Dynamic information storage or retrieval – Control of storage or retrieval operation by a control... – Mechanism control by the control signal
Reexamination Certificate
1998-07-23
2002-05-21
Huber, Paul W. (Department: 2651)
Dynamic information storage or retrieval
Control of storage or retrieval operation by a control...
Mechanism control by the control signal
C369S053270, C369S116000
Reexamination Certificate
active
06392970
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a reproducing light quantity control method adopted in an optical memory device, in which a light beam is projected on an optical recording medium having a reproducing layer and a recording layer, and a magnetic aperture smaller than a spot diameter of the light beam is generated in the reproducing layer so as to reproduce record marks recorded on the recording layer, for controlling a reproducing light quantity of the light beam projected on the optical recording medium optimum, and a reproducing light quantity control device, and an optical recording medium.
BACKGROUND OF THE INVENTION
Conventionally, a technology for improving recording density of an optical recording medium by a so-called super resolution effect has been developed. In this method, a light beam is projected on an optical recording medium having a reproducing layer and a recording layer on a substrate, and a magnetic aperture having a smaller diameter than the light spot diameter is generated on the reproducing layer. As an example of such a method, a so-called magnetic super resolution is known.
The magnetic super resolution is a phenomenon in which a high temperature portion of the reproducing layer by the projection of light beam forms, by the magnetic coupling with the recording layer, a magnetic aperture for reading recorded information. In this phenomenon, the temperature distribution of the portion projected by the light beam takes the form of Gaussian distribution. Also, the temperature distribution is influenced by the heat capacity of the recording medium and the environment temperature. For this reason, it is always required to control the aperture size optimum by controlling the reproducing light quantity. Japanese Unexamined Patent Publication No. 63817/1996 (Tokukaihei 8-63817) discloses a device which carries out this control. The following briefly describes the operation of such a device.
FIG.
16
(
a
) shows a mark string recorded on the optical recording medium and the waveform of reproducing signal obtained when the mark string is reproduced. In FIG.
16
(
a
), when a light beam with a certain reproducing light quantity is projected on the optical recording medium, by the Gaussian temperature of the light beam, the temperature of the center of the light beam projected portion becomes high. In this high temperature portion of the reproducing layer, a magnetic aperture “ap” is generated. When the reproducing light quantity is small, the aperture “ap” takes the form of an aperture “ap
1
” having a smaller diameter, indicated by a solid line, and when the reproducing light quantity is large, takes the form of an aperture “ap
2
” having a larger diameter, indicated by a broken line.
Of the marks recorded on the recording layer, for example, from a long mark
101
larger than the aperture “ap
1
” having a smaller diameter, a signal quantity (for example, peak-to-peak amplitude) v
1
of a reproducing signal cl is detected, and from a short mark
102
smaller than the aperture “ap
2
”, a signal quantity (for example, peak-to-peak amplitude) v
2
of a reproducing signal cs is detected. In this manner, the resolving power when reading the record marks varies depending on the size of the aperture “ap”.
The resolving power can be substituted by a ratio v
2
/v
1
which is a ratio of the reproducing signal quantity v
1
of the long mark
101
to the reproducing signal quantity v
2
of the short mark
102
, and the size of the aperture “ap” can be detected from the value of the ratio.
In a graph of FIG.
16
(
b
), the horizontal axis represents the size Pr of reproducing light quantity, and the vertical axis represents an amplitude ratio of long mark and short mark and an error rate. With respect to reproducing light quantity Pr, the error rate of the reproducing data and the reproducing signal quantity ratio v
2
/v
1
vary in the manner as shown in FIG.
16
(
b
). When the error rate of the reproducing data is minimum, the reproducing signal quantity ratio v
2
/v
1
becomes an optimum amplitude ratio, and the reproducing light quantity becomes an optimum reproducing light quantity Pr
0
.
Thus, in the conventional device, the reproducing light quantity Pr is controlled after deciding the optimum amplitude ratio so that the reproducing signal quantity ratio v
2
/v
1
obtained from the reproducing signal approaches the optimum amplitude ratio. Also, in the conventional device, on the optical recording medium, the long mark
101
and the short mark
102
are pre-recorded, and there are provided (i) a long mark recording region in which long marks
101
are recorded repeatedly and (ii) a short mark recording region in which short marks
102
are recorded repeatedly. The reproducing signal quantity ratio v
2
/v
1
is detected by reproducing respective control patterns of the long mark
101
and the short mark
102
respectively recorded on the long mark recording region and the short mark recording region, and the reproducing light quantity Pr is controlled so that the reproducing light quantity Pr becomes an optimum reproducing light quantity Pr
0
.
However, generally, because the heat capacity of each optical recording medium is different, in a reproducing light quantity control device, it is required to measure the error rate of reproducing data and the amplitude ratio (reproducing signal quantity ratio v
2
/v
1
) of reproducing signal, and determine an optimum amplitude ratio, and set the optimum reproducing light quantity Pr
0
everytime a different optical recording medium is installed.
Here, generally, when a bit rate error is 10
−5
, by an error correction technique, a bit error of 10
−12
is obtained, which is demanded in a computer memory device. When the bit error rate is on 10
−5
, in order to measure the bit error rate with an error of 1 percent, it is required to detect at least 100 error bits, and carry out measurement so that the number of sample bits is 10
7
. Generally, since the transfer rate of an optical disk is 10 Mbps at the maximum, it takes 1 second at the fastest to measure the number of sample bits. Since one measurement takes 1 second, for example, when the change in error rate is to be measured while changing the reproducing light quantity in 10 levels, it takes 10 seconds to determine the optimum value (optimum amplitude ratio). Namely, it is required to wait at least 10 seconds from installing of the optical recording medium to recording and reproducing of information. As a result, a problem is presented that a high-speed device cannot be realized.
Further, the conventional device also has a problem that control malfunction results when the optical disk (optical recording medium) has a defect or scratch.
For example, when an irregular reproducing signal is generated by a defect or scratch on the optical disk, and as shown by x
1
of FIG.
16
(
c
), when the amplitude v
2
of the reproducing signal from the short mark
102
becomes large, or as shown by x
4
, when the amplitude v
1
of the reproducing signal from the long mark
101
becomes small, the reproducing signal quantity ratio v
2
/v
1
, namely, the amplitude ratio v
2
/v
1
of the reproducing signal becomes excessively large. When the reproducing light quantity control device mistakenly responds to this amplitude ratio, the reproducing light quantity is increased, and the temperature of the recording layer exceeds the curie point. As a result, a problem is presented that the following record marks are destroyed by the defect or scratch. In the worst case, a serious problem is caused that the periodically recorded reproducing light quantity control patterns of the following record marks are destroyed and the reproducing light quantity cannot be controlled.
Also, as shown in x
2
of FIG.
16
(
c
), when the amplitude v
2
of the reproducing signal from the short mark
102
becomes small, or as shown in x
3
, when the amplitude v
1
of the reproducing signal from the long mark
101
becomes large, the amplitude ratio v
2
/v
1
becomes excessively sma
Akiyama Jun
Fuji Hiroshi
Inui Toshiharu
Maeda Shigemi
Miyake Tomoyuki
Edwards & Angell LLP
Huber Paul W.
Sharp Kabushiki Kaisha
LandOfFree
Reproducing light quantity control method for optical memory... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Reproducing light quantity control method for optical memory..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Reproducing light quantity control method for optical memory... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2834862