【作者】 叶余千；

【导师】 何赛灵；

【作者基本信息】 浙江大学 ， 光学， 2010， 博士

【摘要】 长久以来,人们一直在寻找一种有效的方法来控制光的传输。在近二十年中,光子晶体和人工电磁媒质,这两种人造材料,由于其局域和控制光传输的能力以及它们所具有的超自然的奇异电磁特性,而逐渐成为了光学、电磁学、物理学等多个领域的研究热点。光子晶体是一种由介质(或者金属-介质)周期性排列而成的人工微结构材料,它的电磁特性主要由结构的周期性决定。由于光子晶体的禁带可以限制光的传输,人们已经将其用于实现高Q腔,小型波导,以及微激光器等。同时,利用其特殊的色散曲线可以实现对于光群速度的控制,光束整形,负折射现象和超棱镜效应等。人工电磁媒质往往是由亚波长的共振金属结构单元组成,它的电磁性质主要由单元结构的共振响应所决定。人工电磁媒质的本构参数是灵活可调的,通过合理的设计共振单元可以实现所需的等效介电常数和磁导率。由于这特性,人工电磁媒质已经被广泛的用于实现负折射率、电磁隐身、完美吸波、超透镜和极化控制等。在本论文中,我们将对于包括光子晶体和人工电磁媒质在内的人工微结构材料的特性和运用进行若干研究和探索。本论文中的主要工作如下：1.我们设计一个纯介质波导实现局域的“光轮”现象,并解释了其形成的物理机理,同时研究了禁带边缘由于反向耦合形成的非局域光轮模式。该模式的存在可以使得这个复合波导在很短的长度上获得较大的Q值。2.我们研究了一维EIT(电磁诱导透明)光子晶体的能带结构和等频率曲线随耦合光拉比频率的变化。对于某一特定频率的探针光,仅通过调节耦合光的拉比频率,实现了正折射和负折射两种情形。并研究通过EIT光子晶体的这种可调性来控制光的传输。3.我们设计了太赫兹波段的广角且极化不敏感的人工吸波材料,在1／25波长的厚度上实现了近完美的吸波。通过数值模拟分析了该人工结构的吸波是由于磁偶极子共振所产生。同时,研究了通过多层人工结构之间的共振耦合实现大带宽的吸波。同时我们在实验上验证了该人工结构的单层吸波特性。4.我们设计了双层结构的人工手征电磁媒质,实现了90°偏振旋转器。分析了该人工手征电磁媒质的巨旋光效应,并指出它是由于磁偶极共振的横向耦合产生。同时,我们研究了结构在传播方向上的手征性和交叉极化透射之间的关系。该人工手征电磁媒质所具有的2700°/λ的旋光强度是目前文献中所报道的最大旋光强度。5.我们研究了TE模式的狭缝透射增强。通过在一层表面镀有二维金属线阵列的覆盖层,我们实现了TE模式透射率的800倍的增强。通过数值模拟,分析了狭缝上方金属线的电偶极子共振对于狭缝透射的增强作用。更多还原

【Abstract】 Scientists have long been seeking effective approaches to control and manipulate the light. In the past two decades, two kinds of man-made materials, namely, photonic crystals and metamaterials, have become hot research topics in multidisciplinary community of optics, electromagnetics, physics and material science, since they have remarkable capability of localizing and guiding radiation and provide unprecedented electromagnetic properties and functionalities unattainable from naturally occurring materials.Photonic crystals are composed of periodic dielectric or metallo-dielectric nanostructures that are designed to affect the propagation of electromagnetic waves. The electromagnetic properties of photonic crystals, e.g. phtonic band gap, result from the periodicity of the whole structure. Due to their great ability of controlling the flow of light, photonic crystals have already been used for e.g. high-Q nanocavities, narrow waveguides and microlasers. The dispersive properties of photonic crystals can also be exploited for manipulating the group velocity of light, shaping and compressing optical pulses, and realizing negative refraction and superprism effects.In contrast, metamaterials are usually composed of metallic elements whose size is much smaller than the resonant wavelength. Therefore, the electromagnetic properties of metamaterials depend on the response of each subwavelength element. By properly designing the resonant elements, metamaterial can be an effective medium with desired permittivity and permeability, which has been used to achieve some interesting phenomena, such as negative reflective index, invisibility cloaking, perfect absorption, super lenses and polarization conversion.In this thesis, we study some properties and applications of photonic crystals and metamaterials. Our original works are listed as follow:1. We design a composite dielectric waveguide for the realization of a localized "light wheel", which is numerically demonstrated and explained physically in detail. A delocalized "light wheel" is found at the band gap edge caused by contra-directional coupling between the two waveguides. The delocalized "light wheel" can be used to trap light as a cavity.2. We study on the band structures and equifrequency contours of one-dimensional photonic crystals (PCs), which consist of an electromagnetically induced transparency (EIT) medium and a common dilectric medium,when the coupling Rabi frequency (CRF) of the EIT medium is tuned. It is found that for a probe light at a fixed frequency, either positive or negative refraction in the EIT PC can be realized with a proper CRF. This tunable optical response enables manipulating light flow.3. We design a nearly omni-directional THz absorber for both TE and TM polarizations. The perfect absorption in a thin thickness about 25 times smaller than the resonance wavelength is numerically demonstrated to be caused by the excitation of magnetic polariton. More importantly, by simply stacking the proposed layer structure, the bandwidth of the absorption can be effectively increased due to the hybridization of magnetic polaritons in different layers, which pave a way for broad bandwidth absorber in THz frequency.4.We design a bilayered chiral metamaterial to realize a 90°polarization rotator, whose giant optical activity is due to the transverse magnetic dipole coupling among the metallic wire pairs of enantiomeric patterns. It is demonstrated that it is the chirality in the propagation direction that makes this efficient cross-polarization conversion possible. The optical activity of the present structure is about 2700°/λ, which is the largest optical activity that can be found in literature.5. We report the enhanced transmission of TE waves through an array of subwavelength slits in a thin metallic film at microwave frequencies. By adding a dielectric layer with a metallization of cut wire array, we obtain an 800 fold enhanced transmission through the slits. We numerically demonstrate that the resonant transmission is to due to the excitation of the electric dipole-like resonances of cut wires in close proximity to the apertures of the slits. which effectively coupled the incident wave into the subwavelength slits.更多还原