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Regarding fiber optic connectors, you need to understand this knowledge

Update:30-07-2020
Summary:

The main function of the optical fiber connector is to […]

The main function of the optical fiber connector is to quickly connect two optical fibers so that the optical signal can be continuous to form an optical path. The optical fiber connector is movable and reusable, and it is also the most indispensable passive component in the current optical communication system. The two end faces of the optical fiber can be precisely connected by the optical fiber connector, so that the light energy output by the transmitting optical fiber can be coupled to the receiving optical fiber to the maximum extent, and it is necessary to minimize the impact of the system due to its intervention. Because the outer diameter of the fiber is only 125um, and the light-passing part is smaller, the single-mode fiber is only about 9um, and the multimode fiber has two types, 50um and 62.5um, so the connection between the fibers needs to be accurately aligned.

Through the function of the optical fiber connector, it can be seen that the core component that affects the performance of the connector is the ferrule. The quality of the ferrule directly affects the precise center connection of the two optical fibers. The ferrule is made of ceramic, metal or plastic. Ceramic ferrules are widely used. The main material is zirconium dioxide, which has the characteristics of good thermal stability, high hardness, high melting point, wear resistance, and high machining accuracy. The sleeve is another important part of the connector, and the sleeve plays an aligning role to facilitate the installation and fixation of the connector. The inner diameter of the ceramic sleeve is slightly smaller than the outer diameter of the ferrule, and the slotted sleeve tightens the two ferrules to achieve precise alignment.

  

In order to make the end faces of the two optical fibers better contact, the end faces of the ferrule are usually ground into different structures. PC, APC, UPC represent the front-end surface structure of the ceramic ferrule. PC is Physical Contact, physical contact. PC is micro-spherical grinding and polishing, the ferrule surface is ground into a slight spherical surface, and the fiber core is located at the highest point of the bend, so that the two fiber end faces are in physical contact. APC (Angled Physical Contact) is called the angled physical contact, and the end face of the optical fiber is usually ground into an 8° bevel.

The 8° angle bevel makes the fiber end face closer, and reflects the light to the cladding through its bevel angle instead of directly returning to the light source, providing better connection performance. UPC (Ultra Physical Contact), super physical end face. UPC optimizes the polishing and surface finish of the end face on the basis of PC, and the end face looks more dome-shaped. The connector connection needs to have the same end surface structure. For example, APC and UPC cannot be combined, which will cause the performance of the connector to decrease.

Due to the different end faces of the ferrule, the loss performance of the connector is also different. The optical performance of optical fiber connectors is mainly measured by two basic parameters, insertion loss and return loss. So, what is insertion loss? Insertion loss (Insertion Loss, usually referred to as "IL") is the optical power loss caused by the connection. It is mainly used to measure the optical loss between two fixed points in the optical fiber. It is usually caused by the lateral deviation between the two optical fibers, the longitudinal gap in the optical fiber connector, and the quality of the end face. The unit is expressed in decibels (dB). The smaller the better, the general requirement should be no more than 0.5dB.

Return Loss (Return Loss, usually abbreviated as "RL") refers to the parameter of signal reflection performance, which describes the power loss of optical signal return/reflection. Generally, the larger the better, the value is usually expressed in decibels (dB). The typical RL value of general APC connector is about -60dB, and the typical RL value of PC connector is about -30dB. In addition to considering the two optical performance parameters of insertion loss and return loss, the performance of optical fiber connectors should also pay attention to the interchangeability, repeatability, tensile strength, and operating temperature of the optical fiber connector when choosing a good optical fiber connector. , Mating times, etc.

Connector type, according to the connection mode, the connector is divided into: LC, SC, FC, ST, MU, MT, MPO/MTP, etc.; according to the fiber end face: FC, PC, UPC, APC. The LC-type connector (Lucent connector) is made with a convenient modular jack (RJ) latch mechanism. The size of the pins and sleeves used in the LC connector is 1.25mm, which is generally the size of ordinary SC, FC, etc., so its appearance size is only half of SC/FC.

The SC connector (‘Subscriber Connector’ or ‘Standard Connector’) is a snap-fit ​​standard square connector, and the fastening method is a plug-in latch type without rotation. This type of connector uses engineering plastics, is low in price, and is easy to plug and unplug. The size of FC fiber optic connector (Ferrule Connector) and SC connector are the same, the difference is that FC uses a metal sleeve and the fastening method is a turnbuckle. The structure is simple, easy to operate, easy to manufacture, durable, and can be used in high vibration environments.

ST optical fiber connector (Straight TIp) has a circular shell, adopts a 2.5mm circular plastic or metal shell, and the fastening method is a turnbuckle, which is often used in optical fiber distribution frames. MTP/MPO fiber optic connector is a special type of multi-fiber connector. The structure of MPO connector is more complicated, it connects 12 or 24 optical fibers in a rectangular optical fiber ferrule. Usually used in high-density connection scenarios, such as data centers.

In addition to the above, there are MU connector, MT connector, MTRJ connector, E2000 connector and so on. SC may be the most commonly used optical fiber connector, mainly due to its low-cost design. LC fiber optic connector is also a commonly used fiber optic connector, especially for connection with SFP and SFP+ fiber optic transceivers. FC is mostly used in single mode, and is relatively rare in multimode fiber. The complicated design and the use of metal make it more expensive. ST fiber optic connectors are usually used in long and short distance applications, such as campus and building multi-mode fiber applications, corporate network environments and military applications.

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