A fiber optic system works by transmitting light pulses generated by a light emitter located at one end of the fiber. This system is a structure consisting of a transparent, centrally located quartz glass core surrounded by a shell and a special protective coating.
Below you will find out what functions a fiber optic cable performs, consider in detail the advantages of fiber optics, and find out what types it is divided into.
Optical fiber - construction
Using suitable materials as the core and cladding of a fiber optic cable having different refractive indices results in the light beam traveling only in the core. The core material has a higher refractive index and thus there is total internal reflection of light from the cladding to the core. The protective coating is made of thermoplastic materials to protect the shell. A distinction is made between single-mode and multi-mode fibers: only single-mode fibers are used in power lines due to the significant reduction in attenuation, which is important for long lines.
Tasks
The main purpose of using fiber optic cables in the power industry is to provide communication between power substations. This is due to the use of modern automation to protect power lines from the effects of short circuits. Safety automation is located at each power plant, and to ensure its normal operation, a fast connection between stations is required. High-voltage overhead power lines (110 kV) and ultra-high voltage (220 and 400 kV) have a considerable length. Using more fiber in power lines makes it possible to lease fiber optic lines to other operators. This allows the creation of a global fiber-optic network intended for commercial use (Internet, telecommunications, multimedia, etc.).
On video: How does optical fiber work?
Advantages, types and types of optical fiber
The intensive growth in the use of fiber optic cables in the world has been going on for more than 40 years. This is due to the many advantages of fiber optics. The most important are: very high throughput of a single fiber, low signal attenuation even over very long distances, small size and light weight, complete immunity to radio interference and electromagnetic fields. Due to current environmental issues, an important feature of fibers is the absence of any environmental impact, which is very important when designing fiber optic lines. These connections are largely reliable, easy to use, provide workplace safety and significant efficiency, which is why they are becoming increasingly popular.
Types of wires with optical fibers in power lines
Fiber optic cables are produced in bundles containing from tens to several hundred fibers in one bundle. Fiber optic cables can be used in power lines as: phase conductors (live) or lightning conductors (grounding potential conductors) and self-supporting dielectric (additional cables in a line containing only fiber optic cables). There are several types of conductors associated with optical fibers.
OPGW (Optical Ground Wire) are lightning rods commonly used in 110 kV overhead power lines.
From a design point of view, there are two types of wires:
- wires consisting of one central tube (made of aluminum or stainless steel) containing optical fibers and an outer layer of aluminum alloys,
- hoses with a stainless steel socket; they consist of several steel wires forming cores and an outer layer of aluminum alloys. Optical fibers are placed in a special stainless steel tube and form the core of the cable.
The most important advantages of these cables are the following:
- possibility of application in existing lines (instead of conventional steel and aluminum wires such as AFL), in most cases without the need to strengthen the column structure,
- easy installation, using existing cable,
- reliability and durability.
— fiber optic cables without metal elements. They are made from a centrally located rod-shaped FRP core surrounded by multiple tubes containing optical fibers.
Between the inner and outer sheath of the cable are very strong aramid fibers, which give ADSS cables adequate mechanical strength.
ADSS cables have a slight increase in sag. When choosing an attachment point for ADSS cables, it is also necessary to take into account the distribution of the electric field strength between the phase wires, since in the event of rain or high air humidity, the outer sheath is exposed to micro-discharges. Placing wires in an area with too much electric field leads to rapid destruction of their sheath. The solution to this problem is the use of semiconductor cables, which, due to the high electromagnetic field strength, are usually used in lines with a voltage of no more than 110 kV. At higher voltages, special cables made of materials resistant to electric fields are used. When designing the suspension of ADSS cables on existing power lines, the additional stress placed on the supporting structures must be taken into account and appropriate reinforcements must be provided.
MASS (Metallic Aerial Self Supporting) - self-supporting cables made of aluminum steel wire in combination with optical fiber. They are very similar to OPGW cables, but do not provide a lightning conductor or electrical function in the line. For this reason, MASS cables typically hang slightly lower than the phase wires.
Special Applications of Optical Fibers
Temperature control in cable lines
One interesting application of fiber optic fibers is the DTS (Distributed Temperature Sensing) system used to monitor the temperature of high-voltage cable lines. This method is based on changing the attenuation of special fibers depending on their temperature. The return conductor of power cables contains optical fibers that are connected to a special device that provides operational monitoring of the temperature of the cable core and structural disturbances in its environment, for example, when performing work near a cable line (here the phenomenon of fiber damping is used depending on the deformation of the fiber). This system can be used by network operators in emergency situations when there is a temporary need to load power lines with high current. This information allows the network operator to plan line shutdowns and carry out appropriate repairs in advance. .
Optical fiber - temperature control of phase conductors in overhead lines
A similar solution can be used in overhead power lines. A special optical fiber placed in an OPPC conductor allows the actual temperature of the phase conductors to be determined under given weather conditions. Monitoring allows the dispatcher to dynamically load the line and, in a broader perspective, so-called intelligent network management or “smart grids”.
Currently, fiber-optic communication lines are firmly in their position and are rapidly developing. Cables with copper cores are being replaced at a rapid pace with fiber-optic cables in all sections of networks. Traditional communication cables with copper conductors are being replaced by fiber-optic waveguides, in which the information carrier is electromagnetic waves in the infrared range. Information transmission via fiber-optic cables is carried out according to the principle of total internal reflection. Reflection is achieved due to a protective coating applied to the optical fiber (core), at this boundary the beam is completely reflected and propagates along the waveguide. Due to the increasing demands placed on telecommunication networks, the use of fiber optic technology is becoming indispensable.
In order to design the route of a fiber-optic communication line and select the desired type of cable, you need to know the operating conditions, cable design and its technical parameters. The demand for fiber optic communication line components is constantly increasing. Growth dynamics are observed not only in the segment of backbone networks built by telecom operators. A steady increase in the number of optical installations is also noticeable in the field of structured cabling systems, which is explained, first of all, by the development of information technology. Already today, the foundation is being laid for the construction of high-speed optical transmission lines with the ability to operate at a speed of 10 Gbit/s. Applications that integrate voice, data and video are becoming in demand, where fiber optics is also the best solution.
Currently, there are a large number of fiber optic cable designs, focused on various application conditions (laying inside buildings, in telephone sewers or in the ground, optical cable can be laid along railway supports, on power lines, in sewer and water pipes, along river beds and the bottom of lakes, along highways, along with power cables.
For many applications, fiber optics is preferable due to a number of advantages.
Advantages of fiber optic cables compared to traditional copper cables:
- Immunity to interference and interference, the complete insensitivity of the cable to external electrical noise and interference ensures stable operation of the systems even in cases where the installers did not pay sufficient attention to the location of nearby power networks, etc.
- The absence of electrical conductivity for fiber optic cable means that problems associated with changes in ground potential, such as those found in power plants or railways, are eliminated. This same property eliminates the risk of equipment damage caused by current surges from lightning, etc.
- Ease of installation, splicing and assembly work.
- No crosstalk or interference, which improves the quality of data transmission.
- Small dimensions and minimal weight (up to 2.2 mm outer diameter and weight 4 g/m for polymer optical fiber, SIMPLEX simplex version). The extremely small size of optical fibers and fiber optic cables allows you to breathe new life into crowded cable channels. For example, one coaxial cable takes up the same amount of space as 24 optical cables, each of which can supposedly carry 64 video channels and 128 audio or video signals simultaneously.
- Possibility of laying over long distances.
- The highest bandwidth of any transmission medium available, optical fiber's wide transmission bandwidth allows high-quality video, audio, and digital data to be transmitted simultaneously over a single fiber optic cable.
- Low loss, fiber optic cables allow image signals to be transmitted over long distances without the use of routing amplifiers or repeaters. This is especially useful for long-distance transmission schemes, such as highway or railway surveillance systems, where repeater-free sections of 20 km are not uncommon.
- A timeless communication line, by simply replacing the terminal equipment rather than the cables themselves, fiber optic networks can be upgraded to carry more information. On the other hand, part or even the entire network can be used for a completely different task, for example, combining a local area network and a closed-circuit TV system in one cable.
- Long service life.
The main element of optical cables is optical fiber. A distinction is made between polymer optical fiber (POF), polymer-coated quartz glass fiber (PCF), and pure high-grade quartz glass fiber (GOF).
For use in industrial environments, LAPP Kabel offers fiber optic cables made from polymer optical fibers and glass fibers, as well as combined cables with copper cores.
Most cables are specially designed for flexible installation in drag chains.
The general concept of transmitting information over fiber optic cables is defined by the use of polymer fiber (POF), polymer coated fiber (PCF) and glass fiber (GOF) cables.
Matching optical connectors, tools and pre-assembled optical fiber patch cables are also available.
Typical applications of fiber optic cables with (POF), (PCF):
- BUS systems for production automation;
- in mechanical engineering and production of industrial equipment.
Due to their special properties, optical fiber cables (POF) find their application:
- where reliable transmission of information is required;
- where the laying of cables is spatially limited;
- short data transmission distances (up to 60 m).
Typical Applications of Optical Fiber Cables (GOF)
Designed for use where large amounts of data need to be transmitted at high speeds and over long distances (from 60 m to several kilometers), for example:
- in local computer networks LAN (Local Area Networks);
- in networks built using MAN (Metropolitan Area Networks) technology;
- in networks built using WAN (Wide Area Networks) technology.
Basic structural elements of fiber optic cables
Several main groups of structural elements can be distinguished: optical fibers with protective coatings, optical modules, cores, power elements, hydrophobic materials, shells and reinforcement. Depending on the purpose and conditions of use, fiber optic cables have certain designs.
Optical fiber (OF) is very sensitive to external influences: mechanical pressure and bending, temperature, humidity. To protect against them, a coating must be applied to the OM. The standardized nominal diameter of the optical fiber is 250 microns. In order to identify the OM, a layer of paint 36 microns thick is applied to the coating. The reliability of the connection of the dye with the coating is ensured by intense ultraviolet irradiation.
The main element of fiber optic cables is optical fiber (OF), made from high-quality quartz steel, which ensures the propagation of light signals.
An optical fiber consists of a central high refractive index portion (core) surrounded by a cladding of low refractive index material, as shown in Fig. 1, the fiber is characterized by the diameters of these regions; for example, 50/125 means a fiber with a core diameter of 50 μm and an outer cladding diameter of 125 μm.
Light propagates along the fiber core by successive total internal reflections at the interface between the core and cladding; its behavior is in many ways similar to what it would be like if it fell into a pipe whose walls were covered with a mirror layer. However, unlike a conventional mirror, whose reflection is rather inefficient, total internal reflection is essentially close to ideal - this is their fundamental difference, allowing light to propagate long distances along the fiber with minimal loss.
In turn, light guides differ depending on the refractive index profile in the direction from the center to the periphery in the cross section of the light guide. The fiber in (Fig. 2a) is called step-index and multimode fiber because there are many possible paths, or modes, for a light beam to propagate. This multiplicity of modes results in pulse dispersion (broadening) because each mode travels a different path through the fiber, and therefore different modes have different transmission delays from one end of the fiber to the other. The result of this phenomenon is a limitation of the maximum frequency that can be effectively transmitted for a given length of fiber; increasing either the frequency or the fiber length beyond the limits essentially causes successive pulses to merge together, making them impossible to distinguish. For typical multimode fiber, this limit is approximately 15 MHz * km, which means that a video signal with a bandwidth of, for example, 5 MHz can be transmitted over a maximum distance of 3 km (5 MHz x 3 km = 15 MHz * km). Attempting to transmit a signal over a greater distance will result in progressive loss of high frequencies.
Single-mode fibers, as they are called (Fig. 2b), are very effective at reducing dispersion, and the resulting bandwidth of many GHz * km makes them ideal for public telephone and telegraph networks (PTT) and cable television networks. Unfortunately, such small-diameter fibers require a high-power, precision-aligned, and therefore relatively expensive laser diode emitter, making them less attractive for many short-range closed-circuit TV surveillance applications.
Ideally, a fiber with the same bandwidth as single-mode fiber but with the same diameter as multimode fiber is required to enable low-cost LED transmitters. To some extent, these requirements are met by multimode fiber with a gradient change in the refractive index (Fig. 2, c). It resembles the multimode step-index fiber discussed above, but the refractive index of its core is not uniform, varying smoothly from a maximum value at the center to lower values at the periphery. This leads to two consequences. First, the light travels along a slightly curved path, and second, and more important, the differences in propagation delay between different modes are minimal. This is because high modes that enter the fiber at a higher angle and travel a longer distance actually start to propagate at a higher speed as they move away from the center into the region where the refractive index decreases, and generally travel faster , than lower-order modes remaining near the axis in the fiber, in the region of high refractive index. The increase in speed just compensates for the larger distance traveled.
Gradient multimode fibers are preferable because, firstly, fewer modes propagate in them and, secondly, their angles of incidence and reflection differ less, and therefore, transmission conditions are more favorable.
However, graded index multimode fibers are not ideal, but they still exhibit very good bandwidth values. Therefore, in most closed-circuit TV surveillance systems of short and medium length, the choice of this type of fiber is preferable. In practice, this means that bandwidth is only rarely a parameter that needs to be taken into account.
However, this is not the case for attenuation. The optical signal attenuates in all fibers at a rate depending on the wavelength of the transmitter of the light source. There are three wavelengths at which optical fiber attenuation is typically minimal, 850, 1310 and 1550 nm. These are known as transparency windows. For multimode systems, the 850 nm window is the first and most commonly used (lowest cost). At this wavelength, good quality graded multimode fiber exhibits an attenuation of about 3 dB/km, making it possible to implement closed-circuit TV communications over distances exceeding 3 km.
At a wavelength of 1310 nm, the same fiber exhibits an even lower attenuation of 0.7 dB/km, thereby allowing the communication range to be proportionally increased to approximately 12 km. 1310 nm is also the first operating window for single-mode fiber optic systems, with an attenuation of about 0.4 dB/km, which, in combination with laser diode transmitters, allows for communication lines in excess of 50 km. A second transparency window of 1550 nm is used to create even longer communication links (fiber attenuation less than 0.24 dB/km) (Fig. 3).
The difference in attenuation values in different transparency windows is quite significant, especially in multimode fibers. Table 1 clearly illustrates the advantage of single-mode fibers over multimode ones.
To ensure stable operation of the fibers and reduce the risk of their rupture under the influence of longitudinal and transverse stresses, the fibers are protected with primary and secondary coatings. The primary coating, applied in a continuous layer directly to the shell of the fiber after it has been drawn out, protects the surface of the fiber from damage and gives it additional mechanical strength. The following are used as a secondary coating of OM: a tube with freely placed OBs with a primary protective coating; continuous polymer coating; a strip element in which OMs with a primary protective coating are placed. In a tubular element (tube), which acts as a secondary protective coating, freely placed fibers with a primary protective coating are usually laid without twisting or by twisting around the central strength element. Multimode light guides are easier to manufacture, it is easier to introduce light rays into them, and they are easier to splice.
Multimode fibers are characterized by a frequency bandwidth expressed in megahertz. In specifications, it is customary to indicate not the bandwidth, but the so-called broadband coefficient inherent in a given type of fiber, in megahertz multiplied by kilometers (MHz x km). For a given broadband coefficient (let's denote it S), the AF passband will depend on the length of the line or its regeneration section modifications AF=S. For 50/125 multimode fibers, the normalized S values are 4001500 MHz*km. For a 10 km line, the bandwidth is 40150 MHz. The longer the line, the smaller the frequency bandwidth and, therefore, the smaller the amount of information transmitted.
In an ideal case, only one wave propagates along single-mode fibers. They have a significantly lower attenuation coefficient (depending on the wavelength by 24 and even 710 times) compared to multimode ones and the highest throughput, since the signal is almost not distorted in them (Fig. 4). But for this, the diameter of the fiber core must be commensurate with the wavelength (in any case, d< А < 10). Практически dc=8 10 мкм.
Depending on the operating conditions, different requirements are placed on the cable design. A cable that is used outdoors, first of all, must be protected from atmospheric influences, such as sunlight, moisture, and temperature changes. The cable, which is intended for laying in cable wells, needs protection from rodents. If the cable is suspended between power line supports, its mechanical strength is important. When choosing a cable, the main focus is usually on two aspects. The first is fire safety, the need for which arises if the cable is laid indoors. The second aspect is the integrity and safety of light guides during storage, installation and operation of the fiber optic cable. At each of these stages, the cable is exposed to mechanical, atmospheric and other influences that can be dangerous to the fiber. Note that here we are not talking about physical destruction of the optical fiber.
The most common material used to make the outer sheath of fiber optic cables is polyethylene. It has excellent physical parameters (high strength, good wear resistance, resistance to ultraviolet radiation, oxidation and other chemical influences) and good dielectric properties. Polyethylene has good resistance to moisture penetration, low and high temperatures, and also has the ability not to change its physical properties under the influence of changes in ambient temperature.
Particular attention should be paid to fiber-optic cables, the sheaths of which meet fire safety requirements. The basis for the manufacture of the corresponding shells is polyethylene, and the necessary properties are achieved by adding special chemical additives. In the description of a fiber optic cable, the presence of such properties is most often indicated by the abbreviation LSZH (Low Smoke Zero Halogen). The presence of a non-flammable sheath on a fiber-optic cable, which does not emit halogens, significantly increases its cost, but when laying the cable indoors, at industrial facilities, in subway tunnels, international and national fire safety standards require the use of this type of cable.
Reinforcing elements
To increase the permissible stretch of a fiber-optic cable, strength elements must be introduced into its design. The permissible elongation value of 1000-2000 N (newtons) can be achieved using Kevlar or glass fibers.
As a rule, this indicator is quite sufficient for general purpose cables. The threads can form a dense layer, or they can intertwine. Kevlar threads are believed to provide greater tensile strength. However, glass fibers also protect against rodents and act as a barrier to the spread of fire. Sometimes one central or a pair of side rods are used in parallel with Kevlar threads. Additional power elements can be dielectric or metal. The design with a central strength element is typical for a cable with a large number of fibers, which are placed in groups around the strength element. High permissible tensile strength in special types of cables, in which this value must be tens of kilonewtons, is achieved using steel rods. In such cables, optical fibers are often located not in thermoplastic, but in gel-filled steel tubes. Tensile performance characterizes the maximum force that can be applied in the longitudinal direction of the cable without changing the characteristics of the optical fiber. When a cable is stretched, the sheath itself is first affected, and only then the optical fiber.
As a result of changes in ambient temperature, the cable length naturally increases or decreases. Therefore, the group of these characteristics also includes the temperature range in which the cable can be stored, operated and installed.
Important Parameters for Fiber Optic Cables
The compressive force characterizes the permissible force with which the cable can be compressed in the transverse direction, provided that the amount of attenuation in the fiber remains within the normal range. Impact load characterizes the cable's resistance to shock.
The maximum cable bend is another important parameter that characterizes the maximum permissible radius of curvature of cable laying. It must be taken into account when it comes to laying fiber optic cable, for example in pipelines or cable ducts. The minimum permissible bend radius is often within 15-20 diameters of the outer sheath of the cable. If you neglect this parameter, the integrity of the light guides in the cable may be damaged.
Torsion determines the ability of the cable sheath to provide protection to the fiber when the sheath is twisted around its axis. For a cable with metal armor, the permissible twisting angle is less than for a cable without armor.
Water penetration is an important parameter for fiber optic cable, especially if it is intended for outdoor use.
Indoor cable
The type of cable sheath is largely determined by operating conditions. For a fiber optic cable that will be used indoors, the main characteristics are:
- Fire safety;
- good flexibility and ease of installation;
- mounting the connector directly onto the optical fiber;
- absence of gel inside the cable sheath;
- absence of metal elements.
Of course, the most important characteristic of a cable for installation inside a building is its resistance to fire. The cable must have a sheath that does not spread combustion, does not smoke, does not emit halogens and other toxic compounds when exposed to flame. It is understood that these properties are possessed not only by the outer shell, but also by the internal elements of the structure. These requirements are met by a cable with a tight buffer (Tight-Buffer), in which each fiber is additionally enclosed in a 900-micron sheath. This shell provides sufficient protection against moisture penetration for the relevant operating conditions. The densely buffered fiber optic cable itself is lightweight and very flexible.
For installation inside buildings, the so-called “dry” cable, which does not contain gel, is most often used. One of the reasons why this type of cable is recommended for indoor use is that the gel can become a fire propagation medium within the cable sheath, even if the outer sheath itself is not flame retardant. Another reason is a phenomenon sometimes called Axial Migration, which can be translated as “gel flow.”
If a gel-containing cable is used for inter-floor communication of network segments, there is a high probability that in the summer there will be gel in the fiber-optic cross-connect panel of the lower floor, and the consequences of this can be very disastrous. Instead of leaking water-repellent composition, moisture may condense in the fiber tube, which deteriorates the parameters of the optical fiber. This problem arises if the cable is located, for example, in an unheated shaft.
In addition, this may lead to changes in the mechanical characteristics of the cable itself. The fact is that the amount of optical fiber in a gel-containing tube exceeds its length; the free placement of the fiber in the tube in the normal state resembles a spiral. The fiber itself is buffered with a diameter of 250 micrometers (µm) and is fixed at the junction with the connectors or pigtail sleeves, that is, at only two points. In the case of a vertical cable arrangement, together with the gel, the fiber also moves from top to bottom, as a result of which in the upper part of the cable the fiber is straightened and can be in a tense state.
Now all the tensile force applied to the outer sheath is equally transferred to the fiber that does not have additional length. Stretching of the outer shell can occur, for example, in the warm season as a result of a natural increase in length with rising temperatures. Ultimately, this will lead to changes in fiber characteristics, microcracks, or even tearing of the light guide from the optical connector. In the lower part of a vertically located cable, on the contrary, there will be an excess of fiber, which can also affect the mechanical strength of the cable and, consequently, the reliability of the fiber-optic communication line as a whole.
For cables used indoors, it is preferable to install connectors directly on the fiber. In this case, additional fastening is provided to a dense buffer with a diameter of 900 microns, which to some extent makes it possible to relieve possible stress from the optical fiber.
In addition, the implementation of Fiber to the Desk technology is based on connecting workstations to SCS using a fiber-optic cable, which must be terminated in a special socket. Such sockets are not suitable for mounting splice cassettes for welded connection sleeves, but require mounting the connectors directly onto the fiber. The Tight Buffer cable with a 900 µm buffer is best suited for this task.
Outdoor cable
The types of fiber optic cables for outdoor installations today are very diverse, which is explained by the operating conditions and methods of their installation. Such cables can be divided into two groups: those that can be directly dug into the ground, and those that are laid in special sewers. Separately, you can also highlight cables that are suspended in the open space between poles on a supporting cable or on brackets along buildings.
Cables suspended between power line supports must have minimal weight, but at the same time provide good protection from the damaging effects of solar radiation and be completely dielectric. In addition, their shell must reliably perform its protective functions not only at low or high temperatures, but also at frequent temperature changes.
However, rodents for cables installed in telecommunications sewers can be an even bigger problem. Metallic or non-metallic armor, a dense layer of fiberglass threads - these are the ways to solve this problem. To reduce the frictional force when pulling the cable into cable ducts, its outer sheath must have a low coefficient of friction and be very durable. This is achieved using special materials, for example, polyamide (PA). Particular attention should be paid to protecting the cable from moisture penetration, taking into account the possibility of flooding of cable ducts with water. In this case, the best cable is one that houses the optical fibers in gel-filled thermoplastic tubes. If there is only one such tube in a cable, then it is called Uni Tube, if there are several tubes, it is called Multi Tube.
Each type of cable has its pros and cons, and you need to choose Uni Tube or Multi Tube depending on the specific task. For example, for ease of use, cables with more than 12 fibers generally have a Multi Tube design. This is due to the fact that the cassette for mounting welded joints, into which the fiber-containing tube is inserted, is most often designed for only 12 fibers. In addition, in cross-connect panels and junction boxes, fiber optic connectors are also often arranged in groups of 12. Therefore, if you need to use a 16-core cable, it is better to choose a Multi Tube, in which each of the four tubes contains four light guides. To maintain the round shape of the cable, together with the four gel-filled tubes, it is necessary to use another pair of plastic rods. For example, a 24-core cable contains six tubes of four fibers or four tubes of six fibers.
In a Multi Tube cable, tubes containing fibers are placed around a central strength element. This cable has a greater allowable stretch than Uni Tube. Naturally, it is heavier and has a larger cross section. For digging into the ground, this is not of decisive importance, but when pulling such a cable into telecommunications sewers, it can directly depend on the diameter of the cable being laid. From an economic point of view, Uni Tube cable is preferable.
Also, do not forget about the length of the cable that can be pulled into the cable duct. This factor should be taken into account, first of all, when calculating the number of couplings that are required for splicing optical fibers. Let us immediately note that the length of the cable that can physically be pulled into the sewer differs from the length that would guarantee the reliable operation of the fiber-optic communication line.
The fact is that during the installation process the cable is successively pulled through a number of telecommunication wells, the distance between which is several tens of meters. Since these wells are not located in a straight line, the cable has to be constantly bent, stretched, and twisted. All these mechanical effects can cause the formation of microcracks in the optical fiber, which can cause harm only after several years.
In addition, when large sections of cable are pulled through manholes, the outer sheath may be worn out or scratched so much that it loses its protective functions. Therefore, the recommended cable length for tightening through telecommunications wells is 1-1.5 km. Of course, you can first tighten 1 km of cable in one direction, then unwind it from the reel and tighten another 1 km in the other. The result will be a segment 2 km long, but only highly qualified specialists can carry out such work.
If it is necessary to bury a cable in the ground, first of all it is worth considering protection from rodents and maintaining mechanical strength, as well as taking into account the influence of ultraviolet radiation, the presence of a smooth sheath and operating conditions at particularly low temperatures. As a rule, such a cable is laid in a trench using special mechanical means. Both Uni Tube and Multi Tube cables can be used for digging into the ground. Protection against rodents can be implemented to the same extent in each of them, but protection against moisture in the Multi Tube will be much more effective if the space between the fiber-containing tubes is additionally filled with a hydrophobic composition. In addition, in a Multi Tube cable it is possible to achieve a greater value of permissible longitudinal stretch, since in the cable design, in addition to Kevlar or glass fibers, there is also a central strength element.
Optical cables for long-distance submarine communications
Underwater long-distance fiber optic communication lines are primarily associated with international lines. Optical cables for long-distance underwater systems are structurally complex and labor-intensive to manufacture. These cables must contain elements that protect optical fibers from moisture and atomic hydrogen. Cables must be produced in large construction lengths, and all optical fibers along the construction length of the cable must not have welds.
In the operating wavelength range, fibers must have low values of attenuation coefficient, chromatic and polarization mode dispersion. Therefore, in modern conditions, fibers with non-zero dispersion shift are chosen as optical fibers in submarine cables.
Submarine optical cables are characterized by high values of mechanical parameters of stretching and crushing. Typically, the grading of these cables according to mechanical parameters involves the production of coastal cables (with the highest values of mechanical parameters), cables for the sea fishing zone (most often these cables are buried in the bottom soil), and cables for the deep-sea zone. In the Black Sea, submarine cables must additionally be resistant to hydrogen sulfide.
Horizontal optics
With the growing demands of new network applications, the use of fiber optic technologies in structured cabling systems is becoming increasingly important. What are the advantages and features of using optical technologies in the horizontal cable subsystem, as well as at user workplaces?
The main advantages of optics include the highest bandwidth of all possible transmission media, including twisted copper and coaxial cables, as well as the longest data transmission range at the lowest cost of active equipment and operation.
Fiber optic segments can be up to 20 times longer than copper segments. A typical multimode fiber intended for use in a LAN today has a bandwidth of more than 500 MHz per kilometer of length. Since existing SCS standards define the length of horizontal optical wiring from the floor distribution point to the subscriber socket as 100 m, each such connection provides a bandwidth of several GHz. Recent advances in multimode fiber technology enable even higher transmission speeds
So, optical fiber has characteristics that far exceed the requirements of today's Ethernet speed standards (100 Mbit/s) for connecting workplaces, and allows you to easily switch to new data transfer protocols, such as, for example, 1 and 10 Gigabit Ethernet or high-speed ATM.
Speaking about the possibilities of modernization, it should be noted that the properties of optical fiber are practically independent of the data transmission speed in the network, since there are no mechanisms (for example, crosstalk) that lead to degradation of the properties of optical fiber with increasing speed of network protocols. Once the optical fiber is installed and tested to meet standards, the cable link can operate at speeds of 1, 10, 100, 500, 1000 Mbps or 10 Gbps.
This ensures that the cable infrastructure installed today will be able to support any network technology for the next 10-15 years, or even more. Only one transmission medium in SCS satisfies these requirements - optics. Optical cables have been used in telecommunications networks for more than 25 years, and recently they have also found widespread use in cable television and LANs.
In LANs, they are mainly used to build backbone cable channels between buildings and in the buildings themselves, while providing high speed data transfer between segments of these networks. However, the development of modern network technologies is actualizing the use of optical fiber as the main medium for connecting users directly.
Structured cabling systems, which use fiber optics for both trunk and horizontal cabling, provide consumers with a number of significant benefits: more flexible design, smaller building footprint, higher security and better manageability.
The use of optical fiber in workplaces will make it possible in the future to switch to new network protocols, such as Gigabit and 10 Gigabit Ethernet, at minimal cost. This is possible thanks to a number of recent advances in fiber optic technology:
- multimode optical fiber with improved optical characteristics and bandwidth;
- optical connectors with a small form factor, which require less area and less installation costs;
- Planar laser diodes with a vertical cavity provide long-distance data transmission at low cost.
A wide range of solutions for building zone optical cable systems ensures a smooth, economically viable transition from copper to all-optical structured cable systems.
Standard designation for fiber optic cables
Almost all European manufacturers mark fiber optic cables in accordance with the DIN VDE 0888 standard system. According to this standard, each type of cable is assigned a sequence of letters and numbers that contain all the characteristics of the fiber optic cable.
For example, I-V(ZN)H 1×4 G50/125 designates a cable for indoor use [I]. The fibers are in a dense buffer with a diameter of 900 microns [V], with non-metallic strength elements, with a non-flammable and low-smoking sheath [N]. Number of fibers 4. Fiber type multimode with core and fiber cladding sizes of 50 and 125 µm, respectively.
A/IDQ(ZN)(SR)H 1×8 G50/125 designates a cable for both outdoor and indoor use. The fibers are placed in a central tube filled with a water-repellent compound. Kevlar or glass fibers in metal corrugated armor. Outer shell LSZH, low smoke, does not emit halogens during combustion [H]. One tube with eight fibers. Fiber type multimode with core and fiber cladding sizes of 50 and 125 µm, respectively.
ADF(ZN)2Y(SR)2Y 6×4 E9/125 cable for outdoor use [A]. It has two polyethylene shells: outer and inner, between which there is metal armor in the form of a corrugated tape. The fibers are located in six tubes, four in each. The inside of the tube, as well as the voids between the tubes, are filled with a water-repellent composition. Kevlar threads and a central non-metallic element are used as power components. Fiber type: single-mode [E9/125] with core and fiber cladding sizes of 9 and 125 µm, respectively.
New standards and technologies
In recent years, several technologies and products have appeared on the market that make it much easier and cheaper to use optical fiber in a horizontal cable system and connect it to user workstations.
Among these new solutions, first of all, I would like to highlight optical connectors with small form factor (small form factor connectors), planar laser diodes with a vertical cavity VCSEL (vertical cavity surface emitting lasers) and optical multimode fibers of the new generation OM-3.
It should be noted that the recently approved type of multimode optical fiber OM-3 has a bandwidth of more than 2000 MHz/km at a laser beam length of 850 nm. This type of fiber provides sequential transmission of 10 Gigabit Ethernet protocol data streams over a distance of 300 m. The use of new types of multimode optical fiber and 850nm VCSEL lasers ensures the lowest cost of implementing 10 Gigabit Ethernet solutions.
The development of new fiber optic connector standards has made fiber optic systems a serious competitor to copper solutions. Traditionally, fiber-optic systems required twice as many connectors and patch cords as copper; telecommunications locations required a much larger area to accommodate optical equipment, both passive and active.
Small form factor optical connectors, recently introduced by a number of manufacturers, provide twice the port density of previous solutions because each small form factor connector contains two optical fibers instead of just one.
At the same time, the sizes of both passive optical elements - cross-connects, etc., and active network equipment are reduced, which makes it possible to reduce installation costs by four times (compared to traditional optical solutions).
It should be noted that the American standardization bodies EIA and TIA in 1998 decided not to regulate the use of any specific type of small form factor optical connectors, which led to the appearance on the market of six types of competing solutions in this area: MTRJ, LC, VF-45, Opti Jack, LX 5 and SCDC. There are also new developments today.
The most popular miniature connector is the M-TRJ type connector, which has a single polymer tip with two optical fibers inside. Its design was developed by a consortium of companies led by AMP Netconnect based on the multi-fiber MT connector developed in Japan. AMP Netconnect has today provided more than 30 licenses for the production of this type of MTRJ connector.
The MTRJ connector owes much of its success to its external design, which is similar to that of the 8-pin modular copper RJ-45 connector. MTRJ connector performance has improved significantly in recent years. AMP Netconnect offers MTRJ connectors with keys to prevent erroneous or unauthorized connection to the cabling system. In addition, a number of companies are developing single-mode versions of the MTRJ connector.
LC connectors are in fairly high demand in the optical cable solutions market. The design of this connector is based on the use of a ceramic tip with a diameter reduced to 1.25 mm and a plastic housing with an external lever-type latch for fixation in the socket of the connecting socket.
The connector is available in both simplex and duplex versions. The main advantage of the LC connector is its low average loss and its standard deviation, which is only 0.1 dB. This value ensures stable operation of the cable system as a whole. Installation of the LC fork follows a standard epoxy bonding and polishing procedure. Today, the connectors have found their use among manufacturers of 10 Gbit/transceivers.
The SCS industry has made its choice in favor of MTRJ and LC connectors. There are also single-mode MTRJ connectors, a feature of which is short installation time. To install the connectors, there is no need to use epoxy glue or polish the ferrules, you just need to clean and chop the fiber and then install it into the connector.
There are a number of proprietary solutions for use in horizontal cabling systems, among which we can note, for example, the Volition Network Solutions system from 3M. It uses VF-45 type connectors.
The VF-45 connector is approximately half the size of a duplex SC connector and does not have a centering tip. To align optical fibers, it uses V-shaped grooves, and the connector and plug itself are equipped with a protective shutter that moves horizontally when they are aligned.
In addition to hybrid optical cords that have VF-45 connectors on one side and ST, SC or other connectors on the other, 3M recently released the VF-45 plug, designed for field installation and allowing for quick termination of cables at consolidation points. In addition, to create high-security optical networks, the company offers six varieties of VF-45 with color coding and security keys.
Although VF-45 connectors were originally designed for horizontal fiber optic cabling applications, they can also be used in backbone applications. The ZM company also considers one of its major achievements to be that currently the price of a network adapter equipped with a VF-45 connector does not exceed $100 (Fig. 5).
Another connector designed for implementing fiber-to-desk cabling solutions is the OptiJack-FJ connector from Panduit.
It has two separate ceramic tips with a diameter of 2.5 mm, and the form factor corresponds to an 8-pin copper RJ-45 connector. OptiJack-FJ modules can be used with Panduit MiniCorn receptacles and patch panels.
Thus, SFFC components, together with new VCSEL lasers (lasers with the characteristics inherent in traditional laser sources, and a low cost comparable to conventional LEDs), make it possible to bring high-speed optical technologies directly to the user's workplace.
Anna FRIESEN, technical consultant at U. I. LAPP GmbH.
Inside are diagrams, gifs, tables and a lot of interesting text.
You are ready?
Conditional classification
Unlike the familiar twisted pair cable, which, regardless of the place of application, has approximately the same design, fiber optic communication cables can have significant differences based on the scope of application and location of installation.The following main types of fiber optic cables for data transmission can be distinguished based on the scope of application:
- For installation inside buildings;
- for cable ducts, unarmored;
- for cable ducts, armored;
- for laying in the ground;
- suspended self-supporting;
- with cable;
- underwater.
Cable for installation inside buildings
Optical cables for laying inside buildings are divided into distribution cables, from which the network as a whole is formed, and subscriber cables, which are used directly for laying throughout the premises to the end user. Like twisted pair, optics are laid in cable trays, cable ducts, and some brands can also be stretched along the external facades of buildings. Typically, such a cable is led to an interfloor distribution box or directly to the subscriber connection point.
The design of fiber optic cables for installation in buildings includes an optical fiber, a protective covering and a central strength element, such as a bundle of aramid threads. Optics installed indoors have special fire safety requirements, such as non-propagation of combustion and low smoke emission, therefore polyurethane, rather than polyethylene, is used as a shell for them. Other requirements are low cable weight, flexibility and small size. For this reason, many models have a lightweight design, sometimes with additional protection against moisture. Since the length of optics inside buildings is usually small, the signal attenuation is insignificant and does not affect data transmission. The number of optical fibers in such cables does not exceed twelve.
There is also a kind of cross between a “bulldog and a rhinoceros” - a fiber-optic cable, which additionally contains a twisted pair cable.
Unarmored sewer cable
Unarmored optics are used for installation in sewers, provided that there are no external mechanical influences on them. Also, such a cable is laid in tunnels, collectors and buildings. But even in cases where there is no external influence on the cable in the sewer, it can be laid in protective polyethylene pipes, and installation is carried out either manually or using a special winch. A characteristic feature of this type of fiber optic cable is the presence of a hydrophobic filler (compound), which guarantees the ability to operate in sewer conditions and provides some protection from moisture.
Armored sewer cable
Armored fiber optic cables are used in the presence of large external loads, especially tensile loads. Reservations can be different, tape or wire, the latter is divided into one- and two-layer. Cables with tape armor are used in less aggressive conditions, for example, when laid in cable ducts, pipes, tunnels, and bridges. Tape armor is a smooth or corrugated steel tube with a thickness of 0.15-0.25 mm. Corrugation, provided that this is the only layer of cable protection, is preferable, as it protects the optical fiber from rodents and generally increases the flexibility of the cable. For more severe operating conditions, for example, when laying in the ground or on the bottom of rivers, cables with wire armor are used.
Cable for laying in the ground
For laying in the ground, optical cables with single-strand or double-strand wire armor are used. Reinforced cables with tape armor are also used, but much less frequently. The optical cable is laid in a trench or using cable layers. This process is described in more detail in my second article on this topic, which provides examples of the most common types of cable layers. If the ambient temperature is below -10 o C, the cable is preheated.
In wet soil conditions, a cable model is used, the fiber-optic part of which is enclosed in a sealed metal tube, and the armored wire is impregnated with a special water-repellent compound. This is where calculations come into play: engineers working on cable laying must not allow tensile and compressive loads to exceed the permissible limits. Otherwise, either immediately or over time, the optical fibers may be damaged, rendering the cable unusable.
Armor also affects the permissible tensile force. Fiber optic cables with double-layer armor can withstand a force of 80 kN, single-layer cables - from 7 to 20 kN, and tape armor guarantees the “survival” of the cable under a load of at least 2.7 kN.
Suspended self-supporting cable
Suspended self-supporting cables are mounted on existing supports of overhead communication lines and high-voltage power lines. This is technologically simpler than laying a cable in the ground, but there is a serious limitation during installation - the ambient temperature during work should not be lower than - 15 o C. Suspended self-supporting cables have a standard round shape, due to which wind loads on the structure are reduced, and the distance The span between supports can reach one hundred meters or more. The design of self-supporting suspended optical cables necessarily contains a central power element - a central strength element made of fiberglass or aramid threads. Thanks to the latter, the fiber optic cable can withstand high longitudinal loads. Suspended self-supporting cables with aramid yarns are used in spans up to one kilometer. Another advantage of aramid threads, in addition to their strength and low weight, is that aramid is by nature a dielectric, that is, cables made on its basis are safe, for example, when struck by lightning.
Depending on the structure of the core, there are several types of overhead cable:
- Cable with a profiled core - contains optical fibers or modules with these fibers - the cable is resistant to stretching and compression;
- Cable with twisted modules - contains optical fibers, loosely laid, the cable is resistant to stretching;
- Cable with one optical module - the core of this type of cable does not have power elements, since they are located in the sheath. Such cables have the disadvantage of inconvenient fiber identification. However, they have a smaller diameter and a more affordable price.
Optical cable with rope
Rope optical cables are a type of self-supporting cables that are also used for aerial installation. In such a product, the cable can be load-bearing and wound. There are also models in which the optics are built into the lightning protection cable.
Reinforcing an optical cable with a cable (profiled core) is considered a fairly effective method. The cable itself is a steel wire enclosed in a separate sheath, which in turn is connected to the cable sheath. The free space between them is filled with a hydrophobic filler. Often this design of an optical cable with a cable is called a “figure eight” because of its external similarity, although I personally have associations with overfed “noodles”. "Eights" are used for laying overhead communication lines with a span of no more than 50-70 meters. There are some restrictions in the operation of such cables, for example, a figure eight with a steel cable cannot be suspended on power lines. I hope there is no need to explain why exactly.
But cables with a winding lightning protection cable (lightning cable) can be easily mounted on high-voltage power lines, being attached to the grounding wire. Ground wire cable is used in places where there is a risk of damage to optics by wild animals or hunters. It can also be used on longer flights than a regular figure eight.
Submarine optical cable
This type of optical cable stands apart from all others, as it is laid in fundamentally different conditions. Almost all types of submarine cables are armored in one way or another, and the degree of armor depends on the bottom topography and burial depth.
The following main types of submarine cables are distinguished (by type of armor):
- Not armored;
- Single (one-step) reservation;
- Enhanced (single-layer) reservation;
- Reinforced rock (two-layer) armor;
I looked at the design of the submarine cable in detail more than a year ago in this article, so here I will give only brief information with a picture:
Paradoxically, there is no direct correlation between cable armoring and burial depth, since the reinforcement protects the optics not from high pressures at depth, but from the activities of marine life, as well as nets, trawls and anchors of fishing vessels. This correlation is rather the opposite - the closer to the surface, the more anxiety, which is clearly visible in the table below:
Table of types and characteristics of submarine cables depending on laying depth
Production
Now that we have become acquainted with the most common types of fiber optic cables, we can talk about the production process of this entire zoo. We all know about fiber optic cables, many of us have dealt with them personally (as subscribers and as installers), but as is clear from the information above, fiber optic, especially trunk, cables can be seriously different from what you dealt with in the past. indoors.Since laying a fiber optic backbone requires thousands of kilometers of cable, entire factories are engaged in their production.
Manufacturing of fiber optic thread
It all starts with the production of the main element - the fiber optic thread. This miracle is produced at specialized enterprises. One of the technologies for producing optical filament is its vertical drawing. And this happens as follows:- At a height of several tens of meters, two tanks are installed in a special shaft: one with glass, the second, lower down the shaft, with a special polymer primary coating material.
- A glass thread is pulled from the precision feed unit of the workpiece or, more simply, the first reservoir with liquid glass.
- Below, the thread passes through a fiber optic diameter sensor, which is responsible for monitoring the diameter of the product.
- After quality control, the thread is coated with a primary polymer coating from a second reservoir.
- After going through the coating procedure, the thread is sent to another oven, in which the polymer is fixed.
- The optical fiber thread is stretched for another N-meters, depending on the technology, cooled and supplied to a precision winder; in other words, it is wound onto a reel, which is then transported as a workpiece to the cable production site.
The most common fiber optic cable sizes are:
- With a core of 8.3 microns and a shell of 125 microns;
- With a core of 62.5 microns and a shell of 125 microns;
- With a core of 50 microns and a shell of 125 microns;
- With a core of 100 microns and a shell of 145 microns.
Control of the diameter of the light guide is of great importance. It is this part of the installation that is responsible for one of the main parameters at all stages of thread production - the constant diameter of the final product (standard - 125 microns). Due to the difficulties in welding threads of any diameter, they strive to make them as long as possible. The linear footage of the fiber optic “blank” on a reel can reach tens kilometers(yes, exactly kilometers) and more, depending on the customer’s requirements.
Already at the enterprise itself, although this can be done at a glass factory, it all depends on the production cycle; for convenience, a colorless thread with a polymer coating can be rewound onto another bobbin, in the process painting it in its own bright color, by analogy with the familiar twisted pair cable. For what? For the glory of sat... for quickly distinguishing channels when, for example, repairing or welding cables.
Cable making
Now we have the heart of our product - the fiber optic thread. What's next? Next, let's look at the cross-sectional diagram of such an average underwater (yes, I like them the most) cable:
At the factory, the resulting optical filaments are launched into machines, which together form an entire conveyor for the production of one type of cable. At the first stage of production of unarmored models, the threads are woven into bundles, which ultimately constitute the “optical core”. The number of threads in the cable may vary, depending on the declared bandwidth. The bundles, in turn, are wound into a “cable” using special equipment, which, depending on its design and purpose. This equipment can also cover the resulting “cable” with a waterproofing material to prevent moisture from entering and fading of the optics in the future (called “in-module hydrophobic filler” in the diagram).
This is how the process of twisting bundles assembled together into a cable takes place at the Perm fiber optic cable plant:
After the required number of optical fiber bundles have been collected into the “cable,” they are filled with polymer or placed in a metal or copper tube. Here, at first glance, it seems that there are no pitfalls and there cannot be, but since the manufacturer strives to minimize the number of connections and seams, everything turns out to be not entirely simple. Let's look at one specific example.
To create a tube-body, shown in the diagram above as a “central tube,” a huge-length strip of the material we need (steel or copper) can be used. The tape is used so as not to have to deal with all the obvious rolling and welding around the entire circumference of the joint that we are familiar with. Agree, then the cable would have too many “weak” points in the design.
So here it is. The metal strip blank passes through a special machine that tensions it and has a dozen or two rollers that perfectly align it. Once the sliver is aligned, it is fed to another machine where it meets our fiber optic strand bundle. An automatic machine on a conveyor bends the tape around the stretched optical fiber, creating a perfectly shaped tube.
This entire, still fragile, structure is pulled further along the conveyor to a high-precision electric welding machine, which at high speed welds the edges of the tape, turning it into a monolithic tube into which a fiber-optic cable is already laid. Depending on those. process, the whole thing can be filled with a hydrophobic filler. Or don’t flood it, it all depends on the cable model.
In general, everything became more or less clear with production. Different brands of fiber optics, primarily trunk cables, may have some design differences, for example, in the number of cores. Here the engineers did not invent a bicycle and simply combine several smaller cables into one large one, that is, such a backbone cable will have not one, but, for example, five tubes with optical fiber inside, which, in turn, are also filled with polyethylene insulation and, when necessary, reinforced. Such cables are called multi-modular.
One of the cross-sectional models of a multi-module cable
Multi-module cables, which are mostly used for long highways, have another mandatory design feature in the form of a core, or as it is also called, a central power element. The CSE is used as a “frame” around which tubes with fiber optic cores are grouped.
By the way, the Perm plant "Inkab", the production process of which is presented in the gifs above, with its volumes of up to 4.5 thousand kilometers of cable per year, is a dwarf in comparison with the plant of the same infrastructure giant Alcatel, which can produce several thousand kilometers fiber optic cable in one piece, which is immediately loaded onto the cable-laying vessel.
A steel tube is the least radical option for armoring optics. For non-aggressive operating and installation conditions, ordinary insulating polyethylene is often used. However, this does not negate the fact that after such a cable is manufactured, it can be “wrapped” in an armor winding made of aluminum or steel wire or cables.
Reservation of cable with polyethylene insulation at the same Perm plant
Conclusion
As you can understand from the material above, the main difference between different types of fiber optic cable is their “winding”, that is, what the fragile glass strands are packaged in, depending on the application and the environment in which the cable will be laid.If you liked this material, then feel free to ask questions in the comments, based on which I will try to prepare another article on this topic.
Thank you for your attention.
Hello friends! Our guru of the Internet and wireless technologies, Borodach, has already written about what fiber optics is (the link to the article will definitely be below). But my colleagues decided that Blonde should also write on this topic and at the same time add knowledge to her beautiful head. Well, it’s necessary - that means it’s necessary! We'll figure out.
Definition for Dummies
Optical fiber is the thinnest wires (threads) made of glass or plastic through which light is transferred due to internal reflection. Optical fiber cable is used as a way to transmit information at high speed over long distances (literally “at the speed of light”). This is how fiber-optic communication lines (FOCL) are built.
A fact from the history of development in Russia. The first fiber-optic line "St. Petersburg-Aberslund" (a city in Denmark) was laid by Rostelecom (then called Sovtelecom).
I immediately suggest watching a documentary on the topic:
Materials
Glass fiber is made from quartz. This provides the following characteristics:
- High optical permeability - this allows you to broadcast waves of different ranges;
- Minimal signal loss (low attenuation);
- Temperature stability;
- Flexibility.
For the far range, chalcogenide glasses, potassium zirconium fluoride or potassium cryolite are used.
The production of optical fiber from plastic is now developing. In this case, the core (core) is made of organic glass, and the shell is made of fluoroplastic. The disadvantage of polymer materials is considered to be low throughput in areas with infrared radiation.
Structure
What does optical fiber consist of? This is a round thread, inside of which there is a core (core), covered on the outside with a sheath. To ensure total internal reflection, the refractive index of the core must be higher than that of the cladding. How it works is that a beam of light directed into the core is reflected repeatedly from the shell.
The diameter of the fiber optic thread used in telecommunications is 124-126 microns. In this case, the diameter of the core may differ - it all depends on the type of optical fiber (I will talk about this in the next section) and national standards.
1 micron is 0.001 mm. I calculated, it turns out that the diameter is only 0.125 mm.
Types and applications
Optical fiber is of two types (depending on the number of rays in the fiber - mod):
- Single-mode. The core diameter is 7-10 microns, light reflection occurs in one mode. Types:
- Standard (with unbiased variance);
- With shifted dispersion;
- With non-zero biased variance.
- Multimode. The core diameter is 50-62 microns (depending on national standards), radiation passes through several modes. Classified into:
- Stepped;
- Gradient.
This section is complicated for the average person, but if someone wants to understand it in more detail, write in the comments. One of the guys will definitely explain everything that was unclear.
The main areas where optical fiber is used are fiber-optic communications and fiber-optic sensors. Other areas:
- Lighting;
- Image formation;
- Creation of a fiber laser.
As I understand it, the main area of application is the construction of fiber optic communication lines. Simply put, these are the lines through which the Internet is transmitted in all major cities.
And here is what the educational program for children and adults “Galileo” says:
Optical cable
So we come to the biggest mystery of our time - the fiber optic cable that connects cities and continents and transmits information at the speed of light. At the same time, the Internet enters our apartment through twisted pair, most often from 8 wires. The maximum speed will reach 1 Gbit/s.
Anyone in the know knows that it is not possible to place an 8-wire wire in every cable channel. This is the main advantage of fiber optics. Optical cable is several times thinner than twisted pair and provides higher speed (up to 10 Gbit/s).
It seems that providers have begun to slowly transfer subscribers to fiber optics - that is, “optics” will go not only to the entrance, but also along it to the apartment. The bad news is that you need a special router to use this cable.
According to the installation method, optical cable is classified into the following types:
- It is laid in the ground;
- Conducted through sewers and sewer pipes;
- Conducted underwater;
- It is laid through the air (suspended).
Depending on the use and signal range, fiber optic cable is:
- Trunk – creating long lines over long distances;
- Zonal – organization of a highway between regions;
- Urban - similar to zonal, but the line length is no more than 10 km;
- Field - laying both by air and underground;
- Water - here the name speaks for itself;
- Object - used for a specific area, easy to install;
- Installation - multimode gradient optical fiber is used.
There is also a classification based on the method of execution of the core and the number of fibers in it. I think this is unlikely to be interesting, but if anything happens, my colleagues will tell you about this too - you just need to write in the comments.
Advantages and disadvantages
Finally, let's look at the pros and cons of fiber optic cable. Let's start with the advantages:
- Low losses with a long relay section;
- Possibility of transmitting information through thousands of channels;
- Small size and weight;
- High protection from interference and external influences;
- Safety.
And now about the disadvantages:
- Exposure to radiation, which increases signal attenuation;
- Glass is susceptible to hydrogen corrosion, which leads to damage to the material and deterioration of properties.
We can finish here. I hope it was useful and my story interesting. Bye everyone!
Fiber optic cables are used for high-speed data transmission in a variety of industries, especially telecommunications. But what exactly is fiber optic cable? How does he work? How is it designed? In this article we will try to provide answers to all these questions.
What are fiber optic cables?
In general, fiber optic cables are not much different from other types of cables. Except that they use light (photons) rather than energy (electrons) to transmit data. Fiber optic transmission is a general term for the transmission of information in the form of light.
How are fiber optic cables constructed?
The fiber optic cable is based on a core consisting of quartz glass or plastic fiber. It is this core that serves as the main conductor of light inside the cable. Between the cable core and its sheath there is another layer called the “boundary layer”. It serves to reflect light. The refractive index directly affects the transmission speed of the light beam.
Next is the core shell itself, which also acts as a conductor of light rays, but has a lower reflection index than core . The shell is covered by the next layer, called the “buffer”. Its function is to prevent moisture from forming inside the core and shell.
And finally, the final layer is the outer covering of the cable, which protects the cable from mechanical damage.
How do fiber optic cables transmit light rays?
To transmit data over optical fiber, the incoming electrical signal is converted into a light pulse using a special electro-optical converter. After this, the light beam begins to move along the cables. At the final point of its route, the beam enters an optoelectronic converter, where it is converted into electronic signals.
Different types of fiber optic cables have different core diameters. Cores with larger diameters can transmit more rays. Fiber optic cables can be bent, but you must ensure that the cable is not bent too much as this may interfere with the transmission of light rays within the cable.
What are the types of fiber optic cables?
There are several types of fiber optic cables. Let's look at them all.
Multi-mode fibers with step-index profile (Multimode Step Index Cables)
Multimode stepped index cables are the simplest fiber optic cables. They consist of a glass core that has a constant reflectance index. This type of cable allows you to simultaneously transmit several beams, which are reflected with different intensities and transmitted along a zigzag path. However, the reflectance index remains constant.
Due to the fact that the rays are refracted many times at different angles, the data transfer speed decreases. Cables of this type provide a bandwidth of up to 100 MHz and allow you to transmit signals over a distance of up to 1 kilometer.The core diameters of cables of this type are usually: 100, 120 or 400 µm.
Multi-mode fibers with graded index
(Graded Index Multimode Cables).
Just like the previous type of cable, this cable allows you to simultaneously transmit many signals, however, the signals inside the optical fiber are not refracted in a zigzag, but along a parabolic path, which allows you to significantly increase the data transfer speed. The disadvantages of these cables include their higher cost. Cables of this type are usually used to build high-speed data transmission networks.
Core diameters: 50 µm, 62.5 µm, 85 µm, 100 µm, 125 µm, 140 µm.
Single-mode fibers (Single mode cables)
Single-mode fiber optic cables have a very small core diameter and can only carry one signal at a time. The absence of refractions has a positive effect on the speed and distance of data transmission. Single-mode cables are quite expensive, but provide excellent throughput and data transmission range, up to 100 (Gbit/s) km.
What are the benefits of using fiber optic cables?
Compared to conventional cables, fiber optics provides the following advantages:
Resistance to radio interference and voltage surges
Increased level of durability
High-speed data transmission over long distances
Electromagnetic Interference Immunity
Compatible with other cable types