Periodic Metal-dielectric Structures Research Articles

Mixing Rules for Left-Handed Disordered Metamaterials: Effective-Medium and Dispersion Properties.

Left-handed materials are known to exhibit exotic properties in controlling electromagnetic fields, with direct applications in negative reflection and refraction, conformal optical mapping, and electromagnetic cloaking. While typical left-handed materials are constructed periodic metal-dielectric structures, the same effect can be obtained in composite guest-host systems with no periodicity or structural order. Such systems are typically described by the effective-medium approach, in which the components of the electric permittivity tensor are determined as a function of individual material properties and doping concentration. In this paper, we extend the discussion on the mixing rules to include left-handed composite systems and highlight the exotic properties arising from the effective-medium approach in this framework in terms of effective values and dispersion properties.

Revising of the Purcell effect in periodic metal-dielectric structures: the role of absorption

Periodic metal-dielectric structures attract substantial interest since it was previously proposed that the spontaneous emission amplification rates (the Purcell factor) in such structures can reach enormous values up to 105. However, the role of absorption in real metals has not been thoroughly considered. We provide a theoretical analysis showing that absorption leads to diminishing values of Purcell factor. We also suggest that using emitting organic compounds such as CBP (4,4-Bis(N-carbazolyl)-1,1-biphenyl) can lead to a moderate increase of about an order of magnitude in the Purcell factor. Defining the experimentally measured Purcell factor as a ratio between the excited state lifetimes in bare CBP and in periodic structure, this increase in the fabricated periodic structure is demonstrated through a 4–8 times decrease in excited state radiative lifetime compared to a bare organic material in a wide emission spectrum.

Spontaneous Emission Amplification in Silver—Organic Periodic Structures and Tamm Plasmon Structures

We have investigated Tamm plasmon structure and periodic metal-dielectric structures with active organic CBP (N,N-dicarbazolyl-4,4-biphenyl) layer. Tamm structure is based on SiO2/TiO2 5 pairs DBR, with 26 nm CBP and 50 nm silver layer on the top of it. Two periodic silver-organic structures using thermal evaporation technique with different CBP layer thickness (15 and 30 nm) was fabricated. The rate of fluorescence intensity decay of Tamm plasmon and periodic structures was experimentally measured in near ultraviolet region. We demonstrate, that decay time of CBP fluorescence intensity in Tamm plasmon structure and periodic metal-organic structures decreases several times.

Modeling of diffraction radiation processes on periodic metal-dielectric structures in millimeter wavelength range

Modeling of diffraction radiation processes on periodic metal-dielectric structures in millimeter wavelength range

Tamm-Langmuir surface waves

In this work we develop a theory of surface electromagnetic waves localized at the interface of periodic metal-dielectric structures. We have shown that the anisotropy of plasma frequency in metal layers lifts the degeneracy of plasma oscillations and opens a series of photonic band gaps. This results in appearance of surface waves with singular density of states - we refer to them as Tamm-Langmuir waves. Such naming is natural since we have found that their properties are very similar to the properties of both bulk Langmuir and surface Tamm waves. Depending on the anisotropy parameters, Tamm-Langmuir waves can be either forward or backward waves. Singular density of states and high sensitivity of the dispersion to the anisotropy of the structure makes Tamm-Langmuir waves very promising for potential applications in nanophotonics and biosensing.

Characteristics of the kinetics of periodic structures CMP for a nonlinear pressure dependence of the polishing rate

For the kinetics of the chemical mechanical polishing (CMP) of wafers containing periodic metal–dielectric structures, a model is developed and theoretically investigated with the use of contact mechanics methods for the nonlinear pressure dependences of the polishing rate. In the steady-state regime, expressions for the dishing effect, which is characterized by the difference in the depths of the polishing metal and dielectric strips, are analytically derived and investigated. The specific characteristics of this effect, which are observed for different kinds of nonlinearities of the polishing rate depending on the pressure and the relative rotation velocity of the pad and wafer, are analyzed. Particularly, it is shown that, under certain conditions, the steady-state regime may be nonunique (the bistability effect).

High-frequency homogenization for layered hyperbolic metamaterials

We propose an analytical approach for calculation of the homogenized dielectric functions ${\ensuremath{\epsilon}}_{\ensuremath{\parallel}}(\ensuremath{\omega})$ and ${\ensuremath{\epsilon}}_{\ensuremath{\perp}}(\ensuremath{\omega})$ of one-dimensional periodic metal-dielectric structure. The obtained formulas are valid at high frequencies near the points of topological transition from an elliptic to hyperbolic regime. The proposed method of high-frequency homogenization takes into account rapidly varying electromagnetic fields within the metallic component of a unit cell, in particular, the evanescent character of the plasmonic mode and oscillatory behavior of the waveguidelike modes. Our results show good correspondence to the exact solution of the Rytov's dispersion equation and significant deviation from the widely used quasistatic formulas obtained by spatial averaging along the direction of periodicity $z$ of $\ensuremath{\epsilon}(z)$ and $1/\ensuremath{\epsilon}(z)$. The quasistatic approach ignores $z$ dependence of the fields that leads to its limited applicability near the frequency of topological transition.

A setup for measuring characteristics of microwave electric vacuum devices with open resonance structures

A new modification of the universal experimental setup for measuring electrodynamic characteristics of microwave generators with open resonance structures of the orotron-diffraction-radiation-generator type is described. To expand the functional capabilities and the electronic frequency-tuning range, an additional periodic metal-dielectric structure is introduced into the open resonator. The experimental results of investigations of the energy, volt-ampere, and frequency characteristics of the modified diffraction-radiation generator prototype are compared to the characteristics of the generator without a metal-dielectric structure.

Bianisotropic metamaterials based on twisted asymmetric crosses

The effective bianisotropic response of 3D periodic metal-dielectric structures, composed of crosses with asymmetrically-cut wires, is investigated within a general homogenization theory using the Fourier formalism and the form-factor division approach. It is found that the frequency dependence of the effective permittivity for a system of periodically-repeated layers of metal crosses exhibits two strong resonances, whose separation is due to the cross asymmetry. Besides, bianisotropic metamaterials, having a base of four twisted asymmetric crosses, are proposed. The designed metamaterials possess negative refractive index at frequencies determined by the cross asymmetry, the gap between the arms of adjacent crosses lying on the same plane, and the type of Bravais lattice.

Effect of the anisotropy of a conducting layer on the dispersion law of electromagnetic waves in layered metal-dielectric structures

The dispersion laws of electromagnetic waves in layered periodic metal-dielectric structures with anisotropic metal layers have been theoretically analyzed. It has been found that the anisotropy of metal layers is responsible for the appearance of additional allowed energy bands for photons. It has been shown that these bands correspond to plasma (Langmuir) waves propagating in anisotropic metal layers of the structure. Conditions under which the directions of group and phase velocities of Langmuir waves coincide or are opposite have been determined. It has been shown that the penetration of the electromagnetic field of Langmuir waves into dielectric layers is exponentially weak and this field is primarily concentrated in metal layers, where it oscillates in the direction perpendicular to the plane of the layers.

A setup for measuring spatial and waveguide characteristics of periodic metal-dielectric structures

An experimental setup and procedure for measuring electrodynamic characteristics of planar periodic metal-dielectric structures, which can be used for manufacturing practical equipment operating in millimeter, submillimeter, and terahertz wavelength ranges. Serviceability of the setup is checked by comparing the waveguide and spatial characteristics obtained experimentally and by numerical methods in a 4-mm wavelength range.

Polarization-independent 2D omni-directional photonic band gaps in a 1D periodic metal-dielectric (anisotropic) structure

It is shown that there is no polarization-independent two-dimensionally (2D) omni-directional photonic band gap (PBG) for any conventional one-dimensional (1D) metal-dielectric (isotropic) structure. Through the study of band diagrams and some asymptotic analysis, a 1D periodic metal-dielectric (anisotropic) structure is proposed to achieve a polarization-independent 2D omni-directional PBG. Theoretical predictions for both the lossless and lossy cases are verified with finite element method (FEM) simulation of a point source in such a structure.

All-angle zero reflection at metamaterial surfaces

The authors study theoretically reflection on the surface of a metamaterial with a hyperbolic dispersion. It is found that reflection is strongly dependent on how the surface is terminated with respect to the asymptote of the hyperbolic dispersion. For a surface terminated normally to the asymptote, zero reflection occurs for all incident angles. It is exemplified by a metamaterial made of a periodic metal-dielectric layered structure with its surface properly cut through numerical simulations.

Optical bistability and multistability in one-dimensional periodic metal-dielectric photonic crystal

The optical bistability and multistability in one-dimensional photonic crystal with the periodic metal-dielectric structure is investigated theoretically. In linear transmission, a structure with N periods will support N−1 resonant modes which correspond to the transmission peaks. Strong localized effect in these resonant modes is obtained. Optical bistability and multistability can be achieved when the incident wavelength is close to a resonance, which can be seen as an effect of the dynamic shifting of the wavelength of the resonant modes. It is found that the threshold for optical bistability in the periodic resonant structure is lower than the nonresonant metal-dielectric structure.

Subwavelength imaging at optical frequencies using a transmission device formed by a periodic layered metal-dielectric structure operating in the canalization regime

Imaging with sub-wavelength resolution using a lens formed by periodic metal-dielectric layered structure is demonstrated. The lens operates in canalization regime as a transmission device and it does not involve negative refraction and amplification of evanescent modes. The thickness of the lens have to be an integer number of half-wavelengths and can be made as large as required for ceratin applications, in contrast to the other sub-wavelength lenses formed by metallic slabs which have to be much smaller than the wavelength. Resolution of $\lambda/20$ at 600 nm wavelength is confirmed by numerical simulation for a 300 nm thick structure formed by a periodic stack of 10 nm layers of glass with $\epsilon=2$ and 5 nm layers of metal-dielectric composite with $\epsilon=-1$. Resolution of $\lambda/60$ is predicted for a structure with same thickness, period and operating frequency, but formed by 7.76 nm layers of silicon with $\epsilon=15$ and 7.24 nm layers of silver with $\epsilon=-14$.

Wave-front adaptive control structure (WACS) for quasi-optical power amplifiers in Intelligent RF front-ends

Tunable electromagnetic crystal (EMXT) surfaces are used as rectangular waveguide sidewalls to provide uniform excitation for quasi-optical power amplifiers. InP hetero-barrier varactors are monolithically integrated into periodic metal-dielectric structures to realize a reconfigurable EMXT surface that has a tunable resonance frequency from 30 to 45 GHz. Real-time reconfigurable (30 - 40 GHz) and low-loss quasi-TEM wave-front control with only 2-mm long EMXT waveguide section is demonstrated. Experimental results are in good agreement with design simulations. Such waveguides can be readily integrated into an intelligent RF front-end with self-assessment and self-adjustment capabilities.