A multiport representation of the step junction of two circular dielectric waveguides of different size and its application to the stepwise approximation of a tapered dielectric waveguide are presented. Continuous spectral modes of the circular dielectric waveguide are discretized at a terminal plane by means of expressing their mode amplitudes in the form of infinite series of orthonormal Gaussian Laguerre functions. Applying the standard mode matching technique at the terminal plane, a rigorous multiport representation of the step junction of two circular dielectric waveguides is derived. Using the multiport representation, a stepwise approximate solution is given for the tapered dielectric waveguide. Numerical examples are given where the results are tested for the conservation of power. Also the numerical results are compared with those from Marcuse’s approximate methods.

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Q-map method is a practical method for the design of high-speed optical communication systems. We applied this method to the optimization of periodically dispersion compensated 40 Gbit/s soliton-based TDM systems. The optimum dispersion compensation is about ±30 ps/nm and does not depend on the compensation periods. In a single-channel 640-km transmission experiment using conventional dispersion shifted fibers and 2-pieces of dispersion compensation fibers, we observed error free transmission in the wavelength range of 1.2-nm by adjusting the location of the dispersion compensation elements. The optimal channel power is about +7 dBm and the transmissible condition shows good agreement with the numerical simulations. We applied these techniques to 80 Gbit/s (40 Gbit/s, 2 PDM) transmission line design and observed error free 800 km transmission. In 40 or 80 Gbit/s/fiber systems, the dispersion-managed soliton scheme is attractive because higher SN-ratio, conventional dispersion shifted fibers and narrow band low cost amplifiers are applicable. The soliton stabilization effect enables stable long distance transmission.

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In this paper, the scattering problems by columnar dielectric gratings will elliptically layered media are analyzed using the combination of improved Fourier series expansion method and the multilayer method. Numerical results are given for the transmitted scattered characteristics for the case of incident angle and frequency by varying the grating shape whose profile is the elliptic cylinders, and whose interior distribution of permittivity is an elliptically layered medium for both TM and TE waves. The influences of the incident angle and frequency of the transmitted power are compared between inhomogeneous case and homogeneous case

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The propagation and switching of short optical pulses in a three-core nonlinear fiber coupler have been investigated with a variational method within the framework of the Lagrange equation. The analytical solutions were directly obtained from the coupled nonlinear Schrodinger equations. It is shown that the soliton switching behavior predicted by our analytical method agrees well with results from numerical analysis. In addition, the coupling length and the switching threshold of solitons in a nonlinear coupler were obtained.

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In the connection of two optical fibers, higher-order modes appear occasionally even for slight shift of the two fibers. In usual fiber, four higher-order modes, TE₀₁, TM₀₁ and two of HE₂₁ modes, have slightly different eigenvalues and field distributions of two-lobe patterns described by linearly polarized E_x and E_y, respectively. Then in order to investigate precisely the occurrence mechanism of such higher-order modes, accurate full-vectorial numerical method is required. In this paper, Fourier series expansion method is applied to the full-vectorial analysis of the connection problem. First, the eigenvalues and the field distributions of the four higher-order modes in step-index type optical fibers are computed by the method, and their accuracies are examined. Then the occurrence mechanism of the higher-order modes caused by the transverse shift of the two fibers is made clear.

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We propose a new method to design 3-branch optical power dividers. According to the scalar Helmholtz equation, if a complex field distribution is given, then one corresponding refractive index distribution is determined uniquely. On the basis of this relationship, we first make up an ideal field which ensures smooth power division in the branching region, and next derive the refractive index distribution from this ideal field. Since the derived refractive index distribution has non-zero imaginary part and a complicated profile, it is almost impossible to fabricate the index distribution as derived. We discretize the real part into several levels and set imaginary part zero from a practical point of view. Three-branch waveguides designed by this procedure accomplish very low loss and equal division.

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We propose a new technique to reduce the influence of timing jitter without increasing the intersymbol interference by utilizing Kerr nonlinearity in normal dispersion fiber. We carried out numerical simulations of 10 Gb/s soliton transmission and confirmed that the proposed method is more effective than the conventional RZ receiver with a Bessel-Thompson filter in reducing the influence of Gordon-Haus timing jitter. We also employed this technique to the 10 Gb/s optical soliton pulses transmitted at 16, 000km in a sliding frequency recirculating loop. The phase and amplitude margins obtained with the proposed method were 18 % and 67 % wider than that with the lowpass filter with 7.5 GHz bandwidth.

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Amplitude and phase perturbations on subionospheric VLF signals (known as Trimpi effect) are thought to be due to the scattering of VLF waves by ionization perturbations caused by either the precipitation of higher energy electrons from the magnetosphere, lightning discharge or earthquakes. In this paper, we examine the VLF scattering by simulating the fast Trimpis due to the direct effect of lightning and we calculate amplitude and phase perturbations by such ionospheric perturbations using the conventional FDTD method. Finally, we compare our computational results with the data measured for Japanese sprite events, to estimate the validity of our modeling.

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The Vacuum arc can remove the oxide layer and evaporate impurities on the metal surface. The removal by vacuum arc is expected to solve the problems of the current chemical and mechanical cleaning. In this paper, the removal of the oxide layer covering the circular hole on the stainless steel surface by using the vacuum arc was carried out by changing its diameter and depth. As the result, the oxide layer can be almost perfectly removed by using the vacuum arc. However it is difficult to remove the oxide layer on the inside of the fine and deep hole, even if the removal time and the arc current are increased. The removal time for the hole is longer than that for the plane without holes. The removal is done in turn of the surface area → the side of the hole → the bottom of the hole. The removal time is little influenced by the placement of the circular holes. But a removal is completed from the circular hole with the lower aspect ratio. A removal limit exists in the circular hole of the highest aspect ratio 1.67∼2.0. In this case, the surface metal is selected more preferentially than the oxide layer inside the hole. When the cathode spots inside the hole reach the critical aspect ratio, the cathode spots work well for “the re-removal” on the metal surface.

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The alternating magnetic flux leakage testing has been applied in the inspection process for detecting cracks on the surface of steel. In order to develop a precise inspection method, the flux and eddy current distribution should be investigated taking account of nonlinearity of steel. This paper describes 3-D numerical analysis and experiment for this testing. The property of leakage flux from the crack of steel under ac excitation is investigated using 3-D edge-based hexahedral finite element method. It is shown that the 3-D analysis is obligatory in the precise analysis of magnetic phenomena of this testing. The effect of crack width and depth on leakage flux is clarified and the relationship between the lift off and the amplitude of leakage flux is also illustrated. The characteristic of leakage flux is confirmed by verification experiment.

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A feasibility study has been conducted to determine if Hollow Cathode Arc (HCA) can be used for a welding heat source in space, that is a high vacuum and a microgravity condition. The HCA method enables the arc discharge to form under low pressure conditions by purging a small amount of gas through the center of the hollow cathode.
In this paper, fundamental characteristics of HCA as a welding heat source, such as volt-ampere characteristics, arc current distribution on anode surface and the electron density and temperature in arc space, have been made clear.
The results are summarized as follows,
(1) The current distribution on anode surface of HCA is extremely diffuse, and the anode diameter reaches to about 55mm under the condition that arc length is 10mm.
(2) The melting process by HCA is significantly affected by the diffuse anode, and it is characterized by shallow and wide penetration.
(3) The electron density of HCA is about 5×10¹⁹/m³ at the center of arc column, and the electron temperature is about 12000∼18000K in arc space.

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This paper deals with the effect of acetophenone coating on dielectric properties such as tanδ and capacitance and on space charge formation up to electrical breakdown under the AC voltage application in low density polyethylene (LDPE) film. The existence of acetophenone at the electrode interface enhances tanδ. Tanδ in acetophenone-coated specimen increased with electric field and decreased with the frequency in the high field and high temperature region. AC breakdown test gave the result that the electric strength in non-coated specimen was higher than that in acetophenone-coated one and that the electric strength also decreased with temperature.

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Recently, the magnetoencephalograph (MEG) measurement is expected as a means to find a higher-order function in the brain. It is physiologically considered that multiple areas in the brain are activated at the latency. Therefore the source localization method to which two or more signal sources can be estimated in short time by high accuracy is requested. Then we developed a method to estimate multiple-dipole sources by combining the genetic algorithm and the simulated annealing. In this combined method, the genetic algorithm is managed for a global search, and then the simulated annealing is applied for a detailed estimation. To assess this method, the simulation was carried out with the data of multiple-dipole sources model including white noise. The results of the simulation suggest that the presented method can be applied to the real MEG data and is useful for multiple source localization in shorter time and with high accuracy.

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Zinc oxide (ZnO) films prepared on quartz-glass substrates using radio-frequency magnetron sputtering have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), Auger electron spectroscopy (AES) and photoluminescence (PL). Crystal structure of ZnO films were dependent on the sputtering condition; argon (Ar) gas pressure and target-substrate distance. The XRD results indicated that the peak intensity of (002)-orientation increases with increasing Ar gas pressure and target-substrate distance. The SEM images showed a pillar structure formed in films with high (002)-orientation. The film composition determined by AES results was Zn_xO_1-x from x=0.482 to 0.501. The optical band gap of 3.25-3.29 eV and the visible transmittance of greater than 80 % were obtained. The PL spectrum with the peak at 620 nm was observed in highly crystallized films. In contrast, non-crystalline films did not show the PL spectrum in the range of 400 to 900 nm. It is clarified that the product of Ar gas pressure (P) and target-substrate distance (D) was strongly related to the film structure. Well crystallized films were obtained at the P·D above 0.4 Torr·mm. It was concluded that the pillar structure of the film could be formed when energy of sputter-particles decreased to the surface migration energy.

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The pulsed electroacoustic(PEA) method has been used to measure space charge distributions in insulations. Since the resolution of ordinary PEA systems is over 10 microns, it is difficult to observe space charges in thin specimens, such as a film which is less than 100 microns-thick. In order to improve the resolution of the current PEA system, the attenuation of pressure waves in the bottom electrode and the frequency bandwidth of the piezoelectric sensor were concerned. In this paper we introduce the new PEA system which has super high resolution of 6 microns.

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This paper describes effect of blending of poly(trifluoropropylmethylvinylsiloxane) (PTFPMVS) with polydimethylsiloxane (PDMS) on the surface properties of the blend, such as hydrophobicity. The surface molecular mobility of the PDMS/PTFPMVS blends was investigated via dynamic contact angle measurement and adhesion tension relaxation. Surface resistance of the blends was also measured under the continuous of salt fog spraying. The advancing contact angle of the PDMS/PTFPMVS blends increased with increasing content of PTFPMVS, but the receding contact angle decreased. We found that a flexible side-chain segment having greater surface energy of the PTFPMVS could be reoriented easily in water to decrease the interfacial tension of the polymer/water interface. This surface functionality seems to play a major role in the decrease of receding contact angle and the surface resistance of PDMS/PTFPMVS blends during wet electrical aging.

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The pulsed electroacoustic (PEA) method has been used to measure space charge distributions in insulating materials. A high-resolution PEA measurement system and signal procedure have been reported in previous papers. Since the signal procedure is necessary for high-resolution measurement, the system must include a computer. A new PEA system without a signal procedure or computer is introduced here. In order to eliminate signal distortion, a step-voltage generator is used in the new system instead of a very narrow pulse generator used in conventionally ones. The resolution of the system is 24 microns, which is lower than that of conventionally systems. The poor resolution can be improved by changing the pulse waveform according to numerical simulations. The new system should be used in portable measurement equipment.

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This paper presents a new method to separate leakage currents into three components which are: conductive current that flows in the water film, partial discharge current as corona discharge and dryband arc discharge current; and analyze each cumulative charges automatically by using FFT and differential techniques.

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