Introduction to fiber optic networking technology. What is Vols

In fiber-optic transmission systems (FOTS), information is transmitted by electromagnetic waves of high frequency, about 200 THz, which corresponds to the near-infrared range of the optical spectrum of 1500 nm. The waveguide that carries information signals into the FOSS is an optical fiber (OF), which has the important ability to transmit light radiation over long distances with low losses. Losses in OF are quantitatively characterized by attenuation. The speed and range of information transmission are determined by the distortion of optical signals due to dispersion and attenuation. A fiber-optic network is an information network, the connecting elements between the nodes of which are fiber-optic communication lines. In addition to fiber optics, fiber optic network technologies also cover issues related to electronic transmission equipment, its standardization, transmission protocols, network topology issues, and general network design issues.

Optical fiber is currently considered the most advanced physical medium for transmitting information, as well as the most promising medium for transmitting large flows of information over long distances. The reasons to think so arise from a number of features inherent in optical waveguides:

- broadband optical signals due to the extremely high carrier frequency Hz. This means that information can be transmitted via an optical communication line at a speed of the order of bits/s (1Tbit/s). In other words, one fiber can carry 10 million telephone conversations and a million video signals simultaneously. Data transmission speed can be increased by transmitting information in two directions at once, since light waves can propagate independently of each other in one fiber. In addition, light signals of two different polarizations can propagate in an optical fiber, which allows doubling the throughput of an optical communication channel. To date, the limit on the density of transmitted information via optical fiber has not been reached;
- very low (compared to other media) attenuation of the light signal in the optical fiber. The best examples of Russian fiber have an attenuation of 0.22 dB/km at a wavelength of 1.55 microns, which makes it possible to build communication lines up to 100 km long without signal regeneration. In comparison, Sumitomo's best fiber at 1.55 µm has an attenuation of 0.154 dB/km. In optical laboratories in the USA, even more “transparent”, so-called fluorozirconate optical fibers with a theoretical limit of about 0.02 dB/km at a wavelength of 2.5 microns are being developed. Laboratory studies have shown that based on such fibers, communication lines can be created with regeneration sites across 4600 km at a transmission speed of about 1 Gbit/s;
- The OM is made of quartz, which is based on silicon dioxide, a widespread and therefore inexpensive material, unlike copper;
- optical fibers have a diameter of about 100 microns, that is, they are very compact and lightweight, which makes them promising for use in aviation, instrument making, and cable technology;
- since optical fibers are dielectrics, therefore, during the construction of communication systems, galvanic isolation of the segments is automatically achieved. In an optical system, they are electrically completely isolated from each other, and many of the problems associated with grounding and potential removal that hitherto arose when connecting electrical cables are no longer relevant. Using especially durable plastic, cable factories produce self-supporting overhead cables that do not contain metal and are therefore electrically safe. Such cables can be mounted on the masts of existing power lines, either separately or built into a phase conductor, saving significant costs on laying cables across rivers and other obstacles;
- communication systems based on optical fibers are resistant to electromagnetic interference, and information transmitted via optical fibers is protected from unauthorized access. Fiber optic communication lines cannot be eavesdropped in a non-destructive manner. Any impacts on the OM can be recorded by monitoring (continuous monitoring) of the integrity of the line;
- an important property of optical fiber is durability. The lifetime of the fiber, that is, its preservation of its properties within certain limits, exceeds 25 years, which allows you to lay a fiber-optic cable once and, as necessary, increase the channel capacity by replacing receivers and transmitters with faster ones.

But there are also some disadvantages of fiber optic technology:

- when creating a communication line, highly reliable active elements are required that convert electrical signals into light, and light into electrical signals. To connect the optical fiber to the receiving and transmitting equipment, optical connectors (connectors) are used, which must have low optical losses and a long connection and disconnection resource. Errors in the manufacture of such communication line elements should be on the order of a fraction of a micron, i.e. match the wavelength of the radiation. Therefore, the production of these optical communication link components is very expensive;
- another disadvantage is that the installation of optical fibers requires precision, and therefore expensive, technological equipment.

As a result, in the event of an optical cable failure (break), restoration costs are higher than when working with copper cables.

The advantages of using fiber-optic communication lines (FOCL) are so significant that, despite the listed disadvantages of optical fiber, these communication lines are increasingly used to transmit information.

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

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

This information transmission system is usually used in the construction of work facilities as external highways that unite isolated structures or buildings, as well as multi-story buildings. It can also be used as an internal carrier of a structured cabling system (SCS), however, complete SCS made entirely of fiber are less common - due to the high cost of building optical communication lines.

The use of fiber-optic communication lines allows you to locally combine workplaces, provide high speed Internet downloads on all machines simultaneously, high-quality telephone communications and television reception.

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

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

Information Security. Fiber-optic communications provide reliable protection against unauthorized access and interception of confidential information. This ability of optics is explained by the absence of radiation in the radio range, as well as high sensitivity to vibrations. In case of wiretapping attempts, the built-in monitoring system can turn off the channel and warn about a suspected hack. This is why fiber-optic communication lines are actively used by modern banks, research centers, law enforcement organizations and other structures that work with classified information.
High reliability and noise immunity of the system. The fiber, being a dielectric conductor, is not sensitive to electromagnetic radiation and is not afraid of oxidation and moisture.
Economical. Despite the fact that the creation of optical systems, due to their complexity, is more expensive than traditional SCS, in general, their owner receives real economic benefits. Optical fiber, which is made from quartz, costs about 2 times less than copper cable; in addition, when building large systems, you can save on amplifiers. If, when using a copper pair, repeaters need to be installed every few kilometers, then in a fiber-optic line this distance is at least 100 km. At the same time, the speed, reliability and durability of traditional SCS are significantly inferior to optics.

The service life of fiber-optic lines is half a quarter of a century. After 25 years of continuous use, signal attenuation increases in the carrier system.
If we compare copper and optical cables, then with the same bandwidth, the second one will weigh about 4 times less, and its volume, even when using protective sheaths, will be several times less than that of copper.
Prospects. The use of fiber-optic communication lines makes it possible to easily increase the computing capabilities of local networks due to the installation of faster active equipment, without replacing communications.

Scope of fiber optic communication lines

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

Connecting cables are a separate type: indoors they are used as connecting cords and horizontal wiring communications - to equip individual workplaces, and outside - to connect buildings.

Installation of fiber optic cable is carried out using special tools and devices.

The length of fiber-optic communication lines can reach hundreds of kilometers (for example, when building communications between cities), while the standard length of optical fibers is several kilometers (including because working with too long lengths is in some cases very inconvenient). Thus, when constructing a route, it is necessary to solve the problem of splicing individual optical fibers.

There are two types of connections: detachable and permanent. In the first case, optical connectors are used for connection (this is associated with additional financial costs, and, in addition, with a large number of intermediate connectors, optical losses increase).

For permanent connection of local sections (installation of routes), mechanical connectors, adhesive splicing and welding of fibers are used. In the latter case, machines for splicing optical fibers are used. Preference is given to one method or another taking into account the purpose and conditions of use of the optics.

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

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

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

The highest quality connection with minimal losses is ensured by welding fibers. This method is used to create high-speed fiber optic lines. During welding, the ends of the light guide melt; for this, a gas burner, an electric charge, or laser radiation can be used as a source of thermal energy.

Each method has its own advantages. Laser welding, due to the absence of impurities, allows you to obtain the purest compounds. Gas torches are typically used to permanently splice multimode fibers. The most common is electric welding, which provides high speed and quality of work. The melting time of different types of optical fibers differs.

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

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

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

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

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

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

FOCL: types of optical fibers

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

The technological age has given us many brilliant inventions and discoveries, but, apparently, it was the ability to transmit information over long distances that made one of the most significant contributions to the development of technology. The media over which data is transmitted have come a long way from copper wire a century ago to modern fiber optic cables. As a result, the volume of information, the speed and distance of its transmission have increased manifold, which has expanded the limits of technological development in all areas.

Modern low-loss glass fiber optic cables provide virtually unlimited bandwidth and have many other advantages over previously created media. The simplest fiber-optic system for transmitting information between two points consists of three main elements: an optical transmitter, a fiber-optic cable and an optical receiver (Fig. 1).

Rice. 1. Diagram of the simplest fiber-optic information transmission system

Optical transmitter converts an analog or digital electrical signal into a corresponding light signal. The light source can be either an LED or a solid-state laser. The most commonly used light sources are wavelengths of 850, 1300 and 1550 nanometers.

Fiber optic cable consists of one or more glass fibers that act as waveguides (light guides) for light. The design of a fiber optic cable is similar to that of an electrical cable, but it contains special elements to protect the light guides inside it. The connection of many kilometers of cables is carried out using detachable and permanent optical connectors.

Optical receiver converts the light signal into a copy of the original electrical signal. The sensing element of the optical receiver is either an avalanche photodiode or (more often) a PIN photodiode.

Fiber optic information transmission systems - an optical receiver and transmitter connected by a fiber optic cable - have many advantages over conventional copper wires and coaxial cables:

Why do fiber optic systems have these beneficial properties? By reading this brochure and understanding the principles behind fiber optic technology, you will have the answer to this question. Each of the three components of fiber optic systems - transmitters, receivers and cables - has its own section.

Optical transmitters

An optical transmitter converts an electrical signal into a modulated light stream for transmission via optical fiber. Depending on the type of signal, various modulation methods can be used - turning the light on and off or smoothly changing it between specified levels in proportion to the input signal. In Fig. 2, these two main modulation methods are shown in graphs of light intensity versus time.

Rice. 2. Basic methods of light flux modulation

The most common light sources used in optical transmitters are light-emitting diodes (LEDs) and semiconductor lasers (laser diodes). For use in fiber optic systems, these devices are manufactured in housings that allow the optical fiber to be brought as close as possible to the area emitting light. This is necessary in order to direct as much light as possible into the light guide. Sometimes the emitter is equipped with a microscopic spherical lens, which allows you to collect all the light “to the last drop” and direct it into the fiber. In some cases, the glass filament is attached directly to the surface of the light-emitting crystal.

The most common light sources used in optical transmitters are light-emitting diodes (LEDs) and semiconductor lasers (laser diodes).

LEDs have a fairly large area of the emitting element, and therefore they do not emit as efficiently as lasers. However, LEDs are widely used on short and medium length communication lines. LEDs are much cheaper than lasers, have an almost linear dependence of the radiation intensity on the magnitude of the electric current, and the intensity of their radiation weakly depends on temperature. Lasers, on the other hand, have a very small emitting surface area and can deliver much more power into the fiber than LEDs. They are also linear in current, but are very susceptible to temperature influence and require the use of more complex electronic circuits to achieve the necessary stability. Since lasers are quite expensive, they are mainly used where data transmission over long distances is required.

Since lasers are quite expensive, they are mainly used where data transmission over long distances is required.

LEDs and lasers used in fiber-optic communications emit in the infrared part of the spectrum of electromagnetic waves and therefore their light is invisible to the human eye without the use of special means. The radiation wavelength was selected taking into account the maximum transparency of the light guide material and the highest sensitivity of the photodiodes. The most commonly used wavelengths today are 850, 1300 and 1550 nanometers. Both LEDs and lasers are available for all three wavelengths.

As already mentioned, the light output of LEDs and lasers is modulated in one of two ways: “on-off” or a linear continuous change in intensity. In Fig. Figure 3 shows simplified circuits that implement both modulation methods. To control the emitter, a transistor is used, the base of which receives a pre-formed digital signal. The maximum modulation frequency is determined by the electronic circuit and the properties of the emitter. With LEDs, frequencies of several hundred megahertz are easily achievable, with lasers - thousands of megahertz. The diagram does not show the thermal stabilization unit (LEDs usually do not require it at all).

Linear modulation is accomplished using an op-amp based circuit (Figure 3B). The modulating signal is applied to the inverting input of the amplifier, the constant bias is supplied to the non-inverting input. The thermal stabilization circuit is also not shown here.

Rice. 3. Methods for modulating the luminous flux of LEDs
and semiconductor lasers

In a digital signal that uses on-off modulation, logic levels can be encoded in various ways. In the simplest of them, a logical one corresponds to the presence of light, and a logical zero corresponds to its absence. In addition, pulse width and pulse frequency modulation are used. Pulse width modulation uses a continuous stream of pulses, with two different durations encoding the logical levels of the signal. With pulse frequency modulation, all pulses have the same duration, but their repetition rate varies depending on the transmitted logic level.

Figure 4. Various methods of optical transmission to analog
and digital information

There are also several methods for analog modulation. The simplest of these is linear modulation, where the intensity of the light source is directly related to the magnitude of the transmitted signal. In other methods, the transmitted signal first modulates a high-frequency carrier (and in some cases multiple carriers), and then this complex signal controls the brightness of the light source.

In Fig. Figure 4 shows the light intensity versus time for these modulation methods.

The frequency of light (which is also electromagnetic radiation) is very high - on the order of millions of gigahertz. The frequency band of light emitters (lasers and LEDs) is quite wide, but, unfortunately, modern technology does not make it possible to selectively use this band, as is done when transmitting information via radio. In an optical transmitter, the entire frequency band is switched on and off at once, as was done in the first spark transmitters at the dawn of the radio era. Eventually, scientists will overcome this obstacle and “coherent transmission” will become possible, which will determine the further development of fiber optic technology.

Light guides

Injecting light into optical fiber

The higher the emitter power, the more light enters the light guide.

After the transmitter has converted the input electrical signal into properly modulated light, it must be inserted into the optical fiber. As already mentioned, there are two ways to do this: directly connecting the emitting element to the light guide, and placing the light guide in close proximity to the emitter. When using the second method, the amount of light that enters the optical fiber depends on four factors: radiation intensity, area of the emitting element, input angle of the light guide, and reflection and scattering losses. Let's take a quick look at all these factors.

Intensity The emission output of an LED or laser depends on its design and is usually expressed as the total radiated power at a specific current. Sometimes this figure is stated as the actual power transferred into a particular type of fiber. All other things being equal, the higher the power of the emitter, the more light enters the light guide.

The ratio of the areas of the radiating element and the core of the optical fiber determines the proportion of the total power that enters the fiber - the lower this ratio, the more light will end up in the fiber.

Only the light that entered the optical fiber at an angle less than or equal to the input angle will propagate along the light guide.

Entrance angle Optical fibers are characterized by their numerical aperture (NA), which is defined as the sine of half the input angle. Typical NA values range from 0.1 to 0.4, corresponding to an entry angle of 11 to 46 degrees. Only the light that entered the optical fiber at an angle less than or equal to the input angle will propagate along the light guide.

Losses. In addition to losses from contamination on the surface of the optical fiber, there is always an inevitable loss of light intensity caused by reflection at the entrance to and exit from the optical fiber. These are the so-called Fresnel losses (named after the French physicist O. J. Fresnel), which account for approximately 4% of the total intensity at each glass-air interface. If necessary, a small amount of special optical gel is applied to the glass surfaces being joined to reduce these losses.

Optical Fiber Types

Now two types of optical fiber are used: with a stepped and smooth change in the refractive index along the radius (profile). In Fig. Figure 5 shows that light propagates through such light guides in different ways.

Figure 5. Light propagation through an optical fiber with stepped and smooth refractive index profiles

As shown in the figure, step index fiber consists of a core of low loss glass surrounded by a lower refractive index glass cladding. This difference in refractive index causes light to be reflected from the interface between the core and the cladding along its entire propagation path. Smooth profile fiber consists of only one type of glass, but it is processed so that its refractive index gradually decreases from the center to the periphery. As a result, the light guide, like an extended lens, constantly deflects the light propagating through it towards the center.

Optical fiber is characterized by the thickness of the core and cladding, which is expressed in micrometers. There are three sizes of general-purpose fiber that are most common today, although there are other sizes for specialized applications. These are multimode fibers 50/125 and 62.5/125 microns and single-mode 8-10/125 microns. The first two sizes are usually used in conjunction with LED emitters on short and medium length transmission lines. Optical fiber with a core of 8-10 microns is most often used in long-distance telecommunication systems in conjunction with laser optical transmitters.

Optical fiber loss

In addition to losses in signal intensity at the connection between the emitter and the light guide, losses also occur when light propagates through the optical fiber. The optical fiber core is made from ultra-pure glass with very low loss. Glass must have the highest transparency, since light must travel kilometers along the fiber made from it. Let's look at ordinary window glass. It is transparent, but only because its thickness is only 3-4 mm. It is enough to look at the end of the glass plate and see its green color to understand how strongly it absorbs light even over a length of ten or two centimeters. It’s easy to imagine how little light will pass through a hundred-meter thickness of window glass!

Most general-purpose light guides produce losses of 4 to 6 decibels per kilometer at a wavelength of 850 nm (that is, 60 to 75% of light is lost per kilometer). At a wavelength of 1300 nm, losses are reduced to 3-4 dB/km (50-60%), and at 1550 nm they are even lower - a value of 0.5 dB/km (10%) is not unusual.

The main cause of losses is the absorption of light by inhomogeneities and scattering by them. Another cause of loss in optical fiber is excessive bending, which causes some of the light to escape from the core. To avoid such losses, the bending radius of the fiber-optic cable during installation must be at least 2.5 cm (and more often even greater).

Fiber Bandwidth

However, the optical fiber's bandwidth for a modulated signal is limited, and the longer the fiber, the more limited it is.

The fewer modes in the radiation, the wider the bandwidth of the optical fiber.

The losses listed above do not depend on the modulation frequency, that is, a loss level of 3 dB means that 50% of the light will not reach the recipient, regardless of whether it is modulated by a 10 Hz or 100 MHz signal. However, the optical fiber's bandwidth for a modulated signal is limited, and the longer the fiber, the more limited it is. The reason for this limitation is illustrated in Fig. 6. Light entering the optical fiber at a small angle to its axis (M1) travels along a shorter path than that entering at an angle close to the maximum input angle (M2). As a result, different beams emanating from the same source (called modes) do not arrive at the far end of the fiber at the same time, which leads to the smearing effect - the broadening of short pulses. This limits the maximum frequency of the signal transmitted over the fiber optic cable. In short, the fewer modes in the radiation, the wider the bandwidth of the fiber. To reduce the number of propagating modes, the fiber core is made thinner. Single-mode fiber with a core diameter of 8 to 10 µm has a significantly wider bandwidth than multimode fibers with a diameter of 50 and 62.5 µm, through which a large number of radiation modes can propagate simultaneously.

Rice. 6. Bandwidth of modulation frequencies transmitted by the optical fiber,
limited by the existence of different light propagation paths

Typical bandwidths for conventional optical fibers are several megahertz per kilometer for very large core diameter fiber, several hundred megahertz per kilometer for standard multimode fiber, and thousands of megahertz for single-mode optical fibers. As the cable length increases, the bandwidth decreases proportionally. For example, a cable with a 500 MHz band over a length of 1 km can provide a 250 MHz band at a length of 2 km, and only 100 MHz at 5 km.

The very wide bandwidth of single-mode fibers makes it possible to practically ignore their length. However, for multimode fibers this factor is important, since often the frequency range of the transmitted signals exceeds the bandwidth of the cables.

Fiber Optic Cable Design

Fiber optic cables are available in different diameters and designs. As with coaxial cables, the design of fiber optic cables is determined by its intended purpose. Externally, fiber optic cable is similar to coaxial cable. In Fig. Figure 7 shows a schematic diagram of a standard fiber optic cable.

The optical fiber has a protective coating that protects it from damage during the production process. It is placed in a form-fitting polyvinyl chloride tube, where it can bend freely when installed around wall corners and in cable ducts.

This tube is surrounded by a Kevlar braid, which absorbs the main mechanical force that acts on the cable during installation. Finally, the PVC outer jacket protects the entire cable and prevents moisture from penetrating inside.

Cables of this design are suitable for installation inside buildings where significant resistance to external influences is not required. There are cables for almost any installation option, such as direct in-ground cables, reinforced rodent-resistant steel outer sheaths, and UL certified non-flammable cables for installation above false ceilings. Color-coded multi-core cables are also available.

Rice. 7. Installation of a standard fiber optic cable

Other types of light guides

Plastic light guides are used to transmit data over very short distances inside electronic equipment in conjunction with inexpensive LEDs. One of the standard applications of such light guides is optical isolation of control circuits in high-voltage power supplies.

Two other types of light guides - quartz with a very large diameter core and made entirely of plastic - are not usually used in telecommunications. Quartz light guides are used to transmit powerful light streams, for example in laser surgery. Plastic light guides are used to transmit data over very short distances inside electronic equipment in conjunction with inexpensive LEDs. One of the standard applications of such light guides is optical isolation of control circuits in high-voltage power supplies.

Optical connectors

Using optical connectors, fiber optic cables are connected to equipment or interconnected. They are similar to electrical connectors in function and appearance, but require very high precision manufacturing. An optical connector requires precise alignment and alignment of the cores of both fibers. Since their diameter is very small (for example, 50 µm), the accuracy requirements are very high: the tolerance is on the order of one micron.

There are many different types of optical connectors in use today. The SMA connector, used before the invention of single-mode fibers, remained the most common until recently. In Fig. 8 shows the design details of this connector.

Rice. 8. SMA connector design

Please note that ST multimode connectors will only work correctly with multimode fibers.

For multimode fibers, the most commonly used connector today is the ST connector developed by AT&T. It uses a bayonet lock, and the overall losses are less than in SMA. A matched pair of ST connectors provides less than 1 dB (20%) loss and does not require additional guide bushings or similar components. A special protrusion that prevents the connector from rotating ensures that when connecting, the optical fibers will always be installed in the same position relative to each other, which ensures stable characteristics of the detachable connection.

ST connectors are available for both multi-mode and single-mode fibers - the main difference is the tolerances. Please note that ST multimode connectors will only work correctly with multimode fibers. The more expensive single-mode ST connectors can be used with either single-mode or multi-mode fibers. The procedures for installing ST and SMA connectors on a cable are similar and take approximately the same time. In Fig. Figure 9 shows the main elements of the industry standard ST connector.

Rice. 9. Basic elements of the ST connector

Permanent connections of light guides

Although optical connectors can be used to connect two light guides, there are other methods that provide significantly lower losses. The two most common are mechanical connection and welded connection. Both provide loss levels of 0.15 to 0.1 dB (3-2%).

For mechanical connection, the ends of the light guides are freed from the shells, their ends are cleaned and precisely aligned using a special mechanical device. An optical gel is applied to the junction, reducing reflection loss to a minimum. The aligned ends of the light guides are held in place by a locking mechanism.

Optical receivers

The main task of an optical receiver is to convert the modulated light stream coming from an optical fiber into a copy of the original electrical signal supplied to the transmitter.

The main task of an optical receiver is to convert the modulated light stream coming from an optical fiber into a copy of the original electrical signal supplied to the transmitter. The detector in the receiver typically uses a PIN or avalanche photodiode, which is mounted on an optical connector (similar to that used for light sources). Photodiodes usually have a fairly large sensing element (several micrometers in diameter), so the requirements for optical fiber positioning accuracy are not as stringent as for transmitters.

It is important to use receivers only with the fiber size for which they are designed, otherwise the amplifier may become overloaded.

The intensity of the radiation coming out of the optical fiber is quite low, and optical receivers have internal amplifiers with high gain. Therefore, it is important to use receivers only with the fiber size for which they are designed, otherwise the amplifier may overload. If, for example, a transmitter-receiver pair designed for single-mode fiber is used with multimode, too much light will enter the receiver, causing it to saturate and severely distort the output signal. Likewise, if you use single-mode fiber with a transmitter and receiver designed for multimode, little light will reach the receiver and the output signal will contain a lot of noise or no signal at all. The only case where mismatching the receiver and transmitter to the fiber type may be useful is if there is excessive loss in the fiber. Then the additional 5-15 dB, which will be obtained by replacing single-mode fiber with multimode, will save the situation and allow us to obtain a workable system. However, this is an extreme situation and is not recommended for normal use.

It should be remembered that electronic signal receivers, unlike fiber optic cables, are susceptible to electromagnetic interference, so when working with them, standard protection measures should be used - shielding, grounding, etc.

Like transmitters, optical receivers are available in analog and digital versions. They both use an analogue preamplifier followed by an analogue or digital output stage.

In Fig. Figure 10 shows a functional diagram of a simple analog optical receiver. The first stage is an operational amplifier, connected as a current-to-voltage converter. The small current generated by the photodiode is converted here into a voltage, the amplitude of which is usually a few millivolts. In the next stage, which is a simple voltage amplifier, the signal is amplified to the required level.

The functional diagram of a digital optical receiver is shown in Fig. 11. As with an analog receiver, the first stage is a current-to-voltage converter. Its output signal is fed to a voltage comparator, which produces a clean digital signal with short swing durations. The comparator trigger level control, if present, is used to fine-tune the symmetry of the reconstructed digital signal.

Often, additional stages are added to receivers for the most accurate reproduction of the input signal, which work as linear amplifiers for coaxial cables, protocol converters, etc. It should be remembered that electronic signal receivers, unlike fiber optic cables, are susceptible to electromagnetic interference, so when working with them, standard protection measures should be used - shielding, grounding, etc.

Rice. 10. The simplest analog optical receiver

Rice. 11. The simplest digital optical receiver

Development of a fiber optic system

There are many factors to consider when designing a fiber optic system, each of which contributes to the end goal of ensuring that sufficient light reaches the receiver. Without achieving this goal, the system will not work correctly. In Fig. 12 identifies many of these factors.

Rice. 12. The most important parameters to consider
when developing a fiber optic system

When engineering a fiber optic system, the following step-by-step procedure is recommended:

Selecting a receiver and transmitter suitable for the type of signal that needs to be transmitted (analog, digital, video, RS-232, RS-422, RS-485, etc.).
Determination of available power sources (AC voltage, DC voltage, etc.).
Determine, if necessary, special requirements (for example, impedances, bandwidth, special connectors and fiber diameter, etc.).
Calculation of total losses in the system (in decibels): summation of losses in cables, in detachable and permanent connections. These specifications are available from electronic device and fiber optic cable manufacturers.
Comparison of the resulting loss figure with the permissible value of the signal level at the receiver input. You should play it safe by adding at least a 3 dB headroom to the entire system.
Checking whether the system bandwidth meets the needs of transmitting the desired type of signal. If calculations show that the bandwidth is insufficient to transmit the signal over the required distance, then you should either choose a different receiver and transmitter (different wavelength), or consider using a more expensive and high-quality fiber optic cable with lower losses.

Checklist of parameters required to design a fiber optic transmission system

Purpose (brief description of the task):
Analog signal parameters:
Input voltage
Input impedance
Output voltage
Output impedance
Signal to noise ratio

Bandwidth
Connectors
Other data
Digital signal parameters:
Interface type (RS-232, 422, 485, etc.)
Data transfer rate
Communication method (DC or AC)
Allowable bit error rate
Connectors
Other data
Power supply requirements:
Voltage
Current
AC or DC voltage
Connectors
Other data

Fiber optic line requirements:
Line length
Wavelength of light
Acceptable losses
Optical connectors
Fiber type
Fiber Diameter
Installation conditions
General requirements:
Case size
Installation method
Environmental Characteristics
Operating temperature range
Storage temperature range
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Slide Communication

Connection in technology - transmitting information (signals) over a distance.

Types of communication

Depending on what phenomena were used to encode messages, you can highlight the connection using:

electrons - telecommunications (wired and radio communications)
photon radiation - modern optical fiber, some types of signal towers, flashlight signals in Morse code, atmospheric and space laser communications
sequences of symbols made from dyes on the material - writing on paper.
relief or change in the shape of the material - optical disk

Depending on the data transmission medium, communication lines are divided into:

satellite
air
ground
underwater
underground

Depending on what the message carries, according to the physical principles underlying communication lines, the following types of communication can be distinguished:

Wire and cable communications - transmission is carried out along the guide medium.

Electrical cable communication
Fiber Optic Communication

Satellite communications - communications using space repeater(s)
Radio relay communication - communication using terrestrial repeater(s)
base stations

Courier service

Pigeon mail

Depending on whether the sources/receivers of information are mobile or not, they distinguish stationary (fixed) And mobile connection ( mobile, communication with moving objects- SPO).

Based on the type of signal transmitted, analogue and digital communications are distinguished.

Signal

Depending on what information is transmitted, there are analog And digital connection. Analogue communication is the transmission of continuous messages (such as sound or speech). Digital communication is the transfer of information in discrete form (digital form). However, discrete messages can be transmitted over analog channels and vice versa. Currently, digital communication is replacing analogue (digitalization is taking place),

Communication line

Communication line(LS) - the physical medium through which information signals of data transmission equipment and intermediate equipment are transmitted.

This is a set of technical devices that ensure the transmission of messages of any kind from the sender to the recipient. It is carried out using electrical signals traveling through wires or radio signals.

Wired communication lines

Communication circuit- conductors/fiber used to transmit one signal. In radio communications the same concept has the name trunk. Distinguish cable chain- chain in the cable and air chain- suspended on supports.

Wired telecommunication lines are divided into cable, overhead and fiber optic. Cable lines were laid underground. However, due to imperfect design, underground cable communication lines gave way to overhead ones. A typical city telephone cable consists of a bundle of thin copper or aluminum wires, insulated from each other and enclosed in a common sheath. Cables are made up of a varying number of pairs of wires, each of which is used to carry telephone signals. The desire to expand the spectrum of transmitted frequencies and increase the capacity of lines of multi-channel systems led to the creation of new types of cables, the so-called coaxial. They are used for transmitting high-frequency television signals, as well as for long-distance and international telephone communications. One wire in a coaxial cable is a copper or aluminum tube (or braid), and the other is a central copper core embedded in it. They are isolated from each other and have one common axis. Such a cable has low losses, emits almost no electromagnetic waves and therefore does not create interference. These cables allow the transmission of energy at current frequencies of up to several million hertz and allow them to transmit television programs over long distances.

Rice. Coaxial cable

Fiber optic communication lines

Telephone lines and television cables are mainly used as wired communication lines. The most developed is telephone wire communication. But it has serious disadvantages: susceptibility to interference, attenuation of signals when transmitting them over long distances and low throughput. Fiber optic lines do not have all these disadvantages - a type of communication in which information is transmitted along optical dielectric waveguides ("optical fiber").

Optical fiber is considered the most perfect medium for transmitting large flows of information over long distances. It is made of quartz, which is based on silicon dioxide - a widespread and inexpensive material, unlike copper. The optical fiber is very compact and lightweight, with a diameter of only about 100 microns.

Fiber optic lines differ from traditional wire lines:

very high speed of information transmission (over a distance of more than 100 km without repeaters);
security of transmitted information from unauthorized access;
high resistance to electromagnetic interference;
resistance to aggressive environments;
the ability to simultaneously transmit up to 10 million telephone conversations and one million video signals over one fiber;
fiber flexibility;
small size and weight;
spark, explosion and fire safety;
ease of installation and installation;
low cost;
high durability of optical fibers - up to 25 years.

Rice. Fiber optic cable (cross section)

Currently, information exchange between continents occurs primarily through undersea fiber optic cables rather than satellite communications. At the same time, the main driving force behind the development of underwater fiber optic communication lines is the Internet.

Rice. Transtelecom fiber optic network

Link May be:

simplex- that is, allowing data transmission only in one direction, for example - radio broadcasting, television;
half duplex one by one;
duplex- that is, allowing data transfer in both directions simultaneously, example - telephone.

Separation (sealing) of channels:

The creation of several channels on one communication line is ensured by separating them by frequency, time, codes, address, and wavelength.

frequency division of channels (FDM, FDM) - division of channels by frequency, each channel is allocated a certain frequency range
time division of channels (TDM, TDM) - division of channels in time, each channel is allocated a time slice (timeslot)
code division of channels (KKK, CDMA) - separation of channels by codes, each channel has its own code, the overlay of which on the group signal allows you to highlight the information of a specific channel.
spectral channel division (SRK, WDM) - separation of channels by wavelength

Wireless communication lines

Radio communication - radio waves in space are used for transmission.

DV, SV, HF and VHF communications without the use of repeaters
Satellite communications - communications using space repeaters
Radio relay communication - communication using terrestrial repeaters
Cellular communication - communication using a network of terrestrial base stations

Communication system comprises terminal equipment, the source and recipient of the message, and signal conversion devices(UPS) from both ends of the line. The terminal equipment provides primary processing of messages and signals, conversion of messages from the form in which they are provided by the source (speech, image, etc.) into a signal (on the source, sender side) and back (on the recipient side), amplification, etc. .UPS can protect the signal from distortion.

Types of modern communications

Mail

Mail(Russian) Mail (info); from lat. posta) - a type of communication and institution for transporting news (for example, letters and postcards) and small goods, sometimes people. Carries out regular shipment of postal items - written correspondence, periodicals, money orders, parcels, parcels - mainly using vehicles.

The postal organization in Russia is traditionally a state enterprise. The post office network is the largest organizational network in the country.

Letter- a means of storing information, for example on paper. Before sending a letter, you need to put the postal codes of the sender and recipient on the envelope in accordance with the stencil applied to it.

Rice. Mailing envelope with postal code stencil

Rice. Russian postal envelope with postal code

Airmail, or air mail(English) airmail), - a type of postal service in which postal items are transported by air using aviation.

Rice. Airmail envelope of the Russian Federation

Pigeon mail- one of the methods of postal communication in which written messages are delivered using carrier pigeons.

Cybermail@

The main advantage of e-mail is the speed of delivery, regardless of the geographical location of the sender of the letter and the recipient. But both the sender and the recipient must have computers and access to email.

What if the sender has these capabilities, but the recipient does not? In the United States, the state postal service ensures the delivery of an email to the post office closest to the addressee. There it is printed and delivered in an envelope by the postman to the recipient. Today, airmail delivers a regular letter from Russia to the USA in 3-4 weeks. A new combined (email - regular) letter can be delivered within 48 hours. Russia also has a plan to equip post offices with Internet and email access. This project is called “Cybermail@”. “Internet salons” – points of public access to the Internet – will be opened in all post offices. In such a salon it will be possible to send an email containing any text, document, drawing, photograph. This letter will be sent to the nearest post office to the recipient, printed, automatically sealed in an envelope and delivered by the postman to any address within 48 hours. In the online salon, a consultant will help you learn how to use e-mail and take a digital photograph. The first such Internet salon already exists at the Moscow Post Office. The cost of one page of such a combined letter is 12 rubles, and on a floppy disk it costs 6 rubles per 2 KB.

Part of the Cybermail@ project is the so-called “Hybrid Mail”. This is a hybrid of the modern Internet and the “traditional postman”. Now anyone can bring an ordinary letter written on paper to the post office. There it will be entered into the computer and sent by e-mail to the post office closest to the addressee. In it, this letter will be printed on a printer, and the postman will take it to the addressee. Then the letter will reach any city in the country no later than 48 hours, since the longest stage of the delivery process - transporting a letter written on paper from city to city - disappears. So the speed of delivery of a letter is equal to that of a telegram. But the cost of such a letter is many times less than a telegram. After all, the cost of just one word of a telegram when transmitted across Russia is 80 kopecks, and the cost of one page of a hybrid letter in A4 format and 2000 characters is only 12 rubles. At the same time, several hundred words fit on an A4 page!

The letter may be closed, i.e. The letter is delivered to the recipient in an envelope, or open, i.e. the letter is delivered without an envelope.
You can submit letters via Hybrid mail, both on paper and on magnetic media.

Later, an addition was added to the “Hybrid Mail” project for users who own the Internet and e-mail. It allows them to send an email to a recipient who does not have email. This letter goes to the post office closest to the addressee, is printed out and sealed in an envelope. The postman takes this envelope to the addressee - the recipient of the letter. This significantly reduces its delivery time.

Pneumatic mail, or pneumatic mail(from the Greek πνευματικός - air), - a system for moving piece goods under the influence of compressed or, conversely, rarefied air. Closed passive capsules (containers) move through a pipeline system, carrying light loads and documents inside.

Rice. Pneumatic mail terminal

It is used in organizations to send original documents, for example, in banks, warehouses and libraries, cash in supermarkets and bank cash desks, tests, medical histories, X-rays in medical institutions, as well as samples in industrial enterprises.

Telegraph(from ancient Greek τῆλε - “far” + γρᾰ́φω - “I write”) - a means for transmitting a signal through wires or other telecommunication channels. In Russia, telegraph communication still exists today. In some countries, the telegraph was considered an obsolete form of communication and all operations for sending and delivering telegrams were curtailed. In the Netherlands, telegraph communications ceased operation in 2004. In January 2006, the oldest American national operator, Western Union, announced a complete cessation of services to the public for sending and delivering telegraph messages. At the same time, in Canada, Belgium, Germany, Sweden, and Japan, some companies still support the service for sending and delivering traditional telegraph messages.

Telegraph(from ancient Greek τῆλε - “far” + γρᾰ́φω - “I write”) - a means for transmitting a signal through wires or other telecommunication channels.

Telegram- a message sent by telegraph, one of the first types of communication using electrical transmission of information.

Rice. Telegram

Telephone communications

Telephone(from the Greek τῆλε - far and φωνή - voice) - a device for transmitting and receiving sound over a distance via electrical signals. Telephone communications are used to transmit and receive human speech.

Is it fiber optic? Research Institute of Communications (FOCL) - a system based on a fiber-optic cable, designed to transmit information in the optical (light) range. In accordance with GOST 26599-85, the term FOCL has been replaced by FOLP (fiber-optic transmission line), but in everyday practical use the term FOCL is still used, so in this article we will stick to it.

FOCL communication lines (if they are installed correctly) compared to all cable systems are distinguished by very high reliability, excellent communication quality, wide bandwidth, significantly greater length without amplification and almost 100% immunity from electromagnetic interference. The system is based fiber optics technology– light is used as an information carrier; the type of information transmitted (analog or digital) does not matter. The work primarily uses infrared light, the transmission medium being fiberglass.

Scope of fiber optic communication lines

Fiber optic cable has been used to provide communications and information transfer for more than 40 years, but due to its high cost, it has become widely used relatively recently. The development of technology has made it possible to make production more economical and the cost of the cable more affordable, and its technical characteristics and advantages over other materials quickly pay for all the costs incurred.

Currently, when one facility uses a complex of low-current systems at once (computer network, access control system, video surveillance, security and fire alarms, perimeter security, television, etc.), it is impossible to do without the use of fiber-optic communication lines. Only the use of fiber optic cable makes it possible to use all these systems simultaneously, ensures correct stable operation and performance of their functions.

FOCL is increasingly used as a fundamental system in the development and installation, especially for multi-storey buildings, long-term buildings and when combining a group of objects. Only fiber optic cables can provide the appropriate volume and speed of information transfer. All three subsystems can be implemented on the basis of optical fiber; in the subsystem of internal trunks, optical cables are used equally often with twisted pair cables, and in the subsystem of external trunks they play a dominant role. There are fiber optic cables for external (outdoor cables) and internal (indoor cables), as well as connecting cords for horizontal wiring communications, equipping individual workplaces, and connecting buildings.

Despite the relatively high cost, the use of optical fiber is becoming more justified and is becoming more widely used.

Advantages fiber optic communication lines (FOCL)) before traditional “metal” transmission means:

Wide bandwidth;
Insignificant signal attenuation, for example, for a 10 MHz signal it will be 1.5 dB/km compared to 30 dB/km for RG6 coaxial cable;
The possibility of “ground loops” is excluded, since optical fiber is a dielectric and creates electrical (galvanic) isolation between the transmitting and receiving ends of the line;
High reliability of the optical environment: optical fibers do not oxidize, do not get wet, and are not subject to electromagnetic influence
Does not cause interference in adjacent cables or in other fiber optic cables, since the signal carrier is light and it remains completely inside the fiber optic cable;
Fiberglass is completely insensitive to external signals and electromagnetic interference (EMI), no matter what power supply the cable runs near (110 V, 240 V, 10,000 V AC) or very close to a megawatt transmitter. A lightning strike at a distance of 1 cm from the cable will not produce any interference and will not affect the operation of the system;
Information security - information is transmitted via optical fiber “from point to point” and it can only be eavesdropped or changed by physically interfering with the transmission line
Fiber optic cable is lighter and smaller - it is more convenient and easier to install than an electrical cable of the same diameter;
It is not possible to make a cable branch without damaging the signal quality. Any tampering with the system is immediately detected at the receiving end of the line, this is especially important for security and video surveillance systems;
Fire and explosion safety when changing physical and chemical parameters

The cost of the cable is decreasing every day, its quality and capabilities are beginning to prevail over the costs of building low-current fiber-optic lines

There are no ideal and perfect solutions; like any system, fiber-optic communication lines have their drawbacks:

Fragility of glass fiber - if the cable is strongly bent, the fibers may break or become cloudy due to the occurrence of microcracks. To eliminate and minimize these risks, cable-reinforcing structures and braids are used. When installing the cable, it is necessary to follow the manufacturer's recommendations (where, in particular, the minimum permissible bending radius is standardized);
The complexity of the connection in case of rupture requires a special tool and the qualifications of the performer;
Complex manufacturing technology of both the fiber itself and the components of the fiber-optic link;
Complexity of signal conversion (in interface equipment);
Relative high cost of optical terminal equipment. However, the equipment is expensive in absolute terms. The price-to-bandwidth ratio for fiber-optic lines is better than for other systems;
Haze of the fiber due to radiation exposure (however, there are doped fibers with high radiation resistance).

Installation of fiber-optic communication systems requires an appropriate level of qualification from the contractor, since cable termination is carried out with special tools, with special precision and skill, unlike other transmission media. Settings for routing and signal switching require special qualifications and skill, so you should not save money in this area and be afraid to overpay for professionals; eliminating disruptions in the system and the consequences of incorrect cable installation will cost more.

Operating principle of fiber optic cable.

The very idea of transmitting information using light, not to mention the physical principle of operation, is not entirely clear to most ordinary people. We will not go deeply into this topic, but we will try to explain the basic mechanism of action of optical fiber and justify such high performance indicators.

The concept of fiber optics relies on the fundamental laws of reflection and refraction of light. Thanks to its design, fiberglass can hold light rays inside the light guide and prevent them from “passing through walls” when transmitting a signal over many kilometers. In addition, it is no secret that the speed of light is higher.

Fiber optics is based on the effect of refraction at the maximum angle of incidence, where total reflection occurs. This phenomenon occurs when a ray of light leaves a dense medium and enters a less dense medium at a certain angle. For example, let’s imagine an absolutely motionless surface of water. The observer looks from under the water and changes his viewing angle. At a certain point, the viewing angle becomes such that the observer will not be able to see objects located above the surface of the water. This angle is called the angle of total reflection. At this angle, the observer will only see objects underwater, it will seem like he is looking into a mirror.

The inner core of a fiber optic cable has a higher refractive index than the sheath and the effect of total reflection occurs. For this reason, a ray of light, passing through the inner core, cannot go beyond its limits.

There are several types of fiber optic cables:

With a stepped profile - the typical, cheapest option, the light distribution occurs in “steps” and the input pulse is deformed due to different lengths of the light ray trajectories
With a smooth “multi-mode” profile – light rays propagate at approximately equal speeds in “waves”, the length of their paths are balanced, this allows improving the characteristics of the pulse;
Single-mode fiberglass - the most expensive option, allows you to stretch the beams straight, the pulse transmission characteristics become almost flawless.

Fiber optic cable is still more expensive than other materials, its installation and termination is more complicated, and requires qualified performers, but the future of information transmission undoubtedly lies in the development of these technologies and this process is irreversible.

The fiber-optic line includes active and passive components. At the transmitting end of the fiber optic cable there is an LED or laser diode, their radiation is modulated by the transmitting signal. In relation to video surveillance, this will be a video signal; for the transmission of digital signals, the logic is preserved. During transmission, the infrared diode is modulated in brightness and pulsates according to signal variations. To receive and convert an optical signal into an electrical signal, a photodetector is usually located at the receiving end.

Active components include multiplexers, regenerators, amplifiers, lasers, photodiodes and modulators.

Multiplexer– combines multiple signals into one, so a single fiber optic cable can be used to transmit multiple real-time signals simultaneously. These devices are indispensable in systems with insufficient or limited number of cables.

There are several types of multiplexers, they differ in their technical characteristics, functions and applications:

spectral division division (WDM) - the simplest and cheapest devices, transmits optical signals from one or more sources operating at different wavelengths via one cable;
frequency modulation and frequency multiplexing (FM-FDM) - devices that are quite immune to noise and distortion, with good characteristics and circuits of medium complexity, have 4.8 and 16 channels, optimal for video surveillance.
Amplitude modulation with partially suppressed sideband (AVSB-FDM) - with high-quality optoelectronics, they allow you to transmit up to 80 channels, optimal for subscriber television, but expensive for video surveillance;
Pulse code modulation (PCM - FDM) - an expensive device, completely digital, used for the distribution of digital video and video surveillance;

In practice, combinations of these methods are often used. A regenerator is a device that restores the shape of an optical pulse, which, propagating along the fiber, undergoes distortion. Regenerators can be either purely optical or electrical, which convert an optical signal into an electrical signal, restore it, and then convert it back to optical.

Amplifier- amplifies the signal power to the required voltage level, can be optical and electrical, carries out optical-electronic and electron-optical signal conversion.

LEDs and Lasers- source of monochrome coherent optical radiation (light for cable). For systems with direct modulation, it simultaneously performs the functions of a modulator that converts an electrical signal into an optical one.

Photodetector(Photodiode) - a device that receives a signal at the other end of a fiber optic cable and performs optoelectronic signal conversion.

Modulator- a device that modulates an optical wave carrying information according to the law of an electrical signal. In most systems, this function is performed by a laser, but in systems with indirect modulation, separate devices are used for this purpose.

Passive components of fiber-optic communication lines include:

Fiber optic cable – acts as a medium for signal transmission. The outer sheath of the cable can be made of various materials: polyvinyl chloride, polyethylene, polypropylene, Teflon and other materials. An optical cable can have various types of armor and specific protective layers (for example, small glass needles to protect against rodents). The design can be:

Optical coupling- a device used to connect two or more optical cables.

Optical cross- a device designed for terminating an optical cable and connecting active equipment to it.

Spikes– designed for permanent or semi-permanent fiber splicing;

Connectors– to reconnect or disconnect the cable;

Couplers– devices that distribute the optical power of several fibers into one;

Switches– devices that redistribute optical signals under manual or electronic control

Installation of fiber-optic communication lines, its features and procedure.

Fiberglass is a very strong but brittle material, although thanks to its protective shell, it can be treated almost as if it were electrical. However, when installing the cable, you must comply with the manufacturers' requirements for:

“Maximum elongation” and “maximum breaking force”, expressed in newtons (about 1000 N or 1 kN). In an optical cable, most of the stress is placed on the strength structure (reinforced plastic, steel, Kevlar, or a combination of these). Each type of structure has its own individual characteristics and degree of protection; if the tension exceeds the specified level, the optical fiber may be damaged.
“Minimum bend radius” – make bends smoother, avoid sharp bends.
“Mechanical strength”, it is expressed in N/m (newtons/meters) - protection of the cable from physical stress (it can be stepped on or even run over by vehicles. You should be extremely careful and especially secure the intersections and connections, the load increases greatly due to small contact area.

The optical cable is usually supplied wound on wooden drums with a durable plastic protective layer or wooden strips around the circumference. The outer layers of the cable are the most vulnerable, so during installation it is necessary to remember the weight of the drum, protect it from shocks and falls, and take safety measures during storage. It is best to store drums horizontally, but if they do lie vertically, then their edges (rims) should touch.

Procedure and features of installation of fiber optic cable:

Before installation, it is necessary to inspect the cable drums for damage, dents, and scratches. If there is any suspicion, it is better to immediately put the cable aside for subsequent detailed examination or rejection. Short pieces (less than 2 km) can be checked for fiber continuity using any flashlight. Fiber cable for infrared transmission transmits ordinary light just as well.
Next, examine the route for potential problems (sharp corners, clogged cable channels, etc.), if any, make changes to the route to minimize risks.
Distribute the cable along the route in such a way that the connection points and connection points for amplifiers are in accessible, but protected from adverse factors, places. It is important that sufficient cable reserves remain at future connections. Open cable ends must be protected with waterproof caps. Pipes are used to minimize bending stress and damage from passing traffic. A portion of the cable is left at both ends of the cable line; its length depends on the planned configuration).
When laying a cable underground, it is additionally protected from damage at local load points, such as contact with heterogeneous backfill material and trench unevenness. To do this, the cable in the trench is laid on a layer of sand 50-150 cm and covered with the same layer of sand 50-150 cm. The bottom of the trench must be flat, without protrusions; when burying, stones that can damage the cable should be removed. It should be noted that damage to the cable can occur both immediately and during operation (after backfilling the cable), for example, from constant pressure; an unremoved stone can gradually push through the cable. Work on diagnostics and search and elimination of violations of an already buried cable will cost much more than accuracy and compliance with safety precautions during installation. The depth of the trench depends on the soil type and the expected surface load. In hard rock the depth will be 30 cm, in soft rock or under the road 1 m. The recommended depth is 40-60 cm, with a sand bed thickness of 10 to 30 cm.
The most common method is to lay the cable in a trench or tray directly from the drum. When installing very long lines, the drum is placed on the vehicle, as the machine moves, the cable is laid in its place, there is no need to rush, the pace and order of unwinding the drum is adjusted manually.
When laying the cable in a tray, the most important thing is not to exceed the critical bending radius and mechanical load. The cable should be laid in one plane, not create points of concentrated loads, avoid sharp angles, pressure and intersections with other cables and routes on the route, and do not bend the cable.
Pulling fiber optic cable through conduits is similar to pulling conventional cable, but do not use excessive physical force or violate manufacturer specifications. When using staple clamps, remember that the load should not fall on the outer sheath of the cable, but on the power structure. To reduce friction, talc or polystyrene granules can be used; for the use of other lubricants, consult the manufacturer.
In cases where the cable already has an end seal, when installing the cable, you should be especially careful not to damage the connectors, contaminate them, or subject them to excessive load in the connection area.
After installation, the cable in the tray is secured with nylon ties; it should not slip or sag. If the surface features do not allow the use of special cable fastenings, the use of clamps is acceptable, but with extreme caution so as not to damage the cable. It is recommended to use clamps with a plastic protective layer; a separate clamp should be used for each cable and in no case should you tie several cables together. It is better to leave a little slack between the end points of the cable attachment rather than putting the cable under tension, otherwise it will react poorly to temperature fluctuations and vibration.
If the optical fiber is damaged during installation, mark the area and leave a sufficient supply of cable for subsequent splicing.

In principle, laying a fiber optic cable is not much different from installing a conventional cable. If you follow all the recommendations we have indicated, then there will be no problems during installation and operation and your system will work for a long time, efficiently and reliably.

An example of a typical solution for laying a fiber-optic line

The task is to organize a fiber-optic communication system between two separate buildings of a production building and an administrative building. The distance between buildings is 500 m.

Estimate for installation of fiber-optic communication system

No.	Name of equipment, materials, work	Unit from-i	Qty	Price per one.	Amount, in rub.
I.	FOCL system equipment, including:				25 783
1.1.	Cross optical wall (SHKON) 8 ports	PC.	2	2600	5200
1.2.	Media converter 10/100-Base-T / 100Base-FX, Tx/Rx: 1310/1550nm	PC.	2	2655	5310
1.3.	Optical coupling through passage	PC.	3	3420	10260
1.4.	Switching box 600x400	PC.	2	2507	5013
II.	Cable routes and materials of the fiber-optic communication system, including:				25 000
2.1.	Optical cable with external cable 6kN, central module, 4 fibers, single-mode G.652.	m.	200	41	8200
2.2.	Optical cable with internal support cable, central module, 4 fibers, single mode G.652.	m.	300	36	10800
2.3.	Other consumables (connectors, screws, dowels, insulating tape, fasteners, etc.)	set	1	6000	6000
III.	TOTAL COST OF EQUIPMENT AND MATERIALS (item I+item II)				50 783
IV.	*Transportation and procurement costs, 10% item III**				5078
V.	Work on installation and switching of equipment, including:				111 160
5.1.	Installation of banners	units	4	8000	32000
5.2.	Cabling	m.	500	75	37500
5.3.	Installation and welding of connectors	units	32	880	28160
5.4.	Installation of switching equipment	units	9	1500	13500
VI.	TOTAL ESTIMATED (item III+item IV+item V)				167 021

Explanations and comments:

The total length of the route is 500 m, including:
- from the fence to the production building and the administrative building is 100 m each (total 200 m);
- along the fence between buildings 300 m.
Cable installation is carried out in an open way, including:
- from buildings to the fence (200 m) by air (hauling) using materials specialized for laying fiber-optic lines;
- between buildings (300 m) along a fence made of reinforced concrete slabs, the cable is secured in the middle of the fence using metal clips.
To organize fiber-optic communication lines, a specialized self-supporting (built-in cable) armored cable is used.