PPLN晶体中谐波转换的时空特性研究
文献类型：学位论文
| 作者 | 林飞 |
| 学位类别 | 硕士 |
| 答辩日期 | 2001 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 钱列加 |
| 关键词 | 准位相匹配 群速度色散 光束质量改善 飞秒光参量放大器 |
| 中文摘要 | 九十年代以来，非线性材料由于技术上的突破，以及光通信等应用领域对其空前的需求，从而变得越加重要。以χ~((2))极性调制铌酸锂(PPLN)品体为代表的准位相匹配(QPM)晶体就是其中之一，它对非线性光学领域产生了极为重要的影响。PPLN晶体有着诸多优秀和新颖的非线性特性，已成为激光技术领域新的研究热点。今天，已被商品化的PPLN晶体被应用于许多重要领域。在对色散效应有特殊要求的飞秒光学领域和高维时空光孤子领域，PPLN晶体提供了一种全新的色散控制方法；在非线性频率变换领域，PPLN晶体被广泛用于二次谐波、光参量振荡器、光参量放大器和光参量产生器；在光通信领域，PPLN晶体已被作为一种极为重要的材料用于各利，光器件，尤其是各种有源和无源的WDM器件。作为一种QPM结构的非线性晶体，PPLN有许多将与应用相关的非线性光学特性有待研究。本论文就是围绕着PPLN晶体中谐波转换的时空特性来展开基础性的研究工作，进一步探索PPLN品体的QPM结构在二阶非线性光学过程中带来的新特性，同时我们又将这些新特性与在非线性光学领域的应用联系起来，拓宽了QPM的应用范围。本论文主要做了三方面的工作，简单介绍如下。首先我们从PPLN的时域特性着手，在第二章里我们对PPLN中感应的群速度色散进行了研究。我们提出一种物理意义清晰且数学形式简洁的方法来研究啁啾PPLN(CPPLN)中的非线性群速度色散。发现不仅谐波可以获得色散，而且在一定条件下基频光也可以在CPPLN中获得色散。讨论了CPPLN的色散特性，并与传统色散元件进行比较。群速度色散控制是飞秒光学领域最为重要的基本问题，因此这章中对QPM物理概念的深入理解和对CPPLN中群速度色散的研究显得十分重要。第三章，我们接着研究PPLN的空域特性。我们通过将PPLN的空域特性和时域特性作一类比，利用时空“等价”性，发现在倾斜非周期PPLN中存在非线性感应的空间相移。我们通过耦合波方程研究了倾斜非周期PPLN中二次谐波感受到的空间相移，结果表明可用来补偿入射基波的任意空间位相畸变。我们发现PPLN晶体的这种全新特性，可为光束质量改善提供一种新的有效途径。我们将其应用在横向位相畸变的半导体激光束的质量改善上，可以获得转换效率近于传统PPLN的具有衍射极限光束质量的谐波输出。PPLN晶体的参量过程中，相互作用光波间的群速度失配非常大，而这是制约其应用于飞秒OPA的关键因素。非共线位相匹配是有望解决此问题的一种全新的方法。因此，在第四章中，我们研究了基于PPLN晶体的飞秒OPA中的非共线位相和群速度匹配，由于其具有准位相匹配结构，非共线匹配方式不同于以BBO为代表的传统晶体。本文分别讨论了非临界位相匹配PPLN和倾斜PPLN两种情况下的匹配过程。对PPLN中非共线参量过程的研究，将为研制低泵浦功率、脉宽小于100飞秒的PPLN OPA提供新的途径。 |
| 英文摘要 | Nonlinear optical materials have become increasingly important since 1990's, owing to the breakthrough in the technology and unprecedented demand driven by rapid expansion in the optical telecommunications network and other applications. As one of these materials, PPLN (period-poled lithium niobate) crystal in which quasi phase matching (QPM) has been implemented through periodic electric field poling, has had a radical impact on nonlinear optics. Recently a wide and strong research interest in it has been excited on account of its many excellent and novel nonlinear optical characteristics. Today PPLN is commercial available, and has been employed in many significant applications. In the fields that require special and strict control of dispersion such as femtosecond optics and hyper-dimension spatiotemporal solitons generation, PPLN provides a novel way to control dispersion; In the fields of nonlinear frequency conversion, PPLN is applied to second harmonic generation (SHG), optical parametric oscillator (OPO), optical parametric amplifier (OPA) and optical parametric generation (OPG); In the fields of optical communication, PPLN is critical materials or a variety of telecom components such as active and passive WDM components. As one of novel crystals with QPM structure, PPLN has more applicable characteristics that need to be investigated. In this thesis, we researched into temporal and spatial nonlinear characteristics induced by second harmonic generation in PPLN, and explored the new characteristics induced by QPM. And we applied these novel characteristics to new significant applications such as beam-quality improvement and femtosecond OPA. So the applications of QPM and PPLN were extended. The main work and achievements are summarized below. Firstly, in chapter 2, we investigated the temporal characteristics in PPLN. A mathematically simple means with clarity of physical concept for investigating nonlinear process induced group velocity dispersion (GVD) in CPPLN was proposed. It was found that not only the second-harmonic pulse but also the fundamental pulse could experience dispersion in CPPLN under certain condition. The characteristic of GVD in CPPLN was discussed and compared with that of conventional dispersion components. In a word, the better understanding of QPM and investigation on nonlinear interactions induced GVD is extremely important because control of dispersion plays a key role in femtosecond optics. Secondly, in chapter 3, we investigated the spatial characteristics in PPLN. First we drew an analogy between the temporal characteristics and spatial characteristics, and found that the harmonic beam experiences a spatial shift in tilted aperiodic PPLN in which the spatial walk-off plays a role analogous to the group velocity mismatching (GVM) in temporal domain. Then by the nonlinear coupled wave equations, we investigated the spatial shift experienced by the harmonic beam in aperiodic PPLN with spatial walk-off, and showed that it can be engineered to compensate arbitrary spatial phase distortions of incident beam. By applying it to improve beam-equality of diode laser beams, diffraction-limited beam quality can be realized without scarifying the conversion efficiency. Finally, in chapter 4, in order to compensate the large GVM accompanied with parametric processes in PPLN, noncollinear phase and group-velocity matching of femtosecond OPA based on periodically poled lithium niobate were discussed, which differ from that based on birefringent phase matched traditional crystals such as BBO. The investigation in PPLN included noncritical phase matched PPLN with d_(33) and tilted PPLN. With noncollinear configuration, the great potentialities to develop a lower energy pumped femtosecond OPA based PPLN with broad tunability were promised. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/16556]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 林飞. PPLN晶体中谐波转换的时空特性研究[D]. 中国科学院上海光学精密机械研究所. 2001. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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