基于磁性表面等离激元的电磁波调控与相关光学器件的设计

Metamaterials are composite, artificial materials, consisting of resonant building blocks designed with state-of-the-art configurations,which leads to many exotic phenomena not occurring in nature such as negative refraction, subwavelength imaging, and cloaking. A particular characteristic of the system made of metallic materials is the excitation of surface plasmon polaritons (SPPs). The present project is devoted to invetigating the optical properties and phenomena relevant to "magnetic surface plasmon" (MSP), the magnetic analogue of SPP. It can be excited in the magnetic metamaterials made of ferrite materials. However, the MSP relevant issues are not examined elaborately as the case for the SPP in metallic materials. Besides, different from SPP the time reversal symmetry is broken in the MSP system under the exertion of external magnetic field. It can induce the nonreciprocal transport of the electromagnetic (EM) wave. Based on this feature, we can observe many interesting phenomena and design a series of useful EM devices. Our research is going to concern (i) extending multiple scattering theory, Mie theory, and effectivel medium theory so that we can analyze and simulate the system; (ii) investigating the feasibility to realize unidirectional transmission, cloaking, and imaging and then we are also going to analyze the corresponding optical properties and design the EM devices such as circulator and EM diode; (iii) examining how to realize the negative refraction and subwavelength focusing based on the the magnetic metamaterials under gradient magnetic field; (iv) in particular, the disorder induced excitation of MSP edge mode will be investigated where some propertes similar to the electronic systems can be observed. We are going to analyze its optical property and discover the underlying physics dominating the phenomenon.

特异电磁介质是由亚波长共振单元所构造人工合成材料，在理论上能够设计具备任意电磁参量的电磁波介质，从而实现了自然界常规介质所不具备的光学性质和光学现象。本项目基于铁磁和铁电材料设计新型可调控的磁性特异电磁介质，在该体系中能够激发磁性表面等离激元共振，并且能够引起时间反演对称性的破坏，从而使其具备了极为特别的性质。本项目就是研究与磁性表面等离激元相关的光学现象和光学特性，主要研究内容包括：（1）推广多重散射理论和Mie散射理论以及等效介质理论，从而对该体系进行理论计算和模拟并提取体系的等效电磁参量；（2）探讨单向透射、单向隐身和单向成像的实现方案，并对相关性质进行分析，以设计相关的电磁波器件，如射频环行器和电磁波二极管；（3）研究梯度磁场下，采用磁性特异电磁介质实现负折射和亚波长聚焦的性质；（4）探讨无序磁性特异电磁介质表面的单向界面态激发、以及与其相关性质和物理机制。

根据本项目所提出的研究课题，我们开展了一系列的研究，基本完成了项目中的各项内容。同时，我们也根据本领域的最新进展开展了相关研究，也取得了一定的结果。截至目前，我们的研究成果可概括为以下四个方面：(1) 基于铁磁散射体为基本的共振单元来设计各种类型的界面，由此来探讨这些体系的单向电磁波特性。包括界面态的特征、单向完美吸收、以及磁表面等离激元共振的物理本质。在理论上，我们验证了单向界面态的强抗干扰能力以及外加磁场对工作频率的调控能力；单向完美吸收对角度的依赖关系和工作频率的可调控性质以及各种无序对性质的影响；对于磁性表面等离激元我们也从光子能带角度进行了研究，探讨了它与 Chern 数间的关系以及共振附近的表面态激发状况。(2) 探讨了零折射率相关的体系，包括：各向异性零折射体系以及该壳层对各向同性电磁波辐射的影响、增强辐射的各种方案以及吸收和增益的影响；基于磁性电磁超介质，我们也设计了零折射材料并探讨了它对波前的调控能力，实现了电磁波的聚焦、分束以及准直效应，并考察了外加磁场和温度场对它的调控能力。(3) 设计了梯度电磁 “超表面” 和 “超界面”，考察了电磁波在该体系中的非对称传输性质。采用磁性散射体阵列设计了梯度磁性电磁“超表面”，既研究了单向界面态的特点也探讨了非互易的古斯－汉欣位移；采用纯介质散射体，在复式光子晶体中设计了引入旋转梯度形成梯度界面，即“超界面”，研究了电磁波在两个相反方向上的非对称传输性质。(4) 探讨了光子与微观粒子的相互作用，考察了光波对微观粒子的纵向光力和横向光力作用，既考察了普通的金属粒子也考察了手性粒子的光力特点。本项目的研究成果为我们下一步更为深入研究电磁超介质和电磁“超表面”的电磁波性质奠定了坚实的理论基础，也为我们后续研究项目的开展做好了准备。