Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Reexamination Certificate
1999-07-16
2002-02-19
Neyzari, Ali (Department: 2651)
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
C369S275300
Reexamination Certificate
active
06349085
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical recording medium having formed thereon along its recording tracks pits indicative of information signal, a master for use to produce the optical recording medium, and an optical recording and/or reproducing apparatus for reading or writing information signal from or to the optical recording medium by irradiating a light to the optical recording medium.
2. Description of Related Art
As the optical recording media, disc-shaped ones are used to and/or from which information signal is optically written and/or read. They are called “optical disc” and include a read-only optical disc having a substrate on which pits for data are formed beforehand and from which data is only read, a magneto-optical disc to and/or from which data is written and/or read by the use of the magneto-optical effect, and a phase-change optical disc to and/or from which data is written and/or read by the use of the phase change of a recording layer of the disc. It should be noted that normally in the optical discs such as magneto-optical disc and phase-change optical disc, pits for address information, etc. are also formed on the disc substrate beforehand.
In the optical disc drives for compact disc (CD) mini disc (MD), etc., the three-spot method is employed for tracking servo control. The 3-spot method is such that a light incident upon an optical disc is split into a main beam to be projected to the center of a recording track, a first sub beam for projection to a position leading the main beam, and a second sub beam for projection to a position following the main beam. The first sub beam is projected perpendicularly to the track direction to a position deviated +¼ of the track from the central spot and the second sub beam is projected perpendicularly to a position deviated −¼ of the track from the central spot.
Thus, a signal necessary for the tracking servo control is obtained by detecting the first and second sub beams reflected from the optical disc. Namely, in the 3-spot method, a difference is determined between a sum signal derived from detection of a whole reflected light of the first sub beam from the optical disc and a sum signal derived from the detection of a whole reflected light of the second sub beam from the optical disc and it is used in the 3-spot method as a signal for the tracking servo control.
For tracking servo control by the 3-spot method in write to and/or read from an optical disc having formed on a disc substrate pits corresponding to data beforehand, it is necessary to set a ratio Pw/Tp (where Pw is a pit width and Tp is a track pitch) to 0.4 or so because the sum signal cannot sufficiently be modulated if the ratio Pw/Tp is larger than such a value.
In the optical discs such as CD, MD, etc., the pit width Pw is on the order of 0.5 to 0.6 &mgr;m and track pitch Tp is on the order of 1.60 &mgr;m. Therefore, in such optical discs, the ratio Pw/Tp is smaller than 0.4, which assures that the tracking servo control by the 3-spot method can be effected stably.
The optical recording media such as optical discs have been required to have an increasing larger recording density. To this end, the pit width should be smaller while the track pitch be also smaller, for example. If the pit width is made too small, no optical reproduction of data from the optical recording media is possible. Therefore, it has been difficult to attain a high recording density with the conventional optical recording media by reducing the track pitch thereof.
Accordingly, the present invention has an object to overcome the above-mentioned drawbacks of the prior art by providing an optical recording medium in which data can be written highly densely.
The present invention has another object to provide a master for use to produce such an optical recording medium capable of writing data with a high density.
The present invention has a further object to provide an optical recording and/or reproducing apparatus adapted to write and/or read data to and/or from the optical recording medium.
SUMMARY OF THE INVENTION
The above object can be attained by providing an optical recording medium having formed along recording tracks thereon pits indicative of information signal so that a ratio Pw/Tp where Pw is the width of the pit and Tp is the pitch of the tracks is within a range of 0.4 to 0.55.
It should be noted that the optical recording medium should preferably be subjected to tracking servo control by the push-pull method or differential push-pull method.
In the optical recording medium according to the present invention, the ratio Pw/Tp of 0.4 to 0.55 between the pit width Pw and tack pitch Tp is larger than those in the conventional optical recording media. Therefore, the optical recording medium according to the present invention is capable of a high density recording with the track pitch Tp being small while the pit width Pw is not so much narrowed. Note that even if the ratio Pw/Tp between the pit width Pw and tack pitch Tp is set large, tracking servo control can be done with a sufficient stability by the push-pull method or differential push-pull method, not by the 3-spot method.
Also the above object can be attained by providing a master for use to produce the optical recording medium according to the present invention, the optical recording medium having formed thereon along recording tracks thereon pits indicative of information signal so that a ratio Pw/Tp where Pw is the width of the pit and Tp is the pitch of the tracks is within a range of 0.4 to 0.55 .
Further the above object can be attained by providing an optical recording and/or reproducing apparatus adapted to write and/or read data to and/or from the optical recording medium according to the present invention by irradiating light to the optical recording medium, the optical recording medium having formed thereon along recording tracks thereon pits indicative of information signal so that a ratio Pw/Tp where Pw is the width of the pit and Tp is the pitch of the tracks is within a range of 0.4 to 0.55.
It should be noted that the push-pull method or differential push-pull method should preferably be employed for tracking servo control of the optical recording medium.
These objects and other objects, features and advantages of the present intention will become more apparent from the following detailed description of the preferred embodiments of the present invention when taken in conjunction with the accompanying drawings.
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Patent Abstracts of Japan, JP 8-235642, Published Sep. 13, 1996, Seiko Epson Corp.
Arima Mitsuo
Endoh Sohmei
Ohtomo Katsuhiko
Neyzari Ali
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Sony Corporation
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