NASDA (National Space Development Agency of Japan) has just finished the Earthquake Remote Sensing Frontier Project (for which the author was the principal scientist) conducted since 1996 within the framework of the Earthquake Frontier Projects by the former S.T.A. (Science and Technology Agency). Main emphasis of NASDA's Frontier Project was the complete understanding of lithosphere-atmosphere-ionosphere (LAI) coupling by making full use of different kinds of observational items and finally we would like to contribute to the short-term earthquake prediction. The most exciting finding from our Frontier project was the discovery of convincing evidence of the presence of seismo-ionospheric perturbations, which has been extensively investigated by using the subionospheric VLF/LF propagation, and several important findings have been presented, including the initial result for the Kobe earthquake and a few case studies from many data. Then, our latest result on seismo-atmospheric perturbation is presented on the basis of the reception of over-horizon FM transmitter signal. Finally, the initial and boundary condition of the LAI system (i.e., lithosphere) has been investigated by means of the measurements of ULF (ultra-low-frequency) emissions and acoustic emissions, whose latest results are summarized as well.

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A 4×4 matri×-based analysis of the electromagnetic waves diffracted by a grounded slab of uniaxial chiralmedium with a plane metallic grating has been presented. In the analysis, the total fields are given by the superposition of the current-independent primary fields and the scattered fields depending on the currentsinduced on the grating. The scattered fields are expanded in terms of Floquet modes. The coupled mode equations which are derived for the uniaxial chiral media give the general solutions of fields as the superposition of left and right-handed elliptically-polarized eigen modes. The unknown currents on the grating are determined by applying Galerkin's method to the condition of the perfect conductivity on the grating. Both the direction of the optical axis of the uniaxial anisotropy and that of the incident wave vector are assumed to be perpendicular to the strip conductors of the grating. In the numerical computation, the polarization characteristics of diffracted waves are investigated.

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Plane wave diffraction by a semi-infinite strip grating is analyzed in order to investigate the end-effect of finite gratings in pure form. In the formulation, the current induced on each strip is divided into periodic current on an infinite strip grating and the correction current induced by the truncation of the periodic structure. These currents are determined by solving a set of integral equations by using the method of moment. Numerical calculations for current distribution, diffraction patterns, and norm of the induced correction currents reveal the end-effects of the semi-infinite grating.

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Amplifiers doped with Ytterbium and Erbium ions are given increasing attention for amplification of signals in the present communication wavelength band of 1.55 μm. Sensitization of Er-doped amplifiers has many advantages such as the possibility of using broader pumping wavelength range. In this paper a thin-film waveguide amplifier based on Er-Yb codoped Garnet crystals is proposed and steady state and transient amplification characteristics, studied numerically using time-dependent rate equations are presented. Understanding the dynamic characteristics of the integrated optic waveguide amplifiers is necessary when the input signal is modulated in various formats. Amplification and pulse distortion effects of short signal pulses are presented, which are shown to be related to the lifetime of the excited states. Comparison is made between the gain characteristics of Er and Er-Yb doped waveguide amplifiers.

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A comprehensive approach of combining the generalized forward-backward method (GFBM) with spectral accelerate algorithm (SAA) is developed. It is applied to numerical simulation of bistatic scattering from two models: (1) an ocean-like surface described by the Pierson-Moskowitz spectrum with a ship presence, and (2) a fractal rough surface described by the Weierstrass-Manderbrot function under the TE and TM tapered wave incidence at low grazing angle (LGA). Numerical simulations of bistatic scattering at LGA show the functional dependence upon polarization, frequency, observation angle and other surface parameters.

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The impedance matrix generated by the discretization of volume integral equation is usually nonsymmetrical and dense. When the direct matrix solver such as Gaussian elimination is employed to solve the impedance matrix, O(N²) memory and O(N³) operations are required, where N is the number of unknowns. Therefore, the direct matrix solver is not suitable for the practical solution of large-scale problems by the volume integral equation. The implement of the iterative-methods is the realistic solution to improve the calculation efficiency in solving the problems. In this paper, we evaluate six well-known iterative-methods in solving the matrix equation obtained by the discretization of volume integral equation. We investigate the convergence characteristics of the residual-norms in this evaluation. In the methods based on Lanczos process, it is found that the convergence characteristics of the residual-norms become unstable under some conditions. In the methods based on Arnoldi process, it is found that the convergence characteristics of the residual-norms are always stable under various conditions. Since we found that GMRES is the most effective iterative-method in solving the matrix equation obtained by the discretization of volume integral equation, we particularly investigate the convergence characteristic of GMRES based on Arnoldi process.

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The problem of suppressing resonances of the power/ground planes in a printed circuit board (PCB) by coating high resistive metal films onto the inner sides of copper layers of the two planes has theoretically been studied. The Q-factor that determines the strength of the resonance, is derived from the surface resistance of the composite conductor. To achieve the smallest Q-factor of a given resonance mode, there is an optimum thickness for a fixed conductivity or reversibly an optimum conductivity for a fixed thickness, for the coating metal films. The numerical results for the reduction rate of the quality factor and the input impedance of a test board have demonstrated the effectiveness of the high resistive metal coating to suppress the resonances of the power/ground planes in PCBs.

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The fundamental mode can be launched in the multimode(MM) fibers with high accuracy by suppressing modal speckle by using broad-bandwidth excitation sources such as ultra-short pluses. As temporal coherence length of broad-bandwidth sources is very short, temporal interference between the modes and thus the presence of speckle is prevented. In this paper, single-mode(SM) excitation of step-index and graded-index multimode fibers with light sources with short temporal coherence lengths is demonstrated using a Ti:Sapphire laser with wavelengths of 790 ran and 836 nm and pulse widths of 60-90 fs. As a result, the stability of the spatial beam profile was verified by coupling the output of a MM fiber into SM fiber and SM excitation in the presence of mode-coupling for the MM fibers was confirmed by experiment.

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An optical pulse compressor using a normal dispersion fiber combined with a linearly chirped fiber grating (instead of a bulk grating pair) is analyzed. A set of modified design rules of the fiber-fiber grating compressor that governs the optimum fiber length; optimum dispersion and length of fiber grating are given.

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With the aid of the multilayer approximation method, growth characteristics of a Cherenkov free-electron laser filled with background plasma with a transversely inhomogeneous density profile are discussed. The accuracy of numerical results is confirmed by comparison with the available analytical solution. From the numerical results, including the effect of electron-ion collisions, we find a great enhancement in the growth characteristics by a proper choice of various parameters, as compared with the corresponding vacuum device. In addition, we can identify the main parameter of the inhomogeneous background plasma which affects growth characteristics of a plasma-filled Cherenkov laser.

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In this paper, propagation characteristics of a single polarization optical fiber with the cross section of arbitrary shape are numerically studied by applying the circular Fourier expansion method. Firstly, for a single elliptical core fiber, an accuracy of the circular Fourier expansion method is discussed by comparing to a rigorous analysis method using Mathieu functions. Secondly, as an application of the circular Fourier expansion method, a single polarization optical fiber composed of an elliptic core with round shoulder and fluctuations in the pit of circular periphery is designed so as to satisfy the zero total dispersion at wavelength 1.55μm and is discussed for the single polarization bandwidth and the wavelength sensitivity of the total dispersion. These results are compared with the case of the single polarization optical fiber without round shoulder and fluctuations.

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This letter describes characteristics of an optical resonator composed of the alternating Δβ coupler from the point view of tuning the resonance wavelength and the sharpness of the resonance curve. The idea of how to tune separately the two matters is described together with the operation principle of the proposed coupler resonator, and simulation results on the tuning characteristics are demonstrated.

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Photonic crystal optical devices are of new candidates for high density integrated optical devices because of the size comparable to wavelength of the light. The propagation property of photonic crystal optical waveguides is different from that of conventional weakly-guiding dielectric optical waveguides. Direct joint with optical waveguides of two kinds different transmits optical powers with low efficiency. In order to make well coupling each other, we propose to load a tapered-end dielectric tip in the joint section. Numerical simulations confirm that loading tapered-end dielectric tip several wavelengths long performs high coupling efficiency more than 90% between photonic crystal optical waveguides and dielectric optical waveguides having almost same core width as the gap of photonic crystal optical waveguides.

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A new fiber-type polarization splitter is proposed. This polarization splitter is constructed from two optical fibers with a circular hollow pit outside a core. The characteristics of the device length, the extinction ratio, and the bandwidth in terms of the structural parameters for the polarization splitter are discussed.

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An algorithm for generating a multi-level NAND logic circuit is proposed. In the algorithm, (a) to cover true (1) cell, permissible cubes described by the product of the affirmative literals are generated; and (b) if false (0) cell is found in the generated cube, new permissible cubes excluding the false cell are added. Procedures (a) and (b) are repeated until no true cell exists together with false cell in the permissible cube. The finally obtained cubes are converted into a NAND gate circuit. The circuit generation is carried out only by the mouse operations and the circuit can easily be displayed on a screen.

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It is difficult in practice to analyze problems dealing with electromagnetic (EM) transmission through high conductivity sheets, such as EM wave shielding materials, in FDTD analysis, because of a high increase in the number of cells. We attempt to introduce the transmission coefficient of a sheet material into FDTD analysis, to obtain a more satisfactory solution. First, we derive the transmission coefficient of a multi-layered material in the case of EM waves incident on the material with an arbitrary direction, employing Maxwell's EM field theory. Then, we numerically calculate the EM shielding effectiveness of TE and TM modes by introducing the transmission coefficient into FDTD analysis. Consequently, this technique is confirmed to be useful, as the results of FDTD analysis using it have agreed well with the values of theoretical analysis.

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