Before figuring out these issues, we first need to understand the following nouns:
Pigtail : It is used in the terminal box to connect the optical fiber in the optical cable, and connect the pigtail and jumper through the terminal box coupler (adapter).
Jumper : Both ends of the jumper are movable connectors, which are used to connect the pigtail to the device.
Optical cable terminal box : It is a box that protects optical cables and pigtails at the end of optical cable laying.
Optical fiber coupler : It is used for the active connection of two optical fibers or pigtails, commonly known as a flange.
Optical fiber terminal box : It is the terminal connector of an optical cable, one end of which is an optical cable, and the other end is a pigtail, which is equivalent to a device that splits an optical cable into a single optical fiber.
Fiber splice box : It is used to connect two optical cables into one long optical cable. The optical fiber terminal box and the optical fiber fusion splicing box cannot be used interchangeably, and the optical cable and the optical terminal are connected through the optical fiber terminal box, that is, only pigtails can be plugged into the optical terminal.
Coupler : Only two pigtails can be connected and divided into SC/PC FC/PC and other interfaces, and the connection between the optical cable and the pigtail is welded by a fusion splicer, which is dead.
Terminal box VS fusion splice box : The former is the fusion of optical cables and pigtails, and the latter is the fusion between optical cables.
Splice box VS terminal box : The splice box is fully sealed and waterproof, but it cannot fix the pigtail; the terminal box is not waterproof, and the internal structure can fix the optical cable and the pigtail on one side.
Pigtail VS jumper : Only one end of the pigtail is a movable connector; both ends of the jumper are movable connectors, there are many types of interfaces, different interfaces require different couplers, and the jumper can be used as a pigtail when it is divided into two.
First, the connection relationship between optical cable, terminal box and pigtail
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The outdoor optical cable is connected to the terminal box, the purpose is to fuse the optical fiber in the optical cable with the pigtail, and lead it out through the jumper.
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The fiber optic jumper is connected to the fiber optic transceiver, the purpose is to convert the optical signal into an electrical signal.
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The optical fiber transceiver leads to electrical signals, and the transmission medium used is twisted pair. At this time, the twisted pair can be connected to the RJ-45 port of the network device. So far, the photoelectric signal conversion has been completed.
Note: Many network devices now have optical ports (optical fiber interfaces), but if there is no optical distribution module (similar to the function of optical fiber transceivers), this port cannot be used.
2. The role of optical cable, terminal box and pigtail
The function of the optical cable terminal box : to terminate the optical cable, connect the core and pigtail in the optical cable, the internal structure of the optical cable terminal box, and the incoming optical cable can have multiple cores.
For example: a 4-core optical cable (there are 4 cores in the optical cable), then, this optical cable can be spliced with up to 4 pigtails after passing through the terminal box, that is, 4 jumpers can be drawn out. If only 2 wires are welded, 2 jumper wires will be drawn out.
Pigtail : There is a connector at one end and a broken end of an optical fiber core at the other end. It is connected to other optical fiber cores by fusion splicing.
Pigtail function : It is mainly used to connect the connectors at both ends of the optical fiber. One end of the pigtail is fused to the optical fiber connector, and the other end is connected to the optical fiber transceiver or optical fiber module through a special connector to form an optical data transmission path. Generally, we can't buy pure pigtails, but jumpers as shown in the figure. Once the middle is cut, it becomes a pigtail.
ST, SC, and FC optical fiber connectors are standards developed by different companies in the early stage. They have the same effect and have their own advantages and disadvantages. The following editor will popularize them in detail for everyone.
ST, SC connector joints are commonly used in general networks.
After the ST head is inserted, it rotates half a circle and has a bayonet to fix it. The disadvantage is that it is easy to break;
The C connector is directly plugged and unplugged, which is very convenient to use, but the disadvantage is that it is easy to fall out;
The FC connector is generally used in telecommunication networks. There is a nut screwed onto the adapter. The advantage is that it is reliable and dust-proof, and the disadvantage is that the installation time is slightly longer.
MTRJ type optical fiber jumper consists of two high-precision plastic molded connectors and optical cables. The outer part of the connector is a precision plastic part, including a push-pull plug-in clamping mechanism. Suitable for indoor applications in telecom and data network systems.
Types of fiber optic interface connectors
TF-FC、TF-ST、TF-FC/APC、TF-SC/APC、TF-SC
There are many kinds of fiber optic connectors , that is, the fiber optic connectors connected to optical modules, and they cannot be used with each other. People who are not often exposed to optical fibers may mistakenly think that the optical fiber connectors of GBIC and SFP modules are the same, but they are not. The SFP module is connected to an LC fiber optic connector, while the GBIC is connected to an SC fiber optic connector. The following is a detailed description of several commonly used fiber optic connectors in network engineering:
① FC 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 distribution frame)
② SC-type optical fiber connector : the connector connected to the GBIC optical module, its shell is rectangular, and the fastening method is plug-in and bolt-type, without rotation. (Most used on router switches)
③ ST type optical fiber connector : often used in optical fiber distribution frames, the outer shell is round, and the fastening method is a turnbuckle. (For 10Base-F connection, the connector is usually ST type. Commonly used in fiber distribution frame)
④ LC-type fiber optic connector : a connector connected to the SFP module, which is made of an easy-to-operate modular jack (RJ) latch mechanism. (commonly used by routers)
⑤ MT-RJ : a square optical fiber connector with integrated transceiver, one end with dual fiber transceiver
Introduction of various fiber optic interface types
- Fiber optic connector
- FC round threaded (mostly used on patch panels)
- ST snap-in round type;
- SC snap-in square type (mostly used on router switches)
- PC microsphere grinding and polishing;
- APC is angled at 8 degrees and microspherically ground and polished
- MT-RJ square, dual-fiber transceiver at one end (useful on Huawei 8850)
Optical fiber module : generally supports hot plugging,
GBIC Giga Bitrate Interface Converter, the optical fiber interface used is mostly SC or ST type
SFP small package GBIC, the optical fiber used is LC type
Fiber used:
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Single mode : L, wavelength 1310, single mode long distance LH wavelength 1310,1550
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Multimode : SM wavelength 850
SX/LH indicates that single-mode or multi-mode fiber can be used
In the label indicating the pigtail connector, we often see "FC/PC", "SC/PC", etc., and their meanings are as follows:
- The part in front of "/" indicates the connector model 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 oxidize. The optical interface on the transmission equipment side generally uses SC connectors.
- The "LC" connector is similar in shape to the SC connector, but smaller than the SC connector.
- The "FC" connector is a metal connector, which is generally used on the ODF side. Metal connectors can be plugged and unplugged more often than plastic ones.
There are many varieties of connector signals, in addition to the three 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 the most widely used in telecom operators' equipment, and its joint 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 ODF racks, mainly to improve the indicators of ODF equipment itself.
The optical fiber connector
Optical fiber connector is a device for detachable (movable) connection between optical fiber and optical fiber. It precisely butts the two end faces of optical fiber so that the optical energy output by the transmitting optical fiber can be coupled into the receiving optical fiber to the maximum extent. And to minimize the impact on the system due to its intervention in the optical link, this is the basic requirement of the fiber optic connector. 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 plastics as transmission media; according to the structure of the connector, it can be divided into: FC , SC, ST, LC, D4, DIN, MU, MT, etc. in various forms. The following are some of the more common fiber optic connectors:
(1) FC fiber optic connector
This connector was first developed by Japan's 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, the FC type connector, uses the docking port of the ceramic pin. This type of connector is simple in structure, easy to operate, and easy to manufacture, but the fiber end is more sensitive to dust and prone to Fresnel reflection, making it difficult to improve return loss performance. Later, this type of connector was improved by adopting a contact pin (PC) with a spherical butt end surface, and the external structure remained unchanged, which greatly improved the insertion loss and return loss performance.
(2) SC type fiber optic connector
This is a fiber optic connector developed by NTT Corporation of Japan. Its shell is rectangular, and the structure dimensions of the pins and coupling sleeves used are exactly the same as those of the FC type. Among them, the end faces of the pins are mostly PC or APC-type grinding; the fastening method is the plug-in pin-bolt type, which does not need to be rotated. This type of connector is cheap, easy to plug and unplug, has small fluctuations 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 Laboratories in the United States. It consists of two precision-molded cylindrical plugs with truncated conical ends and a biconical plastic sleeve inside. The coupling assembly of the cylinder is composed.
(4) DIN47256 fiber optic connector
This is a connector developed in Germany. The structure dimensions of the pin and coupling sleeve used in this connector are the same as those of the FC type, and the end face treatment adopts PC grinding method. Compared with the FC type connector, its structure is more complicated. There is a spring to control 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 latch mechanism as the RJ-45 LAN electrical connector. It is connected to the machine, and the optical fiber on the end face of the connector is designed as a double-core (0.75mm interval) arrangement. It is a 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 (Bell) Research 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 optical fiber connectors in the optical fiber distribution frame. At present, in terms of single-mode SFF, LC-type connectors have actually occupied a dominant position, and their applications in multi-mode are also growing rapidly.
(7) MU type connector
MU (Miniature unit Coupling) connector is the world's smallest single-core fiber optic connector developed by NTT based on the most widely used SC connector. The connector uses a 1.25mm diameter sleeve and a self-retaining mechanism, which has the advantage of enabling high-density installation. Using MU's 1.25mm diameter ferrule, NTT has developed the MU connector series. They are available as receptacle type connectors for optical cable connection (MU-A series); backplane connectors with self-retaining mechanism (MU-B series) and simplified receptacles for connecting LD/PD modules to plugs (MU-SR series) wait. With the rapid development of optical fiber networks towards larger bandwidth and larger capacity and the wide application of DWDM technology, the demand for MU connectors will also increase rapidly.