U.S. patent application number 10/198813 was filed with the patent office on 2002-12-05 for optical fiber feedthrough assembly and method of making same.
Invention is credited to Chipman, Christopher, Currier, Bradley A., Grunbeck, John, Maron, Robert J..
Application Number | 20020181909 10/198813 |
Document ID | / |
Family ID | 24517533 |
Filed Date | 2002-12-05 |
United States Patent
Application |
20020181909 |
Kind Code |
A1 |
Grunbeck, John ; et
al. |
December 5, 2002 |
Optical fiber feedthrough assembly and method of making same
Abstract
In an optical waveguide feedthrough assembly, and method of
making such an assembly, a tubular member defines an axially
elongated, annular surface, and the annular surface forms an
axially elongated optical feedthrough cavity. An optical fiber or
like waveguide is received through the axially-elongated optical
feedthrough cavity, and is spaced radially inwardly relative to the
annular surface to thereby define an axially-elongated annular
cavity between the fiber and annular surface. An epoxy adhesive is
introduced in its liquid phase into one end of the annular cavity,
and is allowed to fill the annular cavity by capillary action. Upon
filling the annular cavity, the epoxy hardens and cures and, in
turn, adhesively secures the optical fiber within the tubular
member. The annular surface defines a plurality of constrictions in
the annular cavity to further secure the solid epoxy plug within
the cavity, and prevent the plug from moving in response to
axially-directed forces encountered in
Inventors: |
Grunbeck, John; (Northford,
CT) ; Chipman, Christopher; (Scotland, CT) ;
Currier, Bradley A.; (Guilford, CT) ; Maron, Robert
J.; (Cromwell, CT) |
Correspondence
Address: |
Cummings & Lockwood LLC
Grantie Square
700 State Street
P.O. Box 1960
New Haven
CT
06509-1960
US
|
Family ID: |
24517533 |
Appl. No.: |
10/198813 |
Filed: |
July 18, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10198813 |
Jul 18, 2002 |
|
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09628114 |
Jul 28, 2000 |
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6445868 |
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Current U.S.
Class: |
385/123 |
Current CPC
Class: |
G02B 6/3644 20130101;
G02B 6/4248 20130101 |
Class at
Publication: |
385/123 |
International
Class: |
G02B 006/02 |
Claims
What is claimed is:
1. An optical waveguide feedthrough assembly for passing at least
one optical waveguide through a feedthrough member, comprising: at
least one axially elongated surface defining an axially elongated
optical feedthrough cavity, wherein the optical feedthrough cavity
is defined by an outer dimension having at least one variation
along the axial direction thereof; at least one optical waveguide
received through the axially-elongated optical feedthrough cavity,
and spaced relative to the axially-elongated surface; and a sealant
received within the cavity and extending between the at least one
optical waveguide and the axially-elongated surface, and extending
axially within the cavity from approximately one end to
approximately another end thereof, wherein the sealant exhibits
adhesive properties at the interface of the sealant and the at
least one optical waveguide, and at the interface of the sealant
and the axially-elongated surface, to secure the at least one
optical waveguide within the optical feedthrough cavity, and
wherein the sealant cooperates with the at least one variation in
the outer dimension defining the cavity to substantially prevent
axial movement of the sealant relative to the axially-elongated
surface.
2. An optical waveguide feedthrough assembly as defined in claim 1,
wherein the axially-elongated surface defines an annular surface,
and an axially-elongated annular cavity between the at least one
optical waveguide and the axially-elongated surface.
3. An optical waveguide feedthrough assembly as defined in claim 1,
wherein the sealant is a polymeric sealant.
4. An optical waveguide feedthrough assembly as defined in claim 1,
wherein the axially-elongated surface defines at least one first
surface area and contiguous second surface area spaced radially
inwardly relative to the first surface area, and wherein the first
and second surface areas form the at least one variation in the
outer dimension defining the optical feedthrough cavity for
preventing axial movement of the polymeric sealant relative to the
annular surface.
5. An optical waveguide feedthrough assembly as defined in claim 4,
wherein the second surface area defines an annular surface area
extending around the at least one optical waveguide.
6. An optical waveguide feedthrough assembly as defined in claim 4,
wherein the axially-elongated surface defines a plurality of first
surface areas spaced relative to each other in the axial direction
of the optical feedthrough cavity, and a plurality of contiguous
second surface areas spaced radially inwardly relative to the
respective first surface areas for preventing axial movement of the
polymeric sealant relative to the annular surface.
7. An optical waveguide feedthrough assembly as defined in claim 4,
further defining at least one transition region between the first
and second contiguous surface areas, and wherein the at least one
transition region forms a rounded surface for facilitating the flow
of sealant through the cavity upon introduction of the sealant into
the cavity.
8. An optical waveguide feedthrough assembly as defined in claim 1,
wherein the axially elongated surface is defined by at least one
tubular member.
9. An optical waveguide feedthrough assembly as defined in claim 8,
further comprising a first support mountable within the feedthrough
member and defining a first mounting surface for receiving and
supporting the tubular member within the feedthrough member.
10. An optical waveguide feedthrough assembly as defined in claim
9, further comprising a second support defining an elongated
aperture for receiving therethrough the at least one tubular
member, and a second mounting surface for receiving and supporting
the first support thereon, wherein the second support is mountable
within the feedthrough member for fixedly mounting the assembly to
the feedthrough member and forming a hermetic seal at the interface
of the second support and feedthrough member.
11. An optical waveguide feedthrough assembly as defined in claim
1, wherein the at least one optical waveguide and axially-elongated
surface are approximately concentric.
12. An optical waveguide feedthrough assembly as defined in claim
1, wherein the axially-elongated surface defines at least one
approximately cylindrical portion.
13. An optical waveguide feedthrough assembly as defined in claim
3, wherein the polymeric sealant is an epoxy.
14. An optical waveguide feedthrough assembly as defined in claim
1, wherein the sealant is capable of exhibiting a liquid phase and
a solid phase, and in the liquid phase the sealant exhibits a
viscosity within the range of approximately 3,000 centipoises
through approximately 85,000 centipoises.
15. An optical waveguide feedthrough assembly as defined in claim
1, wherein the sealant exhibits a liquid phase and a solid phase,
and the cavity defines a width extending between the at least one
optical waveguide and the axially-elongated surface sufficient to
allow the sealant in its liquid phase to fill the cavity from
approximately one end to approximately the other end thereof by
capillary action.
16. An optical waveguide feedthrough assembly as defined in claim
1, wherein the sealant exhibits a liquid phase and a solid phase,
and in its solid phase is substantially free of voids.
17. An optical waveguide feedthrough assembly as defined in claim
14, wherein the sealant is approximately 100% solids.
18. An optical waveguide feedthrough assembly as defined in claim
1, wherein the sealant forms a hermetic seal between the at least
one optical waveguide and the axially-elongated surface.
19. An optical waveguide feedthrough assembly as defined in claim
1, wherein the at least one optical waveguide is an optical
fiber.
20. At least one optical waveguide feedthrough assembly as defined
in claim 1 in combination with an optical sensor assembly, wherein
the optical sensor assembly includes a housing, a sensor cavity
formed within the housing, and an optical sensor located within the
housing, and wherein the feedthrough member of the at least one
optical feedthrough assembly is defined by a wall of the
housing.
21. At least one optical waveguide feedthrough assembly and optical
sensor assembly as defined in claim 20, comprising at least one
optical pressure sensor and at least one optical temperature sensor
optically coupled to the optical waveguide of the optical waveguide
feedthrough assembly.
22. An optical waveguide feedthrough assembly as defined in claim
1, having a relatively high pressure side at one end of the optical
feedthrough cavity, and a relatively low pressure side at the
opposite end of the optical feedthrough cavity, and wherein the
axially-elongated surface defines a first annular portion located
at the high pressure side and defining a first width, and a second
annular portion spaced axially inwardly relative to the first
annular portion and defining a second width, wherein the first
width is less than the second width to thereby minimize forces
applied to the sealant at the high pressure side of the
assembly.
23. An optical waveguide feedthrough assembly as defined in claim
1, wherein the cavity defines a width in a radial direction between
the at least one optical waveguide and the axially-elongated
surface, and defines a length in the axial direction from
approximately one end of the axially-elongated surface to the
other, and wherein the length of the cavity is at least
approximately 50 times the width.
24. An optical waveguide feedthrough assembly as defined in claim
23, wherein the axis of the cavity is defined by a straight
line.
25. An optical waveguide feedthrough assembly for passing at least
one optical waveguide through a feedthrough member, comprising: at
least one axially elongated surface defining an axially elongated
optical feedthrough cavity; at least one optical waveguide received
through the axially-elongated optical feedthrough cavity, and
spaced relative to the axially-elongated surface; first means
received within the optical feedthrough cavity and extending within
the cavity between the at least one optical waveguide and the
axially-elongated surface, and extending axially within the cavity
from approximately one end to approximately another end thereof,
for adhesively securing and hermetically sealing the at least one
optical waveguide within the cavity; and second means for
preventing movement of the first means in the axial direction
relative to the axially-elongated surface.
26. An optical waveguide feedthrough assembly as defined in claim
25, wherein the second means includes at least one first surface
area formed on the axially-elongated surface, at least one
contiguous second surface area spaced radially inwardly relative to
the first surface area on the axially-elongated surface, and at
least one transition surface area formed between the first and
second surface areas, and wherein the first, second and transition
surface areas adhesively engage the first means to prevent axial
movement of the first means.
27. An optical waveguide feedthrough assembly as defined in claim
26, wherein the second surface area forms an annular constriction
within the cavity.
28. An optical waveguide feedthrough assembly as defined in claim
25, wherein the first means includes a tubular body forming the
axially-elongated surface.
29. An optical waveguide feedthrough assembly as defined in claim
25, wherein the at least one optical waveguide and
axially-elongated surface are approximately concentric.
30. An optical waveguide feedthrough assembly as defined in claim
25, wherein the second means includes a sealant substantially
filling the cavity.
31. An optical waveguide feedthrough assembly as defined in claim
30, wherein the sealant exhibits a liquid phase and a solid phase,
and the assembly further comprises means for allowing the sealant
in its liquid phase to fill the cavity from approximately one end
to approximately the other end thereof by capillary action.
32. At least one optical waveguide feedthrough assembly as defined
in claim 25 in combination with an optical sensor assembly, wherein
the optical sensor assembly includes a housing, a sensor cavity
formed within the housing, and an optical sensor located within the
housing, and wherein the feedthrough member is defined by a wall of
the housing.
33. An optical waveguide feedthrough assembly as defined in claim
25, having a relatively high pressure side at one end of the
optical feedthrough cavity, and a relatively low pressure side at
the opposite end of the optical feedthrough cavity, and including
means for reducing the forces applied to the first means at the
high pressure side of the optical feedthrough cavity.
34. An optical waveguide feedthrough assembly as defined in claim
33, wherein the means for reducing the forces applied to the first
means includes the axially-elongated surface defining a first
annular portion located at the high pressure side and defining a
first width, and a second annular portion spaced axially inwardly
relative to the first annular portion and defining a second width,
wherein the first width is less than the second width to thereby
reduce the forces applied to the first means at the high pressure
side of the assembly.
35. A method of making an optical waveguide feedthrough assembly
including a feedthrough member for receiving therethrough at least
one optical waveguide, an axially-elongated surface defining
therein an axially elongated optical feedthrough cavity, at least
one optical waveguide received within the cavity, and a sealant
exhibiting a liquid phase and a solid phase and received within the
cavity for adhesively securing the at least one optical waveguide
within the cavity, said method comprising the steps of: forming the
cavity with a predetermined width between the at least one optical
waveguide and the axially-elongated surface to allow the sealant in
its liquid phase to substantially fill the cavity by capillary
action; selecting a sealant capable of exhibiting a viscosity which
allows the sealant to substantially fill the cavity by capillary
action, and capable of exhibiting a viscosity which substantially
prevents leakage of the sealant out of at least one end of the
cavity upon substantially filling the cavity; and introducing the
sealant in its liquid phase into the cavity and allowing the
sealant to substantially fill the cavity by capillary action;
wherein upon substantially filling the cavity, the sealant
transitions to its solid phase and adhesively secures the at least
one optical waveguide within the cavity and substantially prevents
movement of the sealant and the at least one optical waveguide
relative to the axially-elongated surface.
36. A method as defined in claim 35, further comprising the step of
forming at least one radially projecting interruption in the cavity
to further prevent axial movement of the sealant.
37. A method as defined in claim 35, further comprising the steps
of preheating at least one of the axially-elongated surface and at
least one optical waveguide to a predetermined elevated
temperature, introducing the liquid sealant into the cavity and
heating the sealant upon contacting at least one of the
axially-elongated surface and at least one optical waveguide and,
in turn, reducing the viscosity of the sealant to facilitate
filling the cavity by capillary action.
38. A method as defined in claim 37, wherein the sealant includes
an epoxy, and the predetermined elevated temperature is at least
the approximate first stage cure temperature of the epoxy.
39. A method as defined in claim 35, further comprising the step of
positioning the at least one optical waveguide approximately
concentric with the axially-elongated surface within the optical
feedthrough cavity.
40. A method as defined in claim 39, wherein the axially-elongated
surface is defined by a tubular body, and the positioning step
includes mounting at least one end of the tubular body to a
multi-axis translation stage, applying tension to the at least one
optical waveguide, and adjusting at least one of the translation
stages to align the at least one optical waveguide concentrically
with the axially-elongated surface.
41. A method as defined in claim 35, wherein the sealant exhibits
in its liquid phase a viscosity within the range of approximately
3,000 centipoises through approximately 85,000 centipoises.
42. A method as defined in claim 35, wherein the axially elongated
surface is defined by at least one tubular body, and the optical
waveguide feedthrough assembly further includes a first support
mountable within the feedthrough member and defining a first
mounting surface for receiving and supporting the tubular body
within the feedthrough member, and a second support defining an
elongated aperture for receiving therethrough the at least one
tubular body, and a second mounting surface for receiving and
supporting the first support therein, said method further
comprising the steps of: fixedly securing the tubular body to the
first support; fixedly securing the tubular body and first support
to the second support; installing the at least one optical
waveguide within the optical feedthrough cavity; and then
introducing the sealant in its liquid phase into the optical
feedthrough cavity and allowing the sealant to substantially fill
the cavity by capillary action.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] This application is a continuation of co-pending U.S. patent
application Ser. No. 09/628,114, filed Jul. 28, 2000, the
disclosure of which is hereby incorporated by reference in its
entirety.
TECHNICAL FIELD
[0002] The present invention relates to feedthroughs for optical
waveguides, and more particularly, to hermetically sealed
feedthroughs suitable for use in high pressure, high temperature,
and/or other harsh environments.
BACKGROUND ART
[0003] In many industries and applications, there is a need to have
small diameter wires or optical waveguides penetrate a wall,
bulkhead, or other feedthrough member wherein a relatively high
fluid or gas differential pressure exists across the feedthrough
member. In addition, one or both sides of the feedthrough member
may be subjected to relatively high temperatures and other harsh
environmental conditions, such as corrosive or volatile gas, fluids
and other materials. In the case of electrical wires, these
devices, called feedthroughs or penetrators, typically are
constructed by using electrically conductive metal `pins` having a
low thermal coefficient of expansion. The pins are concentrically
located within a hole in a housing, and the resulting annular space
is filled with a suitable sealing glass. Critical to the success of
such seals is the selection and approximate matching of the thermal
expansion rates of the various materials, i.e., the metal housing,
sealing glass, and electrical pin. As the temperature range over
which the feedthrough is exposed increases, the matching of thermal
expansion rates becomes increasingly important in order to avoid
failure of the feedthrough by excessive thermal stress at the
interface layers between the various materials. This technology is
relatively mature for electrical feedthroughs, and commercial
devices are readily available that meet service temperatures in
excess of 200.degree. C.
[0004] More recently, with the introduction of optical sensors,
particularly sensors for use in oil and gas exploration and
production, a need has emerged for a bulkhead feedthrough that can
seal an optical fiber at high pressures of 20,000 psi and above,
and high temperatures of 150.degree. C. to 250.degree. C., with
desired service lives of 5 to 10 years. The sensing assembly of
FIG. 3 is of the type disclosed in co-pending U.S. patent
application Ser. No. 09/440,555 filed Nov. 15, 1999, entitled
"Pressure Sensor Packaging For Harsh Environments", which is
assigned to the Assignee of the present invention and is hereby
expressly incorporated by reference as part of the present
disclosure (CiDRA Docket No. CC-0198).
[0005] There are several problems associated with constructing such
an optical fiber feedthrough. One of these problems is the
susceptibility of the glass fiber to damage and breakage. This is
due to the small size of the fiber, the brittle nature of the glass
material, the susceptibility of the glass to stress corrosion
cracking due to moisture exposure, and the typical presence of a
significant stress concentration at the point at which the fiber
enters and exits the feedthrough. Attempts to use a hard sealing
glass, such as used with electrical feedthroughs, have had problems
of this nature due to the high stress concentration at the
fiber-to-sealing glass interface.
[0006] Another problem with sealing an optical fiber, as opposed to
sealing an electrically-conductive metal `pin` in an electrical
feedthrough, is that the fused silica material of which the optical
fiber is made, has an extremely low thermal expansion rate.
Compared to most engineering materials, including metals, sealing
glasses, and even the metal `pins` typically used in electrical
feedthroughs, the coefficient of thermal expansion of the optical
fiber is essentially zero. This greatly increases the thermal
stress problem at the glass-to-sealing material interface,
particularly as the application temperatures rise.
[0007] One technique used to produce optical fiber feedthroughs is
the use of a sealed window with a lensing system. In this
technique, the optical fiber must be terminated on each side of a
pressure-sealed window, thus allowing the light to pass from the
fiber into a lens, through the window, into another lens, and
finally into the second fiber. The disadvantages associated with
this system include the non-continuous fiber path, the need to
provide two fiber terminations thus increasing manufacturing
complexity, and the light attenuation associated with these
features.
[0008] Another approach to producing optical fiber feedthroughs
involves passing the fiber through a bulkhead without termination,
while providing a seal around the fiber to prevent leakage across
the bulkhead. One such seal has been implemented by means of a
sapphire compression fitting to take advantage of the pressure
differential typically present across a bulkhead in a harsh
environment. One disadvantage associated with this type of seal,
however, is that it has been found to suffer from creep of material
across the bulkhead in the direction of the decreasing pressure
gradient, which can, in turn, compromise both the optical fiber and
seal.
[0009] It is often desirable to mount fiber optic based sensors in
harsh environments that are environmentally separated from other
environments by physical bulkheads. An exemplary such fiber optic
based sensor is disclosed in co-pending U.S. patent application
Ser. No. 09/205,944 (Docket No. CC-0036) entitled "Tube-Encased
Fiber Grating Pressure Sensor" to T. J. Bailey et al., which is
assigned to the Assignee of the present invention and is hereby
expressly incorporated by reference as part of the present
disclosure. This exemplary optical sensor is encased within a tube
and certain embodiments are disclosed wherein the sensor is
suspended within a fluid. Some such fiber optic sensors have
sensors and tubes that are comprised of glass, which tends to be
relatively fragile, brittle and sensitive to cracking. Thus, the
use of such a sensor in a harsh environment, such as where the
sensor would be subjected to substantial levels of pressure,
temperature, shock and/or vibration, presents a significant threat
of damage to the sensor. In certain environments, such sensors are
subjected to continuous temperatures in the range of 150.degree. C.
to 250.degree. C., shock levels in excess of 100 Gs, and vibration
levels of 5G RMS at typical frequencies between about 10 Hz and 200
Hz and pressures of about 15 kpsi or higher.
[0010] However, as discussed above, the harsh environments where
the sensors are located generally must be isolated by sealed
physical barriers from other proximate environments through which
the optical fiber communication link of the sensor must pass. It is
important to seal the bulkhead around the optical fiber to prevent
adjacent environments from contamination, as well as to protect the
optical fiber as it passes through adjacent environments. If the
optical fiber is compromised by contamination from an adjacent
harsh environment, the optical fiber and all sensors to which it is
connected are likely to become useless.
[0011] Accordingly, it is an object of the present invention to
provide an optical waveguide feedthrough assembly, and a method of
making such an assembly, which overcomes one or more of the
above-described drawbacks and disadvantages of the prior art, and
is capable of relatively long-lasting operation at relatively high
pressures and/or temperatures.
SUMMARY OF THE INVENTION
[0012] The present invention is directed to an optical waveguide
feedthrough assembly for passing at least one optical waveguide,
such as an optical fiber, through a sensor wall, bulkhead, or other
feedthrough member. The feedthrough assembly of the present
invention comprises a tubular member or like support defining an
axially elongated, annular surface, wherein the annular surface
forms an axially elongated optical feedthrough cavity. The optical
fiber or like waveguide is received through the axially-elongated
optical feedthrough cavity, and is spaced radially inwardly
relative to the annular surface to thereby define an
axially-elongated annular cavity between the fiber and annular
surface. A sealant, such as an epoxy adhesive, is received within
and substantially fills the annular cavity. The sealant exhibits
adhesive properties at the interface of the sealant and optical
fiber, and at the interface of the sealant and the annular surface,
to adhesively secure and hermetically seal the optical fiber within
the feedthrough cavity and substantially prevent axial movement of
the sealant and optical fiber relative to the annular surface.
[0013] The optical feedthrough cavity is defined by an outer
dimension having one or more variations along the axial direction
thereof, and the dimensional variations cooperate with the sealant
to further prevent axial movement of the sealant relative to the
annular surface. In accordance with an embodiment of the present
invention, the annular surface of the tubular member defines one or
more annular constrictions or like radially projecting
interruptions forming the variations in the outer dimension of the
annular cavity for further preventing movement of the epoxy or like
sealant plug in the axial direction.
[0014] The present invention is also directed to a method of making
an optical feedthrough assembly, including the following steps: (a)
forming the annular cavity of the tubular member with a
predetermined width between the optical fiber and the annular
surface to allow the epoxy or other sealant in its liquid phase to
substantially fill the annular cavity by capillary action; (b)
selecting a polymeric or other type of sealant capable of
exhibiting a viscosity which allows the sealant to substantially
fill the annular cavity by capillary action, and also capable of
exhibiting a viscosity which substantially prevents leakage of the
sealant out of the ends of the annular cavity upon filling the
cavity; (c) introducing the polymeric or other sealant in its
liquid phase into the annular cavity and allowing the sealant to
substantially fill the annular cavity by capillary action; and (d)
wherein upon filling the annular cavity, the polymeric or like
sealant transitions to its solid phase and adhesively secures the
fiber within the optical feedthrough cavity, and substantially
prevents movement of the solid epoxy or sealant plug out of the
cavity.
[0015] One advantage of the method and assembly of the present
invention is that they are capable of providing an optical
feedthrough assembly with minimal leakage and high longevity in
relatively high pressure, high temperature and other harsh
environments.
[0016] Another advantage of the method and assembly of the present
invention is that they enable the use of polymeric or like sealants
having low elastic moduli to thereby significantly improve the
resistance of the glass fiber to damage and breakage. Epoxies or
like sealants further provide a natural strain relief at the
interface between the glass fiber and the feedthrough assembly at
the points where the fiber enters and exits the feedthrough.
Accordingly, the feedthrough assemblies of the present invention
may exhibit significantly lower stress concentrations and improved
survivability in comparison to the prior art feedthroughs described
above.
[0017] Another advantage of the method and assembly of the present
invention is that they enable the use of a polymeric or like
sealant having a relatively low elastic modulus to minimize any
thermal stress at the interface of the optical fiber or like
waveguide and feedthrough assembly. As a result, the present
invention substantially avoids the problems encountered in the
above-described prior art feedthroughs wherein significant thermal
stresses are created at the interfaces of the optical fibers and
feedthroughs due to the extremely low rate of thermal expansion of
the optical fiber material in contrast to the adjoining material of
the prior art feedthroughs.
[0018] A further advantage of the method and assembly of the
present invention is that the feedthrough assembly may form a
continuous (or uninterrupted) fiber or like waveguide path from one
end of the assembly to the other. As a result, there is essentially
zero light attenuation when using, for example, single mode fiber
with a high numerical aperture (NA). Such high NA single mode
fiber, sometimes called `bend-insensitive` fiber, is typically used
in Bragg grating-based optical fiber sensors employed in oil and
gas exploration and production, where the low light attenuation
properties of the fiber are particularly useful in such systems
having sensors located at great distances from the light source
which interrogates the sensor.
[0019] These and other objects and advantages of the present
invention will become readily apparent in view of the following
detailed description of preferred embodiments and accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a cross-sectional view of an optical waveguide
feedthrough assembly embodying the present invention.
[0021] FIG. 2 is a cross-sectional view of the tubular member of
the feedthrough assembly of FIG. 1 for receiving therethrough at
least one optical waveguide.
[0022] FIG. 3 is a somewhat schematic, cross-sectional view of an
optical sensing assembly employing the optical waveguide
feedthrough assembly of FIG. 1.
BEST MODE FOR CARRYING OUT THE INVENTION
[0023] In FIG. 1, an optical waveguide feedthrough assembly
embodying the present invention is indicated generally by the
reference numeral 10. As shown in FIGS. 1 and 2, the feedthrough
assembly 10 comprises a feedthrough body or tubular member 12
defining an axially elongated, annular surface 14 extending from
approximately one end of the tubular member to the other, and an
optical feedthrough cavity 16 formed within the annular surface.
The annular surface 14 and feedthrough cavity 16 define an
elongated axis 18. As shown in FIG. 1, at least one optical
waveguide 20 is received through the feedthrough cavity 16, and is
spaced radially inwardly relative to the annular surface 14 to
thereby define an axially elongated annular cavity 22 between the
optical waveguide 20 and annular surface 14 and extending from one
end of the tubular member 12 to the other.
[0024] A flowable adhesive or sealant 24, such as a polymeric
sealant as will be more fully described herein below, is received
within the annular cavity 22, surrounds the optical waveguide 20,
and substantially fills the annular cavity 22 from approximately
one end of the tubular member 14 to the other. As described further
below, the sealant 24 exhibits liquid and solid phases, and is
introduced in its liquid phase into one end of the annular cavity
22 and fills the annular cavity by capillary action. Then, the
sealant 24 transitions from its liquid to its solid phase, and
exhibits adhesive properties at the interfaces of the sealant and
both the annular surface 14 and waveguide 20, to adhesively secure
and hermetically seal the waveguide within the tubular member.
[0025] The feedthrough assembly 10 further comprises a first
support 26 defining a first mounting surface 28 formed therethrough
for receiving one end of the tubular member 12, and a second
mounting surface 30 formed along the outer periphery of the first
support. A second support 32 defines an elongated aperture 34 for
receiving therethrough the tubular member 12, and a mounting recess
36 formed at one end of the support for receiving and fixedly
securing thereto the first support 26. The second support 32
defines an external mounting surface 38 for mounting the optical
feedthrough assembly 10 within a feedthrough member 40 in a
conventional manner, such as a metal-to-metal seal, o-ring seal, or
weldment.
[0026] As shown best in FIG. 2, the annular surface 14 defines an
inner dimension (which also defines the outer dimension of the
optical feedthrough cavity 16) having at least one variation along
the axial direction thereof, which, as described further below,
cooperates with the sealant 24 to substantially prevent movement of
the sealant and optical waveguide relative to the annular surface.
In the illustrated embodiment, the inner dimension of the annular
surface 14, and the outer dimension of the optical feedthrough
cavity 16, is the diameter "D", and as can be seen, the diameter
varies along the axial direction between the diameter "D1" and the
diameter "D2". As also shown in FIG. 2, in the illustrated
embodiment, the tubular member 12 defines a plurality of radially
inwardly projecting interruptions 42 in the annular cavity 22 and
axially spaced relative to each other that define the variations in
the diameter "D". The radially projecting interruptions 42 are
defined by first surface areas shown typically at 43, and
contiguous second surface areas shown typically at 44 that are
spaced radially inwardly relative to the first surface areas. In
the illustrated embodiment of the present invention, the radially
projecting interruptions 42 are formed by radially crimping the
tubular member 12 over a gage pin (not shown). As may be recognized
by those skilled in the pertinent based on the teachings herein,
numerous other techniques equally may be employed for creating the
radially inwardly projecting interruptions, such as by employing a
premolded tubular member. In addition, the outer surface of the
tubular member may be uniform and need not include dimensional
variation. As also shown best in FIG. 2, transition regions shown
typically at 45 extend between the first and second surface areas
43 and 44, respectively, and define smooth or rounded surfaces. As
described further below, the rounded transition regions 45 promote
the flow of sealant 24 throughout the annular cavity 22 in a
substantially laminar manner to thereby define a substantially
voidless layer of sealant.
[0027] One advantage of the radial projections 42 is that upon
filling the annular cavity 22 with the sealant 24, and
transitioning the sealant to its solid phase, the radial
projections cooperate with the sealant to further prevent axial
movement of the solid sealant plug and/or waveguide 20 in the axial
direction. In high-pressure applications, the pressure applied to
the sealant 24 at the high-pressure end of the assembly tends to
force the sealant axially within the tube. If sufficient, the high
pressure could over time break the adhesive bond between the
sealant and annular surface of the tube and, in turn, force or
extrude the sealant through the tube. However, the radial
projections 42 (or like dimensional variations) provide a
mechanical resistance to extrusion of the sealant out the
low-pressure end of the feedthrough assembly, thereby providing an
additional safety factor to the adhesive bonds. In addition, the
radial projections 42 of the tubular member provide mechanical
holding to prevent movement of the sealant plug in either the high
or the low-pressure directions due to applied thermal and/or
pressure cycles.
[0028] As may be recognized by those skilled in the pertinent art
based on the teachings herein, the feedthrough assembly of the
present invention may employ one or more such radially projecting
interruptions or like dimensional variations, and the interruptions
or like dimensional variations may take any of numerous different
shapes or configurations. For example, rather than have the second
surface portions 44 project radially inwardly, one or more of these
surface portions may project radially outwardly relative to the
contiguous second surface portion 43. In addition, the radially
projecting surface portions need not extend annularly about the
optical waveguide 20, but rather may extend over a more limited, or
different surface area. For example, the radially projecting
interruptions may be defined by one or more dimples or discrete
protuberances formed on the annular surface 14. Alternatively, the
radially projecting interruptions may be formed by discrete members
fixedly secured to the annular surface, or otherwise projecting
radially inwardly relative to the annular surface. Those skilled in
the pertinent art may further recognize based on the teachings
herein that the axially-elongated, annular surface 14 need not
define a circular cross-sectional configuration, but rather may
define any of numerous different shapes and/or configurations
without departing from the scope of the present invention.
[0029] At the high-pressure end 47 of the feedthrough assembly 10,
the sealant 24 is subjected to high-pressure fluid over its exposed
end face. The force per unit area applied by such high-pressure
fluid to the end face is a function of the outside diameter of the
sealant 24 (or the diameter or other dimension defining the optical
feedthrough cavity 16). Accordingly, as the outside diameter of the
sealant 24 (or the diameter of the annular surface 14 or
feedthrough cavity 16) is reduced, the reduction in total force
applied by the high pressure fluid to the end face of the sealant
24 is a function of the diameter squared (or is a function of the
circumference of the bond line to the annular surface 14 to the
first power). Accordingly, as shown in FIGS. 1 and 2, for
relatively high pressure applications, a radially projecting
interruption 42 is formed on at least the high pressure end 47 of
the tubular member 12 to thereby reduce the outer diameter of the
sealant 24 and, in turn, minimize the forces applied to the sealant
in the axial direction. As shown best in FIG. 2, an embodiment of
the tubular member 12 includes radially projecting interruptions 42
at both ends. The tubular member is similar to that disclosed in
the aforementioned US patent application CiDRA Docket number
CC-0293, filed contemporaneously herewith, the disclosure of which
is hereby incorporated by reference in it's entirety.
[0030] In an embodiment of the present invention, the sealant 24 is
an epoxy capable of withstanding temperatures within the range of
about 150.degree. C. to about 250.degree. C. and capable of
exhibiting a viscosity within the range of about 3,000 centipoises
through about 85,000 centipoises. In addition, the epoxy 24 in a
certain embodiment is a 100% solids epoxy. Epoxies that are
approximately 100% solids do not expel solvents or volatiles during
cure, and therefore create a substantially void-free epoxy layer
filling the annular cavity 22 from one end of the tubular member 12
to the other. Other epoxies may be used, depending on the
particular application; however, epoxies that are not 100% solids
may contain volatile compounds or solvents that escape or evaporate
during cure. Thus, if such epoxies are employed in the apparatus of
the present invention, any such volatiles might expand during cure
and expel some or all of the epoxy within the tubular member 12. As
a result, voids would likely remain within the annular cavity 22.
Any such voids could, in turn, create non-axisymmetric stress
fields, leading to high fiber stress, power attenuation in the
fiber due to fiber bending, and collapse of one or more of the
voids due to applied high pressures.
[0031] For long term service with high reliability, the sealant 24,
such as the epoxies described above, exhibit a glass transition
temperature that is significantly above the service temperature of
the feedthrough assembly. One such sealant is an anhydride cure
epoxy manufactured by Aremco Inc. under the designation "526N". The
glass transition temperature of this epoxy is approximately
160.degree. C. In addition, the viscosity of this epoxy at room
temperature is approximately 85,000 centipoises, which, when
employed in the present invention, is sufficiently high to prevent
capillary action from drawing the epoxy through the annular cavity
22 without first lowering the viscosity by preheating the tubular
member 12 and optical waveguide 20, as described further below.
[0032] As may be recognized by those skilled in the pertinent art
based on teachings herein, the sealant 24 may take the form of any
of numerous different sealants that are currently known or later
become known for performing the functions of the sealant 24. For
example, the sealant may take the form of any of numerous different
polymeric sealants, such as any of numerous different epoxies or
other thermoset resins, and such sealants may include fillers or
other agents for obtaining the desired physical characteristics of
the sealant for a particular application. For relatively high
pressure and/or high temperature environments, such as for use in
oil or gas wells, the sealant is preferably capable of withstanding
continuous temperatures of at least 150.degree. C., and continuous
pressures of at least 15 kpsi, and most preferably is capable of
withstanding continuous temperatures within the range of about
150.degree. C. to about 175.degree. C., and continuous pressures
within the range of about 15 kpsi to about 20 kpsi. In addition,
the preferred sealant for such applications is at such temperatures
and/or pressures capable of resisting creep (i.e., material flow)
and softening, and also is capable of maintaining the adhesive bond
between the sealant and annular surface 14 and between the sealant
and outer surface of the optical waveguide, such as the buffer
layer of an optical fiber.
[0033] As also may be recognized by those skilled in the pertinent
art based on the teachings herein, the optical waveguide 20 may be
any of numerous different devices that are currently or later
become known for conducting optical signals along a desired
pathway. Accordingly, the optical waveguide 20 may include, for
example, an optical fiber (such as a standard telecommunication
single mode optical fiber), an optical fiber having a Bragg grating
impressed (or embedded or imprinted) in the fiber, or any of
numerous other types of optical waveguides, such as multi-mode,
birefringent, polarization maintaining, polarizing, multi-core or
multi-cladding optical waveguides, or flat or planar waveguides,
any of which may be referred to as an optical fiber herein. In
addition, the feedthrough assembly 10 may include a single such
waveguide as shown in FIG. 1, or may include a plurality of such
waveguides.
[0034] As also may be recognized by those skilled in the pertinent
art based on the teachings herein, the body or tubular member 12
may be formed of any of numerous different materials that are
currently or later become known for performing one or more of the
functions of the tubular member (and annular surface) described
herein. For high pressure and/or high temperature applications, the
tubular member preferably exhibits high strength, corrosion
resistance, temperature and pressure stability, and predictably
induced plastic deformation. In an embodiment of the present
invention, the tubular member 12 is formed of an annealed nickel
alloy, such as the alloy sold by Inco Alloys International, Inc.
under the mark "Iconel 600". However, as indicated above, any of
numerous other materials may be suitable for the tubular member,
such as stainless steel, other nickel-based alloys, including
Incoloy.RTM. and Nimonic.RTM. (registered trademarks of Inco Alloys
International, Inc.), carbon, chromium, iron, molybdenum, and
titanium (e.g., Inconel 625). In addition, the tubular member 12
(or other structure forming the annular surface 14) may take any of
numerous different shapes or configurations. For example, rather
than a circular cross-sectional configuration, the tubular member
or annular surface may have a square, rectangular, oval,
elliptical, clam-shall or other desired shape.
[0035] In accordance with the method of the present invention, the
feedthrough assembly 10 is manufactured in accordance with the
following steps: (a) The annular cavity 22 is formed with a
predetermined minimum width "D" (FIG. 1) between the optical
waveguide 20 and the annular surface 14 to allow the sealant 24 in
its liquid phase to substantially fill the annular cavity by
capillary action; (b) A sealant 24 is selected which is capable of
exhibiting a viscosity which allows the sealant to substantially
fill the annular cavity 22 by capillary action, and also is capable
of exhibiting a viscosity which substantially prevents leakage of
the sealant out of one or both ends of the annular cavity upon
substantially filling the cavity. (c) Then, the sealant 24 is
introduced in its liquid phase into the annular cavity, and is
allowed to substantially entirely fill the annular cavity by
capillary action. Although the sealant may be introduced into the
annular cavity at either end, in a current embodiment, the sealant
is introduced at the high pressure end 47. (d) Upon filling the
annular cavity 22, the sealant 24 transitions to its solid phase
and adhesively secures the optical waveguide 20 within the optical
feedthrough cavity 16, and substantially prevents movement of the
sealant and the optical waveguide relative to the annular surface
14.
[0036] With the epoxy or like polymeric sealants of the present
invention, the annular surface 14 and optical waveguide 20 are
preheated to a predetermined elevated temperature prior to
introducing the epoxy into the annular cavity. The annular surface
and waveguide are heated to the first stage cure temperature of the
epoxy. Then, the epoxy is introduced into one end of the cavity and
heated to its first stage cure temperature upon contacting the
preheated annular surface 14 and optical waveguide 20. This, in
turn, reduces the viscosity of the epoxy to facilitate filling the
annular cavity at a relatively rapid rate by capillary action.
[0037] One important step in the method of this embodiment is to
select an adhesive or epoxy with a viscosity within a range that is
low enough to allow it to be drawn by capillary action into the
annular cavity 22, with or without lowering the viscosity by
preheating, within a reasonable period of time. For example, if
heat is applied to lower the viscosity prior to filling, but the
viscosity is still too high for reasonably rapid filling, the epoxy
may begin to harden and cure prior to filling the cavity and may
thereby prevent complete filling of the cavity. Alternatively, if
the viscosity of the epoxy is too low, the epoxy may not remain
contained within the annular cavity 22 for a long enough time for
curing to begin. As a result, the epoxy may leak out of the annular
cavity 22 and cause an incomplete fill.
[0038] As described above, in the current embodiment of the present
invention, an epoxy or other sealant capable of exhibiting a
viscosity within the range of about 3,000 centipoises to about
85,000 centipoises has proven to be effective in manufacturing the
optical feedthrough assemblies in accordance with the present
invention. In one embodiment, the tubular member 12 defines a
nominal inside diameter of about 0.022 inches, the overall length
of the tubular member 12 is about 2.0 inches, the outside diameter
of the fiber 20 over the buffer is about 0.006 inches, and the
epoxy exhibits a viscosity in the range of about 3,000 centipoises
to about 85,000 centipoises. In this embodiment, the diameter D2 is
preferably within the range of about 0.015 to about 0.030 inch, and
most preferably within the range of about 0.020 to about 0.025
inch. When the tubular member 12 and optical fiber 20 are preheated
to about 90.degree. C., the annular cavity 22 can be filled by
capillary action in less than approximate five (5) minutes.
Preferably, the maximum width "D2" (FIG. 1) of the annular plug of
sealant 24 is no more than approximately twice the diameter of the
optical waveguide(s) 20 (or maximum width) in order to fill the
annular cavity by capillary propagation (or "wicking").
[0039] Also in accordance with this embodiment of the present
invention, the tubular member 12 is first assembled to the first
support 26 and second support 32 prior to introducing the sealant
24 into the annular cavity 22. First, the first support 26 is
fixedly secured to the high-pressure end of the tubular member 26
using a technique such as laser welding, which allows precise
welding of relatively thin cross sectional parts like the tubular
member 12. As shown in FIG. 1, the first support 26 is in the form
of a cylinder; however, as may be recognized by those skilled in
the pertinent art based on the teachings herein, the first support
may take any of numerous other shapes or configurations. The first
support/tubular member assembly (26, 12) is then fixedly secured to
the second support 32 by, for example, welding, such as electron
beam welding.
[0040] Next, the optical waveguide or fiber 20 is installed
concentrically within the tubular member 12 with relatively high
precision, typically within a true position of about 0.001 inches.
One particularly versatile method of the invention that will
accommodate geometry variations in the tubular member and/or
waveguide is to utilize a high-precision, three-axis translation
stage (not shown) of a type known to those of ordinary skill in the
pertinent art on each end of the tubular member 12. Proper
adjustment of these stages, while maintaining mild tension on the
optical fiber sufficient to keep it straight, will align the fiber
concentrically within the metal tube. A significant advantage of
the approximately concentric alignment of the waveguide or fiber
with the annular surface is that it provides an axisymmetric stress
field on the fiber during epoxy curing, and during subsequent
thermal and fluid pressure loading.
[0041] Turning to FIG. 3, an optical sensing assembly employing the
optical waveguide feedthrough 10 of the present invention is
indicated generally by the reference numeral 50. The sensing
assembly of FIG. 3 is of the type disclosed in the aforementioned
co-pending U.S. patent application Ser. No. ______.
[0042] As shown in FIG. 3, the sensing assembly 50 comprises an
optical sensor 52 disposed within a volume 54 partially defined by
a sensor housing 56 that is filled with a viscous fluid 58 to
essentially "float" the sensor within the sensor housing. The
viscous fluid 58 "floats" sensor element 52 within sensor housing
56 providing fluid dampening to the sensor and allowing for uniform
pressure distribution about the sensor. The sensor 52 may be any of
numerous different types of optical sensors, such as pressure,
temperature and/or force sensors, that benefit from shock and
vibration protection. For example, the sensor 52 may be a pressure
sensor of the type described in one or both of the above-mentioned
U.S. Patent applications. In the case of a fiber optic based sensor
element 52, waveguide 20 may be comprised of one or more fiber
optic cables.
[0043] Sensing assembly 50 further comprises a pressure
transmission device 60, such as a bellows, disposed within a
pressure housing 64 and in fluid communication with volume 54.
Pressure transmission device 60 is exposed to a viscous fluid 65,
which may be the same or different than viscous fluid 58, having a
pressure P1 entering the pressure housing 64 through an inlet 66
from a source (not shown). Pressure transmission device 60 reacts
to pressure P1 in the direction indicated by arrow 61 and produces
a corresponding pressure P2 within volume 58. Pressure P2 is a
quasi-hydrostatic pressure that is distributed about pressure
sensor 52 enabling the accurate determination of P1. In certain
embodiments, fluid 65 comprises those fluids typically encountered
within an oil production well, including oil, gas, water and air,
among others. Sensor housing 56 is filled with a fluid such as a
viscous fluid, grease, silicone oil, or other fluids that provide
shock and/or vibration isolation and prevent the sensor 52 from
violently contacting the inner walls of the housing when subject to
shock or vibration. Pressure transmission device 60 is coupled to
volume 54 in such a way as to transmit the pressure P1 to volume 54
wherein there will be a corresponding pressure P2 sensed by the
pressure sensor 52. Further, pressure transmission device 60 may be
configured to maintain fluid 58 in a relatively void free
condition, but in any event maintains a minimum pressure within
volume 54 and retains sensor 52 in a suspended or floating position
as described above. The maintenance of this fluid filled, void free
condition is also useful to protect the sensor 52 from shock and
vibration during shipping, deployment, and handling.
[0044] The viscous fluid 54 isolates the sensor 52 from shock or
vibration induced to the sensor assembly 50 by maintaining an
average gap 68, thereby decoupling the sensor 52 from the housing
56. By decoupling the sensor 52 from the housing 56, the sensor
assembly 50 virtually eliminates base strain from the housing, and
in turn achieves essentially a zero base strain sensitivity.
Pressure sensor 52 is exposed to pressure P2 and transmits a signal
corresponding to the level of pressure of fluid 58 via optical
waveguide 20. In order to insure that the sensor 52 is free to
float within housing 56, optical waveguide 20 may be provided with
a strain relief, or flexure portion 70 which creates a low
stiffness attachment between the sensor element 52 and its base
structure, the housing 56.
[0045] As shown in FIG. 3, the optical waveguide feedthrough
assembly 10 of the present invention is mounted within an end wall
of the housing 56, and the optical wave guide (or transmission
cable) 20 exits the housing through the feedthrough 10 and, in
turn, is routed to other sensors or to an instrumentation or
interrogation system (not shown).
[0046] In the operation of the sensor assembly 50, a change in
source pressure P1 causes bellows 60 to react in the direction of
arrow 61, thereby changing the internal volume of the bellows and
the pressure P2 within volume 58. An increase in pressure P1
decreases the internal volume of bellows 60 and increases the
sensed pressure P2, and likewise a decrease in source pressure P1
increases the internal volume of the bellows 60 thereby decreasing
the sensed pressure P2. Bellows 60 has a maximum extension volume
that maintains viscous fluid 54 at a predictable minimum
quasi-hydrostatic pressure P2 suspending sensor 52 within volume 58
with average gap 68 between the sensor and sensor housing 56.
[0047] Although the exemplary sensing assembly of FIG. 3 employs
only a single optical waveguide feedthrough assembly 10, other
sensing assemblies or systems requiring optical waveguide
feedthroughs may employ a plurality of such waveguide feedthroughs
in any of a plurality of different configurations. For example, a
single optical waveguide 20 may enter a sensor housing at one end
through a first feedthrough assembly 10, and exit the sensor
housing at another end (or the same end) through a second
feedthrough assembly 10. Similarly, a single optical waveguide 20
may enter a sensor housing through a feedthrough assembly 10, and
exit the housing by doubling back through the same feedthrough
assembly.
[0048] In some cases, the waveguide 20 may include an external
buffer, particularly in the region where the waveguide passes
through the feedthrough assembly, wherein the buffer is made of a
material to which it is difficult to create a strong and reliable
adhesive bond, such as polyamide or Teflon.RTM.. A relatively weak
bond of this type could cause an eventual failure of the
feedthrough assembly by fluid leakage along the interface, and/or
by allowing movement of the waveguide 20 relative to the tubular
member 12 due to complete adhesive bond failure. In order to
overcome this deficiency, an alternative embodiment of the present
invention involves removing the waveguide or fiber buffer locally
over a fraction of the length of the fiber passing through the
feedthrough assembly to expose the underlying optical glass
surface. Then, the exposed optical glass surface is treated with an
adhesion promoter, such as silane. The epoxy adhesive or other
sealant 24 is then introduced by capillary action into the annular
cavity 22 in the manner described above. Alternatively, the silane
or other adhesion promoter can be pre-mixed with the epoxy adhesive
in a manner known to those of ordinary skill in the pertinent
art.
[0049] In addition to treating the glass for improving the
epoxy-to-glass bond (or other sealant-to-glass bond), the annular
surface 14 of the tubular member 12 may be treated in a like manner
to improve the epoxy-to-metal bond (or other sealant-to-metal
bond). However, the improvement in the epoxy-to-metal bond achieved
with such treatment is typically not as great as is seen with the
epoxy-to-glass bond. In one embodiment, silane sold under the mark
"A-1100" and manufactured by Witco Corp. of Greenwich, Conn. is
employed. However, as may be recognized by those skilled in the
pertinent art based on the teachings herein, any of numerous other
adhesion promoters, or methods for promoting adhesion, which are
currently known or later become known for performing the function
of the adhesion promoter described herein, may be employed.
[0050] One advantage of the present invention is that the
feedthroughs disclosed are resistant to creep and/or extrusion
along the elongated axis of the optical fiber, and therefore are
capable of exhibiting significantly improved service lives in
comparison to the prior art feedthroughs described above.
[0051] Another advantage of the present invention is that the axial
length of the feedthrough is sufficiently long to provide a
sufficient margin of safety, such that some gradual degradation or
failure of the adhesive bond can occur without causing fluid
leakage through the feedthrough, or movement of the fiber relative
to the tubular member. In accordance with certain embodiments of
the present invention, the overall length of the annular cavity 22
preferably is at least approximately 50 times the diameter D2 of
the annular surface 14 (or if the annular surface defines a cross
sectional shape other than circular, the length is preferably 50
times the width of the feedthrough cavity 16), and most preferably
this ratio is at least 100:1.
[0052] A significant advantage of the present invention over
existing optical waveguide feedthroughs is that the feedthrough
assembly of the invention provides for essentially zero optical
loss with certain fiber types, such as single mode, high numerical
aperture `bend-insensitive` fiber, due to the continuous fiber path
through the feedthrough, and the use of low elastic modulus epoxy
adhesives or other sealants surrounding the fiber which create low
micro-bending losses.
[0053] Another advantage of the present invention is the ease of
manufacture, due to the lack of need to create a `break` in an
otherwise continuous fiber, which would require terminating the
fiber in some way which is usually expensive, labor intensive, and
subject to loss or scrapping of valuable optical components which
may be integrally attached to this fiber `pigtail`.
[0054] The feedthrough assembly of the present invention achieves
these advantages while maintaining high reliability for long term
service at very elevated temperatures and pressures. Another
significant advantage of the present invention is the ability to
fill the annular cavity between the tubular member and optical
waveguide or fiber completely using capillary action. Injection of
epoxy or other sealant by conventional means, on the other hand,
into such a small volume is essentially impossible, and injection
into large volumes is subject to the formation of voids in the
epoxy or other sealant, which can, in turn, create non-axisymmetric
stresses on the fiber due to applied pressure and temperature,
leading to failure due to fluid leakage and/or fiber breakage.
[0055] It should be understood that the dimensions, geometries, and
materials described for the embodiments disclosed herein are for
illustrative purposes and as such, any other dimensions,
geometries, or materials may be used if desired, depending on the
application, size, performance, manufacturing or design
requirements, or other factors, in accordance with the teachings
herein. For example, the axially-elongated surface 14 may be
defined by the feedthrough member, such as the bulkhead itself, and
need not be defined by a separate tubular member of other body of
the feedthrough assembly. In addition, numerous changes and
modifications may be made to the above described and other
embodiments of the present invention without departed from the
scope of the invention as defined in the appended claims. It should
also be understood that any of the features, characteristics,
alternatives or modifications described regarding a particular
embodiment herein may also be applied, used, or incorporated with
any other embodiment described herein. Accordingly, this detailed
description of preferred embodiments is to be taken in an
illustrative, as opposed to a limiting sense.
* * * * *