Note: Descriptions are shown in the official language in which they were submitted.
r
~ L7~33~ii
This invention is a division of application Serial
No. 287,510 filed September 26, 1977.
This invention relates general.ly to optical fiber
. waveguides and, more specifically, to connectors for
coupling a pair of multi-fiber cables.
Optical fiber waveguides have potential use in
: communication systems for guiding light beams carrying :.
voice, television and high speed data signals. One
important area of technology that is required if optical
. 10 fiber communication systems are to be implemented, is
the development of useful techniques for fiber coupling.
. Efficient coupling of a pair of optical fibers demands
. minimal lateral and longitudinal separation of the
fiber tips, and angular alignment thereof. The tolerance j.
for longitudinal separation is generally the least critical
of the three owing to the small degree of divergence of
the light travelling between the tips, and to the divergence-
reducing effect of an index-matching fluid which may
be deposited be-tween the fiber tips~
2b Angular misalignment may be minimized by properly ~':
: .~ .~
locating the fibers within channels. Lateral sepa~ation, :
., that is to say the non-coincidence of the optical axes of
the coupled fibers, is the most critical parameter and
must therefore be held withln very exacting tolerances
I 25 when a pair of optical fibers are to be coupled. For
example, a coupling loss of 0.1 db requires a separation
of no more than about 10~ of the fiber core radius or
approximately 0.0001 inch for a typical fiber.
:~ _3_
~i
,
33~ `
.
As a practical matter, optical communication systems
often requi.re the use of multi-fiber cables comprising a
plurality of protectively jacketed optical fiber wave-
guides enclosed by a cable sheath. Many cable connections
within each optical communications system, such as those
to terminal equi.pment and routing lnterconnections
will additionally require connectors having disconnect/
reconnect capabilities
SUMMAR~ OF THE PRIOR ART :~
In U.S. Patent 3,861,781, there is shown a
~:~ separable optical fiber connector comprising a terminal
member having an axial through-hole which ineludes a
first portion having a relatively large diameter equal ~.
to the diameter of the thermoplastic coated protectively
jacketed optical fiber, and a narrow-diameter seeond
portion having a diameter equal to that of the optieal
;~ fiber without the eoating. The fiber is inserted
into the through-hole until it protrudes at the other
end, whereupon it is affixed to the end surface of
the terminal member and polished until it is flat therewith.
In U.S. Patent 3,902,785, there is diselosed a
. dielectrie optical waveguide coupler comprising a pair
of identieal plugs engaged in a double socket. Eaeh plug
eonsists of a sleeve and capillary bore glass tube within -
the sleeve arranged so that an annular spaee exists
between an interior wall of the sleeve and an exterior
; wall of the tube. A dielectric optieal waveguide is
threaded through the capillary bore and rigidly fixed
therein. A slide, consisting of a tube, ean slide
--4--
~73~
within the ~nnular space. A second length of
capillary bore tube is fixed withln the slide and the
dielectric optical waveguide is partially inserted
within, ancl is free to slide with respect to, the bore
of this tube. The socket consists of a third length
of capillary bore tubes surrounded by a collar. On
inserting the plugs into the socket, the slide moves
backwards causing two lengths of dielectric optical
waveguide, one from each plug, to enter the bore of the
third length of capillar~- bore tube. When the two
lengths of dielectric optical waveguide abut, an optical
coupling is formed and the plugs can be locked in position.
In U.S. Patent No. 3,948,582, there is shown an
optical fiber connector comprising separately formed
bodies of substantially elongate form, each having an
axial bore in which an optical fiber can be fitted.
The end of one body defines a flared socket adapted to
mate with the conical plug shaped end of the second
body. An optical fiber waveguide is protrudingly
held by the plug shaped body and is pushed into the
bore of the flared socketed body as the plug mates
with the socket.
In an article entitled `'Optical Fiber Connector"
by J.F. Dalgleish, et al. (Electronics Letters Vol. 11,
No. 1 (January 9, 197S)), bared fiber ends are located
radially at the bottom of an axially extending V-groove
formed in one of a pair of interlocking housings. ~ ~
The second housing fits over the first and provides ,
two fiber-accommodating slots transverse to the length
of the V-groove, and a pair of fiber-retaining wires
which push the fiber ends to the bottom of the groove.
_5_
: ,.
; ~
' ... ' .;,; : :
~7~3~
, .
It may be appreciated in the foregoing U.S. patents
that it is necessary to push the optical ~iber waveguide
in-to the tight capillary bore required to obtain accurate
alignment of the fibers. This is a rather precarious
procedure owing to the fragility of the optical fiber
waveguides; there is a tendency for the fibers to break
when pushed through a tight capillary. Additionally,
for the devices of U.S. Patents 3,9Q2,285 and 3,948,582,
the stresses to which the spliced fibers are subjected
are transmitted along the individual fibers and the
resistances of these splices to the stresses are thereby
limited by the relatively weak strength of the optical
fibers. None of these techniques utilize the practical
aspect of telecommunication systems whereby optical
fiber waveguides will be grouped in multiple fiber
cables. Accordingly, none of these references treat
the eonsideration that the eable sheath may be safely
anchored as part of the connection to distribute the
l stresses induced by the coupler.
; 20 A few connectors having disconnect/reconnect
eapability and adapted for use with multi-fi~er cables
are known in the art. One -type requires the ~ibers to
be fabricated into ribbons in which the fibers must be
co-planar, very accurately spaced, and have outer
diameters and core centerings whieh match to approximately
1%. Examples of these conneetors may be found in
Bell System Tech. Journal; Vol 54, pp. 471-479, (1971).
In U.S. Patent 3,864,018, a connector is disclosed whieh
requires the staeking of rows of fibers alternatively
with grooved plates.
-6
.. .. . . . . . . . ..... . . .. . . . . . . .. ...... ....... ... ... , . .. , . .,, .. , .. ...... ~ .. , ., .. . ., ~ . .
....
3~5
It should be noted that the fiber-accomodating
channels oE the above described devices are rigid and
consequently do not allow for the variations in fiber
diameters which occur in manufacturing. These variations
cause lateral misalignment of opposing fiber tips with
the substantial resulting coupling losses indicated above.
In a connector assembly described in Electronics
Vol. 48, p. 29 (August 21, 1975) the wall of each fiber
is held in an opening formed by the sides of three
compressible plastic cylindrical alignment structures.
One of the cylinders extends axially along the interior
of one connector and rests on two adjacent cylinders
extending axially along the interior of a laterally
mating connector, the groove between the two adjacent
cylinders being thereby enclosed by the surface of
said one cylinder to define the opening. ~lthough this
assembly allows for fiber diameter variations because
of its flexible grooves, it has several disadvantages.
The fibers of one cable associated with the two-cylinder
connector, must be individually inserted into the appropriate
grooves with the accompanying substantial risk of fiber
breakage. The fibers of the second cable, associated
with the one-cylinder connector, do not sit in grooves,- -
but remain on the top surface of the appropriate Fylinder
~ ~ '
~ r~ r
733~ii
and fall into the grooves of the two-cylinder connector
when the connectors are mated.
The connectors used for coupling multi-fiber cables
to each other or to system equipment should have certain
general characteristics. Cable and fiber-end preparation
should be simple and fibers should be easily inserted into
the connector with a minimal danger of breakage. Fibers
having diameter variations within reasonable manufacturing
tolerances should be accommodated with minimal coupling
loss. The connector should be rugged and installed on
the cable in a manner which minimi~es the possibility
of fiber damage during handling or coupIing of the
connectors. The light throughput efficiency of the
coupled connectors should be high, pre~erably greater
than 95%. F.inally/ the connectors should be easily mated.
Accordingly, a multi-fiber cable connector assembly
is disclosed for coupling the opposing pluralit.ies of
protectively jacketed optical fiber waveguides contained
within a pair of multi-fiber cables. The connector
assembly comprises an opposing pair of mating connectors,
each containing a plurality of axially extending fiber-
guiding channels si~ed to freely accommodate respectively
inserted fibers. The connectors each further contain
a like plurality of internal and transversely displaceable
jacket-engaging surface members which project inwardly -
into the respective channels. One of the connectors
is adapted to accommodate the jacketed fibers from
one of the cable pair and to projectingly hold the bared
fiber tips in a predetermined pattern at its mating end.
ill~L~73~;
The second connector is adapted to accommodate the
jacketed fib~rs from the other cable and to internally
hold the bared fiber tips thereof in a similar pattern,
The second connector is further adapted to freely
accommodate the projecting fiber tips from the first
housing upon ma-ting therewith to hold the opposing pairs
of fiber tips in abuttment. The second connector
additionally includes a plurality of internal and
transversely displaceable fiber-engaging surface members
arranged to project into respective channels within
the abuttment area to securely align the abutting fiber ~ ~ -
tips. The cable connector assembly further comprises
first means for transversely displacing the jacket-engaging
surfaces of each housing to secure the accommodated
fibers within their respective channels and second means
for transversely displacing the fiber engaging surfaces
of the second housing to securely align the abutting
fiber tips.
Either of the connectors may additionally be
utilized to couple a multi-fiber cable to system
terminal connectors. Additionally, a connector assembly
for coupling a pair of single fiber waveguides and
including a pair of connectors having a single fiber-
accommodating channel is also within the purview of
the inventicn. These and other features of a multi-
fiber cable connector assembly constructed in accordance~
with the invention disclosed herein will be more fully
described in the following description which is to be '
read in conjunction with the accompanying drawings. ~-
_9_
3~5
One embodiment oE the invention will now be
described, by way oE example, with reference to the
accompanying drawings in which:
Figure 1 is a partially sectioned view of an
assembled mul~iple optical fiber cable connector assembly
constructed in accordance with the in~ention.
Figure 2 is a partially sectioned view, showing a
disassembled one of mating connectors forming the connector
assembly of Figure 1.
Figure 3 is a partially sectioned view showing
the disassembled second mating connector forming the
connector assembly of Figure 1.
Figure 4 is an enlarged fragmentary view showing
features of the jacket-engaging finger-like elements
in Figs. 1-3.
Figure 5 is a cross-sectional view of the first
mating connector taken along line 5-5 in Figure 2.
! It should be noted that like reference numerals will
be used throughout the Figures to dèsignate identical
elements of the multiple optical fiber cable connector
assembly.
,
With initial reference to Figure 1, there lS shown
a multi-fiber cable connector assembly 10, constructed
in accordance with the invention, for coupling the
opposing pluralities of protec-tively jacketed optical
;~ fiber waveguides 12 and 14 contained within a pair of
multi-fiber cables 16 and 18. The connector assembly 10
.
--10--
3~S
,
comprises ~n opposing pair of mating connectors 20
and 22 whicl~, for the sake of clarity, will be
individually described below.
Figure 2 is a partially sectioned view of one
of the mating connectors forming the connector assembly
of Figure 1 and shown in disassembly so that its
various components and their interrelationships may
be more readily appreciated.
The first connector 22, hereinafter referred to
as the female connector, comprises a rigid housing 50,
formed from a metal or a plastic such as acetal or
polycarbonate, and having a generally cylindrical shape
and an axially extending throughbore 51 between and in
communication with, its mating face 60 and its fiber-
receiving face 61. As will be more fully described
below, a plurallty of axially extending, generally
V-shaped, fiber-accommodating channels, illustratively
shown as 56a-f, are disposed within the bore and serve
to individually guide the optical fiber waveguides 1
through the housing 50 and internally hold the bared
wa~eguide 14 tips in a predetermined pattern in an
abuttment region 26. As will also be explained in
greater detail below, the waveguides 14 are secured
within their respective channels by a plurality of
transversely displaceable jacket-engaging surfaces formed
; by finger-like members 62a-f which extend inwardly
into respective channels from a common base 64 located ;
interjacent the end portions 50a, 50b of the housing 50.
At least a portion of the common base 64 forms a generally
.
~L733~ii
wedge-shaped cam surface 6~a extending slightly outward
from the housing 50 periphery.
In the preferred embodiment, the finger-like elements
62a-f are outwardly spaced from the channel surface
so that the waveguides may be freely inserted and
withdrawn, and are inwardly displaceable so as to
contact the protective jacketing of the waveguides 14 and
securely press the waveguides into their respectlve
channels subsequent to insertion. The pressure exerted
by the fingers on the jacketing is sufficient to secure
the fibers against movement but incapable of damaging
them owing to the protective nature of the fiber jacketing
which precludes the waveguides from being scratched or nicked
and additionally distributes the forces exerted thereon.
A like plurality of finger-:Like elements 58a-f, similar
to the elements 62a-f are provided within the abuttment
region 26. The finger elements !;8a-f are also outwardly
biased from the channel surfaces to ~reely accommodate
the insertion or withdrawal of the fiber tips. Unlike
the jacket-engaging surfaces of finger elements ~2a-f,
however, the surfaces of the finger-like elements 58a-f
are adapted to engage the bared fibers when inwardly
displaced and serve, in a manner more fully described
hereinbelow, to align the plurality of abuttingly held
fiber tips in the region 26 when the connectors 20
and 22 are mated. Accordingly, the fiber-engaging
surfaces of the finger-like elements 58a-f are formed
from a resilient material such as polypropylene or
~0 polyethylene, which deforms slightly when in pressing
contact with the bare waveguide tips. In the preferred
embodiment, many features of finger elements 62a-f and
56a-f are identical and the features described immediately
-12-
3;~5
below with reference to Figures 4 and 5 are common
to bo-th unless otherwise indicated.
Figure 4 is a fragmentary view of the finger-like
elements 58a-f of Figure 2. The finger-elements 58a-f
are shown extending from a common base 59, the outer
peripheral portion of which includes a generally
wedge-shaped cam surface 59a and a generally linear
supporting leaf spring 64. In the preferred embodiment,
leaf spring 64 is integral with the base 59 and comprises
iO a resilient material such as polypropylene or polyethylene.
The leaf spring 64 rests upon a contoured shoulder 66
surrounding a slot 88 that extends inwardly from the
housing 50 periphery to the housing through-bore 51.
The leaf spring 64 may thereby be deformed against ~`
the shoulder 66 by the application of an inwardly
directed force against the cam surface 59a to permit
the inward displacement of the finger-like elements 58a-f
into the channels 56a-f. The channels 56a-f and
finger-like elements 58a-f are depicted with greater - `
clarity in Figure 5. i
Figure 5 is a cross-sectional view of the housing 50
of Figure 2 taken along line 5-5 therein. The through-
bore 51 of the housing 50 contains a plurality of
generally V-shaped fiber-accommodating channels 56a-f and
a like plurality of finger-like elements 58a-f, each
extendiny into a respective channel from a common base 59;
The channels are depicted as comprising a linear array,
although as will be apparent, any of a variety of
patterns may be chosen. The clearance between each
finger 58a-f and the base of the respective channels
56a-f prior to any inward displacement of the fingers is
:-
, -13-
73~
such that an optical fiber waveguide may be freely
inserted, within each channel, through the housing 50
to be internally held within the abuttment region 26.
The subsequent inward displacement of the fingers 6~a-f
(Figure 2) -thereby secures the individual waveguides
within their respective channels by engaging the
protectively jacketed portion thereof, while the fingers
58a-f engage the bared fiber tips for optical alignment
with the abutting fibers of a mating connector in a
manner hereinafter described.
In the preferred embodiment, both the finger-like
elements 58a-f and the channels 56a-f are formed from
a resilient material such as polypropylene or polyethylene
which deforms slightly when in pressing contact with
the waveguides. Consequently, the waveguide tips may
be firmly secured without the exertion thereon of
potentially damaging forces. The deformation of the
resilient V-shaped channel material additionally allows
self-centering of waveguides having di-Efering diameters
~0 within manufacturing tolerances.
To ~ully support each fiber and preclude unnecessary
bending, the inner dimensions of the channels 56a-f
are provided with a stepped dimensional change adjacent
to the abuttment region to compPnsate for the relatively
smaller diameter of the bared fiber tip compared to
that of the jacketed length of the fiber. The step
additionally provides the means for accurately locating
- the tips within the abuttment region by engaging the
leading edge of the fiber ~acket to control the depth
of insertlon into the housing 50,
-14-
73~3cj
.
To conveniently manufac-ture rigid connectors with
resilient channels, the channels may be formed as an
insert of resilient material which, as depicted in
Fiyure 5, may be inserted into the housing bore 51.
Returning to Figure 2, it may be additionally
appreciated that the channels 56a-f may extend axially
beyond the fiber-receiving end 50b of the housing 50
to define a shelf 55 that facilitates the placement of
the waveguides 1~ within the channels 38a-f.
Turning now to the means by which the finger-like
elements 62a-f are transversely displaced, it may be
seen from Figures 1 and 2 that the inwardly directed
force exerted upon the cam surface 64a to secure the
jacketed fibers in the channels is derived from a first -
partially internally threaded sleeve-like member 52
which is tightened onto the fiber-receiving end 50b
of the housing 50 by engaging the external threads 68
formed thereon for that purpose. ~s the sleeve member 52
is tightened onto the housing 50, the unthreaded forward
- 20 portion 70 of its inner periphery contacts the cam
surface 6~a and pushes it inwardly into a substantially
flush relationship with the housing 50 periphery. To
prevent the internally threaded region of the sleeve 52
from abrasively contacting the cam surface 64a, the
25 - tightening of the sleeve member 52 onto the housing 50
may be limite~ by si~ing the housing end portion 50a,
located ad~acent to the mating face 2~a, with a larger
outer diameter ~han the internal diameter of the sleeve
member 52.
In addition to inwardly displacing the fingers 58a-f
the sleeve member 52 securely supports the multi-~iber
cable 18 by means of a cable-securing ~aw 72 at its
3;3~
cable-receiving end. The jaw 72 comprises a plurality of
cantilevered elements, depicted as 7~a, 72b extending from
a common externally threaded shaft 74. The cantilevered
elements are spaced apart to freely admit the multi-
fiber cable 18 and function in a manner similar to a
drill chuck to secure the cable 18. Accordingly, a ~
second internally threaded sleeve member 54 is sized to ~ -
tighten onto the externally threaded shaft 74. The
second sleeve member 54 has a conically tapered bore 76
adapted to radially compress the cantilevered elements
72a, 72b, as the sleeve member 54 is tightened onto
the shaft 74, to securely and firmly engage the multi-
fiber cable 18. -
~ttention will next be turned to Figure 3 which
is a partially sectioned view of the other mating
connector 20 in disassembly. Many of the ~eatures of
the connector 20, hereinafter referred to as the male
connector, are similar to those described with reference
to the female connector 22; ~or the sake of brevity,
onl~ differences in the male connector 20 will be discussed.
The male connector 20 is shown to comprise a male housing 24,
and a pair of sleeve-like members 26, 28, respectively
similar in appearance and function to the sleeve-like
members S2, 54 discussed above. The male housing 24
has an axially extending through-bore 30 containing a
pluralit~ of generall~ V-shaped channels 38a-f arranged
in a pattern substantially identical to those of the
female housing 50.
The male housing 24 is, however, adapted to
projectingly hold the bare tips of the fiber waveguides 14
-16-
~L3L733~
in respective channels. ~he clearance between the
female connector channels 56a-f and fingers 5~a-f is
such that the projectingly-held b~re fibe~ tips from
the male connec-tor 20 are freely admitted into, and
accommodated within, the female housing 50 when the
housings 2~, 50 are mated.
Each of the abutting pairs of fiber tips are securely
aligned within their respective channel and in the
aforementioned manner by the transverse displacement
of the fingers 58a-f. The transverse displacement
is induced by the engagement of the cam surface 59a
with the interior periphery of a connector interface
sleeve 76 mounted concentrically about the male connector
housing 2~. The sleeve 76 is partially internally
threaded to mate with external threads 62, respectively
provided for that purpose on the mating end of the
female housing 50. The forward portion of the interior
sleeve 76 periphery is preferably unthreaded to minimize
the wear upon the cam surface 59a. As may be seèn with
reference to Figure 1, the connector interface sleeve 76
insures a secure and rigid connection while precluding
the inadvertent decoupling of the male and female
connectors.
Having thus described the structural features of
~5 the multi-fiber cable connector assembly, attention is
directed to the manner in which the connector assembly
is utilized to couple a pair of such cables. As is
known in the art, multi-fiber cables contain a plurality
o~ protectively jacketed optical fiber waveguides.
The protective jacketing serves to protect the fragile
waveguides from inadvertently caused scratches and nicks,
33~
and additionally serves to distribute potentially
damaging stresses. In the coupling process, this
protective jacketing must first be removed from the
fiber tips.
Accordinyly, a portion of the outer cable sheath
is removed and drawn back and the fibers splayed out
to form an essentially linear array, on a simple support
plate. The individual fibers' protective jacketing can
then be removed by any means known in the art as, for
example, by a hot wire stripper. The fibers can then
be scored and broken simultaneously. Although the
fibers may be splayed subsequent to scoring and breaking,
prior splaying yields fibers with ends having the same
length and minimizes the handling of bare fibers and
consequently, the possibility of fiber breakage.
The male connector 20 may then be assembled by
slipping the sleeve member 28 and the sleeve member 26
onto the cable 16 and inserting the waveguides 12 of
the cable 16 into the V-grooved channels of the housing 24
until the bared fiber tips protrude beyond the face 24a
by a predetermined amount. Since the fibers in the
V-grooves of the housing are protectively jacketed while
the protruding fiber tips are bare, the depth of insertion
of the waveguides may be controlled by internal stops
in the housing 24 which contact the ends of the fiber
¦ jacketing. It may be appreciated that the V-grooved -
extension shelf 55 facilitates the placement of each
waveguide into an appropriate channel. Each V-groove ~ -
in the housing 24 is deep enough to preclude, in
combination with undisplaced finger elements, the
jumping of c~annels by -the fibers.
-18-
1~L7!33~
The sleeve member 26 is then slid along the cable
toward the housing 24 and tightened thereon while the
cable is held in a manner which prevents its rotation.
As the sleeve 26 is tightened onto the housing 24, the
cam surface 36a is depressed so that the finger like
members 34a-f clamp the protectively jacketed fibers
at the bottom of the channels 38a-f. The sleeve member 28
is subsequently tightened onto the opposite remaining
end of the sleeve member 26 to solidly clamp the cable 16
by means of the jaws 44. In this manner~ support and
strain relief for the fibers are provided; in other ~
words, the fibers are isolated from tensions applied ;
on the cable beyond the connector.
The female connec-tor 22 is similarly assembled.
However, the tips of the fiber waveguides 14 inserted
into the female housing 50 are recessed from the mating
face 60 by a predetermined distance corresponding to
the distance by which the waveguides 12 of the housing 24
project.
- 20 The male and female connectors 20, 22 are subsequently
mated. Means for accurately aligning the pro~ectingly-held
fiber tips with the channels of the female connector are
provided by a pair of guide pins 78 in the male connector
which mate with guide holes 80 in the female connector.
I 25 Potentially damaging handling of the waveguides associated
! with conventional couplers during mating is thereby - ;
advantageously eliminated. Although the bare fibers
slide freely into the V-grooves of the emale housing 50,
the clearance between the fingers 58a-f and the channels
is such that the opposing fiber tips will butt against
each other rather than pass each other by. Any take-up
~19 -
3~i
of extra fiber will occur in accumulation chambers
provided on either side of the fingers 58a-f. The
connector interface sleeve 76 is then tightened onto
the female housing 50 to make a firm connection.
A covered access hole through the connector housing
may be provided for the application of index matching
fluid, or the fluid can be preloaded into the V-grooves
of the housing 24, 50.
¦ As explained above, the connector interface sleeve 76
¦ 10 causes the fingers 58a-F to align and clamp the opposing
¦ fiber tips down into the V-groove channels. Because the
fingers and channels comprise a soft resilient material
to compensate for variations of the fiber diameters
within manufacturing tolerances, a high coupling efficiency
is provided. Additionally, the connector halves may be
disconnected and reconnected or disassembled and reassembled
as needed.
It may be appreciated that either of the connectors
20, 22 ~escribed above may be utili~ed in conjunction
with the terminal connector associated with the hardware
comprising a particular system. As a practical matter,
the terminal connector would be similar to the female
housing 50 described herein and internally hold a
plurality of fiber waveguides protected by the housing
structure. A multi-fiber cable terminating in a male
connector, such as hereindescribed connector 20, could
be coupled to the system in the manner described above.
Additionally, a connector and connector assembly
of the type described hereinl but having a single channel
may be used for coupling single fiber waveguides.
,
~73~i
While the preferred embodiment of a multi-fiber
cable coupler has been described above, it is apparent
that numerous variations and modifications are obvious
to one skilled in the art. These variations and
modifications are included within the scope of the
present invention which are defined and limited only
by the appended claims.
