双曲特异材料及特异表面的电磁特性与应用研究

Hyperbolic metamaterials (HMMs) are highly anisotropic mediums with hyperbolic dispersion. Such metamaterials are quite different from conventional (uniaxial) crystals in which one of the principal components of their permittivity (permeability) tensors is opposite in sign to the other two principal components. This metamaterial uses the concept of engineering the basic dispersion relation of waves to provide unique electromagnetic modes. Owing to the hyperbolic dispersion of wavevector, HMMs support propagating modes with very large wave vectors (also called high-k waves), which indicates the ultra-high refractive index of materials. Therefore HMMs provide the novel opportunities for electromagnetic manipulation in subwavelength scale, which brings about a rich variety of new physics and novel applications such as negative refraction, sub-diffraction imaging, sub-wavelength modes, spontaneous and thermal emission engineering and so on. .However, the most studies of HMMs have focused on the high-k waves so far. In fact, HMMs not only support high-k waves, but also possess anomalous wavevector dispersion by contrast with isotropic dielectric. When the periodic structures contain with HMMs, the coherent multiple scattering of high-k waves will be induced, which offer an unprecedented way to control the light propagation and thus activate novel physical phenomena. On the other hand, merging the concept of bulk hyperbolic metamaterials and ultrathin metasurfaces has recently led to hyperbolic metasurface which supports extreme confinement of surface plasmon polaritons (SPPs) and the channeling towards specific directions within the sheet. The properties of hyperbolic metasurfaces originate from the near-field interference between high-k waves in HMMs and evanescent waves in air. More importantly, hyperbolic metasurfaces can be used for manipulating the dipole radiation, which possesses special application for planar antenna design. .In this program, we will theoretically and experimentally explore the unique electromagnetic properties of HMMs and metasurfaces. The main works and challenges can be summarized as follows: We firstly investigate the coherent multiple scattering mechanism of high-k waves in photonic crystals containing with HMMs, and then explore dispersion control of photonic band gap or SPPs. We expect to realize dispersionless photonic band gap or SPPs. Later, we investigate near-field interference mechanism in hyperbolic metasurfaces and its unique manipulation for surface waves, and explore its potential application for planar antenna design with miniaturized size and specific radiated direction. The mentioned work above not only can improve people's understanding of HMMs and metasurfaces, but also provide significant guidance for application of HMMs and metasurfaces and design of novel metadevices.

作为一种极端各向异性的特异材料，双曲特异材料支持高k传输波；而在普通材料中这些电磁波以衰逝波形式存在。因而双曲特异材料有着许多奇异的电磁特性。本项目将围绕双曲特异材料及特异表面的奇异电磁特性与应用展开研究。我们首先研究双曲特异材料中高k传输波的相干多重散射，并探索其对光子带隙和表面电磁模式的调控；然后我们研究双曲特异表面的近场干涉效应，并探索其对表面电磁波的调控以及在天线领域的应用。通过上述问题的研究，我们希望一方面能够揭示双曲特异材料中高k传输波与正常介电材料中电磁波的相位补偿效应，实现特殊色散甚至无色散的光子能带或表面电磁模式；另一方面能够揭示双曲特异表面的近场干涉效应机理，并实现对表面电磁波的调控以及对天线辐射的调控。上述问题的研究成果，不仅会加深人们对双曲特异材料及特异表面中电磁波传播基本物理过程的理解，而且可以为双曲特异材料及特异表面的应用与新型电磁器件的研制提供科学基础。

作为一种极端各向异性的特异材料，双曲特异材料支持高k传输波；而在普通材料中这些电磁波以衰逝波形式存在。因而双曲特异材料有着许多奇异的电磁特性。本项目将围绕双曲特异材料及特异表面的奇异电磁特性与应用展开研究。经过四年的研究，我们完成了两个系列的工作，一个是双曲超材料的反常波矢色散特性及其对光子能带以及Tamm等离激元模式的调控，另一个是超表面中的诱导磁机制及其在毫米波透镜天线上的应用。.首先是双曲超材料及超表面的电磁特性研究。双曲特异材料具有反常波矢色散特性，当用双曲特异材料构造一维光子晶体，其反常波矢色散特性可以用于调控光子带隙的色散，从而实现多种形态的，比如蓝移、红移或者无色散的光子带隙。相关研究结果得到实验证实。其次，双曲特异材料的反常波矢色散特性可用于调控金属表面的等离激元，实现无色散的Tamm等离激元模式。从而实现宽角度的光谱选择完美吸收。另一方面，两种极化的Tamm等离激元模式具有不同的色散特性，其反射相位所构成的椭偏角将对角度变换十分敏感，因而在生物传感方面有着潜在应用。第三，利用极端各向异性表面的类光子霍尔效应，圆极化波中的两种极化成分会沿着极端各向异性表面的不同方向传播，从而实现了两种极化成分的完全分离。.其次是天线领域的应用。超表面是一种超薄的平面超材料，由于其超薄的结构特性，通常只存在电响应而没有磁响应。我们利用超表面原子中电偶极子之间的耦合激发产生磁偶极子，并通过调节两者的谐振频率使得电偶极子与磁偶极子发生简并，从而激发惠更斯谐振。基于惠更斯谐振，我们在单层PCB板上实现了能调谐相位超过360度的透射超表面。我们因此探索了单极化、双极化的高增益宽带毫米波透镜天线原型，其展现了高增益与高口面效率、宽带宽等优良的辐射性能。这类透射型超表面的最大优势是结构简单、制备方便，因而在毫米波阵列天线领域有着巨大的工程应用价值。