Magnetic field sensitivity of Pt/Co multilayers, which are studied as a high density magneto-optical recording material, are worse than those of RE-TM alloy films, so it is necessary to improve the sensitivity of Pt/Co. In this report, Pt/Co multilaryer films were prepared for various period, content and buffer on 64mmφ disk substrate and their magnetic field sensitivity were estimated. Although any change of sensitivity were not observed in Pt/Co films on ZnO buffer layer, 3dB change of sensitivity were observed in the films on SiN buffer layer. It seems that the difference of perpendicular anisotropy of ZnO and SiN buffer films influenced on the magnetic field sensitivity.

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The magnetic and magneto-optical properties of Nd (Tb, Dy)/FeCo which prepared by rf magnetron sputtering method are investigated. By optimizing the bilayer period and composition of multilayers, the perpendicular magnetic anisortropy (PMA) of 5.0 ×10^5J/M^3 is obtained. And square nysteresis loop is Kept at hRE content of 35 at. % in RE layer becauce Tb and Dy have large single ion anisortropy. The magneto-optical Kerr Rotation at blue wavelength is about 1.5 times as large as Tb-FeCo alloy in practice use. The fine structures of Tb/Fe multilayers are analyzed via EXAFS (Extended X-ray Absorption Fine Structure) spectroscopy to clear the change of PMAs for various bilayer periods. The PMA is influenced by Fe-Fe and Fe-Tb correlations.

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We investigated to use W layers as metal boundary layers between recording and protective dielectric layers for a phase change optical disk structure. The W metal boundary layers are proved to be able to control of the crystallization speed, and the absorptance of crystal/amorphous phase change recording medium. High CNR, high erasability and good cycle characteristic were achieved for a high density ZCAV mark-position recording using a 690nm diode laser and a high N.A. objective lens.

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Thermal stability of aluminum-alloy reflective layer is one of the key-factor of archival life of a rewritable phase-change optical disk. The disk using an aluminum-alloy reflective layer having excellent stability at high temperature and a MxGeSbTe-alloy recording layer is extremely stable. The bit-error-rate of the recorded disk did not substantially changed after 7,800 hours acceleration test under the condition of 90℃ 80%RH.

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We confirmed that phase-change recordable (PCR) media is superior to magneto-optical (MO) media by 10 dB in maximum-repeat-frequency at bit length of 0.34μm at 12 m/s by (1,7) RLL digital recording, (CNR for PCR is 50dB and CNR for MO is 40dB). We also fabricated optical head for PCR media by measuring the noise level gap between amplifier and laser noise level. We attained 10 dB for the level gap. The linear recording density for PCR media is 1.3 times larger than that for MO media, because of bit length between 0.34 and 0.45μm at the bit error rate of 10^<-4>.

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Strong point of high density optical disk is exchangeabilty which is secured by international standard. Standard disk, calibration disk and common testing are proposed for standardization and supporting practical use of the standards. Common testing on recording characteristics, testing method of effect by dust, measuring method of laser spot size on rotating disk and temperature dependance of recording characteristics are studied. Disk slipping on turn-table is pointed out and it's measuring method is studied.

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To improve the erasing characteristics at high linear velocity condition for a phase change optical disk, disks of various layer structures have been investegated. It is found that it is effective not only to control the optical absorption of the active layer, but also to reduce the cooling rate of the disk. Especially, the no-reflective-layer disk, with properly controled optical absorption and low cooling rate, shows high erasingratio of >25dB. The no-reflective-layer disk having SiO_2 layer with small thermal expansion coefficient shows half a million cycle stability.

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Crystals doped with Eu^<3+> are known to exhibit ultrasharp holeburning at cryogenic temperatures. In fact, in these materials, the homogeneous widths, or the hole widths, are extremely narrow (<1 kHz, the narrowest in any solid state) compared to the inhomogeneous absorption widths (^-10 GHz), and the holes are persistent. These findings promote the Eu-doped crystals to be a candidate of ultrahigh-density frequency-domain optical memory of capacity 10^7 bits. Not only that, due to short bleaching times, even real-time recording of a moving image in possible using a holographic technique, which is called holographic motion picture. We for the first time succeeded in holographic motion picture using Eu^<3+> : Y_2SiO_5.

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We have developed a quadruple density CD-ROM, which has a recording density four times as high as existing CDs. A 635nm laser diode is used for reading out the data from the CD-ROM. Owing to realizing the CD-ROM, we have developed a 2D/3D moving picture player based on the MPEG2 standard. The player can play back video data at 3Mbps by a 120mm diameter CD-ROM for 135 minutes. Generally, the multimedia product needs a real time processing. So, we have developed real time OS, which works as the kernel of real time processing. And the real time OS is used to control the player.

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