Coherent light generators – Particular component circuitry – For driving or controlling laser
Reexamination Certificate
1999-11-19
2002-05-07
Davie, James W. (Department: 2881)
Coherent light generators
Particular component circuitry
For driving or controlling laser
Reexamination Certificate
active
06385222
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a semiconductor module used in the field of optical transmissions and a method for driving the semiconductor laser module.
BACKGROUND OF THE INVENTION
FIG. 6A
exemplary shows one structural example of a semiconductor laser module, using a cross-sectional view, and
FIG. 6B
shows one example of electric wiring of the semiconductor laser module illustrated in FIG.
6
A. The semiconductor laser module
1
illustrated in
FIG. 6A
is made into a module in which a semiconductor laser element
2
and an optical fiber
3
are optically coupled to each other.
That is, as shown in
FIG. 6A
, a thermomodule
5
is fixed on the wall surface of the inner bottom of a package
4
. The thermomodule
5
is constructed so that a plurality of Peltier elements
5
a
are placed between plate members
5
b
and
5
c
(first substrate and second substrate) of a high temperature conductive body (for example aluminum nitride). In this example, the plate member
5
b
is fixed on the wall surface of the inner bottom
4
a
of the package
4
, and the heat radiating side of the Peltier elements
5
a
is installed on the plate member
5
b
by soldering while the plate member
5
c
is fixed at the heat absorbing side of the Peltier elements
5
a
by soldering.
In such a thermomodule
5
, a heating generating action (heating action) and a heat-absorbing action (cooling action) are changed in compliance with the orientation of a current flowing into the Peltier elements
5
a
, and the heat generating amount and heat absorbing amount thereof are changed in compliance with a current flow amount into the Peltier elements
5
a.
On the upper side (that is, on the plate member
5
c
) of such a thermomodule
5
, a substrate
6
for attaching components is installed and fixed by soldering (for example, InPbAg eutectic solder (Melting point: 148° C.). Supporting members
7
and
8
, and a lens
9
are fixed on the substrate
6
. A semiconductor laser element
2
is disposed at the supporting member
7
, and at the same time a thermistor
10
, which detects the temperature of the semiconductor laser element
2
, is disposed there at. Also, a monitor photodiode
11
for monitoring the light emitting state of the semiconductor laser element
2
is provided on the supporting member
8
. As the semiconductor laser element
2
, those having a signal light wavelength band of, for example, a 131 nm band and 1550 nm band, or those having a wavelength band of a pumping light of an optical fiber amplifier of a 1480 nm band and 980 nm band, etc., are generally used.
A through hole
4
c
is formed at the side wall
4
b
of the package
4
, into which an optical fiber supporting member
12
is inserted and fitted. The optical fiber supporting member
12
has an inserting hole
12
a
, wherein the end portion side of an optical fiber
3
is led from the outside of the package
4
into the interior of the inserting hole
12
a
. In addition, a lens
14
is disposed in the inserting hole
12
a
with spacing from the tip end of the optical fiber
3
.
As shown in
FIG. 6B
, a plurality of lead pins
16
(in the example shown in
FIG. 6B
,
14
lead pins) are formed so as to protrude outward at the package
4
. Also, conductive patterns and conducting means
17
, which electrically connect the semiconductor laser element
2
, thermomodule
5
, thermistor
10
, and photodiode
11
to the corresponding lead pins
16
, are provided in the interior of the package
4
. By these conductive means
17
and lead pins
16
, the semiconductor element
2
, thermomodule
4
, thermistor
10
, and photodiode
11
can be, respectively, electrically connected to an external drive controlling means (not illustrated) for driving a semiconductor laser module.
In detail, in the example shown in
FIG. 6B
, the semiconductor element
2
is electrically connected to the drive controlling means by the conducting means
17
and lead pins
16
(
16
g
,
16
h
), the thermomodule
5
is electrically connected thereto by the conducting means
17
and lead pins
16
(
16
a
and
16
f
), and further the thermistor
10
is electrically connected thereto by the conducting means
17
and lead pins
16
(
16
b
and
16
e
).
The semiconductor laser module
1
shown in FIG.
6
A and
FIG. 6B
is constructed as described above. As such a semiconductor laser module
1
is electrically connected to the drive controlling means and an electric current is provided from the drive controlling means to the semiconductor laser element
2
of the semiconductor laser module
1
, a laser light is emitted from the semiconductor laser element
2
. The emitted laser light is condensed by a coupling optical system consisting of the lenses
9
and
14
and is made incident into an optical fiber
3
, whereby the light is caused to propagate in the optical fiber
3
and is used for an appointed application.
However, the intensity and wavelength of the laser light emitted from the abovementioned semiconductor laser element
2
are caused to fluctuate in response to the temperature of the semiconductor laser element
2
itself. For this reason, in order to control the intensity and wavelength of the laser light so as to become constant, the drive controlling means controls, on the basis of output values outputted from the thermistor
10
, the orientation and amount of current flows to the thermomodule
5
so that the temperature of the semiconductor laser element
2
becomes constant, whereby the heating action and cooling action of the thermomodule
5
are thus controlled. By the temperature control made by the thermomodule
5
, the temperature of the semiconductor laser element
2
can be kept almost constant, whereby the intensity and wavelength of the laser light emitted from the semiconductor laser element
2
can be made constant.
OBJECTS AND SUMMARY OF THE INVENTION
However, for example, there is a case where an abnormal situation arises, in which an overcurrent, in the heating direction, which heats the thermomodule
5
flows into the thermomodule
5
by erroneous operations and/or generation of an overcurrent, etc. In this case, the thermomodule
5
is excessively overheated, whereby such components as the semiconductor laser element
2
, substrate
6
, lens
9
, etc., disposed on the thermomodule
5
are rapidly heated (for example, so that the indication temperature of the thermistor
10
reaches 200° C. in ten seconds).
However, there is a case where the substrate (that is, the plate member
5
c
) at the side of the thermomodule where components such as the semiconductor laser element
2
, etc., are disposed is thermally connected to the side wall of the package
4
or the optical fiber supporting member
12
. In this case, a part of the heat transmitted from the thermomodule
5
is discharged to the periphery via the side wall of the package
4
and the optical fiber supporting member
12
. Therefore, as described above, where the thermomodule
5
is heated to an abnormally high temperature, a part of the high temperature heat is radiated from the thermomodule
5
to the periphery via the optical fiber supporting member
12
. Thereby, the amount of heat transmitted from the thermomodule
5
to the components on the thermomodule
5
can be suppressed, whereby the temperature rise of the components can be reduced.
But, in the example shown in
FIG. 6
, the plate member
5
c
of the thermomodule
5
is thermally isolated from the side wall of the package
4
and the optical fiber supporting member
12
. Accordingly, there is almost no case where the heat transmitted from the thermomodule
5
is dissipated at the periphery through the side wall of the package
4
and the optical fiber supporting member
12
. In such a case, where an abnormally high temperature heating arises at the thermomodule
5
, almost all the high temperature heat of the thermomodule
5
is transmitted to and accumulated in the components on the thermomodule
5
. Therefore, the temperature rise of the components on the thermomodule
5
becomes remarkable, where
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