This article focuses on the parameters that affect available b和width in 光纤s, 和 the 分散 mechanisms of various fiber types 和 non-linear effects. 分散 describes the 过程 of how an input signal broadens out as it travels down the fiber. 我们将介绍几种类型的色散. We’ll also take a cursory look at other important nonlinear effects that can reduce the amount of b和width that is ultimately available over an 光纤.
分散
Most of the traffic traveling through fiber networks takes the form of a laser pulse, 激光在哪里被脉冲打开和关闭, effectively forming a digital square wave comprised of “1”s 和 “0”s. 色散导致脉冲随着时间的推移而扩散, 有效地使边缘变圆, 和 making it harder for the detector to determine whether a “1” or a “0” is being transmitted. When this happens, the effective b和width of the link is reduced. The three main types of 分散 mechanisms are modal 分散, 色散, 偏振模色散. Because these mechanisms affect fiber networks in different ways, we’ll discuss each in some depth. 请下载全文以获取更多信息.
模态色散
总的来说，我们的文章beat365登录 单模光纤选择 focuses on single-mode fibers since they comprise the vast majority of fiber kilometers deployed around the world. 与多模光纤相比，单模光纤 是否用于所有高容量, long-distance networks due to their low attenuation 和 high b和width. 多模光纤的一个主要限制因素是模色散.
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多模光纤同时传输多种模式的光. 而光的模式可以被认为是一束光, a typical multimode fiber can have up to 17 modes of light traveling along it at once. These modes all traverse slightly different paths through the fiber, 有些路径长度比其他的长. 路径更直的模式会更快到达, 和 modes that bounce along the outer edges of the core of the fiber take a longer path 和 arrive later. 对端脉冲的影响称为模态色散, 因为这是由于光纤中的不同模式. Multimode fibers are designed to reduce the amount of modal 分散 with precise control of the index of refraction profile, 通过芯中掺杂剂的用量. However, it isn’t possible to completely eliminate modal 分散 in multimode fibers.
色散
色散描述了一种组合 of two separate types of 分散, namely material 分散 和 waveguide 分散. Light travels at different speeds at different wavelengths, 和 all 激光脉冲在一个波长范围内传输. 光也以 通过不同的材料有不同的速度. 这些不同的速度产生脉冲 沿着纤维传播时展开或压缩. 纤维的设计师 can use these two points to customize the index of refraction profile to 生产不同用途的纤维. 色散并不总是 坏事. 事实上，它可以作为一种工具来帮助优化网络 表演。.
例如，第一个用于光纤的激光器 transmission operated at 1310 nm, 和 many networks still use that wavelength. 纤维的设计师 therefore developed the first single-mode fibers to have 在这个波长上色散最小或为零. 事实上，G.652根纤维静止 这样设计的. 在这些光纤中，色散在1550nm窗口处较高.
今天的网络经常以多种方式运作 波长从它们身上掠过. 在这些网络中，会产生非线性效应 从多个波长可以影响网络的运行. 我们将简要介绍一下 本文概述了其中一些非线性效果. 彩色 分散 is often used as a tool to help optimize these types of networks.
偏振模色散(PMD)
Light is an electromagnetic wave 和 is comprised of two polarizations that travel down the fiber at the same time. In a perfectly round fiber deployed with perfectly balanced external stresses, these polarizations would reach the end of the fiber at the same time. 当然，我们的世界并不完美. Even small amounts of glass ovality/non-concentricity or non-concentric stresses in the 电缆 can cause one of the polarizations to travel faster than the other, 当它们沿着光纤传播时，会及时散开. 这种现象被称为偏振模色散(PMD)。.
布线和安装影响PMD，甚至 things like vibration from trains moving down tracks or wind-induced aerial 电缆振动会影响PMD. 然而，这些相互作用的影响是 typically smaller than the inherent PMD caused by the glass manufacturing 过程.
有一些方法可以减轻PMD. 一个非常 effective method is to make the glass fiber as geometrically round 和 尽可能保持一致. OFS使用一种特殊的技术来实现这一点. 使用 a patented 过程 called fiber “spinning”; half-twists are translated through the fiber during the draw 过程, reducing the non-concentricities 和 ovalities in the glass that are the major contributors to increased PMD.
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非线性效应
还有很多其他的因素 network, equipment, 和 fiber designers have needed to consider as network 这些年来，能力不断增强. 这些因素常常导致我们 collectively add more 和 more wavelengths of traffic at greater speeds 和 更高的功率水平.
本文的目的不是回顾 each of these in depth, but instead to touch on them so the reader can have a 通过熟悉. 这些因素中最引人注目的是四波混频， which led to the development of non-zero 分散-shifted fibers (NZDF). However, other non-linear effects include self-phase modulation, cross-phase 调制，拉曼和布里渊散射等. 如前所述， 色散 can be used to offset the effects of four-wave mixing. 为 those non-linear effects related to 更高的功率水平, increasing the effective area where the light travels down the fiber can help to reduce the 这些非线性效应的影响.
色散和非线性效应是最重要的 least understood issues in the general fiber user population, mainly because the guidelines used to match up today’s fibers 和 electronics typically work so that the end user doesn’t need to have a detailed background to bring up a 系统.
OFS在光纤网络方面拥有数十年的经验. 请与您的 本地海事服务处代表 if you would like additional information regarding any of the items in this article.
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OFS is a market leader in the design 和 manufacture of st和ard 和 custom 分散 Slope Compensating Modules (DSCMs) also known as 色散补偿模块 (还). 我们的固定宽带, 可重构的, 和 tunable colorless modules round out a product line that is well-suited for the major transmission fiber types.