U.S. patent number RE36,146 [Application Number 08/781,276] was granted by the patent office on 1999-03-16 for optical fiber element having a permanent protective coating with a shore d hardness value of 65 or more.
This patent grant is currently assigned to Minnesota Mining and Manufacturing Company. Invention is credited to Bryon James Cronk, David Arnold Krohn, James William Laumer, James Craig Novack, Tracy Ristow Woodward.
United States Patent |
RE36,146 |
Novack , et al. |
March 16, 1999 |
Optical fiber element having a permanent protective coating with a
shore D hardness value of 65 or more
Abstract
An optical fiber element includes an optical fiber having a
numerical aperture ranging from 0.08 to 0.34 and a protective
coating affixed to the outer surface of the optical fiber. The
protective coating has a Shore D .[.hardnees.]. .Iadd.hardness
.Iaddend.value of 65 or more and remains on the optical fiber
during connectorization so that the fiber is neither damaged by the
blades of a stripping tool nor subjected to chemical or physical
attack.
Inventors: |
Novack; James Craig (Hudson,
WI), Cronk; Bryon James (Hudson, WI), Laumer; James
William (White Bear Lake, MN), Woodward; Tracy Ristow
(Cottage Grove, MN), Krohn; David Arnold (Hamden, CT) |
Assignee: |
Minnesota Mining and Manufacturing
Company (St. Paul, MN)
|
Family
ID: |
22541935 |
Appl.
No.: |
08/781,276 |
Filed: |
January 10, 1997 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
152206 |
Nov 15, 1993 |
05381504 |
Jan 10, 1995 |
|
|
Current U.S.
Class: |
385/128; 65/385;
385/141; 427/163.1 |
Current CPC
Class: |
C03C
25/106 (20130101); C03C 25/1065 (20130101); G02B
6/443 (20130101) |
Current International
Class: |
C03C
25/10 (20060101); G02B 6/44 (20060101); G02B
006/16 () |
Field of
Search: |
;385/123,124,126-128,141,144,145 ;427/162,163.1,163.2
;65/385,435 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
1256821 |
|
Jul 1989 |
|
CA |
|
0 169 751 |
|
Jan 1986 |
|
EP |
|
0410622 |
|
Jan 1991 |
|
EP |
|
0 405 549 A1 |
|
Jan 1991 |
|
EP |
|
58-204847 |
|
Nov 1983 |
|
JP |
|
60-71551 |
|
Apr 1985 |
|
JP |
|
2-153308 |
|
Jun 1990 |
|
JP |
|
4-66905 |
|
Mar 1992 |
|
JP |
|
2 096 353 |
|
Oct 1982 |
|
GB |
|
2256604 |
|
Dec 1992 |
|
GB |
|
WO91/03503 |
|
Mar 1991 |
|
WO |
|
Other References
Roberts et al, "Fiber Construction for Improved Mechanical
Reliability", SPIE, vol. 1366, Fiber Optics Reliability (1990), pp.
129-135. .
Lawson, "Contributions and Effects of Coatings on Optical Fibers",
Optical Fiber Coatings Group, DeSoto Inc., 10 pages, No Date. .
Machida et al, "Newly Developed, Small Diameter Optical Link Cord
Using Compound Glass Fiber", International Wire & Cable
Symposium Proceedings, 1992, pp. 401-405. .
Durometer-Plastometer Conversion Chart, Shore Instruments Mfg.,
dated Jul. 27, 1994, p. 1. .
6001 CA, Chemical Abstracts, vol. 97, No. 6, p. 250 (09 Aug. 1982).
.
Aulich, H.A. et al., "Modified UV-Curable Epoxy Silicones and
Urethane Acrylates as Coating Materials for Optical Fibers," ECOC
83--9th European Conference on Optical Communication, Elsevier
Science Publications, Amsterdam, NL, pp. 377-380 (23-26 Oct.,
1983)..
|
Primary Examiner: Lee; John D.
Attorney, Agent or Firm: Gwin, Jr.; H. Sanders
Claims
What is claimed is:
1. An optical fiber element, comprising:
an optical fiber having a numerical aperture ranging from 0.08 to
0.34; .[.and.].
a protective coating affixed to the outer surface of said optical
fiber, said protective coating having a Shore D hardness value of
65 or more.Iadd., wherein the protective coating remains on the
outer surface of the optical fiber during connectorization and
permanently thereafter.Iaddend..
2. The optical fiber element of claim 1 further including a buffer
which substantially encloses said optical fiber and said protective
coating, said buffer comprising an inner, resilient layer and an
outer, rigid layer.
3. The optical fiber element of claim 2 wherein said inner,
resilient layer has a modulus ranging from 0.5 to 20 MPa, and said
outer, rigid layer has a modulus ranging from 500 to 2500 MPa.
4. The optical fiber element of claim 2 wherein said inner,
resilient layer has a thickness ranging from 15 to 38 micrometers,
and said outer, rigid layer has a thickness ranging from 25 to 48
micrometers.
5. The optical fiber element of claim 2 wherein said protective
coating adhesively bonds with said optical fiber and with said
inner, resilient layer, said bond with said optical fiber being
stronger than said bond with said inner, resilient layer.Iadd.,
whereby the buffer may be stripped from the protective coating
during connectorization such that the protective coating remains on
the outer surface of the optical fiber during connectorization and
permanently thereafter.Iaddend..
6. The optical fiber element of claim 1 wherein said protective
coating comprises an epoxy-functional polysiloxane having the
structure: ##STR6## wherein: the ratio of a to b ranges from about
1:2 to about 2:1; and
R is an alkyl group of one to three carbon atoms.
7. The optical fiber element of claim 6 wherein said protective
coating further comprises a bisphenol A diglycidyl ether resin
having the structure: ##STR7## wherein n ranges from 0 to 2.
8. The optical fiber element of claim 7 wherein said bisphenol A
diglycidyl ether resin is present in said protective coating at a
weight percentage ranging from about 0 to about 20, said weight
percentage based on the total amount of epoxy-functional
polysiloxane and bisphenol A diglycidyl ether resin present in said
protective coating.
9. The optical fiber element of claim 7 wherein the ratio of a to b
ranges from about 1:2 to about 1.5:1, and wherein said bisphenol A
diglycidyl ether resin is present in said protective coating at a
weight percentage ranging from about 0 to about 30, said weight
percentage based on the total amount of epoxy-functional
polysiloxane and bisphenol A diglycidyl ether resin present in said
protective coating.
10. The optical fiber element of claim 6 wherein said protective
coating further comprises a cycloaliphatic epoxide having the
structure: ##STR8##
11. The optical fiber element of claim 10 wherein the ratio of a to
b ranges from about 1:2 to about 1.5:1, and wherein said
cycloaliphatic epoxide is present in said protective coating at a
weight percentage ranging from about 0 to about 50, said weight
percentage based on the total amount of epoxy-functional
polysiloxane and cycloaliphatic epoxide present in said protective
coating.
12. The optical fiber element of claim 10 wherein said protective
coating further includes an alpha-olefin epoxide having the
structure: ##STR9## wherein R is an alkyl of 10 to 16 carbon
atoms.
13. The optical fiber element of claim 12 wherein:
the ratio of a to b ranges from about 1.5:1 to about 2:1;
said epoxy-functional polysiloxane is present in said protective
coating at a weight percentage ranging from about 27 to about
53;
said cycloaliphatic epoxide is present in said protective coating
at a weight percentage ranging from about 27 to about 53; and
said alpha-olefin epoxide is present in said protective coating at
a weight percentage of about 20, said weight percentages based on
the total amount of epoxy-functional polysiloxane, cycloaliphatic
epoxide, and alpha-olefin epoxide present in said protective
coating.
14. The optical fiber element of claim 1 wherein said protective
coating comprises a novolac epoxy having the structure: ##STR10##
wherein the average value of n ranges from 0.2 to 1.8.
15. The optical fiber element of claim 1 wherein said protective
coating comprises a bisphenol A diglycidyl ether resin having the
structure: ##STR11## wherein n ranges from 0 to 2.
16. The optical fiber element of claim 1 wherein said protective
coating has a thickness ranging from 8 to 23 micrometers.
17. The optical fiber element of claim 2 wherein said optical fiber
and said protective coating have a combined diameter ranging from
about 120 to about 130 micrometers.
18. The optical fiber element of claim 17 wherein the total
diameter of said optical fiber element ranges from about 240 to
about 260 micrometers.
19. The optical fiber element of claim 1 wherein said optical fiber
is capable of supporting multiple modes and has a numerical
aperture ranging from about 0.26 to about 0.29.
20. The optical fiber element of claim 1 wherein said optical fiber
is capable of supporting one mode and has a numerical aperture
ranging from about 0.11 to about 0.20.
21. A method for producing an optical fiber element comprising the
steps of:
providing an optical fiber having a numerical aperture ranging from
0.08 to 0.34; and
affixing a protective coating to the outer surface of said optical
fiber, said protective coating having a Shore D hardness value of
65 or more.
22. The method of claim 21 further including the step of applying a
buffer which substantially encloses said optical fiber and said
protective coating, said buffer comprising an inner, resilient
layer and an outer, rigid layer.
23. The method of claim 22 wherein said inner, resilient layer has
a modulus ranging from 0.5 to 20 MPa, and said outer, rigid layer
has a modulus ranging from 500 to 2500 MPa.
24. The method of claim 23 wherein said inner, resilient layer is
applied at a thickness ranging from 15 to 38 micrometers, and said
outer, rigid layer is applied at a thickness ranging from 25 to 48
micrometers.
25. The method of claim 22 wherein said protective coating
adhesively bonds with said optical fiber and with said inner,
resilient layer, said bond with said optical fiber being stronger
than said bond with said inner, resilient layer.
26. The method of claim 22 wherein said optical fiber and said
protective coating have a combined diameter ranging from about 120
to about 130 micrometers.
27. The method of claim 26 wherein the total diameter of said
optical fiber element ranges from about 240 to about 260
micrometers.
28. The method of claim 21 wherein said protective coating is
applied at a thickness ranging from 8 to 23 micrometers.
29. The method of claim 21 wherein said protective coating
comprises an epoxy-functional polysiloxane having the structure:
##STR12## wherein: the ratio of a to b ranges from about 1:2 to
about 2:1; and
R is an alkyl group of one to three carbon atoms.
30. The method of claim 29 wherein said protective coating further
comprises a bisphenol A diglycidyl ether resin having the
structure: ##STR13## wherein n ranges from 0 to 2.
31. The method of claim 30 wherein said bisphenol A diglycidyl
ether resin is present in said protective coating at a weight
percentage ranging from about 0 to about 20, said weight percentage
based on the total amount of epoxy-functional polysiloxane and
bisphenol A diglycidyl ether resin present in said protective
coating.
32. The method of claim 30 wherein the ratio of a to b ranges from
about 1:2 to about 1.5:1, and wherein said bisphenol A diglycidyl
ether resin is present in said protective coating at a weight
percentage ranging from about 0 to about 30, said weight percentage
based on the total amount of epoxy-functional polysiloxane and
bisphenol A diglycidyl ether resin present in said protective
coating.
33. The method of claim 29 wherein said protective coating further
comprises a cycloaliphatic epoxide having the structure:
##STR14##
34. The method of claim 33 wherein the ratio of a to b ranges from
about 1:2 to about 1.5:1, and wherein said cycloaliphatic epoxide
is present in said protective coating at a weight percentage
ranging from about 0 to about 50, said weight percentage based on
the total amount of epoxy-functional polysiloxane and
cycloaliphatic epoxide present in said protective coating.
35. The method of claim 33 wherein said protective coating further
includes an alpha-olefin epoxide having the structure ##STR15##
wherein R is an alkyl of 10 to 16 carbon atoms.
36. The method of claim 35 wherein:
the ratio of a to b ranges from about 1.5:1 to about 2:1;
said epoxy-functional polysiloxane is present in said protective
coating at a weight percentage ranging from about 27 to about
53;
said cycloaliphatic epoxide is present in said protective coating
at a weight percentage ranging from about 27 to about 53; and
said alpha-olefin epoxide is present in said protective coating at
a weight percentage of about 20, said weight percentages based on
the total amount of epoxy-functional polysiloxane, cycloaliphatic
epoxide, and alpha-olefin epoxide in said protective coating.
37. The method of claim 21 wherein said protective coating
comprises a novolac epoxy having the structure: ##STR16## wherein n
ranges from 0.2 to 1.8.
38. The method of claim 21 wherein said protective coating
comprises a bisphenol A diglycidyl ether resin having the
structure: ##STR17## wherein n ranges from 0 to 2. .Iadd.
39. A method for connecting an optical fiber element to a device,
wherein the optical fiber element comprises:
an optical fiber with a numerical aperture ranging from 0.08 to
0.34;
a protective coating affixed to the outer surface of said optical
fiber, said protective coating having a Shore D hardness value of
65 or more; and
a buffer which substantially encloses said optical fiber and said
protective coating;
the method comprising:
removing the buffer from the protective coating such that the
protective coating remains affixed to the outer surface of the
optical fiber; and
inserting the optical fiber with affixed protective coating into
the device to provide optical interconnection..Iaddend.
Description
FIELD OF THE INVENTION
The present invention relates to an optical fiber element and, more
particularly, to an optical fiber element comprising an optical
fiber having a protective coating affixed to the outer surface
thereof to protect the optical fiber during connectorization.
BACKGROUND OF THE ART
In the construction of glass-based optical fiber elements, a
coating is usually applied to the glass optical fiber immediately
after drawing to protect the glass surface from the detrimental
effects of chemical and/or mechanical attack which would otherwise
occur. Such forms of attack, to which glass optical fibers are
particularly susceptible, greatly decrease the mechanical strength
of optical fibers and lead to their premature failure.
Conventionally, several coatings are applied to optical fibers,
with each serving a specific purpose. A soft coating is applied
initially to protect the fiber from microbending losses, and a
harder, secondary coating is applied over the soft coating to
provide resistance to abrasion.
The connectorization process (i.e., coupling an optical fiber
element to another optical fiber element or other optical element
via a splicing device or optical connector) conventionally entails
the removal of all coating layers such that the bare glass surface
is exposed. The glass surface is usually cleaned by wiping it with
a soft tissue which has been moistened with an alcohol such as
isopropanol. The fiber is then fixed into a connector ferrule or
splicing device using an adhesive such as an epoxy, hot melt, or
acrylic adhesive. Upon curing (or cooling) of the adhesive, the
fiber end face is polished and the connectorization process is
complete.
During the connectorization process, the optical fiber is very
vulnerable. Initially, the fiber may be nicked by the blades of the
tool used to remove the outer coatings during the stripping
operation. After stripping, the bare fiber is exposed to elements
in the local environment. These are likely to include water vapor
and dust particles. Water acts chemically on the surface of the
glass and dust acts as an abrasive. Both of these effects
contribute to failure of the glass fiber. Most failures in optical
fiber systems tend to occur at the sites of connector
installation.
One solution to the problem of fiber stripping and exposure during
connectorization has been proposed in U.S. Pat. No. 4,973,129. That
patent discloses an optical fiber element wherein a resin
composition having a Shore D hardness value of 65 or more
(specified in the Japanese Industrial Standards at room
temperature) is applied to the surface of a glass optical fiber
having a numerical aperture (NA) value of 0.35 or more. The resin
is then cured to form a primary coating layer which does not have
to be peeled from the optical fiber at the time of
connectorization. Instead, the primary layer remains on the fiber
during connectorization (and thereafter) to prevent the fiber from
being damaged as described above. Useable optical fibers are said
to be limited to those having a NA value of 0.35 or more because
the optical losses caused by microbending ("microbending loss")
increase upon covering the optical fiber with such a hard resin. In
optical fibers with a NA value below 0.35, microbending loss was
found to be so great as to make optical communications impractical.
When the NA of the optical fiber is 0.35 or more, however,
microbending loss was not found to be a problem.
Unfortunately, optical fiber elements which require an optical
fiber having a NA value of 0.35 or more are not commercially
useful. As is known, NA is a measure of the angle of light which
will be accepted and transmitted in an optical fiber. Optical fiber
elements having a NA value of 0.35 or more find limited use in
communication, data transmission, and other high bandwidth
applications for two reasons: 1) limited information-carrying
capacity and 2) incompatibility with existing, standardized
communication fibers (which normally have NA values less than
0.29). The information-carrying capacity of an optical fiber is
usually expressed as bandwidth. Bandwidth is a measure of the
maximum rate at which information can pass through an optical fiber
(usually expressed in MHz-km). Bandwidth is inversely proportional
to NA because the higher order modes (analogous to higher angles of
incident light) have longer paths in the fiber, thereby resulting
in pulse broadening or dispersion. The bandwidth limitation of an
optical fiber element occurs when individual pulses travelling
through that fiber can no longer be distinguished from one another
due to dispersion. Thus, the larger the NA value of an optical
fiber, the smaller is that fiber's bandwidth (and therefore
information-carrying capacity). Most commercially useful optical
fibers have a NA value of 0.29 or less. As compared to the
information-carrying capacity of such commercially useful optical
fibers, fibers having a NA value of 0.35 or more carry far less
information in a given period of time and are therefore
undesirable.
Incompatibility becomes a problem when one optical fiber element is
spliced or connected to another optical fiber element. In this
instance, it is important to minimize signal attenuation at the
point of connection. When an optical fiber element with a higher NA
value is spliced to a fiber with a lower NA value, all light
exceeding the NA value of the receiving fiber will be attenuated.
Light-carrying capacity is proportional to the square of the NA.
Thus, as an example, 38% of the light will be lost when transmitted
from a fiber with a NA value of 0.35 to a fiber with a NA value of
0.275. This is a significant and unacceptable loss in signal.
Accordingly, a need exists in the art for an optical fiber element
which protects the optical fiber during connectorization and which
allows the use of optical fibers having NA values smaller than
0.35.
SUMMARY OF THE INVENTION
The present invention provides an optical fiber element comprising
an optical fiber having a numerical aperture ranging from 0.08 to
0.34 and a protective coating affixed to the outer surface of the
optical fiber. The protective coating has a Shore D hardness value
of 65 or more and remains on the optical fiber (i.e., is not
stripped from the fiber) during connectorization so that the fiber
is neither damaged by the blades of a stripping tool nor subjected
to chemical or physical attack by, e.g., water vapor or dust.
It is preferred that the optical fiber element further include a
buffer which substantially encloses the optical fiber and the
protective coating. The buffer may include an inner, resilient
layer and an outer, rigid layer. The inner, resilient layer is
preferably of sufficiently low modulus (e.g., 0.5 to 20 MPa) to
provide the optical fiber element with protection against
microbending losses. The outer, rigid layer is preferably of
sufficiently high modulus (e.g., 500 to 2500 MPa) to protect the
underlying layers from abrasion and mechanical damage.
The protective coating preferably forms an adhesive bond with both
the optical fiber and with the inner, resilient layer of the
buffer. In this manner, the protective coating and buffer form an
integral coating. During connectorization, however, enough of the
buffer must be removed to allow the optical fiber and protective
coating to be inserted in and adhered to a connector or splicing
device. To facilitate this, the bond formed between the protective
coating and the optical fiber is greater than that formed between
the protective coating and the inner, resilient layer, thereby
allowing the buffer to be easily stripped from the fiber and
protective coating.
The present invention also provides a method for producing an
optical fiber element. The method comprises the steps of:
providing an optical fiber having a numerical aperture ranging from
0.08 to 0.34; and
affixing a protective coating to the outer surface of the optical
fiber, the protective coating preferably having a Shore D hardness
value of 65 or more.
The method may further include the step of applying a buffer which
substantially encloses the optical fiber and the protective
coating, the buffer including an inner, resilient layer and an
outer, rigid layer.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 illustrates an optical fiber element constructed in
accordance with the present invention, including an optical fiber,
a protective coating, and a buffer;
FIG. 2 graphically illustrates a dynamic fatigue analysis (Weibull
plot) for the optical fiber element of Example 1;
FIG. 3 graphically illustrates microbending test results for
Examples 2, 3, 5, and 6; and
FIG. 4 graphically illustrates macrobending test results for
Examples 5 and 6.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an optical fiber element 10 constructed in accordance
with the present invention. Optical fiber element 10 includes an
optical fiber 12, a protective coating 14, and a buffer 16. Optical
fiber 12 further includes a core 12A and cladding 12B. Core 12A and
cladding 12B are preferably constructed of glass, but may also be
constructed of any suitable material. For example, core 12A can
also be made from poly(methyl methacrylate), polystyrene,
polycarbonate, alloys of the foregoing, fluorinated or deuterated
analogs to the foregoing, fluoropolymers and alloys thereof, and
silicones. Cladding 12B can also be constructed from materials
other than glass, such as fluoropolymers, fluoroelastomers, and
silicones. Buffer 16 longitudinally encloses optical fiber 12 and
protective coating 14, and preferably includes an inner, resilient
layer 18 and an outer, rigid layer 20. Inner, resilient layer 18
provides optical fiber element 10 with protection against
microbending losses while outer, rigid layer 20 protects the
underlying layers from abrasion and mechanical damage.
Optical fiber 12 may have any desired numerical aperture (NA)
range, but preferably has a NA value ranging from 0.08 to 0.34.
Further, optical fiber 12 may be either a single mode fiber (i.e.,
supports only one path that a light ray can follow in travelling
down the optical fiber element) or a multi-mode fiber (i.e.,
capable of supporting multiple paths for light rays to follow in
travelling down the optical fiber element). When optical fiber 12
is a single mode fiber, the NA thereof preferably ranges from about
0.11 to about 0.20. When optical fiber 12 is a multi-mode fiber,
the NA thereof preferably ranges from about 0.26 to about 0.29.
Protective coating 14 is affixed to the outer surface of optical
fiber 12 (or, more precisely, to the outer surface of cladding
12B). During the process of connectorization, buffer 16 is stripped
from a predetermined length of a terminal end of optical fiber
element 10 to allow the fiber to be properly inserted into and
bonded with an optical fiber connector or splicing device.
Protective coating 14, however, remains on the outer surface of
optical fiber 12 (i.e., is not stripped from the fiber) during the
process of connectorization and permanently thereafter. In this
manner, protective coating 14 prevents optical fiber 12 from being
damaged by the blades of a stripping tool (used to remove buffer
16) or weakened by chemical or physical attack from, e.g., water
vapor or dust, which would otherwise occur if the bare glass
surface of optical fiber 12 were exposed. Protective coating 14
should have a sufficiently high degree of hardness that the coating
is resistant to mechanical force and abrasion. Specifically,
protective coating 14 should allow optical fiber element 10 to be
handled, stripped, cleaned, and clamped inside of a connector or
splicing device without incurring damage to the surface of optical
fiber 12. Further, once clamped and bonded inside of a connector or
splicing device, protective coating 14 should be hard enough that
optical fiber 12 does not exhibit signal loss due to radial
movement of the coated fiber inside of the connector or splicing
device. Protective coating 14 is sufficiently hard for these
purposes when it has a Shore D hardness value of 65 or more (as
determined in accordance with ASTM D2240).
In addition to a Shore D hardness value of 65 or more, the ideal
protective coating would also provide the following:
1) a barrier to water vapor, dust, and other agents of chemical and
mechanical attack against the glass optical fiber;
2) surface characteristics such that the protective coating adheres
strongly to the glass outer surface of the optical fiber so that it
is not easily removed, and at the same time adheres weakly to the
buffer so that the buffer can be easily stripped from the coated
optical fiber without causing damage to the fiber; and
3) the ability to form strong bonds with the adhesives used to
affix optical fibers to connectors and splicing devices.
Any coating having a Shore D hardness value of 65 or more and which
provides, at least to some degree, all or most of the above-listed
properties may be utilized as protective coating 14. While the
present optical fiber element is not limited to any particular
group of protective coating materials, a number of suitable
materials have been identified. For example, the protective coating
may comprise an epoxy-functional polysiloxane having the structure:
##STR1## wherein: the ratio of a to b ranges from about 1:2 to
about 2:1; and
R is an alkyl group of one to three carbon atoms.
Such epoxy-functional polysiloxanes are described in U.S. Pat. No.
4,822,687, the disclosure of which is incorporated herein by
reference, and in copending U.S. patent application Ser. No.
07/861,647, filed Apr. 1, 1992.
Preferably, the protective coating further includes a bisphenol A
diglycidyl ether resin having the structure: ##STR2## wherein the
average value of n ranges from 0 to 2. More preferably, the average
value of n is less than 1.
Suitable bisphenol A diglycidyl ether resins are commercially
available from The Dow Chemical Company as D.E.R..TM.331 and
D.E.R..TM.332, and also from Shell Oil Company as Epon.TM.828. The
bisphenol A diglycidyl ether resin may be present in the protective
coating at a weight percentage ranging from about 0 to 20, and the
epoxy-functional polysiloxane may be present at a weight percentage
ranging from about 80 to 100. The weight percentage of bisphenol A
diglycidyl ether resin in the protective coating may be extended to
about 30 by decreasing the upper limit of the ratio range of a to b
in the epoxy-functional polysiloxane to about 1.5:1 (so that the
range is from 1:2 to 1.5:1). It should be noted that the protective
coating may contain other constituents (e.g., catalysts,
sensitizers, stabilizers, etc.). Thus, the above weight percentages
are based only upon the total amount of epoxy-functional
polysiloxane and bisphenol A diglycidyl ether resin present in the
protective coating.
As an additional example of a protective coating material, the
bisphenol A diglycidyl ether resin set forth above may alone be
used as the protective coating (i.e., without any epoxy-functional
polysiloxane).
A further example of a suitable protective coating material
includes the above-described epoxy-functional polysiloxane along
with a cycloaliphatic epoxide having the structure: ##STR3##
Suitable cycloaliphatic epoxides are commercially available from
Union Carbide under the .[.tradname.]. .Iadd.trade name
.Iaddend.ERL-4221. In this instance, the ratio of a to b in the
epoxy-functional polysiloxane preferably ranges from about 1:2 to
about 1.5:1, and the cycloaliphatic epoxide is present in the
protective coating at a weight percentage ranging from about 0 to
50 (with the balance comprising epoxy-functional polysiloxane). As
before, the weight percentages are based on the total amount of
epoxy-functional polysiloxane and cycloaliphatic epoxide in the
protective coating.
Another example of an appropriate protective coating includes the
aforementioned epoxy-functional polysiloxane and cycloaliphatic
epoxide along with an alpha-olefin epoxide having the structure:
##STR4## wherein R is an alkyl of 10 to 16 carbon atoms. Such
alpha-olefin epoxides are commercially available as Vikolox.TM.
from Atochem North America, Inc., Buffalo, N. Y. Preferably, the
alpha-olefin epoxide is present in the protective coating at a
weight percentage of about 20, the cycloaliphatic epoxide is
present at a weight percentage ranging from about 27 to 53, and the
epoxy-functional polysiloxane makes up the balance. Further, the
ratio of a to b in the epoxy-functional polysiloxane desirably
ranges from about 1.5:1 to 2:1. Again, the weight percentages are
based on the total amount of epoxy-functional polysiloxane,
cycloaliphatic epoxide, and alpha-olefin epoxide in the protective
coating.
A further example of a protective coating according to the present
invention is a novolac epoxy having the structure: ##STR5## wherein
the average value of n ranges from 0.2 to 1.8. The preferred value
is 0.2. Such novolac epoxies are commercially available from The
Dow Chemical Company as D.E.N..TM.431, D.E.N..TM.438, and
D.E.N..TM.439.
As noted above, buffer 16 preferably includes an inner, resilient
layer 18 and an outer, rigid layer 20. It has been found that by
including a relatively soft, resilient layer (18) to the outer,
longitudinal surface of protective coating 14, microbending losses
are minimized. Thus, even though protective coating 14 has a high
degree of hardness (Shore D hardness of 65 or more), the relatively
soft inner, resilient layer 18 allows optical fibers having
virtually any NA value to be used in the present optical fiber
element without incurring unacceptably high microbending losses.
For this reason, commercially useful optical fibers having NA
values ranging from 0.08 to 0.34 may be used.
In order to provide sufficient protection from microbending losses,
inner, resilient layer 18 preferably has a modulus ranging from 0.5
to 20 MPa. It is also preferred that inner, resilient layer 18 be
capable of bonding with protective coating 14. In this manner,
protective coating 14 and buffer 16 together form an integral
coating for optical fiber 12. However, the bond between protective
coating 14 and inner, resilient layer 18 should be sufficiently
weak that buffer 16 can be easily stripped from protective coating
14. Specifically, the bond between protective coating 14 and
optical fiber 12 should be stronger than the bond between
protective coating 14 and inner, resilient layer 18. In this
manner, buffer 16 can be readily stripped from optical fiber
element 10 without also removing protective coating 14 or causing
damage to optical fiber 12.
Inner, resilient layer 18 may be constructed from any material
having the foregoing physical properties. Examples of suitable
materials include acrylate or epoxy functional urethanes,
silicones, acrylates, and epoxies. Materials which are easily cured
using ultraviolet radiation are preferred. Such materials are
commercially available within the desired modulus range of 0.5 to
20 MPa. Acrylate functional silicones, such as those which are
commercially available from Shin-Etsu Silicones of America, Inc.,
Torrance, Calif., are preferred. A particularly preferred acrylate
functional silicone is Shin-Etsu OF-206, which was determined to
have a modulus of 2.5 MPa at room temperature.
Outer, rigid layer 20 protects the underlying coatings from
abrasion and compressive forces. To this end, it is preferred that
outer, rigid layer 20 has a modulus ranging from 500 to 2500 MPa.
Non-limiting examples of acceptable materials from which outer,
rigid layer 20 may be constructed include acrylate or epoxy
functional urethanes, silicones, acrylates, and epoxies. Acrylate
functional urethanes are preferred. Such acrylated urethanes are
commercially available from DSM Desotech, Inc., Elgin, Ill. A
particularly preferred acrylated urethane, having a modulus of 1300
MPa (23.degree. C.), is available from DeSotech, Inc. as
DeSolite.RTM.950-103.
The diameters of optical fiber element 10 and optical fiber 12, as
well as the thicknesses of protective coating 14 and buffer 16,
will vary depending upon the particular application in which the
optical fiber element is used. Generally, it is preferred that the
combined diameter D.sub.o of optical fiber 12 and protective
coating 14 be compatible with the connector, splicing device, or
other optical element into which the coated optical fiber is to be
inserted. Thus, the diameter D.sub.o should be no larger (nor much
smaller) than that which can be accommodated by such elements. In
this regard, it has been found that when the diameter D.sub.o
ranges from about 120 to 130 micrometers, and is preferably about
125 micrometers, optical fiber element 10 will be compatible with
most commercially available connectors, splicing devices, and other
optical elements. At such a diameter, protective coating 14 may
range in thickness from about 8 to about 23 micrometers, cladding
12B may range in thickness from about 8 to about 24 micrometers,
and core 12A will generally be about 62.5 micrometers in diameter.
It should be understood, however, that such thicknesses/diameters
are merely representative of current industry standards, and may be
changed without deviating from the scope of the present
invention.
In further accordance with current industry standards, the total
diameter of optical fiber element 10 preferably ranges from about
240 to about 260 micrometers. As such, the thickness of inner,
resilient layer 18 preferably ranges from about 15 to about 38
micrometers, and the thickness of outer, rigid layer 20 preferably
ranges from about 25 to about 48 micrometers. Again, such
dimensions are merely representative of current industry standards.
The scope of the present invention is not limited to any particular
set of thicknesses or diameters.
Optical fiber element 10 may be produced by any conventional
optical fiber production technique. Such techniques generally
involve a draw tower in which a preformed glass rod is heated to
produce a thin fiber of glass. The fiber is pulled vertically
through the draw tower. Along the way, the fiber passes through one
or more coating stations in which various coatings are applied and
cured in-line to the newly drawn fiber. The coating stations each
contain a die having an exit orifice which is sized to apply the
desired thickness of the particular coating to the fiber.
Concentricity monitors and laser measuring devices are provided
near each coating station to ensure that the coating applied at
that station is coated concentrically and to the desired
diameter.
To facilitate the coating process, the compositions giving rise to
protective coating 14 and buffer 16 preferably have a viscosity
ranging from 800 to 15,000 cps, and more preferably from 900 to
10,000 cps. Conveniently, inner, resilient layer 18 and outer,
rigid layer 20 can be wet coated in the same coating station and
then cured simultaneously.
In order that the invention may be more readily understood,
reference is made to the following examples, which are intended to
be illustrative of the invention, but are not intended to be
limiting in scope.
FIBER DRAWING PROCESS
Preform Preparation
A fiber optic preform was first prepared in accordance with U.S.
Pat. No. 4,217,027.
Fiber Drawing
The fiber optic draw tower used in the draw process was based on an
enclosed Nokia system which featured a Nokia-Maillefer fiber draw
tower (Vantaa, Finland). To begin the draw process, a downfeed
system was used to control the rate at which the optical preform
was fed into a 15 KW Lapel zirconia induction furnace (Lapel Corp.,
Maspeth, NY) in which the preform was heated to a temperature at
which it may be drawn to fiber (between about 2200.degree. to
2250.degree. C.). Below the heat source, a LaserMike.TM. laser
telemetric measurement system was used to measure the drawn fiber
diameter as well as monitor the fiber position within the
tower.
The newly formed fiber was then passed to a primary coating station
at which the protective coating was applied. The coating station
included a coating die assembly, a Fusion Systems.RTM. Corp.
microwave UV curing system, a concentricity monitor, and another
laser telemetric system. The coating die assembly, based on a
Norrsken Corp. design, consisted of a sizing die(s), back pressure
die and a containment housing which was mounted on a stage having
adjustment for pitch and tilt and x-y translation. These
adjustments were used to control coating concentricity. The
protective coating material was supplied to the coating die
assembly from a pressurized vessel and was applied, cured and
measured within the primary coating station.
The coated fiber then proceeded on to a secondary coating station
where a buffer was applied to the coated fiber. In certain cases it
was desirable to apply two buffer layers simultaneously in a
wet-on-wet application at the secondary coating station. In this
case an additional sizing die was used and an additional vessel was
used to supply material to this die. The coatings were applied, one
after the other, and then cured and the outer diameter measured. As
required, additional coatings could be applied via additional
coating stations. Ultimately, the completed optical fiber element
was drawn through a control capstan and onto a take-up spool
(Nokia).
TESTING
Coating Dimension
Coating dimensions and concentricities are measured using an
Olympus STM-MJS Measuring Microscope and MeasureGraph 123 software
(Rose Technologies). The technique fits a circle to a number of
points selected about the circumference. The size of these circles
and their offset from center (from various components of the fiber
structure) were determined and reported by the software.
Connector temperature Cycle
This test was modeled after Bellcore test TR-NWT-0003236 (Jun.
1992), "Generic Requirements for Optical Fiber Connectors". The
Bellcore test cycles from -45.degree. to 70.degree. C. for 14 days.
The test procedure used herein spanned -45.degree. to 60.degree. C.
for 48 hours. The values reported are the maximum within this
time.
Dynamic Fatigue Testing
This test was performed similarly to Fiber Optic Test Procedure
("FOTP") 28. The exceptions are as follows:
Strain Rate =9% minute
Gauge Length =4 meters
Environment =Ambient Laboratory
Microbending Testing
Microbending testing was done in accord with FOTP-68. The highest
value obtained was reported.
Macrobending Testing
Macrobending testing consisted of determining the transmission of a
fiber that was turned 180.degree. about mandrels of various
diameter. The transmission was determined as the ratio of the power
out of the wrapped fiber/power out of unwrapped fiber. Care was
taken to insure that other loops in the fiber were large enough
(radius>10 cm) such that they did not contribute to the
loss.
Numerical Aperture Testing
The numerical attenuation was determined using a Photon Kinetics
Model FOA-2000 which refers to FOTP-177 for "Numerical Aperture
Measurement of Graded-Index Optical Fibers". The test procedure was
modified to accommodate experimental fiber by using shorter lengths
of fiber (0.2-0.5 Km) rather than the .gtoreq.1 Km lengths
specified in the FOTP.
Pull-Out Test
A tensile pull-out test was utilized to determine how well the
connector adhesive adheres to the protective coating (which remains
on the fiber during connectorization and permanently thereafter).
An "ST" connector design was chosen due to its availability and
compatibility with the test equipment. It consists of a zirconia
ferrule mounted in a barrel to which was attached a bayonet
assembly.
Fiber Preparation
In all of the following examples, 12 inch pieces
of the completed optical fiber element were stripped to reveal
1.5-2.0 cm of the protective coating which was then cleaned with a
tissue moistened with isopropyl alcohol. The fiber ends were
allowed to dry prior to installing connectors.
Two-.[.Pail.]. .Iadd.Part .Iaddend.Epoxy
A standard two-part epoxy for fiber optic connectors (either
Tra-Con #BA-F112 or 3M #8690, Part No. 80-6107-4207-6) was used. It
was mixed according to the manufacturer's instructions and poured
from the mixing envelope into a syringe body. A plunger was
installed taking care to avoid incorporation of air into the
liquid. The syringe was fitted with a blunt-end needle. This
assembly was used to inject adhesive into the ferrule from the
barrel end until adhesive appeared at the tip end. The fiber was
inserted such that the buffer coating bottomed in the barrel. The
adhesive was cured for 25 minutes at 90.degree. C.
Hot Melt Adhesive
A polyamide hot melt adhesive was provided preinstalled in ST
connectors as a product (3M 6100 Hot-Melt.TM. Connector, Part No.
80-6106-2549-5). The connector was heated in the required oven (3M
Part No. 78-8073-7401-8) for two minutes and removed. The optical
fiber was immediately installed such that the buffer coating
bottomed in the barrel. The connector was then left undisturbed
until cool.
Pull-Out Testing
Pull-out testing was performed using an Instron tensile tester
(Model 4201). Peak loads (before pull-out) were recorded. The
average of five or ten tests was reported as the pull-out value for
each sample.
Spectral Attenuation
The spectral attenuation of the fiber was determined using a Photon
Kinetics Model FOA-2000. The operational reference was FOTP-46.
Catalyst Formulation
For each of the examples, the following catalyst formulation was
used:
40 parts of bis(dodecylphenyl)iodonium hexafluoroantimonate
60 parts of a C10-C14 alcohol blend
4 parts 2-isopropylthioxanthone
EXAMPLES
Example 1
Epoxy-Functional Polysiloxane
Protective Coating Formulation
A protective coating formulation was prepared by thoroughly mixing
95 parts of an epoxy-functional polysiloxane with 5 parts of the
above-described catalyst formulation. The epoxy-functional
polysiloxane had the structure set forth above in which the ratio
of a to b was 1:1 and R was a methyl group. This formulation was
then filtered though a 0.2.mu.polysulfone filter disk into a amber
glass bottle. 1 part of 3-glycidoxypropyltrimethoxysilane was added
and thoroughly mixed.
Coating Process
The protective coating formulation was coated to a diameter of 125
.mu.m on a 110 .mu.m optical fiber which was freshly drawn from a
Diasil.TM. preform at a draw speed of 30 MPM (meters per minute).
The coating was cured and a subsequent layer of an acrylated
urethane (Desotech 950-103) buffer was coated and cured to a
diameter of 250 .mu.m.
Dynamic Fatigue Analysis
The completed optical fiber element was subjected to tensile
testing to failure (dynamic fatigue analysis). The Weibull
statistics for such testing are shown in FIG. 2.
Pull-Out Test
The buffer coatings on this and similarly coated fiber elements
were easily removed using conventional stripping tools. Connector
pull-out testing gave the following results:
______________________________________ Hot melt Adhesive 5.2 lbs
Two-Part Epoxy 6.1 lbs ______________________________________
Example 2
Epoxy-Functional Polysiloxane/Bisphenol A: Dual Coat
Protective Coating Formulation
A mixture of 75 parts of the epoxy-functional polysiloxane used in
example 1 was mixed with 25 parts Epon.TM.828 bisphenol A
diglycidyl ether resin (from the Shell Oil Co.). 5.3 parts of the
catalyst formulation was added and thoroughly mixed and filtered
though a 1.0 .mu.m Teflon.TM. filter disc into an amber glass
bottle.
Coating Process
This formulation was coated and cured to a 125 .mu.m diameter on a
100 .mu.m glass fiber which was freshly drawn from a graded index
preform at a draw speed of 45 MPM. A buffer coating of acrylated
urethane (DSM 950- 103 from DSM Desotech, Inc.), having a modulus
of 1300 MPa was coated and cured to a 250 .mu.m diameter.
Microbending Test
The completed optical fiber element was tested for microbending
according to FOTP-68 resulting in a maximum loss of 4.4 dB (see
FIG. 3).
Pull-Out Test
A similarly coated optical fiber element gave the following results
for connector pull-out tests:
______________________________________ Hot melt Adhesive 7.2 lbs
Two-Part Epoxy 4.4 lbs ______________________________________
Example 3
Epoxy-Functional Polysiloxane/Bisphenol A; Triple Coat
Protective Coating Formulation
The protective coating formulation was that described in Example
2.
Coating Process
The material was coated and cured to a 125 .mu.m diameter on a 100
.mu.m glass fiber which was freshly drawn from a graded index
preform at a draw speed of 45 MPM. Inner and outer buffer layers
(DSM 950-075 and DSM 950-103, respectively) were applied then cured
simultaneously to diameters of 183 and 226 .mu.m, respectively. The
inner buffer layer had a modulus of 3.8 MPa while the outer buffer
layer had a modulus of 1300 MPa.
Pull-Out Test
The optical fiber element gave the following results for connector
pull-out tests:
______________________________________ Hot melt Adhesive 2.6 lbs
Two-Part Epoxy 6.2 lbs ______________________________________
Microbending Test
The optical fiber element was tested for microbending according to
FOTP-68 resulting in a maximum loss of 1.15 dB (see FIG, 3).
Example 4
Novolac
Protective Coating Formulation
A protective coating formulation was prepared by thoroughly mixing
95 parts of an epoxy-novolac (Dow DEN 431) with 5 parts of catalyst
formulation, This formulation was filtered to 0.5 .mu.m through a
Teflon.TM. filter disk into an amber bottle.
Coating Press
The protective coating formulation was coated and cured to a 125
.mu.m diameter on a 100 .mu.m glass fiber which was freshly drawn
from an unpolished preform at a draw speed of 45 MPM, A buffer
coating of acrylated urethane (DSM 9-17) was coated and cured to a
250 .mu.m diameter.
Pull-Out Test
The optical fiber element gave the following results for connector
pull-out tests:
______________________________________ Hot melt Adhesive 6.2 lbs
Two-Part Epoxy 6.5 lbs ______________________________________
Example 5
Epoxy-Functional Polysiloxane/Bisphenol A; Triple Coat
Protective Coating Formulation
A mixture of 75 parts of the epoxy-functional polysiloxane used in
example 1 was mixed with 25 parts Epon.TM.828 bisphenol A
diglycidyl ether resin (from the Shell Oil Co.). 10 parts of the
catalyst formulation was added and the formulation was thoroughly
mixed and filtered though a 1.0 .mu.m Teflon.TM. filter disc into
an amber glass bottle.
Coating Process
The protective coating formulation was coated and cured to a 125
.mu.m diameter on a 100 .mu.m glass fiber which was freshly drawn
from a graded index preform at a draw speed of 45 MPM. Inner and
outer buffer layers (Shin-Etsu OF 206 and DSM 950-103,
respectively) were applied and then cured simultaneously to
diameters of 184 and 250 .mu.m, respectively. The inner buffer
layer had a modulus of 2.5 MPa while the outer buffer layer had a
modulus of 1300 MPa.
Pull-Out Test
The optical fiber element gave the following results for connector
pull-out tests:
______________________________________ Hot melt Adhesive 3.0 lbs
Two-Part Epoxy 6.4 lbs ______________________________________
Microbending Test
The optical fiber element was tested for microbending according to
FOTP-68 resulting in a maximum loss of 0.76 dB (see FIG. 3).
Macrobending Test
The fiber was tested for macrobending and the results are shown in
FIG. 4.
Numerical Aperture
The numerical aperture was determined to be 0.258
Spectral Attenuation
The spectral attenuation, based on the modified FOTP-46, was
determined to be as follows:
@850 nm=6.03 db/Km
@1300 nm=3.5 db/Km
(Comparative) Example 6
Corning 62.5/125 .mu.m
The fiber used for this comparative example was Corning.TM. Optical
Fiber with the following identifications:
______________________________________ Product: LNF(.TM.) 62.5/125
Fiber Coat: CPC3 Fiber ID: 262712272304
______________________________________
Pull-Out Test
The fiber gave the following results for connector pull-out
tests:
______________________________________ Hot melt Adhesive 5.9 lbs
Two-Part Epoxy 4.6 lbs ______________________________________
Microbending Test
The fiber was tested for microbending according to FOTP-68
resulting in a maximum loss of 0.42 dB (see FIG. 3 ).
Macrobending Test
The fiber was tested for macrobending and the results are shown in
FIG. 4.
Numerical Aperture A value for numerical aperture of 0.269 was
provided by Corning (method unspecified).
Spectral Attenuation
The spectral attenuation values provided by Corning (method
unspecified) were as follows:
@850 nm =2.7 db/.[.Km.]. .Iadd.km .Iaddend.
@1300 nm =0.6 db/.[.Kin.]. .Iadd.km .Iaddend.
Example 7
Hardness Testing
Shore D hardness values of various protective coating formulations
were evaluated using a Shore D durometer mounted on Shore
Leverloader following the general procedure of ASTM D-2240. The
samples were prepared by curing thin layers on top of each other
such that large discs of the material resulted. Samples were at
room temperature (23.degree. C.) for testing.
______________________________________ Formulation 1 95% Epoxy
functional polysiloxane in which the a:b ratio is 1:1 and R is a
methyl group; and Catalyst Formulation 2 71.2% Epoxy-functional
polysiloxane in which the a:b ratio is 1:1 and R is a methyl group;
23.8% Epon .TM. 828 bisphenol A [piglycidyl] diglycidylether resin;
and Catalyst Formulation 3 31.7% Epoxy-functional polysiloxane in
which the a:b ratio is 2:1 and R is a methyl group; 63.3% ERL-4221
cycloaliphatic epoxide; and Catalyst Formulation 4 95% Dow D.E.N.
.TM. 431 novolac epoxy; and 5% Catalyst
______________________________________ RESULTS: Shore D Hardness
Formulation No. of Tests Average Value Deviation
______________________________________ 1 * * * 2 6 70 2 3 6 71 3 4
7 77 4 ______________________________________ *due to brittleness
of the sample it fractured upon penetration of the durometer point;
therefore, accurate values were unattainable.
* * * * *