Optical pickup head and information recording/reproducing...

Details Optical pickup head and information recording/reproducing... Optical pickup head and information recording/reproducing...

2002-06-04

2004-09-28

Hindi, Nabil (Department: 2655)

Dynamic information storage or retrieval

With servo positioning of transducer assembly over track...

Optical servo system

C369S044420

Reexamination Certificate

active

06798723

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical pickup head used in a apparatus for recording, reproducing, or erasing information on an optical storage medium, and to an information recording/reproducing apparatus.
2. Description of Related Art
Optical memory technologies using optical storage media with a pit-shaped pattern, that are storage media of high density and large capacity, are increasingly adopted for digital audio disks, video disks, text file disks, and data files, for example. In recent years, high-density, large capacity optical storage media known as DVDs have been put into practical use and have garnered widespread attention as information media capable of handling large quantities of information, such as moving pictures. These DVD optical storage media are recorded and reproduced using a so-called red semiconductor laser that emits laser light of a wavelength near 650 nm.
A conventional optical pickup head in an optical disk system capable of recording and reproducing is described using FIG.
22
.
A semiconductor laser light source
101
, serving as the light source, emits a linearly polarized divergent beam
700
with a wavelength &lgr;
2
of 650 nm. The divergent beam
700
emitted from the semiconductor laser light source
101
is incident on a diffraction grating
510
and split into three beams of zero order, −1st order, and +1st order diffracted light. The zero order diffracted beam is a main beam
700
a
for recording/reproducing information and the +1st and −1st order diffracted beams are sub-beams
700
b
and
700
c
used in a differential push-pull method (hereinafter, referred to as DPP) to detect tracking error (hereinafter, referred to as TE) signals stably. The ratio of the diffraction efficiency of the zero order diffracted beam to either one of the 1st order diffracted beams is ordinarily set from 12:1 to 20:1, and here it is 20:1. Accordingly, the sub-beams
700
b
and
700
c
are prevented from affecting the main beam
700
a
, and unintentional recording on an optical storage medium
410
can be avoided.
The three beams created by the diffraction grating
510
, that is, the main beam
700
a
and the sub-beams
700
b
and
700
c
, pass through a polarizing beam splitter
520
and are converted into parallel beams by a collimating lens
530
with a focal length of 15 mm. The parallel beams pass through a quarter wavelength plate
540
and are converted into circularly polarized light, after which they are converted into convergent beams by an objective lens
560
with a 3 mm focal length. The opening of the objective lens
560
is restricted by an aperture
550
, and its numerical aperture NA is 0.6.
The optical storage medium
410
is provided with a transparent substrate
410
a
and an information recording plane
410
b
, and the thickness of the transparent substrate
410
a
is 0.6 mm. The convergent beam from the objective lens
560
passes through the transparent substrate
410
a
and is focused on the information recording plane
410
b.
FIG. 23
shows the relationship between the tracks and the beams on the optical storage medium. As shown in
FIG. 23
, tracks, which are a plurality of continuous grooves, are formed on the information recording plane
410
b
of the optical storage medium
410
(FIG.
22
). Tracks T
m−1
, T
m
, and T
m+1
are lined up in order, and the track pitch P
2
, which is the distance between the track T
m−1
and the track T
m
and between the track T
m
and the track T
m+1
, is 0.74 &mgr;m. The beams are arranged such that when the main beam
700
a
is positioned on the track T
m
, the sub-beams
700
b
and
700
c
are positioned between the tracks T
m
and T
m−1
and the tracks T
m
and T
m+1
, respectively. Consequently, there is a 0.37 &mgr;m wide spacing L
2
between the main beam
700
a
and the sub-beams
700
b
and
700
c
in the direction perpendicular to the track T
m
.
The main beam
700
a
and the sub-beams
700
b
and
700
c
focused on the information recording plane
410
b
are reflected, and after passing through the objective lens
560
and the quarter wavelength plate
540
and being converted into linearly polarized light with a polarization that is rotated by 90° with respect to that of the incident path, they pass through the collimating lens
530
and are converged into convergent light. This convergent light is reflected by the polarizing beam splitter
520
, passes through a cylindrical lens
570
, and is incident on an optical detector
300
. Astigmatism is imparted on the main beam
700
a
and the sub-beams
700
b
and
700
c
when they pass through the cylindrical lens
570
.
The optical detector
300
has eight light receiving portions
300
a
,
300
b
,
300
c
,
300
d
,
300
e
,
300
f
,
300
g
, and
300
h
. The light receiving portions
300
a
,
300
b
,
300
c
, and
300
d
are for receiving the main beam
700
a
, the light receiving portions
300
e
and
300
f
are for receiving the sub-beam
700
b
, and the light receiving portions
300
g
and
300
h
are for receiving the sub-beam
700
c
. The light receiving portions
300
a
,
300
b
,
300
c
,
300
d
,
300
e
,
300
f
,
300
g
, and
300
h
each output a current signal corresponding to the amount of light received.
Using each of the signals output from the light receiving portions
300
a
,
300
b
,
300
c
, and
300
d
for receiving the main beam
700
a
, it is possible to obtain focus error (hereinafter, referred to as FE) signals through the astigmatism method, TE signals through a phase difference method, TE signals through a push-pull method, and information (hereinafter, referred to as RF) signals recorded on the optical storage medium. Also, when recording/reproducing continuous groove disks such as DVD-RW disks, TE signals can be obtained through DPP by jointly using the signals output from the light receiving portions
300
e
,
300
f
,
300
g
, and
300
h
for receiving the sub-beams
700
b
and
700
c
. After being amplified to a desired level and phase compensated, the FE signals and the TE signals are supplied to actuators
910
and
920
, and based on these signals, focusing and tracking control are performed.
In DVDs, ROM disks for read only are standardized as two-layered disks provided with two information planes. Information can be read out from these two-layered disks without any problems by detecting the TE signals through the phase difference method using the conventional optical pickup head.
Moreover, at the research and development level, there have been many publications of research results for two-layered recordable disks having two information recording planes (hereinafter, referred to as two-layered recording disks). Initially, no information is written on two-layered recording disks, so TE signals cannot be detected by a phase difference method. For this reason, the TE signals are detected by DPP, as is the case with single-layered recordable disks.
However, even if two-layered recording disks are used with the above-mentioned conventional optical pickup head and TE signals are detected by DPP, there is the problem that letting the objective lens perform tracking generates an uncorrectable offset in the TE signals.
This is because when information is recorded/reproduced with one of the information recording planes of the two layers (hereinafter, that information recording plane is referred to as the focus plane), a portion of the beam forming a focal point on the focus plane is reflected and a portion passes through the focus plane and arrives at the other information recording plane (hereinafter, that information recording plane is referred to as the non-focus plane). This beam is out of focus on the non-focus plane and is reflected by the non-focus plane toward the optical detector. The beam reflected by the non-focus plane cannot be fully cancelled during detection of the TE signals by DPP due to aberration and variations in the amount of beam light, for example. For this reason, tracking with th

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