Dynamic information storage or retrieval – Control of storage or retrieval operation by a control... – Mechanism control by the control signal
Reexamination Certificate
2000-04-26
2003-06-24
Tran, Thang V. (Department: 2653)
Dynamic information storage or retrieval
Control of storage or retrieval operation by a control...
Mechanism control by the control signal
C369S116000, C369S059110
Reexamination Certificate
active
06584050
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an optical recording device, an optical reproducing device, and an optical memory medium that are arranged so that a control pattern is recorded in the optical memory medium of a magnetic super-resolution type, and that a reproducing power of a light beam is controlled according to a reproducing signal obtained from the control pattern.
BACKGROUND OF THE INVENTION
Recently, magneto-optical disks of the magnetic super-resolution type from which recording marks smaller than a spot diameter of a light beam can be reproduced have drawn attention. Such a magneto-optical disk is, for instance, provided with a recording layer and with a reproducing layer having in-plane magnetization at room temperature, and reproduction of the same is carried out in the following manner. During reproducing, a light beam is projected onto the reproducing layer side of the magneto-optical disk. Then, part of the area of the reproducing layer within the light beam spot is heated to above a predetermined temperature, and the magnetization of this portion (hereinafter referred to as an aperture) shifts from in-plane magnetization to a perpendicular magnetization conforming to that of the recording layer beneath the aperture. In this way, recorded marks smaller in diameter than the light beam spot can be reproduced.
By the foregoing method, however, changes in the ambient temperature during reproducing tend to cause the optimum reproducing power of the light beam to fluctuate accordingly, even in the case where the driving current for generating the light beam is kept constant.
If reproducing power is much stronger than the optimum level, the aperture formed becomes too large. Consequently, output of reproducing signals from tracks adjacent to the track being reproduced is increased, the proportion of noise signals included in the reproduced data increases, and reading errors are more likely to occur. If reproducing power is much weaker than the optimum level, the aperture becomes smaller than the recorded mark, and the reproducing signal output from the target track is reduced. Accordingly, the proportion of noise signals included in the main signal increases, and reading errors are more likely to occur in this case as well.
A technique to cope with the foregoing problem is disclosed in the Japanese Publication for Laid-Open Patent Application No. 7668/1999 (Tokukaihei 11-7668 [publication date: Jan. 12, 1999]). In that technique, two types of patterns for reproducing power control (hereinafter referred to as reproducing-power-control patterns) of different mark-space lengths are reproduced, and reproducing power is controlled so as to bring close to a predetermined value a ratio of amplitudes of reproducing signals obtained from these recorded marks. By this means, reproducing power is maintained at an optimum value, and the likelihood of reading errors is reduced. Here, in the case where the shorter pattern among the two types of reproducing-power-control patterns has a recording length of 1T (T represents the minimum recording length), the S/N ratio becomes too low since a signal from the pattern has a small amplitude value. On the other hand, in the case where the foregoing pattern has a recording length of 2T, sensitivity to changes in the amplitude ratio cannot be obtained at the level required for detection of an optimum aperture since a signal from the pattern has a great amplitude value. Therefore, the technique disclosed by the foregoing publication utilizes 1T- and 2T-patterns that are present together.
FIG. 5
is a block diagram schematically illustrating an arrangement of such a recording-reproducing device.
FIG. 6
is a view schematically illustrating a structure of a magneto-optical disk
20
used in the foregoing recording-reproducing device.
FIG. 7
is an explanatory view of short-mark/space patterns and long-mark/space patterns for reproducing power control. The following description will explain the foregoing recording-reproducing device, particularly its reproducing power control operation, with reference to these figures.
As shown in
FIG. 6
, in a magneto-optical disk
20
, data are recorded in each sector
200
as a unit. A short-mark/space recording area
103
is provided in a front part of each sector
200
, and a long-mark/space recording area
104
is provided therebehind. Furthermore, a data recording area
105
for recording information data is provided behind the long-mark/space recording area
104
.
As shown in FIG.
7
(
a
), a short mark having a mark length of 2T is repeatedly provided at an inter-mark distance (space) of 1T in the short-mark/space recording area
103
. As shown in FIG.
7
(
b
), a long mark having a mark length of 8T is repeatedly provided at an inter-mark distance (space) of 8T in the long-mark/space recording area
104
.
The following description will explain an operation of recording reproducing-power-control patterns in a magneto-optical disk
20
arranged as described above.
A light emitted from a semiconductor laser
2
is projected onto the short-mark/space recording area
103
disposed in the front part of the sector
200
on the magneto-optical disk
20
. Here, a driving current supplied to the semiconductor laser
2
from the laser power control circuit
13
has a high power for recording use.
Besides, simultaneously, an external magnetic field is applied onto the magneto-optical disk
20
from a magnetic head
18
. Here, a power control pattern generating circuit
16
switches the polarity of the magnetic head
18
at time intervals of 1T and 2T.
In so doing, the short marks having a mark length of 2T each are recorded at inter-mark distances of 1T each in the short-mark/space area
103
as shown in FIG.
7
(
a
). Likewise, the power control pattern generating circuit
16
switches the polarity of the magnetic head
18
at time intervals of 8T, thereby causing the long marks having a mark length of 8T each to be recorded at inter-mark distances of 8T each in the long-mark/space area
104
as shown in FIG.
7
(
b
).
The following description will explain a reproducing operation of the foregoing recording-reproducing device. Upon projection of light emitted from the semiconductor laser
2
onto the short-mark/space recording area
103
in the sector
200
on the magneto-optical disk
20
, light is reflected from the short-mark/space pattern recorded in the area. This reflected light is converted by a photo-diode
3
into a reproducing signal. The reproducing signal is sent to an amplifier
4
where the reproducing signal is amplified to a level in a range suitable for input into an A/D converter
5
after low-frequency components are removed from the reproducing signal. The reproducing signal is subsequently subjected to A/D conversion by the A/D converter
5
, and further, it is inputted to the short-mark/space amplitude detecting circuit
9
where an amplitude value of the short-mark/space pattern is determined. Likewise, reflected light from the long-mark/space recording area
104
is processed by means of the photo-diode
3
, the amplifier
4
, the A/D converter
5
, and the long-mark/space amplitude detecting circuit
8
, so that an amplitude value of the long-mark/space pattern is determined.
Incidentally, the A/D conversion is carried out at timings by clocks extracted from the respective reproducing signals by a reproducing clock extracting circuit
19
. The short-mark/space pattern and long-mark/space pattern thus determined are inputted into a division circuit
11
and an amplitude ratio thereof is outputted therefrom. This detected amplitude ratio and a standard amplitude ratio are compared by a differential amplifier
12
. The driving current applied to the semiconductor laser
2
is controlled by a laser power control circuit
13
so that feedback causes the difference as a result of the foregoing comparison to become smaller.
After the laser light driving current is controlled so that an optimum reproducing power is applied, the emitted light is projected onto the
Maeda Shigemi
Okumura Tetsuya
Conlin David G.
Edwards & Angell LLP
Sharp Kabushiki Kaisha
Tran Thang V.
Tucker David A.
LandOfFree
Optical recording device, optical reproducing device, and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical recording device, optical reproducing device, and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical recording device, optical reproducing device, and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3103873