Magneto-optical memory device

Details Magneto-optical memory device Magneto-optical memory device

2000-12-15

2003-05-13

Letscher, George J. (Department: 2653)

Dynamic information storage or retrieval

Storage or retrieval by simultaneous application of diverse...

Magnetic field and light beam

C360S254100

Reexamination Certificate

active

06563768

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an adjustment method for a magneto-optical memory device and a magneto-optical memory device, and more particularly to an adjustment method for a magneto-optical memory device and a magneto-optical memory device for storing data using light beams and magnetic fields.
2. Description of the Related Art
Magneto-optical memory devices, such as magneto-optical disk devices, store data by simultaneously focusing or projecting light emitted from a light source through an objective lens onto a recording surface of a magneto-optical disk comprising the recording medium and applying an external magnetic field to the position on the disk onto which the light beam is projected or focused. An overwrite system, involving magnetic field modulation recording using a magnetic head capable of reduced magnetic field switching time, has been proposed as one method of reducing the data storage time.
As the recording density of the above-described magneto-optical disk increases it becomes increasingly necessary to position the light beam and magnetic field accurately so as to reduce data storage time.
FIG. 1
is a diagram showing the structure of an essential part of a conventional magneto-optical disk device. As shown in the diagram, the conventional magneto-optical disk device comprises a light source
2
provided on an optical head
1
. Light emitted from the light source
2
is emitted from the optical head
1
and supplied to a reflecting mirror
3
.
The reflecting mirror
3
deflects the light supplied from the optical head
1
at an angle of 90°. An objective lens
4
focuses the light supplied from the reflecting mirror
3
on a magneto-optical disk
5
.
The objective lens
4
is supported by a lens holder
6
. The lens holder
6
is movably supported by an actuator (not shown in the diagram) so as to be movable in a focusing direction (arrow A) and a tracking direction, that is, in a direction of a radius of the magneto-optical disk
5
(arrow B).
A magnetic head
7
is provided on a side opposite the objective lens
4
, with the magneto-optical disk
5
positioned between the magnetic head
7
and the objective lens
4
. The magnetic head
7
is attached to a suspension arm
8
and the suspension arm is attached to a carriage
9
. The carriage
9
is movably supported by an actuator (not shown in the diagram) so as to be movable in the direction of the radius of the magneto-optical disk
5
(arrow B).
It should be noted that, because the magnetic head
7
is fixedly mounted on the carriage
9
, the relative positions of the objective lens
4
and the magnetic head
7
, that is, the positions of the objective lens
4
and the magnetic head
7
with respect to each other, do not change even when the carriage
9
is moved.
It should also be noted that the carriage
9
is fixed in such a way that a position of a spot
10
on the magneto-optical disk
5
on which the objective lens focuses light and a position of the magnetic head
7
are roughly identical with respect to a hypothetical horizontal plane parallel to the recording surface of the magneto-optical disk
5
.
In recent years, the size of the magnetic head
7
has been reduced in order to reduce the switching time of an external magnetic field. As a result, the effective range of the external magnetic field generated by passing an electric current through a coil of a magnetic head element within the magnetic head
7
has been narrowed drastically to approximately 100-200 &mgr;m. Given the narrowness of this effective range, even a slight misalignment of the light spot
10
and the magnetic head
7
results in an inability to generate an effective magnetic field for recording and playing back data.
For this reason, then, the positions of the light spot
10
and the magnetic head
7
are adjusted when the magnetic head
7
is mounted on the carriage
9
during manufacture. A description will now be given of one conventional method for adjusting the position of the light spot
10
and magnetic head
7
.
FIG.
2
(A) and
2
(B) are diagrams of the structure of an essential part of a conventional magneto-optical disk device. FIG.
2
(A) is a cross-sectional view of the magnetic head
7
and FIG.
2
(B) is a cross-sectional view of the optical system.
As shown in FIG.
2
(A), the magnetic head
7
comprises coils
11
and a magnetic pole portion
12
. The center magnetic pole
13
of the magnetic pole portion
12
is designed so that a surface of the center magnetic pole
13
opposing the magneto-optical disk
5
has a reflection factor that is greater than that of the adjacent magnetic poles
14
and the surrounding coils
11
.
As shown in FIG.
2
(B), when adjusting the positions of the light spot
10
and the magnetic head
7
a transparent substrate
15
having the same characteristics as those of a typical magneto-optical disk is positioned between the magnetic head
7
and the objective lens
4
. Light emitted from the light source passes through a beam splitter
16
and the objective lens
4
and is trained on the transparent substrate
15
. The light so trained on the transparent substrate
15
passes through the transparent substrate
15
and reaches the magnetic head
7
. The light that reaches the magnetic head
7
is trained on the magnetic pole portion
12
.
The light trained on the magnetic head
7
is reflected by the magnetic head
7
and supplied to the beam splitter
16
via the transparent substrate
15
and the objective lens
4
. The beam splitter
16
supplies the light reflected by the magnetic head
7
to a photodetector
17
. The photodetector
17
outputs an output signal in response to the amount of light reflected from the magnetic head
7
.
It should be noted that a reflecting layer is provided on the center magnetic pole
13
of the magnetic head
7
so that the center magnetic pole
13
has a reflection factor that is greater than that of adjacent members of the magnetic head
7
, and so the amount of light reflected is at a maximum amount at a center core
13
, that is, a center of the magnetic field generated at the magnetic head
7
.
FIG.
3
(A),
3
(B) and
3
(C) are diagrams for explaining the operation of the conventional position adjustment method, the structure of which has been described above. FIG.
3
(A) and FIG.
3
(C) show a state in which the center of the magnetic head
7
and the axis
18
of the light beam
10
do not match, while FIG.
3
(B) shows a state in which the center of the magnetic head
7
and the axis
18
of the light beam
10
do match.
FIG.
3
(A) shows a state of the center magnetic pole
13
of the magnetic head
7
deviating from the axis
18
of the light beam
10
in the direction of the arrow C
1
. In this state, the axis
18
of the light beam
10
is trained not on the reflecting layer of the center magnetic pole
13
of the magnetic head
7
but on an adjacent area of the magnetic head
7
. As a result, the amount of light reflected decreases and, accordingly, the output of the photodetector
17
also decreases.
Similarly, FIG.
3
(C) shows a state of the center magnetic pole
13
of the magnetic head
7
deviating from the axis
18
of the light beam
10
in the direction of the arrow C
2
. As with the state shown in FIG.
3
(
a
) described above, in this state, too, the axis
18
of the light beam
10
is trained not on the reflecting layer of the center magnetic pole
13
of the magnetic head
7
but on an adjacent area of the magnetic head
7
. As a result, the amount of light reflected decreases and, accordingly, the output of the photodetector
17
also decreases.
FIG.
3
(B) shows a state in which the magnetic head
7
and the axis
18
of the light beam
10
do match. In this state, the axis
18
of the light beam
10
is aligned with the center magnetic pole
13
of the magnetic head
7
and, thus, the amount of light reflected is at a maximum amount.
FIG. 4
is a diagram showing the relation between the amount of light reflected and the misalignments of the axis
1

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