Optical disk having high recording density

Details Optical disk having high recording density Optical disk having high recording density

1998-04-22

2001-06-05

Huber, Paul W. (Department: 2651)

Dynamic information storage or retrieval

Storage medium structure

Optical track structure

Reexamination Certificate

active

06243354

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to optical disks having high recording density, and more particularly, to an optical disk such as a compact disk and a video disk that allows recording/reproduction for a long period of time.
2 .Description of the Background Art
Various optical disks such as a compact disk (CD) and a video disk are developed. There are various standards such as CD-DA, CD-ROM, and CD-I even in one type of a compact disk. According to these standards, the physical dimensions such as disk outer diameter, track pitch, and minimum size of pit (shortest pit length) are predetermined.
For example, in a CD-ROM, the track pitch is 1.6 &mgr;m and the shortest pit length is 0.83-0.97 &mgr;m. The shortest pit length varies according to the allowance of the linear velocity (1.2-1.4 m/sec) of the optical disk. More specifically, since the frequency of a reproduction clock is 4.3218 MHz, the physical length of 3T which is the shortest pit length is 0.83 (≈(1.2/4.3218)×3) &mgr;m when the linear velocity is, for example, 1.2 m/second.
In accordance with the technical advance in the field of short-wavelength laser, various research is carried out as to disk fabrication outside the standard range and reproduction thereof. For example, the technique of recording information at a track pitch smaller than that of the standard to store information approximately two times the standard capacity into an optical disk of an outer diameter identical to that of the standard is known. In this case, reproduction from such an optical disk of high density recording can be effected by reducing the diameter of the beam spot employed in reproduction.
One method of increasing the recording density of an optical disk is to compress the physical amount such as the track pitch and the pit length. For example, a double recording density can be achieved by setting the track pitch and the pit length to 1/{square root over (2)} respectively.
However, crosstalk occurs between adjacent tracks at the time of reproduction if the track pitch is too small. Furthermore, if the pit length is reduced, the level of a reproduced signal becomes smaller as the pit has a length more approximating to the shortest pit length. Although the level of the reproduced signal can be easily compensated for, it is difficult to remove the crosstalk component from the reproduced signal.
If the recording density is improved on physical basis as described above, the standard deviation of the jitter of the reproduced signal is increased at the time of reproduction. The frequency of readout error becomes higher as this standard deviation is greater.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of the present invention is to suppress generation of crosstalk in an optical disk.
Another object of the present invention is to suppress jitter from a reproduced signal in an optical disk.
According to an aspect of the present invention, an optical disk includes a track having a track pitch of k times the track pitch of a standard recording format. Here, 0<k<1. The track is formed of a pit having a pit length smaller than k times the pit length of the standard recording format. The standard recording format is preferably a compact disk format.
When a standard compact disk having linear velocity of V m/second is compressed, the track pitch Pgm and the shortest pit length L&mgr;m preferably satisfy the relationship of L<(A/1.6)×P. Here, A=(V/4.3218)×3. Further preferably, the optical disk has a recording density approximately two times the recording density of the standard recording format, and the above track pitch is approximately 1.2 &mgr;m.
Preferably, the optical disk has a recording density n times the recording density of the standard recording format, where n>1. The track pitch is greater than 1.6/{square root over (n)}&mgr;m.
Although the above-described optical disk is reduced in track pitch and pit length to increase the recording density, generation of crosstalk between adjacent tracks is suppressed since the track pitch is not reduced as much as the pit length.
According to another aspect of the present invention, an optical disk has a recording density approximately two times the recording density by a compact disk format, and includes a track having a track pitch of approximately 0.9-1.4 &mgr;m. When the wavelength of the laser beam used in reproduction is approximately 780 &mgr;m and the numerical aperture of the objective lens used in reproduction is approximately 0.52, the track pitch is preferably approximately 1.1-1.3 &mgr;m.
The above-described optical disk has a reproduced signal suppressed in jitter to reduce generation of readout error since the track pitch is set to approximately 0.9-1.4 &mgr;m, preferably approximately 1.11-1.3 &mgr;m to increase the recording density.


REFERENCES:
patent: 6009072 (1999-12-01), Tsuchiya et al.

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