Title: Method and apparatus for removing polymeric coatings from optical fiber in a non-oxidizing environment
Abstract: In accordance with the invention, the polymeric coating is removed from a coated optical fiber by disposing the fiber within a non-oxidizing 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 non-oxidizing environment is inert gas and the heat is provided by resistive filament heaters.
Patent Number: 7,003,985 Issued on 02/28/2006 to Swain, et al.
| Inventors:
|
Swain; Robert F. (Sandy Lodge, Sandy Lane, Broadclyst, Exeter EX5 3AN, GB);
Yablon; Andrew D. (502 W. 113th St., Apt. 3D, New York, NY 10025)
|
| Appl. No.:
|
968094 |
| Filed:
|
October 1, 2001 |
| Current U.S. Class: |
65/473; 65/424; 65/503; 65/509; 65/DIG.9; 134/15; 134/21; 219/539; 373/27; 373/110; 373/117 |
| Current Intern'l Class: |
C03C 25/70 (20060101); B08B 7/00 (20060101) |
| Field of Search: |
65/473,424,157,335,346,502,509,532,DIG.4,900
156/344,584
134/15,19,21
219/50,72-74,155,156,162,538,539,260
373/5,27,28,110,117-122
|
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| 8-248234 | Sep., 1996 | JP.
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Primary Examiner: Hug; Eric
Attorney, Agent or Firm: Lowenstein Sandler PC
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application is related to U.S. patent application Ser. No. 09/968,211 filed
by the present inventors concurrently herewith and entitled "Method and Apparatus
For Removing Polymeric Coatings From Optical Fiber", which is incorporated herein
by reference.
Claims
What is claimed is:
1. A method for removing a coating from a polymeric coated optical fiber comprising
the steps of:
disposing the coated optical fiber within a sealable chamber;
filling the chamber with non-oxidizing gas; and
exposing the fiber to at least one resistive filament heater heated to a glow
temperature in excess of 800° C. to apply to the fiber sufficient heat to
cause the coating to burst away from the fiber.
2. The method of claim 1 wherein the non-oxidizing gas comprises an inert gas.
3. 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.
4. The method of claim 1 wherein the at least one resistive filament heater is
heated to a glow temperature ≧1500° C.
5. Apparatus for removing a coating from a polymeric coated optical fiber comprising:
a sealable chamber, comprising a two-part chamber for sealingly engaging together
about the coated optical fiber;
means for filling the chamber with non-oxidizing gas; and
one or more resistive filament heaters heated to a glow temperature in excess
of 800° C. for heating the coated fiber along the length of coating to be
removed causing the coating to burst away from the fiber.
6. The apparatus of claim 5 wherein the one or more heating elements comprise
a series of resistive filament heaters, the series extending along a length of
coating to be removed.
7. The apparatus of claim 5 wherein each resistive filament heater is comprised
of refractory metal.
8. The apparatus of claim 7 wherein the at least one resistive filament heater
is heated to a glow temperature ≧1500° C.
9. Apparatus for removing a coating from a polymeric coated optical fiber comprising:
a sealable chamber;
means for filling the chamber with non-oxidizing gas; and
one or more heating elements each comprising an open loop resistive filament
for heating the coated fiber along a length of coating to be removed.
10. The apparatus of claim 9 wherein sufficient heat is applied to the fiber
to cause the coating to burst away from the fiber in less than about 3 seconds.
11. The apparatus of claim 9 wherein the one or more open loop resistive filaments
are heated to a glow temperature in excess of 800° C. to apply sufficient
heat to cause the coating to burst away from the fiber.
12. The apparatus of claim 9 wherein each open loop resistive filament is comprised
of refractory metal.
13. The apparatus of claim 9 wherein the one or more open loop resistive filaments
are heated to a glow temperature ≧1500° C.
14. A method for removing the coating from a polymetric coated optical fiber
comprising the steps of:
disposing the coated optical fiber within a sealable chamber;
filling the chamber with non-oxidizing gas; and
applying heat from at least one open loop resistive filament to the fiber sufficient
to cause at least a portion of the coating to burst away from the fiber.
15. The method of claim 14 wherein sufficient heat is applied to the fiber to
cause the coating to burst away from the fiber in less than about 3 seconds.
16. The method of claim 14 wherein the one or more open loop resistive filaments
are heated to a glow temperature in excess of 800° C.
17. The method of claim 14 wherein the one or more open loop resistive filaments
are comprised of refractory metal.
18. The method of claim 14 wherein the one or more open loop resistive filaments
are heated to a glow temperature ≧1500° C.
Description
FIELD OF THE INVENTION
The invention relates to methods for removing polymeric coatings from optical
fiber and to apparatus for practicing such methods. In particular it relates to
an advantageous method of removing such coatings by the application of heat within
a non-oxidizing environment.
BACKGROUND OF THE INVENTION
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.
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.
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
In accordance with the invention, the polymeric coating is removed from a coated
optical fiber by disposing the fiber within a non-oxidizing 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 non-oxidizing
environment is inert gas and the heat is provided by resistive filament heaters.
BRIEF DESCRIPTION OF THE DRAWINGS
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:
FIG. 1 is a block diagram of the steps in removing a polymeric coating from
an optical fiber;
FIG. 2 illustrates apparatus useful in practicing the method of FIG. 1; and
FIG. 3 illustrates a preferred resistive filament heater for use in the apparatus
of FIG. 2.
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
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 a sealable chamber.
The next step (block B) is to form a non-oxidizing environment within the chamber.
The chamber can be evacuated to a low pressure and filled with an inert gas such
as Argon. The inert gas can be at ambient pressure (e.g. 1 atm) or below.
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 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° C.
is adequate to effect such removal.
The heat should be applied uniformly 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.
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 a sealable 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. In accordance with
techniques well known in the art, an arrangement 28 of pumps, valves, tubing
and gas reservoirs can be provided for pumping down the chamber and introducing
non-oxidizing gas into 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.
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.
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 chamber 22 is sealed,
air is pumped out and a non-oxidizing gas such as Argon is introduced. The filament
heaters 21 are then heated by the application of electricity to glow red
at temperatures in excess of about 800° C. and preferably to glow yellow at
temperatures in excess of 1500° 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 3 seconds and preferably less than about 1 second. This leaves
a relatively clean glass surface free of mechanical damage, particulates or hazardous chemicals.
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. Stripping was carried out
in a 1 Atm Ar environment. Unspliced stripped fiber yielded pull strengths of 600-800
kpsia. Best results were obtained in stripping dual acrylate coatings such as those
surrounding Coming 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.
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.
*
