Optical waveguides – With disengagable mechanical connector – Optical fiber to a nonfiber optical device connector
Reexamination Certificate
1998-12-24
2002-03-12
Kim, Ellen E. (Department: 2874)
Optical waveguides
With disengagable mechanical connector
Optical fiber to a nonfiber optical device connector
C385S091000, C385S093000, C385S094000
Reexamination Certificate
active
06354747
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical module applicable to an optical data link used for optical communications; and, in particular, to a structure for attaching a sleeve to a head portion in which an optical device such as light-receiving device or light-emitting device is molded with a resin.
2. Related Background Art
A conventional optical module comprises, at least a can-shaped TO (Transistor Outline) type standard package which incorporates an optical device such as light-emitting device or light-receiving device therein and is mounted with a condenser lens. To the TO type standard package, an alignment sleeve for receiving an optical fiber ferrule attached to a tip of an optical fiber acting as an optical transmission line has been secured with the aid of an adhesive (see U.S. Pat. No. 5,596,665).
Here, since the housing of the TO type standard package accommodating the optical device therein is made of a metal, the optical module tends to become expensive and larger in size, while being hard to be processed into a desirable form and thus being low in its freedom of design. Therefore, in place of such a metal package, optical modules of an integrated structure in which an optical device such as light-emitting device or light-receiving device directly mounted on a lead frame is molded with a plastic resin have been proposed (see U.S. Pat. Nos. 4,410,469 and 4,539,476).
Namely, as shown in
FIG. 1
, a conventional optical module comprises a head portion
2
(resin mold portion) molding an optical device mounted on a lead frame with a transparent resin, a body portion
4
(resin mold portion) molding an electronic device mounted on the lead frame with an opaque resin, and a plurality of lead pins
6
(connecting portion) for electrically and mechanically connecting these resin mold portions
2
and
4
to each other.
Further secured to a front end part
2
a
of the head portion
2
is an opaque cylindrical sleeve
8
for receiving an optical fiber ferrule. As the optical fiber ferrule is inserted into the cylindrical sleeve
8
, the conventional optical module can automatically align the optical fiber and the optical device in the head portion
2
with each other in terms of optical axis.
The operation of securing the cylindrical sleeve
8
to the head portion
2
has been carried out such that, as shown in
FIG. 2
, the front end part
2
a
of the head portion
2
is inserted into an insertion hole
8
a
formed at the rear end part of the cylindrical sleeve
8
, the gap between the inner wall face of the insertion hole
8
a
and the surface of the front end part
2
a
is filled with a UV-curable resin
100
, and then the UV-curable resin
100
is cured upon irradiation with ultraviolet rays UV. Alternatively, the securing operation may be carried out such that a thermosetting resin is injected into the above-mentioned gap in place of the UV-curable resin, and then thus injected resin is cured upon heating.
SUMMARY OF THE INVENTION
Having studied the above-mentioned conventional art from various viewpoints, the inventors have found the following problems.
1) First, when using a UV-curable resin for bonding the sleeve, the irradiation efficiency of ultraviolet rays must be taken into consideration.
As shown in
FIGS. 1 and 2
, the head portion
2
has a structure in which the front end part
2
a
shaped like a circular truncated cone and a rectangular base
2
b
larger than the front end part
2
a
are integrally molded by transfer molding. Consequently, when securing the cylindrical sleeve
8
to the head portion
2
with the aid of the UV-curable resin
100
, these members are irradiated with ultraviolet rays UV in the state where the base
2
b
abuts to the rear end part of the cylindrical sleeve
8
. Here, since the cylindrical sleeve
8
is opaque to the ultraviolet rays UV, it is necessary for the ultraviolet rays UV to be emitted toward the gap between the insertion hole
8
a
of the cylindrical sleeve
8
and the front end part
2
a
of the head portion
2
from the rear side of the base
2
b.
In practice, however, the gap filled with the UV-curable resin
100
is blocked with the base
2
b,
thereby the UV illuminance would inevitably decrease even when the head portion
2
is a resin mold body transparent to the ultraviolet rays. As a consequence, it has taken a long time to fully solidify the UV-curable resin
100
.
2) On the other hand, when using a thermosetting resin for bonding the sleeve, attention has to be paid to the handling of the excess part of the filling resin in particular.
Though the thermosetting resin introduced as an adhesive cures upon the heating processing after the injection, the thermosetting resin has such a characteristic that, with its viscosity once decreasing upon heating, it spreads out into the gap between the inner wall face of the sleeve
8
and the front end part
2
a
before curing. As a consequence, when the viscosity of the thermosetting resin once decreases, there is a possibility of the excess thermosetting resin flowing into a ferrule insertion hole
8
b
positioned on the opposite side of the insertion hole
8
a
or adhering to the condenser lens
2
c
mounted to the front end part
2
a.
This phenomenon is not negligible since the amount of injection of resin cannot be reduced in order to attain a sufficient bonding strength.
For example, if the excess thermosetting resin that has flowed into the insertion hole
8
b
cures, then, upon inserting the ferrule therein, the optical fiber received therein and the condenser lens will shift from each other in terms of optical axis. On the other hand, the excess thermosetting resin attached to the surface of the condenser lens
2
c
causes the optical function of the condenser lens
2
c
to deteriorate, thereby the optical module would lower its optical characteristics. In particular, when the front end part
2
a
and the insertion hole
8
a
of the sleeve
8
are made smaller in response to the demand for reducing the size of the optical module, then the gap between the side wall of the front end part
2
a
and the inner wall face of the sleeve
8
becomes narrower. As a consequence, the thermosetting resin with its viscosity lowered upon heating is more likely to spread out due to the capillary action, thereby flowing into the deep part of the insertion hole
8
b
or adhering to the surface of the condenser lens
2
c
by a large amount.
3) In addition, when taking account of the environment where the optical module is actually used, it is preferred that the adhesion durability of the sleeve be improved.
As a method of molding a resin mold portion (head portion
2
or body portion
4
) or sleeve in conventional modules, it is common to use transfer molding in which a plastic resin is injected into a die having a cavity with a predetermined form and is molded therein. The surface of thus obtained resin mold portion or sleeve is processed as smooth as possible in view of die-cutting or the like.
In the case where a sleeve is secured to such a resin mold portion with the aid of an adhesive such as UV-curable resin, smooth surfaces inevitably face each other with the adhesive interposed therebetween. As a consequence, it has been difficult to improve durability in the conventional optical modules against expected changes in their use environment (e.g., temperature changes within the range from −40° C. to +85° C., moisture changes, and the like).
It is an object of the present invention to provide an optical module comprising a variety of structures for overcoming the problems mentioned above.
The optical module according to the present invention is applicable to an optical data link for connecting an optical fiber transmission line and an electric signal transmission line to each other and comprises an integrated structure constituted by a head portion molding an optical device such as light-emitting device or light-receiving device as a whole with a resin and an alignment sleeve attached thereto. This sleeve is s
Irie Takeshi
Kurima Kazunori
Mizue Toshio
Takagi Daisuke
Tonai Ichiro
Kim Ellen E.
Pillsbury & Winthrop LLP
Sumitomo Electric Industries Ltd.
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