Optical: systems and elements – Optical amplifier – Particular active medium
Reexamination Certificate
2001-11-09
2003-09-02
Black, Thomas G. (Department: 3663)
Optical: systems and elements
Optical amplifier
Particular active medium
C372S043010
Reexamination Certificate
active
06614590
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical semiconductor hermetic sealing package for accommodating an optical semiconductor element in its interior and an optical semiconductor module and an optical fiber amplifier using this optical semiconductor hermetic sealing package.
2. Description of the Related Art
In semiconductor devices for opto-electronics that need to operate at high speed for, for example, optical communication, in particular semiconductor modules such as those of light sources for exciting optical fiber amplifiers or of optical semiconductor amplifiers, hermetic sealing packages are employed for accommodating the optical semiconductor elements, driver ICs, etc., in their interiors.
As shown in FIG.
1
and
FIG. 2
, in a conventional optical semiconductor hermetic sealing package, typically, a bottom plate
2
made of Fe—Ni—Co alloy or Fe—Ni alloy such as 42 alloy, or composite metallic material such as CuW is fixed to a frame made of metal such as Fe—Ni—Co alloy such as Kovar. In particular, a CuW bottom plate
2
is employed in an optical semiconductor hermetic sealing package where there is high power consumption and which is required to have heat-radiating capability.
A frame
1
comprising the side walls of the optical semiconductor hermetic sealing package is made by machining or injection molding of the above-mentioned Kovar etc., and usually comprises ceramic terminals
3
which are made of a plurality of ceramic sheets metallized at the required parts, and the lead terminals
4
made of Kovar. In some cases a construction is adopted in which part of the frame
1
is constituted of ceramic, which is an insulator, and is integrated with the ceramic terminals
3
, or a construction is adopted in which the lead terminals
4
are inserted into through-holes provided in the frame
1
, and fixed by sealing with glass.
In addition, a light transmitting window
5
is formed in the frame
1
to transmit light in the interior and exterior of the package. The light transmitting window
5
normally comprises a pipe of for example Kovar which is provided with a window member made of glass or the like to provide hermetic sealing. In some optical semiconductor hermetic sealing packages, any window material of glass or the like is not employed but the optical fiber is passed through the frame
1
, the optical fiber being hermetically sealed to the transmitting window by solder brazing. In this case, only the window frame pipe is joined to the frame
1
of the package.
These components such as the frame
1
, bottom plate
2
and lead terminals
4
are assembled into an optical semiconductor hermetic sealing package by joining by means of silver brazing or other solder brazing. In order to perform hermetic sealing with a lid, in order to prevent corrosion of the package, and in order to facilitate soldering during assembly of the semiconductor module, usually this entire optical semiconductor hermetic sealing package is subsequently subjected to gold plating. After packaging the optical semiconductor element etc within this optical semiconductor hermetic sealing package, finally, the lid (not shown) is air-tightly fixed to the upper end face of the frame
1
of the package by welding or solder brazing through a ring made of Kovar and so forth.
In the semiconductor module, an optical semiconductor element etc. is packaged in the interior of the optical semiconductor hermetic sealing package mentioned above. Specifically, as shown in
FIG. 3
, in the interior of the optical semiconductor hermetic sealing package, apart from an optical semiconductor element such as a laser diode (LD) element
6
and/or a photodiode (PD) element, a driver IC to drive this, a chip thermistor for temperature detection, and so forth are packaged by being mounted on a circuit board
7
.
Optical semiconductor elements, in particular LD elements, are subject to inconveniences such as that, in addition to change of oscillation wavelength with temperature, their optical output falls at high temperature, with an extremely shortened life and adverse effect on their reliability. An electronic cooling device is therefore employed to control temperatures and cool the LD element and so forth. As shown in
FIG. 3
, the electronic cooling device has a construction in which a plurality of electronic cooling elements (Peltier elements)
8
constituted by crystals or a sintered body of a compound semiconductor BiTe are gripped between two insulating substrates
9
made of a ceramic sheet with metallized electrodes and wiring. Typically alumina or aluminum nitride is employed as the insulating substrates
9
of the electronic cooling device; in particular, aluminum nitride (AlN), which has good thermal conductivity, is employed when high heat radiating ability is required or when power consumption of the electronic cooling device is to be kept low.
The respective electronic cooling elements
8
are electrically connected by the metallized wiring on insulating substrates
9
and are provided with a pair of leads for electrical coupling between these and the semiconductor hermetic sealing package. In assembly of the optical semiconductor module, this electronic cooling device is soldered to the bottom plate
2
of the semiconductor hermetic sealing package and then a circuit board
7
, on which have been pre-mounted optical semiconductor elements, such as an LD element
6
or PD element or other components, are mounted by means of solder brazing on one of the insulating substrates
9
of the electronic cooling device.
In an optical semiconductor hermetic sealing package which are constituted by parts made of different materials, as described above, after being formed into an optical semiconductor module, there was sometimes deterioration of performance of the electronic cooling elements such as BiTe elements in an environment endurance test at −40° C. to +125° C. as specified in MIL-STD. The deterioration of performance of such electronic cooling elements is caused by cracking resulting from thermal stress concentration in the electronic cooling elements such as BiTe elements, whose Young's modulus is low and which is comparatively soft, due to warping of the bottom plate of the optical semiconductor hermetic sealing package and/or the circuit board etc on which the LD element or PD element within the semiconductor module has been mounted. The warping occurs due to the differences of thermal expansion coefficient between the members constituting the module.
When such deterioration of the performance of the electronic cooling elements occurs, the problem is experienced that power consumption becomes large because of a deterioration of cooling efficiency of the electronic cooling device, resulting, in the worst case, in temperature control of the optical semiconductor module becoming impossible to achieve because of its own generation of heat. Also, warping of the bottom plate of the semiconductor hermetic sealing package tends to occur the deviation of the optical axis of the optical system that effects optical coupling between the optical semiconductor element such as the LD element or PD element and the optical fiber, even if it does not give rise to any defects of the electronic cooling device. Such optical axis deviation causes the problem of lowering of output at the optical fiber terminals of the optical semiconductor module.
To deal with such problems, for example Japanese Patent Application Laid-open No. 6-314747 discloses the countermeasure of mitigating and absorbing warping by making the flange of the bottom plate thin, by grinding. Also, in Japanese Patent Application Laid-open No. 6-82659, the same effect is obtained by, instead of making the flange of the bottom plate thin, constructing only the flange of another metal having a small modulus of longitudinal elasticity. However, in both methods, processing is difficult and it was difficult to obtain sufficient strength.
Japanese Patent Application Laid-open No. 5-67844 proposes an
Black Thomas G.
Hughes Deandra M.
McDermott & Will & Emery
Sumitomo Electric Industries Ltd.
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