Optical waveguides – With optical coupler – With alignment device
Reexamination Certificate
2000-08-21
2003-08-12
Robinson, Mark A. (Department: 2872)
Optical waveguides
With optical coupler
With alignment device
C385S091000
Reexamination Certificate
active
06606435
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a laser diode module for use in optical communications and a method for fabricating the same.
PRIOR ART
Conventionally, laser diode modules have been used in optical communications, in which a laser diode element (a semiconductor laser element) and an optical fiber for allowing the light from the laser diode element to propagate therethrough are optically coupled in a module. An example of such laser diode modules is disclosed in the European Patent Application EP 0 717297 A2. One that is disclosed therein is a laser diode module shown in FIG.
3
. For example, as shown in FIG.
3
(
c
), the laser diode module has a metallic base
1
and a laser diode element
3
that is fixedly disposed on a element mount block
2
secured to the upper side of the base
1
.
A lens formed fiber
8
is provided as opposed to the laser diode element
3
. The lens formed fiber
8
has a lens (not shown in the figure) formed on the distal end of the optical fiber for receiving laser beams from the laser diode element
3
. The lens formed fiber
8
is secured to the ferrule
4
with the distal end thereof, on which the lens is provided, protruded through the distal end of a ferrule
4
toward the laser diode element
3
.
Moreover, with the lens formed fiber
8
and the laser diode element
3
aligned with each other, the front side edge portions of the ferrule
4
near the laser diode element
3
are fixedly sandwiched on the both sides thereof by means of a ferrule front fixing part
15
. On the other hand, the rear side edge portions of the ferrule
4
furthest from the laser diode element
3
are fixed to the base
1
via a rear fixing part
16
. Furthermore, the ferrule
4
is formed in a cylindrical shape or in a shape having a U-shaped groove (in
FIG. 3
, a cylindrically shaped one is shown).
The aforementioned ferrule front fixing part
15
is disposed, with the part
15
guided by means of a guide portion
11
, spaced approximately 0 to 5 &mgr;m to a side surface of the ferrule
4
at both sides (on the sides of both side portions) of the ferrule
4
and is fixed to the guide portion
11
. After the part
15
has been fixed to the guide portion
11
, the ferrule
4
is fixedly YAG-welded to the ferrule front fixing part
15
, thus a sandwiched portion
9
is formed.
Furthermore, in such a laser diode module, the lens formed at the distal end of the lens formed fiber
8
is machined to obtain a high optical coupling efficiency with the laser diode element
3
. However, the tolerance for optical fiber dislocation in optical coupling is extremely small. For this reason, it is inevitably necessary to fixedly align the aforementioned lens formed fiber
8
with the laser diode element
3
with an extremely high accuracy. This requires much higher accuracy compared with a case where one or more minute optical lenses such as spherical and aspherical lenses are disposed in between the edge surface of an ordinary optical fiber with no lens attached thereto and the laser diode element
3
to align the laser diode element
3
with the lens and the optical fiber.
When the aforementioned laser diode module is fabricated, the lens formed fiber
8
is aligned to obtain maximum coupling efficiency with laser diode
3
. Thereafter, as shown in FIG.
3
(
a
), the ferrule front fixing part
15
is disposed at the both sides (at the surfaces of the both sides) of the front side (the side near the laser diode element
3
) of the ferrule
4
in between the ferrule
4
and the guide portion
11
, which are provided with a spacing therebetween. Furthermore, the guide portion
11
is fixedly provided on the base
1
or formed in one piece with the base
1
. Then, the ferrule front fixing part
15
is adapted to be guided by means of the guide portion
11
so as to be able to slide on the surface of the base
1
in the direction (toward X direction in the figure) substantially orthogonal to the beam axis of the ferrule
4
. Here, the spacing between the ferrule front fixing part
15
and a side surface of the ferrule
4
is adjusted to within the range of approximately 0 to 5 &mgr;n.
Thereafter, as shown in FIG.
3
(
b
), after the ferrule front fixing part
15
is fixedly welded to the guide portion
11
at a plurality of welded portions
7
, the ferrule front fixing part
15
and the ferrule
4
are fixedly YAG-welded. The lens formed fiber
8
is dislocated to the laser diode
3
by this YAG-welding. This fixed position is the sandwiched portion
9
of the ferrule
4
. After that, for example as shown in
FIG. 4
, the edge of the rear side of the ferrule
4
(the side furthest from the laser diode element
3
) is moved for alignment by a fulcrum at the sandwiched portion
9
. Thus, the laser diode element
3
and the lens formed fiber
8
are re-aligned. Furthermore, in
FIG. 4
, reference number
5
shows a lens provided on the fiber.
Then, under the state of the aforementioned re-alignment, the rear fixing part
16
is disposed on the edge portion of the rear side of the ferrule
4
as shown in FIG.
3
(
c
). After the rear fixing part
16
has been secured to the base
1
, the ferrule
4
is fixedly YAG-welded to the rear fixing part
16
. Then, finally, the rear fixing part
16
is permanently deformed by a fulcrum at the sandwiched portion
9
in order to correct a dislocation occurring when the ferrule
4
is fixed to the rear fixing part
16
. Thus, final alignment is thereby carried out and the plastic deformation of the rear fixing part
16
allows for sustaining the ferrule
4
in a state of re-alignment.
Furthermore, in the aforementioned laser diode module, the ferrule
4
is fixedly YAG-welded at the front side edge portion of the ferrule
4
after the alignment of the laser diode element
3
with the lens formed fiber
8
. However, a certain degree of dislocation will occur upon fixing the ferrule
4
at any cost. Accordingly, in the laser diode module shown in
FIG. 3
, when the front side edge portion of the ferrule
4
is fixed according to the aforementioned method, this dislocation is reduced as follows. That is, the spacing between a side portion of the ferrule
4
and the ferrule front fixing part
15
is adjusted to within a range of approximately 0 to 5 &mgr;m, and thereafter the side portion of the ferrule
4
and the ferrule front fixing part
15
are fixedly welded to each other. This will reduce the displacement of the ferrule at the time of YAG welding between the ferrule front fixing part
15
and the ferrule
4
, thus reducing a dislocation when the front side edge portion of the ferrule
4
is fixed.
Subsequently, the lens formed fiber
8
is re-aligned with the laser diode element
3
. The reduction in dislocation is also intended to reduce re-alignment displacement of the rear side edge portion of the ferrule
4
by a fulcrum at the fixed portion (the sandwiched portion
9
) at this time.
However, in the aforementioned laser diode module, the ferrule
4
is fixedly welded at a re-aligned position using the aforementioned rear fixing part
16
that is fixedly welded to the base
1
. This makes it impossible to accurately secure the ferrule
4
at said re-alignment position since, for example, the position of the rear fixing part
16
to which the ferrule
4
is to be fixed becomes misaligned when the rear fixing part
16
is fixedly welded to the base
1
. Accordingly, in the fabricating method of laser diode modules, it was necessary to perform final alignment of correcting a dislocation between the re-alignment position and the fixing position of the ferrule
4
with plastic deformation of the rear fixing part
16
.
Furthermore, the rear fixing part
16
had to take a complicated shape as shown in FIG.
3
(
c
) with additional cost in order to facilitate the final alignment between the laser diode element
3
and the lens formed fiber
8
by means of the plastic deformation. Consequently, this presented such a problem in that the laser diode module comprising such rear fixing part
16
was provided with an increase in cost.
Irie Yuichiro
Miyokawa Jun
Shimizu Takeo
Amari Alessandro V.
Lacasse & Associates LLC
Robinson Mark A.
The Furukawa Electric Co. Ltd.
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