Group Velocity Modulation and Light Field Focusing of the Edge States in Chirped Valley Graphene Plasmonic Metamaterials
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The valley degree of freedom, like the spin degree of freedom in spintronics, is regarded as a new information carrier, promoting the emerging valley photonics. Although there exist topologically protected valley edge states which are immune to optical backscattering caused by defects and sharp edges at the inverse valley Hall phase interfaces composed of ordinary optical dielectric materials, the dispersion and the frequency range of the edge states cannot be tuned once the geometrical parameters of the materials are determined. In this paper, we propose a chirped valley graphene plasmonic metamaterial waveguide composed of the valley graphene plasmonic metamaterials (VGPMs) with regularly varying chemical potentials while keeping the geometrical parameters constant. Due to the excellent tunability of graphene, the proposed waveguide supports group velocity modulation and zero group velocity of the edge states, where the light field of different frequencies focuses at different specific locations. The proposed structures may find significant applications in the fields of slow light, micro–nano-optics, topological plasmonics, and on-chip light manipulation.Keywords:
Group velocity
Photonic metamaterial
We demonstrate novel chiral photonic metamaterials consisting of physically separated mutually twisted planar metal patterns in parallel planes. Such metamaterials are shown to exhibit very strong gyrotropy (600°/mm) in the visible, near-IR and microwaves.
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We present some of our recent experiments and numerical calculations on photonic metamaterials. In particular, we demonstrate negative-index metamaterials, simultaneous negative phase and group velocity of light, magnetization waves in negative-index metamaterials, and circular dichroism at optical frequencies.
Photonic metamaterial
Negative index metamaterials
Slow Light
Metamaterial cloaking
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Phase velocity
Group velocity
Negative Refraction
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Recent advances in nanofabrication techniques allow for the manufacture of optical metamaterials, bringing their unique and extraordinary properties to the visible regime and beyond. However, an analytical description of optical nanoplasmonic metamaterials is challenging due to the characteristic optical behavior of metals. Here we present an analytical theory that allows us to bring established microwave metamaterials models to optical wavelengths. This method is implemented for nanoscaled plasmonic wire-mesh and trihelical metamaterials, and we obtain an accurate prediction for their dispersive behavior at optical and near-IR wavelengths.
Photonic metamaterial
Transformation Optics
Nanophotonics
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We report on a number of new approaches to control the interaction of light with nanostructured photonic metamaterials and new types of metamaterials. This includes nano-mechanical reconfigurable metamaterials for the visible and near-infrared parts of the spectrum; bas-relief and intaglio full-metal metamaterials and loaded plasmon metamaterials as new types of frequency selective surfaces, perfect absorbers and magnetic walls. We also show how tailoring profile of the excitation optical field can be used to control localization of light in a certain class of plasmonic nanostructures with strongly interacting meta-molecules which has a potential for applications in data storage and imaging.
Photonic metamaterial
Metamaterial cloaking
Transformation Optics
Nanophotonics
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Abstract The scaling down of meta‐atoms or metamolecules (collectively denoted as metaunits) is a long‐lasting issue from the time when the concept of metamaterials was first suggested. According to the effective medium theory, which is the foundational concept of metamaterials, the structural sizes of meta‐units should be much smaller than the working wavelengths (e.g., << 1/5 wavelength). At relatively low frequency regimes (e.g., microwave and terahertz), the conventional monolithic lithography can readily address the materialization of metamaterials. However, it is still challenging to fabricate optical metamaterials (metamaterials working at optical frequencies such as the visible and near‐infrared regimes) through the lithographic approaches. This serves as the rationale for using colloidal self‐assembly as a strategy for the realization of optical metamaterials. Colloidal self‐assembly can address various critical issues associated with the materialization of optical metamaterials, such as achieving nanogaps over a large area, increasing true 3D structural complexities, and cost‐effective processing, which all are difficult to attain through monolithic lithography. Nevertheless, colloidal self‐assembly is still a toolset underutilized by optical engineers. Here, the design principle of the colloidally self‐assembled optical metamaterials exhibiting unnatural refractions, the practical challenge of relevant experiments, and the future opportunities are critically reviewed.
Photonic metamaterial
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Metamaterials have been around for almost two decades, providing great advances in optics and photonics. Despite many fundamental studies and several predicted applications, only recently have metamaterials found niche applications and started to be implemented in products available to the consumer. Applications are still limited by the static nature of conventional metamaterials, meaning that the function of a specifically designed metamaterial cannot be changed after fabrication. For example, a metamaterial which is designed to absorb at a certain wavelength would become far more useful if it could shift its absorption peak in response to an external control signal. A promising way of overcoming this design limitation is through the exploitation of planar nanomechanical photonic metamaterials. Structurally reconfigurable photonic metamaterials, based on dielectric membranes of nanoscale thickness, can provide a simple platform for achieving high levels of modulation contrast and modulation frequency. These metamaterial systems have tuneable optical properties arising from nanomechanical displacements driven externally through different mechanisms. Using different actuation forces and designs, tuneable devices that are able to change their transmission, absorption or reflection characteristics can be attained. In this tutorial, we will focus on planar nanomechanical photonic metamaterials, while also acknowledging the considerable work developed using other tuneable metamaterial platforms, such as bulk, 3D or multilayer reconfigurable metamaterials. Planar reconfigurable photonic metamaterials are reviewed, nanoactuation mechanisms are explained, nanofabrication processes discussed and some conclusions on future challenges are drawn. Planar nanomechanical photonic metamaterials and their tuneable optical properties can become powerful components for optical devices and optical circuitry, and also be introduced to novel applications.
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Transformation Optics
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We review recent progress regarding photonic metamaterials with highly unusual optical properties, including a negative index, magnetization waves, and strong circular dichroism. Furthermore, we discuss experiments on second- and third harmonic generation from magnetic metamaterials.
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Negative index metamaterials
Negative Refraction
Split-ring resonator
Metamaterial cloaking
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Negative Refraction
Superlens
Photonic metamaterial
Split-ring resonator
Transformation Optics
Figure of Merit
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Left-handed metamaterials (i.e. metamaterials with electrical permittivity and magnetic permeability both negative, resulting to negative index of refraction) are becoming recently a subject of continuously increasing interest, owing to their novel and unique properties (like backwards propagation, negative refraction, super-resolution, etc) and thus the new capabilities that they can provide in the manipulation of electromagnetic waves. These novel properties and capabilities of left-handed materials have motivated strong research efforts to push the operation frequency of such materials from the initially achieved microwave regime to the infrared and optical regime. In this talk we will review the current status on the optical left-handed metamaterials research, and we will present our efforts: (a) to understand various aspects of the wave propagation in optical left-handed materials, (b) to obtain novel and/or optimized optical left-handed metamaterial designs, and (c) to explore new phenomena and possibilities available with optical left-handed metamaterials.
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Metamaterial cloaking
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We review the studies conducted in our group concerning electromagnetic properties of metamaterials and photonic crystals with negative effective index of refraction. In particular, we demonstate the true left handed behavior of a 2D composite metamaterial, by analyzing the electric and magnetic response of the material components systematically. The negative refraction, subwavelength focusing, and flat lens phenomena using left handed metamaterials and photonic crystals are also presented.
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