Optical waveguides – Accessories – External retainer/clamp
Reexamination Certificate
1998-10-07
2001-07-24
Font, Frank G. (Department: 2877)
Optical waveguides
Accessories
External retainer/clamp
C385S088000, C385S094000, C385S136000
Reexamination Certificate
active
06266470
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an optical switch module; and, more particularly, to an optical switch module having a buffer device which is capable of effectively minimizing the influence of the temperature variation on the module performance.
DESCRIPTION OF THE PRIOR ART
Generally, an optical switch module includes an optical switch device and optical input output portions, each having an optical array assembled on a V-groove substrate for multi-channel. The optical components, e.g., the optical switch device and the optical fiber array are aligned to have a maximum optical coupling efficiency, and fixed or assembled in a module case.
Referring to
FIGS. 1A and 1B
, there are shown a top plan view and a front elevational view of a conventional optical switch module, respectively and referring to
FIGS. 2A and 2B
, there are shown a top plan view and a front elevational view of a submodule contained in the conventional optical switch module.
The conventional optical switch module includes a submodule and a package case. As shown, in the submodule, an optical switch device
1
is fixed on a ceramic chip carrier substrate
6
by using a die bonding and a wire bonding techniques at a center portion of a submodule substrate
5
. At each side of the submodule substrate
5
, an optical array
4
is assembled on the optical carrier substrate
9
and fixed through an optical fiber housing
7
and an optical fiber support member
8
by using a laser welding technique. The welding points are indicated by welding spots
11
,
12
,
27
,
28
and
29
. The submodule has a project portion on which the chip carrier is mounted to thereby facilitate to align it with the optical fiber. On the other hand, in order to maintaining a constant operating temperature of the optical switch device, a temperature detection device
10
is attached on the submodule substrate
5
. For employing the laser welding technique, a stainless 304L or KOVAR can be preferably used as a structural material, but a material of the submodule substrate
5
can be made of Cu—W in order to obtain an effective thermal propagation from the optical switch device to a thermoelectric cooling device, e.g., a heat sink,
13
and to facilitate the application of the laser welding technique.
As shown, the optical fiber array
4
is fixed on the optical housing
7
of the stainless 304L by using a resin, e.g., epoxy, and aligned to the optical switch device.
That is, in order to provide an uniform optical property to all of optical fibers, the optical fiber array is first aligned in x-, y- and z-axis directions and in rotational directions Rx, Ry and Rz for each axis. Thereafter, in order to obtain a z-axis directional solidification, a first laser welding is provided on a portion between the optical housing
7
and the optical fiber support member
8
. The active alignment is repeatedly executed in x- and y-axis directions and a second laser welding is applied to a portion between the optical support member
8
and the submodule substrate
5
to thereby provide a complete submodule. The complete submodule is shown in
FIG. 2
a.
When the submodule is assembled, the thermoelectric cooling device
13
is mounted on an inner-lower surface of the package case
3
by using In-Sn solder(melting point: 135° C.) and the assembled submodule is fixed on the thermoelectric cooling device
13
by using a thermal conductive epoxy or solder. As shown in
FIG. 1
a,
a Fan-out printed circuit board
14
is fixed to the submodule substrate
5
and through a plurality of signal lines
16
to the package case
3
by using the thermal conductive epoxy or solder. One side signal lines of the printed circuit board
14
are connected to the chip carrier substrate
6
by using a wire bonding, while the other side signal lines thereof are coupled to a number of pins of the package case
17
by using a soldering technique. A protect member made of a rubber material is provided in a hole of the package case surround the optical array. When all of internal components are assembled, the package cap is fixed on the package case by using a seam sealing technique in order to prevent the internal components contacting the outer environment.
An alignment tolerance between the optical switch device and the optical fiber is generally less than about 10 &mgr;m in y-axis, e.g., optical axis of the optical fiber, direction. In contrast, in x- and z-axis, e.g., axes normal to the optical axis, direction, when there is 1 &mgr;m in radial displacement, the coupling efficiency of the optical switch module is decreased below 50% as compared with the maximum optical coupling efficiency. Therefore, a precise and stable aligning and solidifying technique is necessarily required. Furthermore, it is also required that the variation of outer environment does not affect the alignment between the optical fiber and the optical switch device.
In the conventional optical switch module, the submodule substrate
5
is made of Cu—W which has a good thermal conductivity, so that a hetero-junction between the Cu—W and SUS304L is necessarily required in the alignment and solidification of the optical switch module. In the laser welding technique, there is no problem to prepare the optical switch module since the hetero-junction made by using the laser welding can provide a desired high integrity. In contrast, a thermal expansion constant of Cu—W is 6.5×10
−6
/° C., while a thermal expansion constant of SUS304L is 18.7×10
−6
/° C. As a result, there is a thermal mismatching between the Cu—W and SUS304L.
In general, the optical switch module is tested by using a temperature cycling experiment in the range of −40 to +85° C. On the other hand, the distance between the two hetero junctions is 6 mm in x-axis direction (3 mm in a longitudinal direction). Under −40° C., the SUS304L is deformed 7.1 &mgr;m (3.5 &mgr;m in the longitudinal direction), while Cu—W is deformed 2.5 &mgr;m (1.2 &mgr;m in the longitudinal direction) due to thermal contraction. Therefore, the difference between the deformations of SUS304L and Cu—W is about 4.6 &mgr;m (2.3 &mgr;m in the longitudinal direction). On the other hand, it is known that the plasticity recovery rate of a metal is 0.2% and, when the deformation of metal, is less than 0.2% in size, the deformation can be recovered. The size of welding portions is in range of the 300-400 &mgr;m and 0.2% thereof becomes about 0.6-0.8 &mgr;m. Therefore, the above deformation difference cannot be recovered and the welding portion may be destroyed. Furthermore, a mechanical stress may be hardly applied to the welding portion since, in the temperature cycling experiment, the temperature varies in the range from −40 to +85° C. and the deformation difference can reach about, 5-9 &mgr;m. Consequently, there is a disadvantage that the welding portion of the conventional optical switch module can be easily affected by the variation of temperature. Further, since there is a hetero-junction between SUS304L and Cu—W which are welded together in the conventional optical switch module, the deformation thereof is greater than that of the homo-junction.
SUMMARY OF THE INVENTION
It is, therefore, an object of the invention to provide an optical switch module having a buffer device, which is capable of effectively providing a stable structure and a minimum thermal deformation under the variation of temperature.
In accordance with one aspect of the present invention, there is provided an optical switch module for aligning and fixing an optical fiber array relative to an optical switch device, comprising: optical fiber support member for fixing the optical fiber array; first support means forming a homo-junction with the optical fiber support member and including a first thermal deformation buffer device; and second support means forming a hetero-junction with the first support means to support the first support means and including a second thermal deformation buffer device.
REFERENCES:
patent: 4838639 (1989-06-0
Hwang Nam
Kang Seung Goo
Lee Hee Tae
Lee Sang Hwan
Park Seong Su
Electronics and Telecommunications Research Institute
Font Frank G.
Jacobson & Holman PLLC
Nguyen Sang H.
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