What is fiber for what it is used. What is fiber-optic internet and what is its difference. Suspended cable cores are different. According to their type, cables are divided into

Talked about the most common types of fiber optic cable used in Ukraine. And today - a cross-section of the cable, 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 cables. Let's take some averaged typical OK:

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

What does each layer represent when examined in detail?

Central (axial) element

Fiberglass rod with or without polymer sheath. The main purpose is stiffens the cable... Unshelled fiberglass rods are bad because they easily break when bent and damage the fiber around them.

Optical fiber

Optical fiber strands are most often 125 microns thick (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, providing full refraction in the core.

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

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

Depending on the thickness of the core, the optical fiber is subdivided into singlemode(thin core) and multimode(larger diameter). V recent times multimode is 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 patchcords is usually made orange(single mode - yellow).

In turn, single-mode optical fiber can be:

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

V general outline- dispersion-shifted fiber optic cable (including non-zero) is used for much longer distances than conventional one.

The glass filaments are coated with varnish on top of the shell, and this microscopic layer also plays an important role. Fiber optic without varnish is damaged, crumbled and broken by the slightest impact. While in lacquered insulation it can be twisted and subjected to some stress. In practice, fiber-optic filaments can withstand the weight of the cable on the supports for weeks if all other power rods break during operation.

However, you should not place too high hopes on the strength of the fibers - even when varnished, they break easily. Therefore, when installing optical networks, especially when repairing existing highways, the utmost care is required.

Plastic modules for optical fibers

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

There is no one 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 the elements of the additional protection of fibers and modules from friction, as well as moisture- some types of optical cable contain a hydrophobic under the film. The film on top can be additionally reinforced with interlacing of threads and impregnated with a hydrophobic gel.

The plastic shell performs the same function as the film, plus serves as an interlayer between the armor and the modules. There are cable modifications where there is none at all.

Armor

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

• Kevlar it is used in those types of fiber optic cable where the metal content is unacceptable or if it is necessary to reduce its weight.
• Steel Wire Armor Cable intended for underground laying directly into the ground - strong armor protects against many damages, incl. from the shovel.
• Corrugated cable laid in pipes or cable ducts, such armor can only be protected from 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) Was not damaged during installation - otherwise moisture getting inside will increase line losses;

b) Not touched during operation on a tree, wall, corner or rib of the structure, etc., if there is a risk of friction in this place under wind and other loads.

Despite the fact that many have heard about the existence of optical fibers and their use for high-speed information transfer, very few people know what they are and how they transmit data.

Even the simplest optical cable has a rather complex structure. In the middle of it there is a bundle of thin optical fiber wires isolated from each other, while each fiber is in a sheath and has a special insulating coating. All fibers are drawn inside a steel protective tube. On top of the tube there is a braid made of copper current-carrying conductors, covered with a layer of copper foil. The next layer is dielectric insulation, most often made of polyethylene. The uppermost layer is armor-plating to ensure protection of the cable from mechanical damage.

Fiber optic cable device

By itself, an optical fiber is a plastic or glass thread capable of conducting light pulses, and a variable wavelength and refractive index of the light beam provides the transfer of the necessary information.

Optical fiber types

Optical fibers are classified according to the number of modes or rays propagating along the fiber. Distinguish:

• single-mode fiber with a diameter of 7-9 microns;
• multimode fiber with a diameter of 50 or 62.5 microns.

In addition, optical fibers are subdivided into conductors with a gradient refractive index and a stepped profile of the distribution of refractive indices.

Fiber Optic Benefits

The main advantage of optical fiber is its high level of bandwidth compared to coaxial cable. Large data transfer rates over long distances are accompanied by high level protection against external interference and noise reduction. At the same time, the use of fiber provides reliable data protection against unauthorized access. Connecting a cable with optical fibers allows for the simultaneous operation of several systems at once, for example.

And the internet over fiber optic cable is last change way of transferring data around the world. It is much faster than regular cable, faster than dial-up, and can carry large amounts of data, often reaching several terabytes of data transfer quite easily.

Before fiber: DSL and cable

Digital Subscriber Line (DSL) used existing telephone lines for data transmission, which were usually made of copper. DSL is slow, old, and has largely been phased out in favor of cable, but it remains in some rural areas. The average speed for DSL is around 2 Mbps.

Cable internet uses coaxial cable, also made of copper, and usually comes with the same cables that are used to control the television network. This is why many internet service providers offer bundled TV subscription plans and internet access. Average cable speeds vary, but range from 20 Mbps to 100 Mbps.

Optical fiber

Fiber optic cables use small glass fibers to transmit data using pulsed light. Light travels in the same way as electricity through copper wire, but the advantage is that fiber cables can transmit multiple signals at the same time. They are incredibly small, which is why they are often bundled into larger cables called “fiber optic trunk cables,” each containing multiple fiber lines. Fiber cables contain a huge amount of data, and the average speed you will see at home is around 1 Gbps (often referred to as "gigabit internet").

Fiber trunk cables form the bulk modern internet and you will see their benefits even if you don't have a "fiber internet". This is because Internet Exchange Points (IXPs) - the switching and routing stations that connect your home to the rest of the world - use fiber backbones to connect to other IXPs.

But when it comes time to connect all the houses in the city to your local IXP (a term commonly referred to as "last mile"), your ISP will usually use a traditional coaxial cable for your home. This option becomes the bottleneck for your internet speed. When someone says they have “fiber optic internet,” they mean that the connection from their home to the IXP also uses fiber, excluding the speed limit of copper.

Fiber Limitations

There is a reason why fiber optic internet is not publicly available. Fiber is much more expensive to run and does not justify the cost when cable lines are often already available. For most people, the 20-100 Mbps speed they get on cable is sufficient, as most downloads from the Internet will not exceed this connection anyway.

And while fiber is definitely better than copper, you won't see an increase in actual download speeds due to limitations on the server you're downloading from. An app like Steam downloading a 10GB game seems to only take a few seconds on a 1000Mbps fiber connection, but in reality you get maximum speed 50 Mbps from Steam servers.

Optical communication lines are gradually replacing conventional copper wires for transmission over long distances, which significantly reduces the cost of line maintenance.

To understand how fiber optic cable works, imagine an incredibly long, several kilometers long, flexible plastic drinking straw. Now imagine that the inner surface of this mega straw is mirrored and you are looking into it from one side. Several kilometers away, at the other end, your friend is shining inside a straw. Due to the fact that the inner surface of the straw is a perfect mirror, the light from the flashlight is reflected many times from the walls of the straw (even in the places where it bends) and you can see it through the hole at its other end. If your friend begins to send you ordered light signals through this straw, for example, using Morse code, then he will be able to communicate with you from a distance. This is the basic principle of fiber optic cable operation.

Of course, it is possible to make a cable from tubes with a reflective surface, but it will be extremely difficult to turn the inner surface into a perfect mirror. Therefore, a fiber-optic cable, or fiber-optic cable, is made of glass. Glass has incredible transparency, so it is capable of transmitting light over great distances. Imagine an ordinary window glass several kilometers thick - it will still be transparent. Only in optical fiber is the thickness of glass comparable to that of a human hair, and this glass filament is covered with two layers of plastic.

By covering the glass with plastic, you have the equivalent of a mirror around the glass strand. This mirror creates a total internal reflection, as if it were created by the mirror coating of our straw, which you imagined earlier. Light travels along optical fibers, reflecting inside at very small angles, and completely stays inside.

At one end of the optical cable is installed, which is included to transmit each bit of information. Modern fiber optic systems with a single laser are capable of transmitting billions of bits per second by turning the laser on and off several billion times every second. Latest systems with several lasers of different colors, they are capable of transmitting several types of signal at once over one fiber.

Modern fiber optic cables are capable of transmitting a signal over a distance of about 100 kilometers. Approximately every 70-100 kilometers, it is necessary to install special equipment that relays the signal further to the next segment of the fiber-optic line.

And a dozen years ago and at the end of 2013, the optical fiber produced by the industry is standardized and has many types and subtypes. The main types of OV are considered on the pages
Optical fiber types and standards
Optical fiber types

The most drastically different fibers multimode and singlemode.

The theory of transmission along them is discussed on the pages Modal propagation in fibers. The number of mods. Formula. Multimode stepped and stepped refractive index fibers

By appearance optical fibers are no different. That is, without the appropriate devices, it is impossible to figure out which fiber optic fell into your hands. The appearance, color, and some properties of optical fibers are given by a special coating. Several OB sizes are standardized.

250 microns the same glass covered with lacquered insulation. Varnish is usually used in different colors, and in addition to insulating properties, the color of the fiber determines its conditional number in the module. (Color counting of fibers, identification by color in optical cables). The lacquer finish provides additional resistance to bending. This fiber is similar to fishing line and can withstand bends with a radius of 5mm (see photo)

900 μm optical fiber in a buffer polymer coating. Used in making cords and connecting fiber optic crosses. The color of the coating often determines the type of fiber. (Color counting in fiber optic cables)

Optical fiber with varnish (125 microns) and polymer (900 microns) coating,
below the connector is closed with a cap (All photos)

Optical fiber and cable production

Most of the fiber is produced by Fujikura (Japan) and Corning (USA). But more and more technological lines appear, including in Russia, producing one or another type of optical fibers. Some of the steps and principles of this process are described on the pages
Fiber optic production technology. Fiber optic preforms
Fiber extraction from preform

Further, the optical fiber on special drums is supplied to cable factories, where it is used in the production of optical cables. Since cables for fiber-optic communication lines differ in purpose and method of laying, they accordingly have a different number of armor covers and differ in profile.

Optical cable marking

There are many manufacturers of fiber optic cables in the CIS countries, and at the same time, each enterprise develops its own technical conditions(TU) for its products and labels it in its own way. Marking systems are different and the following pages are devoted to the analysis of this problem.
Fiber Optic Labeling and Assignment Handbook
Alphabetical List of Possible Fiber Optic Labels
Fiber optic labeling sorted by manufacturer

Laying of fiber-optic communication lines (FOCL)

FOCLs are laid along overhead power lines, in the ground, cable ducts, along the walls of buildings and indoors. The following official documents are devoted to the laying of fiber-optic cables over overhead power lines:
Rules for the design, construction and operation of fiber-optic communication lines on overhead power lines with a voltage of 0.4-35 kV
Rules for the design, construction and operation of fiber-optic communication lines on overhead power lines with a voltage of 110 kV and above

Other types of laying almost do not differ from the methods of laying cables with metal conductors and their features are described on the page from the "SLSMSS Manual": Features of laying optical cables

Installation of couplings and terminal devices for fiber-optic communication lines

Enlarge photo

Fiber optic cables are similar in appearance to conventional cables. All the complexity of "optics" is precisely in the connection of optical fibers with each other. It will not be possible to connect them "on the knee"; for any type of connection of an optical fiber, specialized tools and devices are required. The following pages are devoted to the methods of installation and measurements on optical fiber when installing couplings, crosses and connectors.
FOCL terminal devices. Connectors
Fiber optic attenuators for FOCL
Fiber optic cleaver. Gel connectors for FOCL
Welding of optical fiber FOCL. Types of welding machines
Description of installation of fiber optic couplings and optical crosses

In the next photo, optical fibers are laid in a cassette of an optical fiber coupling.

Fiber optic in cassette coupling (Enlarge photo)

Fiber measurements

Measurements of optical fibers are made before installation (control of drums with cable), during the installation of fiber-optic couplings and crosses, and during the FOCL process. C measurements are made by two types of instruments: measurement with fiber optic testers and optical time domain reflectometers (OTDR). RH measurements are devoted to the pages
Types of FOCL measurements. Fiber measurements
Measurements of fiber-optic cable (FOCL) during installation

This topic is discussed in more detail on the pages of the book Hardwood Reflectometry of optical fibers.
Loss measurement with optical testers
How the OTDR works
OTDR assignment

Aging of fiber optic (optical) cables

FOCL documentation

Installation of fiber optic couplings and crosses, as well as all measurements of optical cables must be documented in the appropriate protocols and passports. Below are links to pages official rules and guidelines for building communication lines.
Protocol for measuring the attenuation of optical fibers of face-to-face length, serial number "n" before laying (incoming control)