What makes fiber-optic communication different from others. Fiber optic communication lines

Fiber-optic lines are used to transmit information in the optical range. According to the Soviet Information Bureau, at the end of the 80s, the growth rate of the use of fiber-optic lines was 40%. Union experts assumed that some countries would completely abandon the copper core. The congress decreed for the 12th five-year plan a 25% increase in the volume of communication lines. The thirteenth, also designed to develop fiber optics, saw the collapse of the USSR, the first cellular operators appeared. By the way, experts' forecast regarding the growth of demand for qualified personnel failed ...

Operating principle

What are the reasons for the soaring popularity of high frequency signals? Modern textbooks mention a decrease in the need for signal regeneration, cost, and an increase in channel capacity. Soviet engineers found out, reasoning differently: copper cable, armor, screen take 50% of the world's copper production, 25% - lead. An insufficiently known fact became the main reason for the abandonment of the sponsors of Nikola Tesla, the project of the Wardencliff tower (the name was given by the name of the patron who donated the land). A well-known Serbian scientist wanted to transmit information and energy wirelessly, frightening many local owners of copper smelters. 80 years later, the picture has changed dramatically: people realized the need to save non-ferrous metals.

The fiber is made of ... glass. Ordinary silicate, flavored with a fair amount of polymers modifying the properties. Soviet textbooks, in addition to the indicated reasons for the popularity of the new technology, are called:

Low attenuation of signals, which was the reason for a decrease in the need for regeneration.
No sparking, hence fire safety, zero explosion hazard.
Impossibility of short-circuiting, reduced need for maintenance.
Insensitive to electromagnetic interference.
Low weight, relatively small dimensions.

Initially, fiber-optic lines were supposed to unite major highways: between cities, suburbs, automatic telephone exchanges. Experts from the USSR called the cable revolution akin to the emergence of solid-state electronics. The development of technology has made it possible to build networks that are free of leakage currents, cross-talk. A section of one hundred kilometers in length is devoid of active methods of signal regeneration. The coil of single-mode cable is usually 12 km, multimode - 4 km. The last mile is often covered with copper. Providers are used to assigning end sites to individual users. There are no high speeds, transceivers are cheap, the ability to supply power to the device at the same time, ease of use of linear modes.

Transmitter

Semiconductor LEDs, including solid state lasers, are typical beamformer. The spectrum width of the signal emitted by a typical pn junction is 30-60 nm. The efficiency of the first solid-state devices was barely 1%. The basis of connected LEDs is often the indium-gallium-arsenic-phosphorus structure. By emitting a lower frequency (1.3 μm), the devices provide significant spectrum dispersion. The resulting variance severely limits the bitrate (10-100 Mbps). Therefore, LEDs are suitable for building local network resources (distance 2-3 km).

Frequency division multiplexing is performed by multifrequency diodes. Today, imperfect semiconductor structures are being actively replaced by vertical emitting lasers, which significantly improve spectral characteristics. increasing the speed. One order price. The stimulated emission technology brings much higher powers (hundreds of mW). Coherent radiation provides 50% efficiency of single-mode lines. The effect of chromatic dispersion is reduced, allowing you to increase the bit rate.

The short time of charge recombination makes it easy to modulate the radiation by high frequencies of the supply current. In addition to vertical ones, they are used:

Feedback lasers.
Fabry-Perot resonators.

High bitrates of long-distance communication lines are achieved by using external modulators: electro-absorption, Mach-Zehnder interferometers. External systems eliminate the need for supply voltage chirp. The clipped spectrum of the discrete signal is passed on. Additionally, other carrier coding techniques have been developed:

Quadrature Phase Shift Keying.
Orthogonal frequency division multiplexing.
Amplitude quadrature modulation.

The procedure is carried out by digital signal processors. The old techniques only compensated for the linear component. Berenger expressed the modulator in Wien's series, the DAC and the amplifier modeled in truncated, time-independent Volterra series. Khana suggests using a polynomial transmitter model in addition. Each time the series coefficients are found using an indirect learning architecture. Dutel recorded many common variations. Phase cross-correlation and quadrature fields simulate imperfections in synchronization systems. Non-linear effects are compensated in the same way.

Receivers

The photodetector does the reverse light-to-electricity conversion. The lion's share of solid-state receivers use the indium-gallium-arsenic structure. Sometimes there are pin-photodiodes, avalanche. Metal-semiconductor-metal structures are ideal for incorporating regenerators, shortwave multiplexers. Optoelectric converters are often supplemented with transimpedance amplifiers that produce a digital signal. Then practice the recovery of sync pulses with phase-locked loop frequency.

Glass transmission of light: history

The phenomenon of refraction, which makes tropospheric communication possible, is disliked by students. Complicated formulas, uninteresting examples kill the student's love for knowledge. The idea of a light guide was born in the distant 1840s: Daniel Colladon, Jacques Babinet (Paris) tried to embellish their own lectures with tempting, visual experiments. Teachers in medieval Europe were making poor money, so a sizable influx of money-carrying students looked like a welcome prospect. The lecturers lured the audience in any way. A certain John Tyndall took advantage of the idea 12 years later, much later publishing a book (1870), considering the laws of optics:

The light passes the air-water interface, the refraction of the beam relative to the perpendicular is observed. If the angle of contact of the beam to the orthogonal line exceeds 48 degrees, the photons stop leaving the liquid. The energy is completely reflected back. The limit is called the limiting angle of the medium. Water is equal to 48 degrees 27 minutes, for silicate glass - 38 degrees 41 minutes, diamond - 23 degrees 42 minutes.

The origin of the 19th century brought the light telegraph line from St. Petersburg to Warsaw with a length of 1200 km. The message was regenerated by operators every 40 km. The message went on for several hours, the weather and visibility interfered. The advent of radio communication supplanted the old methods. The first optical lines date back to the end of the 19th century. The novelty was liked ... by the doctors! The bent glass fiber made it possible to illuminate any cavity in the human body. Historians suggest the following timeline for the development of events:

Henry Saint-René's idea was continued by the settlers of the New World (1920s), who wanted to improve television. Clarence Hansell, John Logie Baird pioneered. Ten years later (1930) medical student Heinrich Lamm proved the possibility of transferring images with glass guides. The seeker of knowledge decided to examine the insides of the body. The image quality was lame, and the attempt to obtain a British patent failed.

The birth of fiber

Independently Dutch scientist Abraham van Heel, Briton Harold Hopkins, Narinder Singh Kapani invented fiber (1954). The merit of the first in the idea of covering the central vein with a transparent shell, which had a low refractive index (close to air). Surface scratch protection greatly improved the transmission quality (contemporaries of the inventors saw the main obstacle to the use of fiber lines in high losses). The British also made a significant contribution, collecting a bundle of 10,000 fibers, transmitted the image at a distance of 75 cm. The note "Flexible fiberscope using static scanning" adorned the journal Nature (1954).

It is interesting! Narinder Singh Kapani coined the term fiber optic in a note in American Science (1960).

1956 brought the world a new flexible gastroscope, by Basil Hirchowitz, Wilbur Peters, Lawrence Curtiss (University of Michigan). A special feature of the novelty was the glass sheath of the fibers. Elias Snitzer (1961) publicized the idea of creating a single-mode fiber. So thin that only one speck of the interference pattern fit inside. The idea helped doctors examine the insides of a (living) person. The loss was 1 dB / m. The communication needs extended much further. It was required to reach a threshold of 10-20 dB / km.

1964 is considered a watershed year: a vital specification was published by Dr. Kao, introducing the theoretical foundations of long-distance communications. The document made extensive use of the above figure. The scientist has proved: glass of the highest purity will help reduce losses. German physicist (1965) Manfred Börner (Telefunken Research Labs, Ulm) introduced the first workable telecommunication line. NASA immediately transmitted lunar imagery downstairs using novelties (developments were classified). A few years later (1970), three employees of Corning Glass (see the beginning of the topic) filed a patent that implements the technological cycle for smelting silicon oxide. The bureau has been evaluating the text for three years. The new core has increased the bandwidth of the channel by 65,000 times relative to the copper cable. Dr. Cao's team immediately attempted to cover a considerable distance.

It is interesting! 45 years later (2009) Kao was awarded the Nobel Prize in Physics.

Military computers (1975) US Air Defense (NORAD Section, Cheyenne Mountains) received new communications. The optical Internet appeared a long time ago, before personal computers! Two years later, test trials of a 1.5-mile telephone line (suburb of Chicago) successfully transmitted 672 voice channels. Glassblowers worked tirelessly: the early 1980s saw the introduction of 4 dB / km fiber. Silicon oxide was replaced by another semiconductor, germanium.

The production line of the high quality cable was produced at a speed of 2 m / s. Chemie Thomas Mensah developed a technology that increased the specified limit twenty times. The novelty has finally become cheaper than a copper cable. The rest is outlined above: there was a surge in the introduction of new technology. The repeater spacing was 70-150 km. The Erbium ion doped fiber amplifier has drastically reduced the cost of building the lines. The times of the thirteenth five-year plan brought the planet 25 million kilometers of fiber-optic networks.

A new impetus to development was given by the invention of photonic crystals. The first commercial models were brought in 2000. The periodicity of the structures made it possible to significantly increase the power, the fiber design was flexibly adjusted to follow the frequency. In 2012, the Nippon Telegraph and Telephone Company achieved 1 petabits / s over 50 km with a single fiber.

Military industry

The history of the march of the US military industry, published in the Monmouth Message, is reliably known. In 1958, the cable manager at Fort Monmouth (Signal Corps Labs of the United States Army) reported on the dangers of lightning and precipitation. The official disturbed researcher Sam Dee Vit, asking him to find a replacement for the greening copper. The answer included a proposal to try glass, fiber, light signals. However, Uncle Sam's engineers at that time were powerless to solve the problem.

On a hot September 1959, Di Vita asked Lieutenant Second Rank Richard Sturzebacher if he knew the formula for glass capable of transmitting an optical signal. The answer contained information regarding silicon oxide - a sample based at Alfred University. By measuring the refractive index of materials with a microscope, Richard had a headache. 60-70% glass powder freely transmitted radiant light, irritating the eyes. Keeping in mind the need to obtain the purest glass, Sturzebacher studied modern production techniques using silicon chloride IV. Di Vita found the material suitable, deciding to leave negotiations with the Corning glass blowers to the government.

The official knew the workers very well, but decided to publicize the case so that the plant would receive a state contract. Between 1961 and 1962, the idea of using pure silicon oxide was transferred to research laboratories. Federal allocations amounted to about $ 1 million (1963-1970 period). The program ended (1985) with the development of a multi-billion dollar fiber-optic cable industry that was rapidly replacing copper. Di Vita stayed to work advising the industry, having lived for 97 years (year of death - 2010).

Varieties of cables

The cable is formed by:

Core.
Shell.
Protective cover.

The fiber realizes full reflection of the signal. The material of the first two components is traditionally glass. Sometimes they find a cheap substitute - polymer. Optical cables are combined by fusion. Aligning the core will take some skill. Multimode cables over 50 microns thick are easier to solder. The two global varieties differ in the number of mods:

The multimode is equipped with a thick core (over 50 microns).
Singlemode is much thinner (less than 10 microns).

Paradox: the smaller cable provides long-distance communication. The cost of the four-core transatlantic is $ 300 million. The core is coated with a lightfast polymer. The journal New Scientist (2013) published the experiments of the scientific group of the University of Southampton, covering a range of 310 meters ... with a waveguide! The passive dielectric element showed a speed of 77.3 Tbit / s. The walls of the hollow tube are formed by a photonic crystal. The information flow moved at a speed of 99.7% light.

Photonic crystal fiber

The new type of cables is formed by a set of tubes, the configuration resembles a rounded honeycomb. Photonic crystals resemble natural mother-of-pearl, forming periodic conformations, differing in refractive index. Some wavelengths are attenuated inside such tubes. The cable demonstrates the bandwidth, the beam undergoing Bragg refraction is reflected. Due to the presence of forbidden zones, the coherent signal moves along the fiber.

Introduction

Communication plays an important role in our world today. And if earlier copper cables and wires were used to transfer information, now the time has come for optical technologies and fiber-optic cables. Now, making a phone call to the other side of the world (for example, from Russia to America) or downloading our favorite melody from the Internet that is on a website somewhere in Australia, we do not even think about how we manage to do this. And this happens thanks to the use of fiber optic cables. In order to connect people, to make them closer to each other or to the desired source of information, it is necessary to connect continents. Currently, the exchange of information between continents is carried out mainly through submarine fiber optic cables. At present, fiber-optic cables are laid along the bottom of the Pacific and Atlantic oceans and almost the whole world is "entangled" in a network of fiber communication systems (Laser Mag.-1993.-№3; Laser Focus World.-1992.-28, №12; Telecom mag. 1993. No. 25; AEU: J. Asia Electron. Union. 1992. No. 5). European countries across the Atlantic are connected by fiber lines to America. USA, through the Hawaiian Islands and the island of Guam - with Japan, New Zealand and Australia. A fiber-optic communication line connects Japan and Korea with the Russian Far East. In the west, Russia is connected with the European countries Petersburg - Kingisepp - Denmark and St. Petersburg - Vyborg - Finland, in the south - with the Asian countries Novorossiysk - Turkey. At the same time, the Internet is the main driving force behind the development of fiber-optic communication lines.

Fiber optic networks are undoubtedly one of the most promising areas of communication. The throughput of optical channels is orders of magnitude higher than that of information lines based on copper cable.

Optical fiber is considered the most advanced medium for transmitting large flows of information over long distances. It is made of quartz, which is based on silicon dioxide, which is a widespread and inexpensive material, unlike copper. Optical fiber is very compact and lightweight, with a diameter of only about 100 microns.

In addition, optical fiber is immune to electromagnetic fields, which alleviates some of the typical problems of copper communication systems. Optical networks are capable of transmitting a signal over long distances with less loss. Despite the fact that this technology is still expensive, the prices of optical components are constantly falling, while the capabilities of copper lines are approaching their limiting values and require more and more costs for the further development of this direction.

It seems to me that the topic of fiber-optic communication lines is currently relevant, promising and interesting for consideration. That is why I choose it for my term paper and I think that the future is for FOCL.

1. History of creation

Fiber optics, although it is a widely used and popular means of providing communication, the technology itself is simple and developed for a long time. The experiment of changing the direction of a light beam by refraction was demonstrated by Daniel Colladon and Jacques Babinet back in 1840. The practical application of the technology was found only in the twentieth century.

In the 1920s, experimenters Clarence Hasnell and John Berd demonstrated the ability to transmit images through optical tubes.

The invention of optical fiber in 1970 by Corning specialists is considered to be a turning point in the history of the development of optical fiber technology. The developers have succeeded in creating a conductor that is capable of retaining at least one percent of the power of an optical signal at a distance of one kilometer. By today's standards, this is a rather modest achievement, but then, almost 40 years ago, it was a necessary condition in order to develop a new type of wire communication.

E The first large-scale experiments associated with the emergence of the FDDI standard. These first generation networks are still in operation.

E Massive use of fiber optics associated with the production of cheaper components. The growth rate of fiber optic networks is explosive.

E The growth of information transfer rates, the emergence of wavelength division multiplexing technologies (WDM, DWDM) / New types of fibers.

2. Fiber-optic communication lines as a concept

1 Optical fiber and its types

A fiber optic communication line (FOCL) is a type of transmission system in which information is transmitted through optical dielectric waveguides known as optical fiber. So what is it?

An optical fiber is an extremely thin glass cylinder called a core, covered with a layer of glass (Fig. 1) called a cladding, with a refractive index different from that of the core. A fiber is characterized by the diameters of these regions - for example, 50/125 means a fiber with a core diameter of 50 µm and an outer cladding diameter of 125 µm.

Fig. 1 Fiber structure

Light propagates along the fiber core due to successive total internal reflections at the core-cladding interface; his behavior is in many ways similar to that as if he got into a pipe, the walls of which are covered with a mirror layer. However, unlike conventional mirrors, in which reflection is rather inefficient, total internal reflection is essentially close to ideal - this is the fundamental difference between them, which allows light to propagate along the fiber for long distances with minimal loss.

A fiber made in this way ((Fig. 2) a)) is called a stepped refractive index and multimode fiber because there are many possible paths, or modes, for the light beam to propagate.

This multiplicity of modes results in pulse dispersion (broadening) because each mode travels a different path in the fiber, and therefore different modes have different transmission delays from one end of the fiber to the other. The result of this phenomenon is a limitation of the maximum frequency that can be effectively transmitted for a given fiber length - an increase in either frequency or fiber length beyond the limit values essentially leads to the coalescence of successive pulses, making it impossible to distinguish between them. For a typical multimode fiber, this limit is approximately 15 MHz km, which means that a video signal with a bandwidth of eg 5 MHz can be transmitted over a maximum distance of 3 km (5 MHz x 3 km = 15 MHz km). Attempting to transmit the signal over a greater distance will result in progressive loss of high frequencies.

Fig. 2 Optical fiber types

For many applications, this figure is unacceptably high, and a search was made for a fiber design with a wider bandwidth. One way is to reduce the fiber diameter to very small values (8-9 microns), so that only one mode becomes possible. Single-mode, as they are called, fibers ((Fig. 2) b)) are very effective in reducing dispersion, and the resulting bandwidth - many GHz km - makes them ideal for public telephone and telegraph networks (PTT) and cable television networks. Unfortunately, a fiber of such a small diameter requires the use of a powerful, precision aligned, and therefore relatively expensive laser diode emitter, which reduces their attractiveness for many applications associated with the short length of the projected line.

Ideally, a fiber with a bandwidth of the same order of magnitude as a single-mode fiber, but with a diameter similar to that of a multimode fiber, is required to enable the use of inexpensive LED transmitters. To some extent, these requirements are satisfied by multimode fiber with a gradient change in refractive index ((Fig. 2) c)). It resembles a multimode fiber with a step change in refractive index, which was mentioned above, but the refractive index of its core is inhomogeneous - it smoothly changes from a maximum value in the center to a lower value at the periphery. This has two consequences. First, the light travels along a slightly curving path, and second, and more importantly, the differences in propagation delay between different modes are minimal. This is because high modes that enter the fiber at a larger angle and travel a longer path actually propagate at a faster rate as they move away from the center into the region where the refractive index decreases, and generally move faster. than the lower-order modes, which remain near the axis in the filament, in the region of high refractive index. The increase in speed just compensates for the greater distance traveled.

Gradient index multimode fibers are not ideal, but they still exhibit quite good bandwidth. Therefore, in most lines of short and medium length, the choice of this type of fiber is preferable. In practice, this means that bandwidth is rarely a parameter to be considered.

However, this is not the case for fading. The optical signal is attenuated in all fibers, at a rate depending on the wavelength of the transmitter by the light source (Fig. 3). As mentioned earlier, there are three wavelengths at which the attenuation of an optical fiber is usually minimal - 850, 1310 and 1550 nm. These are known as transparency windows. For multimode systems, the 850nm window is the first and most commonly used (lowest cost). At this wavelength, good quality gradient multimode fiber exhibits attenuation of the order of 3 dB / km, which makes it possible to implement communication in a closed-loop TV system at distances over 3 km.

Fig. 3 Dependence of attenuation on wavelength

At a wavelength of 1310 nm, the same fiber shows even less attenuation - 0.7 dB / km, thereby allowing a proportional increase in the communication range to about 12 km. 1310 nm is also the first operating window for single-mode fiber optic systems, with attenuation of about 0.5 dB / km, which, in combination with laser diode transmitters, allows the creation of communication lines longer than 50 km. The second transparency window - 1550 nm - is used to create even longer communication lines (fiber attenuation is less than 0.2 dB / km).

2 Classification of EQA

Fiber optic cable has been around for a long time, and was supported even by early 10 Mbps Ethernet standards. The first of them was named FOIRL (Fiber-Optic Inter-Repeater Link), and the next one - 10BaseF.

Today, there are several dozen companies in the world that produce optical cables for various purposes. The most famous of them: AT&T, General Cable Company (USA); Siecor (Germany); BICC Cable (UK); Les cables de Lion (France); Nokia (Finland); NTT, Sumitomo (Japan), Pirelli (Italy).

The defining parameters in the production of FOC are the operating conditions and the throughput of the communication line. According to the operating conditions, the cables are divided into two main groups (Fig. 4)

Intra-facility are intended for laying inside buildings and structures. They are compact, lightweight and, as a rule, have a short headroom.

Trunk lines are designed for laying cable communications in wells, in the ground, on supports along power lines, under water. These cables are protected against external influences and have a construction length of more than two kilometers.

To ensure high throughput of communication lines, FOCs are produced containing a small number (up to 8) single-mode fibers with low attenuation, and cables for distribution networks can contain up to 144 fibers, both single-mode and multimode, depending on the distances between network segments.

Fig. 4 Classification of EQA

3 Advantages and Disadvantages of Fiber Optic Signal Transmission

3.1 Advantages of FOCL

For many applications, fiber optics are preferred for a number of advantages.

Low transmission loss. Low loss fiber optic cables allow the transmission of image signals over long distances without the use of route amplifiers or repeaters. This is especially useful for long-distance transmission schemes - for example, a highway or railway surveillance system, where 20 km of repeater-free sections are not uncommon.

Broadband signal transmission. The wide transmission bandwidth of optical fiber allows high-quality video, audio and digital data to be transmitted simultaneously over a single fiber-optic cable.

Immunity to interference and interference. The complete insensitivity of the fiber-optic cable to external electrical noise and interference ensures stable operation of the systems even in cases where the installers did not pay sufficient attention to the location of nearby power networks, etc.

Electrical insulation. The lack of electrical conductivity for fiber optic cable means that the problems associated with changes in ground potential, such as those in power plants or railways, are gone. This property also eliminates the risk of equipment damage caused by lightning surges, etc.

Lightweight and compact cables. The ultra-small dimensions of optical fibers and fiber optic cables bring a new lease of life to jam-packed cable ducts. For example, a single coaxial cable takes up as much space as 24 optical cables, each of which can presumably carry 64 video channels and 128 audio or video signals at the same time.

Timeless communication line. By simply replacing the terminal equipment, rather than the cables themselves, fiber optic networks can be upgraded to carry more information. On the other hand, part or even the entire network can be used for a completely different task, for example, combining a local area network and a closed-loop TV system in one cable.

Explosion and fire safety. Due to the absence of sparking, optical fiber increases the safety of the network at chemical, oil refineries, when servicing high-risk technological processes.

Profitability of FOCL. The fiber is made of silica based on silica, a widespread and therefore inexpensive material, unlike copper.

Long service life. Fiber degrades over time. This means that the attenuation in the laid cable gradually increases. However, due to the perfection of modern technologies for the production of optical fibers, this process is significantly slowed down, and the service life of the FOC is approximately 25 years. During this time, several generations / standards of transceiving systems may change.

3.2 Disadvantages of FOCL

High complexity of installation. Highly qualified staff and special tools. Therefore, most often, fiber optic cable is sold in the form of pre-cut pieces of different lengths, on both ends of which the connectors of the required type are already installed. The use of fiber optic cable requires special optical receivers and transmitters that convert light signals into electrical signals and vice versa.

Fiber optic cable is less durable and flexible than electrical cable. Typical bending radii are around 10 - 20 cm; at smaller bending radii, the center fiber may break.

Fiber optic cable is sensitive to ionizing radiation, which reduces the transparency of the glass fiber, that is, increases the signal attenuation.

3. Electronic components of FOCL. Principle of information transfer

In the most general form, the principle of information transmission in fiber-optic communication systems can be explained using (Fig. 5).

Fig. 5 Principle of information transmission in fiber-optic communication systems

1 Transmitters for fiber optics

The most important component of a fiber optic transmitter is the light source (usually a semiconductor laser or LED (Figure 6)). Both serve the same purpose - the generation of a microscopic light beam that can be introduced into the fiber with high efficiency and modulated (changed in intensity) at a high frequency. Lasers provide higher beam intensities than LEDs and allow higher modulation frequencies; therefore they are often used for long-haul broadband lines such as telecommunications or cable TV. On the other hand, LEDs are cheaper and more durable devices, and are also quite suitable for most small to medium-sized systems.

Fig. 6 Methods for introducing optical radiation into optical fiber

In addition to its functional purpose (i.e. what signal it should transmit), a fiber-optic transmitter is characterized by two more important parameters that determine its properties. One is its optical output power (intensity). The second is the wavelength (or color) of the light emitted. Usually these are 850, 1310 or 1550 nm, values selected from the condition of coincidence with the so-called. "Transparency windows" in the transmission characteristic of an optical fiber material.

3.2 Fiber Optic Receivers

Fiber optic receivers solve the vital problem of detecting extremely weak optical radiation emitted from the end of the fiber and amplifying the received electrical signal to the required level with minimal distortion and noise. The minimum level of radiation required by the receiver in order to provide an acceptable quality of the output signal is called the sensitivity; the difference between the receiver sensitivity and the transmitter output power determines the maximum allowable system loss in dB. For most CCTV surveillance systems with an LED transmitter, the typical figure is 10-15 dB. Ideally, the receiver should work well when the input signal changes over a wide range, since it is usually impossible to predict in advance exactly what the attenuation will be in the communication line (i.e., the length of the line, the number of joints, etc.). Many simple receiver designs use manual gain control during installation to achieve the desired output level. This is undesirable, since changes in the amount of line attenuation caused by aging or changes in temperature, etc., are inevitable, which dictates the need to periodically adjust the gain. All fiber optic receivers use an automatic gain control that monitors the average level of the input optical signal and changes the receiver gain accordingly. No manual adjustment is required either during installation or during operation.

optical fiber communication cable

4. Scopes of fiber-optic communication lines

Fiber-optic communication lines (FOCL) allow the transmission of analog and digital signals over long distances. They are also used at shorter, more manageable distances, such as inside buildings. The number of Internet users is growing - and we are rapidly building new data processing centers (DPCs), for the interconnection of which fiber is used. Indeed, when transmitting signals at a speed of 10 Gbit / s, the costs are similar to those of "copper" lines, but optics consume much less energy. For years, fiber and copper adherents have battled each other for priority in corporate networks. Wasted time!

Indeed, the fields of application of optics are becoming more and more, mainly due to the above advantages over copper. Fiber optic equipment is widely used in medical institutions, for example, for switching local video signals in operating rooms. Optical signals have nothing to do with electricity, which is ideal for patient safety.

Fiber optic technologies are also preferred by the military, since the transmitted data is difficult or even impossible to read from the outside. Fiber-optic communication lines provide a high degree of protection of confidential information, allow transferring uncompressed data such as high-resolution graphics and video with pixel precision. Optics have penetrated all key areas - surveillance systems, dispatch and situation centers in areas with extreme operating conditions.

Reducing the cost of equipment made it possible to use optical technologies in traditionally copper areas - at large industrial enterprises for organizing automated process control systems (APCS), in the energy sector, in security and video surveillance systems. The ability to transmit a large flow of information over long distances makes optics ideally suited and in demand in almost all areas of industry, where the length of cable lines can reach several kilometers. If for twisted pair the distance is limited to 450 meters, then for optics and 30 km is not the limit.

As an example of using fiber-optic communication lines, I would like to give a description of a closed-loop video surveillance security system at a typical power plant. This topic has become especially relevant and in demand recently, after the adoption by the Government of the Russian Federation of a decree on countering terrorism and a list of vital objects to be protected.

5. Fiber optic TV surveillance systems

The system development process usually includes two components:

Selection of suitable active components of the transmission path based on the function (s) required, the type and number of fibers available or offered, and the maximum transmission distance.

Passive fiber infrastructure designs, including trunk cable types and specifications, junction boxes, fiber patch panels.

1 Components of a video surveillance transmission path

First of all, what components are actually required to meet the system specifications?

Fixed camera systems - These systems are extremely simple and usually consist of a miniature fiber optic transmitter and either a modular or rack-mountable receiver. The transmitter is often small enough to be mounted directly in the camera body, and is equipped with a coaxial bayonet connector, 'ST' optical connector and terminals for connecting a low voltage power supply (typically 12V DC or AC). The surveillance system of a typical power plant consists of several dozen such cameras, the signals from which are transmitted to the central control room, in which case the receivers are rack mounted on a standard 19-inch 3U card with a common power supply.

Systems based on controlled cameras with PTZ devices - such systems are more complex, since an additional channel is required to transmit camera control signals. Generally speaking, there are two types of remote control systems for such cameras - requiring unidirectional transmission of remote control signals (from the central station to the cameras) and requiring bi-directional transmission. Bidirectional transmission systems are becoming more and more popular, as they allow each camera to receive confirmation of the receipt of each control signal, and therefore provide greater accuracy and reliability of control. Within each of these groups, there is a wide variety of interface requirements, including RS232, RS422, and RS485. Other systems do not use a digital interface, but transmit data as a sequence of beeps over an analog channel, similar to dual-frequency tone dialing in telephony.

Fig. 6 Transmission of signals for remote control of the PTZ device over one fiber

All of these systems can work with fiber optic cables using the appropriate equipment. Under normal circumstances, simultaneous transmission of optical signals along one fiber in opposite directions is undesirable, since mutual interference occurs due to diffuse reflections in the fiber. In closed-circuit TV systems, this effect creates noise in the image whenever the camera controls are activated.

To achieve bi-directional transmission over a single fiber that does not cause mutual interference, it is necessary that the transmitters at different ends of the fiber operate at different wavelengths, for example, at 850 nm and at 1300 nm, respectively (Fig. 6). A wavelength division multiplexer (WDM) coupler is connected to each end of the fiber, ensuring that each receiver receives only the correct wavelength (e.g. 850 nm) light from the transmitter at the opposite end of the fiber. Unwanted reflections from the near end transmitter are in the “wrong” range (ie 1300 nm) and are rejected accordingly.

Additional features - although the choice of a fixed camera or a PTZ camera satisfies the requirements of most closed-circuit TV surveillance systems, there are a number of systems that require additional features, for example, audio information transmission - for general notification, auxiliary messages to the consumer or intercom communication with a remote post ... On the other hand, contacts of sensors that are triggered in the event of a fire or the appearance of strangers can be part of the integrated security system. All of these signals can be transmitted over optical fiber - either over the same one used by the network, or over another.

2 Video multiplexing

Up to 64 video and up to 128 audio or digital data signals can be multiplexed on a single single-mode fiber, or somewhat less on multi-mode. In this context, multiplexing refers to the simultaneous transmission of full-screen video signals in real time, rather than the low-frame or split-screen display, which is often referred to as the term.

The ability to carry many signals and additional information over multiple optical fibers is very valuable, especially for long distance CCTV surveillance systems, such as highways or railways, where minimizing the number of fiber optic cables is often vital. For other applications, with shorter distances and highly scattered cameras, the benefits are less obvious and the first consideration should be given to using a separate fiber line for each video signal. The choice of whether to multiplex or not is quite complex and should only be made after considering all the considerations, including system topology, overall costs, and last but not least, network fault tolerance.

3 Cable infrastructure

After the requirements for the transmission path are determined, the infrastructure of the cable fiber-optic network is developed, which includes not only the cables themselves, but also all the auxiliary components - junction boxes, panels for extending cables, bypass cables.

The first task is to confirm the correctness of the choice of the number and type of optical fibers, determined at the stage of selecting the components of the path. If the system is not very long (i.e., no longer than about 10 km) and does not involve multiplex transmission of video signals, then most likely the best choice would be a 50/125 micron or 62.5 / 125 micron multimode fiber with a gradient refractive index. Traditionally, for closed-circuit TV systems, 50/125 microns fiber is chosen, and for local computer networks - 62.5 / 125 microns. In any case, each of them is suitable for each of these tasks, and in general, in most countries, 62.5 / 125 µm fiber is used for both purposes.

The number of fibers required can be determined based on the number and relative position of the cameras and whether unidirectional or bi-directional remote control or multiplexing is used. Since the pipes. Cables to be routed in external ducts are usually waterproofed either from aluminum tape (dry hollow pipes) or water-repellent filler (gel-filled cables). Fire safety cable.

Many short-haul CCTV systems have a star configuration, where a single piece of cable runs from each camera to the control room. For such systems, the optimal cable design will contain two fibers - for video transmission and remote control, respectively. This configuration provides a 100% headroom for the cable, since, if necessary, both video and remote control signals can be transmitted over the same fiber. More branched networks can benefit from the use of inverted branch & tree topology (Figure 7). In these networks, a two-wire fiber optic cable runs from each camera to a local "hub" where they are connected to form a single multi-wire cable. The hub itself is not much more complicated than a conventional all-weather junction box and can often be combined with the equipment body of one of the cameras.

The cost increase when adding fiber optic lines to an existing cable is negligible, especially when compared to the cost of associated public works, the possibility of installing cables with a margin of capacity should be taken seriously.

Fiber optic trench cables may contain steel wire reinforcement. Ideally, all cables should be made from flame retardant materials with low smoke emission in order to meet local regulations, intended for installation in external cable ducts or directly in trenches, usually of a hollow pipe design containing from 2 to 24 fibers in one or more

Figure 7 Fiber optic tree topology

At the control room, the input fiber optic cable usually arrives at the interface box, mounted in a 19 "rack, with each fiber having its own individual 'ST' connector. No special skill is required to complete all installation work other than a reasonable understanding of the need for careful handling of the optical fiber (for example, do not bend a fiber with a radius of less than 10 fiber diameters) and general hygiene (ie cleanliness).

4
Optical Loss Budget

It may seem odd that the optical loss budget is calculated at such a late stage in the development process, but in fact, it can only be calculated with any accuracy after the cabling infrastructure is fully defined. The purpose of the calculation is to determine the loss for the worst-case signal path (usually the longest) and to ensure that the equipment chosen for the transmission path with a reasonable margin fits within the obtained limits.

The calculation is quite simple and consists in the usual summation of the losses in decibels of all components of the path, including the attenuation in the cable (dB / km x length in km) plus both connectors and the loss at the joints. The biggest challenge is simply extracting the required loss figures from the manufacturer's documentation.

Depending on the result obtained, the equipment selected for the transmission path may need to be reevaluated to ensure acceptable losses. For example, it may be necessary to order equipment with improved optical parameters, and if such equipment is not available, consideration should be given to switching to a transparency window with a longer wavelength, where the losses are less.

5 Testing the system and putting it into operation

Most fiber installers provide optical test results for a commissioned fiber network. As a minimum, they should include the end-to-end optical power transmission measurements for each fiber - this is equivalent to a continuity check for a conventional copper network with electrical signal multiplexers. These results are reported as line loss in dB and can be directly compared with the technical data for the equipment selected for the transmission path. It is generally considered normal to have a minimum 3dB loss margin (hardware promised minus measured value) for the inevitable aging processes occurring in fiber optic lines, especially transmitters.

Conclusion

Often, experts are of the opinion that fiber-optic solutions are much more expensive than copper ones. In the final part of my work, I would like to summarize what was said above and try to find out whether this is so or not by comparing the optical solutions of the 3M Volution company with a typical shielded system of the 6th category, which has the closest multimode optics

The approximate calculation of the cost of a typical system included the price of a port of a 24-port patch panel (per subscriber), subscriber and patch cords, a subscriber module, as well as the cost of a horizontal cable per 100 meters (see Table 1).

Table 1 Calculation of the cost of the SCS subscriber port for "copper" of the 6th category and optics

This simple calculation showed that the cost of a fiber optic solution is only 35% more than a Category 6 twisted pair solution, so rumors about the huge cost of optics are somewhat exaggerated. Moreover, the cost of the main optical components today is comparable or even lower than for shielded systems of the 6th category, but, unfortunately, ready-made optical patch and subscriber cords are still several times more expensive than copper analogs. However, if for some reason the length of subscriber channels in the horizontal subsystem exceeds 100 m, there is simply no alternative to optics.

At the same time, the low attenuation of the optical fiber and "immunity" to various electromagnetic interference makes it an ideal solution for today's and future cable systems.

Structured cabling systems that use fiber for both backbone and horizontal cabling offer customers a number of significant benefits: more flexible structure, less building footprint, higher security, and better manageability.

The use of optical fiber in workplaces will allow in the future to move to new network protocols such as Gigabit and 10 Gigabit Ethernet with minimal costs. This is possible thanks to a number of recent advances in fiber optic technology: multimode fiber with improved optical performance and bandwidth; small form factor optical connectors that require less floor space and less installation; vertical cavity plane laser diodes provide long distance data transmission at low cost.

A wide range of optical cabling solutions provide a smooth, cost-effective transition from copper to fully optical structured cabling.

List of used literature

1. Guk M. Hardware of local networks / M. Guk - SPb: Publishing House "Peter", 2000.-572s.

Solutions for telecom and telecom operators

Energy. Electrical engineering. Connection.

Optical cables

Rodina O.V. Fiber-optic communication lines / O.V. Motherland - M .: Hot line, 2009.-400c.

In the modern world, the needs for communication are constantly growing. Consumers are looking for ever higher transmission rates, quality of communication and broadcast content (for example, the quality of digital television). Providers - companies that provide services of wired Internet, wireless Internet (Wi-Fi), IP-telephony, digital television - need to expand the capabilities of their communication lines. You can find out about these and many other areas of telecommunications on our website rcsz-tcc.ru.

Channels based on ordinary twisted pair, limit the speed when the length of the communication lines and the heavy load (large number of subscribers) on them. The solution was found in the most modern lines - optical. In another way, they are also called Fiber Optic Communication Lines (FOCL). What is the advantage of such lines, and how is it achieved?

First, a little history. For the first time, an experiment on the transmission of a light signal was carried out and presented by Daniel Colladon and Jacques Babinet in the distant 1840. But the first practical application of the technology took place only in the twentieth century. In 1952, physicist Narinder Singh Kapany was able to carry out several studies that sparked the creation of optical fiber. Narinder created a bundle of glassy fibers, which represent an optical waveguide (waveguide is a guiding system for signals). The middle of the fiber has a lower refractive index than the cladding. In this case, the signal will pass completely through the core, and from the cladding will be reflected back into the core. Thus, the shell acts as a mirror. Before the invention of such fibers, the signal did not reach the end of the line. Now the problem could be considered solved. The discovery in 1970 by Corning of a method of making optical fiber, which was not inferior in attenuation to a copper wire for a telephone signal, is considered a turning point in the history of fiber-optic communication.

Optical communication has many advantages over electrical... Firstly, a wide bandwidth due to very high transmission frequencies allows information to be transmitted at a rate of several Tbit / s. Secondly, low signal attenuation makes it possible to build highways up to 100 kilometers or more without relay stations. For example, the Transatlantic Optical Highway is made without a single repeater. Thirdly, FOCL is resistant to any external interference that can be induced from neighboring radio transmitters, other transmission lines, even from weather conditions, unlike other cable systems. One of the most important benefits is information security. It is impossible to connect to a fiber-optic communication line and intercept information - the line will be damaged, and this is easy to fix. Because optical fiber is a dielectric, the likelihood of a fire from such a line is completely excluded, which is important at enterprises with a high risk of fire. And, of course, the service life of the fiber-optic communication line is 25 years or more.

The transmitter (generator of the information signal) in such lines is most often currently lasers, including those made using integral technology. The receivers are photodetecting diodes. These devices form the main disadvantage of fiber-optic communication lines - the cost of active elements. The second significant disadvantage of optical lines is the high cost of service. When fiber is broken, the cost of recovery is much higher than when copper or other lines are broken. At the same time, breaks are not allowed on the main lines (welding places introduce significant attenuation), therefore, large sections have to be replaced with new fiber. It is recommended to repair FOCL only over short distances, within a district or a small town.

Fiber optic technology is constantly evolving - it is the technology of the future. And you can always read about the most advanced innovations on our website rcsz-tcc.ru.

Fiber optic communication- communication based on fiber optic cables. The abbreviation FOCL (fiber-optic communication line) is also widely used. It is used in various spheres of human activity, from computing systems to structures for communication over long distances. It is today the most popular and effective method for providing telecommunication services.

An optical fiber consists of a central conductor of light (core) - a glass fiber surrounded by another layer of glass - a cladding with a lower refractive index than the core. Spreading along the core, the light rays do not go beyond its limits, reflecting from the covering layer of the shell. In optical fiber, the light beam is usually formed by a semiconductor or diode laser. Depending on the distribution of the refractive index and on the size of the core diameter, the optical fiber is divided into single-mode and multi-mode.

Fiber optic li nii communication (FOCL) - a system based on a fiber-optic cable, designed to transmit information in the optical (light) range. In accordance with GOST 26599-85, the term FOCL has been replaced by FOCL (fiber-optic transmission line), but in everyday practice the term FOCL is still used, so in this article we will stick to it.

FOCL communication lines (if they are correctly installed), in comparison with all cable systems, are distinguished by very high reliability, excellent communication quality, wide bandwidth, much longer length without amplification, and almost 100% immunity from electromagnetic interference. The system is based on fiber optics technology- light is used as an information carrier, the type of information transmitted (analog or digital) does not matter. In the work, infrared light is mainly used, the transmission medium is fiberglass.

Scope of FOCL

Fiber-optic cable has been used for communication and information transmission for more than 40 years, but due to its high cost, it has become widely used relatively recently. The development of technologies made it possible to make production more economical and the cost of the cable more affordable, and its technical characteristics and advantages over other materials quickly pay off all the costs incurred.

At present, when a complex of low-current systems is used at one facility (computer network, ACS, video surveillance, burglar and fire alarms, perimeter security, television, etc.), it is not possible to do without the use of fiber-optic communication lines. Only the use of a fiber-optic cable makes it possible to use all these systems at the same time, ensures the correct stable operation and performance of their functions.

FOCL is increasingly used as a fundamental system in the design and installation, especially for multi-storey buildings, long buildings and when combining a group of objects. Only Fiber optic cables can provide adequate volume and speed of information transfer. All three subsystems can be implemented on the basis of optical fiber; in the subsystem of internal highways, optical cables are used equally often with twisted pair cables, and in the subsystem of external highways, they play a dominant role. A distinction is made between fiber optic cables for outdoor cables and indoor cables, as well as connecting cords for horizontal wiring communications, equipping individual workplaces, connecting buildings.

Despite the relatively high cost, the use of fiber is becoming more and more justified and is increasingly being used.

Advantages fiber-optic communication lines (FOCL) in front of traditional "metal" means of transmission:

Wide bandwidth;
Slight signal attenuation, for example, for a 10 MHz signal, it will be 1.5 dB / km compared to 30 dB / km for an RG6 coaxial cable;
The possibility of the occurrence of "earth loops" is excluded, since the optical fiber is a dielectric and creates electrical (galvanic) isolation between the transmitting and receiving end of the line;
High reliability of the optical medium: optical fibers do not oxidize, do not get wet, are not subject to electromagnetic influences
Does not cause interference in adjacent cables or other fiber-optic cables, since the signal carrier is light and it remains completely inside the fiber-optic cable;
Fiberglass is absolutely insensitive to external signals and electromagnetic interference (EMI), it doesn't matter where the cable runs (110 V, 240 V, 10,000 V AC) or very close to the megawatt transmitter. A lightning strike at a distance of 1 cm from the cable will not give any interference and will not affect the operation of the system;
Information security - information on optical fiber is transmitted "from point to point" and it can be eavesdropped or changed only by physical interference in the transmission line
Fiber-optic cable is lighter and smaller - it is more convenient and easier to lay than electric cable of the same diameter;
It is not possible to make a cable branch without damaging the signal quality. Any tampering with the system is immediately detected at the receiving end of the line, this is especially important for security systems and video surveillance;
Fire and explosion safety when changing physical and chemical parameters

The cost of the cable is decreasing every day, its quality and capabilities begin to prevail over the costs of building low-current ones based on fiber-optic communication lines

There are no ideal and perfect solutions, like any system, FOCL has its drawbacks:

Brittleness of fiberglass - if the cable is bent strongly, the fibers may break or become cloudy due to the occurrence of microcracks. To eliminate and minimize these risks, cable reinforcement structures and braids are used. When installing the cable, it is necessary to follow the manufacturer's recommendations (where, in particular, the minimum permissible bending radius is standardized);
The complexity of the connection in the event of a break - requires a special tool and qualifications of the performer;
Sophisticated manufacturing technology of both the fiber itself and the components of the FOCL;
Complexity of signal conversion (in interface equipment);
Relative high cost of optical terminal equipment. However, the equipment is expensive in absolute terms. The price-to-bandwidth ratio for fiber-optic communication lines is better than for other systems;
Fiber clouding due to radiation exposure (however, doped fibers with high radiation resistance exist).

Installation of fiber-optic communication systems requires an appropriate level of qualification from the contractor, since the termination of the cable is carried out with special tools, with special accuracy and skill, unlike other means of transmission. Settings for routing and switching signals require special qualifications and skill, so in this area you should not save money and be afraid to overpay for professionals, eliminating system malfunctions and the consequences of improper cable installation will cost more.

The principle of operation of a fiber-optic cable.

The very idea of transmitting information using light, not to mention the physical principle of work, is not entirely clear to most ordinary people. We will not go deep into this topic, but we will try to explain the main mechanism of operation of fiber and justify such high performance indicators.

The concept of fiber optics is based on the fundamental laws of reflection and refraction of light. Due to its construction, fiberglass can keep light rays inside the fiber and prevent them from “passing through walls” when transmitting a signal for many kilometers. Moreover, it is no secret that the speed of light is higher.

Fiber optics rely on the effect of refraction at the maximum angle of incidence when total reflection occurs. This phenomenon occurs when a ray of light exits a dense medium and enters a less dense medium at a certain angle. For example, let's imagine an absolutely motionless surface of water. The observer looks from under the water and changes the angle of view. At a certain moment, the viewing angle becomes such that the observer will not be able to see objects above the surface of the water. This angle is called the angle of total reflection. At this angle, the observer will see only objects under water, it will seem that you are looking in a mirror.

The inner core of the FOCL cable has a higher refractive index than the sheath, and the effect of total reflection occurs. For this reason, a ray of light passing through the inner vein cannot go beyond its limits.

There are several types of fiber optic cables:

With a stepped profile - a typical, cheapest option, the distribution of light is "steps" and the deformation of the input pulse occurs, caused by different lengths of the trajectories of light rays
With a smooth profile "multimode" - light beams propagate with approximately equal speed "waves", the length of their paths is balanced, this allows to improve the characteristics of the pulse;
Single-mode fiberglass is the most expensive option, it allows you to pull the beams in a straight line, the pulse transmission characteristics become almost flawless.

Fiber-optic cable still costs more than other materials, its installation and termination is more difficult, requires qualified performers, but the future of information transmission is undoubtedly behind the development of these technologies and this process is irreversible.

The FOCL includes active and passive components. At the transmitting end of the fiber optic cable there is an LED or laser diode, their radiation is modulated by the transmitting signal. With regard to video surveillance, this will be a video signal; for the transmission of digital signals, the logic is preserved. During transmission, the infrared diode is modulated in brightness and pulsates in accordance with signal variations. To receive and convert an optical signal into an electrical one, a photodetector is usually located at the receiving end.

Active components include multiplexers, regenerators, amplifiers, lasers, photodiodes and modulators.

Multiplexer- combines several signals into one, so one fiber-optic cable can be used for simultaneous transmission of several real-time signals. These devices are indispensable in systems with an insufficient or limited number of cables.

There are several types of multiplexers, they differ in their technical characteristics, functions and field of application:

spectral division (WDM) - the simplest and cheapest device that transmits optical signals over one cable from one or several sources operating at different wavelengths;
frequency modulation and frequency multiplexing (FM-FDM) - devices are quite immune to noise and distortion, with good characteristics and circuits of average complexity, have 4.8 and 16 channels, are optimal for video surveillance.
Amplitude modulation with partially suppressed sideband (AVSB-FDM) - with high-quality optoelectronics, they can transmit up to 80 channels, optimal for subscriber television, but expensive for video surveillance;
Pulse code modulation (PCM - FDM) - an expensive device, completely digital used for the distribution of digital video and video surveillance;

In practice, combinations of these methods are often used. Regenerator is a device that restores the shape of an optical pulse, which, propagating along the fiber, undergoes distortion. Regenerators can be either purely optical or electrical, which convert an optical signal into an electrical one, restore it, and then convert it back to an optical one.

Amplifier- amplifies the signal power to the required voltage level, can be optical and electrical, carries out optical-electronic and electro-optical signal conversion.

LEDs and Lasers- a source of monochrome coherent optical radiation (light for the cable). For systems with direct modulation, it simultaneously functions as a modulator that converts an electrical signal into an optical one.

Photodetector(Photodiode) - A device that receives a signal at the other end of a fiber optic cable and performs optoelectronic signal conversion.

Modulator- a device that modulates an optical wave, carrying information according to the law of an electrical signal. In most systems, the laser performs this function, but in indirect modulation systems, separate devices are used for this.

Passive components of FOCL include:

Fiber optic cable – serves as a medium for signal transmission. The outer sheath of the cable can be made of various materials: polyvinyl chloride, polyethylene, polypropylene, teflon and other materials. An optical cable can have different types of armor and specific protective layers (for example, small glass needles to protect against rodents). By design it can be:

Optical coupler- a device used to connect two or more optical cables.

Optical cross- a device designed to terminate an optical cable and connect active equipment to it.

Adhesions- designed for permanent or semi-permanent splicing of fibers;

Connectors- to reconnect or disconnect the cable;

Taps- devices that distribute the optical power of several fibers into one;

Switches- devices redistributing optical signals under manual or electronic control

Installation of fiber-optic communication lines, its features and order.

Fiberglass is a very strong but brittle material, although thanks to its protective shell it can be handled almost like electrical. However, when installing the cable, you must comply with the manufacturers' requirements for:

"Maximum tensile" and "maximum breaking force" expressed in newtons (about 1000 N or 1 kN). In an optical cable, the main stress falls on the load-bearing structure (reinforced plastic, steel, Kevlar, or a combination of these). Each type of construction has its own individual characteristics and degree of protection, if the tension exceeds the stipulated level, then the optical fiber can be damaged.
"Minimum bend radius" - make bends smoother, avoid sharp bends.
"Mechanical strength", it is expressed in N / m (newtons / meters) - protection of the cable from physical stress (it can be stepped on or even hit by transport. small contact area.

Optical cable is usually supplied wound on wooden drums with a strong plastic protective layer or wooden strips around the circumference. The outer layers of the cable are the most vulnerable, therefore, during installation, it is necessary to remember the weight of the drum, protect it from impacts, falls, and take safety measures during storage. It is best to store drums horizontally, if they do lie vertically, then their edges (rims) should touch.

The procedure and features of the installation of fiber-optic cable:

Before starting the installation, it is necessary to inspect the drums with the cable for damage, dents, scratches. In case of any suspicion, it is better to put the cable aside immediately for further detailed examination or rejection. Short pieces (less than 2 km) for fiber continuity can be checked for transmission with any flashlight. Fiber cable for infrared transmission transmits ordinary light just as well.
Next, study the route for potential problems (sharp corners, clogged cable channels, etc.), if any, make changes to the route to minimize risks.
Distribute the cable along the route so that the connection and connection points of the amplifiers are accessible, but protected from adverse factors. It is important that there is a sufficient supply of cable in the places of future connections. The exposed cable ends must be protected with waterproof caps. Pipes are used to minimize bending stress and damage from passing traffic. A part of the cable is left at both ends of the cable line, its length depends on the planned configuration).
When laying the cable underground, it is additionally protected from damage at local points of load, such as contact with inhomogeneous backfill material, unevenness of the trench. To do this, the cable in the trench is laid on a layer of sand 50-150 cm. And covered with the same layer of sand 50-150 cm. It should be noted that damage to the cable can occur both immediately and during operation (after backfilling the cable), for example, from constant pressure, an uncleaned stone can gradually push through the cable. The work on diagnostics and search and elimination of violations of the already buried cable will cost much more than the accuracy and observance of precautions during installation. The depth of the trench depends on the type of soil and the expected surface load. In hard rock, the depth will be 30 cm, in soft or under the road 1 m. The recommended depth is 40-60 cm, with a thickness of sandy litter from 10 to 30 cm.
Most often, the cable is laid in a trench or in a tray directly from the drum. When installing very long lines, the drum is placed on the vehicle, as the machine progresses, the cable is laid in its place, and there is no need to rush, the pace and order of unwinding of the drum is manually adjusted.
When laying the cable in the tray, the most important thing is not to exceed the critical bending radius and mechanical stress. The cable should be laid in one plane, do not create points of concentrated loads, avoid sharp corners on the route, pressure and intersection with other cables and routes, do not bend the cable.
Pulling fiber optic cable through cable ducts is similar to pulling conventional cable, but you shouldn't use excessive physical effort or violate manufacturer's specifications. When using the clamp brackets, remember that the load should not be placed on the outer sheath of the cable, but on the load-bearing structure. To reduce friction, talcum powder or polystyrene granules can be used; the use of other lubricants should be consulted with the manufacturer.
In cases where the cable already has an end seal, special care should be taken when installing the cable so as not to damage the connectors, contaminate them and do not overload the connection area.
After laying, the cable in the tray is secured with nylon ties, it should not slip or sag. If the surface conditions do not allow the use of special cable ties, the use of clamps is acceptable, but with extreme care so as not to damage the cable. We recommend the use of clamps with a plastic protective layer, for each cable, use a separate clamp and in no case bundle several cables together. Between the end points of the cable attachment, it is better to leave a little slack, and not put the cable under an interference fit, otherwise it will react poorly to temperature fluctuations and vibrations.
If the optical fiber was damaged during installation, mark the section and leave sufficient cable headroom for subsequent splicing.

Basically, the installation of fiber optic cable is not very different from the installation of conventional cable. If you follow all our recommendations, then there will be no problems during installation and operation and your system will work for a long time, efficiently and reliably.

An example of a typical solution for laying a fiber-optic line

The task is to organize a FOCL system between two separate buildings of the production building and the administrative building. Distance between buildings 500 m.

Estimate for the installation of the fiber-optic communication system

N / a	Name of equipment, materials, works	Unit out of me	Qty	Price per one.	Amount, in rubles
I.	FOCL system equipment, including:				25 783
1.1.	Wall-mounted optical cross (SHKON) 8 ports	PCS.	2	2600	5200
1.2.	Media converter 10/100-Base-T / 100Base-FX, Tx / Rx: 1310 / 1550nm	PCS.	2	2655	5310
1.3.	Optical straightway coupler	PCS.	3	3420	10260
1.4.	Switching box 600x400	PCS.	2	2507	5013
II.	Cable routes and materials of the FOCL system, including:				25 000
2.1.	Optical cable with external cable 6kN, central module, 4 fibers, single-mode G.652.	m.	200	41	8200
2.2.	Fiber optic cable with internal carrier cable, center module, 4 fibers, single-mode G.652.	m.	300	36	10800
2.3.	Other consumables (connectors, screws, dowels, electrical tape, fasteners, etc.)	set	1	6000	6000
III.	TOTAL COST OF EQUIPMENT AND MATERIALS (item I + item II)				50 783
IV.	*Transport and procurement costs, 10% item III**				5078
V.	Installation and switching of equipment, including:				111 160
5.1.	Installation of constriction	units	4	8000	32000
5.2.	Cabling	m.	500	75	37500
5.3.	Mounting and welding of connectors	units	32	880	28160
5.4.	Installation of switching equipment	units	9	1500	13500
Vi.	TOTAL BY AN ESTIMATE (item III + item IV + item V)				167 021

Explanations and comments:

The total length of the track is 500 m, including:
- from the fence to the production building and the office building is 100 m each (total 200 m);
- along the fence between buildings 300 m.
The cable is installed in an open way, including:
- from buildings to the fence (200 m.) by air (hauling) using materials specialized for laying fiber-optic communication lines;
- between buildings (300 m.) along a fence made of reinforced concrete slabs, the cable is fixed in the middle of the fence with metal clips.
For the organization of fiber-optic communication lines, a specialized self-supporting (built-in cable) armored cable is used.

Fiber optic communication

Fiber optic communication- a type of wired telecommunication using electromagnetic radiation of the optical (near infrared) range as a carrier of an information signal, and fiber-optic cables as guiding systems. Due to the high carrier frequency and wide multiplexing capabilities, the throughput of fiber-optic lines is many times higher than the throughput of all other communication systems and can be measured in terabits per second. Low attenuation of light in an optical fiber allows the use of fiber-optic communication over long distances without the use of amplifiers. Fiber-optic communication is free from electromagnetic interference and difficult to access for unauthorized use - it is technically extremely difficult to intercept a signal transmitted over an optical cable unnoticed.

Physical basis

Fiber-optic communication is based on the phenomenon of total internal reflection of electromagnetic waves at the interface between dielectrics with different refractive indices. An optical fiber consists of two elements - a core, which is a direct light guide, and a cladding. The refractive index of the core is slightly higher than the refractive index of the cladding, due to which the light beam, experiencing multiple re-reflections at the core-cladding interface, propagates in the core without leaving it.

Application

Fiber-optic communication is increasingly being used in all areas - from computers and on-board space, aircraft and ship systems, to systems for transmitting information over long distances, for example, a fiber-optic communication line from Western Europe to Japan, a large part of which passes through the territory of Russia. In addition, the total length of submarine fiber-optic communication lines between continents is increasing.

Notes (edit)

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Fiber optic communication lines
Fiber optic cable

See what "Fiber-optic communication" is in other dictionaries:

FIBER OPTICAL COMMUNICATION- A type of wired telecommunication that uses electromagnetic radiation of the optical (near infrared) range as a carrier of an information signal, and fiber-optic cables as guiding systems. Dictionary of business terms. ... ... Business glossary

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Fiber optic transmission line- (FOCL), Fiber optic communication line (FOCL) is a fiber optic system consisting of passive and active elements, designed to transmit information in the optical (usually near infrared) range. Contents 1 ... Wikipedia