U.S. patent application number 09/755258 was filed with the patent office on 2002-07-11 for flexible optical circuit having a protective foam layer.
This patent application is currently assigned to US Conec Ltd.. Invention is credited to Sorosiak, James L..
Application Number | 20020090191 09/755258 |
Document ID | / |
Family ID | 25038370 |
Filed Date | 2002-07-11 |
United States Patent
Application |
20020090191 |
Kind Code |
A1 |
Sorosiak, James L. |
July 11, 2002 |
Flexible optical circuit having a protective foam layer
Abstract
A flexible optical circuit is provided that includes at least
one layer formed of a foam material in order to provide strain
relief for the optical fibers and to improve the crush resistance
of the flexible optical circuit. The flexible optical circuit
includes a substrate and at least one optical fiber disposed upon
the substrate. In one embodiment, the substrate is formed of a foam
material, such as a silicone or polyurethane foam. The flexible
optical circuit can also include a protective layer disposed upon
at least a portion of the substrate so as to overlie at least a
segment of at least one optical fiber, such as those segments at
which the stress is concentrated. In addition to or instead of
forming the substrate from a foam material, the protective layer
may be formed of a foam material.
Inventors: |
Sorosiak, James L.;
(Huntersville, NC) |
Correspondence
Address: |
ALSTON & BIRD LLP
BANK OF AMERICA PLAZA
101 SOUTH TRYON STREET, SUITE 4000
CHARLOTTE
NC
28280-4000
US
|
Assignee: |
US Conec Ltd.
|
Family ID: |
25038370 |
Appl. No.: |
09/755258 |
Filed: |
January 5, 2001 |
Current U.S.
Class: |
385/137 |
Current CPC
Class: |
G02B 6/3608 20130101;
G02B 6/3878 20130101; G02B 6/43 20130101 |
Class at
Publication: |
385/137 |
International
Class: |
G02B 006/36 |
Claims
That which is claimed:
1. A flexible optical circuit comprising: a substrate formed of a
foam material; adhesive disposed upon at least a portion of said
substrate; and at least one optical fiber attached to said
substrate with said adhesive such that the foam material that forms
said substrate provides strain relief for said at least one optical
fiber.
2. A flexible optical circuit according to claim 1 further
comprising a layer of foam material disposed upon at least a
portion of said substrate so as to overlie at least a segment of
said at least one optical fiber.
3. A flexible optical circuit according to claim 2 wherein said
layer of foam material is disposed proximate an edge of said
substrate.
4. A flexible optical circuit according to claim 2 further
comprising at least one fiber optic connector mounted upon a
respective optical fiber, wherein said layer of foam material is
disposed proximate said at least one fiber optic connector.
5. A flexible optical circuit according to claim 2 wherein said
substrate comprises a main section and at least one tab extending
outwardly from said main section, and wherein said layer of foam
material is disposed upon at least a portion of said at least one
tab.
6. A flexible optical circuit according to claim 1 wherein the foam
material that forms said substrate comprises a non-porous surface
upon which said adhesive is disposed.
7. A flexible optical circuit according to claim 1 wherein the foam
material that forms said substrate is flame retardant.
8. A flexible optical circuit according to claim 1 wherein the foam
material that forms said substrate is selected from the group
consisting of silicone and polyurethane.
9. A flexible optical circuit according to claim 1 further
comprising a conformal coating disposed upon said substrate and
overlying said at least one optical fiber.
10. A flexible optical circuit comprising: a substrate; at least
one optical fiber disposed upon said substrate; and a layer of foam
material disposed upon at least a portion of said substrate so as
to overlie at least a segment of said at least one optical fiber
such that the foam material provides strain relief for said at
least one optical fiber as the optical circuit flexes.
11. A flexible optical circuit according to claim 10 wherein said
layer of foam material is disposed proximate an edge of said
substrate.
12. A flexible optical circuit according to claim 10 further
comprising at least one fiber optic connector mounted upon a
respective optical fiber, wherein said layer of foam material is
disposed proximate said at least one fiber optic connector.
13. A flexible optical circuit according to claim 10 wherein said
substrate comprises a main section and at least one tab extending
outwardly from said main section, and wherein said layer of foam
material is disposed upon at least a portion of said at least one
tab.
14. A flexible optical circuit according to claim 10 wherein said
layer of foam material comprises a non-porous surface facing said
substrate and said at least one optical fiber.
15. A flexible optical circuit according to claim 10 wherein said
layer of foam material is flame retardant.
16. A flexible optical circuit according to claim 10 wherein said
layer of foam material is formed of a foam selected from the group
consisting of silicone and polyurethane.
17. A flexible optical circuit according to claim 10 wherein said
substrate is also formed of a foam material.
18. A flexible optical circuit according to claim 10 further
comprising a conformal coating disposed upon said substrate and
overlying said at least one optical fiber, wherein said layer of
foam material is disposed upon said conformal coating.
19. A flexible optical circuit according to claim 10 further
comprising an adhesive disposed upon at least a portion of said
substrate for securing said at least one optical fiber to said
substrate.
20. A flexible optical circuit comprising: a substrate; at least
one optical fiber disposed upon said substrate; and a protective
layer disposed upon at least a portion of said substrate so as to
overlie at least a segment of said at least one optical fiber,
wherein at least one of said substrate and said protective layer
are formed of a foam material in order to provide strain relief for
said at least one optical fiber as the optical circuit flexes.
21. A flexible optical circuit according to claim 20 wherein said
protective layer is disposed proximate an edge of said
substrate.
22. A flexible optical circuit according to claim 20 further
comprising at least one fiber optic connector mounted upon a
respective optical fiber, wherein said protective layer is disposed
proximate said at least one fiber optic connector.
23. A flexible optical circuit according to claim 20 wherein said
substrate comprises a main section and at least one tab extending
outwardly from said main section, and wherein said protective layer
is disposed upon at least a portion of said at least one tab.
24. A flexible optical circuit according to claim 20 wherein both
said substrate and said protective layer are formed of the foam
material.
25. A flexible optical circuit according to claim 20 wherein the
foam material comprises a non-porous surface facing said at least
one optical fiber.
26. A flexible optical circuit according to claim 20 wherein the
foam material is flame retardant.
27. A flexible optical circuit according to claim 20 wherein the
foam material is selected from the group consisting of silicone and
polyurethane.
28. A flexible optical circuit according to claim 20 further
comprising a conformal coating disposed upon said substrate and
overlying said at least one optical fiber, wherein said protective
layer is disposed upon said conformal coating.
29. A flexible optical circuit according to claim 20 further
comprising an adhesive disposed upon at least a portion of said
substrate for securing said at least one optical fiber to said
substrate.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to flexible optical
circuits and, more particularly, to flexible optical circuits
designed to provide strain relief for the optical fibers.
BACKGROUND OF THE INVENTION
[0002] Flexible optical circuits are utilized in a wide variety of
applications in which fiber management is desirable. For example,
flexible optical circuits are commonly utilized as optical
backplanes to interconnect a number of printed circuit boards or
the like. Similarly, flexible optical circuits can serve as ribbons
of optical fibers in order to route the optical fibers in an
organized fashion.
[0003] Regardless of the application, a flexible optical circuit is
commonly formed of a plastic substrate, typically formed of a
polyimide or similar types of engineering thermoplastic materials,
such as polyetherimide or polybutylene terphthalate. Most commonly,
however, the substrate is formed of Kapton.TM. polyimide. The
substrate is coated with an adhesive, such as a silicone adhesive,
and a plurality of optical fibers are placed upon the
adhesive-coated substrate. In particular, the optical fibers are
placed in a predetermined pattern upon the substrate in order to
appropriately route the optical fibers. The flexible optical
circuit is then completed by placing another layer over the optical
fibers. For example, a flexible optical circuit can include another
layer of the plastic material that forms a substrate in order to
effectively sandwich the optical fibers between the layers of
plastic. By way of example, the flexible optical circuit can
include a layer formed of Kapton.TM. polyimide that overlies the
optical fibers and is adhered to the substrate. Alternatively, a
conformal coating can be applied so as to cover the substrate and
the optical fibers adhered to the substrate. For example, a
conformal coating of silicone can be sprayed on the substrate in
order to cover the optical fibers as well as other portions of the
substrate.
[0004] In designing a flexible optical circuit, it is desirable for
the flexible optical circuit and, more particularly, for the
components that form the flexible optical circuit, to be flame
retardant. Additionally, a flexible optical circuit preferably has
good environmental resistance properties. In this regard, the
flexible optical circuit preferably maintains approximately the
same generally small level of attenuation for signals transmitted
via the optical fibers as the temperature and humidity to which the
flexible optical circuit is subjected are varied within a
predetermined range of temperatures and humidities. Still further,
the flexible optical circuit preferably has good handling
characteristics. In other words, the flexible optical circuit is
preferably relatively flexible to facilitate routing of the optical
fibers. As such, the flexible optical circuit must be capable of
being readily bent or otherwise flexed.
[0005] Unfortunately, the substrate of most flexible optical
circuits is much less flexible than the optical fibers. In other
words, the substrate of most flexible optical circuits is
relatively stiff or inflexible relative to the optical fibers. This
relative inflexibility is compounded in instances in which the
flexible optical circuit includes a second layer of plastic, such
as a second layer formed of Kapton.TM. polyimide, that covers the
optical fibers and other portions of the substrate. Accordingly,
conventional flexible optical circuits disadvantageously subject
the optical fibers to stress.
[0006] Typically, the stress is concentrated upon the optical
fibers at one or more points depending upon the configuration of
the flexible optical circuit. For example, most flexible optical
circuits are designed such that the optical fibers extend beyond
the edge of the substrate. As such, the optical fibers are
subjected to stress along the edge of the substrate. Additionally,
fiber optic connectors are commonly mounted upon respective optical
fibers of a flexible optical circuit. In these instances, the
substrate upon which the optical fibers are mounted typically
extends into the connector boot and into the rearward end of the
spring push element of the fiber optic connector. Nevertheless, the
optical fibers are typically subjected to stress at the point
beyond the edge of the substrate at which the fiber optic connector
is mounted to the optical fiber. In embodiments in which the
flexible optical circuit includes a second layer of plastic, such
as a second layer of Kapton.TM. polyimide, that covers the optical
fibers and the substrate, the second layer of plastic may
delaminate and peel back from the substrate as the flexible optical
circuit is bent or otherwise flexed. In these instances, stress is
also concentrated on the optical fibers at the point at which the
second layer of plastic becomes delaminated from the substrate. In
each of these instances, the points along the optical fiber at
which the stress is concentrated will disadvantageously increase
the attenuation of the optical signals transmitted via the optical
fibers.
[0007] In order to protect the optical fibers from the
concentrations of stress, some flexible optical circuits have
included shrink tubing and/or strain relief boots through which
optical fibers extend. By positioning the shrink tubing or the
strain relief boot upon that segment of the optical fiber at which
the stress is concentrated, the optical fiber can be at least
partially shielded from the stress such that the signals
propagating along the optical fibers are not attenuated to the same
degree. For example, the shrink tubing or strain relief boot may be
placed upon an optical fiber proximate the edge of the substrate in
order to protect the optical fiber from the concentration of stress
that typically occurs at the edge of the substrate.
[0008] In addition to increasing the cost of a flexible optical
circuit, strain relief boots and shrink tubing create other
difficulties. In this regard, strain relief boots and shrink tubing
are typically rather bulky, and/or inflexible relative to the
remainder of the flexible optical circuit. As such, the resulting
flexible optical circuit is typically heavier and somewhat more
difficult to handle than conventional flexible optical circuits
that do not include either strain relief boots or shrink tubing.
Additionally, it is generally more difficult and laborious to
fabricate flexible optical circuits that include strain relief
boots and/or shrink tubing, thereby increasing the time required
for fabrication and, in many instances, the cost of the resulting
flexible optical circuit.
[0009] Even in instances in which segments of the optical fibers
are protected from concentrations of stress by strain relief boots
and/or shrink tubing, the majority of the length of the optical
fibers is not protected by strain relief boots and/or shrink
tubing. As such, these other unprotected segments of the optical
fibers are susceptible to damage and therefore increased
attenuation as a result of inadvertent contact with the optical
fibers. For example, flexible optical circuits are typically
deployed in electronics cabinets or other closures that also house
a variety of other components, typically formed of metal or hard
plastic. As such, these other components may inadvertently contact
the flexible optical circuit during installation or subsequently
during the repair, thereby damaging the optical fibers if the
components contact those segments of the optical fibers that are
not protected by a strain relief boot or shrink tubing.
Accordingly, most conventional flexible optical circuits
disadvantageously have a relatively small crush resistance.
SUMMARY OF THE INVENTION
[0010] An improved flexible optical circuit is therefore provided
that includes at least one layer formed of a foam material in order
to provide strain relief for the optical fibers and to improve the
crush resistance of the flexible optical circuit. Accordingly, the
flexible optical circuit need not include strain relief boots
and/or shrink tubing such that the flexible optical circuit is
simpler to manufacture and generally less expensive than
conventional flexible optical circuits having strain relief boots
and/or shrink tubing.
[0011] A flexible optical circuit includes a substrate and at least
one optical fiber disposed upon the substrate. In one advantageous
embodiment, the substrate is formed of a foam material, such as a
silicone or polyurethane foam. As such, the foam substrate provides
both crush resistance and strain relief for the optical fibers.
Preferably, the foam material that forms the substrate includes a
non-porous surface upon which the optical fibers are mounted.
Additionally, the foam material that forms the substrate is
preferably flame retardant. Typically, the flexible optical circuit
also includes an adhesive, such as a silicone adhesive, disposed
upon at least a portion of the substrate for attaching the optical
fibers to the substrate. The flexible optical circuit can also
include a conformal coating disposed upon the substrate and
overlying the optical fibers.
[0012] In addition to the substrate and the optical fibers disposed
upon the substrate, the flexible optical circuit of one
advantageous embodiment also includes a protective layer disposed
upon at least a portion of the substrate so as to overlie at least
a segment of at least one optical fiber. According to this
embodiment, at least one of the substrate and the protective layer
is formed of a foam material to provide strain relief for the
optical fibers. In this regard, the substrate may be formed of the
foam material as described in conjunction with the foregoing
embodiment. Alternatively, the protective layer may be formed of
the foam material, irrespective of whether the substrate is also
formed of a foam material or is formed of another material, such as
a polyimide or other plastic material. In embodiments in which the
protective layer is formed of a foam material, the protective layer
also advantageously provides strain relief for the optical fiber
and, at least some, crush resistance for the optical fibers.
[0013] In embodiments in which the protective layer is formed of a
foam material, the foam material also preferably includes a
non-porous surface facing the optical fibers. In addition, the foam
material that forms the protective layer of these embodiments is
preferably flame retardant and is typically formed of either a
silicone or polyurethane foam. In embodiments in which the
protective layer is formed of a foam material, the protective layer
may cover the entire substrate including all segments of the
optical fibers. Alternatively, the protective layer may be designed
to cover those segments of the optical fibers subjected to the
largest concentrations of stress, while leaving other segments of
the optical fibers exposed. In this regard, the protective layer of
foam material is preferably disposed proximate the edges of the
substrate to protect the optical fibers from the concentrations of
stress that otherwise occur at the edge of the substrate. In this
regard, the substrate can include a main section and at least one
tab extending outwardly therefrom. In this embodiment, the
protective layer of foam material is preferably disposed upon at
least a portion of the at least one tab. Additionally, the flexible
optical circuit may include at least one fiber optic connector
mounted upon a respective optical fiber. In this embodiment, the
protective layer of foam material is preferably disposed proximate
the fiber optic connector in order to protect the optical fiber
from the concentration of stress that otherwise would occur at the
fiber optic connector. Since the protective layer generally does
not cover the entire substrate, the flexible optical circuit can
also include a conformal coating disposed upon the substrate and
overlying the optical fibers. The protective layer of foam material
can then be disposed upon portions of the conformal coating, such
as those portions at which the stress is concentrated upon the
optical fibers.
[0014] In each of these embodiments, the improved flexible optical
circuit provides strain relief for the optical fibers as a result
of the inclusion of a layer of foam material. As a result of the
strain relief, the improved flexible optical circuit can transmit
signals with lower levels of attenuation. Moreover, the improved
flexible optical circuit provides improved crush resistance,
thereby protecting the flexible optical circuit and, in particular,
the optical fibers from physical damage as a result of contact with
other components within an electronics cabinet, closure or the
like. Additionally, the improved flexible optical circuits of the
present invention and, in particular, those embodiments of the
improved flexible optical circuits that include a substrate formed
of a foam material are quite flexible, thereby reducing the
concentration of stress upon the optical fibers and improving the
handling characteristics of the flexible optical circuit so as to
facilitate installation, repair and the like of the improved
flexible optical circuit. Further, the improved flexible optical
circuits of the present invention can be efficiently fabricated,
thereby reducing the time required for manufacture and the costs of
manufacture relative to the fabrication of conventional flexible
optical circuits that include shrink tubing and/or strain relief
boots.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Having thus described the invention in general terms,
reference will now be made to the accompanying drawings, which are
not necessarily drawn to scale, and wherein:
[0016] FIG. 1 is a perspective view of a flexible optical circuit
according to one embodiment of the present invention which includes
a substrate formed of a foam material;
[0017] FIG. 2 is a cross-sectional view of the flexible optical
circuit of FIG. 1 taken along line 2-2;
[0018] FIG. 3 is a perspective view of a flexible optical circuit
according to another embodiment of the present invention which
includes both a substrate and a protective layer formed of a foam
material;
[0019] FIG. 4 is a cross-sectional view of the flexible optical
circuit of FIG. 3 taken along line 4-4; and
[0020] FIG. 5 is a flow chart illustrating the operations performed
to fabricate the flexible optical circuit of FIG. 3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] The present invention now will be described more fully
hereinafter with reference to the accompanying drawings, in which
preferred embodiments of the invention are shown. This invention
may, however, be embodied in many different forms and should not be
construed as limited to the embodiments set forth herein; rather,
these embodiments are provided so that this disclosure will be
thorough and complete, and will fully convey the scope of the
invention to those skilled in the art. Like numbers refer to like
elements throughout.
[0022] Referring now to FIG. 1, a flexible optical circuit 10
according to one advantageous embodiment to the present invention
is illustrated. The flexible optical circuit can be deployed in a
variety of applications in order to route optical fibers in an
organized and managed fashion. For example, the flexible optical
circuits depicted in FIGS. 1 and 3 can be utilized as an optical
backplane or the like. However, the flexible optical circuit may be
an elongated ribbon, thereby defining a ribbon of optical fibers as
commonly utilized for routing optical fibers across relatively long
distances. As such, flexible optical circuits, as used herein,
includes ribbons of optical fibers as well as other flexible
optical circuits utilized for fiber management purposes, such as
for optical backplanes and the like.
[0023] The flexible optical circuit 10 includes a substrate 12 and
at least one and, more commonly, a plurality of optical fibers 14
disposed upon the substrate. As will be apparent, the optical
fibers can be disposed upon the substrate in any desired pattern in
order to provide the proper routing of the optical fibers.
Typically, however, the optical fibers generally extend from beyond
one edge of the substrate to beyond another edge of the substrate
to facilitate connection with the optical fibers. While the
flexible optical circuit of the illustrated embodiments is shown to
include a plurality of individual optical fibers, it is noted that
the flexible optical circuit of the present invention will
typically include optical fibers that extend beyond the edge of the
substrate in a ribbonized format.
[0024] The optical fibers 14 are typically attached to the
substrate 12 such that the position of the optical fibers relative
to the substrate is fixed. As such, the flexible optical circuit 10
also generally includes an adhesive 15, such as silicone adhesive,
as shown in FIG. 2. The adhesive is typically disposed upon at
least that portion of the substrate across which the optical fibers
will be routed in order to attach the optical fibers to the
substrate. More commonly, however, the entire substrate is coated
with the adhesive. Once the optical fibers have been attached to
the substrate, a conformal coating 16 may be applied to the surface
of the substrate to which the optical fibers are attached. In this
regard, the conformal coating is typically formed of a relatively
thin layer of silicone that is sprayed over the optical fibers and
the substrate in order to protect the flexible optical circuit and
to further secure the optical fibers to the substrate. As described
below, in embodiments of the flexible optical circuit that include
a protective layer 18, the conformal coating may be applied over
the protective layer and the exposed portions of the substrate or
the conformal coating may be omitted altogether.
[0025] According to the present invention, the flexible optical
circuit 10 includes at least one layer formed of a foam material.
In the embodiment illustrated in FIG. 1 and, in more detail, in the
cross-sectional view of FIG. 2, the substrate 12 can be formed of a
foam material. As described in more detail hereinbelow, the foam
material serves to provide strain relief for the optical fibers 14
and to improve the crush resistance of the flexible optical
circuit. The substrate can be formed of a variety of different
types of foam materials. Typically, however, the substrate is
formed of a silicone or a polyurethane foam. For example, the
flexible optical circuit of one embodiment includes a substrate
formed of UL94-V0 silicone that is commercially available from
Rogers Corporation of Elk Grove Village, Ill.
[0026] The foam material that forms the substrate 12 can have
various thicknesses depending upon the application and the desired
handling characteristics. In one embodiment, however, the substrate
is formed of a silicone or polyurethane foam having a thickness
within the range of {fraction (1/32)} inches to {fraction (1/16)}
inches. Additionally, the foam material that forms the substrate,
such as the UL94-V0 silicone, is preferably flame retardant. For
example, the foam material may include a halogen or other additive
in order to provide the desired flame retardancy. Further, the foam
material that forms the substrate preferably has at least one and,
most commonly, opposed non-porous surfaces. The adhesive 15 can
therefore be applied to a non-porous surface of the foam material
to facilitate adhesion of the optical fibers 14 to the underlying
substrate.
[0027] In embodiments in which the substrate 12 is formed of a
silicone or polyurethane foam having a thickness within the range
of {fraction (1/32)} inches to {fraction (1/16)} inches, the
flexible optical circuit 10 preferably has environmental resistance
properties that are similar to those of a conventional flexible
optical circuit having a comparably sized, polyimide substrate. In
this regard, the attenuation of the signals propagating along the
optical fibers 14 of the flexible optical circuit is substantially
the same for a flexible optical circuit including a substrate
formed of silicone or polyurethane foam as for a conventional
flexible optical circuit having a polyimide substrate as the
temperature and humidity to which the flexible optical circuit is
subjected are varied throughout predetermined ranges. However, a
flexible optical circuit including a substrate formed of a silicone
or polyurethane foam generally has better handling characteristics,
i.e., is more flexible, than a conventional flexible optical
circuit that includes a polyimide substrate.
[0028] As a result of forming the substrate 12 from a foam
material, the optical fibers 14 will be subjected to less stress
since, among other reasons, the optical fibers will be permitted
some movement into and out of the plane defined by the substrate as
a result of the compressibility of the foam material that forms the
substrate. The reduction in the stress to which the optical fibers
are exposed is particularly evident at those points at which the
stress would otherwise be concentrated, such as along the edges of
the flexible optical circuit 10. In addition, the compressibility
of the foam material that forms the substrate also improves the
crush resistance of the flexible optical circuit by permitting
movement of the optical fibers into and out of the plane defined by
the substrate. As such, additional protection is afforded the
optical fibers in instances in which contact is made between the
flexible optical circuit and other components within an electronics
cabinet or the like. By including a substrate formed of a foam
material, the resulting flexible optical circuit is quite flexible,
thereby reducing the concentration of stress upon the optical
fibers and improving the handling characteristics of the flexible
optical circuit so as to facilitate its installation, repair and
the like.
[0029] As described above, the flexible optical circuit 10 includes
at least one layer formed of a foam material. While the substrate
12 may be formed of a foam material as described above, the
flexible optical circuit 10 of another embodiment of the present
invention includes a protective layer 18 formed of a foam material.
The protective layer is disposed upon the substrate and, in
embodiments that include a conformal coating 16 upon the substrate,
upon the conformal coating that covers the substrate. In instances
in which the protective layer is disposed upon the substrate
without any intervening conformal coating, the adhesive 15 adheres
the protective layer to the substrate. However, in instances in
which the substrate is covered with a conformal coating prior to
disposing the protective layer upon the substrate, another layer of
adhesive, such as silicone adhesive, is preferably applied to
either the protective layer or the surface upon which the
protective layer is to be disposed in order to adhere the
protective layer to the underlying surface. The flexible optical
circuit of the illustrated embodiment also includes a substrate
which may be formed of a foam material as described above.
Alternatively, the substrate may be formed of other materials, such
as a polyimide or other engineering thermoplastic materials, such
as polyetherimide or polybutylene terphthalate.
[0030] As depicted in FIGS. 3 and 4, the protective layer 18 is
disposed upon at least a portion of the substrate 12 so as to
overlie predetermined segments of the optical fibers 14. In this
regard, the protective layer of foam material can overlie the
entire substrate including all optical fibers upon the substrate.
In this embodiment, the flexible optical circuit 10 need not
include a conformal coating between the substrate and the
protective layer, although a conformal coating can be applied over
the protective layer, if so desired. Alternatively, the protective
layer of foam material may be disposed only upon selected portions
of the substrate, such as those portions of the substrate that
support segments of the optical fibers upon which stress will be
concentrated. In these embodiments, the flexible optical circuit
can include a conformal coating between the substrate and the
protective layer and/or a conformal coating over the protective
layer as well as the exposed portions of the substrate.
[0031] As shown in FIG. 3, for example, the protective layer 18 of
foam material may be disposed along those edges of the substrate 12
across which the optical fibers 14 extend. The protective layer of
foam material can therefore protect the optical fibers from the
stress that is otherwise concentrated at the edge of the substrate.
As will be apparent, the protective layer of foam material can
extend inward from the edges of the substrate by any distance. In
one embodiment, however, the protective layer of foam material
extends about 1 to 2 inches from the edge of the substrate.
Similarly, in those embodiments in which fiber optic connectors 20
are mounted upon end portions of the optical fibers, the protective
layer of foam material is preferably disposed upon those portions
of the substrate proximate the fiber optic connectors since stress
would otherwise be concentrated upon the optical fibers at the
point at which the fiber optic connectors are mounted thereto. In
this regard, it is noted that while the flexible optical circuit 10
of the illustrated embodiments is shown to include a plurality of
individual optical fibers, it is noted that the flexible optical
circuit will typically include optical fibers that extend beyond
the edge of the substrate in a ribbonized format. As such, the
fiber optic connectors can be either single fiber connectors, or
multifiber connectors in order to be mounted upon a ribbon of
optical fibers.
[0032] As shown in FIG. 3, the flexible optical circuit 10 of one
advantageous embodiment includes a substrate 12 that has a main
section 12a and at least one and, more typically, a plurality of
tabs 12b extending outwardly from the main section. The flexible
optical circuit of this embodiment also includes a plurality of
optical fibers 14, each of which extends across the main section of
the substrate and along a respective tab. For example, a plurality
of optical fibers in a ribbonized format may be supported by and
extend from each tab. Each tab can flex or otherwise move in
relation to the other tabs and to the main section of the
substrate, thereby permitting the optical fibers supported by the
tabs to be individually moved or positioned. In this embodiment,
the flexible optical circuit also includes a protective layer 18
formed of foam material disposed proximate those edges of the
substrate across which the optical fibers extend. In more detail,
the flexible optical circuit of this embodiment preferably includes
a protective layer of foam material proximate the edges of both the
main section of the substrate and the tabs at which the optical
fibers enter and exit the flexible optical circuit.
[0033] As described above in conjunction with the embodiment in
which the substrate 12 is formed of a foam material, the protective
layer 18 can be formed of a variety of different types of foam
materials, such as silicone or polyurethane foams. In one
embodiment, for example, the protective layer is formed of UL94-V0
silicone foam. The protective layer of foam material is also
preferably flame retardant. The protective layer of foam material
can have various thicknesses depending upon the application.
Typically, however, the protective layer has a thickness of between
{fraction (1/32)} inches and {fraction (1/16)} inches. In order to
facilitate the adhesion of the protective layer of foam material to
the substrate, the protective layer of foam material preferably
includes at least one and, more typically, opposed non-porous
surfaces. In either instance, the protective layer is positioned
such that a non-porous surface faces the substrate.
[0034] The protective layer 18 of foam material provides strain
relief for the optical fibers 14 by accommodating at least some
relative movement of the optical fibers. As such, the protective
layer of foam material is preferably disposed upon at least those
portions of the substrate 12 at which the stress otherwise would be
concentrated upon the optical fibers, as described above.
Additionally, the protective layer of foam material provides at
least some crush resistance for those segments of the optical
fibers that underlie the protective layer of foam material.
[0035] While the flexible optical circuit 10 of the present
invention can be fabricated in various manners, one advantageous
method for fabricating a flexible optical circuit that includes
both a substrate 12 formed of a foam material and a protective
layer 18 formed of a foam material is illustrated in FIG. 5 and
will be described hereinafter for purposes of illustration. As
mentioned above, however, the flexible optical circuit need not
include both a substrate and a protective layer formed of a foam
material and may include only a single layer of foam, if so
desired. In the illustrative method, however, the substrate is
formed of a foam material. Adhesive 15, such as a silicone
adhesive, is initially applied to one surface of the substrate as
shown in block 30 of FIG. 5. In this regard, the foam material that
forms the substrate has at least one and, most commonly, opposed
non-porous surfaces. As such, the adhesive is preferably applied to
a non-porous surface of the foam material to facilitate adhesion
therewith. The substrate is then secured in position. See block 32.
For example, the substrate may be placed upon a vacuum table, may
be secured electrostatically, may be secured with double-sided tape
or may otherwise be fixed in position. In the illustrated
embodiment, the substrate is then formed into the desired shape,
such as by cutting the substrate into the desired shape as shown in
block 34. Alternatively, the substrate may be formed into the
desired shape at other stages in the fabrication process, if so
desired. The optical fibers 14 are then laid upon the adhesive
coated surface of the substrate in the desired pattern, as shown in
block 36. In the illustrated embodiment, a conformal coating 16,
also typically formed of silicone, is then sprayed over the optical
fibers and upon the adhesive coated surface of the substrate. See
block 38. The conformal coating is then cured, typically by heating
or by ultraviolet curing. See block 40. As described above,
however, the conformal coating may be applied at a later stage in
the fabrication process, such as following the application of the
protective layer 18. Still further, the conformal coating may be
omitted altogether, especially in instances in which the protective
layer covers the entire substrate.
[0036] It is then determined if fiber optic connectors 20 are to be
mounted upon one or more of the optical fibers 14. See block 42 of
FIG. 5. If so, the fiber optic connectors are mounted upon the end
portions of the respective optical fibers in a conventional manner
known to those skilled in the art. See block 44. According to this
embodiment that includes both a substrate 12 and a protective layer
18 formed of a foam material, a protective layer of foam material
is then applied, either to the entire substrate or to selected
portions of the substrate. See block 46. As described above, the
protective layer of foam material is typically applied to those
portions of the substrate that support segments of the optical
fibers upon which stress would otherwise be concentrated, such as
along the edges of the substrate and proximate the fiber optic
connectors. In this regard, the fiber optic connectors are
typically mounted upon the end portions of respective optical
fibers such that the substrate extends into the connector boot and
the rearward end of the spring push element, while the protective
layer of foam material is applied to the substrate so as to abut
the rearward end of the connector boot.
[0037] The protective layer 18 is applied by initially forming the
foam material into the desired shape, such as by cutting the foam
material into the desired shape. In embodiments in which the
flexible optical circuit 10 includes a conformal coating 16 between
the substrate 12 and the protective layer, the protective layer is
typically adhered to the conformal coating by means of an adhesive,
such as a silicone adhesive, that is applied to the surface of the
protective layer facing the substrate and/or to the surface upon
which the protective layer will be disposed. As such, at least the
surface of the protective layer that faces the substrate is
preferably non-porous so as to facilitate the adhesion of the
protective layer and the substrate. As the foregoing fabrication
method evidences, the improved flexible optical circuits 10 of the
present invention can therefore be efficiently fabricated by
reducing the time required for manufacture and the costs of
manufacture relative to the fabrication of conventional flexible
optical circuits that include shrink tubing and/or strain relief
boots.
[0038] Regardless of the method by which the flexible optical
circuit 10 is fabricated, the flexible optical circuit 10 provides
strain relief for the optical fibers 14 as a result of the
inclusion of a layer of foam material. As a result of the strain
relief, the improved flexible optical circuit can transmit signals
with lower levels of attenuation. Moreover, the improved flexible
optical circuit provides improved crush resistance, thereby
protecting the flexible optical circuit and, in particular, the
optical fibers from physical damage as a result of contact with
other components within an electronics cabinet, closure or the
like. Additionally, the improved flexible optical circuits of the
present invention and, in particular, those embodiments of the
improved flexible optical circuits that include a substrate formed
of a foam material are quite flexible, thereby reducing the
concentration of stress upon the optical fibers and improving the
handling characteristics of the flexible optical circuit so as to
facilitate installation, repair and the like of the improved
flexible optical circuit.
[0039] Many modifications and other embodiments of the invention
will come to mind to one skilled in the art to which this invention
pertains having the benefit of the teachings presented in the
foregoing descriptions and the associated drawings. Therefore, it
is to be understood that the invention is not to be limited to the
specific embodiments disclosed and that modifications and other
embodiments are intended to be included within the scope of the
appended claims. Although specific terms are employed herein, they
are used in a generic and descriptive sense only and not for
purposes of limitation.
* * * * *