Fiber optic connectors. Optical connectors: purpose, types, characteristics of connectors

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Obviously, in an ideal optical information transmission system, the light flux should freely pass the path from the source to the photodetector. Optical fiber is nothing but the same signal propagation path. Stretching a solid fiber from the source to the receiver is not possible. The technological length of the fiber usually does not exceed several kilometers. And if this problem can still be solved by welding optical fibers, then ensuring the mobility of the local optical subnet is achieved only with the use of cross equipment. The problems of transmitting a light wave from one piece of fiber to another cannot be avoided. For multiple and easy connection of optical links, the light guides can be terminated with optical connectors. Given that modern light guides are micron technologies, terminating the fiber with optical connectors is not an easy task.

Losses in optical connectors

Let us describe the problems that arise when a signal passes from one fiber to another. The loss of power or attenuation of the optical wave occurs when the misalignment of the optical fibers. In this case, some of the rays simply do not pass into the next light guide, or enter at an angle more critical. With incomplete physical contact of the fibers, an air gap is formed. As a result, there is a return loss effect. Part of the rays when passing through transparent media with different densities is reflected in the opposite direction. Reaching the resonator, they are amplified and cause signal distortion.

Non-ideal fiber geometry also contributes to power loss. This may be the ellipticity of the light guide and the non-centricity of its core. The end of the light guide itself may contain deformations: chips and roughness, which in turn reduces the working surface of contact between the fibers.

Tips for optical connectors

Thus, it is necessary to precisely and tightly combine both light guides. To ensure the safety of brittle fibers during repeated alignment, their end segments are placed in ceramic, plastic or steel tips. Most tips are cylindrical in shape with a diameter of 2.5 mm. There are conical designs, and LC connectors have a tip with a diameter of 1.25 mm.
Inside the tips there is a channel into which the light guide cleaned from the sheath is inserted and fixed chemically or mechanically. When removing the protective coating, both special mechanical tools and chemically active solutions can be used. Inside the tip, the light guide can be fixed both along the entire length of the channel (most often these are glue-based methods) and at the point where the fiber enters the tip (mechanical methods). The process of mechanical fixation takes much less time (up to several minutes) and is based on the "pressing down" of the fiber with the help of polymeric materials. But it is less reliable and short-lived. The chemical method speaks for itself. Most often, the fixing composition in this technology is epoxy solutions, as the most reliable. However, the period of complete thickening of such a composition is very long - up to a day. Therefore, if faster assembly of connectors is required, other components or special ovens for drying can be used.

After installing the light guide into the connector, it is necessary to grind the end of the tip. The protruding excess fiber is removed with special tools. The basic principle is to cut and break off the light guide, after which you can proceed to the direct polishing of the surface.
Of particular interest is the shape of the ends of the tips. Their processing is a whole art. The simplest version of the butt is a flat shape. It is characterized by large return losses, since the probability of an air gap in the vicinity of the optical fibers is high. There are enough irregularities even in the non-working part of the end surface. Therefore, convex ends are more often used (the radius of rounding is about 10-15 mm). With good centering, tight contact of the fibers is guaranteed, which means that the absence of an air gap is more likely. An even more advanced solution is to use a rounded end at an angle of several degrees. Rounded ends are less dependent on the deformations formed during the connection of the connectors, therefore, such lugs can withstand a greater number of connections (from 100 to 1000).

The tip material is also important. The vast majority of connectors are built on the basis of ceramic tips, as they are more resistant.
After ending the fibers with connectors, it is necessary to analyze the quality of the tip surface. Most often, microscopes are used for this. Professional devices have a magnification factor of hundreds of times and are equipped with special illumination from various angles. They may also have an interface for connecting to additional measuring equipment.

According to the TIA / EIA 568A standard, the return loss for multimode fiber in optical connectors should not exceed -20 dB, and for single-mode -26 dB. Connectors are divided into classes according to the value of return loss.

Type of	Losses	Type of	Losses
PC	less than 30 dB	Ultra PC	less than 50 dB
Super PC	less than 40 dB	Angled PC	less than 60 dB

PC is an abbreviation of the English Physical Contact.

Connecting optical connectors

Essentially, the connection of two optical connectors cross equipment is built according to the following scheme:
The socket serves as a platform for installing connectors. The connectors included in it are fixed in such a way that the axes of their tips are centered, parallel and tightly pressed. Such sockets are usually installed in patch panels or box inserts.

connector type	Tip	Loss (dB) at 1300 nm
		Multimode	single mode
ST	Ceramics	0.25	0.3
SC	Ceramics	0.2	0.25
LC	Ceramics	0.1	0.1
FC	Ceramics	0.2	0.6
FDDI	Ceramics	0.3	0.4

ST connector

Connectors differ not only in the tips used, but also in the type of fixation of the structure in the socket. The most common representative in local optical networks is the ST-type connector (from the English. Straight Tip). The ceramic tip has a cylindrical shape with a diameter of 2.5 mm with a rounded end. Fixation is performed by turning the frame around the axis of the connector, while there is no rotation of the connector base (theoretically) due to the groove in the socket connector. The guide frames, engaging with the stops of the ST-socket during rotation, press the structure into the socket. The spring element provides the necessary pressure.

The weak point of ST-technology is the rotational movement of the frame when connecting/disconnecting the connector. It requires a large living space for a single link, which is important in multiport cabling systems. Moreover, the rotation of the tip is only theoretically absent. Even minimal changes in the position of the latter lead to an increase in losses in optical connections. The tip protrudes from the base of the structure by 5-7 mm, which leads to its contamination.

SC connector

Weaknesses of ST-connectors are currently being solved through the use of SC-technology (from the English. Subscriber Connector). The cross section of the body is rectangular. Connecting / disconnecting the connector is carried out by translational movement along the guides and is fixed with latches. The ceramic tip also has a cylindrical shape with a diameter of 2.5 mm with a rounded end (some models have a beveled surface). The tip is almost completely covered by the body and is therefore less prone to contamination than in the ST design. The absence of rotational movements causes a more careful pressing of the tips.

In some cases, SC connectors are used in duplex mode. The structure can be provided with clamps for pairing connectors, or special brackets can be used to group the cases. Connectors with singlemode fiber are usually blue, while those with multimode fiber are gray.

LC connector

The LC connectors are a smaller version of the SC connectors. It also has a rectangular body section. The design is made on a plastic base and is equipped with a latch similar to the latch used in modular connectors for copper cable systems. As a result, the connection of the connector is made in a similar way. The tip is made of ceramic and has a diameter of 1.25 mm.

There are both multi-mode and single-mode connector options. The niche of these products is multiport optical systems.

FC connector

In single-mode systems, there is another type of connector - FC. They are characterized by excellent geometry and high tip protection.

FDDI connector

Not only twin SC connectors can be used to connect a duplex cable. Often, FDDI connectors are used for this purpose. The design is made of plastic and contains two ceramic tips. To prevent incorrect connection of the link, the connector has an asymmetric profile.
FDDI technology provides for four types of ports used: A, B, S and M. The problem of identifying the corresponding links is solved by supplying connectors with special inserts that may vary in color or contain letter indices.
This type is mainly used to connect terminal equipment to optical networks.

MT-RJ connectors

Guaranteed parameters of cable assemblies:

• Direct losses<0.5 дБ (типичное значение - 0.25 дБ для ММ)

Areas of use:

• Wiring in buildings (horizontal and backbone)
• Telecommunication networks

Note: MT-RJ cords are assembled in accordance with MFO 86001-0112 procedures.

Peculiarities:

• Same latch size and design as RJ-45
• Duplex ferul
• Low cost
• High port density
• ISO/IEC 11801 and TIA/EIA 568A compliant
• Low direct losses:

< 0.22 дБ для ММ
< 0.19 дБ для ОМ

The development of the MT-RJ connector was based on the following objectives: small size, low cost and ease of installation. Using the MT-RJ connector doubles the port density of standard connectors and makes it ideal for use in fiber-to-the-desk applications. Connector design complies with TIA requirements.

The MT-RJ connector uses an improved version of the industry standard for RJ-45 connectors. It is the small size and convenience of a latch similar to RJ-45 that determine the advantages of this connector when used in horizontal wiring to the workplace.

A feature of the MT-RJ system from Molex is the use of different PN connectors for male (with guide pins protruding from the ferrule) and female (with holes for pins) modifications. There are two versions of the adapter, one of which is installed in the socket for the simplex SC adapter.

Quality and features

The materials were provided by AESP, a well-known manufacturer of network and communication equipment, developer of the cable system SygnaMax.

Optical connectors(connectors) are used when terminating optical fibers for their joining with passive or active telecommunications equipment.

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

ST optical connector type has a tip with a diameter of 2.5 mm with a convex end surface. Fixation of the plug on the socket is carried out by a spring-loaded bayonet element,turning ¼ turn. The guide frames, engaging with the stops of the ST-socket during rotation, 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 by a latch with a latch according to the "push-pull" principle.The linear movement of plugging and unplugging makes this connector particularly suitable for 19" shelf applications, as it allows increased port density by bringing sockets closer together. The latch opens only when pulled out of the housing, which increases operational reliability. An optical SC connector can be combined into a module consisting of several Duplex connectors.

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

miniature optical connectors type LCare about half the size of conventional options SC, FC, ST with a tip diameter of 1.25 mm instead of the standard 2.5 mm. This allows for greater patch panel density and dense rack mounting. The connector is fixed with a clamping mechanism.

We are also pleased to offer you connectors installation method:

One of the easiest methods for installing connectors on fiber is adhesive. This method uses epoxy resin to fix the fiber in the connector core.

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

They are designed to quickly terminate optical cables using the unique Splice-On technology using the Ilsintech Swift F1 splicer.

Dirt, dust and other contaminants are the biggest enemies of optical connectors that prevent high-speed data transfer.

This long article will provide you with detailed systematic information on passive optical components. After reading, you will get a complete idea for what, by what parameters and how to choose components for the operation of FOCL.

Various manufacturers over the years have developed several dozen types of optical connectors (connectors) and pass-through adapters for their connection, but only 4 of them are most widely used: ST, FC, SC, LC. The rest of the connectors that have ever existed are rarely used or have been discontinued altogether.

It should be noted that there is currently no document standardizing the use of any types of connectors. In this regard, depending on the industry, certain types of connectors are more popular.

The main types of optical connectors

ST "Straight Tip" connector

It has a metal bayonet design, the diameter of the ceramic tip is 2.5 mm. The connector was previously popular mainly in networks using multimode optical fiber. However, now it is not recommended for use, since this type of connector lacks the advantages that others have:

the possibility of manufacturing a duplex connector in which it would be physically impossible to confuse the location of the fibers for transmission and reception;

high reliability, stability under vibration loads;

compactness and ease of switching.

FC Ferrule Connector

The design resembles the ST connector, the diameter of the ceramic tip is 2.5 mm, but instead of the bayonet, a metal threaded connection is used. Today, the connector is actively used in active equipment and measuring instruments, due to its high reliability and resistance to vibration.

It is mainly used in long-distance FOCLs (backbone FOCLs), however, its use is limited in access networks, SCS and data centers due to the complexity of switching and the impossibility of manufacturing a duplex connector.

SC Subscriber Connector

Note: The designation SC-D may also be used, emphasizing that the connector is duplex, with a key.

The connector is most widely used due to the convenience of switching (using direct snapping) and the possibility of creating a duplex connector. The SC connector consists of an inner and outer body, the diameter of the ceramic tip is 2.5 mm. It is installed in the pass-through adapter without rotation, which is convenient when switching. The plastic construction is strong enough, is found in active equipment and is widely used in SCS and city-scale data transmission networks, although the connector is not among the compact ones. SC duplex connectors are more commonly used, but simplex connectors can also be used.

LC connector "Lucent Connector"

Unlike the previously listed connectors, the ceramic ferrule is 1.25 mm in diameter and therefore requires more careful handling. Due to their more compact dimensions, LC connectors have become very popular in both active equipment and passive optical cabinets and shelves, especially in high density. The connector belongs to the SFF class - small Form factor, in which the external dimensions of the connector fit into the footprint of an 8-position RJ-45 modular jack. The connector is installed in the pass-through adapter without rotation, by direct snapping. Duplex LC connectors are more commonly used, but simplex connectors can also be used. The body of the connector is made of plastic.

Attention! There is a smaller version of the duplex LC connector where the two shells are spaced less apart than a standard connector. Mini connectorsLCand mini-throughs are not compatible with duplex componentsLCstandard connector!

Among the variety of connectors in the SCS, preference is given to duplex SC and LC connectors with a key that prevents the connector from being inserted incorrectly into the pass-through adapter - thereby ensuring the correct polarity of the optical connection. New models of active equipment and data centers almost always use LC connectors due to their compactness.

Singlemode and multimode connectors and pass-through adapters

All connectors listed are available in 9/125 µm single mode and 50/125 or 62.5/125 µm multimode fiber options. The design of the connectors is fundamentally the same, however, for single-mode systems they are manufactured with the most stringent tolerances, while connectors with wider limits for tip drilling accuracy are suitable for multi-mode systems ( ferrule) and the manufacture of other structural elements. The same applies to pass-through adapters: feed-throughs for single-mode systems are subject to more stringent requirements for manufacturing accuracy.

Polishing types

In the bulk of optical connectors, the end surface is located at an angle of 90º to the longitudinal axis of the light guide. The end face of the ceramic tip can have a certain rounding, bevel of one size or another, but the area at the point of contact between the light guides is flat. Polishing quality may vary:

PC - Physical contact- basic quality acceptable for normal applications in SCS and local networks for not very long distances and speeds up to 1 Gbit / s inclusive. Reflectivity of the order of -35 dB.

SPC - Super Physical contact- improved quality (primarily machine polished), reflectivity -40 ÷ -45 dB or less. This or a higher level of polish is used in factory-made optical cords and pigtails.

UPC - Ultra Physical contact- maximum quality, only machine polished with strict quality control, reflectivity -50 ÷ -55 dB or less. Cords with this finish are used for high-precision measurements in optical system testing and for the most demanding applications at speeds of 10 Gbps or more.

PC, UPC and SPC polished connectors are structurally compatible with each other. The overall performance of the system is most affected by the components with the weakest parameters, so it is recommended to choose products with the same or higher polish quality.

Angle polished connectors

There are connectors with angle polishing APC - Angled Physical contact. In them, the mating surface is deviated by 8º from the usual one, i.e., the angle with the axis of the light guide is 82º. The reflectivity is -65 dB or less.

These connectors provide the best performance available today and minimize back reflections. However, they are not compatible with plain polished connectors. Attempt to dock connectorAPCwith any non-corner connector will cause damage to both! To reduce the risk of mismatching, APC connector bodies, shanks and feed-through adapters are manufactured in bright green.

APC connectors are most widely used in cable TV networks and provider lines.

Color version of conventional connectors

For conventional multimode connectors, it is customary to use black and beige body colors and pass-through adapters. Single-mode connectors and pass-through adapters are most often made in blue.

Note:

- Some manufacturers may manufacture all feed-through adapters with single-mode accuracy, but it is recommended that you always check specifications against datasheets and catalogs.

The coaxiality of the tips when docking optical connectors is provided by a centralizer located inside the pass-through adapter. The centralizer is a sleeve made of bronze, brass or ceramics, which has a longitudinal section along the entire length. Ceramic centralizers provide the best performance; they are made of the same material as the ceramic tips ( ferrule) connectors. For high speed and demanding applications it is recommended to use ceramic centralizer feed through adapters.

Optical patch cords

Cords are selected according to the type of fiber in the system (multi-mode classes OM1-OM4, single-mode classes OS1-OS2), with a certain type of connectors at the ends. The bulk of optical patch cords are duplex. The most popular duplex connectors are LC and SC, but simplex cords are also used. If necessary, cords with different connectors are used at the ends - for example, FC connectors on one end for connecting to active equipment and LC connectors on the other for connecting to an optical distribution box.

The outer diameter of the cable in optical cords was previously usually 3 mm (or twice 3 mm in the case of zip cords), but recently they are trying to make cables more compact, smaller in diameter (for example, 2 or 1.5 mm) to fit in optical cabinets and organizers, the maximum possible number of cords and connections. Regardless of the diameter and type of connectors, all optical cords require careful handling. When disconnecting from the ports, the connectors must be closed with protective caps.

Pigtail - a one-way fiber-optic jumper, "half cord" - has a factory-made and tested connector at one end, the other end is not terminated and is designed to be connected to a laid unterminated cable with a welded or mechanical sleeve. Unlike optical cords, pigtails do not have an outer cable sheath; a fiber comes out of the connector shank in a dense buffer with a diameter of 900 microns or 250 microns. The design of the shank, the diameter of its hole must correspond to the diameter of the buffer. Tails designed for installation on cable with a diameter of 3 mm or less are not intended for installation on fiber in a buffer of any diameter and cannot provide adequate protection to the fiber.

Pigtails are selected according to the type of fiber in the cable to which they are to be connected. The typical length of pigtails is 1 m - this is enough for convenient sealing of the sleeve and subsequent laying in the sleeve tray (splice plate). Manufacturers may offer pigtails in other lengths, but when ordering, consider where and how this fiber will be laid. Since the fiber in the buffer does not have an outer cable jacket, it is critical for it to maintain a bend radius of at least 25 mm and avoid the risk of damage.

Attenuators are designed to artificially attenuate the signal, which is necessary in cases where the optical segments are short and the transmitter produces a too strong signal. To prevent an excessively powerful signal from entering the receiver, it is “muted” by setting an attenuator at some point in the segment.

The attenuator must match the installed system in terms of fiber type and connector. In addition, the attenuator is selected depending on the amount of optical loss in decibels that must be introduced into the segment in order to attenuate the original signal to an acceptable level.

Attenuators are divided into:

active and passive devices;

regulated and unregulated devices;

designs male- female(“father-mother”, are installed on any connector in the segment) and female- female(“mother-mother”, are installed instead of the pass-through adapter).

Attenuators, like any optical component, require careful handling, the use of protective caps, and the timely application of fiber optic cleaners.

Compact devices designed for splicing optical fibers that are not terminated by connectors. There are two types of couplings available on the market: welded and mechanical.

The welded sleeve is a heat-shrinkable tube reinforced with a hard wire - a KDZS sleeve (a set for protecting the welded joint). Splicing is done with a specialized fiber optic splicer, which may have a built-in (or supplied separately) oven for shrink sleeves.

Complicated sleeve designs are also used, designed for flat ribbon cables or multi-fiber cables with a round cross section. Their cases are designed to protect 12 or more welded joints at the same time.

Mechanical couplings have their own rigid body and do not require the use of a welding machine and sleeves KDZS. The stripped and cleaved fibers are mechanically joined and fixed inside the sleeve, and possible voids or irregularities of the chips are filled with a gel, the refractive index of which is equal to the refractive index of the fiber core. The gel is initially located inside the sleeve - this component is fundamentally important for achieving acceptable optical characteristics of a mechanical connection.

Other things being equal, a welded sleeve has better characteristics and leads to significantly lower optical losses than a mechanical one. A well-sealed weld may lose 0.01 dB or less. This method is the leader in popularity and is used both for attaching pigtails to the ends of the cable, and for splicing extended cable sections to each other, especially if the backbone is long and the number of splices is large. In adverse conditions (attics, basements, sewer communications, poles and other areas outside buildings), a welded socket joint certainly outperforms a mechanical one in terms of performance, durability and reliability. Mechanical couplings can be used inside buildings where there are no sudden changes in temperature, vibration and other adverse factors.

Another area of ​​application of mechanical connectors is the operational repair of fiber optic lines when the welding machine is unavailable.

In this case, a high speed of damage repair is ensured at minimal cost (repair requires: mechanical connectors, buffer layer stripper, manual cleaver). The disadvantage of such a connection (not made according to the technology) is the fragility, because during the drying of the immersion gel, losses and reflections from the splice site increase. To prevent such a situation, such a connection should be replaced with a welded one for a short period of time (up to a month).

Any couplings require placement inside the coupling trays, also called splice cassettes, while the capacity of the trays and the shape of the grooves for laying welded and mechanical couplings are different.

Outer housings for accommodating optical couplers

The outer enclosures that house fiber optic splices are also often referred to as splices, which can lead to some confusion. In this case, we are talking about a robust outer casing, designed for installation in outdoor conditions, in sewers, on poles, in trenches (direct burial), in basements, attics and roofs of buildings. Optical couplings are inside the case; the design ensures their safety and protection from adverse external conditions: dust, wind, rain, snow, temperature changes, etc.

Depending on the cable entry points, the structures are divided into two types:

Material prepared
technical specialists of the SvyazKomplekt company.

Currently, there are many optical connectors that differ in size and shape, methods of attachment and fixation. The choice of the type of optical connector depends on the active equipment used, the tasks of fiber installation and the required accuracy. The main ones are - LC, SC, FC, ST.

The use of an optical LC connector allows high-density mounting in a patch panel or cabinet.

Connector tip diameter 1.25 mm, ceramic material. The connector is fixed by a clamping mechanism - a latch, similar to the RJ-45 connector, which prevents unforeseen disconnection.

When using duplex patch cords, it is possible to connect the connectors with a clip. Used for multimode and singlemode fibers.

The SC connector type is used for both multimode and singlemode fiber. Tip diameter 2.5 mm, material - ceramics. The body of the connector is made of plastic. Fixation of the connector is carried out by translational movement with snapping.

FC connectors are typically used in single mode connections. The body of the connector is made of nickel-plated brass. Threaded fixation provides reliable protection against accidental disconnection.

Currently, the ST connector is not widely used due to shortcomings and increased requirements for mounting density. The connector is fixed by turning around the axis, like a BNC connector.

Many people confuse the types of optical connectors, and very few people can immediately tell which connector has which polish. When communicating with colleagues, you probably often heard phrases like: “well, this little blue connector” or “umm .. green”. On the Internet, most of the materials are written chaotically and incomprehensibly, in this article we will try to put everything on the shelves.

Types of polishes

It should be noted that the main problem of optical connectors is optical attenuation, it depends on the misalignment (lateral deviation) of the cores of the joined optical fibers and has a major impact on the amount of total losses.

Another problem with installing an optical connector at the end of a fiber is the loss of optical signal, which is caused by some of the transmitted light being reflected back into the fiber to the source of that light, the laser. Back reflection (RL - Return Loss) can disrupt the operation of the laser and the structure of the transmitted signal. To prevent/reduce this phenomenon, different types of polishing are used.

At the moment, there are 4 types of polishing:

Although the last two are mostly used, let's look at each one in turn.

PC-Physical Contact. In the first variations of polishing, an exclusively flat version of the connector was provided, but life has shown that the flat version makes room for air gaps between the light guides. In the future, the ends of the connectors received a slight rounding. The PC class includes hand polished and glued connectors. The disadvantage of this polishing is that there is such a phenomenon as an "infrared layer" - in the infrared range, negative changes occur on the end layer. This phenomenon limits the use of connectors with such polishing in high-speed networks (>1G).

SPC - Super Physical Contact. In fact, the same PC, only the polishing itself is of better quality, because. It is no longer handmade, but machine-made. The radius of the core was also narrowed and zirconium became the material of the tip. Of course, it was possible to reduce polishing defects, but the problem of the infrared layer remained

UPC Ultra Physically Contact. This polishing is carried out by already complex and expensive control systems, as a result of which the problem of the infrared layer has been eliminated and the reflection parameters have been significantly reduced. This made it possible for connectors with this polishing to be used in high-speed networks.

ARS - Angled Physically Contact. At the moment, it is believed that the most effective way to reduce the energy of the reflected signal is polishing at an angle of 8-12 °. In this design, the reflected light signal propagates at a larger angle than that injected into the fiber. Bias polished connectors are colour-coded and are usually green.

A summary of the data can be found in the table below.

Dependence of insertion loss on the polishing method
Series	Insertion loss, dB	Back reflection, dB
PC	0,2	-25 .. -30
SPC	0,2	-35 .. 0
UPC	0,2	-45 .. 50
APC	0,3	-60 .. 70

Connector types

Optical FC connector. Developed by NTT. Tip with a diameter of 2.5 mm with a convex end surface with a diameter of 2 mm. Fixation is carried out with a threaded cap nut. This makes them resistant to vibrations and shocks, which allows them to be used, for example, near the railway or on moving objects.

optical connector ST. Developed by AT&T. Tip with a diameter of 2.5 mm with a convex end surface with a diameter of 2 mm. Protection of the end of the fiber is carried out by scrolling at the time of installation with a side key that enters the groove of the socket. The plug is fixed with a bayonet lock (from the French ba?onnette - a bayonet. An example of a bayonet lock is a camera lens mount). The connectors are easy to use and quite reliable, but sensitive to vibrations.

optical connector SC. The disadvantage of ST and FC connectors is the rotational movement when turned on, which imposes a restriction on the inclusion density (it is difficult to screw in when there are a lot of plugs in nearby). The SC type is made according to the push-pull principle - pressed inserted / pulled out. The locking mechanism opens by pulling on the housing. The connector can be pulled out by applying a force of 40N, while when "pulling" the ST and FC, it is easier to break the fiber itself. Accordingly, it is not recommended to use the SC connector on moving objects.

optical connector LC. Developed by Lucent Technologies. 1.25 mm diameter ceramic core not bonded to the plastic case. It is fixed with a latch, as in the well-known RJ-45. It is the most popular optical connector. A pair of connectors can easily be combined into a duplex.

Conclusion.

The name of the optical patch cord indicates which connectors are installed at the ends, and through the “/” symbol, the type of polishing. If the type of polishing is not specified, then it is a direct polishing. For example, an LC-SC fiber optic patch cord, which means that there will be an LC connector on one end and a SC connector on the other. In the specification in any store, you can choose the right polish and the right connectors.

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