Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2000-09-15
2003-01-14
Hindi, Nabil (Department: 2653)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044420, C369S044320
Reexamination Certificate
active
06507544
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Korean Application No.99-39831, filed Sep. 16, 1999, Korean Application No. 99-45850, filed Oct. 21, 1999 and Korean Application No. 00-12051, filed Mar. 10, 2000, the disclosures of which are herein incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an error signal detection apparatus for an optical recording/reproducing system, which is capable of detecting a tilting error signal and/or a tracking error signal, based on the phase characteristics of light reflected and diffracted from a recording medium, with improved accuracy and precision, and a reproduction signal detection apparatus for an optical recording/reproducing system and method therefor.
2. Description of the Related Art
Optical pickups record an information signal on or reproduce an information signal from a recording medium, such as an optical disk seated on a turntable and rotating, while scanning the recording medium in the radial direction. However, if the rotating optical disk is tilted with respect to the optical axis, due to bending of the optical disk itself or error in loading the disk, degradation of a recording/reproduction signal can be caused.
When an optical pickup adopts a light source which emits a shorter wavelength of light, and an objective lens having a high numerical aperture (NA), for the purpose of increasing recording density, comma aberration caused by tilting of the optical disk increases, thereby further degrading the recording/reproduction signal. This is because optical aberration is proportional to &lgr;/(NA)
3
.
In an optical recording/reproducing system required for high-density recording and reproduction with a medium, such as a next generation digital versatile disk (DVD), so-called high-definition (HD)-DVD, which has been focused on as a future generation high-density recording medium, there is a need for a tilt error signal detection apparatus capable of preventing degradation of the recording/reproduction signal by detecting the degree of tilting of the disk and correcting for the tilting of the disk based on the result of the detection.
As a conventional tilt error signal detection apparatus, the tilt error signal detection apparatus shown in
FIG. 2
, which detects tilting of a disk
10
with respect to an objective lens
7
, using a signal detected by a photodetector
9
of a general optical pickup as shown in
FIG. 1
, has been suggested.
FIG. 1
illustrates an example of the optical structure of a general optical pickup. Referring to
FIG. 1
, a laser beam emitted from a light source
1
for recording and reproducing an information signal is incident on an objective lens
7
through a beam splitter
5
. The objective lens
7
focuses incident light from the light source
1
to form a light spot on the recording surface of the disk
10
. Light reflected from the recording surface of the optical disk
10
passes through the objective lens
7
, is reflected by the beam splitter
5
, and goes toward the photodetector
9
. Reference numeral
8
indicates a light sensing lens for condensing light reflected by the beam splitter
5
through the objective lens
7
to allow detection of light by the photodetector
9
.
The photodetector
9
includes four divided plates A, B, C and D, as shown in
FIGS. 2 and 3
, for receiving light and performing photoelectric conversion, separately, on incident light. The photodetector
9
sums and/or subtracts the signals detected by the four divided plates A, B, C and D, to detect an information signal and an error signal.
As shown in
FIG. 2
, the conventional tilt error signal detection apparatus includes a photodetector
9
for use in recording and reproducing an information signal, which consists of four divided plates A, B, C and D arranged in a 2×2 matrix, for receiving light reflected by a disk (not shown) and separately performing photoelectric convention on incident light, first and second adders
11
and
13
for summing the signals generated by the divided plates A and D, and the signals generated by the divided plates B and C, respectively, and a differential unit
15
for subtracting the signals from the first and second adders
11
and
13
, and outputting a radial push-pull signal.
The radial push-pull signal output from the differential unit
15
corresponds to a tilt error signal. This radial push-pull signal can be used as a tracking error signal.
The tilt error signal output from the conventional tilt error signal detection apparatus is provided to an apparatus for adjusting relative tilt between the objective lens
7
and the disk
10
, and is used in correcting for the tilt error by the apparatus.
The conventional tilt error signal detection apparatus has an advantage of a simple configuration. However, a tilt error signal is detected by subtracting the detection signals of the two groups of the divided plates, which face each other on either side of the central axis aligned in the tangential direction. For this reason, when the objective lens is shifted or when an objective lens-to-disk distance is beyond On-focus positions, the tilt error signal varies with high sensitivity, and thus it is difficult to detect the degree of tilt error with accuracy.
On the other hand, when recording information on or reproducing information from a disk using the optical pickup as shown in
FIG. 1
, it is required for the optical pickup to accurately trace the tracks of the optical disk. To end this, usually the optical pickup employs a unit for detecting a tracking error signal from the disk by receiving light reflected by the disk after having been emitted from the light source.
As shown in
FIG. 3
, a conventional differential push-pull detection (DPD) type tracking error signal detection apparatus includes a photodetector
9
for use in detecting an information signal, a matrix circuit
21
, two high-pass filters HPF
1
and HPF
2
, two pulse shaping circuits
23
and
25
, and a phase comparator
27
.
The matrix circuit
21
receives signals a, b, c and d, detected by the four divided plates A, B, C and D, respectively, and sums the detected signals of the diagonally opposite divided plates A and C, and diagonally opposite divided plates B and D, respectively. If a light spot is formed beyond the center of the track, a time delay or a phase difference occurs between the sums (a+c) and (b+d) of the signals. Thus, the amount of tracking error can be identified by detecting the time delay between these signals.
The high-pass filters HPF
1
and HPF
2
filter off a low-frequency component of the sums (a+c) and (b+d) of the signals output from the matrix circuit
21
, and pass only a high-frequency component.
The signals (a+c) and (b+d) passed through the high-pass filters HPF
1
and HPF
2
, respectively, are converted to pulse signals through the pulse shaping circuits
23
and
25
. The phase comparator
27
compares the phases of the pulse signals, and outputs a tracking error signal TES'.
The DPD type tracking error signal detection apparatus, which employs the four-section photodetector
9
, is adopted to detect the amount of tracking error of the disk in a read only memory (ROM) type disk drive.
Meanwhile, as shown in
FIG. 4A
, light reflected by the disk for reproduction, after having been focused on the disk, is diffracted into a 0th order diffracted beam and ±1st order diffracted beams by pits (P) or marks (not shown) formed on the tracks of the disk
10
. Thus, the photodetector
9
receives the 0th order diffracted beam and ±1st order diffracted beams, which overlap each other in the radial direction.
FIG. 4A
illustrates light reflected and diffracted in the radial direction from a high-density disk having narrow tracks. This shows the case where ±1st order diffracted beams overlap the 0th order diffracted beam, while separated from each other according to the width of a pit. The signals resulting from the two overlapping
Choi Byung-ho
Chung Chong-sam
Doh Tae-yong
Ma Byung-in
Park In-sik
Hindi Nabil
Samsung Electronics Co,. Ltd.
Staas & Halsey , LLP
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