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For a highly information-oriented society, further enhancement of the capacity and speed of communications and information systems is necessary. For this purpose, all-optical logic elements are expected as a promising solution. In this paper, structures of new all-optical logic elements using a nonlinear medium with its index of refraction varying with the optical intensity are proposed and their properties are analyzed. Most of the all-optical logic elements based on nonlinear materials proposed to date either make use of more than two wavelengths or require a specific phase condition (such as 0° or 180°) for combined lightwaves with identical wavelengths. It is extremely difficult to fix the phase difference between the two lightwaves to be combined. This is a significant problem in practical fabrication. In this paper, all-optical logic elements are proposed in which only one wavelength is used and no specific phase relationship is required. For the numerical analysis, the FD-BPM (Finite Difference Beam Propagation Method) based on the Padé) (1, 1) approximation is used. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 85(9): 1–12, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10048 [ABSTRACT FROM AUTHOR]

This paper considers a model of a Čerenkov laser consisting of a relativistic electron beam and a parallel plate waveguide loaded with a dielectric thin film. By units of numerical analysis, the improvement of the growth characteristics for the electromagnetic wave and the efficiency in energy conversion is discussed. In the Čerenkov laser, the growth of the electromagnetic wave is caused by the transfer of the kinetic energy of the electron beam to the electromagnetic energy. As a result, the drift velocity of the electron beam is decreased gradually so that the synchronism with the phase velocity of the electromagnetic wave cannot be maintained and an efficient transfer of energy is prevented. Thus, the permittivity of the dielectric material composing the waveguide is increased gradually along the direction of the propagation for the electromagnetic wave to reduce the phase velocity of the electromagnetic wave. In this manner, the synchronism with the drift velocity of the electron beam is maintained, leading to an efficient transfer of energy. The variation of the permittivity causes power loss due to the mode scattering of the electromagnetic wave or the reflection or conversion to higher-order uses. In this paper, the effect of the mode scattering is taken into account for detailed numerical analysis of the amplification characteristics for the electromagnetic wave. It is shown that the efficiency in energy conversion from the electron beam to the electromagnetic wave and the amplification characteristics of the electromagnetic wave can be significantly improved. [ABSTRACT FROM AUTHOR]

In this paper, a numerical analysis algorithm has been derived for the analysis of the problem of plane wave diffraction by a multilayered grating. This algorithm is based on the Yasuura method with the smoothing procedure and can be applied to the problems of arbitrary multilayered dielectric (or metallic) grating with smoothly shaped grooves. The convergence of the approximate solution obtained by the present algorithm has been investigated numerically. It was demonstrated that a highly accurate approximate solution can be computed by the introduction of the smoothing procedure. The present algorithm is applicable to problems of a multilayered grating over the range from infrared to visible. As a numerical example, the diffraction efficiency of the multilayered diffraction grating made of alternate lamination of the high-index and low-index dielectric layers deposited on a metal grating is calculated by the algorithm in this paper. The following items are confirmed: (1) by coating dielectric films, the power absorption of the incident light by the metal grating is reduced in a specific wavelength region; and (2) in a multilayered grating, anomalous resonant absorption occurs by the coupling of the guided mode excited by the dielectric thin film and the diffracted wave. [ABSTRACT FROM AUTHOR]

It is necessary to increase the density of fibers of optical cables which are to be used in subscriber lines. To realize such high-density fiber cables, multicore fibers with several cores inside a single cladding have been investigated. However, in multicore fibers, there is the problem of crosstalk between the adjacent cores. This paper investigates the two-core asymmetric single-mode fibers which reduce the crosstalk between adjacent cores. It is shown numerically that the crosstalk can be kept below a certain level for any fiber length, under the condition of fixed-mode field diameter. In a symmetrical structure, the transfer of optical power is perfect and to suppress the crosstalk, the transmission length must be kept limited. However, in asymmetrical structures investigated in this paper, the transmission length is not limited and it becomes possible to design high-density optical transmission lines with small separation between their two cores. [ABSTRACT FROM AUTHOR]

The nonlinear Schrödinger equation (NLSE) is one of the partial differential equations appearing in a number of research areas including mathematics, physics, engineering, and biology. Its applicable area is quite wide. In this paper, as a solution method for an NLSE accompanied with modification or perturbation (generalized NLSE), the - integral method (NM) is used. The basic concept, formulation, and actual numerical calculation algorithm are described. The NM introduced by Feynman is a nonrelativistic quantum mechanical formulation based on the Lagrangian font Since the final formula obtained in this paper takes a standard Fourier transform type, it is possible to use the fast Fourier transform (FFT) so that a quantum jump in numerical efficiency has been attained. it should be noted that only one Fourier transform operation is needed per unit propagating section. As a generalized NLSE, a set of coupled nonlinear Schrödinger equations with a perturbation is considered. As a specific example of application, numerical results for optical solitons are presented. [ABSTRACT FROM AUTHOR]

A new extended integral equation is introduced for three-dimensional electromagnetic scattering problems, and a method is proposed for analyzing this extended integral equation numerically by means of a new boundary element method in which vector shape functions are used. In the conventional boundary integral equation, there is no unique solution to the electromagnetic wave at the angular frequency coinciding with the one characteristic to the system. Several methods are proposed for alleviating this problem; however, each has its own problem. This paper proposes an extended integral equation in which the observation points are allocated on a closed surface in- side the scatterer adjacent to the scatterer surface. Not only does the extended integral equation proposed in this paper a frequencies, hut also it overcomes various deficiencies of the conventional integral equation method. in this paper, the extended integral equation for a three-dimensional perfectly conducting scatterer is derived first and its uniqueness of the solution is proven. Further, for practical examples, this extended integral equation is solved numerically by means of the new boundary element method using vector shape functions. The uniqueness and accuracy of the solution are studied numerically. [ABSTRACT FROM AUTHOR]

A new numerical method is proposed for the analysis of the electromagnetic scattering problem by an inhomogeneous scatterer. Although the finite-element method and the boundary-element method have a high degree of generality, several difficulties occur i they are applied to the electromagnetic scattering problem. First, in the case of the finite-element method, treatment of inhomogeneous regions is easy, but that of an open region is difficult. Hence, the finite-element method is not suited for the scattering problems in which open regions such as the exterior of the scattering body need to be treated. On the other hand, in the case of the boundary-element method, treatment of the open region is easy but that of inhomogeneous regions is difficult. In this paper, a new combination of the finite-element and boundary-element methods is proposed in which the advantages of both are incorporated. The new combined method proposed in this paper solves several difficulties of the conventional combination method by means of the boundary-element method using the extended integral equation for which observation points are placed on the closed loop inside the scatterer. Numerical computations are carried out for a number of examples so that it is proven that the present method can be applied to scatterers with arbitrary shapes and arbitrary permiltivity distributions. Further, it is shown that in addition to the far field, the near field can be found. [ABSTRACT FROM AUTHOR]

This paper proposes an analysis method based on the finite-element method that can be applied to such rotationally symmetric structures as circular cylindrical resonators. In general, the main drawback associated with the finite-element methods for electromagnetic eigenvalue problems is the mixing of the nonphysical or spurious solutions with the physical solutions. However, in the method proposed in this paper, all the spurious solutions have zero eigenvalues and can easily be separated from the physical solutions, thereby eliminating the problem of spurious solutions. Moreover, the computation can be treated as two-dimensional, thus a large saving in computer time and storage is obtained compared to three-dimensional computations. Theoretical equations are derived and by using a numerical example the rightness of this method is demonstrated. [ABSTRACT FROM AUTHOR]

The waveguide bend is an indispensable circuit element in realizing optical integrated circuits. In this paper, the bend in a dielectric slab waveguide is analyzed numerically by means of the integral equation formulation. When a numerical solution of an integral equation is attempted by the boundary-element method, two problems exist: 1) how one can connect the field distributions expressed by the boundary-element method with those by the eigenmodes of the waveguide. In this paper, instead of representing the field at the input/output boundary of the bend in the slab waveguide in terms of the boundary-element method, a new method is proposed in which the field distributions expressed in terms of the eigenmodes are substituted directly into the integral equation; and 2) the treatment of the radiation mode. In this paper, a discretization method based on the sampling theorem is used. As an example, numerical calculations have been carried out for a conventional bend and a reflection bend in a dielectric slab waveguide. It is confirmed that the results agree well with data obtained by other methods. It is pointed out that good results can be obtained for such cases as a structure with large difference in index of refraction between the core and cladding and the one with a large bend angle, which were difficult to analyze by the conventional methods. Further, it is shown that the bending loss of the reflection bend is substantially smaller than that of the conventional bend. [ABSTRACT FROM AUTHOR]

Although Luneburg lenses are already in practical use, few papers have been published on their wave-optical analysis. This is due to the difficulty in the wave-optical analysis of the electromagnetic field in an inhomogeneous medium with a large radius, in addition to the fact that most researchers have been interested so far in a geometrical-optic analysis. Increased applications of this type of lens to a microwave hand require more precise analysis from the wave-optics viewpoint. This paper deals with the wave-optical analysis of a cylindrical Luneburg lens. Taking several numerical analysis methods, the relationship between the number of terms of a truncated series and the accuracy of the analysis, and the relationship between the computation time and the accuracy of the analysis are examined. A method is proposed which can be applied to a lens having a large radius compared with the wavelength. By using this method, actual numerical analyses are carried out, and the focus characteristics and the distribution of the heat generation (the power dissipation density) in the lens are shown. These are compared with the results of published numerical analyses. Some interesting results, which cannot be obtained from a conventional geometrical-optic analysis, are obtained by the proposed method. [ABSTRACT FROM AUTHOR]

In direct transmission of an image by image fiber, the image is blurred by crosstalk due to mode coupling between element fibers, which impairs the resolution. This paper discusses a method of improving the crosstalk characteristics of the image fiber and its effectiveness. First the one-dimensional structure is considered and then the application of the results to improvement of the characteristics of the two-dimensional structure is discussed. The method proposed in this paper reduces the mode coupling and improves the crosstalk characteristics by using two or more kinds of element fibers with different radii, shapes and medium parameters so that element fibers of the same kinds are located as far apart as possible. Numerical analysis of the proposed structure is conducted and its effectiveness is discussed in detail. The analysis in this paper leads to a simple and important conclusion which states that the crosstalk depends mainly on the difference in eigenvalues of the different element fibers if the distances between cores are kept constant, no matter whether the core radius or dielectric constants are varied. Thus, the crosstalk characteristics of the image fiber can be determined from the eigenvalues of the element fibers without calculating the modes (eigenvalues) of the whole image fiber. This property is especially useful in the case of the two-dimensional structure, for which exact analysis is difficult. [ABSTRACT FROM AUTHOR]

A region decomposition technique is proposed for point matching method analysis of electromagnetic scattering problems involving various polygonal cylinders with conducting edges. In this paper, it is verified that the scattering problem is amenable to accurate numerical analysis by the point matching method. The influence of the shape change of the scatterer in the shadow region is investigated. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 90(8): 18–25, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20339 [ABSTRACT FROM AUTHOR]

In surgical navigation systems, system error analysis is performed because of the need for correct superposition of three-dimensional data obtained with three-dimensional position sensors and different coordinate systems for the images. Lea and colleagues proposed a registration graph for providing a systematic description with a graph of the geometrical position of the system and performing error analysis. However, the registration graph requires the explicit input of errors for each 3D data item. The authors expanded this system to automatically calculate individually occurring errors from system design information through a simulation, and to perform direct error analysis from the system design information. As a result, a user without specialized knowledge of error analysis can automatically perform error analysis by virtually designing a 3D data integration system on a computer. In this paper, the authors constructed a system simulator for modeling point-to-point registration and 3D position sensors, performing automatic error calculation with the simulation based thereon, and designing a system easily using a GUI. Furthermore, as a demonstration of the simulator, the simulator was applied to error analysis for a system including point-to-point registration and 3D position sensors, and its effectiveness and reliability were confirmed. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 90(8): 45–59, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20377 [ABSTRACT FROM AUTHOR]

This paper proposes a method for design of the shape and thickness of a dielectric dome by optimization, aiming at achieving multibeam emission with a uniform high gain for a wide range of angles. The dielectric dome has the features that it does not require a tremendous number of elements, as in the constrained lens, and that excellent multibeam characteristics can be realized over a wider range of angles than in the conventional dielectric lens. These features are demonstrated through an example of the design of a dielectric dome in which a decrease in gain is avoided over a wide range of angles up to 70°. The validity of the proposed method is verified by numerical analysis, and also by measurement and evaluation of the radiation pattern of the constructed dielectric dome antenna in the Ka band. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 90(5): 49– 57, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20254 [ABSTRACT FROM AUTHOR]

A new configuration of inner conductor is presented in this paper for a planar branch-line coupler at high-frequency range where the linewidth is not negligible with respect to the guide wavelength. The high characteristic admittance lines with a wide linewidth deteriorating higher-frequency performances of the branch-line coupler are replaced with an equivalent planar circuit consisting of triangular patches and strip conductors. In this way, it is shown theoretically and experimentally that a 3-dB 90° hybrid is obtained in the high-frequency region in which the ratio of the width of the transmission line with a characteristic impedance of 50Ω to the guide wavelength at the center frequency is about 1.35 times that of the conventional case. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 89(5): 1–8, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20240 [ABSTRACT FROM AUTHOR]

In this paper, the integral expressing the field diffracted by an aperture sufficiently larger than the wavelength created in a conducting screen is derived by the aperture field method. By evaluating the integral asymptotically, the extended Fraunhofer approximation and a uniform asymptotic solution for the aperture field methods are derived. By comparison with the reference solution derived by direct numerical integration, the usefulness, applicable range, and physical interpretation of the asymptotic solution are investigated. A new criterion is derived for adopting a nonuniform asymptotic solution applicable outside the transition region and the conventional Fraunhofer approximation from the uniform asymptotic solution. The validity of this technique is demonstrated numerically. The effectiveness of the technique is clarified by comparing a reference solution obtained by the method of moments and uniform asymptotic solutions obtained by the three types of aperture field methods. [ABSTRACT FROM AUTHOR]

In this paper, an improved rooftop mirror is proposed and its characteristics are evaluated by numerical analysis. First, it is shown by FDTD analysis that it is not easy to obtain a high reflection characteristic with fundamental mode incidence in the conventional structure. Next, the reflection characteristics are analyzed for an improved structure in which the incident single-mode waveguide is connected to a multimode interference waveguide inside the rooftop. In such a process, comparison with the results obtained by FDTD analysis demonstrates that the simple guided mode propagation method neglecting the radiation mode is effective for design of a mode interference section. A reflectivity of 96% is attained by introduction of the mode interference section for both fundamental TE and TM mode incidence. Further, the wavelength characteristics of the reflection coefficient are studied. The effects of misalignment of the waveguide axis and shift of the apex angle of the rooftop on the reflection characteristics are discussed. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 87(1): 1–8, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10172 [ABSTRACT FROM AUTHOR]

Three-dimensional optical waveguides with an arbitrary cross section and a periodic configuration have been important as optical IC elements. However, it is not always easy to obtain highly accurate solutions for them without respect to the number of periods. In this paper, the Fourier series expansion method, improved for accurate numerical analysis independently of the number of periods introducing Floquet's theorem, is applied to a fiber grating and various thin-film optical waveguides with index-modulation-type periodic structures and rectangular cross sections. The wavelength characteristics of the transmitted and reflected powers of the guided mode and the radiation field are derived at each period (40 to 1000). As a result, the wavelength characteristics of the power are made clear for periodic optical waveguides of embedded type and raised type with a glass or semiconductor substrate, including inhomogeneous cases. The algorithm thus proves to be useful for detailed analysis of various three-dimensional periodic optical waveguides. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 86(12): 22–31, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10171 [ABSTRACT FROM AUTHOR]

In order to reduce the phase error in FDTD analysis, the NS-FDTD method has been conceived by Cole. However, numerical dispersion characteristics and stability condition were not presented by Cole; only the definition for cubic meshes was given. In the present paper, the three-dimensional NS-FDTD method is extended to rectangular meshes and the numerical dispersion characteristics and stability condition are derived. From the analysis of the stability condition, it is found that the stability condition of the present method is larger than that in the FDTD method. From the analysis of the numerical dispersion characteristics, it is shown that the method has better accuracy than the FDTD method for both cubic and rectangular meshes. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 86(5): 66–76, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.1122 [ABSTRACT FROM AUTHOR]

When a step index waveguide is analyzed by the finite-difference method, the treatment of the discontinuous refractive index profile is a problem. In this paper, while the boundary condition of the field is taken into account, the improved finite-difference equation in which the truncation error is reduced to the fourth order is combined with the alternate direction implicit solution method, formulating a three-dimensional beam propagation method with high computational efficiency. First, by means of the imaginary axis method, an eigenmode analysis of the rib waveguide is carried out so that the effectiveness and validity of the method are proven. Next, a beam propagation analysis is carried out for the rib waveguide taper. By taking into account the discontinuity location of the refractive index, the quantization error is found to be reduced. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 85(12): 20–29, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10061 [ABSTRACT FROM AUTHOR]

Assuming a practical device application of resonant tunneling in a triple-barrier structure, equations for theoretical analysis of the tunneling transmission coefficient and the resonance condition are derived with regard to the tunneling phenomena in asymmetric triple-barrier structures in the presence of an applied bias. From the numerical analysis results, an interesting phenomenon not observed in structures with two or fewer barriers is found. As the bias voltage is increased, the transmission peak value of the resonant spectrum, which initially decreases, begins to increase again and several peaks with a spectral value of 1 (unity resonance) appear. At that time, the resonance condition is studied. Further, the effect of the tunneling transmission characteristics of triple-barrier structures on the voltage–current relationship in a triple-barrier resonant tunneling diode is studied. By means of the equations derived here, the resonant bias voltage in the triple-barrier structure can be determined. The conclusions derived in this paper are considered useful for the design of resonant tunneling devices using triple-barrier structures. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 85(12): 10–19, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10075 [ABSTRACT FROM AUTHOR]

In FDTD analysis, the numerical dispersion caused by the discretization of time and space becomes a problem. Previously, the numerical dispersion was corrected by changing the speed of light. However, such an approach is limited to isotropic meshes. In this paper, a generalized formulation is introduced such that this correction method can also be used in nonisotropic meshes. As an application example, the method is used for the analysis of a large cavity, demonstrating the effectiveness of the method. © 2002 Scripta Technica, Electron Comm Jpn Pt 2, 85(2): 61–69, 2002 [ABSTRACT FROM AUTHOR]

The image NRD guide as a modification of the NRD guide is expected to find applications at millimeter wave frequencies. In order to construct circuits and antennas containing image NRD guides and to evaluate their characteristics, a transition to another waveguide is needed. In this paper, a transition structure from a rectangular waveguide to an image NRD is proposed and its operating principle is explained. Also, by means of numerical calculations based on the effective dielectric constant (EDC) method, a transition intended for use in the R band (30 GHz) is designed. Further, the designed transition is measured and the effectiveness of the proposed transition is demonstrated. © 2001 Scripta Technica, Electron Comm Jpn Pt 2, 84(10): 9–16, 2001 [ABSTRACT FROM AUTHOR]

Nonlinear interactions between neighboring pulses in an optical time division multiplexed (OTDM) system may cause timing jitter of the signal pulse, which degrades transmission quality. A dispersion-managed (DM) soliton is a stable pulse in a DM line and is less influenced by various nonlinear effects than conventional solitons. On the other hand, interactions between DM solitons depend on the strength of the DM line, which is defined as the length of DM period times the variation of the fiber dispersion, and the transmission quality is degraded mainly due to the interactions in a strongly DM line. In this paper, the interactions between DM solitons are studied theoretically and numerically, and we then show that alternating the phases or amplitudes of pulses in the time sequence is effective for reducing the interactions. © 2001 Scripta Technica, Electron Comm Jpn Pt 2, 84(6): 24–29, 2001 [ABSTRACT FROM AUTHOR]

Since subsurface radar is intended to search for objects buried under the ground, the effect of the soil on the radar image is extremely significant. In order to eliminate such an effect, the parameters of the soil medium need to be measured. However, most of the previous measurements determine only the local permittivity of the region where the sample is acquired and hence a desirable result is not obtained. In this paper, a measurement method is proposed for estimating the soil parameters (relative permittivity and conductivity) from the measured resonant frequency and resonant resistance of the antenna in contact with the ground surface. In this method, based on numerical analysis, a monograph indicating the relationship between the parameters of the soil and the characteristics of the antenna is created. By plotting the antenna characteristics obtained by measurement on the monograph, the parameters of the soil are estimated. From the experimental results, it is considered that the measured values obtained by this method provide the spatial average values of the electrical constants of the soil. © 2000 Scripta Technica, Electron Comm Jpn Pt 2, 83(10): 60–68, 2000 [ABSTRACT FROM AUTHOR]

In this paper, the integral equations (guided-mode extracted integral equations) of a near field optics CAD proposed earlier are extended for a two-dimensional near field optics circuit using an aperture probe coated with metal. As a specific example, an aperture-probe manipulator with a two-dimensional configuration is chosen. In particular, a derivation of the boundary integral equation is described in detail for the incident TM mode, in which a simple extension of the previous results is not possible. The validity and effectiveness of the proposed integral equations are demonstrated by simulation using the boundary element method. It is shown that an attractive force directed toward the aperture is exerted on an infinitesimal dielectric cylinder placed near the aperture. The characteristics of the aperture probe coated with metal are compared in detail with those of the uncoated probe reported earlier. © 2000 Scripta Technica, Electron Comm Jpn Pt 2, 83(9): 32–41, 2000 [ABSTRACT FROM AUTHOR]

This paper discusses the potential produced in the development zone, assuming that a charge exists within a finite range on the photosensitive material surface of the copying machine. The detailed value of the electrical potential is numerically calculated, with the x and y lengths of the charge distribution, the thickness, and the kind of photosensitive material as parameters. Based on the result for the electrical potential, an experimental formula for the contrast potential is derived. This formula is accurate enough to reproduce the value of the contrast potential that is derived theoretically. It is seen that the parameters which are effective in enhancing the contrast potential are the bias voltage VB, the permittivity ratio ε3/ε2 between the photosensitive material and the development zone, the thickness of the photosensitive film a, and the effective potential VR. Among these, the parameters that can be used in the design to enhance the contrast potential are VR, VB, and a. © 1998 Scripta Technica, Electron Comm Jpn Pt 2, 81(11): 1–8, 1998 [ABSTRACT FROM AUTHOR]

Design methods for one-dimensional FIR digital filters can be separated into equiripple optimal approximations such as the Remez algorithm, and weighted least-square methods where the weight function is combined with the simple square error in the algorithm. For two-dimensional FIR digital filters, on the other hand, there is no known optimal approximation method, and a weighted least-squares method is generally used. This paper proposes an analytical design method for the one- and two-dimensional digital filters based on the least-squares method and for which matrix inversion and other manipulations are not required. Using this approach, the filter coefficients for a higher-order digital filter can be derived in a computation time similar to that for the lower-order case. We show that by transforming the error obtained for the response of the filter toward the equiripple response, an equiripple solution can be obtained by iteration. This idea is extended to the two-dimensional case, and a design method is offered for a two-dimensional FIR digital filter with a quasi-equiripple response. Finally, design examples are presented, and we show that an equiripple frequency response can be realized in a short time, independently of the filter order. © 1998 Scripta Technica, Electron Comm Jpn Pt 2, 81(1): 56–65, 1998 [ABSTRACT FROM AUTHOR]

In the feed system for an orthogonal two-polarization antenna, a polarization diplexer is used for separating the vertical and horizontal polarizations. In this paper, the three-dimensional (3-D) electromagnetic field analysis by the mode matching method is carried out for the circular-to-rectangular waveguide T-junction used in the polarization diplexer. Its scattering matrix is theoretically derived. As mode functions inside the T-junction, the TE and TM modes in a parallel plate radial waveguide are used. Then, it becomes possible to provide the continuity conditions for the electric and magnetic tangential field components not only at the junction between the junction and the circuit waveguide, but also at the junction between the junction and the rectangular waveguide as well as on the junction wall. Also, by providing an approximate boundary condition at the junction plane between the junction and the rectangular waveguide, the scattering matrix can be formulated in the form that does not contain numerical integration. The numerical results obtained by the present analysis method agreed well with those by the three-dimensional finite-element method and the measured results. © 1998 Scripta Technica. Electron Comm Jpn Pt 2, 80(7), 37–46, 1997 [ABSTRACT FROM AUTHOR]

Nonlinear coupling characteristics taking account of evanescent field overlap were evaluated numerically by assuming a Gaussian field distribution for the mode field in nonlinear directional couplers (NLDC). The nonlinear coefficients Q3to Q5 were found to be Q3 = 3.7 × 10-12 cm-1, Q4 = Q5 = 0 for the plane wave approximation used in Jensen's paper [1], with a core radius of 4 μm, a core spacing of 5 pm, a core refractive index of 1.455, and a nonlinear refractive index of 1.1 × 10-12 esu; and the wavelength of the incident light was 1.06 μm On the other hand, in the case of the Gaussian field approximation, Q3 = 2.5 × 10-12 cm-1 Q4 = 2.2 × 1014, and, and Q5 = 7.3 × 10-14 cm-1 were obtained, indicating that these values cannot be ignored. The full coupling period is increased by increasing the core spacing, and the full coupling period is decreased by using a longer wavelength. Further, from the dependence of nonlinear coupling characteristics on optical wavelength, it is confirmed that wavelength selective characteristics with a sharp bandpass filtering can be realized in NLDC. [ABSTRACT FROM AUTHOR]

In this paper we derive a double-tuned, narrow-band transfer function and illustrate its LC simulation-type active realization with low element sensitivity. First, a new double-tuned function that is adjustable by a single parameter is derived for a circuit using mutual induction. Next, the basic circuit that generates negative feedback with RLC elements and controlled sources is derived. This basic circuit can have a low clement sensitivity within the passband, as confirmed by the numerical analysis. As an example of the implementation for the basic circuit, an active RC circuit with the center frequency f0 = 455 kHz and Q = 30 is constructed; transistor gyrators are used for L element simulation; and a single variable resistor is used for the coupling coefficient adjustment. The experimental tuned characteristics for several coupling coefficients are in good agreement with the calculated values. [ABSTRACT FROM AUTHOR]

In this paper, the formulation of the analysis based on the finite element method is presented for the first time for an anisotropic dielectric grating. By this analysis method, the diffraction characteristics of a plane wave by an anisotropic dielectric grating with an arbitrary shape can be computed easily. The finite element method is applied to the region corresponding to one period containing an anisotropic dielectric grating. The analytical relationships are applied to the boundaries on the incident and transmitted sides while the periodic boundary condition is applied to all other boundaries. Specifically, an index modulated grating and a groove grating are chosen for the analysis of the diffraction characteristics when the TE and TM waves are coupled. From the comparison with the analysis results by the coupled-mode theory and the spatial harmonic expansion method, the validity of the present method is confirmed. [ABSTRACT FROM AUTHOR]

This paper proposes a method for theoretical determination of the circuit parameters in the equivalent circuit for the natural single-phase unidirectional transducer (NSPUDT), which is one type of unidirectional surface acoustic wave interdigital transducers. The finite element method was used to find the upper and lower edge frequencies of the shorted and open-ended gratings corresponding to the shorted and open electrical terminal of the NSPUDT, the potential standing wave distribution and the static capacitance per pair of NSPUDT, needed for determination of the circuit parameters. Due to the analysis method, the anisotropy of the substrate, the electrical perturbation effect, the acoustic perturbation effect, and the energy storage effect can be taken into account. Actually, the equivalent circuit parameters of the NSPUDT on an ST-cut 25° X-propagation quartz substrate were computed and the reflection and excitation characteristics of the surface wave were derived. From a comparison with the experimental values, the validity and usefulness of the present method is confirmed. [ABSTRACT FROM AUTHOR]

The differential equation which analyzes the temperature distribution in the thermoelectric device is non linear and we must implement numerical analysis to solve this equation exactly. If we want analytical considerations using the equation, the equation must be transformed into any linear-approximated differential equation. Before now, we introduced the linearized equation from the exact nonlinear equation under some simple approximation. In this paper, we introduce improved linear-approximated differential equation under more precise approximation. And analytical results for both linearized methods are competed with the numerical method. As the result, values of temperature distribution, beat-flow density, and coefficient of performance (COP) of Peltier cooling system obtained by the new linearized method are considerably agreeable with those by the numerical method. [ABSTRACT FROM AUTHOR]

This paper describes the basic items needed for design and simulation of optical integrated circuits and analysis tools for optical waveguides. Because the finite element method and beam propagation method are emphasized, the scalar wave approximation (which has been extensively used) is used in the discussion. In addition, using examples of analyses on various optical integrated circuits, the design and simulation technologies for optical integrated circuits will be introduced. [ABSTRACT FROM AUTHOR]

Because of the rapid development of quantum effect devices, it is necessary to obtain a synthesis method which can give the expected quantum effect symptoms. Using a triple-barrier structure, quantum effects which cannot be obtained with a double-barrier structure can be realized. However, only a few studies have been made on the triple-barrier structure, in particular, on the asymmetric triple-barrier structure. In this paper, based on the circuit theory, the synthesis method of an asymmetrical triple-barrier structure where a single perfect resonant level is formed in its quantum well is proposed. It is assumed that an original symmetrical double-barrier structure has a first resonant level E1 and a second resonant level E2 whose resonant energy is four times higher than that of E1. One of the single barriers is replaced by another symmetrical double barrier with the first resonant level equal to the second resonant level E2 of the original one. In the nonsymmetrical triple-barrier structure formed by the fore mentioned method, the transmission probability at E1 is 1 and that at higher-energy levels is sufficiently low. This synthesis can be achieved by using the power reflection coefficient and the Smith chart of a complex equivalent circuit. The validity of this method can be established by means of the Smith chart. By carrying out a numerical calculation on the electron transmission characteristic of the synthesized nonsymmetrical triple barrier, it was confirmed that the transmission probability at the energy level that is four times higher than E1 can be around 0.1. [ABSTRACT FROM AUTHOR]

The Yasuura method (mode matching method) was applied to the problem of electromagnetic wave scattering by an obstacle in a rectangular waveguide to prove the usefulness of this method as a general-purpose analysis method. In this paper, the scattering problem of an inductive obstacle with edges placed in a rectangular waveguide is analyzed numerically, taking into account the singularity of the solution at the edges. The inductive obstacle is considered to be a perfect conductor with an asymmetrical triangular cross section with an arbitrary apex angle. Each comer of the triangle is treated as a singularity. The algorithm is presented which takes into consideration the singularity of the solution at the edge, and then the accuracy of the analysis is discussed. As a numerical example, the frequency characteristics of reflection and transmission coefficients versus various parameters are shown including the behaviors of higher-order modes. By taking advantage of the fact that the magnitude of the apex angle can be changed arbitrarily, the effect of the slant angle of the triangle on the incident side exerted on the scattering is discussed. Since the structure can be computed for an apex angle starting from 0°, the solution for an apex angle of 0° or the inductive window is compared with the exact solution by Wiener-Hopf method so that the analysis error is carried out. [ABSTRACT FROM AUTHOR]

In the Črenkov laser, as the electromagnetic wave grows by gaining energy from the electron beam, it loses kinetic energy and, thus, its drift velocity decreases. As a result, the synchronism between the propagation velocity of the electromagnetic wave and the drift velocity of the electron beam ceases to be kept and efficient growth of the electromagnetic wave is prevented. To overcome this difficulty, this paper proposes a model for the Čerenkov laser loaded with a Kerr-like medium, the permittivity of which increases in proportion to the square of electric field. Also, a numerical investigation is made to determine how the growth characteristics for the electromagnetic wave are improved with the aid of the finite element method. The numerical result shows that, by choosing a proper value for the nonlinear coefficient of the Kerr-like medium, the propagation velocity of the electromagnetic wave can be delayed in accordance with the decrease in the drift of the electron beam. Thus, the growth characteristics for the electromagnetic wave can be improved greatly. In addition, it is found that the interaction distance to maximize the electromagnetic wave power extracted from the electron beam can be shortened compared with the case where only a linear dielectric is loaded. [ABSTRACT FROM AUTHOR]

The article presents finite-element analysis of three-dimensional wave-guide transfer problem. This paper proposes a method in which the Galerkin method using the wave-guide modal functions as the weighting functions, is used for connecting the field on the boundary between the wave-guide and the discontinuity. Since, the connecting boundary can be taken very closely to the discontinuity in this method, the size of the matrix equation to be solved is small so that the amount of computation is small. There is no restriction between the number of expansion basis of the field by the finite-element method and that of expansion modes in the eigenmode expansion method.

The article focuses on beam-propagation method. When the wave propagation in an optical circuit is studied by means of the beam-propagation method, a problem is the reflection of the radiated wave at the virtual boundary surrounding a finitely large region to be investigated. In this paper, it is assumed that the field near the virtual boundary is an outward propagation wave. A method is proposed for transmitting this radiation without reflection by using the relationship satisfied by this wave as the boundary condition. The method is then applied to the beam-propagation method based on the finite-element method.

To carry out numerical calculations efficiently based on the discrete Fourier transform (DVF), the filtering operator with regard to the discrete spectrum is defined and its applications are described. First, for the simultaneous equations containing discrete convolution operations similar to the Wiener-Hopf-ype integral equation of the first kind, a study is made to determine if a solution method similar to the Wiener-Hopf technique in the continuous spectrum can be applied. Since the DFT is based on the periodic functions, it is found that such a method is not possible in general except for special cues. To derive numerical solutions, three methods are proposed in this paper. In the first method, the simultaneous equations derived by using the inner product on the discrete spectrum are solved directly. The next method is a successive solution by repetition of the filtering operation. The last method is a successive solution by repetition of the filtering operation. The last method uses a conjugate gradient method based on the filtering operation. As an example of application of the numerical method based on the conjugate gradient method which can be applied to a wide range of problems, the problem of scattering of electromagnetic waves by a planar grating is investigated. It is shown that the transmitted power and the surface current distribution can be accurately. [ABSTRACT FROM AUTHOR]

In principle, the finite element method is an analysis method in which an inhomogeneous waveguide with a closed boundary and a complex geometry. By contrast, the boundary element method is suited for the analysis of an open-region problem. In this paper, as a method for analyzing the propagation characteristics of the guided modes in an open waveguide, the finite element method is applied to the electromagnetic field of the interior region while the boundary element method is applied to the field outside the waveguide. The fields of the two regions are then connected at the boundary. By means of the present method, it is possible to analyze without spurious solutions the guided modes in an open waveguide with a cladding made of a different material and an inhomogeneous interior region with a complex geometry. Also, the coefficient matrix of the matrix equation to be solved becomes square. As practical examples, the dispersion characteristics of the rectangular dielectric waveguides and channel waveguides are analyzed so that the validity of the method is verified. [ABSTRACT FROM AUTHOR]

Conventionally extremely thin gate oxide and high channel-doping concentration are used to reduce the short channel effect of an MOS transistor below the submicron region. However, with these methods, there are problems such as the degradation in design freedom with respect to the breakdown voltage, the considerable decrease in the carrier mobility and the remarkable variation in characteristics of devices due to the statistical fluctuation of the impurity doping profile; and they need to be wived. Through the numerical analysis of the threshold voltage performance and the experimental fabrication of various devices with effective channel length range from 0.26 μm to 1.26 μm, it has been made clear in this paper that a double-gate MOS transistor (XMOS) structure with an- other insulated gate at the lower part of the channel can reduce the short channel effect without the above-mentioned problems. The results also show that the gate swing has reached about 60 mV/decade that is close to the theoretical Limit the short channel effect can even be reduced with a much shorter channel length If a thinner active channel layer is used and that reduction is independent of the channel doping concentration; and the limit to a possible shorter channel length may be less than 0.1 μm. It is concluded that the problems with the conventional MOS transistor can be solved by using XMOS structure [ABSTRACT FROM AUTHOR]

One of the recent trends in the development of magnetic disk devices is the advent of small disks. The small disk has a great influence on the performance of the magnetic disk subsystem. This paper assumes that the small-sized magnetic disk subsystem will be introduced around 1995 and formulates the relation between the disk size and the performance/cost. The disk array subsystem architecture using small disks is considered, and the evaluation is made based on the number of disks for the parallel synchronous transfer. As to the file performance, code and image information are considered and the condition for the subsystem with the best cost/performance ratio for each kind of information is shown. It is shown that small disks of I to 2.5 inches are being developed rapidly at present aiming at the application to the portable equipment and will experience the widest area of application. The requirement for the magnetic disk device, e.g., the relation between the rotation for each size and the number of parallel synchronous transfer in the best configuration, is discussed. [ABSTRACT FROM AUTHOR]

With a view to investigating the operating speed of a quantum effect device, considerable work has been carried out on the lifetime of the resonant state. The lifetime of the resonant state in a multiple bather structure is defined as the time constant with which the existence probability of the electron is attenuated. This is a quantum theoretical transient phenomenon. In this paper, by means of a complex -valued equivalent circuit proposed previously by the authors, this transient problem is discussed from a circuit theoretical viewpoint. First, the complex frequency variable (Laplace variable) is related to the complex energy which permits a circuit theoretical investigation on the lifetime It was found that the real part of the complex frequency, which makes zero the sum of the admittances looking to the left and the right, corresponds to the lifetime. By means of a numerical experiment, a double-bather structure is studied and compared with the research results reported previously. The error of the lifetime estimated from the half-value width also is studied. In addition, a symmetric triple barrier structure is studied. ft is found that a lifetime exists that cannot be estimated from the half-value width. [ABSTRACT FROM AUTHOR]

A heating condition for the collapse of fluoride glass tubes is examined, and a thermal history is discussed. So far, theoretical discussions on the collapse have been made only for the case of a contraction along a tube-radial direction as a viscous flow of glass. This paper discusses an evaluation method of a contraction along not only the radial but also axial directions by taking into account the effect of heat source traverse. The evaluation is made by numerically solving simultaneous equations, a thermal conduction equation and a viscous flow equation. The method provides the information of a thermal history tint temperature relation. Heating conditions are discussed for various traverse speeds and temperature profiles of a heating source. Based on the thermal history thus obtained, the distribution of crystallites grown in a glass is calculated. An excess scattering loss after a collapse is estimated. [ABSTRACT FROM AUTHOR]

Open-type waveguides with homogeneous cladding can be analyzed by the finite element method (FEM) with the multipole expansion method. In this paper, we propose a new connection method in which the fields described by the FEM and by the multipole expansion are combined at the connection boundary between the finite inner region and the infinite outer region by using Galerkin method. By means of this method, we can analyze open-type waveguides with higher accuracy and less amount of calculation than conventional FEM. In addition, there is no difficulty arising from spurious mode and no restriction between the number of the basis functions of the FEM and that of the multipole expansion functions on the connection boundary. The final matrix equation is symmetric. The validity and usefulness of the method has been demonstrated in the example of a rectangular dielectric waveguide and an elliptical fiber. [ABSTRACT FROM AUTHOR]

Differential equation methods often are used for the analysis of the waves scattered by a dielectric grating. It is known that accurate numerical solutions can be obtained if the number of expansion terms of the spatial harmonics is increased. However, when the differential equation method is applied to a dielectric grating with an extremely large permittivity, the convergence speed of the solution becomes excessively slow in the TM wave analysis. Because of the increase of the computation time and the memory capacity, an analysis based on the differential equation method becomes difficult in practice. In this paper, it is shown that a boundary element method using Green's function satisfying the periodic condition is effective for the analysis. By introduction of pseudo-periodic Green's function, the definition region for the integral equation is limited to the grating surface. In comparison to the boundary element method using the Hankel function, the number of linear equations is reduced. By means of numerical examples, it is shown that the convergence speed of the solution by the present method is faster and the computation time is significantly shorter than the solution by the differential equation method even in the TM wave analysis of a dielectric grating with a large loss. [ABSTRACT FROM AUTHOR]

A novel combined integral equation, which is adaptable to the analysis of a general electromagnetic field in a cylindrical structure, is proposed. The unknown quantities of the equation are the transverse electromagnetic field components and the equation is analyzed numerically by the boundary element method. The combined integral equation does not have the difficulty arising from the nonphysical solutions which have been troubled conventionally. In addition, the integral equation does not contain spatial derivatives of the unknown quantities. The coefficient matrix of the matrix equation obtained by the application of the boundary element method is square and is hence suitable for numerical analysis. In this paper, first the combined integral equation for unknown transverse electromagnetic field components are derived. The uniqueness of the solution is proven. Further, the integral equation is analyzed numerically for actual examples by the boundary element method so that the validity and effectiveness of the method are verified. [ABSTRACT FROM AUTHOR]

When the transmission characteristics of an optical fiber with an inhomogeneous core are analyzed, direct numerical analysis of the vector wave equation requires excessive time. To alleviate this deficiency, one may use an analytical solution. When the vector wave equation is solved by a perturbation method in which the scalar solution is used as a nonperturbed solution, it is necesesary to derive the analytical solution in a closed form. In this paper, the index profile is restricted to an even polynomial. The analytical solution of the waist wave equation is constructed as a uniform asymptotic solution by means of a related equation method. This solution is * refinement of a WKB solution. By investigating the accuracy of the uniform asymptotic solution obtained, it is demonstrated that this solution is effective as a nonperturbed solution in vector wave analysis. Also, the accuracy of the WKB solution is studied and it is shown that the WKB solution contains a large error in the single-mode region. [ABSTRACT FROM AUTHOR]