Coherent light generators – Particular temperature control – Heat sink
Reexamination Certificate
2001-01-31
2003-03-04
Leung, Quyen (Department: 2828)
Coherent light generators
Particular temperature control
Heat sink
C372S029020, C372S043010, C385S033000
Reexamination Certificate
active
06529535
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor laser module that is used for optical communication and so on.
2. Description of the Related Art
A development of a high power semiconductor laser module as an exciting light source and the like in an amplifier for an optical fiber that is used for optical communication is in progress.
A conventional semiconductor laser module comprises, as is shown in
FIG. 6
, for example, a semiconductor laser device
1
, an optical fiber
2
that receives laser light emitted from the semiconductor laser device
1
and a photo diode
3
that monitors optical output of the semiconductor laser device
1
. These semiconductor laser device
1
, optical fiber
2
and photo diode
3
are housed in a package
10
.
The semiconductor laser device
1
is optically coupled at its front facet
1
a
(emitting facet) side with the optical fiber
2
and is confronted at its rear facet
1
b
(reflecting facet) side with the photo diode
3
. An anti-reflection coating film whose reflectance is, for example, around several percent is provided on the front facet
1
a
of the semiconductor laser device
1
and a reflection coating film whose reflectance is, for example, around 90 percent is provided on the rear facet
1
b.
The semiconductor laser device
1
is fixed to a base (a base part)
6
via a heat sink
9
and a fixing part
5
, and the photo diode
3
is fixed to the base
6
by a photo diode fixing part
8
.
In the semiconductor laser module shown in
FIG. 6
, ferules
11
a
,
11
b
are provided while keeping a distance from each other in the lengthwise direction of the optical fiber
2
, which is inserted and fixed in these ferules
11
a
,
11
b
. The ferule
11
a
functions as a means for supporting the optical fiber and is made of a Kovar (Trade mark) that is a Fe—Ni—Co alloy, for example.
The base
6
is fixed on a thermomodule
7
and the thermomodule
7
is mounted on a bottom board
10
a
of the package
10
. Here, as is shown in
FIG. 6
, the thermomodule
7
generally comprises a base-side board
17
, a bottom board-side board
18
and a peltier cooler (a peltier device)
19
pinched between these boards
17
and
18
. Both the base-side board
17
and the bottom board-side board
18
of the thermomodule
7
are made of Al
2
O
3
. And the ferule
11
b
is fixed to a side-wall of the package
10
.
In the above mentioned semiconductor laser module, the semiconductor
1
and the optical fiber
2
are aligned, and laser light emitted from the front facet
1
a
of the semiconductor laser device
1
is received by the optical fiber
2
to be transmitted in the optical fiber
2
and is provided for a desired use.
Further, in the above mentioned semiconductor laser module, an optical output from the rear facet
1
b
of the semiconductor laser device
1
is monitored by the photo diode
3
, thereby the optical output from the front facet
1
a
of the semiconductor laser device
1
is controlled. In other words, the output from the emitting facet of the optical fiber
2
is controlled by controlling the laser output based on the monitoring of the photo diode
3
.
Here, as the above mentioned semiconductor laser module monitors the optical output from the rear facet
1
b
of the semiconductor laser device
1
by the photo diode
3
, it is needed to permit light having a certain intensity to be emitted from the rear facet
1
b
of the semiconductor laser device
1
and to reach to a light receiving surface of the photo diode
3
. For that purpose, normally, the reflectance of the rear facet
1
b
of the semiconductor laser device
1
is reduced to a certain extent, for example, to 90 percent or less, intentionally.
However, when the reflectance of the rear facet
1
b
(reflecting facet) of the semiconductor laser device
1
is reduced, there exists a problem in that an optical output form the front facet
1
a
of the semiconductor laser device
1
decreases to reduce the optical output from the semiconductor laser module itself.
In recent years, another constitution for a semiconductor laser module has been proposed in which a fiber grating is provided on the optical fiber
2
of the semiconductor laser module. The fiber grating functions as a diffraction grating reflecting only light having a predetermined wavelength out of the laser beams that are emitted from the semiconductor laser device
1
and enter the optical fiber
2
. Thus, the output wavelength of the semiconductor laser module is stabilized by providing the diffraction grating, such as a fiber grating, on the optical fiber
2
.
However, in this constitution, as the polarization direction of the reflected light selected by the diffraction grating on the basis of the wavelength fluctuates by the change of the positional condition of the optical fiber
2
, a returning light with a changed polarization direction is returned to the semiconductor laser device
1
from the front facet
1
a
of the semiconductor laser device
1
through the optical fiber
2
, when the positional condition of the optical fiber
2
is changed. The power of the optical outputs from the front facet
1
a
and rear facet
1
b
of the semiconductor laser device
1
thus fluctuates. In particular, the amount of the fluctuation of the optical output by the above mentioned disturbance in the case of light emitted from the rear facet
1
b
of the semiconductor laser device
1
is bigger than that in the case of light emitted from the front facet
1
a.
Accordingly, when the fiber grating is provided on the optical fiber
2
of the semiconductor laser device
1
shown in
FIG. 6
, it has been difficult to precisely conduct APC (Automatic Power Control) for controlling optical output from the front facet
1
a
of the semiconductor laser device
1
to a fixed value. Namely, in the constitution shown in
FIG. 6
, when the fiber grating is provided on the optical fiber
2
and the output light from the rear facet
1
b
of the semiconductor laser device
1
is monitored, the fluctuation of monitor current is so large that it was impossible to control the optical output from the front facet
1
a
of the semiconductor laser device
1
to a fixed value.
SUMMARY OF THE INVENTION
The present invention has been made to solve the above mentioned problems, and an object of the present invention therefore to provide a high power semiconductor laser module that can control the optical output to a fixed value.
In order to achieve the above-mentioned object, the present invention provides a semiconductor laser module with the following constitution.
According to a first constitution of the present invention, there is provided a semiconductor laser module comprising: a semiconductor laser device; an optical fiber that receives laser light emitted from the semiconductor laser device; and a photo diode monitoring an optical output of the semiconductor laser device, characterized in that the photo diode monitors an optical output of the semiconductor laser device by receiving scattered light at a laser light receiving end of the optical fiber.
A semiconductor laser module according to a second constitution of the present invention is characterized in that the reflectance at a facet opposite side to the optical fiber of the semiconductor laser device is set to 95 percent or more, in addition to the above mentioned first constitution.
Further, a semiconductor laser module according to a third constitution of the present invention is characterized in that the laser light receiving end of the optical fiber is formed into a lens, in addition to the above mentioned first constitution.
Further, a semiconductor laser module according to a forth constitution of the present invention is characterized in that light emitted from the semiconductor laser device is optically coupled to the laser light receiving end directly, in addition to the above mentioned first (third) constitution.
Further, a semiconductor laser module according to a fifth constitution of the present invention is characterized in that the
Irie Yuichiro
Katayama Etsuji
Miyokawa Jun
Mugino Akira
Leung Quyen
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
The Furukawa Electric Co. Ltd.
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