Plane wave propagation in uniaxial bianisotropic medium

The uniaxial bianisotropic medium is a generalisation of the bi-isotropic and chiral media which recently have been subject to intensive research. Such a medium results, for example, when microscopic helices with parallel axes are positioned in a host dielectric in random locations. Plane wave propagation in such a medium is studied and a simple solution for the dispersion equation is found. Numerical examples for the wave number surfaces of the medium are given.<>     

Green dyadic for a uniaxial bianisotropic medium

An explicit expression for the Green dyadic corresponding to the axially chiral reciprocal uniaxial bianisotropic medium is derived through dyadic analysis with no recourse to Fourier transformations. The result is a generalization of the Green dyadic corresponding to the uniaxial anisotropic medium, which has been known for decades. As a verification, expressions for the field due to an axial dipole are derived and compared to those derived recently through other methods. The medium under study can be realized by laying axially parallel metal helixes in random locations in a host material. Such a medium has recently been shown to possess important polarization-transforming properties     

Plane wave propagation in a uniaxial bianisotropic medium with an application to a polarization transformer

Uniaxial bianisotropic medium is a generalization of the well-studied bi-isotropic and chiral media. It is obtained, for example, when microscopic helices with parallel axes are positioned in a host dielectric in random locations. Plane wave propagation in such a medium is studied and a simple solution for the dispersion equation and for the eigenwaves are found. As a numerical example, polarization properties of a transverse wave propagating in a uniaxial bianisotropic medium is considered. The results give a simple possibility to construct a polarization transformer with a transversely uniaxial chiral medium for changing the polarization of a propagating plane wave.     

Experimental and finite-difference time-domain technique characterization of transverse in-line photonic crystal fiber

We characterize a microstructured photonic crystal fiber in the transverse direction, observing photonic bandgap effects in the transmission spectra. This is modeled using band structure and finite-difference time-domain techniques and reasonable agreement is found, confirming the observation of higher order partial photonic bandgaps. A tapered transverse bandgap fiber is used to create a reduced loss device utilizing the fundamental gap. This technique may be used to monitor the draw process for bandgap fibers, or fibers used in this way may be utilized as microphotonic elements.     

Modeling of power supply noise in large chips using the circuit-based finite-difference time-domain method

In this paper, a multilayered on-chip power distribution network consisting of two million passive elements has been modeled using the finite-difference time-domain (FDTD) method. In this method, a branch capacitor has been used. The use of the branch capacitor is important for simulating multilayered power grids. In addition, a method for including the CMOS inverter characteristics into the FDTD simulation has been presented. As an example of the application of this method, an H-tree clock network was simulated to compute the power supply noise distribution across an entire chip. Various scenarios with varying decoupling capacitances, load capacitances, number of clock buffers, and rise times have been analyzed to demonstrate the importance of circuit nonlinearity on power supply noise. Also, a method has been presented for analyzing package and board planes. Based on the methods presented, the interaction between chip and package has been discussed for capturing the resonant behavior that is otherwise absent when each section of the system is analyzed separately.     

圆环天线的时域有限差分分析

采用时域有限差分算法（FDTD）计算了圆环天线在高斯脉冲激励下的瞬时电流分布，通过付里叶变换，获得天线在不同频率下的稳态电流分布，经过进一步计算，得出天线在这组频率下的辐射方向图和输入阻抗。     

Modeling ultrashort field dynamics in surface emitting lasers by using finite-difference time-domain method

An approach based on the finite-difference time-domain (FDTD) method is developed for simulating the dynamics of vertical-cavity surface-emitting lasers (VCSELs). The material response is incorporated in our FDTD algorithm by the effective semiconductor Bloch equations, and its effects are accounted for through a resonant polarization term in the Maxwell's equations. Moreover, nonlinear gain saturation is incorporated through a gain suppression factor in the equation governing the dynamics of the resonant polarization. This approach is verified by modeling a /spl lambda/-cavity VCSEL, with a multiple quantum-well (MQW) gain region; the corresponding continuous-wave operation is obtained at the expected wavelength. The dynamics of ultrashort pulses generated by a monolithic passively mode-locked one-dimensional VCSEL with a MQW gain region and a single QW saturable absorber are studied and it is demonstrated that a stable mode-locked pulse train can be generated. It is also demonstrated that with our FDTD approach subcycle temporal precision can be achieved. The need for this fine temporal resolution is established by investigating pulse propagation through the semiconductor saturable absorber. Fine features of the spatial profile of the mode-locked pulses are also examined within this approach. This knowledge of the fine spatial features is then used for lowering the current threshold through gain structure optimization. Various approaches for the reduction of the total simulation time are also discussed.     

Analysis of multiport rectangular waveguide devices using pulsed finite-difference time-domain (FDTD) technique

The pulsed FDTD method is used to analyse multiport junctions in rectangular waveguides. Two representative examples are considered, namely the H-plane tee junction and the folded H-plane tee junction. Computed results for the scattering parameters are compared to measurements performed by the authors.<>     

BI-FDTD: a novel finite-difference time-domain formulation for modeling wave propagation in bi-isotropic media

This paper presents a newly developed finite-difference time-domain (FDTD) technique, referred to as BI-FDTD, for modeling electromagnetic wave interactions with bi-isotropic (BI) media. The theoretical foundation for the BI-FDTD method will be developed based on a wavefield decomposition. The main advantage of this approach is that the two sets of wavefields are uncoupled and can be viewed as propagating in an equivalent isotropic medium, which makes it possible to readily apply conventional FDTD analysis techniques. The BI-FDTD scheme will also be extended to include the dispersive nature of chiral media, an important subclass of bi-isotropic media. This extension represents the first of its kind in the FDTD community. Validations of this new model are demonstrated for a chiral half-space and a chiral slab.     

Efficient time-domain finite-difference beam propagation methodsfor the analysis of slab and circularly symmetric waveguides

The generalized Douglas scheme is applied to the time-domain finite difference beam propagation methods (TD-BPMs) in rectangular and cylindrical coordinates. High accuracy and efficiency are demonstrated through the analysis of optical pulse propagation in slab and circularly symmetric waveguides. As an example of a reflection problem, the TD-BPM in cylindrical coordinates is applied to the analysis of a fiber Bragg grating with a sinusoidal index change. Effectiveness of the present scheme is discussed in comparison with the conventional TD-BPM and the finite-difference time-domain method     

Equivalence of propagation characteristics for thetransmission-line matrix and finite-difference time-domain methods intwo dimensions

The equivalence of propagation characteristics for the transmission line matrix (TLM) and finite-difference-time-domain (FD-TD) methods in two dimensions is discussed. A propagation analysis of a TLM shunt node complete with permittivity and loss stubs and a dispersion analysis of the two-dimensional FD-TD method in an arbitrary medium are performed and yield dispersion relations. The relations are identical when the FD-TD method is operated at the upper limit of its stability range     

Numerical analysis of traveling-wave photodetectors' bandwidth using the finite-difference time-domain method

We present full-wave analysis of traveling-wave photodetectors (TWPDs) using the finite-difference time-domain (FDTD) method. Impulse response in the frequency domain is obtained after time-domain data are calculated by the FDTD method. The impulse response includes the optical field profile, carrier transit time, microwave loss, microwave dispersion, and velocity mismatch all together. Three-decibel bandwidth is analyzed with the thickness of an i-layer and waveguide width as the design parameters. It is shown how transit time and microwave characteristics affect the bandwidth according to the TWPD's length. Three-decibel bandwidth is dominated by carrier transit time in case the device length is shorter than 300-500 /spl mu/m under the conditions given in this paper. However, if the device length gets longer, microwave characteristics affect the bandwidth.     

Analysis of shielded membrane microstrip line using the finite-difference time-domain method

A simple and efficient analysis method of the shielded membrane microstrip (SMM) line using the finite-difference time-domain (FDTD) method is presented. New FDTD equations are derived using the contour path FDTD concept for the Yee cell which contains three thin dielectric sheets of membrane. The characteristic impedance and the effective dielectric constant of the SMM line are calculated using our proposed method. The method is validated by comparison with the results shown by Robertson et al. [1996].     

Characterization of microstrip discontinuities using conformalmapping and the finite-difference time-domain method

Microstrip discontinuities are analyzed using Wheeler's waveguide model and the finite-difference time-domain (FDTD) method. Wheeler's model employs a conformal transformation to convert a microstrip into an enclosed waveguide structure. This permits the mapping of a discontinuous microstrip into a discontinuous, but enclosed, waveguide. The enclosed waveguide eliminates the difficulties usually associated with analysis of an open domain geometry. The FDTD technique is then used to calculate the scattering coefficients of the discontinuous waveguide. The features of this approach are: (1) it yields a smaller computational domain than that required to analyze the untransformed geometry; (2) it yields results over a band of frequencies; and (3) it is simple to implement. Results obtained using this scheme show good agreement with previously published results     

Modeling of rough-surface effects in an optical turning mirrorusing the finite-difference time-domain method

A finite-difference time-domain (FDTD) method is applied to calculate the forward-reflected and back-reflected powers of a guided mode from a rough turning mirror in a bent waveguide of a high-power laser array. By segmenting this large problem into a number of smaller problems, the simulation region can be shrunk to a small area containing only the details of the rough-surface mirror. By launching the incident wave judiciously, the computation time grows linearly with the length of the mirror. A farfield transformation of the calculated time-domain scattered field yields forward-reflected and back-reflected powers. The computer time needed to analyze this large turning-mirror system is reduced to about 3 min of CRAY time, compared to several hours for a brute-force approach using a full mesh     

单轴双各向异性媒质柱体的电磁散射

采用广义多极子技术（Ｇｅｎｅｒａｌｉｚｅｄ Ｍｕｌｔｉｐｏｌｅ Ｔｅｃｈｎｉｑｕｅ,ＧＭＴ）分析了单轴双各向异性媒质任意截面柱体的电磁散射,计算结果与解析解和矩量法（Ｍｅｔｈｏｄ ｏｆ Ｍｏｍｅｎｔｓ,ＭｏＭ）所得结果一致,讨论了该方法在电磁散射应用中的优缺点。     

A conformal mesh-generating technique for the conformal finite-difference time-domain (CFDTD) method

This article presents an efficient conformal-mesh generating technique suitable for the conformal finite-difference time-domain (CFDTD) technique. We describe the mesh generation for different types of objects, including planar structures (patch antennas and microwave circuits), as well as for arbitrary three-dimensional structures created by using AutoCAD, GID, or other commercial solid modelers. The versatility of the mesh-generation tool is illustrated through several examples.     

Computer-aided design of two dimensional electric-type hyperthermiaapplicators using the finite-difference time-domain method

A hyperthermia applicator design tool consisting of a finite-difference time-domain (FDTD) technique in combination with a graphical display of electric fields and normalized linear temperature rise is described. This technique calculates, rather than assumes, antenna current distributions; it includes mutual interactions between the body and the applicator, and it calculates driving-point impedance and power delivered to the applicator. Results show that the fundamental limitation of 2-D electric-type applicators is overheating of the fat by normal components of the electric field, which exist because of near fields and capacitive coupling with the muscle. Two factors which contribute to the capacitance are the muscle conductivity and the small antenna size in air. Two examples of applicators designed to avoid fat overheating are described: a 27-MHz segmented dipole for heating large tumors to 7 cm depth, and a 100-MHz dipole for small tumors to 5 cm depth. The first uses a water bolus, and the second uses a water bolus with low-permittivity strips to reduce normal fields at the antenna ends. The results of this study describe fundamental limitations of electric field applicators, and illustrate the use of a powerful applicator design tool that allows rapid evaluation of a wide range of ideas for applicators which would require months and years to test experimentally.     

Analysis of the frequency response of SAW filters using finite-difference time-domain method

The finite-difference time-domain (FDTD) technique was extended to analyze the frequency response of surface acoustic wave (SAW) filters. In this method, the partial derivatives of quasi-static Maxwell's equations and the equation of motion are discretized to centered finite differences. In addition, the perfectly matched layer boundary condition was applied to reduce spurious reflections. Two structures are considered in this paper. First, the model was applied to analyze the influence of the number of electrodes on the frequency response of a SAW filter fabricated on a zinc oxide (ZnO) substrate. Then, the proposed method was further extended to analyze the frequency response of a ZnO/diamond/Si-layered SAW filter. The simulated results are in a good agreement with the existing experimental data, indicating that the FDTD method was an appropriate approach for modeling SAW devices.     

Toward the development of a three-dimensional unconditionallystable finite-difference time-domain method

In this paper, an unconditionally stable three-dimensional (3-D) finite-difference time-method (FDTD) is presented where the time step used is no longer restricted by stability but by accuracy. The principle of the alternating direction implicit (ADI) technique that has been used in formulating an unconditionally stable two-dimensional FDTD is applied. Unlike the conventional ADI algorithms, however, the alternation is performed in respect to mixed coordinates rather than to each respective coordinate direction, Consequently, only two alternations in solution marching are required in the 3-D formulations. Theoretical proof of the unconditional stability is shown and numerical results are presented to demonstrate the effectiveness and efficiency of the method. It is found that the number of iterations with the proposed FDTD can be at least four times less than that with the conventional FDTD at the same level of accuracy