Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
2000-09-26
2002-12-17
Huber, Paul W. (Department: 2653)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S112290
Reexamination Certificate
active
06496469
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical integrated unit, an optical pickup, and an optical recording medium drive device. More specifically, the present invention relates to a flat-package type of optical integrated unit incorporating an integrated laser source for a plurality of operating wavelengths, such as those for DVD-ROM and CD-R disks, for reading signals recorded on an optical recording medium such as an optical disk and writing thereto, and also to an optical pickup using that optical integrated unit and an optical recording medium drive device using that optical pickup.
Digital versatile disk (DVD) systems are being developed for recording large volumes of data within a compact and also portable recording medium. When it comes to implementing such a system, it is preferable to provide compatibility that can also reproduce from disks of prior-art formats, such as compact disk, read-only memory (CD-ROM) and compact disk recordable (CD-R).
A semiconductor laser diode (herein after abbreviated to LD) of a wavelength of approximately 780 nm is used for readout from a CD-R, but an LD of a wavelength of 650 nm is used for DVD, for implementing a recording density of approximately seven times that of a CD-ROM. However, the recording medium used for CD-R is a pigmentation material and it is not possible to obtain sufficient sensitivity therewith in the 650-nm wavelength band used for DVDs. That is why it is essential to use an optical pickup that has two light sources, for implementing a DVD system that is compatible with CDs.
A schematic view of the configuration of a conventional two-light-source type of optical pickup for DVD is shown in FIG.
14
. In this figure, reference number
101
denotes a 650-nm-wavelengthoptical integrated unit for DVD readout,
102
denotes a 780-nm-wavelength optical integrated unit for CD-R and CD-ROM readout,
103
denotes a prism,
104
denotes a collimator lens,
115
denotes a folding mirror,
106
denotes a wavelength selection filter,
107
denotes a focusing lens,
108
denotes a CD-format disk, and
109
denotes a DVD-format disk.
Each of the optical integrated units
101
and
102
is provided with a semiconductor laser that acts as a light source, alight-receiving element for detecting a light beam reflected from a disk, and a monitoring light-receiving element for controlling the output of the semiconductor laser.
An optical pickup that uses two independent light sources, such as that shown in
FIG. 14
, has problems as described below. The first problem relates to the complexity of adjusting the positions of the light sources because there are two optical axes, and the second problem is it is difficult to make the complete assembly smaller and lighter.
In order to solve these two problems, the present inventor and others have developed a integrated semiconductor laser element in which 650-nm and 780-nm light sources are integrated in a monolithic fashion on the same semiconductor substrate, which is designed to greatly simplify optical systems that use such a laser element. This was disclosed as Japanese Patent Application No. 10-181068.
A schematic view of a section through the structure of the integrated semiconductor laser element proposed by the present inventor and others in this application is shown in FIG.
15
.
A perspective view in
FIG. 16
shows essential components of an optical integrated unit in which an integrated semiconductor laser element is mounted in a CAN-type package, and a schematic view of the optical system of an optical pickup that uses this optical integrated unit is shown in FIG.
17
.
As shown in
FIG. 15
, an integrated semiconductor laser element
31
has a 650-nm laser excitation portion
240
and a 780-nm laser excitation portion
241
, formed in a monolithic manner on a common GaAs substrate
210
. Respective p-side electrodes
233
and
234
of these laser excitation portions are attached by an adhesive material
351
, such as an AuSn solder, on top of extraction electrodes
352
and
353
formed separately on top of an insulating substrate
354
of a material such as AlN. Reference number
358
denotes a metal block for heat dissipation.
In the optical integrated unit shown in
FIG. 16
, reference number denotes the previously mentioned integrated semiconductor laser element,
354
denotes an AlN insulating substrate,
358
denotes the metal block for heat dissipation,
359
denotes a photodiode (PD) for monitoring, and
360
denotes a divided PD for error detection and RF signal detection. These components are disposed on a stem
400
and are connected as appropriate by lead pins
404
and wires W through feed-throughs
402
.
Components in
FIG. 17
that are the same as those in
FIG. 14
are denoted by the same reference numbers and further description thereof is omitted. In
FIG. 17
, reference number
361
denotes the optical integrated unit of
FIG. 16
mounted in a CAN-type package.
It is clear that the optical system shown in
FIG. 17
has a far simpler structure than that of the original optical system exemplified in
FIG. 14
, as a result of using a single optical integrated unit, so it can be made smaller and lighter.
However, there are still some technical problems to be solved with both the CAN-type optical integrated unit of FIG.
16
and the optical pickup of FIG.
17
.
The first problem concerns the necessity of a high level of precision in the mounting of the LD
31
(in the X-Z plane) on a surface that is perpendicular to the mounting of the divided PD
360
(in the X-Y plane).
The second problem is that lead pins
361
p,
the metal block
358
for heat dissipation, the integrated semiconductor laser element
31
, and IC chips (not shown in the figure) are disposed in a three-dimensional structure, which imposes a limit on the miniaturization of the assembly.
Concerning the first technical problem: the angle (&agr;) between the LD beam and the Z-axis is required to be within ±1°, the deviation in relative position (in the X-Y plane) between the luminous spot generated by the LD and the divided PD 360 is required to be within ±5 &mgr;m, and the deviation (&bgr;) between the angles of rotation of the LD
31
and the divided PD 360 is required to be within ±0.5°.
Concerning the second technical problem: this presents an obstacle to mounting the assembly in a notebook computer or personal data assistant (PDA) having an external thickness of 30 mm or less.
SUMMARY OF THE INVENTION
The present invention was devised in the light of the above described problems. In other words, an objective thereof is to provide a multi-wavelength optical integrated unit, optical pickup, and optical recording medium drive device which can be made much smaller, lighter, and slimmer than in the prior art, with a reduced number of components, reduced fabrication costs, and, simultaneously, an increased reliability.
In order to achieve this objective, an optical integrated unit in accordance with the present invention comprises a substrate and a semiconductor laser element mounted on a main surface of the substrate; wherein:
the semiconductor laser element has a configuration such that a first laser excitation portion for emitting a laser beam of a first wavelength and a second laser excitation portion for emitting a laser beam of a second wavelength that differs from the first wavelength are integrated in a monolithic manner, and also the laser beam of the first wavelength and the second laser beam are emitted in a substantially parallel direction with respect to the main surface of the substrate;
the substrate comprises:
a mirror surface inclined with respect to the main surface in such a manner that the first and second laser beams are reflected substantially perpendicularly upward with respect to the main surface; and
means for providing electrical separation between a first mount portion corresponding to the first laser excitation portion and a second mount portion corresponding to the second laser excitation portion.
In this case, the means for sepa
Gray Cary Ware & Freidenrich LLP
Huber Paul W.
Kabushiki Kaisha Toshiba
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