Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2001-01-19
2002-11-05
Pyo, Kevin (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S239000, C250S551000, C385S088000, C385S092000
Reexamination Certificate
active
06476379
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an optoelectronic device (semiconductor optical module) and a manufacturing method thereof and, more in particular, it relates to a technique effective for applying a technique of mounting a semiconductor laser chip, a photodetector and an optical fiber on a main surface of a platform referred to as a silicon platform and covering such optical parts with a guard layer r such as ma de of transparent silicone gel.
An optoelectronic device incorporated with a semiconductor laser (semiconductor laser chip) has been used as a light emitting source for an information processing device or as a light emitting source e for optical communication.
“Paper s C-3-33 of the IEICE collection for 1999 Electronic Society Conference of the Institute of Electronics Information and Communication Engineers of Japan” published from the Institute of Electronics Information and Communication Engineers of Japan discloses a surface mount type LD module according to Bellcore standards adopting a passive alignment system. In the surface mount type LD module, optical fibers are fixed with UV epoxy adhesives, and an optical device and an optical coupling portion are potted with an Si series resins. Also, the literature describes data for change of optical power in a temperature cycle test for −40 to 80° C.
Further, a passive alignment mount using the silicon platform is described in “Papers SC-2-77 of the IEICE collection for 1996 General Conference of the Institute of Electronics Information and Communication Engineers of Japan” published from the Institute of Electronics Information and Communication Engineers of Japan. The latter literature describes fixing of the LD module.
SUMMARY OF THE INVENTION
In the manufacture of conventional optoelectronic devices (semiconductor optical module) using silicon platforms (platforms), the top end of an optical fiber fitted along a groove of a silicon platform is adjusted for optical coupling with a semiconductor laser chip fixed to the surface of the silicon platform and then an optical fiber fitted to the silicon platform is fixed with a thermosetting resin (thermosetting epoxy resin) or an adhesive such as UV-ray setting adhesive.
The present applicant has made a study on the technique of fixing the optical fiber to a silicon platform in a short period of time and a technique of suppressing the change of optical power.
The present applicant has already proposed a technique of fixing the optical fiber to a silicon platform in a short period of time (Japanese patent application No. Hei 9-78602 filed on May 28, 1997) (Japanese Patent Laid-Open (Kokai) No. Hei 10-268168). In this technique, the existent method of preparing a silicon platform (platform) having a groove on the surface, then fixing an optoelectronic transducer (semiconductor laser chip) on the surface of the silicon platform at one end of the groove and fitting an optical fiber along the groove and, subsequently, controlling the light transmitting/receiving state between the optoelectronic transducer and optical fiber and fixing the optical fiber to the platform by means of a thermosetting resin is modified such that the optical fiber is provisionally fixed in a state being urged to the platform by a fixing means having shorter fixing time than the curing time of the thermosetting resin and then pressure is removed and the optical fiber is finally fixed by the thermosetting resin.
As an example, after coating a UV-ray setting adhesive to the optical fiber and the platform portion, the UV-ray setting adhesive is set by the irradiation of UV-rays thereby provisionally fixing the optical fiber to the platform and, subsequently, a portion of the optical fiber with the distance from the semiconductor laser chip remote from the provisional fixing position is covered with a thermosetting resin.
In this technique, since the provisional fixing has been completed by the UV-ray setting adhesive, after thermosetting resin is applied, the platform can be moved even before curing of the thermosetting resin, so that the platform can be removed from the fiber fixing machine in a short period of time and curing treatment (main fixing) of the thermosetting resin can be conducted by a batch processing. The batch processing can shorten the fixing time of the optical fiber per platform. Further, the optical coupling has high reliability.
On the other hand, the present applicant has adopted the technique and also made a study on the technique of reducing the package cost. Then, to reduce the package cost, the package main body (casing) and a lid (cap) constituting the package are made of plastic material and a structure of bonding the casing and the cap with a resin was adopted. Further, since the plastic material has less moisture proofness compared with ceramic material, it is intended to improve the moisture proofness by sealing a transparent silicone gel in the casing thereby covering the surface for each of parts including a semiconductor laser chip on a platform with the silicone gel.
However, it has been found by the present applicant that the fixing strength of the optical fiber is lowered and the reliability for fixing is lowered and the moisture proofness is lowered in the silicone gel sealing structure. It has been found that this is attributable to voids formed in the silicone gel.
Further, as a result of experiment and study on the mechanism of forming voids, it has been found that initially formed voids are increased in the subsequent temperature cycle, that is, depending on the temperature of the working circumstances.
Then, the present applicant has already proposed a technique of manufacturing an optoelectronic device having high fixing strength and high fixing reliability of optical fibers (Japanese Patent Application No. Hei 10-270339 filed on Sep. 24, 1998) (Japanese Patent Laidopen (Kokai) No. 2000-137147).
The followings are disclosed in the proposal described above (Japanese Patent Application No. Hei 10-270339) which concerns the problem of voids formed in the silicone gel.
FIG. 8
is a view schematically illustrating a portion in which an optical fiber
3
is fixed in a groove
2
of a silicon platform (platform)
1
by primary fixing (provisional fixing) with a UV-ray setting adhesive
4
and by secondary fixing (main fixing) with a thermosetting resin
5
and the upper surface of the silicon platform
1
is covered with a silicone gel
6
. The optical fiber
3
comprises a clad
3
b
and a core
3
a
situating at the center thereof. A semiconductor laser chip
7
is shown by a dotted chain. Voids
10
tend to be formed, as shown in
FIG. 8
, in a silicone gel in a surrounded region
9
formed with a groove surface forming the groove
2
of the silicone platform
1
and the optical fiber.
Presence of the voids lowers the fixing strength of the optical fiber
3
to the silicon platform
1
and lowers the reliability of the fixing.
Further, the presence of the voids
10
per se lowers the moisture proofness and, when water intrudes, it is trapped around the void as the seed, so that water is less released to the outside to deteriorate the moisture proofness. Since the semiconductor laser chip
7
and the photodetector are disposed on the extended top of the optical fiber, and a wiring layer or wire is present at the periphery, trapping of water to the voids
10
may possibly cause oxidation or corrosion in each of the portions and lowers the moisture proofness of the optical module.
Further, in a state where water is trapped to the voids, water is frozen in a case where the optical module is exposed to the temperature lower than the freezing point and there may be also a worry of trouble caused by the volumic change.
In the experiment, as shown in FIGS.
9
(
a
),
9
(
b
) and FIGS.
10
(
a
),
10
(
b
), a metal frame
16
is placed at the bottom of a vessel
15
, on which two glass capillaries
17
(0.13 mm inner diameter) are arranged in parallel and in contact with each other, and silicone gel
6
is filled in the vessel
15
such that the si
Ando Kazunori
Naka Hiroshi
Takahashi Shoichi
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Pyo Kevin
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