Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
1998-10-01
2001-02-20
Edun, Muhammad (Department: 2753)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S110040, C369S112040, C369S044120, C369S044230
Reexamination Certificate
active
06192020
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor laser device which is preferably used as a light source of a magneto-optical pick-up device for recording and/or reproducing information onto or from an information recording medium.
2. Description of the Related Art
A conventional semiconductor laser device used for magneto-optical pick-up (Japanese Laid-open Publication No. 6-168462) will now be described with respect to its configuration and operation.
First, the configuration of the conventional semiconductor laser device will be described.
FIG. 30
is a diagram showing an optical system of the conventional semiconductor laser device and an information recording medium. Referring to
FIG. 30
, a semiconductor laser element
101
and a servo-signal light-receiving element
102
for detecting a focus error signal and a radial error signal are provided within a semiconductor laser unit
107
. A polarization beam splitter
111
, a collimator lens
112
and an objective lens
113
are sequentially placed in this order in the optical path from the semiconductor laser element
101
to an information recording medium
114
. The polarization beam splitter
111
is secured on the top of the semiconductor laser unit
107
. A diffraction grating
109
is formed at the surface of the polarization beam splitter
111
which faces the semiconductor laser element
101
. Moreover, an information-signal light-receiving element
104
is provided outside the optical path between the semiconductor laser element
101
and the information recording medium
114
. The information-signal light-receiving element
104
is divided into two elements for p-polarized light components and s-polarized light components, respectively. A Wollaston prism
116
is provided at the surface of the polarization beam splitter
111
which faces the information-signal light-receiving element
104
.
Next, the operation of the conventional semiconductor laser device will be described. Light is emitted from the semiconductor laser element
101
onto the information recording medium
114
. The light reflected from the information recording medium
114
(hereinafter, the reflected light is referred to as return light) passes through the objective lens
113
and the collimator lens
112
into the polarization beam splitter
111
. The polarization beam splitter
111
partially reflects the return light into the Wollaston prism
116
, while transmitting the remaining return light therethrough. The Wollaston prism
116
has different refractive indices for p-polarized light and s-polarized light, respectively. Therefore, the return light entering the Wollaston prism
116
is divided into a p-polarized light component and an s-polarized light component in the Wollaston prism
116
. The two elements of the information signal light-receiving element
104
are located at the positions on which the two divided light components for an information signal are focused, respectively. The information signal is calculated based on an output of the information-signal light-receiving element
104
. The remaining return light having passed through the polarization beam splitter
111
is diffracted by the diffraction grating
109
into the servo-signal light-receiving element
102
. The focus error signal and the radial error signal are detected based on an output value from the servo-signal light-receiving element
102
.
According to the conventional semiconductor laser device shown in
FIG. 30
, the information-signal light-receiving element
104
is separately provided outside the semiconductor laser unit
107
, whereby the overall size of the device is increased.
In order to provide a smaller and thinner semiconductor laser device which solves the above-mentioned problem, an information-signal light-receiving element may be placed within a semiconductor laser unit, as shown in FIG.
31
. Such a semiconductor laser device will now be described with respect to its configuration and operation with reference to FIG.
31
.
FIG. 31
shows another conventional semiconductor laser device and an information recording medium. First, the configuration of this conventional semiconductor laser device will be described. Referring to
FIG. 31
, a semiconductor laser element
201
and servo-signal light-receiving elements
202
and
203
are provided within a package
205
. The package
205
is sealed by a transparent seal substrate
206
. Thus, a semiconductor laser unit
207
is configured. A light-transmitting substrate
208
, a collimator lens
212
and an objective lens
213
are sequentially provided in this order in the optical path from the semiconductor laser element
201
to an information recording medium
214
. A hologram optical element
228
includes a diffraction grating
209
and a three-beam generating diffraction grating
210
. The diffraction grating
209
is formed at the surface of the light-transmitting substrate
208
which faces the collimator lens
212
, whereas the three-beam generating diffraction grating
210
is formed at the surface of the light-transmitting substrate
208
which faces the seal substrate
206
.
Hereinafter, the operation of the conventional semiconductor laser device shown in
FIG. 31
will be described. Light emitted from the semiconductor laser element
201
is divided into three light beams by the three-beam generating diffraction grating
210
. More specifically, the three-beam generating diffraction grating
210
divides incident light into positive first-order light which is diffracted in the direction perpendicular to the plane of
FIG. 31
from the rear to the front of the plane of
FIG. 31
, 0th-order light which is not diffracted, and negative first-order light which is diffracted in the direction perpendicular to the plane of
FIG. 31
from the front to the rear of the plane of FIG.
31
. The three light beams thus divided pass through the hologram optical element
228
, and then, through the collimator lens
212
and the objective lens
213
so as to be focused onto the information recording medium
214
. The light beam reflected from the information recording medium
214
, that is return light, is directed back to the hologram optical element
228
through the same optical path. Thereafter, the return light is diffracted by the diffraction grating
209
of the hologram optical element
228
so as to be focused onto a focus-error-signal light-receiving region (not shown) and a radial-error-signal light-receiving region (not shown) of the servo-signal light-receiving elements
202
and
203
. Each of the focus-error-signal light-receiving region and the radial-error-signal light-receiving region is divided into a plurality of elements. A focus error signal is detected by first converting a current output from each element of the focus-error-signal light-receiving region to a voltage, and then, performing a differential operation of the voltages thus converted. A radial error signal is similarly detected by a differential detection method using a three-beam method. An information signal is obtained by first converting a current output from each element of the focus-error-signal light-receiving region to a voltage and then calculating the sum of the voltages thus converted.
The conventional semiconductor laser device shown in
FIG. 31
obtains the information signal by calculating the sum of the signals from the plurality of elements. Therefore, a noise component of the signal from each element is added. As a result, the total noise component is increased according to the number of elements, causing significant reduction in a signal
oise (S/N) ratio.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, a semiconductor laser device includes a semiconductor laser element for emitting laser light onto a recording medium; beam dividing means provided in an optical path between the semiconductor laser element and the recording medium; a hologram optical element including a diffraction grating formed in a light-transmitting substr
Ijima Shin'ichi
Nakanishi Hideyuki
Takasuka Shouichi
Yoshikawa Akio
Edun Muhammad
Matsushita Electronics Corporation
Ratner & Prestia
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