Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Reexamination Certificate
2003-06-11
2004-10-05
Dinh, Tan (Department: 2653)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
C369S013540, C369S013550
Reexamination Certificate
active
06801479
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical disk recording method, an optical disk reproducing method, an optical recording medium using the method, and an optical disk drive, and, in particular, to an optical disk recording method, an optical disk reproducing method, an optical recording medium using the method, and an optical disk drive for recording data at high density and reproducing the data thus recorded at high density.
2. Description of the Related Art
Recently, as optical recording media (optical disk, magneto-optical disk and so forth) come to have large capacities, low costs, high reliabilities, and so forth, they have become used in various fields such as recording/reproducing of image information, recording/reproducing of various code data in computer systems, and so forth.
Especially, optical disk drives are demanded to have further large capacities, and need to use recording/reproducing methods of recording data at high density, and reproducing with high accuracy the data recorded at high density.
As a recording/reproducing method for high-density data recording and high-accuracy data reproducing onto optical recording media, a method of shortening of laser wavelength and relative shortening of spot diameter through improvement of numerical aperture (NA) have been performed, for example.
Further, as a recording/reproducing method for high-density data recording and high-accuracy data reproducing onto an optical recording medium of a magneto-optical recording system, shortening of record mark through magnetic-field modulation recording has been performed, for example.
In the related art, for optical recording media in the magneto-optical recording system, record marks through magnetic-field modulation recording are recorded successively with portions thereof overlapped with one another, a recording density in a track direction (referred to as a line density, hereinafter) is increased in comparison to a track width, and, thus, the total recording density is increased. Further, the track width is shortened, a recording density in a radial direction (referred to as a track density, hereinafter) is increased, and, thus, the total recording density is also increased.
Thus, in order to increase a recording density, a line density is increased, and/or a track density is increased.
However, when a track density is increased, in a case where interference of diffracted light is used as in a tracking error detecting system employing a push-pull method, a tracking signal is degraded when the track width is shortened to be less than a predetermined width. For example, in a case where a laser wavelength is 650 nm and a numerical aperture is 0.6, the tracking signal is degraded when the track width is less than approximately 0.505 &mgr;m. Accordingly, there is a limit of improvement in track density.
When a line density is increased, because record marks are record successively with portions thereof overlapped with one another, crescent patterns of the record marks come to be emphasized. Such crescent record marks have curvature at end portions thereof increased when the track width increases, and portions which are not effective for reproducing increase.
Especially, in a case of MSR (Magnetically-induced Super Resolution) medium of double mask type, the crescent pattern of a record mark and a reproducing aperture (magnetic window) are exactly reverse in curvature. Accordingly, a resulting reproduced signal is degraded.
Thus, there is a limit of increase in recording density for each of the methods of increasing line density and increasing track density.
SUMMARY OF THE INVENTION
The present invention has been devised in consideration of those points, and, an object of the present invention is to provide an optical disk recording method, an optical disk reproducing method, an optical recording medium using the method and an optical disk drive by which it is possible to record a plurality of rows of data in a single track, and reproduce the thus-recorded plurality of rows of data.
An optical disk recording method of recording data on an optical disk by applying laser light to a track of the optical disk, according to the present invention comprises the steps of:
a) driving a plurality of laser light sources in sequence in a time division manner, and applying a light flux to one track of the optical disk successively; and
b) producing a plurality of rows of record marks in the one track.
In this method, a plurality of laser light sources are driven in sequence, and a light flux is applied to one track thereby in sequence. Then, a plurality of rows of record marks are produced in the track of the optical disk. At this time, because the plurality of laser light sources are driven in sequence, there is no case where a plurality of light fluxes are applied simultaneously. Accordingly, it is possible to produce a plurality of rows of record marks in one track, avoiding optical interference between the plurality of light fluxes.
In order to improve the recording density of the optical disk, it is preferable that the step b) produces the plurality of rows of record marks in such a manner that the rows of record marks overlap partially with one another.
In this method, because the rows of record marks overlap partially with one another, it is possible to improve the line density. Further, because the plurality of rows of record marks are cut off by one another at the end portions thereof, it is possible to prevent the curvature of the record marks from increasing. Accordingly, it is possible to reduce problems that the curvature of the record marks and the curvature of the reproduction aperture (window) do not coincide in MSR (Magnetically-induced Super Resolution) reproduction by which record marks smaller than the beam spot can be reproduced using a magnetic mask. With regard to MSR reproduction of double mask type, see Japanese Laid-Open Patent Application No. 7-244877.
In order to apply the method to a magneto-optical disk, a magnetic field may be generated in the track of the magneto-optical disk by one magnetic head.
In this method, it is possible to produce plurality of rows of record marks partially overlapping each other in one track of a magneto-optical disk through a simple configuration.
In order to reproduce data from an optical disk in which a plurality of rows of record marks are recorded in one track, with high accuracy, an optical disk reproducing method of reproducing data recorded on an optical disk on which a plurality of rows of record marks are formed in one track, by applying laser light to the track, according to the present invention, comprises the steps of:
a) driving a plurality of laser light sources in sequence by a time division manner, and applying a light flux to one track of the optical disk successively;
b) causing reflected light to be generated from the plurality of rows of record marks by the incident light flux successively, mixing the reflected light, and reproducing a signal changing according to states of the plurality of rows of record marks; and
c) demodulating the data recorded in the track from the reproduced signal according to a predetermined decoding algorithm.
In this method, a reading light flux is applied to one track, and reflected light is caused to be generated from a plurality of rows of record marks to which the light flux is applied, in sequence. The reflected light is signals changing according to states of the record marks to which the light flux is applied, and, from the signals, the data recorded in the track of the optical disk can be obtained through demodulation according to a predetermined decoding algorithm.
Interference occurs between respective reflected light from record marks of a plurality of rows of record marks to which a light flux is applied. Accordingly, the signal changing according to the states of the plurality of rows of record marks contains interference between the reflected light from the plurality of rows of record marks, and the data may be demodulat
Matsuura Michio
Taguchi Masakazu
Uchida Akiyoshi
Dinh Tan
Fujitsu Limited
Greer Burns & Crain Ltd.
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