Dynamic information storage or retrieval – Condition indicating – monitoring – or testing – Including radiation storage or retrieval
Reexamination Certificate
2001-03-22
2003-08-26
Edun, Muhammad (Department: 2655)
Dynamic information storage or retrieval
Condition indicating, monitoring, or testing
Including radiation storage or retrieval
C369S044320, C369S044410
Reexamination Certificate
active
06611482
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Korean Application No. 00-14550, filed Mar. 22, 2000, in the Korean Patent Office, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an error signal detecting apparatus for an optical recording/reproducing apparatus, and more particularly, to an error signal detecting apparatus for an optical recording/reproducing apparatus which can detect a relative tangential tilt error signal between an objective lens and a recording medium by using a main beam to record/reproduce information signals on/from a recording medium.
2. Description of the Related Art
In general, an optical pickup records and reproduces information signals while moving across a recording medium such as a disc rotating on a turntable. When the rotating disc is tilted due to a warp in the disc or an error in installation of the disc, the recording and reproducing signals deteriorate.
In particular, in the case of an optical pickup adopting a light source for emitting light having a short wavelength and an objective lens having a large numerical aperture (N.A.) to increase the density of recording, since an optical aberration is proportional to &lgr;/(NA)
3
, a large coma due to the tilt of a disc is generated so that recording and reproducing signals are further deteriorated.
Thus, to prevent the deterioration of the recoding/reproducing signals by detecting the amount of the tilt of the disc to compensate for the tilt, a conventional apparatus
100
for detecting a relative tilt between a disc
10
and an objective lens
7
by using a detection signal of a photodetector
9
for reproducing is known, as shown in FIG.
1
.
Referring to
FIG. 1
, laser light emitted from a light source
1
for recording and reproducing information signals passes through a beam splitter
5
and is then input to the objective lens
7
. The objective lens
7
focuses incident light emitted from the light source
1
to form an optical spot on a recording surface of the disc
10
. Light reflected by the recording surface of the disc
10
passes through the objective lens
7
and is reflected by the beam splitter
5
to proceed toward the photodetector
9
. Here, reference numeral
8
denotes a photosensing lens for focusing the incident light reflected by the beam splitter
5
and detected by the photodetector
9
.
The photodetector
9
is formed of four separate plates A, B, C and D, as shown in
FIG. 2
, each independently performing a photoelectric conversion with respect to the incident light thereof. Thus, information and error signals are detected by appropriately adding and/or differentiating detection signals generated by the respective separate plates A, B, C and D.
Referring to
FIG. 2
, the conventional tilt error signal detecting apparatus
100
includes the photodetector
9
for reproducing information signals. The photodetector
9
is formed of four separate plates A, B, C and D, first and second adders
11
and
13
for respectively adding the detection signals of the separate plates A and B and the separate plates C and D, and a differentiator
15
for subtracting the signals input from the first and second adders
11
and
13
to output a tangential push-pull signal as a tilt error signal.
The tilt error signal output from the conventional tilt error signal detecting apparatus
100
having the above structure is input to an apparatus for adjusting the relative tilt between the objective lens
7
and the disc
10
, to thereby correct the tangential tilt error.
Since the conventional tilt error signal detecting apparatus
100
, although it has the advantage of a simple structure, detects the tangential tilt error signal by subtracting the detection signals of the separate plates at either side with respect to a center axis of the photodetector
9
which is parallel to the radial direction of the disc
10
, when the objective lens
7
is shifted or the distance between the objective lens
7
and the disc
10
is deviated from an on-focus position, the signal output therefrom changes, and thus the tangential tilt error cannot be accurately detected.
Also, the profile of a light beam, which is focused on the disc
10
as an optical spot and is reflected/diffracted, as shown in
FIG. 3
, and is detected by the photodetector
9
according to the tangential tilt between the objective lens
7
and the disc
10
, changes. This is shown in
FIGS. 4A
though
4
C. Thus, the conventional tilt error signal detecting apparatus
100
as described with reference to
FIGS. 1 and 2
cannot accurately detect the tangential tilt error signal.
FIG. 3
shows the light reflected by the disc
10
in a land/groove format and diffracted to the 0
th
order and the ±1
st
order. As shown in
FIG. 3
, the 0
th
order and the ±1
st
order diffraction light overlap one another in a radial direction of the disc
10
. Also, some areas of the +1
st
order diffraction light and the −1
st
order diffraction light may overlap one another.
FIGS. 4A through 4C
show the profiles of a light beam reflected by the disc
10
in land/groove format such as next generation DVDs, and so-called HD-DVD RAM discs, in which a track pitch is, for example, 0.37 &mgr;m and is detected by the photodetector
9
.
FIG. 4A
shows the case in which a negative tangential tilt error of about −0.5 degrees occurs.
FIG. 4B
shows the case in which the tangential tilt error does not occur.
FIG. 4C
shows the case in which a positive tangential tilt error of about +0.5 degrees occurs.
As can be seen from
FIGS. 4A and 4C
, when the tangential tilts are generated in opposite directions, light beams landing on the separate plates A and D and the separate plates B and C show patterns of the profiles of the light beams opposing each other with respect to a center axis in the tangential direction. Also, the beam profile mainly lands on the inner portion of the separate plate with respect to the tangential tilt in one direction, and on the outer portion of the separate plate with respect to the tangential tilt in the opposite direction.
As described above, in the conventional tilt error detecting apparatus using the photodetector
9
having four separate plates, a tangential tilt error signal is detected by subtracting a sum signal of the detection signals of the separate plates C and D from a sum signal of the detection signals of the separate plates A and B. Therefore, the conventional tilt error detecting apparatus is not able to accurately detect a change in the beam profile according to the tangential tilt and thus an accurate tangential tilt error signal cannot be detected.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an error signal detecting apparatus for an optical recording/reproducing apparatus which can detect a change in the profile of a light beam according to the tangential tilt by adopting a photodetector so that a highly accurate tangential tilt error signal can be detected.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and, in part, will be obvious from the description, or may learned by practice of the invention.
The foregoing and other objects of the present invention are achieved by providing an error signal detecting apparatus for an optical recording/reproducing apparatus comprising a photodetector to receive [for receiving] light reflected and diffracted by a recording medium, and a signal processor to detect an error signal by calculating a detection signal of the photodetector, in which the photodetector includes a plurality of light receiving areas, each independently receiving light where the profile of a beam changes to the opposite profile according to the tangential tilt of the recording medium, and the signal processor detects a tangential tilt error signal from detection signals of the light receiving areas.
It is preferred in the
Choi Byoung-ho
Chung Chong-sam
Doh Tae-yong
Ma Byung-in
Park In-sik
Edun Muhammad
Samsung Electronics Co,. Ltd.
Staas & Halsey , LLP
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