U.S. patent number RE34,005 [Application Number 07/569,114] was granted by the patent office on 1992-07-21 for contact for terminating an optical fiber.
This patent grant is currently assigned to Raychem Corporation. Invention is credited to Frank H. Levinson, Richard J. McCrae, Mark Ostasiuk, Pravin Soni, Adam C. Tanous.
United States Patent |
RE34,005 |
Levinson , et al. |
July 21, 1992 |
Contact for terminating an optical fiber
Abstract
An optical fiber contact for terminating an optical fiber
includes a solid multi-part thermoset mixture in a cavity in a
front portion of the contact, an optical fiber being terminated by
heating the thermoset so as to cause it to soften and liquify and
subsequently inserting an optical fiber through the contact. The
thermoset when liquified chemically reacts so as to form an epoxy
adhesive which secures the optical fiber within the contact and
keeps the optical fiber in place even when subjected to extremely
wide temperature variations.
Inventors: |
Levinson; Frank H. (Menlo Park,
CA), Soni; Pravin (Union City,both of, CA), Tanous; Adam
C. (Charlottesville, VA), McCrae; Richard J. (Hatfield,
PA), Ostasiuk; Mark (Newark, CA) |
Assignee: |
Raychem Corporation (Menlo
Park, CA)
|
Family
ID: |
27074985 |
Appl.
No.: |
07/569,114 |
Filed: |
August 17, 1990 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
799898 |
Nov 20, 1985 |
04790622 |
Dec 13, 1988 |
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Current U.S.
Class: |
385/80;
385/86 |
Current CPC
Class: |
G02B
6/382 (20130101); G02B 6/3861 (20130101); G02B
6/3887 (20130101); G02B 6/3821 (20130101); G02B
6/3833 (20130101) |
Current International
Class: |
G02B
6/38 (20060101); G02B 006/36 () |
Field of
Search: |
;350/96.2,96.21,96.22,320 ;385/76,77,78,79,80,86,87 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0086266 |
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Aug 1983 |
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EP |
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57-56809 |
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Apr 1982 |
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JP |
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2007869 |
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May 1979 |
|
GB |
|
1567636 |
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May 1980 |
|
GB |
|
2052790 |
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Jan 1981 |
|
GB |
|
2068142 |
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Aug 1981 |
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GB |
|
2111240 |
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Jun 1983 |
|
GB |
|
Other References
Bauman et al, "Fiber-Optic Cable Termination Method," IBM Tech.
Discl. Bull., vol. 24, No. 2, Jul. 1981, p. 1150..
|
Primary Examiner: Lee; John D.
Attorney, Agent or Firm: Kovach; Dennis E. Burkard; Herbert
G.
Claims
What is claimed is:
1. An optical fiber contact for terminating an optical fiber
comprising:
a contact body having a cavity .[.and an aperture.]. through which
an optical fiber to be terminated can extend; and
a solid substantially uncured thermoset disposed within the cavity
through which the optical fiber can be inserted .[.subsequent to
softening the thermoset within the cavity.]., the thermoset
comprising a multi-component room-temperature stable solid mixture
which when heated softens, liquifies, mixes and then cures to form
an adhesive capable of adhering to the optical fiber and the
contact body.Iadd., the thermoset being disposed in the cavity in a
hardened form prior to any part of the optical fiber being inserted
into the contact body.Iaddend..
2. The contact of claim 1, the adhesive consisting essentially of a
solid mixture of novolac epoxy resin, either dicyandiamide or
substituted dicyandiamide, and imidazole.
3. The contact of claim 1, the thermoset being cylindrically shaped
so as to have a bore in a central region thereof through which the
optical fiber can be inserted.
4. The contact of claim 1, the thermoset completely filing a
cross-sectional area of the cavity. .[.5. The contact of claim 1,
an empty reservoir being formed adjacent a front end of the
aperture, the front end of the aperture being on a front of the
contact body whereat a front end
of an optical fiber to be terminated is located..]. 6. The contact
of claim 1, the contact body having a front face adjacent a front
end thereof whereat an end of the optical fiber being terminated
can be optically connected to another optical fiber, a back end of
the contact body having a plurality of flanges extending from an
outer surface thereof, the flanges forming at least one annular
reservoir on the surface of the contact body between the flanges,
and further comprising a second solid adhesive disposed in the
reservoir for adhering to fiber braids subsequent
to softening the second adhesive. 7. The contact of claim 6, the
flanges forming at least one reservoir extending circumferentially
around the contact body along a direction essentially perpendicular
to a longitudinal axis of the contact body, the optical fiber being
terminated being
disposed within the aperture. 8. The contact of claim 7, further
comprising means for urging braids of an optical fiber cable into
the
second adhesive. 9. The contact of claim 8, the urging means
comprising a dimensionally recoverable member which when heated
recovers radially inward and attempts to conform to a shape of the
outer surface of the
contact body and the second adhesive. 10. The contact of claim 6,
the contact body including first and second tubes and a ring, the
ring being press fitted onto the second tube adjacent a flange
thereof, the first tube being telescopically press fitted onto said
second tube so as to form a gap between a back end of the first
tube and a front end of the ring.
An optical fiber contact for terminating an optical fiber,
comprising:
a contact body having a front face adjacent a front end thereof
whereat an end of an optical fiber being terminated can be
optically connected to another optical fiber, a back end of the
contact body having a plurality of flanges extending from an outer
surface thereof, the flanges forming at least one annular reservoir
on the surface of the contact body between the flanges; and
a solid adhesive disposed in the reservoir and secured to the
contact body into which optical fiber braids can be embedded and
secured thereto subsequent to softening the adhesive and forcing
the braids into the softened adhesive;
the contact body including first and second tubes and a ring, the
ring being press fitted onto the second tube adjacent a flange
thereof, the first and second tubes being telescopically press
fitted together such that a back end of the first tube and a front
end of the ring are
separated a predetermined precise distance. 12. The contact of
claim 11, the contact body having an aperture therein through which
the optical fiber being terminated can be inserted, the flanges
forming at least one reservoir and extending circumferentially
around the contact body along a direction essentially perpendicular
to a longitudinal axis of the contact
body, the optical fiber being disposed within the aperture. 13. The
contact of claim 11, further comprising means for urging the braids
of an
optical fiber cable into the adhesive. 14. The contact of claim 13,
the urging means comprising a dimensionally recoverable member
which when heated recovers radially inward and attempts to conform
to a shape of the outer surface of the contact body and the
adhesive, the recoverable member when heated conducting sufficient
heat to the adhesive so as to cause the
braids to be embedded therewithin. 15. The contact of claim 11,
further comprising a spring disposed around the contact body such
that a front end of the spring contacts the ring so as to limit
forward movement of the
spring along an outer surface of the contact body. 16. An optical
fiber contact for terminating an optical fiber, comprising:
a contact body having a cavity therein and an aperture through
which an optical fiber to be terminated can extend, a reservoir
being formed adjacent a front end of the aperture, the front end of
the aperture being on a front of the contact body whereat a front
end of the optical fiber to be terminated is located;
an optical fiber disposed within the contact body, an end of the
fiber having a resiliently deformable index matching solid disposed
thereon, the reservoir being empty so as to allow accommodation of
at least part of said index matching solid therein upon deformation
thereof by contact with
an end of a mating optical fiber. 17. The contact of claim 16, the
optical fiber being terminated by being disposed through the
contact body and the contact body aperture, the reservoir being
sized so as to allow the resiliently deformable index matching
solid disposed on the end of the optical fiber to deform and
substantially flatten when compressed against the end of the mating
optical fiber being optically connected to the
terminated optical fiber. 18. The contact of claim 17, further
comprising a solid thermoset disposed within the cavity, the
thermoset comprising a multicomponent mixture which when heated
softens, liquifies, mixes and cures to form an adhesive capable of
adhering to the optical fiber being terminated and the contact
body, a portion of the cured thermoset comprising the resiliently
deformable index matching solid which is
disposed on the end of the optical fiber. 19. An optical fiber
contact for terminating an optical fiber, comprising:
a contact body having a cavity therein and an aperture through
which the optical fiber to be terminated can extend, the contact
body comprising a ring and first and second tubes, the ring being
disposed against a flange of the second tube, the first and second
tubes being telescopically press fitted together such that a back
end of the first tube is separated from a front end of the ring so
as to form a gap therebetween, a length of the gap being controlled
so as to precisely control a distance between a front end of the
first tube and the front end of the ring, the ring being press
fitted onto the second tube. 20. The contact of claim 19, further
comprising a solid thermoset disposed within the cavity through
which the optical fiber can be inserted, the thermoset comprising a
multicomponent mixture which when heated softens, liquifies, mixes
and cures to form an adhesive capable of adhering to the optical
fiber and the contact body.
The contact of claim 19, a reservoir being formed adjacent a front
end
of the aperture. 22. A method of terminating an optical fiber,
comprising the steps of:
cleaving an end of the optical fiber; and thereafter
inserting the cleaved optical fiber end through an aperture of a
contact body such that the cleaved end of the optical fiber is
substantially flush with a front face of the contact body;
heating the contact body prior to inserting the cleaved optical
fiber end therethrough so as to liquify a solid thermoset material
therewithin such that a portion of the liquid thermoset material is
disposed on and adheres
to the cleaved optical fiber end. .Iadd.23. A method of terminating
an optical fiber, comprising the steps of:
first disposing a solid thermoset within a cavity of a contact body
having the cavity therein through which an optical fiber to be
terminated can extend, the thermoset being disposed in the cavity
in a substantially unreacted form, the thermoset comprising a
multi-component room-temperature stable solid mixture which when
heated softens, liquifies, mixes and then cures to form an adhesive
capable of adhering to the optical fiber and the contact body;
then inserting the optical fiber through the thermoset and through
the contact cavity after the thermoset has been disposed within the
cavity;
heating the thermoset so as to soften and liquify the thermoset.
.Iaddend. .Iadd.24. The method of claim 23, the thermoset being
heated after the optical fiber has been inserted through the
thermoset. .Iaddend. .Iadd.25. The method of claim 24, the
substantially unreacted thermoset having a preformed bore in a
central region thereof through which the optical fiber is inserted.
.Iaddend. .Iadd.26. The method of claim 25, further comprising the
step of disposing an index matching material on an end of the fiber
subsequent to inserting it through the contact body. .Iaddend.
.Iadd.27. The method of claim 23, the thermoset being heated prior
to
inserting the optical fiber through the thermoset. .Iaddend.
.Iadd.28. The method of claim 27, the substantially unreacted
thermoset completely filling the cavity. .Iaddend. .Iadd.29. The
method of claim 23, the contact body including an aperture therein
through which the optical fiber to be terminated can extend, a
front end of the contact aperture being on a front of the contact
body, the contact cavity being adjacent a back of the aperture, and
further comprising a conical-shaped reservoir adjacent the front of
the contact body. .Iaddend. .Iadd.30. The method of claim 23, the
adhesive consisting essentially of a solid mixture of novolac epoxy
resin, either dicyandiamide or substituted dicyandiamide, and
imidazole. .Iaddend. .Iadd.31. The method of claim 23, the contact
body having a front face adjacent a front end thereof whereat an
end of the optical fiber being terminated can be optically
connected to another optical fiber, a back end of the contact body
having a plurality of flanges extending from an outer surface
thereof, the flanges forming at least one annular reservoir on the
surface of the contact body between the flanges. .Iaddend.
.Iadd.32. The method of claim 31, further comprising the step of
disposing a second solid adhesive in the reservoir, the flanges
preferably forming at least one reservoir extending
circumferentially around the contact body along a direction
essentially perpendicular to a longitudinal
axis of the contact body. .Iaddend. .Iadd.33. The method of claim
32, further comprising the step of urging braids of an optical
fiber cable into the second adhesive using a dimensionally
recoverable member which when heated recovers radially inward and
attempts to conform to a shape of the outer surface of the contact
body and the second adhesive. .Iaddend. .Iadd.34. The method of
claim 33, the contact body including first and second tubes and a
ring, and further comprising the steps of press fitting the ring
onto the second tube adjacent a flange thereof, and telescopically
press fitting the first tube onto said second tube so as to form a
gap between a back end of the first tube and a front end of the
ring. .Iaddend. .Iadd.35. The contact of claim 1, the contact body
including an aperture adjacent the cavity, an empty reservoir being
formed adjacent a front end of the aperture, the front end of the
aperture being on a front of the contact body whereat a front end
of an optical fiber to be terminated is located. .Iaddend.
Description
BACKGROUND OF THE INVENTION
The present invention relates to an optical fiber contact for
terminating an optical fiber and methods of terminating optical
fibers.
Numerous methods have been proposed in the prior art for
terminating optical fibers to fiber contacts and interconnecting
such contacts. In severe environments where a relatively wide
temperature range can be expected, such as in aerospace,
geophysical, industrial, and marine applications, it has been
common to mix two liquids together in the field to form a liquid
epoxy which is then used to terminate an optical fiber to a fiber
contact, the contact then being mechanically assembled with
additional hardware to form a connector. This termination method is
disadvantageous since it is messy, very craft sensitive, and time
consuming. In addition, such fiber contacts tend to be intricate in
design in that they include the connector hardware and therefore
are unduly large which makes them hard to use since they are
substantially larger in cross-section than the fiber cable.
Prior art contacts suffer from a further disadvantage in that they
are oftentimes required to be formed to precise longitudinal
lengths to insure that an optical fiber terminated therewith will
be disposed a pre-controlled distance from an optical source when
connected thereto. A further disadvantage of prior art optical
fiber contacts is that oftentimes the user is required to cleave an
end of the optical fiber at a position flush with an end of the
contact, and then subsequently polish the cleaved optical fiber
end, which operations are very craft sensitive and time consuming.
Finally, prior art contacts have relatively short shelf lives.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to eliminate the
above-noted drawbacks of prior art optical fiber contacts and
termination methods, and to provide an optical fiber contact which
is relatively simple in design, small in size, and easy to
install.
These and other objects are achieved by a contact which includes a
contact body having a cavity therein and an aperture therethrough
through which an optical fiber to be terminated can extend, and a
solid thermoset adhesive disposed within the cavity through which
the optical fiber can be inserted, the thermoset comprising a
multi-component mixture which when heated softens, liquifies, mixes
and chemically reacts so as to cure to form an adhesive, capable of
adhering to the optical fiber and to the contact body, one example
of the thermoset being a multipart epoxy. Such a thermoset makes
termination of an optical fiber easy, and being in a solid
multipart unreacted form, the thermoset is inherently stable and
has a relatively long shelf life. A preferred curing mechanism is
chemical crosslinking.
According to one preferred embodiment of the invention, the
thermoset completely fills the cavity, and the optical fiber is
terminated by first heating the contact body so as to liquify the
thermoset, and thereafter an end of the optical fiber is inserted
through the liquified thermoset. Preferably the thermoset is
formulated so as to be optically transparent and so as to have an
index of refraction substantially the same as that of a core of the
optical fiber, and accordingly a portion of the thermoset which
adheres to an end of the optical fiber and cures thereon thus forms
a relatively hard resiliently deformable index matching material on
the end of the terminated optical fiber which can then be pressed
against a similar index matching material disposed on a similarly
terminated optical fiber to eliminate an air gap therebetween.
Accordingly to another preferred embodiment, the thermoset is
shaped so as to form a cylinder having a bore therein through which
the optical fiber being terminated is inserted, and with this
embodiment it is advantageous to dispose an index matching material
on an end of the optical fiber being terminated subsequent to
inserting it through the contact body.
A further feature of the invention is that of forming a reservoir
adjacent the front end of the contact body aperture which allows
the relatively hard resiliently deformable index matching material
disposed on the terminated end of the optical fiber to flatten out
when it is pressed against other similarly terminated optical fiber
so as to eliminate any air gap therebetween and associated optical
losses.
According to a further feature of the invention, the contact body
comprises a ring and first and second tubes, the ring preferably
being press fitted onto the second tube adjacent a flange thereof,
the first and second tubes being telescopically press fitted
together such that a back end of the first tube is separated from a
front end of the ring so as to form a gap therebetween, a length of
the gap being controlled so as to precisely control a distance 1
between a front end of the first tube and the front end of the
ring, this assembly procedure eliminating any need for precisely
machining and controlling a longitudinal length of the first tube
and yet allows a means for accurately positioning an end of the
terminated optical fiber relative to a reference point, e.g. the
front of the ring, which enables the terminated optical fiber end
to be positioned at an optimum focusing point.
Preferably, the contact further includes a plurality of flanges at
a back end of the contact body which extend from an outer
circumferential surface of the contact body, the flanges forming at
least one annular reservoir on the surface of the contact body
between the flanges, the contact further including a second solid
adhesive disposed in the reservoir and secured to the contact body,
the adhesive being capable of tightly adhering to braids of an
optical fiber cable when the braids are forced into the second
adhesive preferably by hoop stresses generated by a sleeve disposed
around the braids when recovered using heat.
The invention further includes improved methods of terminating an
optical fiber, one method being first cleaving the optical fiber
and then inserting the cleaved optical fiber end through the
contact body so as to be precisely positioned flush with a front
end of the contact body. According to an alternative preferred
termination method, the optical fiber is first inserted through the
contact body so as to extend a substantial distance in front of the
front face of the contact body and cleaved thereat, and
subsequently the cleaved optical fiber end is retracted so as to be
flush against the front face of the contact body.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view of a preferred embodiment of an
optical fiber contact constructed according to the present
invention; and
FIG. 2 is an enlarged more detailed cross-sectional view of a front
portion of the optical fiber contact of the invention which lacks a
preformed adhesive bore 53 shown in FIG. 1 but which is otherwise
identical in construction with the contact of FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 illustrates a preferred embodiment of an optical fiber
contact 11 for terminating an optical fiber 73, and FIG. 2
illustrates details of a front end 52 of the contact 11.
Referring to FIGS. 1 and 2, the optical fiber contact 11 comprises
a ring 59 and first and second tubes 50, 58. Preferably, the ring
59 and a flange 60 of the second tube 58 are formed so that an
outside diameter of the flange 60 and an inside diameter of the
ring 59 are closely sized such that a press fit therebetween is
created. Extending forward of the flange 60 is a reduced diameter
section 86 which has an outside diameter which closely corresponds
to an inside diameter of the first tube 50 such that the first and
second tubes 50, 58 telescopically mate in a press fitting
manner.
In many applications, it is advantageous if a distance 1 (FIG. 2)
between a fixed reference point, in this case a front face 85 of
the ring 59, and a front face 61 of the contact is precisely
controlled so that an end 87 of the optical fiber, which is flush
with the front face 61 of the contact 11, can be precisely axially
positioned relative to a light source so as to be optimally
situated with respect thereto so as to receive an optimum amount of
light from the light source. To this end, prior art contacts have
generally been precisely machined so as to precisely control a
longitudinal length thereof relative to a fixed reference point
such as a ring or seating flange so that the front end 87 of the
optical fiber 73 could be precisely positioned longitudinally
relative to another element such as a light source.
However, with the invention, since the first and second tubes 50,
58 are press fit together in a variable manner, a longitudinal
length of the first tube 50 is not required to be precisely
controlled since when the first and second tubes 50, 58 are
telescopically assembled, the first tube 50 is slideably engaged
over the section 86 only a distance sufficient such that the
distance 1 equals a predetermined value. In other words, a gap 63
between the front face 85 of the ring 59 and a back end of the tube
50 compensates for variations in length of the tube 50 such that a
length of the gap 63 plus a length of the tube 50 always equals the
value 1. In practice, it is a relatively expedient matter to
assemble the tubes 50, 58 so to achieve the value 1 between the
front face 61 and the front face 85, whereas it is much more
difficult to precisely fabricate elements so as to have a precise
longitudinal length as is done with prior art contacts.
FIG. 2 further illustrates a cavity 54 within the first tube 50,
the cavity being formed by the assembly of parts 50, 58 and 59. A
thermoset 55 is disposed within the cavity 54, the thermoset
comprising a multipart solid material mixture, one example being an
epoxy mixture. The thermoset 55 is disposed in the cavity 54 in a
substantially unreacted form, and includes chemicals which when
liquified mix and chemically react so as to form an adhesive, the
chemical reaction preferably including crosslinking curing.
Subsequent to curing and cooling, the mixture 55 provides a strong
bond capable of adhering over a wide temperature range.
Specifically, the thermoset 55 when heated softens, liquifies,
mixes and cures to form an adhesive capable of adhering to the
optical fiber 73 and the inside of the tube 50. The use of a solid
multipart thermoset pre-installed within the tube 50 is
advantageous since the user is not required to mix multiple shelf
life sensitive materials in the field so as to form an adhesive for
terminating an optical fiber. However, it should be noted that
contact illustrated in FIGS. 1 and 2 can be used with liquid
epoxies mixed in the field as well as other fiber termination
techniques, the use of the pre-installed solid multipart thermoset
comprising one preferred embodiment of the invention.
If a solid multipart thermoset is used, two further embodiments are
to completely fill the cavity 54 with the thermoset 55 or
alternatively to form the thermoset 55 so as to have a preformed
bore 53 (FIG. 1) in a central regional thereof which aligns with
aperture 51 of the front end 52 of the contact tube 50. If the bore
53 is so preformed, to terminate an optical fiber, the user simply
inserts the optical fiber through the bore 53 and the aperture 51
for termination, accurately positions the front end 87 of the fiber
relative to the contact face 61, and then heats the tube 50 so as
to liquify the thermoset and secure the fiber within the contact.
When liquified, a portion of the thermoset will wick into the
aperture 51.
For the embodiment where the thermoset completely fills a
transverse cross-sectional area and volume of the cavity 54, the
user must heat the contact tube 50 so as to soften and liquify the
thermoset 55 after which the optical fiber 73 can be inserted
through the hot thermoset and through the contact aperture 51. With
this embodiment, since the optical fiber is inserted through the
liquified thermoset 55, the insertion of the optical fiber through
the thermoset 55 will cause a portion of the thermoset to be
disposed within the aperture 51 and enhance the wicking effect so
as to better secure the optical fiber in place, with a portion of
the thermoset 55 further adhering to an end of the optical fiber.
In this case it is advantageous to formulate the thermoset 55 so as
to be substantially optically transparent and so as to have an
index of refraction preferably close to that of a core of the
optical fiber being terminated in which case the portion of the
thermoset 55 on a front end of the optical fiber can function as an
index matching medium when the terminated optical fiber is abutted
against another similarly terminated optical fiber. Preferably,
when the thermoset 55 hardens, it forms a relatively hard but
resiliently deformable material which will conform to a similar
relatively hard resiliently deformable material on an end of the
other contact to be optically connected with the terminated optical
fiber 73. This allows the contact 11 to be resiliently urged
towards its mating contact and eliminates any air gap between the
optically coupled fibers.
A further advantageous feature of the contact 11 is the provision
of a reservoir 62 adjacent the front end 61 in a vicinity of the
aperture or passageway 51 of the contact body 50, the embodiment
illustrated in FIG. 2 being conical in shape. The function of the
reservoir 62 becomes apparent when it is realized that any
relatively hard solid resiliently deformable index matching
material disposed on an end of the optical fiber 73 will tend to be
displaced when urged against a similar index matching material when
the terminated optical fiber is optically connected to another
terminated optical fiber. The reservoir 62 provides an area for the
compressed index matching material to expand into which allows an
excellent continuous interface to be formed between the optical
fibers being interconnected so as to eliminate any air gap and
associated optical losses which an air gap may otherwise
create.
A further feature of the invention, illustrated in FIG. 1, is the
provision of annular flanges 66 formed on a back portion of the
contact 11, and a solid adhesive 72 disposed on the exterior
surface of the contact 11 and in adherence therewith. Adjacent
flanges 66 form annular reservoirs for containing the adhesive 72.
The adhesive 72 and the flanges 66 provide an efficient and
convenient means for clamping onto braids 67 of an optical fiber
cable containing the optical fiber 73 being terminated.
As illustrated in FIG. 1, by disposing the braids 67 longitudinally
along the contact 11 so as to confront the adhesive 72 and the
flanges 66, and by disposing a force means 68 around the braids
which is capable of generating inwardly directed radial forces onto
the braids 67, the braids 67 can be urged into the adhesive 72 and
furthermore pinned between the force means 68 and the flanges 66.
With this structure, axial pull out forces exerted on the cable are
transferred to the exterior surface of the contact 11 via the
braids 67, flanges 66, and adhesive 72 thus isolating the optical
fiber itself from these axial pull out forces. A preferred adhesive
is KYNAR.TM., with polypropylene or nylon being possible as
well.
According to one preferred embodiment, the force means 68 comprises
a dimensionally recoverable member, preferably a heat recoverable
sleeve, which has the property of shrinking and generating radially
inwardly directed forces when heated. Hoop stresses generated by
recovery of the sleeve 68 thus urge the braids 67 into the adhesive
72 and pin the braids 67 against the flanges 66 upon recovery of
the sleeve 68. In addition, the sleeve 68 can further provide an
environmental barrier around a joint between the optical fiber
cable and the contact 11.
The contact 11 further includes a flange 88, which in conjunction
with the ring 59, provide an area for retaining a compression
spring 90. The spring 90 provides a means for urging the contact 11
in an axial direction when the contact 11 is assembled within a
connector for connecting the contact 11 with a similar additional
contact 11.
The invention further includes several means of terminating an
optical fiber. Prior art optical fiber termination techniques
generally require that the optical fiber be inserted into a contact
so that a front end of the fiber extends beyond a front face of the
optical fiber contact, with the optical fiber then being cleaved at
a position flush with the front face of the optical fiber contact
and then being polished thereat.
On the other hand, according to the methods of terminating an
optical fiber according to the invention, according to a first
embodiment, the optical fiber is first cleaved prior to inserting
it within the optical fiber contact 11. Thereafter, the cleaved
optical fiber end is inserted through the contact 11. A hard
resiliently deformable index matching material 87 is then disposed
on the end of the fiber, or alternatively the material 87 can
comprise part of the liquid thermoset 55 in the embodiment where
the thermoset is liquified using heat prior to inserting the fiber
through the passageway 51. Thereafter, the end of the fiber is
precisely positioned so as to be flush with a plane of the front
face 61 of the contact 11.
According to an alternative preferred method of the invention, the
optical fiber is not first cleaved, and is simply inserted through
the contact 11 so as to extend beyond a front face 61 of the
contact to a vicinity of a point such as that illustrated by the X
identified by reference number 91 in FIG. 2. Thereafter, the
optical fiber is cleaved at the point 91, retracted so as to be
flush with the front face 61, and thereafter an index matching
material is disposed on an end of the optical fiber. Such a
termination procedure does not require that the optical fiber be
polished as do prior art techniques. In addition, if a relatively
hard resiliently deformable index matching material is disposed on
the end of the optical fiber subsequent to cleaving, an efficient
means of optically connecting the optical fiber 73 is provided
since substantially no air gap will exist across an optical joint
when the resiliently deformable index matching material is pressed
against another similar type of index matching material. As
explained previously, the reservoir 62 provides a means for
allowing the index matching material to deform when pressed using
compression forces of the spring 90 so as to insure that no air gap
exists across the optical joint.
Finally, if desired, a back end of the contact 11 can contain some
type of potting material, such as a potting adhesive in a vicinity
of reference numberal 80, though this is not required.
According to a preferred embodiment, the thermoset 55 includes an
epoxy resin, a curing agent and an accelerator, all disposed in the
cavity 54 in solid form such that they substantially do not react
over time until heated above a predetermined temperature. One
preferred embodiment is a mixture of 100 parts novolac epoxy
available from Ciba-Geigy as product ECN1299, 2-10 parts
dicyandiamide available from Aldrich Chemical Co. as product
dicyandiamide, a preferred amount being 8 parts, and 0.3-2 parts
imidazole available from Shikokou Chemical Co. as product 2P4MHZ a
preferred amount being 0.5 parts. The latter two chemicals comprise
a curing agent and an accelerator, respectively.
Another thermoset example found useful but less preferred than the
aforementioned mixture is 100 parts of the novolac epoxy as
described above, 2-10 parts, preferably 8 parts, substituted
dicyandiamide available from Ciba-Geigy as product Hardener HT2833
and 0.3-2 parts, preferably 0.5 parts, imidazole as described
above. Another alternative sealant composition comprises 100 parts
of novolac epoxy, 20-40 parts, preferably 30 parts, of Sumicure S
available from Sumitomo Chemical Co. and 0.3-2 parts, preferably
0.5 parts imidazole as described above. It should readily be
understood that other alternative thermoset compositions can be
used in accordance with the invention, the above three being
preferred compositions only.
EXAMPLE
A thermoset mixture comprising 100, 8, and 0.5 parts of novolac,
dicyandiamide and imidazole, respectively, was used to secure an
optical fiber within a stainless steel capillary tube, and after
curing was heated to a temperature of 150.degree. C. whereat a
pull-out strength test was conducted by pulling on the optical
fiber longitudinally relative to the stainless steel capillary
tube, and during this test the optical fiber fractured prior to the
adhesive. A glass transition temperature Tg of this thermoset
composition was measured and found to be 170.degree. C.-180.degree.
C. The thermoset was further used to secure two stainless steel
plates together, and at 150.degree. C. a lap sheer strength test
was conducted whereat the thermoset was found to fail at
approximately 950 psi. No weight loss for the cured thermoset
composition was found to occur until approximately 300.degree. C.
as measured by a thermogravimetric analysis test (TGA).
Although the invention has been described with reference to
particular embodiments thereof, it should be understood that
various modifications thereto can be made within the spirit and
scope of the invention, and accordingly the invention is to be
limited only by the appended claims.
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