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     

Reducing losses in dielectric waveguide discontinuities

Rectangular dielectric waveguides are used in millimeter-wave applications. They have low loss and wide bandwidth at high frequencies. Another major advantage to dielectric waveguides is that they are inexpensive to design and manufacture. However, a major disadvantage to the dielectric waveguide is that they experience relatively high losses at bends and T-junctions. This paper looks at a novel approach in reducing the insertion loss in dielectric waveguide bends and T-junctions. A high dielectric material is inserted at the discontinuity, causing the electromagnetic energy to be coupled and launched toward the output. The dielectric constant of the material, position of the material, and shape of the material are instrumental in reducing the insertion loss. A transition discontinuity in the form of a 45° bend has also been found to reduce insertion loss when properly designed. The size, shape, and location of the discontinuity and the high dielectric material are optimized and compared to the results without a high dielectric material. The 90°- and 45°-bend simulations were verified by building test structures and comparing predictions of the insertion loss to measurements     

任意截面波导管截止频率的MRM-BEM计算

本文基于多重互易边界元法,利用横向谐振技术,计算了对称双脊波导的截止波数,通过截止波数可以进一步求得其他传输特性常数。计算结果与文献有很好的一致性。     

Full-wave analysis of cross-aperture waveguide couplers

This paper presents a full-wave analysis of coupling between rectangular waveguides through a cross-aperture. The rigorous mode-matching method is used to derive the generalized scattering matrix of a waveguide T-junction having a crossed waveguide as the side arm. Two three-port T-junctions are then cascaded together to form a number of cross-aperture couplers. The analysis method can handle both broad-wall and narrow-wall, both parallel and crossed coupling structures. Our numerical results for a variety of couplers are in good agreement with those obtained by Ansoft's HFSS     

Insulated Nonradiative Dielectric Waveguide for Millimeter-Wave Integrated Circuits

An improved version of the nonradiative dielectric waveguide (NRD-guide), called an insulated nonradiative dielectric waveguide, is proposed for millimeter-wave integrated circuits. This dielectric waveguide can overcome some difficulties which arise when high dielectric material is used in the NRD-guide. Guide wavelengths and transmission losses were measured at 50 GHz and compared with theory. In addition, some basic circuit components such as bends, ring resonators, chip resonators, and T-junctions were fabricated on the basis of the insulated NRD-guide and tested to confirm their usefullness in millimeter-wave integrated circuits. The fabricated components operated as expected without suffering from any appreciable radiation at curved sections and discontinuities.     

Rigorous Mode-Matching Method of Circular to Off-Center Rectangular Side-Coupled Waveguide Junctions for Filter Applications

An accurate and efficient method for analyzing circular to multiple off-center rectangular side-coupled waveguide T-junctions is developed based on a rigorous mode-matching technique. The method is very general and not limited by symmetry or other dimensional constraints to the junction. A new way to match fields on the curved interface between subregions is described in detail. The computer code developed based on this theory is highly efficient. The numerical results match with the results obtained by other methods including experimental ones. The method is used to design a side-coupled circular waveguide dual-mode filter.     

Wide-band waveguide and ridge waveguide T-junctions for diplexerapplications

Scattering parameters of E- and H-plane stepped waveguide and E-plane ridge waveguide stepped T-junctions are obtained using an extension of the three-plane mode matching method. An optimization process is applied to find the T-junctions and step dimensions that yield a low reflection coefficient in one of the T-junctions arms over a wide frequency band. An example of the design of a wideband T-junction diplexer is presented. The diplexer filters are inductive window waveguide filters, and are rigorously modeled using mode matching and a novel two-dimensional curve fitting method, which greatly reduces the CPU time for optimization. The diplexer optimization procedure, as well as the filter modeling method, are described. Experimental results on the optimized T-junction and the diplexer are presented; both show excellent agreement with their computed optimum results, without any adjustments or tuning     

Analysis of Optical Waveguide Consisting of a Square-Law Lenslike Medium and its Analogies to Circular TE/sub 01/ waveguide

Propagation behavior of light beams along sinusoidal and serpentine bends as well as circular bends and linearly tapered bends of optical waveguides consisting of a square-law Ienslike medium is investigated in detail, both theoretically and numerically, on the basis of the approximate wave theory. A new design method of the circular bend for removing the effects of the bend is proposed and numerical results are presented. The divergence phenomena of the beam trajectory in both the sinusoidal and serpentine bends of the optical waveguide are discussed in comparison with mode-conversion phenomena occurring in the circular TE/sub 01/ waveguide with the same bends. Several design conditions to eliminate undulations of the beam trajectory and/or the spot size which would occur at a circnlar bend of the optical waveguide are also studied, and interesting analogies to the design conditions proposed so far to prevent mode-conversion losses at a circular bend of the TE/sub 01/ waveguide are shown.     

Vector analysis of optical dielectric waveguide bends usingfinite-difference method

A full-vectorial analysis of optical dielectric waveguide bends using the finite-difference method has been developed. The formulation was based on the transverse electric field components, E_r and E_z. To set up the boundary conditions at each dielectric interface, the continuity of E_&thetas;, H_&thetas;, and the tangential component of the electric field, and the discontinuity of the normal component of the electric field were satisfied. The finite-difference scheme was modified to satisfy these boundary conditions. The results of the analysis using the current method is compared with previous results. The optimal offset for 90° bends was obtained, and the losses for these optimal bend structures are also presented     

A high-gain 58-GHz box-horn array antenna with suppressed gratinglobes

A low-profile high-gain antenna array of box horns for the frequency band 57.2-58.2 GHz is presented. The antenna consists of 256 radiating elements divided into two subgroups of 128 elements fed by a rectangular waveguide feed network. The radiating elements are fed in parallel and the waveguides are connected with T-junctions. The matching of the T-junctions is improved with a matching pin and a splitter. Because of the waveguide feed network, the element spacing is larger than one wavelength, which causes grating lobes. The grating lobes and sidelobes in the H-plane have been suppressed by the use of a combination of subarrays, a special characteristic of the box horn, and an array amplitude tapering. The measured sidelobe levels in the H-plane are below -30 dB at angles larger than 8° from boresight. A gain higher than 35.7 dBi and a return loss higher than 14.4 dB have been measured for the antenna over the band 57.2-58.2 GHz     

波导混合模问题的修正边界元法分析

本文建立了分析波导混合模问题的修正边界元模型;导出了关于混合模的耦合边界积分方程组及其退化形式,并用矩量法将之离散为齐次代数方程组,从而得波导的混合模传输常数;最后以部分介质填充波导为例进行了计算,所得结果与横向谐振法结果吻合得很好。     

五角波导TM模截止波数的边界元分析

推导了常数单元边界元法求解波导本征值问题的矩阵计算公式，应用常数单元和线性单元边界元法计算五角波导TM模的截止波数，两种方法计算所得结果与文献中已有结果吻合良好。     

Field theoretical CAD of open or aperture matched T-junctioncoupled rectangular waveguide structures

The rigorous computer-aided design of rectangular waveguide structures coupled by open or rectangular iris loaded E- or H-plane T-junctions is described. The design theory is based on the full wave mode-matching method for the key-building-block T-junction element associated with the generalized S-matrix technique for composite structures. The waveguide structures may be arbitrarily composed of the T-junction and already known key-building-block elements (such as the double step and the septum discontinuity) combined with homogeneous waveguide sections between them. The E- or H-plane T-junction effect, large apertures, finite iris or septum thicknesses, and higher-order mode interactions at all step discontinuities are rigorously taken into account. Typical design examples, like rectangular iris coupled T-junctions, narrow-stopband waveguide filters, high return loss E-plane T-junction diplexers, an elliptic function E-plane integrated metal insert filter and a simple ortho-mode transducer demonstrate the efficiency of the method. The theory is verified by measurements     

Transmission Characteristics of Ridge Waveguide Loaded with Left-Handed Materials

This paper presents a numerical study of the electromagnetic wave propagation in a double ridge waveguide, loaded with left-handed materials (LHM). The LHM is defined phenomenologically by assigning to it a negative permittivity and negative permeability simultaneously. Transmission characteristics such as cutoff wavelength, single-mode bandwidth, dispersion and field patterns have been investigated by edge-based finite element method. The results are compared to those with air- and dielectric-loaded ridge waveguide. It was found that the LHM-loaded ridge waveguide can greatly increase the cutoff wavelength with the disadvantage of a dramatic reduction in the single-mode bandwidth. The behavior of the dispersion curve of LHM-loaded ridge waveguide is similar to the cases of waveguide loaded with air or dielectric, except for a significant improvement of the propagation constant. The boundary conditions at the interface between the air and the LHM have been well illustrated and the antiparallel wave vector in LHM were obtained by considering the field patterns. The unusual behaviors of the LHM-loaded ridge waveguide provides the potential opportunities to design novel microwave and millimeter devices.     

The method of lines for the analysis of dielectric waveguide bends

The analysis of a wide class of waveguide bends using the method of lines is suggested. The discretization is performed in radial direction. The cross section of the waveguide may consist of many inhomogeneous layers. Loss can be taken into account by using complex permittivities. The radiation loss is calculated by the use of absorbing boundary conditions. The presented algorithm is verified by the analysis of a rib waveguide bend. The results are in good agreement with those published in the literature     

A versatile moment method solution of the conventional and modifiedcoplanar waveguide T-junctions

The conventional and modified coplanar waveguide (CPW) T-junctions, both symmetric and nonsymmetric, are investigated using the full wave moment method with duality for the electric and magnetic currents. The method is shown to be accurate and computationally more efficient than the finite-difference-time-domain (FDTD) method previously used to solve these T-junctions. The results show that the dispersion in the S-parameters of the different types of CPW T-junctions investigated can be minimized by a proper choice of the dimensions and locations of the air bridges. The versatility of the method is demonstrated by its ability to solve complicated CPW structures with different types of air bridges, such as the modified CPW T-junction     

Nonradiative Dielectric Waveguide for Millimeter-Wave Integrated Circuits

A nonradiative dielectric waveguide is proposed in which dielectic strips are sandwiched between two parallel metal plates separated by a distance smaller than half a wavelength. Though the structure is substantially the same as that of the H-guide, it is based on a quite different principle of operation. This dielectric guide is particularly applicable in millimeter-wave integrated circuits, since it is not only small in size, but also allows bends and junctions to be incorporated into the circuits with very little radiation and interference. A design diagram is given. Losses and coupling coefficients of the strips are calculated, as well. Some basic circuit components, such as 90° and 180° bends and T-junctions, made of polystyrene strips, are measured to confirm their usefulness in millimeter-wave integrated circuits.     

Compensation of Discontinuities in Planar Transmission Lines

Compensation of discontinuity reactance associated with steps, right-angled bends, and T-junctions in planar transmission lines has been carried out by removing appropriate triangular portions from the discontinuity configurations. A two-dimensional analysis using a Green's functions approach has been employed.     

Finite element beam propagation method for three-dimensionaloptical waveguide structures

A beam propagation method (BPM) based on the finite element method (FEM) is described for longitudinally varying three-dimensional (3-D) optical waveguides. In order to avoid nonphysical reflections from the computational window edges, the transparent boundary condition is introduced. The present algorithm using the Pade approximation is, to our knowledge, the first wide-angle finite element beam propagation method for 3-D waveguide structures. To show the validity and usefulness of this approach, numerical results are shown for Gaussian-beam excitation of a straight rib waveguide and guided-mode propagation in a Y-branching rib waveguide     

A full-wave analysis of an arbitrarily shaped dielectric waveguideusing Green's scalar identity

An integral equation analysis is proposed to determine the phase constant of an arbitrarily shaped dielectric waveguide. The main feature of this approach is the use of Green's scalar identity in which only simple contour integrals have to be evaluated. Different scalar Green's functions are considered to satisfy the boundary conditions for the electric and magnetic fields in each region. This approach is combined with the boundary element technique with linear elements for the computation. The case of the rectangular dielectric image waveguide is discussed. and numerical results are shown to be consistent with other theories and experiments. The cases of hollow rectangular and semicircular image waveguides are analyzed, and numerical results are presented