Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
1998-06-08
2001-03-27
Huber, Paul W. (Department: 2651)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S112030
Reexamination Certificate
active
06208610
ABSTRACT:
TECHNICAL FIELD
This invention relates to an optical pickup device for writing or reading out information signals on or from an optical recording medium, as a recording medium for information signals, such as an optical disc.
BACKGROUND ART
Up to now, a device configured as shown in
FIG. 1
is used as an optical pickup device for reading out information signals recorded on an optical disc, such as a magneto-optical disc.
This optical pickup device includes a semiconductor laser
2
for radiating a light beam L
1
illuminated on an optical disc
1
and an objective lens
3
for converging the light beam L
1
outgoing from the semiconductor laser
2
for illumination on the optical disc
1
, as shown in FIG.
1
.
On the light path of the light beam L
1
from the semiconductor laser
22
to the objective lens
3
is a grating
4
disposed towards the semiconductor laser
2
for splitting the light beam L
1
outgoing from the semiconductor laser
2
into at least three diffracted light beams, namely a zero-order light beam and ±1 order light beams, as shown in
FIGS. 1 and 2
.
It is noted that, in
FIGS. 1 and 2
, the three diffracted light beams are represented as a sole light beam and these three diffracted light beams are referred to simply as a light beam in keeping with the drawing.
On the light path from the grating
4
to the objective lens
3
are disposed a beam splitter
5
and a reflective mirror
6
. The beam splitter
5
splits the light beam L
1
outgoing from the semiconductor laser
2
from a light beam L
2
reflected by the optical disc
1
to fall on the beam splitter
5
via objective lens
3
, while the reflective mirror
6
causes the light beam L
1
transmitted through the beam splitter
5
to be deflected 90° to fall on the objective lens
3
while causing the light beam L
2
reflected by the optical disc
1
and transmitted through the objective lens
3
to be deflected 90° to fall on the beam splitter
5
.
The optical pickup device includes a photodetector
7
for detecting the return light beam L
2
reflected back from the optical disc
1
to read out the information signals recorded on the disc and for detecting focusing error signals and tracking error signals. The photodetector is comprised of a light detecting element, such as a photodiode. This photodetector
7
is arranged facing the beam splitter
5
at a position perpendicular to the light path from the semiconductor laser
2
to the objective lens
3
for detecting the return light beam L
2
the light path of which has been modified 90° by being reflected back by a boundary surface
5
a
of the beam splitter
5
. Meanwhile, the boundary surface
5
a
of the beam splitter
5
is inclined 45° relative to the optical axis of the light beam incident on the beam splitter
5
for modifying the light path of the light beam incident on the beam splitter
5
by 90°.
In the light path from the beam splitter
5
to the photodetector
7
are arranged a Wollaston prism
8
for detecting the Kerr rotation angle of the return light beam L
2
reflected by the optical disc
1
and a cylindrical lens
9
for producing astigmatic aberration in the return light beam L
2
. The Wollaston prism
8
is mounted as-one with the beam splitter
5
.
The present optical pickup device has a photodiode
10
for detecting part of the light beam L
1
radiated from the front side of the semiconductor laser
2
for controlling the semiconductor laser
2
to render the output level of the light beam radiated from the semiconductor laser
2
substantially constant. This photodiode
10
is arranged facing the beam splitter
5
at a position perpendicular to the light path from the semiconductor laser
2
to the objective lens
3
for detecting a portion of the light beam L
1
from the semiconductor laser
2
having its light path changed 90° by being reflected back by a boundary surface
5
a
of the beam splitter
5
.
The detection output of the photodiode
10
is supplied to an automatic output control circuit
12
configured for controlling the intensity of the driving current supplied from a driving source
11
configured for driving the semiconductor laser
2
. The automatic output control circuit
12
is responsive to a detection output of the photodiode
10
to control the driving current supplied from the driving source
11
so that the semiconductor laser
2
will radiate the light beam L
1
of a constant output level.
Meanwhile, since the return light beam L
2
incident on the photodetector
7
and a portion L
3
of the light beam L
1
radiated from the semiconductor laser
2
to fall on the photodiode
10
are changed in light paths by being reflected by the common boundary surface
5
a
of the sole beam splitter
5
, the photodetector
7
and the photodiode
10
are arranged facing each other on both sides of the beam splitter
5
as shown in FIG.
2
.
In the above-described optical pickup device, if the driving current is supplied from the driving source
11
for driving the semiconductor laser
2
, the light beam L
1
is radiated from the semiconductor laser
2
. The light beam L
1
radiated from the front side of the semiconductor laser
2
is split by the grating
4
into at least three diffracted light beams to fall on the beam splitter
5
. The portion L
3
of the light beam L
1
from the semiconductor laser
2
, having its light path changed 90° by the boundary surface
5
a
of the beam splitter
5
, is received by the photodiode
10
whereby the intensity of the portion L
3
of the light beam
1
is converted to an electrical signal which is detected. This detection output is supplied to an output control circuit
12
for controlling the driving current supplied from the driving source
11
to the semiconductor laser
2
for controlling the driving of the semiconductor laser
2
for providing a constant output level of the light beam L
1
radiated from the semiconductor laser
2
.
The light beam L
1
, transmitted through the beam splitter
5
without being reflected by the boundary surface
5
a
of the beam splitter
5
, falls on the reflective mirror
6
so as to be thereby changed in light path by 90° to then fall on the objective lens
3
. The light beam L
1
, reflected by the reflective mirror
6
, is converged by the objective lens
3
on the signal recording surface of the optical disc
1
. The light beam L
2
, reflected by the signal recording surface of the optical disc
1
, again falls via objective lens
3
on the reflective mirror
6
so as to be thereby re-converted in light path by 90°. The light beam L
2
, the light path of which has been changed by 90° by the reflective mirror
6
, falls on the beam splitter
5
to be then reflected by 90° by the boundary surface
5
a
. The light beam L
2
, reflected by 90° by the reflective mirror
6
, falls on the Wollaston prism
8
for detecting the Kerr effect so as to be then received via cylindrical lens
9
by the photodetector
7
.
Due to the cylindrical lens
9
, the light beam L
2
reflected by 90° by the boundary surface
5
a
undergoes astigmatic aberration depending on changes in the distance between the objective lens
3
and the signal recording surface of the optical disc
1
. The result is that the spot shape is changed on the light receiving surface of the photodetector
7
depending on changes in the distance between the signal recording surface of the optical disc
1
and the objective lens
3
, so that focusing error signals are produced based on an output signal of the photodetector
7
. On the other hand, each spot corresponding to the ±one order diffracted light on the light receiving surface of the photodetector
7
is moved depending on how much the light spot of each of the ±one order diffracted light beams on both sides of the spot of the zero order diffracted light beam radiated on the signal recording surface of the optical disc
1
is shifted relative to the recording track of the optical disc
1
. The result is that the output signal of the photodetector
7
is changed so that the tracking error signals can be ge
Kanada Tokio
Kawakami Takashi
Huber Paul W.
Limbach & Limbach L.L.P.
Sony Corporation
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