通信英语 课文UNIT 6

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 development 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 trunk installations have been dominated, accounting for about 95% of the fiber in the U.S.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.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 commercial 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 October of 1970. 1970年1020 dB/kmThe 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 a major industry would evolve.: 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 light 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 in the marketplace.严重的疑虑。

Although the technological barriers appeared formidable, the economic potential was very significant.As a consequence, research and development activity expanded rapidly, and a number of important issues were resolved during the early 1970s.70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.70Fibers with losses approaching the Rayleigh 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.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 cabling techniques.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 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 the low fiber loss and dispersion in this “longer wavelength region”.开发了工作于 1.3um低色散特性。

everal major field trials were undertaken during this period, including AT&T’s Atlanta experiment and Chicago installation, and Japan’s subscriber access project.这一时期进行的室外试验教重要的有AT&T于19761977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80Fiber soon became the preferred transmission medium for long-haul trunks.光纤很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0.8um1983者们就考虑使用1.3um单模光纤系统了。

The single-mode fiber, used in conjunction 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1.3umData 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围。