Toshimitsu Kaku

Compact magnetooptical disk for coded data storage

A compact magnetooptical disk having 500 times the capacity of a 13.34-cm (5.25-in.) floppy disk has been developed for use in coded data storage applications. Low error rates are attained by the use of advanced highly sensitive polarization detection optics and high-quality recording media. Progress in these fields has been based on noise analysis of readout signals. The disk drive can write and erase data by sectors and can also play current write-once-type optical disks. This disk/disk drive unit promises to lead to enhanced storage capacity and to support the current drive to enhance office automation and other information systems.

Single‐beam overwrite experiment using In‐Se based phase‐change optical media

Single‐beam overwrite in an optical disk is reported using In‐Se‐Tl amorphous‐crystalline phase‐change recording films having very short erasing (crystallization) time of 0.2 μs. The lifetime of the amorphous state in an In‐Se‐Tl film is estimated to be longer than 10 years at 60 °C. This is due to its high crystallization temperature (135 °C) and high activation energy (2.6 eV). The phase‐change cycles can continue over 106 cycles in stationary state experiments using test samples. The possibility of single beam overwrite (rewriting without prior erasing as with a magnetic disk) is verified by using a 1.6‐μm‐diam round laser beam spot irradiated on a 5‐in.‐diam disk rotating at 2400 rpm.

Sn–Te–Se Films for Reversible Phase-Change Optical Recording

Characteristics of optical recording films that consist of Sn–Te–Se and have an amorphous crystalline phase change recording mechanism are analyzed. High crystallization temperatures and high crystallization activation energies, which certify the long life of the recorded dots, can be obtained for compositions whose ratio of Sn concentration to Se concentration is about 1 to 2. Among these compositions, high speed erasing, long life of the recorded dots, and high recording sensitivity are achieved in compositions whose Te concentration is 10 to 20 at%. When the Te concentration is 50 to 60 at% and the Se concentration is 17 to 25 at%, the crystallization temperature of the recorded dots is much lower than that of the as-deposited amorphous state.

Sn-Te-Se Phase Change Recording Film For Optical Disks

Sn-Te-Se amorphous-crystalline phase change recording film is analyzed on write/erase cyclability, erasing speed, and activation energy of crystallization. The Sn-Te-Se thin film, sandwiched by two SiO2 thin film layers, is deposited on an organic-thick-film coated glass substrate. Then, another organic thick film is coated onto these layers. For these samples, the maximum erasure(crystallization) speed by laser beam irradiation and other write/erase characteristics are measured. Information can be written and erased more than 106 times. The crystallization activation energy is also measured and found to be about 2.3eV. The life of the amorphous state is estimated to be about 10 years at 40°C. These experimental results show that Sn-Te-Se thin film is promising as a reversible phase change recording film.

High-speed DVD-multi drive system

High speed DVD-RAM and DVD-R recording technologies have been established for the DVD-multi drive system. The developed key components are LSIs, especially a laser diode driver, and an optical pickup.

Ablative organic films for optical recording

This work presents a new type of optical recording medium for a diode laser which is three times more sensitive than a chalcogenide thin film. This medium has a tetralayer structure of n–hexatriacontane, zinc stearate, Sb2S3 and Bi. The Bi layer absorbs a recording light beam and organic layers are ablated by heat evolved in the Bi layer. The high sensitivity characteristic of this medium is attributed to the use of low‐melting‐point material as the ablating layer and the effective use of the incident beam.

Compact Magneto-Optical Disk for Coded Data Storage

A compact magneto-optical disk drive compatible with current optical disk systems is reported. A tracking detection system enabling use with add-on (non-erasable) optical disks was adopted. High-speed accessing was accomplished by constructing the head from both stationary and moving mechanisms. Noise analyses showed that for large analyzer angles ¿<inf>A</inf>, N<inf>disk</inf> ≫ N<inf>laser</inf> ≫ N<inf>shot</inf>, but when the SN ratio was maximum at ¿<inf>A</inf> ~ 10°, the three noise levels were roughly equal.

On-Land Composite Pregroove Method For High Track Density Recording

In optical disk systems using push-pull tracking method, there have been problems of tracking offset errors caused by a disk skew and low signal-to-noise ratio due to a surface noise of the pregrooved area. In order to achieve higher track density recording, these problems have to be solved. We have developed a new type of on-land composite pregroove method for higher track density recording. In this method, the header data and the user data are recorded on the land area between two pregrooves on the disk. Each pregroove has 10-20 of tracking offset detection flags once per sector at each header area.

Performance and reliability of advanced magneto-optical disk drive

Read/Write characteristics such as 2.2 MB/sec overwriting and 0.6 μm/bit density are obtained by magnetic field modulation and domain edge recording on a magneto-optical disk. Reliability of an interface between a floating magnetic head and a disk is investigated under artificial dusty environment.