中山復(fù)試專業(yè)英語(yǔ)

1、專 業(yè) 英 語(yǔ) Specialized English Unit 7：第二部分 通信技術(shù) Fiber Optic光纖Specialized English on Communication Engineering Snells Law(斯涅爾定律)相關(guān)背景知識(shí)n1n2A1 (angle of incidence)A2(angle of refraction)Specialized English on Communication Engineering NEW WORDS AND PHRASES interference n.干涉;干擾propagate v. 傳播; propagation

2、n. refraction n. 折射；refractive index v. 折射率core n. （光纖）纖芯cladding n. 包層 dispersion n. 色散profile n. 曲線，分布圖 multimode fiber 多模光纖single-mode fiber 單模光纖 graded-index fiber 漸變（折射率）光纖stepped-index fiber 階躍（折射率）光纖 Specialized English on Communication Engineering Optical fiber transmission has come of age a

3、s a major innovation in munications. munications：電訊, 長(zhǎng)途通訊, 無(wú)線電通訊, 電信學(xué)光纖傳輸作為電信業(yè)一項(xiàng)重大變革的時(shí)代已經(jīng)到來(lái)。TEXTSpecialized English on Communication Engineering Such systems offer extremely high bandwidth, freedom from external interference, immunity from interception by external means, and cheap raw material (sili

4、con, the most abundant material on the Earth). bandwidth：帶寬； external interference：外界干擾interception ：中途奪取, 攔截,偵聽(tīng)；raw material：原料 光纖通信系統(tǒng)提供了極寬的帶寬，它不受外界干擾，不能通過(guò)外部手段進(jìn)行信號(hào)截取，它的原材料是廉價(jià)的（硅，地球上最豐富的物質(zhì)）。Specialized English on Communication Engineering Optical fibers guide light rays within the fiber material. Th

5、ey can do this because light rays bend or change direction when they pass from one medium to another. light rays ：光纖medium ：介質(zhì)，媒介Fundamentals of Fiber Optic SystemSpecialized English on Communication Engineering They bend because the speed of propagation of light in each medium is different. This ph

6、enomenon is called refraction. speed of propagation：傳播速度phenomenon：現(xiàn)象refraction：折射光線發(fā)生彎曲是因?yàn)楣獾膫鞑ニ俣仍诟鞣N介質(zhì)中是不同的。這種現(xiàn)象就稱作折射。Specialized English on Communication Engineering One common example of refraction occurs when you stand at the edge of a pool and look at an object at the bottom of the pool. Unless

7、you are directly over the object, it appears to be farther away than it really is. 當(dāng)你站在湖邊，看湖底的一個(gè)物體時(shí)，就會(huì)發(fā)生最普通的折射的例子。如果你不是在物體的正上方，這個(gè)物體就會(huì)看起來(lái)比他真實(shí)的位置更遠(yuǎn)。Specialized English on Communication Engineering This effect occurs because the speed of the light rays from the object increases as the light rays pass f

8、rom the water to the air. light rays：光線發(fā)生這種效應(yīng)是因?yàn)?，?lái)自物體的光線從水中進(jìn)入空氣時(shí)，其速度會(huì)增加。 Specialized English on Communication Engineering This causes them to bend, changing the angle at which you perceive the object. You can obtain an appreciation for the manner by which light flows by focusing upon Snells Law. per

9、ceive ：察覺(jué)，感知, 感到這使得光線發(fā)生彎曲，改變了觀察物體的角度。通過(guò)Snell定律可以理解光線遵循的傳播方式。Specialized English on Communication Engineering How optical fibers work can be explained by Snells Law, which states that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is equal to the ratio of the p

10、ropagation velocities of the wave in the two respective media.the ratio of A to B：表示A與B之比the angle of refraction：折射角 the angle of incidence：入射角propagation velocities：傳播速度光纖的工作原理可通過(guò)斯涅爾折射定律來(lái)解釋，該定理闡明，入射角正弦值與折射角正弦值之比等于光波在兩種媒介中的傳輸速度之比。 Specialized English on Communication Engineering the angle of refract

11、ionthe angle of incidenceconstant refractive index of the second medium refractive index of the first medium Snells Law Specialized English on Communication Engineering (a) Ray Escapes(b) Ray is Absorbed(c) Total Internal ReflectionSpecialized English on Communication Engineering Fig.2-1(b) demonstr

12、ates the condition that exists when A1 is at the critical angle and angle A2 is at 90dg.demonstrate:表示，表明critical angle：臨界角（定義為折射角為90度時(shí)的入射角）dg表示角度單位，dg=degree度。 圖2-1(b)表示當(dāng)A1為臨界角， A2為90度時(shí)的情況。Specialized English on Communication Engineering As shown in Fig.2-1 (c), any light rays that are incident at

13、angles greater than A1 of Fig.2-1 (b) will be reflected back into material 1 with angle A2 equal to A1. incident：入射的reflect：反射如圖2-1 (c)所示，入射角大于圖2-1 (b)中的入射角A1的任何入射光線，都會(huì)被以反射角A2 = A1反射回材料1。Specialized English on Communication Engineering An optical fiber is a dielectric (nonconductor of electricity) w

14、aveguide made of glass or plastic.dielectric：電介質(zhì), 絕緣體waveguide ：波導(dǎo)plastic ：塑料光纖是由玻璃或塑料制成的介質(zhì)（電絕緣體）波導(dǎo)。Fiber Composition (光纖結(jié)構(gòu)) Specialized English on Communication Engineering It consists of three distinct regions: a core, the cladding, and a sheath or jacket. The sheath or jacket protects the fiber b

15、ut does not govern the transmission capability of the fiber. cladding：包層 sheath：涂敷層，外殼jacket ：護(hù)套govern ：控制，統(tǒng)治, 支配transmission capability ：傳輸性能Specialized English on Communication Engineering The index of refraction of the assembly varies across the radius of the cable, and the core has a constant or

16、 smoothly varying index of refraction called nc. The cladding region has another constant index of refraction called n. assembly ：集合，組裝radius ：半徑constant ：常數(shù)光纖的折射率沿著半徑變化,纖芯的折射率nc是常數(shù)或者是平滑變化的。包層的折射率n是另一個(gè)常數(shù)。Specialized English on Communication Engineering The core possesses a high refractive index, whe

17、reas the cladding is constructed to have a lower refractive index. The result of the difference in the refractive indices keeps light flowing through the core after it gets into the core, even if the fiber is bent or tied into a knot. assembly ：集合，組裝radius ：半徑constant ：常數(shù)纖芯具有高的折射率，而構(gòu)建的包層具有較低的折射率。折射率

18、差異這一結(jié)果使得光進(jìn)入光纖以后能夠通過(guò)纖芯傳播，即使光纖發(fā)生彎曲或者打結(jié)。Specialized English on Communication Engineering For a fiber designed to carry light in several modes of propagation at the same time (called a multimode fiber), the diameter of the core is several times the wavelength of the light to be carried. mode：模式 multimod

19、e fiber：多模光纖diameter：直徑 wavelength：波長(zhǎng)能夠同時(shí)攜載多個(gè)傳輸模式的光纖（稱作多模光纖），其纖芯直徑是所攜載波長(zhǎng)的幾倍。Specialized English on Communication Engineering Wavelength is a measure of the distance between two cycles of the same wave measured in nanometers (nm), or billionths of a meter, and the cladding thickness will greater than

20、 the radius of the core. nanometer： 納米，簡(jiǎn)寫(xiě)為nm；billionth：十億分之一radius：半徑nana- (前綴)納（諾），10-9波長(zhǎng)是同一個(gè)光波2周之間距離的量度標(biāo)準(zhǔn)，以納米即一米的十億分之一來(lái)表示，光纖包層厚度要大于光纖纖芯的半徑。Specialized English on Communication Engineering A light source emits light at many angles relative to the center of the fiber. In Fig.2-2, light ray A enters

21、the fiber perpendicular to the face of the core and parallel to the axis. light source：光源relative to：相對(duì)于perpendicular to ：垂直于，正交于parallel to：平行于Specialized English on Communication Engineering For optical fibers in which the diameter of the core is many times the wavelength of the light transmitted,

22、 the light beam travels along the fiber by bouncing back and forth at the interface between the core and the cladding. bounce：反射back and forth：來(lái)來(lái)往往地, 來(lái)回地interface：界面，邊界對(duì)于纖芯直徑是光波長(zhǎng)幾倍的光纖，光束通過(guò)在纖芯和包層界面處來(lái)回反射而沿著傳播。Modal Delay（模式延遲）Specialized English on Communication Engineering Rays entering the fiber at

23、differing angles are refracted varying numbers of times as they move from one end to the other and consequently do not arrive at the distant end with the same phase relationship as when they started.phase relationship ：相位關(guān)系當(dāng)光線從光纖的一端傳到另一端時(shí)，以不同角度進(jìn)入光纖的光線，產(chǎn)生的折射的次數(shù)不同，因此到達(dá)遠(yuǎn)端時(shí)，其相位關(guān)系也與開(kāi)始時(shí)不同。 Specialized Eng

24、lish on Communication Engineering The differing angles of entry are called modes of propagation, and a fiber carrying several modes is called a multimode fiber.modes of propagation：傳播模式 multimode fiber ：多模光纖以不同角度進(jìn)入的光線稱作傳播模式，攜帶多種模式的光纖稱作多模光纖。Specialized English on Communication Engineering Multimode p

25、ropagation causes the rays leaving the fiber to interfere both constructively and destructively as they leave the end of the fiber. This effect is called modal delay spreading. constructively：相長(zhǎng)地 destructively ：相消地modal delay spreading ：模式延遲擴(kuò)散當(dāng)光線從光纖末端傳出時(shí)，多模傳輸引起相長(zhǎng)干涉和相消干涉。這種效應(yīng)稱作模式延遲擴(kuò)散。Specialized Engl

26、ish on Communication Engineering Because most optical communications systems transmit information in digital form consisting of pulse of light, the effect of modal delay spreading limits the capability of the fiber to transport recognizable pulses. pulse of light：光脈沖recognizable：可識(shí)別的因?yàn)榇蠖鄶?shù)光纖通信系統(tǒng)都是以光脈

27、沖這種數(shù)字方式傳輸信息的，所以模式延遲擴(kuò)散限制了光纖傳輸可識(shí)別脈沖的容量。 Specialized English on Communication Engineering TIMETIMETIMETIMEPOWERPOWERSpecialized English on Communication Engineering The effect of pulse spreading is to make it difficult or impossible for an optical receiver to differentiate one pulse from another after

28、a given transmission distance. optical receiver ：光接收機(jī)recognizable：可識(shí)別的經(jīng)過(guò)一段特定的傳輸距離后，脈沖擴(kuò)散使得光接收機(jī)很難或不可能將相鄰脈沖彼此區(qū)分開(kāi)來(lái)。 Specialized English on Communication Engineering Thus, after a predefined transmission distance, a multimode fiber either causes a very high error rate or precludes the capability of the p

29、ulse to be recognized and terminates the capability of the cable to be used for communications. error rate ：誤碼率preclude：阻止, 妨阻礙因此，在經(jīng)歷了預(yù)定的傳輸距離之后，多模光纖要么會(huì)導(dǎo)致很高的誤碼率，要么無(wú)法識(shí)別光脈沖，這樣光纖就無(wú)法用于通信中了。 Specialized English on Communication Engineering If the diameter of the fiber core is only a few times the wavelength of the transmitted light (say, a factor of 3), only one ray or mode will be propagated, and no destructive interference between rays will occur.factor：表示“因數(shù)、倍”如果光纖纖芯的直徑僅僅是傳輸光波波長(zhǎng)的幾倍（比如說(shuō)3倍），那么只有一種光或傳輸模式可以傳輸，并且在光線之間不會(huì)產(chǎn)生干涉相消。Specialized English o