Fiber optic communication cables. How it's done
In several of my posts published more than a year ago, I raised such an interesting and exciting topic for many people, like backbone fiber-optic communication cables, in particular, the topic of “underwater” optics. The information in these publications was incomplete, hastily, and scattered, since the articles were written “on the knee” during the lunch break. Now I would like to share a structured and, as far as possible, full material on the topic of optics, with a maximum of tasty details and geek porn, from which it will be warm to any technician’s soul.
Inside the scheme, gifs, tables and a lot of interesting text.
You are ready?
')
Unlike all of us familiar twisted pair, 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 the place of installation.
The following main types of fiber optic cables for data transmission based on the field of application can be distinguished:
The most simple design have cables for laying inside buildings and sewer unarmored, and the most difficult - for laying in the ground and underwater.
Optical cables for installation inside buildings are divided into distribution cables, from which the network as a whole is formed, and subscriber ones, which are used directly for installation along the premises to the end user. Like the twisted pair, they lay optics in cable trays, cable channels, and some brands can be stretched along the external facades of buildings. Typically, such a cable lead to the interfloor junction box or directly to the place of connection of the subscriber.
The design of fiber optic cables for laying in buildings includes an optical fiber, a protective coating and a central power element, for example, a bundle of aramid filaments . There are special fire safety requirements for optics installed in premises, such as non-proliferation of combustion and low smoke emission, therefore, not polyethylene , but polyurethane is used as a cover 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 from moisture. Since the length of the optics inside buildings is usually small, the attenuation of the signal is insignificant and does not affect the 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 also contains a twisted pair cable.
Unarmoured optics are used for laying in the sewage system, provided that it is not subject to external mechanical effects. Also, a similar cable is laid in tunnels, collectors and buildings. But even in cases where there is no external impact on the cable in the sewage system, it can be laid in protective polyethylene pipes, and installation is done either manually or using a special winch. A characteristic feature of this type of fiber optic cable can be called the presence of a hydrophobic filler ( compound ), which guarantees the possibility of operation in sewage conditions and provides some protection from moisture.
Armored fiber optic cables are used in the presence of large external loads, especially in tension. Reservations can be different, tape or wire, the latter is divided into one- and two-bar. Cables with armor are used in less aggressive conditions, for example, when laying in cable ducts, pipes, tunnels, on bridges. Tape booking is a steel smooth or corrugated tube with a thickness of 0.15-0.25 mm. Shirring, provided that this is the only layer of cable protection, is preferred because it protects the fiber from rodents and generally improves the flexibility of the cable. Under more severe operating conditions, for example, when laying into the ground or on the river bottom, cables with wire armor are used.
For laying in the ground using optical cables with wire single-or double-armor. Reinforced cables with ribbon armor are also used, but much less frequently. Laying of the optical cable is carried out in a trench or with the help of cable-laying machines. This process is described in more detail in my second article on this topic, where examples of the most common types of cable-laying machines are given. 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 wires are impregnated with a special water-repellent compound. The calculations immediately come into play: the engineers who work on laying the cable should not allow the tensile and compressive loads to exceed the allowable ones. Otherwise, immediately or over time, the optical fibers may be damaged, causing the cable to become unusable.
Armor also affects the value of allowable tensile force. Fiber optic cables with double-armor can withstand a force of 80 kN, single-pole ones can withstand from 7 to 20 kN, and tape armor ensures cable survival with a load of at least 2.7 kN.
Suspended self-supporting cables are mounted on existing supports of overhead lines and high-voltage transmission lines. This is technologically simpler than laying the cable into the ground, but during installation there is a serious limitation - the ambient temperature during the work should not be lower - 15 o C. Suspended self-supporting cables have a standard circular shape, due to which the wind loads on the structure are reduced, and the distance the span between the supports can reach one hundred and more meters. In the design of self-supporting suspended optical cables, the TSEC is necessarily present - the central power element made of fiberglass or aramid filaments. Thanks to the latest fiber optic cable withstands high longitudinal loads. Suspended self-supporting cables with aramid yarns are used in spans up to one kilometer . Another advantage of aramid yarns, besides their strength and low weight, is that aramid is by its nature a dielectric, that is, cables made on its basis are safe, for example, when lightning strikes.
Depending on the structure of the core, there are several types of suspension cable:
Optical cable with a cable - a kind of self-supporting cables, which are also used for aerial installation. In such a product, the cable can be carrying and wound. There are still models in which the optics are built into the ground wire.
Strengthening an optical cable with a cable (profiled core) is considered to be quite an 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, such a construction of an optical cable with a cable is called a “figure of eight” due to external similarity, although I personally have associations with overfed “noodles”. "Eight" is used for laying air lines with a span of no more than 50-70 meters. There are some limitations in the operation of such cables, for example, the "eight" with a steel cable cannot be suspended on power lines. I hope, to explain why, it is not necessary.
But cables with a waving ground wire (ground wire) are quietly mounted on high-voltage power lines, while attached to the ground wire. Lightning cable is used in places where there is a risk of optics being damaged by wild animals or hunters. It can also be used for longer spans than the usual G8.
This type of optical cable stands aside from all the others, since it is laid in fundamentally different conditions. Almost all types of submarine cables, one way or another, are armored, and the degree of booking already depends on the topography of the bottom and the depth.
The following main types of submarine cables are distinguished (by booking type):
I looked at the construction of the submarine cable more than a year ago in this article , so here I will give only a brief information with a picture:
Paradoxically, there is no direct correlation between cable reservations and depth, as reinforcement protects 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 inverse - the closer to the surface, the more anxiety, which is clearly seen in the table below:
Table of types and characteristics of submarine cables depending on the depth of installation
Now that we are familiar 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 dealt with them personally (as subscribers and as installers), but as it becomes clear from the information above, fiber-optic, especially trunk, cables can seriously differ from what you dealt with. indoors.
Since the installation of the fiber optic trunk line requires thousands of kilometers of cable, whole factories are involved in their production.
It all starts with the production of the main element - fiber optic yarn. Produce this miracle in specialized enterprises. One of the technologies for the production of optical filament is its vertical hood. And it happens as follows:
The following fiber optic dimensions are most common:
Optics with a core diameter of 8.3 microns can be soldered qualitatively in the field, without high-precision equipment or installation of concentrators, it is not easy or practically impossible.
Of great importance is the control of the diameter of the fiber. This part of the installation is responsible for one of the main parameters at all stages of the production of the thread - the invariance of the diameter of the final product (standard - 125 microns). Because of the difficulties in welding threads of any diameter, they tend to make them as long as possible. The running meter of the fiber-optic “blank” on a reel can reach tens of kilometers (yes, just kilometers) and more, depending on customer requirements.
Already at the enterprise, although it can be done at the glass factory, it all depends on the production cycle, for convenience they can rewind to another reel, in the process of dyeing it in their own bright color, by analogy with the familiar twisted pair. What for?To the glory of Sat .. to quickly distinguish channels with, for example, repair or welding of a cable.
Now we have the heart of our product - a fiber optic thread. What's next? Next, let's look at the scheme of such an average underwater (yes, I like them most) cable in the context of:
At the plant, the obtained optical threads are launched into machines, which together form the whole conveyor for the production of any one type of cable. At the first stage of production of unarmored models, the threads are woven into bundles, which constitute, ultimately, the “optical core”. The number of threads in the cable may vary depending on the stated bandwidth. Bundles, in turn, are wound into a “wire” on special equipment, which, depending on their design and purpose. This equipment can also cover the resulting “tross” with waterproofing material to prevent moisture ingress and tarnishing of optics in the future (in the diagram it is called “intra-modular hydrophobic filler”).
This is how the process of twisting bundles gathered together in a cable at the Perm factory of fiber optic cables goes:
After the required number of fiber bundles have been collected in the “tross”, they are poured with polymer or placed in a metal or copper tube. Here, at first glance, it seems that there are no pitfalls and cannot be, but since the manufacturer seeks to minimize the number of joints and seams, everything turns out to be not quite simple. Consider one specific example.
To create a tube-body, shown in the diagram above as a "central tube", a huge length of tape of material we need (steel or copper) can be used. The tape is used so as not to suffer with everything that is familiar to us and obvious rolling, and welding around the entire circumference of the joint. Agree, then the cable would have too many "weak" places in the structure.
So here. A metal band blank passes through a special machine that pulls it and has about a dozen or two rollers that perfectly align it. After the tape is aligned, it is fed to another machine, where it meets with our bundle of fiber optic fibers. The automatic machine on the conveyor bends the tape around the stretched fiber, creating a tube that is perfect in shape.
All this, still fragile, construction is pulled along the conveyor further, to an electric welding apparatus of high precision, which at great speed conducts the welding of the edges of the tape, turning it into a monolithic tube, in which the fiber-optic cable has already been laid. Depending on those. process, the whole thing can be filled with hydrophobic aggregate. Or do not pour, it all depends on the cable model.
In general, with production everything became more or less clear. Different brands of fiber-optic, first of all, trunk cable, may have some structural differences, for example, in the number of cores. Here, the engineers did not invent a bicycle and simply connect several smaller cables into one large one, that is, such a trunk cable will have not one but, for example, five tubes with optical fiber inside, which, in turn, are also filled with plastic insulation and need reinforced. Such cables are called multi-modular .
One of the models of multi-module cable in the context
Multi-module cables, which, for the most part, are used for long lines, have one more obligatory design feature in the form of a core, or as it is also called - a central power element. The CSA is used as a “frame” around which the tubes with the cores of the optical fiber are grouped.
By the way, the Perm plant “Inkab”, whose production process is presented on gifs above, with its volumes up to 4.5 thousand kilometers of cable per year is a dwarf compared to the plant of the same infrastructure giant Alcatel, which can produce several thousand kilometers of fiber-optic cable in one piece, which is immediately loaded onto the ship-laying layer.
The steel tube is the least radical option for booking optics. For non-aggressive operating conditions and installation often use ordinary insulating polyethylene. However, this does not negate the fact that after the manufacture of such a cable, it can be “wrapped” into an armoring winding of aluminum or steel wire or cables.
Booking cable with polyethylene insulation at the same Perm plant
As can be understood from the material above, the main difference between various types of fiber optic cable is their “winding”, that is, what fragile glass filaments are packed into, depending on the application and the environment in which the cable installation will be carried out.
If you liked this material, you can feel free to ask questions in the comments, based on which I will try to prepare another article on this topic.
Thanks for attention.
Inside the scheme, gifs, tables and a lot of interesting text.
You are ready?
')
Conditional classification
Unlike all of us familiar twisted pair, 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 the place of installation.
The following main types of fiber optic cables for data transmission based on the field of application can be distinguished:
- For laying inside buildings;
- for cable ducts unarmoured;
- for cable ducts; armored;
- for laying in the ground;
- suspended self-supporting;
- with cable;
- underwater.
The most simple design have cables for laying inside buildings and sewer unarmored, and the most difficult - for laying in the ground and underwater.
Cable for laying inside buildings
Optical cables for installation inside buildings are divided into distribution cables, from which the network as a whole is formed, and subscriber ones, which are used directly for installation along the premises to the end user. Like the twisted pair, they lay optics in cable trays, cable channels, and some brands can be stretched along the external facades of buildings. Typically, such a cable lead to the interfloor junction box or directly to the place of connection of the subscriber.
The design of fiber optic cables for laying in buildings includes an optical fiber, a protective coating and a central power element, for example, a bundle of aramid filaments . There are special fire safety requirements for optics installed in premises, such as non-proliferation of combustion and low smoke emission, therefore, not polyethylene , but polyurethane is used as a cover 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 from moisture. Since the length of the optics inside buildings is usually small, the attenuation of the signal is insignificant and does not affect the 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 also contains a twisted pair cable.
Unarmoured sewer cable
Unarmoured optics are used for laying in the sewage system, provided that it is not subject to external mechanical effects. Also, a similar cable is laid in tunnels, collectors and buildings. But even in cases where there is no external impact on the cable in the sewage system, it can be laid in protective polyethylene pipes, and installation is done either manually or using a special winch. A characteristic feature of this type of fiber optic cable can be called the presence of a hydrophobic filler ( compound ), which guarantees the possibility of operation in sewage conditions and provides some protection from moisture.
Armored sewer cable
Armored fiber optic cables are used in the presence of large external loads, especially in tension. Reservations can be different, tape or wire, the latter is divided into one- and two-bar. Cables with armor are used in less aggressive conditions, for example, when laying in cable ducts, pipes, tunnels, on bridges. Tape booking is a steel smooth or corrugated tube with a thickness of 0.15-0.25 mm. Shirring, provided that this is the only layer of cable protection, is preferred because it protects the fiber from rodents and generally improves the flexibility of the cable. Under more severe operating conditions, for example, when laying into the ground or on the river bottom, cables with wire armor are used.
Cable for laying in the ground
For laying in the ground using optical cables with wire single-or double-armor. Reinforced cables with ribbon armor are also used, but much less frequently. Laying of the optical cable is carried out in a trench or with the help of cable-laying machines. This process is described in more detail in my second article on this topic, where examples of the most common types of cable-laying machines are given. 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 wires are impregnated with a special water-repellent compound. The calculations immediately come into play: the engineers who work on laying the cable should not allow the tensile and compressive loads to exceed the allowable ones. Otherwise, immediately or over time, the optical fibers may be damaged, causing the cable to become unusable.
Armor also affects the value of allowable tensile force. Fiber optic cables with double-armor can withstand a force of 80 kN, single-pole ones can withstand from 7 to 20 kN, and tape armor ensures cable survival with a load of at least 2.7 kN.
Suspended self-supporting cable
Suspended self-supporting cables are mounted on existing supports of overhead lines and high-voltage transmission lines. This is technologically simpler than laying the cable into the ground, but during installation there is a serious limitation - the ambient temperature during the work should not be lower - 15 o C. Suspended self-supporting cables have a standard circular shape, due to which the wind loads on the structure are reduced, and the distance the span between the supports can reach one hundred and more meters. In the design of self-supporting suspended optical cables, the TSEC is necessarily present - the central power element made of fiberglass or aramid filaments. Thanks to the latest fiber optic cable withstands high longitudinal loads. Suspended self-supporting cables with aramid yarns are used in spans up to one kilometer . Another advantage of aramid yarns, besides their strength and low weight, is that aramid is by its nature a dielectric, that is, cables made on its basis are safe, for example, when lightning strikes.
Depending on the structure of the core, there are several types of suspension cable:
- Cable with profiled core - contains optical fibers or modules with these fibers - the cable is resistant to stretching and squeezing;
- Cable with twisted modules - contains free-laid optical fibers, the cable is resistant to tension;
- Cable with a single optical module - the core of this type of cable does not have power elements, since they are encased. Such cables have the disadvantage of inconvenient identification of fibers. However, they have a smaller diameter and a more affordable price.
Cable with optical cable
Optical cable with a cable - a kind of self-supporting cables, which are also used for aerial installation. In such a product, the cable can be carrying and wound. There are still models in which the optics are built into the ground wire.
Strengthening an optical cable with a cable (profiled core) is considered to be quite an 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, such a construction of an optical cable with a cable is called a “figure of eight” due to external similarity, although I personally have associations with overfed “noodles”. "Eight" is used for laying air lines with a span of no more than 50-70 meters. There are some limitations in the operation of such cables, for example, the "eight" with a steel cable cannot be suspended on power lines. I hope, to explain why, it is not necessary.
But cables with a waving ground wire (ground wire) are quietly mounted on high-voltage power lines, while attached to the ground wire. Lightning cable is used in places where there is a risk of optics being damaged by wild animals or hunters. It can also be used for longer spans than the usual G8.
Underwater Optical Cable
This type of optical cable stands aside from all the others, since it is laid in fundamentally different conditions. Almost all types of submarine cables, one way or another, are armored, and the degree of booking already depends on the topography of the bottom and the depth.
The following main types of submarine cables are distinguished (by booking type):
- Not armored;
- Single (single-share) reservation;
- Enhanced (single-share) booking;
- Reinforced rock (dual) reservation;
I looked at the construction of the submarine cable more than a year ago in this article , so here I will give only a brief information with a picture:
- Polyethylene insulation.
- Mylar coating.
- Double wire steel wire reservation.
- Aluminum waterproofing tube.
- Polycarbonate.
- Central copper or aluminum tube.
- Intra-modular hydrophobic aggregate.
- Optical fibers.
Paradoxically, there is no direct correlation between cable reservations and depth, as reinforcement protects 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 inverse - the closer to the surface, the more anxiety, which is clearly seen in the table below:
Table of types and characteristics of submarine cables depending on the depth of installation
Production
Now that we are familiar 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 dealt with them personally (as subscribers and as installers), but as it becomes clear from the information above, fiber-optic, especially trunk, cables can seriously differ from what you dealt with. indoors.
Since the installation of the fiber optic trunk line requires thousands of kilometers of cable, whole factories are involved in their production.
Fiber Optic Fabrication
It all starts with the production of the main element - fiber optic yarn. Produce this miracle in specialized enterprises. One of the technologies for the production of optical filament is its vertical hood. And it happens as follows:
- At a height of several tens of meters in a special mine, two tanks are installed: one with glass, the second, lower in the mine, with a special polymer material of the primary coating.
- A glass filament is drawn out of the precision feed assembly, or, more simply, the first tank with liquid glass.
- Below the thread passes through the sensor fiber diameter, which is responsible for monitoring the diameter of the product.
- After quality control, the thread is coated with a primary polymer coating from the second tank.
- After the coating procedure, the thread is sent to another furnace, in which the polymer is fixed.
- The fiber of the fiber is pulled N-meters, depending on the technology, it is cooled and fed to the precision winder, in other words, it is wound on a reel, which is already transported as a blank to the place of cable production.
The following fiber optic dimensions are most common:
- With 8.3 micron core and 125 micron shell;
- C core 62.5 microns and a shell of 125 microns;
- C core 50 microns and a shell of 125 microns;
- With a core of 100 microns and a shell of 145 microns.
Optics with a core diameter of 8.3 microns can be soldered qualitatively in the field, without high-precision equipment or installation of concentrators, it is not easy or practically impossible.
Of great importance is the control of the diameter of the fiber. This part of the installation is responsible for one of the main parameters at all stages of the production of the thread - the invariance of the diameter of the final product (standard - 125 microns). Because of the difficulties in welding threads of any diameter, they tend to make them as long as possible. The running meter of the fiber-optic “blank” on a reel can reach tens of kilometers (yes, just kilometers) and more, depending on customer requirements.
Already at the enterprise, although it can be done at the glass factory, it all depends on the production cycle, for convenience they can rewind to another reel, in the process of dyeing it in their own bright color, by analogy with the familiar twisted pair. What for?
Cable manufacturing
Now we have the heart of our product - a fiber optic thread. What's next? Next, let's look at the scheme of such an average underwater (yes, I like them most) cable in the context of:
At the plant, the obtained optical threads are launched into machines, which together form the whole conveyor for the production of any one type of cable. At the first stage of production of unarmored models, the threads are woven into bundles, which constitute, ultimately, the “optical core”. The number of threads in the cable may vary depending on the stated bandwidth. Bundles, in turn, are wound into a “wire” on special equipment, which, depending on their design and purpose. This equipment can also cover the resulting “tross” with waterproofing material to prevent moisture ingress and tarnishing of optics in the future (in the diagram it is called “intra-modular hydrophobic filler”).
This is how the process of twisting bundles gathered together in a cable at the Perm factory of fiber optic cables goes:
After the required number of fiber bundles have been collected in the “tross”, they are poured with polymer or placed in a metal or copper tube. Here, at first glance, it seems that there are no pitfalls and cannot be, but since the manufacturer seeks to minimize the number of joints and seams, everything turns out to be not quite simple. Consider one specific example.
To create a tube-body, shown in the diagram above as a "central tube", a huge length of tape of material we need (steel or copper) can be used. The tape is used so as not to suffer with everything that is familiar to us and obvious rolling, and welding around the entire circumference of the joint. Agree, then the cable would have too many "weak" places in the structure.
So here. A metal band blank passes through a special machine that pulls it and has about a dozen or two rollers that perfectly align it. After the tape is aligned, it is fed to another machine, where it meets with our bundle of fiber optic fibers. The automatic machine on the conveyor bends the tape around the stretched fiber, creating a tube that is perfect in shape.
All this, still fragile, construction is pulled along the conveyor further, to an electric welding apparatus of high precision, which at great speed conducts the welding of the edges of the tape, turning it into a monolithic tube, in which the fiber-optic cable has already been laid. Depending on those. process, the whole thing can be filled with hydrophobic aggregate. Or do not pour, it all depends on the cable model.
In general, with production everything became more or less clear. Different brands of fiber-optic, first of all, trunk cable, may have some structural differences, for example, in the number of cores. Here, the engineers did not invent a bicycle and simply connect several smaller cables into one large one, that is, such a trunk cable will have not one but, for example, five tubes with optical fiber inside, which, in turn, are also filled with plastic insulation and need reinforced. Such cables are called multi-modular .
One of the models of multi-module cable in the context
Multi-module cables, which, for the most part, are used for long lines, have one more obligatory design feature in the form of a core, or as it is also called - a central power element. The CSA is used as a “frame” around which the tubes with the cores of the optical fiber are grouped.
By the way, the Perm plant “Inkab”, whose production process is presented on gifs above, with its volumes up to 4.5 thousand kilometers of cable per year is a dwarf compared to the plant of the same infrastructure giant Alcatel, which can produce several thousand kilometers of fiber-optic cable in one piece, which is immediately loaded onto the ship-laying layer.
The steel tube is the least radical option for booking optics. For non-aggressive operating conditions and installation often use ordinary insulating polyethylene. However, this does not negate the fact that after the manufacture of such a cable, it can be “wrapped” into an armoring winding of aluminum or steel wire or cables.
Booking cable with polyethylene insulation at the same Perm plant
Conclusion
As can be understood from the material above, the main difference between various types of fiber optic cable is their “winding”, that is, what fragile glass filaments are packed into, depending on the application and the environment in which the cable installation will be carried out.
If you liked this material, you can feel free to ask questions in the comments, based on which I will try to prepare another article on this topic.
Thanks for attention.
Source: https://habr.com/ru/post/267859/
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