Fractal characteristics of far-field diffraction patterns for two-dimensional Thue-Morse quasicrystals

We report a numerical method to analyze the fractal characteristics of far-field diffraction patterns for two-dimensional Thue-Morse (2-D TM) structures. The far-field diffraction patterns of the 2-D TM structures can be obtained by the numerical method, and they have a good agreement with the experimental ones. The analysis shows that the fractal characteristics of far-field diffraction patterns for the 2-D TM structures are determined by the inflation rule, which have potential applications in the design of optical diffraction devices.     

Equivalent network analysis of MIC transmission lines in the spectral domain

The propagation characteristics of planar guiding structures are analyzed by an equivalent network method in the spectral domain. Both the eigenvalues and eigenfunctions of the guided structure are determined by solving the active transmission line network. Numerical results obtained by the network method are compared with those obtained by the other method. It is demonstrated that the present method is simple but accurate and therefore is suitable for analyzing the 3-D discontinuity problems of some complicated planar structures.     

Frequency-dependent transmission characteristics of curved microstrip bends

The frequency-dependent transmission characteristics of curved microstrip bends are calculated by utilising a second-order perturbation analysis of the equivalent curved waveguide model and a mode-matching method that includes the higher-order modes. Computational results for the transmission coefficient of typical curved microstrip bends are presented and compared to results obtained for right-angle and chamfered right-angle bends.<>     

A novel dimension-reduction technique for the capacitanceextraction of 3-D VLSI interconnects

In this paper, a new capacitance extraction method called the dimension-reduction technique (DRT) is presented for three-dimensional (3-D) very large-scale integration (VLSI) interconnects. The DRT converts a complex 3-D problem into a series of cascading simple two-dimensional (2-D) problems. Each 2-D problem is solved separately, thus we can choose the most efficient method according to the arrangement of conductors. We have used the DRT to extract the capacitance matrix of multilayered and multiconductor crossovers, bends, vias with signal lines, and open-end. The results are in close agreement with those of Ansoft's SPICELINK and the Massachusetts Institute of Technology's (MIT) FastCap, but the computing time and memory size used by the DRT are several (even ten) times less than those used by SPICELINK and FastCap     

Photonic-Crystal Heterostructure Waveguides

Photonic crystals (PC) are periodic dielectric structures that, if suitably designed, prohibit light propagation within a frequency band even though the constituent materials may be transparent in this range. One of the remarkable applications of such artificial photonic materials has been to provide guiding of light. Ultimately, to guide light in directions other than straight lines, PC waveguide (PCW) bends are needed, and thus are expected to be essential building blocks of photonic integrated circuits. While bending light through large angles is possible with conventional waveguides, the corner radii of such bends cannot typically be reduced to the electromagnetic wavelength, which hinders the realization of extremely compact devices. And though sharp two-dimensional (2-D) PCW bends have been proposed, the transmission is typically low and/or narrow band. Here we focus on PCWs obtained by introducing line defects in otherwise period 2-D PCs with the aims of enhancing the typical poor and low-bandwidth transmission through tight bends. We show how PCW bends occurring at heterojunctions between different PCs may enable unprecedented flexibility in meeting these aims. The deformation introduced to the usual PC lattice lifted off the angle constraint and resulted in the power transmission greater than 90% over in the 95-nm bandwidth     

A rigorous and efficient method of moments solution for curvedwaveguide bends

An accurate and computationally efficient method of moments solution together with a mode-matching technique for the analysis of curved bends in a general parallel-plate waveguide is presented. In order to exemplify the techniques, the method is applied to study the transmission characteristics of single and cascaded curved E- and H-plane bends in a rectangular waveguide. It is shown that the effect of the orientation of cascaded bends on the transmission properties can be significant, and examples to demonstrate this effect are included. Results of the convergence with increasing number of expansion functions illustrate that only a few terms need to be considered for accurate evaluation of the transmission characteristics of structures with single and multiple bends. Comparison with measurements for single and cascaded curved H-plane bends in a WR-90 waveguide show good agreement with the predicted result     

Air trenches for sharp silica waveguide bends

Air trench structures for reduced-size bends in low-index contrast waveguides are proposed. To minimize junction loss, the structures are designed to provide adiabatic mode shaping between low- and high-index contrast regions, which is achieved by the introduction of "cladding tapers." Drastic reduction in effective bend radius is predicted. We present two-dimensional (2-D) finite-difference time-domain/effective index method simulations of bends in representative silica index contrasts. We also argue that substrate loss, while present, can be controlled with such air trenches and reduced to arbitrarily low levels limited only by fabrication capabilities. The required trench depth, given an acceptable substrate loss, is calculated in three dimensions using an approximate equivalent current sheet method and also by a numerical solver for full-vector leaky modes. A simple, compact waveguide T-splitter using air trench bends is presented.     

High-density integrated optics

This paper presents two dimensional (2-D) finite difference time domain (FDTD) simulations of low-loss right-angle waveguide bends, T-junctions and crossings, based on high index-contrast waveguides. Such structures are essential for the dense integration of optical components. Excellent performance characteristics are obtained by designing the waveguide intersection regions as low-Q resonant cavities with certain symmetries and small radiation loss. A simple analysis, based on coupled mode theory in time, is used to explain the operation principles and agrees qualitatively with the numerical results     

Reversible decorrelation method for progressive transmission of 3-Dmedical image

In this paper, the authors present a new reversible decorrelation method of three-dimensional (3-D) medical images for progressive transmission. Progressive transmission of an image permits gradual improvement of image quality while being displayed. When the amount of image data is very large, as a 3-D medical image, the progressive transmission plays an important role in viewing or browsing the image. The data structure presented in this paper takes account of interframe correlation as well as intraframe correlation of the 3-D image. This type of data structure has been termed the 3-D hierarchy embedded differential image (3-D-HEDI) as was derived from the earlier HEDI structure (Kim et al., 1995). Experiments were conducted to verify the performance of 3-D HEDI in terms of the decorrelation efficiency as well as the progressive transmission efficiency. It is compared with those of conventional hierarchy interpolation (HINT), two-dimensional (2-D) HEDI and differential pulse code modulation (DPCM). Experimental results indicate that 3-D HEDI outperforms HINT, 2-D HEDI and DPCM in both decorrelation efficiency as well as the progressive transmission efficiency on 3-D medical images     

On the Fast and Rigorous Analysis of Compensated Waveguide Junctions Using Off-Centered Partial-Height Metallic Posts

In this paper, we present an efficient and rigorous method, based on the 3-D boundary integral-resonant-mode expansion technique, for the analysis of multiport rectangular waveguide junctions compensated with partial-height cylindrical metallic posts. The electrical performance of a great variety of commonly used wideband microwave circuits has been improved drastically thanks to the introduction of a new design parameter, i.e., the relative position of the metallic post in the structure. To the authors' knowledge, this parameter has not been taken into account in previous studies concerning compensated junctions using partial-height metallic posts. The developed tool has been successfully used to design compensated H- and E-plane right-angled bends and power dividers, as well as optimal magic-T junctions. This novel tool has been fully verified through comparisons between our results and those provided by a well-known commercial finite-element method software     

三维介质频率选择表面结构的多模网络分析

该文采用多模网络与严格模匹配相结合的方法分析了介质周期结构在电磁波斜入射情况下的散射特性。定量地分析了这种三维频率选择表面结构的频率选择特性随入射波的频率、入射角度、周期层和均匀层的厚度与介电常数等结构参数的变化关系,从而为三维介质频率选择表面的设计和应用提供了依据。     

3-D CMOS Circuits Based on Low-Loss Vertical Interconnects on Parylene-N

parylene-N is used as a dielectric layer to create ultra low-loss 3-D vertical interconnects and coplanar waveguide (CPW) transmission lines on a CMOS substrate. Insertion loss of 0.013 dB for a 3-D vertical interconnect through a 15-$mu$ m-thick parylene-N layer and 0.56 dB/mm for a 50- $Omega$ CPW line on the parylene-N layer (compared to 1.85 dB/mm on a standard CMOS substrate) are measured at 40 GHz. L-shaped, U-shaped, and T-junction CPW structures are also fabricated with underpasses that eliminate the discontinuities arisen from the slot-line mode and are characterized up to 40 GHz. A 3-D low-noise amplifier using these post-processed structures on a 0.13-$mu$ m CMOS technology is also presented along with the investigation of parasitic effects for accurate simulation of such a 3-D circuit. The 3-D circuit implementation reduces the attenuation per unit length of the transmission lines, while preserving the CMOS chip area (in this specific design) by approximately 25%. The 3-D amplifier measures a gain of 13 dB at 2 GHz with 3-dB bandwidth of 500 MHz, noise figure of 3.3 dB, and output 1-dB compression point of ${+}$ 4.6 dBm. Room-temperature processing, simple fabrication, low-loss performance, and compatibility with the CMOS process make this technology a suitable choice for future 3-D CMOS and BiCMOS monolithic microwave integrated circuit applications that currently suffer from high substrate loss and crosstalk.      

Periodic bandgap and effective dielectric materials in electromagnetics: characterization and applications in nanocavities and waveguides

The main objectives of this paper are to characterize and develop insight into the performance of photonic bandgap (PBG) periodic dielectric materials and to integrate the results into some novel applications. A powerful computational engine utilizing the finite-difference time-domain technique with periodic boundary conditions/perfectly matched layers integrated with Prony's method is applied to provide an in-depth look at the physics of PBG/periodic bandgap structures. Next, the results are incorporated into two classes of applications in the areas of nanocavity lasers and guidance of electromagnetic (EM) waves in sharp bends. A two-dimensional PBG structure with finite thickness is presented to strongly localize the EM waves in three directions and design a high-Q nanocavity laser. It is shown that the periodic PBG/total internal reflections remarkably trap the EM waves inside the defect region. The effect of the number of periodic cells and defect's dielectric constant on the Q of structure is investigated. It has been found that a seven-layer PBG with a dielectric impurity defect can be used in the design of a laser with a Q as high as 1050. Additionally, potential applications of the PBG structures for guiding the EM waves in sharp bends, namely, 90/spl deg/ and 60/spl deg/ channels are demonstrated. It is shown that shaping the bend by introducing small holes can noticeably improve the guidance of the waves at the bends and channel the EM waves with great efficiency. A comparative study between PBG and effective dielectric materials in controlling the EM waves is also provided and it is observed that the novel characteristics of the PBG cannot be modeled using the effective material for the frequencies within the bandgap.     

Enhanced detectability of small objects in correlated clutter usingan improved 2-D adaptive lattice algorithm

Two-dimensional (2-D) adaptive filtering is a technique that can be applied to many image processing applications. This paper will focus on the development of an improved 2-D adaptive lattice algorithm (2-D AL) and its application to the removal of correlated clutter to enhance the detectability of small objects in images. The two improvements proposed here are increased flexibility in the calculation of the reflection coefficients and a 2-D method to update the correlations used in the 2-D AL algorithm. The 2-D AL algorithm is shown to predict correlated clutter in image data and the resulting filter is compared with an ideal Wiener-Hopf filter. The results of the clutter removal will be compared to previously published ones for a 2-D least mean square (LMS) algorithm. 2-D AL is better able to predict spatially varying clutter than the 2-D LMS algorithm, since it converges faster to new image properties. Examples of these improvements are shown for a spatially varying 2-D sinusoid in white noise and simulated clouds. The 2-D LMS and 2-D AL algorithms are also shown to enhance a mammogram image for the detection of small microcalcifications and stellate lesions.     

一种二维金属电磁带隙结构的电磁传输特性

采用时域有限差分法与Floquet定理相结合，对由正方形金属柱构成的二维电磁带隙结构的传输特性进行了分析和计算，得到了不同频率的平面电磁波在不同角度入射时，该结构的传输参数及电磁特性。通过改变金属方柱的边长和间距，得到了电磁带隙结构的阻带中心频率的变化规律，进而得到了拟合公式，该公式计算结果与仿真结果间最大误差不超过2％，具有较好的可靠性和较高精度，可用于EBG结构的应用研究。     

Modified Gain and Mode Characteristics in Two-Dimensional Photonic Crystal Waveguide With Microcavity Structure

Optical gain spectra of InGaAsP MQW for photonic crystal waveguide (PCWG) were simulated by the method with considering the variation of group velocity and the natural broadening synthetically. The dependence of the first mode's gain maximum on the width of PCWG was discussed. To improve the mode characteristics and the gain performances in the 2-D PCWG with relative large width, we proposed a new structure by combining a microcavity inside the 2-D PCWG. Mode characteristics in proposed structure were analyzed and the transmission performance was simulated by the FDTD method. The simulation results show that improved longitudinal mode characteristics can be obtained even in the W3 PCWG with relative wide waveguide width because of the additional frequency selecting mechanism provided by the microcavity.     

Design and characterization of a 10-Gb/s dual-drive Z-cut Ti:LiNbO/sub 3/ electrooptical modulator

The design and characterization of a dual-drive (DD) Z-cut Ti:LiNbO/sub 3/ electrooptical modulator are presented. Both the radio frequency (RF) electrode layout and the optical splitters and combiners of the Mach-Zehnder interferometer are investigated: The former is designed to avoid RF line crosstalk, whereas the latter is to obtain a low-loss longitudinally short splitter structure, able to properly separate the interferometer straight optical waveguide sections. First, the RF analysis is addressed, simulating the small-signal behavior of the DD coplanar waveguide electrode structure as a function of the central ground width. The performances of different splitter layouts (circular segment bends, sin-bends, and offset bends) are then investigated using the beam propagation method. Finally, experimental results on the electrical and optical test pattern structures, and of the DD Z-cut complete modulator, are discussed and compared with simulations.     

Three-dimensional analysis of a Cherenkov laser via particlesimulation

For a three-dimensional (3-D) Cherenkov laser composed of a dielectric-loaded rectangular waveguide and a finite-width planar relativistic electron beam, the nonlinear characteristics and efficiency enhancement are investigated with the aid of particle simulation, allowing for the nonlinear properties of the electron beam. The numerical results obtained in the paper are compared with those obtained in the two-dimensional (2-D) analysis. The efficiency enhancement scheme, which was previously proposed for the 2-D case, is found to be effective also for the 3-D case     

Study of 3-D magnetic components by means of "double 2-D" methodology

The magnetic field in many magnetic components, namely toroids and EE cores, has a three-dimensional (3-D) distribution. Energy and losses calculation in these particular structures makes necessary the use of 3-D techniques that accounts for all 3-D effects. The calculation of the energy and losses is needed in order to obtain any transformer model. This paper presents a procedure that allows the calculation of energy and losses in 3-D structures using two-dimensional (2-D) approaches. This procedure accounts for 3-D effects, solving each magnetic component by means of two different analyses but using 2-D finite-element analysis (FEA) solvers instead of 3-D. The main advantages of this procedure are that all geometrical and frequency effects are taken into account using 2-D FEA solvers. 3-D FEA solvers are not applicable to analyze most practical cases because of the complexity in the geometry. Therefore, the use of this method is not only advantageous from the point of view of time reduction, but also it is a solution for many cases where 3-D solvers are not a feasible solution. Some experimental results illustrate the application of the methodology, which is especially useful to study the influence of the winding strategy in toroidal structures and to design integrated magnetics in order to adjust the coupling coefficient between each pair of windings before the component construction.     

Calculation of Microstrip Bends and Y-Junctions with Arbitrary Angle

A method is described for calculating the frequency-dependent scattering parameters of microstrip bends and Y-junctions with arbitrary angles. Use is made of a waveguide model and an orthogonal series expansion for the fields around the discontinuity of the bend, so that the excitation and propagation of higher order modes can be considered. The transmission properties of the Y-junctions are derived from those of the bends by a symmetry consideration. Numerical results are given for two different substrates and are compared with experimental data. Neglecting radiation effects, they are in good agreement.