Present Situation And Development Of Optical Fiber Connector

Introduction

Fiber optic connectors, commonly known as live connectors, are proposed to be defined as "passive components that are stable but not permanently connected to two or more optical fibers" (CCITT, group VI, March 1992, passed in Geneva, ITU). It is mainly used to realize the non permanent fixed connection between the equipment, the equipment and the instrument, the equipment and the optical fiber and the optical fiber and the optical fiber in the system. It is an indispensable passive component in the optical fiber communication system. Because of the use of connectors, the removable connection between optical channels becomes possible, which provides the test entrance for optical fiber, facilitates the measurement and maintenance of the optical system, and provides a medium for network management to make the optical system switching more flexible. 

Features of optical fiber connector

The general characteristics of optical fiber connector because fiber optic connector has such an important role in optical fiber communication system, so all manufacturers have invested a lot of manpower and resources, actively and deeply studied, developed a variety of fiber optic connectors, has been widely used in various types of optical fiber communication system. (1) the basic composition of optical fiber connectors - at present, most optical fiber connectors are made up of three parts: two matching plugs and a coupling tube. The two plugs are mounted at the ends of the two fibers, and the coupling tube acts as an alignment sleeve. In addition, the coupling tube is equipped with metal or nonmetal flanges to facilitate the installation and fixation of connectors. (2) the alignment method of optical fiber connector, there are two kinds of alignment methods of optical fiber connector: precise component alignment and active alignment. High precision assembly alignment is the most commonly used method. This method is to penetrate and fix the optical fiber into the supporting sleeve of the plug. After the butt port is polished or polished, the alignment is realized in the sleeve coupling tube. The supporting sleeve of the plug is made of stainless steel, inlaid glass or ceramic stainless steel, ceramic bushing, mold glass fiber plastic and other materials. The butt joint of the plug is treated by grinding, and the other end of the plug is usually bent to support the fiber or fiber cord to release the stress. The sleeve used for coupling alignment is made of two halves of composite, fastened cylindrical components made of ceramic, glass fiber reinforced plastic (FRP) or metal. In order to make the fiber pair correct, this type of connector requires high machining accuracy of the coupling components of the plug and sleeve, and needs to be made by ultra high precision casting mold or mechanical processing technology. The interference loss of this kind of optical fiber connector is in the range of (0.18 ~ 3) dB. Active alignment connector requires low accuracy of components, and can be manufactured by low cost common process. But in the assembly, the optical instrument (microscope, visible light source, etc.) should be used to adjust the fiber core. In order to obtain lower insertion loss and higher return loss, the matching materials of refractive index should be used. 

Performance of optical fiber connector

The performance of optical fiber connector 3 optical fiber connector, fundamentally speaking, is the first optical performance of optical fiber connector; the other is to ensure the normal use of optical fiber connector, but also consider the exchange of optical fiber connector (the same type) performance, mechanical performance, environmental performance and life (i.e., the maximum number of plug). 

(1)optical properties 

At present, the fiber optical connector performance requirements, the focus of interest to the user and manufacturer of propaganda or on the insertion loss and return loss of the two most basic performance parameters. Among them, the intervention loss (or insertion loss) refers to the amount of transmission line effective power reduction due to the involvement of the connector, for the user, the smaller the better. For this performance, ITU recommends that the average loss, standard deviation and maximum loss of the sample should be determined according to the test of 20 samples. Based on average loss value should be less than 0.5dB. Return loss (or reflection attenuation, return loss, return loss) is a measure of the input power component returned from the connector and input along the input channel, and its typical value should be no less than 25dB. For optical fiber communication system, with the continuous improvement of transmission rate, reflection effect of the system is also more and more big, huge reflection from the connector will affect the high-speed laser (switching rate is Gbit / s) stability, and lead to the increase of laser jitter and noise distribution. Therefore, the requirement of echo loss is higher and higher, only meeting the requirements of typical values can not meet the actual requirements, but also need to further improve the return loss. The research shows that the return loss is greater by polishing or lapping the end of the connector butt joint. ITU recommends that this specially handled connector shall not return less than 38dB of return loss. - it is necessary to point out that the numerical requirements for both the ITU that when the system is light power distribution restrictions, these values are appropriate; for distribution network is not high requirements for power distribution occasions, lower performance is acceptable. 

The test method for optical properties of optical fiber connectors, ITU, is recommended according to the method specified in the latest revised edition of IEC874-1. But it should be noted that these methods are specified for production testing and are not completely applicable to the field environment. The interventional loss and reflection can be tested by OTDR. In order to ensure the accuracy of the test, OTDR must be carried out in two directions when the test of the intervention loss is carried out. 

(2)interchangeability performance 

The determination of the interchangeability of optical fiber connectors (with the same type) is not stated in the relevant recommendations of ITU. But in practical application, the optical fiber connector is a common optical interface element, so the optical fiber connectors of the same type, such as no special requirements, any combination of connector assembly and connector combination has good matching phase, additional transmission power consumption should be negligible. At present, the additional loss can not be ignored because of the restriction of connection mode, processing accuracy and intrinsic characteristics of optical fiber (mode field diameter, mode field heart error, etc.). Users and manufacturers generally limit this additional loss to less than 0.2dB. 

(3)mechanical properties

For the test methods of the mechanical properties of optical fiber connectors, ITU is recommended according to the method specified in the latest revision of the IEC874-1 general specification. In addition to the special requirements, IEC specifies that no less than 5 connectors / optical cable assemblies are required. For some test items, the test conditions and evaluation criteria are also specified in the test method specified by IEC. For the axial tensile strength of the paired connectors and the strength retention of the optical cable assemblies with at least 5 connectors, the IEC determines its minimum 90N. For bending performance, IEC specifies that at least 5 connectors / fiber optic cable assemblies shall be tested. The force of 15.0N should be applied to the optical cable at the distance from the connector 1m. Bend 300 loops on a circular shaft with a radius of 1.25cm. Additional loss shall be no more than 0.2dB after the test. For resistance to mechanical properties (i.e., repeated plug performance) IEC provisions from 5 / 1 cable connector combination out samples, using artificial way to access and disconnect at least 200 times, the connector should be cleaned, repeated 25 times to access each one measurement of insertion loss. After completion of the test, the maximum additional loss should not exceed 0.2dB and still work compared with the initial value. For the droop performance, the IEC stipulates that at least 5 optical cable assemblies with connectors should be tested. The maximum additional loss shall not exceed 0.2dB after test. For vibration performance, IEC specifies that the vibration frequency range is (10~55) Hz, and the stable amplitude is 0.75mm.