Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1999-10-27
2001-02-27
Young, W. R. (Department: 2753)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S059160, C369S124020
Reexamination Certificate
active
06195317
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to optical disks, optical disk apparatuses, methods for recording optical disks, and methods for reproducing optical disks, and more particularly, to an optical disk which records information at a high density and its related apparatuses. The present invention improves the recording density of an optical disk in the radial direction by densely forming tracks such that inter-code interference is generated between adjacent tracks, and by forming pits or marks so as to cancel the inter-code interference.
2. Description of the Related Art
A conventional optical disk is formed such that crosstalk caused by interference between codes from adjacent tracks is effectively avoided.
In a compact disc, which is reproduced in a reproduction apparatus for such an optical disk, a track pitch &dgr; is set to 1.6 &mgr;m. In a compact disc player, the wavelength &lgr; and the numerical aperture NA of a reproduction optical system are set against the track pitch &dgr; such that the size of an area image, namely 1.22&lgr;/(2NA), satisfies expression (1).
&dgr;>1.22&lgr;/(2
NA
) (1)
With this setting, the compact disc player reproduces data recorded in a compact disc, with crosstalk between adjacent tracks being effectively avoided.
In contrast, in a magneto-optical disk apparatus, a so-called land/groove recording method is applied. With effective use of the depth-of-focus in a reproduction optical system, crosstalk between adjacent tracks is effectively avoided and information is recorded at higher density. (This method is described, for example, in “LAND/GROOVE RECORDING IN MO SYSTEMS,” A. Fukumoto et al., Technical Digest, Optical Data Storage 1995, PP. 117-118.)
In a magneto-optical disk, since grooves for guiding a laser beam and lands formed between grooves have different depths from the surface of the disk, laser beams are condensed separately on grooves and lands, and changes in light returned from marks formed on the grooves and the lands are effectively avoided. In recording, laser beams are condensed separately on grooves and lands, and increases in temperature to the magnetic Curie point or more at the grooves and the lands are effectively avoided. With this configuration, grooves and lands are densely formed at an interval of the size of an area image or less, and the desired data can be recorded into and reproduced from grooves and lands.
In such an optical disk, however, recording density in the track direction is smaller than that in the circumferential (line) direction. In a compact disc, for example, recording density in the line direction is about 0.6 &mgr;m/bit whereas the track pitch is 1.6 &mgr;m. This means that recording density in the line direction and that in the track direction differ by a factor of 2.7.
To solve this problem, a method of land/groove recording, which is applied to a magneto-optical disk, can be considered. It is, however, practically difficult to apply the method to an optical disk which records information with the use of pits, such as a compact disc. Since a pit and a groove are formed by the same method, it is difficult to form a pit among grooves. In addition, for effectively preventing crosstalk from being generated, grooves must be maintained in their ideal shape, and hence mass production is difficult.
SUMMARY OF THE INVENTION
The present invention is made in consideration of the foregoing points. Accordingly, it is an object of the present invention to provide an optical disk which can record and reproduce the desired data and which has tracks formed at a higher density than that for a conventional disk, an optical disk apparatus therefor, a recording method therefor, and a reproduction method therefor.
The foregoing object is achieved in one aspect of the present invention through the provision of an optical disk, an optical disk apparatus, or a recording method for an optical disk, wherein tracks are densely formed such that inter-code interference is generated between adjacent tracks, and pits or marks are formed such that the inter-code interference is canceled.
The foregoing object is achieved in another aspect of the present invention through the provision of an optical disk or an optical disk apparatus, wherein pits or marks are sequentially formed on a plane, and tracks or a reproduction optical system is formed such that the relationship of &dgr;<1.22&lgr;/(2NA) is satisfied.
The foregoing object is achieved in still another aspect of the present invention through the provision of an optical disk apparatus or a reproduction method for an optical disk, wherein the spot of an optical beam scans a plurality of tracks on a disk-shaped recording medium at the same time, and light changed by and returned from pits or marks on the plurality of tracks is received.
In an optical disk, an optical disk apparatus, or a recording method for an optical disk, when tracks are densely formed such that inter-code interference is generated between adjacent tracks, track density is increased accordingly and recording density is also increased. In this case, when pits or marks are formed such that the inter-code interference is canceled, data can be reproduced from the desired track while the effect from adjacent tracks is effectively avoided.
In an optical disk or an optical disk apparatus, when pits or marks are sequentially formed on a plane, and tracks or a reproduction optical system is formed such that the relationship of &dgr;<1.22&lgr;/(2NA) is satisfied, tracks are formed more densely than in a conventional disk or a conventional disk apparatus. In this case, since a reproduction signal in which inter-code interference is generated between adjacent tracks during reproduction is processed with this interference being taken into account, data can be reproduced from the desired track.
In an optical disk apparatus or a reproduction method for an optical disk, when the spot of an optical beam scans a plurality of tracks on a disk-shaped recording medium at the same time, and light changed by and returned from pits or marks on the plurality of tracks is received, a reproduction signal can be obtained from a narrow-track-pitch optical disk in which tracks are formed such that inter-code interference is deliberately generated.
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Limbach & Limbach L.L.P.
Sony Corporation
Young W. R.
LandOfFree
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