Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Reexamination Certificate
2001-05-24
2002-11-05
Psitos, Aristotelis M. (Department: 2651)
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
C369S275100
Reexamination Certificate
active
06477136
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical recording medium comprising a substrate formed therein with prepits between pregrooves, and an optical absorption layer and an optical reflection layer which are formed on the substrate, and in particular, to a high density optical recording medium which can reduce the error rate of address signals, and the jitter and the block error rate of recording signals.
2. Related Art
These years, that is, in the highly information-oriented era, optical recording media which can deal with several various information become noticeable. These optical recording media are classified into a read-only recording medium on which no data can be recorded, and a write-once type optical recording medium on which date can be only once written, and a rewritable recording medium on which data can be rewritten many times. Of these optical recording media, the write-once type optical recording medium is suitably used as a data storage medium for official documents and important documents since data recorded once thereon cannot be altered for defrauding or the like. As such a write-once type optical recording medium, there has been know, for example, a CD-R (compact disc-recordable).
This CD-R which is a write-once type CD has an optical absorption layer and an optical reflection layer formed on a substrate and made of organic pigment, and which can produce output signals which are in conformity with a CD format during reproduction. The substrate of this CD-R is spirally or concentrially formed thereon with pregrooves for tracking. In order to record data on the CD-R, a laser beam is irradiated on the substrate along the pregrooves so as to decompose or alter the optical absorption layer. Thus, recording marks are formed in the recording beam irradiated part of the optical absorption layer within pregrooves. When a reproduction beam is irradiated along the pregrooves, data can be read since a difference in optical reflectivity is caused between the parts on which the recording marks are formed, and parts on which no recording marks are formed, and since the difference in the optical reflectivity can be used for reading the data. The laser beam used for recording and reproducing to and from the CD-R usually has a wavelength in a range from 770 to 830 nm.
These years, it has been demanded that the recording capacity of a recording medium is further increased. In order to increase the recording capacity, there has been proposed such a method that the wavelength of the laser beam used for recording and reproducing is shortened so as to decrease the diameter of a beam spot in order to enhance the recording density. As to a high density recording medium in association with this method, there have been proposed a DVD (digital versatile disc) and a DVD-R (digital versatile disc-recordable) (refer to, for example, Electronic Technology, August, 1996, on page 101). A laser beam used for recording and reproduction of this DVD-R has a wavelength in the range from 630 to 660 nm.
Pregrooves for tracking are spirally and concentrically formed on a substrate of a DVD-R, as shown in
FIG. 5
, and prepits
41
for address signals are formed at predetermined pitches between adjacent pregrooves
42
,
42
′ (in lands therebetween). Further, these prepets are provided in combination with their inner peripheral side pregrove
42
. Track pitches of the pregrooves in the DVD-R are in a range from 0.7 to 0.8 &mgr;m, which is extremely dense in comparsion with track pitches of the pregrooves in the CD-R, which are 1.6 &mgr;m.
Accordingly, as to the DVD-R, the width of the pregrooves becomes smaller than the diameter of the beam spot for recording and reproduction, and the lands laid on both sides of a pregroove are in part included within the beam spot with which the pegroove is scanned for recording and reproduction. In this case, if the prepits are present in either an inner peripheral side land or an outer peripheral side land in the vicinity of recording pits formed in the pregroove, a part of the prepits is included within the spot for recording and reproduction when the recording pits are reproduced. Thus, a difference in obtained reproduction intensity is caused between a recording pit in the vicinity of a prepit, and a recording pit which is far from a prepit even though the recording pits have one and the same pit length. Accordingly, these pits are reproduced as recording pits having different pit lengths. As a result, there has been caused such a problem that jitter and block error rate become high. Further, in order to solve this problem, there has been proposed such a method that the size of these prepits formed in the land between the pregrooves is decreased. However, in this method, the intentity of prepit signals becomes smaller, and accordingly, there has been caused such a problem that the error rate of address signals becomes high.
SUMMARY OF THE INVENTION
The present invention is devised in order to solve the above-mentioned problems, and accordingly, an object of the present invention is to provide a high dense optical recording medium in which prepits formed (in lands) between pregrooves can be precisely reproduced so as to reduce an error rate of address signals, and recording pits formed in the vicinity of the prepits can be precisely reproduced, thereby it is possible to reduce jitter and a block error rate of recording signals.
To the end, according to an object of the present invention, there is provided an optical recording medium comprising a substrate formed therein prepits in (lands) between pregrooves, the pregrooves and the prepits being set apart from each other by edge parts therebetween, and an optical absorption layer and an optical reflection layer which are formed on the substrate, the prepits are preferably formed so as to satisfy the following inequal equation (1):
0<
b≦a<Dp≦Dg
(1)
where Dg is a maximum depth of the pregrooves, Dp is a maximum depth of the prepits, a is a depth of an edge parts on the inner peripheral side of the prepits,and b is a depth of the edge part on the outer peripheral side of the prepits.
FIGS. 2 and 3
show a specific example of the shape of the prepits formed (in lands) between the pregrooves, which can satisfy the above-mentioned condition, and are a perspective view and an enlarged partly sectional view, respectively, illustrating a sectioned structure obtained by cutting the substrate by a plane that is orthogonal to the longitudinal direction of the pregrooves (pregroove direction) and including prepits. It is noted that the pregrooves and the prepits are set apart from each other by eges parts
23
,
23
′ therebetween.
Referring to
FIG. 3
, the maximum depth Dg of the pregrooves
22
, the maximum depth Dp of the prepits
21
, the depth a of the edge parts
23
on the inner peripheral side of the prepits
22
, and the depth b of edge parts
23
′ on the outer peripheral side of the prepits
21
satisfy the above-mentioned unequal equation (1). As shown in
FIG. 5
, in such a case that no edge parts are formed in the prepits formed (in lands) between grooves
42
,
42
′, as in the conventional one, so that the pregrooves and the prepits are continuously formed, a part of a prepit which is adjacent to the pregroove is recognized as a recording pit. On the contrary, according to the present invention, since the edge part between the pregroove and the prepit is formed so that it is higher than the bottom surface of the prepit, and in more detail, the depth of the edge part between the prepit and the pregroove is set to be less than 95% of the maximum depth Dp of the prepit, it is possible to prevent the prepit from being recognized as a recording pit even though a part of the prepit is contained in the reproduction spot. Thus, recording pits can be appropriately reproduced, irrespective of the presence of a prepit adjacent to a recording pit. Accordingly, the optical recording medium according to the present invention
Hayashi Takuya
Ito Mitsuru
Nagataki Yoshiyuki
Sakurai Yuichi
Takazawa Kouji
Hitachi Maxell Ltd.
Psitos Aristotelis M.
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