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

Fiber optic cables, unlike cables with copper or aluminum conductors, use a transparent optical fiber as a medium for signal transmission. The signal here is not transmitted using electric current but with the help of light. This means that practically not electrons are moving, but photons, and, accordingly, 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 almost unhindered for tens of kilometers, while the light intensity decreases slightly.

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

Fiber optic cable device

The 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) dressed in a protective plastic or glass sheath, which provides total internal reflection of light due to the difference in refractive indices at the boundary of two media.

It turns out that the light, on its entire path from the transmitter to the receiver, cannot leave the central core. In addition, light is not afraid of electromagnetic interference, so such a cable does not need electromagnetic shielding, but only needs to be strengthened.

To give the fiber optic cable mechanical strength, special measures are taken - they make the cable armored, especially when it comes to multi-core optical cables that carry several separate light guides at once. Suspended cables require special reinforcement with metal and Kevlar.

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

In a multilayer armored cable, the load-bearing reinforcing cable is made of metal enclosed in a polyethylene sheath. Around it are light-bearing plastic or glass fibers. Each individual fiber is coated with a layer of colored lacquer as a color marking and to protect against mechanical damage. The bundles of fibers 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 reach up to 288 pieces. The tubes are braided with a thread that tightens the film moistened with a hydrophobic gel - for greater damping of mechanical effects. Tubes and central cable are enclosed in polyethylene. Next come Kevlar threads, which practically provide armor to the stranded cable. Then again polyethylene to protect against 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, single mode is more expensive.

It provides the rays passing through the fiber with almost the same path without significant mutual deviations, as a result, all rays arrive at the receiver simultaneously and without distortion of the signal shape. The diameter of the light guide in a single-mode cable is about 1.3 microns, and light with this wavelength 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 single mode. The rays from the transmitter go in it with a spread, and on the side of the receiver there is some distortion in the shape of the transmitted signal. The diameter of the light guide fiber in a multimode cable is 62.5 µm, and the diameter of the outer sheath is 125 µm.

It uses a conventional (rather than laser) LED on the transmitter side (with a wavelength of 0.85 microns), and the equipment is not as expensive as with a laser light source, and the service life of current multimode cables is longer. Cables of this type do not exceed 5 km in length. Typical signal transmission delay time is on the order of 5 ns/m.

Advantages of fiber optic cables

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

Electromagnetic interference directed at 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 over it.

The bandwidth of a fiber optic 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 kilometer.

By itself, fiber optic cable is not expensive, almost the same as thin coaxial cable. But the bulk of the increase in the cost of the finished network still falls on the transmitting and receiving equipment, whose task is to convert the 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 the advantage of the optical medium over traditional electrical conductors - the attenuation increases slightly. And at frequencies above 0.2 GHz, fiber optic cable is clearly out of competition. It is practically possible to extend the transmission distance up to 800 km.

Fiber optic cables are applicable in networks with "ring" or "star" topologies, while the problems of grounding and matching with the load, which are always relevant for electric cables, are completely absent.

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

Disadvantages of fiber optic cables

In fairness, one cannot fail to mention the shortcomings of fiber-optic information transmission systems, the main of which is the complexity of installing systems and high requirements for the accuracy of installing connectors. A micron deviation during connector assembly can lead to an increase in attenuation in it. Here, high-precision welding or a special adhesive gel is required, the light refractive index in which is similar to that in the most mounted fiberglass.

For this reason, the qualification of personnel does not allow for 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. To branch a signal from an optical fiber, specialized splitters are used for several channels (from 2 to 8), but when branching, light attenuation inevitably occurs.

Of course, optical fiber is less durable and less flexible than copper, and bending the fiber to a radius of less than 10 cm is not safe for its safety. Ionizing radiation reduces the transparency of the optical fiber and increases the attenuation of the transmitted light signal.

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

Fiber optic cable (FOC)- cable products on fiber light guides, which are used in communication lines for transmitting information using optical signals (photons). The technology provides signal transmission over long distances with the preservation of its strength and with little interference.

Scope of application

Optical fiber cable is the basis of modern telecommunication networks. 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 a fiber optic cable varies depending on the installation location, design and size of the central core.

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

• for interior lining

Cable products for internal networks (home, office, shopping center, clinic, etc.) 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 durable sheath that is resistant to atmospheric and mechanical influences is used. In the case of a particularly difficult operational situation, the networks are brought into the main channels.

• special purpose cables

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

When choosing an optical cable, the presence of a reinforced sheath is not always important. When laying inside channels and pipes, reinforced protection is not needed. At the same time, when laying in the mail, the fiber optic cable must be protected from rodents, getting wet, and mechanical influences. And when building air networks - from sagging.

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

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

• 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. Such fiber optic wire is used for data transmission inside and between buildings, it is optimal for computer networks. The core diameter may vary. It is made on the basis of a conventional LED.

Cable manufacturers for optical communication lines

In Russia, optical cables are produced by:

• CJSC TRANSVOK, Kaluga region;
• ZAO Samara Optical Cable Company;
• Eurocable 1 LLC, Moscow region;
• JSC "ELECTRIC CABLE "KOLCHUGINSKY PLANT";
• Plant "Yuzhkabel", Ukraine;
• ZAO OFS Svyazstroy-1 VOKK, Voronezh;
• Cable plant "NPP Starlink";
• Plant "Inkab";
• Plant "Cableelectrosvyaz";
• Plant "MinxKabel" and many others.

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

Installation

Laying networks is allowed only by trained personnel. High price Supplies and installation work, as well as high costs for correcting defects, require strict adherence to the regulations. Splicing uses optical couplers to ensure signal speed and purity are maintained.

There are the following laying methods:

• Suspended (air laying).
• IN open ground in protective sleeves.
• inside cable channels.

An order is issued for work indicating the category of tolerance to delimit responsibility for the installation result.

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:

• The maximum degree of signal security.
• Minimum losses.
• High data transfer rate (from 1 to 10 Gbps at a distance of 1 km).
• High throughput FOC.
• Small dimensions.

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

Where to buy fiber

You can buy a fiber optic cable and mounting systems for it at Tekhkabelsistems LLC.

To buy an optical cable, place an order at e-mail or phone. The manager will provide a selection of products of the required range.

We work with regions and accept orders from companies with any form of payment. 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 company's specialist will calculate the total cost.

At present, fiber-optic communication lines are firmly occupying their positions and are being intensively developed. The replacement of cables with copper conductors by fiber-optic cables is proceeding at a rapid pace in all sections of networks. Traditional communication cables with copper conductors are being replaced by fiber-optic waveguides, in which the information carrier is electromagnetic waves of the infrared range. The transmission of information 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 completely reflected and propagates along the waveguide. Due to the growing demands on telecommunications networks, the use of fiber optic technology is becoming indispensable.

In order to design the route of a fiber-optic communication line and select the desired type of cable, it is necessary to know the operating conditions, the design of the cable and its technical specifications. The demand for fiber-optic communication line components is constantly increasing. Growth dynamics is observed not only in the segment of backbone networks, which are being built by telecom operators. The stable increase in the number of optical installations is also noticeable in the field of structured cabling, which is explained, first of all, by the development information technologies. Already today, the foundation is being laid for building high-speed optical transmission lines with the ability to operate at a speed of 10 Gbit / s. 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 designs focused on various conditions applications (laying inside buildings, in telephone ducts or in the ground, optical cable can be laid on supports railways, on power lines, in sewer and water pipes, along riverbeds and lakebeds, along highways, along with power cables.

For many applications, fiber optics is preferred due to 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 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, which are common, for example, in power plants or railways, are gone. Their same property eliminates the risk of damage to equipment caused by current surges from lightning, etc.
• Ease of work on laying, splicing and confectioning.
• The absence of crosstalk and mutual interference, which improves the quality of data transmission.
• Small dimensions and minimum weight (up to 2.2 mm outer diameter and weight 4 g/m for polymer optical fiber, SIMPLEX simplex version). Extremely small sizes of optical fibers and fiber optic cables allow you to breathe a second life into crowded cable channels. For example, one coaxial cable takes up as much space as 24 optical cables, each of which can supposedly carry 64 video channels and 128 audio or video signals simultaneously.
• Possibility of laying over long distances.
• The highest bandwidth of any transmission medium, the wide bandwidth of optical fiber allows you to simultaneously transmit high-quality video, audio and digital data over a single 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, such as highway or railway surveillance systems, where repeaterless sections of 20 km are not uncommon.
• A never-ending link, by simply replacing the terminal equipment rather than the cables themselves, fiber optic networks can be upgraded to carry more information. On the other hand, part or even the entire network can be used for a completely different task, for example, combining a local area network and a closed-circuit TV system in one cable.
• Long service life.

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

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

Most cables are specially designed for flexible installation in drag chains.

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

Matching optical connectors, tools and pre-assembled 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, fiber optic cables with (POF) find their application:

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

Typical applications for fiber optic cables with (GOF)

Designed for use 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 (Metropolitan Area Networks) technology;
• in networks built using WAN technology (Wide Area Networks).

Basic structural elements of fiber optic cables

There are several main groups structural elements: optical fibers with protective coatings, optical modules, cores, power elements, hydrophobic materials, shells and reinforcement. Depending on the purpose and conditions of use, fiber-optic cables have certain designs.

Optical fiber (OF) is very sensitive to external influences: mechanical pressure and bends, temperature, humidity. To protect against them, a coating is necessarily applied to the OV. The standardized nominal diameter of an optical fiber is 250 µm. In order to identify the OM, a layer of paint 36 µm thick is applied to the coating. The reliability of the connection of the dye with the coating is ensured by intense ultraviolet irradiation.

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

An optical fiber consists of a high refractive index core (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 by successive total internal reflections at the interface between the core and the cladding; its behavior is in many respects similar to that as if it got into a pipe, the walls of which are covered with a mirror layer. However, unlike a conventional mirror, which reflects rather inefficiently, total internal reflection is essentially close to ideal - this is their fundamental difference, allowing light to propagate along the fiber over long distances with minimal loss.

In turn, the light guides differ depending on the refractive index profile in the direction from the center to the periphery in the cross section of the light guide. The fiber in (Fig. 2, a) is called a step-index and multi-mode fiber, 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 through the fiber, and therefore different modes have different transmission delays as they travel from one end of the fiber to the other. The result of this phenomenon limiting the maximum frequency that can be effectively transmitted for a given fiber length increasing either the frequency or the fiber length beyond the limits essentially results in the merging of successive pulses, making them indistinguishable. 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 = 15 MHz * km). Attempting to transmit a signal over a longer distance will result in a progressive loss of high frequencies.

Single-mode fibers, as they are called, (Fig. 2b) are very effective at reducing dispersion, and the resulting bandwidth many GHz * km makes them ideal for telephone and telegraph networks common use(PTT) and cable TV networks. Unfortunately, a fiber of such a small diameter requires a powerful, precision-coupled, and therefore relatively expensive laser diode emitter, which makes them less attractive for many short-haul CCTV applications.

Ideally, a fiber with the same order of bandwidth as a single-mode fiber, but with a diameter similar to a multimode fiber, is required to allow the use of low-cost LED transmitters. To some extent, these requirements are met by a multimode fiber with a gradient change in the refractive index (Fig. 2c). It resembles the stepped index multimode fiber discussed above, but its core index is non-uniform—it fluctuates from a maximum value at the center to lower values ​​at the periphery. This leads to two consequences. First, the light travels along a slightly curving path, and second, and more importantly, the differences in propagation delay between modes are minimal. This is because the high modes entering the fiber at a high angle and traveling 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 travel faster. than lower-order modes remaining near the fiber axis, 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, consequently, the transmission conditions are more favorable.

However, graded index multimode fibers are not ideal, but they still show very good bandwidth. Therefore, in most closed-circuit TV surveillance systems of short and medium length, the choice of this type of fiber is preferable. In practice, this means that bandwidth is only occasionally a parameter that should be taken into account.

However, this is not the case for damping. The optical signal attenuates in all fibers, at a rate that depends on the wavelength of the light source transmitter. There are three wavelengths at which the attenuation of an optical fiber is usually minimal, 850, 1310 and 1550 nm. These are known as transparency windows. For multimode systems, the 850 nm window is the first and most commonly used (least cost). At this wavelength, good quality graded multimode fiber exhibits an attenuation on the order of 3 dB/km, which makes it possible to implement communications in a closed TV system at distances in excess of 3 km.

At 1310 nm, the same fiber shows an even lower attenuation of 0.7 dB/km, thus allowing a proportionate 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 you to create links over 50 km long. 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 ​​in different transparency windows is quite significant, especially in multimode fibers. Table 1 clearly illustrates the advantage of single-mode fibers over multi-mode ones.

To ensure stable operation of optical fibers 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 OF shell after its drawing, protects the OF surface from damage and gives it additional mechanical strength. The following are used as a secondary coating of OV: a tube with OV freely placed in them with a primary protective coating; continuous polymer coating; a tape element in which the OV with a primary protective coating is placed. In a tubular element (tube), which plays the role of a secondary protective coating, freely placed OF with a primary protective coating is usually laid without twisting or by twisting around the central strength element. Multimode fibers are easier to manufacture, easier to introduce light beams into, and easier to splice.

Multimode fibers are characterized by a frequency bandwidth expressed in megahertz. In the specifications, it is customary to indicate not the bandwidth, but the so-called broadband coefficient inherent in this type of fiber, in megahertz multiplied by kilometers (MHz x km). For a given bandwidth factor (let's denote it S), the bandwidth AF will depend on the length of the line or its regeneration section of modifications AF=S. For 50/125 multimode fibers, the specified S values ​​are 4001500 MHz*km. For a 10 km line, the bandwidth is 40150 MHz. The longer the line, the smaller the frequency bandwidth and, consequently, the smaller the amount of information transmitted.

Ideally, only one wave propagates through single-mode fibers. They have a significantly lower attenuation coefficient (depending on the wavelength by 24 and even 710 times) compared to multimode ones and the highest bandwidth, since the signal is almost not distorted in them (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 is subject to different requirements. The cable that is used outdoors, first of all, must be protected from atmospheric influences, such as sunlight, moisture, temperature changes. Rodent protection is required for cable intended for laying in cable wells. If the cable is suspended between transmission towers, its mechanical strength is important. When choosing a cable, the main 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 a fiber-optic cable. At each of these stages, the cable is exposed to mechanical, atmospheric and other influences that can be dangerous for the fiber. Note that here we are not talking about the physical destruction of the optical fiber.

The most common material used to make the outer sheath of fiber optic cables is polyethylene. It has both excellent physical parameters (great strength, good wear resistance, resistance to ultraviolet radiation, oxidation and other chemical attack), 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 ambient temperature changes.

Particular attention should be paid to fiber optic cables, the sheaths of which meet the requirements fire safety. The basis for the manufacture of the corresponding casings is polyethylene, and the necessary 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-combustible sheath that does not emit halogens in a fiber-optic cable significantly increases its cost, but when laying a 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 allowable stretching of a fiber-optic cable, power elements must be introduced into its design. Tensile strengths of 1000-2000 N (Newtons) can be achieved using Kevlar or glass yarns.

As a rule, this indicator is quite enough for general purpose cables. The threads can form a dense layer, or they can intertwine. It is believed that Kevlar threads provide a 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 is used. Additional power elements can be dielectric or metallic. The design with a central strength element is typical for a cable with a large number of fibers, which are placed in groups around the strength element. A high permissible breaking force in special types of cables, in which this value must be in the tens of kilonewtons, is achieved using steel bars. In such cables, optical fibers are often located not in thermoplastic, but in steel gel-filled tubes. Tensile performance characterizes the maximum force that can be applied in the longitudinal direction of the cable and at which there will be no change in the characteristics of the optical fiber. When a cable is stretched, first of all, the sheath itself is affected, and only then - on the optical fiber.

As a result of changes in ambient temperature, a natural increase or decrease in the length of the cable occurs. Therefore, the group of these characteristics also includes the temperature range in which the cable can be stored, operated and installed.

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. Shock load (Impact) characterizes the protection of the cable from shock.

The maximum cable bend (Cable bend) is another important parameter that characterizes the maximum permissible radius of curvature of the cable laying. It must be taken into account when it comes to laying fiber optic cables, 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 optical fibers in the cable may be violated.

Torsion determines 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 allowable twist 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 a 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 sheath;
• absence of metal elements.

By far the most important feature of indoor cable is its 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 flame. This implies that these properties are possessed not only by the outer shell, but also by the internal elements of the structure. These requirements are met by a cable with a dense buffer (Tight-Buffer), in which each fiber is additionally enclosed in a 900 micron sheath. This sheath provides sufficient protection against the ingress of moisture 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 this type of cable is recommended for indoor use is that the gel can become a fire propagation medium inside the cable sheath, even if the outer sheath itself does not support combustion. Another reason is a phenomenon sometimes referred to as Axial Migration, which can be translated as "gel overflow".

If gel-containing cable is used to interconnect network segments, there is a high probability that gel will be in the fiber optic cross panel of the lower floor in summer, and the consequences of this can be dire. Instead of the leaked water-repellent composition, moisture can condense in the tube with the fiber, which degrades the performance of the optical fiber. Such a problem arises if the cable is located, for example, in an unheated mine.

In addition, this may lead to a change in 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 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 is straightened 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, in the warm season as a result of a 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, consequently, the reliability of the fiber-optic communication line as a whole.

For cable that is used indoors, it is preferable to install connectors directly on the fiber. In this case, additional fastening is provided for a dense buffer with a diameter of 900 μm, which, to some extent, makes it possible to remove possible stresses from the optical fiber.

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

Outdoor cable

Types of fiber optic cables for outdoor installation are very diverse today, due to the operating conditions and methods of their installation. Such cables can be 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 select cables that are suspended in an open space between poles on a carrier 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 shell must reliably perform its protective functions not only at low or high temperatures, but also at frequent temperature changes.

However, rodents for cable that is laid in telecommunications sewers can become an even greater problem. Metal or non-metal armor, a dense layer of fiberglass filaments - these are the ways to solve this problem. To reduce the frictional force when pulling a cable into 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 ingress, with the expectation that cable ducts may be flooded with water. In this case, a cable is best suited, in which the optical fibers are placed in gel-filled thermoplastic tubes. If there is only one such tube in the cable, then it is called Uni Tube, if there are several tubes - Multi Tube.

Each type of cable has its 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 the installation of welded joints, into which the fiber-containing tube is inserted, is most often designed for only 12 fibers. In addition, fiber optic connectors are also often arranged in groups of 12 in cross panels, back boxes. Therefore, if you need to use a 16-core cable, it is better to choose a Multi Tube, in which each of the four tubes contains four fibers. To save round shape cable, together with 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 a Multi Tube cable, tubes with fibers are placed around a central strength member. Such a cable has a larger allowable stretch than the Uni Tube. Naturally, it is heavier and has a larger cross section. For digging into the ground, this is not of decisive importance, but when such a cable is pulled into telecommunication sewers, it can directly depend on the diameter of the cable being laid. From an economic point of view, the Uni Tube cable is preferable.

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 sleeves that are required for splicing optical fibers. Let us immediately note 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 a 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 has to be constantly bent, stretched, twisted. All these mechanical effects can cause the formation of microcracks in the optical fiber, which can be harmful only after a few years.

In addition, when tightening large lengths of cable along wells, the outer sheath can be worn out or scratched so much that it loses its protective functions. Therefore, the cable length recommended 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 it from the drum and tighten another 1 km in the other direction. The result will be a segment 2 km long, but only highly qualified specialists can perform such work.

If it is necessary to dig the cable into the ground, rodent protection and preservation of mechanical strength should be taken into account in the first place, as well as the influence of ultraviolet radiation, the presence of a smooth sheath and operating conditions at especially 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. Rodent protection can be equally implemented in each of them, but moisture protection in Multi Tube will be much more effective if the space between the fiber-containing tubes is additionally filled with a hydrophobic composition. In addition, in the Multi Tube cable it is possible to achieve a greater value of the allowable longitudinal stretching, since in the cable structure, in addition to Kevlar or glass fibers, there is also a central strength element.

Optical cables for submarine extended communication lines

Submarine extended fiber-optic communication lines are connected primarily with international lines. Optical cables for extended underwater systems are structurally complex and labor-intensive to manufacture. These cables must contain elements that protect optical fibers from moisture and atomic hydrogen. Cables should be produced in large construction lengths, and, on the construction length of the cable, all optical fibers should not have welds.

In the operating wavelength range, the fibers should have low values ​​of the attenuation coefficient, chromatic and polarization-mode dispersion. Poe to that in modern conditions Fibers with nonzero shifted dispersion are chosen as optical fibers of submarine cables.

Submarine optical cables are distinguished by high values ​​of mechanical parameters of stretching and crushing. Typically, the gradation of these cables in terms of mechanical parameters involves the manufacture of cables for coastal laying (with highest values mechanical parameters), cables for the sea 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.

Optics "horizontally"

As the requirements of new network applications increase, the use of fiber optic technologies in structured cabling systems is becoming increasingly important. What are the advantages and features of using optical technologies in a horizontal cable subsystem, as well as at user workplaces?

The main advantages of optics include the largest bandwidth of all possible transmission media, including copper twisted and coaxial cables, as well as the greatest 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. A typical multimode fiber designed for LAN use today has more than 500 MHz bandwidth per kilometer. Since existing SCS standards define the length of horizontal optical wiring from the floor distribution point to the subscriber outlet at 100 m, each such connection provides a bandwidth of several GHz. Recent advances in multimode fiber technology enable even higher transmission rates

So, fiber has characteristics that far exceed the requirements of today's Ethernet speed standards (100 Mbit / s) for connecting workplaces, and allows you to easily switch to new data transfer protocols, such as, for example, 1 and 10 Gigabit Ethernet or high-speed ATM.

Speaking about the possibilities of modernization, it should be noted that the properties of an optical fiber are practically independent of the data transfer rate in the network, since there are no mechanisms (for example, crosstalk) that lead to degradation of the properties of an optical fiber with an increase in the speed of network protocols. Once the optical fiber is installed and tested to 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, and even more. Only one transmission medium in SCS satisfies these requirements optics. Optical cables have been used in telecommunications networks for more than 25 years, and more recently they have also found wide application in cable television and LANs.

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

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

The use of optical fiber in the workplace will allow in the future with minimal cost migrate to new network protocols such as Gigabit and 10 Gigabit Ethernet. This is possible thanks to a number of recent advances in fiber optic technology:

• multimode optical fiber with improved optical characteristics and bandwidth;
• optical connectors with a small form factor, which require less space and less cost during installation;
• Planar laser diodes with a vertical cavity provide data transmission over long distances at low cost.

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

Standard designation for fiber optic cables

Almost all European manufacturers mark 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 a fiber optic cable.

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

A/IDQ(ZN)(SR)H 1×8 G50/125 designates a cable for both outdoor and indoor applications. The fibers are housed in a central tube filled with a water-repellent compound. Kevlar or glass threads in metal corrugated armor. Outer sheath LSZH, low smoke, does not emit halogens during combustion [H]. The tube is one with eight fibers. Fiber type multimode with a core size and a 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: outer and inner, between which there is a metal armor in the form of a corrugated tape. The fibers are arranged in six tubes, 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 power components. Fiber type single-mode [E9/125] with a core size and a fiber cladding of 9 and 125 µm, respectively.

New standards and technologies

In recent years, several technologies and products have appeared on the market that make it much easier and cheaper to use optical fiber in a horizontal cable system and connect it to user workplaces.

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

It should be noted that the recently approved type of multimode optical fiber OM-3 has a bandwidth of more than 2000 MHz/km at a laser beam length of 850 nm. This type of fiber provides serial transmission of data streams of the 10 Gigabit Ethernet protocol over a distance of 300 m. The use of new types of multimode fiber and 850nm VCSEL lasers provides the lowest 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 have required much more floor space to house optical equipment, both passive and active.

Small form factor optical connectors, recently introduced by a number of vendors, offer twice the port density of previous solutions because each connector contains two optical fibers instead of just one.

At the same time, the size of both optical passive elements (cross-connects, etc.) and active network equipment are reduced, which makes it possible to reduce installation costs by four times (compared to traditional optical solutions).

It should be noted that the American standardization bodies EIA and TIA in 1998 decided not to regulate the use of any particular 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 at once: MTRJ, LC, VF-45, Opti Jack, LX 5 and SCDC. Also today there are new developments.

The most popular miniature connector is the M-TRJ type, which has a single polymer ferrule with two optical fibers inside. Its design was developed by a consortium of companies led by AMP Netconnect based on the multi-fiber MT connector developed in Japan. AMP Netconnect has now issued over 30 licenses for this type of MTRJ connector.

The MTRJ connector owes much of its success to its external design, which is similar to that of the RJ-45 8-pin modular copper connector. The performance of the MTRJ connector has improved markedly in recent years AMP Netconnect offers keyed MTRJ connectors to prevent erroneous or unauthorized connections to the cabling system. In addition, a number of companies are developing single-mode versions of the MTRJ connector.

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

The connector is available in both simplex and duplex versions. The main advantage of the LC connector is the low average loss and its standard deviation, which is only 0.1 dB. This value ensures stable operation of the cable system as a whole. To install the LC plug, use the standard gluing procedure on epoxy resin and polishing. Today, connectors have found their way into 10 Gb/transceiver manufacturers.

The SCS industry has made its choice in favor of MTRJ and LC connectors. There are also single-mode MTRJ connectors, which feature a short installation time. There is no need to use epoxy and polish the ferrules to install the connectors, just clean and cleave the fiber and then install it into the connector.

There are a number of proprietary solutions for use in horizontal cabling systems, such as 3M's Volition Network Solutions. It uses VF-45 type connectors.

The VF-45 connector is about half the size of the duplex SC connector and does not have a centering lug. To align the optical fibers, it uses V-grooves, and the connector itself and the plug are equipped with a protective shutter, which shifts in the horizontal direction when they are combined.

In addition to hybrid optical cords that have 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 variants of VF-45 with color coding and security keys to create optical networks with increased security.

Although VF-45 connectors were originally designed for horizontal fiber optic cabling, they can also be used in backbone networks. 3M also considers one of its major achievements the fact that at present the price of a network adapter equipped with a VF-45 connector does not exceed $100 (Fig. 5).

Another connector for fiber-to-the-desk cabling solutions is Panduit's OptiJack-FJ.

It has two separate 2.5mm ceramic ferrules and is shaped like an 8-pin copper RJ-45 connector. OptiJack-FJ modules can be used with Panduit MiniCorn outlets and patch panels.

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

Anna FRIESEN, technical consultant U. I. LAPP GmbH.

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

The structure of the fiber optic cable is very simple and similar to the structure of the coaxial electrical cable, only instead of the central copper wire here, thin (1-10 microns in diameter) fiberglass is used, and instead of internal insulation, a glass or plastic shell is used to prevent light from escaping the glass fiber. In this case, we are dealing with the regime of the so-called total internal reflection of light from the boundary 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).

It has exceptional characteristics in terms of noise immunity and secrecy of transmitted information. No external electromagnetic interference is in principle capable of distorting the light signal, and this signal itself does not fundamentally generate external electromagnetic radiation. It is practically impossible to connect to this type of cable for unauthorized network eavesdropping, as this requires breaking the integrity of the cable. Theoretically 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 is constantly decreasing and is now approximately equal to the cost of a thin coaxial cable. However, in this case, it is necessary to use special optical receivers and transmitters that convert light signals into electrical signals 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 approximately the same as that of electric 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 over 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 (micron precision is required when installing connectors; the attenuation in the connector strongly depends on the accuracy of fiberglass cleavage and the degree of its polishing). To install the connectors, welding or gluing is used using a special gel that has the same light refractive index 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, at both ends of which connectors of the desired type are already installed.

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

Fiber optic cable is less durable than electrical cable and less flexible (typical allowable bend radius is about 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 fiberglass can crack. At present, optical cables made of radiation-resistant glass are produced (they cost, of course, more expensive).

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

Fiber optic cable is used only in networks with a star and ring topology. There are no problems of matching and grounding in this case. The cable provides ideal galvanic isolation of network computers. In the future, this type of cable is likely to supplant all types of electrical cables, or at any rate to greatly displace them. Copper reserves on the planet are depleted, and there are more than enough raw materials for glass production.

There are two various types fiber optic cables:

1. Multi-mode, or multi-mode, 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 passage of light rays in the cable.

In single mode cable virtually all beams travel the same path, so they all reach the receiver at the same time, and the waveform is virtually undistorted. A single-mode cable has a central fiber diameter of about 1.3 µm and only transmits light at the same wavelength (1.3 µm). Dispersion and signal loss are very small, which allows you 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, using light only with the required wavelength. Such transceivers are still relatively expensive and not very durable. However, in the future, single-mode cable should become mainstream due to its excellent characteristics.

In multimode cable the paths of the light rays have a noticeable spread, as a result of which the signal shape 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 sheath 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 life of the transceivers compared to a single-mode cable. The wavelength of light in a multimode cable is 0.85 µm. The permissible cable length reaches 2-5 km. Currently, multimode cable is the main type of fiber optic cable, as it is cheaper and more affordable. The propagation delay in a fiber optic cable is not much different from the delay in electrical cables. Typical delay for most common cables is around 4-5 ns/m.

Optical fiber is the fastest technology for transmitting information on the Internet today. The structure of an optical cable is distinguished by certain features: such a wire consists of small, very thin wires, protected by a special coating that separates one wire from another.

Each wire carries a light that transmits data. An optical cable is capable of transmitting data simultaneously, in addition to an Internet connection, as well as television and a landline phone.

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

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

An optical cable is made up of tiny fibers, the diameter of which is thousandths of a centimeter. These fibers carry optical beams that carry data as they pass through each fiber's silicon core.

Optical fibers make it possible to establish a connection not only between cities, but also between countries and continents. Communication over the Internet between different continents is maintained through fiber optic cables laid along the ocean floor.

fiber optic internet

Thanks to the 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 data transmission over the network.

Advantages of optical cable:

• Durability, high bandwidth, conducive to fast data transfer.
• Data transmission security - fiber allows programs to instantly detect unauthorized access to data, so access to them for intruders is almost excluded.
• High anti-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 files and audio files.
• When connecting fiber, you can organize a system that implements some additional options, such as video surveillance.

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

Internet connection using fiber optics

The most common Internet in the Russian Federation, the network of which operates on the basis of 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 the provider. The latter must report 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 jacks that allow you to connect an analog home telephone to the fiber optic connection, and several more jacks are provided for connecting television.