When installing any fibre optic system, it is necessary to consider interconnecting the fibres or cables with each other in a low loss method for splicing the optical link. The splicing of optical fibre links can be further classified into permanent and active ones. Permanent splicing, most of the fusion splicing method, bonding method or fixed connectors to achieve; activity of the splicing, generally using movable connectors to achieve. In this paper, the activity of the connector to do a brief introduction.
Fiber optic activity connector , commonly known as a live connector, generally known as fiber optic connector, is used to connect two optical fibers or fiber optic cables to form a continuous optical pathway can be reused passive devices, has been widely used in fiber optic transmission lines, fiber optic distribution frames and fiber optic test instruments, instrumentation, is currently the largest number of passive optical devices.
2. The general structure of the optical fibre connector
The main purpose of optical fibre connector is to achieve the optical fibre connection. Now has been widely used in optical fibre communication systems in the optical fibre connector, its many types, different structures. But in detail, the basic structure of various types of fiber optic connectors is the same, that is, the vast majority of fibre optic connectors are generally used in high-precision components (consisting of two pins and a coupling tube composed of a total of three parts) to achieve optical fibre alignment connection.
This method is the optical fibre is threaded and fixed in the pins, and the surface of the pins are polished, in the coupling tube to achieve alignment. The outer components of the pins are made of metallic or non-metallic materials. The butted end of the pin must be ground and the other end is typically constructed with a bend limiting member to support the fibre or fibre optic flexible cable to relieve stress. The coupling tube is generally made of two halves of a composite, tightly-fitting cylindrical member made of ceramic, or bronze, etc., and is often fitted with a metal or plastic flange to facilitate the mounting of the connector. In order to align the optical fibre as accurately as possible, the pin and the coupling tube of the machining precision requirements are very high.
3. Fibre optic connector performance
Fiber optic connector performance, first of all, optical properties, in addition to consider the interchangeability of optical fibre connectors, repeatability, tensile strength, temperature and the number of insertion and removal.
(1) Optical performance: optical performance requirements for optical connectors, mainly insertion loss and return loss of the two most basic parameters.
Insertion loss (Insertion Loss) that is, connection loss, refers to the connector due to the introduction of the link caused by the loss of effective optical power. Insertion loss is as small as possible, the general requirement should not be greater than 0.5dB.
Return loss (Return Loss) refers to the connector on the link optical power reflection suppression ability, its typical value should not be less than 25dB. practical application of the connector, the pin surface has been specially polished, can make the return loss is greater, generally not less than 45dB.
(2) interchangeability, repeatability
Fiber optic connector is a universal passive device, for the same type of fiber optic connector, generally can be used in any combination, and can be repeated many times, which leads to additional loss is generally less than 0.2dB within the range.
(3) Tensile strength
For a good optical fibre connector, the general requirements of its tensile strength should not be less than 90N.
General requirements, fibre optic connectors must be in -40 ℃ ~ +70 ℃ temperature can be used normally.
(5) Plugging and unplugging times
Currently used fibre optic connectors can generally be inserted and removed more than l000 times.
4. Part of the common fibre optic connectors
According to different classification methods, fiber optic connectors can be divided into different types, according to the different transmission media can be divided into single-mode fiber optic connectors and multi-mode fiber optic connectors; according to the different structures can be divided into FC, SC, ST, D4, DIN, Biconic, MU, LC, MT and other types; according to the connector pin end face can be divided into PC (UPC) and APC; according to the number of fiber optic core points There are also single-core, multi-core points.
In the actual application process, we generally follow the different structure of the optical fibre connector to distinguish. The following is a brief introduction to some of the more common fibre optic connectors:
(1) FC optical fibre connector
This connector was first developed by **NTT. FC is the abbreviation of Ferrule Connector, indicating that its external reinforcement is the use of metal sleeve, fastening method for the screw buckle. At the earliest, FC type connector, using the ceramic pins of the docking end face is flat contact (FC). This type of connector structure is simple, easy to operate, easy to produce, but the optical fibre end face is more sensitive to microdust, and easy to produce Fresnel reflection, to improve the return loss performance is more difficult. Later, the type of connector to make improvements, the use of butt end face is a spherical pin (PC), while the external structure has not changed, so that the insertion loss and return loss performance has improved substantially.
(2) SC type optical fibre connector
This is an optical fibre connector developed by **NTT. Its shell is rectangular, the pin and coupling sleeve used in the structure of the dimensions and FC-type exactly the same, of which the end face of the pin more PC or APC-type grinding method; fastening method is the use of insertion and removal of the pin latch type, do not need to rotate. Such connectors are inexpensive, easy to insert and remove the operation, intervene in the loss fluctuation is small, high compressive strength, high installation density (router switches on the most used).
(3) ST-type fibre optic connectors
ST-type fiber optic patch cord: commonly used in fibre-optic distribution frame, the shell is round, the fastening method for the screw buckle. (For 10Base-F connection, the connector is usually ST type. Commonly used in fibre optic distribution frame)
(4) LC type fibre optic connector
LC type connector is the famous Bell Research Institute research and development, using easy to operate modular jack (RJ) latch mechanism made. The size of the pins and sleeves used is half the size of the ordinary SC, FC, etc., for 1.25 mm, which can improve the density of fibre-optic connectors in the optical distribution frame. At present, in the single-mode SFF, LC-type connectors have actually dominated the multi-mode applications are also growing rapidly.
(5) Biconic connector (Biconic Connector)
This type of fiber optic connector in the most representative products developed by the United States Bell Labs development, which consists of two precision moulding forming the end of the truncated conical cylinder plug and an internal double cone plastic sleeve coupling components.
(6) DIN4 type optical fibre connector
This is a connector developed by Germany. This connector pin and coupling sleeve structure using the same dimensions as the FC-type, end face processing using PC grinding. Compared with the FC-type connector, its structure is a little more complex, the internal metal structure of the control pressure of the spring, you can avoid damage to the end face due to excessive mating pressure. In addition, the mechanical precision of this connector is higher, so the intervention loss value is smaller.
(7) MT-RJ type connector
MT-RJ started in the NTT development of MT connectors, with RJ-45-type LAN electrical connector with the same latch mechanism, installed in a small sleeve on both sides of the guide pin aligned with the optical fibre, in order to facilitate the connection with optical transceivers, connector end face optical fibre for the double-core (spacing of 0.75mm) arrangement design is mainly used for the transmission of data in the next generation of high-density optical connectors.
8) MU type connector
The MU connector is the world's smallest single-core optical fibre connector developed by NTT based on the SC-type connector, which is currently the most widely used connector. The connector uses a 1.25 mm diameter sleeve and a self-holding mechanism, and has the advantage of being able to be installed at high density. Utilising the MU's l.25mm diameter sleeve, NTT has developed a series of MU connectors. They include socket-type optical connectors (MU-A series) for optical cable connection, baseboard connectors (MU-B series) with a self-holding mechanism, and simplified sockets (MU-SR series) for connecting LD/PD modules to plugs. With the rapid development of fibre 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 grow rapidly.
With the continuous development of fiber-optic communication technology, especially the development of high-speed LANs and optical access networks, the application of fibre optic connectors in the optical fiber system will be more widely used. At the same time, it also puts forward more and higher requirements for fibre optic connectors, and its main development direction is: miniaturization of appearance, low cost, while the performance requirements are increasingly high. In the coming period of time, a variety of newly developed fibre optic connectors will be with the traditional FC, SC and other connectors, the formation of "each show their strengths, each used" pattern.