Optical head device with zero-cross point correction

Details Optical head device with zero-cross point correction Optical head device with zero-cross point correction

2000-08-17

2001-12-04

Hindi, Nabil (Department: 2651)

Dynamic information storage or retrieval

With servo positioning of transducer assembly over track...

Optical servo system

C369S044320, C369S044410

Reexamination Certificate

active

06327231

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical head device for recording information to, or reproducing or erasing information from, an information memory medium, for example, an optical disk or optical card. The present invention also relates to an optical information processing apparatus, and an inclination angle detection apparatus for detecting an angle made by a beam collected by a light collection system in an optical information processing apparatus and an information memory medium.
2. Description of the Related Art
Optical memory technologies which use optical disks or optical cards as high density, large capacity memory media are used in progressively wider fields, for example, in digital audio disks, video disks, document file disks and data files. By such optical memory technologies, information is recorded to, or reproduced from, an optical disk with sufficiently high precision and satisfactory reliability through a light beam which is focused to have a microscopic diameter. The performance of a recording and reproduction apparatus using the optical memory technologies significantly relies on the optical system.
Exemplary basic functions of the optical head device, which is a main part of the optical system, are rough classified into:
(1) light collection in order to form a smallest possible light spot only limited by the diffraction;
(2) focusing and tracking control of the optical system, and reproduction of information signals; and
(3) erasing and writing of information signals by collected light.
These functions are realized by a combination of various optical systems and a light detector of a photoelectric conversion system.
As a first conventional example comparative to the present invention, a conventional optical head device will be described with reference to FIG.
42
.
FIG. 42
is a schematic view of an optical system of the conventional optical head device. In the optical head device shown in
FIG. 42
, focusing is performed by the non-point aberration method and tracking is performed by the push-pull method and the phase contrasting method.
The optical head device shown in
FIG. 42
operates in the following manner.
Light emitted by a semiconductor laser
101
as a light source is reflected by a plane-parallel beam splitter
102
and collimated by a collimator lens
103
, which is included in a light collection system. The light is then collected by an objective lens
104
which is also included in the light collection system, and collected on an information layer
108
of an optical disk
105
, which is an information memory medium. An actuator
107
moves the objective lens
104
and a holding device
106
in accordance with fluctuations or decentration of the optical disk
105
.
The light is then diffracted and reflected by the information layer
108
of the optical disk
105
to be reflected light
108
a.
The reflected light
108
a
is converged by the collimator lens
103
. The reflected light
108
a
is then provided with an non-point aberration when passing through the plane-parallel beam splitter
102
. The light provided with the non-point aberration is received by a light detector
150
. The above-described elements in the optical system shown in
FIG. 42
are arranged so that, when a focal point F
0
of the light from the objective lens
104
is on the information layer
108
, a light detecting surface of the light detector
150
is in the least circle of confusion of the converged light provided with the non-point aberration.
FIG. 43A
shows a pattern of a light detection area of the light detector
150
and the shape of a cross section of the reflected light
108
a
detected by the light detector
150
. The light detector
150
includes four light detection areas
251
through
254
. Signals obtained in accordance with the amount of light received by the light detection areas
251
through
254
are referred to herein as s
1
through s
4
. Although an operation circuit for generating a tracking error signal is not shown, a tracking error signal TE
1
is generated according to expression (1).
TE
1
=(
s
1
+s
4
)−(
s
2
+s
3
)  (1)
By the phase contrasting method, a tracking error signal TE
2
is obtained by comparing the phase of a sum signal of s
1
and s
3
and the phase of a sum signal of s
2
and s
4
.
A focusing error FE signal by the non-point aberration method is generated according to expression (2).
FE=
(
s
1
+s
3
)−(
s
2
+s
4
)  (2)
When the information layer
108
of the optical disk
105
is distanced from the objective lens
104
so as to be beyond the focal point F
0
of the light from the objective lens
104
, the cross section of the reflected light
108
a
detected by the light detector
150
is as shown in FIG.
43
B. When the information layer
108
of the optical disk
105
approaches the objective lens
104
so as to be between the objective lens
104
and the focal point F
0
of the light from the objective lens
104
, the cross section of the reflected light
108
a
detected b the light detector
150
is as shown in FIG.
43
C.
An RF signal, which is an information reproduction signal, is a sum of the signals s
1
through s
4
obtained from all the light detection areas and thus is generated according to expression (3).
RF=s
1
+
s
2
+
s
3
+
s
4
  (3)
The conventional optical head device described above have the following problems.
(1) The tracking error signal is generated by a differential signal which indicates the difference between the signals respectively obtained from the two light detection areas defined by simply equally dividing the light detection surface (aperture) of the light detector
150
into two by a central line of the aperture. In such a structure, the light is incident off the track or tracking is not stably controlled when an aberration occurs due to an inclination of the objective lens
104
and/or the optical disk
105
(tilt), or when the objective lens moves in a direction perpendicular to the tracks with respect to the optical axis in accordance with the decentration of the optical disk
105
.
(2) When the focal point of the light from the objective lens
104
scans the position off the track in which the information to be reproduced is stored, if a reproduction signal is generated by a signal indicating the difference between the signals respectively obtained from the two light detection areas defined by simply equally dividing the aperture of the light detector
150
into two by a central line of the aperture, a sufficient margin with respect to the disturbance cannot be secured.
Regarding an inclination angle detection apparatus for detecting an inclination of a beam collected by a light collection system in an optical information processing apparatus with respect to the information memory device, various structures have been proposed in order to accurately read information from, and write information to, the information memory device.
As a second conventional example comparative to the present invention, a conventional inclination detection apparatus will be described with reference to FIG.
44
.
FIG. 44
is a schematic view of an inclination detection apparatus. The inclination detection apparatus shown in
FIG. 44
operates in the following manner.
A linearly polarized scattering beam
70
emitted from a semiconductor laser
101
as a light source is collimated by a collimator lens
103
and then is incident on a polarizing beam splitter
130
. Next, the beam
70
is transmitted through the polarizing beam splitter
130
and then through a ¼-wave plate
122
to be converted into a circularly polarized beam. The circularly polarized beam is collected on an optical disk
105
as an information memory medium by an objective lens
104
.
FIG. 45
shows a structure of the optical disk
105
. In
FIG. 45
, Gn−1, Gn, Gn+1, . . . each represent a guide groove. Information is stored in the guide grooves as a mark or a space. Accord

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