【正文】 地方外，不包含其他人或組織已經發(fā)表或公布過的研究成果，也不包含我為獲得 及其它教育機構的學位或學歷而使用過的材料。電光調制器可以對光波進行調幅、調強、調頻、調相和調偏振，應用領 域非常廣闊。通過設定倒格矢參數(shù)，從而彌補晶體雙折射時 o光和 e光折射率不同造成的相位失配，得到較高的電光效率。 關鍵詞：鈮酸鋰，電光效應，耦合波，轉換效率 長沙學院 畢業(yè)設計 (論文 ) II ABSTRACT Electrooptic modulation， based on linear electrooptic effect， is one of widely used modulation technologies． Electrooptic modulator has been widely used for the modulation of the signals of light， including the modulation of amplitude， intensity, frequency phase and polarization. Our works presented in the thesis are based on the wave coupling theory of linear electrooptic effect, a new electromagic theory put forward by She et. al., whose advantage is with rigorous solution for a light wave with arbitrary polarization propagating along any direction under an arbitrary external electric field. The quasiphasematched (QPM) theory was applied to the electrooptic effect. We derived a general wave coupling equations of QPM linear electrooptic effect， and used resultant equations to investigate the electrooptic effect in periodically poled LiNb03 (PPLN)． By setting the parameters of PPLN grating, we pensated for the phase mismatched which is caused by different index of refraction of the oray and eray when birefringence happens. As a result, high conversion efficiency was obtained. By use of Matlab, the influence of temperature, wavelength, electric field intensity and duty cycle of PPLN on the conversion efficiency of the electrooptical effect were investigated numerically. The results indicate that the QPM condition plays an important role in electrooptic coupling； in addition， the coupling is very sensitive to the temperature and incident light wavelength， but has a large tolerance to the incident direction of light. Our research results will be useful for designing the electrooptic modulator. Keywords: LiNbO3, electrooptic effect, coupled wave, conversion efficiency 長沙學院 畢業(yè)設計 (論文 ) III 目 錄 摘 要 ................................................................................................................ I ABSTRACT...................................................................................................... II 第 1 章 緒論 .................................................................................................... 1 電光效應的基本概念 ................................................................................................. 1 線性電光效應的應用 ................................................................................................. 2 電光效應研究的理論發(fā)展 ......................................................................................... 2 本論文的主要工作及其意義 ..................................................................................... 3 第 2 章 LiNbO3的晶體結構和性質 ................................................................. 5 LiNbO3晶體結構 .......................................................................................................... 5 LiNbO3晶體基本性質 .................................................................................................. 6 LiNbO3晶體特點 .......................................................................................................... 6 周期性極化 LiNbO3晶體（ PPLN）的制備 ................................................................. 7 PPLN 晶體的應用 ........................................................................................................ 8 LiNbO3晶體折射率方程 .............................................................................................. 9 第 3 章 線性電光效應的耦合波理論 ............................................................11 第 4 章 LiNbO3 晶體電光效應理論 ............................................................... 17 LiNbO3晶體電光效應的折射率橢球分析法 ............................................................ 17 LiNbO3晶體電光效應線性耦合波理論分析法 ........................................................ 19 第 5 章 PPLN 結構參數(shù)設定 ......................................................................... 22 相關參數(shù)說明 ........................................................................................................... 22 PPLN 結構參數(shù) .......................................................................................................... 22 有效電光系數(shù)設定 ................................................................................................... 23 第 6 章 數(shù)值模擬與討論 .............................................................................. 25 長沙學院 畢業(yè)設計 (論文 ) IV 溫度 T 的改變對轉換效率η的影響 ....................................................................... 25 波長λ的改變對轉換效率η的影響 ....................................................................... 28 外電場 E的改變對轉換效率η的影響 ................................................................... 30 晶體占空比 D的改變對轉換效率η的影響 ........................................................... 30 結 論 ............................................................................................................. 32 參考文獻 ......................................................................................................... 33 附 錄 ............................................................................................................. 34 致 謝 ............................................................................................................. 41 長沙學院 畢業(yè)設計 (論文 ) 1 第 1 章 緒論 電光效應的基本概念 光在各向異 性介質中傳播時 將產生雙折射現(xiàn)象，這種現(xiàn)象是由于晶體結構自身的各向異性所造成的，通常把這種現(xiàn)象稱為自然雙折射。在有些晶體內部由于自發(fā)極化存在著固有電偶極矩 ，當對這種晶體施 加電場時，外電場使晶體中的固有偶極矩的取向傾向于一致或某種優(yōu)勢向， 從而改變晶體的折射率，使本來是各向同性的介質產生雙折射，而使本來是光學各向異性的晶體的雙折射特性發(fā)生變化。可見外加電場后使介質產生極化，從而使介質的折射率發(fā)生改變，進而改變光波在其中的傳播規(guī)律通常用下式表示電場 E引起的折射率的變 化： 20 ......n n aE bE? ? ? ? （ ） 式中 a和 b為常數(shù)， 0n 是不加電場時晶體的折射率。不同的非線性光學現(xiàn)象的產生由所用非線性介質的性質和所產生 現(xiàn)象的物理條件 定。正是 由于這種可控性，使電光效應在光電子技術中獲得了廣泛的應用。這些年來，