Mitsubishi Chemical Corporation

Hideharu Takeshima

Masae Kubo

Toshifumi Kawano

Hidemi Yoshida

Chiga Ueda

Kyuuya Narita

Masanobu Hodohara

A magneto-optical recording medium having a writing layer formed on a transparent substrate provided with a groove having a flat bottom surface and a flat land, so that writing or readout is carried out on either the groove or the land only by irradiating a laser beam from the substrate side, wherein the sum (.alpha.+.beta.) of a phase shift .alpha. of a reflected light of a readout beam by the substrate and a phase shift .beta. thereof by a layer structure on the transparent substrate, is made to have an opposite sign to a phase shift .gamma. by interference of reflected lights from the groove and the land.

Magneto-optical recording medium and writing and readout method therefor

A magneto-optical disk has a recording film on a substrate for defining a data area. The data area is divided into a plurality of zones in the radial direction, and each zone has a plurality of physical tracks divided into a plurality of sectors along the tracks. Number of sectors per physical track in each zone is increased as viewed toward the outer edge of the disk one by one. The shortest mark length in specified zones in the vicinity of the inner and outer edges of the disk is longer than that in other zones to thereby improve reliability in recording/reproducing characteristics in the specified zones, which have otherwise degraded recording/reproducing characteristics due to inferior physical characteristics of the recording film.

Optical disk having a large storage capacity

A high density optical disk having data tracks and pre-grooves disposed in a track pitch not higher than 1.2 .mu.m provides groove signals to a disk drive having a two-divided optical detector for tracking control. The groove signal characteristics of the optical disk is such that an envelope cross-track signal, an envelope cross-track minimum signal and an envelope push-pull signal are not less than 0.10, not less than 0.12 and between 0.10 and 0.70, respectively, when normalized by a virtual mirror surface. The optical disk may be any of a magneto-optical (MO) disk, a ROM disk and a partial ROM disk and can provide any type of disk drives with sufficient groove signals for tracking control in both a magneto-optical area and a ROM area.

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Kanagawa, Japan

Hideharu Takeshima