Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Reexamination Certificate
1999-03-26
2003-10-07
Edun, Muhammad (Department: 2655)
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
C369S047100, C369S053100, C369S059100, C369S044130
Reexamination Certificate
active
06631114
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical disc having spiral grooves formed on a data recording surface thereof and in which information is written to, and read from, both a land between the grooves and the grooves as tracks, a tracking controlling apparatus and method for the optical disc, and a focus controlling apparatus for the optical disc.
2. Description of Related Art
Various optical recording media, disc- and card-shaped, adopting an optically or magneto-optically signal recording/reproducing method, have been developed and are commercially available. These optical recording media include a read-only memory (ROM) type recording medium such as so-called compact disc (CD), well known as CD-ROM, a write-once type recording medium to which the user can write data once, a rewritable (spo-called overwrite) type recording medium such as magneto-optical disc (MO), etc.
The optical disc drive to write and read data to and from a disc-shaped recording medium uses an optical head incorporating a laser diode to emit a light beam for writing and reading information to and from the optical disc, a photodetector to detect a reflected light of the light beam focused on the optical disc, etc. and is adapted for servo control of the focus and tracking of the optical head based on a reflected light detection output provided from the photodetector. In the optical disc drive, the optical head writes and reads data to and from the optical disc by scanning the light beam on a recording track on the optical disc while driving to spin the optical disc at a constant angular velocity or constant linear velocity by a spindle motor running at a servo-controlled speed. For example, the tracking is servo-controlled by the one-beam pushpull method or three-beam method, for example. However, taking in consideration the recent highly increased storage capacity and recording density of optical discs, highly improved control of the laser diode output power and optical system, and related improvements in the art, the pushpull method should desirably be used for servo control of the optical head tracking.
In the optical disc drive adopting the pushpull method, a light beam reflected and diffracted by grooves on the optical disc is detected by two photodetectors disposed symmetrically with respect to the track center, and a difference between outputs from the photodetectors is detected as a pushpull signal. The pushpull signal is used as a tracking error for servo control of the biaxial actuator, etc. for tracking of the optical head.
Recently, ROM (read-only memory) and RAM (random access memory) discs proposed as optical recording media show a considerably large storage capacity. Semiconductor lasers of shorter wavelengths have been proposed for use in the optical heads of optical disc drives, and objective lenses of a larger numerical aperture (NA) have been proposed for use to focus a light beam onto the information recording surface of an optical disc.
To implement a phase-change type optical disc having a larger storage capacity and higher density than DVD-RAM, it is known to use a smaller focused light spot size. The size of a focuses spot on the recording medium is given generally as &lgr;/NA. The focused spot size can be reduced by using a short-wave semiconductor laser such as GaN, ZnSe or the like or by using a two-group lens or the like, typically, a solid immersion lens (SIL) to increase the objective lens NA.
Assume here that &lgr;=640 nm and NA=0.85, for example. The diameter of a laser spot focused on the recording medium will be about 0.75 &mgr;m. In this case, when signal is written using RLL (
1
,
7
) for example, a recording density of about 0.21 &mgr;m/bit can be attained.
Well-known modulation codes in a modulation system using a wide channel detection window suitable for a high-density recording and reproduction include RLL (
1
,
7
) and RLL (
2
,
7
).
Further, in an optical disc system adopting an optical head in which an objective lens of a large NA is used, to accommodate an error caused by the influence on the light beam of dust or scratch on the surface of the optical, the error correction capability should be improved by increasing the code and ECC block.
Assume here that the optical disc spins without run-out. As shown in FIG.
1
(A) for example, a photodetector
70
is irradiated at the center thereof with a reflected light of the laser beam. However, if the optical disc spins with a run-out, the photodetector
70
will be irradiated at a position off the center thereof with the reflected light of the laser beam as shown in FIGS.
1
(B) to
1
(D). Thus, a DC offset will take place in a pushpull signal produced from the reflected light of the laser beam from the groove. FIG.
2
(A) shows a pushpull signal offset, indicated with a solid line, from an ideal pushpull signal indicated with a dashed line.
In an optical disc in which data is written on lands as well as in grooves, the reflected light of the laser beam from the lands and grooves results in a pushpull signal suffering from an offset. As in FIG.
2
(A), a pushpull signal produced from a reflected light of the laser beam from the land is offset from an ideal pushpull signal as shown in FIG.
2
(B).
If a pushpull signal offset takes place, no accurate tracking is possible. Especially in a large storage capacity, high recording density optical disc, since the space between land and groove is decreased correspondingly to the increase of the storage capacity and recording density, tracking of the optical head has to be done more accurately.
In some of so-called on-land/in-groove recording type optical discs in which both the land track and groove track have a generally same width and the groove depth is ⅙ to ⅕ of the wavelength of a write/read laser light, embossed pits are used as addresses.
In writing or reading information to or read from an on-land track, for example, however, since the polarity of a tracking error signal in an address area is reversed, a tracking tried with the laser spot in an address area after seeking cannot be performed. The actuator makes a big jump, the laser spot is far from a target address, and thus the access time is longer.
Even with the laser spot focused on a track, a tracking error will be a disturbance when the optical head is in an address area, and also a focus error will be a disturbance when the optical head is in the address area.
Furthermore, in an on-land/in-groove recording, a focus error offset on a land track is detected to be different from one on a groove track in some cases.
Also, in an optical head using a one-beam optical system, a tracking error offset caused by a light intensity off the center of on the photodetector when the optical disc runs out, is a problem.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to overcome the above-mentioned drawbacks of the prior art by providing an optical disc, a tracking controlling apparatus and method, and a focus controlling apparatus and method, in which an offset arisen in a tracking error signal and focus error signal is removed to accurately control the tracking and focus of the optical head.
The above object can be achieved by providing an optical disc having spiral grooves formed on a data recording surface thereof and in which information is written to, and read from, both a land between the grooves and the grooves as tracks,
each track having formed thereon a plurality of address areas and user areas;
each of the address areas having formed thereon embossed pits for a groove header and embossed pits for a land header; and
each of the address areas having provided in a leading part thereof a header mark area formed from a mirror finished surface.
The above object can be achieved also by providing an optical disc having spiral grooves formed on a data recording surface thereof and in which information is written to, and read from, both a land between the grooves and the grooves as tracks,
each track having formed
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