Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
1999-10-07
2002-07-30
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
Reexamination Certificate
active
06426933
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an optical pickup apparatus used for recording and reproducing an optical disc, and more particularly to an optical pickup apparatus that is capable of eliminating the crosstalk component of a high density optical disc effectively.
2. Description of the Prior Art
Generally, an optical pickup apparatus irradiates a light on the recording surface of an optical disc to detect the reflected light, thereby performing the information recording and reproducing operation. To this end, the optical pickup apparatus is composed of a laser diode for emitting a light, an objective lens for focusing the emitted light on the recording surface of the disc, and other optical system required for concentrating and receiving the light.
An optical disc, such as a compact disc(CD) or a digital versatile disc(DVD) having more improved recording capacity, has been commercially available. This optical disc has more enlarged use for recording and reproducing audio and video data and computer data, etc. Recently, an optical disc having much more improved recording capacity is expected owing to the development of a blue laser generating a short wavelength of light. There have been suggested several schemes increasing the numerical aperture(NA) of an objective lens or narrowing the track pitch along with the use of a light source such as a blue laser, etc. so as to enlarge a recording capacity of the optical disc. However, it has a problem in that a crosstalk is caused between the adjacent tracks in the case of narrowing the track pitch of the optical disc.
More specifically, since an optical spot irradiated so as to reproduce a certain pit P
1
has a larger size than a width of the pit as shown in
FIG. 1
, it also is irradiated onto the pits in the adjacent tracks. As a result, a crosstalk component caused by the pits in the adjacent tracks is involved in the reproduced signal. A strategy employing a polarizing phase plate as shown in
FIG. 2
has been known as one of methods for eliminating such a crosstalk component.
FIG. 2
shows the conventional optical pickup apparatus for eliminating the crosstalk component. In
FIG. 2
, the optical pickup apparatus includes a light source
12
for generating a light beam, an objective lens
20
for focusing a light beam from the light source
12
on the recording surface of an optical disc
22
, first and second photo detectors
30
and
32
for converting a reflective light beam from the optical disc
22
into an electrical signal, a beam splitter
18
arranged among the light source
12
, the objective lens
20
and the first and second photo detectors
30
and
32
, a polarizing beam splitter(PBS)
26
arranged among the beam splitter
18
and the first and second photo detector
30
and
32
, a polarizing phase plate
16
arranged between the light source
12
and the beam splitter
18
, a first collimator lens
14
arranged between the polarizing phase plate
16
and the beam splitter
18
, a second collimator lens
24
arranged between the beam splitter
18
and the PSB
26
, and a sensor lens arranged between the PBS
26
and the first photo detector
30
. The light source
12
generates two polarized beams having a polarizing characteristic moving perpendicularly to each other The first collimator lens
14
converts a divergent light beam progressing from the light source
12
, via the polarizing phase plate
16
, toward the beam splitter
18
into a parallel light beam to prevent a leakage of the light beam. The beam splitter
18
passes a light beam received via the first collimator lens
14
and the polarizing phase plate
16
in such a manner to be progressed toward the objective lens
20
, and reflects a reflective light beam reflected from the recording surface of the optical disc
22
and passing through the objective lens
20
in such a manner to be progressed toward the second collimator lens
24
. The objective lens
20
focuses an incident light beam from the beam splitter
18
on the recording surface of the optical disc
22
. The polarizing phase plate
16
consists of two phase zones
16
A and
16
B having a phase difference of 180° in the left and right phases thereof as shown in
FIG. 3
, and which is responsible for selectively changing a phase of the light beam received, via the first collimator lens
14
, from the light source
12
in accordance with a polarizing characteristic thereof. More specifically, the polarizing phase plate
16
passes the first polarized beam in any one direction of two polarized beams emitted from the light source
12
as it is, thereby allowing the first polarized beam to be irradiated, via the collimator lens
16
the beam splitter
18
and the objective lens, on the recording surface of the optical disc
22
as a main beam MB as shown in FIG.
2
A. On the other hand, the polarizing phase plate
16
passes the second polarized beam in a direction perpendicular to the first polarized beam of two beams from the light source
12
with a phase being modulated, thereby allowing the second polarized beam to be irradiated on the recording surface of the optical disc
22
as a twin-mountain shaped sub-beams SB
1
and SB
2
superposed at each side of the main beam MB as shown in FIG.
2
A. The main beam MB in the light beams irradiated on the recording surface of the optical disc
22
in this manner is irradiated on the signal track to be accessed and is used to reproduced an information signal. On the other hand, the sub-beams SB
1
and SB
2
are irradiated on the adjacent tracks and is used to detect a crosstalk component included in the reproduced signal. The second collimator lens
24
plays a role to focus a parallel light beam reflected from the optical disc
22
and received via the objective lens
20
and the beam splitter
18
. The PBS
26
passes the main beam MB with the first polarization component in a reflective light beams reflected from the beam splitter
18
and received via the second collimator lens
24
as it is in such a manner to be progressed, via the sensor lens
28
, toward the first photo detector
30
. On the other hand, the PBS
26
reflects the sub-beams SB
1
and SB
2
with the second polarization component in the reflective light beam in such a manner to be progressed toward the second photo detector
32
. The sensor lens
28
focuses the main beam MB with the first polarization component passing through the PBS
26
as it is and being received thereto onto the first photo detector
30
. The first photo detector
30
detects a main beam MB received via the sensor lens
28
and the second photo detector
32
detects sub-beams SB
1
and SB
2
received separately from the PBS
26
, thereby converting them into electrical signals.
In other words, the first photo detector
30
detects a radio frequency signal including an reproducing signal from the main beam MB while the second photo detector
32
detects a crosstalk component in the adjacent tracks from the sub-beams SB
1
and SB
2
. A crosstalk component detected at the second photo detector
32
is eliminated from the radio frequency signal detected at the first photo detector
30
to thereby detect a reproducing signal.
The first and second sub-beams SB
1
and SB
2
reflected from the adjacent tracks have a frequency characteristic different from each other. In particular, when a tilt is generated between the objective lens and the optical disc, two sub-beams SB
1
and SB
2
have a greatly different frequency characteristic. Accordingly, in order to eliminate a crosstalk component from the radio frequency signal detected at the first photo detector
30
effectively, it is necessary to detect the first and second sub-beams SB
1
and SB
2
and filter the same with a filter suitable for a frequency characteristic of each sub-beam so as to make an operation on the radio frequency signal detected from the main beam MB. To this end, the second photo detector
32
includes two photo detecting cells for detecting the first and second sub-beams SB
1
and SB
2
. Howe
Jeong Seong Yun
Park Kyung Chan
Birch & Stewart Kolasch & Birch, LLP
Huber Paul W.
LG Electronics Inc.
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