《通信与电子信息科技英语》课件unit 12.ppt

1、Fiber OpticNew words and phrases 1 fiber n.纤维 fiber optic(optical fiber)光纤(光纤电缆)2 innovation n.革新，技术革新，新方法3 immunity n.抗扰性，免除性，免疫(性)immune adj.免疫的;免受(伤害)的4 direct vt.引导，导引5 propagate v.传播6 refraction n.折射，折射度 refract vt.折射refractiveadj.折射的7 index n.指数，指标，索引 (pl.indices)refractive index（index of refr

2、action）折射率8 external adj.外部的；n.外部,外面 external interference 外界干扰9 interception n.截取，窃听，监听10 abundant adj.丰富的,充裕的11 perceive v.察觉,感知Fiber Optic12 appreciation n.了解,懂得13 sine n.正弦14 incidence n.入射 angle of incidence（incidence angle）入射角15 critical adj.临界的，决定性的，极限的 critical angle 临界角16 dielectric n.电介质,绝

3、缘材料17 waveguide n.波导,波导管18 core n.（光纤）纤芯19 cladding n.包层20 sheath n.外皮，护层21 jacket n.护套，外壳22 govern v.支配，决定，起决定影响23 assembly n.装配,组合Fiber Optic24 radius n.半径(pl.radii)25 possess vt.有，具有，拥有26 knot n.结点，节27 diameter n.直径28 wavelength n.波长29 nanometer n.纳米，毫微米 30 perpendicular adj.垂直的，正交的 perpendicular

4、 to 与垂直，垂直于31 zigzag adj.之字形的，Z字形的32 opaque adj.不传导的,不透明的33 destructive adj.破坏(性)的destructivelyadv.破坏地34 modal adj.n.模态(的)，形式(上的)35 bounce vi.反跳(弹);反射36 broaden vt.加宽，扩展Fiber Optic37 differentiate vt.区分,区别38 predefine n.预先确定（规定），预定义39 preclude vt.阻碍，妨碍40 outline vt.略述，概括地论述 41 uniform adj.均匀的，一致的42

5、mono (前缀)单，单一，一monomoden.单模43 dispersion n.色散 44 profile n.曲线，分布图refractive index profile 折射率分布45 devise vt.设计，发明46 chromatic adj.有色的，彩色的chromatic dispersion色散1 come of age 成年,到法定年龄,发达,充分发展2 freedom from 免除3 at the edge of 在的边缘4 Snells law 斯涅尔（折射）定律Fiber Optic5 multimode fiber 多模光纤6 single mode fibe

6、r(singlemode fiber)单模光纤7 clad fiber 包层光纤,涂层纤维8 parallel to 与平行,平行于9 light ray 光线10 light beam 光束11 back and forth 来来往往地,来回地12 modes of propagation（propagation mode）传播模，传播波型13 multimode propagation 多模传播14 optical receiver 光接收器 optical communication receiver 光通信接收机15 error rate 误码率Fiber Optic16 destru

7、ctive interference 破坏性干扰，相消(性)干扰17 gradedindex fiber 渐变折射率光纤 gradedindex multimode fiber 渐变折射率多模光纤18 steppedindex fiber 阶跃折射率光纤19 intermodal dispersion 模间色散Fiber Optic Optical fiber transmission has come of age as a major innovation in telecommunications.Such systems offer extremely high bandwidth,f

8、reedom from external interference,immunity from interception by external means,and cheap raw materials(silicon,the most abundant material on Earth).Fundamentals of Fiber Optic Systems Optical fibers guide light rays within the fiber material.They can do this because light rays bend or change directi

9、on when they pass from one medium to another.They bend because the speed of propagation of light in each medium is different.This phenomenon is called refraction.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 you ar

10、e directly over the object,it appears to befarther away than it really is.This effect occurs because the speed of the light rays from the object increases as the light rays pass from the water to the air.This causesthem to bend,changing the angle at which you Fiber Opticperceive the object.them to b

11、end,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.Snells Law 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 th

12、e angle of refraction is equal to the ratio of the propagation velocities of the wave in the two respective media.This is equal to a constant that is the ratio of the refractive index of the second medium to that of the first.Written as an equation,Snells Law looks like this:sinA1/sinA2=V1/V2=K=n2/n

13、1In this equation,A1 and A2 are the angles of incidence and refraction,respectively.V1 and V2 are the velocities of propagation of the wave in the two media.n1 and n2 are the indices of refraction of the two media.The parameters are demonstrated graphically in Fig.12.1.In each case,A1 is the angleof

14、 incidence,and A2 is the angle of refraction.The index of refraction(n1n2)of refraction of material 1,n1,is greater than the index of refraction of material 2,n2.This means that the velocity of Fiber Opticpropagation of light is greater in material 2 than in material 1.Fig.12.1(a)demonstrates how a

15、light ray passing from material 1 to material 2 is refracted in material 2 when A1 is less than the critical angle.Fig.12.1(b)demonstrates the condition that exists when A1 is at the critical angle and the angle A2 is at 90dg.The light ray is directed along the boundary between the two materials.As

16、shown in Fig.12.1(c),any light rays that are incident at angles greater than A1 of Fig.121(.b)will be reflected back into material 1 with angle A2 equal to angle A1.The condition in Fig.12.1(c)is the one of particular interest for optical fibers.Exercises.Please translate the following words and phr

17、ases into Chinese.1.light beam2.propagation mode3.refractive index profile 4.chromatic dispersion 5.optical receiver 6.external interference 7.error rate8.dielectric 9.light ray10.clad fiber11.destructive interference12.steppedindex fiber光束光束传播模传播模折射率分布折射率分布色散色散光接收器光接收器外界干扰外界干扰误码率误码率电介质电介质,绝缘材料绝缘材料光

18、线光线包层光纤，涂层纤维包层光纤，涂层纤维破坏性干扰，相消破坏性干扰，相消(性性)干扰干扰阶跃折射率光纤阶跃折射率光纤Exercises.Please translate the following words and phrases into English.1.波导（管）2.临界角 3.纳米4.光纤通信系统5.光纤传输6.单模光纤7.渐变折射率多模光纤waveguidecritical anglenanometeroptical communications systemoptical fiber transmissionsingle mode fiber(singlemode fiber

19、)gradedindex multimode fiberExercises8.波长9.斯涅尔定律10.折射率11.折射角12.破坏性干扰13.多模传输14.光通信接收机15.入射角16.光纤wavelength Snells lawrefractive index(index of refraction)refraction angle(angle of refraction)destructive interferencemultimode transmissionoptical communication receiver angle of incidence(incidence angl

20、e)fiber optic(optical fiber)Exercises.Fill in the blanks with the missing word(s).1.Optical fiber transmission has come of age as a major innovation in telecommunications.2.The ray propagates in this zigzag fashion down the core until it reachesthe other end.3.Light ray A enters the fiber perpendicu

21、lar to the face of the core and parallel to the axis.4.In addition to pointers,a significant portion of the overhead bytes in the STS1 frame are reserved for management data,enabling networkmanagement functions to include loopback,bit error rate testing,and collection and reporting of performance st

22、atistics to be carried(carried,to be carried,carrying,having carried)within the SONET frame.5.This is because modal delay spreading broadens the pulses in the time doain.Exercises6.Rays entering the fiber at differing angles are refracted varying numbers of times as they move from one end to the oth

23、er and consequently do not arrive at the distant end with the same phase relationship as when they started.7.The effect of pulse spreading is to make it difficult or impossible for an optical receiverto differentiate one pulse from another after a given transmission distance.8.Because most optical c

24、ommunications systems transmit information in digital form consisting of pulses of light,the effect of modal delay spreading limits the capability of the fiber to transport(transporting,to transport,transported)recognizable pulses.9.The result of the difference in the refractive indices keeps light

25、flowing(flowing,flow,flowed,to flow)through the core after it gets into the core,even if the fiber is bent(bent,bending,bend)or tied(tied,tying,tie)into a knot.10.The ray enters into the cladding and propagates into,or is absorbed,into the cladding and jacket(which is opaque to light).Exercises.Answ

26、er the following questions according to the text.1.What are the benefits of optical fiber transmission systems?Opticalfiber systems offer extremely high bandwidth,freedom from external interference,immunity from interception by external means,and cheap raw materials(silicon,the most abundant materia

27、l on Earth).2.Tell the Snells law in your own words in English.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 propagation velocities of the wave in the two respectivemedia.Exercises3.Please give some typical parameter values design

28、ed for a multimode fiber.Following are some typical values for a multimode fiber:An operating light wavelength of 0.8 micrometers(m)A core index of refraction nc of 1.5A cladding index of refraction nof 1.485(=0.99nc)A core diameter of 50,62.5,or 100 m A cladding thickness of 37.5 m4.What is a multi

29、mode fiber and what is a singlemode fiber?What are the differences between them?Singlemode fiber,also known as monomode,has a uniform refractive index.This type of fiber permits only a single light ray to pass through the cable,and no destructive interference between rays will occur.These fibers are

30、 called single mode fibers.The differing angles of entry are called modes of propagation(or just modes),and a fiber carrying several modes is called a multimode fiber.One of the principal differences between singlemode and multimode fibers is that most of the power in the multimode fiber travels in

31、the core,whereas,in singlemode fibers,a large fraction of the power is propagated in the cladding near the core.Exercises5.How many kinds of optical fibers can we classify by its type of refractive index and what are they?4 classifications.They are:stepped index fiber,graded index fiber,singlemode f

32、iber,graded index multimode fiber6.Please describe the composition of the optical fiber.An optical fiber is a dielectric(nonconductor of electricity)waveguide madeof glass or plastic.It consists of three distinct regions:a core,the cladding,and a sheath or jacket.The sheath or jacket protects the fiber but does not govern the transmission capability of the fiber.