通信工程外文翻譯

1、<p><b>　　附 錄</b></p><p><b>　　一、英語原文</b></p><p>　　Optical fiber</p><p><b>　　Abstract:</b></p><p>　　An optical fiber (or optical

2、 fiber) is a flexible, transparent fiber made of a pure glass (silica) not much thicker than a human hair. It functions as a waveguide, or “l(fā)ight pipe”[1], to transmit light between the two ends of the fiber.[2] The fiel

3、d of applied science and engineering concerned with the design and application of optical fibers is known as fiber optics. Optical fibers are widely used in fiber-optic communications, which permits transmission over lon

4、ger distances and at higher band</p><p>　　Optical fibers typically include a transparent core surrounded by a transparent cladding material with a lower index of refraction. Light is kept in the core by tota

5、l internal reflection. This causes the fiber to act as a waveguide. Fibers that support many propagation paths or transverse modes are called multi-mode fibers (MMF), while those that only support a single mode are calle

6、d single-mode fibers (SMF). Multi-mode fibers generally have a wider core diameter, and are used for short-distance</p><p>　　Joining lengths of optical fiber is more complex than joining electrical wire or c

7、able. The ends of the fibers must be carefully cleaved, and then spliced together, either mechanically or by fusing them with heat. Special optical fiber connectors for removable connections are also available.</p>

8、<p>　　【keywords】 optical Fiber Multi-mode fiber Index of refraction</p><p>　　Total internal reflection absorption </p><p>　　Fiber optics, though used extensively in the modern world,

9、 is a fairly simple, and relatively old, technology. Guiding of light by refraction, the principle that makes fiber optics possible, was first demonstrated by Daniel Colladon and Jacques Babinet in Paris in the early 184

10、0s. John Tyndall included a demonstration of it in his public lectures in London, 12 years later.[3] Tyndall also wrote about the property of total internal reflection in an introductory book about the nature of light in

11、 1</p><p>　　Practical applications, such as close internal illumination during dentistry, appeared early in the twentieth century. Image transmission through tubes was demonstrated independently by the radio

12、 experimenter Clarence Hansell and the television pioneer John Logie Baird in the 1920s. The principle was first used for internal medical examinations by Heinrich Lamm in the following decade. Modern optical fibers, whe

13、re the glass fiber is coated with a transparent cladding to offer a more suitable ref</p><p>　　In 1880 Alexander Graham Bell and Sumner Tainter invented the 'Photophone' at the Volta Laboratory in Wa

14、shington, D.C., to transmit voice signals over an optical beam.[9] It was an advanced form of telecommunications, but subject to atmospheric interferences and impractical until the secure transport of light that would be

15、 offered by fiber-optical systems. In the late 19th and early 20th centuries, light was guided through bent glass rods to illuminate body cavities.[10] Jun-ichi Nishizawa, a Ja</p><p>　　Principle of operatio

16、n</p><p>　　An optical fiber is a cylindrical dielectric waveguide (nonconducting waveguide) that transmits light along its axis, by the process of total internal reflection. The fiber consists of a core surr

17、ounded by a cladding layer, both of which are made of dielectric materials. To confine the optical signal in the core, the refractive index of the core must be greater than that of the cladding. The boundary between the

18、core and cladding may either be abrupt, in step-index fiber, or gradual, in graded-i</p><p>　　Index of refraction</p><p>　　The index of refraction is a way of measuring the speed of light in a m

19、aterial. Light travels fastest in a vacuum, such as outer space. The speed of light in a vacuum is about 300,000 kilometers (186,000 miles) per second. Index of refraction is calculated by dividing the speed of light in

20、a vacuum by the speed of light in some other medium. The index of refraction of a vacuum is therefore 1, by definition. The typical value for the cladding of an optical fiber is 1.52.[34] The core value is typ</p>

21、<p>　　Total internal reflection</p><p>　　When light traveling in an optically dense medium hits a boundary at a steep angle (larger than the "critical angle" for the boundary), the light will

22、 be completely reflected. This is called total internal reflection. This effect is used in optical fibers to confine light in the core. Light travels through the fiber core, bouncing back and forth off the boundary betwe

23、en the core and cladding. Because the light must strike the boundary with an angle greater than the critical angle, only light tha</p><p>　　Multi-mode fiber</p><p>　　Fiber with large core diamet

24、er (greater than 10 micrometers) may be analyzed by geometrical optics. Such fiber is called multi-mode fiber, from the electromagnetic analysis (see below). In a step-index multi-mode fiber, rays of light are guided alo

25、ng the fiber core by total internal reflection. Rays that meet the core-cladding boundary at a high angle (measured relative to a line normal to the boundary), greater than the critical angle for this boundary, are compl

26、etely reflected. The critical an</p><p>　　In graded-index fiber, the index of refraction in the core decreases continuously between the axis and the cladding. This causes light rays to bend smoothly as they

27、approach the cladding, rather than reflecting abruptly from the core-cladding boundary. The resulting curved paths reduce multi-path dispersion because high angle rays pass more through the lower-index periphery of the c

28、ore, rather than the high-index center. The index profile is chosen to minimize the difference in axial propagation</p><p>　　Single-mode fiber</p><p>　　Fiber with a core diameter less than about

29、 ten times the wavelength of the propagating light cannot be modeled using geometric optics. Instead, it must be analyzed as an electromagnetic structure, by solution of Maxwell's equations as reduced to the electrom

30、agnetic wave equation. The electromagnetic analysis may also be required to understand behaviors such as speckle that occur when coherent light propagates in multi-mode fiber. As an optical waveguide, the fiber supports

31、one or more confined t</p><p>　　The waveguide analysis shows that the light energy in the fiber is not completely confined in the core. Instead, especially in single-mode fibers, a significant fraction of th

32、e energy in the bound mode travels in the cladding as an evanescent wave.</p><p>　　The most common type of single-mode fiber has a core diameter of 8–10 micrometers and is designed for use in the near infrar

33、ed. The mode structure depends on the wavelength of the light used, so that this fiber actually supports a small number of additional modes at visible wavelengths. Multi-mode fiber, by comparison, is manufactured with co

34、re diameters as small as 50 micrometers and as large as hundreds of micrometers. The normalized frequency V for this fiber should be less than the first zer</p><p>　　Special-purpose fiber</p><p>

35、;　　Some special-purpose optical fiber is constructed with a non-cylindrical core and/or cladding layer, usually with an elliptical or rectangular cross-section. These include polarization-maintaining fiber and fiber desi

36、gned to suppress whispering gallery mode propagation.</p><p>　　Photonic-crystal fiber is made with a regular pattern of index variation (often in the form of cylindrical holes that run along the length of th

37、e fiber). Such fiber uses diffraction effects instead of or in addition to total internal reflection, to confine light to the fiber's core. The properties of the fiber can be tailored to a wide variety of application

38、s.</p><p>　　Mechanisms of attenuation</p><p>　　Attenuation in fiber optics, also known as transmission loss, is the reduction in intensity of the light beam (or signal) with respect to distance

39、traveled through a transmission medium. Attenuation coefficients in fiber optics usually use units of dB/km through the medium due to the relatively high quality of transparency of modern optical transmission media. The

40、medium is usually a fiber of silica glass that confines the incident light beam to the inside. Attenuation is an important factor lim</p><p>　　Light scattering</p><p>　　The propagation of light

41、through the core of an optical fiber is based on total internal reflection of the lightwave. Rough and irregular surfaces, even at the molecular level, can cause light rays to be reflected in random directions. This is c

42、alled diffuse reflection or scattering, and it is typically characterized by wide variety of reflection angles.Light scattering depends on the wavelength of the light being scattered. Thus, limits to spatial scales of vi

43、sibility arise, depending on the fr</p><p>　　Thus, attenuation results from the incoherent scattering of light at internal surfaces and interfaces. In (poly)crystalline materials such as metals and ceramics,

44、 in addition to pores, most of the internal surfaces or interfaces are in the form of grain boundaries that separate tiny regions of crystalline order. It has recently been shown that when the size of the scattering cent

45、er (or grain boundary) is reduced below the size of the wavelength of the light being scattered, the scattering no lon</p><p>　　UV-Vis-IR absorption</p><p>　　In addition to light scattering, att

46、enuation or signal loss can also occur due to selective absorption of specific wavelengths, in a manner similar to that responsible for the appearance of color. Primary material considerations include both electrons and

47、molecules as follows:</p><p>　　1) At the electronic level, it depends on whether the electron orbitals are spaced (or "quantized") such that they can absorb a quantum of light (or photon) of a spec

48、ific wavelength or frequency in the ultraviolet (UV) or visible ranges. This is what gives rise to color.</p><p>　　2) At the atomic or molecular level, it depends on the frequencies of atomic or molecular vi

49、brations or chemical bonds, how close-packed its atoms or molecules are, and whether or not the atoms or molecules exhibit long-range order. These factors will determine the capacity of the material transmitting longer w

50、avelengths in the infrared (IR), far IR, radio and microwave ranges.</p><p>　　The design of any optically transparent device requires the selection of materials based upon knowledge of its properties and lim

51、itations. The Lattice absorption characteristics observed at the lower frequency regions (mid IR to far-infrared wavelength range) define the long-wavelength transparency limit of the material. They are the result of the

52、 interactive coupling between the motions of thermally induced vibrations of the constituent atoms and molecules of the solid lattice and the incident </p><p>　　Thus, multi-phonon absorption occurs when two

53、or more phonons simultaneously interact to produce electric dipole moments with which the incident radiation may couple. These dipoles can absorb energy from the incident radiation, reaching a maximum coupling with the r

54、adiation when the frequency is equal to the fundamental vibrational mode of the molecular dipole (e.g. Si-O bond) in the far-infrared, or one of its harmonics.</p><p>　　The selective absorption of infrared (

55、IR) light by a particular material occurs because the selected frequency of the light wave matches the frequency (or an integer multiple of the frequency) at which the particles of that material vibrate. Since different

56、atoms and molecules have different natural frequencies of vibration, they will selectively absorb different frequencies (or portions of the spectrum) of infrared (IR) light.</p><p>　　Reflection and transmiss

57、ion of light waves occur because the frequencies of the light waves do not match the natural resonant frequencies of vibration of the objects. When IR light of these frequencies strikes an object, the energy is either re

58、flected or transmitted.</p><p>　　References</p><p>　　Gambling, W. A., "The Rise and Rise of Optical Fibers", IEEE Journal on Selected Topics in Quantum Electronics, Vol. 6, No. 6, pp.

59、1084–1093, Nov./Dec. 2000.</p><p>　　Hecht, Jeff, Understanding Fiber Optics, 4th ed., Prentice-Hall, Upper Saddle River, NJ, USA 2002 (ISBN 0-13-027828-9).</p><p>　　Mirabito, Michael M.A; and Mo

60、rgenstern, Barbara L., The New Communications Technologies: Applications, Policy, and Impact, 5th. Edition. Focal Press, 2004. (ISBN 0-24-080586-0).</p><p>　　Nagel S. R., MacChesney J. B., Walker K. L., &quo

61、t;An Overview of the Modified Chemical Vapor Deposition (MCVD) Process and Performance", IEEE Journal of Quantum Electronics, Vol. QE-18, No. 4, p. 459, April 1982.</p><p>　　Ramaswami, R., Sivarajan, K.

62、 N., Optical Networks: A Practical Perspective, Morgan Kaufmann Publishers, San Francisco, 1998 (ISBN 1-55860-445-6).</p><p>　　VDV Works LLC Lennie Lightwave's Guide To Fiber Optics, http://www.vdvworks.

63、com/LennieLw/ © 2002-6.</p><p><b>　　二、漢語譯文</b></p><p><b>　　摘 要 ：</b></p><p>　　光導(dǎo)纖維，簡稱光纖，是一種達(dá)致光在玻璃或塑料制成的纖維中的全反射原理傳輸?shù)墓鈧鲗?dǎo)工具。微細(xì)的光纖封裝在塑料護(hù)套中，使得它能夠彎曲而不至于斷裂。通常

64、光纖的一端的發(fā)射裝置使用發(fā)光二極管或一束激光將光脈沖傳送至光纖，光纖的另一端的接收裝置使用光敏元件檢測脈沖。包含光纖的線纜稱為光纜。由于光在光導(dǎo)纖維的傳輸損失比電在電線傳導(dǎo)的損耗低得多，更因為主要生產(chǎn)原料是硅，蘊藏量極大，較易開采，所以價格便宜，促使光纖被用作長距離的信息傳遞工具。隨著光纖的價格進(jìn)一步降低，光纖也被用于醫(yī)療和娛樂的用途。</p><p>　　光纖主要分為兩類，漸變光纖與突變光纖。前者的折射率是漸變

65、的，而后者的折射率是突變的。另外還分為單模光纖及多模光纖。近年來，又有新的光子晶體光纖問世。</p><p>　　光導(dǎo)纖維是雙重構(gòu)造，核心部分是高折射率玻璃，表層部分是低折射率的玻璃或塑料，光在核心部分傳輸，并在表層交界處不斷進(jìn)行全反射，沿“之”字形向前傳輸。這種纖維比頭發(fā)絲還細(xì)，這樣細(xì)的纖維要有折射率截然不同的雙重結(jié)構(gòu)分布，是一個非常驚人的技術(shù)。各國科學(xué)家經(jīng)過多年努力，創(chuàng)造了內(nèi)附著法、MCVD法、VAD法等等，

66、制成了超高純石英玻璃，特制成的光導(dǎo)纖維傳輸光的效率有了非常明顯的提高。現(xiàn)在較好的光導(dǎo)纖維，其光傳輸損失每公里只有零點二分貝；也就是說傳播一公里后只損失4.5％。</p><p>　　【關(guān)鍵詞】 光纖 多模 折射 全反射 散射 </p><p>　　光纖雖然在現(xiàn)代世界中廣泛使用，但仍是一個相當(dāng)簡單陳舊的技術(shù)。最早在19世紀(jì)40年代初由丹尼爾·Colladon和巴比涅雅克首次在巴黎展

67、示了通過折射導(dǎo)光的光纖的導(dǎo)光原理。12年后約翰·廷德爾在他的倫敦的公共講座中作了示范。在1870年左右廷德爾還寫了關(guān)于自然光在內(nèi)部全反射的理論的入門書：“當(dāng)光線從空氣中傳遞入水，折射光正朝著垂直彎曲，當(dāng)光線從水到空氣垂直彎曲通過......如果在水中的光與表面垂直包圍的角度大于48度，射線一點也不會穿出水面，將被水面完全反射.這標(biāo)志著限制全反射開始的角度被稱為介質(zhì)的限制角。水，這個角度是48°27'，火石玻璃

68、，它是38°41'，而鉆石，它是23°42'”。未染色的人的頭發(fā)也被作為光纖。</p><p>　　實際應(yīng)用出現(xiàn)在20世紀(jì)初的牙科密切內(nèi)部照明，在20世紀(jì)20年代顯像管傳輸圖像通過被無線電實驗者克拉倫斯·漢塞爾和電視的先驅(qū)約翰·洛吉貝爾德獨立證實。該原則最早是由海因里希·拉姆在其后的十年內(nèi)體檢。</p><p>　　10年之

69、后出現(xiàn)現(xiàn)代光學(xué)纖維是以玻璃纖維涂用透明覆面，以提供更適合的折射率。這之后的發(fā)展則側(cè)重于圖像傳輸?shù)睦w維束。哈羅德·霍普金斯大學(xué)和倫敦帝國學(xué)院的納林德·辛格Kapany通過一個75厘米長束結(jié)合幾千纖維，實現(xiàn)低損耗光傳輸。他們于1954年在“自然”雜志發(fā)表了題為“一個靈活采用靜態(tài)掃描的纖維內(nèi)窺鏡”的文章。在1956年第一個光纖半靈活的胃鏡由羅勒Hirschowitz，C.威爾伯·彼得斯，和Lawrence E.柯

70、蒂斯在密歇根大學(xué)的研究人員獲得專利。在胃鏡發(fā)展的過程中，柯蒂斯生產(chǎn)出第一包層玻璃纖維;而以前的光纖依賴于空氣或不切實際的油脂和蠟為低折射率的包層材料。</p><p>　　1880年亞歷山大·格雷厄姆·貝爾和薩姆納弧形在華盛頓特區(qū)沃爾特實驗室Photophone發(fā)明了通過光束傳輸語音信號。這是電子通信的一種先進(jìn)形式，但是要受大氣干擾，是不切實際的，直到光纖系統(tǒng)提供的可靠的光的傳輸。在19世紀(jì)末

71、和20世紀(jì)初，光被用來透過彎曲的玻璃棒引導(dǎo)燈老照亮體腔。西澤俊一，一個日本東北大學(xué)的科學(xué)家，還提出在1963年使用的光纖通信，正如他于2004年在印度出版的書上所說。西澤發(fā)明的其他技術(shù)，如半導(dǎo)體激光器的光傳輸通道的梯度折射率光纖，對光纖通信的發(fā)展作出了貢獻(xiàn)。第一臺運作的光纖數(shù)據(jù)傳輸系統(tǒng)被證實是德國物理學(xué)家曼弗雷德B?rner于1965年在烏爾姆的德律風(fēng)根實驗室研制成功，這項技術(shù)于1966年獲得了第一項專利。高錕和英國公司的標(biāo)準(zhǔn)電話和電纜

72、（STC）的喬治·A·Hockham率先推廣光纖的衰減可以減少每公里低于20分貝（分貝/公里）的想法，使光纖成為實用的通訊媒介。他們提出可用纖維的衰減是由應(yīng)該被去除的雜質(zhì)而不是由基本物理效應(yīng)如散射所致。他們正確和系統(tǒng)的分析了光纖的光損耗特性，并指出了生產(chǎn)這種纖維所使用的正確材料 - 高純度石英玻璃。這一發(fā)現(xiàn)使得高錕在2009年獲得諾貝</p><p><b>　　運作原理：</

73、b></p><p>　　光纖是圓柱形的介質(zhì)波導(dǎo)，應(yīng)用全反射原理來傳導(dǎo)光線。光纖的結(jié)構(gòu)大致分為里面的核心部分與外面的包覆部分。為了要局限光信號于核心，包覆的折射率必須小于核心的折射率。漸變光纖的折射率是緩慢改變的，從軸心到包覆，逐漸地減小；而突變光纖在核心-包覆邊界區(qū)域的折射率是急劇改變的。</p><p><b>　　折射率</b></p>&l

74、t;p>　　折射率可以用來計算在物質(zhì)里的光線速度。在真空里，及外太空，光線的傳播速度最快，大約為 3 億米／秒。一種物質(zhì)的折射率是真空光速除以光線在這物質(zhì)里傳播的速度。所以，根據(jù)定義，真空折射率是 1 。折射率越大，光線傳播的速度越慢。通常光纖的核心的折射率是 1.48 ，包覆的折射率是 1.46 。所以，光纖傳導(dǎo)信號的速度粗算大約為 2 億米／秒。電話信號，經(jīng)過光纖傳導(dǎo)，從紐約到悉尼，大約 12000 公里距離，會有最低 0.0

75、6 秒時間的延遲。</p><p><b>　　全反射</b></p><p>　　當(dāng)移動于密度較高的介質(zhì)的光線，以大角度入射于核心-包覆邊界時，假若這入射角（光線與邊界面的法線之間的夾角）的角度大于臨界角的角度，則這光線會被完全地反射回去。光纖就是應(yīng)用這種效應(yīng)來局限傳導(dǎo)光線于核心。在光纖內(nèi)部傳播的光線會被邊界反射過來，反射過去。由于光線入射于邊界的角度必須大于臨界角

76、的角度，只有在某一角度范圍內(nèi)射入光纖的光線，才能夠通過整個光纖，不會泄漏損失。這角度范圍稱為光纖的受光錐角，是光纖的核心折射率與包覆折射率的差值的函數(shù)。更簡單地說，光線射入光纖的角度必須小于受光角的角度，才能夠傳導(dǎo)于光纖核心。受光角的正弦是光纖的數(shù)值孔徑。數(shù)值孔徑越大的光纖，越不需要精密的熔接和操作技術(shù)。單模光纖的數(shù)值孔徑比較小，需要比較精密的熔接和操作技術(shù)。</p><p><b>　　多模光纖<

77、;/b></p><p>　　核心直徑較大的光纖（大于 10 微米）的物理性質(zhì)，可以用幾何光學(xué)的理論來分析，這種光纖稱為多模光纖，用于通信用途時，線材會以橘色外皮做為辨識。 </p><p>　　在一個多模突變光纖內(nèi)，光線靠著全反射傳導(dǎo)于核心。當(dāng)光線遇到核心-包覆邊界時，假若入射角大于臨界角，則光線會被完全反射。臨界角的角度是由核心折射率與包覆折射率共同決定。假若入射角小于臨界角，則

78、光線會折射入包覆，無法繼續(xù)傳導(dǎo)于核心。臨界角又決定了光纖的受光角，通常以數(shù)值孔徑來表示其大小。較高的數(shù)值孔徑會允許光線，以較近軸心和較寬松的角度，傳導(dǎo)于核心，造成光線和光纖更有效率的耦合。但是，由于不同角度的光線會有不同的光程，通過光纖所需的時間也會不同，所以，較高的數(shù)值孔徑也會增加色散。有些時候，較低的數(shù)值孔徑會是更適當(dāng)?shù)倪x擇。</p><p>　　漸變光纖的核心的折射率，從軸心到包覆，逐漸地減低。這會使朝著包

79、覆傳導(dǎo)的光線，平滑緩慢地改變方向，而不是急劇地從核心-包覆邊界反射過去。這樣，大角度光線會花更多的時間，傳導(dǎo)于低折射率區(qū)域，而不是高折射率區(qū)域。因此，所形成的曲線路徑，會減低多重路徑色散。工程師可以精心設(shè)計漸變光纖的折射率分布，使得各種光線在光纖內(nèi)的軸傳導(dǎo)速度差值，能夠極小化。這理想折射率分布應(yīng)該會非常接近于拋物線分布。</p><p><b>　　單模光纖</b></p>&

80、lt;p>　　核心直徑小于傳播光波波長約十倍的光纖，不能用幾何光學(xué)理論來分析其物理性質(zhì)。替而代之，必須改用麥克斯韋方程組來分析，導(dǎo)出相關(guān)的電磁波方程。視為光學(xué)波導(dǎo)，光纖可以傳播多于一個橫模的光波。只允許一種橫模傳導(dǎo)的光纖稱為單模光纖。用于通信用途時，線材會以黃色外皮做為辨識[來源請求]。大直徑核心、多橫模的光纖的物理性質(zhì)，也可以用電磁波波動方程分析。結(jié)果會顯示出，這種光纖允許多于一個橫模的光波。這樣的解析多模光纖，所得到的結(jié)果，與

81、幾何光學(xué)的解析結(jié)果大致相同。</p><p>　　波導(dǎo)分析顯示，在光纖內(nèi)的光波的能量，并不是全部局限于核心里。令人驚訝地，特別是在單模光纖里，有很大一部分的能量是以衰減波的形式傳導(dǎo)于包覆。 </p><p>　　最常見的一種單模光纖，核心直徑大約為 7.5–9.5 微米，專門用于傳導(dǎo)近紅外線。多模光纖的核心直徑可以小至 50 微米，或者大至幾百微米。</p><p>

82、;<b>　　特用光纖</b></p><p>　　有些特用光纖的核心或包覆會特別地制作成非圓柱形，通常像橢圓形或長方形。這包括維護(hù)偏極化光纖。</p><p>　　光子晶體光纖是一種新型的光纖，其折射率以規(guī)律性的模式變化（通常沿著光纖的軸向會有圓柱空洞）。光子晶體光纖應(yīng)用衍射效應(yīng)（單獨的或加上全反射效應(yīng)）來局限光波于光纖核心。</p><p>

83、;<b>　　衰減機制</b></p><p>　　在介質(zhì)內(nèi)，光纖的衰減，又稱為傳輸損失，指的是隨著傳輸距離的增加，光束（或信號）強度會減低。由于現(xiàn)代光傳輸介質(zhì)的高質(zhì)量透明度，光纖的衰減系數(shù)的單位通常是 dB/km （每公里長度介質(zhì)的分貝）。因為硅石玻璃纖維能夠滿足嚴(yán)格的規(guī)定，局限光束于內(nèi)部，傳輸介質(zhì)材料大多是由硅石玻璃纖維制成的。 </p><p>　　阻礙數(shù)字信號

84、遠(yuǎn)距離傳輸?shù)囊粋€重要因素就是衰減。因此，減少衰減是光纖光學(xué)研究的必然目標(biāo)。經(jīng)過多次實驗得到的結(jié)果，顯示出光散射和吸收是造成光纖衰減的主要原因之一。</p><p><b>　　光散射</b></p><p>　　因為光線的全反射，光線可以傳輸于光纖核心。粗糙、不規(guī)則的表面，甚至在分子層次，也會使光線往隨機方向反射，稱這現(xiàn)象為漫反射或光散射，其特征通常是多種不同的反射角

85、。大多數(shù)物體因為表面的光散射，可以被人類視覺偵測到。光散射跟入射光波的波長有關(guān)?？梢姽獾牟ㄩL大約是 1 微米。人類視覺無法偵測到超小于這尺寸的物體。所以，位于可見物體表面的散射中心也有類似的空間尺寸。光波入射于內(nèi)部的邊界面時，會因為不同調(diào)散射而造成衰減。對于結(jié)晶材料或多晶材料，像金屬或陶瓷，除了細(xì)孔以外，大部分內(nèi)部接口的形式乃晶界，分隔了晶粒尺寸的微小區(qū)域。材料學(xué)專家發(fā)現(xiàn)，假若能將散射中心（或晶界）的尺寸減小到低于入射光波的波長，則光散

86、射的影響會減小很多，可以被忽略。這發(fā)現(xiàn)引起更多有關(guān)透明陶瓷材料的研究。 類似地，在光學(xué)光纖內(nèi)，光散射是由分子層次的不規(guī)則玻璃結(jié)構(gòu)所造成的。很多材料學(xué)專家認(rèn)為玻璃無疑是多晶材料的極限案例。而其展現(xiàn)出短距離現(xiàn)像的疇域 ，則是金屬、合金、玻璃、陶瓷等等的基礎(chǔ)建筑材料。散布在這些疇域之間，有很多微結(jié)構(gòu)缺陷，是造成光散射的最理想地點。當(dāng)光學(xué)倍率變高時，光纖的非線性光學(xué)行為也可能會造成光散射。</p><p><b&g

87、t;　　紫外線和紅外線吸收</b></p><p>　　除了光散射以外，光纖材料會選擇性地吸收某些特定波長的光波，這也會造成衰減或信號損失。吸收光波的機制類似顏色顯現(xiàn)的機制。</p><p>　　1.在電子層次，光纖材料的每種組成原子，其不同的電子軌域的能級差值，決定了光纖材料能否吸收某特定頻率或頻率帶的光子。這些特定頻率或頻率帶的光子，大多屬于紫外線或可見光的頻區(qū)。這就是很多

88、可見物質(zhì)顯示出顏色的機制。</p><p>　　2.在原子或分子層次，振動頻率、堆積結(jié)構(gòu)、化學(xué)鍵強度等等，這些重要因素共同決定了材料傳輸紅外線，遠(yuǎn)紅外線，無線電波，微波等等長波的能力。 </p><p>　　在設(shè)計任何透明光學(xué)元件前，必須先知道材料的性質(zhì)和限制，然后才能選擇適當(dāng)?shù)牟牧?。任何材料在低頻率區(qū)域的晶格吸收特性，也賦予了這材料對于這低頻率光波的透明限制。這是組成的原子或分子的熱感應(yīng)

89、振動，和入射光波之間，相互耦合的結(jié)果，在。因此，在紅外線頻區(qū)（＞ 1 微米），每一種材料都要避開這些由于原子或分子振動機制而產(chǎn)生的吸收區(qū)域。因為某特定頻率的紅外線光波，恰恰好匹配了，某種材料的原子或分子的自然振動頻率，這種材料會選擇性地吸收這特定頻率的光波。由于不同的原子或分子有不同的自然振動頻率，它們會選擇性地吸收不同頻率（或不同頻率帶）的紅外線光波。由于光波頻率不匹配光纖材料的自然振動頻率，會造成光波的反射或透射。當(dāng)紅外線光波入射于

90、這不匹配的光纖材料，一部分能量會被反射，另一部分能量會被透射。</p><p><b>　　參考文獻(xiàn)：</b></p><p>　　Gambling, W. A., "The Rise and Rise of Optical Fibers", IEEE Journal on Selected Topics in Quantum Electronic

91、s, Vol. 6, No. 6, pp. 1084–1093, Nov./Dec. 2000.</p><p>　　Hecht, Jeff, Understanding Fiber Optics, 4th ed., Prentice-Hall, Upper Saddle River, NJ, USA 2002 (ISBN 0-13-027828-9).</p><p>　　Mirabit

92、o, Michael M.A; and Morgenstern, Barbara L., The New Communications Technologies: Applications, Policy, and Impact, 5th. Edition. Focal Press, 2004. (ISBN 0-24-080586-0).</p><p>　　Nagel S. R., MacChesney J.

93、B., Walker K. L., "An Overview of the Modified Chemical Vapor Deposition (MCVD) Process and Performance", IEEE Journal of Quantum Electronics, Vol. QE-18, No. 4, p. 459, April 1982.</p><p>　　Ramasw

94、ami, R., Sivarajan, K. N., Optical Networks: A Practical Perspective, Morgan Kaufmann Publishers, San Francisco, 1998 (ISBN 1-55860-445-6).</p><p>　　VDV Works LLC Lennie Lightwave's Guide To Fiber Optics