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

Basic data on FOCL for the design of telecommunications systems

Optical fiber allows you to organize communication without regenerators (signal repeaters) up to 120 km for single-mode and up to 5 km for multimode cables.

As signals in optical cables, not electrical impulses are used, but modes ( light streams). The walls of the central core are dielectrics and have the reflective properties of glass, due to which light fluxes propagate inside the cable.

Singlemode and multimode fibers

It is customary to divide fiber optic fibers (cables and patch cords) into two types:

Single mode (Single Mode), abbreviated: SM;

Multimode (Multi Mode), abbreviated: MM.

At the same time, both types have their advantages and disadvantages, which means that each of them can be used for various purposes.

Single mode optical fibers (SM)

8/125, 9/125, 10/125 is the marking of single-mode fiber optic patchcords. The first number in the marking is the diameter of the central core, and the second is the diameter of the sheath. It is worth noting that the diameters of FOCL (fiber-optic transmission line) are measured in microns (micrometers).

A single-mode cable uses a focused, narrowly focused laser beam with a light wave range of 1.310-1.550 µm (1310-1550 nm).

Due to the fact that the diameter of the central core is small enough, the light modes move in it almost parallel to the central axis. Therefore, there are practically no signal distortions in the fiber, and low attenuation makes it possible to transmit an optical pulse over distances up to 120 km without regeneration at speeds up to 100 Gbit/s and higher.

There are single-mode optical fibers:

Unbiased dispersion (standard, SMF);

Dispersion Shifted (DSF);

And with non-zero shifted variance (NZDSF).

Multimode optical fibers (MM)

Multimode stepped fiber

Multimode Gradient Coefficient Fiber

Multimode fibers are labeled, for example, 50/125 or 62.5/125. This suggests that the diameter of the central core can be 50 or 62.5 µm, and the diameter of the cladding is the same as that of the single-mode type - 125 µm.

A multimode cable uses scattered beams from LEDs or a laser with a light wave range of 0.85 µm - 1.310 µm (850-1310 nm).

Due to the fact that the diameter of the central core of a multimode patch cord is larger than that of a single-mode patch cord, the number of paths for the propagation of light modes increases. Several light streams at once move along different trajectories, reflecting from the mirror surface of the central core.

However, stepped multimode fiber has a rather high intermode dispersion (gradual expansion of the optical beam due to reflections), which limits the signal transmission distance to 1 km and the transmission rate to 100 - 155 Mbps. The operating wavelength is typically 850 nm.

Multimode graded-index fibers are characterized by lower intermode dispersion due to a smooth change in the refractive index in the fiber. This allows you to transmit an optical signal over distances up to 5 km at speeds up to 155 Mbps. Working wavelength - 850 nm and 1310 nm.

Differences between single-mode and multi-mode optical fibers

Signal attenuation plays a rather important role in single-mode and multimode optical fibers. This is the reason for the short working distance of multimode fibers (1-5 km). Despite the fact that it would seem that more light fluxes travel through a multimode cable, the throughput of such cables and patch cords is lower than that of single-mode ones.

A narrowly directed (single-mode) beam in single-mode fibers attenuates several times less than a scattered (multi-mode) beam in multi-mode fibers, which makes it possible to increase the distance (up to 120 km) and the speed of the transmitted signal.

Optical connectors

An optical connector, or connector (Optical Connector) is an inexpensive and effective method switching fiber optic cables. It provides reliable connection and integrity of transmitted packets.

Today on the market there is a large number of various types connectors for FOCL. All of them have different parameters and purpose. Docking of two identical or different connectors is carried out using an optical adapter.

Various types of optical connectors have different shape and connection technology. Also in the production of such connectors can be used various materials whether it be metals or polymers.

The main types of optical connectors (connectors)

SC connectors

SC is the most popular optical connectors.

The housing of the SC connector is made of plastic, cross section- rectangular. The connection and disconnection of this connector is linear, in contrast to the FC and SC connectors, in which the connection is rotational. Thanks to this, as well as a special "latch", a fairly rigid fixation in the optical socket is provided. SC connectors are mainly used in fixed installations. The price is slightly more expensive than FC and SC connectors.

Single-mode SC connectors are marked in blue, in gray- multi-mode connectors, in green- single-mode connectors with APC polishing class (beveled end).

LC connectors

The optical LC connector is similar in appearance to the SC connector, but smaller than it in size, which makes it easy to implement high-density optical cross-connects using LC connectors. Fixation in the optical socket is carried out using a latch.

FC Connectors

FC connectors are made of a ceramic core and a metal ferrule. Fixation in the optical socket occurs due to threaded connection. FC connectors provide a low level of losses and a minimum of back reflections, and due to reliable fixation, they are used to organize communication on moving objects, communication networks railways and other critical applications.

ST connectors

ST connectors are characterized by simplicity and reliability in operation, ease of installation and relatively low price. Outwardly similar to FC connectors, but, unlike FC, in which fixation in the socket is carried out using a threaded connection, ST connectors belong to the category of BNC connectors (the connection is made using a bayonet connector). ST connectors are sensitive to vibration and are subject to these limitations.

ST connectors are mainly used to connect optical equipment to trunk lines and in local area networks.

DIN connectors

The DIN connector is similar to the FC connector but is smaller. 2.5mm diameter ceramic core protrudes beyond plastic case, which, in turn, has a latch that prevents the core from rotating around its own. DIN connectors are often used in measuring equipment.

Connectors E-2000

E-2000 is one of the most complex optical connectors. Connection and disconnection is carried out linearly (push-pull), and opening - by means of a special key insert. Therefore, it is almost impossible to mistakenly remove such a connector.

The E-2000 connectors have special plugs in their design, which automatically close the end of the connector when it is disconnected from the optical socket, which prevents dust from getting inside.

E-2000 connectors are distinguished by high reliability and density of mounting. square section connector provides easy implementation of duplex connections.

High Density Connectors

Connectors MT-RJ

MT-RJ connectors are manufactured as duplex pairs.

Connectors VF-45 (SJ)

The shank of the connector is inclined approximately at an angle from the plane of the connection of the fibers. The VF-45 (SJ) connector is equipped with a self-locking dust cover.

MU Connectors

Analogue of the SC connector, smaller in size. The centralizer is ceramic, with a diameter of 1.25 mm, the rest of the parts are plastic.

Colors of optical connectors (connectors).

FC and ST - nickel-plated brass

SC and LC duplex or simplex multimode - beige or gray

SC and LC duplex or simplex single mode - blue

SC/APC simplex (simplex) - green

Polishing grades for optical connectors

Perhaps the main characteristics of optical connectors are insertion attenuation and back reflection. Optical attenuation has a stronger effect on signal quality than back reflection.

The return attenuation index depends primarily on the transverse deflection of the cores of the connected optical fibers.

The polishing of optical connectors ensures that the optical fibers are tightly connected to each other and reduces the air gap, which, in turn, reduces the back reflection of the signal.

There are 4 polish grades: PC, SPC, UPC and APC.

Polishing PC, SPC, UPC:

RS (Physically Contact)

The PC class includes hand-polished connectors, as well as connectors manufactured using adhesive technology. Application speed - up to 1 Gbps.

SPC (Super Physically Contact)

Mechanical polishing of ends of optical connectors. Provides a tighter fit and use in systems with speeds greater than 1.25 Gbps.

UPC (Ultra Physically Contact)

Automatic polishing. The planes of the connected connectors fit even more tightly than in PC and SPC, therefore, such connectors are used in information transmission systems with speeds of 2.5 Gb / s and higher.

Polishing APC (Angled Physically Contact):

The contact surface of these connectors is beveled by 8 - 12 degrees from the perpendicular. This grinding method is used to reduce the energy level of the reflected signal (at least 60 dB). APC connectors are used only in conjunction with other APC connectors and cannot be used in conjunction with other types of connectors (PC, SPC, UPC). Differ in green marking of plastic tips.

Types of optical patch cords

Simplex (SX) and duplex (DX) patch cords

Optical patch cords can be simplex (for one connection) and duplex (for two connections).

Patch cord SC-SC simplex (SX)		Patch cord SC-SC duplex (DX)

Transition patchcords

Transitional optical patch cords are used to switch from one type of optical connector to another. The need for their use arises quite often, when switching equipment for various purposes and production. To do this, transitional patch cords are terminated with different optical connectors: for example, at one end - LC, at the other end - FC.

Transitional patch cords are simplex and duplex.

Patch cord colors

The sheath of optical patch cords is different, depending on the type of optical fiber, and has a color:

• yellow - for single-mode fiber;
• orange - for multimode fiber with a diameter of 50 microns;
• blue, black - for multimode fiber with a diameter of 62.5 microns.

Differences from the generally accepted color coding may be in the manufacture of duplex patch cords.

Marking of optical patch cords

Usually, the marking of optical patch cords indicates:

• connector type: usually SC, FC, LC, ST, MTRJ;
• fiber type: single mode (SM) or multimode (MM)
• polishing class: PC, SPC, UPC or APC;
• number of fibers: one (simplex, SX) or two (duplex, DX);
• diameter of the light-conducting core and buffer: usually 9/125 for single-mode patch cords and 50/125 or 62.5/125 for multi-mode patch cords;
• patchcord length.

The growth in the number of operated ports, the speed and range of information transmission requires new approaches to organizing the connection of equipment ports and SCS. One approach is to use LC connectors, which are available in a variety of designs. However, not all of them are effective in high-density passive and active ports.

LC connector

The optical interface type LC (Lucent Connector) is one of the most widely used plug-in connector types today. The connector was introduced to the market in 1996 by Lucent Technologies and has been recognized by experts due to a number of advantages that the user receives in real-life operating conditions of the final passive and active equipment, along with the use of SFP transceivers. Analysts estimate that over 60 million LC connectors have been installed worldwide to date. Currently, about 30 companies officially have a license to manufacture of this type interface.

Among the main advantages of the optical LC connector is the ability to place a duplex optical port on the same footprint as an RJ45 copper port (Figure 1), and the LC connector uses a similar latch mechanism.

In the original version, the optical LC socket had landing dimensions, equal to the size of the hole for a copper socket, which allowed " reuse» existing copper patch panels and their combination.

Until the recent past specific gravity optical wiring in total cable system was less than 10%, since the main tasks of connecting active equipment were effectively solved using traditional copper-core SCS various categories. The situation has started to change with the advent of 10G Ethernet applications and the development of SAN infrastructure using the Fiber Channel protocol, which requires a lower level of channel loss.

Limited space available in machine rooms of data centers and overall growth The number of units of active equipment per unit area of ​​the hall has led to the emergence of more efficient - in terms of size, power consumption and cooling - active equipment. In turn, this has forced structured cabling manufacturers to adapt their solutions to accommodate more passive optical ports due to the introduction of a new small-sized duplex LC socket (the so-called SC foot print type), the landing dimensions of which coincide with the dimensions of a standard SC simplex socket (Fig. 2).

Density or comfort

The advent of the small-sized duplex LC receptacle made it possible to increase the density of installation due to the closer placement of ports on the optical patch panel. Today, up to 48 duplex LC sockets can be accommodated per standard height unit. From the point of view of data center infrastructure, this means, for example, the ability to significantly reduce the number of units used in a rack with active equipment, to make the switching field more compact. However, from an operational point of view, the issue of serviceability of connected optical LC connectors remains unresolved. It is here that most SCS manufacturers have not managed to make significant progress in terms of technology.

The ease of use of any plug-in connection generally means that you can get free access to the optical connector without affecting adjacent, already connected connectors. This problem is especially critical in high-density installations, which are typical today for central switching optical distribution frames, as well as when connecting a number of types of network switches or routers.

It's no secret that a few years ago, operations department specialists perceived the LC interface extremely negatively, referring to the fact that it is extremely small in comparison with the usual SC connector, that it is difficult to remove it from the socket (often SCS manufacturers even suggested using a special tool, facilitating this operation), which forms a "beard" of entangled patch cords, since the latches of the connectors cling to the cable all the time, complicating the process of removing the optical cord.

Since the density of connections in the case of LC is two or more times higher compared to other connectors (for example, SC), and the design of the latch of the LC connector and the copper RJ45 connector is implemented in a similar way, access to the latches is significantly limited when the cords are connected (Fig. 3a). I think most experts remember well the best tool for servicing duplex LC connections - ordinary tweezers.

Developers and manufacturers of optical LC connectors, taking into account this limitation, made design changes to the shape of the latch (Fig. 3, b). Various options offered by different manufacturers, suggest, for example, the creation of an additional platform for pressing the connector latch (the platform is part of either the connector housing or the duplex clip), increasing the usable working area of ​​the latch, or complicating the geometry of its surface so that pressing the connector latch works more efficiently.

The presence of an additional platform simplifies access to the connector latches and reduces the tangling of optical cords. On the other hand, due to the characteristics of the deformation polymer material and small dimensions of the latch, it is impossible to ensure uniform pressure on the latches in the duplex version of the LC connector. This usually causes the duplex connector to stick when unplugged, with one latch engaged and the other not. As well as additional costs time and effort, this can lead to the destruction of the connector housing due to an asymmetrical side load.

Among the interesting non-standard solutions available on the market, it should be noted the design of the LC connector with the so-called inverted latch (Fig. 4). Keeping full compatibility with standard sockets, this connector design provides good access to the latches due to the increased area, reduces the likelihood of tangling optical cords due to the fact that the optical cord cable will catch on the latch. In addition, in the duplex design, due to the design of the used clip, the applied force is evenly distributed on both latches.

Flexible shanks

One alternative approach to improve serviceability detachable connections LC in high-density mounting conditions, - use of shortened flexible shanks (Fig. 5). Manufacturers offering these solutions report that optical ports are easily accessible and patch cords can be safely managed even in tight spaces between the equipment plane and the cabinet door.

Note, however, that the use of a shortened body of the connector and/or a flexible shank, however, does not solve the issue of ease of access to the latches of the connector itself.

Design LC-HD

From the point of view of the use of plug-in connections, it is of particular interest to be able to combine the high density of connections inherent in the LC interface with the option of fixing the push-pull interface of the SC. In this case, access to the connector latches, especially in duplex versions, is not required at all. Such a design is on the market today (Fig. 6) under the trade name LC-HD (subject of a valid patent), where the abbreviation HD stands for High Density.

The manufacturer, while maintaining full compatibility with standard LC sockets and SFP/SFP+ transceivers, has created a solution for organizing high-density connections both on patch panels and on cards/blades of active equipment. Its main feature is the use of a special clip, thanks to which there is no need for access to the connector latches at all.

Proposed constructive solution works equally effectively in cases of horizontal and vertical orientation of LC sockets or optical transceivers, for example, on the blades of a heavy multiport switch (Fig. 7).

By applying even and symmetrical force to the connector latches, the user can connect or disconnect the duplex connector from the switch port almost blindly - this is a typical situation, for example, when using blades with ultra-dense mounting of transceivers.

A little about prospects

And in conclusion, I would like to draw attention to special kind optical duplex interface - mini-LC. This decision arose as a result of an attempt to increase the density of mounting transceivers on the switch blade. Its characteristic feature is the reduced distance between the geometric centers of the connectors - 5.25 mm instead of 6.25 mm for the standard version. Corresponding changes were made to the design of transceivers, which were called mini-SFP.

Apparently, the practical future of such a solution is not yet obvious, although a number of manufacturers of optical connectors have announced the availability for ordering mini-LC connectors and patch cords based on them. Anyway this decision cannot be adapted within the framework of a complete cabling system, since the requirement of compatibility and universality of cabling with respect to active equipment of various vendors in the data center computer room is not met.

In general, the developers and manufacturers of passive components are only at the very beginning of their journey, and, of course, new interesting engineering solutions will still be presented to the market.

The body of the optical connector is made of plastic and has a rectangular shape. The ferrule has a diameter of 2.5 mm and is almost completely covered by the body, which protects it from mechanical damage and dirt. The body color depends on the type of connector polishing: UPC - blue, APC - green. SC multimode (MM) connectors are manufactured gray color. Often, duplex SC connectors are used, in this case 2 connectors are connected to each other using a clip (holder).

LC connector.

The LC optical connector is a smaller copy of the SC connector. Its body is rectangular. The ferrule of the connector has a diameter of 1.25 mm and is made of ceramic. There is a latch on the connector body, the connector is fixed with the help of translational movement. This type of connector is designed for use in high-density mounting. The body color depends on the type of connector polishing: UPC - blue, APC - green. LC multimode (MM) connectors are available in grey. The duplex LC connector consists of two connectors fastened with a clip (holder).

Types of terminated fiber:

Polishing types: PC, UPC, SPC, APC.

Types of terminated fiber: SM, MM.

Fiber sheath diameter: 0.9, 2, 3 mm.

FC connector.

The body of the FC connector is made of plastic and has a rounded shape. The connector is fixed by screwing the movable part of the connector onto the optical adapter. On the front of the connector there is a notch (key) that prevents the connector from turning when it is fixed. The color of the shank depends on the type of polishing. The ferrule of the connector is made of ceramic and has a diameter of 2.5 mm. Compared to LC and SC connectors, it has both positive and negative sides. On the positive side, the FC connector is rigidly fixed to the optical adapter, which makes it resistant to vibrations and gives an undeniable advantage of using it on backbone connections. Of the negative - just a rigid fixation makes it inconvenient during installation, the possibility of circular rotation at the junction of optical fibers negatively affects wear resistance.

Types of terminated fiber:

Polishing types: PC, UPC, SPC, APC.

Types of terminated fiber: SM, MM.

Fiber sheath diameter: 0.9, 2, 3 mm.

ST connector.

The body of the optical connector is made of metal and has a rounded shape. The connector is fixed by means of latches on the rotating frame of the connector. The clamping force is achieved by a spring installed between the body and the movable frame. On the front of the connector there is a notch (key) that prevents the connector from turning when it is fixed. The color of the connector depends on the type of polishing. The ferrule of the connector is made of ceramic and has a diameter of 2.5 mm. If we compare the ST connector with the three previous ones, then we can only answer a couple of its positive aspects - a fairly strong fixation in the optical adapter (strong in terms of not being able to fall out or accidentally pull out) and ease of installation. But there are a lot of negative ones - a ferrule strongly protruding from the body, the possibility of circular rotation, low vibration resistance (since the connector is not rigidly fixed on the optical adapter). At present, this type of connector can be classified as endangered, although it is not yet often found in fiber-optic communication lines.

Types of terminated fiber:

Polishing types: PC, UPC, SPC.

Types of terminated fiber: SM, MM.

Fiber sheath diameter: 0.9, 2, 3 mm.

To date, more than 70 types of connectors for various purposes for FOCL have been developed. The most common are symmetrical optical connectors with design plug type. To connect such connectors, special optical adapters are used. Thanks to these devices, the connected optical connectors can be either one or several types.

Description of the design of the optical connector

Plug-in optical connectors look like this: the optical fiber is fixed in a special precision tip of the "ferule" type, which is inserted into the centralizer insert. Fastener connectors in the adapter can be either bayonet type or threaded or lockable. Some types of equipment require the connection of duplex pairs of optical fiber, duplex type optical connectors have been developed specifically for this. Initial implementation similar devices was achieved by a symmetrical plastic clip containing sockets into which a pair of connectors were inserted, after which they were fixed with a latch. Most of all, connectors with square housings were suitable for this. However, over time, it became necessary to develop duplex-type optical connectors in a single package.

The next stage in the development of the production of fiber optic connectors was the creation of special ribbon-type connectors in a solid buffer coating. Nevertheless, today this type is not very popular due to the high complexity of obtaining a high-quality joint, even using the welding method. Currently, the main consumers of the mentioned connectors are Japan and the USA.

Main technical characteristics

The main parameters of optical connectors are: long-term durability and stability external conditions. On the throughput back reflection and insertion attenuation are affected. These characteristics depend on the transverse displacement of the axes, as well as the angle between them. And also from the Fresnel reflection of the signal at the boundary of the separation of two media. The maximum amount of loss introduced by the connector is the optical attenuation. This characteristic affects the amount of total losses in a given path. This parameter directly depends on the transverse deviation (misalignment) of the cores of the connected

The next important parameter is the inverse reflection. The main source influencing this characteristic, is the separation boundary of two media (air and fiber). This component can reach significant values. Moreover, the back reflection can be changeable in time, that is, under the influence of external factors it can eventually disrupt the performance of the entire system.

Optical audio cable

Now they are gaining great popularity in the device of audio systems. The main advantage of such wires is the absence of interference, which means that the signal will remain clean and clear, despite the length of such an extension cord. have proven themselves to be reliable in harsh electromagnetic environments where copper wires were unable to cope with the interference. In computer technology, the SPDIF (Sony-Philips Digital Interface) cable is especially popular - this is an interface for transmitting audio signals in digital form. It transmits between devices without the quality loss that inevitably occurs when using the analog method.

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. Connector design provides reliable protection ceramic tip from contamination, and the use for fixing the union nut gives greater tightness connection zones and connection reliability 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 most simple methods for installing connectors on fiber - adhesive. To fix the fiber in the connector core, this method uses epoxy resin.

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 welding machine Ilsintech Swift F1.

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