Vols transcript. Fiber optic communication lines: unlimited possibilities

Introduction

Today, communication plays an important role in our world. And if earlier copper cables and wires were used to transmit information, now the time has come for optical technologies and fiber optic cables. Now, when making a phone call to the other side of the world (for example, from Russia to America) or downloading a favorite melody from the Internet that is on a website somewhere in Australia, we don’t 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, bring them closer to each other or to the desired source of information, continents have to be connected. Currently, information exchange between continents is carried out mainly through undersea fiber optic cables. Currently, fiber-optic cables are laid along the bottom of the Pacific and Atlantic oceans and almost the entire world is “entangled” in a network of fiber communication systems (Laser Mag.-1993.-No. 3; Laser Focus World.-1992.-28, No. 12; Telecom mag.-1993.-No. 25; AEU: J. Asia Electron.-1992.-No. 5). European countries are connected across the Atlantic 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 of St. Petersburg - Kingisepp - Denmark and St. Petersburg - Vyborg - Finland, in the south - with the Asian countries of Novorossiysk - Türkiye. At the same time, the main driving force behind the development of fiber optic communication lines is the Internet.

Fiber optic networks are certainly one of the most promising areas in the field of communications. The capacity of optical channels is orders of magnitude higher than that of information lines based on copper cable.

Optical fiber is considered the most perfect medium for transmitting large flows of information over long distances. It is made of quartz, which is based on silicon dioxide - a widespread and inexpensive material, unlike copper. The 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 eliminates some of the typical problems of copper communication systems. Optical networks are capable of transmitting signals over long distances with less loss. Despite the fact that this technology is still expensive, prices for optical components are constantly falling, while the capabilities of copper lines are approaching their limit values and require more and more costs for the further development of this area.

It seems to me that the topic of fiber-optic communication lines is currently relevant, promising and interesting to consider. That's why I choose her for mine course work and I think that FOCL is the future.

1. History of creation

In the 1920s, experimenters Clarence Hasnell and John Berd demonstrated the possibility of transmitting images through optical tubes.

The invention of fiber optics in 1970 by Corning specialists is considered to be a turning point in the history of the development of fiber optic technologies. The developers managed to create a conductor that is capable of maintaining at least one percent of the optical signal power 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 for developing new look wired connection.

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

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

E Increase in information transmission speeds, emergence of wave multiplex 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 along optical dielectric waveguides, known as optical fiber. So what is it?

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

Fig.1 Optical fiber structure

Light propagates along the fiber core by successive total internal reflections at the interface between the core and cladding; its behavior is in many ways similar to what it would be like if it fell into a pipe whose walls were covered with a mirror layer. However, unlike a conventional mirror, whose reflection is rather inefficient, total internal reflection is essentially close to ideal - this is their fundamental difference, allowing light to travel long distances along the fiber with minimal loss.

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

This multiplicity of modes results in pulse dispersion (broadening) because each mode travels a different path through the fiber, and therefore different modes have different transmission delays as they travel from one end of the fiber to the other. The result of this phenomenon is limitation maximum frequency that can be transmitted efficiently for a given fiber length - increasing either the frequency or the fiber length beyond the limits essentially causes successive pulses to merge together, making them impossible to distinguish. For typical multimode fiber, this limit is approximately 15 MHz km, which means that a video signal with a bandwidth of, for example, 5 MHz can be transmitted over a maximum distance of 3 km (5 MHz x 3 km = 15 MHz km). Attempting to transmit a signal to b ó Any further distance will result in progressive loss of high frequencies.

Fig.2 Types of optical fiber

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

Ideally, a fiber with the same bandwidth as single-mode fiber but with the same diameter as multimode fiber is required to enable low-cost LED transmitters. To some extent, these requirements are met by multimode fiber with a gradient change in refractive index ((Fig. 2) c)). It resembles the multimode step-index fiber discussed above, but the refractive index of its core is not uniform - it varies smoothly from a maximum value at the center to lower values at the periphery. This leads to two consequences. First, the light travels along a slightly curved path, and second, and more important, the differences in propagation delay between different modes are minimal. This is due to the fact that high modes entering the fiber under b ó larger angles and traveling a longer distance actually begin to propagate at a higher speed as they move away from the center into the region where the refractive index decreases, and generally move faster than the lower order modes that remain near the axis in the fibers, in areas of high refractive index. The increase in speed just compensates for the larger distance traveled.

Multimode graded index fibers are not ideal, but they still exhibit very good bandwidth. Therefore, in most short and medium length lines, the choice of this type of fiber is preferable. In practice, this means that bandwidth is only rarely a parameter that needs to be taken into account.

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

Fig.3 Dependence of attenuation on wavelength

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

2 Classification of FOC

Fiber optic cable is already known for a long time, even early Ethernet standards supported it for 10 Mbps throughput. The first of them was called FOIRL (Fiber-Optic Inter-Repeater Link), and the subsequent one was called 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 determining parameters in the production of fiber optic cables are operating conditions and communication line capacity. According to operating conditions, cables are divided into two main groups (Fig. 4)

In-house ones are intended for installation inside buildings and structures. They are compact, lightweight and, as a rule, have a short overall length.

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

To ensure high throughput of communication lines, fiber optic cables 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 FOC

3 Advantages and disadvantages of fiber optic signal transmission

3.1 Advantages of fiber optic communication lines

For many applications, fiber optics is preferable due to a number of advantages.

Low transmission loss. Low loss fiber optic cables allow you to transmit image signals over long distances without the use of routing amplifiers or repeaters. This is especially useful for long-distance transmission schemes - for example, highway or railway surveillance systems, where repeater-free sections of 20 km 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 absence of electrical conductivity for fiber optic cable means that problems associated with changes in ground potential, typical for example in power plants or railways. This same property eliminates the risk of equipment damage caused by current surges from lightning, etc.

Lightweight and compact cables. The extremely small size of optical fibers and fiber optic cables allows you to breathe new life into crowded cable channels. For example, one coaxial cable takes up the same amount of space as 24 optical cables, each of which can supposedly carry 64 video channels and 128 audio or video signals simultaneously.

Timeless line of communication. 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-circuit TV system in one cable.

Explosion and fire safety. Due to the lack of sparking, optical fiber increases network security in chemical plants, oil refineries, and maintenance technological processes increased risk.

Cost-effectiveness of fiber-optic communication lines. The fiber is made from quartz, which is based on silicon dioxide, a widespread and therefore inexpensive material, unlike copper.

Long service life. Over time, the fiber experiences degradation. This means that the attenuation in the installed cable gradually increases. However, thanks to perfection modern technologies production of optical fibers, this process is significantly slowed down, and the service life of the fiber optic fiber optic fiber is approximately 25 years. During this time, several generations/standards of transceiver systems may change.

3.2 Disadvantages of fiber optic lines

High complexity of installation. Highly qualified personnel and special tools. Therefore, most often, fiber optic cable is sold in the form of pre-cut pieces of different lengths, at both ends of which the required type of connectors 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. The typical allowable bend radius is about 10 - 20 cm, with smaller bend radii the central fiber may break.

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

3. Electronic components of fiber optic lines. Principle of information transfer

In the most general view the principle of information transfer 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 - generating a microscopic light beam that can be injected into the fiber with high efficiency and modulated (changed in intensity) at a high frequency. Lasers provide b ó higher beam intensity than LEDs and allow a higher modulation frequency; therefore they are often used for long-distance broadband lines, such as telecommunications or cable television. On the other hand, LEDs are cheaper and more durable devices, and are also quite suitable for most small or 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 his output power(intensity) of optical radiation. The second is the wavelength (or color) of the light emitted. Typically this is 850, 1310 or 1550 nm, values selected from the condition of matching the so-called. transparency windows in the transmission characteristics of the optical fiber material.

3.2 Receivers for fiber optics

Fiber optics receivers perform the vital task of detecting extremely weak optical radiation emitted from the end of a fiber and amplifying the resulting electrical signal to the required level with minimal distortion and noise. The minimum level of radiation required by a receiver to provide acceptable output signal quality is called sensitivity; the difference between receiver sensitivity and transmitter output power determines the maximum acceptable losses in the system in dB. For most closed-circuit TV surveillance systems with an LED transmitter, the typical figure is 10-15 dB. Ideally, the receiver should operate normally when the input signal varies widely, since it is usually impossible to predict in advance exactly what the degree of attenuation in the communication line will be (i.e., line length, number of junctions, etc.). Many simple receiver designs use manual gain adjustments during system installation to achieve the desired output level. This is undesirable because changes in line attenuation are inevitable due to aging or temperature changes, etc., which necessitates the need to periodically adjust the gain. All fiber optic receivers use automatic gain control, which 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. Areas of application of fiber-optic communication lines

Fiber-optic communication lines (FOCL) allow you to transmit analog and digital signals over long distances. They are also used over smaller, 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 optical fiber is used. Indeed, when transmitting signals at a speed of 10 Gbit/s, the costs are similar to “copper” lines, but the optics consume significantly less energy. For many years Fiber and copper advocates battled each other for priority in corporate networks. Waste of time!

Indeed, the number of applications for optics is increasing, mainly due to the above-mentioned 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 lines provide a high degree of protection of confidential information and allow the transmission of uncompressed data such as high-resolution graphics and video with pixel accuracy. Optics has penetrated into all key areas - surveillance systems, control rooms and situation centers in areas with extreme operating conditions.

Reduced equipment costs have made it possible to use optical technologies in traditionally copper areas - large industrial enterprises for organization automated systems process control (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 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 in lately, after the Government of the Russian Federation adopted a resolution on countering terrorism and a list of vital objects to be protected.

5. Fiber optic TV surveillance systems

The system development process typically includes two components:

Selecting the right ones active ingredients transmission path, based on the required function (or functions), the type and number of fibers available or offered, and the maximum transmission range.

Fiber optic cable passive infrastructure designs, including backbone cable types and specifications, junction boxes, fiber patch panels.

1Video Surveillance Path Components

First of all - what components are actually required to satisfy technical specifications systems?

Fixed camera systems - These systems are extremely simple and typically consist of a miniature fiber optic transmitter and either a modular or rack-mounted receiver. The transmitter is often small enough to be mounted directly into the camera body, and is equipped with a coaxial bayonet connector, optical connector ST and terminals for connecting a low voltage power source (usually 12 V DC or AC). The surveillance system of a typical power plant consists of several dozen of these cameras, the signals from which are transmitted to the central control station, and in this 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 system remote control such cameras require unidirectional transmission of remote control signals (from the central station to the cameras) and those requiring bidirectional transmission. Bidirectional transmission systems are becoming increasingly popular because they allow each camera to acknowledge the receipt of each control signal, and therefore provide greater control accuracy and reliability. Within each of these groups there is a wide range of interface requirements, including RS232, RS422 and RS485. Other systems do not use a digital interface but transmit data as a sequence sound signals via an analog channel, similar to dual-frequency signals tone dialing in telephony.

Fig.6 Transmission of remote control signals for a rotary device over one fiber

All of these systems can also work with fiber optic cables using the appropriate equipment. Under normal circumstances, simultaneous transmission of optical signals in opposite directions on the same fiber is undesirable, as cross-talk will occur due to scattered reflection in the fiber. In closed-circuit TV systems, this effect creates noise in the picture whenever camera controls are engaged.

To achieve bidirectional transmission over a single fiber without causing mutual interference, it is necessary that the transmitters at different ends of the fiber operate at different wavelengths, for example, 850 nm and 1300 nm, respectively (Fig. 6). A wavelength division multiplexer (WDM) coupler is connected to each end of the fiber, which ensures that each receiver receives only the required wavelength of light (for example, 850 nm) from the transmitter at the opposite end of the fiber. Unwanted reflections from the near-end transmitter end up in wrong range (i.e. 1300 nm) and are cut off accordingly.

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

2Video multiplexing

Up to 64 video and up to 128 audio or digital data signals can be multiplexed on a single single-mode fiber, or a slightly smaller number on multimode. In this context, multiplexing refers to the simultaneous transmission of full-screen video signals in real time, rather than the small-frame or split-screen display that the term is more commonly referred to.

The ability to transmit multiple signals and additional information over multiple optical fibers is highly valuable, especially for long-distance closed-circuit TV 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 widely dispersed cameras, the benefits are not as clear, and here the first consideration should be the use of a separate fiber link for each video signal. The choice of whether to multiplex or not is quite complex and should only be made after considering all aspects, including system topology, overall costs and, last but not least, network fault tolerance.

3Cable network infrastructure

Once the transmission path requirements are determined, the fiber optic cable network infrastructure is developed, which includes not only the cables themselves, but also all the auxiliary components - junction boxes, cable extension panels, 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 path components. 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 optimal choice there will be 50/125 µm or 62.5/125 µm graded index multimode fiber. Traditionally, 50/125 µm fiber is selected for closed-circuit TV systems, and 62.5/125 µm for local area networks. In any case, each of them is suitable for each of these tasks, and in general, in most countries, 62.5/125 micron fiber is used for both purposes.

The number of fibers required can be determined based on the number and relative positioning of cameras and whether unidirectional or bidirectional remote control or multiplexing is used. Because the pipes. Cables intended for installation in external ducts are usually waterproofed with either aluminum tape (dry hollow pipes) or water-repellent filler (gel-filled cables). Fire safety cable.

Many short-circuit TV systems have a star configuration, where a single section of cable is laid from each camera to the control station. For such systems, the optimal cable design will contain two fibers - respectively for transmitting video signals and remote control. This configuration provides 100% cable capacity since, if necessary, both video and remote control signals can be transmitted over the same fiber. More extensive networks may benefit from using reverse tree topology (inverted branch & tree topology) (Fig. 7). In such networks, a two-core fiber optic cable leads from each camera to a local “hub” where they are connected into a single multi-core cable. The concentrator itself is not much more complicated than a conventional all-weather junction box and can often be combined with the equipment housing of one of the cameras.

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

Trenched fiber optic cables may contain steel wire reinforcement. Ideally, all cables should be constructed of flame retardant, low smoke emission materials to comply with local codes intended for outdoor installations. cable duct or directly in trenches, usually have a hollow tube design containing from 2 to 24 fibers in one or more

Fig.7 Tree topology of a fiber optic network

At the control station, the input fiber optic cable usually comes into an interface unit mounted in a 19" rack, with each fiber having its own individual ST -connector. For final interfacing with the receiver, short adapter cables of increased rigidity with mating cables are used. ST - connectors at each end. To fulfill all installation work no special skill is required beyond a reasonable understanding of the need for careful handling of optical fiber (e.g., do not bend fiber to a radius less than 10 times the fiber diameter) and the requirements of general hygiene (i.e., cleanliness).

4Optical Loss Budget

It may seem strange that optical loss budget calculations occur so late in the design process, but in fact, any accurate calculations are only possible once the cable network infrastructure has been fully defined. The purpose of the calculation is to determine the losses for the worst-case signal path (usually the longest) and to ensure that the equipment selected for the transmission path fits within the obtained limits with a reasonable margin.

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

Depending on the result obtained, it may be necessary to re-evaluate the equipment selected for the transmission path to ensure acceptable losses. For example, it may be necessary to order equipment with improved optical parameters, and if this is not available, you should consider switching to a transparency window with a longer wavelength, where losses are lower.

5System testing and commissioning

Most fiber optic network installers provide optical test results for the fiber optic network being commissioned. At a minimum, they should include end-to-end optical power measurements for each fiber link - this is equivalent to an integrity test 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 specifications for the equipment selected for the transmission path. It is generally considered normal to have a minimum loss margin (promised equipment parameters minus the measured value) of 3 dB for the inevitable aging processes that occur in fiber optic lines, especially in transmitters.

Conclusion

Experts often have 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 earlier and try to find out whether this is true or not, by comparing the optical solutions of the 3M Volution company with a standard shielded system of the 6th category, which has the closest properties to multimode optics

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

Table 1 Calculation of the cost of an SCS subscriber port for category 6 copper 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 of the enormous 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 patching and subscriber cords are still several times more expensive than their copper counterparts. 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 value of optical fiber and its immunity to various electromagnetic interference makes it an ideal solution for today's and future cable systems.

Structured cabling systems, which use fiber optics for both trunk and horizontal cabling, provide consumers with a number of significant benefits: a more flexible design, a smaller building footprint, greater security and better manageability.

The use of optical fiber in workplaces will make it possible in the future to switch to new network protocols, such as Gigabit and 10 Gigabit Ethernet, at minimal cost. This is possible thanks to a number of recent advances in fiber optic technologies: multimode fiber with improved optical performance and bandwidth; small form factor optical connectors that require less footprint and installation costs; Planar vertical cavity laser diodes enable long-distance data transmission at low cost.

Fiber optic communication lines

(FOCL), optical communication lines in which information is transmitted using fiber-optic elements. FOCL consists of transmitting and receiving optical modules, fiber-optic cables and fiber-optic connectors. Optical fiber is the most perfect medium for transmitting large flows of information over long distances. It is made from silica-based quartz, a common and inexpensive material, unlike the copper used in conventional wires. The optical fiber is very compact and lightweight, its diameter is only approx. 100 microns. Fiber light guides are optical fiber bundles, glued or sintered at the ends, protected by an opaque sheath and having ends with a polished surface. Glass fiber is a dielectric, therefore, during the construction of fiber-optic communication systems, individual optical fibers do not need to be isolated from each other. The durability of optical fiber is up to 25.

When creating fiber-optic communication lines, highly reliable electronic elements are needed that convert electrical signals into light and light into electrical signals, as well as optical connectors with low optical losses. Therefore, the installation of such lines requires expensive equipment. However, the advantages of using fiber-optic communication lines are so great that, despite the listed disadvantages of optical fibers, these communication lines are increasingly used to transmit information. Data transmission speed can be increased by transmitting information in two directions at once, since light waves can propagate independently of each other in one optical fiber. This makes it possible to double the capacity of the optical communication channel.

Fiber-optic communication lines are resistant to electromagnetic interference, and those transmitted through light guides are protected from unauthorized access. It is impossible to connect to such communication lines without violating the integrity of the line. Signal transmission over optical fiber was first carried out in 1975. Nowadays, long-distance optical communication systems over distances of many thousands of kilometers are rapidly developing. Transatlantic communication lines USA - Europe, Pacific line USA - Hawaiian Islands - Japan are successfully operated. Work is underway to complete the construction of a global fiber optic communication line Japan - Singapore - India - Saudi Arabia– Egypt – Italy. In Russia, TransTeleCom has created a fiber-optic communication network with a length of more than 36,000 km. It is duplicated by satellite communication channels. In con. 2001 A unified backbone digital communication network was created. It provides long-distance and international telephone services, Internet, and cable television in 56 of the 89 regions of Russia, where 85–90% of the population lives.

Encyclopedia "Technology". - M.: Rosman. 2006 .

See what “fiber-optic communication lines” are in other dictionaries:

A fiber-optic communication line (FOCL) is a fiber-optic system consisting of passive and active elements designed to transmit an optical signal via a fiber-optic cable. Contents 1 Elements of fiber-optic communication lines 2 Installation ... ... Wikipedia

fiber optic communication system- - [E.S. Alekseev, A.A. Myachev. English Russian explanatory dictionary in computer systems engineering. Moscow 1993] fiber-optic communication system Transmission of modulated or unmodulated optical energy through a fiber-optic medium, ... ...

RD 45.047-99: Fiber-optic transmission lines on the backbone and intra-zonal primary networks of the VSS of Russia. Technical operation. Guiding technical material- Terminology RD 45.047 99: Fiber optic transmission lines on the backbone and intra-zonal primary networks of the VSS of Russia. Technical operation. Leading technical material: 3.1.18 “EMERGENCY” quality parameters exceeded the limits... ... Dictionary-reference book of terms of normative and technical documentation

fiber optic cable- A cable containing one or more optical fibers and intended for data transmission. fiber optic cable [Luginsky Ya. N. et al. English-Russian dictionary of electrical engineering and... ... Technical Translator's Guide

fiber optic adapter- A passive device used to connect optical plugs and connect optical fibers. [SN RK 3.02 17 2011] fiber optic adapter A component of switching equipment designed for positioning and connecting two... ... Technical Translator's Guide

fiber optic line- A set of fiber optic segments and repeaters that, when connected, form a transmission path. [Source] Topics: optical communication lines EN fiber optic link ... Technical Translator's Guide

fiber optic attenuator- A component installed in a fiber optic transmission system to reduce the power of the optical signal. Often used to limit the optical power received by the photodetector to the sensitivity limits of the optical... ... Technical Translator's Guide

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

Check information. It is necessary to check the accuracy of the facts and reliability of the information presented in this article. There should be an explanation on the talk page... Wikipedia

A technique for transmitting information from one place to another in the form of electrical signals sent through wires, cables, fiber optic lines, or without any guide lines at all. Directional transmission through wires is usually carried out from one... ... Collier's Encyclopedia

Books

Reducing signal degradation in fiber-optic communication systems, Maxim Velichko. A review of the results of theoretical and experimental studies describing the propagation of light radiation in a single-mode fiber is presented. The joint effect of...
Principles of building primary networks and optical cable communication lines. Textbook for universities, E.L. Portnov. Information about primary communication networks, principles of design, construction, measurements and operation, and the place of fiber-optic lines in these networks is systematized. Considered...

Fiber optic communication- communications built on the basis of fiber optic cables. The abbreviation FOCL (fiber-optic communication line) is also widely used. It is used in various fields of human activity, ranging from computing systems to structures for communication over long distances. Today it is the most popular and effective method to provide telecommunications services.

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

Market of fiber optic products in Russia

Story

Although fiber optics is a widely used and popular means of communication, the technology itself is simple and developed a long time ago. An experiment with changing the direction of a light beam by refraction was demonstrated by Daniel Colladon and Jacques Babinet back in 1840. A few years later, John Tyndall used this experiment in his public lectures in London, and already in 1870 he published a work on the nature of light. The practical application of the technology was found only in the twentieth century. In the 1920s, experimenters Clarence Hasnell and John Berd demonstrated the possibility of transmitting images through optical tubes. This principle was used by Heinrich Lamm for medical examination of patients. It wasn't until 1952 that Indian physicist Narinder Singh Kapany conducted a series of his own experiments that led to the invention of optical fiber. In fact, he created the very same bundle of glass threads, and the shell and core were made of fibers with different refractive indices. The shell actually served as a mirror, and the core was more transparent - this solved the problem of rapid dispersion. If previously the beam did not reach the end of the optical filament, and it was impossible to use such a means of transmission over long distances, now the problem has been solved. Narinder Kapani improved the technology by 1956. A bunch of flexible glass rods transmitted the image with virtually no loss or distortion.

The invention of optical fiber by Corning specialists in 1970, which made it possible to duplicate the telephone signal data transmission system over a copper wire over the same distance without repeaters, is considered to be a turning point in the history of the development of fiber-optic technologies. The developers managed to create a conductor that is capable of maintaining at least one percent of the optical signal power 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 wired communication.

Initially, optical fiber was multiphase, that is, it could transmit hundreds of light phases at once. Moreover, the increased diameter of the fiber core made it possible to use inexpensive optical transmitters and connectors. Much later, they began to use higher-performance fiber, through which it was possible to transmit only one phase in the optical environment. With the introduction of single-phase fiber, signal integrity could be maintained for greater distance, which contributed to the transfer of considerable amounts of information.

The most popular fiber today is single-phase fiber with zero wavelength offset. Since 1983, it has been the industry's leading fiber optic product, proven to operate over tens of millions of kilometers.

Advantages of fiber optic communication

Broadband optical signals due to extremely high carrier frequency. This means that information can be transmitted over a fiber optic line at a speed of about 1 Tbit/s;
Very low attenuation of the light signal in the fiber, which makes it possible to build fiber-optic communication lines up to 100 km or more in length without signal regeneration;
Resistance to electromagnetic interference from surrounding copper cabling systems, electrical equipment (power lines, electric motors, etc.) and weather conditions;
Protection against unauthorized access. Information transmitted over fiber-optic communication lines is practically impossible to intercept in a non-destructive manner;
Electrical safety. Being, in fact, a dielectric, optical fiber increases the explosion and fire safety of the network, which is especially important at chemical and oil refineries, when servicing high-risk technological processes;
Durability of fiber-optic communication lines - the service life of fiber-optic communication lines is at least 25 years.

Disadvantages of fiber optic communication

The relatively high cost of active line elements that convert electrical signals into light and light into electrical signals;
Relatively high cost of splicing optical fiber. This requires precision, and therefore expensive, technological equipment. As a result, if an optical cable breaks, the cost of restoring a fiber-optic line is higher than when working with copper cables.

Fiber Optic Line Elements

Optical receiver

Optical receivers detect signals transmitted along a fiber optic cable and convert them into electrical signals, which then amplify and then restore their shape, as well as clock signals. Depending on the transmission speed and system specifics of the device, the data stream can be converted from serial to parallel.

Optical transmitter

The optical transmitter in a fiber optic system converts the electrical data sequence supplied by the system components into an optical data stream. The transmitter consists of a parallel-serial converter with a clock synthesizer (which depends on the system installation and bit rate), a driver and an optical signal source. Various optical sources can be used for optical transmission systems. For example, light-emitting diodes are often used in low-cost local networks for short distance communication. However, the wide spectral bandwidth and the inability to work in the wavelengths of the second and third optical windows do not allow the use of LEDs in telecommunication systems.

Preamplifier

The amplifier converts the asymmetric current from the photodiode sensor into an asymmetric voltage, which is amplified and converted into a differential signal.

Data synchronization and recovery chip

This chip must restore the clock signals from the received data stream and their clocking. The phase-locked loop circuitry required for clock recovery is also fully integrated into the clock chip and does not require external control clock pulses.

Serial to parallel code conversion block

Parallel-to-serial converter

Laser shaper

Its main task is to supply bias current and modulating current to directly modulate the laser diode.

Optical cable, consisting of optical fibers located under a common protective sheath.

Singlemode fiber

If the fiber diameter and wavelength are small enough, a single beam will propagate through the fiber. In general, the very fact of selecting the core diameter for the single-mode signal propagation mode speaks about the particularity of each individual fiber design option. That is, single-mode refers to the characteristics of the fiber relative to the specific frequency of the wave used. The propagation of only one beam allows you to get rid of intermode dispersion, and therefore single-mode fibers are orders of magnitude more productive. On at the moment a core with an outer diameter of about 8 microns is used. As with multimode fibers, both step and gradient material distribution densities are used.

The second option is more productive. Single-mode technology is thinner, more expensive and is currently used in telecommunications. Optical fiber is used in fiber-optic communication lines, which are superior to electronic communications in that they allow lossless, high-speed transmission of digital data over vast distances. Fiber optic lines can either form a new network or serve to combine existing networks - sections of optical fiber highways, connected physically at the light guide level, or logically at the level of data transfer protocols. Data transmission speeds over fiber-optic lines can be measured in hundreds of gigabits per second. The standard is already being finalized to allow data transmission at a speed of 100 Gbit/s, and the 10 Gbit Ethernet standard has been used in modern telecommunications structures for several years.

Multimode fiber

In a multimode optical fiber, a large number of modes—rays introduced into the fiber at different angles—can propagate simultaneously. Multimode OF has a relatively large core diameter (standard values 50 and 62.5 μm) and, accordingly, a large numerical aperture. The larger core diameter of multimode fiber simplifies the coupling of optical radiation into the fiber, and the more relaxed tolerance requirements for multimode fiber reduce the cost of optical transceivers. Thus, multimode fiber predominates in short-range local and home networks.

The main disadvantage of multimode optical fiber is the presence of intermode dispersion, which arises due to the fact that different modes follow different optical paths in the fiber. To reduce the influence of this phenomenon, a multimode fiber with a gradient refractive index was developed, due to which the modes in the fiber propagate along parabolic trajectories, and the difference in their optical paths, and, consequently, the inter-mode dispersion, is significantly less. However, no matter how balanced gradient multimode fibers are, their throughput cannot be compared with single-mode technologies.

Fiber Optic Transceivers

To transmit data over optical channels, the signals must be converted from electrical to optical, transmitted over a communications link, and then converted back to optical at the receiver. electric type. These transformations occur in the transceiver device, which contains electronic components along with optical components.

Widely used in transmission technology, the time division multiplexer allows the transmission speed to be increased to 10 Gb/s. Modern high-speed fiber optic systems offer the following transmission speed standards.

SONET standard	SDH standard	Baud rate
OC 1	-	51.84 Mb/sec
OC 3	STM 1	155.52 Mb/s
OC 12	STM 4	622.08 Mb/s
OC 48	STM 16	2.4883 Gb/sec
OC 192	STM 64	9.9533 Gb/sec

New methods of multiplexing wavelength division or wavelength division multiplexing make it possible to increase data transmission density. To achieve this, multiple multiplexed streams of information are sent over a single fiber optic channel using each stream's transmission at a different wavelength. The electronic components in the WDM receiver and transmitter are different from those used in a time division system.

Application of fiber optic communication lines

Optical fiber is actively used to build city, regional and federal communication networks, as well as to install connecting lines between city automatic telephone exchanges. This is due to speed, reliability and high throughput fiber networks. Also, through the use of fiber optic channels, there are cable television, remote video surveillance, video conferences and video broadcasts, telemetry and others information systems. In the future, it is planned to use transformation in fiber-optic networks speech signals to optical.

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

Market of fiber optic products in Russia

Story

Initially, optical fiber was multiphase, that is, it could transmit hundreds of light phases at once. Moreover, the increased diameter of the fiber core made it possible to use inexpensive optical transmitters and connectors. Much later, they began to use higher-performance fiber, through which it was possible to transmit only one phase in the optical environment. With the introduction of single-phase fiber, signal integrity could be maintained over greater distances, which facilitated the transfer of considerable amounts of information.

Advantages of fiber optic communication

Broadband optical signals due to extremely high carrier frequency. This means that information can be transmitted over a fiber optic line at a speed of about 1 Tbit/s;
Very low attenuation of the light signal in the fiber, which makes it possible to build fiber-optic communication lines up to 100 km or more in length without signal regeneration;
Resistance to electromagnetic interference from surrounding copper cabling systems, electrical equipment (power lines, electric motors, etc.) and weather conditions;
Protection against unauthorized access. Information transmitted over fiber-optic communication lines is practically impossible to intercept in a non-destructive manner;
Electrical safety. Being, in fact, a dielectric, optical fiber increases the explosion and fire safety of the network, which is especially important at chemical and oil refineries, when servicing high-risk technological processes;
Durability of fiber-optic communication lines - the service life of fiber-optic communication lines is at least 25 years.

Disadvantages of fiber optic communication

The relatively high cost of active line elements that convert electrical signals into light and light into electrical signals;
Relatively high cost of splicing optical fiber. This requires precision, and therefore expensive, technological equipment. As a result, if an optical cable breaks, the cost of restoring a fiber-optic line is higher than when working with copper cables.

Fiber Optic Line Elements

Optical receiver

Optical transmitter

The optical transmitter in a fiber optic system converts the electrical data sequence supplied by the system components into an optical data stream. The transmitter consists of a parallel-serial converter with a clock synthesizer (which depends on the system installation and bit rate), a driver and an optical signal source. Various optical sources can be used for optical transmission systems. For example, light-emitting diodes are often used in low-cost local area networks for short-distance communications. However, the wide spectral bandwidth and the inability to work in the wavelengths of the second and third optical windows do not allow the use of LEDs in telecommunication systems.

Preamplifier

The amplifier converts the asymmetric current from the photodiode sensor into an asymmetric voltage, which is amplified and converted into a differential signal.

Data synchronization and recovery chip

Serial to parallel code conversion block

Parallel-to-serial converter

Laser shaper

Its main task is to supply bias current and modulating current to directly modulate the laser diode.

Optical cable, consisting of optical fibers located under a common protective sheath.

Singlemode fiber

If the fiber diameter and wavelength are small enough, a single beam will propagate through the fiber. In general, the very fact of selecting the core diameter for the single-mode signal propagation mode speaks about the particularity of each individual fiber design option. That is, single-mode refers to the characteristics of the fiber relative to the specific frequency of the wave used. The propagation of only one beam allows you to get rid of intermode dispersion, and therefore single-mode fibers are orders of magnitude more productive. Currently, a core with an outer diameter of about 8 microns is used. As with multimode fibers, both step and gradient material distribution densities are used.

Multimode fiber

Fiber Optic Transceivers

To transmit data over optical channels, the signals must be converted from electrical to optical, transmitted over a communications link, and then converted back to electrical at the receiver. These transformations occur in the transceiver device, which contains electronic components along with optical components.

SONET standard	SDH standard	Baud rate
OC 1	-	51.84 Mb/sec
OC 3	STM 1	155.52 Mb/s
OC 12	STM 4	622.08 Mb/s
OC 48	STM 16	2.4883 Gb/sec
OC 192	STM 64	9.9533 Gb/sec

Application of fiber optic communication lines

Optical fiber is actively used to build city, regional and federal communication networks, as well as to install connecting lines between city automatic telephone exchanges. This is due to the speed, reliability and high capacity of fiber networks. Also, through the use of fiber optic channels, there are cable television, remote video surveillance, video conferences and video broadcasts, telemetry and other information systems. In the future, it is planned to use the conversion of speech signals into optical signals in fiber-optic networks.