電子信息類專業(yè)英語第二版十九單元

1、Passage B Advantages of Optical Fiber Communication光纖通信的優(yōu)點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. 使用沿著玻璃纖維引導的光學載波的通信有許多極具吸引力的特性,當技術被最初構想出來其中一些是明顯的。此外,技術的進步到目前為止已經(jīng)超過甚至最樂觀的預測,而產生額外的優(yōu)勢。因此它對于考慮提供的優(yōu)點和光纖通信在更傳統(tǒng)的電子通信的特色是有用的。在這種情況下我們著手于最初預測的優(yōu)勢然后考慮已成為明顯的技術的附加功能。(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、大的潛在帶寬。頻率在1013赫茲到1016赫茲范圍(通常在1014 Hz的近紅外或105 GHz)的光學載波比金屬電纜系統(tǒng)(即，同軸電纜帶寬約500 MHz)甚至毫米波無線電系統(tǒng)(即，系統(tǒng)目前操作的調制帶寬700 MHz)產生一個更具潛在的傳輸帶寬。目前,對于光纖系統(tǒng)的可用帶寬不是被完全利用,而在幾兆赫超過一百公里的速度調制和數(shù)百兆赫超過三百公里沒有干預電子(中繼器)是可能的。因此,光纖系統(tǒng)的信息傳送能力證明它優(yōu)于最好的銅電纜系統(tǒng)。相比之下，在寬帶同軸電纜系統(tǒng)的損失限制了在一百兆赫帶寬只有幾公里的距離傳輸。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.雖然可用光纖帶寬將進一步擴展到光載波頻率,很明顯,這個參數(shù)由于使用單一光載波信號而被限制。因此提高了帶寬利用率的光纖可以通過傳輸多個光信號,每個信號在處在不同中心波長,同時在相同的纖維來實現(xiàn)。波分多路復用操作,特別是致密堆積的光波長(或者,從本質上講,良好的頻率間隔),為纖維信息提供了潛力承載能力，即許多數(shù)量級超過獲得使用的銅電纜或寬帶無線電系統(tǒng)。(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。光纖有非常小的直徑,通常不超過一根頭發(fā)絲的直徑。因此,即使當這些纖維被保護膜覆蓋也遠比相應的銅電纜更小、更輕。這是巨大的好處，對于減輕在城市的管道擁堵,以及允許擴大手機內的信號傳輸，例如飛機、衛(wèi)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)電氣隔離。被玻璃、有時一個塑料聚合物制成的光纖是電絕緣體,因此,與金屬類不同的是,他們并沒有表現(xiàn)出接地環(huán)路和接口問題。此外,這個屬性使光纖傳輸理想地適合電危險環(huán)境中的通信，因為纖維沒有制造處于磨損或短路的電弧或火花危險。(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)免疫干擾和串音。光纖組成一個介質波導,因此不受電磁干擾(EMI),射頻干擾(RFI),或切換瞬變電磁脈沖(EMP)。因此,光纖通信系統(tǒng)的操作不會被通過電噪聲環(huán)境和不需要屏蔽EMI的光纖電纜的傳輸所影響。光纖電纜如果架在頂部而不是地下也不容易受到雷擊。此外,它是相當容易確保沒有光學纖維之間的干擾,因此,不同于通信電導體的交流，串聲是可以忽略的,即使許多纖維連接在一起。(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)安全信號。來自光纖的光不會有顯著地輻射,因此它們提供高級的信號安全。不像銅電纜的情況,傳輸光信號不能用非侵入性的方式(即沒有畫從光纖光功率)從纖維獲得。因此,理論上,任何試圖想獲得一個光信號傳輸?shù)南⒖赡鼙粰z測到。這個特性顯然是對軍事,銀行和通用數(shù)據(jù)傳輸(即計算機網(wǎng)絡)

20、應用程序有吸引力。(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)低傳輸損耗。在過去的20年，相比最好的銅導體，光纖的發(fā)展導致光纖電纜的生產表現(xiàn)出非常低的衰減或傳輸損失。制造的纖維損失只有

23、0.2 dB /公里,這一特性已成為光纖通信的主要優(yōu)勢。它有助于實現(xiàn)連接長中繼器間距(長傳輸距離沒有中間電子)，因此降低系統(tǒng)的成本和復雜性。與已經(jīng)證實的光纖電纜的調制帶寬能力一起提供了一個完整的引人注目的理由，在大多數(shù)長途電信應用程序采用光纖通信。(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)強度和靈活性。雖然防護涂料是必不可少的,非常高的抗拉強度的光纖也許被制造。也許令人驚訝的是玻璃態(tài)物質,纖維也可能傾向于相當小的半徑或無傷害的扭曲。此外,電纜結構已經(jīng)開發(fā)出來,已經(jīng)證明了它靈活、緊湊,非常堅固?？紤]到尺寸和重量的優(yōu)勢,這些光纜一般在儲存、運輸、裝卸和安裝相應的銅電

26、纜具有優(yōu)越性，同時至少表現(xiàn)出類似的強度和耐用性。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)系統(tǒng)可靠性和易于維護。這些特性主要來源于光纖電纜的低損耗特性,這降低了對中間中繼器或線性放大器來提高傳輸信號強度的要求。因此，與傳統(tǒng)的電導體系統(tǒng)相比，用更少的中繼器,系統(tǒng)的可靠性通常是增強的。此外,現(xiàn)在很常見，光學組件的可靠性不再是20到30年的預測壽命的問題。這兩個因素也傾向于減少維修時間和成本。(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)潛在的低成本。通常提供光纖傳輸介質的玻璃是由一種稀缺資源砂制成。所以,與銅導體相比,光纖提供潛在的低成本的有線溝通。盡管近年來這種潛力很大程度上光纖傳輸介質的成本被實現(xiàn)，批量購買它現(xiàn)在成為銅導線(即雙絞線)競爭。它還沒有在所有其他組件與光纖通信相關的領域實現(xiàn)。例如,高性能半導體激光器和探測器光敏二極管的成本仍然相對較高,以及一些關聯(lián)的連接技術(可拆卸連接器、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,當利用光纖通信在遠程鏈接時，整體系統(tǒng)成本大大低于那些等效電氣線路系統(tǒng)，這是因為低損耗和寬帶光傳輸介質的屬性。(f)表示,中繼器和相關電子產品的需求減少,提供了巨大的成本優(yōu)勢。雖然這個成本效益為長途連接并非總是有額外成本的短途應用程序鏈接提供了凈收益，電力光學轉換(反之亦然),可能是一個決定性因素。然而,可能存在其他與運輸、搬運、安裝和維護相關的的成