Kunihiko Hayashi

Recording Capacity Enhancement of Micro-Reflector Recording

Micro-reflector recording is a potential candidate for sub-terabyte optical storage systems. In this paper, the latest progress on increasing storage capacity and on improving recording transfer rate of micro-reflector recording is presented. With our dynamic tester, we successfully recorded ten signal layers dynamically in a monolithic recording material. For every signal layer, moderate bit error rate was obtained by employing readout signal processing. Our experimental results indicate the potential for increasing recording transfer rate and recording density.

Raman Scattering from Magnon Excitations in RFeO3

Raman scattering from one- and two-magnon excitations in various rare-earth orthoferrites are studied. The magnetic in-plane and out-of-plane anisotropy energies of these systems are obtained and discussed based on the two-sublattice model of ironspins. Detailed temperature dependence of the frequencies of two (k{cong}0) magnons are also examined on YFeO 3 , ErFeO 3 , SmFeO 3 , Er 0.7 Sm 0.3 FeO 3 and DyFeO 3 . It is shown that the softening behaviors of one-magnon peak frequencies are different between the rotational- and abrupt-type spin-reorientation (SR) systems. This is explained by different anisotropy terms which contribute to the magnon softening associated with SR transitions. The exchange interactions between the iron and rare-earth ions are considered to interpret the magnon softening in the vicinity of SR temperatures. The temperature and polarization properties of two-magnon Raman spectra are also discussed.

Single Crystal ESR Study of Y2BaCuO5

Single-crystal ESR measurements were made in insulating Y2BaCuO5. The principal values of the g tensor of Cu2+ ions in Y2BaCuO5 are gX=2.050(4), gY=2.094(4) and gZ=2.222(4), which reflects the rhombic symmetry. The principal X-axis is parallel to the crystallographic c-axis, the Y to the b, and the Z to the a. The crystal habits with Miller indices and the crystallographic axes are shown. The temperature dependence of the ratio of the ESR intensity to that of DPPH at room temperature, which agrees well with that observed for the magnetic susceptibility, is also reported.

Structure and Superconductivity in a New Type of Oxygen Deficient Perovskites Y1Ba2Cu3O7

We have succeeded in obtaining a new single phase of oxygen-deficient perovskite ABO3-x type. The sample of nominal composition Y1/3Ba2/3CuO3-x exhibits the superconductivity at 125 K and a zero resistance state at 83 K. X-ray diffraction patterns of this compound show the oxygen deficient tetragonal perovskite to be of a nearly single phase of the formula Y1Ba2Cu3O7. This structure is a layered perovkite which is associated with the high-Tc superconductivity.

Preparation and Characterization of Ba-Y-Cu-O Single Crystals

Single crystals of Ba2YCu3O7-y were prepared from molten Ba-Y-Cu-O. The shape of the crystals was thin rectangular slab and the size of the largest crystal was 1.5×1.5×0.04 mm3. The crystals were characterized by resistivity measurement, Meissner effect study and structure analysis. Superconductivity was found with transition temperature of about 90 K by resistivity measurement. The resistivity parallel to the c-axis is 30-90 times larger than in-plane resistivity just above Tc. The Meissner effect was also observed in the same sample. The unit cell was orthorhombic with space group Pmmm and the lattice parameters a = 3.857(1), b = 3.865(1) and c = 11.723(4) A.

Drive system and readout characteristics of micro-reflector optical disc

This paper reviews the analyses and the experimental results of Micro-reflector optical disc system. In Micro-reflector optical disc, data are recorded on multiple virtual planes in a monolithic holographic medium. We have demonstrated the possibility of huge capacity from our analyses of readout characteristics of the Micro-reflector. In addition, we have developed the five-axis servo control system in order to achieve precise control of two counter-propagating light spots in recording media. Using this system, we succeeded in four-layer recording/readout.

Growth and Domain Structures of Ba2YCu3O7-y Single Crystals

Crystallographic and superconducting properties of single crystals of Ba2YCu3O7-y grown by the flux method are studied. The single crystals were superconductors in as-grown atates. Domain observation by an interference microscope revealed that there were a few kinds of single crystals with a single domain and a few with several domains. A single-domain crystal had a tetragonal structure and a Tc onset of ~45 K while a multidomain crystal had an orthorhombic structure and a Tc onset of ~95 K. The latter crystal with no twins had several rectangular shape domains. It is thought that long one-dimensional chains of oxygens with a few 100 µm in length were realized in each domain of the crystal. The reason for the appearance of such domain structures is discussed.

Dynamic Recording of 200 Gbytes in Three-Dimensional Optical Disk by a 405 nm Wavelength Picosecond Laser

We present experimental results of our volumetric optical data storage system. To achieve volumetric recording over a wide depth range of 250 µm in a recording medium, we developed a relay lens system for compensating for the spherical aberration of a high-numerical-aperture (0.85) objective lens. The disk employs a single monolithic recording layer and a reference layer for servo control. A 405-nm-wavelength titanium:sapphire laser that exhibits 2 ps pulse duration and a more than 2 kW peak power is used for recording. We adopted void formation and mark position as recording principles. We have experimentally demonstrated 34-layer dynamic recording, corresponding to a capacity of 200 Gbytes.

Fabrication of Transparent PLZT Ceramics with a High Transmittance and Their Application to Optical Light Shutter

Lanthamun-modified lead zirconate titanate (PLZT) powders were produced by chemical preparation method and these powders were sintered by ordinal atmosphere sintering method with O2-gas flow. As a result of combination both high quality powder and atmosphere sintering, high transparent PLZT ceramics with a transmittance as high as 67% at the wavelength of 600 nm were obtained. Optical light shutters were produced using these PLZT ceramics and proved to be applicable for commercial use.

Electro-optic lens composed of transparent electrodes on PLZT ceramic towards optoelectronic devices

Combination of numerous fine-electrodes with an electro-optic (E-O) material is much expected to be various optoelectronic key-devices. However, since a metallic opaque electrode has usually been used in most of the devices reported,2 the loss of intensity due to the electrode portion is serious disadvantage. In addition, the devices with the opaque electrode are not suitable to focusing or defocusing function such as a lens. In the present paper proposed are two types of E-O lenses, i.e., an E-O zoom lens and a Fresnel-zone plate (FZP) E-O lens which consist of numerous transparent fine-electrodes on a flat E-O material, and are experimentally demonstrated by composing the E-O lenses with the ITO transparent electrodes on a PL7T (9/65/35) ceramic plate, in comparison with theoretical calculations.