Biomedical subjects

C M Soukoulis

Publications and source records attributed to C M Soukoulis.

12 recordsLinked to original sources

PubMed2004

Effective medium theory of left-handed materials.

We analyze the transmission and reflection data obtained through transfer matrix calculations on metamaterials of finite lengths, to determine their effective permittivity epsilon and permeability micro. Our study concerns metamaterial structures composed of periodic arrangements of wires, cut wires, split ring resonators (SRRs), closed SRRs, and both wires and SRRs. We find that the SRRs have a strong electric response, equivalent to that of cut wires, which dominates the behavior of left-handed materials (LHM). Analytical expressions for the effective parameters of the different structures are given, which can be used to explain the transmission characteristics of LHMs. Of particular relevance is the criterion introduced by our studies to identify if an experimental transmission peak is left or right handed.

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PubMed2004

High-bandwidth transmission of an efficient photonic-crystal mode converter.

We have investigated both theoretically and experimentally the spectral behavior and the transmission and reflection performance of a photonic-crystal (PhC) mode converter upon an InP substrate. This taper exhibits 70% transmission efficiency on an 80-nm bandwidth when it couples a ridge access guide to a strongly confined single-missing-row PhC guide. Such a taper design included in a PhC bend contributes a large benefit to the overall transmission budget of the PhC-based link.

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PubMed2004

Highly directional emission from photonic crystal waveguides of subwavelength width.

Recently it has been shown that it is possible to achieve directional emission out of a subwavelength aperture in a periodically corrugated metallic thin film. We report on theoretical and experimental studies of a related phenomenon concerning light emitted from photonic crystal waveguides that are less than a wavelength wide. We find that the termination of the photonic crystal end facets and an appropriate choice of the wavelength are instrumental in achieving very low numerical apertures. Our results hold promise for the combination of photonic crystal waveguides with conventional optical systems such as fibers, waveguides, and freely propagating light beams.

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PubMed2003

Resonant and antiresonant frequency dependence of the effective parameters of metamaterials.

We present a numerical study of the electromagnetic response of the metamaterial elements that are used to construct materials with negative refractive index. For an array of split ring resonators (SRR) we find that the resonant behavior of the effective magnetic permeability is accompanied by an antiresonant behavior of the effective permittivity. In addition, the imaginary parts of the effective permittivity and permeability are opposite in sign. We also observe an identical resonant versus antiresonant frequency dependence of the effective materials parameters for a periodic array of thin metallic wires with cuts placed periodically along the length of the wire, with roles of the permittivity and permeability reversed from the SRR case. We show in a simple manner that the finite unit cell size is responsible for the antiresonant behavior.

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PubMed2003

Subwavelength resolution in a two-dimensional photonic-crystal-based superlens.

We experimentally and theoretically demonstrate single-beam negative refraction and superlensing in the valence band of a two-dimensional photonic crystal operating in the microwave regime. By measuring the refracted electromagnetic waves from a slab shaped photonic crystal, we find a refractive index of -1.94 that is very close to the theoretical value of -2.06. A scanning transmission measurement technique is used to measure the spatial power distribution of the focused electromagnetic waves that radiate from a point source. The full width at half maximum of the focused beam is measured to be 0.21 lambda, which is in good agreement with the finite difference time domain method simulations. We also report a subwavelength resolution for the image of two incoherent point sources, which are separated by a distance of lambda/3.

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PubMed2003

Absorption losses in periodic arrays of thin metallic wires.

We analyze the transmission and reflection of electromagnetic waves calculated from transfer matrix simulations of periodic arrangements of thin metallic wires. The effective permittivity and the absorption of the arrangements of wires are determined. Their dependence on the wire thickness and the conductance of the metallic wires is studied. The cutoff frequency, or effective plasma frequency, is obtained and compared with analytical predictions. It is shown that the periodic arrangement of wires exhibits a frequency region in which the real part of the permittivity is negative while its imaginary part is very small. This behavior is seen for wires with thickness as small as 17 microm with a lattice constant of 3.33 mm.

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PubMed2003

Refraction in media with a negative refractive index.

We show that an electromagnetic (EM) wave undergoes negative refraction at the interface between a positive and negative refractive index material, the latter being a properly chosen photonic crystal. Finite-difference time-domain (FDTD) simulations are used to study the time evolution of an EM wave as it hits the interface. The wave is trapped temporarily at the interface, reorganizes, and, after a long time, the wave front moves eventually in the negative direction. This particular example shows how causality and speed of light are not violated in spite of the negative refraction always present in a negative index material.

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PubMed2002

Transmission losses in left-handed materials.

We numerically analyze the origin of the transmission losses in left-handed structures. Our data confirms that left-handed structures can have very good transmission properties, in spite of the expectable dispersion of their effective permeability and refraction index. The large permittivity of the metallic components improves the transmission. High losses, observed in recent experiments, could be explained by the absorption of the dielectric board.

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PubMed2002

Numerical studies of left-handed materials and arrays of split ring resonators.

We present numerical results on the transmission properties of the left-handed materials (LHMs) and split-ring resonators (SRRs). The simulation results are in qualitative agreement with experiments. The dependence of the transmission through LHMs on the real and imaginary part of the electric permittivity of the metal, the length of the system, and the size of the unit cell are presented. We also study the dependence of the resonance frequency of the array of SRRs on the ring thickness, inner diameter, radial and azimuthal gap, as well as on the electrical permittivity of the board and the embedding medium, where the SRR resides. Qualitatively good agreement with previously published analytical results is obtained.

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PubMed2002

Localized random lasing modes and a path for observing localization.

We demonstrate that a knowledge of the density of states and the eigenstates of a random system without gain, in conjunction with the frequency profile of the gain, can accurately predict the mode that will lase first. Its critical pumping rate can also be obtained. It is found that the shape of the wave function of the random system remains unchanged as gain is introduced. These results were obtained by the time-independent transfer matrix method and finite-difference time-domain methods in a one-dimensional model. They can also be analytically understood by generalizing the semiclassical Lamb theory of lasing in random systems. These findings provide a path for observing the localization of light, such as looking for the mobility edge and studying the localized states.

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PubMed2001

Ministop bands in single-defect photonic crystal waveguides.

We numerically study single-defect photonic crystal waveguides obtained from a triangular lattice of air holes in a dielectric background. It is found that, for medium-high air filling ratios, the transmission has very small values in narrow frequency regions lying inside the photonic band gap-the so-called ministop bands. Two types of ministop bands are shown to exist; one of which is due to the multimode nature of the waveguide. Their dependence on the length of the waveguide and on the air filling ratio is presented.

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PubMed2000

Parametric localized modes in quadratic nonlinear photonic structures.

We analyze two-color spatially localized nonlinear modes formed by parametrically coupled fundamental and second-harmonic fields excited at quadratic (or chi(2)) nonlinear interfaces embedded in a linear layered structure--a quadratic nonlinear photonic crystal. For a periodic lattice of nonlinear interfaces, we derive an effective discrete model for the amplitudes of the fundamental and second-harmonic waves at the interfaces (the so-called discrete chi(2) equations) and find, numerically and analytically, the spatially localized solutions--discrete gap solitons. For a single nonlinear interface in a linear superlattice, we study the properties of two-color localized modes, and describe both similarities to and differences from quadratic solitons in homogeneous media.

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