Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Reexamination Certificate
1999-04-01
2001-05-01
Dinh, Tan (Department: 2651)
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
C428S064400
Reexamination Certificate
active
06226256
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to an optical recording disc and a method for recording and reproducing such an optical recording disc.
2. Discussion of the Background
Highlight is recently focused on optical recording media capable of recording information at a high density and erasing the recorded information for overwriting. For example, Specification (Ver. 1.0) for DVD-RAM which is a phase change optical recording disc was published in July, 1997. A phase change optical recording medium is a medium wherein a laser beam is directed to the recording layer to change its crystalline state whereupon a change of reflectance by the crystallographic change is detected for reproduction of the information. The phase change optical recording media are of great interest since the optical system of the drive unit used for their operation is simple as compared with magneto-optical recording media.
When information is recorded in the optical recording medium of phase change type, the laser beam applied is of high power (recording power) that the recording layer is heated to a temperature higher than the melting point. In the region where the recording power is applied, the recording layer is melted and thereafter quenched to form an amorphous record mark. When the record mark is erased, a laser beam of relatively low power (erasing power) is applied so that the recording layer is heated to a temperature higher than the crystallizing temperature and lower than the melting temperature. The record mark to which the laser beam of erasing power is applied is heated to a temperature higher than the crystallizing temperature and then allowed to slowly cool to recover the crystalline state. Accordingly, in the optical recording media of the phase change type, the medium can be overwritten by modulating the intensity of a single laser beam.
Phase change-type optical recording discs which found relatively widespread use include PD and CD-RW. These optical recording discs are of the format wherein a spiral guide groove (which is hereinafter referred to as a groove) formed on the surface of the substrate is used for the recording track. In such disc, the recording track is continuous, and jump of optical pickup is not required even when the information is continuously recorded and reproduced in two or more turns of the recording tracks.
Recently, so-called land/groove recording wherein land (the region between two adjacent grooves) in addition to the groove is used for the recording track in order to increase the recording density has gone into practical use. When a disc having a single spiral groove is recorded by such land/groove recording, the recording track will be discontinuous, and the optical pickup is required to jump to the next track, namely, the adjacent land or groove once per one rotation of the disk. Such jumping to the adjacent recording track is herein referred to as a track jump.
Therefore, it is general in the optical recording disc for land/groove recording to preform a synchronization mark pattern (typically a pit train) in the land or groove of the substrate so that the optical pickup can read such pattern to effect the track jump. Such synchronization mark pattern may be formed in the disc substrate simultaneous with the injection molding of the disc, and for such simultaneous formation of the pattern, a pit train-forming pattern may formed in the stamper which functions as the mold in the injection molding. Production of such stamper adapted for simultaneous formation of the pit train in the groove or on the land, however, is quite difficult since track pitch has been reduced with the increase in the recording density, and formation of an accurate pattern is difficult. Such difficulty has been reflected on the track jump error.
SUMMARY OF THE INVENTION
An object of the present invention is to enable a convenient formation of a highly readable synchronization mark pattern indicative of the track jump position in an optical recording disc wherein track jump is required once per one disc rotation.
Such an object is realized by the constitution of any one of (1) to (7), below.
(1) An optical recording disc comprising a disc substrate and a recording layer on the disc substrate, wherein
at least one surface-irregularity region having an irregularity pattern is formed on the substrate in its non-recording region, and said surface-irregularity region is circumferentially adjacent to a smooth region.
(2) An optical recording disc according to the above (1) wherein said surface-irregularity region is in the form of an arc which is concentric with the substrate.
(3) An optical recording disc according to the above (1) or (2) wherein said irregularity pattern includes a plurality of circumferentially extending grooves.
(4) An optical recording disc according to any one of the above (1) to (3) wherein said irregularity pattern includes a plurality of projections.
(5) An optical recording disc according to any one of the above (1) to (4) wherein said surface-irregularity region has radial width of at least 1 mm.
(6) An optical recording disc according to any one of the above (1) to (5) wherein said substrate is formed with grooves and/or pits in its data recording region, and said surface-irregularity pattern has a depth or height substantially equal to groove or pit.
(7) An optical recording disc according to any one of the above (1) to (6) wherein said disc has a recording layer of phase change type, and wherein said recording layer in its crystalline state covers said surface-irregularity region and said smooth region.
(8) An optical recording disc according to any one of the above (1) to (7) wherein said disc has a reflective layer, and wherein said reflective layer covers said surface-irregularity region and said smooth region.
(9) A method for recording and reproducing an optical recording disc according to anyone of any one of the above (1) to (8) wherein track jump is conducted in synchronicity with change of reflectance in said surface-irregularity region induced by the disc rotation.
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Kato Tatsuya
Utsunomiya Hajime
Dinh Tan
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
TDK Corporation
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