Analysis of the structure and performance of various optical fiber connectors

      I. Introduction 　　

      When installing any optical fiber system, consideration must be given to connecting optical fibers or optical cables to each other in a low-loss method to achieve optical fiber link connections. The connection of optical fiber links can be divided into two types: permanent and active. Permanent connections are mostly achieved by welding, bonding or fixed connectors; movable connections are generally achieved by movable connectors. This article will give a brief introduction to active connectors. 　　

      Fiber optic movable connectors, commonly known as movable joints, are generally called fiber optic connectors. They are reusable passive components used to connect two optical fibers or optical cables to form a continuous optical path. They have been widely used in optical fiber transmission lines and optical fiber distribution frames. Among optical fiber testing instruments and meters, it is currently the most widely used optical passive device. 　　

      2. General structure of optical fiber connector 

      The main purpose of fiber optic connectors is to connect optical fibers. Optical fiber connectors, which have been widely used in optical fiber communication systems, have many types and different structures. However, upon closer inspection, the basic structure of various types of fiber optic connectors is the same, that is, the vast majority of fiber optic connectors generally use high-precision components (consisting of three parts: two pins and a coupling tube) to realize the fiber optic connection. alignment connection.

      This method is to insert the optical fiber into and fix it in the pin, polish the surface of the pin, and achieve alignment in the coupling tube. The outer components of the pins are made of metal or non-metallic materials. The butt end of the pin must be ground, and the other end usually uses a bend limiting member to support the fiber or fiber optic cable to relieve stress. The coupling tube is generally made of two halves of a synthetic, fastened cylindrical component made of ceramic, bronze or other materials. It is often equipped with a metal or plastic flange to facilitate the installation and fixation of the connector. In order to align the optical fiber as accurately as possible, the processing accuracy of the pins and coupling tubes is very high.

      3. Performance of optical fiber connectors

      The performance of optical fiber connectors, first of all, is the optical performance. In addition, the interchangeability, repeatability, tensile strength, temperature, and number of plugging and unplugging of the optical fiber connector must also be considered.

      1. Optical performance: The optical performance requirements of optical fiber connectors are mainly the two most basic parameters of insertion loss and return loss. 

      Insertion Loss (Insertion Loss) is connection loss, which refers to the loss of effective optical power of the link caused by the introduction of the connector. The smaller the insertion loss, the better, and the general requirement should be no more than 0.5dB.

      Return loss refers to the connector's ability to suppress link optical power reflection, and its typical value should be no less than 25dB. In practical connectors, the pin surface has been specially polished, which can make the return loss greater, generally not less than 45dB.

      2. Interchangeability and repeatability

Optical fiber connectors are universal passive components. The same type of fiber optic connectors can generally be used in any combination and can be used repeatedly. The additional loss introduced thereby is generally less than 0.2dB.

      3. Tensile strength

      For finished optical fiber connectors, it is generally required that the tensile strength should not be less than 90N.

      4. Temperature 

      As a general requirement, fiber optic connectors must be able to be used normally at temperatures between -40°C and +70°C.

      5. Number of plugging and unplugging

      The fiber optic connectors currently used can generally be plugged and unplugged more than 1,000 times.

      4. Some common optical fiber connectors

      According to different classification methods, optical fiber connectors can be divided into different types. According to different transmission media, they can be divided into single-mode optical fiber connectors and multi-mode optical fiber connectors; according to different structures, they can be divided into FC, SC, ST, and D4 , DIN, Biconic, MU, LC, MT and other types; according to the pin end face of the connector, it can be divided into PC (UPC) and APC; according to the number of fiber cores, it can be divided into single core and multi-core.