Optical waveguides – With optical coupler – Particular coupling structure
Reexamination Certificate
2001-04-25
2004-08-10
Ullah, Akm Enayet (Department: 2874)
Optical waveguides
With optical coupler
Particular coupling structure
C385S147000
Reexamination Certificate
active
06775440
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a carrier for optical semiconductor device and a mounting structure thereof used in optical fiber communication system or optical local area network, and further relates to an optical semiconductor module on which optical wave guide elements such as the carrier for optical semiconductor device, an optical fiber coupled thereto and an optical wave guide channel are mounted.
2. Description of the Related Art
In recent years, optical fiber communication is realized in fields of cable television (CATV) and public data network. Furthermore, an optical module having high speed and high accuracy is realized by a module structure called “coaxial type” or “dual-inline type”. These elements are practiced mainly in a field called “trunk line”.
On the other hand, another optical module is developed by using a technology for mounting an optical semiconductor device and an optical fiber on a silicon substrate with high positioning accuracy owing to mechanical precision. This optical module is aimed to be practiced mainly in a field called “subscriber system”, so that it is required to be downsized, to be thinner and to be inexpensive.
Examples of conventional mounting structure of a surface sensing type optical semiconductor device (photodiode) are described.
FIG. 26
shows an example of a carrier (mounting base)
40
having a cubic shape. A photodiode will be mounted on the carrier
40
. Electrodes
411
and
412
, to which anode and cathode of the photodiode are respectively connected, are formed on adjoining first face
41
and second face
42
of the carrier
40
. Portions of the electrodes
411
and
412
on the first face
41
are electrically connected to the other portions on the second face
42
at the boundary of the first face
41
and the second face
42
.
FIG. 27
shows that the optical semiconductor device such as a PIN type photodiode
20
is mounted on the carrier
40
. A size of the photodiode
20
is, for example, a square of about 500 &mgr;m and a thickness of about 200 &mgr;m. A photo sensing area of the photodiode
20
is a circular having a diameter about 200 &mgr;m. An electrode
21
formed on a photo sensing plane is electrically connected with the electrode
412
by a bonding wire
31
. Another electrode
22
formed on a rear face is directly connected with the electrode
411
by a connecting element such as a solder of AuSn.
FIGS. 28A
to
28
C show a mounting structure of the carrier
40
with the photodiode
20
on a silicon substrate
30
. The photodiode
20
is held in a manner so that the photo sensing plane is vertical to a principal plane of the silicon substrate
30
via the carrier
40
. By such a configuration, an optical fiber (not shown in the figure) mounted in parallel with the principal plane on the silicon substrate
30
is optically coupled with the photodiode
20
. The portions of the electrode
411
and
412
on the first face
41
are respectively connected to electrodes (not shown) formed on the silicon substrate
30
by bonding wires
32
and
33
, so that electric power can be supplied to the photodiode
20
. The carrier
40
is generally formed by a ceramic material such as alumina. The electrodes
411
and
412
on the carrier
40
are formed on the first face
41
and the second face
42
of the carrier
40
by printing method using a paste including a filler.
In a process for forming the electrodes
411
and
412
on the first face
41
and the second face
42
of the carrier
40
, the portions of the electrodes
411
and
412
on the first face
41
and the other portions of them on the second face
42
cannot be formed at the same time. At first, the carrier
40
is disposed in a manner so that the first face
41
be disposed at the top end. The portions of the electrodes
411
and
412
on the first face
41
are formed. After that, the carrier
40
is picked up and turned by a handle so that the second face
42
be disposed at the top. Subsequently, the other portions of the electrodes
411
and
412
on the second face
42
are formed. Thus, the process for forming the electrode
411
and
412
on the first face
41
and the second face
42
of the carrier
40
is complex, and the productivity thereof is much lower.
Furthermore, accuracy of the relative position of the portions of the electrode
411
and
412
on the first face
41
and the other portions of them on the second face
42
depends on the positioning accuracy of the carrier
40
by the handle, so that the gap between the electrodes
411
and
412
and the width of them cannot be made so narrower, for example, less than about 70 &mgr;m. This limitation of the width of the electrodes
411
and
412
disturbs to decrease the impedance of the electrodes
411
and
412
, to improve the high frequency characteristics of the optical semiconductor device and to downsize the optical semiconductor module.
Furthermore, the smaller the size of the carrier becomes, the more difficult to handle the carrier, so that the productivity becomes much lower. Thus, it is substantially impossible to downsize the carrier smaller than the cubic having each side length of 2 mm by the conventional method.
In other words, the size and the cost of the carrier for optical semiconductor device are in a relation of trade off, so that the cost of the carrier becomes very expensive by downsizing and high accuracy of the carrier, and there are physical limitations in the downsizing and high accuracy.
Another mounting structure of the photodiode directly mounted on the silicon substrate without using the carrier is shown in Publication Gazette of Japanese Patent Application Hei 8-94887. A slant face, on which the photodiode is fixed, is formed on the silicon substrate at a position on production of mounting groove for the optical fiber. When the optical fiber and the photodiode are mounted on the silicon substrate, the exit plane of the optical fiber faces the photo sensing plane of the photodiode but they are not parallel. The electrode on the rear face of the photodiode directly contacts the electrode formed on the slant face, and the electrode on the photo sensing plane is connected to the electrode by the bonding wire.
Since the electrode of the photodiode is slanted with respect to the principal plane, the wiring process for connecting the electrode of the photodiode and the electrode on the silicon substrate becomes very difficult. Furthermore, the angle of the slant surface with respect to the principal plane of the silicon substrate is restricted by workability for forming and/or for wiring the electrode on the slant face, so that tolerances of photosensitivity and positioning of the photodiode become smaller than those when the photo sensing plane of the photodiode is disposed perpendicular to the optical path of the light beam emitted from the optical fiber.
Still another method for mounting the photodiode directly on the silicon substrate is shown in Publication Gazette of Japanese Patent Application Hei 9-54228. A total reflection mirror having a reflection angle about 45 degrees with respect to the exit plane of the optical fiber is formed on an end of the mounting groove for the optical fiber on the silicon substrate. The photodiode is directly mounted on the silicon substrate in a manner so that a part of the photo sensing plane overhangs for facing the mirror. An optical path of a light beam emitted from the exit plane of the optical fiber is bent about 90 degrees toward the photo sensing plane of the photodiode by the mirror.
Since the total reflection mirror is formed on an end of the mounting groove, the shape and the manufacturing process of the mounting groove becomes complex. A part of the photo sensing plane of the photodiode is used for mounting the photodiode on the silicon substrate, so that the reduction of the sensitivity of the photodiode is inevitable.
For solving the problems in the above-mentioned conventional mounting structure, a carrier for optical semiconductor device having a slant face wit
Kishida Yuji
Oda Keiko
Hogan & Hartson LLP
Kyocera Corporation
Ullah Akm Enayet
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