Electric heating – Metal heating – For bonding with pressure
Reexamination Certificate
1999-10-26
2002-05-28
Copenheaver, Blaine (Department: 1771)
Electric heating
Metal heating
For bonding with pressure
C219S086900, C219S081000, C219S082000, C219S083000, C219S084000, C219S105000, C219S107000, C134S001000, C134S001300, C134S026000, C134S040000, C134S039000, C257S432000, C257S433000, C257S081000, C257S082000, C257S083000, C257S084000, C438S706000, C438S707000, C438S708000, C438S709000, C372S006000
Reexamination Certificate
active
06396023
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for hermetically sealing a high output semiconductor laser element used for an optical fiber amplifier, etc., and a hermetic-sealing apparatus for semiconductor laser elements in the field of optical transmissions.
BACKGROUND OF THE INVENTION
Conventionally, a semiconductor laser module has been frequently utilized as a signal light source and a pumping light source for an optical fiber amplifier in the field of optical transmissions.
In particular, those having wavelength bands of 980 nm, 1020 nm and 1480 nm have been known as a light source module for pumping rare metal doped optical fibers in optical fiber amplifiers. There are many cases where an optical output of more than 100 mW is required with respect to the use of such a light source.
FIG. 1
shows an example of the structure of such a high output semiconductor laser module. In
FIG. 1
, light emitted from a semiconductor laser element
11
is optically coupled with an optical fiber
12
disposed in proximity of the front end face
11
a
of the semiconductor laser element
11
, and is led to the exterior, where the light is used for an appointed application. The semiconductor laser element
11
is fixed on a thermomodule
14
for adjusting a temperature, and these devices
11
and
14
are hermetically enclosed in a package
13
.
In order to produce such high output semiconductor laser modules
10
, first, the lower plate
14
a
of the thermomodule
14
is fixed by soldering on the bottom plate
13
b
of a package
13
. At the thermomodule
14
, a lead line
14
c
is soldered to a lead terminal (not illustrated) of the package
13
for electrical connection with the exterior of the package
13
.
Next, a substrate
15
having a fixed semiconductor laser element
11
is soldered to and fixed on the upper plate
14
b
of the thermomodule
14
. An optical fiber
12
is inserted through a through hole
13
a
provided at the sidewall of the package
13
and is introduced into the interior of the package
13
, and is positioned so that most of light from the semiconductor laser element
11
is coupled thereto. And, the optical fiber
12
is fixed on the substrate
15
by YAG laser welding in the positioned state. In addition, the optical fiber
12
is also soldered at the through hole
13
a.
After that, a cover
13
c
is placed on the upper surface of the package
13
, and the circumferential portion thereof is welded by resistance welding to be hermetically sealed from the exterior.
OBJECTS AND SUMMARY OF THE INVENTION
A degradation mechanism of a high output semiconductor laser module is a PIF (Packaging Induced Failure).
The PIF is produced by a slight amount of hydrocarbons in the module being subjected to a polymerization reaction by a photochemical reaction and being adhered to the light emitting end face of a semiconductor laser element as solid organic substances. That is, the adhered organic substances absorb a laser light, thereby causing the temperature at the end face of the semiconductor laser element to rise, whereby the end face of the semiconductor laser element is melted and broken.
Herein, hydrocarbons may be ah organic solvent used for cleaning in a production process of semiconductor laser modules, flux used for soldering, etc. Even though a slight amount of hydrocarbons should remain in a package at a ppm level or less, they will become a cause of such a degradation.
The phenomenon results from a photochemical reaction made by a laser light, especially in cases where the optical output from a semiconductor laser element is large, and the laser light has a great optical energy with a very short wavelength. This is a failure mode which remarkably occurs, for example, in a case of 980 nm and 1020 nm bands which emit an optical output of 100 mW or more. A detailed report regarding the failure has been published, for example, “Requirements to avert packaging induced failure of high power 980 nm laser diodes”, Jackobson et al, LEOS, November 1993.
In order to prevent a failure of a semiconductor laser element by the PIF, a method for containing oxygen in a hermetically sealed gas
16
of the package
13
has been employed previously.
That is, since polymerization of a slight amount of hydrocarbons in the package can be suppressed due to the existence of oxygen, or by oxidation of the adhered organic substances, the organic substances can be prevented from being accumulated on the end face of the semiconductor laser element.
However, in a prior art high output semiconductor laser module, which is sealed with a sealing gas containing oxygen, although it is possible to prevent organic substances from being adhered to and being accumulated on the light emitting end face of a semiconductor laser element by actions of the oxygen sealed within, water is generated by a reaction of oxygen and the residual hydrocarbons or reaction of oxygen and organic substances adhered to the light-emitting end face, whereby the water content in the package is increased. The water generated is condensed to dew at the light-emitting end face to hinder optical coupling, whereby the optical output is lowered or short-circuits result therefrom in the interior electric wiring.
As a principle, the above phenomenon can be avoided by reducing the amount of the residual organic substances in the package. But, PIF may occur due to the existence of a very slight amount of organic substances at a level of ppm or less. In a fact, it was difficult to repeatedly achieve a very low level of organic substance which does not produce any PIF.
The present invention was developed to propose a method for maintaining the cleanliness of packages in a stabilized state and in a good condition in order to prevent organic substances from being adhered to the end face of the abovementioned high output semiconductor laser element due to photochemical reactions.
That is, a method for hermetically sealing a semiconductor laser element according to a first aspect of the invention comprises a first step of introducing oxygen into a chamber of a hermetic-sealing apparatus and irradiating ultraviolet rays to an unsealed package where a semiconductor laser element is mounted in the chamber; and a second step for purging the inside of the chamber with an inert gas and hermetically sealing an unsealed package in the inert gas atmosphere after the first step is completed.
A method for hermetically sealing a semiconductor laser element according to a second aspect of the invention is featured in that, in the second step of the method for hermetically sealing a semiconductor laser element according to the first aspect, ultraviolet rays are irradiated onto the purging inert gas, and an unsealed package is hermetically sealed in the inert gas atmosphere onto which the ultraviolet rays are irradiated.
A method for hermetically sealing a semiconductor laser element according to a third aspect of the invention comprises a first step for introducing oxygen and an inert gas into a chamber of a hermetic-sealing apparatus and irradiating ultraviolet rays onto an unsealed package having a semiconductor laser element mounted in the chamber, and a second step for hermetically sealing the unsealed package in the atmosphere consisting of the oxygen and inert gas without being exposed to any outer atmosphere.
Further, a method for hermetically sealing a semiconductor laser element according to a fourth aspect of the invention comprises a first step for introducing oxygen and an inert gas into a chamber of a hermetic-sealing apparatus and irradiating ultraviolet rays onto an unsealed package having a semiconductor laser element mounted in the chamber; and a second step for purging the inside of the chamber with the inert gas and hermetically sealing the unsealed package in the inert gas atmosphere after the first step is completed.
Further, a method for hermetically sealing a semiconductor laser element according to a fifth aspect of the invention comprises a step of introducing a package having a semiconductor laser element
Copenheaver Blaine
Lacasse & Associates
The Furukawa Electric Co. Ltd.
Vo Hai
LandOfFree
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