Afonso M. Barbosa

A linear-operator formalism for the analysis of inhomogeneous biisotropic planar waveguides

Using the theory of linear operators, guided electromagnetic wave propagation in inhomogeneous (nonreciprocal) biisotropic planar structures is analyzed in terms of a 2*2 matrix differential operator. Based on the concept of adjoint waveguide, a new biorthogonality relation for the guided hybrid modes is derived. For the special case of reciprocal biisotropic media or chiral media, the linear-operator formalism leads to a self-adjoint problem. As an application example, a general analysis of the radiation modes of a grounded chiroslabguide is also presented. >

Full-wave analysis of a nonradiative dielectric waveguide with a pseudochiral /spl Omega/-slab

This paper presents a new microwave device - a non-radiative dielectric (NRD) waveguide with a dielectric pseudochiral /spl Omega/-slab - the /spl Omega/-NRD waveguide. A rigorous full-wave analysis is presented and the modal equations for the longitudinal-section magnetic (LSM) and longitudinal-section electric (LSE) modes are derived. The dispersion curves and operational diagrams for the first hybrid LSM modes are presented. The effect of the pseudochiral /spl Omega/-medium is discussed. New interesting modal features are revealed, showing that the propagation characteristics may differ considerably from the common isotropic case.

Dispersion and Losses in Surface Waveguides Containing Double Negative or Chiral Metamaterials

In this article the in∞uence of both dispersion and losses on waveguides with metamaterials is investigated. The analysis is focused on surface waveguides (planar interfaces and grounded slabs) containing either double-negative (DNG) or chiral metamaterials. The main goal is to show how the combined efiect of material dispersion and losses with the structural dispersion afiect the solutions of the modal equations. It is shown that this interplay is essential to obtain a correct modal analysis of these waveguides. Namely, the overall behavior can qualitatively change | so that it is not possible to state that the corresponding lossy case | even when a very small amount of losses is introduced | can be interpreted as a small perturbation of the lossless case.

Modified split-step Fourier method for the numerical simulation of soliton amplification in erbium-doped fibers with forward-propagating noise

Using a modified version of the split-step Fourier method, we analyze the effect of noise on soliton propagation inside erbium-doped fiber amplifiers. In fact, noise from forward-propagating amplified spontaneous emission, associated with a Markov immigration process, is included in the analysis of soliton amplification. Moreover, this algorithm accounts for the real spectral gain profile of the fiber amplifier. The frequency jitter, induced during soliton amplification, is compared with the Gordon-Haus effect where optical amplifiers are considered as noisy point-like devices.

Effect of Losses in a Layered Structure Containing DPS and DNG Media

The problem of re∞ection and transmission of plane electromagnetic waves in a periodic multilayered structure containing double-negative (DNG) media is analyzed using a matrix formalism. A Lorentz model with a single resonance is used to describe the dispersion of the DNG medium. It is shown that the introduction of losses, in accordance with the Kramers- Kronig relations, is essential in order to obtain correct results on the performance of the structure.

A method to overcome the limitations of G.O. in axis-symmetric dielectric lens shaping

The design of a cylindrically symmetric dielectric lens antenna is presented for the case of a very squeezed fan-beam. One makes use of geometrical optics (G.O.) to establish the profile of the lens in a first step. A half-integrated solution of Greens formula for bodies with cylindrical symmetry and circularly polarized surface fields is then derived to calculate the radiation pattern. Since the use of G.O. is restricted to some conditions which were observed unsatisfied in our study, a two-steps procedure to reach an acceptable lens shape is then presented. The first step is based on weighting the source beam of the antenna; and the second one is based on simple geometrical interpolation. Prototypes provided experimental results that are consistent with the predicted radiation characteristics and interesting features of such antennas are pointed out.

ELECTROMAGNETIC WAVE PROPAGATION IN CHIRAL H-GUIDES

Guided-wave propagation in chiral H-guides is analyzed, using a building-block approach. In a flrst stage, a 2D chiral parallel-plate waveguide is studied using a lossless frequency dispersion model for the optically active medium, where the constitutive chiral parameter is assumed to be dependent on the gyrotropic parameter. In the second stage, the mode matching technique and the transverse resonance method are used to characterize the 3D structure. A full parametric study is presented for a flxed frequency. The operational and dispersion diagrams for the chiral H-guide are presented. By replacing the common isotropic slab with a chiral slab, chirality provides an extra degree of freedom in the design of new devices.

Semileaky waves in dielectric chirowaveguides.

The occurrence of semileaky waves in dielectric chirowaveguides is investigated. It is shown that a thinfilm dielectric chiroslabguide with an achiral superstrate and in which both the film and substrate are chiral can support semileaky modes radiating energy into the substrate, provided that the chirality parameters are properly chosen.

Spectral representation of self-adjoint problems for layered anisotropic waveguides

Layered waveguides with lossless anisotropic layers in the polar configuration are analyzed through the unifying concept of a real self-adjoint operator. For a suitable definition of two-vector transverse eigenfunctions, general properties such as orthogonality and completeness relations are derived. The linear operator formalism is applied to closed waveguides inhomogeneously filled with anisotropic materials, including crystals and gyrotropic media. As an extension of the former theory to open waveguides, a grounded uniaxial dielectric slab with a coplanar optic axis is also analyzed: as for open isotropic waveguides, a complete spectral representation including the surface (proper eigenfunctions) and the pseudosurface modes (improper eigenfunctions) is presented. >

New biorthogonality relations for inhomogeneous biisotropic planar waveguides

Using a linear operator formalism this paper presents new biorthogonality relations for the hybrid modes supported by planar waveguides inhomogeneously filled with general biisotropic media. In the special case of lossless biisotropic media, the linear operator is self-adjoint, the original and adjoint waveguides are identical and new orthogonality relations can be derived. As an example of application, the radiation modes of a grounded nonreciprocal and lossless biisotropic slab waveguide are analyzed in terms of a pair of incident transverse electric (ITE) and incident transverse magnetic (ITM) continuous modes, which have the advantage of being mutually orthogonal and of having a clear physical interpretation. >