Dielectric substrate effect on the metamaterial resonances in terahertz frequency range

We report on the effect of dielectric substrate on the resonance shift of metallic metamaterials operating in the terahertz frequency region. The resonance frequencies for various metamaterials obtained by time-domain spectroscopy agree well with calculations based on the finite-difference time-domain method. The dependencies of the resonance frequency to substrate index are studied, and are systematically determined by introducing an effective substrate index. The relative contributions of the substrate index for various metamaterials are obtained by fitting the numerically obtained effective refractive indices as a function of substrate index, which is found to be ∼0.63 regardless of the metamaterial geometry.     

Classification of electromagnetic resonances in finite inhomogeneous three-dimensional structures

We present a simple and unified classification of macroscopic electromagnetic resonances in finite arbitrarily inhomogeneous isotropic dielectric 3D structures situated in free space. By observing the complex-plane dynamics of the spatial spectrum of the volume integral operator as a function of angular frequency and constitutive parameters, we identify and generalize all the usual resonances, including complex plasmons, real laser resonances in media with gain, and real quasistatic resonances in media with negative permittivity and gain.     

基于零折射磁性特异电磁介质的波前调控

本文基于二维磁性柱周期阵列设计了具有等效零折射率的磁性特异电磁介质. 通过多重散射理论计算体系的光子能带和等效介质理论提取体系的等效电磁参量可以确定该磁性特异电磁介质可以实现等效介电常数和等效磁导率同时为零. 利用该双零磁性特异电磁介质可以实现电磁波在无相位延迟下的传输, 从而可以调控电磁波的空间相位变化. 进而, 通过设计具有不同电磁波输出界面的构型实现了高斯光束的波前由平面转变成柱面, 还可以实现高斯光束的聚焦和高斯光束的分束. 也可以根据需要设计具有更为一般的输出界面, 实现更为多样的电磁波波前的调控. 而且, 磁性材料的电磁特性可以通过温度和外加磁场进行调制, 因此该双零磁性特异电磁介质的工作频率可以灵活控制, 这更便于电磁波器件的设计和应用.     

Annular aperture arrays: study in the visible region of the electromagnetic spectrum

Baida and Van Labeke recently proposed a structure that exhibits a supertransmission of light through an array of nanometric coaxial apertures in a metallic film that has been named an annular aperture array (AAA) [Opt. Commun. 209, 17 (2002); Phys. Rev. B 67, 155314 (2003); J. Microsc. 213, 140 (2003)]. We present the first experimental study, to our knowledge, of an AAA structure in the visible region. For technological reasons, the structure under study does not produce a supertransmission of 80% as in Baida and Van Labeke [Opt. Commun. 209, 17 (2002)]. We built the nanostructure and experimentally recorded its far-field spectral response. This transmission shows only one broad band with a maximum around lambda = 700 nm, giving a maximum efficiency around 17%. A finite-difference time-domain simulation reproduces quite well the obtained transmission spectrum.     

Photonic band gap in the visible range in a three-dimensional solid state lattice

We report on the photonic band gap effect in the visible range in a three-dimensional dielectric lattice formed by closely packed silica spherical clusters and by interconnected cavities filled with various liquids. The spectral position and the spectral width of the optical "stop-band" depend on the lattice period and on the relative sphere/cavity refraction indexn. The stop band peak wavelength shows a linear dependence on n. Transmission characteristics of the lattice have been successfully simulated by numerical calculations within the framework of a quasicrystalline approximation.     

Application of texture analysis methods to computer microscopy in the visible range of electromagnetic radiation

The application of the textural analysis methods based on computer microscopy in the visible region of electromagnetic radiation to classify blood cells into lymphoblasts and lymphocytes is considered. The model of digital processing of cell images is proposed. To quantitatively describe cells in diagnostics and differential diagnostics of acute lymphoblastic leucoses (ALLs), textural characteristics of nucleus images with estimation of their parameters are used.     

A candidate three-dimensional GHz left-handed metamaterial composed of coplanar magnetic and electric resonators

GHz left-handed metamaterials (LHMs) composed of coplanar magnetic and electric resonators were proposed in this paper. On each of the unit cells, the electric resonator is placed in the center space of the magnetic resonator. By adjusting the geometrical dimensions of the resonators, negative magnetic response of the magnetic resonator and negative electric response of the electric resonator can be tuned to be coexistent at the same frequencies. The effective constitutive parameters were retrieved. The results verified simultaneous negative permeability and permittivity as well as negative index of the proposed LHMs. Based on the above work, two- and three-dimensional LHMs that make use of coplanar magnetic and electric resonators were proposed. The work done in this paper is of great reference values in fabricating three-dimensional LHMs.     

A method for measuring the phase of the reflection coefficient in the visible range of the spectrum

A method for measuring the phase of the reflection coefficient in the optical wavelength range is proposed. The method is simple in experimental implementation and is based on measuring the energyreflection coefficients of a sample in two media with different refractive indices. Analytical and numerical estimates show that the measurement accuracy of the phase is on the order of 1°. The possibilities of using the results of the phase measurement in practice for a more complete characterization of materials and structures under investigation are considered.     

Simulation study on reconstruction model of three-dimensional temperature distribution within visible range in furnace

This paper presents a reconstruction model of three-dimensional temperature distribution in furnace based on radiative energy images captured by charge-coupled device （CCD） cameras within the visible wavelength range. Numerical simulation case was used in this study and a zigzag eccentric temperature distribution was assumed to verify the model. Least square QR-factorization （LSQR） method was introduced to deal with reconstruction equation. It is found that the reconstructed temperature distributions in low-temperature areas had some fluctuations and high-temperature areas were reconstructed well. The whole reconstruction relative error was mainly due to errors in low-temperature areas and the relative error for highest-temperature reconstruction was quite small.     

Tunable femtosecond laser in the visible range with an intracavity frequency-doubled optical parametric oscillator

We demonstrated experimentally a synchronously pumped intracavity frequency-doubled femtosecond optical parametric oscillator (OPO) using a periodically-poled lithium niobate (PPLN) as the nonlinear material in combination with a lithium triborate (LBO) as the doubling crystal. A Kerr-lens-mode-locked (KLM) Ti:sapphire oscillator at the wavelength of 790 nm was used as the pump source, which was capable of generating pulses with a duration as short as 117 fs. A tunable femtosecond laser covering the 624-672 nm range was realized by conveniently adjusting the OPO cavity length. A maximum average output power of 260 mW in the visible range was obtained at the pump power of 2.2 W, with a typical pulse duration of 205 fs assuming a sech2 pulse profile.     

High-gain composite microstrip patch antenna with the near-zero-refractive-index metamaterial

A high-gain rectangular microstrip patch antenna which is covered by a single layer metamaterial (MTM) superstrate with the near zero refractive index is proposed. The refraction of the metamaterial at frequency 3.51 GHz–3.57 GHz is very close to zero. The metamaterial with the near zero refractive index is placed 42 mm above an ordinary rectangular microstrip patch antenna. The effectively zero refractive index behavior of metamaterial superstrate can gather the wave emitted from the microstrip patch antenna and collimate it toward the normal direction of the antenna. The finite element method (FEM) and the finite difference time domain (FDTD) method are used to study the characteristics of this antenna. The results of the two methods indicate that the realized gain of the proposed antenna is increased by more than 6 dB, and the antenna has a flatness high gain in the predicted frequency band, where the proposed MTM is designed to have a near zero index of refraction. Therefore, the high-gain antenna is effectively enhanced based on the near-zero-refractive-index metamaterial.     

Determination of the electromagnetic properties in magnetic composite materials by inverse homogenisation

The paper proposes a numerical procedure for evaluating the geometrical and electromagnetic properties of the microstructure of a heterogeneous medium starting from the material effective characteristics. The identification process is developed by applying an inverse homogenisation technique, based on multiple scale expansion theory. The Newton–Raphson scheme and the Rosenbrock algorithm are tested. The efficiency of the second approach is proved by reporting several numerical results.     

Trapping of electromagnetic wave in single-negative metamaterial waveguides

We study the trapping properties of transverse magnetic (TM) waves in single-negative metamaterial waveguides including epsilon-negative (ENG) metamaterial and mu-negative (MNG) metamaterial. The relationship between effective refractive index and reduced core width is analyzed when the permittivities of ENG and MNG metamaterials are different, and the inflection on this curve can be regarded as the trapping point. Simulation results show that the properties in an ENG–MNG–ENG metamaterial waveguide are contrary to that in a MNG–ENG–MNG metamaterial waveguide. The sensitivity of trapping point to the change of permittivity makes the single-negative metamaterial waveguides to be an effective method to detect the permittivity variation and can be used as a new kind of waveguide sensor.     

Total reflection of electromagnetic waves propagating from an isotropic medium to an indefinite metamaterial

The existence conditions for total reflection and the corresponding critical angle at the interface separating an isotropic medium and an indefinite metamaterial for TE- and TM-polarized electromagnetic waves are obtained. For different kinds of indefinite metamaterial, there appear different total reflection phenomena. Particularly, the anomalous total reflection in which the incident angle is smaller than the critical angle and the Brewster’s angle can be smaller than the critical angle can occur for anti-cutoff medium. Furthermore, the omnidirectional total reflection exists for the always cutoff medium and anti-cutoff medium. The total reflection depends on the thickness of indefinite metamaterial when the indefinite metamaterial is finite, and the photon tunneling phenomenon can occur when the thickness of indefinite metamaterial is smaller than wavelength.     

Experimental demonstration of electromagnetic tunneling through an epsilon-near-zero metamaterial at microwave frequencies

Silveirinha and Engheta have recently proposed that electromagnetic waves can tunnel through a material with an electric permittivity (epsilon) near zero (ENZ). An ENZ material of arbitrary geometry can thus serve as a perfect coupler between incoming and outgoing waveguides with identical cross-sectional area, so long as one dimension of the ENZ is electrically small. In this Letter we present an experimental demonstration of microwave tunneling between two planar waveguides separated by a thin ENZ channel. The ENZ channel consists of a planar waveguide in which complementary split ring resonators are patterned on the lower surface. A tunneling passband is found in transmission measurements, while a two-dimensional spatial map of the electric field distribution reveals a uniform phase variation across the channel--both measurements in agreement with theory and numerical simulations.