Takumi Minemoto

Measurement of the displacement distribution by speckle photography using a BSO crystal

Abstract The use of Bi 12 SiO 20 crystal plates for recording media of specklegrams in speckle photography enables one to measure the distribution of in-plane displacement on a rough surface of an object in situ and in quasi real time. For the purpose of measuring the distribution of any in-plane displacement in quasi real time by speckle photography using a BSO crystal plate, the dependence of the visibility of Youngs fringes on the readout beam diameter for specklegram and the magnitude of the object displacement has been investigated. The fact is cleared that the visibility of Youngs fringes depends on the number of speckles consisting of a Youngs fringe, which is decided by the ratio of the displacement magnitude to the readout beam diameter.

Optical parallel logic gate using spatial light modulators with the Pockels effect

This paper describes a new optical gate for logical processing in parallel. The gate consists of two spatial light modulators which spatially modulate a lightwave by the longitudinal electrooptic or Pockels effect. The gate can perform in parallel all sixteen logic functions of two binary variables in both the bright-true logic and the dark-true logic. The gate has the capability of operating on large arrays of binary variables.

Influence of silver on critical current of the Y–Ba–Cu–O superconductor

Electrical properties of Y--Ba--Cu--O superconductors, such as the critical current density and the zero-resistance temperature, are systematically improved by changing the compression pressure during the formation process of the specimens. Also, by changing the silver powder content of the superconducting Y--Ba--Cu--O powder, the critical current density and the zero-resistance temperature are remarkably improved. The resistance-drop temperature is insensitive to changes in the compression pressure, silver content, and magnetic field, whether the field is applied perpendicular to the specimens. The critical current density of the specimens with and without silver decreases exponentially with the perpendicular magnetic field. The critical current densities of specimens without silver showed much lower sensitivity to perpendicularly applied magnetic fields than those of the specimens having a silver content. Along with the above improvements, the present paper also examines several factors that affect the superconducting characteristics. These factors include impurities in the air and strong magnetic fields.

Improvement in magnetic shielding by the superposition of a magnetic cylinder over a copper-oxide superconducting cylinder

Magnetic shielding was shown to be improved by superimposing a magnet cylinder over a superconducting cylinder. Examples of such configurations are soft iron and electromagnetic steel cylinders over a copper-oxide superconducting cylinder. The value of the magnetic shielded field for the superimposed cylinder was found to be several times more than that of single superconducting cylinders such as YBCO or a BPSCCO cylinder. Experimental results reveal good characteristics which include the effects of the excitation magnetic field on the inner magnetic field within both the single superconducting and superimposed cylinders, the temporal change of the trapped magnetic field within the superconducting cylinder, the distribution of the magnetic shielded field along the axial direction of the superimposed cylinders, and the relationship between the length of the magnetic cylinder and the shielding effect.<<ETX>>

Optical implementation of a wavelet transform by the use of dynamic holographic recording in a photorefractive material

An optical system that employs holographic recording in a photorefractive material is proposed and experimentally demonstrated for the implementation of a wavelet transform of two-dimensional mages. A scaling operation, to derive the family of wavelet filters from a mother wavelet filter, is performed by the use of an optical feedback loop. The selection of a desired wavelet filter from the family and the correlation for a wavelet transformation are made by the use of a holographic recording in a photorefractive material. The principle of operation of the system relies on the frequency detuning introduced inside the loop and the subsequent variation in the holographic grating diffraction. Experimental results on wavelet-filter selection and wavelet transformation are presented. This nonlinear optical wavelet-transform system is advantageous for pattern recognition applications.

Successful Pattern Matching with a Large Number of Reference Patterns Using a Joint Fourier-Transform Correlator

Two kinds of modification of the joint transform correlator to perform pattern matching are proposed and the mechanisms are analyzed. Simulation and experimental results show that pattern matching is executed correctly by the modified JTCs; it is shown that one of the two modified joint transform correlators is equivalent to matched filtering and the other corresponds to pure-phase-only filtering.

Readout properties of the specklegram recorded in photorefractive Bi(12)SiO(20) crystal.

The readout properties of the specklegram recorded in a photorefractive Bi(12)SiO(20) (BSO) crystal plate have been investigated by observing the Young fringes and the polarization change of the light transmitted from the BSO plate. The Young fringes can be obtained without an analyzer by any linearly polarized readout beam; they have higher visibility than those obtained from a photographic plate specklegram, since the specklegram recorded in the BSO crystal can be read out by the spatial distribution of both the degree of polarization and the azimuth angle of polarization. Selective interference of a kind is performed.

Numerical analysis of the modulation transfer function of a Pockels readout optical modulator device

We present a new model in which the drift of photoinduced carriers in the transverse direction of a Bi12SiO20 single-crystal plate is newly taken into account in addition to the drift in the longitudinal direction considered with the previous models. According to the new model, the charge distributions in the crystal plate are calculated by an iterative method and the electric potentials in the device by the boundary element method. The modulation transfer function curve is obtained from the potentials and compared with the experimental one. The calculated result agrees fairly well with the experimental result in the entire region of spatial frequency. It is shown that the transverse drift of carriers in the crystal plate plays an important role in the write-in process of a Pockels readout optical modulator device and under certain operational conditions cannot be disregarded in the calculation of the modulation transfer function curve of the device.

Highly sensitive magnetic sensor made with a superconducting Y-Ba-Cu-O thick film

In the research, Y-Ba-Cu-O (YBCO) thick film was fabricated to form a highly sensitive magnetic sensor, constructed to maintain the superconducting state at the boiling point of liquid nitrogen (77.4 K). Superconducting film will, in general, break the superconducting state of the flow of current at the value of current density J greater than that of the critical current density J/sub c/, when the resistance R/sub sen/ to the flow of current occurs. The magnetic sensitivity increases as the value of the resistivity /spl rho//sub seu/ of R/sub sen/ decreases. The value of /spl rho//sub sen/ can be readily controlled by the value of J. The average sensitivity S of this magnetic sensor was determined as about 154%/gauss, over the magnetic range of 0 gauss to /spl plusmn/40 gauss. In addition,the sensitivity is about 154 times that of a giant magneto-resistance sensor. The paper examines the fabrication process and conditions, the characteristics of S as related to /spl rho//sub sen/, and the magnetic response of the highly sensitive magnetic sensor.

Surface-roughness measurement using Fourier transformation of doubly scattered speckle pattern

The statistical properties of the doubly scattered speckle pattern generated from a rough surface, under a fully developed and static speckle pattern illumination, have been investigated by numerical analysis. The real-time Fourier transformation of the doubly scattered speckle pattern by an optical process enables us to measure the surface roughness in quasi real time.