Coherent light generators – Particular temperature control – Heat sink
Reexamination Certificate
2001-09-14
2004-10-12
Vu, David (Department: 2828)
Coherent light generators
Particular temperature control
Heat sink
C372S049010, C372S045013, C372S043010, C372S046012
Reexamination Certificate
active
06804276
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-282852, filed Sep. 19, 2000, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor laser device and particularly to a semiconductor laser device including a semiconductor laser element adapted for an optical pickup based on a tracking servo system using a three-beam method.
2. Description of Related Art
A CD-ROM (Compact Disk-Read Only Memory) has come to be indispensable as a recording medium for a personal computer (PC). In an optical pickup used for an optical disk, tracking control generally adopts a system called a 3-beam method.
FIG. 9
shows a schematic view of an optical system adopted to the 3-beam system. A laser beam
601
emitted from a semiconductor laser element such as a laser diode (not shown) is guided to a diffraction grating
602
. The diffraction grating
602
generates diffraction lights of 0-order, 1-order, and −1-order. The diffraction lights pass through a collimator lens
603
, a half-mirror
604
, and an objective lens
605
and have a focus point on an optical disk
610
. That is, three beams of a main beam
606
and sub-beams
607
and
608
are focused on the optical disk
610
. Reflection lights from the optical disk
610
are guided to the half-mirror
604
passing again through the objective lens
605
and are reflected on the half-mirror
604
, to enter into patterned PDS (photo diodes)
611
. Incident light is photoelectrically converted at each PD
611
. The signal outputted from each PD
611
is calculated to obtain a position shift of the beam. The calculation result is fed back to a drive part of the optical pickup and is controlled so as to let the main beam
606
follow the track
609
.
The tracking control based on the 3-beam method covers a wide following range, and no limitation is put on the density and phase of the disk. Therefore, the tracking control is less influenced by variations in the disk quality. Accordingly, this is suitable for an optical pickup for reading. This method, however, has a problem of returning light from sub-beams.
That is, as shown in
FIG. 10
, two sub-beams
705
reflected from the disk partially return to the upper and lower sides of the laser diode chip (hereinafter called a LD chip)
701
(this is hereinafter called 3-beam returning light). The two sub-beams
705
are distant from the laser beam
703
by a distance d. For example, when the 3-beam returning light
705
is guided to the side of the sub-mount, the beams are reflected again on the side surface of the sub mount
704
. Therefore, reflection light
707
is generated from the 3-beam returning light and is mixed into the optical system. Consequently, a tracking error is caused in some cases.
To avoid this problem, a sub-mount
801
as shown in
FIG. 11
is used. A side surface of this sub-mount
801
that is positioned just below the laser beam emission facet of the LD chip
701
has three parts. That is, an upper part of the side surface of the sub-mount is formed to be vertical to the upper surface
802
of the sub-mount. A part of the side surface near a position at a distance d (see
FIG. 10
) from the emission point is inclined at an angle &thgr;. A lower part of the side surface of the sub-mount is also formed to be vertical to the upper surface
802
of the sub-mount. The beam direction of the 3-beam returning light
705
is refracted in correspondence with the inclination angle &thgr; of the inclined part. For example, the beam direction of the returning light
705
which returns in a direction vertical to the laser beam emission side surface
808
is refracted by 2&thgr;, according to Snell's law. NA (Numerical Aperture) of a collimator lens for a CD is about 0.1. An estimated half angle is about 5.7 degrees where the relationship of NA=n×sin &thgr;. At this time, if the inclination angle is 3 degrees or more, the returning light reflected on the side surface of the sub-mount is incident again to the collimator lens
603
(see FIG.
9
), and is thus prevented from mixing into the optical system. Thus, influences from the 3-beam returning light can be eliminated by inclining the side surface of the sub mount
801
at an angle corresponding to the NA of the collimator lens.
If a countermeasure is taken only against the returning light of the 3 beam optical system, the entire side surface of the sub-mount may be inclined. However, in case of die-bonding the sub-mount to a metal heatsink or die-bonding the LD chip to the sub-mount, the optimal axis direction must be set precisely. Therefore, operation for letting the laser beam emission facet of the LD chip collide with a positioning pin is required. Hence, constant areas on the upper and lower parts of the side surface of the sub-mount are formed to be vertical to the upper surface of the sub-mount. That is, an inclined part is formed only on a part of the side surface of the sub-mount upon requirements, as shown in FIG.
11
.
The sub-mount
801
is formed by a dicing process as shown in
FIGS. 12A and 12B
. At first, as shown in
FIG. 12A
, a sub-mount substrate
902
is partially cut by a blade
901
having a substantial V-shape. In this manner, a vertical part and an inclined part at an upper part of a side surface of the sub-mount are formed. Next, as shown in
FIG. 12B
, the sub-mount substrate
902
is cut and divided by a blade
903
having a normal shape. At this time, another vertical part at a lower part of the side surface of the sub-mount in the laser-beam emission side is formed. Thus, a sub-mount
904
having three side surfaces corresponding to the laser-beam emission facet is formed. That is, this sub-mount
904
has two flat parts respectively having heights a and e for abutting with a pin, and an inclined part as a countermeasure against 3-beam returning light, which has a height b and a depth c. The heights a and b and the depth c need to be highly precise, within a margin of error of about 10 &mgr;m. Therefore, when cutting is carried out by the V-shape blade
901
, the position of the blade must be controlled precisely in the plane direction and in the depth direction. In addition, when cutting is carried out by the blade
903
having a normal shape, the blade must be positioned precisely. Further, the shape of the V-shape blade changes due to friction as cutting continues. To cope with the effect of friction, the cutting depth must be changed, and the inclined part must be matched with the required dimensions. Therefore, a complicated adjustment operation is required.
As described above, the sub-mount having the structure shown in
FIG. 11
has a very complicated structure and is difficult to manufacture. The cost for the sub-mount is too high to enable an effective entire cost reduction for the semiconductor laser device.
Hence, there has been a demand for a semiconductor laser device and a method for manufacturing the same, which are capable of consistently removing the influences of the returning light of three beams, and enable excellent mass-productivity.
BRIEF SUMMARY OF THE INVENTION
According to an aspect of the invention, there is provided a semiconductor laser device comprising: a semiconductor laser chip having an emission facet for emitting a laser beam; and a sub-mount having a first surface on which the semiconductor laser chip is provides, and at least one second surface vertical to the first surface, wherein one of the second surface, which is arranged in line with the emission facet of the semiconductor chip, is inclined at an angle of 3 to 30 degrees to the emission facet, and the second surface which is inclined reflects reflection light of a sub-beam diffracted from the laser beam emitted from the semiconductor laser chip.
REFERENCES:
patent: 4844581 (1989-07-01), Turner
patent: 5517479 (1996-05-01), Nakanishi et al.
patent: 5923692 (1999-07-01), Stasku
Fukuoka Kazuo
Gen-ei Koichi
Iida Seiji
Okada Makoto
Hogan & Hartson LLP
Kabushiki Kaisha Toshiba
Nguyen Dung T
Vu David
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