Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Electromagnetic or particle radiation
Reexamination Certificate
2002-12-24
2004-09-14
Wojciechowicz, Edward (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Electromagnetic or particle radiation
C257S084000, C257S085000, C257S092000, C257S094000, C257S096000, C257S461000, C257S470000
Reexamination Certificate
active
06791150
ABSTRACT:
BACKGROUND OF THE INVENTION
1) Field of the Invention
The present invention relates to an optical module that comprises an optical element and a thermoelectric semiconductor.
2) Description of the Related Art
The Internet has become popular. As a result, there is an increasing demand for large-capacity data transmission. For the large-capacity data transmission, it is necessary to have an optical system that can transmit optical signals via an optical fiber faster.
A laser diode is used as a light source in the optical system. An optical module transmits the light generated by the laser diode to the optical fiber.
In order to increase the transmission speed of optical signals, it is necessary to execute at high speed the intensity modulation of the light generated by the laser diode. It is also necessary to improve the performance of the optical module.
Optical modules that transmit optical signals at a high-speed bit rate of 2.5 Gb/s have been put into practical use. Moreover, development of optical modules that transmit optical signals at still higher speed of 10 Gb/s have been progressed.
In order to realize large-capacity optical communications, it is necessary to provide a high-density optical fiber network by using an optical module that can transmit optical signals at a high-speed bit rate. For this purpose, a stable supply of low-cost optical modules has been desired.
FIGS. 9A and 9B
show structures of a conventional optical module disclosed in Japanese Patent Application Laid-Open No. H11-121862.
FIG. 9A
shows a top plan view of the conventional optical module in a state that an upper lid is dismounted.
FIG. 9B
shows a side view of this optical module cut along a line A—A.
In
FIGS. 9A and 9B
, a reference number
1
denotes a laser diode that converts an electric signal into an optical signal,
2
denotes a mount on which the laser diode
1
is mounted, and
3
denotes a carrier on the upper surface of which the mount
2
is installed. A reference number
4
denotes a package that accommodates the carrier
3
and seals the laser diode
1
, and
5
denotes a thermistor that is provided on the upper surface of the carrier
3
. A reference number
6
denotes a thermo-module that heats or cools the laser diode
1
to avoid a fluctuations in the temperature of the laser diode
1
due to the heating of the laser diode
1
by itself or the heat from the outside of the package
4
. Such heating or cooling of the laser diode
1
is performed to stabilize the characteristic of the laser diode
1
. A reference number
7
denotes a terminal that transmits signals between the carrier
3
and the outside of the package
4
. The elements
1
to
7
constitute an optical module
8
.
An automatic temperature control (ATC) circuit
9
is provided outside of the package
4
.
To execute intensity modulation of optical signals, a bias current Ib and a modulation current Im is applied to the laser diode
1
. When there is a rise in the temperature of the laser diode
1
, the light output of the laser diode
1
decreases, or the oscillation stops. When there is a fall in the temperature of the laser diode
1
, the light output increases. The temperature of the laser diode
1
rises even as a result of self-heating.
The ATC circuit
9
inputs-outputs control signals to/from the optical module
8
via the terminal
7
. The ATC circuit
9
receives information from the thermistor
5
, which detects the temperature of the laser diode
1
, about the temperature of the laser diode
1
, and adjusts a driving current Is supplied to the thermo-module
6
based on the temperature of the laser diode
1
so that the laser diode
1
is always kept at a constant temperature. Since the temperature of the laser diode
1
is always constant, a stable optical output can always be obtained from the laser diode
1
.
The thermo-module
6
is usually constructed of about 12 to 40 thermoelectric semiconductors. Each thermoelectric semiconductor consists of an N-type semiconductor
10
a
and a P-type semiconductor
10
b
. The thermoelectric semiconductors are arranged parallel to each other. The thermoelectric semiconductors conduct heat in a direction (heat transmission direction) that is parallel to the long side of the paper on which the
FIG. 9B
has been drawn. Each thermoelectric semiconductor is connected to a dielectric substrate at each end of the thermoelectric semiconductor in the heat transmission direction. For example, dielectric substrate
11
a
is connected to one end and dielectric substrate
11
b
is connected to the other end of the N-type semiconductor
10
a
. Wiring patterns are prepared in the dielectric substrates. The dielectric substrates of one thermoelectric semiconductor are electrically connected to the dielectric substrates of adjoining thermoelectric semiconductor such that all the thermoelectric semiconductors are connected in series.
The thermoelectric semiconductors operate according to the Peltier effect. Whether to perform heating or cooling, can be decided by simply changing the direction of the current supplied to the thermoelectric semiconductors. Therefore, the thermoelectric semiconductors are suitable for the temperature control of the laser diode
1
.
In the conventional optical module, the thermo-module
6
is mounted on the base of the package
4
, and the carrier
3
is mounted on the thermo-module
6
, so that the heat transmission direction of the thermoelectric semiconductors becomes parallel to the height direction of the thermoelectric semiconductor. However, because the thermo-module
6
is mounted on the base, and the carrier
3
is mounted on the thermo-module
6
, there has been a problem that the height of the optical module increases. Consequently, the package becomes large, and this has been a barrier for the cost reduction of the optical module.
Moreover, since a large number of the thermoelectric semiconductors are used, the workload on the thermo-module
6
increases, and the total power consumption increases. Further, the assembling becomes complex and takes time. In addition, the ATC circuit
9
, which is expensive, has to be provided. These factors have also interrupted the cost reduction of the optical module.
Optical modules that do not have the above mentioned problems have been developed and appeared in the market. These optical modules use a mini dual in-line (mini-DIL) type package. Moreover, these optical modules do not have a thermo-module. Therefore, it is possible to decrease the height of the optical module, and realize low cost.
However, in order to output a stable optical signal at the transmission speed of the order of 10 Gb/s or more, it is necessary to minimize the operation temperature of the laser diode. Concretely, it is necessary to set the operation temperature of the laser diode to about 70° C. or below. However, there is a demand that the optical module even functions at the environmental temperature of about 70° C. If the environmental temperature is 70° C., the temperature of the laser diode becomes higher and exceeds the operation temperature of the laser diode due to self-heating. Consequently, it is not possible to stably operate the laser diode if the environmental temperature is 70° C. or higher.
Therefore, there have been problems that, if the environmental temperature is 70° C. or higher, then either that laser diode does not exhibit desired characteristics or a provision has to be made to cool the surrounding of the laser diode so that the environmental temperature falls to 65° C. or below.
Various technical developments have been carried out so far to expand the range of operation temperature of the laser diode. However, expansion of the operation temperature of the laser diode has always been a difficult task.
To conclude, the conventional optical modules have a problem that the overall height is tall and cost reduction is not possible. Moreover, the optical modules that use the mini dual in-line (mini-DIL) type package and do not have a thermo-module have a problem that the temperature control of the laser di
Burns Doane Swecker & Mathis L.L.P.
Mitsubishi Denki & Kabushiki Kaisha
Wojciechowicz Edward
LandOfFree
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