBM redbook
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