Semiconductor element module

A semiconductor element module of the invention comprises a sleeve, a stem, a semiconductor light-emitting or light-receiving element, and a converging lens. In the sleeve, a fitting portion in which a ferrule for positioning an optical fiber is to be fitted is formed from its one open end toward the interior, an element housing portion coaxial with the fitting portion is formed from the other open end toward the interior, and a lens holding portion is formed to connect the fitting portion and the element housing portion. The stem is fixed to the sleeve at the other open end. The semiconductor light-emitting or light-receiving element is fixed on a surface of the stem on the element housing portion side. The converging lens is housed in the element housing portion and fixed to the sleeve, and optically couples an end face of the optical fiber to the light-emitting end face of the semiconductor light-emitting element or the light-receiving end face of the semiconductor light-receiving element. The material constituting the sleeve includes a metal having a thermal expansion coefficient close to that of a material constituting the converging lens.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a semiconductor element module used in a 
reception unit and a transmission unit in an optical communication system. 
2. Related Background Art 
An optical communication system using an optical fiber technique has been 
attracting attention in recent years. Since light-emitting and 
light-receiving elements are generally very small and are inconvenient for 
use as they are, they are usually provided in a semiconductor element 
module. A sleeve is formed in this semiconductor element module to connect 
this module to a ferrule having an optical fiber inserted therein. 
A light-emitting diode is generally used as a light-emitting element. Since 
emitted light diffuses, the light is generally converged by a lens and 
guided into the optical fiber. Since light emitting from the end face of 
the optical fiber also diffuses, a lens must be provided between the 
optical fiber and the light-receiving element, thereby improving the ratio 
of light guided to the light-receiving element. 
Hence, a lens must be provided between a semiconductor element, e.g., a 
light-emitting or light-receiving element, and the optical fiber. An 
example of a conventional module has a structure in which a lens is 
directly provided with a semiconductor element (e.g., Japanese Patent 
Laid-Open No. 4-165312 and the like). Another example has a structure in 
which a lens is provided in a module. When a lens is provided in a module, 
a metal holder 101 holding a lens 120 therein, as shown in FIG. 1, is 
mounted to a sleeve (not shown) which is formed separately from the metal 
holder 101. To hold a lens in a metal holder, a lens is held on a metal 
cylinder or the like. 
At this time, SUS430, which is a material having a thermal expansion 
coefficient close to that of a glass material constituting the lens, is 
used as the material of the cylinder holding the lens. SUS303-based 
material having a good machining performance is used as the material 
constituting the sleeve. 
Alternatively, as shown in FIG. 2, a light-emitting element is hermetically 
sealed by using a cap 201 that fixes a lens 220, and the cap 201 is 
mounted to a sleeve. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a semiconductor element 
module for optical communication which has a small number of components 
and a high endurance against a connecting/disconnecting operation and 
which can be aligned easily. 
According to the present invention, there is provided a semiconductor 
element module comprising: a sleeve with a first hollow portion, in which 
a ferrule for positioning an optical fiber is to be fitted, is formed 
having a first open end which extends toward an interior; a second hollow 
portion coaxial with the first hollow portion, is formed from a second 
open end thereof toward the interior; and a third hollow potion is formed 
to link the first and second hollow portions; a stem fixed to the sleeve 
at the second open end; a semiconductor light-emitting or light-receiving 
element fixed on a surface of the stem on the second hollow portion side; 
and a converging lens, housed in the third hollow portion and fixed to the 
sleeve, for optically coupling an end face of the optical fiber to a 
light-emitting end face of the semiconductor light-emitting element or a 
light-receiving end face of the semiconductor light-receiving element, 
wherein the sleeve is integrally formed using a metal having a thermal 
expansion coefficient close to that of a material constituting the 
converging lens (within 30%). 
In the above semiconductor element module, the sleeve is preferably made of 
a corrosion-resistant metal, stainless steel, ferrite-based stainless 
steel, an SUS430-based metal, an SUS430F metal, or a metal having a nature 
corresponding to that of the aforementioned metals. 
The converging lens is preferably made of BK7 optical glass. TaF-3, HE-2, 
K-2, LF-5, F-3, SF-2, and LaF-3 optical glass are also usable. 
The converging lens is preferably hermetically fixed to close the third 
hollow portion, and the stem is preferably hermetically fixed to close the 
second open end. The converging lens is preferably fixed to the lens 
holding portion with a low-melting point glass or an inorganic or organic 
glue. 
According to the above arrangement, since the third hollow portion holding 
the lens and the first hollow portion in which the ferrule is to be 
inserted are integrally formed as a sleeve, they are coaxial positioned 
relative to each other at high precision. Therefore, the centering 
operation of the optical fiber, the lens, and the semiconductor element, 
which operation is required when the optical fiber is fitted in the sleeve 
through the ferrule and the stem fixing the semiconductor element (a 
light-emitting or light-receiving element) is mounted to the sleeve, can 
be performed easily. Since the first and second hollow portions are 
integrally formed as the sleeve by using the same material, the number of 
components can be decreased. 
Furthermore, since the thermal expansion coefficient of the material 
constituting the sleeve and that of the material constituting the lens are 
close to each other, even if the module is exposed to a large temperature 
change, a gap will not be formed between the sleeve and the lens, and the 
material glueing the lens and the sleeve will not be separated. 
When the lens and the stem are fixed to the sleeve in contact therewith, 
the air-tightness of the second hollow portion housing the semiconductor 
element is maintained. Hence, impurities will not enter the second hollow 
portion from the outside. 
If ferrite-based stainless steel, a SUS430-based metal, a SUS430F metal, or 
a metal having a nature corresponding to that of these metals is used as 
the material of the sleeve, cohesion of the sleeve and the ferrule can be 
avoided. 
As described above, according to the present invention, since the third 
hollow portion holding the lens and the first hollow portion are 
integrally formed as the sleeve from the same material, the centering 
operation of the optical fiber, the lens, and the semiconductor element, 
which operation is required when the optical fiber is fitted in the first 
hollow portion and the stem fixing the semiconductor element 
(light-emitting or light-receiving element) is mounted to the sleeve, can 
be easily performed, and the optical axes of these components can be 
aligned with high precision. Also, the number of components can be 
decreased. Therefore, the manufacturing cost can be decreased, and the 
yield can be increased. 
Since the thermal expansion coefficient of the material constituting the 
sleeve and that of the material constituting the lens are close to each 
other, even if a large temperature change occurs, a gap will not be formed 
between the sleeve and the lens, and the material adhering the lens and 
the sleeve will not be separated. Therefore, the air-tightness of the 
second hollow portion can be maintained even if a large temperature change 
takes place. 
Since the lens and stem are fixed to the sleeve in tight contact therewith, 
the air-tightness of the second hollow portion is maintained. Hence, 
impurities will not enter the second hollow portion from the outside. 
Therefore, a semiconductor element module having a high reliability can be 
obtained. 
If ferrite-based stainless steel, the SUS430-based metal, the SUS430F 
metal, or a metal having a nature corresponding to that of these metals is 
used as the material of the sleeve, cohesion of the sleeve and the ferrule 
can be avoided. 
Thus, according to the present invention, a high-reliability, low-cost, 
high-performance semiconductor element module can be provided. 
The present invention will become more fully understood from the detailed 
description given hereinbelow and the accompanying drawings which are 
given by way of illustration only, and thus are not to be considered as 
limiting the present invention. 
Further scope of applicability of the present invention will become 
apparent from the detailed description given hereinafter. However, it 
should be understood that the detailed description and specific examples, 
while indicating preferred embodiments of the invention, are given by way 
of illustration only, since various changes and modifications within the 
spirit and scope of the invention will become apparent to those skilled in 
the art form this detailed description.

DETAILED DESCRIPTION OF THE INVENTION 
The embodiment of the present invention will be described with reference to 
the accompanying drawings. In the description of the drawings, the same 
elements will be denoted by the same reference numerals. 
The embodiment of the present invention will be described with reference to 
FIGS. 3 and 4. 
As shown in FIGS. 3 and 4, a fitting portion 11 serving as the first hollow 
portion in which an optical fiber positioning ferrule is to be fitted is 
formed in a sleeve 1 from one open end toward its interior. An element 
housing portion 13 serving as the second hollow portion coaxial with the 
fitting portion 11 is formed in the sleeve 1 from the other open end 
toward its interior. The inner diameter of the element housing portion 13 
is larger than that of the fitting portion 11. A lens holding portion 12 
serving as the third hollow portion is defined in the sleeve 1 and links 
the first and second hollow portions. The inner diameter of the lens 
holding portion 12 is smaller than that of the fitting portion 11. The 
sleeve 1 may be made of SUS430F metal. 
The inner circumferential surface of a distal end portion of the fitting 
portion 11 is formed in a tapered manner to be wider toward the outer 
portion. This aims at facilitating fitting of the ferrule. In other words, 
the distal end portion is tapered so that it functions as a ferrule guide. 
The wall of the lens holding portion 12 is thicker than that of the fitting 
portion 11, and a ball lens 20 is fixed in the inner side of the lens 
holding portion 12 with a low-melting point glass. The low-melting point 
glass is a glass to which selenium, thallium, arsenic, or sulfur is added 
to give a low melting point. The lens material of the ball lens 20 may be 
BK7 optical glass. The material for fixing the ball lens 20, may be an 
organic glue, an inorganic glue, or the like, used in place of the 
low-melting glass. 
A disk-shaped stem 31 is fixed to the open end of the sleeve 1 on the 
element housing portion 13 side by projection welding. 
The element housing portion 13 is hermetically maintained, and its interior 
is a dry N.sub.2 gas atmosphere. When the element housing portion 13 is 
hermetically maintained in this manner, dust or a corrosive gas will not 
enter the element housing portion 13 from the outside, thereby maintaining 
a high reliability. 
As a method of glueing the stem 31 to the sleeve 1, a solder sealing 
method, or the like, are available in addition to projection welding. The 
interior of the element housing portion 13 is not limited to the N.sub.2 
gas atmosphere but can be other inert gas atmospheres, e.g., an Ar gas 
atmosphere, or can be set at a vacuum state. 
The stem 31 is obtained by plating Ni to cold-rolled steel and plating Au 
to the Ni-plated cold-rolled steel. A semiconductor light-emitting element 
41 is placed on the upper surface of the stem 31. Three stem pins 32a, 
32b, and 32c are attached to predetermined positions, as shown in FIG. 3, 
of the stem 31 respectively through seal tubes 34. The upper ends of the 
stem pins 32a, 32b, and 32c projecting through the upper surface of the 
stem 31 are connected to the semiconductor light-emitting element 41 
respectively through wires 33. The stem pin 32b may be directly welded to 
the stem 31 to serve as a ground terminal, thereby providing an 
electromagnetic shield effect. 
As described above, according to the semiconductor element module of this 
embodiment, since the fitting portion 11 and the lens holding portion 12 
of the sleeve 1 are integrally formed from the same material, one 
centering operation is sufficient for aligning the light-emitting element 
and the optical fiber. More specifically, the ball lens 20 can be 
positioned by fixing it in the lens holding portion 12 of the sleeve 1, 
and centering can be performed by fitting the ferrule having an optical 
fiber in the fitting portion 11 and aligning the stem 31, to which the 
semiconductor light-emitting element 41 is fixed, to the open end of the 
sleeve 1. Thus, the centering operation is simple, increasing yield, and 
reducing machining cost. Also, since the entire structure is made of a 
same material, the number of components can be decreased. 
To form the sleeve 1 as indicated in the above embodiment, it may be formed 
in accordance with, e.g., coaxial machining by using an NC lathe. When 
coaxial machining is performed by using the NC lathe, the coaxial degree 
of the fitting portion 11 and the lens holding portion 12 can be 
increased. When the coaxial degree of the fitting portion 11 and the lens 
holding portion 12 is increased, the optical axis of the optical fiber and 
the center of the ball lens 20 can be aligned at a high precision by 
fitting and fixing the ball lens 20 in the lens holding portion 12. 
In the above embodiment, SUS430F metal is used as the material of the 
sleeve 1. However, a corrosion-resistant metal, stainless steel, 
ferrite-based stainless steel, an SUS430-based metal, an SUS430F metal, or 
a metal having a nature corresponding to that of these metals may also be 
used. Of these materials, when ferrite-based stainless steel, an 
SUS430-based metal, an SUS430F metal, or a metal having a nature 
corresponding to that of these metals, which are represented by SUS430F, 
is used, cohesion of the ferrule and the sleeve can be prevented even if 
the connecting/disconnecting operation of the ferrule is repeated. 
As the material of the ball lens 20, BK7 optical glass is used. However, 
any other material can be used as far as it has a thermal expansion 
coefficient close to that of the metal constituting the sleeve. In other 
words, the material of the ball lens may be determined first and a metal 
having a thermal expansion coefficient k.sub.2 close to that of the 
material of the ball lens may be selected to form the sleeve. Or, the 
metal of the sleeve may be determined first and a material having a 
thermal expansion coefficient (k.sub.1) close to that of the metal of the 
sleeve may be selected to form the ball lens which expressed by the 
following equation 
##EQU1## 
When the thermal expansion coefficients of the ball lens and the metal 
forming the sleeve are close, even if a large temperature change occurs, a 
gap will not be formed between the ball lens and the lens holding portion, 
and the material which adheres the ball lens and the lens holding portion 
will not be removed. As a result, the air-tightness in the element housing 
portion 13 can be maintained even if a large temperature change occurs. 
If a light-receiving element is housed in the element housing portion 13 
described in the above embodiment, the module can be used as the 
light-receiving element module. In this case, the ball lens converges the 
light from the optical fiber onto the light-receiving end face of the 
light-receiving element. 
From the invention thus described, it will be obvious that the invention 
may be varied in many ways. Such variations are not to be regarded as a 
departure from the spirit and scope of the invention, and all such 
modifications as would be obvious to one skilled in the art are intended 
to be included within the scope of the following claims.