Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
2001-05-24
2004-11-09
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
C369S121000
Reexamination Certificate
active
06816450
ABSTRACT:
The present disclosure relates to the subject matter contained in Japanese Patent Application No. 2000-155358 filed May 25, 2000, which is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical pickup apparatus enabling to read two or more kinds of recording medium, which are different in read wavelength, such as a compatible optical pickup apparatus for DVD/CD and the like. Particularly, the present invention relates to an optical pickup apparatus using a semiconductor laser element formed of a one-chip laser diode emitting two laser beams, which are different in wavelength from each other.
2. Description of the Related Art
Conventionally, a DVD/CD compatible reproducing apparatus sharing an optical pickup for a CD reproducing apparatus and a DVD reproducing apparatus has actively been proposed, and there are a DVD/CD compatible reproducing apparatus using a one-wavelength/bifocal optical pickup and a DVD/CD compatible reproducing apparatus using a two-wavelengths/bifocal optical pickup.
When a CD is compared with a DVD, a thickness of a protective layer of the DVD is about one-half (0.6 mm) that of a protective layer of the CD. Thus, in case of reproducing both of optical disks using a unifocal optical pickup, when a light beam is gathered so as to achieve optimization to an information record surface of the DVD, the protective layer of the CD, through which the light beam passes, is thicker than that of the DVD, therefore, aberration such as spherical aberration and the like occurs in the light beam so that the light beam cannot be gathered optimally to an information record surface of the CD. Also, since the CD is different from the DVD in a size of information pits formed for recording, it is necessary to form a beam spot with optimum size to the respective information pits on the information record surface of the CD or the DVD in order to exactly read the respective information pits.
Also, a size of the beam spot is proportional to a ratio of a wavelength of the light beam to a numerical aperture of an objective lens for gathering the light beam to the information record surface. That is, when it is assumed that a wavelength of the light beam is constant, the beam spot becomes smaller as the numerical aperture becomes larger. Accordingly, in the case of reproducing the CD and the DVD by the unifocal optical pickup, when it is constructed so that a wavelength of the light beam is constant and the numerical aperture is adapted for, for example, the information pits of the DVD, the beam spot becomes too small with respect to the information pits of the CD and distortion occurs in a reproduction signal on reproducing the CD and an exact reading becomes difficult. Hence, a DVD/CD compatible reproducing apparatus using a bifocal optical pickup enabling to focus at different positions on the same straight line and applying two laser beams for forming a beam spot with a proper size in correspondence with a size of each information pit has become the mainstream.
For example, an optical pickup apparatus shown in
FIG. 13
is a DVD/CD compatible reproducing apparatus in which an optical path of a light beam emitted from a first light source
10
for CD and an optical path of a light beam emitted from a second light source
15
for DVD are mixed by a first beam splitter
13
acting as a prism to apply any one of two light beams emitted from the two light source, respectively, to a bifocal lens comprising an objective lens and a diffraction element, and a configuration and operation will be described briefly.
In
FIG. 13
, the first light source
10
generates a laser beam (shown by a broken line) with a wavelength (780 nm) most suitable for an information reading from a CD according to a driving signal from a first driving circuit
11
, and the laser beam is applied to the first beam splitter
13
through a grating
12
for generating three beams. The first beam splitter
13
reflects the laser beam emitted from the first light source
10
and guides the reflected light to a second beam splitter
14
.
On the other hand, the second light source
15
placed at a 90° with respect to the first light source
10
generates a laser beam (shown by a solid line) with a wavelength (650 nm) most suitable for an information reading from a DVD according to a driving signal from a second driving circuit
16
, and the laser beam is applied to the first beam splitter
13
through a grating
17
. The first beam splitter
13
transmits the laser beam emitted from the second light source
15
and guides the laser beam to the second beam splitter
14
.
The second beam splitter
14
guides the laser beam supplied through the first beam splitter
13
, namely the laser beam emitted from the first light source
10
or the second light source
15
to a bifocal lens
19
through a collimator lens
18
. The bifocal lens
19
gathers the laser beam from the second beam splitter
14
at one point to be information reading light beam and the information reading light beam is applied to an information record surface of an optical disk
21
rotated and driven by a spindle motor
20
.
The laser beam emitted from the first light source
10
(shown by a broken line) is gathered by the bifocal lens
19
to focus on an information record surface C of the optical disk
21
. Also, the laser beam emitted from the second light source
15
(shown by a solid line) is gathered by the bifocal lens
19
to focus on an information record surface D of the optical disk
21
.
The reflected light occurring by applying the information reading light beam from the bifocal lens
19
to the optical disk
21
passes through the bifocal lens
19
and the collimator lens
18
, is reflected at the second beam splitter
14
, passes through a cylindrical lens
22
, which is an astigmatism generation element, and is applied to a photodetector
23
. The photodetector
23
generates a signal having a level corresponding to light intensity of the applied light and supplies the signal to an information data reproducing circuit
24
and a disk determination circuit
25
as a reading signal.
The information data reproducing circuit
24
generates a digital signal based on the obtained reading signal and further performs demodulation and error correction to the digital signal to reproduce information data. The disk determination circuit
25
identifies a kind of the optical disk
21
based on a size of a beam spot formed at the time of applying a laser beam to the optical disk
21
and supplies the kind to a controller
26
as disclosed in, for example, Japanese Unexamined Patent Application No. Hei. 10-255274 by the present applicant. According to a disk identification signal, the controller
26
drives and controls any one of the first driving circuit
11
and the second driving circuit
16
selectively in a drive state. The controller
26
drives only the first driving circuit
11
when a disk identification signal indicating a CD is obtained from the disk determination circuit
25
. Therefore, the laser beam emitted from the first light source
10
is applied to the optical disk
21
through an optical system comprising the grating
12
, the first beam splitter
13
, the second beam splitter
14
, the collimator lens
18
, and the bifocal lens
19
. Then, the reflected light (return light) reflected at the information record surface of the optical disk
21
passes through the bifocal lens
19
and the collimator lens
18
, and is reflected at the second beam splitter
14
, and passes through the cylindrical lens
22
, and is applied to the photodetector
23
.
Also, the controller
26
drives only the second driving circuit
16
when a disk identification signal indicating a DVD is obtained from the disk determination circuit
25
. Therefore, the laser beam emitted from the second light source
15
is applied to the optical disk
21
through an optical system comprising the grating
17
, the first beam splitter
13
, the second beam splitter
14
, the coll
Miura Akira
Suzuki Yoshiharu
Huber Paul W.
Pioneer Corporation
Sughrue & Mion, PLLC
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