Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Back~round of the Invention
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1. Field of the Invention ~
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- - This invention relates to optical fibers, and more
~- particularly, to apparatus and methods for splicing such
fibers. - ;~
2. Descri~tion of the Prior Art
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Success of future optical co~munications systems
depends on the development of quick, convenient, and
inexpensive means of splicing optical fibers. Splicing is
difficult due to the small size of fibers and accurat~
transverse alignment needed for low-loss splices. To
achieve a splice loss of 0.1dB, approximately a ~0.1 fiber
core radius alignment accuracy is required.
One known method of transversely aligning two
mating fibers is with a snug-fitting aligning sleeve. While -
such a sleeve is desirable for effecting simple and small
splices, practical problems exist. To achieve the desired '~
- low-loss splice, the sleeve and mating fibers must be
manufactured to very close tolerances. Also, there is
difficulty in initially inserting fibers into such a sleeve.
A third problem is that contamination is scraped off the
interior surfaces of the sleeve and trapped between the
fibers during fiber insertion.
It is therefore desirable to develop a transverse i~!`' '
aligning technique which allows for simple and small J`.'' ', '
splices, yet avoids the problems of a snug-fitting sleeve.
It is also desirable that the aligning technique effect - , -
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low-loss splic~s. -
Summary of the Invention
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Pursuant to this invention, accurate transverse
alignment of one or more pairs of mating optical fibers is
facilitated by a loose-fitting optical fiber receiving tube
having a longitudinally uniform interior cross section with
` at least one corner. The corner forms a fiber-aligning
: groove in the interior surfaces substantially parallel to
the longitudinal axis of the tube, hence combining the
aligning accuracy of grooves and the small completed splices
of sleeves.
Mating fibers are introduced into opposite ends of the
optical fiber receiving tube with no particular orientation
with respect to the tube. The fibers are then bent at an ;-
angle with respect to the longitudinal axis of the tube to
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bias the fibers against the interior surfaces of the tube.
The stiffness of the fibers generates forces against the
tube; in response to these forces, the tube rotates to align ;
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itself with respect to the fibers until the mating fiber
ends are lodged against the fiber-aligning groove. This ;
procedure effects transverse alignment of the ~ating fibers,
after which the fibers, still bent, are moved toward each
other into abutment. The tube forms part of the completed
joint.
In accordance with one aspect of the present invention
there is provided a method of joining the mating ends of a
pair of optical fibers comprising the steps of:
inserting said fibers into opposite ends of a loose-
fitting optical fiber receiving tube being capable of
rotating about its longitudinal axis and having a uniform
interior cross section comprising at least one corner, said
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corner forming a fiber-aligning groove in thc intcrior
surfaces of said tube substantially parallel to said longitudinal
axis;
bending said fibers with respect to said longitudinal
axis to bias said fibers against said interior surfaces,
said biasing generating sufficient forces to rotate said
~ube until said mating fiber ends are lodged against said
fiber-aligning groove to effect transverse alignment of said
fibers;
advancing said bent fibers into abutment with each ~:
other; and ;:.: ~
joining said fibers while they are held in the bent and 1 ;
abutting position.
In accordance with another aspect of the present invention `.~
there is provided apparatus for joining a mating pair of `~:.
optical fibers comprising: a loose-fitting optical fiber ~
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. receiving tube capable of rotating in response to forces
generated when said fibers are biased against the interior
surfaces of said tube, said tube comprising: .
a uniform interior cross section comprising at least .
one corner, said corner forming a fiber-aligning groove in
the interior surfaces substantially parallel to the longitudinal
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axis of said tube; :~
means for inserting said fibers until they are a small
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distance apart; .: :
means for bending said fibers with respect to said ~;
longitudinal axis to bias them against the interior surfaces `~
of said tube, said biasing causing rotation of said tube to .
effect transverse alignment by lodging said fiber ~ends .
against said fiber-aligning groove; ~ .
means for abutting said bent fibers; and
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: means for joining said fibers while they are held in
the bent and abutting position.
The inven~ion and its objects, features, and advantages
will be readily discerned from a reading of the description
to follow of illustrative embodiments.
Brief Description of the Drawing
FIG. 1 is a schematic perspective view of an abutted
joint made with an optical fiber receiving tube in accordance
with the present invention;
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FIGS.-2A and 2B are illustrations of various
alternative configurations for the optical fiber receiving
tube;
FIG. 3 is an illustration of two mating fibers
inserted into the optical fiber receiving tube as taught
by this invention;
FIGS. 4A and 4B are illustrations of a temporary
splicing fixture;
. FIG. 5 illustrates an apparatus for joining a
10 mating pair of optical fibers in accordance with this
: invention;
FIG. 6 illustrates an apparatus for joining linear
- arrays of optical fibers;
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. FI&S. 7A and 7B are illustrations of optical . .
. fiber receivlng structures as taught by this invention;
and
FIG, 8 depicts the bell~shaped configuration for ~ .
a mating pair of fibers.
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; Detalled Deficription ~
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20 Illustrated in FIG. 1 is an optical fiber receiving ~ :
. tube 20, adapted for joining two mating optical fibers 11 :
and 12. Tube 20, which is a hollow elongated member~ has a
uniform interior cross section 21 that is larger than the ;
- diameter of fibers 11 and 12 to loosely receive either
fiber, 11 or 12, at any point along interior cross section
21, hance permitting easy insertion of the fibers and forming
a loose fit. The interior cross section 21 and tube 20 are
~ preferably selected so that tube 20 is sufficiently small
to retain the benefits of a small splice of which tube 20
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~ 3~ forms a part, while allowing easy insertion. For example, .~
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where the interlor cross section 21 of tube 20 is square-
shaped as shown in FIG. 1, the interior side edge 23 is
preferably 10 to 70 percent grea~er in length than the
diameter of fibers 11 and 12. The upper limit is chosen
so that the fibers cannot accidentally pass each other in
tube 20 during iiber insertion.
In accordance with this invention, interior cross
section 21 comprises at least one corner 22, defined by two
interior surfaces 26 disposed at an angle, depicted by ~,
with respect to each other, to form a fiber-aligning groove
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24 in the interior surfaces 26 of tube 20 substantially
parallel to the tube's longitudinal axis, which is depicted
by line 28. Corner 22 constitutes a region of torsional
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equilibrium for tube 20 when interior surfaces 26 are impinged
by fibers 11 and 12, inserted into opposite ends 27 and 29
of tube 20, respectively, and bent with respect to axis 28.
Also illustrated in FIG. 1 is the completed joint
comprising optical fibers 11 and 12, transversely aligned
and abutted in tube 20. Bent fibers 11 and 12 are
positioned in a stable state as their fiber ends, 13 and 14
respectively, are lodged against fiber-aligning groove 24.
Groove 24 preferably has an angle ~ of approximately 90
degrees to maintain the transversely aligned fibers in a
stable state. A greater angled groove would provide less
stability in holding fiber ends 13 and 14 in place. Also,
as the angle ~ of groove 24 decreases from 90 degrees, Piber
insertion becomes more difficult due to flattening of the
interior cross section. An angle 0 from 60 degrees to 150
degrees is preferred. --
In the preferred embodiment, tube 20 has a square
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cross~sectional configuration comprising four corners, each
of which would suffice as a fiber aligning groove 24.
Advantageously, the angle ~ of each groove 24 is 90 degrees.
Insertion is relatively easy since all the sides are
substantially of an identical dimension. ;
Furthermore, upon transverse alignment, fibex
ends 13 and 14 are lodged against a first fiber-aligning
groove 24, while the fibers, 11 and 12, further along their
length, are biased against the diagonally opposite second
fiber-aligning groove 25 near the ends 27 and 29 of tube 20 `
for more stability. The second groove 25 advantageously
assures continual alignment of bent fibers 11 and 12 as
they are moved into abutment.
Other cross-sectional configurations can be readily
envisioned. A tube 30 having a uniform interior cross
section with one corner, such as illustrated in FIG. 2A, may
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be utilized. FIG. 2B illustrates a two-cornered tube 32.
Preferably, the two corners are diagonally opposite to each
other for greater stability of the aligned fibers as ,
permitted in a square-shaped tube. Cross-sectional
configurations having more than four-fiber aligning grooves
are possible; however, the angles of the grooves would
increase and hence provide less stable positioning of the
fibers as mentioned earlier.
Optical fiber receiving tube 20 is capable of
rotatlng about its longitudinal axis 28 in response to
forces generated when mating fibers 11 and 12 are bent
against the tube's interior surfaces 26. Advantageously,
tube 20 is thin-walled to minimize the forces necessary to
3~ rotate tube 20 and to effect a smaller completed splice.
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Also, the interior surfaces 26 are advantageously smooth to
allow easy movement of tube 20 with respect to fibers 11
and 12.
In one embodiment of the invention, tube 20 is
advantageously made of glass. It is sometimes preferred
that the glass be transparent for easy visual detection of
the completed joint. Tubes made of plastic are also
- considered quite suitable.
To make an aligned joint, mating optical fibers 11
; 10 and 12 are introduced into opposite ends 27 and 29 of
- tube 20 with no particular orientation with respect to
tube 20 as illustrated in FIG. 3. The fiber ends, 13 and
14, are advantageously flat, though they need not be
optically polished. Fibers 11 and 12 are inserted prefer-
ably until they are substantially adjacent; their separation
prevents any physical contact between the fiber ends which
might thwart their movement during the alignment process
described.
Inserted fibers 11 and 12 are then bent at an
angle with respect to longitudinal axis 28 to bias fibers
- 11 and 12 against the interior surfaces of tube 20. The
amount of bending desired depends on the size of tube 20
and fiber stiffness. Fibers 11 and 12 should be biased
sufficiently against the interior surfaces 26 to generate
the required rotational forces upon tube 20. ~n response
to these forces, tube 20 rotates until fiber ends 13 and
14 are lodged against fiber~aligning groove 24 as shown
in FIG. 1, thereby effecting ~ransverse alignment of the
fiber ends. After alignment, fibers 11 and 12, still bent,
are moved toward each other into abutment. The bending of
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fibers 11 and 12 is exaggerated in FIG. 1 to more clearly
visualize the invention. Also, the dimensions of the tube ~;
are not accurate. In the actual inventive technique, the
tube length is substantially longex relative to the interior
cross section than depicted and the fibers are stiffer.
The length of tube 20 is not so short with respect ;
to the interior cross section 21 so that the longitudinal -
axes of the fibers are substantially skewed with respect to `~
each other, even though the fibers are transversely aligned.
Yet the tube length is short enough relative to interior
cross section 21 to allow the bending needed in generating
rotational forces for tube 20. ;~
Upon transverse alignment, it is desirable that
the longitudinal axes of mated fibers 11 and 12 be within
one degree of each other on a common longitudinal axis. To
assure that the longitudinal axes of fibers 11 and 12 are
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not more than one degree off, a tube leng~h 0.5 inch has
been suitably used for a square-shaped tube with an interior
side edge 23 of 0.006 inch.
: 20 To permanently complete the splice, an index-
matching fluid, such as curable epoxy, may be applied and
allowed to cure in and around the abutted joint. Sometimes,
` it is advantageous that the index matching fluid be applied
into tube 20 prior to ~iber insertion; the fluid can then
serve to wash away contamination on the fiber ends 13 and
; 14 during fiber insertion.
-~ Where a temporary splice is desired, a thermo-
plast-ic material, such as polymethylmethacrylate, can
be used to hold the abutted fibers in place. To terminate
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the joint, the material is then heated, hence allowing the
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fibers to separate.
Another approach for completing a temporary splice
. . is to place the abutted joint in a fixture such as illustra-
ted in FIG. 4A. The fixture comprises a top and bottom
clamp, 35 and 36 respectively, adapted to be fastened
together. The clamping surfaces 38 and 39 are lined with
. thick, soft layers 37 of a materia:L such as ethylene-vinyl ~:
acetate copolymer (EVA). The soft layer 37 on each clamp
has a recessed space 40 for placement of tube 20, such that
the jo.in~ is suspended in air when the clamps are fastened
together. The fastened clamps hold the abutted joint by
maintaining the bent fiber configuration as shown in FIG.
:. 4B.
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Illustrated in FIG. 5 is an apparatus for joining
a mating pair of optical fibers. Mounted on an assembly
baseplate 41 is a positioning block 42 having a tube-
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positioning furrow 44 across its top surface 46 for place~
ment of optical fiber receiving tube 20. Near either end
of furrow 44 is an optical fiber guide assembly 50~ Each ~;
20 fiber guide assembly 50 comprises a guiding block 52 having ~ .
a fiber guiding channel 54 in axial alignment with furrow ~. .
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Pivotally mounted on each guiding block 52 is a
.. fiber guiding plate 56 located adjacent to positioning
block 42. The top surface 58 of plate 56 also has a fiber ^
~; guiding channel 60 which is in axial alignment with channel
54 and furrow 44 during initial insertion of fibers 11 and ..
. 12 into tube 20. .
The guiding channels 54 and 60 of each assembly ~ .
50 direct the insertion of respective fibers ll and 12, into
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the opposite ends of tube 20, after which the fibers, 11 ;~
and 12, are held with a clamp 48 respectively, to each
guiding block 52. The clamps 48 are advantageously lined
with a material such as EVA.
Each plate 56 rotates about an axis substantially
perpendicular to the longitudinal axis of the furrow 44 and
is preferably pivotal in an upward direction. AS both
inserted fibers 11 and 12 are bent relati~e to tube 20 by
~ pivoting plates 56 upwards, tube 20 is lifted from position-
; 10 ing block 42 and allowed to freely rotate in response to
the forces generated by the bent fibers against the interior -;
surfaces 26 until fiber ends 13 and 14 are lodged against a
fiber-aligning groove 24. The plates 56 may be pivoted with
any known conventional means.
In an alternative embodiment, positioning block
42 can be lowered a~ter fiber insertion wherein guiding ;~
plates 56 can be rotated in a lateral direction to effect
: ~iber bending and rotation of tube 20.
It is recognized that furrow 44 can be made very
- 20 shallow and tube 20 he made cylindrical externally so as to
allow rotation of tube 20 while tube 20 is still in contact
with furrow 44.
Each guiding block 52 is slidably mounted on
assembly baseplate 41 through a male-female interlocking
guide track 62. The guide tracks 62 allow movement of
guiding blocks 52 in a direction parallel to the longitud~ ~-
inal axis of furrow 44 so as to advance the transversely
~ aligned fibers 11 and 12 into abutment. The splice is then
- completed with epoxy or a holding fixture as desired.
3Q Advantageously, when a splice is made with epoxy~
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the apparatus maintains a bell-shaped curve as shown in
FIG. 8 for the abutted fibers; such a bend generates
-sufficient forces to prevent fibers 11 and 12 from
separating during curing of the epoxy.
This apparatus as illustrated in FIG. 5 can easily
be modified to join two mating groups of fibers such as
linear arrays 64 in the form of ribbons.
Advantageously, the fibers 11 or 12 of each ribbon
64 are substantially parallel to each other along their
longitudinal axes and have a specific center-to-center
spacing. The embedding materials of the ribbon structures
are stripped away to prepare the fibers 11 and 12 for
: splicing. As illustrated in FIG. 6, the top surface 46 of
positioning block 42 then comprises a plurality of -
furrows 44', for placement of a plurality of optical fiber
receiving tubes 2Q. The furrows 44' are parallel to each
other and have substantially the same center-to-center
spacing as the arrayed fibers 11 and 12. Each guiding
block 52, of which only one is illustrated, can be adapted
to position an optic ribbon structure as shown by ribbon
guide 66. The alignment abutment process is similar to
that for single mating fibers.
As the number of fibers being joined simultaneously
increases, it is sometimes advantageous to align the grooves
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of the tubes in a specific orientation with respect to the
bending. For example with joining apparatus shown in
FI~. 6, a plurality of square-shaped tubes also correspond
ingly square-shaped externally in configuration can
; advantageously be poaitioned in V-shaped furrows 44' on
~- 3Q the top surface of positloning block ~6. This minimizes the
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amount of rotation needed by tubes ~0 to align the fibers as
- the grooves are initially oriented for the movement of fiber
ends 13 and 14 towards them.
In another embodiment, an optical fiber receiving
structure 72 comprising a plurality of parallel tube-like
cavities 74 as depicted in FIG. 7A, may be utilized to join
linear arrays 64 of optical fibers. No tube-holding
fixtures are needed in this embodiment. Each cavity 74,
continuous with respect to either end, is adapted to receive
and align the respective mating fibers 11 and 12. Having
interior dimensions similar to that of tube 20, each
cavity 74 has a uniform cross section 76 for loosely fitting
the inserted fibers. The cross section 76 of each cavity
comprises at least one corner 77 which forms a fiber-
aligning groove 78 substantially parallel to the cavity's
longitudinal axis. Advantageously the fiber-aligning
grooves 78 of the cavities 74 are oriented with respect to
`~ each other and the direction of bending such that when the
mating arrays 64 are bent to bias the fibers against the
cavity walls, the fiber ends are simultaneously directed
toward the respective ~iber~aligning grooves 78.
- To achieve the splice, the arrayed fibers are
first inserted into the opposite ends of the corresponding
~ cavities 74 with no particular orientation to the cavities
- 74. The arrays are then bent with respect to the longi-
udinal axes o~ cavities 7~ to urge the plurality of fiber
ends 13 and 14 against the respective cavity walls 79 and
towards the corresponding grooves 78. The bending generates
su~ficient fiber biasing forces to cause fibers 11 and 12
to move along the respective cavity walls 79 until the
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plurality of fiber ends 13 and 14 are lodged in their
; respective grooves 78. Structure 72 forms a part of
-completed joint. The structure 72 may be extended to splice
a plurality of linear arrays 64 as depicted in FIG~ 7B in a
cross-sectional view.
- It is to be understood that the embodiments
described herein are merely illustrative of the princîples
of the invention. Various modifications may be made thereto
by persons skilled in the art without departing from the
10 spirit and scope of the invention. --
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