本文主要讨论影响光纤可用带宽的参数, 以及各种纤维类型的色散机理和非线性效应. 色散描述了输入信号在光纤中传播时如何变宽的过程. There are several types of 分散s that we will cover. 我们还将粗略地了解其他重要的非线性效果，这些效果可能会减少网络中最终可用的带宽 optical fiber.
分散
大部分通过光纤网络传输的信息都是以激光脉冲的形式传输的, where the laser is pulsed on 和 off, 有效地形成由“1”和“0”组成的数字方波. 分散 causes a pulse to spread out over time, effectively rounding the edges, 这使得探测器更难确定传输的是“1”还是“0”. 当这种情况发生时，链路的有效带宽会减少. 色散机制的三种主要类型是模态色散, chromatic 分散, 和 polarization mode 分散. 由于这些机制以不同的方式影响光纤网络，因此我们将对每种机制进行深入讨论. Please download the full article for more information.
Modal 分散
In general, our article on Single-Mode Optical Fiber Selection 重点关注单模光纤，因为它们构成了世界上部署的绝大多数光纤公里. In contrast to multimode fibers, single-mode fibers are used for all high-capacity, 远距离网络由于其低衰减和高带宽. A main limiting factor of multimode fibers is modal 分散.
Multimode fibers carry multiple modes of light at the same time. While a mode of light can be thought of as a ray of light, 一根典型的多模光纤可以同时有多达17种模式的光通过. 这些模式通过光纤的路径都略有不同, with some path lengths longer than others. Modes that take a straighter path will arrive sooner, 而沿着光纤核心外缘反射的模式路径较长，到达时间也较晚. The effect on the end pulse is called modal 分散, since it is due to the different modes in the fiber. 多模光纤的设计目的是通过精确控制折射率来减少模态色散, through the quantity of dopants used in the core. 然而，要完全消除多模光纤中的模色散是不可能的.
彩色 分散
彩色 分散 describes a combination 两种不同类型的色散，即材料色散和波导色散 分散. 光以不同的波长以不同的速度传播，等等 laser pulses are transmitted over a wavelength range. Light also travels at different speeds through different materials. These varying speeds cause pulses to either spread out or compress as they travel down the fiber. Fiber designers 可以用这两点来定制折射率剖面来吗 produce fibers for different applications. 彩色 分散 isn’t always a 坏事. In fact, it can be used as a tool to help optimize network performance.
为 example, the first lasers used for fiber 传输工作在1310nm，许多网络仍在使用该波长. 因此，光纤设计师开发了第一种单模光纤 minimum or zero 分散 at this wavelength. 事实上，G.652 fibers are still designed this way. In these fibers, 分散 is higher in the 1550 nm window.
Today’s networks often operate with multiple wavelengths running over them. In these networks, nonlinear effects that result from the multiple wavelengths can affect network operation. We’ll give a brief overview of some of these non-linear effects in this article. 彩色 分散常被用作帮助优化这类网络的工具.
Polarization Mode 分散 (PMD)
光是一种电磁波，由两种极化组成，这两种极化同时沿着光纤传播. 在一个完美的圆形纤维与完美平衡的外部应力展开, 这些偏振会同时到达光纤的末端. Of course, our world isn’t perfect. 即使是少量的玻璃椭圆/非同心圆或非同心圆应力在 电缆 能使其中一个极化比另一个传播得快吗, spreading out in time as they travel along the fiber. This phenomenon is called polarization mode 分散 (PMD).
Cabling 和 installation affect PMD, 和 even 比如火车沿着轨道行驶时产生的振动，或者风引起的天线 电缆 vibrations can affect PMD. However, the impacts of these interactions are 通常小于由玻璃制造引起的固有PMD 过程.
There are ways to mitigate PMD. 一个非常 有效的方法是使玻璃纤维呈几何圆形 consistent as possible. OFS uses a special technique to accomplish this. 使用 a patented 过程 called fiber “spinning”; half-twists are translated through 纤维在拉伸过程中，减少了非同心度和 玻璃中的椭圆是PMD增加的主要原因.
Non-Linear Effects
There are a host of other factors that 网络、设备和光纤设计人员都需要将其作为网络来考虑 capabilities have grown over the years. These factors often result as we 以更快的速度和速度增加越来越多的交通波长 higher power levels.
It is not the intent of this article to review 每一个都是深入的，而不是接触它们，以便读者可以有一个 passing familiarity. The highest profile of these factors is four-wave mixing, 这导致了非零色散位移光纤(NZDF)的发展. 然而，其他非线性效应包括自相位调制，交叉相位 modulation, Raman 和 Brillouin scattering, 和 others. As mentioned earlier, 色散可以用来抵消四波混频的影响. 为 这些非线性效应与更高的功率水平有关，增加了 光在光纤中传播的有效面积可以帮助减少 impact of these other non-linear effects.
分散s 和 non-linear effects are the 一般光纤用户群体中最不了解的问题，主要是因为 用于匹配当今光纤和电子设备的指导方针通常是有效的 这样终端用户就不需要有详细的背景知识 系统.
OFS has multiple decades of experience with fiber optic networks. Please contact your local OFS representative 如果您想了解有关本文中任何项目的其他信息.
OFS是设计和制造标准和定制色散斜率补偿模块(dscm)的市场领导者 分散 Compensating Modules (还). Our fixed broadb和, reconfigurable, 可调的无色模块完善了产品线，非常适合主要的传输光纤类型.