电子信息类专业英语第二版十九单元

1、Passage B Advantages of Optical Fiber Communication光纤通信的优点Communication using an optical carrier wave guided along a glass fiber has a number of extremely attractive features, several of which were apparent when the technique was originally conceived. Furthermore, the advances in the technology to d

2、ate have surpassed even the most optimistic predictions, creating additional advantages. Hence it is useful to consider the merits and special features offered by optical fiber communications over more conventional electrical communications. In this context we commence with the originally foreseen a

3、dvantages and then consider additional features which have become apparent as the technology has been developed. 使用沿着玻璃纤维引导的光学载波的通信有许多极具吸引力的特性,当技术被最初构想出来其中一些是明显的。此外,技术的进步到目前为止已经超过甚至最乐观的预测,而产生额外的优势。因此它对于考虑提供的优点和光纤通信在更传统的电子通信的特色是有用的。在这种情况下我们着手于最初预测的优势然后考虑已成为明显的技术的附加功能。(a) Enormous potential bandwidth.

4、 The optical carrier frequency in the range 1013 to 1016 Hz (generally in the near infrared around 1014Hz or 105GHz) yields a far greater potential transmission bandwidth than metallic cable systems(i.e. coaxial cable bandwidth up to around 500MHz) or even millimeter wave radio systems(i.e. systems

5、currently operating with modulation bandwidths of 700 MHz). At present, the bandwidth available to fiber systems is not fully utilized but modulation at several gigahertz over a hundred kilometers and hundreds of megahertz over three hundred kilometers without intervening electronics(repeaters)is po

6、ssible.Therefore, the information-carrying capacity of optical fiber systems has proved far superior to the best copper cable systems. By comparison the losses in wideband coaxial cable systems restrict the transmission distance to only a few kilometers at bandwidths over one hundred megahertz.(1) 巨

7、大的潜在带宽。频率在1013赫兹到1016赫兹范围(通常在1014 Hz的近红外或105 GHz)的光学载波比金属电缆系统(即，同轴电缆带宽约500 MHz)甚至毫米波无线电系统(即，系统目前操作的调制带宽700 MHz)产生一个更具潜在的传输带宽。目前,对于光纤系统的可用带宽不是被完全利用,而在几兆赫超过一百公里的速度调制和数百兆赫超过三百公里没有干预电子(中继器)是可能的。因此,光纤系统的信息传送能力证明它优于最好的铜电缆系统。相比之下，在宽带同轴电缆系统的损失限制了在一百兆赫带宽只有几公里的距离传输。Although the usable fiber bandwidth will be

8、extended further towards the optical carrier frequency, it is clear that this parameter is limited by the use of a single optical carrier signal. Hence much enhanced bandwidth utilization for an optical fiber can be achieved by transmitting several optical signals, each at different center wavelengt

9、hs, in parallel on the same fiber. This wavelength division multiplexed operation, particularly with dense packing of the optical wavelengths (or, essentially, fine frequency spacing), offers the potential for a fiber information- carrying capacity which is many orders of magnitude in excess of that

10、 obtained using copper cables or a wideband radio system.虽然可用光纤带宽将进一步扩展到光载波频率,很明显,这个参数由于使用单一光载波信号而被限制。因此提高了带宽利用率的光纤可以通过传输多个光信号,每个信号在处在不同中心波长,同时在相同的纤维来实现。波分多路复用操作,特别是致密堆积的光波长(或者,从本质上讲,良好的频率间隔),为纤维信息提供了潜力承载能力，即许多数量级超过获得使用的铜电缆或宽带无线电系统。(b) Small size and weight. Optical fibers have very small diameters

11、which are often no greater than the diameter of a human hair. Hence, even when such fibers are covered with protective coatings they are far smaller and much lighter than corresponding copper cables. This is tremendous boon towards the alleviation of duct congestion in cities, as well as allowing fo

12、r an expansion of signal transmission within mobiles such as aircraft, satellites and even ships.(b)小尺寸和重量。光纤有非常小的直径,通常不超过一根头发丝的直径。因此,即使当这些纤维被保护膜覆盖也远比相应的铜电缆更小、更轻。这是巨大的好处，对于减轻在城市的管道拥堵,以及允许扩大手机内的信号传输，例如飞机、卫星和船只。(c) Electrical isolation. Optical fibers which are fabricated from glass, or sometimes a pl

13、astic polymer, are electrical insulators and therefore, unlike their metallic counterparts, they do not exhibit earth loop and interface problems. Furthermore, this property makes optical fiber transmission ideally suited for communication in electrically hazardous environments as the fibers create

14、no arcing or spark hazard at abrasions or short circuits.(c)电气隔离。被玻璃、有时一个塑料聚合物制成的光纤是电绝缘体,因此,与金属类不同的是,他们并没有表现出接地环路和接口问题。此外,这个属性使光纤传输理想地适合电危险环境中的通信，因为纤维没有制造处于磨损或短路的电弧或火花危险。(d) Immunity to interference and cross-talk. Optical fibers form a dielectric wave-guide and are therefore free from electromagnet

15、ic interference (EMI), radio frequency interference (RFI), or switching transients giving electromagnetic pulse(EMP).Hence the operation of an optical fiber communication system is unaffected by transmission through an electrically noisy environment and the fiber cable requires no shielding from EMI

16、. The fiber cable is also not susceptible to lightning strikes if used overhead rather than underground. Moreover, it is fairly easy to ensure that there is no optical interference between fibers and hence, unlike communication using electrical conductors, cross-talk is negligible, even when many fi

17、bers are cabled together.(d)免疫干扰和串音。光纤组成一个介质波导,因此不受电磁干扰(EMI),射频干扰(RFI),或切换瞬变电磁脉冲(EMP)。因此,光纤通信系统的操作不会被通过电噪声环境和不需要屏蔽EMI的光纤电缆的传输所影响。光纤电缆如果架在顶部而不是地下也不容易受到雷击。此外,它是相当容易确保没有光学纤维之间的干扰,因此,不同于通信电导体的交流，串声是可以忽略的,即使许多纤维连接在一起。(e) Signal security. The light from optical fibers does not radiate significantly and th

18、erefore they provide a high degree of signal security. Unlike the situation with copper cables, a transmitted optical signal cannot be obtained from a fiber in a noninvasive manner (i. e. without drawing optical power from the fiber). Therefore, in theory, any attempt to acquire a message signal tra

19、nsmitted optically may be detected. This feature is obviously attractive for military, banking and general data transmission (i.e. computer network) applications.(e)安全信号。来自光纤的光不会有显著地辐射,因此它们提供高级的信号安全。不像铜电缆的情况,传输光信号不能用非侵入性的方式(即没有画从光纤光功率)从纤维获得。因此,理论上,任何试图想获得一个光信号传输的消息可能被检测到。这个特性显然是对军事,银行和通用数据传输(即计算机网络)

20、应用程序有吸引力。(f) Low transmission loss. The development of optical fibers over the last twenty years has resulted in the production of optical fiber cables which exhibit very low attenuation or transmission loss in comparison with the best copper conductors. Fibers have been fabricated with losses as lo

21、w as 0.2 dB/km and this feature has become a major advantage of optical fiber communications. It facilitates the implementation of communication links with extremely wide repeater spacing (long transmission distances without intermediate electronics), thus reducing both system cost and complexity. T

22、ogether with the already proven modulation bandwidth capability of fiber cable this property provides a totally compelling case for the adoption of optical fiber communication in the majority of long-haul telecommunication applications.(f)低传输损耗。在过去的20年，相比最好的铜导体，光纤的发展导致光纤电缆的生产表现出非常低的衰减或传输损失。制造的纤维损失只有

23、0.2 dB /公里,这一特性已成为光纤通信的主要优势。它有助于实现连接长中继器间距(长传输距离没有中间电子)，因此降低系统的成本和复杂性。与已经证实的光纤电缆的调制带宽能力一起提供了一个完整的引人注目的理由，在大多数长途电信应用程序采用光纤通信。(g) Ruggedness and flexibility. Although protective coatings are essential, optical fibers may be manufactured with very high tensile strengths. Perhaps surprisingly for a glas

24、sy substance, the fibers may also be bent to quite small radii or twisted without damage. Furthermore, cable structures have been developed, which have proved flexible, compact and extremely rugged. Taking the size and weight advantage into account, these optical fiber cables are generally superior

25、in terms of storage, transportation, handling and installation to corresponding copper cables, whilst exhibiting at least comparable strength and durability.3(g)强度和灵活性。虽然防护涂料是必不可少的,非常高的抗拉强度的光纤也许被制造。也许令人惊讶的是玻璃态物质,纤维也可能倾向于相当小的半径或无伤害的扭曲。此外,电缆结构已经开发出来,已经证明了它灵活、紧凑,非常坚固。考虑到尺寸和重量的优势,这些光缆一般在储存、运输、装卸和安装相应的铜电

26、缆具有优越性，同时至少表现出类似的强度和耐用性。3(h) System reliability and ease of maintenance. These features primarily stem from the low loss property of optical fiber cables which reduces the requirement for intermediate repeaters or line amplifiers to boost the transmitted signal strength. Hence with fewer repeaters,

27、system reliability is generally enhanced in comparison with conventional electrical conductor systems. Furthermore, the reliability of the optical components is no longer a problem with predicted lifetimes of 20 to 30 years now quite common. Both these factors also tend to reduce maintenance time an

28、d costs.(h)系统可靠性和易于维护。这些特性主要来源于光纤电缆的低损耗特性,这降低了对中间中继器或线性放大器来提高传输信号强度的要求。因此，与传统的电导体系统相比，用更少的中继器,系统的可靠性通常是增强的。此外,现在很常见，光学组件的可靠性不再是20到30年的预测寿命的问题。这两个因素也倾向于减少维修时间和成本。(i) Potential low cost. The glass which generally provides the optical fiber transmission medium is made from sandnot a scarce resource. So

29、, in comparison with copper conductors, optical fibers offer the potential for low cost line communication. Although over recent years this potential has largely been realized in the costs of the optical fiber transmission medium which for bulk purchases is now becoming competitive with copper wires

30、 (i.e. twisted pairs), it has not yet been achieved in all the other component areas associated with optical fiber communications. For example, the costs of high performance semiconductor lasers and detector photodiodes are still relatively high, as well as some of those concerned with the connectio

31、n technology (demountable connectors, couplers, etc).(i)潜在的低成本。通常提供光纤传输介质的玻璃是由一种稀缺资源砂制成。所以,与铜导体相比,光纤提供潜在的低成本的有线沟通。尽管近年来这种潜力很大程度上光纤传输介质的成本被实现，批量购买它现在成为铜导线(即双绞线)竞争。它还没有在所有其他组件与光纤通信相关的领域实现。例如,高性能半导体激光器和探测器光敏二极管的成本仍然相对较高,以及一些关联的连接技术(可拆卸连接器、耦合器等)。Overall system costs when utilizing optical fiber communic

32、ation on long-haul links, however, are substantially less than those for equivalent electrical line systems because of the low loss and wideband properties of the optical transmission medium. As indicated in (f), the requirement for intermediate repeaters and the associated electronics is reduced, g

33、iving a substantial cost advantage. Although this cost benefit gives a net gain for long-haul links it is not always the case in short-haul applications where the additional cost incurred, due to the electrical-optical conversion (and vice versa), may be a deciding factor. Nevertheless, there are ot

34、her possible cost advantages in relation to shipping, handing, installation and maintenance, as well as the features indicated in (c) and (d) which may prove significant in the system choice.然而,当利用光纤通信在远程链接时，整体系统成本大大低于那些等效电气线路系统，这是因为低损耗和宽带光传输介质的属性。(f)表示,中继器和相关电子产品的需求减少,提供了巨大的成本优势。虽然这个成本效益为长途连接并非总是有额外成本的短途应用程序链接提供了净收益，电力光学转换(反之亦然),可能是一个决定性因素。然而,可能存在其他与运输、搬运、安装和维护相关的的成