Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Reexamination Certificate
2003-02-14
2004-06-01
Dinh, Tan (Department: 2653)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
C369S116000, C369S047530
Reexamination Certificate
active
06744700
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical output adjustment apparatus and an optical output adjustment method for adjusting an optical output level of a reproducing laser used for reproducing a record mark recorded on a magneto-optical recording medium.
2. Description of Related Art
In recent years, attention has been paid to a magneto-optical disk as a high-density recording medium which enables rewriting of information signals. For example, the Japanese Patent Application KOKAI Publication No. 6-290496 (hereinafter called a reference 1) discloses a magneto-optical reproducing method which utilizes a point that a magneto-optical disk including at least three layers of a displacement layer, a switching layer, and a memory layer as magnetic layers are used so that the size of magnetic sectors recorded on the memory layer is substantially magnified on the moving layer. For example, the magneto-optical reproducing method is a so-called DWDD (Domain Wall Displacement Detection) in which a reproducing laser beam is irradiated during reproducing such that an area in the switching layer is set to a curie temperature or more, and magnetic connection between the memory layer and the displacement layer, which corresponds to the area, is disconnected to detect a magnetic wall which moves within the area of the moving layer corresponding to an area where the magnetic connection is disconnected. In this manner, the size of the magnetic sectors recorded on the memory layer is substantially magnified on the displacement layer to enlarge the reproducing carrier signal.
In the magneto-optical reproducing method based on this DWDD, i.e., in a so-called magnetic wall displacement detection reproducing method (hereinafter called a DWDD reproducing method), it is possible to reproduce a very large information signal even from an optical limit resolution of a reproducing laser, so the recording density can be heightened without changing the wavelength of the reproducing laser beam and the numerical aperture NA of the objective leans.
Meanwhile, in the DWDD reproducing method, the output level of the reproducing laser beam must be set to a certain level which causes magnetic displacement. However, no optimal output level for the reproducing laser beam has been known. This is because the optimal output level differs depending on the conditions such as a peripheral temperature change, variants of sensitivity of between magneto-optical disks, and the like. However, if the optimal value of the output level of the reproducing laser beam cannot be grasped and the output level of the reproducing laser beam is too large, record marks recorded on adjacent recording tacks may be deteriorated.
BRIEF SUMMARY OF THE INVENTION
Hence, the present invention has been made in view of the above situation and has an object of providing an optical output adjustment apparatus and an optical output adjustment method which are capable of adjusting the reproducing laser beam to an optimal output level.
To achieve the above object, an optical output adjustment apparatus according to the present invention is constructed as an apparatus for adjusting an output level of a reproducing laser beam, in a signal reproducing device which adopts a magnetic wall movement detection reproducing method, irradiates the reproducing laser beam onto a magneto-optical information recording medium on which data is recorded by recording marks having different recording lengths according to a predetermined modulation method, and magnifies a magnetic sector by magnetic wall movement, thereby to perform reproducing of the data.
The optical output adjustment apparatus comprises: a light source for emitting the reproducing laser beam; reproducing signal detector means for detecting a shortest recording mark reproducing signal corresponding to a component of a shortest recording mark in a reproducing signal obtained by reproducing the magneto-optical information recording medium; signal amplitude level detector means for detecting an amplitude level of the shortest recording mark reproducing signal; comparator means for comparing the amplitude level with a predetermined threshold value; and optical output control means for adjusting the reproducing laser beam to an output level which makes the amplitude level equal to or higher than the predetermined threshold value.
In the optical output adjustment apparatus having the structure as described above, based on a comparison result between a predetermined threshold value and an amplitude level of a shortest recording mark reproducing signal corresponding to a component of a shortest recording mark in a reproducing signal obtained by reproducing the magneto-optical information recording medium, the reproducing laser beam is adjusted to an output level which makes the amplitude level equal to or higher than the predetermined threshold value.
By the reproducing laser beam whose output level is thus controlled, it is possible to obtain a reproducing signal with a lowered jitter.
Also, to achieve the above object, an optical output adjustment method according to the present invention is a method for adjusting an output level of a reproducing laser beam, in a signal reproducing device which adopts a magnetic wall movement detection reproducing method, irradiates the reproducing laser beam onto a magneto-optical information recording medium on which data is recorded by recording marks having different recording lengths according to a predetermined modulation method, and magnifies a magnetic sector by magnetic wall movement, thereby to perform reproducing of the data, characterized in that, based on a comparison result between a predetermined threshold value and an amplitude level of a shortest recording mark reproducing signal corresponding to a component of a shortest recording mark in a reproducing signal obtained by reproducing the magneto-optical information recording medium, the reproducing laser beam is adjusted to an output level which makes the amplitude level equal to or higher than the predetermined threshold value.
By the reproducing laser beam whose output level is thus controlled, it is possible to obtain a reproducing signal with a lowered jitter.
Also, to achieve the above object, an optical output adjustment apparatus according to the present invention is constructed as an apparatus for adjusting an output level of a reproducing laser beam, in a signal reproducing device which adopts a magnetic wall movement detection reproducing method, irradiates the reproducing laser beam onto a magneto-optical information recording medium on which data is recorded by recording marks having different recording lengths according to a predetermined modulation method, and magnifies a magnetic sector by magnetic wall movement, thereby to perform reproducing of the data.
The optical output adjustment apparatus comprises: a light source for emitting the reproducing laser beam; first reproducing signal detector means for detecting a first recording mark reproducing signal corresponding to a component of a first recording mark in a reproducing signal obtained by reproducing the magneto-optical information recording medium; second reproducing signal detector means for detecting a second recording mark reproducing signal corresponding to a component of a second recording mark in a reproducing signal obtained by reproducing the magneto-optical information recording medium; first signal amplitude level detector means for detecting a first amplitude level of the first recording mark reproducing signal; second signal amplitude level detector means for detecting a second amplitude level of the second recording mark reproducing signal; difference value calculator means for calculating a difference value between the first and second amplitude levels; comparator means for comparing the amplitude level with a predetermined threshold value; and optical output control means for adjusting the reproducing laser beam to an output level which makes the amplitude level equal to o
Takeshita Yasuyuki
Tsutsui Keiichi
Dinh Tan
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Sony Corporation
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