Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Reexamination Certificate
2001-07-03
2003-12-09
Dinh, Tan (Department: 2653)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
Reexamination Certificate
active
06661744
ABSTRACT:
BACKGROUND OF THE INVENTION
This application claims the benefit of a Japanese Patent Application No. 2001-028714 filed Feb. 5, 2001, in the Japanese Patent Office, the disclosure of which is hereby incorporated by reference.
1. Field of the Invention
The present invention generally relates to optical recording media, recording and reproducing methods and storage units, and more particularly to an optical recording medium such as a magneto-optical recording medium which uses magnetic super resolution (MSR), and to a recording and reproducing method and a storage unit which are suited for reproducing information from such an optical recording medium.
Recently, the recording densities of optical recording media have increased, and of the magneto-optical recording media such as the magneto-optical disk, there are recording media which were developed to use the MSR. In this specification, a recording medium which uses the MSR will be referred to as a MSR recording medium. When reproducing information from the MSR recording medium, it is desirable to obtain a stable reproduced output regardless of changes in temperature and laser power.
2. Description of the Related Art
For example, a Japanese Laid-Open Patent Application No. 7-29238 proposes a method which records a reference signal on a disk in advance, stores values such as a reproduced signal amplitude and a carrier-to-noise (C/N) ratio, and compares the reference signal which is reproduced from the disk and a reference value when the disk is loaded into a storage unit (disk unit) or the storage unit is started. According to this proposed method, a reproducing laser power is appropriately controlled to carry out a temperature compensation for cancelling a change in the magnetic characteristic caused by a temperature change at the time of the reproduction, based on a comparison result. In other words, the changes in the environmental temperature and the laser power are detected, and the laser power, the pulse width or the like are controlled based on the detected results.
Such a method is also proposed in Japanese Laid-Open Patent Applications No. 4-258831 and No. 7-262643.
However, the proposed method described above does not take into consideration the peculiar problems which are generated at the time of reproduction of the MSR recording medium. In other words, in the case of the MSR recording medium, even if the temperature at the time of the reproduction is the same, the optimum conditions such as the laser power and the reproducing magnetic field at the time of the reproduction differ if the temperatures at the time of the recording differ. Hence, unless the temperature at the time of the recording is known in advance, it is extremely difficult to obtain the optimum conditions for the reproduction. In addition, since the information recording with respect to the MSR recording medium is carried out at arbitrary timings, the temperatures at the time of the recording in many cases differ depending on the recording regions on the MSR recording medium, thereby making it further difficult to obtain the optimum conditions for the reproduction for each of the recording regions.
FIG. 1
is a diagram showing a relationship between a reproducing magnetic field and an error rate of a MSR recording medium for four different recording and reproducing conditions.
FIG. 1
shows the reproducing magnetic field with respect to one track on the MSR recording medium for a case where the MSR recording medium is a disk. In
FIG. 1
, a solid line indicates the relationship for a room-temperature recording (hereinafter referred to as a write) and a room-temperature reproduction (hereinafter referred to as a read), a dotted line indicates the relationship for a room-temperature write and a high-temperature read, a one-dot chain line indicates the relationship for a high-temperature write and a high-temperature read, and a double line indicates the relationship for a high-temperature write and a room-temperature read. In this case, the room temperature is 25° C., and the high temperature is 55° C. Furthermore, H
1
denotes a point of inflection (hereinafter referred to as an inflection point) for the room-temperature write and room-temperature read, H
2
denotes a inflection point for the high-temperature write and high-temperature read, H
3
denotes a inflection point for the room-temperature write and high-temperature read, and H
4
denotes a inflection point for the high-temperature write and room-temperature read.
As may be seen from
FIG. 1
, in the case of the MSR recording medium, the optimum read conditions change when the write temperature changes, even if the read temperature is the same, and a relationship H
1
<H
2
<H
3
stands. In addition, the values of the inflection points H
1
, H
2
, H
3
and H
4
change depending on the radial position on the MSR recording medium, production lot and the like of the MSR recording medium.
In the conventional magneto-optical disk unit, a test write and read is carried out with respect to a test track region on the magneto-optical disk, so as to determine a write laser power (hereinafter simply referred to as a write power), a read laser power (hereinafter simply referred to as a read power), and a reproducing magnetic field which are optimum. When determining such optimum values, a value which is obtained by adding a constant value &agr; to the inflection point is regarded as the optimum reproducing magnetic field, by taking into consideration the inconsistencies in the read power and the reproducing magnetic field. This constant value &agr; is obtained by actual measurement or calculation, by taking into account the effects such as the inconsistencies within one track on the magneto-optical disk and the crosstalk from the adjacent tracks.
However, when the reproducing conditions are determined by carrying out the test write and read with respect to the test track region, in the case of the room-temperature write and high-temperature read, it is only possible to obtain the inflection point H
1
of the reproducing magnetic field for the room-temperature write and room-temperature read in
FIG. 1
by the test read during the write, and the inflection point H
2
of the reproducing magnetic field for the high-temperature write and high-temperature read in
FIG. 1
by the test read during the read. The inflection point H
3
of the reproducing magnetic field for the room-temperature write and high-temperature read shown in FIG.
1
and the inflection point H
4
of the high-temperature write and room-temperature read shown in
FIG. 1
, which are actually required, cannot be obtained.
Similarly, when the reproducing conditions are determined by carrying out the test write and read of the reference signal in advance at the room temperature as in the proposed method described above, it is only possible to obtain the inflection point H
1
of the reproducing magnetic field for the room-temperature write and room-temperature read shown in
FIG. 1
by the room-temperature test read, and the inflection point H
3
of the reproducing magnetic field for the room-temperature write and high-temperature read shown in
FIG. 1
by the high-temperature test read. The inflection point H
2
of the reproducing magnetic field for the high-temperature write and high-temperature read shown in
FIG. 1
, and the inflection point H
4
of the reproducing magnetic field for the high-temperature write and room-temperature read shown in
FIG. 1
, which are actually required, cannot be obtained.
Accordingly, when the optimum values for the read power and the reproducing magnetic field with respect to the temperature at the time of the test read are obtained by the test read but the error rate is poor if the actual data read is carried out using these optimum values, it is possible to update the optimum values by carrying out a retry by changing the read power and the reproducing magnetic field. A method of updating the optimum values while carrying out the retry in such a manner is proposed in a Japanese Laid-Open Patent Application
Dinh Tan
Greer Burns & Crain Ltd.
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