Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
2000-09-28
2003-05-06
Huber, Paul W. (Department: 2653)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S120000, C369S121000
Reexamination Certificate
active
06560188
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a compound optical unit as a combination light receiving/emitting optical element suitably used in an optical device, such as an optical pickup, which applies light onto an optical disk and receives returned light from the optical disk in order to perform writing or reading of information on the optical disk.
2. Description of the Related Art
As an example of compound optical units, a combination light receiving/emitting optical element has been proposed and used which applies laser beam onto an optical disk or which receives laser beam from the optical disk in order to perform recording or reproduction of information on the optical disk.
To write information on an optical disk, such as a CD (compact disk), a CD-R (write-once compact disk), or a DVD (“digital versatile disk” or “digital video disk”), or to read information on an information-recording surface of the optical disk, an optical pickup is used, and an optical unit is mounted on the optical pickup.
When various types of optical components are mounted on the optical pickup, positions or angles of the optical components with respect to the optical pickup are adjusted so as to optimally perform writing or reading of information on the-optical disk. In this case, in an optical unit having a combination of a light receiving section and a light emitting section, the relationship between light receiving position and a light emitting position is not changed even by the adjustment. Therefore, wide allowable ranges of the positions and the angles of the optical components can be ensured, and the positions and the angles can be easily adjusted. Such an optical unit has been widely used. In order to reduce the size of the optical pickup, an optical unit has been developed of reduced size.
In recent years, DVD apparatuses for writing/reading information on a DVD, which is an optical disk having a higher recording density than a CD, have been commercialized, and reduction in cost of the DVD apparatuses is essential in order for the DVD apparatuses to become more popular. Accordingly, a reduction in cost of an optical unit used in an optical pickup to be mounted on the DVD apparatuses has been demanded.
In addition, compatibility with CDs (including CD-Rs) has been demanded for the DVD apparatuses. Therefore, the DVD apparatuses should include a laser light source (with a wavelength of 650 nm) for a DVD, and a laser light source (with a wavelength of 780 nm) for writing and reading information on the CD-R which cannot be read by a laser light source with a wavelength of 650 nm.
FIG. 5
is a plan view showing an optical pickup
20
having conventional optical units
4
and
8
mounted thereon. The optical pickup
20
is primarily composed of the optical unit
4
for a DVD (high-density optical disk)
17
, the optical unit
8
for a CD (low-density optical disk)
18
, a beam splitter
10
for guiding laser beams of various wavelengths, emitted from the optical units
4
and
8
, to the same optical axis, a wavelength filter
15
serving as a diaphragm for restricting the diameter of the laser beam in accordance with the wavelength of the laser beam, an objective lens
16
, and a carriage
21
for disposing the above components at predetermined positions so as to be able to read information from both the DVD
17
and CD
18
.
The above components will now be described in detail.
The optical unit
4
is composed of a light source
2
, which is a laser diode chip for emitting laser beam of a wavelength of 650 nm for the DVD
17
; a light-receiving element
3
consisting of a photo-diode serving as a light receiving member for receiving laser beam reflected by the DVD
17
; a base plate
4
a
having the light source
2
and the light-receiving element
3
, a side wall
4
b
fixed to the base plate
4
a
contains the light source
2
and the light-receiving element
3
; an emergent section
4
d
that is a window in the side wall
4
b
; and a highly transmissive optical member
5
, such as glass, bonded to cover the emergent section
4
d
. The light source
2
is fixed on the base plate
4
a
so as to oppose the optical member
5
, and the light-receiving element
3
is formed on the surface of the base plate
4
a
in close proximity to the light source
2
. In addition, laser beam (returned light) emitted from the light source
2
and reflected by the DVD
17
is diffracted by a diffraction grating
5
a
formed on the optical member
5
so as to be guided to a predetermined position of the light-receiving element
3
. Since a sufficiently large diffraction angle of the returned light diffracted by the diffraction grating
5
a
is not obtained because narrowing of the pitch of the diffraction grating
5
a
is limited (the narrower the pitch of the grating, the larger the diffraction angle obtained), the light-receiving element
3
is formed in close proximity to the light source
2
. The optical member
5
is fixed to the emergent section
4
d
after the position thereof has been adjusted so that the light diffracted by the diffraction grating
5
a
is guided to a predetermined position of the light-receiving element
3
by a predetermined reference optical system.
The optical unit
8
is composed of a light source
6
that is a laser diode chip for emitting laser light of a wavelength of 780 nm for the CD
18
; a light-receiving element
7
consisting of a photo-diode for receiving laser beam reflected by the CD
18
; a base plate
8
a
having the light source
6
and the light-receiving element
7
, a side wall
8
b
fixed to the base plate
8
a
to contain the light source
6
and the light-receiving element
7
; an emergent section
8
d
that is a window in the side wall
8
b
; and a highly transmissive optical member
9
, such as glass, bonded to cover the emergent section
8
d
. The light source
6
is fixed on the base plate
8
a
so as to oppose the optical member
9
, and the light-receiving element
7
is formed on the surface of the base plate
8
a
in close proximity to the light source
6
. Returned light emitted from the light source
6
and reflected by the CD
18
is diffracted by a diffraction grating
9
a
formed on the optical member
9
so as to be guided to a predetermined position of the light-receiving element
7
.
The light-receiving element
7
is formed in close proximity to the light source
6
for the same reason as for the optical unit
4
. In order to effect tracking control by a three-beam method, the optical member
9
is provided with a beam formation section
9
b
. The optical member
9
is fixed to the emergent section
8
d
after the position thereof has been adjusted so that the light diffracted by the diffraction grating
9
a
is guided to a predetermined position of the light-receiving element
7
by a predetermined reference optical system.
The beam splitter
10
guides both laser beams from the light source
2
and the light source
6
to the DVD
17
(CD
18
). The beam splitter
10
is shaped like a rectangular parallelepiped in which two prisms are bonded to each other, and a bonding surface is coated with an optical film (dichroic film) having a wavelength selecting function. The dichroic film is formed so as to transmit the laser beam for the CD
18
and to reflect the laser beam for the DVD
17
.
The wavelength filter
15
is formed so as to transmit the laser beam emitted from the light source
2
, and to reflect or absorb the laser light emitted from the light source
6
, thereby restricting diameters of laser beams emitted from the light source
2
and the light source
6
. Therefore, when spots of laser beams emitted from the light sources
2
and
6
and condensed by the objective lens
16
are applied onto the DVD
17
and CD
18
, respectively, aberration is reduced.
Dispositions of the optical units
4
and
8
, and reading of information of the DVD
17
and CD
18
will now be described in detail.
The optical unit
4
and the optical unit
8
are disposed to form an angle of about 90° starting from
Kyoya Shoichi
Yamashita Tatsumaro
Alps Electric Co. ,Ltd.
Huber Paul W.
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