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题名	铌酸锂薄膜微腔中的非线性过程研究
作者	汪旻
文献子类	博士
导师	程亚
关键词	铌酸锂 Lithium niobate 回音壁模式微腔 Whispering gallery mode microresoantor 非线性光学 Nonlinear optics 相位匹配 Phase matching 光子学分子 Photonic molecule
其他题名	Nonlinear optical processes in lithium niobate thin film whispering-gallery-mode microresonators
英文摘要	回音壁模式微腔的几何结构具有高度旋转对称性。在透明衬底上制备出的回音壁模式光学微腔腔体具有非常光滑的表面，且腔体与外界空气之间存在着明显的折射率差异，因此回音壁模式光学微腔可以有效地通过界面全内反射约束光场，获得光场的显著增强。这一特点使得回音壁微腔成为研究非线性光学的理想载体。在构建回音壁模式光学微腔的各种介质材料中，作为一种传统的非线性光学晶体，铌酸锂晶体兼具较宽的透明窗口（0.4 ~ 5.5 μm）、较大的非线性系数（d33= ? 41.7±7.8 pm/V）和电光系数、极低的吸收损耗（~ 0.17% cm^-1 @1.32 μm）、双折射效应等多种特质，并且与离子掺杂、铁电畴极化等工艺兼容，因此是实现非线性光学微腔中备受关注的衬底材料。 近年来，利用智能剥离技术制备的铌酸锂薄膜逐渐被用于构建铌酸锂微盘腔。相比传统机械抛光工艺制备的毫米级微腔，铌酸锂薄膜微腔在保留了铌酸锂单晶的优良特质的同时，极大地减小了微腔的模式体积，且与多种平面光刻工艺兼容，有望与其他光子学元件（波导、定向耦合器、分束器、微电极等）耦合组成功能更加复杂的光子学回路集成芯片，并已经实现低阈值激射、光频梳、量子光源、光机械等前沿应用，具有更加广阔的应用前景。 目前，铌酸锂薄膜微腔的制备方法主要以电子束光刻和紫外光刻结合反应离子束干法腐蚀为代表的平面光刻技术和以飞秒激光直写结合聚焦离子束研磨的飞秒激光微加工技术两种。前一种技术工艺成熟，具有并行加工的特点，易于实现大规模生产，但是制备工艺相对复杂，需要对薄膜样品做前期的匀胶、曝光复刻等工序，所使用的掩模板造价昂贵，研发周期较长，对仍处于原型制备阶段的铌酸锂薄膜微腔及相关研究而言缺少灵活性。而飞秒激光直写结合聚焦离子束研磨的薄膜微腔制备技术利用飞秒激光直写技术灵活的三维加工特性和聚焦离子束的超高加工精度，可快速实现高品质铌酸锂微腔及其他微纳结构的制备。本论文工作在对飞秒激光直写结合聚焦离子束研磨制备回音壁微腔的工艺进行优化和提升的基础上，拓展以高品质铌酸锂薄膜微腔为基础的集成光子学结构，并开展微腔中非线性光学新现象的研究，主要内容包括： 1、 利用飞秒激光直写结合聚焦离子束研磨技术，优化后期湿法腐蚀工艺实现高Q/V比的悬空铌酸锂微腔，所制备的铌酸锂微腔直径最小可达3.13 μm，品质因子可达~10^4，Purcell因子为884.35。 2、 结合飞秒激光诱导选择性化学镀铜和微腔制备技术，在同一芯片上同平面集成高品质铌酸锂微腔与平行微电极，并演示腔模的电光调制过程。在该系统中观测到共振波长平移量与外加电压的非线性关系，调制效率最高为3.41 pm/V。 3、 成功制备强耦合铌酸锂微盘双腔，当泵浦功率达到21.9 mW以上时，在倍频光附近观测到了级联的四波混频，以及对应振动模式分别为578 cm^-1、581 cm^-1和252 cm^-1的级联受激拉曼散射峰。; Whispering gallery mode (WGM) microresonators possess a high rotational symmetric geometry. WGM optical microresonators fabricated in transparent dielectric materials can provide a smooth equatorial surface and distinct refractive index (RI) differences between the dielectric resonator and surrounding. Light can be tightly confined in the microresonator via a total internal reflection (TIR) and experience an apparent intensity enhancement. This significant characteristic renders WGM microresoantor an ideal platform for nonlinear optics research. Compared with various materials available for constructing WGM microresoantors, lithium niobate (LiNbO3, LN), as a conventional nonlinear optical crystal, is well known for its wide transparent window (0.4 ~ 5.5 μm), large nonlinear coefficients (i.e., d33= ? 41.7±7.8 pm/V), low absorption loss (~0.17 % cm^-1@1.32 μm) and intrinsic birefringence. In addition, the optical properties of LN can be engineered by ion doping and poling the domain structure of ferroelectrics. Therefore, LN has become a prominent substrate for realizing nonlinear optical microresonators. With the development of the ion slicing technique, lithium niobate on insulator (LNOI) platform has been used to build LN thin film microresonator. Unlike millimeter scale LN microresoantor fabricated by mechanical polishing, the LN thin film microresoantor greatly reduces the WGM volume while maintains the intrinsic single crystalline property of LN. The LNOI platform is also compact with lithography techniques. The construction of on-chip integrate photonic circuits on LNOI can be easily achieved by coupling the WGM microresonator with some other functional components such as waveguides, directional couplers, splitters and microelectrodes. Nowadays, WGM microresoantors fabricated on LNOI have been widely used in nonlinear optical frequency conversions, low-threshold lasing, frequency comb, quantum light sources and optomechanics. Currently, LN thin film microresonators are mainly fabricated based on two approaches. The first approach utilizes electron-beam lithography (EBL) or photolithography followed by plasma dry etching, whilst the second approach combines femtosecond laser direct writing with focused ion beam (FIB) milling. The first approach is a mature parallel process with complex procedures, such as spin-coating and development. The mask plates used in the process are expensive and take long design cycle, which lacks of efficiency for microresonator prototyping. However, the second approach offers an extreme flexibility in prototyping high quality LN microresoantors and other types of micro/nano structures by taking the advantages of the 3D micromachining ability of femtosecond laser direct writing as well as the fabrication precision of focused ion beam (FIB). In this dissertation, I utilize the second fabrication technique to develop the integrate photonic structures based on LN thin film microresonators. The performance of the fabricated devices in nonlinear optical frequency conversions is investigated in great detail. The main results and innovations are as follows: 1. We propose a method for fabricating freestanding LN microresonators with high Q/V ratio by femtosecond laser direct writing followed with FIB milling. The subsequent wet etching step is optimized for precise control of the etching rate. The minimum diameter of the LN microresoantor can be 3.13 μm and the Q factor is ~10^4. The Purcell factor of the LN microresonator is calculated to be 884.35. 2. We fabricate an on-chip lithium niobate microresonator with integrated in-plane microelectrodes and demonstrate electro-optic tuning of the WGM of the microresonator. We observed that the resonant wavelength of the WGM possesses a nonlinear dependence on the voltage between the microelectrodes. A high electro-optical tuning coefficient of 3.41 pm/V has been obtained. 3. We demonstrate a photonic molecule (PM) structure composed of two strongly coupled X-cut lithium niobate microdisks of different diameters fabricated using femtosecond laser micromachining and focused ion beam milling. When the pump power is above 21.9 mW, cascaded FWM processes occurr around the second harmonic signal. Meanwhile, stimulated Raman scattering peaks corresponding to LN vibrational modes of 578 cm^-1, 581 cm^-1 and 252 cm^-1 also appears at the wavelengths farther away from the SH wavelength .
学科主题	光学
内容类型	学位论文
源URL	[http://ir.siom.ac.cn/handle/181231/31112]
专题	中国科学院上海光学精密机械研究所
作者单位	中国科学院上海光学精密机械研究所
推荐引用方式 GB/T 7714	汪旻. 铌酸锂薄膜微腔中的非线性过程研究[D].

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