Optical pick-up device

Details Optical pick-up device Optical pick-up device

2001-08-31

2003-04-01

Schwartz, Jordan M. (Department: 2873)

Optical: systems and elements

Lens

With reflecting element

C369S112010

Reexamination Certificate

active

06542315

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an optical pick-up device, and more particularly, to an optical pick-up device constructed so as to reflect and focus light from a light emitting unit onto a storage surface of a storage medium.
2. Description of the Related Art
Optical pick-up devices exist for reading and/or writing information to and from a disk-like rotating storage medium such as, for example, a CD-ROM. The advantages of optical storage and retrieval systems over other types of information storage and retrieval systems have spurred efforts to make such optical pick-up devices slim enough to be incorporated in portable information storage devices, most notably the popular laptop-type personal computer.
An optical pick-up device as described in Japanese Laid-Open Patent Application No. 5-120723 represents a conventional way to reduce the thickness of such optical pick-up devices.
FIG. 1
is a schematic diagram of an optical system of the conventional optical pick-up device as described in Japanese Laid-Open Patent Application No. 5-120723, a printed publication.
As shown in
FIG. 1
, a read-only optical pick-up device
1
has a light emitting unit
3
that directs a laser beam onto a storage surface
2
a
of an optical disk storage medium
2
and that picks up the light reflected from the storage surface
2
a
, a reflecting member (that is, a mirror)
4
tilted at an angle &thgr;
0
with respect to a hypothetical horizontal plane, and a focusing member (that is, an object lens)
5
that focuses the light from the reflecting mirror
4
onto the storage surface
2
a
of the optical disk storage medium
2
. The laser unit
3
that forms a light emitting unit is mounted in a tilted state, at an angle such that a central axis of light L
1
of the light emitted from the laser unit
3
and a central axis of light L
2
of the light reflected toward the optical disk storage medium
2
together form an angle that is less than 90 degrees.
In such a configuration of the optical pick-up device
1
, a distance H
0
between the storage surface
2
a
of the optical disk storage medium
2
and a hypothetical horizontal plane formed by a bottom surface of the reflecting mirror
4
can be reduced and thus the thickness of the optical pick-up device can be reduced, because the position at which the laser unit
3
is mounted is above the hypothetical horizontal plane formed by the bottom surface of the reflecting mirror
4
. Even with such a configuration it is still possible to maintain a minimum safe separation distance d between the upper edge of the laser unit
3
and the optical disk storage medium
2
, so that there is no danger that the optical disk storage medium
2
will contact an upper edge of the laser unit
3
. It should be noted that the above-described distance d is a distance at which there is no danger that the optical disk storage medium
2
will contact the upper edge of the laser unit
3
when the optical disk storage medium
2
is rotatably driven even if there is unevenness in the rotation of the optical disk storage medium
2
.
FIG. 2
is a schematic diagram of the optical system of a conventional read-write optical pick-up device.
As shown in
FIG. 2
, a read-write optical pick-up device
6
interposes a collimator lens
7
between the laser unit
3
and the reflecting mirror
4
. The collimator lens
7
refracts the light emitted from the laser unit
3
, changing it into parallel rays, such that the parallel rays of light are directed toward the reflecting mirror
4
. In such a read-write optical pick-up device
6
, the laser unit
3
is mounted at an angle such that an angle formed by an axis L
1
of the light emitted from the laser unit
3
and an axis L
2
of the laser beam reflected onto the optical disk storage medium
2
by the reflecting mirror
4
form an angle of less than 90 degrees.
As a result, as with the optical pick-up device
1
noted previously, in such a configuration of the optical pick-up device
6
as described above, the distance H
0
between the storage surface
2
a
of the optical disk storage medium
2
and a hypothetical horizontal plane formed by the bottom surface of the reflecting mirror
4
and a bottom surface of the collimator lens
7
can be reduced and thus the thickness of the optical pick-up device can be reduced, because the position at which the laser unit
3
is mounted is above the hypothetical horizontal plane formed by the bottom surface of the reflecting mirror
4
and the bottom surface of the collimator lens
7
. Even with such a configuration it is still possible to maintain the minimum safe separation distance d between the upper edge of the laser unit
3
and the optical disk
2
, so that there is no danger that the optical disk storage medium
2
will contact an upper edge of the laser unit
3
.
In order to facilitate an understanding of the present invention, a description will now be given of the light emitting unit used to generate the laser beam in an optical pick-up device.
FIG. 3
is an enlarged front view of a conventional light emitting unit.
As shown in
FIG. 3
, a laser unit
3
is composed of an integrated circuit (IC) chip, with a plurality of input/output terminals
8
a
projecting outward from both lateral surfaces of a unit package
8
. A laser diode
9
, a reflecting mirror
10
that reflects light emitted from the laser diode
9
at a right angle, and a pair of photodiodes
11
that detect the light reflected from the storage surface of the optical disk storage medium
2
are mounted atop a substrate
8
c
of the unit package
8
. The photodiodes
11
convert the light reflected from the storage surface of the optical disk storage medium
2
into electrical signals.
Additionally, the laser unit
3
is configured so that the mirror
10
is provided at a center of the unit package
8
. Accordingly, a point of emission of the light emitted from the laser unit
3
coincides with a hypothetical perpendicular line passing through the center position of the mirror
10
.
FIG. 4
is a schematic diagram of a conventional optical system, illustrating a conventional solution to the problem of how to reduce the thickness of a read-only optical pick-up device.
FIG. 5
is a schematic diagram of a conventional optical system, illustrating a conventional solution to the problem of how to reduce the thickness of a read-write optical pick-up device.
As shown in FIG.
4
and
FIG. 5
, the conventional solution to the problem of how to reduce the thickness of the optical pick-up devices described above is to mount the laser unit
3
in a tilted state and to reduce the angles of inclination &thgr;
0
, &thgr;
1
′ of the reflecting mirror
4
to smaller angles &thgr;
0
′, &thgr;
1
′, thus allowing the distance (that is, the thickness of the optical system) H
0
, H
1
to be reduced to H
0
′, H
1
′.
It should be noted the read-write optical pick-up device
6
described above, for example, specific values for the angles and distances involved are as follows:
&thgr;
0
′=43.6 degrees;
&thgr;
1
′=42.788 degrees;
H
0
′=7.46 mm; and
H
1
′=7.36 mm,
with the result that the thickness of the device can be reduced by approximately 0.1 mm.
However, there is a problem with the conventional solution, in that the minimum safe separation distance d between an upper edge
8
b
of the unit package
8
of the laser unit
3
and the optical disk storage medium
2
cannot be maintained, because the mirror
10
which reflects the light from the laser unit
3
onto the storage surface
2
a
of the optical disk storage medium
2
is positioned at the center of the unit package
8
of the laser unit
3
.
As a result, there is a danger that the optical disk storage medium
2
will contact the upper edge
8
b
of the laser unit
3
, and accordingly, there is a limit to the extent to which the thickness of the optical pick-up device can be reduced in the conventional art.
SUMMARY OF THE INVENTION
Accordingly, it

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