Optical system with tracking controller

Details Optical system with tracking controller Optical system with tracking controller

2002-09-30

2004-06-01

Young, W. R. (Department: 2652)

Dynamic information storage or retrieval

With servo positioning of transducer assembly over track...

Optical servo system

C369S044340, C369S275400, C369S044260

Reexamination Certificate

active

06744706

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to: an optical information recording medium which utilizes both groove regions (i.e., guide grooves) and land regions (i.e., regions between grooves) as information tracks, the grooves and lands having been previously formed on the optical information recording medium; and an optical information recording/reproduction device for recording an information signal on the optical information recording medium.
2. Description of the Related Art
In recent years, there have been vigorous research and development activities for realizing optical information recording media for recording and reproducing information signals (e.g., video signals and audio signals) thereon. One example of such an optical information recording medium is an optical disk. A recordable optical disk includes guide grooves (hereinafter referred to as “grooves”) previously engraved on a substrate, the grooves constituting information tracks. Any region between adjoining grooves is referred to as a “land”. Information signals can be recorded or reproduced on the optical disk by converging a laser light beam on the flat portions of grooves or lands.
In the case of common commercially-available optical disks, information signals are typically recorded on either grooves or lands. When information signals are recorded on the grooves, for example, the lands serve as guard bands for separating adjoining tracks defined by the grooves. In the case where information signals are recorded on the lands, the grooves serve as guard bands.
FIG. 9
is a magnified perspective view of a conventional optical disk having the above-mentioned structure. In
FIG. 9
, reference numeral
85
denotes a recording layer (which may be composed of a phase-change material, for example);
86
denotes a recording pit;
87
denotes a laser beam spot;
88
,
90
, and
92
denote guide grooves defining “grooves”;
89
and
91
denote “lands”;
93
denotes a transparent substrate through which light enters. As seen from
FIG. 9
, grooves are made wider than lands in this exemplary conventional optical disk.
In an attempt to increase the recording capacity of the above conventional optical disk, the interspaces between tracks are shortened by narrowing the widths of the lands
89
. However, a smaller interspace between tracks results in a larger diffraction angle of light reflected from the grooves. This results in a lower level of tracking error signal, which is employed to ensure accurate tracing of the beam spot
87
on the tracks.
Moreover, there is a limit to the increase in track density achieved by merely reducing land widths. However, reducing the groove widths might lower the amplitude of the reproduced signal due to thinner recording pits
86
.
On the other hand, there are techniques for increasing the track density, such as that disclosed in Japanese Patent Publication No. 63-57859, according to which information signals are recorded on both grooves and lands.
FIG. 10
is a magnified perspective view of such an optical disk. In
FIG. 10
, reference numeral
85
denotes a recording layer;
86
denotes a recording pit;
87
denotes a laser beam spot;
93
denotes a transparent substrate;
94
,
96
, and
98
denote grooves;
95
and
97
denote lands.
As shown in
FIG. 10
, the grooves and the lands have substantially the same width. Pre-pits
99
, which are formed for both grooves and lands, are engraved at the beginnings of sectors of both information tracks (i.e., groove and lands) as identification signals representing locational information on the optical disk.
In the above optical disk, the recording pits
86
are formed for both grooves and lands as shown in FIG.
10
. Although the grooves have a period equal to the period of grooves in the optical disk shown in
FIG. 9
, each interspace between adjoining recording pit rows in
FIG. 10
is half of that of the optical disk shown in FIG.
9
. As a result, the optical disk in
FIG. 10
has twice as large a recording capacity as that of the optical disk in FIG.
9
.
Rewritable optical disks require identification signals (indicating location information on the disk), etc., to be previously recorded on the disk. The inventors of the present invention have proposed in Japanese Laid-Open Patent Publication No. 6-176404 a technique of recording one identification signal for an adjoining pair consisting of a groove and a land so as to be located between the groove and the land.
However, in the above-mentioned optical information recording media, the track pitch is reduced to half of that of conventional optical information recording media, thereby requiring an even more accurate track servo control. Particularly when an identification signal is recorded between a land and its corresponding groove, only one half of the beam spot will be incident on the pre-pits. Therefore, when the beam spot shifts away from the track center, toward regions where the identification signal is not present, it may be impossible to detect the identification signal.
SUMMARY OF THE INVENTION
An optical information recording medium according to the present invention includes at least one groove track and at least one land track allowing information to be recorded on or reproduced from the groove track and the land track, the groove track and the land track adjoining each other, wherein the optical information recording medium further includes: an identification signal region including a pre-pit array, the pre-pit array indicating identification information concerning the groove track and the land track; and a servo control region disposed ahead of the identification signal region along the groove track and the land track, the servo control region including wobble pits positioned so as to shift to opposite sides of a center line of either the groove track or the land track.
In one embodiment of the invention, the wobble pits include a plurality of pairs of pre-pits positioned so as to shift to opposite sides of the center line.
In another embodiment of the invention, the plurality of pairs of pre-pits indicate a reproduction synchronization signal.
In still another embodiment of the invention, a synchronization signal section indicating the beginning of the wobble pits is provided immediately before the wobble pits, and the synchronization signal section includes a pit array positioned on the center line of either the groove track or the land track.
In still another embodiment of the invention, at least a portion of the pre-pit array in the identification signal region is formed so as to be shifted away from the center line of either the groove track or the land track.
In still another embodiment of the invention, the identification signal region includes a pit indicating a track identification signal.
In still another embodiment of the invention, the pit indicating the track identification signal is shifted away from the center line of either the groove track or the land track.
In still another embodiment of the invention, the groove track and the land track are divided into a plurality of sectors, the pre-pit array in the identification signal region includes an address pit array indicating address information of a corresponding sector.
In still another embodiment of the invention, the groove track and the land track are formed in a spiral or concentric shape on a disk substrate.
In still another embodiment of the invention, the identification information includes a track number.
In still another embodiment of the invention, a portion of the pre-pit array indicating the identification signal that indicates the track number is shifted away from the center line of either the groove track or the land track along a direction across the groove track and the land track.
In still another embodiment of the invention, pre-pits in the pre-pit array indicating the identification signal which are formed so as to be shifted away from the center line of either the groove track or the land track are shifted away from the center line of either the gro

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