Hello everyone, I'm Brother Xue. In network cabling, optical cables are usually used for the connection between outdoor buildings, and optical fibers or network cables are used for indoor buildings. So how to convert between the optical cable transmission medium outside the building and the Ethernet transmission medium in the building? What kind of equipment is used? What do they do? What about the relationship between them?
Before we get to the bottom of these questions, we first need to understand the following terms:
Pigtail: Used in the terminal box, connecting the optical fiber in the fiber optic cable, through the terminal box coupler (adapter), connecting the pigtail and the jumper.
Jumper: Both ends of the jumper are movable joints, which play the role of connecting the pigtail and the equipment.
Optical cable terminal box: It is a box that protects the welding of optical cable and pigtail at the terminal of optical cable laying.
Fiber Optic Coupler: is a movable connection for two fibers or pigtails, colloquially known as a flange.
Optical fiber terminal box: It is the terminal joint of a fiber optic cable, one end of which is the fiber optic cable, and the other end is the pigtail, which is equivalent to the device that splits a fiber optic cable into a single optical fiber.
Optical fiber splice box: It is used for two optical cables to be docked into a long optical cable. The optical fiber terminal box and the optical fiber fusion box cannot be used interchangeably, and the optical cable and the optical transceiver are connected through the optical fiber terminal box, that is, only pigtails can be inserted into the optical transceiver.
Coupler: It can only connect two pigtails and divide SC/PC FC/PC and other interfaces, and the optical cable and pigtail are welded with a fusion splicer.
Terminal box VS splice box: The former is the splicing of the optical cable and the pigtail, and the latter is the splicing between the optical cable.
Splice box VS terminal box: The splice box is fully sealed and can be waterproof, but it cannot fix the pigtail; The terminal box is not waterproof, and the internal structure can fix the fiber optic cable on one side and the pigtail on the other.
Pigtail VS jumper: Only one end of the pigtail is a movable joint; Both ends of the jumper are movable joints, there are many kinds of interfaces, different interfaces need different couplers, jumpers are divided into two can be used as pigtails.
1. The connection relationship between optical cable, terminal box and pigtail
1: The outdoor optical cable is connected to the terminal box, the purpose of which is to fuse the optical fiber and pigtail in the optical cable, and lead it out through the jumper.
2: Connect the fiber patch cord to the fiber optic transceiver, the purpose is to convert the optical signal into an electrical signal.
3: The optical fiber transceiver is the electrical signal, and the transmission medium used is the twisted pair. At this time, the twisted pair cable can be connected to the RJ-45 port of the network device. At this point, the conversion of the photoelectric signal is completed.
Note: Many network devices also have optical ports (optical fiber interfaces), but if they do not have optical distribution modules (similar to optical fiber transceivers), this port cannot be used.
Second, the role of optical cables, terminal boxes, and pigtails
Function of the optical cable terminal box: terminate the optical cable, connect the fiber core and pigtail in the optical cable, the internal structure of the optical cable terminal box, and the connected optical cable can have multiple cores.
For example, if a 4-core cable (with 4 cores in the cable) can be spliced through the terminal box to produce up to 4 pigtails, i.e. 4 jumpers outward. If only 2 are spliced, 2 jumpers will be drawn outward.
Pigtail: There is a connector at one end and a broken end of a fiber optic cable core at the other end. Through splicing, it is connected to other fiber optic cable cores.
Pigtail function: It is mainly used to connect the joints at both ends of the optical fiber. One end of the pigtail is welded with an optical fiber connector, and the other end is connected to a fiber optic 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, and as soon as the middle is cut, it becomes pigtails.
ST, SC, FC optical fiber connector is a standard developed by different enterprises in the early stage, and the use effect is the same, each has its own advantages and disadvantages.
ST and SC connector connectors are commonly used in general networks.
After the ST head is inserted, there is a bayonet fixed in the rotation half a week, and 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, and there is a nut screwed onto the adapter, which has the advantage of being reliable and dust-proof, and the disadvantage is that the installation time is slightly longer.
The MTRJ fiber optic patch cord consists of two high-precision plastic-molded connectors and optical cables. The external parts of the connector are precision plastic parts, including a push-pull plug-and-pull clamping mechanism. Suitable for indoor applications in telecommunications 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 optical fiber connectors, that is, optical fiber connectors that access optical modules, and they are not interoperable 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 type, 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 connector. The following is a detailed description of several commonly used optical fiber connectors in network engineering:
(1) FC type optical fiber connector: the external reinforcement method is metal sleeve, and the fastening method is screw buckle. Generally used on the ODF side (most commonly used on patch panels)
(2) SC type optical fiber connector: the connector connected to the GBIC optical module, its shell is rectangular, and the fastening method is plug-and-unplug pin latch, which does not need to be rotated. (Most used on routers and switches)
(3) ST type optical fiber connector: commonly used in optical fiber distribution frame, the shell is round, and the fastening method is a screw buckle. (For 10Base-F connections, the connector is usually ST type.) Commonly used in optical fiber distribution frames)
(4) LC type fiber optic connector: The connector connected to the SFP module, which is made of the easy-to-operate modular jack (RJ) latching mechanism. (commonly used by routers)
(5) MT-RJ: square optical fiber connector with integrated transceiver and transceiver, one end with two fibers integrated transceiver
Introduction to various types of optical fiber interfaces
Fiber optic connectors
FC round with thread (most used on patch panels)
ST Snap-on Round;
SC snap-on square type (most used on router switches)
PC microsphere grinding and polishing;
The APC is at an angle of 8 degrees and is polished with a microsphere
MT-RJ square type, one end and two fibers in one transceiver (useful on Huawei 8850)
Optical fiber module: generally supports hot swapping,
GBIC Giga Bitrate Interface Converter, 使用的光纤接口多为SC或ST型
SFP GBIC in small package, using LC type fiber
Fibers used:
Single-mode: L, wavelength 1310, single-mode long-distance LH wavelength 1310, 1550
Multimode: SM wavelength 850
SX/LH means that single-mode or multimode fiber can be used
In the annotations that represent pigtail joints, we often see "FC/PC", "SC/PC", etc., which have the following meanings:
The preceding part of the "/" indicates the connector model of the pigtail.
The "SC" joint is a standard square joint, made of engineering plastic, which has the advantages of high temperature resistance and not easy oxidation. The optical interface on the side of the transmission equipment generally uses SC connectors.
The "LC" fitting is similar in shape to the SC fitting and is smaller than the SC fitting.
The "FC" connector is a metal connector, which is generally used on the ODF side, and the metal connector can be plugged and unplugged more times than the plastic one.
There are many varieties of signals for connectors, in addition to the three introduced above, there are MTRJ, ST, MU, etc.
The "/" after indicates the fiber optic splice cross-section process, i.e., the grinding method.
"PC" is the most widely used in the equipment of telecom operators, and its connector cross-section is flat.
The attenuation of "UPC" is smaller than that of "PC", and is generally used for equipment with special needs.
Fiber optic connectors
Optical fiber connector is a detachable (active) connection between optical fiber and optical fiber, it is the two end faces of the optical fiber precision docking, so that the optical energy output of the transmitting optical fiber can be coupled to the receiving optical fiber to the maximum extent, and the impact on the system due to its involvement in the optical link is minimized, which is the basic requirement of optical fiber connector. To a certain extent, optical fiber connectors also affect the reliability and performance of optical transmission systems.
Optical fiber connectors can be divided into single-mode and multi-mode connectors of common silicon-based optical fibers according to different transmission media, as well as other optical fiber connectors with 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. Here are some of the more common fiber optic connectors today:
(1) FC type fiber optic connector
This connector was first developed by NTT in Japan. FC is the abbreviation of Ferrule Connector, which indicates that its external reinforcement is made of a metal sleeve and the fastening method is a screw buckle. The earliest, FC type connectors, using the mating port of ceramic pins. This kind of connector has a simple structure, easy to operate, and easy to make, but the end of the optical fiber is more sensitive to fine dust, and it is easy to produce Fresnel reflection, and it is difficult to improve the return loss performance. Later, this type of connector was improved, and the pin (PC) with a spherical end face was adopted, and the external structure was not changed, so that the insertion loss and return loss performance were greatly improved.
(2) SC type fiber optic connector
This is a fiber optic connector developed by NTT Corporation in Japan. The housing is rectangular, and 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 made of PC or APC type grinding; The fastening method is a plug-and-pull pin latch type, which does not need to be rotated. These connectors are inexpensive, easy to plug and unplug, have small fluctuations in intervention loss, high compressive strength, and high installation density.
ST and SC interfaces are the two types of fiber optic connectors, for 10Base-F connections, the connector is usually ST type, 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) 双锥型连接器(Biconic Connector)
The most representative product of this type of fiber optic connector is developed by Bell Laboratories in the United States, which consists of two precision-molded cylindrical plugs with truncated conical ends and a coupling assembly with a double conical plastic sleeve inside.
(4) DIN47256-type fiber optic connectors
This is a connector developed in Germany. The pins and coupling sleeves used in this connector are the same as those of the FC type, and the end face is treated using a PC grinding method. Compared with the FC type connector, its structure is more complex, and there is a spring to control the pressure in the internal metal structure, which can avoid damage to the end face due to excessive mating pressure. In addition, the connectors have a high mechanical accuracy and therefore low intervention losses.
(5) MT-RJ type connector
MT-RJ is a next-generation high-density optical fiber connector mainly used for data transmission with the same latching mechanism as the RJ-45 type LAN connector, which is aligned with the optical fiber by means of guide pins mounted on both sides of the small sleeve to connect to the optical transceiver.
(6) LC type connector
The LC type connector was developed by the famous Bell Research Institute and is made by the easy-to-operate modular jack (RJ) latching mechanism. The size of the pins and sleeves used is 1.25 mm, which is half the size of ordinary SC and FC. This increases the density of fiber optic connectors in the fiber distribution frame. At present, LC type connectors have actually dominated the single-mode SFF, and the application of multimode is also growing rapidly.
(7) MU type connector
The MU (Miniature unit Coupling) connector is the world's smallest single-core fiber connector developed by NTT based on the most widely used SC type connector. The connector features a 1.25mm diameter sleeve and self-retaining mechanism, which has the advantage of enabling high-density mounting. NTT has developed the MU connector series using MU's l.25mm diameter bushing. They are available with socket type connectors for fiber optic cable connections (MU-A series); Backplane connectors with self-locking mechanism (MU-B series) and simplified sockets (MU-SR series) for connecting LD/PD modules to plugs, etc. With the rapid development of optical fiber networks in the direction of larger bandwidth and larger capacity and the wide application of DWDM technology, the demand for MU connectors will also grow rapidly.
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