Detailed knowledge of fiber optic connectors

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. Optical fiber connectors are movable and reusable, and they are also the most indispensable and most used passive components in optical communication systems. Through the optical fiber connector, the two end faces of the optical fiber can be precisely butted together, so that the light energy output by the transmitting fiber can be coupled to the receiving fiber to the maximum extent, and the influence of the system caused by its intervention needs to be minimized. 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 multi-mode fiber is 50um and 62.5um, so the connection between the fibers needs to be precisely aligned.

ZR Cable Fiber Connector

Core component: ferrule

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 docking of the two fibers. Ferrules are made of ceramic, metal or plastic. Ceramic ferrules are widely used, and the main material is zirconium dioxide, which has the characteristics of good thermal stability, high hardness, high melting point, wear resistance, and high processing accuracy. The sleeve is another important part of the connector, and the sleeve plays the role of alignment 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 clamps the two ferrules to achieve precise alignment.

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

The 8° angled bevel allows for tighter fiber endfaces and provides better connection performance by reflecting light through its bevel angle to the cladding rather than directly back to the source. UPC (Ultra Physical Contact), ultra-physical end face. UPC is based on PC with more optimized end surface polishing and surface finish, and the end surface looks more dome-shaped. The connector connection needs to be in the same end face structure, for example, APC and UPC cannot be combined together, which will cause the performance of the connector to degrade.

Basic parameters: insertion loss, return loss

Due to the difference in the end face of the ferrule, the performance of the connector loss is also different. The optical performance of a fiber optic connector is mainly measured by two basic parameters, insertion loss and return loss. So, what is Insertion Loss? Insertion Loss (often abbreviated as “IL”) is the loss of optical power due to a connection. It is mainly used to measure the optical loss between two fixed points in the optical fiber, which is usually caused by the lateral deviation between the two optical fibers, the longitudinal gap in the optical fiber joint, the quality of the end face, etc. 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 referred to 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 the general APC connector is about -60dB, and the typical RL value of the PC connector is about -30dB.

In addition to 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 optical fiber connectors when selecting a good optical fiber connector. , times of plugging and unplugging, etc.

connector type

Connectors are divided by connection method: LC, SC, FC, ST, MU, MT, MPO/MTP, etc.; by fiber end face: FC, PC, UPC, APC.

LC connector

The LC type connector (Lucent connector) is made with an easy-to-operate modular jack (RJ) latch mechanism. The size of the pins and sleeves used by the LC connector is 1.25mm, which is the size of ordinary SC, FC, etc., so its appearance size is only half of SC/FC.

SC connector

The connector of SC connector (‘Subscriber Connector’ or ‘Standard Connector’) is a snap-on standard square connector. This type of connector is made of engineering plastic, which is low in price and convenient for plugging and unplugging.

FC connector

The size of the FC fiber optic connector (Ferrule Connector) is the same as that of the SC connector. The difference is that the FC adopts a metal sleeve and the fastening method is a turnbuckle. The structure is simple, the operation is convenient, the manufacture is easy, the durability is durable, and it can be used in a high vibration environment.

ST connector

The outer shell of ST fiber optic connector (Straight Tip) is round, using a 2.5mm annular plastic or metal shell, and the fastening method is turnbuckle, which is often used in fiber optic distribution frames.

MTP/MPO connector

MTP/MPO fiber optic connector is a special type of multi-fiber connector. The structure of the MPO connector is more complicated. It connects 12 or 24 fibers in a rectangular fiber ferrule. Usually used in high-density connection scenarios, such as data centers.

In addition to the above, the connector types include MU connectors, MT connectors, MTRJ connectors, E2000 connectors, etc. SC is probably the most commonly used fiber optic connector today, mainly due to its low cost design. The 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 multi-mode fibers. The complex design and the use of metal make it more expensive. ST fiber optic connectors are commonly used in long and short reach applications such as campus and building multimode fiber optic applications, enterprise network environments and military applications.