U.S. patent application number 13/365603 was filed with the patent office on 2013-01-31 for methods for centering optical fibers inside a connector ferrule and optical fiber connector.
The applicant listed for this patent is James P. Luther, Darrin M. Miller. Invention is credited to James P. Luther, Darrin M. Miller.
Application Number | 20130028561 13/365603 |
Document ID | / |
Family ID | 42057585 |
Filed Date | 2013-01-31 |
United States Patent
Application |
20130028561 |
Kind Code |
A1 |
Luther; James P. ; et
al. |
January 31, 2013 |
METHODS FOR CENTERING OPTICAL FIBERS INSIDE A CONNECTOR FERRULE AND
OPTICAL FIBER CONNECTOR
Abstract
An optical fiber connector assembly includes at least one
ferrule, the ferrule having a front end, at least one bore for
receiving at least one optical fiber, and an optical fiber at least
partially disposed in the bore, at least a portion of the at least
one optical fiber being disposed in the at least one ferrule bore
so that a section of the at least one fiber portion has an end face
that is essentially even with the ferrule front end, a section of
the optical fiber having a bulge which has a size which is larger
than the bare optical fiber diameter, the fiber at least partially
contacts a surface of the ferrule bore, and the contact defining a
fiber-to-ferrule interface region. The fiber-to-ferrule interface
region includes substantial contact between the bulge and a portion
of the surface of the bore such that movement of the fiber in the
bore is inhibited and the remaining portion of the optical fiber is
substantially centered in the at least one bore.
Inventors: |
Luther; James P.; (Hickory,
NC) ; Miller; Darrin M.; (Conover, NC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Luther; James P.
Miller; Darrin M. |
Hickory
Conover |
NC
NC |
US
US |
|
|
Family ID: |
42057585 |
Appl. No.: |
13/365603 |
Filed: |
February 3, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12241558 |
Sep 30, 2008 |
8132971 |
|
|
13365603 |
|
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Current U.S.
Class: |
385/80 ;
385/78 |
Current CPC
Class: |
G02B 6/02342 20130101;
G02B 6/3834 20130101; G02B 6/403 20130101; G02B 6/3847 20130101;
G02B 6/3861 20130101; G02B 6/02366 20130101 |
Class at
Publication: |
385/80 ;
385/78 |
International
Class: |
G02B 6/36 20060101
G02B006/36 |
Claims
1. An optical fiber connector assembly with at least one ferrule,
the ferrule having a front end at least one bore for receiving at
least one optical fiber, and an optical fiber at least partially
disposed in the bore, said assembly comprising: at least a portion
of the at least one optical fiber is disposed in the at least one
ferrule bore so that a section of the at least one fiber portion
has an end face that is essentially even with the ferrule front
end, a section of the optical fiber comprising a bulge which has a
size which is larger than the bare optical fiber diameter, the
fiber at least partially contacts a surface of the ferrule bore,
and the contact defining a fiber-to-ferrule interface region; and
the fiber-to-ferrule interface region comprises substantial contact
between the bulge and a portion of the surface of the bore whereby
movement of the fiber in the bore is inhibited.
2. The assembly of claim 1, wherein the interface region comprises
a force-fit aligning the at least one optical fiber in the
bore.
3. The assembly of claim 1, wherein the bulge is has a size of
about 25 .mu.m to about 50 .mu.m larger than the bare fiber
diameter, and the fiber end face is essentially flat.
4. The assembly of claim 1, wherein the optical fiber includes
collapsed void regions and void regions that have not been
collapsed, and the fiber end face protrudes from the ferrule front
end.
5. The assembly of claim 1, wherein the substantial contact
comprises a bulge size being larger than a ferrule bore inside
diameter, thereby causing a tight fit.
6. The assembly of claim 1, wherein the bulge has a size of up to
about 0.8% larger than the bare fiber diameter.
7. The assembly of claim 1, wherein the size associated with the
bulge is about 0.8% to about 20% larger compared to the bare fiber
diameter.
8. The assembly of claim 1, wherein the size associated with the
bulge is about 2% to about 5% larger compared to the bare fiber
diameter.
9. The assembly of claim 1, wherein the ferrule includes an epoxy
material and the optical fiber is at least partially bonded to the
ferrule by the epoxy.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a divisional of U.S. patent application Ser. No.
12/241,558 filed on Sep. 30, 2008, which is related to (a) U.S.
patent application Ser. No. 11/595,365, entitled "Method of
splicing an optical fiber with holes in the cladding," filed in the
United States on Nov. 9, 2006; (b) U.S. patent application Ser. No.
12/077,694, entitled "Connectorized nano-engineered optical fibers
and methods of forming same," filed in the United States on Mar.
20, 2008; and (c) U.S. patent application Ser. No. 12/220,266,
entitled "Connectorized nano-engineered optical fibers and methods
of forming same, filed in the United States on Jul. 23, 2008, all
of which are incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to optical fibers
and optical fiber connectors, and more specifically to methods for
centering one or more optical fibers in an optical fiber connector
ferrule.
[0004] 2. Technical Background of the Invention
[0005] With the ever growing demand for lower loss fiber optic
connections, the centering of one or more optical fibers in a
ferrule of an optical fiber connector is becoming more and more
critical. The ideal position of an optical fiber in a ferrule bore
is the "dead center" of the ferrule bore--i.e., the optical fiber
centerline is exactly aligned with the bore central axis. However,
achieving such exact alignment has proven to be difficult. Also,
with the introduction of bend insensitive fibers, it is preferred
that the holes, voids or "airlines" within the optical fiber be
closed off at the point where two fibers connect--namely, at or
near the end of the ferrule--to prevent contaminants from gathering
in the exposed airlines and adversely impacting the transmission of
light between the connected optical fibers. The voids can include a
gas such as Nitrogen or Krypton, or a mixture of such gases, such
as air, Nitrogen, and/or Krypton.
[0006] One reason why centering one or more optical fibers in a
single-fiber or multi-fiber connector ferrule is difficult is
because it is not practical to use an interference fit between an
optical fiber and a ferrule bore. Optical fibers can vary in size
by up to +/-1 micron or so, so that sizing a ferrule bore to have
an interference fit with the optical fiber would result in
significant amounts of optical fiber not fitting into the bore. In
addition, those optical fibers that can barely be fit into the bore
have a higher risk of being damaged due to the tight fit. In
addition, an optical fiber is typically secured within the ferrule
bore using an epoxy, so that some space within the bore must be
maintained to accommodate the epoxy.
[0007] Once an optical fiber is exactly aligned in the ferrule
bore, it must be locked into place. It is therefore important to
have a simple and efficient way of maintaining the optical fiber in
its centered position within the bore until the epoxy curing
process or other fixing process can be carried out.
SUMMARY OF THE INVENTION
[0008] A first aspect of the invention is a method of centering at
least one optical fiber having a centerline and an end, within at
least one bore of a connector ferrule having a front end and a
central axis. The method includes inserting at least one bare-fiber
portion of the at least one optical fiber into the at least one
ferrule bore so that a section of the at least one bare-fiber
portion extends beyond the ferrule front end. The method also
includes selectively applying an amount of energy to the at least
one bare-fiber section so as to form a locally deformable region.
The method further includes forming at least one bulge in the
locally deformable region. The method also includes causing the at
least one bulge to form a force-fit with the at least one bore at
the ferrule front end, thereby substantially centering the at least
one optical fiber centerline along the at least one bore central
axis.
[0009] A second aspect of the invention is a method of centering at
least one nano-engineered optical fiber within a connector ferrule
having a front end and at least one bore with a central axis. The
at least one nano-engineered optical fiber has a core, a cladding
surrounding the core, and non-periodically disposed voids formed in
the cladding. The method includes inserting at least one bare-fiber
portion of the at least one optical fiber into the at least one
ferrule bore so that at least a section of the at least one
bare-fiber portion extends beyond the ferrule front end. The method
also includes selectively heating the at least one bare-fiber
section, thereby forming a locally deformable region and
substantially collapsing the voids at least within the locally
deformable region, thereby forming a substantially void-free
region. The method further includes forming at least one bulge in
the locally deformable region and force-fitting the at least one
bulge with the at least one bore at the ferrule front end, thereby
substantially centering the at least one optical fiber centerline
along the at least one bore central axis. The method also
optionally includes creating at least one end of the at least one
optical fiber from the substantially void-free region so as to form
a substantially void-free fiber end that substantially coincides
with the ferrule front end (or in the case of a "long-short"
multifiber ferrule, substantially coincides with the standoff
plane).
[0010] A third aspect of the invention is a method of centering at
least one optical fiber having a centerline in a connector ferrule
having at least one bore with a central axis. The method includes
inserting at least one bare-fiber portion of the at least one
optical fiber into the at least one connector ferrule bore so that
a section of the at least one bare-fiber portion extends beyond a
front end of the ferrule. The method also includes locally heating
a region of the at least one bare-fiber section, thereby forming at
least one locally deformable region. The method further includes
forming a bulge in the at least one locally deformable region, and
force-fitting the bulge into the front end of the at least one
ferrule bore so that the optical fiber centerline is substantially
aligned with the bore central axis. The method further includes
cleaving the at least one bare-fiber section to form at least one
corresponding fiber end that substantially coincides with the
ferrule front end. The cleaving can be performed using a laser,
which can also simultaneously cleave and polish a fiber.
[0011] A fourth aspect of the invention is an optical fiber
connector assembly with at least one ferrule, the ferrule having a
front end at least one bore for receiving at least one optical
fiber, and an optical fiber at least partially disposed in the
bore. The portion of the at least one optical fiber is disposed in
the at least one ferrule bore so that a section of the at least one
fiber portion extends beyond the ferrule front end, and a section
of the optical fiber comprises a bulge which has a size which is
larger than the bare optical fiber diameter. The fiber at least
partially contacts a surface of the ferrule bore, and the contact
defines a fiber-to-ferrule interface region. The fiber-to-ferrule
interface region comprises substantial contact between the bulge
and a portion of the surface of the bore whereby movement of the
fiber in the bore is inhibited and the fiber is aligned in relation
to the bore.
[0012] Additional features and advantages of the invention are
forth in the detailed description that follows, and in part will be
readily apparent to those skilled in the art from that description
or recognized by practicing the invention as described herein,
including the detailed description that follows, the claims, and
the appended drawings. It is to be understood that both the
foregoing general description and the following detailed
description present exemplary embodiments of the invention, and are
intended to provide an overview or framework for understanding the
nature and character of the invention as it is claimed. The
accompanying drawings are included to provide a further
understanding of the invention, and are incorporated into and
constitute a part of this specification. The drawings illustrate
various embodiments of the invention, and together with the
detailed description, serve to explain the principles and
operations thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] These and other features, aspects and advantages of the
present invention are better understood when the following detailed
description of the invention is read with reference to the
accompanying drawings, in which:
[0014] FIG. 1 is a side view of a section of an example optical
fiber;
[0015] FIG. 2 is a cross-sectional view of an example optical fiber
of FIG. 1 in the form of a nano-engineered optical fiber as viewed
along 2-2 therein, along with an example effective refractive index
profile for the various fiber regions;
[0016] FIG. 3 is a schematic side view of an example single-fiber
ferrule;
[0017] FIG. 4 is a length-wise cross-sectional view of the ferrule
of FIG. 3;
[0018] FIG. 5 is a close-up view of a portion of the ferrule of
FIG. 4 and that includes an optical fiber contained therein;
[0019] FIG. 6A is a perspective view of an example "long-short"
single-fiber ferrule that facilitates laser processing of the fiber
adjacent the ferrule front end;
[0020] FIG. 6B is a close-up perspective view of the notched front
end of the "long-short" single-fiber ferrule of FIG. 6A;
[0021] FIG. 7A is a front perspective view of an MT-type multifiber
ferrule;
[0022] FIG. 7B is a plan view of the MT-type multifiber ferrule of
FIG. 7A;
[0023] FIG. 7C is similar to FIG. 7B, and illustrates an example
embodiment of a "long-short" MT-type multifiber ferrule that
facilitates laser processing of the fibers adjacent the ferrule
front end;
[0024] FIG. 8 is a schematic side view of single-fiber ferrule that
holds an optical fiber;
[0025] FIG. 9 is a schematic side view similar to FIG. 8, and
illustrates the local heating of the optical fiber via an
electrical arc for forming the locally deformable region;
[0026] FIG. 10 is similar to FIG. 9, and illustrates the fiber
bulge positioned to have an interference fit with the front end of
the ferrule bore;
[0027] FIG. 11 is a close-up view of the ferrule front end as shown
in FIG. 10, illustrating the interference fit of the fiber bulge
with the front end of the ferrule bore, and showing the locally
deformable region and the substantially void-free fiber region for
the case of a nano-engineered optical fiber;
[0028] FIG. 12 is a close-up view of the ferrule front end similar
to FIG. 11, illustrating the laser processing of the fiber end so
that the fiber end substantially coincides with the ferrule front
end;
[0029] FIG. 13 is a schematic side view similar to FIG. 8, showing
an example finalized single-fiber ferrule assembly along with a
close-up inset view of the substantially void-free fiber end in the
case where a nano-engineered optical fiber is used;
[0030] FIG. 14 is an exploded view of an example single-fiber
connector that includes the single-fiber ferrule assembly formed
using the methods of the present invention;
[0031] FIG. 15 is a schematic plan view of a generalized multifiber
ferrule as described above in connection with the MTP-type ferrule
of FIG. 7A and FIG. 7B, shown adjacent an electrode pair;
[0032] FIG. 16 is similar to FIG. 15, and shows twelve optical
fibers contained in the ferrule bores and held by a fiber holder,
with bare-fiber sections extending out of the ferrule front end in
between the electrode pair;
[0033] FIG. 17 is similar to FIG. 16, and illustrates the localized
heating of the optical fibers via an electrical arc from the
electrode pair;
[0034] FIG. 18A is similar to FIG. 17, and illustrates the step of
forming the optical fiber bulges in the locally deformable region
and forming a force-fit of the fibers at the front ends of the
ferrule bores;
[0035] FIG. 18B is similar to FIG. 18A, and illustrates an example
embodiment wherein a "long-short" multifiber ferrule is used;
[0036] FIG. 19 is similar to FIG. 18A, illustrating the laser
processing of the fiber ends;
[0037] FIG. 20 is an front end-on view of a "long-short" multifiber
ferrule, illustrating the laser processing of the fiber ends by
scanning the laser beam across the ferrule front end;
[0038] FIG. 21A is similar to FIG. 19 and shows an example
finalized multifiber ferrule assembly, along with a close-up inset
view of the substantially void-free fiber end in the case where
nano-engineered optical fibers are used;
[0039] FIG. 21B is similar to FIG. 21A, and illustrates an example
embodiment wherein a "long-short" multifiber ferrule is used so
that the fiber ends substantially coincide with the standoff
plane;
[0040] FIG. 22 is similar to FIG. 19, except that the multifiber
ferrule includes a rectangular cross-section protrusion at the
front end, and also shows a laser beam performing laser cleaving of
the optical fiber ends on the sides of the bulges opposite the
ferrule;
[0041] FIG. 23 is similar to FIG. 22 and shows a secondary
multifiber ferrule in the process of engaging the "main" multifiber
ferrule;
[0042] FIG. 24 is similar to FIG. 23, and shows the secondary
multifiber ferrule engaged with the main multifiber ferrule so that
the optical fiber ends substantially coincide with the secondary
ferrule front end; and
[0043] FIG. 25 is an exploded perspective view of an example
multifiber connector that includes the multifiber ferrule assembly
formed by the methods of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0044] Reference is now made to preferred embodiments of the
invention, examples of which are illustrated in the accompanying
drawings. Whenever possible, the same or similar reference numbers
and symbols are used throughout the drawings to refer to the same
or similar parts.
[0045] In the description below, the term "void-free" in connection
with an optical fiber means that there are no voids visible when
the fiber end face is viewed at a magnification of 400.times. using
an optical microscope. The smallest feature that is visible at such
magnification is about 0.4 .mu.m in diameter, so that any voids
smaller than this size may be present, but would not be considered
sufficiently large to be of significance in relation to the
performance of the fiber. The term "substantially void free" means
that there may be present voids having diameter of 0.4 .mu.m or
greater, but the number of voids (i.e., the air-fill percent) is so
reduced as compared to that prior to thermally processing the fiber
that they do not have a substantial impact on the performance of
the fiber.
[0046] In an example embodiments of the invention as discussed
below, reducing the number of voids (i.e., reducing the air-fill
percent from its initial value) in a given fiber cross-section by a
factor of 5 or greater is considered as forming a "substantially
void free" fiber region. In other preferred embodiments, the
initial air-fill percent is reduced by at least a factor of 50, and
more preferably is reduced by at least a factor of 500 when forming
the "substantially void-free region" of the fiber.
[0047] In example embodiment of the present invention, the fiber
end face can have one or more voids, provided that the number of
voids (i.e., the air-fill percent) is sufficiently small so that
the potential for contamination of the fiber end face due to the
presence of the one or more voids is insubstantial--e.g., has an
insubstantial impact on the attenuation of light as it passes
through the fiber end face. While having no voids at the fiber end
face is generally preferred, allowing the fiber end face to have
one or more voids but still be "substantially void free" allows for
a larger process window for the methods described herein.
[0048] In some example embodiments, the substantially void-free
region includes "void transition zones" between completely
"void-free" portions and the void-containing portion of the optical
fiber. The transition zones each include one or more voids (e.g.,
partially collapsed voids) and have a reduced air-fill percent as
compared to the void-containing portion of the fiber, which is that
portion of the fiber that remains unaffected by the localized
heating of the mid-span portion of the fiber.
[0049] FIG. 1 is a side view of an example embodiment of a section
of an optical fiber 10 having opposite ends 12 and 14, and a
centerline 16. The methods of the present invention are
particularly well suited to so-called "nano-engineered" fibers that
include nano-engineered features in the form of relatively small
aperiodically arranged voids that facilitate the guiding of
optical-frequency electromagnetic waves in a glass fiber core in a
manner that makes the optical fiber resistant to optical loss even
when the fiber is bent to a small bending radius (i.e., the fiber
is "bend resistant"). The nano-engineered optical fibers otherwise
operate in the same manner as standard optical fibers.
Nano-engineered optical fibers are discussed in detail below. Thus,
in the discussion below "optical fiber 10" can refer to either a
"standard" or "nano-engineered" optical fiber, or both, and one
skilled in the art will understand whether a particular one of
these two types of optical fibers is being considered based on the
context of the discussion.
Nano-Engineered Optical Fibers
[0050] Nano-engineered optical fibers have voids limited to a
relative small void-containing region in the fiber cladding wherein
the air-fill percent (the area fraction of voids to the area of the
optical fiber times 100%, at a pre-selected cross-section) is less
than about 1% and is usually about 0.02% to about 0.2% or about
0.3%. The term "nano-engineered optical fiber" (also sometimes
referred to as a "micro-structured" or "nanostructured" optical
fiber) refers to an optical glass fiber comprising these
nanometer-size features.
[0051] FIG. 2 is a cross-sectional view of an example
nano-engineered version of optical fiber 10 of FIG. 1 as viewed
along the direction 2-2 of FIG. 1. Nano-engineered optical fiber 10
includes a core region ("core") 20 made up of a single core segment
having a radius R.sub.1 and positive maximum relative refractive
index .DELTA..sub.1, a cladding region ("cladding") 30 having an
annular inner cladding region ("inner cladding") 32 with an inner
radius R.sub.1, an outer radius R.sub.2 an annular width W.sub.12
and a relative refractive index .DELTA..sub.2. Optical fiber 10
also includes annular nano-engineered or "void containing" region
34 having an inner radius R.sub.2, an outer radius R.sub.3 an
annular width W.sub.23 and a relative refractive index
.DELTA..sub.3. Optical fiber 10 also includes an outer annular
cladding region ("outer cladding") 36 having an inner radius
R.sub.3, an outer radius R.sub.4, an annular width W.sub.34 and a
relative refractive index .DELTA..sub.4. Outer annular cladding 36
represents the outermost silica-based portion of nano-engineered
optical fiber 10. The total diameter of the "bare" fiber 10 is
D.sub.10=2R.sub.4.
[0052] In an example embodiment D.sub.10=125 microns (.mu.m),
.DELTA..sub.1=approximately 0.34%, R.sub.1=approximately 4.5
microns, R.sub.2=approximately 10.7 microns, region 34 is comprised
of 100 holes having a mean diameter of approximately 300 nm and a
maximum diameter of <700 nm, W.sub.23=approximately 4 microns
and .DELTA..sub.2=.DELTA..sub.4=approximately 0%.
[0053] In another example embodiment D.sub.10=125 microns,
.DELTA..sub.1=approximately 0.34%, R.sub.1=approximately 4.5
microns, R.sub.2=approximately 13.6 microns, region 34 is comprised
of 200 holes having a mean diameter of approximately 200 nm and a
maximum diameter of <700 nm, W.sub.23=approximately 3 microns
and .DELTA..sub.2=.DELTA..sub.4=approximately 0%.
[0054] In yet another example embodiment D.sub.10=125 microns,
.DELTA..sub.1=approximately 0.34%, R.sub.1=approximately 4.5
microns, R.sub.2=approximately 13.6 microns, region 34 is comprised
of 400 holes having a mean diameter of approximately 150 nm and a
maximum diameter of <700 nm, W.sub.23=approximately 3 microns
and .DELTA..sub.2=.DELTA..sub.4=approximately 0%.
[0055] In yet another example embodiment D.sub.10=125 microns,
.DELTA..sub.1=approximately 0.34%, R.sub.1=approximately 4.5
microns, R.sub.2=approximately 12.2 microns, region 34 is comprised
of 500 holes having a mean diameter of approximately 120 nm and a
maximum diameter of <700 nm, W.sub.23=approximately 3 microns
and .DELTA..sub.2=.DELTA..sub.4=approximately 0%. These fibers when
measured by cable cutoff show that they are single-moded above 1260
nm.
[0056] A protective cover 50 is shown surrounding outer annular
cladding 36. In an example embodiment, protective cover 50 includes
one or more polymer or plastic-based layers or coatings, such as a
buffer coating or buffer layer. Protective cover 50 is thus also
referred to below as "buffer layer" 50.
[0057] In an example embodiment, annular void-containing region 34
is comprised of periodically or non-periodically disposed holes or
"voids" 40 that run substantially parallel to centerline 16 and
that are configured such that the optical fiber is capable of
single mode transmission at one or more wavelengths in one or more
operating wavelength ranges. By "non-periodically disposed" or
"non-periodic distribution," it will be understood to mean that
when one takes a cross-section (such as a cross-section
perpendicular to the longitudinal axis) of the optical fiber, the
non-periodically disposed voids are randomly or non-periodically
distributed across a portion of the fiber. Similar cross sections
taken at different points along the length of the fiber will reveal
different cross-sectional void patterns, i.e., various
cross-sections will have different void patterns, wherein the
distributions of voids and sizes of voids do not match. That is,
the voids are non-periodic, i.e., they are not periodically
disposed within the fiber structure. These voids are stretched
(elongated) along the length (i.e. in a direction generally
parallel to centerline 16) of the optical fiber, but do not extend
the entire length of the entire fiber for typical lengths of
transmission fiber. Typically, voids 40 extend less than 10 meters,
e.g., 0.2 to 1 meter or less.
[0058] As mentioned above, the nano-engineered optical fibers 10
suitable for use in example embodiments of the present invention
preferably include an air-fill percent less than about 1%, more
preferably less than about 0.7%, even more preferably less than
about 0.3%, and even more preferably between about 0.02% and about
0.2%.
[0059] An example nano-engineered optical fiber 10 suitable for use
in the present invention further has an average hole size of about
0.3 microns or less, such as 0.15 or 0.09 microns and greater than
0.005 microns. In contrast, holey fiber available from NTT, Japan,
has an average hole size of about 12 microns and an air-fill
percent of >1%, and typical photonic crystal fibers have
air-fill percents >5%. Thus, as mentioned above, it is the small
void size of the nano-engineered optical fibers considered herein
that allows the fibers to retain their circularity and nominally
their original size when the voids are substantially collapsed.
Note that the above-mentioned air-fill percentages are considered
"initial" air-fill percentages since voids 40 are substantially
collapsed to form a "substantially void-free region" in one or more
nano-engineered optical fibers 10, as described below.
[0060] For a variety of applications, it is desirable for the voids
40 of the nano-engineered optical fibers 10 considered herein to
have greater than about 95% of and preferably all of the voids
exhibit a mean void size in cladding 30 for the optical fiber that
is less than 1550 nm, more preferably less than 775 nm, most
preferably less than 390 nm and in some embodiments less than 250
nm and greater than 5 nm. Likewise, it is preferable that the
maximum diameter of the voids in the fiber be less than 7000 nm,
more preferably less than 4000 nm, more preferably less than 1550
nm, and most preferably less than 775 nm and in some embodiments
less than 300 nm. In some embodiments, the fibers disclosed herein
have greater than 50 voids, in some embodiments also greater than
200 voids, and in other embodiments the total number of voids is
greater than 500 voids, while still in other embodiments the total
number of voids is greater than 1000 voids in a given optical fiber
perpendicular cross-section. Of course, the most preferred fibers
will exhibit combinations of these characteristics.
[0061] Thus, for example, an embodiment of optical fiber 10 would
exhibit greater than about 200 voids in the optical fiber, the
voids having a maximum diameter less than 1550 nm and a mean
diameter less than 775 nm, for example, the maximum diameter is
less than 775 nm and the mean diameter of about 200 nm, although
useful and bend resistant optical fibers can be achieved using
larger and greater numbers of voids. The number of voids, mean
diameter, max diameter, and total void area percent of voids can
all be calculated with the help of an optical microscope at
400.times. or a scanning electron microscope at a magnification of
about 800.times. and image analysis software, such as ImagePro,
which is available from Media Cybernetics, Inc. of Silver Spring,
Md., USA.
[0062] Because example nano-engineered optical fibers 10 considered
herein rely on the core-cladding index difference to guide light,
the fiber can generally include germania or fluorine to also adjust
the refractive index of the core and/or cladding of the optical
fiber, but these dopants can also be avoided in the intermediate
annular region. The voids 40 (in combination with any gas or gases
that may be disposed within the voids) can be used to adjust the
manner in which light is guided down the core of the fiber,
particularly when the fiber is bent. Void-containing region 34 may
consist of undoped (pure) silica, thereby completely avoiding the
use of any dopants in the void-containing region, to achieve a
decreased refractive index, or the void-containing region may
comprise doped silica, e.g. fluorine-doped silica having a
plurality of voids.
[0063] In one set of embodiments, the core region 20 includes doped
silica to provide a positive refractive index relative to pure
silica, e.g. germania doped silica. The core region 20 is
preferably free of voids 40.
[0064] Such a nano-engineered optical fiber 10 can be made to
exhibit a single-mode behavior with a cable cutoff of less than
1400 nm, more preferably less than 1260 nm; a 20 mm diameter
macrobend induced loss at 1550 nm of less than 1 dB/turn,
preferably less than 0.5 dB/turn, even more preferably less than
0.1 dB/turn, still more preferably less than 0.05 dB/turn, yet more
preferably less than 0.03 dB/turn, and even still more preferably
less than 0.02 dB/turn; a 10 mm diameter macrobend induced loss at
1550 nm of less than 5 dB/turn, preferably less than 1 dB/turn,
more preferably less than 0.5 dB/turn, even more preferably less
than 0.2 dB/turn, still more preferably less than 0.01 dB/turn,
still even more preferably less than 0.05 dB/turn.
[0065] Example nano-engineered optical fibers 10 considered herein
also include multi-mode nano-engineered optical fibers that
comprise, for example, a graded-index core region and a cladding
region surrounding and directly adjacent to the core region, the
cladding region comprising a depressed-index annular portion
comprising a depressed relative refractive index, relative to
another portion of the cladding (which preferably is silica that is
not doped with an index of refraction altering dopant such as
germania or fluorine). Preferably, the refractive index profile of
the core has a parabolic shape. The depressed-index annular region
34 may comprise glass comprising a plurality of voids 40,
fluorine-doped glass, or fluorine-doped glass comprising a
plurality of voids. The depressed index region 34 can be adjacent
to or spaced apart from the core region.
[0066] Example multi-mode nano-engineered optical fibers 10
considered herein also exhibit very low bend induced attenuation,
in particular very low macrobending attenuation. In some
embodiments, high-bandwidth is provided by a low maximum relative
refractive index in the core, and low bend losses are also
provided. In some embodiments, the core radius is large (e.g.
greater than 10 microns, for example 25 microns and 31.25 microns),
the core refractive index is approximately 2% or less (e.g. 2.0%,
1.0%, 0.90% or 0.50%), and the macrobend losses are low.
Preferably, the multi-mode nano-engineered optical fiber 10
disclosed herein exhibits a spectral attenuation of less than 3
dB/km at 850 nm.
[0067] In an example embodiment, core 20 and cladding 30 are
configured to provide improved bend resistance, and single-mode
operation at wavelengths preferably greater than or equal to 1500
nm, in some embodiments also greater than about 1310 nm, in other
embodiments also greater than 1260 nm. Example embodiments of the
nano-engineered optical fibers 10 considered herein provide a MFD
at a wavelength of 1310 nm preferably greater than 8.0 microns,
more preferably between about 8.0 and 10.0 microns.
Example Effective Index Parameters
[0068] In one set of example embodiments, a single-mode
nano-engineered optical fiber 10 has the following parameters:
0.30%<.DELTA..sub.1<0.40%, and 3.0 .mu.m<R.sub.1<5.0
.mu.m. In some embodiments, core 20 has a refractive index profile
with an alpha shape, where in some embodiments alpha is 6 or more,
while in other embodiments alpha is 8 or more. An example
embodiment of a multi-mode nano-engineered optical fiber 10 has the
following parameter range: 12.5 .mu.m.ltoreq.R.sub.1.ltoreq.40
microns. In some embodiments, 25 .mu.m.ltoreq.R.sub.1.ltoreq.32.5
.mu.m, and in some of these embodiments, R.sub.1 is greater than or
equal to about 25 microns and less than or equal to about 31.25
microns.
[0069] In an example embodiment, core 20 preferably has a maximum
relative refractive index (sometimes called .DELTA..sub.1MAX) of
0.5%.ltoreq..DELTA..sub.1.ltoreq.2.0%. In yet another embodiment,
core 20 has a maximum relative refractive index
0.9%.ltoreq..DELTA..sub.1.ltoreq.1.1%. In yet another embodiment,
core 20 has a maximum relative refractive index
0.4%.ltoreq..DELTA..sub.1.ltoreq.0.5%. Such multi-mode
nano-engineered optical fibers 10 preferably exhibit a one-turn 10
mm diameter mandrel attenuation increase of no more than a 1 turn
10 mm diameter mandrel wrap attenuation increase at a wavelength of
1550 nm, in dB, (also called 1.times.10 mm dia. bend loss at 1550
nm) of less than or equal to the product of two times
(1/.DELTA..sub.1MAX).sup.2. Thus for a multi-mode nano-engineered
optical fiber 10 having a core .DELTA..sub.1MAX of 2% the
1.times.10 mm dia. bend loss at 1550 nm.ltoreq.2(1/2).sup.2=1 dB;
for a multi-mode fiber having a core .DELTA..sub.1MAX of 1% the
1.times.10 mm dia. bend loss at 1550 nm.ltoreq.2(1/1).sup.2=1 dB;
and for a multi-mode nano-engineered optical fiber 10 having a core
.DELTA..sub.1MAX of 0.5% the 1.times.10 mm dia. bend loss at 1550
nm.ltoreq.2(1/0.5).sup.2=4 dB.
[0070] In an example embodiment, the void-containing region 34 has
an inner radius R.sub.2.ltoreq.20 .mu.m. In some example
embodiments, 10 .mu.m.ltoreq.R.sub.2.ltoreq.20 .mu.m. In other
embodiments, 10 .mu.m.ltoreq.R.sub.2.ltoreq.18 .mu.m. In other
embodiments, 10 .mu.m.ltoreq.R.sub.2.ltoreq.14 .mu.m. In some
embodiments, the inner annular cladding radial width W.sub.12>1
.mu.m. In an example embodiment, radius R.sub.2>5 .mu.m, and
more preferably R.sub.2>6 .mu.m.
[0071] Again, while not being limited to any particular width, in
an example embodiment, the void-containing region 34 has a radial
width 0.5 .mu.m.ltoreq.W.sub.23, while in other example embodiments
0.5 .mu.m.ltoreq.W.sub.23.ltoreq.20 .mu.m. In other embodiments, 2
.mu.m.ltoreq.W.sub.23.ltoreq.12 .mu.m. In other embodiments, 2
.mu.m.ltoreq.W.sub.23.ltoreq.10 .mu.M. In an example embodiment,
the annular void-containing region 34 has a regional void area
percent of less than about 30 percent and greater than 0.5 percent,
and the non-periodically disposed voids 40 have a mean diameter of
less than 1550 nm. In some embodiments, void-containing region 34
has a regional void area percent of less than about 10% and greater
than 0.5% and a mean void diameter of less than 775 nm and greater
than 5 nm. In some embodiments region 34 has a regional void area
percent of less than about 6% and greater than 0.5% and a mean void
diameter of less than 300 nm and greater than 5 nm.
[0072] Multimode nano-engineered optical fibers 10 are discussed in
U.S. patent application Ser. No. 12/004,174, entitled
"Bend-resistant multimode optical fiber," filed on Dec. 20, 2007,
and incorporated by reference herein. The bandwidth of the
multi-mode version of nano-engineered optical fiber 10 varies
inversely with the square of .DELTA..sub.1MAX. For example, a
multi-mode nano-engineered optical fiber 10 with
.DELTA..sub.1MAX=0.5% can yield a bandwidth 16 times greater than
an otherwise identical multi-mode optical fiber 10 with
.DELTA.1.sub.MAX=2.0%.
Ferrule Types
[0073] The methods of the present invention apply to both
single-fiber connector ferrules and multifiber connector ferrules.
Examples of these two types of ferrules are discussed below, and
then example methods of centering at least one optical fiber 10
therein are set forth. Some of the example methods are applied to
one or more nano-engineered optical fibers, and the methods as
applied to such fibers include substantially collapsing voids 40 so
as to form substantially void-free fiber ends 14.
Single-Fiber Ferrule
[0074] FIG. 3 is a schematic side view of an example single-fiber
ferrule 100. FIG. 4 is a length-wise cross-sectional view of
ferrule 100, and FIG. 5 is a close-up view of a portion of ferrule
100 of FIG. 4 and that includes a nano-engineered optical fiber 10.
Cartesian X-Y-Z coordinates are shown in FIG. 3 through FIG. 5 for
the sake of reference.
[0075] Ferrule 100 includes a cylindrical ferrule body 102 having a
substantially circular cross-section and that extends lengthwise
along a central axis .DELTA..sub.C. An example material for ferrule
body 102 is ceramic. Ferrule body 102 includes opposite first and
second ends 104 and 106. First (rear) end 104 optionally includes a
conical notch 110 centered on central axis .DELTA..sub.C, while
second (front) end 106 is preferably planar or includes a planer
portion that defines a front end face.
[0076] Ferrule body 102 defines a single central bore 120 having
respective rear and front open ends 124 and 126 at rear and front
ends 104 and 106. Bore 120 is centered on central axis
.DELTA..sub.C and has a diameter D.sub.B. In an example embodiment
where ferrule 100 is to be used with an optical fiber 10 having a
diameter D.sub.10 that is nominally 125 .mu.m, the bore diameter
D.sub.B is nominally 125.7 .mu.m. Voids 40 are shown in FIG. 5 as
dashed lines surrounding fiber core 20 to indicate the case where
optical fiber 10 is a nano-engineered optical fiber. FIG. 5 also
shows an epoxy 127, such as a heat-activated epoxy, within bore
120. As discussed below, epoxy 127 serves to fix optical fiber 10
to ferrule body 102 after the optical fiber is substantially
centered in bore 120.
[0077] FIG. 6A is a perspective view of an example single-fiber
ferrule 100, while FIG. 6B is a close-up perspective view of rear
end 104 of the ferrule of FIG. 6A. The single-fiber ferrule of
FIGS. 6A and 6B includes at front end 106 a notch 107 that runs
across ferrule body 102 and through central axis .DELTA..sub.C.
Notch 107 facilitates the laser processing (e.g., cleaving,
polishing or simultaneous cleaving and polishing) of fiber section
10S that extends from bore 120 at front end 106. Specifically,
notch 107 allows for the laser beam to process fiber section 10S
far enough away from ferrule body 100 to prevent damaging the
ferrule body. Moreover, front end 106 serves as the standoff
surface (which defines a standoff plane SP), so that the length of
fiber section 10S extending beyond the plane of front end 106 is
significantly shorter than that which actually extends from bore
120. This type of ferrule is thus referred to in the art as a
"long-short" (LS) ferrule.
Multi-Fiber Ferrule
[0078] FIG. 7A is a perspective view and FIG. 7B is a plan view of
an MT-type multifiber ferrule 100 having a ferrule body 102 that is
generally rectangular in lateral cross-section. An example material
for multifiber ferrule body 102 is plastic. Although an MT-style
ferrule is illustrated and described herein in certain example
embodiments, multifiber ferrule 100 need not be an MT-type ferrule
and may be any other type of multifiber ferrule. Multifiber ferrule
100 may be, for example, of the type used for connectors such as
SC/APC, SC/UPC, FC/APC, FC/UPC, LC/APC, and LC/UPC connectors.
Ferrule body 102 defines a plurality of bores 120 each having rear
and front open ends 124 and 126 at respective ferrule rear and
front ends 104 and 106. Bores 120 are arranged in a laterally
extending linear row along respective central axes .DELTA..sub.C
for receiving the bare-fiber portions of respective optical fibers
10.
[0079] Although the embodiments of the multifiber ferrule 100
illustrated herein define a total of twelve bores 120 such that the
multifiber ferrule 100 can support twelve individual optical fibers
10, the multifiber ferrule may define any number of bores, such as
2, 4, 6, 8, 10 or more. In addition, the multifiber ferrule 100 may
comprise more than a single linear row of bores 120, such as two
rows of 12 bores. Furthermore, bores 120 need not be arranged in
one or more laterally extending linear rows. For example, any
number of bores 120 may be arranged in any predetermined pattern.
Like the single-fiber ferrule 100, the multifiber ferrule bores 120
each have a diameter D.sub.B slightly larger than the nominal fiber
diameter D.sub.10 for the optical fibers 10 intended for use with
the multifiber ferrule.
[0080] The ferrule body 102 may also define at least one and
elongate guide pin hole 140 (FIG. 7A) also referred to in the art
as an "alignment hole." Two guide pin holes 140 in front end 106
are shown in FIG. 7A. Guide pin holes 140 are adapted to receive
respective guide pins 142 to align ferrule 100 with an opposing
ferrule (not shown) of a mating connector (not shown) in a known
manner.
[0081] FIG. 7C is a plan view of the front end 106 of an example
"long-short" (LS) multifiber ferrule 100. Front end 106 of LS
multifiber ferrule 100 includes outer protrusions 106P (e.g.,
pedestals) that extend out from the otherwise planar surface 106S
of front end 106. Protrusions 106P serve as the standoff surface
for front end 106 and define a standoff plane SP. Protrusions 106P
allow fiber sections 10S to protrude from bores 120 over a "long"
length from surface 106S and over a "short" length from standoff
plane SP.
[0082] As in the case of the single-fiber LS ferrule discussed
above, protrusions 106P allow for a laser beam to cleave (or
simultaneously cleave and polish) fiber sections 10S at a safe
distance from ferrule body 102. When LS multifiber connector 100 is
mated to another connector, protrusions 106P serve as the standoff,
so that the effective fiber length extending from the connector is
the "short" length as measured relative to standoff plane SP. Fiber
ends 14 can thus be formed to substantially coincide with standoff
plane SP.
Single-Fiber and Multifiber Fiber-Centering Methods
[0083] Various example methods of centering at least one optical
fiber 10 in a single-fiber or multifiber ferrule are now described
for single-fiber and multiple-fiber ferrules. As discussed above,
the methods of the present invention are applicable to both
"standard" optical fibers and nano-engineered optical fibers. In
some of the example embodiments below, the optical fibers 10 are
nano-engineered optical fibers, and the methods include
substantially collapsing the voids 40 to form a localized
substantially void free region in the at least one fiber so as to
form at least one substantially void-free fiber end 14.
Single-Fiber Embodiments
[0084] FIG. 8 is a schematic side view of an single-fiber ferrule
100 that supports a single optical fiber 10, which in an example
embodiment is a nano-engineered optical fiber. A bare-fiber portion
13 adjacent fiber end 14 of optical fiber 10 and that includes the
fiber end has its protective coating ("buffer layer") 50 removed
("stripped") so that this portion can be inserted into bore 120.
The remaining "buffered-fiber" portion 15 of optical fiber 10 is
supported by a fiber holder 200 adjacent rear ferrule end 104.
Buffered-fiber portion 15 and includes a "buffer edge" 17 where the
buffered-fiber portion terminates at bare-fiber portion 13.
[0085] A pair 220 of opposing electrodes 222 is arranged adjacent
ferrule front end 106 to provide localized heating of optical fiber
10 as described below. In an example embodiment, bore 120 is filled
with an epoxy 127 (see FIG. 5) to fix optical fiber 10 to ferrule
100 once the fiber-centering procedure is completed.
[0086] Bare-fiber portion 13 is inserted into epoxy-containing
ferrule bore 120 so that a bare-fiber section 10S of the bare-fiber
portion extends from front ferrule end 106 and in between opposing
electrodes 222. Optical fiber 10 is preferably held in a seated
position at ferrule rear end 104 with buffer edge 17 placed up
against rear ferrule end 104 so that there is no exposed bare fiber
when the resultant ferrule assembly is incorporated into a
connector.
[0087] With reference now to FIG. 9, a current is applied to
opposing electrodes 222 so as to generate a high-temperature arc
230. The energy from arc 230 acts to locally soften optical fiber
10 to form a locally deformable region 19, introduced and described
in greater detail below in connection with FIG. 11. In the case
where optical fiber 10 is a nano-engineered optical fiber, the
localized heating also acts to substantially collapse voids 40,
thereby form a substantially void-free region 11, at least of
portion of which is contained in locally deformable region 19.
[0088] In an example embodiment, a small amount of an axial force F
is applied to optical fiber 10 during the arcing process (or within
a sufficiently short time thereafter) so that the locally
deformable region deforms to form a bulge 250. The formation of
bulge 250 also forms a fiber-to-ferrule interface region. The
fiber-to-ferrule interface region includes positive contact between
at least portions of the optical fiber and the surface of bore 120.
Preferably, the contact between the fiber-to-ferrule interface
region is substantial contact whereby movement of the fiber in the
bore is inhibited. In another embodiment the fiber-to-ferrule
contact region comprises a force fit of the optical fiber to at
least portions of the bore 120 at front ferrule end 106, as
illustrated in FIG. 10 and in the close-up view of FIG. 11.
[0089] In an example embodiment, surface tension effects caused by
the localized heating cause an increase in the fiber diameter,
thereby creating bulge 250. In an example embodiment, bulge 250
formed using surface tension effects has a size of about 25 .mu.m
to 50 .mu.m larger than the normal fiber diameter D.sub.10. The
phrase "force fit" means the fiber is, through the use of force,
assembled into the hole formed in the ferrule, which hole has a
slightly smaller diameter than the bulge on the fiber. The fiber
can be essentially permanently or temporarily force fit into the
ferrule hole. The force fit is such that axial and radial movement
of the fiber relative to the ferrule is, in one embodiment,
inhibited, and in other embodiments substantially prevented. The
force can be due to expansion of the fiber in the hole, and/or
pushing or pulling of the bulge into the hole.
[0090] With reference to FIG. 11, locally deformable region 19 has
a length L19, while the substantially void-free region has a length
L11. The axial extents of these regions are indicated by respective
dashed lines. Substantially void-free region 11 may extend beyond
locally deformable region 19 because collapsing voids 40 does not
necessarily require heating a nano-engineered optical fiber to the
point of deformation.
[0091] In one example embodiment, axial force F is applied by
generating pressure to fiber end 14 directed towards ferrule
100--i.e., by "pushing" on the optical fiber in the -X direction.
In another example embodiment, axial force F is applied by
"pulling" (i.e., by placing a load on) optical fiber 10 the -X
direction.
[0092] Bulge 250 causes optical fiber 10 to be substantially
centered in bore 120 along the bore central axis .DELTA..sub.C,
i.e., so that optical fiber centerline 16 is substantially aligned
with the bore central axis. Furthermore, bulge 250 serves to tack
optical fiber 10 within bore 120 at ferrule front end 106 and
inhibits or prevents the optical fiber from being pulled out of
ferrule 100.
[0093] In an example embodiment, arc 230 is preferably positioned
close enough to ferrule front end 106 so as to not damage ferrule
100 but still provide enough energy in the form of heat to
substantially collapse voids 40 close to the ferrule front end. In
example embodiment, enough heat is generated by arc 230 to
substantial collapse voids 40 to the extent that substantially
void-free region 11 extends into ferrule bore 120 by at least a
small distance D.sub.AF.
[0094] In an example embodiment, fiber bulge 250 as formed for
single-fiber and multiple fiber centering applications (the latter
are discussed below) need only have a size such that it makes
optical fiber diameter D.sub.10 only slightly larger than bore
diameter D.sub.B. By way of example, for a fiber diameter
D.sub.10=125 .mu.m (nominal), and a bore diameter D.sub.B=125.7
.mu.m, an increase in fiber diameter D.sub.10 of about 1 .mu.m, or
to D.sub.10=126 .mu.m, is generally sufficient to carry out the
centering methods of the present invention. This is a diameter
change .DELTA.D.sub.10=0.8%. In an example embodiment, the fiber
diameter increase .DELTA.D.sub.10 associated with bulge 250 is in
the range defined by 0.8%.ltoreq..DELTA.D.sub.10.ltoreq.20%, is
more preferably in the range defined by
0.8%.ltoreq..DELTA.D.sub.10.ltoreq.20%, and is more preferably in
the range defined by 2%.ltoreq..DELTA.D.sub.10.ltoreq.5%. Thus, the
relative size of bulges 250 as shown in the Figures for both the
single-fiber embodiments and multifiber embodiments are exaggerated
for the sake of illustration.
[0095] In an example embodiment, bulges 250 are formed so as not to
substantially affect the waveguiding properties of one or more
optical fibers 10, except for those properties associated with
substantially collapsing the voids when the one or more optical
fibers being considered are nano-engineered optical fibers.
[0096] Once optical fiber 10 is force-fitted into bore 120, the
optical fiber is bonded to ferrule body 102, e.g., by applying heat
H to the heat-activated epoxy 127 contained in bore 120, as shown
in FIG. 5.
[0097] With reference now to FIG. 12, at this point, bare-fiber
section 10S that extends from ferrule front end 106 is cut (e.g.,
precision-cut or "cleaved") at or close to the ferrule front end
and then polished so that resulting fiber end 14 substantially
coincides with the ferrule front end. One or both of the cutting
and polishing steps can be performed, for example, using either a
laser beam LB from a laser source LS as shown in FIG. 12, or with a
diamond scribe and conventional mechanical polishing techniques. In
an example embodiment, laser beam LB simultaneously cleaves and
polishes fiber end 14. Note that the laser cleaving and polishing
process is facilitated by the use of the LS single-fiber ferrule
100 as discussed above in connection with FIGS. 6A and 6B.
[0098] In an example embodiment, electrode pair 220 is part of a
fusion splicer configured to provide a select amount of current for
a select duration. A suitable fusion splicer for use in carrying
out the method of the present invention is, for example, the
Corning miniMASS.RTM. Fusion Splicer, available from Corning Cable
Systems, Inc., Hickory, N.C. An example amount of current for
forming electric arc 230 is in the range of about 12 mA to about 16
mA for a single optical fiber 10. Larger amounts of current would
be used for multiple fibers, such as fiber ribbons.
[0099] While localized heating of optical fiber 10 is described
above using an electric arc 230 by way of example, the localized
heating may be generated in various ways including using other
means, such as a heated filament, a flame or a laser, among
others.
[0100] If heat-activated epoxy 127 is contained in bore 120 prior
to inserting bare portion 13 of optical fiber 10 therein, then it
is important to perform the above steps in a manner that does not
prematurely heat-activate the epoxy. In an example embodiment,
bulge 250 is first formed far enough from the ferrule front end 106
so that the preinstalled epoxy 127 is not substantially affected,
and then the bulge moved (e.g., "pulled" or "pushed") into bore 120
at ferrule front end 106.
[0101] In an alternative example embodiment, epoxy 127 is added to
bore 120 after heat treating optical fiber 10 with arc 230. This is
accomplished, for example, by wicking epoxy 127 into bore 120. In
an example embodiment, the wicking action of epoxy 127 is assisted
by heating the ferrule and/or by applying a vacuum to pull the
epoxy into bore 120.
[0102] The above steps form an example ferrule assembly 101,
wherein optical fiber end 14 is substantially coincident with front
ferrule end 106 (e.g., is polished to be flush therewith), as shown
in FIG. 13. In the case where optical fiber 10 is a nano-engineered
optical fiber, fiber end 14 has substantially no voids. In an
example embodiment where the single-fiber ferrule 100 is an LS-type
ferrule, fiber end 14 is formed substantially coincident with
standoff plane SP.
[0103] In an example embodiment, single-fiber ferrule assembly 101
is incorporated into a single-fiber optical fiber connector 270,
such as shown in the exploded view of FIG. 14, and that is
disclosed in, for example, U.S. Pat. Nos. 4,923,274 and 7,104,702,
which patents are incorporated by reference herein. Example
connector 270 includes, in order along axis A1 from the front to
the back of the connector: a spring retainer 271, a spring 272, a
connector housing 273, the single-fiber ferrule assembly 101, a
ferrule holder 274, splice members 275A and 275B, a lead-in tube
276, a crimp tube 277, a cam member 278 and trigger member 279, a
crimp band 280, a boot 281, and an optical fiber cable 282 that
carries optical fiber 10.
Multi-Fiber Embodiments
[0104] FIG. 15 is a schematic plan view of a generalized multifiber
ferrule 100 as described above in connection with the MTP-type
ferrule of FIG. 7A and FIG. 7B. Cartesian X-Y-Z coordinates are
shown in FIG. 15 for the sake of reference. Twelve bores 120 are
shown by way of example. The twelve bores 120 span a distance
D.sub.A across ferrule front end 106, and example embodiment
D.sub.A=2.875 mm for an MTP-type connector.
[0105] FIG. 16 is similar to FIG. 15, and shows twelve optical
fibers 10 contained in respective bores 120, with respective
bare-fiber sections 10S extending in between electrodes 222.
Optical fibers 10 are held by fiber holder 200 adjacent ferrule
rear end 104. As with the single-fiber ferrule embodiment, epoxy
127 is preferably contained with bores 120 for fixing the fibers to
the ferrule to complete the fiber-centering procedure. Generally,
less epoxy is required for multifiber ferrules than for a
single-fiber ferrule. Also, epoxy 127 can be wicked into bores 127
after the fiber-centering procedure is carried out. In this regard,
it is noted that fiber bulges 250 serve to prevent epoxy 127 from
leaking out of ferrule front end 106.
[0106] With reference now to FIG. 17, a current is applied to
opposing electrodes 222 so as to generate high-temperature arc 230.
The energy from arc 230 acts to locally soften optical fibers 10 to
form respective locally deformable regions 19, as discussed above
in connection with the single-fiber embodiment (see also FIG. 11).
In the case wherein one or more of optical fibers 10 are
nano-engineered optical fibers, arc 230 also acts to substantially
collapses voids 40 therein, thereby forming corresponding
substantially void-free regions 11, at least portions of which are
contained in the corresponding locally deformable regions 19. Note
that in FIG. 17 the one example locally deformable region 19 is
shown as being smaller than the one example substantially void-free
region 11.
[0107] If a small amount of an axial force F is applied to optical
fiber 10, such as a small amount of pressure ("pushing") applied to
fiber ends 14 and directed towards ferrule 100 during the arcing
process (or within a sufficiently short time thereafter), the
locally deformable regions 19 deform to form respective bulges 250
for each fiber 10, as illustrated in FIG. 18A. Bulges 250 form a
force fit to bores 120 at front ferrule end 106, similar to the
single-fiber ferrule embodiment as shown in FIG. 10 and the
close-up view of FIG. 11. Another example of applying an axial
force F is to pull optical fibers 10 the -X direction. Also, as
discussed above for the single-fiber embodiment, surface tension
effects alone may be used to form bulges 250.
[0108] Bulges 250 also cause optical fiber 10 to be substantially
centered in bores 120 so that the respective optical fiber
centerlines 16 are substantially aligned with the respective bore
central axes .DELTA..sub.C. Furthermore, bulges 250 serve to tack
optical fibers 10 within bores 120 and prevent the optical fibers
from being pulled out of ferrule 100.
[0109] As with the single-fiber ferrule embodiment, arc 230 is
preferably positioned close enough to front ferrule end 106 as to
not damage ferrule 100 but to still provide enough heat to
substantially collapse voids 40 for nano-engineered optical fibers
10. In example embodiment, enough heat is generated by arc 230 to
soften optical fibers 10 so that substantially void-free regions 11
extend into respective ferrule bores 120 by at least a small amount
D.sub.AF, in the same manner as discussed above and shown in FIG.
11 for the single-fiber ferrule embodiment.
[0110] Also as in the single-fiber ferrule example, in this
multifiber ferrule embodiment, in an example embodiment electrode
pair 220 is part of a fusion splicer configured to provide a select
amount of current for a select duration. A suitable fusion splicer
for use in carrying out the method of the present invention is, for
example, the Corning miniMASS.RTM. Fusion Splicer, available from
Corning Cable Systems, Inc., Hickory, N.C.
[0111] While localized heating of optical fibers 10 is described
above using an electric arc 230, the localized heating may be
generated in various ways including using other means for
generating energy, such as a heated filament, a flame or a laser,
among others.
[0112] Once optical fibers 10 are force-fitted into bores 120, the
optical fibers are bonded to ferrule body 102, e.g., by applying
heat H to the heat-activated epoxy 127 contained in bores 120, as
shown in the single-fiber example of FIG. 5. In an example
embodiment, bulges 250 are first formed far enough from the ferrule
front end 106 so that the preinstalled epoxy 127 is not
substantially affected, and then the bulges moved (e.g., "pulled"
or "pushed") into bores 120 at ferrule front end 106.
[0113] FIG. 18B is similar to FIG. 18A, but illustrates an example
embodiment where multifiber ferrule 100 is an LS-type ferrule.
[0114] With reference now to FIG. 19 and FIG. 20, at this point
fiber sections 10S that extend from ferrule front end 106 are cut
(e.g., precision-cleaved) at or close to the ferrule front end and
are then polished so that resulting fiber ends 14 substantially
coincide with the ferrule front end. These cutting and polishing
steps can be performed, for example, either with a laser beam LB
from a laser source LS as shown in FIG. 19 and FIG. 20, or with a
diamond scribe and conventional mechanical polishing techniques.
FIG. 20 shows laser beam LB being scanned over the ferrule front
end 106 of an LS multifiber ferrule 100 (see FIG. 18B) to cleave
fiber sections 10S, as discussed above in connection with FIG. 7C.
Note that in the embodiment of FIG. 20, fiber ends 14 are formed
substantially coincident with standoff plane SP (see FIG. 7C).
[0115] FIG. 21A shows an example multifiber ferrule assembly 101
wherein optical fiber ends 14 substantially coincide with ferrule
end 106 (e.g., polished to be flush therewith). In the case where
optical fibers 10 are nano-engineered optical fibers, fiber ends 14
have substantially no voids, as shown in the close-up inset
view.
[0116] FIG. 21B is similar to FIG. 21A, but illustrates a LS
multifiber ferrule embodiment that includes "long" and "short"
portions of fiber sections 10S as measured relative to surface 106S
and protrusions 106P, respectively. Note that fiber ends 14 are
substantially coincident with standoff plane SP.
[0117] If a heat-activated epoxy 127 is contained in bores 120
prior to inserting bare portions 13 of optical fibers 10 therein,
then it is important to perform the above steps in a manner that
does not prematurely heat-activate the epoxy. In an example
embodiment, bulges 250 are first formed far enough from the ferrule
front end 106 so that the preinstalled epoxy 127 is not
substantially affected, and then the bulges moved (e.g., "pulled"
or "pushed") into bores 120.
[0118] In an alternative example embodiment, epoxy 127 is added to
bores 120 after heat-treating optical fiber 10 with arc 230. This
is accomplished, for example, by wicking epoxy 127 into bore 120.
In an example embodiment, the wicking action of epoxy 127 is
assisted by heating the ferrule and/or by applying a vacuum to pull
the epoxy into bore 120.
[0119] Another example embodiment of a method for centering
standard optical fibers utilizes a two-piece multifiber ferrule
100. This example method is now described in connection with FIGS.
22 through 24. FIG. 22 is similar to FIG. 19, except that
multifiber ferrule 100 includes a rectangular cross-section
protrusion 112 at front ferrule end 106 that contains an end
portion of bores 120. FIG. 22 also shows laser cleaving (and
optionally laser polishing) being carried by out by laser beam LB
on bare-fiber sections 10S next to bulges 250 but opposite ferrule
front end 106 so that the bulges remain in place adjacent the front
ferrule end. The laser cleaving (and optional polishing) is
performed at a select distance from the ferrule front end 106,
leaving shortened fiber sections 10S, as shown.
[0120] FIG. 23 is similar to FIG. 22, and shows a secondary
multifiber ferrule 300 having a body 302, a rear end 304 and a
front end 306. In this particular embodiment, multifiber ferrule
100 is referred to as the "main ferrule" and secondary multifiber
ferrule 300 is referred to as the "secondary ferrule." Secondary
ferrule body 302 defines a rectangular-cross-sectioned recess 312
open at rear end 304, and plurality of secondary bores 320 each
having an open end 324 at recess 312 and an open end 326 to front
end 306. Secondary recess 312 is configured to mate with protrusion
112 of main ferrule 100. Main ferrule 100 and secondary ferrule 300
form a two-piece multifiber ferrule.
[0121] Secondary bores 320 are arranged in a laterally extending
linear row along respective secondary central axes .DELTA..sub.CS
and correspond in size and position to bores 120 of main ferrule
100. Recess 312 is sized to accommodate bulges 250 formed in
optical fibers 10. Secondary ferrule body 302 includes guide pins
340 sized and positioned on rear end 304 to mate with guide pin
holes 140 at main ferrule front end 106.
[0122] FIG. 24 is similar to FIG. 23, and shows the secondary
ferrule 302 engaged with main ferrule 100 to form a multifiber
ferrule assembly 101. Optical fiber sections 10S fit within bores
320 with the fiber central axes 16 substantially aligned with
respective secondary bore central axes .DELTA..sub.CS. The mating
fit between recess 312 and protrusion 112 facilitates the insertion
of optical fiber sections 10S into secondary bores 320 while guide
pins 340 mate with guide pin holes 140 to fix secondary ferrule 300
to main ferrule 100. In this position, optical fiber ends 14 that
terminate optical fiber sections 10S substantially coincide with
ferrule front end 306 and are preferably flush therewith. In an
example embodiment, ferrule front end 306 has a recessed portion
(not shown) where optical fiber ends 14 reside.
[0123] The substantial centering of optical fibers 10 within bores
120 of main ferrule 100 results in the center lines 16 of optical
fiber sections 10S being substantially aligned with the central
axes .DELTA..sub.CS of secondary bores 320. It is also noted here
that an epoxy 127 need not be used to secure optical fiber sections
10S to secondary ferrule 300. The use of secondary ferrule
facilitates the laser cleaving and polishing of optical fiber ends
14.
[0124] Once optical fibers 10 are fixed within multifiber ferrule
100 as described above to form ferrule assembly 101, then in an
example embodiment the multifiber ferrule assembly is incorporated
into a multi-fiber optical fiber connector 370, such as shown in
the exploded view of FIG. 25, and such as disclosed in U.S. Pat.
Nos. 6,816,661 and 7,077,576, which patents are incorporated by
reference herein. Connector 370 includes, in order along axis A1
from the front of the connector to the back: guide pins 340, a
connector housing 273, multifiber ferrule assembly 101, a guide pin
retainer 371, a spring seat 271, a spring 272, a spring push 372, a
crimp body 280, a lead-in tube 276, and an optical fiber cable 282
that carries a plurality of optical fibers 10 (six fibers are shown
for the sake of illustration).
[0125] It will be apparent to those skilled in the art that various
modifications and variations can be made to the present invention
without departing from the spirit and scope of the invention. Thus,
it is intended that the present invention cover the modifications
and variations of this invention provided they come within the
scope of the appended claims and their equivalents.
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