Fibers are charged into the splicing machine
Hello, Habr readers! Everyone has heard about optical fibers and cables. There is no need to tell where and what optics are used for. Many of you come across it at work, some develop backbone networks, some work with optical multiplexers. However, I have not come across a story about optical cables, couplings, cross-connects, or the technology itself for splicing optical fibers and cables. I am an optical fiber solder, and in this (my first) post I would like to tell and show you how all this happens, and in my story I will also often be distracted by other related things. I will rely mainly on my own experience, so I fully admit that someone will say “this is not entirely correct”, “this is non-canonical”.
There was a lot of material, so it became necessary to break the topic into parts.
In this first part you will read about the design and cutting of cables, about optical instruments, and about preparing fibers for welding. In other parts, if the topic turns out to be interesting to you, I will talk about the methods and show on video the process of splicing the optical fibers themselves, about the basics and some nuances of measurements in optics, touch on the topic of welding machines and reflectometers and others measuring instruments, I will show the welder’s workplaces (roofs, basements, attics, hatches and other fields with offices), tell you a little about cable fastening, about wiring diagrams, about placing equipment in telecommunication racks and boxes. This will certainly be useful to those who are planning to become a solder. I flavored all this with a large number of pictures (I apologize in advance for the paint quality) and photographs.
Be careful, there are a lot of pictures and text.
Introduction
First, a few words about me and my work.I work as an optical solder. He started as a telephone operator and installer, then worked in an emergency crew servicing trunk optics. Now I work in an organization that takes out general contracts for the construction of facilities and communication lines from various companies. A typical construction project is cable line, connecting several containers of GSM base stations. Or, for example, several FTTB rings. Or something smaller - for example, laying a cable between two server rooms on different floors of a building and welding cross-connects at the ends of the cable.
If the tender is won, suitable subcontractors are sought to carry out the work (design, survey and construction). In some regions these are our subsidiaries, in some we have our own equipment and resources, in some we hire independent companies. On our shoulders falls mainly control, elimination of jambs of subcontractors and various force majeure, all kinds of coordination with land owners and administrations, sometimes drawing up executive documentation on the constructed facility (documentation - mainly RD 45.156-2000, here is a list, plus a section with different licenses is added) and so on. Often you need to work with optics: weld or weld an optical coupling or cross somewhere, eliminate the consequences of a support knocked down by a street racer or a tree falling on a cable, input control cable drum, take reflectograms of the area, etc. These are the tasks I perform. Well, along the way, when there are no optics tasks, other tasks: from loading and installation through courier and delivery to copying and paper work. :)
Optical cable, its types and internals
So what is an optical cable? Cables are different.
The design ranges from the simplest (a shell, underneath there are plastic tubes-modules containing the fibers themselves) to the super-sophisticated (many layers, two-level armor - for example, in underwater transoceanic cables).
By place of use - for external and internal installation (the latter are rare and usually in data centers high class, where everything should be perfectly correct and beautiful). According to installation conditions - for suspension (with Kevlar or cable), for soil (with armor made of iron wires), for installation in cable ducts (with corrugated metal armor), underwater (complex, ultra-protective multi-layer structure), for suspension on power line supports (in addition to transmitting information, they play the role of a lightning protection cable). In my practice, the most common cables used are for hanging on poles (with Kevlar) and for laying in the ground (with armor). Less often you come across them with a cable and with corrugated armor. Another common cable is that it is essentially a thin paired optical patch cord (yellow jacket for single mode and orange jacket for multimode, a bit of Kevlar and one fiber; two jackets are paired). Other optical cables (without protection, underwater, for installation indoors) are exotic. Almost all the cables I work with are designed like the picture below.
1 - central power element(in other words, a rod made of fiberglass, although there may also be a cable in a polyethylene sheath). Serves to center tube modules and impart rigidity to the entire cable. The cable is also often secured to it in a coupling/cross-connection, clamped under a screw. When the cable is strongly bent, it has the sneaky property of breaking, breaking the modules with some of the fibers along the way. More advanced cable designs contain this rod, covered in a polyethylene sheath: then it is more difficult to break and will cause less damage to the cable if broken. The rod can be the same as in the picture, and very thin. The tip of such a rod is an excellent abrasive tool for fine work: for example, cleaning relay contacts or an area of a copper part for soldering. If you burn it a couple of centimeters, you get a nice soft brush. :)
2 -
themselves optical fibers(in the picture - in varnish insulation). Those very thin fibers-light guides, for the sake of which everything is started. The article will only talk about glass fibers, although plastic fibers also exist somewhere in nature, but they are very exotic, cannot be welded with devices for welding optics (mechanical connection only) and are suitable only at very short distances and I personally have not encountered them . Optical fibers come in single-mode and multi-mode, I have only encountered single-mode, since multi-mode is a less common technology, can only be used over short distances and in many cases can be perfectly replaced by single-mode. The fiber consists of a glass “shell” made of glass with certain impurities (I won’t dwell on chemistry and crystallography, since I don’t know the topic). Without varnish, the fiber has a thickness of 125 microns (slightly thicker than a hair), and in the center of it there is a core with a diameter of 9 microns made of ultra-pure glass with a different composition and with a refractive index slightly different from the shell. It is in the core that radiation propagates (due to the effect of total reflection at the core-cladding boundary). Finally, on top of the 125-micron cylinder of the “shell” is covered with another shell - made of a special varnish (transparent or colored - for color coding fibers), which EMNIP is also two-layer. It protects the fiber from moderate damage (without varnish, although the fiber bends, it is difficult and easy to break; the fiber will simply crumble if a mobile phone is accidentally placed on it; but with varnish, you can safely wrap it around a pencil and pull it quite hard - it will withstand). It happens that a cable span sags on just the fibers: all the sheaths, Kevlar, are torn (burned, cut), the central rod bursts, and some 16 or 32 125-micrometer glass fibers can support the weight of the cable span and wind loads for weeks! However, even in varnish, fibers can be easily damaged, so the most important thing in a solder’s work is meticulousness and accuracy. One awkward move can ruin the results of a whole day of work or, if you are particularly unlucky and there is no redundancy, you can drop the trunk connection for a long time (if, while delving into the “battle” trunk coupling, you break the DWDM fiber under the spine at the cable exit).
There are many types of fibers: regular (SMF or simply SM), dispersion-shifted (DSF or simply DS), non-zero dispersion-shifted (NZDSF, NZDS or NZ). It is impossible to distinguish them externally; the difference lies in the chemical/crystalline composition and, possibly, in the geometry of the central core and in the smoothness of the boundary between it and the shell (unfortunately, I have not fully clarified this issue for myself). Dispersion in optical fibers is a harsh and difficult thing to understand, worthy of a separate article, so I’ll explain it more simply - dispersion-shifted fibers can transmit a signal further without distortion than simple ones. In practice, solders know two types: simple and “with offset”. In a cable, the first module is often allocated for “offset”, and the rest - for simple fibers. It is possible to join a “displaced” fiber and a simple fiber, but it is undesirable; this causes one interesting effect, which I will talk about in another part, about measurements.
3 - plastic tube modules, in which fibers float in a hydrophobe.
Cable stripped into modules
They easily break (or rather, suddenly bend) when bent, like telescopic antennas on household receivers, breaking the fibers inside them. Sometimes there is only one module (in the form of a thick tube), and it contains a bundle of fibers, but in this case too many are needed different colors for marking fibers, therefore several modules are usually made, each of which has from 4 to 12 fibers. Single standard there is no difference in color and number of modules/fibers; each manufacturer does it their own way, displaying everything in the cable passport. The passport is attached to the cable drum and is usually stapled to the wood directly inside the drum.
Cable passport
Typical cable passport. Sorry for the quality.
However, there is hope that, say, the DPS cable from the manufacturers Transvok and Beltelekabel will still be the same in configuration. But you still need to look at the datasheet for the cable, which always shows detailed colors and what type of fibers are in which modules. The minimum capacity of an “adult” cable that I have seen is 8 fibers, the maximum is 96. Usually 32, 48, 64. It happens that out of the entire cable 1 or 2 modules are occupied, then instead of the remaining modules, black dummy plugs are inserted (to ensure the overall parameters cables have not changed).
4 - film, braiding the modules. It plays a secondary role - damping, reducing friction inside the cable, additional protection from moisture, holding the hydrophobe in the space between the modules and, possibly, something else. It is often additionally tied with threads crosswise and moistened on both sides with a hydrophobic gel.
5 - thin inner shell made of polyethylene. Additional protection from moisture, protective layer between Kevlar/armor and modules. May be missing.
6 - Kevlar threads or armor. In the picture, the armor is made of rectangular rods, but much more often it is made of round wires (in imported cables, the wires are steely and difficult to cut even with cable cutters; in domestic ones, they are usually made of nail iron). The armor can also be in the form of fiberglass rods, the same as the central element, but in practice I have not encountered this. Kevlar is needed so that the cable can withstand high tensile strength without being heavy. It is also often used instead of a cable where there should be no metal in the cable to avoid interference (for example, if the cable hangs along the railway, where there is a contact wire with 27.5 kV nearby). Typical values of permissible tensile force for a cable with Kevlar are 6...9 kilonewtons, this allows it to withstand a long span under wind load. When cutting, Kevlar is terribly dull cutting tool. :) Therefore, it is better to cut it either with special scissors with ceramic blades, or bite it off with cable cutters, which is what I do.
As for the armor, it is designed to protect an underground cable lying directly in the ground, without protection in the form of a plastic pipe, cable duct, etc. However, the armor can only protect against a shovel; an excavator will still tear any cables in flight. Therefore, the underground cable is laid in the ground at a depth of 1 m 20 cm, and above it at a depth of 60 cm a yellow or orange warning tape with the print “Caution” is placed. Don't dig! Below is the cable,” and also bollards, warning signs and notices are placed along the route. But they still dig and tear.
7 - external thick polyethylene sheath. She is the first to bear all the burdens during cable installation and operation. Polyethylene is soft, so it is easy to cut it if the cable is not carefully tightened. It happens that when laying an underground cable, the contractor will tear this sheath several meters down to the armor and not notice that moisture gets into the cable in the ground despite the hydrophobe, and then upon delivery, when testing the outer sheath with a megohmmeter, the megohmmeter shows low resistance (high leakage current) . 
If a hanging cable touches a concrete pole or tree, the polyethylene can also quickly wear down to the fibers.
Between the outer shell and the armor there may be polyethylene film and some hydrophobic gel.
In Russia, unfortunately, optical fibers are no longer produced (here, alas, a joke about polymers would be appropriate). There is a Russian laboratory that produces experimental fibers for special purposes, as suggested by esvaf.
They are bought from companies such as Corning, OFS, Sumitomo, Fujikura, etc. But cables are made in Russia and Belarus! Moreover, in my practice, 95% of the cables I worked with are cables from Russia or Belarus. In this case, imported fiber is laid into the cable. Offhand, from my experience, I recall such cable manufacturing companies as Beltelekabel, MosCable Fujikura (MKF), Eurocable, Transvok, Integra-cable, OFS Svyazstroy-1, Saransk-cable, Incab. There are others too. Of the imported cables, only Siemens remains in my memory. Subjectively, all cables are similar in design and materials and do not differ much in quality.
Here, in fact, I talked about the design of optical cables. Let's move on.
Cable cutting: necessary tools and techniques
Cable cutting, like welding, requires a number of specific tools. A typical set of an assembler-soldier is a suitcase with tools “NIM-25”, it contains all the necessary strippers, cable cutters, screwdrivers, side cutters, pliers, a breadboard knife and other tools, as well as a pump or bottle for alcohol, a supply of hydrophobic solvent “D- Gel", non-woven lint-free wipes, electrical tape, self-adhesive number markers for cables and modules and other consumables.
After completing the supply with consumables (ties, worm-drive clamps, etc.) and some auxiliary tools it is quite sufficient for working with optics. There are also other sets, richer and poorer in configuration (“NIM-E” and “NIM-K”). The weak point of most sets is the poor quality of the “aluminum type” case, which only looks nice, but in fact consists of thin fiberboard covered with textured/corrugated foil, and aluminum thin corners with rivets. It does not withstand long-term use in field and urban conditions, and has to be repaired and strengthened. In my case, the case lasted 3 years and, being all tattered, held together with corners and bolts, with a “collective farm” organizer instead of the original one, it was replaced with a regular one plastic box for tools. Some tools and materials from the standard set may be low quality. I personally didn’t need some tools. Some have already been replaced within 3 years of operation. As the “branded” consumables are used up, some are replaced with “improvised” ones without compromising the quality of work. Thus, factory-made non-woven lint-free wipes for wiping fibers are easily replaced toilet paper"Zeva plus" type. :) The main thing is that it is unflavored. Instead of expensive (about 800 rubles/liter) D-Gel, if the work is going on outdoors, you can use AI-92 gasoline.
When cutting cables, it is important to maintain the lengths of the cable elements in accordance with the requirements of the instructions for the coupling: for example, in one case it may be necessary to leave a long power element to secure it in the coupling/cross-connect, in another case it is not required; in one case, a pigtail is braided from Kevlar cable and clamped under a screw, in another case, the Kevlar is cut off. It all depends on the specific coupling and the specific cable.
Let's look at the cutting of the most typical cable:
A) Before cutting a cable that has been in damp for a long time or without a waterproofed end, you should cut off about a meter of cable with a hacksaw (if reserve allows), since prolonged exposure to moisture negatively affects the optical fiber (it may become cloudy) and other elements of the cable. Kevlar threads in a cable are an excellent capillary that can “pump” water into itself for tens of meters, which is fraught with consequences if, for example, wires run parallel to the cable high voltage: currents can begin to flow through wet Kevlar, the water evaporates, crushes the outer shell from the inside, the cable runs in bubbles and new moisture gets in through the bubbles from the rain.
B) If the cable design has a separate cable for suspension (when the cable in cross section has the shape of a figure “8”, where there is a cable at the bottom and a cable at the top), it is bitten out with cable cutters and cut off with a knife. When cutting the cable, it is important not to damage the cable.
B) To remove the outer sheath of the cable, use a suitable stripper knife. NIM-25 is usually equipped with a “Kabifix” knife as in the photo below, but you can also use a stripper knife for electrical cables, which has a long handle. 
This stripper knife has a blade that rotates in all directions, which can be adjusted in length according to the thickness of the outer sheath of the cable, and a clamping element for holding it on the cable. Important: if you have to cut cables of different brands, then before cutting a new cable you need to try the knife on the tip and, if you cut too deeply and damaged the modules, you need to tighten the blade shorter. It can’t be worse when the coupling has already been welded, and suddenly, when laying the fibers, one fiber suddenly “pops out” of the cable, because during cutting the knife caught the module and broke this fiber: all the work is in vain.
Using a stripper knife to remove the outer sheath of the cable, a circular cut is made on the cable, and then from it two parallel cuts are made with opposite sides cable toward the end of the cable so that the outer sheath splits into two halves. 
It is important to set the length of the blade of the stripper knife correctly, since if the blade is too short, the outer shell will not easily separate into two halves and it will take a long time to tear it off with pliers, and if the blade is long, you can damage the modules deep in the cable or dull the rotating blade on the armor.
D) If the cable is self-supporting with Kevlar, then the Kevlar is cut with cable cutters or scissors with special ceramic blades. 
Wire Bites
Kevlar should not be cut with a knife or simple scissors without ceramic linings on the blades, as Kevlar quickly dulls the metal cutting tool. Depending on the design of the coupling, it may be necessary to leave a certain length of Kevlar for fixation; this will be stated in the coupling installation instructions.
If the cable is intended for laying in a telephone sewer and the armor contains only a metal corrugation (so that rats do not gnaw through it), it can be cut longitudinally with a special tool (a reinforced plow knife). Or it can be carefully cut with a small pipe cutter or even with a regular knife there is a circular mark on the corrugation and, by swaying, increase metal fatigue at the place of the mark and the appearance of a crack, after which you can remove part of the corrugation, bite the modules and pull off the corrugation. This cutting must be carried out especially carefully, since it is easy to damage the modules and fibers: the corrugation is not very strong, it can wrinkle in the place where it is picked with tools, and when pulled from the fibers, sharp edges at the break point can pierce the modules and damage the fibers. A cable with corrugation is not the most convenient for cutting.
If the cable is armored with round wires, they should be cut off with cable cutters in small batches, 2-4 wires each. With side cutters it takes longer and is harder, especially if the wire is steel. Some couplings require a certain length of armor for fixation, and armor (including corrugated armor) often needs to be grounded.
E) For the inner, thinner sheath found in some cables (for example, self-supporting ones with Kevlar), you should use a separate, pre-set stripper knife (can be the same as for removing the outer sheath of the cable) so as not to interfere with the knife length settings every time when cutting the cable. In this case, it is especially important to correctly set the length of the blade in the stripper knife; it will be less than in a stripper for removing the outer sheath of the cable, since the inner sheath is much thinner, and immediately below it are modules with fibers. With a certain skill, you can use a regular breadboard knife to remove the inner shell, making a longitudinal cut with it, but there is a significant risk of damaging the modules. You can also use a clothespin stripper to cut coax.
E) Threads, plastic film and other auxiliary elements are removed from the modules using napkins and D-Gel/gasoline. The threads can be twisted one at a time, or can be torn off with a special sharp “plow” hook (may be included in the design of some stripper knives for removing the sheath). To remove the hydrophobe, use D-Gel solvent (colorless oily liquid, has an orange smell, toxic) or gasoline. However, be careful with gasoline: office employees who have gasoline pouring next to them will not be happy about the aroma. Yes, and it's a fire hazard.
You should work in disposable gloves (surgical, polyethylene or construction), since hydrophobe is a very unpleasant muck (the most unpleasant thing in the work of a solder!), it is difficult to wash, after using gasoline or hydrophobe, your hands remain greasy for some time, and after cutting the cable you have to weld the fibers, requiring clean hands and workplace. In winter, hands stained with hydrophobe get very cold. However, once you get the hang of it, you can cut cables almost without getting your hands dirty.
After removing the threads and dividing the bundle of modules into separate modules, each module is wiped with napkins or rags with D-Gel solvent/gasoline, and then with alcohol until clean. Although, in order to save time and get less dirty, you can proceed in the following way - initially, not completely cut the cable to the modules, but in the place where the cutting begins, 30 centimeters, without wiping anything, bite the modules (see point “e”) and pull off the entire bundle of modules with winding and threads from the fibers, holding the clean end of the cable with your hand like a handle. Hands remain almost clean, time is saved. However, with this cutting method there is a risk of breaking some of the fibers or applying excessive tensile force to the fibers, which will negatively affect the attenuation of the fibers in the future, and there is also a greater likelihood of damaging the modules, so this method is not recommended, especially in winter time when the hydrophobic filler thickens. First you need to learn how to do it correctly, and then try different optimizations.
f) At the required length, each module (except for dummy modules, they are bitten out at the root, but first you should make sure that they really have no fibers) is bitten with a stripper for modules (suitable for copper coaxial), after which the module can be pulled off without much effort from fibers. 
Biting the modules with a stripper is a very important moment. It is necessary to choose a recess of the exact diameter, since if the recess is larger than necessary, the module will not bite enough to be easily removed; if it is smaller, there is a risk of cutting through the fibers in the module. In addition, you should carefully monitor the stripper locking pawl: if, at the moment of biting the module, it blocks the reverse movement of the stripper, fixing it in the “closed” state, then in order to separate the stripper and fold back the lock, you will have to close the tool again on the already bitten module, in this case there is a high probability that the module will be cut, which will lead to the need to re-cut the cable. We remember that when biting one of the modules, we are actively interfered with by other modules that need to be held with the other hand, and the cable itself also needs to be held suspended somehow. Therefore, at first it will be very inconvenient and you should cut the cable together.
There are cable designs where the module is single and has the form of a rigid plastic tube in the center of the cable. To remove such a module efficiently, it should be cut in a circle with a small pipe cutter (not included in NIM-25), and then carefully broken at the place of the circular mark.
When tightening the modules, make sure that all fibers are intact and not a single fiber is left sticking out from the tightened module.
If the temperature is low, the modules are thin, the cable design in the modules contains little hydrophobe (=lubricant) or the length of the removed modules is significant - the module may not be pulled off the fibers without effort. In this case, you cannot pull too hard, since stretching may affect the attenuation of the fibers in this place, even if the fibers do not break. You should bite and remove the module in 2-3 steps, in parts and slowly.
When cutting the cable, you should pay attention to the length of the fibers. It must be no less than specified in the instructions, usually 1.5-2 meters. In principle, you can cut it into 15 cm and then even somehow weld it, but then when laying the fibers in the cassette, problems will arise. big problems: a large supply of fibers is needed just so that there is room for “maneuvers” during installation, so that you can “play” with the length and beautifully lay all the fibers in the cassette.
Sometimes it becomes necessary to weld into a transit cable without cutting it. In this case, it is cut into modules just like a regular one, but the requirements for careful cutting are stricter: after all, communication can already go through the cable. It is cut down to modules and the modules are carefully inserted into the “oval” coupling input (they won’t fit into a regular round one - they will break), for this input a special set of heat shrink and metal clips with a block of hot-melt adhesive are used. This glue shrinks from high temperature melts and fills the space between the two cables, ensuring tightness. Next, the module that needs to be welded into is cut, those fibers from it that do not need to be soldered are welded back in transit, and those that we need are welded to the “unsoldered” (branch) cable. Very rarely a situation may arise when we need to take a fiber from a module, but we cannot cut the module (an important connection runs through it). Then applies kit for longitudinal cutting of modules: a “chamfer” is removed longitudinally from the module, the fibers are removed from it, wiped off the hydrophobe and sorted. The ones we need are cut and welded onto another cable according to the diagram, and the rest are simply placed in a cassette. In this case, if a continuous cable is installed, the length of the fibers should be twice as long (2-3 m), this is understandable.
The fibers must be clean (carefully wiped free of hydrophobe); special care should be taken to ensure that all fibers are intact. Fibers require careful handling, because in the case when the cables are cut and inserted, the welding is almost completed and some fiber breaks at the cable exit, you will have to re-cut the cable and weld, which will take a lot of time and is extremely undesirable and unprofitable when quickly restoring communication on an existing highway. 
Optical fibers damaged as a result of careless cable cutting (the length of the stripper blade was incorrectly set to remove the inner sheath of the cable, as a result of which the modules were cut and some of the fibers were damaged)
G) The fibers should be thoroughly wiped with lint-free wipes and alcohol to completely remove the hydrophobic filler. First, the fibers are wiped with a dry cloth, then with wipes soaked in isopropyl or ethyl alcohol. This order is special because on the first napkin there remains a huge drop of hydrophobe (alcohol is not needed here), but on the 4th-5th napkin you can already call on alcohol to dissolve the remains of the hydrophobe. The alcohol from the fibers evaporates quickly.
Used napkins (as well as scraps of cable sheath, chipped fibers and other debris) must be cleaned up after yourself - have mercy on nature!
The purity of the fibers, especially towards the ends, has great value for quality welding. Where work is done with microns, dirt and dust are unacceptable. The fibers should be inspected for the integrity of the varnish coating, the absence of dirt, and broken parts of the fibers. If the varnish on some fiber is damaged, but has not yet broken, it is better not to risk it and recut the cable. Spend 10-15 minutes, otherwise you risk spending the whole day.
H) The cut cables are covered with special adhesive heat shrinks, which are often included in the coupling kit (if the coupling has a cable entry pipe). If the coupling provides for clamping the cable in wet rubber with sealant, then heat shrinkage is not needed. A very common and very unpleasant mistake made by a beginner is to forget to put on the heat shrink! When the coupling is welded, the heat shrink is pushed onto the coupling pipe and shrinked with a gas torch, blowtorch or industrial hair dryer, providing a hermetically sealed cable entry into the coupling and additional fixation of the cable. The most practical way to seat is with a small torch placed on a canister of tourist gas with a price clamp: one canister is enough for dozens of welded couplings, it just ignites, unlike blowtorch, weighs little, there is no dependence on electricity, unlike an industrial hair dryer.
Before shrinking, the coupling pipe and the cable itself must be sanded with coarse sandpaper for better glue adhesion. If you neglect this, you may end up with a misunderstanding like this: 
If you still forgot to put on the heat shrink, a heat shrink cuff with a lock (known as XAGA) will help. Collective farming cannot be sealed with electrical tape!
Some heat shrinks (for example, from Raychem) are covered with dots of green paint, which turns black when heated, indicating that this place no longer needs to be heated, but here it should be heated some more. This was done because the heat shrink can burst if it is overheated in some place.
It is better to seat after the coupling is welded. If something goes wrong during welding (for example, the fiber breaks and you have to recut the cable), then you won’t have to pick at the hardened thick adhesive heat shrink with a knife, and the heat shrink itself won’t be wasted.
I) The cut cables are inserted into the coupling or cross-connect, fixed, and the coupling or cross-connect itself is fixed on the desktop. When fixing a cable in a coupling or in a cross-connection, you should follow the installation instructions - everything is different for different couplings. In some cases (armored cable and, for example, an MTok A1 coupling with the corresponding entry kit), fixing the cable in a coupling is a separate difficult operation with cutting the armor, winding sealant, etc.
So we have inserted the cut cable into the coupling/cross, now we need to measure and strip the fibers, put on the KDZS and cook according to the diagram. I’ll talk about this in the next part, since it’s a bit much for one article.
Optical couplings
I'll tell you a little about optical couplings and cross connects. I'll start with the couplings.The optical coupling is plastic container, into which the cables are inserted and connected there. Previously, in the late 90s - early 2000s, when all specialized materials for optics were in short supply with exorbitant prices, some smart guys sculpted sewer fittings or plastic bottles. Sometimes it even worked for several years. :) Today this is certainly wild, normal couplings can be bought in any average and big city and prices start from 1500-2000 rubles. There are many designs of couplings. The most widespread and familiar design for me personally is like that of the Svyazstroydetal series of couplings “MTOC”. There is a headband from which pipes for cable entry protrude from the outside. A metal frame is attached to the inside of the headband, to which optical cassettes are attached. A cap is placed on top (which can be made with stiffening ribs for strength), sealed with an elastic band. The cap is fixed with a detachable plastic clamp: the coupling can always be opened and closed without wasting a repair kit made from heat shrink. 
In general, Svyazstroydetal makes generally good couplings for different applications. From the MTOC series, I personally like the L6 coupling the most: it’s universal, inexpensive, and easy to install. 
There are other couplings in the MTOC series - small-sized, for sewerage, for inserting armored cables, for burying underground. For each coupling, it is possible to purchase additional components and kits for cable entry: for example, cast iron armor protection for the underground coupling "MChZ", an extra set of optical cassettes with consumables, or an additional kit for inserting another cable.
If you need something cheaper, they have a series of couplings “MOG”, of which the most popular is the coupling “MOG-U” (Optical Urban Coupling, Shortened): at a price of less than 2000 rubles we get a simple and high-quality coupling, which, in fact, some believe inconvenient for installation. 
Such a coupling will not look very good on a pole, and it is inconvenient to wind up a supply of cable with such a coupling while standing on a ladder, so they are usually placed in hatches. This coupling is designed to be placed in the telephone hatch on special standard consoles. The downside of the “mogushka” is that it does not have a locking detachable clamp and to open it you will have to cut off the heat shrink, and when closing it, use a repair kit made of wide heat shrinks (if the cables are wound in at one end) or a heat shrink sleeve (if the cables are on both sides). The same applies to A-series MTOKs. In addition, if you insert cables from both sides, it is important not to forget to put on plastic pipe on one of the “sides” of the cables, otherwise you won’t be able to put it on without cutting it: this also affects beginners.
Also, sometimes there are couplings without pipes, in which the cables are sealed by clamping them in damp rubber or sealant. Here, for example, is the “SNR-A” coupling, which my partner and I welded together as part of the construction of the FTTB ring. 
This method of sealing cables requires great care, since otherwise water may get into the coupling, which is undesirable. Firstly, water in the coupling can over time cause clouding of the glass fibers and deterioration of the varnish. Secondly, all sorts of metal structural elements will rust, and the armor grounding wire, if any, will rot. Thirdly, Kevlar will draw water into itself. And most importantly, a muff full of water in cold weather will simply be crushed along with the fibers.
At least two cables are usually inserted into an optical sleeve. Of course, you can come up with a wild welding scheme, when one cable is inserted and welds on itself, but usually 2-3 cables are inserted. If 4-5 cables are introduced, and all the cables are different with different colors And different amounts fibers in the modules, the coupling turns out to be difficult for installation and subsequent disassembly of what is soldered where. My partner and I cooked my first such coupling for 3 days! :) So it is better to design the network so that no more than 3 cables enter the coupling.
Optical crosses
The optical cross-connect is designed to terminate the cable in the place where it was connected: at the base station, in the information center, in the data center, in the server room. A typical cross is metal box 19" standard size for mounting in a standard rack; a terminated cable is inserted into it at the rear; strips with ports are located at the front.
Welded crossover for 24 ports of FC/APC type, single-unit
Welded cross-connect for 64 ports, LC type, 2-unit
Working cross-over for 96 FC ports
There is also a cheaper option - when everything that is possible is thrown out of the cross, then it turns out something like this: 
Open cross-connect for 8 SC/APC ports, 1 unit. The bad thing is that the optical pigtails are not protected in any way and can be broken by those who rummage through the box/rack, dragging, say, a new cable.
All of these crosses are rack-mounted, but there are also wall-mounted options and other rare ones. 
Wall distribution for 16 FC ports. By the way, it is welded poorly: the yellow shells of the pigtails do not fit into the KDZS and the fibers can break, and the fibers in the cassette are laid with small bending radii
The cable inserted into the cross is welded to the so-called pig tails: in the photographs these are thin yellow laces inside the crosses. Each fiber belongs to its own pigtail. The other side of the pigtail contains an optical connector-plug, which is inserted into the optical adapter-socket from inside the cross-connect. Outside the cross-connect, switching is performed with optical patch cords (thick yellow cords). The patch cord differs from the pig tail in that it has a more durable connector and the presence of Kevlar inside, so that if someone gets caught on the patch cord and pulls, it is difficult to pull it out. Well, patch cords have connectors on both sides, while pig tails have connectors on only one. If necessary, a temporary patch cord can be welded from two pig tails.
In principle, several cables can be inserted into a cross-connect, some of the fibers from them can be welded together, and some can be brought out to the ports. Then we get something that can be called a “cross coupling”, while we save on materials and welding. This is sometimes done when installing FTTB, but it is undesirable to do this, as the complexity of the circuit increases.
Adapters and connectors
Optical cross connects are characterized by the adapters used in them (simply - optical sockets). There are also a large number of standards and substandards.
This picture shows only part of the “genera” and “types” of optical sockets
The standard is a complex of an adapter (socket) and a connector (plug). Of course, there are adapters between different standards, but these are crutches that are only suitable for measurements and should be avoided in a constantly working communication line. The less in the line all kinds of welded and especially mechanical connections, the better. Of course, if the distance is small, the line will work even if a couple of decibels are lost on some of the crosses. In the case of short lines, optical attenuators are sometimes specially installed. But for very long lines, where the equipment is working at its limit, adding another cross-connect or coupling (that is, some 0.05-0.1 dB of loss) can be fatal: the line will not rise.
The tip of the “fork” is, roughly speaking, a cylinder with a thin through hole under the fiber in the center. The end of this cylinder is not flat, but slightly convex. The tip consists of an incredibly hard and scratch-resistant cermet, although metal ones are very rare. There are rumors of people breaking side cutters trying to cut through this tip. :) I myself easily scratched steel and glass with these tips. Nevertheless, they must be handled with care, do not allow dust to enter, do not touch the end of the connectors with your finger, and if you touch them, wipe them with a cloth soaked in alcohol. Ideally, a special microscope (optical or with a camera) is used to monitor the condition of the patch cords. Dirty - clean, scratched, if the scratch crosses the center with the glued fiber - scrap or polish. Dirty and scratched sockets and patch cords are a common cause of line attenuation.
The optical fiber is fixed in the tip by gluing it with epoxy (or some other) glue and then grinding it on a special machine, although this is only done if you need to make long non-standard patch cords: it’s easier and cheaper to buy ready-made ones. The price of a regular optical patch cord 2 meters long is about 200-400 rubles. 
Manufacturing of patch cords. Emilink
In practice, standards such as FC, SC, LC are most often used. Less common are FC/APC, SC/APC, ST. LC can be either duplex or single.
F.C.
Pros - excellent connection quality, therefore suitable for critical highways. An old proven standard. Metal (hard to break). If you move a well-screwed connector with your hand, this will not affect the connection.
Cons: It takes a long time to unscrew/tighten when switching. If they are located closely on the cross, it can be very inconvenient to crawl up to unscrew one of the connectors in a crowd of others.
The connector itself is fixed motionless thanks to the groove on it and the notch on the adapter, and only the knurled nut turns with your fingers.
S.C.
Everything is the same as in FC, only the adapter and connector are square, plastic, and the connector is fixed by clicking, not screwing. Pros - cheaper than FC, more convenient and faster to switch, cons - plastic is easier to break, shorter connection and disconnection life. It sometimes happens that the amount of reflection and attenuation on a connection changes noticeably after touching the connected connector, which is undesirable for critical lines. The color of the connectors is usually blue.
LC and LC Duplex
They have similar properties to SC, but have much smaller dimensions: a two-unit cross-connect on an LC accommodates as many as 64 ports, and on an SC - only 32. Due to their small dimensions, they are often mounted directly on optical multiplexer boards.
FC/APC, SC/APC, LC/APC
Same as FC, SC and LC, but with bevel (A - angle) tip polishing.
Difference between ceramic ferrules with regular and bevel polishing. The image is a little inaccurate: in fact, in the case of both polishings, the ends are not flat, but slightly convex; accordingly, when connecting, only the centers of the tips, where the fiber is, will touch.
Such adapters and connectors are made in green color and when compared with conventional UPC (or simply PC) polishing, the difference is visible to the eye. This is necessary to reduce back reflection at the junction of two connectors. As far as I know, this type of polishing was developed for transmitting analog television via optics to avoid ghosting on the screen, but I could be wrong.
It is possible to combine “regular” and “oblique” polishing with each other, but only if it is necessary to take a reflectogram according to the principle “if only the length of the path can be seen”: a large air gap will lead to strong losses and strong back reflection.
My story is over for today. Ask questions, I will try to answer. If you find this topic interesting, I will write a continuation.
Sleeve for welding fiber optic connection: KDZS
Despite its apparent simplicity, it is a rather complex and, in its own way, irreplaceable detail. Designed to protect and seal the welding site and the fiber area cleared of varnish. Consists of three components.
- Metal core. It serves as a rigid frame and prevents the sleeve from “warping” in the stove, distributing the heat evenly.
- Hot melt adhesive. Fixes the fiber after cooling and seals the joint.
- Heat shrink tube. It shrinks in the oven and forms external protection connections.
Sleeve with HERE for protection of welding joint OV (KDZS)
Enlarge photos
In their original state, they are a tube 3 to 6 cm long. The fiber is inserted into the sleeve before welding. After welding and checking the joint with a reflectometer, the sleeve is moved to the joint location and placed in the oven of the casing device.
Can be supplied complete with coupling.
12.27.13 Information supplemented with the page Fiber optic sleeves - KDZS
Laying OM in a splice plate (cassette)
Laying optical fibers in a cassette (fiber organizer or splice plate)
The welded fiber together with the sleeve cased at the joint looks like a thin fishing line with a weight-sleeve in the middle. To carefully secure such a “web” in all optical couplings and terminal cross-connects, a special box is used, somewhat similar to a VCR cassette. People often call this box a cassette, but there is also official name— light guide organizer (splice plate). Cassettes (splice plates) for laying optical fiber sometimes differ slightly in design, but as a rule they contain cells for attaching sleeves and some space for laying out cable fibers or optical cords. Photos of various cassettes:
Cassette (fiber organizer or splice plate)
for laying optical fiber in the distribution box. Red inserts for attaching sleeves
A cassette with laid optical fiber in the optical cross box.
The sleeves are not only placed in the cells, but also secured with a special fastener
Fiber optic cassette for installation in a coupling
Sequence of assembly of couplings and terminal devices of fiber-optic communication lines
Installation technology for fiber optic couplings and termination devices
Couplings and fiber optic cross-connects have different shapes and, accordingly, different assembly sequences. As a rule, suppliers or manufacturers include installation instructions in each coupling. In terms of design, I will only note that some types of couplings remain partially dismountable after final installation (clip-latch) or are completely welded.
1. Start with pruning. According to old, perhaps unwritten rules, 2 meters of cable is simply cut off. This is due to the fact that when tightening, the end of the cable experiences a maximum of impacts and kinks; moreover, if the sheath is broken, water could get inside the module, which would subsequently cause clouding of the fiber glass.
2. Cable reserves are left on the fiber optic coupling, the purpose of which is to replace or remake the coupling. Its length has changed over the years (initially 15 meters, now less). On intercity lines, everything is documented, see protocol forms. Much of this stage can be specified by the customer or written down in the project. Sometimes a much larger reserve may be left due to the peculiarities of cable disposal in communication construction organizations.
Optical fiber in modules
(4 pieces each)
3. Protective sheaths are removed from the cable for a length of about 1 meter, up to the optical modules, only a certain section of armor is left for its fixation and electrical connection. Optical modules are wiped with nefras or alcohol to remove any remaining hydrophobic filler.
4. Partially cut ends are inserted into the holes of the coupling or cross and secured. In cross-connections, the armor is connected to a soft wire and brought out to the ground terminal of the rack. Secure the cassette.
5. Next, usually with a special clothespin-knife, cut off the shell of the optical module so that the ends of the module shell are secured in the cassette clamps. The fibers are also wiped with nefras.
Fiber optic coupling installation stage
7. A heat-shrinkable sleeve KDZS is put on one of the fibers to be welded.
8. Next, a tool called a striper comes into action. They remove the varnish from the ends of the optical fiber by about 2 - 3 cm (under the cleaver).
9. The cleaned optical fiber is wiped with alcohol or a special cloth and placed in a cleaver, and the fiber is cleaved.
10. The welding process is described on the welding page. The welding joint is measured and controlled using an optical reflectometer.
11. The fiber optic sleeve is encased.
12. The welded fibers are placed in a cassette (light guide organizer or splice plate).
Fiber optic cassette with laid fibers
13. Points 7 to 12 are repeated for the remaining optical fibers.
14. After casing and laying all fibers, control with a reflectometer is carried out again.
15. For the coupling, everything is sealed and placed in a pit (well). For cross laying and connecting connectors.
Official procedure for installing fiber optic cable revealed on the pages
12.6 Installation of optical couplings(Guide to the construction of linear structures of local communication networks, M., 2005)
10.3 Laying optical cables from (Manual for the operation of line-cable structures of local communication networks)
Information on the organization of terminal devices is also available on the pages of the book "Fiber optics. Theory and practice" - Connection panels, connection devices and terminal compartments. Covering connections
Coupling installation instructions:
Short fiber optic coupling MOGU
Dead-end fiber optic coupling MTOC
A fiber-optic network for several premises (buildings) usually consists of connecting several lines into a common backbone, which is then sent through a single multi-module cable to a switching node. This branching of the highway into several lines can be carried out by the most in a variety of ways depending on the conditions and technical means, but the simplest option would be to use a special optical cross connector to connect a multi-fiber cable to a single-channel optical cord.
First, it is necessary to explain what an optical cross-connect actually is. IN in a general sense This is a box designed to protect the connection of optical fibers, including organizational and connecting elements. However, unlike, which also serve to protect the connection point, cross-connects are equipped with sockets, to which the optical fibers of the main cable are connected through special devices - optical pittails. It is through these sockets that single-channel lines terminated with the appropriate connector on a conventional optical patch cord are connected to the main line.
Network installation using cross-connect boxes
This is the most convenient solution, when you extend a single backbone along the building, branching fiber optic modules from it as they pass by the premises. The same situation usually occurs if a powerful fiber-optic backbone runs along the street and sends out branches to houses. If in case of internal network wiring you need cross-connects wall-mounted for rooms with sockets for a patch cord, then to connect the lines to the street main it is necessary to select a box depending on the characteristics of the cable of this line and the technical conditions of the installation. For sequential removal of lines from a common backbone, cross-connects equipped with an input and output channel for the backbone cable and sockets according to the number of lines planned for connection at a given point are suitable. Most often, one outlet is enough. If the distribution of a single main line occurs immediately from one point, then there is only one input for the main cable, but there can be quite a lot of sockets. Most often, this method of routing the highway is carried out in switching nodes and technical rooms. For ease of installation of cross-connects in such cases, they are also made in the RAC version for placement in switching cabinets. In addition, optical cross-connections can be designed with the possibility of subsequent opening without complete dismantling connection and without it. Thus, to choose the most suitable optical cross-connect you need to know:
.type of connection (transit branch of one, several communication lines or terminal branch);
.technological conditions (external or internal installation, wall or RAC version, maximum possible dimensions and weight, possibility of opening without dismantling);
.type of connectors to be connected (for exact matching with sockets).
It would be useful to know the type of both the main cable and the cable of the connected lines.
Installation of optical cross
Actually, the installation of the crossover box itself is quite simple. The main cable is inserted into the box opening intended for this purpose, the sheaths are removed and the cable is divided into modules. The retractable module is dissected, the fibers are stripped and prepared for connection to the pittails. A pittail is a connector with a small section of optical fiber that connects to the inside of the cross-connect socket. The connection to the end of the pittail fiber is most often made by welding, but you can also glue it and use splices - many optical cross-connects contain splice cassettes. The cable supply is placed inside the cross-connect box without sharp bends or twists; usually there are special brackets to secure the cable inside the case. Sleeves (or splices) of connected fibers are placed in organizing cassettes, pittails are connected and installation is completed by sealing the cable inlets and outlets and closing the cross-connect box.
An optical cross-connect is a passive optical device for connecting multi-core optical cables with single-fiber optical cords with optical plugs (connectors) at the ends. Optical cross-connections are used to connect a cable network with active network equipment and transmit an optical signal from active equipment to the network.
Optical cross connects come in various modifications and are divided into:
For correct installation optical cross-connects they are equipped with:
splice cassette;
splice plates;
KDZS sleeves;
pigtails;
adapters;
a set of fastening elements (ties, bolts, clamps, lugs, marking stickers).
At first glance, installation of an optical crossover may seem simple process, but in fact this is not entirely true. Assembling the optical cross is enough important point in the construction of a distribution network. In case of incorrect and careless installation, the signal may not pass through at all due to high attenuation in places where fibers are welded or in places where pigtails are laid and cable fibers are stored in splice plates or in cross-connects. Also, attenuation or breakage of fibers can be due to improperly fastened cable in the cross-connect or improper placement of sleeves in the cassette holders.
Installation of the optical cross-connect must be carried out by a certified, experienced specialist with all necessary equipment and a tool.
Important to know! When installing an optical cross-connect, there should be no figure-of-eights of pigtail fibers in the cassettes, and there should be no excess supply of fibers that interferes with installation. After installing and fastening the pigtails into the adapters, the adapters on the other side must be plugged to avoid dust and debris getting into the joint. After installing the cross-connects, it is necessary to illuminate the fibers for compliance with the circuit.
Navikom specialists have everything necessary for prompt installation and restoration of optical cross-connections.
8.1 ODF is included in the PON exchange section. ODF must have the following capabilities:
− providing free access to any of the optical ports and the ability to quickly perform cross-connection work;
− increasing the cross-connection capacity during operation;
− ensuring prompt production of installation, installation and switching of OV;
− system for laying fiber optics and patch cords, guaranteeing compliance with the requirements for the bending geometry of fiber optics;
− constructively support the installation of splitters directly in the ODF;
− occupy a minimum area.
The cross must match " Technical requirements to station optical cross-connections high density", approved by the Chief technical director JSC Kazakhtelecom.
The basic principle of installing a high-density ODF of a modular design is to separate the optical station and line cables (fibers) supplied to the cross-connect onto the mounting modular tubes, through the adapters shown in Figure 19.
Figure 19 Figure 20
Mounting modular tubes with 12 or 16 optical fibers are fed to the splicing and switching module shown in Figure 20, where the fibers are boiled into factory-prepared picktails. Welded joints fibers reinforced with KDZS sleeves are placed in cassettes. The design of the optical cross-connect should ensure the extension of the splicing and switching module from modular blocks to a length of up to 1.5 meters due to the supply of mounting modular tubes laid in the switching and splicing module, only when installing (unbonding) optical fibers of station and linear fiber optics. SC/APC type connecting sockets are installed in special sockets of patch panels.
8.2 Due to the large number of different designs of optical cross-connections, including the top or bottom feed of the fiber optic cable from a cable rack or through a raised floor, detailed description installation is not advisable; in each specific case, you should use the manufacturer’s instructions. The length of the supply of linear cable fibers and picktails left on the cassette in the terminal device must be at least 0.5 m, and the length of the fiber supply left on the cable rack or in the raised floor is at least 2 m. Placement options are shown in Appendix 3.
NOTE For any optical cross-connect design, station cables or station patch cords must be fed to station splicing and switching modules installed in the upper part of the cabinet, in the middle part of the cabinet it is necessary to install splitter modules with input and output splitters welded into connectors (optical switching ports), and onto linear modules installed in the lower part of the cabinet, it is necessary to supply the main linear fiber optics. There are 2 options for mounting (feeding) OLT linear terminations to the optical cross-connect:
When installing an OLT in a combined room in close proximity to the ODF and the capacity of a GPON network node for up to 2 thousand subscribers, the OLT outputs can be connected directly to the ODF trunk ports using patch cords of the appropriate length;
When installing an OLT in a containment zone and the capacity of a GPON network node exceeds 2 thousand subscribers, the connection of the OLT outputs to the ODF station ports should be carried out using 3-meter pigtails terminated on the OLT side with 48-96 station cables, and on the ODF side the station cable should be inserted and welded into station splicing and switching modules. In the latter option, switching of OLT outputs with any port of a linear trunk cable should be carried out using short patch cords inside the ODF rack between the linear and station ports of the optical cross-connect.
8.3 Inside the premises of the telephone exchange, up to the terminal cable equipment ODF should be laid OK with a non-flammable sheath. The margin for cutting the optical station cable from the station and linear parts of the cross-connect must be at least 3-3 meters.
