【正文】 als. 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 core and cladding may either be abrupt, in stepindex fiber, or gradual, in gradedindex fiber.Index of refraction The index of refraction is a way of measuring the speed of light in a material. 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 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 .[34] The core value is typically .[34] The larger the index of refraction, the slower light travels in that medium. From this information, a good rule of thumb is that signal using optical fiber for munication will travel at around 200 million meters per second. Or to put it another way, to travel 1000 kilometers in fiber, the signal will take 5 milliseconds to propagate. Thus a phone call carried by fiber between Sydney and New York, a 12000 kilometer distance, means that there is an absolute minimum delay of 60 milliseconds (or around 1/16 of a second) between when one caller speaks to when the other hears. (Of course the fiber in this case will probably travel a longer route, and there will be additional delays due to munication equipment switching and the process of encoding and decoding the voice onto the fiber).Total internal reflection 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 be pletely 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 between the core and cladding. Because the light must strike the boundary with an angle greater than the critical angle, only light that enters the fiber within a certain range of angles can travel down the fiber without leaking out. This range of angles is called the acceptance cone of the fiber. The size of this acceptance cone is a function of the refractive index difference between the fiber39。首先我要感謝我的導(dǎo)師，他在我完成論文的過程中，給予了我很大的幫助。 　　31．通道跟蹤 跟蹤一個(gè)通道地信號(hào)值，演示信號(hào)值變化的圖。 圖形演示 ，OSA頻譜、示波器和眼圖，探針和可視化工具列出信號(hào)功率、增益、噪聲系數(shù)和OSNR ，眼圖中超過70次的測量，圖形生成工具可以對(duì)任何參數(shù)掃描的任意結(jié)果進(jìn)行比較 ，直觀的圖形管理器使用戶可以畫出設(shè)計(jì)中使用的幾乎所用的參數(shù)的曲線，生成的圖形組尺寸可變、視角可變換，并將這些視圖轉(zhuǎn)變成可以保存和重新使用的結(jié)果方案圖 ，將復(fù)合圖合并成3D圖 OptiSystem的改進(jìn)這個(gè)軟件的新特性更好的滿足光系統(tǒng)和器件設(shè)計(jì)者的需要，并且反映了Optiwave于客戶之間緊密的聯(lián)系。OptiSystem能使用戶選擇不同的模型，例如自定義增益和噪聲系數(shù)的理想放大器，或者是基于測量或者速率方程靜態(tài)或者動(dòng)態(tài)的解的黑匣子模型。 　　13．并行計(jì)算 如果能夠?qū)蓚€(gè)器件同時(shí)進(jìn)行計(jì)算，那么它們也能在不同的線程中更有效的被調(diào)度。 　　6． 高級(jí)的可視化工具 高級(jí)的可視化工具可以生成OSA頻譜、示波器和眼圖（EYE Diagram）。先進(jìn)的軟件工具使得這些系統(tǒng)的設(shè)計(jì)和分析變得迅速而有效。載波在數(shù)字信號(hào)1或0的控制下通或斷，在信號(hào)為1的狀態(tài)載波接通，此時(shí)傳輸信道上有載波出現(xiàn)；在信號(hào)為0的狀態(tài)下，載波被關(guān)斷，此時(shí)傳輸信道上無載波傳送。所謂穩(wěn)態(tài)波，即是隨機(jī)序列 s(t)的統(tǒng)計(jì)平均分量，即： （）其波形顯然是一個(gè)周期為的周期函數(shù)。對(duì)于馬赫—澤德調(diào)制器，其有較好的啁啾特性，適合用于超長距離的高速率傳輸。其賴以實(shí)施的手段是補(bǔ)償應(yīng)變超晶格生長。超高速通信系統(tǒng)要求外調(diào)制器具有足夠的調(diào)制帶寬、低驅(qū)動(dòng)電壓和高飽和功率，此外高消光比、低啁啾、低插入損耗和低偏振相關(guān)性也是重要因素。先進(jìn)的調(diào)制碼技術(shù)是光通信研究的熱點(diǎn)10Gb/s及以下速率的光通信系統(tǒng)通常使用的是NRZ碼,其實(shí)現(xiàn)簡單成本也較低但是對(duì)40Gb/s和更高速率系統(tǒng)NRZ碼由于對(duì)噪聲、偏振模色散和非線性非常敏感，其傳輸能力受到限制?！娟P(guān)鍵詞】高速 光纖通信 碼型 光譜 模擬仿真ABSTRACTIn recent years, with a new round of technological revolution, human society entered the information age, munication mode has undergone a qualitative change, the people to the performance of the munication system requirements are also increasing,40Gb / s high speed optical fiber transmission system has bee a research hot topic in recent years. 40Gb / s high speed optical fiber transmission system has the following several key technology is the focus of current research:（1）Referring to domestic and foreign literatures, discusses the 40Gb / s high speed optical fiber transmission system relates to the key technology and development status. On the significance and the code selection in high speed optical fiber transmission system mainly uses several code are discussed.（2）Introduced a two modulation technique, and analyzed by using external modulation used by Maher Zehnder modulator ( MZM ) and electric absorption modulator ( EAM ) advantages and disadvantages.（3）This paper analyzes on the zero code (NRZ), zero code (RZ) and carrier inhibition to zero code (CSRZ) and the corresponding difference phase shift keying code (DPSK) several MaXing spectra, and by use of the Fourier transform39。通過計(jì)算，對(duì)三種碼型的光譜進(jìn)行理論分析，同時(shí)對(duì)光的傳輸特性做相應(yīng)的介紹。40Gb/s 高速光纖傳輸系統(tǒng)中有以下幾項(xiàng)關(guān)鍵技術(shù)是目前研究的重點(diǎn)：①低噪聲及寬帶寬的光放大器；②前向糾錯(cuò)碼（FEC ）技術(shù)；③高效的信號(hào)復(fù)用及解復(fù)用技術(shù)；④對(duì)光噪聲及光纖的非線性效應(yīng)有著更高容忍度和更高光譜效率的碼型。盡管如此，10Gb/s的光傳輸系統(tǒng)帶寬仍然有限。光纖技術(shù) 光纖技術(shù)的研究重點(diǎn)就是優(yōu)化色散系數(shù)、色散斜率、有效面積和工作波長范圍以適應(yīng)DWDM系統(tǒng)的傳輸速率、信道間隔、工作波長的不斷變化需要。而且既可用于強(qiáng)度調(diào)制也可用于相位調(diào)制，所以在一般的碼型產(chǎn)生中都采用MZM。馬赫澤德調(diào)制器（MZM）馬赫澤德調(diào)制器又即馬赫澤德干涉儀型調(diào)制器，MZ 型光調(diào)制器有LiNbO3MZ 調(diào)制器、GaAsMZ 調(diào)制器和聚合物MZ 調(diào)制器等幾種。 外調(diào)制 把激光器的產(chǎn)生和調(diào)制分開，用獨(dú)立的調(diào)制器調(diào)制激光器的輸出光而實(shí)現(xiàn)。但在許多實(shí)際的數(shù)字傳輸系統(tǒng)中卻往往采用多進(jìn)制的數(shù)字調(diào)制方式?？梢?guī)定為：前后有相位差 л 代表數(shù)字信息“1”，相位差為 0 代表數(shù)字信息“0”。其主要特點(diǎn)為： 　　1. 器件庫 為了完全發(fā)揮效率，器件模塊應(yīng)該再現(xiàn)真實(shí)器件的實(shí)際的性能，確定由于選擇精度和效率引起的影響。 　　11．狀態(tài)技術(shù)計(jì)算數(shù)據(jù)流 計(jì)算調(diào)度程序根據(jù)選擇的數(shù)據(jù)流模式，通過確定器件模塊的執(zhí)行等級(jí)來控制模擬過程。使用OptiSystem，用戶可以輸入測量過的數(shù)據(jù)來評(píng)估速率方程所需的那些參數(shù)。 　　22． 觀察儀 客戶可以在任何器件使用觀察儀來打開端口數(shù)據(jù)監(jiān)視器，并且存取結(jié)果。用密碼來保護(hù)器件以增加安全性。 由Optisystem 軟件模擬所得的眼圖結(jié)果可知，從圖中可以看出 RZ 和CSRZ 的眼圖差別很小，這是因?yàn)樗鼈兺瑸闅w零碼，區(qū)別在于兩者的占空比不同，CSRZ 的占空比大于 RZ的。4139。4239。第三節(jié) 本章小結(jié)本章節(jié)主要介紹了Optisystem軟件的功能等，以及利用Optisystem軟件對(duì)RZ碼、NRZ碼、CSRZ碼進(jìn)行了模擬仿真，得到了各個(gè)碼型的模擬光譜圖和相應(yīng)的眼圖，并加以簡單分析得出結(jié)論。拖動(dòng)的功能可以更容易和快速的建立連接和在圖形窗口中加入圖形。因此，一個(gè) OSA或WDM分析儀可以加在相同的監(jiān)視器上，一旦一個(gè)計(jì)算完成，就不需要再次運(yùn)算。 對(duì)于隨即數(shù)字發(fā)生器，編碼器和比特序列產(chǎn)生器允許用戶在不同的調(diào)制模式和算法之間進(jìn)行選擇。CIDF域使用運(yùn)行調(diào)度法、支持條件、數(shù)據(jù)相關(guān)迭代和真循環(huán)。 　　2． 器件測量 OptiSystem能讓用戶進(jìn)入那些可以從實(shí)際的器件中測量的參數(shù)。從波形上看不出它們的差別，因此它們的光譜是一樣的。但由此付出的代價(jià)是增加信號(hào)功率和實(shí)現(xiàn)上的復(fù)雜性。如下圖所示： （直接調(diào)制） （外調(diào)制）圖11直接調(diào)制與外調(diào)制而對(duì)于外調(diào)制方式，有兩種相關(guān)的調(diào)制器，即上文所述馬赫澤德干涉儀型調(diào)制器和電吸收（EA）調(diào)制器。用LiNbO3 材料制作的MZ 光調(diào)制器與分布反饋激光器組合應(yīng)用時(shí)，從原理上說，波長啁啾可以為零，且容易滿足系統(tǒng)對(duì)調(diào)制帶寬的要求。每層的折射率和厚度根據(jù)中心波長按光學(xué)增反膜堆設(shè)計(jì)，依靠應(yīng)變超晶格結(jié)構(gòu)實(shí)現(xiàn)與襯底間的晶格匹配。色散管理技術(shù) 目的是在同時(shí)考慮色散和非線性效應(yīng)時(shí)使系統(tǒng)帶寬最大化，從而使色散在光纖鏈路上具有最佳的分布。從10Gbit/s到40Gbit/s，信號(hào)速率提高了4倍，但