Differences between ST, SC, FC, LC fiber optic connectors

ST, SC, FC fiber optic connectors are the standards developed by different companies in the early days. They have the same effect and have their own advantages and disadvantages. ZR Cable will popularize them in detail below.

ST, SC connector joints are often used in general networks. After the ST head is inserted, it is fixed by a bayonet in half a circle, but the disadvantage is that it is easy to break; the SC connector is directly inserted and unplugged, which is very convenient to use, but the disadvantage is that it is easy to fall out; It is reliable and dust-proof, but the disadvantage is that the installation time is slightly longer.

The MTRJ type fiber patch cord consists of two high precision plastic molded connectors and fiber optic cables. The outer parts of the connector are precision plastic parts, including a push-pull plug-in clamping mechanism. Suitable for indoor applications in telecommunication and data network systems.

There are also many types of optical fiber connectors, that is, optical fiber connectors that connect to optical modules, and they cannot be used with each other. People who are not in frequent contact with optical fibers may mistakenly think that the optical fiber connectors of GBIC and SFP modules are the same kind, but they are not. The SFP module is connected to the LC fiber optic connector, while the GBIC is connected to the SC fiber optic fiber connector. The following is a detailed description of several commonly used optical fiber connectors in network engineering:

① FC-type fiber optic connector: The external strengthening method is a metal sleeve, and the fastening method is a turnbuckle. Generally used on the ODF side (the most used on the patch panel)

② SC-type optical fiber connector: the connector for connecting the GBIC optical module, its shell is rectangular, and the fastening method is the plug-in type, which does not need to be rotated. (Most used on router switches)

③ ST-type optical fiber connector: commonly used in optical fiber distribution frame, the outer shell is round, and the fastening method is turnbuckle. (For 10Base-F connections, the connectors are usually ST type. Often used in fiber optic distribution frames)

④ LC-type fiber optic connector: a connector for connecting SFP modules, which is made with a modular jack (RJ) latch mechanism that is easy to operate. (commonly used by routers)

⑤ MT-RJ: a square fiber optic connector with integrated transceiver, one dual-fiber transceiver integrated

Fiber Optic Connector Differences

Several common fiber optic lines

Introduction of various fiber optic interface types

fiber optic connector

FC round with thread (most used on patch panels)

ST snap-on round;

SC card connection type (the most used on router switches)

PC microsphere grinding and polishing;

APC is at an 8-degree angle and is ground and polished with microspheres

MT-RJ square, one dual fiber transceiver (useful for Huawei 8850)

Optical fiber modules: generally support hot swap,

GBIC Giga Bitrate Interface Converter, the fiber interface used is mostly SC or ST type

SFP small package GBIC, the fiber used is LC type

Fiber used:

Single mode: L, wavelength 1310 single mode long distance LH wavelength 1310,1550

Multimode: SM wavelength 850

SX/LH means single mode or multimode fiber can be used

In the annotations representing pigtail connectors, we often see "FC/PC", "SC/PC", etc. The meanings are as follows: 

The part before "/" indicates the connector type of the pigtail.

The "SC" joint is a standard square joint, made of engineering plastics, which has the advantages of high temperature resistance and not easy to be oxidized. The optical interface on the side of the transmission equipment generally uses the SC connector.

The "LC" connector is similar in shape to the SC connector and is smaller than the SC connector.

The "FC" connector is a metal connector, which is generally used on the ODF side. The metal connector can be plugged more frequently than plastic.

There are many varieties of connectors, in addition to the three types described above, there are MTRJ, ST, MU, etc.

The back of "/" indicates the cross-section process of the optical fiber connector, that is, the grinding method. 

"PC" is most widely used in telecom operators' equipment, and its connector section is flat.

The attenuation of "UPC" is smaller than that of "PC". It is generally used for equipment with special needs. Some foreign manufacturers use FC/UPC for the internal jumper of the ODF frame, mainly to improve the indicators of the ODF equipment itself.

In addition, the "APC" model is more widely used in radio and television and early CATV. Its pigtail head adopts an inclined end face, which can improve the quality of the TV signal. The main reason is that the TV signal is analog light modulation. When the connector is coupled When the face is vertical, the reflected light returns along the original path. Due to the uneven distribution of the refractive index of the fiber, it will return to the coupling surface again. At this time, although the energy is small, the noise cannot be completely eliminated by the analog signal, so it is equivalent to superimposing a weak signal with time delay on the original clear signal. The performance on the screen is ghosting. The inclination of the pigtail headband prevents the reflected light from returning along the original path. General digital signals generally do not have this problem.

The optical fiber connector

Optical fiber connector is a device for detachable (active) connection between optical fiber and optical fiber. It precisely connects the two end faces of optical fiber, so that the light energy output by the transmitting fiber can be coupled to the receiving fiber to the maximum extent. And minimize the impact on the system due to its involvement in the optical link, which is the basic requirement of fiber optic connectors. To a certain extent, fiber optic connectors also affect the reliability and performance of optical transmission systems.

Optical fiber connectors can be divided into common silicon-based optical fiber single-mode and multi-mode connectors according to different transmission media, and other optical fiber connectors such as plastic as the transmission medium;

According to the structure of the connector, it can be divided into: FC, SC, ST, LC, D4, DIN, MU, MT and so on. Among them, ST connectors are usually used for wiring equipment, such as fiber distribution frames, fiber modules, etc.; while SC and MT connectors are usually used for network equipment.

According to the shape of the fiber end face, there are FC, PC (including SPC or UPC) and APC; according to the number of fiber cores, there are single-core and multi-core (such as MT-RJ) points. Optical fiber connectors are widely used and have a wide variety. In the actual application process, we generally distinguish according to the structure of the optical fiber connector. The following are some of the more common fiber optic connectors:

(1)FC type fiber optic connector

This connector was first developed by Japanese NTT. FC is the abbreviation of Ferrule Connector, indicating that its external reinforcement method is a metal sleeve, and the fastening method is a turnbuckle. The earliest, FC type connectors, used ceramic pins for mating ports.

Such connectors are simple in structure, easy to operate, and easy to manufacture, but the fiber ends are more sensitive to dust, and are prone to Fresnel reflections, making it difficult to improve return loss performance. Later, this type of connector was improved, and the contact pin (PC) with spherical end face was adopted, and the external structure was not changed, so that the performance of insertion loss and return loss was greatly improved.

(2) SC type fiber optic connector

This is a fiber optic connector developed by Japan's NTT company. Its shell is rectangular, and the structure and dimensions of the pins and coupling sleeves used are exactly the same as those of the FC type. Among them, the end face of the pin is mostly PC or APC type grinding method; the fastening method is a plug-in latch type, without rotation. This type of connector is inexpensive, easy to plug and unplug, small fluctuation in insertion loss, high compressive strength, and high installation density.

ST and SC interfaces are two types of fiber optic connectors. For 10Base-F connection, the connector is usually ST type, and for 100Base-FX, the connector is mostly SC type. The core of the ST connector is exposed, and the core of the SC connector is inside the connector.

(3) Biconic Connector

The most representative product of this type of fiber optic connector was developed by Bell Labs in the United States. It consists of two precision-molded cylindrical plugs with frusto-conical ends and a double-conical plastic sleeve inside. The coupling components of the cylinder are composed.

(4) DIN47256 fiber optic connector

This is a connector developed in Germany. The pins and coupling sleeves used in this connector have the same structural dimensions as the FC type, and the end face treatment adopts PC grinding. Compared with the FC type connector, its structure is more complicated, and there is a spring that controls the pressure in the internal metal structure, which can avoid damage to the end face due to excessive insertion pressure. In addition, the mechanical precision of this connector is high, so the insertion loss value is small.

(5) MT-RJ type connector

MT-RJ started from the MT connector developed by NTT. It has the same latching mechanism as the RJ-45 type LAN electrical connector. It is aligned with the optical fiber through the guide pins installed on both sides of the small sleeve. The optical fiber on the end face of the connector is designed in a double-core (0.75mm interval) arrangement. It is the next-generation high-density optical fiber connector mainly used for data transmission.

(6) LC type connector

The LC type connector is researched and developed by the famous Bell Institute, and is made of a modular jack (RJ) latch mechanism that is easy to operate. The size of the pins and sleeves used is half the size of ordinary SC, FC, etc., which is 1.25mm. This can increase the density of fiber optic connectors in the fiber optic distribution frame. At present, in terms of single-mode SFF, LC-type connectors have actually occupied a dominant position, and the application in multi-mode is also growing rapidly.

(7) MU type connector

MU (Miniature unit Coupling) connector is the world's smallest single-core optical fiber connector developed by NTT based on the SC-type connector that is currently most used.

The connector uses a 1.25mm diameter sleeve and a self-retaining mechanism, which has the advantage of enabling high-density mounting. Utilizing MU's 1.25mm diameter sleeve, NTT has developed the MU connector series. They have receptacle type connectors (MU-A series) for fiber optic cable connection;

Backplane connectors with self-retaining mechanism (MU-B series) and simplified sockets for connecting LD/PD modules and plugs (MU-SR series), etc. With the rapid development of fiber optic networks in the direction of larger bandwidth and larger capacity and the wide application of DWDM technology, the demand for MU-type connectors will also increase rapidly.