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通信英语 课文UNIT 6.doc

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1、UNIT 8Introduction to Optical Fiber Communication光纤通信介绍One of the most important technological developments during the 1980s has been the emergence of optical fiber communication as a major international industry.光纤通信介绍 80 年代一项最重要的技术发展是光纤通信成为一个主要的国际性产业。One indication of the extent of this developmen

2、t is the total length of installed fiber, which was estimated to be 3.2million kilometers in the U.S. alone by the end of 1987. 用光纤敷设总长度可以表明其发展程度,据估计,到 1987 年底仅美国的关切敷设总长将达 320 万公里Over 90% of this fiber was placed in service during the time period of 1982-1987. 其中 90%以上是在 1982-1987 年间敷设并开通的Long-haul

3、trunk installations have been dominated, accounting for about 95% of the fiber in the U.S. 而长途干线占主导地位 数量约为光纤总长的 95%Although telecommunication is the rationale for most of the current interest in fiber optics, this was not the case during the early days of the technology. 虽然现在人民对纤维光学的兴趣主要在于通信 但早期发展纤维

4、光学的目的并不在此。The researchers who produced the first clad glass optical fibers in the early 1950s were not thinking of using them for communications; they wanted to make imaging bundles for endoscopy. 50 年代初研究人员制造出第一根具有包层玻璃光纤时,并不想用于通信而是想用它们传送内窥镜需要的成像光束。Fiber optics was already a well-established commerc

5、ial technology when the famous paper by Kao and Hockham, suggesting the use of low-loss optical fibers for communication, appeared in 1966. 1966 年 Kao 和 Hockham 发表了那篇著名的论文 建议将低损耗光纤用于通信 此时纤维光学已发展为一项很实用的技术了。 The first low-loss (20dB/km) silica fiber was described in a publication which appeared in Oct

6、ober of 1970. 1970 年 10 月 第一根低损耗 20 dB/km 石英光纤问世了。The date of this publication is sometimes cited as the beginning of the era of fiber communication. 有时将这以日期作为光纤通信时代的开端。Although this development did receive considerable attention in the research community at the time, it was far from inevitable that

7、 a major industry would evolve. 然这一成果当时在研究领域确实引起了极大的关注 但因此就认为一项产业会发展起来尚为时太早: The 20dB/km loss figure was still too high for long-hall telecommunication systems. 虽每千米 20dB 的损耗对于长途通信系统仍然是太大The fibers were fragile, and a way to protect them would have to be found.光纤易断裂,必须寻找保护方法There were no suitable li

8、ght sources. 没有合适的光源。Researchers did not know whether field termination and splicing of optical cables would ever be practical. 研究人员不知道光缆终结和拼接是否会发展到实用阶段Finally, there were serious doubts as to whether these components could ever be produced economically enough for the technology to play a major role

9、 in the marketplace. 最后 这些部件是否能够足够经济的生产出来 从而使之在市场上占用重要的地位 它们更是存有严重的疑虑。 Although the technological barriers appeared formidable, the economic potential was very significant. 虽然技术障碍好像不可逾越 但经济潜力却非常明显。As a consequence, research and development activity expanded rapidly, and a number of important issues

10、were resolved during the early 1970s. 正因为如此 在 70 年代早期研究和开发工作开展迅速 一些重要问题得以解决。 During the middle and late 1970s, the rate of progress toward marketable products accelerated as the emphasis shifted from research to engineering. 70 年代中后期 由于发展重点研究领域转入工程 因而加速发展了适应市场的产品。Fibers with losses approaching the R

11、ayleigh limit of 2 dB/km at a wavelength of 0.8um,0.3 dB/km at 1.3um, and 0.15 dB/km at 1.55um,were produced in the laboratory. 在实验室研制的光纤衰减值接近瑞利极限值 0.8um 波长处为 2 dB/km 1.3um 波长处为 0.3 dB/km和 1.55um 波长处为 0.15 dB/km。Microbend loss problems were overcome through the use of improved fiber coatings and cab

12、ling techniques. 通过改进光纤外涂层方法和成缆技术 克服了微弯损耗。Rugged cables and multifibre connectors were produced for field installation. 生产了加强型光纤和多纤和多纤连接器用于室外作业。Room temperature threshold currents for commercial gallium aluminum arsenide lasers operating in the 0.8 to 0.85um spectral region were reduced to the 20 to

13、 30 mA range, and projected lifetimes in the 100 000 to 1000 000 hour range were claimed for both lasers and LEDs. 工作在 0.8-0.85um 波长区的商用镓铝砷激光器的室温阈值电流减少到 20-30mA 范围。据称 激光器和发光管的设计寿命达 10 万-100 万小时。Light sources and improved photodetectors which operated near 1.3um were developed to take advantage of th

14、e low fiber loss and dispersion in this “longer wavelength region”. 开发了工作于 1.3um 波长附近的光源和改进的光检测器 从而可以利用光纤在长波长区的低损耗和低色散特性。everal major field trials were undertaken during this period, including AT&Ts Atlanta experiment and Chicago installation, and Japans subscriber access project. 这一时期进行的室外试验教重要的有 A

15、T&T 于 1976 年在亚特兰大的实验 1977 年在芝加哥的实验和 1977 年日本的用户通路项目。 Improvements in component performance, cost, and reliability by 1980 led to major commitments on the part of telephone companies. 到了 80 年代 光纤器件在性能、价格和可靠性方面的改善使众多电话公司受益匪浅。Fiber soon became the preferred transmission medium for long-haul trunks. 光纤很

16、快成为长途干线的首选传输媒质。Some early installations used 0.8um light sources and graded-index multimode fiber, but by 1983, designers of intercity links were thinking in terms of 1.3um, single-mode systems. 一些早期敷设的光纤线路采用 0.8um 光源和渐变折射率多模光纤 但到 1983 年 城市间线路的设计者们就考虑使用 1.3um 单模光纤系统了。The single-mode fiber, used in c

17、onjunction with a 1.3um laser, provides a bandwidth advantage which translates into increased repeater spacings for high data rate systems. 单模光纤与 1.3um 激光器连接 可以提供宽带特性 增加了高数据速率系统的中继距离。 Data rates for installed fiber optic system have recently move into gigabit per second range. 近敷设的光纤系统的数据速率已移至每秒吉比特范

18、围。Such system use the spectrally pure distributed-feedback lasers to minimize fiber dispersion effects. 最这种系统采用光谱纯的分布反馈激光器 将光纤色散效应减至最小。Fibers designed for low dispersion at 1.55UM wavelength, which corresponds to minimum fiber loss, are now commonly used in long distance transmission. 在 1.55um 波长上设计

19、的低色散光纤 相应地具有低损耗特性 目前广泛用于长途通信。The use of wavelength multiplexing to further increase the fiber information capacity is becoming more widespread.为进一步增加光纤的信息容量 逐渐广泛采用波分复用的方法。 The potential of fiber optics in other areas is only beginning to be realized. 人们对于光纤在其他领域的潜力刚刚开始认识。Fiber optic networks for com

20、puter systems and offices are becoming more prominent. 用于计算机系统和办公室的光纤网络逐渐变的更加重要。In the telephone system, the use of fiber optics for interconnecting central offices within a metropolitan area and for lower levels in the switching hierarchy is still increasing rapidly. 在电话系统中 光纤在主要城市地区中心交换局间互联和低级交换中的

21、使用继续迅速增加。Fiber links to the home have been used in demonstration projects. 入户光缆已经有了示范工程。Many observers believe that national telephone systems will eventually be upgraded to handle video bandwidths by using fiber optics. 许多观察家相信 全国电话系统将使用光纤传输视频宽带信号而逐渐升级。These wideband subscriber loop systems would provide access to services such as picturephone, video entertainment. 这些宽带用户环路系统将可视电话、视频娱乐节目等业务提供通路。Widespread installation of these broadband services will become economically feasible. 宽带业务广泛使用光纤将会变的经济可行。

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