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Ministry of Transport of the Russian Federation
Federal Agency for Railway Transport
Omsk State University means of communication
Taiga Institute of Railway Transport - a branch of the federal state budgetary educational institution higher professional education
"Omsk State Transport University"
Thematic abstract
P about the discipline: "History of the development of systems and networks of telecommunications of railway transport"
On the topic: "The history of the development of cable and fiber-optic transmission systems"
Taiga 2015
Introduction
1. The history of the development of cable information transmission systems
2. History of fiber optic information transmission systems
Conclusion
Bibliographic list
Introduction
In recent decades, the cable industry has played an important role in the development information technologies. The constant need of people to expand the transmission of cable networks, which was stimulated by the emergence of increasingly resource-intensive programs, as well as the development of the Internet, which includes email, which has become the most widespread means of communication, has made the evolution of cable networks an important condition for the continued progress in this industry.
Cabling technologists and designers have improved the performance of copper cabling networks in an attempt to keep them up to date with technology requirements.
We have witnessed a growing need to transmit vast amounts of information over long distances. Intensively used for the transmission of information over the past 20 years, technologies such as coaxial cables, satellite and microwave communications have very quickly exhausted their capabilities. The transmission capacity requirements far exceeded the capabilities of existing systems.
In industrial systems with a high level of interference, where the need for data transmission and networking of control systems grew rapidly, a growing need was felt for a new transmission medium. Solving the problems of limited transmission bandwidth and advanced level interference in industrial environments has been successfully found with the advent of fiber optic communication systems.
The purpose of this essay is to consider the history of the development of cable and fiber-optic transmission systems, the significance of these inventions and future prospects.
1. The history of the development of cable information transmission systems
The entire history of the development of cable communication systems is associated with the problem of increasing the amount of information transmitted over a wired communication channel.
In turn, the amount of transmitted information is determined by the bandwidth. It has been established that the achievable information transfer rate is the higher, the higher the frequency of oscillations of an electric current or a radio wave. In order to encode any letter of the alphabet, it is necessary to use 7-8 bits. Thus, if wired communication with a frequency of 20 kHz is used to transmit text, then a standard book of 400-500 pages can be transmitted in about 1.5-2 hours. When transmitting over a 32 MHz line, the same procedure will require only 2-3 seconds.
Let us consider how with the development of wired communication, i.e. with the development of new frequencies, the throughput of the communication channel changed.
As noted above, the development of electrical information transmission systems began with the invention by P. L. Schilling in 1832 of a telegraph line using needles. A copper wire was used as a communication line. This line provided information transfer rate - 3 bit / s (1/3 letters). The first Morse telegraph line (1844) provided a speed of 5 bps (0.5 letters). The invention in 1860 of a printing telegraph system provided a speed of 10 bits / s (1 letter). In 1874, the Baudot six-fold telegraph system already provided a transmission rate of 100 bits / s (10 letters). The first telephone lines, built on the basis of the telephone invented by Bell in 1876, provided an information transfer rate of 1000 bit / s (1 kbit / s - 100 letters).
The first practical telephone circuit was single-wire with telephone sets connected at its ends. This principle required a large number of not only connecting lines, but also the telephone sets themselves. This simple device was replaced in 1878 by the first switch, which made it possible to connect several telephone sets through a single switching field.
Prior to 1900, the originally used single-wire grounded-wire circuits were replaced by two-wire transmission lines. Despite the fact that by this time the switchboard had already been invented, each subscriber had his own communication line. A way was needed to increase the number of channels without laying additional thousands of kilometers of wires. However, the advent of this method (the sealing system) was delayed until the advent of electronics in the early 1900s. The first commercial multiplexing system was created in the United States, where a four-channel frequency division system began operating between Baltimore and Pittsburgh in 1918. Prior to the Second World War, most developments were directed towards increasing the efficiency of overhead line sealing systems and multi-pair cables, since almost all telephone circuits were organized over these two transmission media.
The invention in 1920 of six to twelve channel transmission systems made it possible to increase the speed of information transmission in a given frequency band up to 10,000 bps, (10 kbps - 1000 letters). The upper limiting frequencies of overhead and multi-pair cable lines were 150 and 600 kHz, respectively. The need to transmit large amounts of information required the creation of broadband transmission systems.
In the 1930s and 1940s, coaxial cables were introduced. In 1948, between cities located on the Atlantic and Pacific coasts of the United States, the Bell System put into operation the L1 coaxial cable system. This coaxial-cable system made it possible to increase the bandwidth of the linear path up to 1.3 MHz, which ensured the transmission of information over 600 channels.
After the Second World War, active developments were carried out to improve coaxial cable systems. If initially coaxial circuits were laid separately, then they began to combine several coaxial cables in a common protective sheath. For example, the American company Bell developed in the 1960s an intercontinental system with a bandwidth of 17.5 MHz (3600 channels over a coaxial circuit or “tube”). For this system, a cable was developed in which 20 "tubes" were combined in one sheath. The total capacity of the cable was 32,400 channels in each direction, and two "tubes" remained in reserve. cable fiber transmission information
In the USSR, at about the same time, the K-3600 system was developed on the domestic cable KMB 8/6, which has 14 coaxial circuits in one sheath. Then comes the coaxial system with a larger bandwidth of 60 MHz. It provided a capacity of 9000 channels in each pair. 22 pairs are combined in a common shell.
High-capacity coaxial cable systems in the late 20th century were commonly used for communication between closely spaced centers with high population density. However, the cost of installing such systems was high due to the small distance between the intermediate amplifiers and due to the high cost of the cable and its laying.
2. History of fiber optic information transmission systems
According to modern views, all electromagnetic radiation, including radio waves and visible light, have a dual structure and behave either as a wave-like process in a continuous medium or as a stream of particles called photons, or quanta. Each quantum has a certain energy.
The idea of light as a stream of particles was first introduced by Newton. In 1905, A. Einstein, on the basis of Planck's theory, revived in new form corpuscular theory of light, which is now called quantum theory Sveta. In 1917, he theoretically predicted the phenomenon of stimulated or induced radiation, on the basis of which quantum amplifiers were subsequently created. In 1951, Soviet scientists V. A. Fabrikant, M. M. Vudynsky and F. A. Butaeva received a copyright certificate for the discovery of the principle of operation of an optical amplifier. Somewhat later, in 1953, a proposal for a quantum amplifier was made by Weber. In 1954, N. G. Basov and A. M. Prokhorov proposed a specific project for a molecular gas generator and amplifier with theoretical justification. Gordon, Zeiger, and Towns independently came up with the idea of a similar generator, publishing in 1954 a report on the creation of an operating quantum generator based on a beam of ammonia molecules. Somewhat later, in 1956, Blombergen established the possibility of building a quantum amplifier based on a solid paramagnetic substance, and in 1957 such an amplifier was built by Skovel, Feher, and Seidel. All quantum generators and amplifiers built before 1960 operated in the microwave range and were called masers. This name comes from the first letters of the English words “Microwave amplification by stimulated emission of radiation”, which means “microwave amplification by stimulated emission of radiation”.
The next stage of development is associated with the transfer of known methods to the optical range. In 1958, Towns and Shavlov theoretically substantiated the possibility of creating an optical quantum generator (OQG) on a solid state. In 1960 Meiman built the first pulsed laser on a solid - ruby. In the same year, the question of lasers and quantum amplifiers was independently analyzed by N. G. Basov, O. N. Krokhin, and Yu. M. Popov.
In 1961, the first gas (helium-neon) generator was created by Janavan, Bennett and Erriot. In 1962, the first semiconductor laser was created. Optical quantum generators (OQGs) are called lasers. The term "Laser" was formed as a result of replacing the letter "m" in the word maser with the letter "l" (from the English word "light").
After the creation of the first masers and lasers, work began on their use in communication systems.
Fiber optics, as an original branch of technology, emerged in the early 1950s. At this time, they learned how to make thin two-layer fibers from various transparent materials (glass, quartz, etc.). Even earlier, it was predicted that if the optical properties of the inner (“core”) and outer (“cladding”) parts of such a fiber are chosen appropriately, then a beam of light introduced through the end into the core will only propagate along it and be reflected from the cladding. Even if the fiber is bent (but not too sharply), the beam will obediently be held inside the core. Thus, a light beam - this is a synonym for a straight line - falling into an optical fiber, it turns out to be able to propagate along any curvilinear trajectory. There is a complete analogy with electric shock flowing through a metal wire, so a two-layer optical fiber is often called a light guide or light guide. Glass or quartz fibers, 2-3 times the thickness of a human hair, are very flexible (they can be wound on a spool) and strong (stronger than steel threads of the same diameter). However, the light guides of the 1950s were not transparent enough, and with a length of 5-10 m, the light was completely absorbed in them.
In 1966, the idea was put forward of the fundamental possibility of using optical fibers for communication purposes. Technological search ended in success in 1970 - ultra-pure quartz fiber was able to transmit a light beam at a distance of up to 2 km. In fact, in the same year, the ideas of laser communication and the possibilities of fiber optics "found each other", the rapid development of fiber-optic communication began: the emergence of new methods for manufacturing fibers; creation of other necessary elements, such as miniature lasers, photodetectors, optical connectors, etc.
Already in 1973-1974. the distance that the beam could travel along the fiber reached 20 km, and by the beginning of the 1980s it had exceeded 200 km. By the same time, the speed of information transmission over FOCL had increased to unprecedented values - several billion bits / s. In addition, it turned out that FOCLs not only have an ultra-high data transfer rate, but also have a number of other advantages.
The light signal is not affected by external electromagnetic interference. Moreover, it is impossible to eavesdrop, that is, to intercept. Fiber light guides have excellent weight and size characteristics: the materials used have a low specific gravity, there is no need for heavy metal sheaths; ease of laying, installation, operation. Fiber light guides can be laid in a conventional underground cable duct, can be mounted on high-voltage power lines or power networks of electric trains, and generally combined with any other communications. The characteristics of FOCLs do not depend on their length, on switching on or off additional lines - in electrical circuits, all this is not the case, and each such change requires painstaking tuning work. In principle, sparking is impossible in fiber light guides, and this opens up the prospect of using them in explosive and similar industries.
The cost factor is also very important. At the end of the last century, fiber communication lines, as a rule, were commensurate in cost with wire lines, but over time, given the shortage of copper, the situation will certainly change. This belief is based on the fact that the optical fiber material - quartz - has an unlimited raw material resource, while the basis of wire lines is made up of now rare metals such as copper and lead. And it's not just about the cost. If communication develops on a traditional basis, then by the end of the century all the mined copper and all the lead will be spent on the manufacture of telephone cables - but how to develop further?
Conclusion
We examined the history of the development of cable and fiber-optic transmission systems and found that at present, optical communication lines occupy a dominant position in all telecommunication systems, from backbone networks to the home distribution network. Thanks to the development of fiber-optic communication lines, multi-service systems are being actively introduced, which make it possible to bring telephony, television and the Internet to the end user in one cable.
Bibliographic list
1. Samarsky P. A. Fundamentals of structured cable systems - M .: Company IT; DMK Press, 2013 - 216 p.
2. Bailey D, Wright E. Fiber optics. Theory and practice - M.: Kudits-Obraz, 2012 -- 320 s.
3. Lomovitsky V.V., Mikhailov A.I. Fundamentals of building systems and networks for information transmission - M .: Stereotype, 2011 - 382 p.
4. Levin D.Yu. History of technology. The history of the development of the control system for the transportation process in railway transport - Novosibirsk: UMTs ZHDT, 2014. - 467 p.
5. Rodina O.V. Fiber-optic communication lines - M.: Grif, 2014 - 400 p.
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The history of the development of communication lines in Russia The first long-distance overhead line was built between St. Petersburg and Warsaw in 1854. In the 1870s, an overhead communication line from St. Petersburg to Vladivostok L = 10 thousand km was put into operation. In 1939, a high-frequency communication line was put into operation from Moscow to Khabarovsk L = 8,300 thousand km. In 1851, a telegraph cable was laid from Moscow to St. Petersburg, insulated with gutta-percha tape. In 1852, the first submarine cable was laid across the Northern Dvina. In 1866, a cable transatlantic telegraph line between France and the United States was put into operation.
The history of the development of communication lines in Russia In the years in Russia, the first overhead city telephone networks were built (the cable totaled up to 54 wires with air-paper insulation) In 1901, the construction of an underground city telephone network began in Russia winding to artificially increase the inductance. Since 1917, a telephone amplifier based on vacuum tubes has been developed and tested on the line, in 1923 telephone communication with amplifiers on the Kharkov-Moscow-Petrograd line was carried out. Since the beginning of the 1930s, multichannel transmission systems based on coaxial cables began to develop.
The history of the development of communication lines in Russia In 1936, the first coaxial HF telephone line for 240 channels was put into operation. In 1956, an underwater coaxial telephone and telegraph trunk was built between Europe and America. In 1965, the first experimental waveguide lines and cryogenic cable lines with very low attenuation appeared. By the beginning of the 1980s, fiber-optic communication systems had been developed and tested in real conditions.
Types of communication lines (LS) and their properties There are two main types of LS: - lines in the atmosphere (RL radio links) - guide transmission lines (communication lines). typical wavelengths and radio frequencies Extra long waves (VLF) Long waves (LW) Medium waves (MW) Short waves (HF) Ultrashort waves (VHF) Decimeter waves (DCM) Centimeter waves (CM) Millimeter waves (MM) Optical range km ( kHz) km (kHz) 1.0... 0.1 km (0. MHz) m (MHz) m (MHz) .1 m (0. GHz) cm (GHz) mm (GHz) .1 µm
The main disadvantages of RL (radio communications) are: -dependence of the quality of communication on the state of the transmission medium and external electromagnetic fields; -low speed; insufficiently high electromagnetic compatibility in the range of meter waves and above; - the complexity of the transmitter and receiver equipment; - narrow-band transmission systems, especially at long wavelengths and higher.
In order to reduce the shortcomings of the radar, higher frequencies (centimeter, optical ranges) decimeter millimeter range are used. This is a chain of repeaters installed every 50 km-100 km. RRL allow you to receive the number of channels () over distances (up to km); These lines are less susceptible to interference, provide a fairly stable and high-quality connection, but the degree of transmission security through them is insufficient. Radio relay lines (RRL)
Centimeter wave range. SLs allow for multi-channel communication over an “infinite” distance; Satellite communication lines (SL) Advantages of SL - a large area of coverage and transmission of information over long distances. The disadvantage of SL is the high cost of launching a satellite and the complexity of organizing duplex telephone communication.
Advantages of guiding drugs -high quality signal transmission, -high transmission speed, -great protection from the influence of third-party fields, -relative simplicity of terminal devices. Disadvantages of directing LS - high cost of capital and operating costs, - relative duration of establishing a connection.
Radar and LS do not oppose, but complement each other At present, signals from direct current to the optical frequency range are transmitted over communication lines, and the operating wavelength range extends from 0.85 microns to hundreds of kilometers. - cable (CL) - air (VL) - fiber optic (FOCL). The main types of directional drugs:
BASIC REQUIREMENTS FOR COMMUNICATION LINES - communication over distances up to km within the country and up to for international communication; - broadband and suitability for transmission various kinds modern information (television, telephony, data transmission, broadcasting, transmission of newspaper pages, etc.); - protection of circuits from mutual and external interference, as well as from lightning and corrosion; - stability of the electrical parameters of the line, stability and reliability of communication; - efficiency of the communication system as a whole.
Modern development cable technology 1. Predominant development of coaxial systems, which make it possible to organize powerful communication bundles and transmit television programs over long distances via a single-cable communication system. 2.Creation and implementation of promising communication OKs that provide a large number of channels and do not require scarce metals (copper, lead) for their production. 3. Widespread introduction of plastics (polyethylene, polystyrene, polypropylene, etc.) into cable technology, which have good electrical and mechanical characteristics and make it possible to automate production.
4. The introduction of aluminum, steel and plastic shells instead of lead. The sheaths must be airtight and ensure the stability of the electrical parameters of the cable throughout the entire service life. 5. Development and introduction into production of economical designs of cables for intrazonal communication (single-coaxial, single-quad, unarmoured). 6. Creation of shielded cables that reliably protect the information transmitted through them from external electromagnetic influences and thunderstorms, in particular cables in two-layer sheaths such as aluminum steel and aluminum lead.
7. Increasing the electrical strength of the insulation of communication cables. A modern cable must simultaneously have the properties of both a high-frequency cable and a power electric cable, and ensure the transmission of high voltage currents for remote power supply of unattended amplifying points over long distances.
Since ancient times, as a carrier of information, a person has mainly used acoustic waves - sound and electromagnetic waves - light. People at a distance of line of sight exchanged messages using conventional signs; outside the line of sight, to cover a significant area, messages were transmitted using the sounds of a horn or a battle trumpet. To increase the range and a certain decrease in the angle of direction of message transmission, people used light: the fires of fires on the tops of mountains, later on - torches and "bonfires of alarms or victories" on high towers. Sailors used signal lamps to transmit information. Information has been preserved that in the XII century. BC, the news of the fall of Troy was transmitted to Greece precisely by optical means.
In the early 1890s, the Russian inventor I.P. Kulibin and the Frenchman K. Chapp (Claude Chapp) independently developed an optical telegraph, intended mainly for the transmission of military and government messages. Optical telegraph K. Chapp used during the war of the French Republic against Austria, more than 20 stations connected Paris with Lille (230 km). Messages were transferred from one end to the other in 15 minutes. In Russia, for military and government purposes, the optical telegraph connected St. Petersburg with Shlisselburg (1824), Kronstadt, Tsarskoye Selo and Gatchina. The world's longest (1200 km) optical telegraph line was opened in 1839 between St. Petersburg and Warsaw. In the devices of both inventors, only the design of the semaphore was the same.
English physicist John Tyndall in 1870 demonstrated the possibility of controlling light based on internal reflections. At a meeting of the Royal Society, it was shown that light propagating in a stream of purified water can go around any corner. In the experiment, water flowed over the horizontal bottom of one chute and fell along a parabolic trajectory into another chute. The light entered the stream of water through a transparent window at the bottom of the first trough. When Tyndall directed the light tangentially to the jet, the audience could observe the zigzag propagation of light within the curved part of the jet. A similar zigzag propagation of light occurs in an optical fiber.
A decade later, Alexander Graham Bell, an American engineer who invented the telephone, patented a photophone that used directional light to transmit voice. In this device, using a system of lenses and mirrors, light was directed to a flat mirror mounted on a horn. Under the influence of sound, the mirror oscillated, which led to the modulation of the reflected light. The receiving device used a selenium-based detector, the electrical resistance of which varies depending on the intensity of the incident light. Voice-modulated sunlight falling on a sample of selenium changed the strength of the current flowing through the circuit of the receiving device and reproduced the voice. This device (Fig. 1.6) made it possible to transmit a speech signal over a distance of more than 200 m.
Rice. 1.6 Alexander Bell Photophone
Inventions of I.P. Kulibina, K. Chappa and A.G. Bell are based on the straightness of light propagation, for example, between repeater stations passing through the atmosphere. All these devices belong to open optical communication lines.
The possibility of using an intense, weakly diverging laser beam for information transmission aroused interest in optical methods of signal transmission and stimulated work in this direction. As a result, optical transmission systems with open propagation of signals immediately appeared, the main advantage of which is the huge information capacity due to the extremely high frequency of the optical carrier (about 10 14 Hz).
I must say that the weather prevents the creation of reliable laser communication lines. It turned out that rain, dust, snow, fog, cloud cover and other atmospheric phenomena sharply limit visibility, reduce transmission quality, and can generally disrupt optical communication. Since laser communication was originally conceived as wireless optical communication, in which a laser beam is launched in open space, many began to doubt that optical communication lines would find wide application in the earth's atmosphere.
However, practice has shown that open laser communication systems can be used at a distance of up to 2-3 kilometers (Fig. 1.7)
Rice. 1.7 Laser link
Open communication systems are most effective in outer space.
The disadvantages of open optical transmission systems, primarily the strong attenuation and distortion of signals in the propagation medium (except for space), necessitated the use of a guide system - an optical fiber in which signals are not subject to external interference.
The use of light as an information carrier makes it possible to transmit super-huge volumes of information at the speed of light in a medium. These and other advantages of optical communication have set before man the task of creating devices that are closed from the external environment for transmitting light over long distances, moreover, along a path that is complexly curved in space.
For the first time, the possibility of creating light guides was expressed by the Russian engineer V.N. Chikolev in the 60s of the XIX century. And already in the middle of the 70s of the XIX century V.N. The light source was a coal arc - a Yablochkov candle. The light guides were hollow metal tubes, the inner surface of which was mirrored.
At the beginning of the 20th century, theoretical and experimental studies dielectric waveguides, including flexible glass rods.
A new stage began in 1951, when Van Heel in Holland, Brien O'Brien, who worked at the American Optical Company, and Narinder Kapani and colleagues at the Imperial College of Science and Technology in London, independently of each other, began to study the problem of image transmission along a bundle of The work of these researchers was limited to the flexible fiber endoscope. Van Hiel's main achievement is the fundamental development of glass fibers in a sheath of plastic. Capani developed a fiber-laying technology that, in a modified form, is used in industry as a standard. He was the first to obtain an image without distortion using a bundle of regularly laid glass fibers with a diameter of 50 μm without a sheath.
In 1956, Capani first proposed the term "fiber optics". According to him, fiber optics is an optic based on active or passive fibers used to transmit light (ultraviolet, visible and infrared regions of the spectrum) along a given path. In 1973, Dr. Kapani founded Kaptron, a company specializing in fiber optic splitters and switches.
In 1961, Snitzer obtained laser fibers from neodymium-doped glasses and investigated their use as light amplifiers.
The world's first research on the possibility of creating communication lines based on optical dielectric waveguides - fiber light guides - was started in the USSR in 1957 by O.F. Kosminsky, V.N. Kuzmichev (specialists in communications technology) and A.G. Vlasov, A.M. Ermolaev, D.M. Croup and others (specialists in optics). Already in 1961, in the first article devoted to part of the results of these collective and complex studies, the broadbandness of optical waveguides was shown.
In 1958, Soviet specialists V.V. Vargin and T.I. Weinberg showed that the "light absorption" of glasses is due to the impurities of coloring metals introduced by the charge and the products of refractory erosion; It has been experimentally shown that the light absorption of ideally pure glass is very small and lies beyond the limits of the sensitivity of measuring instruments. In the same work, for the first time, the possibility of a further significant reduction in the attenuation of light in glasses was shown using much purer initial chemical reagents and a fundamental improvement in the technology of glass synthesis.
To the conclusions of Soviet scientists V.V. Vargin and T.I. Weinberg eight years later (1966), employees of the English laboratory of telecommunication standards of the company STL - Charles Kao and Charles Hockham came. They were the first foreign specialists in communication technology to publish an article that optical fibers can be used as a transmission medium when transparency is achieved, providing an attenuation of less than 20 dB / km (decibels per kilometer). They also indicated a way to create fibers suitable for telecommunications, associated with a decrease in the level of impurities in the glass.
In 1970 Robert Maurer and his colleagues at Corning Glass Work! received the first fiber with attenuation less than 20 dB/km. By 1972, a level of 4 dB/km had been achieved in laboratory conditions, which met the criterion of Cao and Hockham. Currently, the best fibers have a loss level of 0.2 dB/km.
In 1973, the US Navy introduced a fiber optic link aboard the Little Rock. In 1976, under the ALOFI program air Force the cable equipment of the A-7 aircraft was replaced with a fiber-optic one. At the same time, a cable system of 302 copper cables, which had a total length of 1260 m and weighed 40 kg, was replaced by 12 fibers with a total length of 76 m and a weight of 1.7 kg. The military was also the first to introduce a fiber-optic line. In 1977, a 2 km system was launched with an information transfer rate of 20 Mbps (megabits per second), linking the satellite earth station to the control center.
In 1977, AT&T and GTE installed fiber optic commercial telephone systems. These systems surpassed previously unshakable performance standards, leading to their rapid adoption in the late 1970s and early 1980s. In 1980, AT&T announced an ambitious fiber optic system linking Boston and Richmond. The implementation of the project has personally demonstrated the high-speed qualities new technology in serial high-speed systems, and not only in experimental setups. After that, it became clear that in the future the stake should be placed on fiber-optic technology, which showed the possibility of wide practical application.
While the computer industry, computer network technology, and manufacturing management have not been as quick to adopt fiber optics as the military and telecommunications companies, these areas have also produced experimental work research and implementation of new technology. The advent of the information age and the resulting need for more efficient telecommunications systems only spurred the further development of fiber optic technology. Today, this technology is widely used outside the field of telecommunications. For example, IBM, a leader in computer manufacturing, announced in 1990 the release of a new high-speed computer that uses a link controller for disk and tape external drives based on fiber optics. This was the first use of fiber optics in commercial equipment.
In 1990, Lynn Mollinar of Bellcore demonstrated the ability to transmit a signal without regeneration at a rate of 2.5 Gb / s over a distance of about 7500 km. Typically, the fiber optic signal needs to be amplified and reshaped periodically about every 25 km. During transmission, the fiber optic signal loses power and is distorted. In the Mollinar system, the laser operated in the soliton mode and a self-amplifying fiber with erbium additives was used. Soliton (in a very narrow range of the spectrum) pulses do not scatter and retain their original shape as they propagate through the fiber.
At the same time, the Japanese company Nippon Telephone & Telegraph achieved a speed of 20 Gb / s, however, over a significantly shorter distance. The value of soliton technology lies in the fundamental possibility of laying along the bottom of the Pacific or Atlantic Ocean fiber-optic telephone system that does not require the installation of intermediate amplifiers.
The whole complex of works carried out under the guidance of academicians Zh.I. Alferova, M.G. Basova, Yu.V. Gulyaeva, G.G. Devyatykh, V.A. Kotelnikova, A.M. Prokhorov at the institutes of the USSR Academy of Sciences with the participation of a number of industry research institutes, has led to the fact that by now, FOCL from fashionable exotic novelties have become ordinary irreplaceable structures in the architecture of many thousands of information systems of the widest and most diverse purposes.
Optical fiber plays the same role as the copper wire used to carry telephone conversations or computer data. But unlike copper wire, the fiber carries light, not an electrical signal. In this regard, there are many advantages, which allows the use of optical fiber as a carrier medium in various areas technology - from telephony to computers and automation systems.
A fiber optic system is a line connecting a receiver and a transmitter.
On fig. 1.8 shows the main components of such a system:
Rice. 1.8 Basic elements of a fiber-optic communication line
Fiber optics affects the lives of every person, sometimes almost imperceptibly. Here are a few examples: voice broadcast across the country; distribution of a television image to your home via cable; industrial process control.
Fiber optics is being used in a variety of applications, and there are good reasons for this. Fiber optic communications have a number of advantages over electronic systems using metal-based transmission media.
Among the advantages of optical fibers are the following:
1. The wide bandwidth is due to the extremely high frequency of the optical carrier - about 10 14 Hz, which provides the potential for transmitting several Tbps of information over a single optical fiber. Large bandwidth is one of the most important advantages of optical fiber over copper or any other information transmission medium.
2. Small attenuation of the light signal in the fiber. The currently produced domestic and foreign optical fiber has an attenuation of 0.2-0.3 dB at a wavelength of 1.55 microns per one kilometer. Low attenuation and low dispersion make it possible to build sections of lines without retransmission with a length of more than 100 km.
3. High noise immunity. Since the fiber is made of a dielectric material, it is immune to electromagnetic interference from surrounding copper cabling systems and electrical equipment capable of inducing electromagnetic radiation (power lines, electric motors, etc.). Multi-fiber optical cables also do not have the problem of electromagnetic radiation cross-talk that is inherent in multi-pair copper cables.
4. Light weight and volume. Fiber optic cables (FOCs) are lighter and lighter than copper cables for the same bandwidth. For example, a 900-pair 7.5 cm telephone cable with a metal base can be replaced with a single fiber with a diameter of 1 mm.
5. High security against unauthorized access. Since the FOC practically does not radiate in the radio range, it is difficult to eavesdrop on the information transmitted over it without disturbing the transmission and reception. Monitoring systems (continuous control) of the integrity of the optical communication line, using the high sensitivity properties of the fiber, can instantly turn off the “hacked” communication channel and give an alarm.
Thus, optical fiber (OV) is used: in trunk, zonal, urban communication cables; in the construction of local computer networks, as an element of a structured cabling system (SCS). OV has found wide application in the creation of cable television networks. OV is used in the creation of perimeter protection systems.
The central office of the company is located in the capital of Kazakhstan - the city of Astana. The company employs about 30 thousand people. Kazakhtelecom JSC has regional divisions in each region of the country and provides communication services throughout the country.
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
Chapter 1. General characteristics of the enterprise. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
1.Historical reference. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Organizational structure of the enterprise. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Organization of the production process. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4. Basic economic and financial indicators. . . . . . . . . . . . . . . . . . . . . . 8
Chapter 2. Marketing research of OJSC Rostelecom. . . . . . . . . . . .. . . . . . . 12
Chapter 3. Conclusions and suggestions for the entire main part of the report. . . . . . . . . . . . . . .17
Conclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
Bibliography. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
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1. History of the development of communication lines
Communication lines arose simultaneously with the advent of the electric telegraph. The first communication lines were cable. However, due to the imperfection of the cable design, underground cable communication lines soon gave way to overhead ones. The first long-distance overhead line was built in 1854 between St. Petersburg and Warsaw. In the early 70s of the last century, an overhead telegraph line was built from St. Petersburg to Vladivostok, about 10 thousand km long. In 1939, the world's largest high-frequency telephone line Moscow-Khabarovsk, 8300 km long, was put into operation.
The creation of the first cable lines is associated with the name of the Russian scientist P.L. Schilling. As early as 1812, Schilling in St. Petersburg demonstrated the explosions of sea mines, using an insulated conductor he had created for this purpose.
In 1851, simultaneously with the construction railway between Moscow and St. Petersburg a telegraph cable was laid, insulated with gutta-percha. The first submarine cables were laid in 1852 across the Northern Dvina and in 1879 across the Caspian Sea between Baku and Krasnovodsk. In 1866, the transatlantic cable telegraph line between France and the United States was put into operation.
In 1882-1884. in Moscow, Petrograd, Riga, Odessa, the first urban telephone networks in Russia were built. In the 90s of the last century, the first cables, numbering up to 54 wires, were suspended on the city telephone networks of Moscow and Petrograd. In 1901, the construction of an underground city telephone network began.
The first designs of communication cables, dating back to the beginning of the 20th century, made it possible to carry out telephone transmission over short distances. These were the so-called urban telephone cables with air-paper insulation and twisted in pairs. In 1900-1902. was
a successful attempt was made to increase the transmission distance by artificially increasing the inductance of cables by including inductors in the circuit (Pupin's proposal), as well as the use of conductive wires with a ferromagnetic winding (Kruppa's proposal). Such methods at that stage made it possible to increase the range of telegraph and telephone communications several times.
An important stage in the development of communication technology was the invention, and starting from 1912-1913. mastering the production of electronic lamps. In 1917 V.I. Kovalenkov developed and tested on the line a telephone amplifier based on electronic tubes. In 1923, a telephone connection was made with amplifiers on the Kharkov-Moscow-Petrograd line.
In the 1930s, the development of multichannel transmission systems began. Subsequently, the desire to expand the range of transmitted frequencies and increase the bandwidth of the lines led to the creation of new types of cables, the so-called coaxial. But their mass production dates back only to 1935, when new high-quality dielectrics such as escapon, high-frequency ceramics, polystyrene, styroflex, etc. appeared. These cables allow the transmission of energy at a frequency of currents up to several million hertz and allow them to transmit television programs over long distances. The first coaxial line for 240 HF telephony channels was laid in 1936. The first transatlantic submarine cables, laid in 1856, organized only telegraph communications, and only 100 years later, in 1956, an underwater coaxial trunk was built between Europe and America for multichannel telephony.
In 1965-1967. Experimental waveguide communication lines appeared for transmitting broadband information, as well as cryogenic superconducting cable lines with very low attenuation. Since 1970, work has been actively developed on the creation of light guides and optical cables using visible and infrared radiation in the optical wave range.
The creation of a fiber light guide and the obtaining of continuous generation of a semiconductor laser played a decisive role in the rapid development of fiber-optic communication. By the beginning of the 1980s, fiber-optic communication systems had been developed and tested in real conditions. The main areas of application of such systems are the telephone network, cable television, intra-object communication, computer technology, the control and management system for technological processes, etc.
In Russia and other countries, urban and long-distance fiber-optic communication lines have been laid. They are given a leading place in the scientific and technological progress of the communications industry.
2. Design and characteristics of optical communication cables
Varieties of optical communication cables
An optical cable consists of quartz glass optical fibers (light guides) twisted according to a certain system, enclosed in a common protective sheath. If necessary, the cable may contain power (strengthening) and damping elements.
Existing OKs according to their purpose can be classified into three groups: trunk, zone and city. Underwater, object and installation OK are allocated in separate groups.
Trunk OK are intended to transmit information over long distances and a significant number of channels. They must have low attenuation and dispersion and high information throughput. A single-mode fiber with a core and cladding of 8/125 µm is used. Wavelength 1.3...1.55 µm.
Zonal OKs serve to organize multi-channel communication between the regional center and regions with a communication range of up to 250 km. Gradient fibers with dimensions of 50/125 µm are used. Wavelength 1.3 µm.
City OK are applied as connecting between city automatic telephone exchanges and communication centers. They are designed for short distances (up to | 10 km) and big number channels. Fiber-gradient (50/125 µm). Wavelength 0.85 and 1.3 µm. These lines, as a rule, operate without intermediate linear regenerators.
Submarine OK intended for communication through large water barriers. They must have high mechanical tensile strength and have reliable moisture-resistant coatings. It is also important for submarine communications to have low attenuation and long regeneration lengths.
Object OKs serve to convey information within an object. This includes institutional and video telephone communications, the internal cable television network, as well as on-board information systems of mobile objects (aircraft, ship, etc.).
Mounting OK are used for intra- and inter-unit mounting of equipment. They are made in the form of bundles or flat ribbons.
Optical fibers and features of their manufacture
The main element of the optical fiber is an optical fiber (optical fiber), made in the form of a thin cylindrical glass fiber, through which light signals are transmitted with wavelengths of 0.85 ... 1.6 μm, which corresponds to a frequency range of (2.3 ... 1 ,2) 1014 Hz.
The light guide has a two-layer design and consists of a core and a cladding with different refractive indices. The core serves to transmit electromagnetic energy. The purpose of the shell is to create the best conditions for reflection at the “core-shell” interface and protection from interference from the surrounding space.
The core of the fiber, as a rule, consists of quartz, and the cladding can be quartz or polymer. The first fiber is called quartz-quartz, and the second is called quartz-polymer (organosilicon compound). Based on the physico-optical characteristics, preference is given to the first. Quartz glass has the following properties: refractive index 1.46, thermal conductivity coefficient 1.4 W/mk, density 2203 kg/m3.
Outside the light guide there is a protective coating to protect it from mechanical influences and apply colors. The protective coating is usually made in two layers: first, an organosilicon compound (SIEL), and then an epoxy acrylate, fluoroplastic, nylon, polyethylene, or varnish. Overall fiber diameter 500...800 µm
Three types of optical fibers are used in existing optical fiber designs: stepped with a core diameter of 50 μm, gradient with a complex (parabolic) refractive index profile of the core, and single-mode with a thin core (6 ... 8 μm)
In terms of frequency bandwidth and transmission range, single-mode fibers are the best, and stepped ones are the worst.
The most important problem of optical communication is the creation of optical fibers (OF) with low losses. Quartz glass is used as a starting material for the manufacture of optical fibers, which is a good medium for the propagation of light energy. However, as a rule, glass contains a large amount of foreign impurities, such as metals (iron, cobalt, nickel, copper) and hydroxyl groups (OH). These impurities lead to a significant increase in losses due to the absorption and scattering of light. To obtain OF with low losses and attenuation, it is necessary to get rid of impurities so that there is a chemically pure glass.
At present, the most widely used method for creating OF with low losses is by chemical vapor deposition.
Obtaining OF by chemical vapor deposition is carried out in two stages: a two-layer quartz preform is manufactured and a fiber is drawn from it. The workpiece is made as follows
A jet of chlorinated quartz and oxygen is fed into a hollow quartz tube with a refractive index 0.5...2 m long and 16...18 mm in diameter. As a result of a chemical reaction at a high temperature (1500...1700°C), pure quartz is deposited in layers on the inner surface of the tube. Thus, the entire internal cavity of the tube is filled, except for the very center. To eliminate this air channel, an even higher temperature (1900° C.) is applied, due to which the collapse occurs and the tubular billet is transformed into a solid cylindrical billet. The pure deposited quartz then becomes the core of the refractive index optical fiber, and the tube itself acts as a refractive index shell. The drawing of the fiber from the workpiece and its winding on the receiving drum is carried out at the glass softening temperature (1800...2200°C). More than 1 km of optical fiber is obtained from a preform 1 m long.
The advantage of this method is not only obtaining OF with a core of chemically pure quartz, but also the possibility of creating gradient fibers with a given refractive index profile. This is done: through the use of doped quartz with titanium, germanium, boron, phosphorus or other reagents. Depending on the additive used, the refractive index of the fiber may vary. So, germanium increases, and boron reduces the refractive index. By selecting the recipe of doped quartz and observing a certain amount of additive in the layers deposited on the inner surface of the tube, it is possible to provide the required pattern of change over the cross section of the fiber core.
Optical cable designs
OK constructions are mainly determined by the purpose and scope of their application. In this regard, there are many constructive options. Currently, a large number of types of cables are being developed and manufactured in various countries.
However, the whole variety of existing types of cables can be divided into three groups
concentric stranded cables
shaped core cables
flat ribbon cables.
The cables of the first group have a traditional twisted concentric core, similar to electric cables. Each subsequent winding of the core has six more fibers compared to the previous one. Such cables are known mainly with the number of fibers 7, 12, 19. Most often, the fibers are located in separate plastic tubes, forming modules.
The cables of the second group have a figured plastic core in the center with grooves in which the optical fibers are placed. The grooves and, accordingly, the fibers are located along the helicoid, and therefore they do not experience a longitudinal effect on the gap. Such cables can contain 4, 6, 8 and 10 fibers. If it is necessary to have a high capacity cable, then several primary modules are used.
A ribbon type cable consists of a stack of flat plastic tapes in which a certain number of optical fibers are mounted. Most often, there are 12 fibers in the tape, and the number of tapes is 6, 8 and 12. With 12 tapes, such a cable can contain 144 fibers.
In optical cables, in addition to optical fiber, as a rule, there are the following elements:
power (reinforcing) rods that take on the longitudinal load, at break;
fillers in the form of continuous plastic threads;
reinforcing elements that increase the resistance of the cable under mechanical stress;
outer protective sheaths that protect the cable from the penetration of moisture, vapors of harmful substances and external mechanical influences.
In Russia, various types and designs of OK are manufactured. For the organization of multi-channel communication, mainly four- and eight-fiber cables are used.
Are of interest OK French production. They, as a rule, are completed from unified modules consisting of a plastic rod with a diameter of 4 mm with ribs along the perimeter and ten OBs located along the periphery of this rod. Cables contain 1, 4, 7 such modules. Outside, the cables have an aluminum and then a polyethylene sheath.
The entire history of the development of cable communication systems is associated with the problem of increasing the amount of information transmitted over a wired communication channel.
In turn, the amount of transmitted information is determined by the bandwidth. It has been established that the achievable information transfer rate is the higher, the higher the frequency of oscillations of an electric current or a radio wave. In order to encode any letter of the alphabet, it is necessary to use 7-8 bits. Thus, if wired communication with a frequency of 20 kHz is used to transmit text, then a standard book of 400–500 pages can be transmitted in about 1.5–2 hours. When transmitting over a 32 MHz line, the same procedure will require only 2-3 seconds.
Let us consider how with the development of wired communication, i.e. with the development of new frequencies, the throughput of the communication channel changed.
As noted above, the development of electrical information transmission systems began with the invention by P. L. Schilling in 1832 of a telegraph line using needles. A copper wire was used as a communication line. This line provided information transfer rate - 3 bit / s (1/3 letters). The first Morse telegraph line (1844) provided a speed of 5 bps (0.5 letters). The invention in 1860 of the printing telegraph system provided a speed of 10 bps (1 letter). In 1874, the Baudot six-fold telegraph system already provided a transmission rate of 100 bits / s (10 letters). The first telephone lines, built on the basis of the telephone invented by Bell in 1876, provided an information transfer rate of 1000 bps (1 kbps - 100 letters).
The first practical telephone circuit was single-wire with telephone sets connected at its ends. This principle required a large number of not only connecting lines, but also the telephone sets themselves. This simple device was replaced in 1878 by the first switch, which made it possible to connect several telephone sets through a single switching field.
Prior to 1900, the originally used single-wire grounded-wire circuits were replaced by two-wire transmission lines. Despite the fact that by this time the switchboard had already been invented, each subscriber had his own communication line. A way was needed to increase the number of channels without laying additional thousands of kilometers of wires. However, the advent of this method (the sealing system) was delayed until the advent of electronics in the early 1900s. The first commercial multiplexing system was created in the United States, where a four-channel frequency division system began operating between Baltimore and Pittsburgh in 1918. Prior to the Second World War, most developments were directed towards increasing the efficiency of overhead line sealing systems and multi-pair cables, since almost all telephone circuits were organized over these two transmission media.
The invention in 1920 of six to twelve channel transmission systems made it possible to increase the transmission rate of information in a given frequency band up to 10,000 bps, (10 kbps - 1000 letters). The upper limiting frequencies of overhead and multi-pair cable lines were 150 and 600 kHz, respectively. The need to transmit large amounts of information required the creation of broadband transmission systems.
In the 1930s and 1940s, coaxial cables were introduced. In 1948, between cities located on the Atlantic and Pacific coasts of the United States, the Bell System put into operation the L1 coaxial cable system. This coaxial cable system made it possible to increase the bandwidth of the linear path up to 1.3 MHz, which ensured the transmission of information over 600 channels.
After the Second World War, active developments were carried out to improve coaxial cable systems. If initially coaxial circuits were laid separately, then they began to combine several coaxial cables in a common protective sheath. For example, the American company Bell developed in the 1960s an intercontinental system with a bandwidth of 17.5 MHz (3600 channels over a coaxial circuit or “tube”). For this system, a cable was developed in which 20 "tubes" were combined in one sheath. The total cable capacity was 32,400 channels in each direction, with two "tubes" held in reserve.
In the USSR, at about the same time, the K-3600 system was developed on the domestic cable KMB 8/6, which has 14 coaxial circuits in one sheath. Then comes the coaxial system with a larger bandwidth of 60 MHz. It provided a capacity of 9000 channels in each pair. 22 pairs are combined in a common shell.
High-capacity coaxial cable systems in the late twentieth century were commonly used for communication between closely spaced centers with high density population. However, the cost of installing such systems was high due to the small distance between the intermediate amplifiers and due to the high cost of the cable and its laying.
6.4.2. History of fiber optic communication systems
According to modern views, all electromagnetic radiation, including radio waves and visible light, have a dual structure and behave either as a wave-like process in a continuous medium or as a stream of particles called photons, or quanta. Each quantum has a certain energy.
The idea of light as a stream of particles was first introduced by Newton. In 1905, on the basis of Planck's theory, A. Einstein revived in a new form the corpuscular theory of light, which is now called the quantum theory of light. In 1917, he theoretically predicted the phenomenon of stimulated or induced radiation, on the basis of which quantum amplifiers were subsequently created. In 1951, Soviet scientists V. A. Fabrikant, M. M. Vudynsky and F. A. Butaeva received a copyright certificate for the discovery of the principle of operation of an optical amplifier. Somewhat later, in 1953, a proposal for a quantum amplifier was made by Weber. In 1954, N. G. Basov and A. M. Prokhorov proposed a specific project for a molecular gas generator and amplifier with theoretical justification. Gordon, Zeiger, and Towns independently came up with the idea of a similar generator, publishing in 1954 a report on the creation of an operating quantum generator based on a beam of ammonia molecules. Somewhat later, in 1956, Blombergen established the possibility of building a quantum amplifier based on a solid paramagnetic substance, and in 1957 such an amplifier was built by Skovel, Feher, and Seidel. All quantum generators and amplifiers built before 1960 operated in the microwave range and were called masers. This name comes from the first letters of the English words “Microwave amplification by stimulated emission of radiation”, which means “microwave amplification by stimulated emission of radiation”.
The next stage of development is associated with the transfer of known methods to the optical range. In 1958, Towns and Shavlov theoretically substantiated the possibility of creating an optical quantum generator (OQG) on a solid state. In 1960 Meiman built the first pulsed laser on a solid - ruby. In the same year, the question of lasers and quantum amplifiers was independently analyzed by N. G. Basov, O. N. Krokhin, and Yu. M. Popov.
In 1961, the first gas (helium-neon) generator was created by Janavan, Bennett and Erriot. In 1962, the first semiconductor laser was created. Optical quantum generators (OQGs) are called lasers. The term "Laser" was formed as a result of the replacement of the letter "m" in the word maser with the letter "l" (from English word"light - light").
After the creation of the first masers and lasers, work began on their use in communication systems.
Fiber optics, as an original branch of technology, emerged in the early 1950s. At this time, they learned how to make thin two-layer fibers from various transparent materials (glass, quartz, etc.). Even earlier, it was predicted that if the optical properties of the inner (“core”) and outer (“cladding”) parts of such a fiber are chosen appropriately, then a beam of light introduced through the end into the core will only propagate along it and be reflected from the cladding. Even if the fiber is bent (but not too sharply), the beam will obediently be held inside the core. Thus, a light beam - this is a synonym for a straight line - falling into an optical fiber, it turns out to be able to propagate along any curvilinear trajectory. There is a complete analogy with an electric current flowing through a metal wire, so a two-layer optical fiber is often called a light guide or light guide. Glass or quartz fibers, 2-3 times the thickness of a human hair, are very flexible (they can be wound on a spool) and strong (stronger than steel threads of the same diameter). However, the light guides of the 1950s were not transparent enough, and with a length of 5–10 m, the light was completely absorbed in them.
In 1966, the idea was put forward of the fundamental possibility of using optical fibers for communication purposes. Technological search ended in success in 1970 - ultra-pure quartz fiber was able to transmit a light beam at a distance of up to 2 km. In fact, in the same year, the ideas of laser communication and the possibilities of fiber optics "found each other", the rapid development of fiber-optic communication began: the emergence of new methods for manufacturing fibers; creation of other necessary elements, such as miniature lasers, photodetectors, optical connectors, etc.
Already in 1973-1974. the distance that the beam could travel along the fiber reached 20 km, and by the beginning of the 1980s it had exceeded 200 km. By the same time, the speed of information transmission over FOCL had increased to unprecedented values - several billion bits / s. In addition, it turned out that FOCLs not only have an ultra-high data transfer rate, but also have a number of other advantages.
The light signal is not affected by external electromagnetic interference. Moreover, it is impossible to eavesdrop, that is, to intercept. Fiber light guides have excellent weight and size characteristics: the materials used have a low specific gravity, there is no need for heavy metal sheaths; ease of laying, installation, operation. Fiber light guides can be laid in a conventional underground cable duct, can be mounted on high-voltage power lines or power networks of electric trains, and generally combined with any other communications. The characteristics of FOCL do not depend on their length, on the inclusion or disconnection of additional lines - in electrical circuits, all this is not the case, and each such change requires painstaking tuning work. In principle, sparking is impossible in fiber light guides, and this opens up the prospect of using them in explosive and similar industries.
The cost factor is also very important. At the end of the last century, fiber communication lines, as a rule, were commensurate in cost with wire lines, but over time, given the shortage of copper, the situation will certainly change. This conviction is based on the fact that the fiber material - quartz - has an unlimited raw material resource, while the basis of wire lines is made up of now rare metals such as copper and lead. And it's not just about the cost. If communication develops on a traditional basis, then by the end of the century all the mined copper and all the lead will be spent on the manufacture of telephone cables - but how to develop further?
At present, optical communication lines occupy a dominant position in all telecommunication systems, from backbone networks to home distribution networks. Thanks to the development of fiber-optic communication lines, multi-service systems are being actively introduced, which make it possible to bring telephony, television and the Internet to the end user in one cable.
