Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Reexamination Certificate
1998-09-11
2002-01-29
Huber, Paul W. (Department: 2651)
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
C369S275300, C369S053200
Reexamination Certificate
active
06343062
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an optical disk and an optical disk device for recording and reproducing high-density signals by irradiating high-energy beams such as laser beams or the like onto a thin film formed on a substrate.
BACKGROUND OF THE INVENTION
Recently, optical disks on which information can be recorded and from which the information can be reproduced and erased and optical disk devices that can record information on and reproduce information from the optical disks have been commercialized. Furthermore, high-density rewritable optical disks and optical disk devices capable of recording and reproducing high-quality animation have been actively researched and developed.
Well-known rewritable optical disks include phase-change optical disks with chalcogenide thin films on a disc-shape substrate. The chalcogenide thin films comprise, for example, Ge—Sb—Te, In—Se, or the like. Magneto-optical recording media having metal thin films such as Fe—Tb—Co as their recording layers also are well known.
In phase-change optical disks, for example, laser beams are irradiated onto and focused on recording thin films comprising the above-mentioned phase-change materials to heat the irradiated parts partially to a predetermined temperature. When the temperature of the irradiated portion becomes equal to or higher than the crystalline temperature, the irradiated portion is changed to the crystalline state. When the irradiated portion is melted at a temperature higher than its melting point and is quenched, its state is changed to the amorphous state. Once either the crystalline state or the amorphous state is determined so as to correspond to the recording state, and the other to the erasing state (unrecorded state), information can be recorded or erased reversibly by forming each state according to a pattern corresponding to information signals. Since the crystalline state and the amorphous state are different from each other in their optical characteristics, recorded signals can be reproduced by optically detecting such different characteristics as a reflectivity change or a transmittance change.
In a magneto-optical recording medium, for example, laser beams are irradiated onto and focused on a magneto-optical recording thin film to heat the irradiated portions partially to a predetermined temperature. While heating the irradiated portions, a magnetic field also is applied. The magnetizing direction of the magneto-optical recording thin film is reversed according to information, thus recording and erasing the information.
In such optical disks mentioned above, a substrate is grooved in advance so as to be provided with uneven guide grooves (hereafter also referred to as “guide tracks”), thus forming information tracks. In an uneven guide groove, an information track nearer to a light-incidence side is referred to as a “groove”, and an information track further from the light-incidence side is referred to as a “land”. Information signals are recorded or reproduced by focusing laser beams on the groove or the land and scanning it. These information signals can be recorded by users themselves, thus being referred to as “user data”.
In common commercial optical disks, information signals are recorded either on a groove or on a land, and the other serves as a guard band that separates adjoining tracks.
Means for increasing recording capacity in optical disks include a technique for increasing track density by recording information signals on both groove tracks and land tracks as described in Examined Japanese Patent Application Tokkou Sho 63-57859.
In order further to increase the track density, there is a method of making the track pitch of guide tracks smaller while recording information on both the land tracks and the groove tracks mentioned above. In this case, in order to cut off the heat transfer from a track heated by laser beams to the adjacent track, a technique for making guide grooves deeper can be applied.
On the other hand, in rewritable optical disks, it is necessary to record address signals as uneven pits that indicate position information on a medium or the like in advance. As a means for recording the address signals, an intermediate address method is proposed in, for example, Unexamined Japanese Patent Application Tokkai Hei 6-176404.
An optical-beam tracking control method for reading information from an optical disk will be explained with reference to drawings as follows.
FIG. 7
is a schematic block diagram of a conventional optical disk device. An information track
501
is formed on an optical disk
500
.
FIG. 8
is an enlarged view of the information track
501
. The information track
501
comprises a groove track
606
and a land track
607
. The information track
501
has a data area
602
for recording information and an address area (an identifying signal area)
601
in which position information of an information track and the like are recorded. The groove track
606
and the land tracks
607
are arranged alternately at an interval of a track pitch Tp. Prepits
604
of projection or pit are formed in the address area (the identifying signal area)
601
. The center of a prepit
604
is arranged at a position shifted from the center of the groove track
606
in the radial direction of the optical disk by Tp/2. The arrangement of these prepits
604
enables the address signals to be reproduced from both the groove track and the land track. Generally, the depth or height of the prepits
604
is the same as the depth of the groove in the data area
602
.
In
FIG. 8
, recording marks
605
are formed on both the groove track
606
and the land tracks
607
. A beam spot
502
scans the groove track
606
and the land tracks
607
in the direction shown by an arrow.
Referring to
FIG. 7
, the operation during reproducing information recorded on the optical disk
500
will be explained.
A laser driving circuit
525
receives a signal L
3
from a controller
518
to be changed to a reproducing mode and outputs a driving current to a semiconductor laser
510
, which results in emission at a constant reproducing intensity.
As a next step, the beam-spot position in the focus direction is controlled. For this purpose, a general focus controlling method such as a spot size method or an astigmatism method may be used. Therefore, a detailed explanation of the method is not necessary herein.
A laser beam emitted from the semiconductor laser
510
provided to an optical head
514
is focused on the information track
501
by an objective lens
511
. A laser beam reflected from the information track
501
enters a photodetector
512
after receiving information recorded on the information track
501
according to the reflected-light quantity distribution. Light receivers
512
a
and
512
b
comprised in the photodetector
512
convert the change in the light quantity distribution of the incident optical beam into electric signals. Each of the light receivers
512
a
and
512
b
output the electric signals to a differential amplifier
515
and a summing amplifier
521
. After converting each input current into voltage, the differential amplifier
515
outputs a differential signal obtained by differentiation to a LPF (low pass filter)
516
. The LPF
516
extracts a low-frequency component from the differential signal and outputs it as a signal S
1
to a polarity inverting circuit
517
.
The polarity inverting circuit
517
outputs a signal S
2
to a tracking control circuit
519
by transmitting the signal S
1
without polarity change or inverting the polarity of the signal S
1
according to a control signal L
1
from the controller
518
. The signal S
2
is a so-called push-pull signal and corresponds to a tracking error quantity between the beam spot
502
and the information track
501
. In this case, when the track on which information should be recorded (or erased, hereafter the same) or from which information should be reproduced is a groove, the polarity inverting circuit
517
transmits the signal S
1
without polarity change. On the other hand,
Furukawa Shigeaki
Ishida Takashi
Nishiuchi Ken'ichi
Huber Paul W.
Matsushita Electric Industrial Co. Ltd
Merchant & Gould
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