What types of optical fiber connectors are there?

The main function of an optical fiber connector is to quickly connect two optical fibers, allowing the optical signal to be continuously transmitted and forming an optical path. Optical fiber connectors are movable and reusable, and are currently indispensable and the most widely used passive components in optical communication systems. Through the optical fiber connector, the two end faces of the optical fibers can be precisely aligned, allowing the maximum coupling of the light energy output by the emitting optical fiber to the receiving optical fiber, and minimizing the impact on the system caused by its intervention. Due to the outer diameter of the optical fiber being only 125um and the light-transmitting part being even smaller, single-mode optical fibers have a diameter of about 9um, and multimode optical fibers have two types: 50um and 62.5um. Therefore, the connection between optical fibers requires precise alignment.

Core component: Insertion core

From the effect of the optical fiber connector, it can be seen that the core component that affects the performance of the connector is the insertion core. The quality of the insertion core directly affects the precise center alignment of the two optical fibers. The materials used to make the insertion core include ceramics, metals, or plastics. Ceramic insertion cores are the most widely used, with the main material being zirconium dioxide, which has good thermal stability, high hardness, high melting point, wear resistance, and high processing accuracy. The sleeve is another important component of the connector, serving as a positioning function 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 insertion core. The slit sleeve clamps the two insertion cores and achieves precise alignment.

To enable the end faces of the two optical fibers to have better contact, the end faces of the insertion core are usually ground into different structures. PC, APC, and UPC represent the front-end surface structures of the ceramic insertion core. PC is Physical Contact, physical contact. PC is micro-spherical grinding and polishing, with the surface of the insertion core ground into a slightly spherical shape, with the optical fiber core located at the highest point of the curvature, achieving physical contact between the two optical fiber end faces. APC (Angled Physical Contact) is called inclined physical contact, and the optical fiber end face is usually ground into an 8° inclined surface. The 8° angle inclined surface makes the optical fiber end faces more compact and reflects the light through its inclined angle onto the cladding rather than directly returning to the light source, providing better connection performance. UPC (Ultra Physical Contact), ultra physical end face. UPC is an optimization of the end face polishing and surface smoothness on the basis of PC, with the end face looking more like a dome. The connection requires the same end face structure, such as APC and UPC cannot be combined together, which will lead to a decline in the connector performance.

Basic parameters: insertion loss, return loss

Due to the different end faces of the core insertion, the performance of the connector's loss varies. The optical performance of the optical connector is mainly measured by two basic parameters: insertion loss and return loss. What is insertion loss? Insertion loss (Insertion Loss, usually abbreviated 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, usually caused by the lateral deviation between the two optical fibers, the longitudinal gap in the optical connector, the end face quality, etc. The unit is decibel (dB), and the smaller the value, the better. Generally, it should not exceed 0.5 dB.

Return loss (Return Loss, usually abbreviated as "RL") refers to the parameter of signal reflection performance, describing the power loss of the return/reflection of the optical signal. The larger the value, the better. The value is usually expressed in decibel (dB). The typical RL value of APC connectors is approximately -60 dB, and the typical RL value of PC connectors is approximately -30 dB.

In addition to considering the two optical performance parameters of insertion loss and return loss, when choosing a good optical connector, attention should also be paid to the interchangeability, repeatability, tensile strength, operating temperature, and insertion/拔出 times of the optical connector.

Connector types

Connectors are classified by connection methods： LC， SC， FC， ST， MU， MT， MPO/MTP， etc.； by optical fiber end faces： FC， PC， UPC， APC.

LC connector

The LC connector (Lucent connector) is made using the modular plug-in mechanism (RJ) latch mechanism. The size of the pins and sleeves used by the LC connector is the same as that of ordinary SC， FC， etc.， which is 1.25mm. Therefore， its appearance size is only half of that of SC/FC.

SC connector

The connector of the SC connector ('Subscriber Connector' or 'Standard Connector') is a snap-fit standard square connector. The fastening method is plug-in latch type， without rotation. This type of connector is made of engineering plastic， is inexpensive， and is convenient for insertion and removal.

FC connector

The FC optical connector (Ferrule Connector) has the same size as the SC connector. The difference is that FC uses a metal sleeve， and the fastening method is a screw buckle. The structure is simple， the operation is convenient， the production is easy， and it is durable， suitable for high-vibration environments.

ST connector

The ST optical connector (Straight Tip) has a circular shell， uses a 2.5mm circular plastic or metal shell， and the fastening method is a screw buckle， often used in fiber distribution frames.

MTP/MPO connector

The MTP/MPO optical connector is a special type of multi-fiber connector. The structure of the MPO connector is relatively complex. It connects 12 or 24 optical fibers in a rectangular optical core. It is usually used in high-density connection scenarios， such as data centers.

In addition to the above， there are MU connectors， MT connectors， MTRJ connectors， E2000 connectors， etc. SC may be the most commonly used optical connector at present， mainly due to its low-cost design. The LC optical connector is also a commonly used optical connector， especially for connections with SFP and SFP+ optical transceivers. FC is mostly used for single-mode， and is less common in multi-mode optical fibers. The complex design and use of metal make it relatively expensive. ST optical connectors are usually used for long and short-distance applications， such as campus and building multi-mode optical fiber applications， enterprise network environments， and military applications. Qingying Industry provides various specifications and different types of optical connectors, including SC, FC, LC, ST, MPO, MTP, etc. Dongguan Qingying Industry Co., Ltd. is a national-level high-tech enterprise that focuses on the research and development, manufacturing, sales and service of passive optical components for optical communication. The company's main products are: optical connectors (high-density optical connectors for data centers), optical quick connectors, optical adapters, etc., which are the three core optical passive basic components and are widely used in fiber-to-the-home, 4G/5G mobile communication, and Internet data centers and other fields.

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