Fiber optic cable. What is the function of fiber? Types of fiber optic cables. What is fiber optic? — How to connect fiber optic internet Optical fiber cable in the network

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, fiber optic cable is fundamentally different from conventional electrical cables 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.

Attenuation of the light signal when passing through a fiber optic cable 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.

It was told about the most common types of fiber optic cable used in Ukraine. And today - a cable in a section, and in the course of the story - some practical moments of its installation.

We will not dwell on the detailed structure of all types of cable. Let's take some average typical OK:

1. Central (axial) element.
2. Optical fiber.
3. Plastic modules for optical fibers.
4. Film with hydrophobic gel.
5. Polyethylene shell.
6. Armor.
7. Outer polyethylene sheath.

What does each layer represent when viewed in detail?

Central (axial) element

Fiberglass rod with or without polymer sheath. Main purpose - stiffens the cable. Unsheathed fiberglass rods are bad because they break easily when bent and damage the optical fiber located around them.

optical fiber

Optical fiber strands most often have a thickness of 125 microns (about the size of a hair). They consist of a core (through which, in fact, the signal is transmitted) and a glass shell of a slightly different composition, which ensures complete refraction in the core.

In cable marking, the diameter of the core and sheath is indicated by numbers through a slash. For example: 9/125 - core 9 microns, shell - 125 microns.

The number of fibers in the cable varies from 2 to 144, this is also fixed by a number in the marking.

Based on the thickness of the core, fiber optics are classified into single mode(thin core) and multimode(larger diameter). Recently, multimode has been used less and less, so we will not dwell on it. We only note that it is intended for use over short distances. The sheath of multimode cable and patch cords is usually made orange color (single mode - yellow).

In turn, single-mode optical fiber is:

• Standard (marking SF, SM or SMF);
• Dispersion-shifted ( DS, DSF);
• With non-zero shifted variance ( NZ, NZDSF or NZDS).

In general terms, a dispersion-shifted (including non-zero) fiber optic cable is used over much longer distances than a conventional one.

On top of the shell, the glass threads are varnished, and this microscopic layer also plays an important role. Optical fiber without varnish coating damaged, crumbled and broken at the slightest impact. While in lacquer insulation, it can be twisted and subjected to some stress. In practice, fiber optic strands can withstand the weight of the cable on supports for weeks if all other power rods break during operation.

However, do not rely on the strength of the fibers too big hopes- even varnished, they break easily. Therefore, when installing optical networks, especially when repairing existing highways, extreme accuracy is required.

Plastic modules for optical fibers

These are plastic shells, inside of which there is a bundle of fiber optic filaments and a hydrophobic lubricant. There can be either one such tube with fiber optics in the cable, or several (the latter is more common, especially if there are a lot of fibers). Modules perform the function of protecting fibers from mechanical damage and along the way - their association and marking (if there are several modules in the cable). However, it must be remembered that the plastic module breaks quite easily when bent, and breaks the fibers in it.

There is no single standard for the color marking of modules and fibers, but each manufacturer attaches a passport to the cable drum, in which this is indicated.

Film and polyethylene sheath

These are elements of additional protection of fibers and modules from friction, as well as moisture- some types of optical cable contain a hydrophobe under the film. The top film can be additionally reinforced with interweaving threads and impregnated with a hydrophobic gel.

The plastic shell performs the same functions as the film, plus it serves as a layer between the armor and modules. There are cable modifications where it is not available at all.

Armor

This can be either Kevlar armor (woven threads), or a ring of steel wires, or a sheet of corrugated steel:

• Kevlar used in those types of fiber optic cable where the metal content is unacceptable or if you need to reduce its weight.
• Steel wire armored cable designed for underground laying directly into the ground - strong armor protects against many damages, incl. from a shovel.
• Cable with corrugated armor laid in pipes or cable ducts, such armor can only protect against rodents.

Outer polyethylene sheath

The first and practically the most important level of protection. Dense polyethylene is designed to withstand all the loads that fall on the cable, so if it is damaged, the risk of damage to the cable increases significantly. You need to make sure that the shell:

a) Has not been damaged during installation - otherwise moisture getting inside will increase the losses on the line;

b) Do not touch a tree, wall, corner or edge of a structure, etc. during operation, if there is a risk of friction in this place under wind and other loads.

Hello friends! Our guru of the Internet and wireless technologies Borodach has already written about what fiber is (the link to the article will definitely be below). But my colleagues decided that the Blonde should also write on this topic and at the same time add knowledge to her beautiful head. Well, it is necessary - it means that it is necessary! We'll figure out.

Definition for dummies

Optical fibers are the thinnest wires (threads) made of glass or plastic, along which light is transferred due to internal reflection. Optical fiber cable is used as a way to transmit information at high speed over long distances (in the truest sense of the word "at the speed of light"). This is how fiber-optic communication lines (FOCL) are built.

Fact from the history of development in Russia. The first FOCL "St. Petersburg-Aberslund" (a city in Denmark) was laid by Rostelecom (then called Sovtelecom).

I suggest you take a look documentary on this topic:

materials

Glass fiber is made from quartz. This provides the following features:

• High optical permeability - this allows you to broadcast waves of different ranges;
• Minimum signal loss (low attenuation);
• Temperature stability;
• Flexibility.

For the far range, chalcogenide glasses, potassium zirconium fluoride or potassium cryolite are used.

Now the production of optical fiber from plastic is developing. In this case, the core (core) is made of organic glass, and the shell is made of fluoroplastics. disadvantage polymer materials consider low throughput in areas with infrared radiation.

Structure

What is optical fiber made of? This is a thread that is round in section, inside of which there is a core (core), which is covered with a sheath on the outside. To ensure total internal reflection, the refractive index of the core must be higher than the same parameter for the shell. How it works - a beam of light directed into the core is repeatedly reflected from the shell.

The diameter of the fiber optic thread used in telecommunications is 124-126 microns. However, the core diameter may vary depending on the type of fiber (I will talk about this in the next section) and national standards.

1 micron is 0.001 mm. I calculated, it turns out that the diameter is only 0.125 mm.

Types and applications

Optical fiber can be of two types (depending on the number of rays in the fiber - mod):

1. Singlemode. The core diameter is 7-10 microns, light reflection takes place in one mode. Types:

• Standard (dispersion unbiased);
• Dispersion-shifted;
• With non-zero shifted variance.

1. Multimode. The core diameter is 50-62 microns (depending on national standards), the radiation passes through several modes. Classified into:

• Stepped;
• Gradient.

This section is difficult for a simple layman, but if someone wants to understand in more detail, write in the comments. One of the guys will definitely explain everything that was not clear.

The main areas where optical fiber is used are fiber optic communication and fiber optic sensor. Other areas:

• Lighting;
• Image formation;
• Creation of a fiber laser.

As I understand it, the main area of ​​application is the construction of backbones of fiber optic communication lines. Simply put, these are the lines through which the Internet is transmitted in all major cities.

And here is what the educational program for children and adults "Galileo" tells:

Optical cable

So we got to the biggest secret of our time - a fiber optic cable that connects cities and continents and transmits information at the speed of light. At the same time, the Internet enters our apartment through a twisted pair cable, most often from 8 wires. Max Speed will reach a value of 1 Gbps.

Those who are in the subject know that it is not possible to place an 8-core wire in every cable channel. This is the main advantage of fiber optics. Optical cable several times thinner than twisted pair and provides higher speed (up to 10 Gbps).

It seems that providers began to slowly transfer subscribers to optical fiber - that is, "optics" will go not only to the entrance, but also to it to the apartment. The bad news is that you need a special router to use such a cable.

According to the method of installation, optical cable is classified into the following types:

• laid in the ground;
• Conducted through collectors and sewer pipes;
• Conducted underwater;
• Laid in the air (suspended).

Depending on the use and range of the signal, fiber optic cable is:

• Trunk - the creation of long lines over long distances;
• Zonal - organization of a highway between regions;
• Urban - similar to the zone, but the length of the line is not more than 10 km;
• Field - laying both in the air and underground;
• Water - here the name speaks for itself;
• Object - used for a specific site, easy to lay;
• Mounting - multimode gradient fiber is used.

There is also a classification according to the method of execution of the core and the number of fibers in it. I think this is unlikely to be interesting, but if anything, colleagues will tell about it - you just need to write in the comments.

Advantages and disadvantages

Finally, let's look at the pros and cons of fiber optic cable. Let's start with the benefits:

• Low losses with a large length of the relay section;
• Ability to transmit information over thousands of channels;
• Small size and weight;
• High protection against interference and external influences;
• Safety.

And now for the disadvantages:

• Exposure to radiation, due to which signal attenuation increases;
• The susceptibility of glass to hydrogen corrosion, which leads to material damage and deterioration of properties.

You can end there. I hope it was useful, and my story is interesting. Bye everyone!

Buy fiber optic cable from Layta at an attractive price.
For the convenience of customers, the description of the equipment is provided with reviews from other customers, characteristics, certificates, instructions, passports, photographs, accessories.
You can buy fiber optic cable both through the website and by phone.
If you have any questions when choosing, delivery or warranty, you can always consult with specialists by phone.
Delivery is made to Moscow, St. Petersburg, Kazan, Saratov, Rostov, Krasnodar, Stavropol, Yekaterinburg, Novosibirsk, Voronezh, Volgograd and other cities of Russia

It's hard to imagine security system without wires and cables. Their diversity, variations and performance are very diverse, which is why choosing a high-quality fiber optic cable is not so easy. variety of models and specifications allows you to create unique security systems, however, in order to buy a fiber optic cable, you need to understand its features and understand what it is.

fiber optic cable- This is a cable consisting of fiber-type light guides and used as an optical signal transmitter. A feature of this cable option is the ability to transmit a signal over a decent distance without loss of image quality, so fiber optic cables are perfect for video surveillance systems in places with large areas and increased remoteness of cameras from the control center. Also, the fiber optic cable is characterized by increased resistance to interference: even with a significant length of the cable, the signal goes with minimal interference.

The scope of fiber optic cable is so wide that it can rightly be called a leader among analogues. This type of cable is widely used in almost all areas: from standard computer networks to intercontinental lines. Such a wide popularity of the product is due to its excellent performance.

Today, manufacturers offer a huge number of modifications and variations of fiber optic cables, depending on the purpose of their use. If you are going to buy a fiber optic cable, decide on the scope of its application: temperature differences, location inside the building or on the street, maximum loads, interaction with the environment, etc.
Fiber optic cable models are used even under extreme conditions - special purpose fiber optic cable is designed for non-standard option applications: underground or water, as well as in areas with increased risks. The main difference between fiber optic cables lies in the sheath, thanks to which the products can easily cope with their tasks even in non-standard conditions.

Despite the high cost of fiber optic cable (this is due to the high price of fiber optics) and its fragility, the presence of a number of positive qualities made it virtually indispensable. Fiber optic models provide high quality signal, low attenuation and high data rate. All these advantages make it possible to achieve the clearest picture necessary to create a high-quality and efficient video surveillance system.

In the Light company, you can always buy a fiber optic cable on favorable terms and at an attractive price. Competent specialists will select for you suitable model meeting all standards and requirements. Having decided on the model and type of cable, special attention should be paid to its installation. Properly selected and installed equipment is guaranteed to provide you with reliable operation for many years.

A fiber optic system works by transmitting light pulses generated by a light emitter located at one end of the fiber. This system is a structure consisting of a transparent, centrally located core of quartz glass, surrounded by a sheath and a special protective coating.

Below you will find out what functions a fiber-optic cable performs, consider in detail the advantages of fiber, find out what types it is divided into.

Optical fiber - construction

Usage suitable materials as the core and sheath of a fiber optic cable, having different refractive indices, leads to the fact that the light beam travels only in the core. The core material has a higher refractive index and thus there is total internal reflection of light from the cladding to the core. The protective cover is made of thermoplastic materials to protect the shell. Single-mode and multi-mode fibers are distinguished: only single-mode fibers are used in power lines, due to the significant reduction in attenuation, which is important for long lines.

Tasks

The main purpose of using fiber optic cables in the electric power industry is to provide communication between power substations. This is due to the use of modern automation to protect power lines from the effects of a short circuit. Protective automation is located at each power plant, and to ensure its normal operation, a fast connection between stations is required. High-voltage overhead power lines (110 kV) and extra-high voltage (220 and 400 kV) have a significant length. The use of more fiber in power lines makes it possible to lease fiber optic lines to other operators. This allows you to create a global fiber optic network designed for commercial use (Internet, telecommunications, multimedia, etc.).

Video: How does fiber work?

Advantages, types and types of optical fiber

The intensive growth in the use of fiber-optic cables in the world has been going on for more than 40 years. This is due to the many benefits of fiber optics. The most important are: very high bandwidth of a single fiber, low signal attenuation even over very long distances, small size and light weight, complete immunity to radio interference and electromagnetic field. Due to topical environmental issues, important feature fibers is the absence of any environmental impact, which is very important when designing fiber optic lines. These connections are largely reliable, easy to use, safe in the workplace and highly effective, which is why they are becoming more and more popular.

Types of wires with optical fibers in power lines

Fiber optic cables are produced in bundles containing from ten to several hundred fibers in one bundle. Cables with fiber optic cables can be used in power lines as: phase conductors (live) or lightning rods (earthing potential conductors) and self-supporting dielectric (additional cables in a line containing only fiber optic cables). There are several types of conductors associated with optical fibers.
OPGW (Optical Ground Wire - optical ground wire) - lightning rods commonly used in overhead power lines with a voltage of 110 kV.

In terms of design, there are two types of wires:

• wires consisting of one central tube (made of aluminum or stainless steel) containing optical fibers and an outer layer of aluminum alloys,
• hoses with a stainless steel flare, they consist of several steel wires forming veins and an outer layer of aluminum alloys. Optical fibers are placed in a special stainless steel tube and are the core of the cable.

The most important advantages of these cables are as follows:

• the possibility of using in existing lines (in place of conventional steel and aluminum wires type AFL), in most cases without the need to strengthen the structure of the column,
• simple installation, using existing cable,
• reliability and durability.

- fiber optic cables without metal elements. They are made from a centrally located FRP rod-shaped core surrounded by several tubes containing optical fibers.
Between the inner and outer sheath of the cable are very strong aramid fibers, which give ADSS cables adequate mechanical strength.

ADSS cables are characterized by a slight increase in sag. When choosing an attachment point for ADSS cables, it is also necessary to take into account the distribution of the electric field strength between the phase conductors, since in the event of rain or high humidity, the outer sheath is subjected to microdischarges. Placing wires in an area with too large an electric field leads to the rapid destruction of their sheath. The solution to this problem is the use of semiconductor cables, which, due to the high intensity of the electromagnetic field, are usually used in lines with a voltage of no more than 110 kV. With more high voltage special cables are used, made of materials resistant to electric field. When designing the suspension of ADSS cables on existing transmission lines, the additional stress on the bearing structures, and create the appropriate gains.

MASS (Metallic Aerial Self Supporting)) - self-supporting cables made of aluminum steel wire in combination with optical fiber. They are very similar to OPGW cables but are not a lightning rod or an in-line electrical function. For this reason, MASS cables usually hang a little lower than the phase wires.

Special application of optical fibers

Temperature control in cable lines

One interesting application of fiber optic fibers is the DTS (Distributed Temperature Sensing) system used to monitor the temperature of high-voltage cable lines. This method is based on the change in attenuation of special fibers depending on their temperature. Optical fibers are placed in the return conductor of power cables, which are connected to a special device that provides operational monitoring of the temperature of the cable core and violations of the structure in its environment, for example, when working near a cable line (the phenomenon of fiber damping depending on the fiber deformation is used here). This system can be used by network operators in emergency situations when there is a temporary need to load power lines with high current. This information allows the network operator to plan for line shutdown and take appropriate action. repair work in advance. .

Optical fiber - temperature control of phase conductors in overhead lines

A similar solution can be used in overhead power lines. A special optical fiber placed in an OPPC type conductor makes it possible to determine the actual temperature of the phase conductors under given weather conditions. Monitoring allows the dispatcher to dynamically load the line and, in a broader perspective, the so-called intelligent network management or "smart networks".