Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Reexamination Certificate
1999-07-14
2003-05-20
Neyzari, Ali (Department: 2655)
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
C369S275300
Reexamination Certificate
active
06567372
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical disk and to an optical disk apparatus which is capable of detecting off-tracking based on a reproduction signal from the optical disk and compensating for the off-tracking.
2. Description of the Related Art
Optical disks such as compact optical disks (CDs) and digital video (or versatile) disks (DVDs) are used as information recording media for recording data, images, and/or sounds, and are widely utilized in OA (office automation) apparatuses, AV (audio visual) apparatuses, and the like. In the field of large-capacity rewritable optical disks, one attempt to realize increased surface capacity has been to allow information to be recorded in both “grooves” (i.e., concave portions formed by guide grooves of spiral tracks) and “lands” (i.e., interspaces between “grooves”) so that the information recorded in the grooves and lands can be reproduced.
There is a class of optical disks, called single spiral land groove format (hereinafter referred to as SS-L/GFMT) optical disks, which are capable of consecutively reproducing or recording the information on the lands and the grooves from the inner periphery to the outer periphery of the optical disks, in which the lands and the grooves are provided so as to alternate per rotation of the optical disks.
On the other hand, an optical disk apparatus is generally arranged so as to be capable of reproducing or recording information on an optical disk. An optical disk apparatus usually generates a tracking error signal from a light beam which is radiated on an optical disk and reflected therefrom, by using a known push-pull method or the like. A tracking error signal indicates the state of shift or offset of a light beam which is radiated on an optical disk, with respect to the center of a target track on the optical disk. Based on the generated tracking error signal, an optical disk apparatus performs tracking control by controlling the converged light beam to follow a given target track on the optical disk.
Hereinafter, a conventional SS-L/GFMT disk will be described.
FIGS. 19A
to
19
C schematically show the structure of a conventional SS-L/GFMT disk.
FIG. 19A
illustrates a single spiral structure. As shown in
FIG. 19A
, a single spiral optical disk is constructed by forming land tracks and groove tracks so as to alternate at a L/G (land/groove) switching point per rotation of the optical disk.
FIG. 19B
is an enlarged view showing a L/G switching point. As shown in
FIG. 19B
, a track on an optical disk is constructed of a data region and an address region which indicates a physical location on the optical disk. An address region includes first and second address pit arrays as well as third and fourth address pit arrays. At a L/G switching point, the first and second address pit arrays are disposed so as to be shifted from the end of each groove track toward the inner periphery side by 1/2 of the track pitch. Conversely, in address regions which do not correspond to L/G switching points, the first and second address pit arrays are disposed so as to be shifted from the end of each groove track toward the outer periphery side by 1/2 of the track pitch.
The third and fourth address pit arrays are disposed so as to be shifted from the beginning of each groove track toward the inner periphery side by 1/2 of the track pitch, in all address regions, whether they correspond to L/G switching points or not.
FIG. 19C
is a further enlarged view of the vicinity of an address region which does not correspond to a L/G switching point. As shown in
FIG. 19C
, each data region is constructed of tracks, groove or land, which meander with respect to the direction of rotation of the optical disk. As explained with reference to
FIG. 19B
, the first address pit array and the second address pit array are disposed so as to be shifted from the end of each groove track toward the outer periphery side by 1/2 of the track pitch, and the third and fourth address pit arrays are disposed so as to be shifted from the beginning of each groove track toward the inner periphery side by 1/2 of the track pitch.
However, a conventional SS-L/GFMT disk and a conventional optical disk apparatus for reproducing and/or recording information on a conventional SS-L/GFMT disk have the following problems.
The principle of detecting a tracking error signal from a light beam which is converged and radiated on a conventional SS-L/GFMT disk by using a known push-pull method will be described.
FIGS. 20A and 20B
illustrate the relationship between a tracking error signal obtained when a light beam crosses a track on an optical disk and an offset of the light beam with respect to the optical disk surface (hereinafter referred to as the “optical disk tilt”). Specifically,
FIG. 20A
illustrates a tracking error signal which is obtained when a light beam crosses a track with zero radial tilt and a tracking error signal which is obtained when a light beam crosses a track with a radial tilt of 1.0 degree, shown against a cross section of an optical disk having land tracks and groove tracks. It is assumed that the tracks extend in a direction which is perpendicular to the plane of FIG.
20
A.
FIG. 20B
is a graph illustrating the relationship between the optical disk tilt along the radial direction and an offset of a light beam from a track center (hereinafter referred to as “off-tracking”), where a tracking error signal indicating off-tracking of the light beam is detected and tracking control is performed so as to attain a zero value of the detected tracking error signal. As used herein, a radial tilt is defined as the tilt of an optical disk occurring along the scanning direction of a track.
As shown by the solid-line waveform in
FIG. 20A
, when there is no optical disk tilt, the tracking error signal indicating the position of a light beam with respect to a track has a zero value when the light beam is located on the track center. A tracking servo system of the optical disk apparatus operates so as to reduce the difference between the zero level of the tracking error signal and the reference control value to zero, thereby achieving feedback control so that the converged light beam follows the track center.
However, when the optical disk has a radial tilt, as shown by the broken-line waveform in
FIG. 20A
, the actual tracking center does not correspond to the zero level of the tracking error signal. On the other hand, as shown in
FIG. 208
, the off-tracking versus radial tilt characteristics are such that an optical disk tilt of a bout 1.0 degrees along the radial direction results in an off-tracking of about 0.104 &mgr;m. Accordingly, there is a problem in that under the presence of an optical disk tilt of about 1.0 degrees, an off-tracking of about 0.104 &mgr;m may result even if the tracking servo functions successfully.
SUMMARY OF THE INVENTION
An optical disk according to the present invention includes tracks and grooves, the grooves being formed with a pitch equal to or greater than about &lgr;/NA, wherein a first array of pits is provided at a position which is shifted by a predetermined amount with respect to each track in one of two directions substantially perpendicular to the tracks, the first array of pits being formed with a predetermined pitch, where the predetermined pitch is a function of a pitch of the grooves taking a value within a range from about 0 to about &lgr;/NA, wherein a second array of pits is provided at a position which is shifted by a predetermined amount with respect to the track in the other one of the two directions substantially perpendicular to the tracks, the second array of pits being formed with a predetermined pitch, where the predetermined pitch is a function of the pitch of the grooves taking a value within the range from about 0 to about &lgr;/NA, wherein &lgr; is a wavelength of a light beam which is radiated on the optical disk; and NA is a numerical aperture of a lens.
In one embodiment of the invention, the first array of pits and the secon
Ishida Takashi
Nakamura Atsushi
Nishiwaki Seiji
Takamine Kouichi
Yamada Shin-ichi
Matsushita Electric - Industrial Co., Ltd.
Neyzari Ali
RatnerPrestia
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