Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2001-06-19
2004-11-23
Klimowicz, William (Department: 2652)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044320, C369S044350, C369S044410
Reexamination Certificate
active
06822934
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical disc apparatus, and in particular to an optical disc apparatus for finding an accurate tracking error signal for an optical disc.
2. Description of the Related Art
An optical disc is known as an information recording medium for storing a large amount of data. An optical disc can store information on tracks thereof, and also allow information recorded thereon to be reproduced. An optical disc apparatus is capable of mounting an optical is other on and is used for recording information on the optical disc and/or reproducing information stored on the optical disc. In order to allow the optical disc apparatus to record information to or reproduce information from an appropriate track accurately, a laser beam needs to accurately follow the tracks on the optical disc. The operation of the laser beam to follow the tracks on the optical disc is referred to as “tracking”. A tracking error signal shows whether the laser beam is accurately following the tracks on the optical disc.
Hereinafter, a conventional optical disc apparatus and a tracking error signal provided by the conventional optical disc apparatus will be described.
FIG. 10A
shows a conventional optical disc apparatus
1000
. Laser light emitted by a laser light source
1010
is converged on an optical disc
1070
through an optical system
1015
. The light reflected by the optical disc
1070
is detected by a photodetector
1050
. Based on a result detected by the photodetector
1050
, a control device
1085
controls an element or elements among the light source
1010
, the optical system
1015
, and the optical disc
1070
as necessary. The optical system
1015
includes, for example, a polarizing beam splitter
1020
having a splitting face
1025
, a collimator lens
1030
, a quarter-wave plate
1042
, a reflecting mirror
1040
, and an objective lens
1060
.
A more specific operation of the optical disc apparatus
1000
will be described.
Laser light emitted by the light source
1010
is incident on the polarizing beam splitter
1020
, transmitted through the splitting face
1025
of the polarizing beam splitter
1020
, and then converted into parallel light by the collimator lens
1030
. The parallel light, which is linearly polarized (P wave) is converted into circular polarization, by the quarter-wave plate
1042
, and then reflected by the reflecting mirror
1040
. The reflected light is converged by the objective lens
1060
on a signal face
1074
of the optical disc
1070
.
The optical disc
1070
has the signal face
1074
between a substrate
1072
and a protection film
1076
. The signal face
1074
has pits (or grooves) formed in a diameter direction of the optical disc
1070
(indicated by arrow X). The pits each have a depth d and a width w, and are arranged at a pitch p. The diameter direction of the optical disc
1070
is perpendicular to the direction of the light incident on the optical disc
1070
and parallel to the sheet of paper of FIG.
10
A.
The light reflected by the signal face
1074
, which is circular polarization, is transmitted through the objective lens
1060
, reflected by the reflecting mirror
1040
, and then converted into linear polarization (S wave) by the quarter-wave plate
1042
. The light is made convergent by the collimator lens
1030
, reflected by the splitting face
1025
of the polarizing beam splitter
1020
, and then collected on the photodetector
1050
as light
1080
. Based on a signal detected by the photodetector
1050
, the control device
1085
controls an element or elements among the light source
1010
, the optical system
1015
, and the optical disc
1070
as necessary.
In
FIG. 10A
, reference numeral
1210
represents an optical axis of the optical disc apparatus
1000
.
FIG. 10B
shows a structure of the photodetector
1050
. The photodetector
1050
includes sub-photodetectors
1050
A and
1050
B. A separation line
1051
shows the border between the sub-photodetectors
1050
A and
1050
B. The sub-photodetector
1050
A and
1050
B each provide a respective light amount. A tracking error signal
1091
s
(TE1 signal) is obtained by subjecting the light amounts provided by the sub-photodetectors
1050
A and
1050
B to subtraction performed by a subtracter
1091
. A reproduction signal
1092
is obtained by subjecting the light amounts provided by the sub-photodetectors
1050
A and
1050
B to addition performed by an adder
1092
. The separation line
1051
substantially equally divides a convergence spot
1081
on the photodetector
1050
. The control device
1085
controls an element or elements among the light source
1010
, the optical system
1015
, and the optical disc
1070
as necessary, so as to make the level of the TE1 signal zero in order to eliminate a tracking error.
FIG. 11A
shows another conventional optical disc apparatus
1100
. Laser light emitted by a laser light source
1110
is converged on an optical disc
1170
through an optical system
1115
. The light reflected by the optical disc
1170
is detected by a photodetector
1190
, Based on a result detected by the photodetector
1190
, a control device
1185
controls an element or elements among the light source
1110
, the optical system
1115
, and the optical disc
1170
as necessary. The optical system
1115
includes, for example, a collimator lens
1130
, a quarter-wave plate
1142
, a polarizing holographic element
1145
, and an objective lens
1160
.
A more specific operation of the optical disc apparatus
1100
will be described.
Laser light emitted by the light source
1110
is converted into parallel light by the collimator lens
1130
and incident on the polarizing holographic element
1145
.
The polarizing holographic element
1145
is integrated into a lens holder
1165
together with the objective lens
1160
. The polarizing holographic element
1145
has the quarter-wave plate
1142
. A surface of the polarizing holographic element
1145
is a polarizing holographic face
1150
.
The light, which is linear polarization (P wave) incident on the polarizing holographic element
1145
is transmitted through the polarizing holographic face
1150
and converted into circular polarization by the quarter-wave plate
1142
, collected by the objective lens
1160
, and then converged on a signal face
1174
of the optical disc
1170
.
The optical disc
1170
has the signal lace
1174
between a substrate
1172
and a protection film
1176
. The signal face
1174
has pits (or grooves) formed in a rotation direction of the optical disc
1170
. The pits each have a depth d and a width w, and arranged at a pitch p.
The light reflected by the signal face
1174
, which is circular polarization, is transmitted through the objective lens
1160
, converted into linear polarizatlon (S wave) by the quarter-wave plate
1142
, and then diffracted by the polarizing holographic face
1150
. The diffraction light is transmitted through the collimator lens
1130
and incident on the photodetector
1190
. Based on a signal detected by the photodetector
1190
; the control device
1185
controls an element or elements among the light source
1110
, the optical system
1115
, and the optical disc
1170
as necessary.
FIG. 11B
shows a structure of the polarizing holographic face
1150
. The polarizing holographic face
1150
includes two areas
1150
a
and
1150
b
which are separated from each other by a separation line
1152
. The light reflected by the optical disc
1170
is substantially equally divided into two by the separation line
1152
.
FIG. 11C
shows a structure of the photodetector
1190
. The photodetector
1190
includes two sub-photodetectors
1190
A and
1190
B separated from each other by a separation line
1191
. The light diffracted by the area
1150
a
(
FIG. 11B
) of the polarizing holographic face
1150
is collected on the sub-photodetector
1190
A as a spot
1181
a.
The light diffracted by the area
1150
b
(
FIG. 11B
) of the polarizing holographic face
1150
is collected on the
Momoo Kazuo
Nagashima Kenji
Nishiwaki Seiji
Saito Yoichi
Agustin Peter Vincent
Klimowicz William
Matsushita Electric - Industrial Co., Ltd.
Renner , Otto, Boisselle & Sklar, LLP
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