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A FIELD INSTALLABLE
OPTICAL FIBER CONNECTOR AND AN ASSOCIATED
METHOD OF FABRICATION
Field of the Invention
The present invention relates generally to
optical fiber connectors and associated methods of
fabrication and, more particularly, to optical fiber
connectors adapted for field installation and their
associated methods of fabrication.
Fsackaround of the Invention
Optical fibers are widely used in a variety
of applicationso, including the telecommunications
l0 industry in which optical fibers are employed in a
number of telephony and data transmission applications.
Due, at least in part, to the extremely wide bandwidth
and the low noise operation provided by optical. fibers,
the use of optical fibers and the variety of
applications i.n which optical ffibers are used are
continuing to increase. For example, optical fibers no
longer serve as merely a medium for long distance
signal transmission, but are being increasingly routed
directly to the home or, in some instances, directly to
a desk or other work location.
With the ever increasing and varied use of
optical fibers, it is apparent that efficient methods
of coupling optical fibers, such as to other optical
fiber, to a patch panel in a telephone central office
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or in an office building or to various remote terminals
or pedestals, i:a required. However, in order to
efficiently couple the signals transmitted by the
respective optical fibers, an optical fiber connector
S must not significantly attenuate or alter the
transmitted signals. In addition, the optical ffiber
connector must be relatively rugged and adapted to be
connected and disconnected a number of times in order
to accommodate changes in the optical fiber
transmission path.
In order to provide the desired signal
transmission characteristics, a number of optical ffiber
connectors have been developed which are mounted to the
end portion of an optical fiber during a factory
assembly process. By mounting the optical fiber
connector to t:he optical fiber and/or optical fiber.
cable (herein~ifter optical fiber) during an assembly
process at the factory, the assembly of the optical-
fiber connector can be standardized such that
inconsistent assembly and other problems associated
with the field installation of the connector are
avoided.
HoHiever, the factory installation of fiber
optic connectors is not altogether satisfactory for
every application. In particular, the factory
installation of fiber optic connectors does not
customize the installation process to account for the
myriad of design variations experienced in the field.
For example, by installing fiber optic connectors to
the end portion of an optical fiber at the factory, the
length of the connectorized optical fiber is fixed,
thus requiring excess length and coiling to insure
sufficient :Length for all applications. In addition,
in many instances, it is desirable to cut a length of
optical fiber into a plurality of shorter lengths of
optical fiber, each of which must be individually
connected, such as by an optical fiber connector, to
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another optica:~ fiber or to a patch panel or other type
of terminal. 33owever, the respective lengths of the
shorter optical fibers cannot generally be determined
until the optical fibers are installed in the ffield.
Thus, in this instance., the requisite optical ffiber
connectors cannot be mounted to the fibers at the
factory prior to installation of the optical (fiber.
Still further, it is desirable, in many instances, to
package and ship optical fiber prior to the
l0 installation of the fiber optic connectors since the
fiber optic connectors generally have a greater
diameter than the respective optical fiber, and may
unnecessarily complicate the packaging and shipping of
the optical fiber.
Consequently, several optical fiber
connectors have been developed which can be mounted to
the end portion of an optical fiber in the ffield once
the particular application of the optical f ibex has
been determined. For example, U.S. Patent No.
5,040,867 which issued August 20, 1991 to Michael de
Jong et al. and which is assigned to Siecor
Corporation, the assignee of the present invention,
discloses an. optical fiber connector which is adapted
for installation in the field. One embodiment of the
2S optical fiber connector of U.S. Patent No. 5,04D,867 is
the Camlite« connector which is also manufactured and
distributed by Siecor Corporation.
The Camlite° connector includes a lengthwise
extending ferrule defining a longitudinal bore
therethrough attached to a V-groove splice with a
camming means for securing a fiber in the splice. A
short length of optical fiber, typically termed an
optical fiber stub, is disposed in the bore of the
ferrule and extends into the V-groove splice. In the
field, the end portion of an optical fiber, typically
termed the field fiber, to which the optical fiber
connector is to be connected can be inserted in the V-
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groove splice from the end opposite the ferrule. Due
to the precise alignment of the longitudinally
extending V-groove within the Camlite° connector, the
end portion of t:he field fiber is aligned with the '
S optical fiber st:ub and thereafter held in place by
activating the ramming means.
The C;amlite° connector can also include a
crimp tube mounted to the end of the V-groove opposite
the ferrule such that the field fiber extends
therethrough. By compressing the crimp tube radially
inward so as to contact the buffer of the field fiber
cable, the field fiber is fixed in position relative to
the ferrule and the aligned optical fiber stub. The
ferrule of the Camlite° connector can, in turn, be
disposed within any of the standard connector housings.
For example, the ferrule of the Camlite° connector is
compatible with and can be mounted within an FC, ST or
SC connector housing. The resulting Camlite° connector
can then be connected, such as with a coupling sleeve,
to the end portion of another optical fiber which also
has an appropriate connector mounted to an end portion
thereof. Alternatively, the resulting Camlite°
connector can be connected to a patch panel, remote
terminal or pedestal.
While the Camlite° connector is a great
advance in th.e art, the Camlite~ connector mechanically
splices the field fiber to the optical fiber stub.
Even though mechanical splices generally provide
acceptable signal transmission characteristics, a
mechanical splice can reflect a portion of the
transmitted signal so as to produce a corresponding
return loss. This reflectance is due, at least in '
part, to differences between the respective indices of
refraction of the field fiber, the optical fiber stub
and the index matching gel which fills the bore of
ferrule between the optical fiber stub and the end
portion of 1=he field fiber. In particular, mhile the
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respective indices of refraction of the field fiber,
the optical fiber stub and the index matching gel can
be matched at a. predetermined temperature, the
respective indices of refraction vary in different
manners as the temperature fluctuates such that a
portion of the transmitted signal can be reflected by
the mechanical splice to thereby create a return loss.
Consequently, optical.fiber connectors in
which an optical fiber stub is fused to the field fiber
have been developed. For example, U.S_ Patent No.
4,598,974 which issued July 8, 1986 to Robert D. Munn
et al. and is assigned to International Business
Machines Corporation discloses an optical ffiber
connector which includes an optical fiber stub fused to
a field fiber. In particular, the optical ffiber
connector of U.S. Patent No. 4,598,974 includes a
ferrule defining a bore in which an optical ffiber stub
is disposed. This optical fiber connector is also
adapted to receive an end portion of the ffield ffiber
within the internal bore such that the end portion of
the field fiber is adjacent to and aligned with the
optical fiber stub within an internal splice chamber
defined within the ferrule.
The optical fiber connector of U.S. Patent
No. 4,598,974 further includes a pair of diametrically
opposed electrodes. The electrodes are permanently
mounted in the ferrule during its factory fabrication
and extend into the splice chamber so as to form an arc
gap therebet~ween. Therefore, by creating an arc
between the electrodes, the end portion of the field
fiber can be fused to the fiber optic stub. However,
as will be apparent to those skilled in the art, the
permanently mounted pair of electrodes can increase
both the mmterial cost and complexity of the optical
fiber connector.
7lnother optical fiber connector which welds
an optical fiber stub to the end portion of a field
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fiber is disclosed in U.S. Patent No. 4,220,394 which
..
issued September 2, 1980 to Andre Tardy and is assigned
to Societe Anonyme Bite: Campagnie Geperale
diElectricite. As described in U.S. Patent No.
4,220,394, the optical fiber stub is disposed within a
connection part and is aligned by a plurality of guide
rods and holding rods. An end portion of the field
fiber can likewise be held by a grouping element which
can, in turn, be mounted in an aligned relationship, by
means of an intermediate part, to the connection part.
Thereafter, tr.e optical fiber stub and the end. portion
of the field fiber can be welded with an oxyhydrogen
micro-blowpipe:. The optical fiber connector of U.S.
Patent No. 4,:?20,394 requires, however, several
different parts to hold and align the optical ffiber
stub and the field fiber, each of which must be ._
assembled so as to properly align and weld the optical
fiber stub to the field fiber.
Summary of the Invention
It is therefore an object of the present
invention to provide an improved optical fiber
connector.
It is another object of the present invention
to provide an improved optical fiber connector adapted
for field installation.
It is a further object of the present
invention tc> provide an optical fiber connector having
increased strength and durability.
It. is yet another object of the present
invention to provide an improved method for fabricating
an optical fiber connector.
These and other objects are provided,
according to the present invention, by an optical fiber
connector a.nd an associated method of fabricating an
optical fiber connector which includes an integral
ferrule and fusion access means such that an optical
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fiber stub and a field fiber can be fused within the
optical fiber cor~nector in the field. In one
embodiment, thc: fusion access means includes a fusion
access slot whale, in another embodiment, the fusion
access means includes at least one fusion access port.
In either embodiment, the optical ffiber
connector includes a longitudinally extending ferrule
having first a.nd second opposed ends and a bore deffined
longitudinally therethrough. According to the first
embodiment, a fusion access slot is formed in the
ferrule. During this formation process, a fluid stream
is preferably directed through the bore of the ferrule
from one or both ends to clear debris from the bore.
The fusion access slot extends transversely across the
ferrule from a first side of the ferrule to a bottom
portion of th.e fusion access slot.
The: fusion access slot is sufficiently deep
that the loncfitudinal bore of the ferrule opens into
the fusion access slot. However, the radial distance
between the bottom portion of the fusion access slat
and the second side of the ferrule, opposite the first
side, is greater than a predetermined radial distance
such that the ferrule remains structurally intact
during use. Thus, the optical fiber connector can be
connected and disconnected a number of times and
various loads can be placed on the optical fiber
connector without fracturing or otherwise damaging the
ferrule.
The optical fiber connector also preferably
includes an optical fiber stub, disposed within the
bore of the ferrule, which extends from a first end
adjacent the first end of the ferrule to a second end
disposed within the fusion access slot. The ffirst end
of the opt_Lcal fiber stub is preferably polished such
that the signal transmission characteristics of the
optical fiber connector are enhanced. In addition, the
second end of the optical Fiber stub preferably has a
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cleave angle of less than about 1°. The ferxule is
also adapted for receiving a second optical fiber, such
as a field fiber, which extends through the bore from
the second end of the ferrule to the fusion access
slot. The ferrule maintains the second optical fiber
and the optical fiber stub in general alignment so that
the.second optical fiber and the optical fiber stub can
be fused within the fusion~access slot during a field
installation procedure.
According to this embodiment, the fusion
access slot includes first and second opposed sidewalls
extending from a respective transversely extending edge
of the bottom 'portion of the fusion access slot to the
first side of the ferrule. In one embodiment, each
respective edge of the bottom portion of the fusion
access slot is curved to further increase the
structural integrity of the ferrule. More
particularly, the curved edges of the bottom portion of
the fusion access slot preferably have a predetermined
radius of cur'rature which is greater than a
predetermined minimum radius of curvature.
The radial distance between the longitudinal
axis defined by the bore of the ferrule and the bottom
portion of the fusion access slot is also preferably
greater than a predetermined minimum radial distance
such that the. second optical fiber and the optical
fiber stub ca:n be properly fused therein. The fusion
access slot also has a predetermined width. The
predetermined width of the fusion access slot is
preferably lE~ss than a predetermined maximum width to
further provide that the ferrule remains structurally
intact during use. However, the predetermined width of
the fusion access slot is also preferably greater than
a predetermined minimum width such that the second
optical,fiber and the optical fiber stub can be
properly fudged therein.
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In another embodiment, the fusion access
means of the ferrule includes a cylindrical fusion port
extending tran:wersely through the ferrule. The fusion
access port is in communication with the longitudinal
bore to thereby define a splice cavity within the
ferrule. The fusion access port also has a
predetermined diameter which, in preferred embodiments,
is less than a predetermined maximum diameter such that
the ferrule remains structurally intact during use.
In this embodiment, the optical fiber stub is
preferably di:~posed within the bore of the ferrule so
as to extend 1_rom a ffirst end adjacent the ffirst end of
the ferrule to a second end disposed within the splice
cavity. In addition, the ferrule is also adapted for
receiving the second optical fiber, such as a field
fiber, which extends through the bore from the second
end of the ferrule and into the splice cavity such'that
the second optical fiber and the optical fiber stub can
be fused therein. Thus, in addition to being less than
a predetermined diameter, the predetermined diameter of
the fusion access port is preferably greater than a
predetermined minimum diameter such that the second
optical fiber and the optical fiber stub can be
properly fused within the splice cavity.
Th.e ferrule of this embodiment can also
include at least one viewing port extending
transversely through the ferrule. The viewing port is
in communication with the splice cavity such that the
fusion process can be monitored. In one embodiment,
3D the fusion access port and the viewing port define a
fusion access port axis and a viewing port axis,
respectively. In this embodiment, the fusion access
port axis and the viewing port axis define a
predetermined angle therebetween, such as 90°.
:=n either embodiment, the optical fiber
connector can also include an annular alignment key
mounted to the ferrule such that the ferrule extends
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therethrough. The alignment key provides a position
indication such that the fusion access means can be
oriented in a predetermined angular relationship.
The optical fiber connector can also include
a crimp tube assembly mounted to the second end of the
ferrule. The crimp tube assembly defines a lengthwise
extending aperture which is aligned with the bore
defined by the ferrule. Thus, the second optical fiber
preferably extends through both the aperture defined by
the crimp tube: assembly and the bore defined by the
ferrule. In one embodiment, the crimp tube assembly
includes a crimp tube adapted to receive the second
optical fiber and an adapter housing adapted to couple
the crimp tubes to the second end of the ferrule. In
particular, the adaptor housing of this embodiment
preferably defines an internal cavity having first and
second cavity portions having first and second internal
diameters, respectively. The first internal diameter
of the adapter housing is preferably sized to receive
the second end of the ferrule, while the second
internal diameter of the second cavity portion is sized
to receive the crimp tube.
The' optical fiber connector can also include
a lengthwise extending tubular crimp body mounted over
the crimp tu:~e assembly to the second end of the
ferrule. The tubular crimp body also defines a
longitudinal bore through which the second optical
fiber extends. In addition, the tubular crimp body can
include a first ring extending radially inward into the
longitudinal. bore. Once assembled, the first ring of
the tubular crimp body is longitudinally inward of the
crimp tube <assembly and is sized smaller than the crimp
tube assembly such that the tubular crimp body is
securely mounted to the ferrule. In order to
3~. facilitate assembly, the tubular crimp body can also
define a lateral slot which e5a ends from a first end of
the tubular crimp body longitudinally inward beyond the
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first ring to thereby divide a portion of the tubular
crimp body into first and second crimp body segments.
The first and second crimp body segments axe adapted to
resiliently deflect outwardly such that the tubular
crimp body car be mounted over the crimp tube assembly.
The optical fiber connector of one embodiment
of the present. invention can also be mounted to the end
portion of a single fiber cable which includes a
buffered optical fiber and one or more lengthwise
extending strength members surrounded by a protective
jacket. According to the present invention, an end
portion of the jacket is removed to expose the buffered
optical fiber and the buffer coating is then removed
from an end portion of the exposed optical fiber.
The: end portion of the exposed optical fiber
can be extended through the bore of a tube which is
inserted within the single fiber cable between the
protective jacket and the buffered optical fiber.
Thereafter, 'she end portion of the exposed optical
fiber is inserted into the second end of the ferrule.
In one embodiment, the end portion of the exposed field
fiber is then fused to an optical fiber stub and the
components of a connector housing are assembled. The
crimp body c:an then be radially compressed about the
portion of t_he single fiber cable in which the tube has
been insertE~d. Thus, the jacket and the strength
member of the single fiber cable can be securely held
in a fixed 'position relative to the optical fiber
connector.
Therefore, according to the present
invention, a durable optical fiber connector which
includes a monolithic ferrule and fusion access means,
such as a fusion access slot or a fusion access port,
is provided such that an optical fiber stub and a field
fiber can )~e fused in the field. In particular, the
fusion access means of the ferrule is formed without
significantly wea~:Gning tine fGrrulG such that the
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ferrule will remain structurally intact without
fracturing or being otherwise damaged during use.
Thus, the optical fiber connector can be connected and
disconnected numerous times without damaging the
connector. In addition, the optical fiber connector of
the present invention can readily be installed by
technicians in the field by fusing the optical stub
fiber to the field fiber while maintaining the
excellent sigr.~al transmission properties of the optical
fiber.
Brief Description of the Drawings
Figure 1 is an exploded perspective view of
one embodiment of an optical fiber connector of the
present invention illustrating the various components
of the housing as well as a ferrule having a fusion_
access slot defined therein.
Figure 2 is a perspective view of a portiolz
of one embodiment of an optical fiber connector
according to the present invention illustrating a
ferrule having a fusion access slot defined therein.
Figure 3A is a longitudinal cross-sectional
view of the embodiment of the ferrule of the present
invention shown in Figure 2 and taken along line 3A-3A
of Figure 3B which illustrates the width of the
transversely extending fusion access slot.
Figure 3B is a longitudinal cross-sectional
view of the embodiment of the ferrule of the present
invention shown in Figure 2 and taken along line 3B-3B
of Figure 3A which illustrates the depth and rounded
edges of the bottom portion of the fusion access slot.
Figure 4 is a perspective view of an optical
fiber connector of one embodiment of the present
invention which has been partially assembled in
preparation for the fusing of the optical fiber stub to
a field fib>er.
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Figure= S is a perspective view of one
embodiment of the optical fiber connector of the
present invention illustrating the fusing of the
optical fiber stub and the field fiber.
Figure 6 is a perspective view of one
embodiment of an optical fiber connector of the present
invention following the assembly and fusion process.
Figure 7 is a longitudinal cross-sectional
view of the embodiment of the optical fiber connector
l0 of the present invention illustrated in Figure 6 and
taken along line 7-7.
Figure 8 is a perspective view of a portion
of one embodiment of an optical fiber connector
according to the present invention illustrating a
ferrule having a fusion access port and a viewing port
defined transversely therethrough. _
Figure 9 is a longitudinal cross-sectional
view of an embodiment of the optical fiber connector' of
the present invention illustrating its connection to an
end portion o:E a single fiber cable.
Detailed Description of the Preferred Embodiments
The present invention will now be described
more fully hereinafter with reference to the
accompanying drawings, in which a preferred embodiment
of the invention is shown. This invention may,
however, be embodied in many different forms and should
not be construed as limited to the embodiments set
forth herein; rather, this embodiment is provided so
that this disclosure will be thorough and complete and
will fully convey the scope of the invention to those
skilled in the art. Like numbers refer to like
elements throughout.
Referring now to Figure 1, an optical fiber
connector lid according to one embodiment of the present
invention is illustrated in an exploded perspective
view. The optical fiber connector includes a
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longitudinally extending ferrule 12 having first and
second opposed ends 14 and 16, respectively, and a
bore 18 defined longitudinally therethrough. The
ferrule is typically comprised of a ceramic material,
such as zirconi.a, but can also be comprised of a glass,
plastic or composite material without departing from
the spirit and scope of the present invention. As
shown in more detail in Figure 2, the ferrule is
generally cylindrical and the bore defined therethrough
is generally d.=_fined along the longitudinal axis 12a of
the ferrule.
The ferrule I2 includes fusion access means
such that a pair of optical fibers aligned by the
ferrule can be. fused as explained hereinafter. In the
embodiment illustrated in Figures 2, 3A and 3B, the
fusion access means includes a fusion access slot 20
defined by the ferrule. In particular, the fusion
access slot e;ttends transversely across the ferrule
from a first aide 22 of the ferrule to a bottom portion
24 of the fusion access slot. Thus, the fusion access
slot has a predetermined width 26 and a predetermined
depth 28, as best shown in Figures 3A and 3B,
respectively.
As illustrated, the fusion access slot 20 is
sufficiently deep that the bore 18 opens through each
of the first and second opposed sidewalls 30 of the
fusion acces;~ slot. According to the present
invention, h~~wever, the predetermined depth 28 of the
fusion access slot is such that a significant amount of
the material which forms the ferrule connects the two
portions of the ferrule which are separated by the
fusion acce~;s slot. In particular, the radial distance
32 between t:he bottom portion 24 of the fusion access
slot and a second side 34 of the ferrule, opposite the
first side 22, is greater than a predetermined radial
distance such that the fusion access slot does not
significantly weaken the ferrule so that the ferrule
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remains structurally intact during use. Consequently,
the ferrule will remain integral and will not break or
otherwise fracr_ure during normal use, including during
repeated connections and disconnections.
As explained hereinafter, a sufficient
distance 36 must also be maintained between the
longitudinal axis 12a defined by the bore 18 and the
bottom surface. 24 of the fusion access slot 20, such
that the optical fibers can be fused within the fusion
access slot. For example, fox a ferrule 12 having a
diameter of 2..5 mm, the depth 28 of the fusion access
slot is prefewably 1.5 mm to 2.0 mm and, more
preferably, about 1.75 mm. Correspondingly, the radial
distance 32 between the bottom portion of the fusion
access slot of this embodiment and the second side 34
of the ferrule is preferably between 1.0 mm and 0.5. mm
and, more preferably is about 0.75 mm.
In addition, the predetermined width 26 of
the fusion a<:cess slot 20 is also preferably less than
a predetermined maximum width to further improve the
structural i:ztegrity of the ferrule. However, the
predetermined width of the fusion access slot must also
be sufficiently large that the optical fibers can be
fused within. the fusion access slot as explained
hereinafter. Thus, for a ferrule 12 having a length of
about 15.5 mm, the fusion access slot preferably has a
width of between about 1 mm and about 2 mm and, more
particularly, has a width of about 1.5 mm.
The transversely extending bottom surface 24
3C of the fusion access slot 20 is preferably parallel to
a line tangent to the surface of the first side 22 of
the ferrule 12 from which the fusion access slot
extends. 'thus, the depth 28 of the fusion access slot
as well as the radial distance 32 between the bottom
3S portion of the fusion access slot and the second side
34 of the ferrule are preferably measured between the
deepest port=ion of the bottom surface of the fusion
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access slot and lines tangent to the first and second
sides of the ferrule, respectively.
As bent shown in Figures 3A and 3B, the
optical fiber connector l0 also preferably includes an
optical fiber stub 40 disposed within the bore 18 of
the ferrule 12 <~nd extending from a first end adjacent
a first end 14 of the ferrule to a second end disposed
within the fusion access slot 20. The second end of
optical fiber stub 40 is preferably cleaved with a good
l0 finish, the cleave angle being preferably less than one
degree. Typically, the optical fiber stub is secured
within the bores of the ferrule, for example with an
epoxy. For example, for a ferrule having a length of
15.5 mm, an optical fiber stub having a length of 11 mm
can be secured within the bore of the ferrule. As also
illustrated, t'~e second end of the optical (fiber stub
preferably extends about halfway across the fusion
access slot. Thus, for a fusion access slot having a
width 26 of 1.5 mm, the optical fiber stubs preferably
extends approximately 0.75 mm across the fusion access
slot.
The ferrule 12 is also adapted to receive a
second optical fiber 42, such as a field fiber, which
extends through the bore 18 of the ferrule from the
second end 16 of the ferrule to the fusion access
slot 20. The second optical fiber can have various
coating diameters, including 250um and 900um buffered
optical fibers, without departing from the spirit and
scope of the present invention. The glass fiber is
typically 125~m, and the bore is sized accordingly. As
illustrated, the second optical fiber also preferably
extends about halfway across the fusion access slot.
Due to the precise alignment of the bore defined
through the ferrule, the second optical fiber and the
optical fiber stub 40 are maintained in general
alignment so that the second optical fiber and the
optical fiber stub can be fused within the fusion
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access slot. In particular, the ferrule of the present
embodiment preferably maintains the alignment of the
second optical fiber and the optical fiber stub such
that single mode optical fibers can be reliably fused
S without introducing significant reflections or modal
interference.
As illustrated, the fusion access slot 20
defined by the ferrule 12 also includes first and
second opposed sidewalls 30 extending radially from a
respective transversely extending edge of the bottom
portion 24 of the fusion access slot to the first
side 22 of the ferrule. In one embodiment, each
respective edc;e of the bottom portion of the fusion
access slot i:> curved to further strengthen the
ferrule. In particular, each curved edge of the bottom
portion of the fusion access slot preferably has a
predetermined radius of curvature. The predetermined
radius of curvature of each curved edge is
advantageously greater than a predetermined minimum
radius of curvature to further increase the structural
integrity of ferrule. For example, for a ferrule
having a fusion access slot having a width of 1.5 mm
and a depth of 1.75 mm, the radius of curvature of each
curved edge.of~the bottom portion of the fusion access
slot is preferably greater than about 0.2 mm and, more
particularly, is about 0.25 mm.
According to another embodiment of the
ferrule 12 cf the present invention illustrated in
Figure 8, the fusion access means of the ferrule
includes at least one cylindrical fusion access port 44
extending transversely through the ferrule. As
illustrated, the fusion access port is in communication
with the longitudinal bore 18 of the ferrule to thereby
define a splice cavity 46. As shown, the fusion access
port preferably extends diametrically through the
ferrule. Ln addition, the fusion access port
preferably has a predetermined diameter 48 and, more
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preferably, has a predetermined diameter which is less
than a predeterrnined maximum diameter such that the
fusion access port does not significantly structurally
weaken the ferrsle so that the ferrule will remain
structurally intact during use. However, the
predetermined diameter of the fusion access port must
also preferably be greater than a predetermined minimum
diameter such that a second optical fiber 42 and an
optical fiber stub 40 can be properly fused within the
l0 splice cavity as described hereinbelow,
As dea cribed above, the ferrule 12 of this
embodiment also includes an optical fiber stub 40
disposed within the bore 18 of the ferrule and
extending from a first end adjacent to the first end 14
of the ferrule to a second end disposed within the
splice cavity 46 defined within the ferrule. The
ferrule of this embodiment is also adapted for
receiving a second optical fiber 42 through the bore of
the ferrule from the second end 16 of the ferrule to
d
the splice cavity such that the ferrule maintains the
second optical fiber and the optical fiber stub in
general alignment.
As .also illustrated in Figure 8, the
ferrule 12 of this embodiment can also define at least
one viewing port 50 extending transversely through the
ferrule. The viewing port is also in communication
with the splice cavity 46 such that the fusion of the
second optical fiber 42 and the optical fiber stub 40
can be monitored as described hereinbelow. In
addition, as described above in conjunction with the
fusion access port 44, the viewing port preferably has
a predetermined diameter SZ and, more preferably, has a
predetermined diameter that is less than a
predetermined maximum diameter such that the viewing
port does not significantly structurally weaken the
ferrule so that the ferrule remains structurally intact
during use. The predetermined diameter of the viewing
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port can be le:>s than the predetermined minimum
diameter of the: fusion access port, however, as the
viewing port need not be large enough to permit fusion
of the optical fiber stub and the second optical fiber
therethrough.
In addition, the fusion access port 44 and
the viewing port 50 define a fusion access port
axis 44a and a viewing port axis 50a, respectively. As
illustrated in Figure e, the fusion access port axis
and the viewing port axis define a predetermined
angle 54 there:between. For example, in the illustrated
embodiment, the predetermined angle defined between the
fusion access port axis and the viewing port axis is 90
degrees. By orienting the fusion access port and the
viewing port ;substantially orthagonally, the strength
of the ferrule can be further enhanced.
According to the present invention, a method
of fabricating an optical fiber connector 10 is also-
' provided. According to this method, the longitudinally
extending ferrule 12 having first and second opposed
ends 14 and 7.6, respectively, and a bore 18 deffined
longitudinal7_y therethrough is formed. In order to
fabricate the ferrule of the first embodiment described
above, a fusion access slot 20 is then formed, such as
by grinding the ferrule. Alternatively, a fusion
access port 44 and, in some embodiments, a viewing
port 50, can be formed, such as by drilling, through
the ferrule. During the forming of either the fusion
access slot or the fusion access port, a fluid stream,
such as a stream of compressed air, is preferably
directed through the bore of the ferrule from one or
both ends such that the bore remains clear and
unobstructed.
Once the fusion access means has been formed,
the optical fiber stub 40 can be disposed within the
bore 18 of the ferrule 12 so as to extend from a first
end adjacent the first end 14 oz the ferrule to a
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_20_
second end positioned within the fusion access slot 20
or the splice cavity 46. The second end of optical
fiber stub is preferably cleaved with a good finish,
the cleave angle being preferably less than one degree.
S The optical fiber stub is preferably secured within the
bore, such as with an epoxy, and the first end of the
optical fiber ;tub is preferably polished to facilitate
optical transmission therethrough.
Typically, an annular alignment key 56 is
provided to fi;{ the ferrule 12 against rotation after
the assembled optical fiber connector 1Q has been
installed in t:he field, such as to a coupling sleeve or
other type of connector. As known to those skilled in
the art, rotation of the optical fiber connector could
damage the end. face of the ferrule. The annular
alignment key also can provide an angular position
indication for use in aligning the eccentricity of the
fiber-ferrule assembly to maximize optical power
transmission .~or a mated pair of optical fiber
2o connectors. ,3uch angular position indicatian can be
established by optical detection during rotation.
In addition, the annular alignment key 56 may
be used to establish the, angular position of the fusion
access means relative to the ferrule 12. Thus, the
fusion acces~~ means can be properly positioned in the
fusion fixtu~-a during the fusion process as described
hereinafter :in conjunction with Figure 5.
The annular alignment key 56 is typically
comprised of a plastic or metallic material and has a
position indicator 58, such as a tab extending radially
outwardly, which is mounted in a predetermined angular
position relative to the ferrule 12 as shown in Figure
4. For example, the alignment key can be press-fit on
the ferrule c>r can be secured to the ferrule, such as
with an epoxy. Thereafter, the fusion access means,
such as a fusion access slot 20 or the fusion access
port 44 can be formed in a predetermined angular
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relationship to the position indicator of the alignment
key.
As shown in Figures 1, 4 and 7, a crimp tube
assembly 60 can also be mounted to the second end 16 of
the ferrule 12 for securing the second optical fiber 42
to the ferrule :in a manner which will protect the fused
joint from subsequent axial forces (e.g., tension and
torsion)~to which the second optical fiber is
subjected. As illustrated, the crimp tube assembly is
mounted to the second end of the ferrule such that the
lengthwise extending aperture defined by the crimp tube
assembly is aligned with the bore 18 of the ferrule.
Thus, the second optical fiber can extend through both
the aperture defined by the crimp tube assembly and the
bore defined by the ferrule.
More particularly, the crimp tube assembly- 60
generally includes a crimp tube 62 having first and
second opposed. ends 64 and 66, respectively. The crimp
tube assembly also generally includes an adapter
housing 68 defining an internal cavity having first and
second cavity portions 70 and 72, respectively. The
first and second cavity portions preferably have ffirst
and second internal diameters, respectively. The ffirst
internal diameter of the first cavity portion of the
adapter housing is preferably sized to receive the
second end 16 of the ferrule 12. In contrast, the
second internal diameter of the second cavity portion
is preferably sized to receive the first end of the
crimp tube.
Although the adapter housing 68 and the crimp
tube 62 are shown in Figure 1 as separate components,
the adapter housing and the crimp tube can be
integrally formed without departing from the spirit and
scope of the present invention. In addition, the crimp
tube assembly 60 can be comprised of either a plastic
or a metallic material and can be mounted to the second
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end 16 of the ferrule 12 in a press fit relationship or ,
can be secured thereto, such as with an epoxy_
Once a crimp tube assembly 60 has been
mounted to the second end 16 of the ferrule 12, the
buffer of an end portion of the second optical (fiber 42
is preferably removed so as to expose the glass optical
fiber itself as shown in Figure 1. The end portion of
the second optical fiber can then be cleaved and
inserted through the aperture defined by the crimp tube
assembly and the bore 18 defined by the ferrule such
that the end portion of the second optical ffiber is
disposed within the fusion access slot 20 or within the
splice cavity 46 in a generally aligned relationship
with the optical fiber stub 40. The end portions of
the optical fiber stub and the second optical (fiber can
then be fused. After fusion, an end portion 62a of -the
crimp tube 62 is crimped to secure the second optical
fiber as shown in cross-.section in Figure 7.
In particular, as illustrated in Figure 5,
the partially-assembled optical fiber connector can be
disposed between a pair of electrodes 91 such that the
electrodes are aligned with the fus~.on access slot 20
or the fusion access part 44. For example, the ferrule
can be controllably positioned by a fusion fixture 90
such that the electrodes are appropriately aligned with
the fusion access slot or the fusion access port_ The
fusion fixture can also include fiber viewing means,
such as a microscope or other type of magnifying
viewing instrument 92 which allows a technician to
monitor the separation and cleave quality respective
end faces of the optical fiber stub 40 and the second
optical fiber 42 such that the separation can be
adjusted, if necessary, prior to the fusion process.
It is generally unnecessary to adjust the relative
positions of the optical fiber stub and the second
optical fiber, however, since the bore 18 of the
ferrule 12 is typically precisely aligned along the
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longitudinal axis 12a of the ferrule, and the end face
separation is reliably controlled by a combination of
fiber preparation and the fusion fixture.
Once the optical fiber stub 40 and the second
optical fiber 42 axe positioned,-an arc.can be
established between the pair of electrodes 91 such that
the optical fiber stub and the second optical ffiber are
fused into an integral~optical fiber. In addition,
during the fusion process, the surface tension of the
molten glass fibers further aligns the resulting
optical fiber.
As described above, the depth 28 of the
fusion access slot 20 is preferably greater than a
predetermined minimum depth and the width 26 of the
fusion access slot is preferably greater than the
predetermined minimum width such that the optical ffiber
stub 40 and the second optical fiber 42 can be
efficiently fused_ In particular, if the depth of the
fusion access slot is too shallow or if the width -of
the fusion access slot is too narrow, a portion of the
energy imparted by the electrodes will be expended in
heating the ferrule instead of fusing the optical fiber
stub and the second optical fiber, thereby decreasing
the efficiency ~f the fusion process. In addition, if
the depth of the fusion access slot is too shallow or
the width of the fusion access slot is too narrow, the
arc formed by the opposed electrodes 91 can deviate so
as to further decrease the efficiency with which the
optical fiber stub and the second optical fiber are
fused.
After fusing the optical fiber stub 40 and
the second optical fiber 42, various fiber protection
methods can be employed to prevent contamination of the
fused joint. For example, the fusion access slot 20 or
the fusion access port 44 can be filled with a gel,
such as a silicone adhesive, to protect the fused end
portions of the optical fiber stub and the second
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optical fiber. In addition, the interior cavity of the
crimp tube assembly 60 can be filled with a gel, such
as a silicone adhesive, to further protect the second
optical fiber. However, the optical fiber connector l0
need not include a fiber protecting gel since the
optical fibers are generally adequately protected by
the surrounding housing of the optical fiber connector
as described below.
In addition, once the optical fiber stub 40
1D and the second optical fiber 42 have been fused, a
portion of the crimp tube 62a, adjacent second end 66,
can be radially compressed about the buffer of the
second optical.fiber such that rotational and axial
forces to which the second optical fiber is
subsequently subjected will not be translated to the
fused joint_ This crimping may be accomplished by
means of a crimping means provided by the fusion
fixture. Thereafter, the optical fiber connector 10-
can be mounted within any one of the standard connector
housings, such as an SC connector housing, an FC
connector housing or an ST connector housing. In
addition to providing a standard connector for coupling
to coupling sleeves, patch panels or other terminals,
the connector housing generally prevents bending forces
from being applied to the ferrule 12 and, instead,
typically limits the forces applied to the ferrule, if
any, to tensile forces. Accordingly, the structural
integrity and durability of the ferrule is further
improved.
For purposes of illustration, an ST connector
housing is illustrated in Figures I, 6 and 7. As best
shown in Figure 4, several components of the housing
including the strain relief boot 72 the crimp body 74,
the bayonet housing 76 and a spring 78 are preferably
disposed upon the second optical fiber 42 prior to the
insertion of the second optical fiber into the second
end 16 of the ferrule 12. Once the optical fibe=r
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stub 40 and thE: second optical fiber have been fused,
the spring, the bayonet housing, the crimp body and the
strain relief boot can be slid along the second optical
fiber and mounted to the ferrule and, more
S particularly, can be mounted to the crimp tube
assembly 60.
In particular, the crimp body 74 generally
has a tubular shape which defines a longitudinal bore
through which the second optical fiber 42 extends. As
shown in Figures 1 and 7, the tubular crimp body
typically includes a first ring 80 extending radially
inward into the longitudinal bore. In addition, the
tubular crimp body preferably defines a lateral slot 82
which extends from a first end of the tubular crimp
body longitudinally inward beyond the first ring to
thereby divide a portion of the tubular crimp body into
first and second crimp body segments 84. The first and
second crimp :body segments are adapted to resiliently
deflect outwardly as tubular crimp body is mounted over
or slid over the crimp tube assembly 60. In addition,
the first ring of the tubular crimp body is adapted to
securely mour..t behind or longitudinally inward of the
crimp tube a~>sembly relative to the second end 16 of
the ferrule 7_2 such that the crimp tube assembly is
securely mounted thereto.
As illustrated in Figures 1, 6 and 7, the
bayonet housing 76 is also preferably disposed about at
least a portion of the ferrule 12. In particular, the
tubular crimp body 74 of this embodiment can also
include means for engaging the bayonet housing, such as
a second raised ring 86 extending radially outward from
an outer surface of the tubular crimp body.
Correspondingly, the bayonet housing includes a
complimentarily shaped surface 88 extending radially
inward into the bayonet housing for engaging the second
raised ring once the tubular crimp body has been
mounted about= the crimp tube assembly 60.
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As also shown in Figure 7, the spring 78 is
accordingly disposed between the alignment key 56 and
the complimentarily shaped surface 88 of the bayonet
housing 76 so as to maintain the bayonet housing in
position. In addition, the crimp body 74 can include a
third raised ring 81 extending radially outward as
shown in Figures 1 and 7. The second raised ring
serves as a step to further prevent the bayonet housing
from being disassembled from the crimp body. In
particular, the second raised ring is adapted to
contact the inwardly extending complimentarily shaped
surface 88 of the bayonet housing so as to prevent
inadvertent disassembly of the bayonet housing.
Furthermore, a dust cover 95 can also be mounted over
the portion of. first end 14 of the ferrule which
extends beyond the bayonet housing to protect the
optical fiber connector 10 from environmental
contamination prior to connection as shown in Figure 1.
The optical fiber connector 10 of the present
invention can also be mounted to an end portion of a
single fiber cable 94 as shown in cross-section in
Figure 9. As known to those skilled in the art,.the
single fiber cable includes a buffered optical fiber 42
and one or more lengthwise extending strength members
96, such as aramid yarn, surrounded by a protective
jacket 9B. According to the present invention, end
portions of the jacket and aramid yarn are removed to
expose the buffered optical fiber. Furthermore, the
buffer coating is removed from an end portion of the
exposed optical fiber.
The end portion of the exposed optical fiber
42 is extended through the bore of a tube 100,
typically comprised of plastic or metallic material,
and the tube is inserted within the single fiber cable
between the strength member 96 and the buffered optical
fiber. For a}:ample, the tube can be identical to the
crimp tube 62 illustrated and described herein.
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Thereafter, the end portion of the exposed optical
fiber is inserted into the second end 16 of the
ferrule 12. In one embodiment, the end portion of the
exposed field fiber is then fused to an optical fiber
stub 4D and the' components of a connector housing are
assembled as described herein and as illustrated in
Figure 9.
As also illustrated in Figure 9, the crimp
body 74 can be radially compressed about a portion of
the single fiber cable in which the tube 100 has been
inserted. Thus, the jacket 98 and the strength member
96 of the single fiber cable can be securely held in a
fixed position, relative to the optical fiber connector
10 and between the crimp body and tube 100 while the
optical fiber 42 is not damaged.
As described above, an optical fiber
connector 10 of the present invention can be readily
fabricated. In particular, the ferrule 12 can be
formed and the optical fiber stub 40 disposed therein
in a factory setting such that the first end of the
optical fiber stub can be polished while disposed in
the first enc. of the ferrule. Thereafter, an end
portion of a second optical fiber 42, such as a field
fiber, can be. inserted through the second end 16 of the
ferrule and fused to the optical fiber stub in the
field. Once the field fiber and the optical fiber stub
have been fused, the various components of the housing
can be assembled to form the resulting optical fiber
connector. Thereafter, the optical fiber connector can
be mounted, such as via a coupling sleeve, to another
optical fiber or to a patch panel, remote terminal,
pedestal or other type of terminal as known to those
skilled the art.
Accordingly, the optical fiber connector 10
of the pres~=_nt invention includes a ferrule 12 having
fusion access means, such as a fusion access slot 20 or
a fusion access pore 44, such that an optical_ fiber
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stub 40 and a ~~econd optical fiber 42 can be fused in
the field. The. ferrule and, more particularly, the
fusion access means, is formed such that the ferrule is
relatively strong and durable and will remain
structurally intact during normal use. Thus, the
optical fiber connector can be connected and
disconnected numerous times without impairing the
structural integrity of the connector. In addition,
due to the design of the optical fiber connector, the
to connector can be readily installed by technicians in
the field while maintaining excellent signal
transmission properties due, at least in part, to the
fusion of the optical fiber stub and the second optical
fiber and to the polishing of the first end of the
optical stub fiber.
In t:he drawings and the specification, there
has been set forth a preferred embodiment of the
invention and, although specific terms are employed,
the terms are used in a generic and descriptive sense
only and not for purpose of limitation, the scope of
the invention being set forth in the following claims.
