We investigated optical properties of nanostructured metal-dielectric multilayered lattices under the conditions of epsilon-near-zero (ENZ), a concept derived from the effective-medium approach (EMA). We theoretically found that the periodic array of metallic nanolayers may exhibit either superlensing driven by broadband canalization from point emitters or single-polarization double refraction, and conventional positive as well as negative, even at subwavelength regimes. For the latter case, we formulated a modified EMA, and subsequently a generalized refraction law, that describes both refractive behaviors concurrently. The modal coupling of plasmonic lattice resonances, and nonlocality induced by partial screening across the nanolayer length, are responsible for these distinct effects. Numerical simulations show that deep-subwavelength lensing along the optical axis of Ag-GaAs metamaterial is clearly enhanced at optical wavelengths. On the other hand, transverse-magnetic-polarized radiation that is obliquely incident on the ENZ periodic nanostructures with the same materials in the infrared (around 1.55 μm ) undergoes double refraction neighboring 50/50 beamsplitting.
We investigated surface waves guided by the boundary of a semi-infinite layered metal-dielectric nanostructure cut normally to the layers and a semi-infinite dielectric material. Using the Floquet-Bloch formalism, we found that Dyakonov-like surface waves with hybrid polarization can propagate in dramatically enhanced angular range compared to conventional birefringent materials. Our numerical simulations for an Ag-GaAs stack in contact with glass show a low to moderate influence of losses.
Recent disclosures on subwavelength plasmonic crystals, like the potential excitation of a pair of coexisting wave-fields
with opposite refraction, only can be understood by considering two dispersion branches with completely
different features that characterize the metamaterial. One branch gives elliptic-like dispersion and the other
provides hyperbolic-like dispersion. However the effective medium approximation, also known as Rytov approximation,
is not consistent with both curves simultaneously. We follow an approach leading to a single curve that
allows a complete description of both diffraction behaviors concurrently. Importantly only two parameters of the
closed curve, together with the lattice period, fulfill such a complete picture. In addition, our semi-analytical
approach may include more general situations straightforwardly.
We investigate spatial-dispersion properties of hybrid surface waves propagating in the boundary of a semi-infinite
layered metal-dielectric nanostructure. Electromagnetic fields can be dramatically affected by a nonlocal optical
response of the plasmonic lattice. We demonstrate that the use of the so called effective medium approximation
(EMA) is not justified if the thickness of a metallic layer becomes of the order of the metal skin depth. We
compare the results obtained by means of EMA with computer solutions of Maxwell's equation, including losses
in the metal.
We present recent progress in nondiffracting subwavelength fields propagating in complex plasmonic nanostructures.
In particular, diffraction-free localized solutions of Maxwell's equations in a periodic wire medium are
discussed thoroughly. The Maxwell-Garnett model is used to provide analytical expressions of the electromagnetic
fields for Bessel beams directed along the cylinders axes. Large filling factors of the metallic composite
induce resonant-plasmonic spots with a size that remains far below the limit of diffraction. Some numerical
simulations based on the finite-element method support our analytical approach.
This paper reviews the main properties and applications of nanomembrane-based plasmonic structures, including some results presented here for the first time. Artificial nanomembranes are a novel building block in micro- and nanosystems technologies. They represent quasi-two-dimensional (2D) freestanding structures thinner than 100 nm and with giant aspect ratios that often exceed 1,000,000. They may be fabricated as various quasi-2D metal-dielectric nanocomposites with tailorable properties; they are fully symmetric in an electromagnetic sense and support long-range surface plasmon polaritons. This makes nanomembranes a convenient platform for different plasmonic structures such as subwavelength plasmonic crystals and metamaterials and applications such as plasmon waveguides and ultrasensitive bio/chemical sensors. Among other advantages of nanomembrane plasmonics is the feasibility to fabricate flexible, transferable plasmonic guides applicable to different substrates and dynamically tunable through stretching. There are various approaches to multifunctionalization of nanomembranes for plasmonics, including the use of transparent conductive oxide nanoparticles, but also the incorporation of switchable ion channels. Since the natural counterpart of the artificial nanomembranes are cell membranes, the multifunctionalization of synthetic nanomembranes ensures the introduction of bionic principles into plasmonics, at the same time extending the toolbox of the available nanostructures, materials and functions.
We studied the propagation of plasmonic modes along planar multilayer metal-dielectric structures with finite number of bi-layer unit cells. The dispersion relations for various investigated waveguide structures with the multilayer core and symmetric or asymmetric cladding have been analyzed. In the case of symmetric metallic cladding we have found both TE and TM modes within the light cone, while TM modes only exist outside the light cone. Both symmetric and asymmetric dielectric claddings support modes outside the light cone and of TM-polarization only. Formation of photonic bands and gaps, the structure of their edge lines, and the behavior of modes that cross the edge lines has been investigated. In the subwavelength regime, we have found ordinary surface plasmon polariton dispersion in the forbidden gap that is created via coalescence of the two modes that cross the neighboring band-gap edges. One of those modes can exhibit negative group velocity.
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