Two-stage mode finder for waveguides with a 2D cross-section

We present a fast and efficient method to find the vectorial eigenmodes of waveguides with an arbitrary 2D cross-section. The method can deal with both material losses and radiation losses (through perfectly matched layer boundary conditions). In the first stage of the method, a coarse estimate of the propagation constants is found using a plane-wave method. In the second stage, these estimates are refined using a mode-matching method.     

Perfect plane-wave source for a high-order symplectic finite-difference time-domain scheme

The method of splitting a plane-wave finite-difference time-domain (SP-FDTD) algorithm is presented for the initiation of plane-wave source in the total-field / scattered-field (TF/SF) formulation of high-order symplectic finite-difference time-domain (SFDTD) scheme for the first time. By splitting the fields on one-dimensional grid and using the nature of numerical plane-wave in finite-difference time-domain (FDTD), the identical dispersion relation can be obtained and proved between the one-dimensional and three-dimensional grids. An efficient plane-wave source is simulated on one-dimensional grid and a perfect match can be achieved for a plane-wave propagating at any angle forming an integer grid cell ratio. Numerical simulations show that the method is valid for SFDTD and the residual field in SF region is shrinked down to -300 dB.     

Effective-dielectric-constant method for the problem of wave diffraction by a close-spaced dielectric grating

A simple method for determination of effective dielectric constants is proposed that allows a close-spaced two-dimensionally periodic dielectric layer with rectangular elements to be replaced by a homogeneous and anisotropic layer of the same thickness. The method makes it unnecessary to solve the complicated problem of determination of the fields within the elements for calculation of the plane-wave reflection and transmission coefficients in a long-wave approximation, which considerably simplifies the calculations. Comparison with known solutions obtained by rigorous methods for one-dimensionally periodic gratings shows exact agreement of the results. The method is easily extended to magnetodielectric media as well as to multicomponent media, including those whose dielectric constants are functions of the coordinate perpendicular to the layer.Academician A. L. Mints Radio-Engineering Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 36, No. 3-4, pp. 286–294, March–April, 1993.     

Calculation and optimization of parameters of deep groove gratings with multilayer dielectric coating for compression of high-power laser pulses

The method of calculating the electromagnetic wave field diffracted by a holographic grating with a multilayer dielectric coating is developed. The method consists of the representation of the field inside dielectric layers in the form of a plane-wave expansion for weakly damped harmonics and an expansion over functions of the concomitant coordinate system for strongly damped orders. This modification of the method allows calculation of the diffraction efficiency and the electric field strength for the deep groove gratings. It is shown that a diffraction element that possess high efficiency and radiation strength can be obtained even when the profile of the dielectric layers flattens with an increase in the distance from the grating’s metallic layer.     

Determination of embedded layer properties using adaptive time-frequency domain analysis

A general model for determination of the complete set of acoustical and geometrical properties of an isotropic layer embedded between isotropic or anisotropic multilayered solids is developed. These properties include density, longitudinal and shear elastic moduli, layer thickness, and loss factors, simultaneously determined from two measurements, one at normal and one at oblique incidence. The inversion model is an extension of the method proposed by Lavrentyev and Rokhlin [J. Acoust. Soc. Am. 102, 3467 (1997)] which is applicable to thick substrates. In this new method, the inversion model mimics an experiment by using the same time-domain gating of the signal reflected from the embedded layer. This allows application of this method to layered solids when reflections from different layers overlap in the time domain. The sensitivity of the method, its stability against data scatter, and the effect of the oblique incident angle are evaluated. The effect of plane-wave approximation versus beam approximation in the inverse algorithm is discussed. Experimental results are given to demonstrate examples of adhesive layer property reconstruction.     

等效介质理论在光子晶体平面波展开分析方法中的应用

应用等效介质理论,提出了一种理论分析光子晶体的新平面波展开法,通过计算光子晶体的能带作收敛性分析,结果表明,新方法具有精度高、收敛快的优点,明显优于目前通用的二种平面波展开法;与已有的理论方法相比,新平面波展开法更适用于分析任意介电分布的高维光子晶体结构 关键词： 光子晶体 平面波展开法 禁带     

The calculation of reactions of the type (a,ab) using the plane-wave expansion method: (I). General formalism for the direct one-step process

A formalism for the evaluation of the transition matrix element for reactions of the type (a, ab) in the direct distorted-wave approximation is presented. The plane-wave expansion method is used to represent the optical model wave function for the entrance and exit channels. Because of the use of the plane-wave expansion method the completely off-the-energy-shell behavior is easily demonstrated when distorted waves are used. The use of this expansion method also shows how difficult it is to extract the momentum dependence of the bound particle. We also apply the plane-wave expansion method to evaluate the transition matrix element for the effective f-operator DWTA approach. We also discuss an approximation to the complete transition matrix element which seems equivalent to the DWTA but yet makes use of completely off-the-energy-shell matrix elements.     

The influence of impurity on the critical thickness of the CeO_2 buffer layer for coated conductors

The lattice parameters, band structure, density of state and elastic constant of RE-doped CeO2 (RE=Sm, Gd, Dy), the buffer material for coated HTS conductors, are calculated using the plane-wave method with pseudopotentials based on the density functional theory (DFT) of first-principle. The rule and mechanism of the effect of rare earth impurity on the critical thickness of the CeO2 buffer layer are investigated. It is found that, in the range of the calculation, the changes of the lattice volume V and ela...     

Engineering absolute band gap in anisotropic hexagonal photonic crystals

We analyze the band gap spectra of two-dimensional anisotropic photonic crystals created by a hexagonal lattice of rods covered by an interfacial layer (e.g. tellurium tubes). Using the plane-wave numerical expansion method, we study the modification of the band gap spectrum when the rods are infiltrated with other material, and discuss the optimization strategies leading to the maximum value of the absolute band gap.     

Numerical implementation of complex geometrical optics

We propose a numerical scheme for calculation of the wave field, based on the geometrical-optics method generalized for complex values. The main advantage of the complex-value method is a possibility to take into account diffraction effects using only the ordinary differential equations of the geometrical optics. This allows one to significantly reduce the amount of computations and, hence, computation time. The efficiency of this algorithm is illustrated by two numerical examples that allow comparison with the known analytical solutions: the plane-wave field behind the caustic in the linearly inhomogeneous layer and the field of a Gaussian beam in a homogeneous medium. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 43, No. 7, pp. 630–637, July, 2000.     

Theoretical study of magnetism and electronic structure of Fe3/Crn(1 1 0) superlattices

The electronic structure and magnetism of Fe₃/Cr_n(1 1 0) (n=1, 3, 5) superlattices (SL) with varying layer thickness have been studied using the full-potential linearized augmented plane-wave (FLAPW) method within the first-principle formalism. The results show that the ferromagnetic state is the preferable phase in the ground state. The magnetic moments of the Fe layers are slightly modified by the presence of the Cr layers. The Cr magnetic moments alternate direction from layer to layer, and an antiferromagnetic coupling between Fe and Cr at the interfacial layer is seen. The magnetic moments of the Cr layers are suppressed because there is a strong hybridization between d-states of both Fe and Cr atoms. Only a small moment is found in the Cr layer. The Cr moment alignment is determined by a delicate balance between the different magnetic interaction.     

Photonic band gaps in two-dimensional photonic crystals of core-shell-type dielectric nanorod heterostructures

A new type of two-dimensional photonic crystal (PC) called core-shell-type PC composed of a nanorod heterostructure array in a square or triangular lattice such that a dielectric nanorod is covered by a thin interfacial layer is studied. Using the plane-wave numerical expansion method, we study the modification of the band gap spectrum when the nanorods are covered by other material, and reveal that the photonic band gap is considerably enhanced in size for both square and triangular lattice. The effects of structural parameters on the band gaps are also studied. The results show that there exist optimal parameters to open large gaps, and TE (Transverse-electric) band gaps are favored in a triangular lattice.     

由介质球构成的三维光子晶体能带结构的平面波研究

采用平面波展开方法计算由介质球构成的面心立方三维光子晶体的能带结构及透射性质.选 用合适的平面波个数研究了SiO₂蛋白石结构光子晶体的能带及透射性质，并采 用转移矩阵 方法计算了电磁波沿［111］方向的传输特性，两种方法得到的结果相符合.还研究了反蛋白 石结构光子晶体的全带隙.最后，研究了壳层介质球构成的面心立方结构光子晶体的能带特 性，发现在高介质球外面包裹适当厚度的低介电常数介质壳层所构成的光子晶体，可以增大 L点相对带隙宽度50％，并证明了其优化内外半径比值约为0．69. 关键词： 光子晶体 光子能带 平面波展开方法 Core-Shell结构     

Transformation of Nanosecond Laser Pulses under the Conditions of Total Internal Reflection from a Layer with Thermal Nonlinearity

The nonlinear, total internal reflection of a laser pulse from an absorbing layer of finite thickness in the presence of a retrodirective mirror has been considered in the framework of the plane-wave approximation. The dynamics of reflection of a pulse from a nonlinear layer has been investigated on the basis of the solution of Maxwell equations for a refracted wave and constitutive equations for a medium with thermal nonlinearity. The numerical solution of the unsteady equations obtained allows one to determine the evolution of the reflectance of a layer. The time evolution of the energy parameters and the shape of the reflected and transmitted pulses has been numerically simulated.     

The effect of etching interfacial layers on the absolute photonic band gap in two-dimensional photonic crystals

The photonic band structures of two-dimensional (2D) photonic crystals with etched interfacial layers between air rods and the background dielectric is studied theoretically. The effect of etching interfacial layers on absolute photonic band gap (PBG) is analyzed quantitatively. Numerical calculations are carried out based on Maxwell's equations and the plane-wave expansion method. It is shown that the physical property of interfacial layers influence the absolute PBG, and the existence of interfacial layers cannot enlarge the largest absolute PBG of an ideal case without interfacial layers.     

Fabrication and optical reflection behavior of a two-dimensional barium titanate ceramic photonic crystal

We demonstrate a method for fabricating a two-dimensional hexagonal array of nanoscale barium titanate ceramic pillars. A precursor array was prepared by introducing a sol solution into an electron-beam resist mold with air holes and subsequently dry etching the unnecessary gel layer formed on the mold. A ceramic array, consisting of barium titanate ceramic pillars with a radius of 85 nm, a lattice constant of 450 nm, and a height of 500 nm, was fabricated by sintering the precursor array at 1073 K. The reflection spectra for the ceramic array in the visible range revealed the underlying photonic band gaps, which were in good agreement with results calculated using a plane-wave method. PACS 77.84.-s; 42.70.-a; 42.70.Qs     

Half-metallic exchange bias ferromagnetic/antiferromagnetic interfaces in transition-metal chalcogenides

To investigate half-metallic exchange bias interfaces, magnetic structures at ferromagnetic (FM)/antiferromagnetic (AFM) interfaces in the zinc blende transition-metal chalcogenides, and with compensated and uncompensated AFM interfaces, were determined by the full-potential linearized augmented plane-wave method. With the uncompensated AFM interface, an antiparallel alignment of the Cr and Mn moments induces an excellent half-metallicity. More striking still, in the compensated AFM interface the Cr moments in the FM layer lie perpendicular to the Mn moments in the AFM layer but the Mn moments strongly cant to induce a net moment so as to retain the half-metallicity. These findings may offer a key ingredient for exchange biased spintronic devices with 100% spin polarization, having a unidirectional anisotropy to control and manipulate spins at the nanoscale.     

Design and fabrication of highly dispersive semiconductor double-chirped mirrors

We report on the development of semiconductor double-chirped mirrors with the group delay dispersion of ?3,800 ± 100 fs² in the wavelength range between 1,058 ÷ 1,064 nm and reflectivity of 99.1 %. The simplified plane-wave reflection transfer method was used to design the mirror multilayer stack. The mirror contains an epitaxial AlAs/GaAs structure topped with a SiNx antireflective layer.     

Ground-state inversion method applied to calculation of molecular photoionization cross-sections by atomic extrapolation: Interference effects at low energies

The ground-state inversion method, which we have previously developed for the calculation of atomic cross-sections [ 29 ], is applied to the calculation of molecular photoionization cross-sections. These are obtained as a weighted sum of atomic subshell cross-sections plus multi-centre interference terms. The atomic cross-sections are calculated directly for the atomic functions which when summed over centre and symmetry yield the molecular orbital wave function. The use of the ground-state inversion method for this allows the effect of the molecular environment on the atomic cross-sections to be calculated. Multi-centre terms are estimated on the basis of an effective plane-wave expression for this contribution to the total cross-section. Finally the method is applied to the range of photon energies from 0 to 44 eV where atomic extrapolation procedures have not previously been tested. Results obtained for H₂, N₂ and CO show good agreement with experiment, particularly when interference effects and effects of the molecular environment on the atomic cross-sections are included. The accuracy is very much better than that of previous plane-wave and orthogonalized plane-wave methods, and can stand comparison with that of recent more sophisticated approaches. It is a feature of the method that calculation of cross-sections either of atoms or of large molecules requires very little computer time, provided that good quality wave functions are available, and it is then of considerable potential practical interest for photoelectron spectroscopy.     

Control of laser pulse parameters in a cavity with a thermal-nonlinearity shutter

The light pulse generation by a laser controlled by shutter from a finite-thickness absorbing layer with thermal nonlinearity has been studied theoretically. The layer placed in the cavity is oriented with respect to the mirror so that conditions for nonlinear total internal reflection of generated radiation are created. In the plane-wave approximation, a self-consistent system of nonlinear truncated equations for the field amplitudes together with constitutive equations has been obtained. Numerical simulation with the use of the obtained system has shown that it is possible to control the form and duration of the generated pulse by varying the absorption coefficient of the nonlinear medium and the angle of incidence on the absorbing layer, as well as the layer thickness.Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 71, No. 6, pp. 771–777, November–December, 2004.This revised version was published online in April 2005 with a corrected cover date.