电子类专业英语电子教案第十四课

null14 Optical Communications14 Optical Communications学习重点： （1）掌握有关光通信的基本单词、词组和缩略语的基本含义及用法 （2）培养阅读翻译有关光通信的科技文献和产品说明书的能力 （3）学习如何撰写科技论文英文摘要并初步掌握在内容、句法、时态、语态等方面的特点 null生词 avalanche [ 'ævəlɑ:nʃ ] n. 雪崩 attenuation [ əˌtenju'eiʃən ] n. 衰减 cladding [ 'klædiŋ ] n. 金属包层；电镀 Passage A Optical Fibre and it’s Applications in Communicationnullcoaxial [ kəu‘æksəl ] a 同轴的 distortion [ dis'tɔ:ʃən ] n. 扭曲；崎变 dispersion [ dis'pə:ʃən ] n. 散布, 分散 drawback [ 'drɔ:.bæk ] n. 不利点 eliminate [ i'limineit ] v. 除去；排除；消除 incoherent [ .inkəu'hiərənt ] a. 不相干的 interference [ .intə'fiərəns ] n.干涉 index ['indeks] n. 索引；指针；指数 modal [ 'məudl] a. 模态的 refractive [ri'fræktiv] a. 折射的 silica [ 'silikə ] n. 矽土；二氧化硅 sophisticate [ sə'fistikeit ] v. 掺合；弄复杂 spectrum [ 'spektrəm ] n. 光谱 stray [ strei ] a. 杂散的 n. [pl.]杂散电容；天电干扰2. 课文翻译讲解2. 课文翻译讲解 Fibre-based systems have largely replaced radio transmit systems for long-haul data transmission, and largely used for telephony, Internet traffic, long high-speed local area networks (LANs), cable-TV, and increasingly also used for shorter distances. In most cases, silica fibers are used, except for very short distances, where plastic optical fibres can be advantageous. 翻译：基于光纤的系统已大部分取代了无线电传输系统长距离传输数据，并主要用于 电话、互联网通信、长距离高速局域网（ LAN ）、有线电视，并且现在已越来越多 地用于短距离通信。除了非常短距离的通信之外，大多情况下用二氧化硅光纤，在短 距离通信中使用塑胶光纤是有利的。 nullCompared with the systems based on electrical cables, there are a number of compelling advantages, which lead to the widespread adoption of fibre optic cable for telecommunications, the most important are: (1) Much lower levels of signal attenuation, ≈0.2 dB/km for modern single-mode silica fibers, so that many tens of kilometers can be bridged without amplifying the signals. 翻译：与电缆系统相比，光纤电缆具有一些极据竟争性的优点，这使得它被广泛 应用于通信系统，这些优点最重要的是： （1）低得多的衰减，现代的单模二氧化硅光纤信号衰减约为0.2 dB/km，这样， 无需放大信号就可跨越数万公里。null (2) Fibre optic cabling provides a much higher bandwidth allowing more data to be delivered. For example, the wavelength range from 1.3 μm to 1.6 μm corresponds to a bandwidth as large as 43 THz, which are some orders of magnitude higher than that of any electrical cable. Even so, the theoretical potential of this bandwidth has not been fully utilized so far. (3) Fibre optic cables are much lighter than the coaxial cables, so that the cost of laying a fiber-optic cable is much lower than the coaxial cables. 翻译：2）光缆可提供高得多的带宽，从而传递更多的数据。举例来说，波长范围 从1.3 μ m至1.6 μ m所对应的带宽是43THz，比普通电缆高出了几个数量级。即 便如此，从理论讲，此带宽的潜力至今仍未被充分利用。 （3）光纤电缆远轻于同轴电缆，这就使得铺设光纤电缆的成本远低于同轴电缆。null (4) Fibre optics does not suffer from stray interference, such as ground loops or electromagnetic interference that often occurs with coaxial cabling. Just for reasons of these advantages, optical data transmission is increasingly used in various areas today, such as for example telephony, Internet traffic, and cable TV, mostly for longer transmission distances of at least a few kilometers. There is, however, a tendency for optical systems to penetrate areas with smaller and smaller transmission distances. 翻译：4）光导纤维不会遭受杂散干扰，而诸如接地环路或电磁干扰之类的杂散干 扰却在使用同轴电缆时常常发生。 正是由于具有这些优势，光数据传输在今天被越来越多地应用在各个领域，如 电话、互联网通讯、有线电视等，这些多数用于至少有几公里的较长传输距离。然 而，目前有将光系统以越来越小的传递距离渗透到各个领域的趋势。 nullCurrent local area networks (LANs) work well with electrical cables for data rates of 100 Mbit/s, but electrical cables do not serve that well at rates of e.g. 10 Gbit/s, so that optical connections will become important. Supercomputers may soon extensively use optical interconnects for rather short distances. Optical board-to-board connections, optical chip-to-chip and even intra-chip connections are seriously considered, partly already developed. 翻译：目前，使用电缆的局域网很好地工作于100 Mbit/s数据速率，但在数据率 达到如10 Gbit/s时电缆的服务不是很好，所以光纤系统将变得很重要。超级计 算机可能很快会在相当短的距离内使用光纤连接。光的板对板连接，光的片对片 连接，甚至内部芯片连接都在认真考虑，部分已进行了开发。 nullHowever, fiber systems are somewhat more sophisticated to install and operate, so that they tend to be less economical if their full transmission capacity is not required. Therefore, usually the connection to the homes and offices are still bridged with electrical cables, while fiber-based communications do the bulk of the long-haul transmission. Any fibre optic data transmission system is comprised by a number of different elements, mainly are: transmitter (light source), fibre optic cable, optical repeater and amplifier, receiver (detector).翻译：不过，光纤系统的安装和操作有点复杂，以至于如果不充分利用它们的全部 传输容量，使用它们往往就不太经济。因此，家里和办公室的连接线通常还是使用 电缆，而基于光纤的通信大部分用于远距离传输。 任何光纤数据传输系统都由一些不同的部分组成，主要是：发射机（光源）， 光纤光缆，光中继器和放大器，接收器（探测器）。nullOriginally, large lasers have been used for optical fibre telecommunication systems. Today, however, a variety of semiconductor devices can be used. The most commonly used devices are light emitting diodes (LEDs), and other semiconductor laser diodes. The simplest transmitter device is the LED, main advantage of which is cheap, and this makes it ideal for low cost applications where only short runs are needed. 翻译： 最初，大型激光器用于光纤电信系统。但是现在可以使用各种各样的半导体 设备。最常用的器件是发光二极管（ LED ），以及其它半导体激光二极管。最简单 的发射装置是LED。它的主要优点在于价格便宜，因而，它成为低成本短距离应用的 理想选择。 nullHowever they have a number of drawbacks. The first is that they offer a very low level of efficiency. Only about 1% of the input power enters the optical fibre. The other disadvantage of LEDs is that they produce incoherent light that covers a relatively wide spectrum, typically between 30 and 60 nm. This means that any chromatic dispersion in the fibre will limit the bandwidth of the system. In view of their performance, LEDs are used mainly in local-area-network applications where the data rates are typically in the range 10-100 Mb/s and transmission distances are a few kilometres. 翻译：不过，它们也有一些弊端：第一个问 题 快递公司问题件快递公司问题件货款处理关于圆的周长面积重点题型关于解方程组的题及答案关于南海问题 是它们所提供的工作效率非常低，只有 约10 ％的输入功率进入光纤；LED的另一个缺点是，他们所生产的非相干光覆盖比 较宽的频谱，通常是30到60纳米，这意味着在光纤中任何颜色的色散都将限制系统的 带宽。鉴于它们的性能，目前发光二极管主要用于局域网，这些地方数据传输率通常 在10-100 Mb/s，并且传输距离为几公里远。 nullThen lasers are used, although more costly, they offer some significant advantages. The first instance is that they are able to provide a much higher level of efficiency in the transfer of the light into the fibre optic cable. Typically the coupling efficiency into a single mode fibre may be as high as 50%. A further advantage is that lasers have a very narrow spectral bandwidth, which enables the lasers to transmit data at much higher rates because modal dispersion is less apparent. 翻译：然后使用激光，虽然较昂贵，他们却有着显著的优势。首先，在把光信号 转换进入光纤电缆时，他们具有高得多的效率，耦合成为一个单模光纤的通常效 率可能高达50 ％。更进一步的好处是激光有一个很窄的谱带宽度，它使激光以高 得多的速率传送数据，因为模式的色散不是那么明显。 nullAnother advantage is that semiconductor lasers can be modulated directly at high frequencies because of short recombination time for the carriers within the semiconductor material. Because the laser diodes are often directly modulated, this provides a very simple and effective method of transferring the data onto the optical signal, achieved by controlling current applied directly to the device. This in turn varies the light output from the laser. 翻译：另一个好处是半导体激光器可在高频率直接调制，由于在半导体材料中载 流子的复合时间很短。因为激光二极管往往直接进行调制，这就提供了将数据转 换成光信号一个非常简单而有效的方法，这一转换是用控制直接加到激光设备上 的电流来达到的。这反过来又改变了由激光器输出的光信号。 nullHowever for very high data rates or very long distance links, it is more effective to run the laser at a constant output level (continuous wave). The light is then modulated using an external device, the advantage of which is that it increases the maximum link distance because an effect known as laser chirp is eliminated. This chirp broadens the spectrum of the light signal and this increases the chromatic dispersion in the fibre optic cable. 翻译：但是对于非常高的数据传输速率或非常长距离的链接，以恒定的输出（连续 波）运行激光更为有效。用外部设备进行光调制，其优点是增加了最大链路距离， 因为一种被称为激光啾声的现象被消除了。这种激光啾声拓宽了光信号的频谱，增 加了光纤电缆中的色散。null A fibre optic cable consists of a core, a cladding, and a protective coating outside of the cladding, as schematically shown in Figure 14-1. The cladding is a layer around the core and the refractive index of which is slightly lower than that of the core. This means that the light passing down the core undergoes total internal reflection when it reaches the core / cladding boundary, and it is thereby contained within the core of the optical fibre.翻译：光缆由缆芯、包层以及外部有覆层的保护涂层组成，此保护涂层是在包层的外 面，如图14-1所示。包层是在缆芯的周围且其折射率相对缆芯的要低。这意味着当在 缆芯中进行传输的光到达核心/包层边界时要进行全内反射，因而光被包围在缆芯中。null Repeaters and amplifiers must be used in order to overcome the attenuation and the distortion of the light signal along the cable as the signals transmitted over longer distances. The heart of the receiver is a photo-detector, which normally is a semiconductor device and may be a p-n junction, a p-i-n photo-diode or an avalanche photo-diode. 翻译：随着信号传输距离加长，必须使用中继器和放大器，以克服光信号沿电缆传 输时产生的衰减和失真。 接收器心脏是一个光电探测器，它通常是半导体器件，也可能是一个PN结，一 个PIN光电二极管或雪崩光电二极管。 nullPhototransistors are not used because they do not have sufficient speed. Once the optical signal from the fibre optic cable has been applied to the photo-detector and converted into an electrical format, it can be processed to recover the data, which then can be passed to its final destination. 翻译：没有使用光电晶体管是因为它们速度不够。一旦光纤电缆中光信号传递给光 电探测器并转换成电气格式，它就可被加工处理以恢复原始数据，然后传给最终目 的地。3.疑难解析3.疑难解析1) In most cases, silica fibers are used, except for very short distances, where plastic optical fibers can be advantageous. 除了短距离通信之外，大多情况下用二氧化硅光纤，短距离通信使用塑胶光纤是有利的。in most cases 意为“在大多数情况下”，这里case意为 “状况、情形、场合”。 比较：in that case意为“如果那样的话”；in one’s case意为“就…的情况而言”；in any case意为“无论如何、不管怎样”。null2) Compared with the systems based on electrical cables, there are a number of compelling advantages which lead to the widespread adoption of fibre optic cable for telecommunications, the most important are : 与电缆系统相比，光纤电缆具有一些极据竟争性的优点，这使得它被广泛应用于通信系统，这些优点最重要的是： (be ) based on / upon意为“以…为基层；以…为根据”。 4 语法应用4 语法应用如何撰写科技论文英文摘要 1) 写科技论文英文摘要的重要性 任何科技论文，不管是在国外刊物还是在国内刊物发表，都要求有英文摘要。如果是全英文论文，英文摘要置于正文之前；如果是全中文论文，中文摘要置于正文之前，英文摘要置于正文之后。科技论文摘要概述了全篇论文的主要内容，便于他人阅读，了解论文内容。许多读者只阅读摘要而不读全文，或常根据摘要来判断是否需要阅读全文。一般检索系统只收录论文的摘要，在网上检索时，一般也只能免费查到摘要。好的英文摘要能吸引读者、增加论文的被检索和引用机会。所以，摘要的清楚表达十分重要。null2) 撰写科技论文英文摘要要点： (1) 内容： 英文摘要的写作并没有一成不变的格式，但英文摘要应是原始文献准确而简短的概括，并要反映原始文献的主要信息。简述论文所描述的主要内容，力求简洁、清晰、准确； (2) 长度： 科技论文英文摘要一般为3到8句，500-1000字符，不能只写一句（即使一句有1000字符也不可）； (3) 语句特点： 句法：英文摘要以陈述事实、描写过程为主，故而主要使用陈述句，并往往带有多种修饰短语。 时态：时态常用一般现在时及一般过去时，少用现在完成时、过去完成时。 语态：一般用被动语态。