Wireless optical communication channels. Fiber optic communication What is fiber optic communication

09.11.2020

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

Quartz glass, which is the carrier medium of fiber-optic links, in addition to unique transmission characteristics, has another valuable property - low losses and insensitivity to electromagnetic fields. This sets it apart from conventional copper cabling systems.

This information transmission system is usually used in the construction of work facilities as external highways that unite isolated structures or buildings, as well as multi-story buildings. It can also be used as an internal carrier of a structured cabling system (SCS), however, complete SCS made entirely 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, provide high speed Internet downloads on all machines simultaneously, high-quality telephone communications and television reception.

With proper design future system(this stage involves solving architectural issues, as well as choosing suitable equipment and methods of connecting support cables) and professional installation, the use of fiber optic lines provides a number of significant advantages:

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

Information Security. Fiber-optic communications provide 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 high sensitivity to vibrations. In case of wiretapping attempts, the built-in monitoring system can turn off the channel and warn about a suspected hack. This is why fiber-optic communication lines are 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. The fiber, being a dielectric conductor, is not sensitive to electromagnetic radiation and is not afraid of oxidation and moisture.
Economical. 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 from quartz, costs about 2 times less than copper cable; in addition, when building large systems, you can save on amplifiers. If, when using a copper pair, repeaters need to be installed every few kilometers, then in a fiber-optic line 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 copper and optical cables, then with the same bandwidth, the second one will weigh about 4 times less, and its volume, even when using protective sheaths, will be several times less than that of copper.
Prospects. The use of fiber-optic communication lines makes it easy to expand computing capabilities local networks thanks to the installation of faster active equipment, without replacing communications.

Scope of fiber optic communication lines

As mentioned above, fiber optic cables (FOC) are used to transmit signals around (between) buildings and within objects. When building external communication highways, preference is given to optical cables, and inside buildings (internal subsystems) traditional cables are used along with them. twisted pair. Thus, a distinction is made between FOCs for external (outdoor cables) and internal (indoor cables) installations.

Connecting cables are 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 fiber-optic communication lines can reach hundreds of kilometers (for example, when building communications between cities), while the standard length of optical fibers is several kilometers (including because working with too long lengths is in some cases 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 permanent. 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 permanent connection of local sections (installation of routes), mechanical connectors, adhesive splicing and welding of fibers are used. In the latter case, machines for splicing optical fibers are used. Preference is given to one method or another, taking into account the purpose and conditions of use of the optics.

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

In particular, before connection, optical cables undergo preliminary preparation: in places of future connections, the protective coating and excess fiber are removed (the prepared area is cleaned of hydrophobic composition). To securely fix the light guide in the connector, epoxy glue is used, which fills the internal space of the connector (it is inserted into the connector body using a syringe or dispenser). To harden and dry the glue, a special oven is used that can create a temperature of 100 degrees. WITH.

Once the glue has cured, excess fiber is removed and the connector tip is ground and polished (chip quality is of utmost importance). To ensure high accuracy, the performance of these works is controlled using a 200x microscope. Polishing can be done by hand or using a polishing machine.

The highest quality connection with minimal losses is ensured by welding fibers. This method is used to create high-speed fiber optic lines. During welding, the ends of the light guide melt; 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. Laser welding, due to the absence of impurities, allows you to obtain the purest compounds. Gas torches are typically used to permanently splice multimode fibers. The most common is electric welding, which provides high speed and quality of work. The melting time of different types of optical fibers differs.

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

After fusion, the joint is protected by tightly fitted tubes, which provide additional mechanical protection.

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

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

Mechanical splicing involves the use of special connectors - so-called splices. There are several types of mechanical connectors, which are an elongated structure with a channel for entering and fixing spliced optical fibers. The fixation itself is ensured using the latches provided by the design. After connection, the splices are additionally protected by couplings or boxes.

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

FOCL: types of optical fibers

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

In the modern world, communication needs are constantly increasing. Consumers need everything high speeds transmission, quality of communication and broadcast content (for example, quality of digital television). Providers - companies that provide services wired internet, wireless Internet (Wi-Fi), IP telephony, digital television- it is necessary to expand the capabilities of your communication lines. You can learn about these and many other areas of telecommunications on our website rcsz-tcc.ru.

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

First, a little history. The first experiment on the transmission of a light signal was carried out and presented by Daniel Colladon and Jacques Babinet back in 1840. But the first practical application of the technology occurred only in the twentieth century. In 1952, physicist Narinder Singh Kapany was able to conduct several studies that led to the creation of optical fiber.

Narinder created a bundle of glassy fibers, which constitute an optical waveguide (a waveguide is a guiding system for signals). The middle of the fiber has a lower refractive index than the cladding. In this case, the signal will completely pass through the core, and from the cladding will be reflected back into the core. Thus, the shell acts as a mirror. Before the invention of such fibers, the signal did not reach the end of the line. Now the problem could be considered solved. The discovery in 1970 by Corning of a method for producing optical fiber, which was not inferior in attenuation to copper wire for a telephone signal, is considered a turning point in the history of fiber optic lines. Optical communication has many advantages over electrical communication

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

Fiber optic technologies are constantly evolving - they are the technologies of the future. And you can always read about the most advanced new products on our website rcsz-tcc.ru.

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.

Fiber Optic Communication

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

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 - the core, which is the direct light guide, and the cladding. The refractive index of the core is slightly greater than the refractive index of the cladding, due to which the light beam, experiencing multiple reflections at the core-cladding interface, propagates in the core without leaving it.

Application

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

Notes

Wikimedia Foundation.

2010.
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 an information signal carrier, and fiber-optic cables as guide systems. Dictionary of business terms.… …

Dictionary of business terms- - [L.G. Sumenko. English-Russian dictionary on information technology. M.: State Enterprise TsNIIS, 2003.] Topics information Technology in general EN fiber optic connectionFOCoptical fiber communication …

worldwide fiber optic communications- - [L.G. Sumenko. English-Russian dictionary on information technology. M.: State Enterprise TsNIIS, 2003.] Topics information technology 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. used with con. 18th century (e.g. semaphore alphabet). With the advent of lasers, it became possible to transfer to optical technology. range of means and principles of production, processing... ... Physical encyclopedia

Fiber Optic Transmission Line- (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

Application

Fiber-optic communications are increasingly used in all areas - from computers and on-board space, aircraft and ship systems, to long-distance information transmission systems, for example, the fiber-optic communication line Western Europe - Japan is currently being successfully used, most of which passes through the territory of Russia. In addition, the total length of underwater fiber-optic communication lines between continents is increasing.

Fiber optic channel to every home(English) Fiber to the premises (FTTP) or Fiber to the home (FTTH)) is a term used by telecommunications providers to designate broadband telecommunication systems based on the implementation of a fiber optic channel and its completion at the end user's territory by installing optical terminal equipment to provide a range of telecommunications services (Triple Play), including:

high-speed Internet access;
telephone services;
television reception services.

The cost of using fiber optic technology is decreasing, making this service competitive with traditional services. The KMI Research forecast estimates the volume of the FTTP market, including equipment and cable systems, at 28 billion rubles per year.

Story

The history of long-distance data transmission systems should begin in ancient times, when people used smoke signals. Since that time, these systems have improved dramatically, with first the telegraph, then coaxial cable. In their development, these systems sooner or later ran into fundamental limitations: for electrical systems this is the phenomenon of signal attenuation at a certain distance, for microwaves it is the carrier frequency. Therefore, the search for fundamentally new systems continued, and in the second half of the 20th century a solution was found - it turned out that signal transmission using light is much more effective than both electrical and microwave signals.

In 1966, Kao and Hockman of STC Laboratory (STL) introduced optical filaments made from ordinary glass that had an attenuation of 1000 dB/km (while the attenuation in coaxial cable was only 5-10 dB/km) due to impurities that they contained and which, in principle, could be removed.

There were 2 global problems in the development of optical data transmission systems: the light source and the signal carrier. The first was resolved with the invention of lasers in 1960, the second with the advent of high-quality fiber optic cables in 1970. This was a development of Corning Glass Works. The attenuation in such cables was about 20 dB/km, which was quite acceptable for signal transmission in telecommunication systems. At the same time, fairly compact semiconductor GaAs lasers were developed.

After intensive research between 1975 and 1980, the first commercial fiber optic system was developed using 0.8 µm wavelength light using an AsGa semiconductor laser. The bitrate of the first generation systems was 45 Mbit/s, the distance between repeaters was 10 km.

On April 22, 1977, in Long Beach, California, General Telephone and Electronics first used an optical channel to transmit telephone traffic at a speed of 6 Mbit/s.

The second generation of fiber optic systems was developed for commercial use in the early 1980s. They operated with light with a wavelength of 1.3 microns from InGaAsP lasers. However, such systems were still limited by the dispersion occurring in the channel. However, already in 1987, these systems operated at speeds of up to 1.7 Gbit/s, the distance between repeaters was 50 km.

The first transatlantic telephone fiber optic cable - TAT-8 - was put into operation in 1988. It was based on the optimized Desurvire laser amplification technology.

TAT-8 was developed as the first submarine fiber optic cable between the United States and Europe.

The electrical signal is sent to a transmitter - a transceiver, which converts the electrical signal into a light pulse, which is fed into the optical cable through an optical connector. At the receiving location, the optical cable is connected using an optical connector to a receiver - a transceiver, which converts the light beam into an electrical signal.

Depending on the purpose of the fiber-optic line, its length, the quality of the components used structural scheme may change. At significant distances between transmission and reception points, a repeater is introduced - a signal amplifier. If the length of the optical cable is short (if the construction length of the optical cable is sufficient), cable welding is not necessary. The construction length is the length of a single piece of cable supplied by the manufacturer.

Fiber optic communication lines have the following advantages:

1. High noise immunity from external electromagnetic interference and from inter-channel interference.

2. A wide range of operating frequencies allows information to be transmitted via such a communication line at a speed of 10 12 bit/s = Tbit/s.

3. Security from unauthorized access: the fiber-optic line produces almost no radiation into the surrounding space, and the manufacture of optical energy taps without destroying the cable is practically impossible. And any impacts on the fiber can be recorded using monitoring (continuous monitoring) of the integrity of the line.

4. Possibility of hidden transmission of information.

5. Potentially low cost due to the replacement of expensive non-ferrous metals (copper) with materials with unlimited raw material resources (silicon dioxide).

6. Galvanic isolation of line segments is automatically ensured.

However, fiber optic technology also has its disadvantages:

1. High cost of equipment.

2. Expensive technological equipment is required, both during installation and during operation. If an optical cable breaks, the cost of restoring it is much higher than restoring a copper cable.

3. Relatively low durability. Lifetime + preservation of its properties within certain acceptable limits - optical cable 25 years. Note that to date in Moscow they have been operating telephone lines laid at the beginning of the century (see Hard & Soft, 1998, N11).

4. Optical cables are not resistant to radiation.

The basis of fiber-optic lines are optical cables, made from individual light guides - optical fibers.

The transmission of optical energy through an optical fiber is achieved using the effect of total internal reflection. The optical fiber is a two-layer cylindrical light guide (Fig. 4.3.)

Fig.4.3. Propagation of radiation and change and change of refractive index in an optical fiber

The material of the inner core has a refractive index n 1, and the material of the outer layer n 2, while n 1 >n 2, i.e. The inner core material is optically denser than the sheath material. For radiation entering the cylinder at small angles relative to the cylinder axis, the condition of total internal reflection is satisfied: when the radiation is incident on the boundary with the shell, all the radiation energy is reflected inside the fiber core. The same thing happens with all subsequent reflections; As a result, radiation propagates along the axis of the light guide without exiting through the cladding. The maximum angle of deviation from the axis, at which there is still total internal reflection, is determined by the expression A 0 = sin y 0 =.

The quantity A 0 is called the numerical aperture of the light guide and is taken into account when matching the light guide with the emitter. Radiation incident on the end at angles y>y 0 (extra-aperture rays) when interacting with the shell is not only reflected, but also refracted; part of the optical energy leaves the light guide. Ultimately, after repeated encounters with the core-cladding interface, such radiation is completely scattered from the fiber.

Radiation propagates along the light guide even if the decrease in the refractive index from the center to the edge occurs not stepwise, but gradually. In such light guides, the rays entering the end are refracted and focused near the axial line (see Fig. 4.4).

Fig.4.4. Propagation of radiation and change in refractive index in a self-focus.

Any segment of such a light guide acts as a short-focus lens, causing a self-focusing effect.

These light guides are called self-focuses (self, focus).

The industry of many countries has mastered the production of a wide range of products and components of fiber-optic communication lines. It should be noted that optical fiber production is concentrated mainly in the USA. Two types of optical fiber are used for signal transmission: single-mode and multimode. In a single-mode fiber, the light guide core has a diameter of 8-10 microns. In a multimode fiber, the diameter of the light guide core is 50-60 microns.

Optical fiber is characterized by two important parameters: attenuation and dispersion.

Attenuation is quantitatively determined by the formula

Pin – power of the input optical signal;

Pout – output optical signal power;

l is the length of the light guide.

The unit of attenuation is decibels per kilometer (dB/km).

Attenuation is determined by losses due to absorption and scattering of radiation in the optical fiber. Absorption losses depend on the frequency of the material, and scattering losses depend on the inhomogeneity of its refractive indices. Attenuation also depends on the wavelength of the radiation introduced into the optical fiber. Currently, signals are transmitted via fiber in three ranges: 0.85 microns, 1.3 microns, 1.55 microns, since it is in these ranges that quartz has increased transparency. Optical fiber is characterized by very low attenuation. The best examples of Russian fiber have an attenuation of 0.22 dB/km at a wavelength of 1.55 µm, which makes it possible to build communication lines up to 100 km long without signal regeneration. Optical fiber from Sumitoto (Japan) has an attenuation of 0.154 dB/km at a wavelength of 1.55 µm. There are reports of the development of so-called fluorozirconate optical fibers with an attenuation of about 0.02 dB/km, which will provide transmission speeds of the order of 1 Gbit/s with regenerators after 4600 km.

Dispersion, i.e. The dependence of the signal propagation speed on the radiation wavelength is another important parameter of an optical fiber. Since an LED or laser emits a certain spectrum of wavelengths when transmitting information, dispersion leads to broadening of pulses as they propagate along the fiber and thereby generates signal distortion. When assessing dispersion, the term “bandwidth” is used - the reciprocal value of the pulse broadening when it travels along an optical fiber over a distance of 1 km.

Bandwidth is measured in megahertz per kilometer (MHz * km). Dispersion imposes restrictions on the transmission range and the upper value of the frequency of transmitted signals.

The amount of attenuation and dispersion varies for different types optical fibers.

Single-mode fibers have better attenuation and bandwidth characteristics. However, single-mode radiation sources (diode lasers operating at a wavelength of 1.55 µm) are several times more expensive than multimode radiation sources (light-emitting diode operating at a wavelength of 0.85 µm). Splicing single-mode fibers and installing optical connectors at the ends of single-mode cables is more expensive. However, the bandwidth of multimode fibers reaches 1000 MHz * km, which is only acceptable for local communication networks.

To connect the receiver and transmitter, a fiber-optic cable (FOC) is used, in which the optical fibers are supplemented with elements that increase the elasticity and strength of the cable.

The main indicators of the FOC are operating conditions and throughput.

Relationship between the correcting ability of a code and the code distance

The degree of difference between any two code combinations is characterized by Hamming distance between them or simply code distance.

Hamming distance d expressed by the number of positions in which code combinations differ from one another.

Example 1. Find the Hamming distance d between code combinations 10101011 and 11111011.

Wireless optical communication channels. Fiber optic communication What is fiber optic communication

Scope of fiber optic communication lines

FOCL connection technologies

FOCL: types of optical fibers

Physical basis

Application

see also

Notes

Fiber Optic Cable

Application

Story

see also

See what “fiber optic communication” is in other dictionaries:

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Wireless optical communication channels. Fiber optic communication What is fiber optic communication

Scope of fiber optic communication lines

FOCL connection technologies

FOCL: types of optical fibers

Physical basis

Application

see also

Notes

Fiber Optic Cable

Application

Story

see also

See what “fiber optic communication” is in other dictionaries:

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