Note: Descriptions are shown in the official language in which they were submitted.
91LI,011
97'~
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CONNECTOR FOR FLAT ~IBBON OPTICAL FIBER C~BLES
This invention relates to fiber optic connectors
and in particular to such connectors adapted for use with
flat ribbon cables containing a plurality of optical fibers
such as may be particularly useful in data communication
systems.
The concept of using optical fibers in data
communications is now well established. See~ for example,
` "Fiber Optic Developments Spark Worldwide Interest",
R. Gundlach, Electronics~ August 5, 1976. Regardless of
the desirable features of interference-free, large band-
width communications which are envisioned, the commercial
utilization of such data transmitting links has been
impeded by the problems of making reliable, inexpensive
~` and low-loss connection between fibers or between a given
fiber and an associated optical element such as a light
source or photodetector. Such connections must address
at least three types of problems, axial allgnment,
longitudinal alignment or gap between associated members
` and angular alignment.
Axial alignment is commonly achieved by use of
precision sleeves which conform precisely to the outer
diameter of the fiber, thereby guiding flbers inserted
therein into axial position such that they may then be
secured in place. U.S. Patent Nos. 3,972,585, 4,005,522,
and 4,oo8,g48 (Dalgleish et al) depict various connectors
employing sleeves into which exposed fiber ends are
~ directly inserted. '
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While various systems have been disclosed using
fiber optic receiver-transmitter modules, see, for example,
U.S. Patent Nos. 3,809,908 (Clanton) and 4,019gO48 (Malone
et al), such systems are complex, utilize non-standardized
componenks, and may not be amenable to data communication
links where a multiplicity of discrete optical fibers are
provided for coupling between a given light source and
photodetector.
Recently, a fiber opti.cal cable system has been
introduced by Quadri Corporation, Tempe, Ari~.ona (Model
2403) which includes a single optical fiber cable connect-
ing a transmitter module to a receiver module. That system
is designed for use with 12.5 mm centered card cage
assemblies and requires separate interfacing receiver and
transmitter modules and provides for only one way slgnal
flow.
In contrast to prior art optical fiber connectors
and communicatlons s~stems in which a bundle of cables are
provided or in which isolated fibers are included in a
coaxial-like cable, the present invention is directed to a
fiber optic data link system based on the use of a flat
rib~on cable containing a plurality of optical fibers
supported in a flexible matrix. The advantages of such
cables in conventional electrical communications links are
now well known, and include advantages including low cost
construction, ease of installation in existing building,
and low profile, thus achieving an inconspicuous appearance.
Despite such known advantages in electrical applications,
flat ribbon cables containing optical fibers are not
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commercially avallable.
The de~elopmen~ of such a cable has led to the
connector of the present invention, which connector
inrlude~, a substantially flat housing member having
internal support means defining a passageway corresponding
in shape and size to a cable to be used therewith. The
passageway provides access for fibers of the cable
received into the housing to protrude beyond the support
means and in~o a channel wlthin the housing such that the
; 10 ends of the fiber terminate proximate an opening through
a front portion of the housing memberO The fiber ends are
thus accessible through the opening and ma~ be optically
coupled to fibers within a mated connector abutting the
front portion.
The connector further includes a plurality of
fiber retaining members, each of which is adapted to be
positioned within a corresponding channel in the housing
member in axial alignment with the fiber. Each of these
members have a smooth substantially cylindrical periphery
and have a circular bore extending therethrough along the
cylindrical axls for receiving an end of a fiber and for
permanently anchoring the fiber end therein substantially
~.o-planar with the end of the bore, the ends of the fiber
and of the retaining member being substantially normal to
the axis of the bore.
- An alignment means is also provided, having a
plurality o~ bores extending therethrough of substantially
the same size and shape as the cylindrical periphery of
the retalning members. Each bore of the allgnment means
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is thus adapted to receive one of the retaining members in
close fitting relationship at one end~ and to receive
another retaining member of a mated connector into the
other end so as to butt against the first member, thus
optically coupling the fibers. Typically, the optical
fibers have a circular cross-section, hence the retaining
member will preferably comprise a tube having a circular
cross-section, the inside diameter o~ which is slightly
larger than the diameter of a fiber to be used therewith
such that the fiber may be inserted and anchored therein,
such as by a suitable adhesive while yet maintaining the
fiber axially centered within. The outside diameter of
such tubes are preferably slightly rounded at the end to
facilitate insertion into the alignment meansO Further,
each retaining member is preferably constructed to include
a flange to be fitted into the housing in order to position
and anchor the member.
Likewise, in that the bore of each alignment
member is adapted to receive the periphery, i.e.~ the out-
side diameter, of retaining members in close fittingrelationship, the ends of those bores are preferably
sllghtly flared. Preferably, the alignment means comprises
a plurality of sleeves having an lnside diameter slightly
greater than that of the outside diaméter of the fiber
retaining tubes. In such an embodiment, each of the
sleeves and tubes preferably include flanges o~ substan-
tially the same radial size and shape such that when one
end of the retaining member is inserted approximately half-
way into the bore of the alignment member, both flanges are
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butted together. The channels in the housing are also
: shaped to receive and lock together in axial al,ignment each
fiber retaining tube at least partially inserted into one
end of its companion sleeve and to position the alignment
sleeves such that their ends are accessible through the
opening in the front portion of the housing for optical
coupling to the mated connector. Preferably, the channels
in the housing are provided with cavities corresponding to
the dimensions of the butted-up flanges such that the
butted-up members inserted into the cavities are anchored
within the housing, while yet allowing limited movement
bet~een the members to relieve strains on the fibers.
, The connector may be utilized to optically couple
: together a pair of flat ribbon cables enclosing a plurality
of optical fibers in which case the housings of the
conneckor and a mating connector are each shaped to
receive and anchor an end of a ribbon cable. Alternatlvely,
the connector may also be utiliz,ed to optically couple
fibers within a flat ribbon cable to an associated optical
element such as a ].ight source or photodetector.
Figure 1 is an exploded view of a connector
assembly utili~ing the connector of the present invention
'. to couple a flat ribbon optical fiber cable to a termina-
, tion connector,
Figure 2 is a similar exploded view of connectors
o~ the present invention adapted for coupling or splicing
' together flat ribbon optical fiber cables; and
Figure 3 is a cross section of the connector
', ' assembly of Figure 1.
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A preferred embodiment of the connector of the
present invention is shown in an exploded view ln Figure 1.
The connector 10 is adapted for coupling to a flat ribbon
optlcal fiber cable 12 containing a pair of optical fibers
14 and 16, and Gomprises two identical housing members 18
and 20, together with a pair of fiber retaining members 22
and 24, respectively, and a matching pair of alignment
sleeves 26 and 28. The housing members 18 and 20 are
preferably injection molded of a thermoplastic such as
polycarbonate or the like. Each member includes projecting
pins such as the pins 30 and 32 on member 20 which mate
with corresponding openings in the respective opposite
member, such as openings 34 and 36 in member 18 such that
when the members are pressed together, the pins are pressed
into the holes to maintain the connector halves together
in appropriate alignment. The interior of the housing
members 18 and 20 are shaped to provide a rear opening 38
into a cable support section 40 which defines a passageway
corresponding in size and shape to a cable such as that of
the cable 12 which is to be received and anchored in the
housing. The section 40 has an extended planar portion
into which the flexible matrix of the cable 12 may be
inserted. The flat portion is provided with a projecting
pin 42 which mates with a similar pin in the half 18 of
the housing. When a cable 12 is to be assembled with the
connector, a hole 44 is punched between the fibers 14 and
16 through the flexible matrix of the cable 12. This hole
`~ thus anchors the cable on the pin 42 wlkhin the housing
and relieves strain on the optical fibers should pressure
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be placed on the cable independent of the connector housing.
Furthermore, the positioning of a hole 44 in the end of the
cable facilitates subsequent jigging operatlons in order to
appropriately position the ends of the fiber within
5 associated connector elements. Extending forward of the
passageway 40 and in general alignment with the axis of the
optical fibers within the cable ].2 are channel means
through which the fibers may extend and which includes a
pair of larger cavities 46 and 48, respectively. The
channel means thus includes a pair of small openings lead-
ing from the passageway 40 into the larger cavities 46
and 48, and larger axial openings 54 and 56 which terminate
at a forward portion 58 of the connector housing. Each of
the cavities 46 and 48 is adapted to receive one of the
retaining members 22 or 24 inserted into one of the align-
ment members 26 or 28, respectively.
The fiber retaining members 22 and 24 comprise a
short section of stainless steel tubing press fitted into
brass flanges 60 and 62 such that a short end protrudes
20 beyond one side of the flanges, facilitating alignment of
the members within the small openings from the passageway
Lio. Such tubing is commercially obtainable in a variety of
inside and outside diametersg and is thus readily selected
to provide an inside diameter slightly greater than that of
25 the optical fibers to be utilized therewith. Accordingly,
- an optical fiber 14 or 16 may be inserted into the retain-
ing members 22 or 24 such that the end of the fiber is
subst~ntially co-planar with the end of the retaining
member 22 or 24. The fiber is then permanently secured
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within tlle retaining member such as with an epoxy resin.
The outside diameter of the members 22 and 24 is similarly
selected to be received into a close fitting relationship
within the alignment members 26 or 28. The radial flanges
5 60 and 62 are of appropriate size to fit within the larger
cavities 46 and 48 while allowing for a slight radial and
axial movement therein, thereby providing for strain relief
for the fibers and limited freedom of movement to opt~mize
optical coupling therebetween.
The alignment members 26 and 28 are also prefer-
ably constructed of brass and are fabricated to have an
inside diameter which is slightly greater than the outside
diameter of the retaining sleeves 22 and 24. ~he alignment
members 26 and 28 are also provided with radial flanges 64
and 66 of similar size and shape as the flanges 60 and 62
such that when the retaining members 22 and 24 are inserted
into the alignment members 26 and 28, the flanges abutt and
may be Jointly received into one of the cavities 46 or 48.
The forward portion of each alignment member 26 or 28 is
20 thus adapted to fit into the forward portions of the
channels 54 and 56 in axial ali~nment with the cable 12
such that the forward opening portions thereof are
accessible through the front portion 58 of the housing.
When thus assembled, the fiber retaining members 22 and 24
25 having the ends of the fibers 14 and 16 permanently anchored
coplanar therewith are inserted approximately half-way into
the alignment members 26 and 28. These assembled members
are received into the cavity such that the forward end of
each alignment member 26 and 28 protrudes a slight distance
ahead of the front portion 58 of the housing. Each align-
ment member 26 and ~8 is preferably flared on botn ends to
facilitat.e entry of a retaining member 22 or 24 into the
rear opening and to further facilitate entry of a similar
retaining member of a mated connector into the front open-
ing.
The connector further includes a latch providing
means for engaging the connectors such as a pair of
resilient fingers 68 and 70, having latching detents 72 and
74 on the forward ends, which fingers are adapted to mate
with corresponding members on a mated connector.
The connector halves 18 and 20 are preferably
formed of an injection molded plastic and are of identical
construction. The upper half 18 thus includes the same
cavities as those shown in the lower half 20. When the
halves are mated together, portions of each half cooperate
to complete the inner cavities. Similarly, the resilient
fingers 68 and 70 on the lower half 20 have corresponding
counterparts 76 and 77 in the other connector half 18.
In the embodiment shown in Figure 1, the connec-
tor 10 is adapted for use with a flat ribbon optical fiber
cable 12 having a pair of optical fibers approximately
.25 mm diameter embedded within an extruded flexible vinyl
matrix having an outer width approximately 12.5 mm and
approximately 1.5 mm thick. The optical fibers are spaced
apart approximately 7 mm. In such an embodiment, the
connector housings 18 and 20 are approximately 3mm thick,
approximately 25 mm overall width~ and are approximately
32 mm in overall length. The platform 40 is shaped to
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contain the 7 mm by 1.5 mm cable 12. Accordingly, the
platform portion of each half of the housing 18 and 20
comprises a recess approximately .75 mm by 12.5 mm. The
projections 42 are similarly shaped to abutt with each
other when the housings are assembled so as to mate with a
hole 44 punched in the cable 12.
The retaining stainless steel sleeves 22 and 24
have an inside diameter approximately -.33 mm so as to be
able to receive the fibers 14 and 16. The fibers are
anchored therein by a suitable resin such as epoxy resin
Type 96-083 manufactured by Dow Corning Corporation. In
the preferred embodiment shown in Figure 1, the ~langes 60,
62 ~ 64 and 66 have an outside diameter approximately 4. 5 mm
and inside diameters enabling them to be press fit onto the
15 steel tubing.
The companion mated connector 78 shown in the
left portion of ~igure 1 is adapted to provide a termina-
tion interface between optical signals on a flber cable
such as the cable 12 and corresponding electrlcal signals.
The connector 78 includes a housing formed of two identical
molded plastic support members 80 and 82, which members are
in turn sandwiched between a base member 84 and a cover
plate 86. The connector further includes a circuit board
88 on which are positioned electronic circuit components
25 shown generally as 90 as desired for a given application.
The connector 78 further includes a pair of fiber retaining
members 92 and 94 within which may be anchored short
optical fibers 96 and 98 to provide optical coupling
between associated optical elements within the electronic
circuit module 90 and optlcal fibers in the other connector
10. The housing halves 80 and 82 are desirably formed of
molded plastic such as a polycarbonate resin or the like.
Each half contains at least one pro~ecting pin 100 and a
corresponding opening 102 such that when the halves are
assembled, the pin 100 of one half of the housing is
received into a corresponding hole such as the opening 104
in the opposite housing half. The cover member 86 is
desirably also formed of injection molded plastic and
includes a plurality of projecting pins, three of which are
shown as elements 106, 108 and 110, respectlvely. These
pins are designed to be inserted through matchlng holes
shown as elements 112, 114 and 116 in side legs of the
members 80 and 82. The base member 84 is similarly provid-
ed with a plurality of openings through which the pinscorresponding to elements 106, 108 and ]10 may be inserked
when the connector is assembled. Following assemblage,
the projecting pins may then be staked to permanently lock
the assembly together. A rear end portion 118 on the cover
20 plate 86 closes the rear portion of the termination
connector 78 while allowing access for electrical connec-
tions 120 to extend from the eleckronic module 90. The
fiber retaining members 92 and 94 are subskantially
identical to the retaining members 22 and 24 in the firsk
recited connector 10 and are made of skainless steel tubing
press-fit within brass flanges 124 and 126. These members
fit within appropriately shaped recesses 128 and 130 within
the support members 80 and 82 such that the front end pro-
trudes beyond a front portion 131 Or the members 80 and 82.
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The optical fibers 96 and 98 may be permanently
anchored within the retaining members 92 and 94 with a front
end of the fibers substantially co~planar with the ends of
the members 92 and 94. The rear end of the fibers may then
be optically coupled to associated optical elements (not
shown) within the electronic module 90~ such as by a trans-
parent adhesive, mechanical clips or the like.
The support members 80 and 82 are further shaped
to have matching latch means such as the indented portions
positioned on the opposite sides of the members, one of
which is shown as element 132. The indented portions are
thus adapted to receive the ends of the resilient fingers
72 and 74 and 76 and 77 of the first recited connector so
as to lock the connectors together and maintain the
respective fiber retaining members substantially butted
together and in axial alignment within the alignment
members 26 and 28.
While the members shown in Figure l may all be
formed of injection molded plastic, in a particularly
preferred embodiment, the base member 84 may be desirably
constructed to include a heat conducting metal or the like
having means such as a corrugated outer surface for provid-
ing additional heat dissipation. In such an instance, the
circuit board 88 may be desirably constructed of an
insulating material such as an electronic grade ceramic.
In the connector 10 shown in the right portion of
Figure l, the alignment members 26 and 28 are included
within the housing members 18 and 20 and the fiber retaln-
ing members 22 and 24 are inserted into one end of the
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alignment members 26 and 28. When the connectors 10 and 78
are mated, the second set of retaining members 92 and 94
retained within the members 80 and 82 of the mated connector
78 are inserted into the alignment members 26 and 28 such
that the front portions of both sets o~ fiber retaining
members are abutted together~ thereby optically coupling
together the fibers anchored therein. Similarlyg it is
within the scope of the present invention that the alignment
members 26 and 28 may be positioned in either of the mated
connectors, it being essential only that the f'iber retain~
ing members nf each connector be inserted into the align-
ment members such that the retaining members become butted
together in axial alignment so as to appropriately opti-
cally couple the optical fibers retained therein.
In another embodiment of the present invention
shown in Figure 2, the connectors are adapted to couple or
splice together a pair of flat ribbon optical fiber cables.
In such an embodiment, the housinL of connector 134 is
formed of inJection molded plastic in identical members 138
and 140, while the housing of connector 136 is inJection
molded in two identical members 160 and 162. ~he connector
134 is substantially the same as the connector 10 shown in
Figure 1 and includes an opening into a platform 142 having
means such as a pro;ection thereon for receiving and anchor-
ing a flat ribbon optical fiber cable 144 having a pair ofoptical fibers 146 and 148 therein. The respective housing
members 138 and 140 also include a pair of channels into
which may be received a pair of fiber retaining members
150 and 152 inserted into and abutted against respective
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alignment members 154 and 156, and resilient fingers 194 ~
196, 198 and 200 proximate the side portions of the respec-
tive housing members as described in con;unction with
Figure 1. A ~ront porti~n 158 of the housing formed from
members 138 and 140 is provided with openings through which
the front of the alignment members 154 and 156 may protrude,
thus allowing access into the retaining members 150 and 152
for optically coupling to the fibers 146 and 148 anchored
therein.
In this embodiment, the mated connector 136 is
provided with an opening into a platform 164 for receiving
and anchoring a cable 166. The platform includes a
p.ro;ection 168 which mates with a hole 170 punched between
the optical fibers 172 and 174 o~ the cable 166 such that
15 the cable is anchored within the housing when the members
160 and 162 are assembled by inserting the mating projec-
tions 188 and 190 into corresponding holes in the opposite
members. The connector 136 also includes a pair of fiber
retaining members 176 and 178 into which the fibers 172 and
20 174 of the cable 166 may be anchored such that the ends of
the fibers are substantially parallel with the front end of
the retaining members 176 and 178. When these members are
inserted into the corresponding cavities 184 and 186 and
the members 160 and 162 are pressed together, the fiber ends
of the two cables 144 and 166 may then be coupled by press-
ing the connector halves together, such that the ends of
the respective sets of fiber retaining means 150 and 152
and 176 and 178, respectively, are butted together within
the alignment means 154 and 156. When thus inserted~ the
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resilient fingers 194, 196, 198 and 200 of the rlght hand
connector 134 are received into the indented por~ions 202
of the mated connector 136 so as to lock the respective
members substantially butted together and in axial align-
ment.
While the connectors shown in Figures 1 and 2 are
depicted for use with a flat ribbon cable having a pair of
optical fibers contained therein, it ls similarly within
the scope of the present in~ention that the connectors may
be expanded so as to provide for coupling of any number of
optical ~ibers contained within a flat ribbon type cable.
Similarly, while the connectors are depicted as having
mechanical means for aligning and maintaining each
connector half in an aligned relationship, it is similarly
within the scope of the invention that the connector halves
may be heat-fused or bonded together adhesively, and may be
of dissimilar shapes depending upon the specific applica-
tions required. Similarly, while in the embodiments shown
in Figures 1 and 2 the housings anchor the optical fibers
via a projection mating with holes punched in the cables,
it is similarly within the scope of the present invention
that other mechanical holding means such as a molded bar
across the platform 142 and 164 may similarly be utilized.
The details of the mated connectors adapted ~or
coupling a flat ribbon optical cable to a termination
module are shown in the cross-sectional view of Figure 3
in which the connectors are slightly spaced apart for
improved clarity. In this ~igureg a connector 204 sub-
stantially like ~hat of Figure 1, is shown to have secured
6~a
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thereto a flat ribbon optical fiber cable 206 in which a
pair o~ optical ~ibers 208 and 210 are embedded. The cable
is anchored to the housing 204 by means of a projecting
pin 212 which protrudes through a similarly shaped opening
in the cable 206 between the fibers 208 and 210. The
~ibers 208 and 210 thus protrude in axial alignment with
the cable through the channels 213 and 214 and enter a
respective fiber retaining member 216 and 218 within which
the fiber ends are permanently anchored by means of a suit-
able adhesive such as the epoxy resin type 96~083 manu-
factured by Dow Corning Corporation.
During assembly of the connector and optical
fiber cable, once the opening into which the pro~ecting
pln 212 is to be inserted has been punched within the
cable 206, such that a suitable length of the cable pro-
trudes beyond the location of the hole, the flexible matrix
of the cable is then removed such that a suitable length
of fibers 208 and 210 extends beyond the end of the
flexible matrix. The cable is subsequently inserted into
a suitable jig (not shown) having a projecting pin and
cavlties into which the cable and the fiber retaining
members 216 and 218 are positioned, such that the location
of the retaining members may be accurately positioned
with respect to the opening through the cable. The
optical fibers are inserted into the retaining members and
are then cut off slightly projecting beyond the forward
ends. The fibers are then permanently anchored therein
as described above. The respective ends are ground and
polished smooth. Preferably~ the ends of the fibers may
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thus become recessed within the ends of the respective
retaining members, thereby avoiding subsequent chipping or
scratching of the fiber ends. When the fibers and respec-
tive retaining members are thus assembled, they are inserted
into the alignment members 224 and 226 such that the flanges
on both sets of members are butted together. The butted
together ~langes are then inserted within the cavities 228
and 230 of the housing assembly and the respective halves
of the assembly are pressed together as described herein-
above.
In a similar fashion, the termination connector234 includes a housing member which is adapted to mate with
the housing of connector 204. Thus the housing 234 includes
a front portion 236 which is adapted to mate with the front
portion 231 of the first recited connector 204. The
connector 234 further includes a pair of retaining members
238 and 240, which members have anchored therein short
sections of optical fibers 242 and 244. The fibers 242 and
244 are permanently anchored within the respective retain-
ing members 238 and 240 by suitable adhesive means asdescribed hereinbefore such thak the fiber ends are
proximate the front portion of the retaining members. The
members are then mounted within corresponding cavities
within the housing 234 so as to maintain the optical fibers
in axial alignment with the front portion 236 of the hous-
ing 234. Upon coupling of the connector 234 with the
connector 204, the retaining members 238 and 240 are
inserted into the alignment members 224 and 226 of the
connector 204 so as to cause the optical fibers therewithin
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to be optically coupled. The end portions of the fibers 242
and 244 are optically coupled to a light source 246 and to
a photodetector 248, respectively, mounted within the elec-
tronic module 250. In a preferred embodiment, the light
source 246 may be a light emitting diode such as Type
FPX-2000, manufactured by Fairchild Semiconductor Corpora-
tion. Similarly, in a pref'erred embodiment, the photo-
detector 248 may be a photodiode such as Type C-30807
manufactured by RCA Corporation. Electrical inputs and out-
puts to and from the light source 246 and photodetector 248may be provided in a conventional manner such as by leads
(not shown).
Preferably, the allgnment members 224 and 226 are
tapered at both ends to facilitate entry to the respective
retaining members 216, 218 and 238, 240. Further, the
forward portion 236 of the housing 234 is shaped such that
when the retaining members 238 and 240 are inserted into
the corresponding cavities there provided, the forward ends
of the retaining members protrude beyond the plane of the
front portion such that the end of the retaining members and
the respective optical f'iber anchored therein may be ground
and polished as described hereinabove. ~lso, the front
portion 236 is desirably relieved such that the correspond-
ing front portion 231 may be entered into the relieved
portion 236 to provide a f'irm connection while the
resilient fingers 252 and 254 are mated with the corres-
ponding indent portions 256 and 258 of the housing 234.
By thus first positioning the optical fibers 242
and 244 within their respective retaining members 238 and
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240, t~le other end of the fibers may then be connected to
the respective associated optical element to maximize
optical coupling. In the event a light emitting diode is
used as the light source 246, the positioning may particul-
arly be optimized inasmuch as such diodes frequently emitnonuniformly across the light emitting surface. According-
ly, the most optimum position for the fiber with respect to
the emitting surface of the source 246 may be determined by
monitoring the light output at the forward end of the fiber
242 and by then permanently anchoring the fiber adjacent
the particular portion of the light emitting surface found
to correspond to the maximum light output. When the fibers
are permanently anchored such as by means of a suitable
light transmitting adhesive, the respective halves of
housing 23l1 may be joined as described hereinabove, thus
completing the connector assemblies.
In the embodiments described hereinabove, the
flat connector housings are shown to include resilient
fingers providing means for engaging the respective
connectors. It is similarly within the scope of the
present invention that such latch means may also include
captured screws and associated threaded portions in the
mated connector. Likewise, additional sealing means such
as rubber and outer shrouds and the like may be included
to provide environmental protection. In a further pre-
ferred embodiment, the cavity within which the electronic
module 250 is positioned may be provided with electrical
shielding means to minimize electrical interference.
Having thus described the invention, we claim:
