U.S. patent application number 10/176470 was filed with the patent office on 2003-04-03 for method and apparatus for removing polymeric coatings from optical fiber.
Invention is credited to Swain, Robert F., Yablon, Andrew D..
Application Number | 20030062070 10/176470 |
Document ID | / |
Family ID | 25513913 |
Filed Date | 2003-04-03 |
United States Patent
Application |
20030062070 |
Kind Code |
A1 |
Swain, Robert F. ; et
al. |
April 3, 2003 |
Method and apparatus for removing polymeric coatings from optical
fiber
Abstract
In accordance with the invention, the polymeric coating is
removed from a coated optical fiber by disposing the fiber within a
low pressure environment and applying sufficient heat to volatilize
at least a portion of the polymeric coating. The result is that the
coating material bursts from the fiber, yielding a clean glass
surface virtually free of surface flaws. In a preferred embodiment
the heat is provided by a resistive filament heater within a vacuum
chamber.
Inventors: |
Swain, Robert F.;
(Broadclyst, GB) ; Yablon, Andrew D.; (New York,
NY) |
Correspondence
Address: |
LOWENSTEIN SANDLER PC
65 LIVINGSTON AVENUE
ROSELAND
NJ
07068
US
|
Family ID: |
25513913 |
Appl. No.: |
10/176470 |
Filed: |
June 20, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10176470 |
Jun 20, 2002 |
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09968211 |
Oct 1, 2001 |
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6436198 |
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Current U.S.
Class: |
134/105 |
Current CPC
Class: |
G02B 6/245 20130101;
B08B 2240/02 20130101; B08B 7/0071 20130101 |
Class at
Publication: |
134/105 |
International
Class: |
B08B 007/00 |
Claims
What is claimed is:
1. A method for removing the coating from a polymeric coated
optical fiber comprising the steps of: disposing the coated optical
fiber within an evacuable chamber; evacuating the chamber to a
pressure of less than about 2 Torr; and applying to the fiber
sufficient heat to volatilize at least a portion of the polymeric
coating thereby causing the coating to burst away from the
fiber.
2. The method of claim 1 wherein the chamber is evacuated to a
pressure of less than about 200 mTorr.
3. The method of claim 1 wherein heat is applied to the fiber by at
least one resistive filament heater.
4. The method of claim 3 wherein the resistive filament heater is
heated to a glow temperature in excess of 800.degree. C.
5. The method of claim 3 wherein the resistive filament heater is
heated to a temperature in excess of 1500.degree. C.
6. The method of claim 1 wherein sufficient heat is applied to the
fiber to cause the coating to burst away from the fiber in less
than about 3 seconds.
7. Apparatus for removing the coating from a polymeric coated
optical fiber comprising: an evacuable chamber; and one or more
heating elements for heating the coated fiber along the length of
coating to be removed.
8. The apparatus of claim 7 wherein the one or more heating
elements each comprise a resistive filament heater.
9. The apparatus of claim 7 wherein the one or more heating
elements comprise a series of resistive filament heaters, the
series extending along the length of coating to be removed.
10. The apparatus of claim 7 wherein the evacuable chamber
comprises a two-part chamber for sealingly engaging together about
the coated optical fiber.
11. The apparatus of claim 7 wherein each heating element comprises
an open loop resistive filament.
12. The apparatus of claim 8 wherein each heating element comprises
a resistive filament heater of refractory metal.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is related to U.S. patent application Ser.
No.______ filed by the present inventors concurrently herewith and
entitled "Method and Apparatus For Removing Polymeric Coatings From
Optical Fiber in a Non-Oxidizing Environment", which is
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The invention relates to methods for removing polymeric
coatings from optical fiber and apparatus for practicing such
methods. In particular it relates to an advantageous method of
removing such coatings by the application of heat within a low
pressure environment.
BACKGROUND OF THE INVENTION
[0003] Optical fibers are key components in modem
telecommunications systems. Basically, an optical fiber is a thin
strand of glass capable of transmitting optical signals containing
a large amount of information over long distances with very low
loss. In its simplest form, it is a small diameter waveguide
comprising a core having a first index of refraction surrounded by
a cladding having a second (lower) index of refraction. A polymeric
coating surrounding the cladding protects the fiber from
contamination and mechanical damage and maintains mechanical
strength. Typical optical fibers are made of high purity silica
glass with minor concentrations of dopants to control the index of
refraction. Typical coatings are dual coatings of urethane
acrylates. An inner (primary) coating having a relatively low in
situ equilibrium modulus is applied directly to the glass, and an
outer (secondary) coating having a relatively high modulus
surrounds the primary coating.
[0004] While protective coatings are critical for most applications
of optical fiber, short lengths of coating must be temporarily
removed in the fabrication of optical fiber devices and during the
assembly of fiber networks. Because the surface of the glass fiber
is susceptible to damage from abrasion and contamination, the
surface is coated with protective polymer immediately after the
fiber is drawn. However the coating must be temporarily removed in
the fabrication of important optical fiber devices such as fiber
Bragg gratings, long period gratings, fused couplers and
metalcoated regions. Moreover end portions of the coating need to
be removed in fusing successive fiber segments to form a network.
The fiber may be recoated after such operations.
[0005] A variety of approaches have been used to remove fiber
polymeric coatings, but none have been completely satisfactory. One
method is to mechanically scrape the coating off the glass using a
blade and then to chemically clean the exposed glass. This approach
inevitably creates surface flaws on the fiber, reducing the
strength and the reliability of devices produced from it. A second
method uses chemical solvents to soften or completely remove the
coating. While this approach has been used in manufacturing, it is
difficult to automate and involves the use of hazardous chemicals,
typically in the form of concentrated acids at high temperatures. A
third method uses heat to soften the coating and mechanical removal
of the softened coating followed by ultrasonic cleaning with a
solvent such as acetone or alcohol. Accordingly there is a need for
an improved method of removing polymeric coatings from optical
fiber.
SUMMARY OF THE INVENTION
[0006] In accordance with the invention, the polymeric coating is
removed from a coated optical fiber by disposing the fiber within a
low pressure environment and applying sufficient heat to volatilize
at least a portion of the polymeric coating. The result is that the
coating material bursts from the fiber, yielding a clean glass
surface virtually free of surface flaws. In a preferred embodiment
the heat is provided by a resistive filament heater within a vacuum
chamber.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The nature, advantages and various additional features of
the invention will appear more fully upon consideration of the
illustrative embodiments now to be described in connection with the
accompanying drawings. In the drawings:
[0008] FIG. 1 is a block diagram of the steps in removing a
polymeric coating from an optical fiber;
[0009] FIG. 2 illustrates apparatus useful in practicing the method
of FIG. 1; and
[0010] FIG. 3 illustrates a preferred resistive filament heater for
use in the apparatus of FIG. 2.
[0011] It is to be understood that these drawings are for purposes
of illustrating the concepts of the invention and are not to
scale.
DETAILED DESCRIPTION
[0012] Referring to the drawings, FIG. 1 is a block diagram of the
steps involved in removing a polymeric coating from an optical
fiber. The first step shown in block A is to dispose the coated
fiber within an evacuable chamber.
[0013] The next step (block B) is to evacuate the chamber. The
chamber should be evacuated to a low pressure below about 2 Torr
and preferably below about 200 mTorr.
[0014] The third step shown in block C is to apply heat to the
coated fiber. The heat should be sufficient to volatilize at least
a portion of the coating without changing the phase of the glass.
The heat should volatilize at least the most volatile components in
the coating and cause the coating to burst from the fiber
(explosive removal). The heat is preferably applied by radiation as
from a resistive filament within the evacuated chamber or from a
laser, such as an infrared laser, within or outside the chamber. In
typical cases involving two-layer acrylate coatings on silica
fibers, the heat provided by a resistive filament glowing at a
temperature in excess of about 800.degree. C. is adequate to effect
such removal.
[0015] The heat should be applied over the length of the coating to
be removed, either by use of an elongated heat source or series of
sources, by translating the fiber, or by translating the source of
the heat.
[0016] FIG. 2 is a perspective view of preferred apparatus useful
in practicing the method of FIG. 1. In essence, the apparatus 20
comprises one or more resistive filament heaters 21 disposed within
an evacuable (vacuum) chamber 22. The chamber 22 advantageously is
a two-part chamber comprising a first part 22A and a second part
22B which can be sealed together against an O-ring 22C and over the
coated fiber 27. The chamber can include a viewing window 22D to
permit the passage of light. An evacuation pump and valves (not
shown) are provided for pumping down the chamber. Preferably a
serial succession of heaters 21 is placed between a pair of
V-groove guides 23, 24. The succession of heaters extends along the
length of coated fiber 27 from which the coating is to be removed.
Fiber holders 25, 26 facilitate and maintain placement of the fiber
27.
[0017] As shown in FIG. 3, each filament heater 21 is
advantageously a high melting temperature metal and preferably a
refractory metal (e.g. iridium, tungsten or tantalum) ribbon bent
in an open loop 30 shaped like the Greek letter omega. The coated
fiber 27 advantageously passes through the center of the loop.
[0018] In typical operation, the coated fiber 27 is loaded into
holders 25, 26 with an exposed intermediate length guided by
V-grooves 23, 24 through the centers of filament heaters 21. The
vacuum chamber 22 is sealed and pumped down to a pressure below
about 2 Torr and preferably below about 200 mTorr. The filament
heaters 21 are then heated by the application of electricity to
glow red at temperatures in excess of about 800.degree. C. and
preferably to glow yellow at temperatures in excess of about
1500.degree. C. The heat volatizes portions of the coating causing
the coating to burst from the fiber without mechanical assistance.
Advantageously the heater is sufficiently hot to cause the coating
to burst from the fiber in less than about three seconds and
preferably less than about 1 second. This leaves a clean glass
surface free of mechanical damage, particulates or hazardous
chemicals.
[0019] The invention can now be more clearly understood by
consideration of the following example. The polymeric coating was
stripped from a 1 inch section of coming SMF28 fiber using
apparatus similar to that of FIG. 2 but having a series of 8
iridium filaments (0.001 in. thick by 0.12 inch wide) wired in
parallel. Stripping was effected by sinking about 300 Watts for 1
second at a 200 mTorr vacuum. Under these conditions the filaments
glowed yellow/white hot. With this configuration there was nearly
flawless surface quality over the stripped 1 inch section.
Unspliced stripped fiber yielded pull strengths of 600-800 Kpsia.
Best results were obtained in stripping dual acrylate coatings such
as those surrounding Corning SMF28, Fuji Panda and 3M Tiger fibers.
Dual coated fibers manufactured by Alcatel, Lucent, Fibercore and
Sumitomo were found to strip in a similar manner.
[0020] It is understood that the above-described embodiments are
illustrative of only a few of the many possible specific
embodiments, which can represent applications of the invention.
Numerous and varied other arrangements can be made by those skilled
in the art without departing from the spirit and scope of the
invention.
* * * * *