Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
1999-12-22
2002-05-28
Tran, Thang V. (Department: 2653)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S112210, C369S094000
Reexamination Certificate
active
06396791
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical pick-up apparatus for recording and reading an optical disc, which is different in an substrate thickness and a wavelength to be used.
2. Description of the Prior Art
Conventionally, in an optical disc being used at present, there are variations such as a CD, a CD-ROM and a DVD, and higher density optical disc has been developed. These informations to be recorded on optical discs have been recorded with a bit on the recording surface of an optical disc by forming a pit or a mark corresponding to the pit, it is adapted to determine the existence if any information by illuminating a light beam on the surface recorded with information and detecting the reflected light beam strength.
According to the kind of an optical disc, there is a difference in the pit shape or the shape of mark corresponding to the pit, recording system and the thickness of the substrate, in the case where reading of different kinds of discs is carried out, a light beam in accordance with the wavelength due to the kind of disc has to be illuminated. For example, to a CD and a CD-ROM (hereinafter referred to “standard density optical disc”) having the substrate thickness of 1.2 mm, a light source to emit a light beam having a wavelength of 780 nm band should be applied, and to a DVD (hereinafter, referred to “high density optical disc) having the substrate thickness of 0.6 mm, a light source to emit a light beam having a wavelength of 635-650 nm band should be applied.
For that purpose, in order to read different kinds of optical discs with a single optical pick-up apparatus, such pick-up apparatus comprises light sources having different wavelengths corresponding to each optical disc and an objective lens to condense a light beam on the recording layer of each disc.
However, it is a main trend that an optical pick-up apparatus comprises such constitution that is made to condense the light beam on the recording surface of different kinds of optical discs with a single objective lens in order to make it small-sized, light-weighted and low-cost.
A general constitution of such kind of an optical pic-up apparatus is shown in FIG.
11
and explained below.
FIG.
11
(
a
) shows a schematic drawing in the case where a high density optical disc
1
a
having a substrate thickness of 0.6 mm is read and FIG.
11
(
b
) shows a schematic drawing in the case where a standard density optical disc
1
b
having a substrate thickness of 1.2 mm is read.
Hereinafter, a constitution of an optical pick-up apparatus is explained referring to FIG.
11
(
a
).
On the light path of a light beam emitted from a first light source
2
corresponding to the high density optical disc
1
a
, from the close side to the first light source
2
are disposed, in turn, a wavelength selection mirror
3
, a beam splitter
4
, a collimator lens
5
and a raising mirror
6
, wherein the raising mirror
6
is disposed in such a manner as it opposes to the recording surface of the high density optical disc
1
a
. Between the high density optical disc
1
a
and the raising mirror
6
an actuator movable portion
7
is disposed. Here, a two-dotted chain line shows an axis A which connects the first light source
2
and the raising mirror
6
. And a position perpendicular to the axis A and opposing to the wavelength selection mirror
3
, a second laser light source
8
corresponding to the standard density optical disc
1
b
is disposed. Further, at a position perpendicular to the axis A and opposing to the beam splitter
4
, a wavelength selection mirror
9
and a cylindrical lens
10
are disposed, and at a position where the cylindrical lens
10
condenses on a first photo detector
11
which the light beam reflected on the recording surface of the high density optical disc
1
a
enters is disposed. And, at a position opposing to the wavelength mirror
9
, a cylindrical lens
12
and a second photo detector
13
are disposed in parallel with the axis A.
The wavelength selection mirror
3
and the wavelength selection mirror
9
are adapted to transmit the light beam emitted from the first light source
2
and to reflect the light beam emitted from the second light source
8
, and the beam splitter
4
transmits the light beams from the light sources
2
and
8
, and reflects the signal light beams reflected on the optical discs
1
a
and
1
b
to the photo detector
11
and
13
. The collimator lens
5
is adapted to convert the light beam into a parallel light beam, and the raising mirror
6
is adapted to reflect the light beam which is transmitted the collimator lens
5
toward the vertical direction and to enter the actuator movable portion
7
by changing the light progressing direction.
On the actuator movable portion
7
, an objective lens
14
and an opening limiting plate
15
are mounted, and the objective lens
14
is designed to have the most suitable opening diameter when the high density optical disc
1
a
is read. Since the opening limiting plate
15
is adapted to transmit the light beam emitted from the first light source
2
and has an aperture formed with a wavelength filter film
16
which cuts off the light beam emitted from the second light souce
8
, the diameter of the light beam emitted from the second light source
8
can be limited. Therefore, when this limited light beam is transmitted the objective lens
14
, the aperture is designed to have the most suitable opening diameter to read the standard density optical disc
1
b.
And the cylindrical lenses
10
and
12
are rod-like lens, and give an astigmatism the light beam which enters the first photo detector
11
and the second photo detector
13
. Further, the first photo detector
11
detects the signal light from the high density optical disc
1
a
and the second photo detector
13
detects the signal light from the standard density optical disc
1
b.
The thus-constituted optical pick-up apparatus of the high density optical disc
1
a
will be explained.
The light beam emitted from the first light source
2
is transmitted the wavelength selection mirror
3
and the beam splitter
4
and progresses in the collimator lens
5
and is converted into parallel light beams having an equally widened angle with each other. The converted parallel light beams progress toward the high density optical disc
1
a
with the raising mirror
6
and is transmitted the opening limiting plate
15
and are condensed most suitably on the recording surface of the high density optical disc
1
a
with the objective lens
14
.
And, the light beam reflected on the recording surface of the high density optical disc
1
a
becomes a signal light and traces the same path reversely, which, however, is branched toward the photo detector
11
through the beam splitter
4
. Further, by being transmitted the wavelength selection mirror
9
and the rear cylindrical lens
10
, the light beam is given with the astigmatism to be detected with the first photo detector
11
.
Next, the reading operation of the standard density optical disc
1
b
is explained referring to FIG.
11
(
b
).
The light beam emitted from second light source
8
is reflected on the wavelength selection mirror
3
, and is transmitted the beam splitter
4
and is converted into a parallel light beam with the collimator lens
5
. Then, the parallel light beam progresses toward the standard density optical disc
1
b
with the raising mirror
6
. Further, since the light beam is cut-off with the wavelength filter film
16
of the opening limiting plate
15
, the light beam of only a central portion can be transmitted the opening limiting plate
15
. The light beam thus limited in the beam diameter is condensed on the recording surface of the standard density optical disc
1
b
with the objective lens
14
.
And, the light beam reflected on the recording surface of the standard density optical disc
1
b
becomes a signal light, traces the same path reversely and is branched toward the photo detector
11
with the beam splitter
4
.
Further, the lig
Matsumoto Kozo
Wakao Sadayuki
Minebea Co. Ltd.
Tran Thang V.
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