Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
2000-04-21
2004-04-27
Tran, Thang V. (Department: 2753)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S112050, C369S112230, C369S044230
Reexamination Certificate
active
06728193
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an optical pickup device and an optical disc drive, and more particularly to those using a laser array in which two light sources with center wavelengths of 650 nm and 780 nm are formed on a common semiconductor substrate for the purpose of simplifying data recording/reading system for both DVD (digital versatile disc) and CD (compact disc) or CD-R (compact disc-recordable).
2. Related Background Art
Today, DVD systems have been brought into practice and are being spread as optical disc systems that can record massive data more than seven times than that of CD or CD-R (hereinafter called “CDs”). On the other hand, CD systems have been widely spread as optical disc systems. Therefore, in order to promote diffusion of DVD systems, it is desirable to provide DVD systems with compatibility with CD systems so that they can reproduce data not only from DVDs but also from CDs.
For reading of data from CDs, semiconductor lasers (laser diodes: LDs) for the wavelength around 780 nm are used. DVD systems, however, use LDs for the center wavelength 650 nm to realize the recording density about seven times of CDs. On the other hand, since the recording medium of CDs (particularly CD-R) is a pigment system material, sufficient sensitivity is not expected with LDs with the center wavelength 650 nm, and for providing DVD system with compatibility with CD systems, they are required to have a two-light-source optical pickup device for two center wavelengths 650 nm and 780 nm.
FIG. 1
is an explanatory diagram schematically showing configuration of a conventional optical pickup device having two independent light sources.
The conventional pickup device with two independent light sources shown in
FIG. 1
includes a first optical integrated unit
101
for detection by emitting light with the center wavelength 650 nm, a second optical integrated unit
102
for detection by emitting light with the center wavelength of 780 nm, a dichroic filter
103
that transmits light whose center wavelength is 650 nm and reflects light whose center wavelength is 780 nm, a collimator lens
104
that collimates transmitted beams which are beams from the first optical integrated unit
101
and the second optical integrated unit
102
into parallel beams, a folding mirror
105
that change the direction of beams from the parallel direction to the vertical direction relative to an optical disc, a wavelength-selective iris
106
for adjusting the numerical aperture (NA) in accordance with the wavelength of light, and an objective lens
107
focalizing beams with center wavelengths of 650 nm and 780 nm which have been aligned in parallel by the collimator lens
104
onto optical discs. The first optical integrated unit
101
as the light source of light whose center wavelength is 650 nm and the second optical integrated unit
102
as the light source of light whose center wavelength is 780 nm are provided independently from each other.
Beams having the center wavelength 650 nm from the first optical integrated unit
101
pass through the dichroic filter
103
while spreading the beam diameter, and they are collimated into parallel beams when they pass through the collimator lens
104
.
Thereafter, they are reflected by the folding mirror
105
to the vertical direction relative to the DVD
109
, introduced into the objective lens
107
under adjustment of the numerical aperture by the wavelength-selective iris
106
, focused onto the DVD
109
by the objective lens
107
,and reflected by the DVD
109
. Reflected beams from the DVD
109
contain data about the presence or absence of any record pits on the DVD
109
, then return along the path of the emitted light in the opposite direction, and are detected by the first optical integrated unit
101
.
On the other hand, the beams from the second optical integrated unit
102
having the center wavelength 780 nm are reflected by the dichroic filter
103
while spreading outward to impinge on the collimator lens
104
, and are aligned into parallel beams when they pass through the collimator lens
104
. Then, they are reflected into the vertical direction relative to the CD
108
by the folding mirror
105
, then introduced into the objective lens
107
after being adjusted in numerical aperture by the wavelength-selective iris
106
, focused onto the CD
108
by the objective lens
107
and reflected from the CD
108
. Reflected beams from the CD
108
contain data about the presence or absence of any record pits on the CD
108
, return along the path of the emitted light in the opposite direction, and are detected by the second optical integrated unit
102
.
Since the CD
108
and the DVD
109
are different in spot size by the objective lens
107
, the effective numerical aperture is usually adjusted by the wavelength-selective iris
106
, for example, in accordance with the wavelength of light.
However, the conventional optical pickup device having two independent light sources requires complicated positional adjustment of two light sources to align their optical axes, and the use of two independent light sources makes it difficult to decrease the size of the device.
For the purpose of overcoming these two problems in the optical pickup device having two light sources, a double-source built-in semiconductor laser array having two light sources for center wavelengths of 650 nm and 780 nm on a common semiconductor substrate was developed to simplify the optical system (Japanese Patent Application No. hei 10-181068).
FIG. 2
is a cross-sectional view showing configuration of the double-source built-in semiconductor laser array.
The semiconductor laser array shown in
FIG. 2
includes double heterostructures having different parameters, which are formed on different locations of a common semiconductor substrate, by substantially commonly designing upper parts of cladding layers of the double heterostructures in respective regions to integrate resonant elements which generate the light with the center wavelength 650 nm and the light with the center wavelength of 780 nm, respectively. Thus, this semiconductor laser array includes a laser element portion
240
for the oscillation wavelength of 780 nm and a laser element portion
241
for the oscillation wavelength of 650 nm.
In the laser element portions
240
and
241
, sequentially stacked on a common gallium-arsenic GaAs substrate
21
are: n-type (n-) GaAs buffer layer
211
,
221
; n-In
0.5
(Ga
0.3
Al
0.7
)
0.5
P first cladding layers
212
,
222
; In
0.5
(Ga
0.5
Al
0.5
)
0.5
P optical guide layer
213
,
223
; multi-quantum well (MQW) active layers
214
,
224
; In
0.5
(Ga
0.5
Al
0.5
)
0.5
P optical guide layers
215
,
225
; p-In
0.5
(Ga
0.3
Al
0.7
)
0.5
P second cladding layers
216
,
226
; p-In
0.5
Ga
0.5
P etching stop layers
217
,
227
; p-In
0.5
(Ga
0.3
Al
0.7
)
0.5
P third cladding layers
218
,
228
; p-In
0.5
Ga
0.5
P cap layers
219
,
229
; n-GaAs current blocking layer
231
; and p-GaAs buried layer
232
.
In the laser element portion
240
for the oscillation wavelength 780 nm, the active layer
214
has a MQW structure including Ga
0.9
Al
0.1
As well layers and Ga
0.65
Al
0.35
As barrier layers. In the laser element portion
241
for the oscillation wavelength 650 nm, the active layer
224
has a MQW structure including In
0.5
Ga
0.5
As well layers and In
0.5
(Ga
0.5
Al
0.5
)
0.5
P barrier layers.
In the structure of the semiconductor laser array configuration shown in
FIG. 2
, by combination of the third cladding layers
218
,
228
having a convex stripe configuration and the GaAs current blocking layer
231
, steps of refractive indices are formed in the horizontal direction, and both laser element portions
240
,
241
form refractive index-guided lasers. The GaAs current blocking layer
231
also functions to confine the current within the ridge stripe portion in each laser element portion. These element portions
240
,
241
are electrically isolated by a separation groove
236
, and they are independently driven via el
Tsunoda Kazuya
Uchizaki Ichiro
Kabushiki Kaisha Toshiba
Tran Thang V.
Vuong Bach
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