Fiber optic communication. Vols: main characteristics and areas of application. New standards and technologies of wols

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 greater 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 is 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 a guide system. Dictionary of business terms. ... ... Business glossary

fiber optic communication- - [L.G. Sumenko. The English Russian Dictionary of Information Technology. M .: GP TsNIIS, 2003.] information Technology overall EN fiber optic connectionFOCoptical fiber communication…

worldwide fiber optic communications- - [L.G. Sumenko. The English Russian Dictionary of Information Technology. M .: GP TsNIIS, 2003.] Topics information technologies in general EN fiber optic link around the globeFLAG ... Technical translator's guide

OPTICAL COMMUNICATION- transmission of information using light. The simplest (uninformative) types of O. s. were used from the end. 18th century (e.g. semaphore alphabet). With the advent of lasers, it became possible to transfer to optical. range of means and principles of obtaining, processing ... ... Physical encyclopedia

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

Introduction

1. Main part

1. Fiber-optic communication lines as a concept

Physical features

Technical features

Fiber technology has its drawbacks

Optical fiber and its types

Fiber optic cable

Electronic components of optical communication systems

Laser modules for fiber-optic communication lines

Photoreceiving modules for FOCL

The use of fiber-optic communication lines in computer networks

Conclusion

Bibliography

Introduction

Since the beginning of development computer technology not a few sixty years have passed. During this time, we have received such speeds of calculations, such speeds of data transmission, which sixty years ago could not even have dreamed of. It all started with the publication of the books by K. Shannon "Mathematical theory of communication" and N. Wiener "Cybernetics, or control and communication in animals and machines" in 1948. They determined a new vector for the development of science, as a result of which a computer appeared: first a tube giant, then a transistor one and on integrated circuits, on microprocessors. And then in 1989 appeared Personal Computer IBM. In the same year, the MS-DOS program was released, and in 1990 - Windows-3.0, and then the rapid improvement of hardware and software... By the end of the century, humanity has received a tremendous miniaturization of computer technology, a reduction in the distance between a computer and a person, total penetration computer technology in the household sphere. 1986 - the birth of the Internet, global network, covering almost all countries of the world, providing each user with current information. Having received such fast data processing, people came to the conclusion that it is possible to stop wasting time and money, also on the transfer of this data, as well as to increase the access speed and data transfer speed. This has become possible thanks to the use of new types of communication, such as optical fiber, which have come to replace the commonplace aluminum and copper wires.

The topic of the fiber-optic communication line is relevant for this moment time, as the number of people on the planet is growing, and the need to improve life is also increasing. Since ancient times, a person has been improving: he improves his knowledge, strives to improve his life, creating and modeling household items. And now many firms create televisions, telephones, tape recorders, computers and much more, that is, household appliances that simplify a person's life. But for the introduction of these new technologies it is necessary to change or improve the old. As an example of this, we can cite our communication lines on a coaxial (copper) cable, which have already been mentioned above. Their speed is low, even for video transmission. And fiber optics is exactly what we need - its information transfer rate is very high. Plus, low signal transmission losses allow laying long cable sections without installing additional equipment. Fiber optic has good noise immunity, ease of installation and long cable life in almost any conditions. And, besides, it makes no sense to steal fiber for the purpose of scrapping. At present, fiber optic is mainly used in tele - and Internet communications. But it is believed that today's use of fiber is only the tip of the iceberg of its use.

1. Fiber-optic communication lines as a concept

Fiber optic communication lines are a form of communication in which information is transmitted over optical dielectric waveguides known as "optical fiber". Optical fiber is currently considered the most advanced physical medium for transmitting information, as well as the most promising medium for transmitting large flows of information over long distances. For example, at present, fiber-optic cables are laid along the seabed 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, No. 12; Telecom mag. 1993. No. 25; AEU: J. Asia Electron. Union 1992. No. 5). European countries across the Atlantic are linked 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. In Europe, as well as in America, they have long been widely used in almost all spheres of communications, energy, transport, science, education, medicine, economics, defense, state-political and financial activities. So, the grounds to consider optical fiber as the most promising medium for transmitting large flows of information follows from a number of features inherent in optical waveguides.

2. Physical features

Broadband optical signals due to extremely high carrier frequencies. This means that information can be transmitted over an optical communication line at a rate of about 1 Terabit / s.

In other words, one fiber can simultaneously transmit 10 million telephone conversations and a million video signals. The data transfer speed can be increased by transmitting information in two directions at once, since light waves can propagate in one fiber independently of each other. In addition, light signals of two different polarizations can propagate in an optical fiber, which makes it possible to double the bandwidth of the optical communication channel. To date, the limit on the density of information transmitted over optical fiber has not been reached. And this means that until now, with such a heavy load on our Internet, there has not been so much information that, with simultaneous transmission, would lead to a decrease in the speed of the transmitted data stream.

Very low (compared to other media) attenuation of the light signal in the fiber. In other words, signal loss due to the resistance of the conductor material. The best examples of Russian fiber have such a low attenuation that it allows building communication lines up to 100 km long without signal regeneration. Optical laboratories in the United States are developing even more "transparent" fibers, the so-called fluorozirconate fibers. Laboratory studies have shown that on the basis of such fibers, communication lines with regeneration sections across 4600 km can be created at a transmission speed of the order of 1 Gbit / s.

3. Technical features

The fiber is made of quartz, the basis of which is silicon dioxide, a widespread and therefore inexpensive material, unlike copper, hence the relatively low price and practically no cases of theft for the purpose of scrapping

Optical fibers have a diameter of about 1 - 0.2 mm, that is, they are very compact and lightweight, which makes them promising for use in aviation, instrumentation, and cable technology.

Glass fibers are not metal; during the construction of communication systems, galvanic isolation of the segments is automatically achieved. Using extra strong plastic, cable factories produce self-supporting overhead cables that do not contain metal and are thus electrically safe. These cables can be mounted on the masts of existing power lines, either separately or embedded in the phase conductor, saving significant costs on laying the cable through rivers and other obstacles.

Communication systems based on optical fibers are resistant to electromagnetic interference, and information transmitted through optical fibers is protected from unauthorized access. Fiber optic communication lines cannot be overheard in a non-destructive manner. Any impacts on the fiber can be recorded by monitoring (continuous control) the integrity of the line. In theory, there are ways to bypass protection through monitoring, but the costs of implementing these methods will be so great that they exceed the cost of intercepted information. For example, you still decided to do it. To detect the intercepted signal, you need a tunable Michelson interferometer of a special design. Moreover, the visibility of the interference pattern can be weakened by a large number of signals simultaneously transmitted through the optical communication system. It is possible to distribute the transmitted information over multiple signals or transmit several noise signals, thereby worsening the conditions for intercepting information. Significant power take-off from the fiber would be required to tamper with the optical signal, and this interference is easily detected by monitoring systems.

An important property of optical fiber is durability. The lifespan of a fiber, that is, it retains its properties within certain limits, exceeds 25 years, which makes it possible to lay a fiber-optic cable once and, if necessary, increase the channel capacity by replacing receivers and transmitters with faster ones, without replacing the cable itself ...

4. Fiber technology has its drawbacks

When creating a communication line, active, highly reliable elements are required that convert electrical signals into light and light into electrical signals. Optical connectors (connectors) with low optical loss and a large connection-disconnection resource are also required.

The manufacturing accuracy of such line elements should correspond to the radiation wavelength, that is, the errors should be of the order of a fraction of a micron. Therefore, the production of such components for optical communication lines is very expensive.

Another disadvantage is that the installation of optical fibers requires expensive processing equipment. a) tools for termination. b) connectors. c) testers. d) couplings and spice cassettes.

The highest throughput among all existing communication facilities, optical fiber (dielectric waveguides) has. Fiber-optic cables are used to create - fiber-optic communication lines capable of providing the highest information transfer rate (depending on the type of active equipment used, the transfer rate can be tens of gigabytes or even terabytes per second).

Quartz glass, which is the carrier medium of FOCL, in addition to unique transmission characteristics, has another valuable property - low losses and insensitivity to electromagnetic fields. This compares favorably with conventional copper cabling systems.

This information transmission system, as a rule, is used in the construction of work facilities as external highways that unite disparate structures or buildings, as well as multi-storey buildings. It can also be used as an internal carrier of a structured cabling system (SCS), however, complete SCS completely made of fiber are less common due to the high cost of building optical communication lines.

The use of fiber-optic communication lines allows you to locally combine workplaces, to ensure high speed Internet downloads simultaneously on all machines, high-quality telephone connection and a television reception.

With the competent design of the future system (this stage implies the solution of architectural issues, as well as the choice of suitable equipment and methods for connecting the carrier cables) and professional installation, the use of fiber-optic lines provides a number of significant advantages:

High bandwidth due to high carrier frequency. The potential of one optical fiber is several terabits of information in 1 second.
Fiber optic cable is different low level noise, which has a positive effect on its throughput and the ability to transmit signals of various modulations.
Fire safety (fire resistance). Unlike other communication systems, FOCL can be used without any restrictions at high-risk enterprises, in particular in petrochemical industries, due to the absence of sparking.
Due to the low attenuation of the light signal, optical systems can combine working sections at significant distances (more than 100 km) without the use of additional repeaters (amplifiers).

Information Security. Fiber-optic communication provides reliable protection against unauthorized access and interception of confidential information. This ability of optics is explained by the absence of radiation in the radio range, as well as by its high sensitivity to vibrations. In case of eavesdropping attempts, the built-in monitoring system can disable the channel and warn of a suspected tamper. That is why FOCL is actively used by modern banks, research centers, law enforcement organizations and other structures that work with classified information.
High reliability and noise immunity of the system. Fiber, being a dielectric conductor, is not sensitive to electromagnetic radiation, is not afraid of oxidation and moisture.
Profitability. Despite the fact that the creation of optical systems due to their complexity is more expensive than traditional SCS, in general, their owner receives real economic benefits. Optical fiber, which is made of quartz, costs about 2 times cheaper than a copper cable; in addition, when building extensive systems, you can save on amplifiers. If, when using a copper pair, repeaters need to be installed every few kilometers, then in FOCL this distance is at least 100 km. At the same time, the speed, reliability and durability of traditional SCS are significantly inferior to optics.

The service life of fiber-optic lines is half a quarter of a century. After 25 years of continuous use, signal attenuation increases in the carrier system.
If we compare a copper and an optical cable, then with the same bandwidth, the second will weigh about 4 times less, and its volume, even with the use of protective sheaths, will be several times less than that of copper.
Perspectives. The use of fiber-optic communication lines makes it easy to increase the computing capabilities of local networks due to the installation of faster active equipment, and without replacing communications.

Scope of FOCL

As mentioned above, fiber optic cables (FOC) are used to carry signals around (between) buildings and within facilities. When building outdoor communication highways, preference is given to optical cables, and inside buildings (internal subsystems), traditional twisted pair... Thus, a distinction is made between outdoor cables and indoor cables.

Connecting cables belong to a separate type: indoors they are used as connecting cords and horizontal wiring communications - to equip individual workplaces, and outside - to connect buildings.

Installation of fiber optic cable is carried out using special tools and devices.

FOCL connection technologies

The length of FOCL communication lines can reach hundreds of kilometers (for example, when building communications between cities), while the standard length of optical fibers is several kilometers (also because working with too long lengths in some cases is very inconvenient). Thus, when constructing a route, it is necessary to solve the problem of splicing individual optical fibers.

There are two types of connections: detachable and one-piece. In the first case, optical connectors are used for connection (this is associated with additional financial costs, and, in addition, with a large number of intermediate connectors, optical losses increase).

For the permanent connection of local sections (installation of routes), mechanical connectors, adhesive splicing and fiber splicing are used. In the latter case, optical fiber splicers are used. Preference for one method or another is given taking into account the purpose and conditions of use of the optics.

The most common is the gluing technology, for which special equipment and tools are used and which includes several technological operations.

In particular, before connection, optical cables pass through preliminary preparation: in the places of future connections, the protective coating and excess fiber are removed (the prepared area is cleaned of the hydrophobic composition). To securely fix the light guide in the connector (connector), epoxy glue is used, which fills the inner space of the connector (it is introduced into the connector housing using a syringe or dispenser). To harden and dry the glue, a special stove is used, capable of creating a temperature of 100 degrees. WITH.

After the glue has hardened, excess fiber is removed and the connector tip is ground and polished (chip quality is paramount). To ensure high accuracy, these works are monitored using a 200x microscope. Polishing can be done by hand or with a polished machine.

The highest quality connection with minimal loss ensures fiber splicing. This method is used to create high-speed FOCLs. During welding, the ends of the fiber are melted; for this, a gas burner can be used as a source of thermal energy, electric charge or laser radiation.

Each method has its own advantages. Due to the absence of impurities, laser welding allows to obtain the cleanest joints. Gas torches are commonly used to permanently weld multimode fibers. The most common is electric welding, which ensures high speed and quality of work. Melting time different types wholesale fibers is different.

For welding, special tools and expensive welding equipment are used - automatic or semi-automatic. Modern welders allow you to control the quality of welding, as well as to test the joints in tension. Advanced models are equipped with programs that allow you to optimize the welding process for a specific type of fiber.

After splicing, the joint is protected by tight fitting tubes that provide additional mechanical protection.

Another method of splicing optical fiber elements into a single fiber-optic line is mechanical connection. This method provides less cleanliness of the connection than welding, but the signal attenuation in this case is still less than when using optical connectors.

The advantage of this method over the others is that it uses simple fixtures(for example, assembly table), which allow work in hard-to-reach places or inside small-sized structures.

Mechanical splicing involves the use of special connectors - the so-called splice. There are several varieties of mechanical connectors, which are elongated structures with a channel for entry and fixation of spliced optical fibers. The fixation itself is provided using the latches provided by the design. After connection, the splices are additionally protected with sleeves or boxes.

Mechanical connectors can be used multiple times. In particular, they are used during repair or restoration work on the line.

FOCL: types of optical fibers

Optical fibers used to build FOCL differ in the material of manufacture and in the mode structure of light. In terms of material, a distinction is made between all-glass fibers (with a glass core and glass optical cladding), all-plastic fibers (with a plastic core and cladding) and combined models (with a glass core and a plastic jacket). The best throughput is provided by glass fibers, a cheaper plastic option is used if the requirements for attenuation and throughput are not critical.

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 end 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.-No.3; Laser Focus World.-1992.-28, No.12; Telecom mag. 1993. No. 25; AEU: J. Asia Electron. Union. 1992. No. 5). European countries across the Atlantic are linked 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 by far one of the most promising directions in the field of communications. 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, a widespread and inexpensive material, unlike copper. Optical fiber is very compact and lightweight, with a diameter of only about 100 microns.

In addition, the optical fiber is immune to electromagnetic fields, which removes some typical problems 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, 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 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

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 managed to create 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, - necessary condition in order to develop a new kind 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 transmission 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; its behavior is in many ways similar to that of being caught in 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 fiber and multimode 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 the frequency or the 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. Singlemode, 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 switched telephone and telegraph networks (PTT) and cable television networks. Unfortunately, a fiber of such a small diameter requires the use of a powerful, precisely aligned, and therefore a 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 in order to be able to use inexpensive LED transmitters. To some extent, these requirements are satisfied by a 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 filaments, 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 850 nm window is the first and most commonly used (lowest cost). At this wavelength, a good quality gradient multimode fiber exhibits an attenuation of about 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 intended for laying cable communications in wells, in the ground, on supports along power lines, under water. These cables are protected against external influences and a construction length of over two kilometers.

To ensure high throughput of the communication line, 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 the fiber optic cable means that the problems associated with changes in ground potential, such as in power plants or railways... 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 one 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 simultaneously.

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 in chemical, oil refineries, and when servicing high-risk technological processes.

Profitability of FOCL. The fiber is made of quartz, which is based on silicon dioxide, a widespread and therefore inexpensive material, in contrast to 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 can 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 connectors are already installed. the right type... 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, with smaller bending radii the central fiber may break.

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

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 systems of short to medium length.

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.). In many simple constructions Receivers to achieve the required output signal level, manual gain control is used, which is made during the installation of the system. 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 FOCL

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 situational centers in areas with extreme operating conditions.

Reducing the cost of equipment made it possible to use optical technology in traditionally copper areas - in large industrial plants for organizing 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 a 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 required function (s), 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 satisfy technical specifications systems?

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, an '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 '' 3U card with common block nutrition.

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 of 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 the same 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 desired 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 Capabilities - While the choice of a fixed camera or PTZ camera will satisfy the requirements of most CCTV surveillance systems, there are a number of systems that require additional features, for example, the transmission of audio information - for general announcements, 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 an 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 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, which is often referred to as this term.

The ability to carry many signals and additional information over multiple optical fibers is very valuable, especially for CCTV surveillance systems over long distances, 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, optimal choice will be a 50/125 µm or 62.5 / 125 µm 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 micron 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 with either 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 the 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 have a hollow tube 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 an 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 is possible to calculate it with some accuracy only 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 joint loss. The biggest challenge is simply extracting the required loss figures from the manufacturer's documentation.

Depending on the result obtained, it may be necessary to reevaluate 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 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 optic installers provide optical test results for a commissioned fiber optic 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 loss margin (promised hardware parameters minus measured value) of 3 dB for the inevitable aging processes occurring in fiber lines, especially in 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 value of the optical fiber and "immunity" to various electromagnetic interference makes it ideal solution for today's and future cabling 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 with minimal cost migrate to new network protocols such as Gigabit and 10 Gigabit Ethernet. 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 costs; 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 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. Homeland - M .: Hotline, 2009.-400c.

An optical fiber consists of a central light conductor (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.

The market of fiber optic products in Russia

History

Fiber optics, although a ubiquitous 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. A few years later, John Tyndall used this experiment in his public lectures in London, and already in 1870 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 ability to transmit images through optical tubes. This principle was used by Heinrich Lamm for the medical examination of patients. It was only in 1952 that the 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 filaments, 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 was how the problem of fast scattering was solved. If earlier the beam did not reach the end of the optical fiber, 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 bundle of flexible glass rods transmitted the image with virtually no loss or distortion.

The invention of optical fiber in 1970 by Corning specialists, which made it possible to duplicate a telephone signal transmission system over a copper wire for the same distance without repeaters, is considered to be a turning point in the history of the development of fiber-optic technologies. The developers have managed to create 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.

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, fiber of higher performance began to be used, through which only one phase could be transmitted in an optical medium. With the introduction of single-phase fiber, signal integrity could be maintained over a greater distance, which facilitated the transfer of considerable amounts of information.

The most sought-after fiber today is zero wavelength offset single phase fiber. Since 1983, it has been at the forefront of the fiber optic industry, proving its performance over tens of millions of kilometers.

Advantages of fiber-optic communication

Broadband optical signals due to extremely high carrier frequencies. This means that information can be transmitted over a fiber-optic line at a speed of the order of 1 Tbit / s;
Very low attenuation of the light signal in the fiber, which makes it possible to build fiber-optic communication lines with a length of up to 100 km or more without signal regeneration;
Immunity to electromagnetic interference from surrounding copper cable systems, electrical equipment (power lines, electric motor installations, etc.) and weather conditions;
Protection against unauthorized access. Information transmitted over fiber-optic communication lines is practically impossible to intercept in a non-destructive way;
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 optical fiber splicing. This requires precision, and therefore expensive, technological equipment. As a result, when an optical cable is broken, the cost of restoring a fiber-optic link is higher than when working with copper cables.

Fiber optic line elements

Optical receiver

Optical receivers detect the signals transmitted over the fiber optic cable and convert it into electrical signals, which then amplify and then reconstruct their shape, as well as clock signals. Depending on the baud rate and system specificity of the device, the data stream can be converted from serial to parallel.

Optical transmitter

An optical transmitter in a fiber optic system converts the electrical sequence of data supplied by system components into an optical data stream. The transmitter consists of a parallel-to-serial converter with a sync synthesizer (which depends on system installation and bit rate), driver and 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 impossibility of working in the wavelengths of the second and third optical windows do not allow the use of LED 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 IC

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

Unit for converting serial code to parallel

Parallel to serial converter

Laser shaper

Its main task is to supply bias current and modulating current for direct modulation of the laser diode.

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

Single mode fiber

With a sufficiently small fiber diameter and corresponding wavelength, a single beam will propagate through the fiber. In general, the very fact of the selection of the core diameter for the single-mode signal propagation mode speaks of the particulars of each individual version of the fiber design. That is, single-mode is to be understood as the characteristics of the fiber with respect to a specific frequency of the used wave. Propagation of only one beam allows one to get rid of intermode dispersion, and therefore single-mode fibers are orders of magnitude more efficient. At the moment, a core with an outer diameter of about 8 µm is used. As in the case of multimode fibers, both stepped and gradient material distributions are used.

The second option is more productive. Single-mode technology is thinner, more expensive and currently used in telecommunications. Optical fiber is used in fiber optic communication lines that surpass electronic means due to the fact that they allow transmission of digital data over great distances without loss and at high speed. Fiber optic lines can both form new network and serve to unite already existing networks - sections of optical fiber trunk lines, physically united at the level of an optical fiber, or logically - at the level of data transmission protocols. The speed of data transmission over fiber-optic lines can be measured in hundreds of gigabits per second. Already, a standard is being finalized that allows data transfer at a speed of 100 Gb / s, and the 10 Gb Ethernet standard has been used in modern telecommunication structures for several years.

Multimode fiber

A multimode optical fiber can propagate simultaneously a large number of modes - beams introduced into the fiber at different angles. A multimode optical fiber has a relatively large core diameter (standard values of 50 and 62.5 μm) and, accordingly, a large numerical aperture. The larger core diameter of multimode fiber makes it easier to inject optical radiation into the fiber, and the softer tolerance requirements for multimode fiber can reduce the cost of optical transceivers. Thus, multimode fiber is prevalent in short-haul LANs and home networks.

The main disadvantage of a multimode optical fiber is the presence of intermode dispersion, which arises due to the fact that different modes make 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 paths, and the difference in their optical paths, and, consequently, the intermode dispersion is much less. However, no matter how balanced graded multimode fibers are, their bandwidth is not comparable to singlemode technologies.

Fiber Optic Transceivers

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

The time division multiplexer, widely used in transmission technology, allows to increase the transmission speed up to 10 Gb / s. Modern high speed fiber optic systems offer the following transmission rate standards.

SONET standard	SDH standard	Transmission speed
OC 1	-	51.84 Mb / s
OC 3	STM 1	155.52 Mb / s
OC 12	STM 4	622.08 Mb / s
OC 48	STM 16	2.4883 GB / s
OC 192	STM 64	9.9533 GB / s

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

Application of fiber optic communication lines

Fiber optic is actively used to build city, regional and federal communication networks, as well as for the installation of connecting lines between city automatic telephone exchanges. This is due to the speed, reliability and high bandwidth of fiber networks. Also, through the use of fiber-optic channels, there is cable television, remote video surveillance, video conferencing and video broadcasting, 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.