The buffer layer of optical fiber should be composed of one or several layers of the same or different materials. If the optical fiber is not further strengthened and protected, it can not be used directly. The reason is that the elongation at break of most optical fibers is very low. The tensile, bending and torsional strains will affect the service life of optical fiber and increase the loss. Therefore, the optical fiber must be protected by additional coating before actual use.
在室内光缆中的光纤多采用紧套结构,光纤的紧套结构通常有两种:一种使用紫外线固化一次涂覆光纤，直接紧套;另一种是将光纤外面涂覆一层缓冲层(缓冲层外径为 350-500 μm)后再紧套，这层缓冲层就是光纤缓冲层。
In the indoor optical fiber cable, the tight sleeve structure is often used. There are two kinds of tight sleeve structure: one is to coat the optical fiber with UV curing once, and tighten the sleeve directly; the other is to coat a buffer layer (the outer diameter of the buffer layer is 350-500 μ m) on the outside of the optical fiber, and then tighten the sleeve again. This buffer layer is the optical fiber buffer layer.
The buffer layer of optical fiber should be composed of one or several layers of the same or different materials. If the optical fiber is not further strengthened and protected, it can not be used directly. The reason is that the elongation at break of most optical fibers is very low. The tensile, bending and torsional strains will affect the service life of optical fiber and increase the loss. Therefore, the optical fiber must be protected by additional coating before actual use
Reason for adding buffer layer
为使光纤具有高的强度, 须在刚拉出的光纤上涂上一次增强涂层为减少微弯损耗, 改善温度特性, 增加机械保护等还须在一次被复光纤上涂复上缓冲层和二次被复层, 构成光纤单元以供成缆。
In order to make the optical fiber have high strength, it is necessary to coat the first reinforced coating on the optical fiber just pulled out. In order to reduce the micro bending loss, improve the temperature characteristics and increase the mechanical protection, it is also necessary to coat the buffer layer and the second clad layer on the primary clad optical fiber to form the optical fiber unit for cabling.
There are many kinds of coatings on optical fibers. One is a thin (several μ m) one shot reinforced coating. This can be achieved by means of a soft coater with taper
The diameter of buffer layer is 250 μ M
用于室内及野战通信、舰船、飞行器等特殊应用场合的光纤, 要求在其使用期内可承受多次人工处理(如移动等) , 使之易于安装、维护。其中, 比较好的解决方案就是在光纤成缆之前, 先涂覆缓冲层, 用带有缓冲层的光纤挤包 PVC (聚氯乙烯) 或其它材料制成紧套光纤, 然后再成缆。这就要求缓冲层必须具有好的弯曲性能、阻隔水汽性能和极小的附加损耗。
The optical fiber used for indoor and field communication, ships, aircraft and other special applications should be able to withstand many times of manual processing (such as mobile) during its service life, so as to make it easy to install and maintain. Among them, a better solution is to coat the buffer layer before the optical fiber is cabled, and use the optical fiber with buffer layer to extrude PVC (polyvinyl chloride) or other materials to make the tight sleeve optical fiber, and then the optical fiber is cabled. This requires that the buffer layer must have good bending performance, water vapor barrier performance and minimal additional loss.
缓冲层通常所采用的材料有丙烯酸酯类、有机硅树脂类等。缓冲层涂料涂覆到光纤上以后, 可以采用多种固化方式, 其中以紫外(UV ) 固化最为适合。UV 固化具有效率高、速度快、清洁、环保等特点。目前国外已有合格的 UV 固化光纤缓冲层涂料, 但是价格昂贵, 交货周期长, 并且有时对国内禁运。为了改变这种局面, 一些国内厂家和研究机构进行了 UV 固化光纤缓冲层涂料的研制工作。但到目前为止, 尚无公认的合格产品可以替代进口涂料使用。
The buffer layer is usually made of acrylate, silicone resin and so on. After the buffer coating is applied to the optical fiber, a variety of curing methods can be used, among which UV curing is the most suitable. UV curing is characterized by high efficiency, high speed, cleanness and environmental protection. At present, there are qualified UV curable optical fiber buffer coatings abroad, but the price is expensive, the delivery time is long, and sometimes the domestic embargo. In order to change this situation, some domestic manufacturers and research institutions have developed UV curable optical fiber buffer coatings. However, up to now, there is no recognized qualified product to replace imported coatings.
近年来典型光纤结构的包层外径为 125Lm, 一次涂覆内外涂层均采用 UV 固化丙烯酸酯树脂, 标称直径分别为 180～ 200Lm、245Lm (或 250Lm)。UV 固化光纤缓冲层涂料涂覆在一次涂覆后的光纤上,标称直径是 500Lm (或 400Lm )。一般来说, 光纤缓冲层涂料首先必须满足粘度、润湿性能的要求。粘度太大或太小, 都不能得到适当厚度的涂层。润湿性能不好, 涂料就难以涂覆上去。另外, 光纤缓冲层涂料固化后, 外面要再挤包 PVC 或尼龙等材料, 标称外径为 900Lm, 称为紧套光纤。固化应满足如下要求:
In recent years, the cladding outer diameter of typical optical fiber structure is 125lm. UV curable acrylic resin is used for both inner and outer coatings, and the nominal diameter is 180-200lm, 245lm (or 250lm) respectively. UV curable optical fiber buffer coating is applied on the optical fiber after one coating, and the nominal diameter is 500lm (or 400lm). Generally speaking, the optical fiber buffer coating must first meet the requirements of viscosity and wettability. If the viscosity is too large or too small, the coating with proper thickness can not be obtained. If the wettability is not good, the coating is difficult to apply. In addition, after the coating of optical fiber buffer layer is cured, PVC or nylon and other materials shall be extruded outside. The nominal outer diameter is 900Lm, which is called tight sleeve optical fiber. Curing shall meet the following requirements:
1) Low water penetration;
2) It has a certain tensile strength;
3) The curing speed is fast;
4) 具有较低的玻璃化温度 (T g ) , 以保证其具有优良
4) It has low glass transition temperature (TG) to ensure its excellent properties
Low temperature performance of the system;
5) 既具有优异的附着力 , 又具有合适
5) It not only has excellent adhesion, but also has suitable adhesion
The strippability of the system;
6) The additional loss of the coated fiber is small.
On line monitoring of concentricity of optical fiber buffer layer
涂层同心度定义为涂复光纤横剖面上的涂层最厚部分 b 与其最薄部分 a(在同一直径上)的比, 即涂层同心度
Coating concentricity is defined as the ratio of the thickest part B of the coating on the cross section of the coated optical fiber to its thinnest part a (on the same diameter)
Examples of coating concentricity
让一束 He 一 Ne 激光通过分光片分成二束光, 然后通过二片反射镜让二束光互成 90 度地一起垂直于光纤轴照射到光纤上, 得到二幅位相差度的前向散射图形。这样就可判定二维方向上的光纤缓冲层同心度的“ 大小” , 据此就可调整涂复器位置使同心度接近于“1 ” 。
A beam of He Ne laser is divided into two beams through a splitter, and then the two beams are irradiated on the fiber perpendicular to the axis of the fiber through two mirrors, and two forward scattering patterns with phase difference are obtained. In this way, the concentricity of the fiber buffer layer in the two-dimensional direction can be determined, and the position of the coater can be adjusted so that the concentricity is close to “1”.
目前研究了光纤缓冲层同心度的在线监测技术—前向散射技术。从静态的前向散射图形可以判断出同心度优于盯的情况。建立了一套在线监测缓冲层同心度的装置。使用这套装置后缓冲层同心度已从 2 左右提高到优于 1.3。
At present, the on-line monitoring technology of concentricity of fiber buffer layer forward scattering technology is studied. It can be judged from the static forward scattering pattern that the concentricity is better than that of the target. A set of on-line monitoring device for concentricity of buffer layer is established. After using this device, the concentricity of buffer layer has been improved from about 2 to better than 1.3.
Composition of UV curable optical fiber buffer coating
Selection of basic components of coatings
The basic components of coatings have a decisive influence on the properties of coatings. The coating with silicone resin as the basic component has heat resistance, cold resistance, weather resistance
Properties of silicone resins with different organic groups
涂料 UV 光引发体系的选择
Selection of UV photoinitiator system for coatings
UV 光引发体系是 UV 固化光纤缓冲层涂料的基本组分之一 , 直接影响缓冲层涂料固化交联速度和缓冲层各种性能。
UV photoinitiator system is one of the basic components of UV curable optical fiber buffer coating, which directly affects the curing speed and properties of the buffer coating.
光敏引发剂的种类繁多, 如阳离子型、安息香型、苯乙酮类、芳香酮类和酰基氧化膦类等, 它们具有不同的结构、特性和引发机理。
There are many kinds of photoinitiators, such as cationic type, benzophenone type, aromatic ketone type and acylphosphine oxide type. They have different structures, properties and initiation mechanisms.
Properties of buffer layer after coating
Optical fiber attenuation is one of the transmission characteristics of optical fiber, which is mainly caused by absorption loss, scattering loss, bending loss and micro bending loss.
对石英光纤来说, 吸收损耗来源于光纤材料的本征吸收、杂质吸收和结构中的原子缺陷吸收。材料的本征吸收是由于紫外区电子跃迁和从近红外到远红外区的晶格振动或多声子过程引起的吸收。杂质吸收主要是石英玻璃中过渡金属离子产生的吸收。原子缺陷吸收是由于在光纤制造过程中, 玻璃受到某种热激励或强辐照而感生的。散射损耗包括固有的瑞利散射损耗和结构不完善引起的损耗。材料密度不均匀以及掺杂浓度不均匀产生折射率分布的微观不均匀, 从而引起瑞利散射。结构缺陷包括纤芯与包层交界面存在的微小凹凸缺陷, 纤芯与包层直径的微小变化及沿纵轴方向形状的改变。
For quartz fiber, the absorption loss comes from the intrinsic absorption, impurity absorption and atomic defect absorption. The intrinsic absorption of materials is due to the electron transition in the ultraviolet region and the lattice vibration or multiphonon process from near infrared to far infrared region. Impurity absorption is mainly caused by transition metal ions in quartz glass. Atomic defect absorption is induced by some kind of thermal excitation or strong irradiation in the process of optical fiber manufacturing. Scattering loss includes inherent Rayleigh scattering loss and loss caused by imperfect structure. The inhomogeneity of material density and doping concentration results in micro inhomogeneity of refractive index distribution, which leads to Rayleigh scattering. Structural defects include micro concave convex defects at the interface between core and cladding, micro change of core and cladding diameter and shape change along the longitudinal axis.
在成缆过程中, 光纤的轴线因发生随机的微小变化, 即微弯而引起的损耗, 称为微弯损耗。在生产紧套光纤时, 在一次被覆后的光纤上再涂覆一定厚度的光纤缓冲层, 就可以进一步防止横向力对光纤的作用, 减少微弯损耗。当然光纤缓冲层要有适当的模量和适当的厚度。如果太厚, 缓冲层则会在冷却过程中由于内外冷却速度不一致而出现分层现象, 反而导致光纤衰减增加。
In the process of cabling, the loss caused by the random small change of the axis of the optical fiber is called micro bend loss. In the production of tight sleeve optical fiber, a certain thickness of optical fiber buffer layer is coated on the coated optical fiber, which can further prevent the effect of transverse force on the optical fiber and reduce the micro bending loss. Of course, the optical fiber buffer layer should have proper modulus and thickness. If the buffer layer is too thick, the delamination will occur due to the different cooling rates inside and outside the buffer layer, which will lead to the increase of fiber attenuation.