Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Reexamination Certificate
2000-02-28
2001-07-17
Neyzari, Ali (Department: 2651)
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
C369S013010
Reexamination Certificate
active
06262968
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical recording medium and more particularly to a high-density optical recording medium having a track width smaller than an optical spot diameter.
An example of a medium for performing high-density (narrow track) recording is disclosed in, for example, JP-A-6-176404. According to this example, in an optical recording medium having grooves and lands which are formed on a substrate and information recording areas which are formed in association with both the groove and the land, prepits are disposed on a virtual extension line of the boundary between a groove and a land. In particular, the prepits are located on only one side of any specific position of the center line of each groove.
With this construction, recording information is formed on both the groove and the land, the prepits have charge of address data representative of the recording areas and one prepit is used in common to a pair of adjacent groove and land to provide address data therefor. When the technique as above is applied to, for example, a phase change recording medium or a magneto-optical recording medium, interference of information (crosstalk) between adjacent lands or grooves due to the optical interference effect within an optical spot can be prevented, thereby permitting narrowing of track.
On the other hand, in the prepit area free from the optical interference effect, the address data can be common to the paired groove and land and the effective track pitch can be increased to reduce crosstalk.
In the example of JP-A-6-176404, however, the disposition of the prepit area is offset on one side of the center line of the groove or land, so that when an optical spot is caused to track a groove or a land, a tracking error (tracking offset) increases, making it difficult to perform high-density recording in which the track pitch is narrowed.
SUMMARY OF THE INVENTION
The present invention achieves elimination of the above problems and it is a first object of the present invention to provide an optical recording medium which can suppress the tracking offset to a value or level which is sufficiently low for the practical use and permit efficient disposition of address data even when recording is effected on both the groove and the land.
A second object of the present invention is to provide a high-density optical recording medium which can ensure simple mastering and easy replica preparation and can permit decoding even when a readout error takes place.
To accomplish the above first object, the following expedients are employed.
(1) Grooves and lands are formed on a substrate of a recording medium, information recording areas are formed in association with both the groove and the land, and prepits are disposed on a virtual extension line of the boundary between a groove and a land.
The disposition of prepits satisfies the following requirements (a) to (c) at the same time.
(a) Prepits are located on both sides of a virtual extension of the center line of a groove;
(b) Prepits are located on both sides of a virtual extension of the center line of a land;
(c) Prepits are not located on the both sides of any specific position of the center line of a groove; and
(d) Prepits are not located on the both sides of any specific position of a land.
With this construction, the arrangement of prepits is not offset on either one side of a virtual extension of the center line of the groove or the land to ensure that tracking offset hardly occurs and the prepits do not exist on both sides of any specific position of the center line of the groove or the land to prevent interference of prepit information between adjacent tracks from taking place within a reproduced spot so as to permit high-density narrow track recording.
(2) When prepits are disposed in the circumferential direction such that those on one side of a groove are not discriminative from those on the other side or those on one side of a land are not discriminative from those on the other side, at least consecutive two dispositions of prepits associated with the groove or the land are made to be different from each other to provide the same disposition of prepits periodically every two dispositions.
As the other option,
(3) A groove associated with at least one pair of pits disposed on both sides of the center line of the groove in a prepit area and an adjacent groove not associated with pits disposed on both sides of the center line of this groove within the prepit area are disposed alternately in the radial direction.
Through this, by merely reproducing the pits, prepits associated with the groove can be discriminated from those associated with the land to improve reliability of information recording reproduction.
(4) Either one of synchronous information and address data is represented by prepits disposed on either one of the both sides of a groove.
As the other option,
(5) Only one of synchronous information and address data is represented by prepits arranged on one side of a groove and both the synchronous information and the address data are represented by prepits arranged on the other of the both side of the groove.
Through this, address data can be reproduced under accurate synchronization. In addition, since the phase margin between prepits on the both sides can be extended, fabrication of a recording medium can be facilitated.
(6) The groove and the prepit have the same depth which is 70 nm or less. More preferably, the depth is 40 nm or more and 60 nm or less.
With this construction, an advantage of suitable crosstalk cancellation can be obtained between the groove and the land and besides an excellent tracking servo signal can be obtained. Formation and fabrication of the recording medium can be facilitated. With the groove depth exceeding 70 nm, the formation of the groove is difficult to achieve. When the groove depth is about 50 nm, the tracking servo is maximized and with the groove depth being about 50±10 nm, substantially the same effect can be attained.
(7) The groove and the land have substantially the same width which is between 0.3 &mgr;m and 0.75 &mgr;m.
With this construction, excellent tracking is compatible with high-density recording. If the groove and land have a width of not greater than 0.3 &mgr;m, then two of the groove and land will be confined within one optical spot and an excellent tracking signal cannot be obtained. On the other hand, if the groove and land have a width exceeding 0.75 &mgr;m, then effective high-density recording cannot be permitted.
(8) Of prepits, the smallest one has a diameter which is smaller than a width of each of the groove and the land. More preferably, the diameter is in the range from 0.25 &mgr;m to 0.55 &mgr;m.
Through this, an excellent prepit signal can be obtained without crosstalk. With the diameter being not greater than 0.25 &mgr;m, the prepit signal decreases in the extreme and with the diameter exceeding 0.55 &mgr;m, crosstalk is generated.
In the present invention, prepits are arranged on the both sides of a virtual extension line of the center line of a groove or a land in the optical spot scanning direction. Consequently, offset is decreased to make the tracking offset hardly occur and the prepits do not exist on the both sides of any specific position of the center line of the groove or the land to ensure that interference of prepit information between adjacent tracks within a reproduced spot can be prevented and high-density narrow track recording can be permitted.
Further, even in the presence of tracking offset, the amount of tracking offset can be detected accurately by comparing amplitudes of signals representative of prepits on the both sides. Accordingly, by feedback-controlling the information indicative of a comparison result to a scanning unit, the tracking offset can be suppressed.
At a portion between a groove and a prepit area, between a land and a prepit area or between prepit areas, a gap takes place when a prepit train on a virtual extension line of the boundary between a groove and a land shifts to a
Andou Tetsuo
Minemura Hiroyuki
Miyamoto Harukazu
Sukeda Hirofumi
Terao Motoyasu
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Neyzari Ali
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