English for IT and EE-08

科技英语信息科学与电子工程专业英语

信息科学与电子工程专业英语

Technical EnglishFor Information Science and Electronic Engineering

科技英语信息科学与电子工程专业英语

信息科学与电子工程专业英语

Unit 8Optical Communications

科技英语信息科学与电子工程专业英语

信息科学与电子工程专业英语

Part IElectromagnetic Spectrum

科技英语信息科学与电子工程专业英语

New Wordsperusal 精读，细读 精读， impress 印，铭刻，加载 铭刻， resonator 谐振器 at will 随心所欲 synchronous 同步的 throughput 吞吐量 femtosecond 毫微微秒(10 15sec) 毫微微秒(10 obviate 避免，使成为不必要 避免， miniature 小型的 counterpart 对等物，对等的角色 对等物， gigahertz 吉赫(109Hz) 吉赫(109Hz) directionality 方向性 tTerahertz 特赫(1012Hz) 特赫(1012Hz) incur 招致，蒙受，引起 招致，蒙受， interleave 交织 nonlinearity 非线性 coherent 相干的 micron 微米 miniaturization 小型化 cladding 光纤包层3

科技英语信息科学与电子工程专业英语

New Wordsproximity 接近，亲近 接近， photon 光子 bias 偏置 fruition 结果实，成就 结果实， granular 颗粒状 benign 良性的

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科技英语信息科学与电子工程专业英语

1Various observations relating to the potential of optical technology for transmission of information can be made from perusal of the frequency line of Table 8.1. 与用于信息传输的光学技术 的潜力有关的

仔细研究表8.1中的频率表可以看到各种用于信息传输的光学 仔细研究表8.1中的频率表可以看到各种用于信息传输的光学 技术的潜力。 技术的潜力。

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科技英语信息科学与电子工程专业英语

1Table 8.1 A frequency line which gives the wavelengths , the frequencies frequencies

, and the photon energy ∑p for the various regions of the frequencyspectrumName λ ν(Hz) εp audio 300km 103 radio 300m 106 µwave 30cm 109 3µeV mmwave 3mm 1011 0.3meV IR 30µm 1013 30meV OPT/UV 0.3µm 1015 3eV x-ray 30Å 1017 300eV Gamma 0.03Å 1020 0.3MeV

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科技英语信息科学与电子工程专业英语

2The information rates in which one is interested in conventional “modern-day” communications systems “moderngenerally correspond to audio rates in telephone systems, radio rates in commercial broadcast systems, or digital television rates in the most advanced video distribution systems.1 … 的信息传播速率通常相应于 …

“现代”常规通信系统中人们所感兴趣的信息传输速率通常 现代” 对应于电话系统中的音频，商用广播系统中的无线电频率， 对应于电话系统中的音频，商用广播系统中的无线电频率， 或是在最先进的视频节目分配系统中的数字电视信息速率。 或是在最先进的视频节目分配系统中的数字电视信息速率。7

科技英语信息科学与电子工程专业英语

2These rates are generally below several GHz. If one were to transmit such information without impressing it on an optical carrier but instead on a radio frequency (RF) carrier a bit higher than the maximum rate, the transmission wavelength of the RF carrier would be centimeters or larger.2

如果要传输这样的信息而不将它加载于 光纤上， 光纤上，而是加载在略高于

最大速率的 射频载波上， 射频载波上，则此射频载波就会是厘米 波或波长再长一些的波。 波或波长再长一些的波。8

科技英语信息科学与电子工程专业英语

2There can, however, be great advantages to using optical carriers. An obvious one is the low loss and directionality of the optical fiber. Clearly, the carrier must have a higher rate than the information rate. A major principle that has appeared in communications systems has been that the higher the frequency, the greater the technical complexity. Microwaves are harder to handle than are radio waves. 通信系统的一个基本原则是

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科技英语信息科学与电子工程专业英语

2As wavelengths decrease to approach the size of circuit components, circuit elements are no longer lumped, and leads can act as reflective components and/or antennas and lumped elements as electromagnetic resonators.3

随着… ,电路单元就不再是集总的 随着… … ,电路单元就不再是集总的， 电路单元就不再是集总的， 导线可起到反射元件以及( 导线可起到反射元件以及(或)天线的 作用，集总单元则成为电磁谐振器。 作用，集总单元则成为电磁谐振器。

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科技英语信息科学与电子工程专业英语

2This has generally meant that sending more information would cost more and there was therefore a cost per bit/sec (bps) of transmitted information in the sense that going to a higher information rate requires a higher frequency. Thus, the frequency. first observation from the frequency line would be that, for optical carriers, which have frequencies in the hundreds of THz, information bandwidth is in some sense free. free. 信息的带宽在 某种意义上是 免费的 因此在较高的信息率要求较高 的频率这层意义上， 的频率这层意义上，要考虑传 输信息的每个bps成本问题 输信息的每个bps成本问题11

科技英语信息科学与电子工程专业英语

2That is to say, the optical wavelength is so small compared to most devices that the technology has changed drastically from electrical and microwave. Once we assume that we have such microwave. technology, no matter how high an information rate one might want it will not be necessary to change the carrier, as the carrier, carrier frequency is higher than any realistic information rate could become. 无论信息率有多高， 无论信息率有多高，再 也没有必要改变载波了 所用技术与电和微波 有根本的不同

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科技英语信息科学与电子工程专业英语

2Bandwidth is not completely free, though, as encoders and decoders must necessarily operate at the information rate, but much of the rest of the system must necessarily handle only the carrier plus modulation. modulation.

而系统其余部分大都只需要 处理载波和调制

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科技英语信息科学与电子工程专业英语

2If a component can handle a frequency of 5×1014 Hz, an 5× information shift in that frequency of a part in a thousand (corresponding to a 500 GHz information rate) will have little or no effect on device performance. performance.

在这个频率，信息偏移千分之一(相应 在这个频率，信息偏移千分之一( 500吉赫兹的

信息率 吉赫兹的信息率) 于500吉赫兹的信息率)对器件的性能 将没有什么影响

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科技英语信息科学与电子工程专业英语

2Therefore, once the system is already set up, one can upgrade system speed more or less at will without the kind of costs incurred by changing the electromagnetic carrier in conventional systems. systems.

就可以随意升级系统而不会涉及 常规系统中改变电磁载波所需付 出的那种代价

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