Uniaxial Medium Research Articles

The Huygens Principle for a Uniaxial Dielectric-Magnetic Medium with Gyrotropic-Like Magnetoelectric Properties

The dyadic Green functions for a uniaxial dielectric-magnetic medium, together with a reversible field transformation, were implemented to derive a formulation of the Huygens principle appropriate to a uniaxial dielectric-magnetic medium with gyrotropic-like magnetoelectric properties.

Exact Solution to Electromagnetic Scattering by an Impedance Sphere Coated With a Uniaxial Anisotropic Layer

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Electromagnetic fields in uniaxial anisotropic media can be obtained based on spherical vector wave functions in isotropic media. Applying the boundary conditions of electromagnetic fields on each interface of an impedance sphere coated with a uniaxial anisotropic layer, the expansion coefficients of electromagnetic fields in the uniaxial anisotropic medium and free space can be derived. The present method is very general, which can be reduced to many isotropic subcases. The present method has been validated in those subcases. Scattering by an impedance sphere with an anisotropic coating is presented and discussed. </para>

RECONSTRUCTION PERMITTIVITY TENSOR AND PRINCIPAL AXIS FOR UNIAXIAL MEDIUM IN MICROWAVE BAND

The relationship of permittivity tensor of anisotropic medium in principal coordinate system and laboratory coordinate system is given. The characteristic of permittivity tensor of uniaxial anisotropic medium in the laboratory coordinate system is discussed. The transverse permittivity of an anisotropic plate is reconstructed in laboratory coordinate system based on the resonance and polarization characteristics of backscattering radar cross section (RCS) in wide band. Then, a new scheme of reconstructing the principal axis direction for a uniaxial sample plate is proposed, subject to the principal axis is unknown. The backscattering characteristics of a sample plate are discussed when the electromagnetic (EM) wave of different polarization is incident perpendicular to the sample plate. Three sample plates, which are cut perpendicularly to the x � , y � ,a nd zaxes in the laboratory coordinate system, are required. A numerical reconstruction example is given to demonstrate the availability of presented scheme.

A finite difference time domain absorbing boundary condition for general frequency-dispersive media

The dispersion relations and the reflectionless conditions are obtained by the Maxwell’s curl equations in a uniaxial anisotropic medium and the phase-matching. Using the shift operator finite difference time domain （SO-FDTD） method and the transform relationship of frequency domain to time domain （jω replaced by /t）, an FDTD absorbing boundary condition for three kinds of general dispersive media model, i.e. the Debye model, Lorentz model and Drude model, is given. The characteristics of our absorbing boundary condition are tested. The computed results illustrated the generality and the feasibility of the scheme.

STUDY OF MODE PROPAGATION IN PSEUDOCHIRAL TRANSMISSION LINES

In this paper, a generic planar transmission line fllled, homogeneously, with a pseudochiral omega medium is considered. It is shown that only a uniaxial omega medium can support TE and TM modes separately. Thus, for such a medium, the flelds and modal equations for TE, TM and TEM mode propagation are obtained. The special case of parallel plate waveguide is solved, and the efiect of pseudochirality parameter › on the propagation constant and cutofi frequency is considered. For TEM propagation, an equivalent circuit is given which is difierent from the common isotropic transmission line model. Finally, a pseudochiral stripline is analyzed, and the elements of the equivalent circuit are calculated. The results show that the properties of the line vary as the pseudochirality parameter changes.

ZERO AXIAL PARAMETER (ZAP) MEDIUM SHEET

Plane-wave reflection from and transmission through a slab of uniaxial anisotropic medium is studied and the concept of ZAP (Zero-Axial-Parameter) medium sheet is defined as the limiting case when the axial parameters and the thickness of the slab vanish simultaneously. It is shown that the ZAP sheet may act as a spatial filter for the incident waves with transmission in a narrow cone around normal direction. Such a sheet may find application in narrowing the radiation beam and reducing sidelobes of an antenna or as a computer privacy filter in optical frequencies.

Self-induced transparency in an optically dense medium of nonsymmetric quantum objects

This paper discusses the soliton propagation regime of a laser pulse consisting of optical ordinary and terahertz extraordinary components in optically uniaxial media that contain nonsymmetrical resonance nanoobjects of the type of quantum filaments. The treatment takes into account dipole-dipole interaction between the nanoobjects. The conditions are explained under which a terahertz pulse can be efficiently generated when a near-IR optical signal is supplied to the input of the medium. It is shown that this generation process is accompanied by displacement of the spectrum of the optical component into the red region, with this displacement increasing as the pulse width becomes shorter.

Interface between transparent isotropic and uniaxial absorbing dielectric media: equations for ray tracing and for the direction of propagation

In this work we analyze the propagation of a plane wave that passes from an isotropic transparent medium to a uniaxial absorbing medium. Detailed expressions that give the real directions of propagation of the wave and the energy of the reflected and refracted ordinary and extraordinary waves are obtained. These expressions are valid for every orientation of the optic axis of the uniaxial medium and for every direction of propagation of the incident wave. Expressions are tested in the case of an interface between a transparent and an absorbing isotropic media and for the air-rutile (TiO2) interface. The effect of absorption has been evaluated by comparing the results obtained in rutile with the results obtained in a transparent uniaxial medium with the same real refractive indices. Results are presented for different values of the angle of incidence and the orientation of the plane of incidence.

Use of the Techniques for Uniaxial Medium in General Curvilinear Coordinates

In this work, it was introduced some considerations about the formulation of the method to uniaxial medium and its implementation in the electromagnetic scattering and of problems in 2-D and 3-D. The methodology used was the technique LN-FDTD, developed to reduce the instability of the method. So that the characteristics of the electromagnetic structures of complex geometry (head), it can be explored.

Surface Integral Equation Solutions for Modeling 3-D Uniaxial Media Using Closed-Form Dyadic Green's Functions

In this paper, a method of moments (MoM) implementation of surface integral equations (SIEs) is presented for uniaxial dielectric materials using closed-form dyadic Green's functions. The standard Poggio-Miller-Chang-Harrington-Wu-Tsai (PMCHWT) SIE is adapted for homogeneous uniaxial materials. A challenge in the implementation was the evaluation of the self impedance matrix elements and singularities due to the distinguished axis of the uniaxial media. For validation, bistatic scattering patterns of uniaxial targets are computed and compared with the well-known finite-element boundary integral (FE-BI) method solutions. A parametric study of the radiation by dipoles placed within high-contrast uniaxial layers is also presented for various distinguished axis orientations.

Hertz potentials in uniaxially anisotropic regions

Hertz potentials are used as an alternative to Fresnel's equation of wave normals to analyse harmonic plane wave propagation in uniaxially anisotropic media. Wave vector and amplitudes of ordinary and extraordinary waves are explicitly given. Refraction of a TM field at the plane face of a uniaxial medium is discussed and it is shown that in this particular situation, the refracted wave is identified with the extraordinary wave. Hertz potentials are also a powerful tool to tackle the same problems when harmonic plane waves are changed into Gaussian beams.

이방성 매질의 편광투과특성 분석을 위한 확장된 존스 행렬식의 개선

확장된 존스 행렬법을 응용하여 등방성 매질과 이방성 매질의 경계면에서 투과계수를 근사적인 방법을 사용하지 않고 정확히 계산하였다. 광학 이방성이 작은 경우(<TEX>$|n_e-n_o|\;{\ll}\;n_o,\;n_e$</TEX>), 계산된 투과계수가 근사식에 의한 투과계수와 일치하는 것을 확인하였다. 정확한 투과계수 표현을 사용하여 임의의 편광상태로 입사한 빛이 단축이방성 a-판을 투과한 후의 편광상태를 임의의 입사각과 방위각에 대하여 계산하였다. 또한 광축이 수직으로 교차된 이상적인 두 o-타입 편광자에 편광되지 않은 빛이 투과한 경우 투과율을 임의의 입사각과 방위각에서 계산한 후, 기존의 근사식과 비교하였고, 완전하지 않은 두 편광자의 소광계수와 두께의 변화에 따른 투과율을 계산하여 실제의 편광자를 상정한 소광도를 평가하였다. 근사식이 적용되지 않는 이방성이 큰 이방성 매질을 통과한 후의 빛의 편광상태를 분석할 때 적용될 수 있도록 정확한 투과계수를 사용하는 방법을 제시함으로써 액정 디스플레이 분야 광소자의 편광 분석에 기여하고자 하였다. The exact transmission coefficients at the interface between a uniaxial anisotropic medium and an isotropic medium at? oblique incidence are derived by applying the extended Jones matrix method. When the birefringence of the uniaxial anisotropic medium is small (<TEX>$|n_e-n_o|\;{\ll}\;n_o,\;n_e$</TEX>), the exact transmission coefficients are compared with those by the conventional extended Jones matrix method by Yeh et al. They showed an excellent agreement with each other. In addition, using the exact transmission coefficients, we calculated the polarization characteristics of a light through a uniaxial medium to an incident light with arbitrary polarization state at? oblique incidence. We compared the transmittances of an unpolarized light through a pair of crossed o-type polarizers by two different methods and calculated the transmittance as the variation of the optical constants of the polarizers to evaluate of the extinction ratio. The polarization analysis method using the exact transmission coefficients can be applied to polarization characteristics of a light through a uniaxial medium with large birefringence as well as to liquid crystals and to optical anisotropic material.

Surface Polaritons at the Planar Interface of Twinned Dielectric Gyrotropic Media

The closed-form dispersion equation for surface polaritons localized near the planar interface of the semi-infinite halves of the same transparent uniaxial dielectric gyrotropic medium was derived for the case when the gyration vectors of the contacting materials are perpendicular to the interface and oppositely directed to each other. Surface electromagnetic waves can be excited only if the medium is both anisotropic and gyrotropic. Numerical analysis of the phase velocity, decay coefficients, and polarization of the surface polaritons as functions of the gyration parameter was undertaken. It turned out that, for a weakly gyrotropic medium, the characteristic penetration depth of the surface polaritons is inversely proportional to the squared gyration parameter.

Complex ray tracing in uniaxial absorbing media

We theoretically analyze waves propagating between an isotropic nonabsorbing medium and a uniaxial absorbing medium in the general case where the incidence plane does not coincide with the principal section of the uniaxial crystal. Expressions for the reflection and transmission coefficients are derived by a combination of complex ray tracing and the 4 x 4 matrix method. The work presented here is useful for the design of optical systems that incorporate the use of birefringent absorbing components.

LATERAL DISPLACEMENT OF AN ELECTROMAGNETIC BEAM REFLECTED FROM A GROUNDED INDEFINITE UNIAXIAL SLAB

A theoretical analysis of the lateral shift for an electromagnetic beam reflected from an uniaxial anisotropic slab coated with perfect conductor is presented. The analytic expression for the lateral shift is derived by using the stationary-phase approach, and the conditions for negative and positive lateral shifts are discussed. It is shown that the lateral shift depends not only on the slabthickness and the incident angle, but also on the constitutive parameters of the uniaxial medium. Enhancement and suppression of lateral shift are observed and are attributed to the interference between the reflected

Possible Abnormal Group Velocity in the Normal Dispersive Anisotropic Media

We introduce a possible method to realize the negative group velocity of electromagnetic wave in the normal dispersive media. Theoretical analysis from the k-surface of the proposed normal dispersive uniaxial media reveals that the group velocity can be negative if the loss of the media is taken into account. Since the proposed normal dispersive media can be constructed in the GHz frequency by metamaterial, our result may provide an alternative way to the investigation of the abnormal group velocity.

An Alternative Description of Multi-Dimensional Optics in Liquid Crystals and Uniaxial Media Solved by Operators and Sparse Linear Systems

An alternative description of multidimensional optics in liquid crystals and uniaxial media, which combines the geometrical optics approximation (GOA) with the beam propagation method (BPM), is presented. In this description, the two orthogonal GOA eigenmodes are used as a basis for development of beam propagation equations for the fields. The general treatment of this approach is developed both theoretically and numerically. The formalism is applied to liquid crystal devices with pixilated structures, and numerical results are compared with the GOA results.

Asymptotic Fields in Frequency and Time Domains Generated by a Point Source at the Horizontal Interface Between Vertically Uniaxial Media

For a point current source placed at the interface between two half-space media, investigation is made of the far-zone asymptotic fields in the frequency domain and their transient waveforms. The media are electrically uniaxial with the uniaxis normal to the interface. The leading-order fields contributed by the stationary-phase points serve as good approximations well off the critical angles. Near the critical angles, the uniform asymptotic techniques need to be employed for a proper approximation. Unlike the ordinary wave, the extraordinary wave cannot be correctly described merely by taking into account the proximity of the stationary and branch points, except in some rare cases. Consideration must also be given to the combined effect associated with the pole introduced in the formulation. The validities of the asymptotic approximations are examined in the time domain by comparing the asymptotic-field waveforms with the wavenumber-synthetic waveforms, around the critical angle of the extraordinary wave.

The largest negative refractive angles in uniaxial bicrystals

Using the Maxwell’s equations, we carry out theoretical analysis on the maximum incident and refractive angles at which negative refraction can be realized at the interfaces associated with conventional uniaxial media. In the numerical analysis, the largest incident and refractive angles at which refraction arises are obtained by optimizing directions of the optical axis of the uniaxial bicrystal. Meanwhile, the optical parameters of the ordinary uniaxial bicrystals (including homogeneity-junction and heterogeneity-junction) are given, and some representative laser wavelengths, the largest incident and refractive angles are obtained. The relation between the largest incident angles (or refractive angles) and refractive index is also discussed.

Laser-induced anisotropy in Ag+-doped glasses

An induced optical anisotropy is observed as a result of interaction of a high-power CW Ar+ laser beam, with silver-ion-exchanged glasses. We have shown that the absorption of the beam by the thin layer of Ag+ produces a temperature gradient resulting in a radial stress on the surface of the sample. The induced anisotropy makes the sample behave as a thin uniaxial optical medium with axis along the direction of the beam propagation. For the polarized light, the induced anisotropy restricts the application of micro-lenses, which are made by this method. The average refraction index of the interaction area is measured.