Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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DEFORM~BLE FIE~ER OPTIC CONNECTION ALIGNMENT` DEVICE
BACKGROUND OF THE INVENTION
Field of the In~ention
_ _ . _ _
The present invention relates to connectors for fi~er
optic cables.
Description of the Prior Art
The employment of fi~er optic cables or light guides~ also
someiimes referred to as optical communication fi~ers, for the
transmission of information-bearing light signals, is now an
established art. Much development work has ~een devoted to the
provision of practical low-loss glass materials and production
techniques for producing glass fi~er ca~les ~ith protective
outer coatings or jackets~ The jacket makes them resemble
ordinary metallic-core electrical ca~le upon superficial external
' inspection. O~viously, if fi~er optic ca~les are to be used in
practical signal transmission and processing systems, practical
connectors for the connection and disconnection of fi~er optic
ca~les must ~e provided.
Before the prior art in respect to connectors, per se, is `
discussed, some references will ~e given for the ~enefit of the
skilled reader in understanding the state of fi~er optic art in
general. ~ -
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104~143 R. L. McCartney 6X
An article entitled "Fiber Optics" by Narinder S. Kapany,
published in the SCIENTIFIC AMERIC~, Vol. 203, Pages 72-81,
dated November 1960, provides a useful background in respect to
some theoretical and practical aspects of fiber optic transmis-
sions.
Of considerable relevance to the problem of developingpractical fiber optic connectors, is the question of transfer
efficiency at the connector. Various factors, including separa-
tion at the point of abutment, and lateral separation or offset,
are among the factors effecting the light transfer efficiency at
a connector. In this connection, attention is directed to the
Bell System Technical Journal, Vol. 50, No. 10, December 1971,
specifically to an article by D. L. Bisbee, entitled "Measurement
of Loss Due to Offset, and End Separations of Optical Fibers".
Another Bell System Technical Journal article of interest appeared
in Vol. 52, No. 8, October 1973 and was entitled "Effect of
Misalignments on Coupling Efficiency on Single-Mode Optical
Fiber Butt Joints" by J. S. Cook, W. L. Mammel and R. J. Grow.
The patent literature also contains much information relative
to the state of this art. For example, ~. S. Patent 3,624,816
describes a "Flexible Fiber Optic Conduit". The device described
therein uses a plurality of light conducting fibers in a flexible
cable type arrangement.
Concerning the utility of fiber optic cables and therefore
the utility of connectors for such cables, various systems are
described in the patent literature which employ fiber optic
cables. One example of such a utilization system is described
in U. S. Patent 3,809,908.
Yet, another patent of interest is entitled "Glass Fiber
Optical Devices", U. S. Patent 3,589,793. That reference re-
lates to the fiber optic bundles and the glass fibers themselves,
as well as to a method of fabrication for the fiber optic ele-
ments themselves.
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A selection of U. S. patents relating more particularly to
optical cable connectors includes U. S. Patents 3,790,791;
- 3,637,284; 3,572,891; 3,806,225; 3,758,189 and 3,508,807 are
representative of the connector prior art.
S It ls known in this art that efficient fiber-to-fiber opti-
cal interconnections require that lateral misalignments to be
~ held to the diameter of a single fiber of the fiber bundle, or
; less.
U. S. Patent No. 38734,594 to Tranbarulo discloses a de-
formable elastomeric core for aligning the ends of a plurality
of pairs of single optical fiber. The core contains bores for
receiving the ends of fiber pairs. The diameter of each bore
in the core is greater than the diameter of the fibers so that
the latter may be easily inserted into the bore. After the
- 15 fibers of each pair are inserted into the bore and axially abut
at their mating end faces, the core is axially compressed by a
pair of pressure plates radially deforming the core so that it
simultaneously aligns and mechanically secures the fibers. This
arrangement has distinct disadvantages. If the fiber end faces
20 touch in the bore under any significant axial compression ~ -
force, the fibers may break, since they are bare; i.e., they
are not terminated by rigid termination pins. If the fibers
do not break, relatively high axial pressures may be created
therebetween due to the small diameters of the fibers and axial
variations in their positions due to tolerances. These pres-
sures may be so high that the radial deformation of the elasto-
meric core by axial compression thereof is insufficient to alter
the relative lateral positions of the mating faces of the fibers.
As a result, the Trambarulo arrangement may be inadequate, if not
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inoperable, for effectively achieving axial alignment
of optical fibers. It is the purpose of the present
invention to provide a fiber optic cabie alignment
sleeve which minimizes, if not completely overcomes,
the foregoing disadvantages of the prior art com-
pressible alignment sleeve, and thus is completely
suitable for a commercially practical type of fiber
optic connector.
SUMMARY OF THE INVh'NTION
,
The present invention is based on the use of an
alignment sleeve in the form of an elongated tubular
member fabricated from an eIast;cally deformable
material having a reIatively lo~ bul~ modulus of
eIasticity. Many known rubbers and synthetic plastic
materials fit this description.
WheneYer a pair of fiber optic cables to be signal
connected are ~eId collinearly wlt~in a pair of
mating connector shells so that they abut each
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R. L. McCartney 6X
104~143
other axially at their ends, the present invention may be em-
ployed to eliminate or greatly reduce the lateral misalignments
discussed hereinbefore.
The ends of the fiber optic cables are inserted into the
opposite ends of the alignment sleeve according to the invention.
The bore in the alignment sleeve has a central portion of uni-
form diameter and outwardly tapering end portions. The diameter
of the central portlon is less than the outside diameters of the
cable ends so that when the latter are pushed into the sleeve
so that their mating end faces abut in the central section of
the bore, the end faces will become self-aligned due to the
interference fit between ends of the cables and the restricted
central region of the sleeve. Thereafter, an axial compression
force may be applied to the alignment sleeve to cause the end
regions thereof to construct radially inward to seal against
the cables and provide vibration dampening for the ends of the
cables.
The manner of implementing the concepts of the present in-
` vention in a practical fîber optic cable connector will be under-
stood as this description proceeds.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a partially cutaway connector assembly showing
a pair of mated connector shells, with corresponding socket
members and a single pair of signal-connected fiber optic -
cables.
Fig. 2 is an enlarged view of a typical form of elastomeric
alignment sleeve according to the invention prior to the inser-
tion of the fiber optic bundles.
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Fig. 3 shows a pair of fiber ~undles with termination
pins typîcally abutted within the alignment sleeve of Fig. 2.
DESCRIPTIOW OF THE PREFERRED EMBODIMENT
.
Referring now to Fig. 1, a partially cutaway view of a
mated connector assem~ly for optical fifier connections is
shown generally at 10. Connector shell parts 11 and 12 are
shown mated, firinglng about the afiutment of opposing fiber
optic fiundles at the interface memfier 24. The said interface
memfier will be her'einafter additionally described.
Socket mem~ers generally shown at their extremities 30
and 31, may be single pieces or multiple piece arrangements
within each connector sheIl. For clarity, only a single mat-
ing pair of fiber optic cables is illustrated, comprising the
fiber optic fiundle'l4 on the'left, with its jacket 15, and on
15 the right, fiber opt;c ~undle 16 with its jacket 17. The
general connector sheIl and socket member arrangement is not
unlike corresponding~memfiers in the weIl known electrical
connector art. The socket member 30 ~ill fie recognized as
being capa~le'of accommodating four fi~er optic cafiles, con-
nectable'to four opposite'numfier cables, held in the socketmem~er 3I. The'engagement nut 13 operates against a projec-
tion 32 for the'securing of connector sheIl mating in a way
already well understood in the'connector art.
Although the present invention does not require the split-
tine terminating pin depicted, that particular termination pin
- 6 -
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is a useful one for the compaction and stabilization of the
end fibers of a fiber bundle for abutment and light path con-
- nection, as at 24 in Fig. 1. Each shell part of the connector
- embodies an axial tolerance relief arrangement, shown gener-
ally at 19 in Fig. 1.
The eIastomeric sleeve according to the present invention
is s~own at 20'of Fig.. 1 and, in more'detail, in Figs. 2 and 3.
In Fig. 2, slee~Je'20 is shown closeIy fit into a bore in
a part 21, which may actually be a socket member, typically
10 illustrated at 28 in ~ig. 1.
A typical eIastomeric sleeve 2a might be fabricated from
.any of a num~er of't~.e known eIastically deformafile materials, l:
synt~etic or natural. The part 21 ~ay have a radial chamfer
22, to provide for easy insertion of the fiber bundle termina- ¦
tion pin Ctypically 18~ at the opposite end of the sleeve 20.
.~ A chamfer 23'in the'end of the'sieeve 20 may be provided for ..
the'same purpose. The'term;nation-pin for the fiber bundle
may be'a metal sleeve'longitudinally slotted on opposite sides, ..
as indicated at 25, to provide'a split-tine arrangement which .-
produces a compression force on the'fifiers in the bundle so :
that the fibers are'arranged in a closed pack array. ''~
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10~143
The relatively thin membrane 24 operates as an inter-
face member and protects the mating fiber surfaces against
abrasion. The membrane may be integral with sleeve 20. In
addition, membrane 24 provides a refractive index matching
function which reduces reflective losses, this particular device
for that purpose being known in the art.
The use of interface gel material is also known
and the connector, according to the present invention, may be
assembled with, or without, such a gel, although ordinarily
the interface part 24 provides essentially the same optical
function as a gel and provides better mechanical protection
for the riber bundle terminal ends. As a further alternative,
a metal protective sleeve (not shown) may be mounted on each
termination pin. The sleeve has an inwardly directed annular
flange which extends over the outer peripheral region of the
mating end of the pin so as not to cover the end of the fiber
bundleO The flanges on the protective sleeves on mating
termination pins prevent the end faces of the fiber bundles
from contacting, and abradding, when the pins are mated to-
gether.
According to the invention, as depicted in Figure
2, the diameter of the bore in the sleeve gradually increases
from the central portion in the vicinity of the part 24 to the
outside extremities on both right and left, thereby providing
outwardly tapered portions as indicated at 33O The diameters
of the tapered portions 33 of the sleeve bore at the ends of
the sleeve are greater than the outside diameter of the pins
18 on the fiber bundles. Thus, the tapered portions of the
bore facilitate easy insertion of the pins into the boreO
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The central region of the sleeve bore has a uniform diameter
and such diameter is less than the outside diameter of the
termination pins 1~ as seen by comparing Figs. 2 and 3. Thus,
there will be an interference fit between the pins and the cen-
tral portion of the bore in sleeve 20 when the pins are pushedinto the opposite ends of the sleeve. When the connector
shells 11 and 12 are initially partially mated, the ends of the
termination pins 18 are pushed into the opposite ends of sleeve
20 until the mating end faces of the pins abut the interface
member 24. Due to the interference fit between the pins and
central region of the sleeve, the wall of the sleeve in that
region will expand or be deformed radially outwardly, thereby
exerting a radially inwardly directed compression force that
effects lateral alignment of the termination pins. Thus, it is
seen that the sleeve and pins cooperate to produce automatic
self-alignment between the fiber bundles terminated by the pins.
This alignment is achieved without axially compressing the
sleeve 20 in contrast to the alignment core disclosed in the
aforementioned Trambarulo patent.
Referringnow to Fig. 3, the mating of the fiber bundles at
the interface member 24, is depicted. This may be thought of
as a detail of the parts of Fig. 1, within and immediately sur-
rounding part 20.
In Fig. 3, after the termination pins reach the interface
member 24 and are self-aligned, continued mating of the con-
nector shells 11 and 12 cause one socket part 35 to apply axial
pressure at the end 26 of sleeve 20. This pressure is operative
between the shoulder 27 and the part 35, and, due to the relatively
low bulk modulus of elasticity of the part 20, produces an inwardly
directed deformation at the end regions of the sleeve (on opposite
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- sides of the uniform diameter central portion of the bore). Such
deformation of the sleeve produces an effective seal between the
sleeve and pins 18, thus preventing intrusion of dust or other
contaminants into the interface between the fiber bundles. In
addition, the inward deformation of the outer end regions of the
sleeve provides vibration dampening for the fiber bundles.
In a rectangular, rack and panel type commercial connector
embodying the alignment sleeve of the present invention up to
ten pounds of force lS required to couple each pair of mating
termination pins of the connector together. Such a force re-
sults in pressures up to a maximum of about 2600 psi between
the mating faces of the termination pins. In such connector
axial compression of the elastomeric alignment sleeve produces
radially inwardly directed forces which are frequently inadequate
to alter the relative lateral positions of the termination pins
once they have abutted under such high pressures. Thus, if the
aforementioned prior art alignment core were utilized in the
above commercial connector in which the pins are inserted loosely
into a uniform diameter enlarged bore, lateral alignment of the
misaligned pins will often not be achieved by axially compress-
ing the elastomeric core due to the high mating pressure which
can occur on the pins.
The present invention achieves effective lateral alignment
between mating fiber optic bundles by a self-aligning operation
due to the interference fit between the pins and the central
portion of the alignment sleeve, and alignment of the pins is not
dependent upon nor does it require axial compression of the align-
ment sleeve. Axial compression occurs after alignment of the
pins has been achieved, and occurs only to provide sealing con-
tact with the pins and dampening of vibrations of the pins whichfrequently occurs during normal use of connectors.
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It will be realized from Figs. 1, ~ and 3 that the parts
21 and 29 might actually not be individual parts, but rather might
be in the nature of face plates with plural fiber connections made
through corresponding axial holes therethrough.
Various modifications of the described structure will sug-
gest themselves to those skilled in this art, for example, in
Fig. 2, the interface part 24 might be an integral part of the
elastomeric sleeve 20, or it may be a separate piece fitted therein.
In either event, any expansion radially outward of the part 24,
due to axial compression between the termination pins l~, can
be absorbed within the deformable body material of 20. The mate-
rials of the various parts in the connector, according to the
present invention, may be selected from a wide variety of known
materials. The connector shells 11 and 12 may be die-cast metallic
parts, and the socket members including 30 and 31, as well as 21
and 29, may be the same relatively hard plastics which are common
in electrical connectors. Since there are no electrical insula-
tion considerations, metallic parts can be used in these places.
The mechanical and environmental performance requirements will
be obvious to persons of skill in this art. There are no electri-
cal insulation problems, per se.
If, as hereinabove indicated, the individual connector
employing the invention were of the multiple cable type, the parts
21 and 29, which might be more actually described as rigid face-
plates with plural axial openings therein, could readily be fabri-
cated from metallic materials or from the same well known plastic
electrical connector socket materials.
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In accordance with the foregoing, it is not intended that
the drawings and this description should be regarded as limiting
the scope of the present invention.
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