Optical head for land and groove recording

Details Optical head for land and groove recording Optical head for land and groove recording

1999-12-17

2002-08-13

Tran, Thang V. (Department: 2653)

Dynamic information storage or retrieval

With servo positioning of transducer assembly over track...

Optical servo system

Reexamination Certificate

active

06434092

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to an optical head for detecting a focusing error signal in optical information read and write apparatuses, wherein both land and groove of recording medium are employed for reading and writing by optical beam from the optical head.
2. Description of the Prior Art
The astigmatic aberration method is often employed conventionally in order to obtain the focusing error signal, because it is easily combined with the push pull method for obtaining the tracking error signal.
A conventional optical head according to the astigmatic aberration method is shown in FIG.
7
. The light from semiconductor laser
101
is collimated by collimator lens
102
. Then, about 50% of the light passes through beam splitter
103
. Further, the light is focused on optical disk
105
by objective lens
104
. The light reflected by optical disk
105
passes through objective lens
104
. Then, about 50% of the reflected light is reflected by beam splitter
103
, and is detected by photo-detector
108
through cylindrical lens
106
and convex lens
107
.
A plan view of cylindrical lens
106
is shown in FIG.
8
. As shown in
FIG. 8
, the angle between the axis
110
of cylindrical lens
106
and the radial direction of optical disk
105
is &thgr;. Here, &thgr; is 45°.
Photo-detector
108
and beam spot thereon are shown in
FIGS. 9A
,
9
B, and
9
C, wherein the focused positions of the beam are different from each other. Photo-detector
108
comprises four light detecting portions
111
to
114
on which the light passing through cylindrical lens
106
is detected. The left to right direction in
FIG. 8
is the radial direction of optical disk
105
and the down to up direction in
FIG. 8
is the tangential direction of optical disk
105
, while the left to right direction in
FIG. 9
is the tangential direction of optical disk
105
and the down to up direction in
FIG. 9
is the radial direction of optical disk
105
, due to cylindrical lens
106
.
In
FIG. 9A
, the major axis of elliptic beam spot
115
is directed from the lower left to the upper right, because optical disk
105
is positioned nearer to objective lens
4
than the focusing point. In
FIG. 9B
, the beam spot is circular, because optical disk
105
is positioned just on the focusing point. In
FIG. 9C
, the major axis of beam spot
115
is directed from the upper left to the lower right, because optical disk
105
is positioned farther from objective lens
4
than the focusing point.
The focusing error signal FE equals to ((V
111
+V
114
)−(V
112
+V
113
)), when the outputs from light detecting portions
111
to
114
are V
111
to V
114
, respectively. FE becomes negative, zero, and positive, in
FIGS. 9A
,
9
B, and
9
C, respectively.
Further, the tracking error signal TE for the push pull method equals to ((V
111
+V
112
)−(V
113
+V
114
)). Furthermore, the read out signal RF equals to (V
111
+V
112
+V
113
+V
114
).
Another conventional optical head which detects focus error signal, according to the astigmatic aberration method is shown in FIG.
10
. This optical head is disclosed in Applied Optics/Vol.32, No.29/Oct. 10 ,1993, pp 5789 to 5796. Light beam from semiconductor laser
101
is collimated by collimator lens
102
. Then, about 50% of the light passes through beam splitter
103
. Further, the light is focused on optical disk
105
by objective lens
104
. The light beam reflected by optical disk
105
passes through objective lens
104
. Then, about 50% of the reflected light is reflected by beam splitter
103
. Then, the beam reflected by beam splitter
103
is divided into 50% transmission beam and 50% reflection beam by beam splitter
109
. The 50% transmission beam is detected by photo-detector
108
a
through cylindrical lens
106
a
and convex lens
107
a
, while the 50% reflection beam is detected by photo-detector
108
b
through cylindrical lens
106
b
and convex lens
107
b.
A plan view of cylindrical lens
106
a
is shown in
FIG. 11A
, while a plan view of cylindrical lens
106
b
is shown in FIG.
11
B. The angle between the axes
110
a
and
10
b
of cylindrical lenses
106
a
and
106
b
and the radial direction of optical disk
105
is &thgr;. Here, &thgr; is 45°.
Photo-detector
108
a
and beam spot thereon are shown in
FIGS. 12A
,
12
B, and
12
C, while photo-detector
108
b
and beam spot thereon are shown in
FIGS. 12D
,
12
E, and
12
F. Photo-detector
108
a
comprises four light detecting portions
111
a
to
114
a
on which the 50% transmission beam from beam splitter
109
becomes beam spot
115
a, while photo-detector
108
b
comprises four light detecting portions
111
b
to
114
b
on which the 50% reflection beam from beam splitter
109
becomes beam spot
115
b.
The left to right direction in
FIGS. 11A and 11B
is the radial direction of optical disk
105
and the down to up direction in
FIGS. 11A and 11B
is the tangential direction of optical disk
105
, while the left to right direction in
FIGS. 12A
to
12
F is the tangential direction and the down to up direction is the radial direction, due to cylindrical lenses
106
a
and
106
b
. Beam spot
115
a
and beam spot
115
b
are mirror symmetrical in respect to the down to up direction.
In
FIG. 12A
, the major axis of elliptic beam spot
115
a
is directed from the lower left to the upper right, because optical disk
105
is positioned nearer to objective lens
104
than the focusing point. In
FIG. 12B
, the beam spot
115
a
is circular, because optical disk
105
is positioned just on the focusing point. In
FIG. 12C
, the major axis of elliptic beam spot
115
a
is directed from the upper left to the lower right, because optical disk
105
is positioned farther from the objective lens
104
than the focusing point.
In
FIG. 12D
, the major axis of elliptic beam spot
115
b
is directed from the upper left to the lower right, because optical disk
105
is positioned nearer to objective lens
104
than the focusing point. In
FIG. 12E
, the beam spot
115
b
is circular, because optical disk
105
is positioned just on the focusing point. In
FIG. 12F
, the major axis of elliptic beam spot
115
b
is directed from the lower left to the upper right, because optical disk
105
is positioned farther from the objective lens
104
than the focusing point.
The focusing error signal FEa detected by photo-detector
108
a
equals to ((V
111
a
+V
114
a
)−(V
112
a
+V
113
a
)), when the outputs from light detecting portions lila to
114
a
are V
111
a
to V
114
a
, respectively. Similarly, the focusing error signal FEb detected by photo-detector
108
b
equals to ((V
111
b
+V
114
b
)−(V
112
b
+V
113
b
)), when the outputs from light detecting portions
111
b
to
114
b
are V
111
b
to V
114
b
, respectively. Here, FEa becomes negative, zero, and positive, in
FIGS. 12A
,
12
B, and
12
C, respectively, while FEb becomes positive, zero, and negative, in
FIGS. 12D
,
12
E, and
12
F, respectively. Therefore, the focusing error FE obtained by the optical head as shown in
FIG. 10
becomes (FEa−FEb) which is negative in
FIGS. 12A and 12D
, zero in
FIGS. 12B and 12E
, and positive in
FIGS. 12C and 12F
.
Further, the tracking error signal TEa detected by photo-detector
108
a
for the push pull method equals to (V
111
a
+V
112
a
)−(V
113
a
+V
114
a
), while the tracking error signal TEb detected by photo-detector
108
b
equals to ((V
111
b
+V
112
b
)−(V
113
b
+V
114
b
)). Therefore, the tracking error signal TE detected by the optical head as shown in
FIG. 10
becomes (TEa+TEb).
Furthermore, the read out signal RF is calculated on the basis of the outputs from
108
a
and
108
b.
The read out signal RFa obtained by photo-detector
108
a
is (V
111
a
+V
112
a
+V
113
a
+V
114
a
), while the read out signal RFb obtained by photo-detector
108
b
is (V
111
b
+V
112
b
+V
113
b
+V
114
b
). Therefore, the

Affiliated with

Also associated with

Rating

Optical head for land and groove recording does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Optical head for land and groove recording, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical head for land and groove recording will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2913694