Despite all the advantages of optical fibers, to install networks they must be connected. It is the complexity of this process for quartz glass fibers that is the main limiting factor for fiber optic technology.

Despite all the technological progress in recent years, non-professionals can only connect cables that do not have special quality requirements. Serious work on the installation of regional highways requires expensive equipment and highly qualified personnel.

But to create inter-house wiring of the “last mile” such difficulties are no longer needed. The work is available to specialists without serious training (or without it at all); a set of technological equipment costs less than $300. In combination with this, the huge (I’m not afraid of this word) advantages of optical fiber over copper cables when laying overhead make it very attractive material for home networks.

Let's take a closer look at the types and methods of connecting optical fibers. To begin with, you need to fundamentally separate splices (one-piece connections) and optical connectors.

In comparatively small networks(up to several kilometers in diameter) intergrowths are not desirable and should be avoided. The main method of creating them today is electric discharge welding.

Optical fiber welding principle.

Such a connection is reliable, durable, and introduces negligible attenuation into the optical path. But welding requires very expensive equipment (in the region of several tens of thousands of dollars) and a relatively highly qualified operator.

This is due to the need for high-precision alignment of the ends of the fibers before welding, and maintaining stable parameters of the electric arc. In addition, it is necessary to ensure smooth (and perpendicular to the fiber axis) ends (chips) of the welded fibers, which in itself is a rather difficult task.

Accordingly, performing such work “from time to time” on your own is not rational, and it is easier to use the services of specialists.

A similar method is also often used for terminating cables by welding cable fibers with small sections of flexible cables with already installed connectors (pig tail, literally - pig tail). But with the spread of adhesive joints, welding is gradually losing ground when terminating lines.

The second way to create permanent connections is mechanical, or using special connectors (splices). The original purpose of this technology is a fast temporary connection used to restore the line in the event of a break. Over time, some companies began to provide a guarantee for “repair” splices for up to 10 years, and up to several dozen connection-disconnection cycles. Therefore, it is advisable to separate them into a separate method for creating permanent connections.

The principle of operation of the splice is quite simple. The fibers are fixed in a mechanical conductor and brought closer to each other with special screws. For good optical contact, a special gel with optical properties similar to quartz glass is used at the joint.

Despite its apparent simplicity and attractiveness, the method is not widely used. There are two reasons for this. Firstly, it is still noticeably inferior in reliability and durability to welding, and is not suitable for trunk telecommunications channels. Secondly, it is more expensive than installing adhesive connectors and requires more expensive technological equipment. Therefore, it is rarely used when installing local networks.

The only thing in which this technology has no equal is the speed of work completion and the lack of demands on external conditions. But today this is clearly not enough to completely conquer the market.

Let's consider detachable connections. If the range limit of high-speed electrical lines based on twisted pair depends on the connectors, then in fiber-optic systems the additional losses they introduce are quite small. The attenuation in them is about 0.2-0.3 dB (or several percent).

Therefore, it is quite possible to create complex topology networks without the use of active equipment, by switching fibers on conventional connectors. The advantages of this approach are especially noticeable in short but extensive last mile networks. It is very convenient to divert one pair of fibers for each house from the common backbone, connecting the remaining fibers in a junction box “for passage”.

What is the main thing in a detachable connection? Of course, the connector itself. Its main functions are to fix the fiber in the centering system (connector), and protect the fiber from mechanical and climatic influences.

The basic requirements for connectors are as follows:

introducing minimal attenuation and back reflection of the signal;

minimal dimensions and weight with high strength;

long-term operation without deterioration of parameters;

ease of installation on cable (fiber);

Easy to connect and disconnect.

Today, several dozen types of connectors are known, and there is no single one on which the development of the industry as a whole would be strategically oriented. But the main idea of ​​all design options is simple and quite obvious. It is necessary to accurately align the axes of the fibers and press their ends tightly against each other (create contact).

The operating principle of a pin-type fiber optic connector.

The bulk of connectors are produced according to a symmetrical design, when a special element - a coupler (connector) is used to connect the connectors. It turns out that first the fiber is fixed and centered in the tip of the connector, and then the tips themselves are centered in the connector.

Thus, it can be seen that the signal is influenced by the following factors:

Internal losses - caused by tolerances on the geometric dimensions of the optical fibers. These are the eccentricity and ellipticity of the core, the difference in diameters (especially when connecting fibers of different types);

External losses, which depend on the quality of the connectors. They arise due to radial and angular displacement of the tips, non-parallelism of the end surfaces of the fibers, and the air gap between them (Fresnel losses);

Reverse reflection. Occurs due to the presence of an air gap (Fresnel reflection luminous flux in the opposite direction at the glass-air-glass interface). According to the TIA/EIA-568A standard, the back reflection coefficient is normalized (the ratio of the power of the reflected light flux to the power of the incident light). It should be no worse than -26 dB for single-mode connectors, and no worse than -20 dB for multimode;

Contamination, which in turn can cause both external losses and back reflection.

Despite the absence of a connector type officially recognized by all manufacturers, ST and SC are actually common, very similar in their parameters (attenuation 0.2-0.3 dB).

Optical fiber connectors.

ST. From the English straight tip connector (straight connector) or, informally, Stick-and-Twist (insert and twist). It was developed in 1985 by AT&T, now Lucent Technologies. The design is based on a ceramic tip (ferule) with a diameter of 2.5 mm with a convex end surface. The plug is secured to the socket by a spring-loaded bayonet element (similar to BNC connectors used for coaxial cable).

ST connectors- the cheapest and most common type in Russia. It is slightly better suited to heavy-duty use than the SC thanks to its simple and robust design. metal structure(allows more opportunities for the use of brute physical force).

The main disadvantages include the complexity of marking, the complexity of connection, and the impossibility of creating a duplex plug.

S.C. From the English subscriber connector (subscriber connector), and sometimes the unofficial decoding Stick-and-Click is used (insert and snap). It was developed by the Japanese company NTT, using the same ceramic tip with a diameter of 2.5 mm as in the ST. But the main idea is a lightweight plastic housing that protects the tip well and allows for smooth connection and disconnection in one linear motion.

This design allows for high packing density and easily adapts to convenient dual connectors. Therefore, SC connectors are recommended for creating new systems, and are gradually replacing ST.

Additionally, two more types should be noted, one of which is used in a related industry, and the other is gradually gaining popularity.

F.C. Very similar to ST, but with threaded fixation. It is actively used by telephone operators in all countries, but is practically never found in local networks.

L.C. New "miniature" connector, structurally identical to SC. So far it is quite expensive, and for “cheap” networks its use is pointless. The creators cite greater installation density as the main argument in favor. This is a fairly serious argument, and in the distant (by telecommunications standards) future it is quite possible that it will become the main type.

Last year we held a number of seminars on information transmission systems via fiber optic cable. Communicating with students, we often came across a situation where people are ready to use these systems: they have projects, the advantages of the solution prevail over the cost - install and deliver the project, receive money and the confidence that the customer will have no complaints about the quality of the work performed. But the fact that the specialists had no experience working with such equipment stopped them. Everyone has repeatedly heard about the difficulties and the need for highly qualified specialists. Many people believe that splicing fiber optics and installing equipment using fiber optic cable is a risky process that requires expensive materials and highly paid employees, and that it is not for them.

S.A. Karachunsky
Head of Marketing Department at V1 Electronics

In fact, although working with fiber optics requires certain experience and skills, acquiring them is not so easy. difficult task. Moreover, the market now offers a large number of tools and equipment for cutting and installing cables. This article is devoted to this issue.

Introductory information

One of the main requirements when working with fiber optic cables is careful attention to all stages of the cable system installation process: laying, cutting, connection and termination. A mistake is costly - the cost of finding the location of the damage and replacing the cable section. Replacing a damaged section not only increases labor costs, but also reduces the quality of the entire system: each connecting element, each solder introduces its own distortions into the transmitted signal, reduces the signal transmission distance, and requires an increase in the optical budget of the system. For specialists who are just starting their work on installing fiber optics, it is recommended to purchase a ready-made set of basic tools and materials necessary for the work: containers, dispensers, distributors, Consumables and protective equipment. After some time, when you gain initial skills in working with fiber-optic cable and form preferences in the variety of tools and materials used, you will be able to combine the set to suit your needs.

Cutting fiber optic cable

A fiber optic cable consists of several optical fibers, which, together with reinforcing threads, are enclosed in a protective polymer sheath. To protect against aggressive external influences the cable is placed in armor protection made of corrugated aluminum or steel protective tape or steel wire. Due to the fact that optical fiber is quite sensitive to axial and radial deformations, inexpensive cable cutters that are used to work with copper cables are not suitable for cutting it. It is recommended to use a tool whose blades are designed to cut steel.

The initial stage of cutting fiber-optic cables - removing the top layer of protective and armor coverings - is performed with the same tools as cutting conventional cables. Polymer insulation and foil are opened with cutters, and steel wire is cut out with side cutters. It is recommended to use cable knives: they allow you to remove the polymer coating from a cable with a diameter of 4 to 35 mm, and the cable knife has a special nozzle that limits the depth of the sheath cut, which prevents damage to the fiber optic cores.

But in further work you still can’t do without special tools:

• scissors or wire cutters with ceramic blades - used to remove reinforcing threads from Kevlar. Ordinary scissors do not cut these thin, flexible and durable fibers, but squeeze them out or bend them;
• strippers - designed to remove the buffer layer. Their use reduces the risk of damage to the optical fiber: primarily due to the fact that its working surfaces have a fixed setting;
• Optical fiber cleaver - used to cut off excess fiber at an angle of 90 degrees. Cleavers can be manual or automatic. When preparing optical fiber for subsequent welding or joining fibers using splicing, it is recommended to use automatic cleavers, which allow you to obtain a clean and even cleavage without defects at an angle of 90±0.5 degrees. For example, a chip with an angle of more than 2 degrees. can lead to an increase in connection losses of up to 1 dB, which, given the total optical budget of the system of 15-25 dB, is often an unaffordable luxury;
• microscopes allow you to diagnose optical fiber connectors for the quality of polishing of the core, the presence of cracks, scratches;
• crimpers are designed for crimping tips, connectors and contacts.

Fiber Optic Cable Connection Methods

Three methods of installing fiber optics are widely used:

• welding of optical fibers;
• connection using mechanical connectors;
• connection using a splice.

Optical fiber welding

It is carried out using special welding machines and is usually performed in three stages:

• preparing and stripping the cable, obtaining a high-quality end;
• welding with a welding machine;
• testing and evaluation of connection quality. The welding machine connects the optical fiber with good parameters connection points are simple and fast. Modern welding machines can reduce losses at the joint to 0.04 dB or less. The device automatically performs all necessary operations: aligns optical fibers, melts the ends of optical fibers, and welds them. The most functional (but, unfortunately, more expensive) models also check the quality of the connection. After which the welding site is protected, usually using heat-shrinkable tubing.

Connection using mechanical connectors

Optical fiber splicing is also used when terminating fibers with connectors. For these purposes, ready-made fiber-optic jumpers - pigtails (English pigtail - flexible conductor) are used. A pigtail is usually manufactured in a factory; it is a piece of fiber optic cable that has an optical connector on one side. The fiber of the optical cable is welded with the pigtail fiber, and with the help of a connector it is connected to the equipment.

Connection using splice

Splice is a device for splicing a fiber-optic cable without welding. The prepared ends of the optical fibers are inserted into the splice through special guides towards each other and fixed in it. To reduce insertion losses, the joint between the fibers is placed in a special (immersion) gel, which is often located inside the splice.

The connection technology using splice includes several stages:

• cutting of fiber optic cable;
• end processing;
• making a connection;
• testing and assessing connection quality;
• application protective coatings, restoration of the protective shell and armor.

The use of splices facilitates the process of splicing optical fibers, but working with them requires practical skills. Insertion loss with this fiber connection method is less than using a pair of fiber optic plugs and an adapter, but can still be 0.1 dB or higher. According to the requirements of the SCS standards IS0 11801, TIA EIA 568B, the insertion loss in the splice should not exceed 0.3 dB. To do this, during installation the position of the fibers relative to each other is adjusted, and during the work it is also necessary to constantly measure losses at the connection point.

In addition, it should be taken into account that over time, losses at the splice joint may increase due to spatial displacement of the fibers or drying out of the immersion gel.

conclusions

The material presented here may seem incomplete to some, superficial to others. I did not set myself the task of presenting all the information about the tools and equipment used when working with fiber optics - and I’m not sure that the entire magazine will be enough for this: there is a lot of information, it is varied.

But in order to get started, basic knowledge and skills are quite enough. Read, ask, come to seminars and trainings - equipment suppliers themselves should be interested in improving your literacy. It was not the gods who fired the pots - and we will succeed.

Today there will be a scientific and educational post :)

Fortunately, this time there was no accident, but planned work, so the process took place, one might say, smoothly. greenhouse conditions.

Typically, an optical cable is welded into a special cross-connect, each fiber to its own port, from where it is already connected to equipment or another cross-connect. But this time it was necessary to weld two cables together, bypassing the optical cross-connects. The process is, in general, similar to welding a cable at break, with the exception that the cable does not need to be pulled out of the cross-connect first.

This is what two working optical cross connects look like, which you will need to get rid of and connect the cables directly. For now, the data is running along the yellow patch cords between the crosses.

Optical crossover from the inside. Carefully unravel and pull the cable out of the cassette.

Colored wires are fiber optic cables, only insulated for now. The optical fiber itself is colorless, and the insulation is specially colored to distinguish the fibers.

There can be many fibers in a cable. It can be 4, 12, or 38. As a rule, a pair of fibers is used for data transmission, one fiber in each direction. Such a single pair can transmit from 155 Mbit/s to several tens of Gbit/s, depending on the equipment at the ends of the fiber-optic route.

This cable contains 12 fibers, which are packaged 4 pieces in 3 colored (white, green, red) modules.

Since the fiber splice is a potentially fragile area, this part of the cable is packaged in an optical sleeve. Before welding, the cables are inserted into the coupling through special holes.

Now you can begin the welding process. First from fiber using precision instruments The insulation is removed and the fiber optic core itself is exposed.

Before welding, it is necessary that the end of the fiber is as smooth as possible, i.e. a very precise perpendicular cut is required. There is a special machine for this.

Chick! The angle of the chip should deviate from the plane by no more than 1 degree. Typical values ​​are from 0.1 to 0.3 degrees.

Scraps of clean fiber are immediately tidied up. You’ll find it on the table later, but it can easily get stuck under the skin, break off there and stay there.

And here is the most important device in this process - the welder. Both fibers are placed in special grooves in the middle of the device on both sides (in the picture - blue color), and are fixed with clamps.

After that comes the hardest part. Press the "SET" button and look at the screen. The device itself positions the fibers, aligns them, and briefly electric arc instantly solders the fibers and shows the result. The whole process happens faster than I wrote these three sentences above, and takes about 10 seconds.

A heat-shrinkable tube with a metal rod is placed on the fiber to strengthen the welding site, and the fiber is placed in an oven in the same apparatus, only in its upper part.

Each fiber is then carefully placed into the coupling cassette. Creative process.

And the result.

To seal the cable entry point into the coupling, heat-shrinkable tubes are put on and treated with a special hair dryer. Tube from high temperature compresses, preventing water and air from entering the coupling.

And the final touch. A cap is placed on the coupling and secured with special fasteners. Now you are not afraid of either humidity, heat or frost. Such couplings can float in a swamp for years without damaging the cable inside.

The entire process of welding two 12-fiber cables together takes about an hour and a half.

Well, now you know all the intricacies of this process, you can safely buy a welding machine and entangle whatever you want with fiber optic networks.

One of the final stages of installing a fiber optic line is the wiring and connection of the incoming fiber optic cable directly at the destination: in the server room, data center, etc. To do this, the cable is inserted into the optical cross-connect and the fibers are connected to the connectors. At this stage, a group such as optical components is used - these are pigtails, and all kinds of clamps. They are also combined under the name passive fiber optic equipment.

Pigtail- this is a piece of optical cable terminated with a connector on only one side.

Patch cord has connectors at both ends, the types of connectors may differ (adapter patch cord) or be the same (connecting).

Optical adapter- this is, in fact, the outlet into which the pigtail or patch cord is connected.

What is important to consider?

It may seem that there is nothing complicated at the stage of connecting a connector to an optical adapter. How to plug a plug into a socket. However, no.

Let's look at least from a technology point of view. What is a kit - patchcord/pigtail + adapter? This is the joining of two optical fibers, the thickness of which is approximately equal to the thickness of a human hair. In this case, a connection shift of even 1 micron causes a loss of power.

That is, the cross connection must provide:

• perfectly precise contact cores (fiber optics);
• protection of this ideal contact from external influences - shifts, the appearance of an air gap, etc.;
• mechanical protection of fibers with repeated connection and disconnection;
• mechanical protection of the cable in the connector during bending, pulling, etc.

In particular, this is why so many types of optical connectors have been created. Each manufacturer strived to create the ideal connector specifically for their equipment.

But that's not all the difficulties

To ensure precise connection, optical connector tips should not have cracks(if a crack crosses the optical fiber, such a connector is replaced), should not be dusty or dirty. Even if you just touched it with your finger, the mark must be thoroughly wiped off with an alcohol wipe. Every speck of dust, pollution, etc. - this is weakening, attenuation of the signal, back reflections.

Therefore, optical connectors are regularly wiped with alcohol, and sockets are blown with compressed air or cleaned with special sticks.

The picture on the right shows the tip of the connector after touching it with a finger. and after cleaning.

The mechanical strength of connections is ensured differently in each type of connector, but basically it is:

• especially durable material connector tip - ceramics, metal ceramics;
• protective plastic and metal caps over the connectors;
• latches and clamps positions both in optical adapters and in “plugs”;
• Kevlar and other reinforcing threads under the sheath of the cable section leading to the connector.

Types of optical patchcords, pigtails, adapters

The classification of optical pigtails, patch cords and adapters is generally the same and is based on the following parameters:

• connector standard;
• type of grinding;
• fiber type - multimode or single-mode;
• type of connectors - single or duplex.

As a result of various combinations of all these types, a huge variety of modifications of connectors and adapters are obtained. Not everything is in this picture:

What do all these letters mean?

Let's take typical optical patch cord markings. Eg, .

• S.C. And L.C.- These are the types of connectors. Here we are dealing with a patch cord - an adapter, since two different types connector;
• UPC- type of grinding;
• Multimode- type of fiber, here multimode fiber, can also be designated by the abbreviation MM. Single-mode is labeled as SingleMode or SM;
• Duplex- two connectors in one housing, for a more dense arrangement. The opposite case is Simplex, one connector.

Duplex example:

Types of polishing (grinding) of fiber optic connectors

The purpose of grinding or polishing fiber optic connectors is to ensure that the fiber optic cores are in perfect contact. There should be no air between their surfaces, as this degrades the signal quality.

Currently, the following types of polishing are used: PC, SPC, UPC and APC.

PC- the progenitor of all other types of polishing. The connector, processed using the PC method (including manually), has a rounded tip.

Please note that the figure shows that connecting connectors with a flat end is fraught with the formation of an air gap. While the rounded ends are connected more tightly.

Can be used in short-range networks that require low data transfer rates.

SPC- an improved version of PC, but grinding is done only by machine.

UPC- an almost flat (but not flat) connector, which is produced using high-precision surface treatment. It provides excellent reflectivity (compared to PC and SPC), therefore it is actively used in high-speed optical networks.

Connectors with this type of connector are most often blue.

APC- a connector processed according to a completely different principle: the ends are beveled at an angle of 8 degrees. This surface polishing gives the most top scores. Back reflections of the signal leave the optical fiber almost immediately, and due to this, losses are reduced.

APC polished connectors are used in networks with high requirements for signal quality: transmission of voice, video data. As an example - cable TV.

Connectors with this type of connector are green.

Attention!

APC Ground Connectors unsuitable to connectors with other polishing (PC, SPC, UPC) and cause mutual damage.

PC, SPC, UPC polishes are mutually compatible.

Comparison of tip shape and reflected signal path in UPC and APC polished connectors:

Dependence of line losses on polishing type optical connector is presented in the table:

As you can see, UPC (rounded ends) and APC (beveled ends) polishing is the most effective. Therefore, patchcords and pigtails with this type of grinding are most often used.

Types of optical connectors

In practice, our fiber optic network installers work in the vast majority of cases with types FC, LC, SC. For more rare species We won’t stop with connectors just yet.

F.C.

• spring-loaded connection, due to which “pressing” and tight contact are achieved;
• metal cap - durable protection;
• the connector is screwed into the socket, which means it cannot jump out, even if accidentally pulled;
• Moving the cable does not affect the connection.

However, it is not suitable for dense placement of connectors - space is required for screwing in/unscrewing.

S.C.

Cheaper and more convenient, but a less reliable analogue of FC. Easy to connect (latch), connectors can be placed tightly.

However, the plastic shell can break, and even touching the connector affects signal attenuation and back reflections.

In general, it is used most often, but is not recommended on important highways.

L.C.

A smaller version of the SC. Due to its small size, it is used for cross connections in offices, server rooms, etc. - indoors, where high density of connectors is required.

The author of the development of this type of connector - a leading manufacturer of telecommunications equipment, Lucent Technologies (USA) - initially predicted the fate of a market leader for his brainchild. In principle, this is how it is. Especially considering that this type of connector refers to connections with increased installation density.

In the following releases:

More articles on the topic "Fiber Optic Networks":

website

Optical connectors(connectors) are used when terminating optical fibers to connect them with passive or active telecommunications equipment.

Today there are a large number of specializedoptical connectors.The most widespreadoptical connectors types SC, FC, ST having standard sizes and miniature L.C. The principle of operation is the same, only the methods of fixation or the type of attachment to the socket are different.

Optical connector ST type has a tip with a diameter of 2.5 mm with a convex end surface. The plug is fixed to the socket using a spring-loaded bayonet element,turning ¼ turn. The guide frames, engaging with the stops of the ST-socket when rotating, press the structure into the socket. The spring element provides the necessary pressure.

SC type optical connectortype is the most popular among connectors with a rectangular cross-section.Fixation is carried out using a latch with a lock according to the “push-pull” principle.The linear movement of plugging and unplugging makes this connector particularly suitable for 19-inch shelf applications, as it allows for increased port density by bringing the receptacles closer together. The latch only opens when pulled by the housing, which increases operational reliability. Optical SC connector can be combined into a module consisting of several Duplex connectors.

FC type optical connectorfixed with a threaded connection. oriented , mainly for use in single-mode long-distance communication lines, specialized systems and cable television networks. The connector design provides reliable protection ceramic tip from contamination, and the use of a union nut for fixing provides greater tightness of the connection area and reliability of the connection when exposed to vibrations.

Miniature LC type optical connectorsare approximately half the size of regular options SC, FC, ST with a tip diameter of 1.25 mm, instead of the standard 2.5 mm. This allows for high-density patch panel mounting and dense rack-mount layouts. The connector is fixed using a clamping mechanism.

We are also pleased to offer you connectors differing in installation method:

One of the most simple methods for installing connectors on fiber - adhesive. This method uses epoxy resin to secure the fiber into the connector core.

The quick connector allows you to easily and quickly terminate optical cables. In the store you can find everything you need to install a quick connector.

They are designed for quick termination of optical cables using the unique “Splice-On” technology using welding machine Ilsintech Swift F1.

The main enemies of optical connectors that prevent high-speed data transfer are dirt, dust and other contaminants.