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This paper describes a novel fabrication technique for constructing a polymer-based large-core single-mode rib waveguide. A negative tone SU8 photoresist with a high optical transmission over a large wavelength range and stable mechanical properties was used as a waveguide material. A waveguide was constructed by using a polydimethylsiloxane stamp combined with a solvent-assisted microcontact molding technique. The effects on the final pattern's geometry of four different process conditions were investigated. Optical simulations were performed using beam propagation method sol, ware. Single-mode beam propagation was observed at the output of the simulated waveguide as well as the actual waveguide through the microscope image. OCIS codes: 050.2770, 130.5460, 130.7408, 160.5470, 220.4000, 230.1480.

To model electrically large waveguiding structures, the compact-finite-difference time-domain (FDTD) algorithm needs to use severely scaled down time steps to properly contain the rapidly growing numerical dispersion errors with increased operating frequency. In this work, a high-order compact-FDTD algorithm based on fourth-order spatial central finite differencing and fourth-order temporal backward finite differencing is developed. The accuracy and efficiency of this proposed algorithm are verified through its dispersion relation analysis and validated by modeling high-frequency wave propagation through an earth tunnel. The obtained computational efficiency allows this high-order algorithm to model wireless propagation through longitudinally-invariant road and railway tunnels using several hundred compact-FDTD cells as opposed to the several million FDTD cells required by three-dimensional FDTD algorithms. Index Terms--Compact finite-difference time-domain (FDTD) method, earth tunnels, electrically large waveguides, high-order finite-difference time-domain (FDTD) methods, numerical dispersion.

The high-speed optoelectronic memory system project is concerned with the reduction of latency within multiprocessor computer systems (a key problem) by the use of optoelectronics and associated packaging technologies. System demonstrators have been constructed to enable the evaluation of the technologies in terms of manufacturability. The system combines fiber, free space, and planar integrated optical waveguide technologies to augment the electronic memory and the processor components. Modeling and simulation techniques were developed toward the analysis and design of board-integrated waveguide transmission characteristics and optical interfacing. We describe the fabrication, assembly, and simulation of the major components within the system. OCIS codes: 200.0200, 200.0220.

An efficient analytical and accurate model to predict the shielding effectiveness of a rectangular enclosure with numerous small apertures is presented. In this paper, an appropriate equivalent admittance for the perforated side is suggested amid the free space and the enclosure, utilizing the traditional waveguide circuit model where the enclosure is represented by a short-circuited rectangular waveguide. The simulation results of this model are in better agreement with measurements than that of the original waveguide equivalent circuit model. This method is applicable to an array of square and circular holes of staggered and square configurations. Index Terms--Enclosures with numerous apertures, rectangular shielding enclosure, shielding effectiveness (SE).

Exact equivalent straight waveguide representation is given for a waveguide of arbitrary curvature and torsion. No assumptions regarding refractive index contrast, isotropy of materials, or particular morphology in the waveguide cross section are made. This enables rigorous full-vector modeling of in-plane curved or helically wound waveguides with use of available simulators for straight waveguides without the restrictions of the known approximate equivalent-index formulas. Index Terms--Coordinate transformation, equivalent straight waveguide, helical coordinates.

In the effective index method, which models photonic crystal fibers by means of a step-index waveguide analogy, two critical parameters are the effective index of the cladding and the effective core radius. It has been shown that the use of an effective core radius as a function of the relative air hole diameter, or also of the relative wavelength, can improve the accuracy of this method. We show, by comparison with a rigorous finite-difference frequency-domain method, that the reported improved fully vectorial effective index methods have commonly adopted a radius of the equivalent circular unit cell, which does not give the best accurate effective cladding index as compared with the use of an equivalent circular unit cell having the same area as the hexagonal unit cell. Furthermore, by defining both the radius of the equivalent circular unit cell and the effective core radius as a function of the relative air hole diameter, and the relative wavelength, we believe that the fully vectorial effective index method can be further enhanced in terms of accuracy of both the effective cladding index and the modal index. OCIS codes: 060.2310, 060.2400, 000.4430.

The finite-difference time-domain (FDTD) method incorporating an equivalent resonant cavity model is presented for the modeling and analysis of guided-wave propagation characteristics of complex periodic structures. By transforming electromagnetic field variables into a new set of periodic variables, which can also be resolved from the Maxwell's equations, one can convert a periodic guided-wave problem into an equivalent resonator problem. Thus, the FDTD method used for a resonant cavity problem can be adopted to simulate periodic guided-wave structures. In addition, the proposed FDTD algorithm can be extended to model lossy periodic propagation problems. In this study, the substrate integrated nonradiative dielectric waveguide, which is a special type of periodic guided-wave structure subject to a potential leakage loss due to its periodic gaps, is investigated as a showcase. The proposed method is first validated and is then used to analyze the guided-wave characteristics of substrate integrated nonradiative dielectric waveguides. It is shown that the substrate integrated nonradiative dielectric waveguide structure, which can easily be fabricated in planar form, has a well-behaved propagation property suitable for high-performance millimeter-wave circuit design. Index Terms--Complex propagation constant, equivalent resonant cavity model, finite-difference time-domain (FDTD) method, periodic guided-wave structure, quality factor, substrate integrated nonradiative dielectric waveguide.

The unidirectional grating-assisted codirectional coupler (U-GACC) has recently been proposed. This unique structure permits irreversible coupling between orthogonal waveguide eigenmodes by means of simultaneous modulation of both the real and imaginary parts of the refractive index in the coupling region. Analysis of the U-GACC has until now relied on coupled mode theory, which can be restrictive in its application as a design tool. We analyze the U-GACC by the transfer matrix method, which demonstrates in a simple fashion why the device operates in a unidirectional manner. In addition, we show that for all practical designs, there is a limit to the minimum cross talk between outputs, a phenomenon that has not been previously identified. OCIS codes: 060.1810, 130.3120, 250.4480.

The body-of-revolution finite-difference time-domain (BOR-FDTD) method is applied to the analysis of a tapered cylindrical-dielectric-rod fed by a metallic waveguide with a launching horn. Before evaluating the wave propagating along the tapered rod, we design the launching horn to efficiently excite the fundamental guided-mode of a uniform rod. After confirming the effectiveness of the launching horn, guided-mode conversion properties are evaluated in linearly and curvilinearly tapered rods. As a result, the guided mode excited at the feed end is smoothly converted into that at the free end in a curvilinearly tapered rod. It is numerically revealed that the smooth guided-mode conversion leads to the expansion of the equiphase field region in a terminal aperture with a subsequent increase in the gain. The calculated radiation patterns are in good agreement with experimental data. Index Terms--Antenna theory, dielectric antennas, dielectric waveguides, endfire antennas, finite-difference time-domain (FDTD) methods.

Several new uni-planar coplanar-waveguide-fed slot surface-wave launchers are presented in this paper. The launchers are used to efficiently excite the dominant transverse-magnetic surface-wave mode inside a grounded dielectric slab for possible use in power combiners and other applications. Analysis of the surface waves and optimization of the slab thickness and other needed parameters are presented. Next, the launchers design and optimization using two commercially available software are described. The launchers were fabricated and tested. Good agreement is obtained between the numerical and experimental results. Index Terms--Power combiners, surface-wave launchers, Yagi--Uda coplanar slot antennas.

Conformal-mapping techniques are used to derive an effective and advanced calculation model for the microwave properties of a light-intensity traveling-wave electroabsorption modulator, resulting in a quasi-TEM computer-aided-design circuit model. For a given device geometry, the model provides the transmission-line (TML) parameters' characteristic impedance and waveguide (WG) propagation constant. Closed-form expressions are derived for the reactive circuit elements. The calculation model includes both the effect of metal conduction loss, as well as losses due to induced currents in the semiconductor substrate. We treat both the buried heterostructure, as well as the ridge-mesa optical WG implementations. The model is validated with full-wave simulations and compared to measured TML parameters. Index Terms--Coplanar waveguides (CPWs), electroabsorption, intensity modulation, optical modulation, skin effect, substrate losses, traveling wave.

We present an empirical model for the waveguiding properties of directly UV-written planar waveguides in silica-on-silicon. The waveguides are described by a rectangular core step-index profile, in which model parameters are found by comparison of the measured waveguide width and effective index with modal field calculations. The model is used as input for beam propagation method calculations to design UV-written optical components. Subsequent fabrication of such components showed a good agreement with the model predictions. Using the model will reduce the number of iterations and thereby the development time of new optical devices. OCIS codes: 130.0130, 130.2790, 130.3120, 220.0220, 220.4610, 230.7390.

A horizontal waypoint guidance algorithm is proposed by applying line-following guidance to waypoint line segments in sequence. The line-following guidance is designed using an LQR (linear quadratic regulator). Then, the optimal waypoint changing points are derived by minimizing the accelerations required for changing the waypoint line segments. Also derived is a sufficient condition for the stability bound of ground speed changes based on the Lyapunov Stability Theorem. Simulation results show that the proposed algorithm can effectively guide a vehicle along the sequence of waypoint line segments.

Anisotropic lossy waveguides are analyzed by applying the finite-element method with higher order interpolatory vector elements. The problem is formulated in terms of the electric field only. The transverse vector component of the electric field is numerically represented by higher order curl-conforming interpolatory vector functions, whereas the longitudinal component of the field is represented by higher order scalar basis functions. Due to the better interpolatory capabilities of the expansion functions, the metallic and material losses are modeled with a higher precision with respect to that provided by the other available numerical models. Furthermore, the use of higher order elements permits the correct modeling of the discontinuity of the normal field component at the interfaces between different materials. Index Terms--Finite-element method, guided-mode analysis, higher order basis functions.

Research describing an ultrasonic resonant technique for characterizing liquids is presented. An important aspect of this method is that it requires only small liquid samples.

In this paper, a new finite-difference time-domain (FDTD) algorithm is proposed in order to eliminate the Courant-Friedrich-Levy (CFL) condition restraint. The new algorithm is based on an alternating-direction implicit method. It is shown that the new algorithm is quite stable both analytically and numerically even when the CFL condition is not satisfied. Therefore, if the minimum cell size in the computational domain is required to be much smaller than the wavelength this new algorithm is more efficient than conventional FDTD schemes in terms of computer resources such as central-processing-unit time. Numerical formulations are presented and simulation results are compared to those using the conventional FDTD method. Index Terms: ADI method, CFL condition, FDTD method.

An electric-field integral-equation formulation discretized via the method of moments (MoM) is proposed for the analysis of arbitrarily shaped planar conductive layers in a shielded guided-wave structure. The method results in a generalized scattering matrix (GSM) for the planar structure and can be used with other GSM's, derived using this or other techniques, to model cascaded structures in waveguide. The Kummer transformation is applied to accelerate slowly converging double series expansions of impedance matrix elements obtained in the MoM solution. In this transformation, the quasi-static part associated with a singularity of the electric-type Green's function in the region of a conductive layer is extracted and evaluated in terms of modified Bessel functions, resulting in a dramatic reduction of terms in a double series summation. The proposed technique permits the modeling of a variety of conductive frequency-selective surfaces, including quasi-optical grids and patch arrays for application to spatial power combining. Index Terms - Acceleration techniques, electromagnetic analysis, Green's functions, layered waveguide, method of moments, planar conductive layers.

This paper presents a set of newly developed computer-aided-design-oriented formulas for the evaluation of the quasi-static even- and odd-mode characteristics of conductor-backed coplanar-waveguide (CBCPW) coupled lines. This set of expressions is evaluated using a conformal mapping method based on the assumption of pure transverse-electromagnetic propagation. The result for the odd- and even-mode characteristic impedance and effective dielectric constants computed by these formulas agrees well with the result evaluated from the existing formulas of both Wadell and Hanna. However, the new expressions derived provide a more systematic and efficient method for calculating the essential parameters of CBCPW coupled lines as compared to the existing ones in [1] and [2]. Index Terms - Coplanar waveguide, coupled lines, directional coupler.

This paper presents an alternative approach to the method of [Mathematical Expression Omitted] for constructing the complete eigenfunction expansions of the dyadic Green's functions for circular waveguides with perfectly conducting walls and filled with homogeneous biisotropic media. The eigenfunction expansions are constructed using the discontinuity relations obtained from Maxwell's dyadic equations treated in the distribution sense. The orthoganality relations for waveguide modes are derived based on the modified reciprocity theorem involving a complementary medium. To illustrate the distinctions between different sets of biisotropic constitutive relations, the dyadic Green's functions are determined for Post-Jaggard and Drude-Born-Federov relations. Index Terms - Biisotropic media, circular waveguide, dyadic Green's function.

In this paper, the surface current density excited by a delta-gap voltage source on shielded printed lines is computed and its medal decomposition analyzed. This analysis specifically aims to determine the practical excitation of complex and/or backward modes in this kind of structures. It has been found that complex modes in reciprocal structures are always excited in pairs whose propagation constants and amplitudes of excitation have the same imaginary part and opposite sign real part. The combination of the pair of complex modes gives rise to an evanescent mode whose amplitude is modulated by a sinusoidal function. Backward modes have also been found to be part of the modal spectrum excited by the source and, thus, in a frequency swept, they appear after the attenuation constant of a pair of complex modes goes to zero. Index Terms - Complex and backward modes, modal decomposition, shielded planar lines, spectral-domain techniques, waveguide excitation.

We present a rigorous differential method describing the propagation of an electromagnetic wave in an elementary mitred bent waveguide (H- and E-planes). Maxwell's equations are used in tensorial form, written in a nonorthogonal coordinate system where the boundary surfaces coincide with coordinate surfaces. Therefore, the expression of boundary conditions on the perfectly conducting walls becomes simplified. The electric and magnetic fields are expanded on trigonometric series, which satisfy the boundary conditions. For this problem, the interesting results are the magnitude and phase of the reflected and transmitted modes (transverse-electric modes for H-plane bend, longitudinal-section electric modes for E-plane bend). The transition conditions between the bent waveguide and access waveguides enable us to determine the scattering matrix of this structure. The knowledge of the scattering matrix enables us to simulate any uniform bent waveguides, even those with radii of curvature equal to zero. Index Terms - Electromagnetic wave, mitred bent waveguide, propagation, scattering matrix, tensorial form.

Absorption and emission cross sections in Er(super 3+)-doped waveguides from transversal fluorescence spectra for transitions involving thermalized states are measured in situ. The method is based on the McCumber theory and is tested in Er-doped Ti:LiNbO3 waveguides to derive accurate cross-section values for the 550-nm band. It is shown that the measurement approach is efficient in providing absorption and emission cross sections, and is especially attractive for transitions between excited states.

An acoustooptic tunable filter with collinear TE-TM mode conversion in a GaAs-AlAs multiquantum well rib waveguide is described. The high form birefringence occurring in the waveguide is utilized to analyze the theoretical basis of the tunable filter. It is shown that the TE-TM mode conversion exhibits a relatively low acoustic frequency, a high diffraction efficiency and a figure of merit which is 14 times higher than that of conventional LiNbO3 filters based on an acoustooptic tunable filter.

Full-wave modeling of the coupling structure between a double-ridge waveguide and dielectric-loaded resonator in a rectangular cavity through an iris is presented. Eigen modes of the double-ridge waveguide, and the discontinuities of the structures are obtained by rigorous mode-matching method. By applying the cascading procedure, the reflection coefficients of the coupling structure can be obtained. From the phase variation of the reflection coefficient and circuit theory, resonant frequency and input/output coupling of the structure are accurately determined. An equivalent circuit model of the resonant structure is established. The computed results are compared with those obtained by other methods and shown to be in good agreement, which verify the theory. Index Terms - Couplings, dielectric resonators, filters, ridge waveguides.

A ray analysis of periodically segmented waveguides with parabolic-index variation in the high-index region is presented. We carried out the analysis using ray transfer matrices, which is convenient to implement and which can be extended to study different types of graded-index segmented waveguide. Results of this ray tracing approach clearly illustrate the waveguiding properties and the existence of stable and unstable regions of operation in segmented waveguides. We also illustrate the tapering action exhibited by segmented waveguides in which the duty cycle varies along the length of the waveguide. This analysis, although restricted to multimode structures, provides a clear visualization of the waveguiding properties in terms of ray propagation in segmented waveguides.

A new leaky-wave antenna was presented and discussed in Part I that possesses many desirable performance features. The antenna structure is also simple in form, consisting of a rectangular waveguide with an offcenter stub on its top wall. Part I presented the principle of operation and the basic theory in which the stub guide was idealized to be infinitely long (or high) in order to stress the essential features. In practice, however, the stub guide has a finite length (or height) and it may be terminated by a flange or a ground plane or simply remain in the form of a pair of baffles. The modifications in the theory and the associated performance considerations under these practical circumstances are treated in the present paper - Part II. Index Terms - Leaky-wave antennas.

A new leaky-wave antenna is presented here that possesses many desirable features and is suitable for application to both the millimeter-wave and microwave ranges. These desirable features, some of which are unusual, include a simple configuration, a wide flexibility in the range of available beamwidths, the ability to control the beamwidth and the direction of the beam essentially independently, and negligible cross polarization at all scan angles. The antenna structure consists of a parallel-plate stub guide of small height, less than a half wavelength, located off center on the top of rectangular waveguide. The beamwidth is easily controlled from very wide to very narrow by adjusting the stub width or location. Part I presents the principle of operation and the theory, employing a new transverse equivalent network that is accurate, but also simple, so that it permits rapid and inexpensive numerical calculations. Part II describes and derives the modifications required in the theory to account for flanges and/or finite stub length, and Part III is devoted to measurements at X-band and from 40 to 60 GHz on both the propagation properties and the radiation patterns; excellent agreement with the theory is demonstrated. Index Terms - Leaky-wave antennas.

In this paper, the character of the propagation in the microcellular urban and suburban environments in the 902-928-MHz frequency band in line-of-sight (LOS) conditions is investigated both theoretically and experimentally for the purpose of wireless radio local loop (WRLL) prediction. The path-loss characteristics and the range of a break point, at which the polynomial character of field intensity decay along the street level is changed, are analyzed for various parameters of street widths, for different average building heights, and for the actual electrical impedance properties of building walls. A multislit waveguide with randomly distributed gaps between the sides of buildings is considered as a model of straight streets. Results of experiments for VHF/UHF wave propagation along the straight streets in urban environment in the conditions of direct visibility between receiver and transmitter are compared with theoretical analysis of field intensity decay, path-loss distribution, and dependence of the break point on street topography in LOS conditions.

Semiconductor quantum-well (QW) lasers at 980 nm show unique spontaneous emission spectra. The transfer matrix method was used to numerically calculate the modal gain spectra of the waveguide structure. The exhibited modulation results in modulation of the emission spectra. The results of the numerical modeling are explained and clarified, using an analytical approach based on coupled mode equations.

Characteristics of coplanar transmission lines on multilayer substrates expressed in analytic formulas have been obtained using conformal mapping. The accuracy of these formulas has been verified experimentally on a variety of coplanar transmission lines using differential electro-optic (DEOS) sampling. For coplanar waveguides, the theory differs from the experiment by less than 3%; for coplanar striplines, the differences are less than 6%.

A general analysis approach for strip metallization structures enclosed in rectangular or square waveguide is presented. The technique involves the novel application of a commercially available 2.5-dimensional (2.5-D) method-of-moments-based (MoM) electromagnetic (EM) analysis tool to a three-dimensional (3-D) waveguide problem. Very good agreement is demonstrated between computed and measured results for several printed strip linear polarizers embedded within a square waveguide environment. This paper, to the authors' knowledge, represents the first such comparison of phase and magnitude between computed and measured data for strip grid polarizers in a waveguide environment. The developed approach involves construction of a theoretical waveguide 'test fixture' and an associated theoretical de-embedding procedure. Computational advantages are expected over the alternative approach of using a finite-element-based fully 3-D analysis approach. The polarizer results have potential application to shielded versions of quasi-optic array components that have been demonstrated in open geometries, as well as to multimode antenna feeds, waveguide filters, and matching networks. Index Terms - Electromagnetic analysis, polarizers, waveguide.

A simple semi-empirical high-frequency equivalent circuit model for characterizing the coplanar waveguide structure composed of relatively thick metal line on very thick polyimide over lossy substrate such as Si BiCMOS wafer is shown. Modified models for the equivalent circuit elements were derived taking into account the geometric dependence of the conductive loss and the skin effect of the substrate loss.

In this paper a detailed analysis of a sandwich coupled slotline with axially or transversely magnetised ferrite layer has been carried out by using FEM with edge elements. Comparison of dispersion characteristics and phase shift shows that the variable reciprocal phase shift is larger with axial bias field than with transverse field, and that non-reciprocal phase shift per unit length (with transverse field) increases with frequency whereas reciprocal phase shift per unit length (with axial field) decreases with frequency. Also conductor-backed coplanar structures may be more suitable than suspended structures.

Several finite element formulations based on edge elements have been developed in recent years, avoiding the appearance of spurious modes in waveguides. However, no formulation of this kind dealing with general lossy inhomogeneous and anisotropic waveguides has been found in the literature. In this paper, a new finite element scheme for the most general linear waveguides has been derived from vector wave equations via a Galerkin procedure. In this formulation, triangular and quadrilateral edge elements have been used in order to avoid the spurious solutions. Furthermore, the final eigensystem involves only very sparse matrices, thus allowing important savings in time and memory. Index Terms - Anisotropic waveguides, edge elements, finite-element method.

A rigorous analysis combining the orthogonal expansion method and Galerkin method for the higher order eigenmodes in a circular-rectangular (C-R) waveguide is presented in this paper. The Bessel-Fourier series is employed to merge the circular and rectangular coordinate systems used in the analysis. The cutoff frequencies of the higher order modes are determined with the singular value decomposition (SVD) technique. The computed results are in excellent agreement with results obtained using the finite element method. Because of its analytic form, the solution will be useful in the rigorous analysis of many practical microwave components and circuits.

In this paper, two contributions to the study of the elliptical waveguides are given: an efficient technique to obtain the modal spectrum for elliptical waveguides and the analysis of the junctions between rectangular, circular, or elliptical to elliptical waveguides. In addition to theoretical results, experimental results are also presented finding good agreement between prediction and measurement.

Many hybrid modes are required in computing the fields scattered from discontinuities in structures such as finline, coplanar waveguide, or microstrip. The authors present a new analytical method based on an eigenvalue formulation of the generalized telegrapher's equations discretized by using the modes at cutoff as an expanding set. This approach produces a compact theoretical model while providing at the same time an effective algorithm for finding the characteristics of many modes, including their below cutoff and complex behavior. The theoretical approach gives some direct insights about the appearance of complex modes. Due to the explicit formulation of the eigenvalue equation for the complex propagation constant, the proposed method overcomes some of the typical drawbacks of the currently used algorithms, such as the limited numerical accuracy and efficiency, the numerical degeneracy and appearance of spurious solutions, the inability to trace the characteristics of degenerate modes. Numerical results for ordinary and complex propagation in finline show excellent agreement with existing data.

A method is presented to model electromagnetic radiation, combining the finite-element technique in the penetrating portion of a three-dimensional (3-D) radiating structure with an integral equation on the outer surface of the computational domain, and with a waveguide mode-matching technique on a cross section of the feeding waveguide. The antenna can be of general shape, provided a portion of the surrounding medium up to a surface of revolution is chosen as part of the computational domain. This truncation scheme and the accurate source representation are more general than those existing in the literature for radiation modeling. An open-ended waveguide and a waveguide with a choke ring are analyzed and their radiation patterns are obtained and compared with available measurements. Index Terms - Mode-matching methods, electromagnetic radiation.