U.S. patent application number 09/876192 was filed with the patent office on 2001-10-11 for methods and apparatusses for packaging long-period fiber gratings.
Invention is credited to Carberry, Joel P., Chen, Gang, Knowles, Peter, Kohnke, Glenn E., Miller, William J., Modavis, Robert A., Weller-Brophy, Laura A..
Application Number | 20010028763 09/876192 |
Document ID | / |
Family ID | 23572243 |
Filed Date | 2001-10-11 |
United States Patent
Application |
20010028763 |
Kind Code |
A1 |
Carberry, Joel P. ; et
al. |
October 11, 2001 |
Methods and apparatusses for packaging long-period fiber
gratings
Abstract
Packages for long period fiber gratings and other optical
components (and methods for forming the packages) are described.
According to an aspect of the invention, a hollow tube surrounding
an optical fiber containing a long-period grating is collapsed in
two areas, forming a seal at each end of the tube. According to
another aspect of the invention, a hollow tube with a shelf section
at each end surrounds an optical fiber containing a long-period
grating. The hollow tube is sealed at each end with a fused frit.
According to another aspect of the invention, a hollow tube
surrounding an optical fiber containing a long-period grating is
sealed at each end with a glass plug.
Inventors: |
Carberry, Joel P.;
(Horseheads, NY) ; Chen, Gang; (Horseheads,
NY) ; Knowles, Peter; (Horseheads, NY) ;
Kohnke, Glenn E.; (Painted Post, NY) ; Miller,
William J.; (Horseheads, NY) ; Modavis, Robert
A.; (Santa Rosa, CA) ; Weller-Brophy, Laura A.;
(Corning, NY) |
Correspondence
Address: |
CORNING INCORPORATED
SP-TI-3-1
CORNING
NY
14831
|
Family ID: |
23572243 |
Appl. No.: |
09/876192 |
Filed: |
June 6, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09876192 |
Jun 6, 2001 |
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09397690 |
Sep 16, 1999 |
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6269207 |
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Current U.S.
Class: |
385/37 ;
385/31 |
Current CPC
Class: |
G02B 6/02209 20130101;
G02B 6/02095 20130101; G02B 6/2558 20130101; G02B 6/02123
20130101 |
Class at
Publication: |
385/37 ;
385/31 |
International
Class: |
G02B 006/26 |
Claims
What is claimed is:
1. An optical waveguide device package comprising: a tube having a
first end, a second end, and a cavity extending at least partially
between said first end and said second end, said tube including a
pair of collapsed sections; and an optical fiber longitudinally
disposed within said cavity and in engagement with said pair of
collapsed sections such that a length of said optical fiber is
tensionally secured between said pair of collapsed sections and a
seal is formed by each of said pair of collapsed sections.
2. The optical waveguide device of claim 1 further comprising: a
long-period grating formed at least partially within the length of
the optical fiber.
3. The optical waveguide device of claim 1 wherein the tube is
boron-doped silica glass.
4. The optical waveguide device of claim 1 wherein the tube is
Pyrex.RTM..
5. The optical waveguide device of claim 1 wherein the tube is
encased in a carbon wrap.
6. The optical waveguide device of claim 1 wherein the tube has a
first predetermined melting temperature, the optical fiber has a
second predetermined melting temperature, and said first
predetermined melting temperature is less than said second
predetermined melting temperature.
7. The optical waveguide device of claim 1 further comprising: a
first epoxy plug disposed in the first end of the tube and a second
epoxy plug disposed in the second end of the tube.
8. The optical waveguide device of claim 1 wherein the tube is
generally cylindrical and has a cross-section which is generally
circular.
9. The optical waveguide device of claim 1 wherein the tube defines
a hollow bore, and the optical fiber is generally centered within
said hollow bore.
10. A method for forming an optical waveguide device comprising the
steps of: providing a tube having an inner wall and defining a
cavity, said cavity having a first predetermined diameter;
providing an optical fiber of a second predetermined diameter,
wherein said second predetermined diameter is less than said first
predetermined diameter; inserting said optical fiber into said
cavity; collapsing a first section of said tube to form a first
collapsed section with said inner wall contacting said optical
fiber in a first location such that a first seal is formed; and
collapsing a second section of said tube to form a second collapsed
section with said inner wall contacting said optical fiber in a
second location such that a second seal is formed, and a length of
said optical fiber is held between said first collapsed section and
second collapsed section.
11. The method of claim 10 further comprising, before the step of
collapsing the first section, the step of: applying a vacuum to the
cavity.
12. The method of claim 10 further comprising, before the step of
collapsing the first section, the step of: tensioning the optical
fiber.
13. The method of claim 10 further comprising, before the step of
collapsing the second section, the step of: tensioning the optical
fiber.
14. The method of claim 10 further comprising the step of: wrapping
the tube in a carbon fiber wrap.
15. The method of claim 10 wherein a long-period grating is formed
within the length of the optical fiber.
16. The method of claim 10 wherein the tube is boron-doped silica
glass.
17. The method of claim 10 wherein the tube is Pyrex.RTM..
18. The method of claim 10 wherein the tube has a first
predetermined melting temperature, the optical fiber has a second
predetermined melting temperature, and said first predetermined
melting temperature is less than said second predetermined melting
temperature.
19. An optical waveguide device comprising: a tube having a center
section, a first shelf section, a second shelf section, a first
end, and a second end, said center section defining a cavity
extending at least partially between said first end and said second
end; an optical fiber longitudinally disposed within said cavity
and adjacent to said first shelf section and said second shelf
section; and a first frit and a second frit, said first frit fused
to said optical fiber and said first shelf section at said first
end to form a first seal, and said second frit fused to said
optical fiber and second shelf section at said second end to form a
second seal, such that a length of said optical fiber is
tensionally secured between said first frit and said second
frit.
20. The optical waveguide device of claim 19 further comprising: a
long-period grating formed within the length of the optical
fiber.
21. The optical waveguide device of claim 19 wherein the tube is
boron doped silica glass.
22. The optical waveguide device of claim 19 wherein the tube is
encased in a carbon wrap.
23. The optical waveguide device of claim 19 wherein the first frit
and the second frit are composed of copper alumino silicate.
24. The optical waveguide device of claim 19 further comprising: a
first epoxy plug disposed on both the first shelf section and the
optical fiber; and a second epoxy plug disposed on both the second
shelf section and the optical fiber, such that the optical fiber is
secured to both the first shelf section and the second shelf
section.
25. The optical waveguide device of claim 19 wherein the tube is
generally cylindrical and has a cross-section which is generally
circular.
26. The optical waveguide device of claim 29 wherein the tube
defines a hollow bore, and the optical fiber is generally centered
within said hollow bore.
27. A method for forming an optical waveguide device comprising the
steps of: providing a tube having a center section, a first shelf
section, a second shelf section, a first end, and a second end,
said center section defining a cavity of a first predetermined
diameter extending at least partially between said first end and
said second end; providing an optical fiber of a second
predetermined diameter, wherein said second predetermined diameter
is less than said first predetermined diameter; inserting said
optical fiber into said cavity such that said optical fiber is
adjacent to said first shelf section and said second shelf section;
fusing a first frit to said optical fiber and said first shelf
section at said first end to form a first seal; and fusing a second
frit to said optical fiber and said second shelf section at said
second end to form a second seal.
28. The method of claim 27 further comprising the steps of:
depositing a first epoxy plug on both the first shelf section and
the optical fiber, such that the optical fiber is secured to the
first shelf section; and depositing a second epoxy plug on both the
second shelf section and the optical fiber, such that the optical
fiber is secured to the second shelf section.
29. An optical waveguide device comprising: a tube having a first
and a second end and defining a cavity extending at least partially
between said first end and said second end; an optical fiber
longitudinally disposed within said cavity; and a first plug and a
second plug disposed within said cavity forming a first seal and a
second seal, such that a length of said optical fiber is
tensionally secured between said first plug and said second
plug.
30. The optical waveguide device of claim 29 wherein the first plug
and the second plug are composed of copper glass.
31. The optical waveguide device of claim 30 further comprising: a
long-period grating formed within the length of the optical
fiber.
32. The optical waveguide device of claim 29 wherein the tube is
boron-doped silica glass.
33. The optical waveguide device of claim 29 wherein the tube is
encased in a carbon wrap.
34. The optical waveguide device of claim 29 further comprising: a
first epoxy plug disposed within the first end and a second epoxy
plug disposed within the second end.
35. The optical waveguide device of claim 29 wherein the tube has a
first predetermined melting temperature, the first plug has a
second predetermined melting temperature, and said second
predetermined melting temperature is less than said first
predetermined melting temperature.
36. The optical waveguide device of claim 29 wherein the tube is
generally cylindrical and has a cross-section which is generally
circular.
37. The optical waveguide device of claim 29 wherein the tube
defines a hollow bore, and the optical fiber is generally centered
within said hollow bore.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to packaging of
fiber optic components, and particularly to methods and apparatuses
for packaging long-period fiber gratings, filters, and other fiber
optic components to provide support and protection.
[0003] 2. Technical Background
[0004] Long-period fiber gratings are formed by the addition of
gratings to a length of optical fiber. Such gratings have an index
of modulation along the waveguiding axis of the fiber, and may be
formed by writing with UV radiation, etching, or other means of
making periodic perturbations. One function of long-period fiber
gratings is to couple light between the fundamental mode
propagating in the waveguide core and a guided cladding mode.
[0005] For high performance applications such as gain-flattening
filters (GFFs) in optical fiber amplifiers, long-period fiber
gratings must operate over large temperature ranges with minimal
change in spectral properties. While the peak loss of the grating
will change with temperature, the primary effect of a temperature
change is a shift in peak wavelength. Previously, this temperature
dependence has been minimized by a variety of techniques including
fiber design, fiber composition, and coating material. By varying
fiber and grating parameters, both positive and negative wavelength
shifts with increasing temperature are possible. The packaging of
the optical fiber can compensate for this temperature dependence by
attaching the long-period fiber grating to a negative or positive
thermal expansion substrate. The packaging is therefore strongly
dependent on the characteristics of the long-period fiber grating,
which can be tailored to have a variety of strain and temperature
dependencies.
[0006] Since long-period fiber gratings operate by coupling light
between core and cladding modes, they are very sensitive to
external perturbations. The grating is typically left uncoated
because coatings change the optical properties of the grating. The
long-period fiber grating package must therefore protect the region
of fiber containing the grating. Some type of tube or rectangular
box is therefore desirable to
[0007] protect the bare fiber from moisture or physical damage, and
prevent premature failure. Since long-period fiber gratings are
sensitive to bending, the fiber is normally kept relatively
straight within the package.
[0008] To obtain a typical hermetic (sealed against air and
moisture) packaging of a long-period fiber grating, the fiber is
metalized and soldered to a high quality package, such as an
expensive Kovar.RTM. metal box. The package is then usually
attached to a supporting substrate or fixture in a separate step.
This solution is expensive both in terms of materials and
processing time.
[0009] Accordingly, it would be highly advantageous to combine both
the fiber support and protective functions in a single package that
should protect the fiber from physical deformation as well as
protect it from various environmental conditions. The process in
which the package is constructed must not impart excessive thermal
load to the grating area or damage the optical fiber at the point
of contact between the package and the optical fiber.
SUMMARY OF THE INVENTION
[0010] The present invention provides advantageous methods and
apparatus for packaging long-period fiber gratings and other fiber
optic components to maintain support and protection. According to
one aspect of the invention, a hollow tube surrounding an optical
fiber containing a long-period grating is collapsed in two areas,
forming a seal. The collapsed areas can be formed by a ring burner,
Vytran.TM. splicer, CO.sub.2 laser, or other methods.
[0011] According to another aspect of the invention, a hollow tube
with a shelf section at each end is employed to form a frit sealed
package. The hollow tube surrounds an optical fiber containing a
long-period grating, and is sealed at each end by a copper alumino
silicate frit fused to each shelf section.
[0012] According to another aspect of the invention, a hollow tube
with a glass plug at each end is employed to form a glass sealed
package.
[0013] A more complete understanding of the present invention, as
well as further features and advantages of the invention, will be
apparent from the following detailed description and the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a cross-sectional view of an optical fiber and a
hollow tube in accordance with the present invention;
[0015] FIG. 2 is a cross-sectional view of a collapsed tube package
in accordance with the present invention;
[0016] FIG. 3 is a flowchart of a method of forming the collapsed
tube package of FIG. 2 in accordance with the present
invention;
[0017] FIG. 4 is a view of an insertion apparatus in accordance
with the present invention;
[0018] FIG. 5 is a view of a coupler draw apparatus used to form
the collapsed tube package of FIG. 2;
[0019] FIG. 6 is view of a frit sealed tube package in accordance
with the present invention;
[0020] FIG. 7 is a flowchart of a method of forming the frit sealed
tube package of FIG. 6 in accordance with the present
invention;
[0021] FIG. 8 is a view of an apparatus used for forming the frit
sealed tube package of FIG. 6 in accordance with the present
invention;
[0022] FIG. 9 is a cross-sectional view of a glass sealed tube
package in accordance with the present invention;
[0023] FIG. 10 is an end view of a glass disc in accordance with
the present invention;
[0024] FIG. 11 is a perspective view of an apparatus used for
forming the glass sealed tube package of FIG. 9;
[0025] FIG. 12 is a top view of the apparatus of FIG. 11; and
[0026] FIG. 13 is a flowchart of a method of forming the glass
sealed tube package of FIG. 9 in accordance with the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] The present invention now will be described more fully with
reference to the accompanying drawings, in which several currently
preferred embodiments of the invention are shown. However, this
invention may be embodied in various forms and should not be
construed as limited to the exemplary embodiments set forth herein.
Rather, these representative embodiments are described in detail so
that this disclosure will be thorough and complete, and will fully
convey the scope, structure, operation, functionality, and
potential of applicability of the invention to those skilled in the
art.
[0028] Referring to the drawings, FIG. 1 shows a cross-sectional
view of an optical fiber 12 and a hollow tube 14 in accordance with
the present invention. The optical fiber 12 is partially enclosed
by the hollow tube 14 having an inner diameter "a" (e.g., 255-300
.mu.m), an outer diameter "b" (e.g., 2.65 mm) and a length "c"
(e.g., 101.60 mm). The optical fiber 12 has an outer diameter "d"
(e.g., 250 .mu.m) and includes a coating 13 which has been stripped
from a length of optical fiber 12 which is contained within the
tube 14. The hollow tube 14 is composed of boron-doped silica or
Pyrex.RTM.. The glass material of the hollow tube 14 has a
coefficient of thermal expansion (CTE) similar to the CTE of the
optical fiber 12, in order to minimize thermal stresses resulting
from temperature changes. While presently preferred materials and
dimensions are disclosed herein, one skilled in the art would
appreciate that the hollow tube 14 of the present invention may be
composed of a variety of materials and sizes, and should not be
construed as limited to the embodiments or dimensions shown and
described herein. The optical fiber 12 has written into it a
long-period grating 20 along a portion of the length which has been
stripped of the coating 13.
[0029] FIG. 2 shows a cross-sectional view of a collapsed tube
package 10 in accordance with the present invention. Collapsed tube
package 20 is formed, by methods described below, from the optical
fiber 12 and tube 14 of FIG. 1. The tube 14 includes two collapsed
regions 22, each collapsed region 22 having an inner wall 24 which
is in concentric contact with the optical fiber 12, forming a seal.
The hollow tube 14 with the collapsed regions 22 tensionally
maintains and supports the region of the optical fiber 12
containing the long-period grating 21, and protects the long-period
grating 21 from external perturbations (such as mechanical stress)
and environmental conditions (such as moisture).
[0030] To provide strain relief, the collapsed tube package 20 also
includes two epoxy plugs 26 disposed at each end 28 of the hollow
tube 14. The epoxy plugs 26 generally cover a semicircular
(180.degree.) portion of each end 28. The ends 28 of the hollow
tube 14 are funnel-shaped at an angle of 45.degree. to facilitate
placement of the epoxy plugs 26.
[0031] According to another aspect of the present invention, the
collapsed tube package 20 may be encased in a carbon wrap (not
shown) to provide another protective layer (e.g., 0.040-0.055
inches), providing additional protection from fracture. The carbon
wrap is described in greater detail in U.S. Pat. No. 5,426,714
entitled "Optical Fiber Couplers Packaged For Resistance To Bending
Or Breakage, and Methods Of Making The Same" which is incorporated
by reference herein in its entirety.
[0032] FIG. 3 shows a method 80 of forming a collapsed tube package
20 utilizing the coupler draw apparatus 50 as shown in FIG. 5 in
accordance with the present invention. In a first step 82,
funnel-shaped ends (such as the funnel-shaped ends 28) are formed
in a hollow tube (such as the hollow tube 14). To accomplish this,
the hollow tube 14 is mounted in a vertical orientation and
nitrogen triflouride (NF.sub.3) gas is forced through a center bore
15 of the hollow tube 14. The hollow tube 14 is then rotated, and
an angled oxygen and gas torch bums the NF.sub.3, forming the
funnel-shaped end 28. The oxygen and hydrogen gas torch is mounted
at a 45.degree. angle with respect to an outer surface 17 of the
hollow tube 14.
[0033] In a second step 84, an optical fiber (such as the optical
fiber 12) is placed within the hollow tube 14 utilizing an
insertion apparatus 40 shown in FIG. 4. To thread the optical fiber
12 into the hollow tube 14, a fixture 42 holds the hollow tube 14.
The fiber 12 is placed into a precision V-groove 44 and held by a
magnet 46, then aligned concentrically to the inside diameter of
the hollow tube 14 with an X, Y, Z positioning stage 48. The
positioning stage 48 is mounted onto a precise bearing slide 50 for
transverse positioning. The fiber 12 is traversed axially into the
tube 14 and centered. This individual alignment of the hollow tube
14 and optical fiber 12 with separate fixtures 42, 44 ensures there
is no damage to the optical fiber 12 during the packaging process.
During insertion, the coating 13 acts as a guide for the uncoated
section of optical fiber 12 containing the grating 20, preventing
the uncoated section from contacting the inner wall of the hollow
tube 14.
[0034] Next, in a tensioning step 86, the optical fiber 12 is
tensioned to between 5-20 thousand pounds per square inch by a
weight 52. In a next tacking step 88, the ends 28 of the hollow
tube 14 are tacked with epoxy plugs 26 to maintain the fiber 12
under tension in the center of the tube 14. Suitable epoxies are
described in greater detail in U.S. Pat. No. 5,552,092 entitled
"Waveguide Coupler" which is incorporated by reference herein in
its entirety. Each epoxy plug 26 is applied manually into the ends
28 with a small syringe and is then UV cured. Nominal post cure
time is 1.5 hr. at 125.degree. C., or 16 hr. at 90.degree. C. The
epoxy plugs 26 also provide the additional benefit of preventing
the optical fiber 12 from making contact with the inside surface of
the hollow tube 14, which would lower the strength of the optical
fiber 12.
[0035] As shown in FIG. 5, in a further embodiment of the present
invention, a Multiclad.RTM. coupler draw apparatus 100 with an
oxygen methane gas ring burner 102 is used to form the collapsed
regions 22 of the collapsed tube package 10. The coupler draw 100
includes a first stage 104 and a second stage 106.
[0036] In step 90, tube 14 and optical fiber 12 are mounted on the
coupler draw apparatus 100. A vacuum is applied to the hollow
center of tube 14 in step 92 by a vacuum pump 108 (maximum vacuum
.about.25 inches) which is connected to the ends of hollow tube 12
by tubing 109.
[0037] Next, in a heating step 94, the ring burner 102 heats a
first section 28 of the tube 14 to a temperature (700.degree. C.
for a Pyrex.RTM. tube, 1600.degree. C. for an 8% boron-doped silica
tube) allowing the tube 14 to flow and form a first collapsed
region (such as the first collapsed region 22 of FIG. 2). The ring
burner 102 has a profile that heats a .about.5-10 mm length of the
hollow tube 14. To minimize thermal damage to the optical fiber 12
from the heating, the material of tube 14 preferably has a melting
temperature lower than the melting temperature of the optical fiber
12. This results in reduced stress during the packaging process 80
and the lifetime of the package 10.
[0038] The stages 104, 106 move in opposite directions during the
heating step 94 to compensate for the loss of initial tension
caused by the larger area of glass flow associated with the profile
of the ring burner 102. The stages 104, 106 are driven by a
computer controlled motor with a stepping motor resolution of
.about.25,000 steps per revolution with a resulting stage response
of 100,000 steps per cm. As the tube 14 is heated, the vacuum
assists in collapsing the tube 14 to form the collapsed section 22
which holds the optical fiber 12 evenly around its entire
circumference. Due to the heat sensitivity of a grating (such as
the grating 21) the tube 14 should be of sufficient length to
assure that the grating 21 is not affected by heat from the ring
burner 102. Furthermore, the heat must be evenly applied around the
circumference of the tube 14 to ensure a uniform collapse in
forming the collapsed sections 22. The heat profile is localized to
keep the package 20 length to a minimum and ensure that the grating
21 is not exposed to a significant increase in temperature. In a
positioning step 96, the stages 104, 106 move the optical fiber 12
and hollow tube 14 into position where a second section 28 of the
tube 14 is contained within the ring burner 102. The ring burner
102 heats the second section 28 of the tube 14 to form the second
collapsed region 22.
[0039] According to another aspect of the present invention, a
CO.sub.2 laser can be used to form each collapsed region 22 by
heating two sections of the tube 14 (700.degree. C. for a
Pyrex.RTM. tube, or to 1600.degree. C. for an 8% boron-doped silica
tube). Use of the CO.sub.2 laser allows heating a more localized
section (e.g., 2 mm) of the tube 14, which in turn allows the use
of a shorter overall length of the tube 14. Furthermore, the
localized heating of the CO.sub.2 minimizes any change in tension
of the optical fiber 12 by reducing the length of optical fiber 12
which is exposed to thermal stress.
[0040] According to another aspect of the present invention, a
Vytran.TM. large-diameter glass splicer (Vytran Corporation,
Morganville, N.J. 07751) can be used to form each collapsed region
22 by heating two sections of the tube 14 (700.degree. C. for a
Pyrex.RTM. tube, or to 1600.degree. C. for an 8% boron-doped silica
tube).
[0041] Another embodiment of the present invention is shown in FIG.
6, which depicts a view of a frit sealed tube package 200. The frit
sealed tube package 200 comprises an optical fiber 212 which is
partially enclosed by a hollow tube 214 having openings 223 at each
end. The tube 214 has an inner diameter (ID) (e.g., 255-300 .mu.m),
an outer diameter (OD) (e.g., 2.65 mm), and a length (e.g., 101.60
mm). A minimum ID of 255 .mu.m allows the use of optical fiber 212
with a coating 213 having a combined diameter of 250 .mu.m. The
coating 213 has been removed from a length of optical fiber 212
which is contained within the tube 214. The tube 214 includes first
and second shelf sections 221, each shelf section 221 having a
length (e.g., 11.10 mm). In one embodiment, the hollow tube 214 is
composed of boron-doped silica or Pyrex.RTM., but should not be
construed as limited only to the embodiments shown and described
herein. The optical fiber 212 has written into it a grating 220
along a length 224 (e.g., 5-30 mm). A first frit 222 is fused to
the optical fiber 212 and first shelf section 221. A second frit
222 is fused to the optical fiber 212 and second shelf section 221.
Each frit 222 forms a hermetic seal in each opening 223. In one
embodiment, each frit 222 is composed of copper alumino silicate. A
CO.sub.2 laser (or other heating methods) is used to fuse the frits
222 in place. An epoxy deposit 226 is disposed on each shelf
section 221, holding the optical fiber 212 in place and providing
strain relief. The epoxy deposit 226 is tailored to withstand at
least 2.0 lb. tensile test, is UV curable, and has a coefficient of
thermal expansion (CTE) of .about.10.times.10.sup.-7 parts per
million (ppm).
[0042] FIG. 7 shows a method 250 of forming a frit sealed tube
package 10 in accordance with the present invention. In a first
placement step 252, an optical fiber (such as the optical fiber
212) is placed within the hollow tube 214 utilizing an insertion
apparatus 270 shown in FIG. 8. To thread the optical fiber 212 into
the hollow tube 214, a fixture 272 holds the hollow tube 214. The
fiber 212 is placed into a precision V-groove 284 and held by a
magnet 286, then aligned concentrically to the inside diameter of
the hollow tube 214 with an X, Y, Z positioning stage 288. The
positioning stage 288 is mounted onto a precise bearing slide 290
for transverse positioning. The fiber 212 is traversed axially into
the tube 214 and centered. This individual alignment of the hollow
tube 214 and optical fiber 212 with separate fixtures 272, 284
ensures there is no damage to the optical fiber 212 during the
packaging process. During insertion, the coating 213 acts as a
guide for the uncoated section of optical fiber 212 containing the
grating 220, preventing contact with the tube 214.
[0043] Next, in a tensioning step 254, the optical fiber 212 is
tensioned to 5-20 thousand pounds per square inch by a weight 292.
In a next fusing step 256, a first frit (such as the frit 222) is
fused to the first opening 223 by a CO.sub.2 laser 294. Next, in a
positioning step 258, the laser 294 is repositioned, and the second
frit 222 is then fused to the second opening 223. To provide strain
relief, in a tacking step 260 an epoxy deposit 226 is placed on
each shelf section 221 holding the optical fiber 212 in place. The
epoxy is then UV exposed to initiate cure and then subjected to a
final dark cure in an oven for 1.5 hr. at 125.degree. C., or 16 hr.
at 90.degree. C. Suitable epoxies are described in greater detail
in U.S. Pat. No. 5,552,092 entitled "Waveguide Coupler", which is
incorporated by reference herein in its entirety.
[0044] Another alternative embodiment of the present invention is
shown in FIG. 9, which depicts a cross-sectional view of a glass
sealed tube package 300. The glass sealed tube package 300
comprises an optical fiber 312 which is partially enclosed by a
hollow tube 314. The tube 314 has an inner diameter (ID) (e.g., 1
mm), an outer diameter (OD) (e.g., 2-3 mm), and a length (e.g., 3
inches). The optical fiber 312 includes a coating 313 which has
been removed from a length of optical fiber 312, and is contained
within tube 314. While in one embodiment, the hollow tube 314 is
composed of glass silica, one skilled in the art would appreciate
that the hollow tube 314 of the present invention can be composed
of a variety of materials and sizes, and should not be construed as
limited to the embodiments shown and described herein. The optical
fiber 312 has written into it a grating 320. First and second glass
plugs 325 are disposed within the tube 314 to form a hermetic seal
at both ends of the tube 314. The glass plugs 325 are composed of a
low melting temperature glass, such as copper glass, which has a
melting temperature of 800.degree. C. Glass sealed tube package 300
also includes two epoxy plugs 326 which are disposed at each end
328 of the hollow tube 314 and provide strain relief. The epoxy
plugs 326 are composed of Corning epoxy MCA-91.
[0045] Each glass plug 325 is formed from a glass disk 331 (shown
in FIG. 10) placed within the tube 314. When each glass disk 331 is
heated to the melting temperature of the glass disks 331
(800.degree. C. for copper glass), the glass disk 331 melts and
flows, forming the glass plug 325. For an optical fiber 312 of 250
.mu.m diameter, the glass disks 331 include an inner diameter 333
(e.g., 270 .mu.m) which is slightly larger than the diameter of the
optical fiber 312 and coating 313 removed (e.g., 250 .mu.m). The
glass disks 331 also have an outer diameter 335 (e.g., 950 .mu.m)
and a thickness (e.g., 475 .mu.m).
[0046] The heating of the glass disks 331 can be accomplished by
the use of a coupler draw apparatus (such as the coupler draw
apparatus 50) a Vytran.TM. large diameter glass splicer 400 (shown
in FIG. 11 and FIG. 12), an induction heater, a CO.sub.2 laser, or
other heaters and glass holding mechanisms. In one embodiment, the
Vytran.TM. large diameter glass splicer 400 is utilized. The glass
splicer 400 includes a pair of clamps 402 which hold the optical
fiber 312 and the tube 314 in place. A tungsten filament 404
operates as the heat source and can traverse the length of the tube
314, allowing the tube and optical fiber to remain fixed while both
glass disks 331 are heated. A camera 406 or other magnified visual
inspection system can be used to ensure proper alignment of the
optical fiber within the tube.
[0047] In one method 450 (shown in FIG. 13) of forming a glass
sealed tube package (such as the glass sealed tube package 300),
the Vytran.TM. large diameter glass splicer 400 is utilized. In a
first placement step 452, a pair of glass disks (such as the glass
disks 331) are threaded onto the optical fiber 312. In a next
placement step 454, the optical fiber 312 is placed within the tube
314 and locked in place by clamps 402. Next, in a tensioning step
456, the optical fiber is tensioned to 5-20 thousand pounds per
square inch by a weight (not shown). In a heating step 458, the
splicer 400 heats an area of the tube 314 causing the first glass
disk 331 to melt and form a first glass plug. Next, in a heating
step 460, the filament 404 moves so that a second area of the tube
314 is heated, causing the second glass disk 331 to melt and form a
second glass plug. The heating temperature in the heating steps
458, 460 is 800.degree. C. for glass disks 331 composed of copper
glass. In order to preserve the strength of the optical fiber 312,
the heating steps 458, 460 should be done with the tube 314 and
optical fiber 312 in a vertical orientation as shown in FIG. 12.
This ensures the glass disks 331 adhere evenly to the tube 314 and
fiber 312. In other words, if the heating is done in a horizontal
orientation, the glass disks 331 will tend to flow transversely
towards the bottom of the tube 314 and form a radially uneven seal.
In a tacking step 462, an epoxy plug 326 is deposited at each end
328 and UV cured for 30 seconds followed by a thermal post cure of
at 125.degree. C. for 4 hours.
[0048] It will be apparent to those skilled in the art that various
modifications and variations can be made in the present invention
without departing from the spirit and scope of the present
invention. Thus, it is intended that the present invention cover
the modifications and variations of this invention provided they
come within the scope of the appended claims and their
equivalents.
* * * * *