Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package
Reexamination Certificate
2001-10-09
2004-05-25
Davie, James (Department: 2828)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
C372S034000, C372S036000
Reexamination Certificate
active
06740963
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical module employed for a high-density wavelength division multiplex optical transmission system.
2. Description of the Prior Art
FIG. 17
is a schematic sectional view showing the structure of a conventional optical module. Referring to
FIG. 17
, the conventional optical module mainly includes a semiconductor laser
20
converting an electric signal to an optical signal, a thermistor
70
serving as temperature detection means, a mounting unit
50
mounting the semiconductor laser
20
and the thermistor
70
, a thermoelectric cooling element
80
for heating/cooling the mounting unit
50
for controlling the temperature thereof, a driver IC (integrated circuit)
30
, a feeder line
110
, a package
60
storing these members, and a signal input connector
40
electrically connected to an electric signal input/output unit of the package
60
.
The feeder line
110
is employed for electrically connecting the semiconductor laser
20
and the electric signal input/output unit of the package
60
with each other. The driver IC
30
is electrically connected between the feeder line
110
and the electric signal input/output unit of the package
60
for amplifying the electric signal input in the semiconductor laser
20
.
FIGS. 18 and 19
are a perspective view and a sectional view schematically showing the structure of the feeder line
110
respectively. Referring to
FIGS. 18 and 19
, the feeder line
110
is a microstrip line prepared by forming conductor films
102
and
103
on an alumina ceramic substrate
101
mainly composed of aluminum oxide. Each of the conductor films
102
and
103
consists of a multilayer structure including at least two layers, i.e., a lower conductor layer
102
b
or
103
b
actually fed with a high-frequency electric signal and a gold plating layer
102
a
or
103
a
necessary for soldering or wire bonding.
A wavelength division multiplex transmission system is watched with interest as an application of such an optical module. This system, multiplexing a plurality of signals in an optical wavelength region and transmitting the same, readily increases the capacity of an optical communication system. Recently, a high-density wavelength division multiplex transmission system narrowing the multiplexed wavelength interval to 200 GHz or 100 GHZ has been defined under international standards for attaining a higher capacity. The optical module must have a sufficiently stable wavelength (preferably not more than about 1/100 the wavelength interval) with respect to this wavelength interval.
In the optical module shown in
FIG. 17
, heat flows into the mounting unit
50
mounting the semiconductor laser
20
and the thermistor
70
mainly through the aforementioned feeder line
110
. The temperature of the optical module is so controlled that the temperature detected by the thermistor
70
is constant.
In practice, however, the portion provided with the semiconductor laser
20
and the portion provided with the thermistor
70
are different in thermal resistance from each other as viewed from the heat inflow path, to exhibit different temperatures, as shown in FIG.
20
. When the ambient temperature for the optical module changes, therefore, the temperature of the semiconductor laser
20
disadvantageously changes even if the temperature of the optical module is so controlled that the temperature detected by the thermistor
70
is regularly constant.
Referring to
FIG. 20
, the descending solid line shows temperature distribution in the case where the package
60
has a higher temperature than the semiconductor laser
20
while the ascending solid line shows temperature distribution in the case where the package
60
has a lower temperature than the semiconductor laser
20
.
Assuming that the thickness of the substrate
101
of alumina (thermal conductivity: 33 W/m/K) is 254 &mgr;m and the thickness of the conductor films
102
and
103
of gold (thermal conductivity: 315 W/m/K) is 3 &mgr;m in the microstrip line shown in
FIGS. 18 and 19
, thermal conduction between the alumina part and the conductor parts is about 9:1 and a larger quantity of heat is transmitted through the alumina part. While thermal conductivity can be lowered by reducing the thickness of the substrate
101
consisting of alumina, the substrate
101
is readily cracked if the thickness thereof is reduced. Therefore, the thermal conductivity cannot be much reduced in practice.
Wires
90
a
for the driver IC
30
define another heat inflow path, as shown in FIG.
21
. The wires
90
a
connected to the driver IC
30
for amplifying the electric signal input in the semiconductor laser
20
are formed on an electric circuit mounting unit
90
A. When the electric signal is input in the connector
40
, the wires
90
a
for the driver IC
30
must be coupled to leads
90
C arranged oppositely to the connector
40
. Therefore, the wires
90
a
are electrically connected to the leads
90
C through wires
90
d
located on the mounting unit
50
and conductor patterns
90
b
located on a lead mounting substrate
90
B.
In the conventional optical module, the wires
90
a
are coupled to the leads
90
C located oppositely to the driver IC
30
through the mounting unit
50
mounting the semiconductor laser
20
, and hence heat flows into the mounting unit
50
through the wires
90
a
or other wires. When the ambient temperature for the optical module changes, therefore, the temperature of the semiconductor laser
20
disadvantageously changes although the temperature of the optical module is so controlled that the temperature detected by the thermistor
70
is regularly constant, similarly to the aforementioned case where heat flows into the optical module through the feeder line
110
.
Temperature dependency of the oscillation wavelength of the semiconductor laser
20
is about 10 GHz/°C., and hence the temperature thereof must be controlled with precision of not more than about 0.1° C. within the category temperature range. Therefore, wavelength change of the semiconductor laser
20
caused by heat flowing into the mounting unit
50
through the feeder line
110
or the wires
90
a
comes into question.
Further, a conventional optical communication system performs no multiplexing in the wavelength region, and hence thermal design is simply based on whether or not the mounting unit
50
can be heated/cooled to a prescribed temperature in the category temperature range. Therefore, the aforementioned problem has been first clarified when the high-density wavelength division multiplex transmission system performing high-density multiplexing in the wavelength region has been watched with interest.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an optical module capable of suppressing wavelength change of a semiconductor laser caused by inflow of heat in a high-density wavelength division multiplex optical transmission system multiplexing a plurality of signals in an optical wavelength region in high density and transmitting the same.
The optical module according to the present invention comprises a package, an optical device, a mounting unit and a feeder line. The package has an electric signal input/output unit. The optical device is arranged in the package. The mounting unit mounts the optical device. The feeder line is employed for electrical connection between the optical device and the electric signal input/output unit, and includes a dielectric substrate having thermal conductivity smaller than the thermal conductivity of aluminum oxide and a conductor film formed on the dielectric substrate.
In the optical module according to the present invention, the thermal conductivity of the dielectric substrate employed in the feeder line is smaller than the thermal conductivity of aluminum oxide. Thus, heat can be inhibited from flowing into the optical device through the feeder line as compared with a conventional feeder line employing a dielectric substrate of aluminum oxide. Therefore,
Kaneko Shinichi
Takagi Shin-ichi
Burns Doane Swecker & Mathis L.L.P.
Davie James
Mitsubishi Denki & Kabushiki Kaisha
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