Mitsubishi Chemical Corporation

Chiga Ueda

Hidemi Yoshida

Masaaki Mizuno

Hideharu Takeshima

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

Disclosed herein are an optical recording method of conducting recording/reading out for information by irradiating a laser beam at a wavelength of not more than 500 nm onto a recording layer of an optical disc having a track pitch of not less than 0.4 .mu.m and less than 0.9 .mu.m, the laser beam being incident from a disc substrate side of the optical disc using an objective lens having numerical aperture of 0.55 to 0.70, a recording area for information recording on the disc substrate being a flat area not having a guide groove for each track, and the disc substrate having a in-plane birefringence of not more than 20.times.10.sup.-6 and a vertical birefringence of not more than 300.times.10.sup.-6, and an optical recording medium suitable for use in the optical recording method.

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Tokyo, Japan

Chiga Ueda