Compatible optical pickup

Details Compatible optical pickup Compatible optical pickup

2000-03-29

2003-04-22

Tran, Thang V. (Department: 2653)

Dynamic information storage or retrieval

With servo positioning of transducer assembly over track...

Optical servo system

Reexamination Certificate

active

06552974

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to optical pickups capable of adopting disc type recording media having different formats, and more particularly, to a compatible optical pickup for a compact disc rewritable (CD-RW), a member of the CD family media, and a digital video disc read only memory (DVD-ROM).
2. Description of the Related Art
Recently, the need for an optical pickup capable of recording and/or reproducing information on and/or from a DVD at a high density be compatible with CD family media such as CD, recordable CD (CD-R), CD-RW, CD interactive (CD-I) and CD plus graphics (CD+G) has arisen.
The standard thickness of existing CD family media is 1.2 mm, whereas the thickness of DVDs has been standardized to 0.6 mm in consideration of the allowable error in the tilt angle of a disc and the numerical aperture (NA) of an objective lens. Accordingly, when recording or reproducing information on or from a CD using an optical pickup for DVDs, spherical aberrations occur due to a difference in the thicknesses therebetween. Such spherical aberration cannot provide a light intensity sufficient for recording an information (radio frequency) signal or may deteriorate the signal reproduced from the CD. Also, DVDs and CD family media utilize different wavelengths of light for reproduction: CDs use light having a wavelength of about 780 nm as a light source for reproduction, whereas DVDs use light having a wavelength of about 650 nm as a light source therefor. Thus, for the compatibility with CDs, an optical pickup adopting a light source capable of emitting different wavelengths of light, and a structure in which optical spots can be formed at different focal positions is required.
Referring to
FIG. 1
, a conventional compatible optical pickup comprises a first light source
21
for emitting light having a wavelength of about 650 nm and a second light source
31
for emitting light having a wavelength of about 780 nm. The first light source
21
is appropriate for a DVD
10
a
, which is a relatively thin disc, and the second light source
31
is appropriate for a CD
10
b
, which is a relatively thick disc. The first and second light sources
21
and
31
are selectively driven according to the type of adopted optical disc, a DVD or a CD.
Light emitted from the first light source
21
is condensed by a first collimator lens
23
, parallel incident onto a first polarization beam splitter (PBS)
25
, and then reflected by the first PBS
25
toward the DVD
10
a
. After reflected by the DVD
10
a
, the reflected light is transmitted through the first PBS
25
and is then received by a first photodetector
27
. Here, an interference filter
41
for changing the paths of light emitted from the first and second light sources
21
and
31
, a ¼-wavelength plate
43
for delaying the phase of light incident thereto to change the polarization characteristic, a variable diaphragm
45
, and an objective lens
47
for condensing light incident thereto are situated on an optical path between the first PBS
25
and the disc
10
.
Light emitted from the second light source
31
is condensed by a second collimator lens
33
, parallel incident onto a second PBS
35
, transmitted through a condenser lens
37
, and then incident onto the interference filter
41
. The light is reflected by the interference filter
41
and passes through the ¼-wavelength plate
43
, the variable diaphragm
45
and the objective lens
47
in sequence to form an optical spot on the CD
10
b.
Light reflected by the CD
10
b
is incident onto the interference filter
41
through the objective lens
47
, the variable diaphragm
45
and the ¼-wavelength plate
43
, and then reflected by the interference filter
41
heading toward the second PBS
35
. The light is reflected by the second PBS
35
and received by a second photodetector
39
.
The interference filter
41
, an optical element for transmitting or reflecting incident light depending on the wavelength of the incident light, transmits the light emitted from the first light source
21
and reflects the light emitted from the second light source
31
.
Referring to
FIG. 2
, the variable diaphragm
45
comprises a first region
45
a
, which is variable in size, and a second region
45
b
bounding the first region
45
a
, and selectively transmits the light incident onto a region of the objective lens
27
having a NA of 0.6 or less. The first region
45
a
, which corresponds to a region of the objective lens
47
having a NA of 0.45 or less, completely transmits the light emitted from the first and second light sources
21
and
31
. The second region
45
b
, which corresponds to a region of the objective lens having a NA of 0.45 to 0.6, completely transmits light having a wavelength of 650 nm and completely reflects light having a wavelength of 780 nm.
In the conventional compatible optical pickup, the variable diaphragm completely reflects the light for recording on a CD-R, which is emitted from the second light source and incident onto a region having a NA of 0.45 or more, and thus it cannot be applied to an optical pickup for CD-RWs, which requires a NA of 0.5 or more and high optical efficiency for recording. Also, the need for the variable diaphragm having first and second regions, which is manufactured through sophisticated and expensive processes makes assembling of such optical pickup complicates and increases the manufacturing cost.
SUMMARY OF THE INVENTION
It is an object of the present invention is to provide a compatible optical pickup capable of reproducing information from a digital video disc read only memory (DVD-ROM), in addition to writing or reproducing information on or from a compact disc rewritables (CD-RWs), which ensures output of a wavelength of 780 nm with a high optical power, and a high numerical aperture (NA) of approximately 0.5 or more.
To achieve the above object, the present invention provides a compatible optical pickup comprising: a first light source for emitting a first light having a predetermined wavelength; a second light source for emitting a second light having a long wavelength relative to the first light; an optical path changing means for changing the traveling path of an incident light; an objective lens for condensing the first and second lights onto optical discs having different thicknesses, respectively; and a main photodetector for detecting an information signal and error signals from the first and second lights which have been reflected by the optical discs and passed through the optical path changing means, wherein the optical path changing means includes a planar first beam splitter disposed on the optical path between the first light source and the objective lens, for changing the traveling path of the first light from the first light source, and a planar second beam splitter disposed on the optical path between the first beam splitter and the objective lens, for changing the optical paths of the first and second lights, and the main photodetector comprises a first photodetector having four divided regions, a second photodetector having two divided regions, and a third photodetector having two divided regions, the second and third photodetectors being disposed at both sides of the first photodetector.


REFERENCES:
patent: 4733065 (1988-03-01), Hoshi et al.
patent: 5703856 (1997-12-01), Hayashi et al.
patent: 5910938 (1999-06-01), Kimura
patent: 5933401 (1999-08-01), Lee et al.
patent: 5974020 (1999-10-01), Ju et al.
patent: 6031667 (2000-02-01), Sugiura et al.
patent: 0 776 003 (1997-05-01), None
patent: 0 855 701 (1998-07-01), None
patent: 4-117637 (1992-04-01), None
patent: 7-272303 (1996-10-01), None
patent: 10-79138 (1998-03-01), None
patent: 10-269607 (1998-10-01), None
patent: 10-269608 (1998-10-01), None
patent: 10-302289 (1998-11-01), None

Affiliated with

Also associated with

Rating

Compatible optical pickup does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Compatible optical pickup, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Compatible optical pickup will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3088924