Optical waveguides – Accessories
Reexamination Certificate
2002-07-12
2004-06-01
Prasad, Chandrika (Department: 2839)
Optical waveguides
Accessories
C385S136000, C385S088000
Reexamination Certificate
active
06744961
ABSTRACT:
BACKGROUND OF THE INVENTION
This application claims the benefit of a Japanese Patent Application No. 2002-007815 filed Jan. 16, 2002, in the Japanese Patent Office, the disclosure of which is hereby incorporated by reference.
1. Field of the Invention
The present invention generally relates to optical modules, and more particularly to an optical module which is made up of a semiconductor package and a metal casing, where the semiconductor package is provided with a semiconductor optical element and a metal base which is connected to the metal casing while maintaining an insulated state with respect to the metal casing.
2. Description of the Related Art
FIGS. 1A through 1C
are diagrams for explaining an example of a semiconductor package.
FIG. 1A
shows a side view of a semiconductor package
1
,
FIG. 1B
shows a plan view of the semiconductor package
1
, and
FIG. 1C
shows a rear view of the semiconductor package
1
. The semiconductor package
1
has a well known internal structure, and a description and illustration thereof will be omitted.
The semiconductor package
1
has a vacuum structure inside, and an optical element is mounted inside the semiconductor package
1
so that the optical element can optically couple to an optical fiber
2
which extends outside from a tip end of the semiconductor package
1
. In order to achieve the vacuum structure and to maintain a sufficient mechanical strength, a circular base
3
is made of a metal. A cover
4
covers the tip end periphery of the semiconductor package
1
. This cover is made of a synthetic resin, and has a generally cone shape towards the optical fiber
2
.
A flange
6
having holes
5
used for mounting is provided on the base
3
. For example, this flange is formed by removing top and bottom portions of a circular plate. As shown in
FIG. 1C
, four terminals
7
-
1
through
7
-
4
extend outwardly from the flange
6
. The terminal
7
-
1
directly penetrates the metal portion of the base
3
. The other terminals
7
-
2
through
7
-
4
are electrically insulated with respect to the base
3
. Accordingly, the terminal
7
-
1
also functions as a ground (GND) terminal which is electrically connected to the base
3
.
As shown in
FIG. 1C
, the terminals
7
-
2
and
7
-
4
are connected to a connection pattern on a terminal plate
8
by soldering. The terminal plate
8
is formed by a printed circuit board. The terminals
7
-
2
and
7
-
4
are connected to corresponding terminals
9
-
1
and
9
-
2
on both sides of the terminal plate
8
via a wiring pattern on the terminal plate
8
. The terminals
7
-
1
and
7
-
3
extend via a cutout in the terminal plate
8
. As may be seen from
FIGS. 1A and 1B
, the terminals
7
-
1
and
7
-
3
and the terminals
9
-
1
and
9
-
2
of the terminal plate
8
are arranged linearly in a horizontal direction.
Conventionally, in the optical module for use in optical transmission at a high bit rate of 600 Mbps or higher, a power supply voltage of a driving integrated circuit (IC) for driving the optical element such as a laser diode is −5 V. For this reason, the terminal
7
-
1
and the base
3
are electrically connected as shown in
FIGS. 1A through 1C
so as to connect an anode circuit terminal and the base
3
.
When combining the semiconductor package
1
and a driving LSI using a negative power supply voltage, the semiconductor package
1
is mounted on the metal casing so that the cathode of the laser diode is connected to −5 V, for example, and the anode of the laser diode is connected to the ground (GND).
Recently, the driving IC for driving the laser diode uses a CMOS structure when transmitting at a high bit rate, and it has become possible to drive the laser diode using a power supply voltage of +3 V, for example. Hence, the laser diode of the semiconductor package
1
shown in
FIGS. 1A through 1C
which is conventionally combined with the driving IC using the negative power supply voltage, needs to be combined with the driving IC using a positive power supply voltage. But according to the conventional mounting method, the entire metal casing of the optical module including the semiconductor package
1
will have the potential of the positive power supply voltage.
More particularly, the terminals are connected so that the positive power supply voltage of an anode circuit of the laser diode is connected to the ground (GND) terminal
7
-
1
, a cathode circuit of the laser diode is connected to the terminal
7
-
2
(
9
-
1
), and a monitoring photodiode for controlling light emission of the laser diode is connected to the terminals
7
-
3
and
7
-
4
(
9
-
2
).
When mounting the optical module described above on an apparatus, the terminal
7
-
1
is connected to a ground circuit of the apparatus, which would in turn short-circuit the power supply. Accordingly, it is necessary to electrically insulate the optical module. It is conceivable to form the metal casing by an electrically insulative material such as a synthetic resin, but the resistance of the circuit against electromagnetic noise deteriorates if the casing is not made of a metal.
FIGS. 2A through 2C
are diagrams for explaining the semiconductor package
1
mounted on a metal casing
11
.
FIG. 2A
shows a side view in cross section of the semiconductor package
1
and the metal casing
11
,
FIG. 2B
shows a plan view of the semiconductor package
1
and the metal casing
11
, and
FIG. 2C
shows a front view of the semiconductor package
1
and the metal casing
11
.
The metal casing
2
has a box shape which is formed by bending four sides of a plate member such as a steel plate. An L-shaped metal fitting
12
is provided inside on the bottom surface of the metal casing
11
by soldering, for example. Four mounting terminals
13
with stepped portions extend inwards by being bent from the bottom surface of the metal casing
11
, and four mounting terminals
14
extend outwards by being bent from the bottom surface of the metal casing
11
. A pair of engaging projections
15
is press-molded on each of the two sidewalls of the metal casing
11
. The entire metal casing
11
is subjected to a suitable rust-proofing process, such as nickel plating, which permits soldering thereon.
The mounting terminals
13
fit into corresponding through holes formed in a conductor pattern formed on a printed circuit board
16
. The printed circuit board
16
is positioned to a predetermined height from the bottom surface of the metal casing
11
by the stepped portions of the mounting terminals
13
. The mounting terminals
13
are soldered onto the conductor pattern in the state where the printed circuit board
16
is positioned. A plurality of lead terminals
17
are arranged in parallel on both sides of the printed circuit board
16
, and these lead terminals
17
extend outside via cutouts formed in the bottom surface of the metal casing
11
. Various circuit parts and circuit patterns are provided on the printed circuit board
16
, but the illustration thereof is omitted in
FIGS. 2A through 2C
so as to simplify the drawing.
The flange
6
of the semiconductor package
1
connects to a vertical surface of the metal fitting
12
via an insulator plate
18
which is made of an electrically insulative material such as a synthetic resin. Screws
21
are inserted through the holes
5
via an insulator bush
19
made of a synthetic resin, from the front side of the flange
6
, and are screwed into screw holes in the metal fitting
12
, so that the flange
6
is fixed to the metal fitting
12
. Accordingly, the flange
6
of the base
3
of the semiconductor package
1
is mounted with respect to the metal casing
11
in a state making no electrical contact to the metal casing
11
. The tip end of the semiconductor package
1
projects outside the metal casing
11
towards the front side via a cutout
22
which is formed at the front side of the metal casing
11
.
FIGS. 3A through 3C
are diagrams for explaining a state where a metal cover is mounted on the structure shown in
FIGS. 2A through 2C
.
FIG.
Fujitsu Limited
Prasad Chandrika
Staas & Halsey , LLP
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