Dynamic information storage or retrieval – Condition indicating – monitoring – or testing – Including radiation storage or retrieval
Reexamination Certificate
2000-01-12
2001-03-27
Edun, Muhammad (Department: 2651)
Dynamic information storage or retrieval
Condition indicating, monitoring, or testing
Including radiation storage or retrieval
C369S116000
Reexamination Certificate
active
06208601
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical information recording method and apparatus which can reduce the degree of quality deterioration of recorded information due to inclination of the information recording surface of an information recording medium.
2. Description of the Related Art
Conventionally, the capacity and the recording speed have increased in the technology for recording information on an optical information recording medium. In recent years, techniques of recording information at high speeds have become commonplace. For example, recording speeds of two to six times the basic speed or even higher speeds are used.
Write-once optical discs (CD-R) are commonly used as optical information recording media.
In recording information on an optical disc, a digital signal is generated by digitizing recording subject information. Pits are formed on the optical disc by applying pulse laser light from an optical pickup to the rotating optical disc based on the digital signal.
In forming pits on the optical disc by using a digital signal generated by digitizing recording subject information, the intensity of laser light that is applied from the optical pickup to the optical disc is increased during periods when, for example, the digital signal is at a high level. As a result, the recording layer of the optical disc is changed by the laser light energy and pits are formed. On the other hand, during periods when the level of the digital signal is low, low-intensity laser light that is necessary for tracking control is applied from the optical pickup to the optical disc.
The information recording surface of an optical disc may incline due to a warp or deformation of the disc. As shown in
FIG. 2
, in most cases inclination of the information recording surface is not uniform and gradually increases as the position on an optical disc
1
goes outward. The inclination angle &thgr; of the information recording surface with respect to a plane
3
that is perpendicular to the rotation axis
2
of the optical disc
1
is generally called a tilt angle.
Where the information recording surface has no inclination, as shown in
FIG. 3
, laser light
5
that is emitted from an optical pickup
4
is applied approximately vertically to the information recording surface. Pits are formed by the laser light
5
.
However, where the emitting direction of laser light
5
is constant and the information recording surface has inclination, the spot of the laser light
5
that is formed on the information recording surface is distorted in shape. Therefore, the illumination light quantity per unit area on the information recording surface decreases and the pit size decreases. As a result, jittering during information reproduction becomes worse.
To solve the above problem, as shown in
FIG. 4
, the emitting direction of laser light
5
is varied so as to be kept vertical to the information recording surface of an optical disc
1
. This is done in such a manner that an inclination (tilt angle) of the information recording surface of the optical disc
1
is detected and the optical pickup
4
is inclined based on the detected tilt angle.
However, the mechanism of inclining the optical pickup
4
in accordance with the tilt angle &thgr; is complex, which increases the cost of the apparatus.
There is a method for performing appropriate recording (appropriateness: &bgr;) without using a tilt angle correction mechanism. That is, Japanese Patent Laid-Open No. 8-147701 entitled “Power Calibration Method of an Optical Disc Recording/Reproducing Apparatus” discloses a method for optimizing the recording laser light intensity even at an outer area (OPC: optimum power control). However, this method has a problem that the OPC takes long time. The above parameter &bgr;, which represents asymmetry, is given by &bgr;=(A
1
+A
2
)/(A
1
−A
2
) in the case of CD-R, where A
1
and A
2
are a top-level value and a bottom-level value, respectively, of pulses of 11T.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an optical information recording method and apparatus which can record information with a constant laser light emitting direction even if the information recording surface of an optical information recording medium is inclined.
In the following manner, the invention makes it possible to perform information recording with a constant laser light emitting direction even if the information recording surface is inclined.
That is, pits are formed while the intensity of laser light is set higher as the acute angle that is formed by the information recording surface and the optical axis of the laser light at a pit forming position decreases.
First, an imaginary plane that is perpendicular to the laser light that is applied from an optical pickup to an optical information recording medium is assumed. Next, an inclination, at the pit forming position, of the information recording surface of the optical information recording medium with respect to the imaginary plane is detected. The laser light intensity is set higher as the detected inclination increases, and pits are formed by using the thus-set laser light intensity.
In this optical information recording method, pits are formed while the laser light intensity is set higher as the inclination, at a pit forming position, of the information recording surface of the optical information recording medium increases.
As the inclination of the information recording surface increases, the illumination light quantity per unit area decreases because of distortion of the laser light spot. However, since the laser light intensity is set higher as the detected inclination increases, reduction of the illumination light quantity per unit area that is associated with inclination of the information recording surface can be compensated for. Therefore, it is not necessary to correct the laser light emitting direction.
This optical information recording method makes it possible to form pits having necessary shapes at proper positions even if the information recording surface of an optical information recording medium has inclination, and hence to perform information recording that is superior in information reproduction characteristics.
In the invention, in the above information recording method, a corresponding relationship between the inclination of the information recording surface of an optical information recording medium and the laser light intensity is prepared in advance as intensity setting information and laser light intensity is set based on the intensity setting information during information recording.
By preparing in advance, as the intensity setting information, the corresponding relationship between the inclination of the information recording surface of an optical information recording medium and the laser light intensity, the time required for setting of laser light intensity during actual information recording can be shortened.
Further, in the invention, pieces of intensity setting information are prepared for respective types of optical information recording media. During actual information recording, laser light intensity is set by using intensity setting information corresponding to the type of an optical information recording medium as a subject of information recording.
By determining, in advance, pieces of intensity setting information for respective types of optical information recording media, laser light intensity corresponding to the type of an optical information recording medium can be set in a short time.
According to another aspect of the invention, the above-described method is applied to an optical information recording apparatus for forming pits by applying pulse laser light to an optical information recording medium, based on a digital signal corresponding to recording subject information, from laser light emitting means that moves relatively to the optical information recording medium.
That is, the optical information recording apparatus according to the inventi
Negishi Akira
Shimizu Atsuo
Sunagawa Ryuichi
Edun Muhammad
Lowe Hauptman Gopstein Gilman & Berner
Taiyo Yuden Co. Ltd.
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