Glass manufacturing – Processes of manufacturing fibers – filaments – or preforms – Process of manufacturing optical fibers – waveguides – or...
Reexamination Certificate
2001-06-18
2003-06-10
Derrington, James (Department: 1731)
Glass manufacturing
Processes of manufacturing fibers, filaments, or preforms
Process of manufacturing optical fibers, waveguides, or...
C065S413000, C065S414000, C065S415000, C065S416000, C065S417000, C065S419000, C065S421000, C065S428000, C065S435000, C065S412000, C065S397000, C065S398000
Reexamination Certificate
active
06574994
ABSTRACT:
TECHNICAL FIELD
This invention relates to a method for producing an optical fiber preform and fiber. More specifically, the method relates to efficiently producing optical fiber preforms and fibers having multiple segments therein.
BACKGROUND OF THE INVENTION
Manufacturing of optical fiber preforms, i.e., the article from which optical fiber is drawn, is typically accomplished by methods such as Outside Vapor Deposition (OVD), Vapor Axial Deposition (VAD), Modified Chemical Vapor Deposition (MCVD) and Plasma Chemical Vapor Deposition (PCVD). In accordance with one method, a multi-segment profile in the preform (corresponding to a multi-segment profile in the optical fiber drawn therefrom) is formed by an OVD method. In the OVD method, silica-containing soot
22
is deposited onto a rotating and traversing mandrel
24
as indicated by arrows A and A′ of
FIG. 2
to form a porous core soot preform
20
. To form the soot
22
, a glass precursor
28
is provided, preferably in gaseous form, to the flame
30
of a burner
26
. The flame
30
is formed by combusting a fuel
32
, such as methane, while providing a combustion supporting gas, such as oxygen
34
. The core soot preform
20
may be up-doped with a dopant such as germania oxide, for example, to raise its refractive index. This may be accomplished, for example, by providing a glass precursor
28
, such as SiCl
4
, to the burner
26
in gaseous form along with a gaseous dopant compound, such as GeCl
4
. The doped silica-containing soot preform
20
is then dried and consolidated in a consolidation furnace
29
, such as shown in Prior Art
FIGS. 3 and 4
to form a consolidated core blank
31
. A helium and chlorine gas atmosphere, for example, in the consolidation furnace is used to dry the preform and remove water prior to vitrification into glass at a temperature of about 950° C. to 1250° C. Pure helium is generally provided during consolidation and the temperature is higher, for example, between about 1390° C. to 1535° C.
Following consolidation, next, as shown in
FIG. 5
, the consolidated core blank
31
is placed in a cane draw furnace
37
and is stretched into a length of core cane
33
from which multiple core cane segments
35
are derived. At the same time, the centerline aperture is closed by application of, for example, a vacuum. The draw tension and preform downfeed rates (indicated by arrow B) are controlled by suitable control method
38
to provide a core cane length
33
of preferably substantially constant, predetermined diameter d
o
. The diameter d
o
is controlled by feedback of a measured diameter signal from an appropriate non-contact sensor
39
to the control apparatus
38
. In response, the controls
38
may adjust the tension applied at the tension apparatus
40
whereby lowering the tension raises the diameter d
o
and raising it lowers the diameter d
o
. At predetermined lengths, the cane is cut, such as by a flame cutter
42
, to form a predetermined length core cane segment
35
(FIG.
6
). This core cane
35
represents the first segment
44
of the final preform, as illustrated in FIG.
1
.
The second preform segment
45
, which is a down-doped moat, is formed by depositing on the core cane segment
35
additional silica-containing soot. This step looks identical to
FIG. 2
except that the mandrel is now the previously made core cane
35
. The soot deposited is preferably silica soot formed by providing the glass precursor
28
such as SiCl
4
to the flame
30
and oxidizing the precursor to form SiO
2
. Next, the soot-laden core cane
41
is placed in a furnace
29
as is described in Berkey U.S. Pat. No. 4,629,485 and the soot, after being dried, is subjected to a fluorine-containing atmosphere. This dopes the soot with fluorine. Subsequently, the doped-soot preform
41
is consolidated, as shown in FIG.
7
. Again, the resultant consolidated preform (now containing two core segments) is drawn into a core cane as is shown in FIG.
5
. The only difference is that the consolidated preform now includes a core at its centerline, rather than a centerline aperture as shown in FIG.
5
.
To make the third up-doped segment
46
(FIG.
1
), the process of
FIG. 2
is again repeated where a glass precursor
28
is provided to the flame
30
. A desired amount of dopant compound, such as GeCl
4
, is also provided to achieve the profile preferably as shown in the third segment
46
of FIG.
1
. This is accomplished by gradually turning on the supply of dopant compound
36
at the innermost part of the segment and gradually turning it off towards the outermost portion of the segment
46
by controlling the mass flow controllers V. Once the additional soot segment is formed, it is again dried and consolidated as shown in FIG.
7
. Once consolidated, it is again drawn into a core cane segment as described with reference to FIG.
5
. As should be recognized, the core cane
10
segment now contains three segments
44
,
45
and
46
therewithin.
In the final step, the core cane segment is overclad with silica-containing soot by the method shown in
FIG. 2
wherein the cladding preferably comprises essentially SiO
2
. Again, the soot preform is dried and consolidated as heretofore mentioned to form a fourth segment
48
and to form the final consolidated optical fiber preform. The resulting final consolidated preform
50
is then placed in a draw furnace
52
as shown in
FIG. 8
, heated and drawn into an optical fiber
54
in a helium gas atmosphere by conventional methods and apparatus. The fiber
54
is then cooled in cooling chamber
55
and measured for final diameter by non-contact sensor
56
. One or more coatings are applied and cured by coating apparatus
58
, as is also conventional. During draw, the fiber
54
passes through a tension assembly
60
whereby tension is applied to draw the fiber
54
from the preform
50
. The tension is controlled via control apparatus
61
to maintain the fiber diameter at a predetermined set point. Finally, the coated fiber
54
is wound by feedhead
62
onto a fiber winding spool
64
.
It should be readily apparent that the prior art, multi-step, OVD process is complex, and therefore time intensive. Moreover, because of the multiple steps involved to arrive at the final optical fiber preform, it is sometimes difficult to achieve consistent profiles. Further, it is also possible to experience high levels of scrap.
Thus, it should be apparent that there is a long felt and unmet need to produce optical fiber preforms cost effectively, efficiently and with greater control of the optical parameters and index profiles.
BRIEF SUMMARY OF THE INVENTION
The manufacturing method in accordance with a first embodiment of the invention provides a multi-segment preform that may be produced in a highly efficient manner with improved profile predictability and possibly lessened scrap. The method of manufacturing a multi-segment optical fiber preform, comprises the steps of forming a core cane segment, which preferably has a germania dopant therein, providing a delta of between about 0.2%-3%, inserting the segment into a sleeve formed by and inside method such as MCVD or PCVD and then collapsing the sleeve onto the cane. Other suitable inside methods may alternatively be employed. Fiber may then be drawn therefrom by conventional methods. The result is a detailed refractive index profile that can be readily made with fewer steps than the prior art method.
In particular, it has been found that the ring shape can be manufactured advantageously with a great amount of precision and, in particular, latent rings (rings that are positioned some finite distance away from the outer edge of the moat) may be manufactured very precisely. Further, the refractive index profile may be made with better repeatability and possibly with a lesser amount of scrap. Advantageously, new refractive index profiles may be made in accordance with the present method whereby heretofore using prior art methods, glass crizzling at the segment interfaces has occurred. The core cane, in accordance with the
Cain Michael B.
dePaor Liam R.
Desorcie Robert B.
Fiacco Richard M.
Giroux Cynthia B.
Corning Incorporated
Derrington James
Wayland Randall S.
LandOfFree
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