Note: Descriptions are shown in the official language in which they were submitted.
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OPTICAL MODULE AND PROCESS-OF PRODUCING THE SAME
BACKGROUND OF THE INVENTION
The present invention relates to an optical module
used for optical communication system such as a data link and
an optical LAN using light as data transmitting medium, more
particularly to an optical sub-module including at least one
optical operation element such as a light emitting element or
a light receiving element which is optically connected to an
optical fiber, an optical module comprising the sub-module
and a receptacle, and a process of producing the optical sub-
module and the optical module.
A single-core optical sub-module including a single
optical operation element optically connected to an optical
fiber, is made into one of two types. That is, one is a
transmission sub-module using a light emitting element such
as a semiconductor laser as the optical operation element,
and the other is a receiving sub-module using a light
receiving element such as a pinphoto diode as the optical
operation element.
Fig. 1 shows a conventional single-core optical sub-
module. In the conventional single-core optical sub-module,
after an optical axis of an optical operation element 2 such
as a light emitting element or a light receiving element is
aligned, the optical operation element is fixed to an optical
connector 1 fitted to a ferrule (not shown) fixed to an end
portion of an optical fiber (not shown) by an adhesive and
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the like. The optical connector~1 fixing the optical
operation element 2 is fixed to a ceramic package 3 by an
adhesive and the like. In addition to the optical connector
1, a substrate 6 supporting an electronic circuit portion
composed of electronic circuit parts such as a bare chip IC 5
is fixed to the ceramic package 3. The bare chip IC 5 and
the like on the substrate 6 as well as wires for connecting
the bare chip IC to a wiring pattern of the substrate 6 are
sealed by a lid 7. Also, the ceramic package 3 is provided
with lead pins 8 including inner leads 8a provided inside the
package and outer leads 8b provided outside the package. The
inner leads 8a and the electronic circuit portion on the
substrate 6, as well as the electronic circuit portion and a
terminal of the optical operation element 2 are electrically
connected by wire bonding and the like. Then, a cover 10 is
fixed to the ceramic package 3 so that the single-core
optical sub-module is constructed.
As shown in Figs. 2 and 3, a plurality of thus
constructed single-core optical sub-modules 11 are attached
to a receptacle 12 so that a conventional multi-core optical
module is constructed.
In the thus constructed multi-core optical module,
optical fibers are concurrently inserted in the respective
optical connectors 1 so that a plurality of data links are
formed at the same time.
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The single-core optical sub-module 11 is constructed
by many elements, and each element is assembled one by one.
Thus, assembling steps are complicated, and many steps are
required for the assembling. Further, since expensive
materials such as ceramic are used, it is difficult to lower
the cost and to mass-produce the single-core optical sub-
module.
On the other hand, the conventional multi-core
optical module is constructed by combining a plurality of
single-core optical sub-modules 11. Accordingly, it is also
difficult to lower the cost and to mass-produce the multi-
core optical module composed of the plurality of single-core
optical sub-modules. Further, at the practical use, the
optical connectors are attached to and off a multi-core plug
having a plurality of ferrules in the receptacle 12. Thus,
when the single-core optical modules 11 are attached to the
receptacle 12, high accuracy of positioning is required.
That is, if the positioning accuracy is insufficient, smooth
attachment and detachment of the optical connectors become
impossible. In the worst case, partial abrasion or damage of
the ferrules of the plug or the optical connectors 1 is
caused. The positioning accuracy must be high as the number
of optical connectors included in the multi-core optical
module increases. For the multi-core optical module with
more than three cores, very high positioning accuracy is
required. Accordingly, assembling portions of the single-
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core optical sub-module 11 and the receptacle must be formed
at high accuracy, and at the assembling, as shown in Figs. 2
and 3, an alignment tool 15 including the same number of
ferrules 13 as the optical connectors of the multi-core
optical module must be used to carry out precise positioning.
Further, as shown in Fig. 4, when the multi-core
optical module precisely positioned as described above is
mounted on a printed circuit board 16 by screwing, soldering
or the like, relative positional relation between the single-
core optical sub-modules 11 or between the sub-modules 11 and
the receptacle 12 may be distorted. In order to solve the
problem, the alignment tool 15 must be attached to the multi-
core optical module until the multi-core optical module is
completely mounted. Therefore, operational efficiency of the
mounting is inferior.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to
provide an optical sub-module and an optical module
comprising the sub-module and a receptacle with a low cost
and in mass-production.
The optical sub-module of the present invention is
provided with a molding resin member for holding in a body at
least one optical connector, at least one optical operation
element, electronic circuit parts, a substrate and lead pins
except for one end of the at least one optical connector at
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which an end of an optical fiber is received and outer leads
of the lead pins.
The process of producing the optical sub-module of
the present invention comprises the steps of preparing a lead
frame having a substrate formation portion formed into a
substrate and lead pin formation portions formed into lead
pins, forming an electronic circuit portion by mounting
electronic circuit parts on the substrate formation portion
of the lead frame, electrically connecting at least one
optical operation element fixed to at least one optical
connector and parts of the lead pin formation portions formed
into inner leads to the electronic circuit portion, holding
one end of the at least one optical connector with a mold die
for resin molding, and holding the at least one optical
connector, the at least one optical operation element, the
electronic circuit parts, and the lead frame except for one
end of the at least one optical connector at which an end of
an optical fiber is received and parts of the lead frame
formed into outer leads.
The optical module of the present invention comprises
at least one optical connector, at one end of which an end of
an optical fiber is received, a molding resin member made of
a molding resin for holding the other end of the optical
connector, and a receptacle including a first fitting portion
into which the optical connector is inserted so that the
first fitting portion is fitted to the molding resin member,
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and a second fitting portion fitting to an optical plug for
holding an end of the optical fiber inserted into the optical
connector and communicating with the first fitting portion.
According to the structure of the optical sub-module
of the present invention, elements constituting the sub-
module can be decreased. Also, assembling steps of the sub-
module can be simplified.
According to the structure of the multi-core optical
module of the present invention having more than two optical
connectors, with the dimensional accuracy realized in the
mold die used at the formation of the molding resin member,
intervals between the plurality of optical connectors held by
the molding resin member in a body are determined, and the
outer dimension of the molding resin member and relative
positional relation o the optical connectors to the outer
figure of the connector holder member are determined.
Further, with the dimensional accuracy realized in the mold
die used at the formation of the receptacle, the inner
dimension of the receptacle is determined. Accordingly, the
fitting accuracy of the molding resin member and the
receptacle is also determined by the dimensional accuracy
realized in the mold dies. The relative positional accuracy
of the optical connectors to the second fitting portion of
the receptacle fitted to the optical plug is also determined
by the dimensional accuracy realized in the mold dies.
BRIEF DESCRIPTION OF THE DRAWINGS
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Fig. 1 is an exploded view showing a conventional
single-core optical sub-module;
Figs. 2 and 3 are views showing a conventional multi-
core optical module and an alignment tool;
Fig. 4 is a view showing the step o mounting a
conventional multi-core optical module to a printed circuit
board;
Fig. 5 is a perspective view showing an optical sub-
module of the present invention;
Fig. 6 is a perspective view showing an optical sub-
module of the present invention before resin molding;
Fig. 7 is a perspective view showing an optical sub-
module of the present invention after resin molding;
Fig. 8 is a perspective view showing a lead frame
supporting an electronic circuit portion on a substrate
formation portion;
Fig. 9 is a perspective view showing a mold die for
transfer molding used for forming an optical sub-module of
the present invention;
Fig. 10 is a perspective view showing an optical
module of the present invention;
Fig. 11 is a sectional view showing an optical module
of the present invention; and
Fig. 12 is a partially perspective view showing a
fitting portion of the sub-module and a receptacle.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
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The preferred embodiments of the present invention
will be described with reference to Figs. 5 through 12.
Fig. 5 shows one example of an optical sub-module
according to the present invention. As shown in the drawing,
in the optical sub-module, parts for constituting the sub-
module such as optical connectors 21, lead pins 22 are held
by an insulative molding resin member 25 in a body.
Although Fig. 5 does not show, parts for constituting
the sub-module except for the optical connectors 21 and the
lead pins 22, that is, optical operation elements fixed to
the optical connectors 21, electronic circuit portion
electrically connected to the optical operation elements and
the lead pins 22, respectively, electronic circuit parts
constituting the electronic circuit portion, and the
substrate for supporting the electronic circuit portion are
held inside the molding resin member 25.
The structure and the process of the optical sub-
module shown in Fig. 5 will be described with reference to
Figs. 6 to 9.
Fig. 6 shows the state before parts constituting the
optical sub-module such as optical connectors are resin
molded. Fig. 7 shows the state after parts constituting the
optical sub-module such as optical connectors are resin
molded. Fig. 8 shows a lead frame 27 before the optical
connectors 21 are held.
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The process of producing~the optical sub-module of
the present invention will be described.
First, as shown in Fig. 6, after the optical axis of
the optical operation elements 26 such as laser diodes or
photodiodes are aligned, they are fixed to the optical
connectors 21 by welding and the like.
Next, a lead frame 27 is prepared. As shown in Fig.
8, the lead frame includes lead pin formation portions 22a
formed into the lead pins 22, frame portions 27a supporting
the portions 22a, a substrate formation portion 28 supported
by the frame portions 27a or lead pin formation portions 22a,
and a connector holding portion 23a for holding the optical
connectors 21 at the outer side thereof. The entire of the
lead frame 27 can be made at the same time by etching a thin
plate of about 0.25 mm thickness made of Fe-42% Ni alloy or
copper, or by punching the thin plate using a press machine.
Alternatively, after the substrate formation portion 28 and
the connector holding portion 23a, and other parts are
separately formed, the substrate formation portion 28 is
fixed to tip ends of the lead pin formation portions 22a or
the frame portions 27a by welding or the like, and the
connector holding portion 23a is fixed to the frame portions
27a by welding or the like, so that the lead frame 27 is
formed. Further, as described below, the lead frame 27 is
provided with holder bars 31 for holding the optical
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connectors 21 which are inserted~into ferrule insertion holes
of the optical connectors 21.
An insulation film of alumina (Al203) or the like is
formed on the surface of the substrate formation portion 28,
and conductive wiring patterns including bonding pads are
formed on the insulation film by aluminum and the like. The
electronic circuit parts such as bare chip ICs 32 are mounted
on the substrate formation portion 28 with the wiring
patterns by die-bonding and the like, and wire-bonded to the
wiring patterns, so that the electronic circuit portion is
formed. As is understood from the above, the substrate
formation portion 28 serves as a substrate for supporting the
electronic circuit parts of the bare chip ICs 32 and the
like.
After the electronic circuit parts are mounted on the
substrate formation portion 28, the holder bars 31 are bent
upward as shown by two dot chain line in Fig. 8. At the same
time, two portions of the connector holding portion 23a are
transformed by a press machine, etc. to correspond to the
outer shape of the optical connector 21. When the connector
holding portion 23a is formed separately from the frame
portions 27a and then fixed to the frame portion 27a, the two
portions of the connector holding portion 23a are previously
formed to correspond to the outer shape of the optical
connector.
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The bent holder bars 31 as shown by the two dot chain
line in Fig. 8 are inserted into the ferrule insertion holes
21a of the optical connectors 21 to which the optical
operation elements 26 are fixed (Figs. 6 and 7). ~hus, the
width of the holder bars 31 is smaller than that of the inner
diameter of the ferrule insertion holes 21a. The holding
bars 31 are returned to the original position while inserted
in the ferrule insertion holes 21a of the optical connectors
21. As a result, as shown in Fig. 6, the optical connectors
21 are held by the connector holding portion 23a.
After the optical connectors 21 are held by the
connector holding portion 23a, the electronic circuit portion
formed on the substrate 28 is connected to the lead pin
formation portions 22a by wire-bonding. Further, as shown in
Fig. 6, the electronic circuit portion and the terminals of
the optical operation elements 26 are electrically connected
by wires 33.
Thereafter, parts such as the lead frame 27 are
mounted to the mold die for transfer molding as described
below, and fluid molding resin is poured in the mold die, so
that respective parts are held by the molding resin member 25
except for ends of the optical connectors 21 into which ends
of the optical fibers are inserted and portions formed into
the outer leads.
Fig. 9 shows one example of a mold die for transfer
molding which enables formation of two two-core optical sub-
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modules at the same time. As shown in the drawing, the molddie is composed of an upper mold die 35 and a lower mold die
36. ~n the opposed surfaces of the upper and the lower mold
dies 35 and 36, two cavities 35a and two cavities 36a are
respectively formed. A pair of semicylindrical recess
portions 35b and a pair of semicylindrical recess portions
36b are formed to communicate with each of the cavities 35a
and 36b. When parts such as the lead frame 27 are mounted to
the mold die in such a way that the parts are held between
the upper mold di-e 35 and the lower mold die 36, one end of
each optical connector 21 at which an end of an optical fiber
is received, is closely fitted in the recess portions 35b and
36b. Thàt is, a pair of optical connectors are fitted in the
recess portions 35b and 36b, so that the relative positional
relation of the optical connectors is precisely determined.
The technical level of manufacturing the mold die is so high
that very high dimensional accuracy can be attained, since if
a gap is formed between the upper and the lower mold dies,
such problems that molding resin protrudes from the gap are
caused. Thus, the dimensional accuracy required between a
pair of optical connectors 21 in the optical sub-module is
also sufficiently satisfied.
Accordingly, if the recess portions 35b and 36b are
formed with the dimensional accuracy required for the
relative positional relation between a pair of optical
connectors 21 in the optical sub-module, the sub-module can
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also be made with high accuracy by mounting parts such as the
lead frame 27 to the mold die, pouring the molding resin into
the cavities in the mold die, and molding the resin.
In the above described process of producing the
optical sub-module, steps of forming single-core optical sub-
modules and combining the single-core optical sub-modules can
be eliminated.
Further, the molding resin member 25 formed by
transfer molding is molded under a high pressure as in the
case of sealing common ICs and the like, so that good sealing
property can be attained. Thus, a lid and a cover for
sealing the bare chip ICs used at the formation of the
conventional single-core optical sub-module can be
eliminated. Further, since inexpensive resin as compared
with a conventional ceramic package is used for packaging, so
that package cost can be decreased.
In the process of producing the optical sub-module
according to the present invention, the optical connectors 21
are held by the connector holding portion 23a of the lead
frame 27 and the holder bars 31, so that it is possible to
prevent the movement of the optical connectors 21 relative to
the lead frame 27 during the handling such as transportation
from the wire-bonding to mounting of the parts to the mold
die. Accordingly, it is possible to eliminate the
possibility of breakage of the wires 33 connecting the
terminals of the optical operation elements 26 fixed to the
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optical connectors 21 to the bonding pads on the substrate
formation portion 28 due to the movement of the optical
connectors 21. Therefore, manufacturing yield is improved
and reliability of the optical sub-module is improved.
After resin molding, unnecessary portions of the lead
frame 27 are cut away by a press machine and r~m~;ning lead
pin formation portions are formed into the outer leads, so
that the optical sub-module is obtained as shown in Fig. 5.
The outer leads are formed by cutting away the unnecessary
portions of the lead frame and bending the remaining portions
after resin molding.
In the above embodiment, a portion of the connector
holding portion 23a extruding from the molding resin member
25 are cut away. However, if the portion is left like the
outer leads and fixed to a fixed object such as a printed
circuit board by soldering and the like, the optical sub-
module can be strongly fixed to the fixed object such as the
printed circuit board.
In the above embodiment, although two-core optical
sub-module including two optical connectors are exemplified,
the present invention is applicable to a multi-core optical
sub-module including more than three optical connectors, as
well as a single-core optical sub-module including a single
optical connector.
As described above, in the optical sub-module of the
present invention, manufacturing steps are simplified.
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Further, due to the structure that parts are held by the
inexpensive molding resin member formed by transfer molding,
a plurality of optical sub-modules can be made at the same
time and mass-produced. Accordingly, it is possible to
provide the optical sub-module at a low cost and in mass-
production as compared with the prior art.
When a multi-core optical sub-module is formed by the
above described method, since a plurality of optical
connectors are fixed by the molding resin member, the multi-
core optical sub-module can be mounted on the fixed object
such as a printed circuit board without distortion of the
relative positional relation between the optical connectors
even if an alignment tool is not used, so that the working
efficiency of mounting is improved.
When the single-core optical sub-module is formed by
the above described method, it is also possible to provide
the sub-module with advantages that costs of parts are
decreased, manufacturing cost is decreased, and dimensional
accuracy is improved.
Next, an optical module comprising the above optical
sub-module and a receptacle will be described with reference
to Figs. 10 to 12.
Figs. 10 and 11 respectively show a two-core optical
module embodying the present invention. In the illustrated
two-core optical module, two optical connectors 120 for
receiving ends of respective optical fibers (not shown) at
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ends of the connectors, as well as lead pins 121, are
integrally held by a molding resin member 122 to provide an
optical sub-module 123. The sub-module 123 is fitted to a
first fitting portion 125a of a receptacle 125. The sub-
module 123 is fitted to the receptacle 125 in such a manner
that the optical connectors 120 held by the molding resin --
member 122 are inserted in the receptacle 125, and in order
to make this fitting firm, an adhesive is beforehand applied
to the fitting portions.
The sub-module 123 is produced through the transfer
molding as described above. Thus, the dimensional accuracy
of the intervals between the optical connectors 120
integrally held by the molding resin member 122 are
determined by the dimensional accuracy realized in the mold
die used for the molding of the sub-module. Also the
dimensional accuracy of the external shape of the molding
resin member 122, as well as the position of each optical
connector 120 relative to the external shape of the molding
resin member 122, is determined by the dimensional accuracy
realized in the mold die.
The receptacle 125 to be fitted to the sub-module 123
can also be produced by pouring a fluid molding resin into a
mold die for the transfer molding or the injection molding
and by effecting the molding under a predetermined pressure.
As shown in Figs. 10 and 11, the generally tubular receptacle
125 thus obtained has the first fitting portion 125a adapted
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to fit to the molding resin member 122, and a second fitting
portion 125b communicating with the first fitting portion
125a and adapted to fit to an optical plug (not shown)
holding the ends of the optical fibers.
As in the sub-module 123, the dimensional accuracy of
the various portions of the receptacle 125 are determined by
the dimensional accuracy realized in the mold die used for
the molding of the receptacle 125.
The technique of manufacturing the mold die has now
reached a level achieving very high dimensional accuracy, and
suficiently satisfies the dimensional accuracy required for
the various parts of the sub-module 123 and the receptacle
125. Therefore, the sub-module 123 and the receptacle 125
both having high dimensional accuracy can be mass-produced by
the resin molding with a high reproducibility.
As described above, in the multi-core optical module
according to the present invention, the molding resin member
122 holding the optical connectors 120, as well as the
receptacle 125, are formed by the resin molding, and the two
members are fitted relative to each other. Therefore, the
accuracy of the relative position between the first and
second fitting portions 125a and 125b of the receptacle 125
is determined by the high dimensional accuracy realized in
the mold die, and fitting portions of the molding resin
member 122 and the receptacle 125 are formed precisely due to
the high dimensional accuracy realized in the respective mold
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dies. As a result, merely by fitting the molding resin
member 122 to the first fitting portion 125a of the
receptacle 125 as shown in Fig. 10, the positioning of the
optical connectors 120 relative to the second fitting portion
125b of the receptacle 125 for receiving the optical plug can
be achieved highly precisely, thus constituting the optical
module without the use of any alignment tool necessitated for
the prior art. Further, the optical module can be mounted on
a fixed object such as a printed circuit board, without the
use of the alignment tool. The strength of connection
between the molding resin member 122 and the receptacle 125
is increased by applying an adhesive to fitting portions of
the two members before this fitting is effected. When it is
desired to further increase such connection strength,
recesses 122a are formed in the molding resin member 122, and
through holes 125c are formed through the receptacle 125 in
such a manner that the through holes 125c can be disposed to
coincide with the recesses 122a, respectively. After the
molding resin member 122 is fitted to the receptacle 125, an
adhesive is applied to each through hole 125c and each recess
122a, and then fixing plates 133 are inserted and fixed to
the hole 125c and recess 122a. By doing so, the fixing
plates 133 serve as stoppers for preventing a relative
movement between the sub-module 123 and the receptacle 125,
and therefore when the load is applied to the sub-module 123
upon insertion of the optical plug into the receptacle 125,
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the sub-module 123 will not be moved relative to the
receptacle 125 in the direction of insertion of the optical
plug, thereby preventing the disengagement of the sub-module
123 from the receptacle 125. In the above embodiment,
although the receptacle 125 is formed by the resin molding,
the receptacle 125 can be formed by die casting or lost wax
casting of molten metal, or by the molding using the
sintering of metal powder. When the receptacle is formed by
such metal casting or molding, the dimensional accuracy is
lower than that achieved by the resin molding; however, such
lower dimensional accuracy of the receptacle can be
sufficiently covered by the improved dimensional accuracy of
the molding resin member 122.
As described above, in the present invention, the
molding resin member holding the optical connectors, as well
as the receptacle fitting to the molding resin member, is so
molded as to have high dimensional accuracy, and therefore
there is no need to use an alignment tool as is the case with
the prior art, and merely by fitting the two members relative
to each other, there can be provided the optical module which
can be mounted efficiently and can be manufactured on a mass-
production basis at low costs.
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