光纤通信必考填空题、计算题及答案 知识点

光纤通信必考填空题、计算题及其答案知识点一、填空题1The main constituents of an optical fiber communications link . The key sections are a transmitter consisting of a light source and its associated drive circuitry, a cable offering mechanical and environmental protection to the optical fibers contained inside, and a receiver consisting of a photodector plus amplification and signal-restoring circuitry.光纤通信链路的主要成分。

的关键部分是一个发射机包括一个光源及其相关的驱动电路，一个电缆提供机械和环境保护于光纤内部包含，和一个接收器包括一个光电探测器加放大和信号复原电路。

2 Attenuation of a light signal as it propagates along a fiber is an important consideration in the design of an optical communication system, the basic attenuation mechanisms in a fiber are absorption, scattering, and radiative losses of the optical energy.因为它传播沿纤维是在光通信系统的设计中的重要考虑因素的光信号的衰减，在一个光纤中的基本衰减机制是吸收，散射，以及光学能量的辐射损失。

3 Intermodal dispersion or modal delay appears only in multimode fibers. This signal-distorting mechanism is a result of each mode having a different value of the group velocity at a single frequency.模间色散或模延迟只出现在多模光纤。

这个信号扭曲机构是在单一频率具有群速度的不同值的每个模式的结果。

4 In general, LEDs are used with multimode fibers, since normally t is only into a multimode fiber that the incoherent optical output power from an LED can be coupled in sufficient quantities to be useful.在一般情况下，使用LED与多模光纤，因为通常t是只有到多模光纤，从一个LED的非相干光输出功率可被耦合以足够的量是有用的。

5 At the output end of an optical transmission line, there must be a receiving device that interprets the information contained in the optical signal. The first element of this receiver is a photodetecor. It senses the luminescent power falling upon it and converts the variation of this optical power into a corresponding varying electric current.在光传输线的输出端，必须有用于解释包含在光学信号中的信息的接收装置。

该接收器的第一个元素是光检测器。

它检测在发光功率落下后，它与该光功率的变化转换成相应的不同的电流。

6 An optical receiver consists of a photodetector , an amplifier, and signal-processing circuitry. The receiver has task of first converting the optical energy emerging from the end of a fiber into an electric signal, and then amplifying this signal to a large enough level.光接收器由一个光检测器，放大器，和信号处理电路。

该接收器具有第一转换的光能新兴从光纤的端部转换成电信号，然后放大该信号到一个足够大的电平的任务。

7 A characteristic of WDM is that the discrete wavelengths form an orthogonal set of carriers that can be separated, routed ,and switched without interfering with each other.波分复用的一个特点是，该离散波长形成正交载波集合可被分离，路由和交换而不相互干扰的。

8 Chromatic dispersion causes pulse broadening , which leads bit-error rates.色散导致脉冲展宽，从而导致误码率。

9 The function of an OADM is to insert or extract one or more selected wavelengths at a designated point in an optical network.一个OADM的功能是插入或在光网络中提取在一个指定点的一个或多个选择的波长。

10 Although the structure of such an optical amplifier is similar to that ofa laser, it does not have the optical feedback mechanism. thus an amplifier can boost incoming signal levels, but it cannot generate a coherent optical output by itself.虽然这样的光放大器的结构类似于激光的，它不具有光学反馈机制。

因而放大器可以放大输入的信号的水平，但它本身不能产生一个相干光输出。

11 The pump light is usually injected from the same direction as the signal flow, this is known as codirectional pumping泵浦光通常从相同的方向的信号流注入，这被称为同向泵送12 In any fiber transmission system using optical amplifiers, the dynamic characteristics of network traffic, particularly in a metro network, can create large, rapid fluctuations in the input optical power level to an EDFA.在使用光放大器的任何光纤传输系统，网络流量的动态特性，尤其是在一个城域网络，可以建立在输入光功率电平到EDFA大，快速波动。

13 The SONET and SDH rings are commonly called self-healing rings because the traffic flowing along a certain path can automatically beswitched to an alternate or standby path following failure or degradation of the link segment.在SONET和SDH环通常被称为自愈环，因为沿着某个路径流动的流量能够自动切换到下面的链路段的故障或降解的替代或备用路径。

14 The performance characteristics of OBS lie between those of a wavelength-routed network and an optical packet-switched networkOBS的性能特征在于那些波长路由网络和光分组交换网络之间15 In single-mode fibers, chromatic and polarization-mode dispersions are important factors that can limit the transmission distance or data rate 在单模光纤，套色和偏振模分散体是可以限制的传输距离或数据速率的重要因素16 Polarization-mode dispersion is important for data rates above 10Gb/s, since its statistical behavior ultimately can limit the highest achievable data rate.偏振模色散是以上的数据速率10Gb / s的很重要，因为它的统计行为最终可以限制可达到的最高数据速率。

17 When a link is being installed and tested, the operational parameters of interest include bit-error rate, timing jitter, and signal-to-noise ratio as indicated by the eye pattern.当链路正在安装和测试，感兴趣的操作参数包括误码率，定时抖动和信噪比由眼图所指示的。

二、计算题一 Consider a multimode silica fiber that has core refractive index 1 1.480n =and a cladding index 2 1.478n =. Find (a) the critical angle, (b) the numerical aperture, and (c) the acceptance angle. 考虑的多模石英光纤具有纤芯折射率和包层的折射率。