Mitsuo TATEIBA Kiyotaka FUJISAKI
Holographic imaging by satellite radars is precisely analyzed on a wave propagation theory in turbulent media. The variance of reconstructed images is expressed in an analytic form for strip objects. The turbulence effects on the image resolution are made clear numerically.
This letter discusses BiSrCaCuO microbridges, fabricated using an MgO-contact annealing process and nitrogen ion beam etching with a Ta/resist multilayer mask. This higher precision microbridge was confirmed to respond more sensitively to both microwave and magnetic fields by annealing at a temperature just below the melting point.
Etsuko INAMURA Kazuhito FURUYA
The electron wave device requires large current density as well as high coherence to increase the speed. This letter describes a relation between the coherence and the current density of the ballistic electron transport. The product of the degree of the coherence and the current density is a constant determined by the electron group velocity. Decrease of the coherence in the direction(s) not essential for the interference increases the current density.
Shigeru OHO Hisao SONOBE Jun-ichi MAKINO Hiroshi KAJIOKA Tatsuya KUMAGAI
A down sampling technique was applied to signal processing for optical fiber gyroscopes. It lowered the higher speed requirement for the sampling system and numerical operations. Utilizing the technique, a digital signal processing circuit extracted rotational information from the gyroscope signal.
Backscattered pulses from three-dimensional ocean waves, the first order statistics of which pulses is similar to that of received pulses by satellite altimeters, can be simulated by using the stationary phase method and the random sampling technique for picking up stationary points.
Hiroyasu TAKAHASHI Akio YAMASHITA Nobuyasu ITOH Tomio AMANO
A new character recognition algorithm with a capacity for easy learning has been developed. This algorithm incorporates two different kinds of processes: a triadic decision tree and a pattern matching method. Its significant features are that (1) a user can generate a reliable recognition dictionary by using only a limited number of characters, (2) the user can easily add new categories to the recognition dictionary or modify it for matching to actual patterns, and (3) the recognition speed is fast. We have also developed a unique OCR system on a personal computer, adopting this recognition algorithm. The system has several unique functions: (1) A user does not need to prepare special sample sheets on which all categories of unknown font are printed in alphabetical order. New dictionaries can be generated by using general texts. (2) It provides him with a concurrent spelling correction capability in order to facilitate learning and recognition. We conducted tests on the system to investigate the effect of the number of learning times and the quantity of sample data on the recognition accuracy. In our tests, the dictionary that was generated from eight data per category (the original and the first to third successive copies of two printed sets) attained a recognition accuracy of 99.6%. In another test, the recognition accuracy of the test documents was improved from 92.3% to 99.5% by modifying a different font dictionary four times with the test font data. A recognition speed of 120 char/sec was achieved by our software program on an IBM PS/55 personal computer.
Shu YAMAMOTO Hidenori TAGA Hiroharu WAKABAYASHI
The chromatic dispersion limitation for the longspan high-speed transmission using a LiNbO3 Mach-Zehnder modulator was estimated by computer simulation techniques taking account of the chirping effect in the modulator. The simulation result shows that the allowable chromatic dispersion to satisfy the 10% eye closure is around 10,000 ps/nm at 2.5 Gbit/s.
Toshitaka KOJIMA Seishi MATSUBA
The present paper deals with the scattering of a H-polarized Gaussian beam from a conducting cylinder with an irregular surface by using the perturbation technique. The correlation function and the variance of the far-zone scattered field are derived under the first-order perturbation and several numerical examples are shown.
A mode-matching method in the sense of least squares are proposed for analyzing grating coupler having a periodic groove structure of finite extent which is formed on the surface of the core region of the thin-film waveguide. The grating couplers are analyzed for the plane wave incidence when the Bragg condition is satisfied. The discussion is developed about the grating couplers formed on the asymmetric and symmetric waveguides. The approximate scattered fields of each region of the grating coupler are described by the superpositions of the plane waves with band-limited spectra, respectively. These approximate wave functions are determined by the minimization of the mean-square boundary residual. This method results in the simultaneous Fredholm type integral equations of the second kind for these spectra. Results of analyses based on the first order approximate solutions are presented. A comparison between our results and those of Green's function approach for grating couplers having rectangular, triangular and sinusoidal grooves of different depth is presented.
Naomichi OKAMOTO Kazuyuki IZAWA
The propagation properties of the TE0 mode in an optically nonlinear tapered waveguide are examined and discussed. It is assumed that the nonlinear core has the Kerr-like refractive index of self-focusing type. The size of the tapered waveguide is so chosen that for a small input power, the guided light is cut off on the way to the taper end, and so the transmitted power becomes nearly zero. If the input power exceeds a threshold, the increment of the core index makes the nonlinear guide break away from the cut-off state, and the output power abruptly goes up at the threshold. Hence, the guide can be used as an all-optical threshold device which has a strong point that the very abrupt increase of the output at the threshold can easily be obtained for its length. Some applications of the tapered guide to pulse compression, optical AND gates, and optical differential amplification are also shown. The above abrupt increase gives the differential amplifier with very high gain.
The queueing system with multiple servers of possibly different rates under a threshold-type scheduling is analyzed. We first derive the general expressions for state probabilities and the average queueing delay in which the conventional M/M/n queueing system is also included as the special case of zero-threshold policy. Next, the numerical calculation is carried out for the queueing system with 3 servers under a threshold-type scheduling to consider the impact of the multiple thresholds on the average queueing delay of the system. It is found that the average queueing delay of the queueing system with multiple servers of different rates can be reduced under a threshold-type scheduling by selecting the threshold values appropriately. The threshold-type scheduling is more effective as the difference of the service rates becomes larger.
Won Ho CHUNG Ha Ryoung OH Myunghwan KIM
Petri net based satisfiability testing for non-clausal propositional calculus is presented. Every formula in propositional calculus is hierarchically represented by an acyclic free-choice Petri net called logic Petri net. Then a logic Petri net is combined with two way alternating modules, whose number depends upon the number of atoms used in the formula. It is shown that the satisfiability of a formula with non-clausal form can be tested by obtaining reachable firing set of the complete logic Petri net corresponding to the formula under the maximum firing rule.
Static characteristics between self-lubricating composite materials, of which resistivities were lowered by modifying the conventional material compositions, and copper, molybdenum, and carbon, which were selected as the mating materials, were examined. As the results, it was found that the contact resistances were lowered as much as by 1/10, and was ascertained that the formations of films due to Joule's heat were lessened through the verification of the Fritting phenomena. It was further found, however, that contact resistances were increased along with the increases of the resistivities of the mating materials in the order of copper, molybdenum, and carbon to indicate the reduction of the modification effects of the properties of the composite materials.
Hiroo UKITA Yasuyuki SUGIYAMA Yoshitada KATAGIRI
Phase change recording with an optically switched laser (OSL) head is realised for the first time. This head consists of a 1.3µm wavelength laser diode monolithically integrated with a photodetector (LD-PD) and a flying slider. The lensless OSL head has a minimum power of 18 mW (1 MHz) for writing information on a 1200 rpm, 130 mm diameter, SbTe based alloy disk. The bit shape and crystalized level are uniform and the readout signals are of high quality.
Kazushige HORIO Yasuji FUSEYA Hiroyuki KUSUKI Hisayoshi YANAI
A simplified two-dimensional model that includes only an electron current equation is shown to be successfully applied to the calculation of current-voltage characteristics of GaAs MESFET's with a p-beffer layer or with the semi-insulating substrate including hole traps.
A parallel binary tree traversal algorithm in Ada is analyzed, its performance profile is derived, and the optimal numbers of parallel processors to be used for the algorithm are determined.
Masaharu OHASHI Nobuo KUWAKI Yutaka SASAKI Fumihiro ASHIYA
A low-loss dispersion-modified single-mode fiber with low dispersion in the 1.5µm wavelength region has been designed and fabricated by using VAD method. A minimum loss of 0.23 dB/km at 1.55 µm and a small dispersion slope less than 0.023 ps/km/nm2 have been achieved around the zero-dispersion wavelength. Moreover, for the fist time, the tolerance of the core radius has been estimated by waveguide dispersion measurement.
Kuniaki YOSHITOMI Takeshi MOMII
The radiation characteristics of a rectangular waveguide with a flange coated with an absorbing material is studied. The impedance boundary condition is applied at the surface of the coated flange. From the numerical results, it is found that the coated flange reduces the maximum amplitude of the radiation field and makes the half-power beamwidth narrow in the E-plane.
Makoto TSUBOKAWA Yutaka SASAKI
Polarization dispersion of a 120-km long submarine optical cable has been experimentally shown to be approximately 1 psec. The length dependence of polarization dispersion is theoretically simulated with a simple model using structural fiber parameters. This reports clarifies how polarization dispersion grows along a fiber axis as a function of the birefringence perturbation mainly caused by core deformation, fiber twist and stress transversely acting on the fiber.
Progress of corrosion of contact surfaces on the printed circuit board both for thin Au plated (0.1µm) and for thick solder plated (10µm) were examined in H2S environment. The corrosion was evaluated by thickness of contaminant film and contact resistance. The Au plated surface easily degraded by pore corrosion. On the other hand, the film on the solder plated surface grew very slowly. For the solder plated surface, acceptable low contact resistance which corresponds to the low growth rate of the film was found.