Masafumi Yoshihiro

Magneto-Optical Disk Structure with High Write/Erase Repeatability

Over 107 write/erase repeatability has been achieved in magneto-optical (MO) disk by optimizing thermo-structural design through thermal conduction analyses. By combining this technology with that for anti-corrosion measures, a highly reliable and durable 5 1/4 inch MO disk has been developed. Carrier level degradation through write/erase repetition, which was observed in the cource of the development, is thought to be interpreted as a structure relaxation by annealing leading to a localized change in magnetic properties.

Direct overwriting capability of magnetic multivalued MO media

As one of the most promising schemes for high density MO recording, a new media for magnetic multivalued recording has been proposed. By switching the external field on four levels, the quadri-valued signal was obtained. On the MMV media, field sensitivity is improved by controlling composition of PtCo capping layer coupled to TbFeCo. The external filed for recording four levels is reduced down to 350 Oe and direct overwriting capability is confirmed on 0.8micrometers mark length recording.

Highly field sensitive (150 Oe) quadri-valued magnetooptical media for high-speed overwriting

For high-density and high-speed magnetooptical (MO) recording, the use of magnetic multi-valued (MMV) MO media has been proposed. [rf:1] A quadri-valued recording has been achieved using this media and a field modulation recording method. For practical use of this media, it is important to reduce the critical magnetic field to minimize the applied field for realizing the quadri-valued recording. We have achieved reduction of the critical magnetic field down to 150 Oe using a new coupled film, TbFeCo/GdTbFeCo.

Write/Erase Cyclability of TbFeCo for Mark-Edge Recording

Write/erase cyclability for mark-edge recording is studied using rare-earth element[RE]-rich TbFeCo media. Mark-edge jitter for the (1-7) random pattern is small enough even after millions of cycles of data writing and erasing.

Basic Characteristics and Predicted Lifetime of Stacked Volumetric Optical Disks

A stacked volumetric optical disks (SVOD) system has been developed to achieve an over 1 Tbytes cartridge capacity using a commercialized drive and conventional recording layers. To confirm the reliability of thin optical disks in SVOD, several feasibility tests were conducted. The recording power margin, tilt margin and read stability of the thin optical disks were measured, and the lifetime of the thin optical disks was estimated. The results were similar to those of conventional 1.2-mm-thick optical disks regardless of the disk thickness.

High Performance Magneto-Optical Disk Using A New Plastic Substrate

To realize high data rate and high reliability 5.25 inch Magneto-Optical(MO) disks, suitable materials for a tri-layer structure(substrate/Kerr enhancement layer/magnetic layer/protective layer) and substrates were studied. By optimizing the composition of TbFeCo film, micron-size and regular-shaped recorded domains were obtained. SiNx film showed enough Kerr rotation enhancement and good protectivity to be used as an enhancement layer and a protective layer for a TbFeCo magnetic film. Those films were constructed on newly developed plastic substrates of photocurable casting resin(PHC) which have as low retardation and as high heat-resistance as glass/2p(photo-polymerization) substrates. MO disks with the tri-layer structure on PHC showed high reliability even in severe circumstances.

Optimization of Pit Depth for Concurrent Read Only Memory?Random Access Memory Optical Disk

We have studied a concurrent read only memory?random access memory (ROM?RAM) optical disk system without laser feedback by optimizing pit depth. When the pit depth was 47 nm (optical depth about 1/11 ?) and the pit width 0.45 ?m, about 8% jitter in both pit and magneto-optical (MO) signals was obtained with a 785 nm wavelength laser diode and 0.55 NA objective lens by employing magnetic-field-modulation (MFM) MO recording. Both pit data and MO data were recorded with eight to fourteen modulation (EFM) code with a minimum mark length of 0.83 ?m and a track pitch of 1.6 ?m and thus the areal density is comparable to 1.3 GB for ?120 mm single sided disk. By the optimization of the pit depth, sufficient system margins for practical use were obtained without laser feed back for the simultaneous reproduction of both pit and MO signals.

Media design of iD PHOTO disk with the CAD structure

We have developed a new MO(Magneto-Optical) disk, which is named iD(image/intelligent disk) PHOTO, as a promising candidate for a digital still camera memory. The iD PHOTO disk achieves 730MB/disk in a 50.8mm diameter by adopting some techniques mainly as follows, CAD (center aperture detection) type Magnetic Super Resolution reading, recording both on land and in groove, magnetic field modulation writing with irradiation of a pulsed laser beam, and PR(1,1) code. The iD PHOTO disk is required high performance in various environments, for it is used in a portable drive. As one of the most important factors, we have previously reported a reduction of electric power consumption by reducing the recording magnetic field. Here, we introduce thermal structure design of iD PHOTO disk to be suit for a drive in a digital still camera.