In optical fiber communication, data communication, multimedia communication and other communication systems that use optical fiber and cable as the transmission medium, it is necessary to fiber connector to optical fibers, or optical cables to optical cables, and optical fibers to optical terminal equipment.

With the rapid development of optical communication technology, the connection of optical fibers and optical cables has now developed into a specialized technology, that is, optical fiber connection technology. It can be seen from the actual application of the optical transmission network that the optical fiber connection technology is divided into two categories: one is a permanent connection, and the other is a detachable active connection. For permanent connection, there are two kinds of mechanical splicing and fusion splicing. In the optical cable transmission network, the connection between optical fibers and cables adopts permanent connection. The connection between the optical terminal equipment and the optical cable line requires various active connection methods.

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What is a fiber optic connector?

fiber connector to optical fibers

Optical fiber connectors, also known as movable joints, are used for the connection between equipment and optical fibers, between optical fibers and optical fibers, or between optical fibers and other passive devices.

It is an indispensable and important instrument for composing optical fiber communication systems and measurement systems.

In the optical fiber communication transmission link, it is necessary to meet the needs of flexible connection between different modules, devices and systems. Due to the difference between optical signal transmission and electrical signal transmission, it is absolutely impossible to directly twist the heads of two optical fibers together (unless For fusion splicing, and fusion splicing is impossible to achieve the flexibility of connection), there must be a device that can be detachably connected between the optical fiber and the optical fiber, so that the optical signal can be transmitted according to the required channel to ensure the optical fiber chain. The smooth flow of the road to achieve the intended purpose and requirements.

The device that can realize this function is the optical fiber active connector, hereinafter referred to as the optical fiber connector, which is the most widely used optical passive device in the optical system.

What are the ways to align the pins of fiber optic connectors?

Fiber optic connectors are now widely used in fiber optic communication systems. There are many types of optical fiber connectors and different structures, but after careful study, the basic structure of various types of optical fiber connectors includes three parts: centering, pins and end faces. The alignment can adopt the structure of sleeve, double cone, groove, lens and so on. The representative and in-use connector structures are mainly the following types:

Casing structure

Casing structure

Consists of two pins and a sleeve as shown. The pin is a precision cylinder with a micro-hole. After inserting the optical fiber into the micro-hole, it is fixed with special glue and processed accordingly to form the pin body. The sleeve is a machined precision sleeve, usually divided into two types: open and non-open. Among them, the open sleeve is the most common. When aligning, the outer cylindrical surface of the pin is used as the reference plane, and the pin is inserted into the sleeve and then closely matched with it, so as to ensure the precise alignment of the two optical fibers.

Because the structural design of the sleeve is reasonable, the required precision can be achieved through processing, and mass production is relatively easy, so it has become the mainstream of connector development.

FTTH (Fiber to the Home), The Ultimate Guide

Double cone structure

Double cone structure

The outer end face of the pin is processed into a conical surface, and the inner hole of the base is also processed into a double conical surface. When the two pins are inserted, use the taper surface positioning for butt joint, as shown in the figure. This method requires extremely high machining accuracy. The pins and bases are usually molded by polymer. The precise combination of the inner and outer cone surfaces not only ensures the alignment of the fiber cores, but also ensures that the distance between the two fiber end faces just meets the requirements. This structure is created and used by.

V-groove structure

V-groove structure

Put the two pins into the precisely designed groove, as shown in the figure, and then use the cover plate to press the pins tightly to align the fiber core, which constitutes the groove structure. This structure is a patented technology of Philips of the Netherlands, which is usually not used in single-fiber connection.

Lens coupling structure

Lens coupling structure

The alignment of the fiber is achieved by a ball lens and a self-focusing lens, as shown. Its working principle is that the lens converts the outgoing light of one fiber into parallel light, and then enters another lens to focus and combine into the second fiber. This structure can greatly reduce the precision requirements for machining, but due to its complex structure, large volume, many adjustment components, and large loss, it is usually only used for convenient communication in short distances.

The pin body of the above structures plus a number of external parts constitute a connector plug, which is used to realize the plugging and unplugging function of the optical fiber between the converters, and its mechanical structure must ensure that the optical fiber is not damaged by the outside world. A patch cord is formed by attaching a plug to both ends of an optical fiber. Jumper is the most commonly used optical connector functional vision, used for interconnection between terminal equipment and optical cable lines and various optical passive devices to form an optical fiber transmission system.

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What is the plug structure of fiber optic connectors?

the general structure of fiber connector plug

Usually the connector plug is to pass the optical fiber into the pin, and then fix it in the pin by gluing and baking. Alignment is then achieved in the compression sleeve after the pin surface is polished by an appropriate process.

When mating, in order to obtain high performance, the splicing end must be ground, and the other end usually adopts a limiting member to support the optical fiber, or release the stress through the optical fiber cable. Coupling tubes are generally made of cylindrical members made of ceramics, bronze, etc., and are mostly equipped with flanges to fix the connectors. Usually, the machining accuracy of the pins and the weighing tube is very high.

What does a fiber optic connector do?

What is a fiber optic connector

The function of the optical fiber connector is to closely align the end faces of the single or multiple optical fiber cores that need to be connected and can be reused many times. Since the core of the optical fiber is very thin, which is 10μm, the performance indicators of the optical fiber connector should meet the following requirements.

(1) The connection loss should be small: it is the most important indicator for evaluating optical fiber connectors, and it is generally required that this indicator be less than 0.5dB. At present, the index of high-quality products is less than 0.2dB.
(2) Reusable performance: Generally, this indicator is required to be greater than 1000 times.
(3) Stable performance: Mainly the temperature characteristics generally require the index to be less than 0.2dB in the range of (-40±2)℃~(+70±2)℃.

How many types of fiber optic cable connectors?

performance indicators of optical fiber connector

Fiber optic connectors are now widely used in fiber optic communication systems. There are many types of fiber optic connectors with different structures.

According to different classification methods, it can be divided into different types. According to different structures, it can be divided into LC, FC, MU, ST, SC, MT-RJ and other types; according to different transmission media, it can be divided into single-mode optical fiber connectors and multi-mode optical fiber connectors;

According to the difference of the pin end face of the connector and the connector material can be divided into oxide ceramic materials, materials, glass materials, plastic materials, etc.

Simply put, the fiber optic connector widely used in the telecom industry is composed of three parts: two plugs and a socket (flange or adapter).

Optical fiber connectors are generally classified according to their structure, and are classified into four types: FC, PC, UPC and APC according to the physical contact surface of the optical fiber connector plug.

Among them, FC means that it is a plane; PC means that it is a spherical surface; UPC means that it is a precise spherical surface; APC means that it is an inclined surface.

According to the locking part of the fiber optic connector plug, it can be classified into FC, SC and ST3 types. FC is screw type, SC is socket type, ST is plug-in rotary type.

When using different locking types of fiber optic connector plugs, the corresponding socket (flange or adapter) should be selected.

The socket (flange or adapter) is selected according to the locking part of the fiber optic connector plug it is connected to, and there are many models.

The two ends of the socket (flange or adapter) can be flexibly configured as required to realize the connection of optical fiber connectors with different locking methods.

For example, the socket (flange or adapter) configured as FC/PC-SC/UPC can connect different types of FC and SC fiber optic connector plugs.

When selecting fiber optic connectors, special attention should be paid to whether single-mode fiber or multi-mode fiber is connected, as well as the outer diameter of the fiber optic connector insert.

Classification of fiber optic connectors

In optical fiber communication engineering, optical fiber connections can be classified as follows according to factors such as the type of optical fiber, transmission rate, and occasions of use.

Classification by fiber type

Optical fibers in modern optical communication engineering can be divided into three categories: single-mode optical fibers, multi-mode optical fibers, and special optical fibers. Corresponding to the types of optical fibers, fiber optic cable connectors can be basically divided into 3 types: single-mode fiber optic connectors, multi-mode fiber optic connectors, and special fiber optic connectors.

Classification by connector shape and structure

The connector types that have been published in IEC874 series standards are: BAM type, CF04 type, CF08 type, D type, DS type, FC type, F-SMA type, LSA type, MT type, OF type, OCCA-PC type, OCCA- BU type, SC type, ST type.

With the development of data and multimedia optical fiber communication technology, there are FSD type, FSD-MC type, RSD type, DNP type and CP type.

At present, the most widely used in digital communication systems are FC type, ST type, SC type and D type fiber optic cable connectors.

The common feature of these 4 fiber optic connectors is that they all have optical ports that contact each other.

According to the IEC874 series of standards, the fiber optic connector specifications can be derived from 12 different forms of connection according to 12 changes in the plug.

It can be seen from this that due to the development of optical fiber and cable connection technology, its connectors have formed a specialized industry in the field of communication.

Classification according to the physical status of the plug

For FC, SC, ST and D-type optical port connectors with mutual contact, no matter what type of device it is, it can always be classified into the following three types; that is, the common PC connection, SPC connection, APC connect.

What is FC type fiber optic cable connector?

FC is the abbreviation of Ferrule Connector, which was first developed by Ben. Its external strengthening method is to use a gold flex sleeve, and the fastening method is a turnbuckle.


FC fiber optic cable connector is one of the common models of single-core fiber optic connectors, with a plug-adapter-plug structure, it is a high-performance fiber optic connector with very low connection attenuation and very low Reflection, can be made into super PC and angle PC when used for multimode fiber connection.

FC/PC fiber optic cable connector is characterized by a cylindrical zirconia ceramic pin body with an outer diameter of 2.5mm and a threaded locking mechanism with M8 thread. It has excellent performance and reliability, and is widely used in fiber optic cable transmission networks. and digital communication systems.

FC is an early product of optical fiber connector plugs. Because its physical contact surface is flat, dust and temperature have a greater impact on its connection loss, and it is generally less used now. However, the equipment and instruments that are still used in the past, and the number of fiber optic connector plugs of this model are still relatively large.

The FC connector is one of the fiber optic connectors, and it has a wide range of applications in the communication industry. The FC connector with a metal sleeve device can strengthen the external structure and use a turnbuckle to tighten and fix it.

The initial FC connector uses the design structure of ceramic pins, which is easy to be allergic to fine dust, and then Fresnel reflection occurs, which will bring serious consequences and generate huge return loss. Spherical pinning will improve this situation.

Another type of commonly used fiber optic connectors is the SC type. This type of connector can be plugged and unplugged at any time, with flexible use and control, and easy installation. The installation task can be completed within 1 minute. use;

At the same time, it also has the advantages of small loss fluctuation, high compressive strength, high installation density, high temperature resistance, and oxidation resistance.

What is SC type fiber optic cable connector?

This is a fiber optic connector developed by NTT Corporation in 2008. Its outer casing is made of plastic and is rectangular, of course, its sleeve is still cylindrical. The connection is made by pushing the connector into the mating sleeve. When the clip is engaged, the housing of the connector and the mating sleeve lock together. The end face of the pin is mostly ground by or type.

To remove the connection, the plastic clip simply disengages by pulling the housing out of the mating sleeve, so it appears to be a push-pull design. The and interface are two types of fiber optic connectors. The type is a button-controlled and spring-loaded device with a weighing sleeve attached. Usually, the ferrule of the connector is exposed, and the core of the type connector is inside the joint.

SC-type optical fiber connector is a common type of optical cable connector. Its shape is rectangular. It is a common optical fiber connector with a plug-in connection mechanism. It also has a plug-plug-adapter-plug structure. Type fiber optic connector has a cylindrical sleeve centering mechanism with an outer diameter of 2.5mm,

The design feature of SC type optical fiber cable connector is that it is formed by pressing PBT type plastic, and the pin body is made of zirconia ceramics, which has the characteristics of small size and light weight, and is especially suitable for mass production.

Therefore, SC type fiber optic connectors are widely used in digital communication systems, optical access networks, high-density installation distribution frames, etc.

Due to the push-pull method of connection and separation, it is suitable for high-density installation applications, excellent performance and reliability, and its SC-type fiber optic connector has a wide range of uses. When used for multimode fiber connections, it can be used to make SPC and APC type, with low return loss light.

What is a PC type fiber optic cable connector?

PC fiber optic cable connector is an improved product of FC fiber optic connector plug. Because its physical contact surface is spherical, dust and temperature have little effect on its connection loss, and are now used more.

What is a UPC type fiber optic cable connector?

UPC is an improved product of PC fiber optic connector plug. Because its physical contact surface is a precision spherical surface, its connection loss is the smallest, and it is the current mainstream product. The fiber optic connectors of UPC, FC and PC fiber optic cable connectors can be freely interconnected, and the connection loss is generally less than 0.5dB. APC is mostly used in places that require a large return loss, such as the transmission of cable TV models. Because its physical contact surface is an inclined plane, it is interconnected with the first three types of optical fiber connectors, and the connection loss is relatively large, and the actual test value is about 14dB.

What is ST-type fiber optic cable connector?

ST-type optical fiber cable connector is a kind of single-core optical cable connector. Its main features are a bayonet locking mechanism and a cylindrical sleeve centering mechanism with a diameter of 2.5mm. and plug/socket structure. The ST style connector design is a bayonet twist lock connection coupling that is suitable for field assembly.

ST-type fiber optic cable connectors are characterized by good repeatability, small size and light weight, and are mainly used in local networks and communication networks.

What is a D-type fiber optic cable connector?

The D-type optical fiber cable connector is a kind of single-core optical cable connector. It is based on the plug-adapter-plug structure. It has a cylindrical pair of sleeves with an outer diameter of 2mm and an M8 thread locking mechanism.

The design features of the D-type fiber optic cable connector are smooth and stable coupling, accurate spring pressure, and excellent repeatability. Because of the use of a 2mm diameter pin body, the structure has the characteristics of small size and light weight, and is mainly suitable for use in local networks.

According to the standard, the D-type fiber optic cable connector has the same structure and performance as the FC-type connector except that the pin body is 2mm in diameter.

What is an LC type fiber optic cable connector?

The LC type connector is developed by Bell (laboratory research and is made by a modular jack (lock mechanism). The dimensions of the sleeve and pin used are those used in the common type and type connectors described below. half of .

At present, in the aspect of single-mode optical fiber, the type connector has occupied the dominant position, and the application in the multi-mode optical fiber connector has also grown rapidly.

What is a MU-type fiber optic cable connector?

MU (Minature unit Coupling) connector is the world’s smallest single-core optical fiber connector developed and issued by NTT, based on the most used type of connector.

The structure of MU (Minature unit Coupling) connector includes outer shell, inner shell, ceramic ferrule, spring, fastener, tailstock, tail sleeve and dust cap.

When the device is assembled, the tail of the 1.25mm ceramic ferrule is inserted into the spring, the fastener presses the two into the inner shell together, and the positioning key of the fastener is locked into the positioning hole of the inner shell. At this time, the 1.25mm ceramic ferrule is inserted. The core is exposed from the front end of the inner shell.

The optical cable is stripped and passed through the tailstock, and the optical fiber is inserted into the 1.25mm ceramic ferrule. The tailstock is combined with the tail of the fastener to fix the optical cable and clamp it with a special clamp.

Finally, put the outer shell on the inner shell, put the tail cover on the tailstock, and put the dust cap on the 1.25mm ceramic ferrule.

With the rapid development of optical fiber networks in the direction of larger bandwidth and larger capacity and the wide application of technology, the demand for MU-type connectors will also increase rapidly.

What is MT-RJ type fiber optic cable connector?

MT-RJ (Mechanical Transfer Registered Jack) started from the connector developed by NTT. The fiber end face of this connector is designed in a dual-core arrangement, that is, it can connect two fibers at the same time. It inserts two end-finished fibers into the connector, aligns and mates with the two received fibers in the V-groove. Next-generation high-density optical connectors mainly used for data transmission.

What is MC type fiber optic cable connector?

In 2012, a Chinese communication company independently developed a MC connector with a smaller volume and higher density than the connector.

MC fiber optic connector is a high-density single-core fiber optic connector, suitable for various high-density occasions, such as large-capacity central computer rooms and high-density data centers.

The MC optical fiber active connector has a high density, which can reach up to twice that of the connector in the same space, making it the smallest and highest density connector in the world.

What are the performance indicators of optical fiber connectors?

type fiber optic cable connector

The performance of the optical fiber connector, first of all, the optical performance, in addition to the mechanical properties of the optical fiber connector, the performance of the temperature and the number of insertion and removal. The indicators used to describe these performances mainly include insertion loss, return loss, spectral loss, crosstalk, etc., of which the most commonly used are insertion loss and return loss, and there are repeatability and interchangeability indicators for active connectors.

Insertion loss

Inertion Loss refers to the optical power attenuation caused by the connected connector to the system. It usually refers to the decibel ratio of the output optical power to the input optical power after the optical signal in the light passes through the connector.

There are many factors that affect insertion loss, mainly including the following:

1. Core dislocation loss: as long as it is the loss caused by the lateral dislocation of the fiber core
2. Optical fiber tilt loss: mainly due to the optical power loss at the connection caused by the angle of the two fiber axes
3. End face gap loss: the loss caused by the gap between the fiber connection end face.
4. Fresnel reflection loss: due to the existence of different media in the gap between the two fiber end faces, when light enters it, it will
5. Multiple reflections are generated, resulting in loss.
6. Core diameter mismatch loss: when light is emitted from a fiber with a core radius of 1 to a fiber with a core radius of
7. Numerical aperture mismatch loss: The loss generated in transmission due to the difference in numerical aperture.

Return loss

Return Loss, also known as reflection loss, is a parameter used to measure the size of the retroreflected light from the end face. Specifically expressed as the number of decibels of the ratio of the retroreflected light from the fiber to the input optical power.

Repeatability and Interchangeability

Repeatability refers to the change of insertion loss after multiple insertion and removal of optical fiber connectors; interchangeability is the performance index of the arbitrary exchange or conditional exchange of the two parts of the plug and the converter, which can be used to investigate the structural design and process of the connector. Reasonable, generally requires that the additional loss of the interchangeable connector be less than.

Tensile strength

For a good optical fiber connector, its tensile strength is generally not lower than that.

Temperature requirements

The fiber optic connector must be able to function normally at the temperature.

Times of plugging and unplugging

Generally qualified optical fiber connectors are required to be able to be plugged and unplugged more than once.