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Existence Conditions of High-k Modes in Finite Hyperbolic Metamaterials
摘要： The capability to support optical waves with very large wave vectors (high-k) is one of the principle features of hyperbolic metamaterials (HMMs). These waves play the key role in HMM applications such as imaging and lifetime engineering. E?ective medium approximation (EMA) as widely used analytical method to predict HMMs behavior, has shortcomings in calculating high-k modes of practical structures. EMA is applicable to a subwavelength unit cell of implicitly in?nite periodic structures. Using conventional EMA, in the present paper, boundary e?ects and spatial dispersion are taken into consideration to properly compute the high-k modes of ?nite-thickness multilayer HMMs. Applying nonlocal homogenization to stacks of alternating metal-dielectric layers, the corresponding e?ective medium is examined as a high-k waveguide sandwiched between the substrate and an ambient superstrate. The developed theory enables us to recognize two types of bulk waves coined as short-range and long-range propagating modes. Number of such modes as well as their cuto? conditions are quanti?ed for the ?rst time. Validity of the developed theory is veri?ed both numerically by rigorous simulations of the multilayer structures with the transfer matrix method and experimentally by optical characterization of the HMMs in infrared regime.
关键词： subwavelength metal-dielectric multilayers,e?ective medium theory,high-k modes,hyperbolic metamaterials
更新于2025-09-19 17:15:36
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Soft Plasmonic Assemblies Exhibiting Unnaturally High Refractive Index
摘要： The increases in refractive indices (n) of materials are crucial for transformative optical technologies. With the progress of monolithic lithography, large advances have been achieved with several semiconductors, including silicon, germanium, and gallium arsenide, which generally provide higher n of ～4.0 compared to those of other elements. Nevertheless, above this upper limit of naturally available n, light?matter interactions could be unprecedentedly expanded, which in turn enriches the possible applications. Here, we present a soft self-assembly of polyhedral Au colloids as a promising method to achieve unnaturally high n values. The interfacial assembly of Au nanocubes provides n of 6.4 at the resonant wavelength (near-infrared) and 4.5 in the o?-resonant regimes (mid-infrared), which have not been previously reached. The soft self-assembly of polyhedral Au colloids can be a versatile and highly e?ective route for the fabrication of optical metamaterials with unnaturally high n values.
关键词： Metamaterials,Self-assembly,Plasmonic colloids,E?ective medium theory,Refractive index
更新于2025-09-19 17:13:59