本文選題：中心對(duì)稱晶體　切入點(diǎn)：b軸偏壓　出處：《山東大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：光折變空間孤子具有在低功率、短時(shí)間內(nèi)形成且能穩(wěn)定傳播的特性,在光纖通信、光波導(dǎo)等方面也存在著較大的應(yīng)用價(jià)值,因而其一直是科研人員研究的熱門(mén)課題。本文將在實(shí)驗(yàn)中平移中心對(duì)稱光折變晶體鉭鈮酸鉀使其產(chǎn)生空間光孤子,并對(duì)此在理論上進(jìn)行分析。鑒于此,本文的主要工作如下:首先,綜述了光折變空間孤子的相關(guān)研究,重點(diǎn)介紹了國(guó)內(nèi)外關(guān)于中心對(duì)稱光折變晶體中空間光孤子的研究進(jìn)展。其次,簡(jiǎn)述了鉭鈮酸鉀晶體的結(jié)構(gòu)特點(diǎn)、物理性質(zhì)及其相關(guān)應(yīng)用。鉭鈮酸鉀晶體在室溫下具有較強(qiáng)的二次電光效應(yīng);晶體加壓后會(huì)由光學(xué)各向同性體變?yōu)楦飨虍愋泽w,折射率橢球由一個(gè)球體變成橢球體。據(jù)此,推導(dǎo)了不同軸向偏壓的立方相鉭鈮酸鉀折射率變化An的表達(dá)式和晶體光軸的變化;重點(diǎn)分析了 b軸偏壓下晶體折射率變化及折射率橢球方程的數(shù)學(xué)表達(dá)式,分析了施加電場(chǎng)前后晶體折射率曲面、晶體折射率橢球方程的變化情況。再次,通過(guò)在偏壓條件下相對(duì)平移晶體的方式,增強(qiáng)了晶體的光折變效應(yīng),實(shí)驗(yàn)研究了鉭鈮酸鉀晶體中空間光孤子的傳播特性。(1)觀測(cè)了外電場(chǎng)條件對(duì)對(duì)光束傳播形態(tài)的影響,實(shí)驗(yàn)結(jié)果表明:當(dāng)只給晶體施加電壓時(shí),光束會(huì)出現(xiàn)短暫的自聚焦現(xiàn)象,隨后便又恢復(fù)到自散焦?fàn)顟B(tài);當(dāng)給晶體施加不同的電壓時(shí),光束的自聚焦程度會(huì)隨著電壓值的不斷增加而加強(qiáng)。(2)采用控制變量法進(jìn)行了外電場(chǎng)、平移兩個(gè)外勢(shì)場(chǎng)下的對(duì)比實(shí)驗(yàn),結(jié)果表明:只有在外電場(chǎng)作用下進(jìn)行實(shí)驗(yàn),才有可能通過(guò)平移的方法使晶體中形成穩(wěn)定的空間光孤子。(3)觀測(cè)了平移條件對(duì)晶體內(nèi)光束傳播形態(tài)的影響,實(shí)驗(yàn)結(jié)果表明:外電場(chǎng)作用下,移動(dòng)晶體可以使晶體內(nèi)光束發(fā)生自聚焦現(xiàn)象并有自陷成亮空間孤子的趨勢(shì);晶體移動(dòng)的速度越大,光束的自聚焦效應(yīng)越明顯;從外形上看,伴隨著移動(dòng)速度的增加,晶體內(nèi)光束會(huì)逐漸變細(xì)。若晶體在特定的速度下平移,改變給其施加的電壓值,光束的傳播行為也會(huì)發(fā)生相類似的變化效果。最后,根據(jù)文獻(xiàn)及相關(guān)理論分析,修正了平移機(jī)制下中心對(duì)稱光折變晶體中的空間電荷場(chǎng)理論模型。利用模型,理論上分析了晶體平移導(dǎo)致空間光孤子現(xiàn)象形成的原因;數(shù)值求解了新模型理論下光束傳播的波動(dòng)方程;模擬了光束在不同平移速度下的傳播行為及其演化過(guò)程。
[Abstract]:Photorefractive spatial solitons have the characteristics of low power, short time formation and stable propagation. They also have great application value in optical fiber communication, optical waveguide and so on. In this paper, we will translate the center symmetry photorefractive crystal potassium tantalum niobate to produce spatial optical soliton, and analyze it theoretically. The main work of this paper is as follows: firstly, the research on photorefractive spatial solitons is reviewed, and the research progress of spatial solitons in centrosymmetric photorefractive crystals at home and abroad is introduced. The structure, physical properties and related applications of potassium tantalum niobate crystals are briefly described. Potassium tantalum niobate crystals have a strong secondary electro-optic effect at room temperature. The refractive index ellipsoid changed from a sphere to an ellipsoid. Based on this, the expression of refractive index change an of cubic phase potassium tantalum niobate with different axial bias and the change of optical axis of crystal were derived. The mathematical expressions of refractive index change and refractive index ellipsoid equation under b axis bias are analyzed, and the change of crystal refractive index surface and refractive index ellipsoid equation before and after application of electric field are analyzed. The photorefractive effect of the crystal is enhanced by the relative translation of the crystal at bias voltage. The propagation characteristics of spatial soliton in potassium tantalum niobate crystal are experimentally studied. The effect of external electric field on the beam propagation morphology is observed. The experimental results show that when only the voltage is applied to the crystal, the beam will appear a transient self-focusing phenomenon, and then return to the self-defocusing state, and when different voltages are applied to the crystal, The self-focusing degree of the beam will be strengthened with the increasing of the voltage. (2) the control variable method is used to carry out the experiment of the external electric field, and the results show that the experiment is carried out only under the action of the external electric field. It is possible to form a stable spatial soliton in the crystal by the method of translation. The effect of the translational condition on the propagation morphology of the beam in the crystal is observed. The experimental results show that: under the action of the external electric field, The moving crystal can cause the self-focusing of the beam in the crystal and has the tendency of self-trapping into the bright spatial soliton. The faster the crystal moves, the more obvious the self-focusing effect of the beam is. The beam in the crystal will gradually become thinner. If the crystal moves at a specific velocity and changes the voltage applied to it, the propagation behavior of the beam will have a similar effect. Finally, according to the literature and related theoretical analysis, The theoretical model of space charge field in centrosymmetric photorefractive crystals with translational mechanism is modified. By using the model, the causes of spatial soliton phenomena caused by crystal translation are analyzed theoretically. The wave equation of beam propagation under the new model theory is numerically solved, and the propagation behavior and evolution process of the beam at different translational velocities are simulated.
【學(xué)位授予單位】：山東大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：O734

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