JPH08203085A - Disk-like recording medium - Google Patents

Abstract

PURPOSE: To attain a high density recording by effectively using the margin of track recording in an inner peripheral part by narrowing the pitch of an information signal sequence in the inner peripheral part than the pitch in the outer peripheral part in an information recording layer. CONSTITUTION: An information area Aw as an information recording region is divided into a first recording area Aw1 and a second recording area Aw2 from the inner peripheral side. The information area Aw is formed in a range between a radius of >=24mm and a radius of <58mm from the central point 0. In this case, the first recording area Aw1 is formed in a range between the radius of >=24mm and a radius of <40mm and the second recording area Aw2 is formed in a range between the radius of >=40mm and the radius of <58mm. In this optical disk, the track pitch in the first recording area Aw1 is set, for instance, to 0.80μm and the track pitch in the second recording area Aw2 0.85μm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disc-shaped recording medium used for recording / reproducing information signals.

[0002]

2. Description of the Related Art Conventionally, an optical disc such as a compact disc in which information pits are spirally recorded at intervals of 1.6 μm, for example, has a recording layer for the information pits formed on a plastic substrate such as polycarbonate. The recording layer was formed and covered with an aluminum reflective film and a protective film.
In such an optical disc, the polycarbonate substrate occupies most of the thickness, so that due to aging and moisture absorption,
As shown in FIG. 5, a tilt α _i occurs due to the warp in the radial direction R indicated by the arrow. Since the warp in the radial direction R becomes larger toward the outer circumference of the disk, the inclination α _i also becomes larger. The inclination that occurs in the optical disc also includes the inclination α ₀ due to the warp of the disc in the tangential direction T indicated by the arrow.
It is a small value within 15 to 0.20 °, and there is almost no change due to the difference between the inner circumference and the outer circumference. Therefore, in the optical disc, the inclination α _i due to the warp in the radial direction R has been a problem. When the inclination α _i is large, the coma aberration of the spot of the light irradiated on the information pit increases and the crosstalk increases, so that the track pitch cannot be reduced, which hinders an increase in recording density. That is, there is a limit to the track pitch due to the inclination α _i . Therefore, the track recording density is determined in consideration of the value of the inclination α _{i on} the outer circumference. In practice, it is determined according to the inclination of the system, which is the sum of the inclination α _i and the inclination generated by mechanical accuracy.

[0003]

By the way, in the above-mentioned optical disk, since there is little warpage in the radial direction R at the inner peripheral portion and the inclination α _i is small, it is determined by the inclination α _i at the outer peripheral portion as described above. If the track pitch is applied as it is, there is a margin in the track recording density.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a disk-shaped recording medium capable of achieving high density recording by effectively using the margin of the track recording density at the inner peripheral portion.

[0005]

A disc-shaped recording medium according to the present invention is a disc-shaped recording medium in which an information signal sequence is formed in an information recording area. The above problem is solved by making the pitch narrower than the pitch in the outer peripheral portion.

In this case, the pitch of the information signal train is narrowed for each zone formed from the outer peripheral portion to the inner peripheral portion of the information recording area. In addition, the pitch of the information signal sequence,
The information recording area may be gradually narrowed from the outer peripheral portion to the inner peripheral portion.

[0007]

The track pitch is not determined according to the inclination of the disc-shaped recording medium due to the warp in the radial direction only at the outer periphery,
The track pitch is determined in a stepwise or gradual manner in accordance with the above-mentioned inclination that is generated from the inner peripheral portion to the outer peripheral portion.

[0008]

Embodiments of the disk-shaped recording medium according to the present invention will be described below with reference to the drawings. This embodiment is an optical disc in which an information signal is reproduced according to a change in the amount of reflected light caused by laser light irradiation, and an information pit string is formed in an information recording area. As shown in FIGS. 1 and 4, in this optical disc, the pitch of the information pit row in the inner peripheral portion of the information recording area is made narrower than the pitch in the outer peripheral portion. In particular,
The optical disc of the first embodiment is an example in which the pitch is narrowed in two steps for each zone formed from the outer peripheral portion to the inner peripheral portion. Proceed with the explanation.

Generally, in an optical disc, the information recording area is formed on a polycarbonate substrate. Therefore, this optical disc is warped in the radial direction as shown in FIG. 2 depending on the usage conditions such as moisture absorption. In FIG. 2, the horizontal axis represents the radial distance from the center point of the disk, and the vertical axis represents the camber angle α _{I of the} disk.
Indicates. Here, the case of an optical disc having a diameter of 64 mm is shown. The warp angle α _{I of the} disk is about 0.2 ° at the innermost peripheral portion, but increases toward the outer peripheral portion and reaches a maximum of about 0.35 °. Therefore, it is conceivable to determine the track pitch in consideration of the change in the warp angle α _{I in} the inner peripheral portion and the outer peripheral portion. In the optical disc of the present embodiment, the above information is gradually increased in the inner peripheral portion and the outer peripheral portion. The pitch of the pit row is changing.

First, the optical disc of the first embodiment will be described with reference to FIG. This optical disc, as shown in FIG.
The information recording area A _W , which is the information recording area, is divided into a first recording area A _W1 and a second recording area A _W2 from the inner circumference side. The information recording area A _W is formed within a radius of 24 mm or more and less than 58 mm from the center point O of the disc, and the first recording area A _W1 is within a radius of 24 mm or more and less than 40 mm, and the second Recording area A _W2
Is formed within the radius of 40 mm or more and less than 58 mm.

In this optical disc, the track pitch in the first recording area A _W1 is, for example, 0.80 μm, and the track pitch in the second recording area A _W2 is, for example, 0.85 μm. Hereinafter, the reason why the track pitches of the first recording area A _W1 and the second recording area A _W2 of this optical disk are set to 0.80 μm and 0.85 μm, for example, will be described.

When the optical disc is set in a reproducing device for reproducing information pits from the disc, the inclination of the entire system generated in the optical disc is caused by the warp angle α _I and the mechanical precision generated in the pickup system. It consists of a mechanical tilt. Here, when the relationship between the inclination of the entire system and the track pitch is examined by using the jitter as an evaluation function, a margin as shown in FIG. 3 is allowed. This figure 3
In, the horizontal axis represents the track pitch and the vertical axis represents the allowable value of the inclination of the entire system with respect to the reproduction optical axis. In general, the allowable value of the mechanical tilt, that is, the mechanical margin is set to 0.27 °. Then, the margin of the warp angle α _I of the disk is 0.38 ° for a track pitch of 0.85 μm and 0.28 ° for a track pitch of 0.8 μm from FIG.

Therefore, the warp angle α of the worst state of the disk
Assuming that _I is 0.35 ° as shown in FIG. 2, the track pitch of the first recording area A _{W1 is} , for example, 0.80 μ.
m, and the track pitch of the second recording area A _W2 is 0.85 μm, the track pitch of the information recording area A _W is uniformly 0.85 μm as in the conventional case.
It was possible to improve the recording density by 2.3% as compared with the case of using m.

In order to form the optical disc of the first embodiment, the switching of the feed voltage zone of the cutting machine may be increased stepwise so as to switch from 0.8 μm track pitch to 0.85 μm. .
As described above, in the optical disc of the first embodiment, the pitch of the information pit row in the first recording area A _W1 is set to the second recording area A _W1 .
_Since the pitch is made narrower than the pitch in _W2 in stages, it is possible to effectively use the margin of the track recording density in the inner peripheral portion and achieve high density recording.

Next, an optical disk of the second embodiment is shown in FIG. As shown in FIG. 4, this optical disc divides the information recording area a _w from the inner circumference side into a first recording area a _w1 , a second recording area a _w2, and a third recording area a _w3 . The information recording area a _w has a radius of 24 m from the center point O of the disc.
The first recording area a _w1 has a radius of 40 mm or more and a radius of 40 mm or more.
Within the range of less than m, and the second recording area a _w2 has the radius 4 described above.
The third recording area a _w3 is formed within a range of 0 mm or more and a radius of less than 50 mm, and the third recording area a _w3 is within a range of 50 mm or more and a radius of less than 58 mm.

The optical disc of the second embodiment is
The track pitch in the first recording area a _w1 is, for example, 0.78 μm, the track pitch in the second recording area a _w2 is, for example, 0.8 μm, and the third recording area a _w3
The track pitch is set to, for example, 0.85 μm. Hereinafter, the first recording area a _w1 , the second recording area a _w2 , and the third recording area a _w3 of the optical disc of the second embodiment will be described.
Then, the track pitch is 0.78 μm, 0.80 μm, for example.
The reason for setting m and 0.85 μm will be described with reference to FIG.

In the optical disc of the second embodiment, the mechanical margin is 0.20 °. Then, the margin of the warp angle α _I of the disk is 0.78 μ from the track pitch shown in FIG.
0.33 ° to m, track pitch 0.8μ
0.35 ° to m, track pitch 0.85
It becomes 0.45 ° with respect to μm. Therefore, the warp angle α _I of the worst state of the disk is 0.35 as shown in FIG.
Assuming that the track pitch is 0.7,
m, 0.80 μm, and 0.85 μm. In the optical disc of the second embodiment, the recording density can be improved by 6.9% as compared with the conventional case where the track pitch of the information recording area a _w is uniformly set to, for example, 0.85 μm.

To form the optical disc of the second embodiment, the switching of the feed voltage zone of the cutting machine may be increased little by little. From the above,
Optical disc of the second embodiment, than the pitch of the pitch information pit rows in the first recording area a _w1 in the second recording area a _w2, the pitch of the pitch in the second recording area a _w2 in the third recording area a _w3 Also, since the track recording density is gradually narrowed, it is possible to effectively use the margin of the track recording density on the inner peripheral side and achieve high density recording.

Further, in the first and second embodiments, the information recording area is divided into zones and the track pitch is divided into two and three stages. However, the track pitch is gradually narrowed gradually from the outer peripheral portion to the inner peripheral portion. Good. Also, the diameter is 64mm
However, it may be 120 mm or larger. Although the optical disk is used as the embodiment, the present invention is also applicable to a disk-shaped recording medium in which a warp in the radial direction occurs due to the influence of the material of the disk.

[0020]

In the on-disk recording medium according to the present invention, the pitch of the information signal train in the inner peripheral portion of the information recording layer is made narrower than the pitch in the outer peripheral portion, so that there is a margin of track recording density in the inner peripheral portion. It can be used effectively and high density recording can be achieved.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a first embodiment of a disc-shaped recording medium according to the present invention.

FIG. 2 is a characteristic diagram for explaining a warp angle generated in the disc-shaped recording medium according to the present invention.

FIG. 3 is a characteristic diagram for explaining the relationship between the track allowance and the tilt allowable value of the entire system that is allowed for the optical discs of the first and second embodiments.

FIG. 4 is a schematic configuration diagram of a second embodiment of a disc-shaped recording medium according to the present invention.

FIG. 5 is a diagram showing a radial warp and a tangential warp that occur on an optical disc.

[Explanation of symbols]

A _W , a _w information recording area A _W1 , a _w1 first recording area A _W2 , a _w2 second recording area a _w3 third recording area

Claims (3)

[Claims] 1. A disc-shaped recording medium in which an information signal sequence is formed in an information recording area, wherein the pitch of the information signal sequence in the inner peripheral portion of the information recording area is narrower than the pitch in the outer peripheral portion. Disc-shaped recording medium. 2. The disc-shaped recording medium according to claim 1, wherein the pitch of the information signal train is narrowed for each zone formed from the outer peripheral portion to the inner peripheral portion of the information recording area. 3. The disk-shaped recording medium according to claim 1, wherein the pitch of the information signal train is gradually narrowed from the outer peripheral portion to the inner peripheral portion of the information recording area.