What is fiber optic cable. Fiber optic cable. Types and device. Installation and application. Indoor cable

Fiber optic cables, in contrast to cables with copper or aluminum conductors, use a transparent optical fiber as a signal transmission medium. The signal here is not transmitted using electric current, but with the help of light. This means that it is practically not electrons that move, but photons, respectively, and the losses during signal transmission turn out to be negligible.

These cables are ideal as a means of transmitting information, because light is able to pass through transparent fiberglass practically unhindered for tens of kilometers, while the light intensity decreases slightly.

There are GOF-cables (English glass optic fiber cable) - with glass fiber, and POF cables (plastic optic fiber cable) - with transparent plastic fiber. Both are traditionally referred to as fiber optic or fiber optic cables.

Fiber optic cable device

Fiber optic cable has a fairly simple device. In the center of the cable there is a fiberglass light guide (its diameter does not exceed 10 microns), clothed in a protective plastic or glass sheath, which provides complete internal reflection of light due to the difference in refractive indices at the interface of two media.

It turns out that light, all the way from transmitter to receiver, cannot leave the central vein. In addition, the light is not afraid of electromagnetic interference, therefore, such a cable does not need electromagnetic shielding, but only needs strengthening.

To give the optical fiber cable mechanical strength, special measures are taken - they make the cable armored, especially when it comes to multicore optical cables carrying several separate optical fibers at once. Suspended cables require special reinforcement with metal and Kevlar.

The simplest fiber optic cable design is glass fiber in plastic sheath... A more complex design is a multi-layer cable with reinforcing elements, for example, for underwater, underground or suspended installation.

In a multilayer armored cable, the carrying reinforcing cable is made of metal enclosed in a polyethylene sheath. Light-carrying plastic or glass fibers are located around it. Each individual fiber is coated with a layer of colored varnish for color coding and for protection against mechanical damage. The fiber bundles are wrapped in plastic tubes filled with a hydrophobic gel.

One plastic tube can contain from 4 to 12 such fibers, while the total number of fibers in one such cable can be up to 288 pieces. The tubes are braided with a thread that tightens the film moistened with hydrophobic gel - for greater damping of mechanical influences. The tubes and the central cable are enclosed in polyethylene. Next come Kevlar threads, which practically provide armor to the multicore cable. Then again polyethylene to protect it from moisture, and finally the outer shell.

The two main types of fiber optic cables

There are two types of fiber optic cables: multimode and singlemode. Multimode is cheaper, singlemode is more expensive.

Provides the beams passing through the fiber practically the same path without significant mutual deviations, as a result, all beams arrive at the receiver simultaneously and without distortion of the signal shape. The diameter of an optical fiber in a single-mode cable is about 1.3 μm, and it is precisely with this wavelength that light should be transmitted through it.

For this reason, a laser source with monochromatic light of a strictly required wavelength is used as a transmitter. It is cables of this type (single-mode) that are considered today as the most promising for communications over long distances in the future, but so far they are expensive and short-lived.

Less "accurate" than singlemode. The beams from the transmitter go in it with a spread, and on the side of the receiver there is some distortion of the transmitted signal shape. The optical fiber diameter in the multimode cable is 62.5 µm and the outer cladding diameter is 125 µm.

It uses a conventional (not laser) LED on the transmitter side (0.85 micron), and the equipment is not as expensive as a laser light source, and current multimode cables have a longer lifespan. Cables of this type do not exceed 5 km in length. Typical signal transmission latency is in the order of 5 ns / m.

Advantages of fiber optic cables

One way or another, a fiber-optic cable is fundamentally different from ordinary electrical cables in exceptional noise immunity, which ensures maximum safety of both the integrity and confidentiality of the information transmitted through it.

Electromagnetic interference directed to a fiber optic cable is not capable of distorting the light flux, and the photons themselves do not generate external electromagnetic radiation. Without violating the integrity of the cable, it is impossible to intercept the information transmitted through it.

The bandwidth of an optical fiber cable is theoretically 10 ^ 12 Hz, which cannot be compared with current-carrying cables of any complexity. You can easily transfer information at speeds up to 10 Gbps per kilometers.

Fiber optic cable itself is not expensive, almost as much as thin coaxial cable. But the main share of the rise in the cost of the finished network still falls on the transmitting and receiving equipment, the task of which is to convert an electrical signal into light and vice versa.

The attenuation of a light signal when passing through a fiber-optic cable of a local network does not exceed 5 dB per 1 kilometer, that is, almost the same as that of a low-frequency electrical signal. Moreover, the higher the frequency - the more pronounced is the advantage of the optical medium over traditional electrical conductors - the attenuation increases insignificantly. And at frequencies above 0.2 GHz, fiber optic cable is definitely out of competition. It is practically possible to bring the transmission distance up to 800 km.

Fiber optic cables are applicable in networks with ring or star topologies, while completely eliminating the grounding and load balancing problems that are always relevant to electrical cables.

Ideal, along with the above advantages, allows analysts to predict that in network communications, fiber-optic cables will soon completely replace electrical ones, especially given the growing copper deficit on the planet.

Disadvantages of fiber optic cables

In fairness, one cannot fail to mention the shortcomings of fiber-optic data transmission systems, the main of which is the complexity of the installation of systems and high requirements for the accuracy of installation of connectors. Micron deviations during connector mounting can lead to an increase in attenuation in it. Here, high-precision welding or a special glue gel is required, the refractive index of light in which is similar to that in the mounted fiberglass itself.

For this reason, the qualifications of the staff do not allow indulgence, special tools and high skill in their use are required. Most often, they resort to using ready-made pieces of cable, at the ends of which ready-made connectors of the required type are already installed. For branching the signal from the optical fiber, specialized splitters are used for several channels (from 2 to 8), but when branching, light attenuation inevitably occurs.

Of course, fiber is a less strong and less flexible material than copper, and it is unsafe to bend the fiber to a radius of less than 10 cm for its safety. Ionizing radiation reduces the transparency of the optical fiber, increases the attenuation of the transmitted light signal.

Radiation resistant fiber optic cables are more expensive than conventional fiber optic cables. A sudden temperature drop can lead to the formation of a crack in the fiber. Of course, fiber is vulnerable to mechanical stress, shock, and ultrasound; to protect against these factors, special soft sound-absorbing materials of the cable sheaths are used.

Fiber optic cable (FOC) - cable products based on fiber optics, which are used in communication lines to transmit information using optical signals (photons). The technology enables signal transmission over long distances while maintaining signal strength and with little interference.

Scope of application

Fiber optic cable is the basis of modern telecommunication networks. It is used in local networks and in the construction of transcontinental communication lines. Regardless of the length of the route, the signal remains stable, high-quality and protected. Today it is the main type of wire for building federal and local channels (in Moscow and the regions).

The price of fiber optic cable varies depending on the installation location, design and size of the center conductor.

Taking into account the place of laying, the following types of FOC are distinguished:

• for internal laying

Cable products for internal networks (home, office, shopping center, clinic, etc.) An optical cable with a semi-dense or dense buffer coating is used. There are no special requirements.

• for external laying

For overhead lines between buildings within settlements. An optical communication cable with a strong sheath resistant to atmospheric and mechanical influences is used. In the case of a particularly difficult operational situation, the networks are brought into the main canals.

• special cables

For the transit of networks in extreme conditions - in the soil, water, in heaving and swampy soils. The cable sheath depends on the specific operating conditions.

When choosing an optical cable, the presence of a ruggedized sheath is not always important. No reinforced protection is required when laying inside ducts and pipes. At the same time, when laying in the mail, the fiber optic cable must be protected from rodents, getting wet, and mechanical stress. And when building air networks - from sagging.

To protect against rodents, corrugated tape armor is used, when laying in the ground, armor made of steel round wire is used, when mounting on non-supports, a reinforced OK with a sealed frame is used.

According to the design and size of the central core, they are distinguished:

• Optical single mode cable

For long distances (up to 50 km). It has a small core diameter, it is used for telephone networks, provider networks, ensuring the operation of data centers. Provides high speed digital data transfer.

• Optical multimode cable

For distances up to 1 km. This fiber-optic cable is used to transfer data inside and between buildings, and is optimal for computer networks. The core diameter can be different. It is made on the basis of a conventional LED.

Fiber Optic Cable Manufacturers

In Russia, optical cables are produced:

• CJSC TRANSVOK, Kaluga Region;
• Samara Optical Cable Company CJSC;
• LLC "Eurocable 1", Moscow region;
• OJSC "ELECTROCABLE" KOLCHUGINSKIY ZAVOD ";
• Plant "Yuzhkabel", Ukraine;
• CJSC OFS Svyazstroy-1 VOKK, Voronezh;
• Cable plant "NPP Starlink";
• Plant "Incab";
• Kabellelectrosvyaz plant;
• MinksKabel plant and many others.

Fiber optic cables can be purchased from leading foreign suppliers: Phoenix Contact GmbH & Co. KG / 1923, Germany, Lapp Lapp Group, Germany (there is production in the Russian Federation) and others.

Mounting

Laying of networks is allowed only by trained personnel. High price supplies and installation work, as well as the high costs of correcting shortcomings, require strict adherence to the regulations. Optical couplings are used for splicing to ensure that the signal remains fast and clear.

There are the following laying methods:

• Suspended (air gasket).
• Outdoors in protective sleeves.
• Inside the cable channels.

A work order is issued with an indication of the category of admission to delineate responsibility for the result of installation.

Pros and cons of fiber optic cable

FOCs have almost completely replaced communication lines based on copper cables. The main advantages of fiber optic cable are:

• Maximum signal security.
• Minimal losses.
• High data transfer rate (from 1 to 10 Gbit / s at a distance of 1 km).
• High throughput of the fiber optic cable.
• Small dimensions.

At the same time, it is worth noting the high cost of cable products and materials for installation, rather high costs of maintaining communication lines, as well as high requirements for the level of specialists performing broaching and operational service. However, these disadvantages outweigh the high stability and quality of FOC-based networks.

Where to buy fiber

You can buy a fiber-optic cable and installation systems for it at Tekhkabelsystems LLC.

To buy an optical cable, place an order by email or phone. The manager will provide a selection of products of the required nomenclature.

We work with regions and accept orders from companies with any form of calculation. The price for 1 meter in the product cards may vary depending on the volume and specifics of the order. You can buy an optical cable with delivery. The full cost will be calculated by a specialist of the company.

At present, fiber-optic communication lines are firmly taking their positions and are developing intensively. The replacement of copper cables with fiber-optic cables is progressing at a rapid pace at all sections of the network. The traditional communication cables with copper conductors are being replaced by fiber-optic waveguides, in which the information carrier is infrared electromagnetic waves. Information transmission over fiber-optic cables is carried out according to the principle of total internal reflection. Reflection is achieved by a protective coating applied to the optical fiber (core), at this boundary the beam is fully reflected and propagates along the waveguide. Due to the growing requirements for telecommunication networks, the use of fiber optic technology is becoming indispensable.

In order to design the route of the fiber-optic communication line and select the required type of cable, you need to know the operating conditions, the design of the cable and its technical specifications... The demand for components of fiber optic communication lines is constantly increasing. The dynamics of growth is observed not only in the segment of backbone networks that are being built by telecom operators. A steady increase in the number of optical installations is also noticeable in the field of structured cable systems, which is explained, first of all, by the development of information technology. The foundation is already being laid for the construction of high-speed optical transmission lines capable of operating at 10 Gbps. Applications that integrate voice, data and video are in demand, where fiber optics is also the best solution.

Currently, there are a large number of FOC structures, focused on various conditions of use (laying inside buildings, in a telephone duct or in the ground, an optical cable can be laid along supports railways, on power lines, in sewer and water pipes, along riverbeds and the bottom of lakes, along highways, together with power cables.

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

Advantages of Fiber Optic Cables Compared to Traditional Copper Cables:

• Immunity to interference and interference, complete insensitivity of the cable to external electrical interference 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.
• The lack of electrical conductivity for fiber optic cable means that the problems associated with changes in ground potential, such as those in power plants or railways, are gone. This property also eliminates the risk of damage to equipment caused by current surges from lightning, etc.
• Ease of execution of works on laying, splicing and confection.
• No crosstalk and mutual interference, which improves the quality of data transmission.
• Small dimensions and minimal weight (up to 2.2 mm - outer diameter and weight 4 g / m for polymer optical fiber, SIMPLEX simplex version). The ultra-small dimensions of optical fibers and fiber optic cables bring a new lease of life to jam-packed cable ducts. For example, a single coaxial cable takes up as much space as 24 optical cables, each of which can presumably carry 64 video channels and 128 audio or video signals simultaneously.
• Possibility of laying over long distances.
• The highest bandwidth of all possible transmission media, wide optical fiber transmission bandwidth allows high-quality video, sound and digital data to be simultaneously transmitted over one fiber-optic cable.
• Low loss, fiber optic cables allow image signals to be transmitted over long distances without the use of route amplifiers or repeaters. This is especially useful for long-distance transmission schemes - for example, highway or railway surveillance systems, where 20 km of repeat-free sections are not uncommon.
• A 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.
• Long service life.

The main element of optical cables is optical fiber. A distinction is made between polymer optical fiber (POF), high quality quartz glass fiber with a protective polymer coating (PCF) and pure high quality quartz glass fiber (GOF).

For use in industrial conditions LAPP Kabel offers fiber optic cables made of polymer optical fiber and glass fiber, as well as combined cables with copper conductors.

Most cables are specially designed for flexible routing in towed cable chains.

The general concept of information transfer over fiber optic cables is defined by the use of polymer fiber (POF), protective polymer coated fiberglass (PCF) and glass fiber (GOF) cables.

Suitable optical connectors, tools and prefabricated fiber optic patch cables are also available.

Typical applications for fiber optic cables with (POF), (PCF):

• BUS systems for production automation;
• in mechanical engineering and production of industrial equipment.

Due to their special properties, optical fiber cables (POF) are used in:

• where reliable information transfer is required;
• where the laying of cables is limited in space;
• short data transmission distances (up to 60 m).

Typical Applications of Fiber Optic Cables (GOF)

They are intended for applications where large amounts of data must be transmitted at high speeds and over long distances (from 60 m to several kilometers), for example:

• in local computer networks LAN (Local Area Networks);
• in networks built using MAN technology (Metropolitan Area Networks);
• in networks built using WAN (Wide Area Networks) technology.

Main structural elements of fiber optic cables

Several main groups of structural elements can be distinguished: optical fibers with protective coatings, optical modules, cores, power elements, hydrophobic materials, cladding and reinforcement. Depending on the purpose and conditions of use, fiber optic cables have specific designs.

Optical fiber (OF) is very sensitive to external influences: mechanical pressure and bending, temperature, humidity. To protect against them, a coating must be applied to the OM. The standardized nominal fiber diameter is 250 µm. In order to identify OM, a paint layer with a thickness of 3… 6 µm is applied to the coating. Reliability of the connection of the dye with the coating is ensured by intense ultraviolet radiation.

The main element of fiber-optic cables is an optical fiber (OF) made of high-quality quartz stele, which ensures the propagation of light signals.

An optical fiber consists of a high refractive index center (core) surrounded by a low refractive index material cladding, as shown in Fig. 1, the 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.

Light propagates along the fiber core through successive total internal reflections at the core-cladding interface; his behavior is in many ways similar to that of falling into a pipe, the walls of which are covered with a mirror layer. However, unlike a conventional mirror, 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 over long distances with minimal loss.

In turn, the fibers differ depending on the profile of the refractive index in the direction from the center to the periphery in the cross section of the fiber. The fiber in (Fig. 2, a) is called a fiber with a stepped refractive index and multimode, since there are many possible paths, or modes, for the propagation of a light beam. This set 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 - increasing either the frequency or the fiber length beyond the limit values \u200b\u200bessentially leads to the fusion of successive pulses, making it impossible to distinguish them. For a typical multimode fiber, this limit is approximately 15 MHz * km, which means that a video signal with a bandwidth of, for example, 5 MHz can be transmitted over a maximum distance of 3 km (5 MHz x 3 km \u003d 15 MHz * km). Attempting to transmit the signal over a greater distance will result in progressive loss of high frequencies.

Single-mode, as they are called, fibers (Fig. 2, b) very effectively reduce dispersion, and the resulting bandwidth - many GHz * km - makes them ideal for telephone and telegraph networks common use (RTT) 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 emitter based on a laser diode, which reduces their attractiveness for many applications associated with short-range closed-loop TV systems.

Ideally, a fiber with a bandwidth of the same order of magnitude as a single-mode fiber, but with a diameter similar to that of a multimode fiber, is required to enable the use of inexpensive LED transmitters. To some extent, these requirements are satisfied by a multimode fiber with a gradient change in the refractive index (Fig. 2c). 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 higher angle and travel a longer path actually start to 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 modes of the lowest orders, which remain near the axis in the filament, in the region of high refractive index. The increase in speed just compensates for the greater distance traveled.

Gradient multimode fibers are preferable, since, firstly, fewer modes propagate in them and, secondly, their angles of incidence and reflection differ less, and, therefore, the transmission conditions are more favorable.

Gradient index multimode fibers are not ideal, however, but still exhibit quite good bandwidth. Therefore, in most closed-loop TV surveillance systems of small and medium length, the choice of this type of fiber is preferable. In practice, this means that bandwidth is only 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 dependent on the transmitter wavelength of the light source. There are three wavelengths at which the attenuation of an optical fiber is usually minimal - 850, 1310 and 1550 nm. These are known as transparency windows. For multimode systems, the 850nm window is the first and most commonly used (lowest cost). At this wavelength, 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.

At 1310 nm, the same fiber exhibits even lower attenuation - 0.7 dB / km, thus allowing a proportional increase in communication range to about 12 km. 1310 nm is also the first operating window for single-mode fiber optic systems, with an attenuation of about 0.4 dB / km, which, in combination with laser diode transmitters, allows for 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 0.24 dB / km) (Fig. 3).

The difference in attenuation values \u200b\u200bin different transparency windows is quite significant, especially in multimode fibers. Table 1 clearly illustrates the advantage of single-mode fibers over multimode ones.

To ensure the stable operation of the OF and reduce the risk of their rupture under the influence of longitudinal and transverse stresses, the fibers are protected by primary and secondary coatings. The primary coating applied in a continuous layer directly on the OM shell after its drawing protects the OM surface from damage and gives it additional mechanical strength. The following are used as the secondary coating of OM: a tube with freely placed OM with a primary protective coating; continuous polymer coating; tape element, which houses the OF with a primary protective coating. In a tubular element (tube) acting as a secondary protective coating, freely placed OFs with a primary protective coating are usually laid without twisting or by twisting around the central strength element. Multimode fibers are easier to manufacture, easier to insert light rays into, and easier to splicate.

Multimode fibers are characterized by a bandwidth expressed in megahertz. It is customary in the specifications to indicate not the bandwidth, but the so-called bandwidth factor inherent in this type of fiber, in megahertz times kilometers (MHz x km). For a given bandwidth factor (let us denote it as S), the bandwidth AF will depend on the length of the line or its regeneration section of modifications AF \u003d S. For multimode 50/125 fibers, the normalized S values \u200b\u200bare 400 ... 1500 MHz * km. For a 10 km line, the bandwidth is 40 ... 150 MHz. The longer the line, the lower the frequency bandwidth and, therefore, the lower the amount of information transmitted.

Ideally, only one wave propagates through single-mode fibers. They have a much lower attenuation coefficient (depending on the wavelength by 2 ... 4 and even 7 ... 10 times) compared to multimode and the highest bandwidth, since they almost do not distort the signal (Fig. 4). But for this, the diameter of the fiber core must be commensurate with the wavelength (in any case d< А < 10). Практически dc=8…10 мкм.

Depending on the operating conditions, the cable design requires different requirements... A cable that is used outdoors, first of all, must be protected from atmospheric influences, such as sunlight, moisture, temperature extremes. A cable that is designed to be installed in cable ducts requires rodent protection. If the cable is suspended between transmission towers, its mechanical strength is important. When choosing a cable, the focus is usually on two aspects. The first is fire safety, the need for which arises if the cable is laid indoors. The second aspect is the integrity and safety of optical fibers during storage, installation and operation of fiber-optic cable. At each of these stages, the cable is exposed to mechanical, atmospheric and other influences that can be dangerous to the fiber. Note that here we are not talking about the physical destruction of the optical fiber.

The most common material used for the outer jacket of fiber optic cables is polyethylene. It possesses both excellent physical parameters (high strength, good wear resistance, resistance to ultraviolet radiation, oxidation and other chemical influences), and good dielectric properties. Polyethylene has good resistance to moisture penetration, low and high temperatures, and also has the ability not to change its physical properties under the influence of changes in ambient temperature.

Particular attention should be paid to fiber optic cables, the sheathing of which meets the requirements fire safety... The basis for the manufacture of the corresponding casings is polyethylene, and the required properties are achieved by adding special chemical additives. In the description of a fiber-optic cable, the presence of such properties is most often indicated by the abbreviation LSZH (Low Smoke Zero Halogen). The presence of a non-flammable sheath that does not emit halogens in a fiber-optic cable significantly increases its cost, but when laying the cable indoors, at industrial facilities, in metro tunnels, international and national fire safety standards oblige the use of this type of cable.

Reinforcing elements

To increase the permissible stretching of a fiber-optic cable, force elements are necessarily introduced into its structure. Allowable tensile values \u200b\u200bof 1000-2000 N (Newtons) can be achieved using Kevlar or glass yarns.

As a rule, this figure is quite sufficient for general-purpose cables. The threads can form a dense layer, or they can intertwine. Kevlar threads are believed to provide greater allowable tensile strength. However, glass fibers also protect against rodents and are a barrier to the spread of combustion. Sometimes, in parallel with Kevlar threads, one central or a pair of side rods are used. Additional power elements can be dielectric or metallic. A central strength member design is characteristic of a cable with a large number of fibers that are placed in clusters around the strength member. High permissible tensile strength in special types of cables, in which this value should be tens of kilonewtons, is achieved with the help of steel rods. In such cables, optical fibers are often located not in thermoplastic, but in gel-filled steel tubes. Tensile performance is the maximum force that can be applied in the longitudinal direction of the cable without changing the characteristics of the optical fiber. When the cable is stretched, the impact on the sheath itself occurs first, and only then on the optical fiber.

As a result of changes in ambient temperature, there is a natural increase or decrease in cable length. Therefore, the group of these characteristics also includes the temperature range in which you can store, operate and install the cable.

Important parameters for fiber optic cables

The compressive force characterizes the allowable force with which the cable can be squeezed in the transverse direction, provided that the attenuation in the fiber remains within the normal range. Impact refers to the impact resistance of the cable.

Cable bend is another important parameter that characterizes the maximum permissible radius of curvature of the cable. It must be considered when it comes to laying fiber optic cable, for example, in pipelines or cable ducts. The value of the minimum allowable bending radius is often in the range of 15-20 diameters from the outer sheath of the cable. If this parameter is neglected, the integrity of the fibers in the cable may be compromised.

Torsion defines the ability of the cable sheath to provide fiber protection when the sheath is twisted around its axis. For a cable with metal armor, the permissible twisting angle is less than for a cable without armor.

Water penetration is an important parameter for fiber optic cable, especially if it is intended for outdoor use.

Indoor cable

The type of cable sheath is largely determined by the operating conditions. For fiber optic cable to be used indoors, the main characteristics are:

• fire safety;
• good flexibility and ease of installation;
• mounting the connector directly on the optical fiber;
• no gel inside the cable jacket;
• lack of metal elements.

By far the most important characteristic of indoor cables is their resistance to fire. The cable must have a sheath that does not spread combustion, does not smoke, does not emit halogens and other toxic compounds when exposed to a flame. It is understood that these properties are possessed not only by the outer shell, but also by the internal structural elements. These requirements are met by a Tight-Buffer cable, in which each fiber is additionally enclosed in a 900 micron sheath. This enclosure provides adequate protection against moisture penetration for the respective operating conditions. The tightly buffered fiber optic cable itself is lightweight and highly flexible.

For laying inside buildings, the so-called "dry" cable, which does not contain gel, is most often used. One of the reasons why such a cable is recommended for indoor use is that the gel can become a fire propagation medium inside the cable jacket, even if the outer jacket itself does not support combustion. Another reason is a phenomenon that is sometimes called Axial Migration, which can be translated as "gel overflow".

If gel-based cable is used to interconnect network segments, there is a high likelihood of gel in the fiber-optic cross-panel of the lower floor in the summer, and the consequences of this can be dire. Instead of the leaked out water-repellent compound, moisture can condense in the tube with the fiber, which degrades the parameters of the optical fiber. This problem occurs if the cable is located, for example, in an unheated shaft.

It can also change the mechanical characteristics of the cable itself. The fact is that the amount of optical fiber in the gel-containing tube exceeds its length - the free placement of the fiber in the tube in the normal state resembles a spiral. The fiber itself in a buffer with a diameter of 250 micrometers (μm) is fixed at the junction with the connectors or pigtail sleeves, that is, only at two points. In the case of a vertical cable arrangement, the fiber moves along with the gel from top to bottom, as a result of which the fiber straightens in the upper part of the cable and can be in a taut state.

Now all the tensile force applied to the outer sheath is equally transferred to the fiber that does not have an additional length margin. Stretching of the outer shell can occur, for example, during the warmer months as a result of the natural increase in length with increasing temperature. Ultimately, this will lead to a change in the characteristics of the fiber, microcracks or even tearing of the fiber from the optical connector. In the lower part of a vertically located cable, on the contrary, there will be an excess of fiber, which can also affect the mechanical strength of the cable and, therefore, the reliability of the fiber-optic communication line as a whole.

For indoor cables, it is preferable to mount the connectors directly onto the fiber. In this case, additional fastening is provided for a dense buffer with a diameter of 900 microns, which to some extent allows you to remove possible stresses from the optical fiber.

In addition, the implementation of Fiber to the Desk technology is based on connecting workplaces to the SCS using a fiber-optic cable, which must be terminated in a special socket. Such sockets are not suitable for mounting splice cassettes for sleeves of welded joints in them, but require mounting the connectors directly on the fiber. The 900 µm Tight Buffer cable is the best choice for this task.

Outdoor cable

The types of fiber optic cables for outdoor installation today are very diverse, due to the operating conditions and methods of their installation. Such cables can be conditionally divided into two groups: those that can be directly dug into the ground, and those that are laid in special sewers. Separately, you can also distinguish cables that are suspended in an open space between poles on a supporting cable or on brackets along buildings.

Cables suspended between power transmission towers should have a minimum weight, but at the same time provide good protection against the damaging effects of solar radiation and be completely dielectric. In addition, their casing must reliably perform its protective functions not only at low or high temperatures, but also at frequent temperature changes.

However, rodents for cable that runs in telecommunications ducts can be an even bigger problem. Metallic or non-metallic armor, a dense layer of fiberglass filaments - these are the ways to solve this problem. To reduce the frictional force when pulling the cable into the cable ducts, its outer sheath must have a low friction coefficient and be very strong. This is achieved using special materials such as polyamide (PA). Particular attention should be paid to protecting the cable from moisture penetration, taking into account the possibility of flooding the cable ducts with water. In this case, a cable is best suited in which the optical fibers are placed in gel-filled thermoplastic tubes. If the cable has one such tube, then it is called Uni Tube, if there are several tubes - Multi Tube.

Each type of cable has its own pros and cons, and you need to choose Uni Tube or Multi Tube depending on the specific task. For example, for ease of use, cables with more than 12 fibers are mainly of the Multi Tube design. This is due to the fact that the cassette for mounting welded joints, into which the fiber-containing tube is inserted, is usually designed for only 12 fibers. In addition, fiber optic connectors are often arranged in groups of 12 in junction panels and junction boxes. Therefore, if you need to use a 16-core cable, it is better to choose Multi Tube, in which each of the four tubes contains four fibers. To save round shape In addition to the four gel-filled tubes, be sure to use a couple more plastic rods. For example, a 24-core cable contains six tubes of four fibers or four tubes of six fibers.

In Multi Tube, the fiber tubes are placed around a central strength member. This cable has a higher allowable stretch than Uni Tube. Naturally, it is heavier and has a larger cross section. For digging into the ground, this is not decisive, but when such a cable is pulled into telecommunication ducts, it can directly depend on the diameter of the cable being laid. From an economic point of view, Uni Tube is the preferred cable.

Also, do not forget about the length of the cable that can be pulled into the cable duct. This factor should be taken into account, first of all, when calculating the number of couplings that are required for splicing optical fibers. Let us note right away that the length of the cable that can physically be pulled into the sewer differs from the length that would guarantee the reliable operation of the fiber-optic communication line.

The fact is that during the installation process, the cable is sequentially pulled through a number of telecommunication wells, the distance between which is several tens of meters. Since these wells are not located in a straight line, the cable must be constantly bent, stretched, twisted. All these mechanical influences can cause the formation of microcracks in the optical fiber, which can be harmful only after a few years.

In addition, when pulling large lengths of cable through the wells, the outer sheath can wear off or burst so badly that it loses its protective functions. Therefore, the recommended cable length for pulling through telecommunication wells is 1-1.5 km. Of course, you can first tighten 1 km of the cable in one direction, then unwind from the drum and tighten another 1 km in the other. The result will be a segment with a length of 2 km, but only highly qualified specialists can perform such work.

If it is necessary to dig the cable into the ground, first of all, it is necessary to take into account the protection against rodents and the retention of mechanical strength, as well as take into account the influence of ultraviolet radiation, the presence of a smooth sheath and the working conditions at extremely low temperatures. As a rule, such a cable is laid in a trench using special mechanical means. For digging into the ground, both Uni Tube and Multi Tube cables can be used. Protection against rodents can be implemented to the same extent in each of them, but the protection against moisture in Multi Tube will be much more effective if the space between the fiber-containing tubes is additionally filled with a hydrophobic compound. In addition, in the Multi Tube cable, it is possible to achieve a greater value of the permissible longitudinal stretching, since in the cable design, in addition to Kevlar or glass threads, there is also a central strength element.

Optical cables for long-distance submarine communication lines

Long-distance underwater fiber-optic communication lines are connected primarily with international lines. Optical cables for extended submarine systems are structurally complex and laborious to manufacture. These cables must contain elements that protect the optical fibers from moisture and atomic hydrogen. Cables must be produced in large face-to-face lengths, and all optical fibers must not have splices along the length of the cable.

In the operating wavelength range, the fibers should have low values \u200b\u200bof the attenuation coefficient, chromatic and polarization mode dispersion. Therefore, in modern conditions As optical fibers for submarine cables, fibers with non-zero dispersion shifted are selected.

Submarine fiber optic cables are characterized by high tensile and expansion properties. Usually, the gradation of these cables by mechanical parameters involves the manufacture of cables for coastal laying (with the highest values \u200b\u200bof mechanical parameters), cables for the marine fishing zone (most often these cables are buried in the bottom soil), cables for the deep water zone. In the Black Sea, submarine cables must additionally be resistant to hydrogen sulfide.

Horizontal optics

In connection with the growing requirements for new network applications, the use of fiber optic technologies in structured cabling systems is becoming increasingly important. What are the advantages and features of the use of optical technologies in the horizontal cable subsystem, as well as at user workstations?

The main advantages of optics should be attributed to the large bandwidth of all possible transmission media, including copper twisted and coaxial cables, as well as the longest data transmission distance at the lowest cost of active equipment and operation.

Fiber optic segments can be up to 20 times longer than copper segments. Typical multimode fiber for use on a LAN today has a bandwidth of more than 500 MHz per kilometer. Since the existing SCS standards define the length of the horizontal optical conduit from the distribution point of the floor to the subscriber socket in 100 m, each such connection provides a bandwidth of several GHz. Recent advances in multimode fiber technology allow even higher transmission speeds

So, optical fiber has characteristics that are much higher than the requirements of today's Ethernet speed standards (100 Mbit / s) for connecting workplaces, and allows you to easily migrate to new data transmission protocols, such as, for example, 1 and 10 Gigabit Ethernet or high speed ATM.

Speaking about the possibilities of upgrading, it should be noted that the properties of optical fiber are practically independent of the data transmission rate in the network, since there are no mechanisms (for example, crosstalk) that lead to degradation of the properties of optical fiber with an increase in the speed of network protocols. Once the optical fiber is installed and its parameters are tested for compliance with the standards, the cable channel can operate at speeds of 1, 10, 100, 500, 1000 Mbps or 10 Gbps.

This ensures that the cabling infrastructure installed today will be able to support any network technology for the next 10-15 years or more. Only one transmission medium in SCS satisfies these requirements - optics. Optical cables have been used in telecommunication networks for over 25 years, and recently they have also found widespread use in cable TV and LAN.

In LANs, they are mainly used to build backbone cable channels between buildings and within buildings themselves, while ensuring high data transfer rates between segments of these networks. However, the development of modern network technologies actualizes the use of fiber as the main medium for connecting users directly.

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

The use of optical fiber in workplaces will allow in the future to move to new network protocols such as Gigabit and 10 Gigabit Ethernet with minimal costs. This is possible thanks to some of the latest advances in fiber optic technology:

• multimode fiber with improved optical performance and bandwidth;
• small form factor optical connectors that require less floor space and less installation;
• vertical cavity plane laser diodes provide long distance data transmission at low cost.

A wide range of solutions for building zonal optical cabling systems provide a smooth, cost-effective transition from copper to all-optical structured cabling systems.

Standard notation for fiber optic cables

Almost all European manufacturers mark the fiber optic cable according to the DIN VDE 0888 system. According to this standard, each type of cable is assigned a sequence of letters and numbers, which contain all the characteristics of the fiber optic cable.

For example, I-V (ZN) H 1 × 4 G50 / 125 denotes indoor cable [I]. The fibers are in a dense buffer 900 µm in diameter [V], with non-metallic strength elements, with a non-combustible and slightly smoky sheath [H]. The number of fibers is 4. The type of fiber is multimode with a core size and fiber sheath of 50 and 125 µm, respectively.

A / IDQ (ZN) (SR) H 1 × 8 G50 / 125 designates cable for both outdoor and indoor use. The fibers are placed in a central tube filled with a water-repellent compound. Kevlar or glass yarns in metal corrugated armor. The outer shell is LSZH, low smoke, does not emit halogens during combustion [H]. One tube with eight fibers. The fiber type is multimode with a core and fiber cladding of 50 and 125 microns, respectively.

ADF (ZN) 2Y (SR) 2Y 6 × 4 E9 / 125 - cable for outdoor use [A]. It has two polyethylene shells: an external and an internal one, between which there is a metal armor in the form of a corrugated tape. The fibers are arranged in six tubes of four in each. The inside of the tube, as well as the voids between the tubes, are filled with a water-repellent compound. Kevlar threads and a central non-metallic element are used as strength components. Fiber type - single-mode [E9 / 125] with core size and fiber cladding 9 and 125 µm, respectively.

New standards and technologies

In recent years, several technologies and products have appeared on the market that make it possible to significantly simplify and reduce the cost of using fiber in a horizontal cable system and connecting it to user workstations.

Among these new solutions, first of all, I would like to single out optical connectors with small form factor connectors, plane laser diodes with a vertical cavity - VCSELs (vertical cavity surface emitting lasers) and optical multimode fibers of the new generation OM-3.

It should be noted that the recently approved OM-3 type of multimode optical fiber has a bandwidth of more than 2000 MHz / km at a laser beam length of 850 nm. This type of fiber provides sequential transmission of 10 Gigabit Ethernet data streams over a distance of 300 m. The use of new types of multimode fiber and 850nm VCSEL lasers provides least cost the ability to implement 10 Gigabit Ethernet solutions.

The development of new standards for fiber optic connectors has made fiber optic systems a serious competitor to copper solutions. Traditionally, fiber-optic systems have required twice as many connectors and patch cords as copper systems — telecom sites required a much larger area to accommodate optical equipment, both passive and active.

Small form factor optical connectors, recently introduced by a number of manufacturers, provide twice the port density of previous solutions, since each such connector contains two optical fibers at once, rather than one as before.

This reduces the size of both optical passive elements - crosses, etc., and active network equipment, which makes it possible to reduce the installation costs by four times (in comparison with traditional optical solutions).

It should be noted that the American standards bodies EIA and TIA in 1998 decided not to regulate the use of any specific type of optical connectors with a small form factor, which led to the appearance on the market of six types of competing solutions in this area: MTRJ, LC, VF-45, Opti Jack, LX 5 and SCDC. There are also new developments today.

The most popular miniature connector is the M-TRJ connector, which has one polymer tip with two optical fibers inside. Its design was designed by a consortium of companies led by AMP Netconnect based on the Japan-developed MT multi-fiber connector. AMP Netconnect has already presented more than 30 licenses for this type of MTRJ connector.

Much of the success of the MTRJ connector is due to its external design, which is similar to that of the 8-pin RJ-45 modular copper connector. In recent years, the performance of the MTRJ connector has improved markedly - AMP Netconnect offers MTRJ connectors with keys to prevent erroneous or unauthorized connection to the cable system. In addition, a number of companies are developing single-mode versions of the MTRJ connector.

LC connectors are in high demand in the market of optical cable solutions. The design of this connector is based on the use of a ceramic ferrule with a diameter reduced to 1.25 mm and a plastic housing with an external lever-type latch for locking into the socket of the connecting socket.

The connector is available in both simplex and duplex versions. The main advantage of the LC connector is its low average loss and its rms deviation of only 0.1 dB. This value ensures the stable operation of the cable system as a whole. Standard epoxy bonding and polishing procedures are used to install the LC fork. Today the connectors have found their way into 10 Gbps country receiver manufacturers.

The SCS industry has made its choice in favor of MTRJ and LC connectors. There are also singlemode MTRJ connectors, which feature short installation times. There is no need to use epoxy glue and polish the tips to install the connectors, you just need to clean and chip the fiber, and then install it into the connector.

There are a number of proprietary solutions for use in horizontal cabling systems, among which, for example, 3M's Volition Network Solutions system can be noted. It uses VF-45 connectors.

The VF-45 connector is approximately half the size of an SC duplex connector and does not have a centering lug. It uses V-shaped grooves to align optical fibers, and the connector and plug itself are equipped with a protective shutter that moves horizontally when they are aligned.

In addition to hybrid optical cords with VF-45 connectors on one side and ST, SC or other connectors on the other, 3M recently released the VF-45 plug, designed for field installation and allowing quick termination of cables at consolidation points. In addition, the company offers six color-coded VF-45s with dongles to create security-enhanced optical networks.

Although the VF-45 connectors were originally designed for horizontal fiber optic cabling, they can also be used in backbone networks. ZM also considers one of its major achievements that the current price of a network adapter equipped with a VF-45 connector does not exceed $ 100 (Fig. 5).

Panduit's OptiJack-FJ is another connector designed for fiber-to-the-workplace cabling solutions.

It has two separate ceramic lugs with a diameter of 2.5 mm, and the form factor corresponds to an 8-pin copper RJ-45 connector. The OptiJack-FJ modules can be used with Panduit's MiniCorn receptacles and patch panels.

Thus, SFFC components together with new VCSEL lasers (lasers have the characteristics inherent in traditional laser sources and a low cost comparable to conventional LEDs) make it possible to deliver high speed optical technologies directly to the user's workplace.

Anna FRIZEN, technical consultant for U. I. LAPP GmbH.

(aka fiber optic) is a fundamentally different type of cable compared to other types of electrical or copper cables. Information on it is transmitted not by an electrical signal, but by a light signal. Its main element is transparent fiberglass, through which light travels over huge distances (up to tens of kilometers) with insignificant attenuation.

The structure of the fiber optic cable is very simple and similar to the structure of a coaxial electrical cable, only instead of the center copper wire it uses thin (about 1-10 microns in diameter) glass fiber, and instead of internal insulation, a glass or plastic shell, which prevents light from leaving the glass fiber. In this case, we are dealing with the regime of the so-called total internal reflection of light from the interface of two substances with different refractive indices (the refractive index of the glass shell is much lower than that of the central fiber). The metal braid of the cable is usually absent, since shielding from external electromagnetic interference is not required here, but sometimes it is still used for mechanical protection from the environment (such a cable is sometimes called armored, it can combine several fiber-optic cables under one sheath).

Possesses exceptional characteristics in terms of noise immunity and secrecy of transmitted information. In principle, no external electromagnetic interference is capable of distorting the light signal, and this signal itself, in principle, does not generate external electromagnetic radiation. It is almost impossible to connect to this type of cable for unauthorized eavesdropping on the network, as it requires breaking the integrity of the cable. Theoretically, the possible bandwidth of such a cable reaches 1012 Hz, which is incomparably higher than that of any electrical cables. The cost of fiber optic cable has been steadily decreasing and is now approximately equal to the cost of thin coaxial cable. However, in this case, it is necessary to use special optical receivers and transmitters that convert light signals into electrical ones and vice versa, which sometimes significantly increases the cost of the network as a whole.

Typical signal attenuation in fiber optic cables at frequencies used in local area networks is about 5 dB / km, which is roughly the same as electrical cables at low frequencies. But in the case of a fiber-optic cable, with an increase in the frequency of the transmitted signal, the attenuation increases very slightly, and at high frequencies (especially above 200 MHz) its advantages over an electric cable are undeniable, it simply has no competitors.

However, fiber optic cable also has some disadvantages. The most important of them is the high complexity of installation (when installing connectors, micron accuracy is required, the attenuation in the connector greatly depends on the accuracy of the fiberglass chip and the degree of its polishing). To install the connectors, welding or gluing is used using a special gel that has the same refractive index of light as fiberglass. In any case, this requires highly qualified personnel and special tools. Therefore, most often, fiber optic cable is sold in the form of pre-cut pieces of different lengths, on both ends of which the connectors of the required type are already installed.

Although fiber-optic cables allow for signal branching (for this, special splitters for 2-8 channels are produced), as a rule, they are used for transmission. After all, any branching inevitably weakens the light signal, and if there are many branches, then the light may simply not reach the end of the network.

Fiber optic cables are less durable than electrical cables and less flexible (typical bending radii are around 10-20 cm). It is also sensitive to ionizing radiation, due to which the transparency of the glass fiber decreases, that is, the signal attenuation increases. It is also sensitive to sudden changes in temperature, as a result of which the fiberglass can crack. Currently, optical cables are produced from radiation-resistant glass (they are, of course, more expensive).

Fiber optic cables are also sensitive to mechanical influences (shock, ultrasound) - the so-called microphone effect. To reduce it, soft sound-absorbing shells are used.

Use fiber optic cable only in networks with a "star" and "ring" topology. In this case, there are no problems of matching and grounding. The cable provides perfect galvanic isolation of network computers. In the future, this type of cable is likely to supersede electrical cables of all types, or, at any rate, strongly suppress them. The reserves of copper on the planet are depleting, and there are more than enough raw materials for the production of glass.

There are two different types fiber optic cables:

1. Multimode, or multimode, cable, cheaper but of lower quality;
2. Single-mode cable, more expensive but with better performance.

The differences between these types are associated with different modes of transmission of light rays in the cable.

Singlemode cable almost all beams travel the same path, with the result that they all reach the receiver at the same time, and the waveform is practically not distorted. Singlemode cable has a center fiber diameter of about 1.3 µm and only transmits light at the same wavelength (1.3 µm). The dispersion and signal loss are very insignificant, which makes it possible to transmit signals over a much greater distance than in the case of using a multimode cable. For single-mode cable, laser transceivers are used that use light exclusively with the required wavelength. Such transceivers are still relatively expensive and not very durable. However, in the future, single mode cable should become the main one due to its excellent characteristics.

In multimode cable the paths of the light rays have a noticeable spread, as a result of which the waveform at the receiving end of the cable is distorted. The central fiber has a diameter of 62.5 microns, and the diameter of the outer cladding is 125 microns (this is sometimes referred to as 62.5 / 125). A conventional (non-laser) LED is used for transmission, which reduces the cost and increases the lifespan of the transceivers compared to single mode cable. The wavelength of light in a multimode cable is 0.85 µm. The permissible cable length is 2-5 km. Currently, multimode cable is the main type of fiber optic cable, as it is cheaper and more affordable. The propagation delay of a signal in a fiber optic cable is not very different from that in an electrical cable. Typical latency for most common cables is around 4-5 ns / m.

Optical fiber is the fastest information transmission technology on the Internet today. The structure of an optical cable has certain features: such a wire consists of small, very thin wires, shielded with a special coating, which separates one wire from another.

Light is transmitted along each wiring, which transmits data. An optical cable is capable of simultaneously transmitting data, in addition to an Internet connection, as well as television and a landline phone.

Therefore, the fiber-optic network allows the user to combine all 3 services of one provider, connecting the router, PC, TV and telephone to a single cable.

Another name for fiber optic connection is fiber optic communication. Such communication makes it possible to transmit data using laser beams over distances measured in hundreds of kilometers.

An optical cable consists of the smallest fibers, the diameter of which is thousandths of a centimeter. These fibers carry optical beams that carry data by passing through the silicon core of each fiber.

Optical fibers make it possible to establish connections not only between cities, but also between countries and continents. Internet communication between different continents is supported by fiber optic cables laid along the ocean floor.

Fiber optic internet

Thanks to optical cable, you can set up a high-speed internet connection, which plays a huge role in today's world. Fiber optic wire is the most advanced technology for transmitting data over a network.

Optical cable advantages:

• Durable, high bandwidth, conducive to fast data transfer.
• Data transmission security - fiber optic enables programs to instantly detect unauthorized access to the data, therefore, access to them for intruders is almost impossible.
• High immunity to interference, good noise suppression.
• The structural features of an optical cable make the data transfer rate through it several times higher than the data transfer rate through a coaxial cable. This primarily applies to video and audio files.
• When connecting optical fiber, you can organize a system that implements some additional options, for example, video surveillance.

However, the most important advantage of fiber-optic cable is its ability to establish a connection between objects located at a great distance from each other. This is possible due to the fact that the optical cable has no restrictions on the length of the channels.

Internet connection using fiber optic

The most widespread Internet in the Russian Federation, the network of which operates on the basis of optical fiber, is provided by the provider Rostelecom. How to connect fiber-optic internet?

First, you just need to make sure that the optical cable is connected to the house. Then you need to order an internet connection from your provider. The latter must provide the data that provides the connection. Then you need to configure the equipment.

It is done like this:

The terminal is equipped with a special socket that allows you to connect to a computer and connect the router to the Internet.

In addition, the terminal has 2 additional sockets that allow you to connect an analog home telephone to the fiber-optic connection, and several more sockets are provided for connecting a television.