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类型 基础研究 预答辩日期 2018-03-09
开始(开题)日期 2016-07-01 论文结束日期 2018-01-22
地点 四牌楼校区五五楼305室 论文选题来源 国家自然科学基金项目     论文字数 6.4 (万字)
题目 复合结构磁光材料的非互易性理论研究
主题词 磁光效应,有效介质理论,滤波器,单向传输,相干背散射
摘要 光是一种电磁波,如何调控光是一个世界性的热点话题,也是集成光子学领域长期存在的难题。不像电子,光子不带电荷,无法直接利用电场或磁场来控制,但是光能跟物质发生相互作用,只要有效地调控物质的属性,就能达到调控光的目的。通过磁场调控光和磁光材料相互作用的法拉第磁光效应和克尔磁光效应就是调控光的有效手段。自然界中材料的磁光效应在可见光频段非常弱,大大限制了磁光效应的应用,因此重新设计材料来增强磁光效应变得非常重要。从最基本的麦克斯韦方程组出发,结合有限元法,分析了磁光效应的电磁特性,并提出了磁光效应的增强方案。利用磁光效应的时间反演对称破缺和洛伦兹非互易性,设计出了左/右旋圆偏振光滤波器和单向传输器件,并研究了磁光材料随机介质的相干背散射现象。具体内容包括: 1、以线偏振光沿磁化方向传播的情况为例,通过非共振和共振的方法增强磁光效应。对于非共振增强方法,利用有效介质理论,在铋铁石榴石薄层中加入负介电常数的金属薄层,调节结构的有效介电常数,使得有效介电常数张量的对角项为真空介电常数,能将克尔旋转角增大到约90°,并且工作带宽非常宽。在共振增强方法中,利用光在铋铁石榴石薄层中的共振,可以同时增强克尔磁光效应和法拉第磁光效应,但是这个方法的工作带宽很窄。 2、光沿磁化方向传播时的两个本征态为左/右旋圆偏振光,对磁光介质重新设计后,使其中一个本征态波矢为虚数,就设计出了衰减型左/右旋圆偏振光滤波器。当设计出来的磁光介质的厚度大于衰减长度时,就能高效地滤出高质量的左旋或右旋圆偏振光,而且工作带宽很宽。此外,在铋铁石榴石薄层中,通过共振情况下的光反射,也能滤出左/右旋圆偏振光,只是这种滤波器的效率不高,且工作带宽很窄。 3、利用磁光材料的非互易性,在一维周期性磁光材料异质结构中和磁光材料异质结的界面处,都能实现光的单向传输。对于TM光在垂直磁化方向的平面内传播,利用准二维传递矩阵法计算后发现,只要包含一层以上的磁光介质层,一维周期性三层异质结构将打破空间反演对称性,能让TM光单向传输,工作带宽取决于能带的非对称区域,并且开关比可以很大。在磁光材料异质结的界面处,光的发散具有“手性”特征,只要利用金属和磁化方向相反的磁光介质阻止光向外发散,就能将TM光束缚在边界上,形成单向传输,工作带宽非常宽,但开关比不大。 4、利用时域有限差分法研究了二维磁光材料随机介质的相干背散射,发现相干散射锥的增强因子不再趋于2,而是趋于1.5。根据多重背散射阶段的时间演化数据分析,发现磁光效应越强时,散射锥的增强因子越快地趋于1.5。另外,所接收到信号散射矩阵的奇异值分布满足随机矩阵理论中的四分之一圆定理,可以确定光在二维磁光材料随机介质中的多重背散射是一个随机散射过程。
英文题目 Theoretical study on the nonreciprocity of magneto-optical hybrid structures
英文主题词 magneto-optical effect, effective medium theory, filter, one-way transmission, coherent backscattering
英文摘要 Light is a kind of electromagnetic wave. Controlling light is a hot topic in this word, which is also a long-standing problem in integrated photonics. Unlike electrons, a photon does not carry a charge and therefore it cannot be manipulated directly by electric or magnetic fields. Fortunately, one can make it by the interaction between light and matter. Faraday magneto-optical effect and Kerr magneto-optical effect are the effective ways to control light through adjusting the interaction between light and magneto-optical materials by magnetic field. However, the weak level of magneto-optical effect goes against the application of natural magneto-optical materials in visible wavelengths, so designing new materials is necessary for enhancing magneto-optical effect. Based on Maxwell equations and finite-element method, the electromagnetic property of magneto-optical effect is analyzed in detail, and then some approaches about the enhancement are introduced. By breaking the time reversal symmetry and the Lorentz reciprocity theorem, light filters and one-way devices are designed with magneto-optical materials, and the coherent backscattering effect is studied numerically from the random magneto-optical media. The main work can be summarized as follows: 1. Focus on the case that linearly polarized light propagates along the magnetization direction of Bismuth iron garnet, the magneto-optical effect can be enhanced by nonresonant and resonant mechanisms. According to the effective medium theory, the permeability tensor of Bismuth iron garnet can be tailored after inserting metallic films. When diagonal terms of the effective permeability tensor are tuned to the vacuum permeability, the corresponding Kerr rotation can be enhanced up to 90° nonresonantly with wide bandwidth. The resonance of light in thick Bismuth iron garnet film can also enhance both Faraday and Kerr magneto-optical effects, while with small rotation and narrow bandwidth. 2. The eigenstates along the magnetization direction of magneto-optical materials are left/right circularly polarized light. The decay-style filters for left or right circularly polarized light can be obtained when the wave vector of one eigenstate is designed to be imaginary by the effective medium theory. Left or right circularly polarized light can be filtered effectively with high quality when the thickness of the filter is longer than the decay length. In addition, Left or right circularly polarized light can also be resonantely reflected by Bismuth iron garnet film. However, both efficient and bandwidth of resonate-style filters are theoretically lower than those of decay-style filters. 3. With the nonreciprocity of magneto-optical materials, one-way transmission of light can be realized both in the one-dimensional magneto-optical heterostructures and on the eage of the magneto-optical heterostructure. For the case that TM light propagates perpendicular to the magnetization direction, it is found by quasi-two-dimensional transfer matrix method that the spatial inversion symmetry can be broken when the unit of periodic heterostructures consists of three different films, in which one or more films are magneto-optical materials. And then, one-way transmission appears with high on-off ratio in the asymmetric part of the band structure. The divergent light manifests chirality along the eage of magneto-optical materials. With the help of metal or other magneto-optical material with opposite magnetization, TM light can be bounded on the eagle and performs one-way transmission with wide bandwidth. 4. By finite-difference time-domain method, the coherent backscattering effect of two-dimentional random magneto-optical media is studied numerically, and it is found that the enhancement factor of the coherent scattering cone tends to 1.5, but not 2 any more. After analyzed the time-evolution data of multiple scattering, it is shown that stronger magneto-optical effect can accelerate the tendency. Furthermore, the distribution of singular values of the scattering matrix follows quarter circle law, indicating the multiple scattering is random in two-dimentional random magneto-optical media.
学术讨论
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学术会议
会议名称时间地点本人报告本人报告题目
中国物理学年会2017年秋季会议 2017/9/7-2017/9/10 成都 非共振和共振增强磁光效应的理论研究
南昌大学物理系学术交流会议 2018/1/15-2018/1/16 南昌 磁光材料中光的单向传输
     
代表作
论文名称
Optimum analysis of a Brownian refrigerator
The impact of energy spectrum width in the energy selective electron low-temperature thermionic heat
A theoretical study on the performances of thermoelectric heat engine and refrigerator with two-dime
Performance analysis of a tunneling thermoelectric heat engine with nano-scaled quantum well
Efficiency at maximum power of thermochemical engines with near-independent particles
 
答辩委员会组成信息
姓名职称导师类别工作单位是否主席备注
黄高山 正高 教授 博导 复旦大学
程迎春 正高 教授 博导 南京工业大学
倪振华 正高 教授 博导 东南大学
吕俊鹏 正高 教授 博导 东南大学
范吉阳 正高 教授 博导 东南大学
      
答辩秘书信息
姓名职称工作单位备注
蒋红燕 其他 讲师 东南大学