Optical pickup and optical disk unit

Details Optical pickup and optical disk unit Optical pickup and optical disk unit

1998-12-23

2001-03-27

Psitos, Aristotelis M. (Department: 2651)

Dynamic information storage or retrieval

With servo positioning of transducer assembly over track...

Optical servo system

C369S109010

Reexamination Certificate

active

06208596

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical pickup for recording and/or reproducing a signal on and/or from an optical disk such as a minidisk (MD), a magneto optical disk (MO), a compact disk (CD) and a CD-ROM, and further to an optical disk unit equipped with this optical pick up.
2. Description of the Related Art
So far, as an optical pickup for an optical disk, various types using a hologram device have been proposed for the purpose of simplifying, stabilizing and size-reducing an optical system, for example, constructed as shown in FIG.
3
.
In
FIG. 3
, an optical pickup, generally designated at numeral
1
, is made up of a light-emitting device
2
, a hologram device
3
, an objective lens
4
and an optical detector
5
.
The hologram device
3
has two surfaces perpendicular to the optical axis of a light beam from the light-emitting device
2
, with a diffraction grating
3
a
being formed in the first surface (lower surface in
FIG. 3
) existing on the light-emitting device
2
side and on the optical axis of the light beam from the light-emitting element
2
.
In addition, the hologram device
3
has a hologram
3
b
formed in its second surface (upper surface in
FIG. 3
) existing on an optical disk D side and on the optical axis of the light beam from the light-emitting device
2
.
The hologram
3
b
allows the light beam from the light-emitting device
2
to directly pass, and makes the light returning from the optical disk D to diffract to be led into the aforesaid optical detector
5
.
In this instance, the hologram
3
b
is, as illustrated, composed of two hologram sections
3
b
-
1
,
3
b
-
2
made by division along a direction parallel to a track direction of the optical disk D, and the hologram sections
3
b
-
1
,
3
b
-
2
have discontinuous spatial frequencies with respect to each other.
In the case of being illustrated, the optical detector
5
comprises a central light-receiving section
5
a
for receiving a main beam after the division by the diffraction grating
3
a
and light-receiving portions E, F provided on both sides of the light-receiving section
5
a
to receive side beams, and further, the light-receiving section
5
a
is composed of four light-receiving portions A, B, C and D established by vertically and horizontally dividing the light-receiving section
5
a
into four.
Furthermore, in a non-shown processing circuit, detection signals from the aforesaid light-receiving portions A, B, C, D, E and F are amplified by a head amplifier into output signals Sa, Sb, Sc, Sd, Se and Sf.
In addition, in an arithmetic circuit, for instance, a reproduction signal RF
1
is calculated according to the following equation (1).
RF
1=(
Sa+Sb
)+(
Sc+Sd
)   (1)
Further, a focus error signal FE
1
is given according to the following equation (2) or (3).
FE
1=(
Sa−Sb
)   (2)
FE
1=(
Sa+Sd
)−(
Sc+Sb
)   (3)
Still further, a tracking error signal TE
1
is given by the following equation (4).
TE
1=(
Se−Sf
)   (4)
In the optical pickup
1
thus constructed, a light beam from the light-emitting device
2
is divided through the diffraction grating
3
a
of the hologram device
3
into a main beam and two side beams, and subsequently, passes through the hologram
3
b
to reach a signal recorded surface of the optical disk D by means of the objective lens
4
.
A returning optical beam reflected on this signal recorded surface again passes through the objective lens
4
to be incident on the hologram
3
b,
where this returning light is diffracted by each of the hologram portions
3
b
-
1
,
3
b
-
2
of the hologram
3
b
so that the returning light due to the main beam is incident on the light-receiving section
5
a
of the optical detector
5
while the returning light resulting from the side beams are incident on the light-receiving portions E, F of the optical detector
5
.
Whereupon, on the basis of the detection signals from the respective light-receiving portions A, B, C, D, E and F of the optical detector
5
, the detection of the reproduction signal RF
1
, the focus error signal FE
1
and tracking error signal TE
1
are possible.
In addition, there has also been known an optical pickup shown in FIG.
4
.
In
FIG. 4
, an optical pickup, generally designated at numeral
6
, includes a light-emitting/receiving device
7
, a hologram device
3
and an objective lens
4
.
The light-emitting/receiving device
7
is, as illustrated, constructed integrally on one semiconductor substrate
7
a.
More specifically, in the light-emitting/receiving device
7
, a light-emitting section is made up of a semiconductor laser element
7
b
formed on a semiconductor substrate
7
a
and a reflecting mirror
7
c
formed to be inclined obliquely from a surface of the semiconductor substrate
7
a.
In addition, an optical detector is composed of first and second optical detectors
8
,
9
placed on the semiconductor substrate
7
a.
In this case, the aforesaid hologram device
3
has two surfaces perpendicular to the optical axis of a light beam from the light-emitting/receiving device
7
, and a diffraction grating
3
a
is formed in the first surface (lower surface in
FIG. 4
) existing on the light-emitting/receiving device
7
side and on the optical axis of the light beam from light-emitting/receiving device
7
while a hologram
3
c
is formed in the second surface (upper surface in
FIG. 4
) existing on an optical disk D side and on the optical axis of the light beam from light-emitting/receiving device
7
.
In this instance, the aforesaid hologram
3
c
is constructed as being one continuous area, and allows the light beam from the light-emitting/receiving device
7
to directly pass and diffracts the returning light from the optical disk D so that 1 order light and −1 order light are led into the first and second optical detectors
8
,
9
, respectively.
As illustrated, each of the optical detectors
8
,
9
comprises a central light-receiving section on which a main beam divided by the diffraction grating
3
a
is incident and light-receiving sections
8
e,
8
f
or
9
e,
9
f
located on both sides of this central light-receiving section for receiving side beams, with the central section having light-receiving portions
8
a,
8
b
and
8
c
or
9
a,
9
b
and
9
c
established by dividing the central section into three along division lines parallel to the track direction of the optical disk D.
Furthermore, in a non-shown processing circuit, the detection signals from the light-receiving portions
8
a,
8
b,
8
c,
8
e
and
8
f
or
9
a,
9
b,
9
c,
9
e
and
9
f
are amplified by a head amplifier into output signals SA, SB, SC, SE, SF, SG, SH, SI, SK and SL. In addition, for example, a reproduction signal RF
2
is given according to the following equation (5).
RF
2=(
SA+SB+SC
)+(
SG+SH+SI
)   (5)
Further, a focus error signal FE
2
is given by the following equation (6).
FE
2=(
SA+SH+SC
)−(
SG+SB+SI
)   (6)
Still further, a tracking error signal TE
2
is given by the following equation.
TE
2=(
SE+SK
)−(
SF+SL
)   (7)
In the optical pickup
6
thus constructed, a light beam from the light-emitting/receiving device
7
is divided into a main beam and two side beams, and subsequently, passes through the hologram
3
c
to reach a signal recorded surface of the optical disk D through the objective lens
4
.
The returning light beam from this signal recorded surface is incident on the hologram
3
c
after again passing through the objective lens
4
. In this instance, the returning light is diffracted by the hologram
3
c
so that 1 order light and −1 order light are incident on the first and second optical detectors
8
,
9
, respectively.
Whereupon, on the basis of the detection signals of the light-receiving portions of the optical detectors
8
,
9
, the detection of the reproduc

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