Glass manufacturing – Processes of manufacturing fibers – filaments – or preforms – Process of manufacturing optical fibers – waveguides – or...
Reexamination Certificate
2002-03-15
2004-08-03
Griffin, Steven P. (Department: 1731)
Glass manufacturing
Processes of manufacturing fibers, filaments, or preforms
Process of manufacturing optical fibers, waveguides, or...
C065S417000, C065S421000
Reexamination Certificate
active
06769275
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a method and apparatus for making an optical fiber preform and, more particularly, to a method and apparatus for making an optical fiber preform using a plasma torch and including one or more steps of substantially simultaneous inside deposition and/or consolidation and outside deposition and/or consolidation.
2. Statement of the Problem
Various methods and apparatus for making optical fiber preforms are known in the optical fiber industry and described in its related publications. For example, U.S. Pat. No. 6,253,580 (“the '580 patent”) describes a Plasma Outside Vapor Deposition (“POVD”) process for making synthetic silica tubes. The synthetic silica tubes made in accordance with the '580 invention can be used as a substrate or as a jacketing tube in fabricating optical fiber preforms by the Modified Chemical Vapor Deposition (“MCVD”) methods. Further, the processing rate and quality of synthetic silica tubes made in accordance with the '580 patent is favorable based on many of the presently established criteria. However, improved processing rate and quality are always desirable. Cost, though, is another factor that must always be considered.
The prior art shows numerous methods for making preforms and other fiber-related glass and silica products. These include the MCVD process such as disclosed by, for example, U.S. Pat. No. 3,982,916 to Miller and Pat. No. 4,217,027 to MacChesney. These also include the Plasma Chemical Vapor Deposition process such as disclosed by, for example, U.S. Pat. Nos. 4,741,747 and 4,857,091, both to Geittner et al. Further included is the MCVD with radio frequency (“rf”) plasma process such as disclosed by, for example, U.S. Pat. No. 4,262,035 to Jaeger et al. and Pat. No. 4,331,462 to Fleming et al., and the method of MCVD with a plasma torch such as disclosed by, for example, U.S. Pat. Nos. 5,397,372 and 5,692,087, both to Partus et al.
The present inventors have identified that the processes and methods disclosed by the above-listed patents have various shortcomings with respect to current and future requirements for production rate and fiber quality.
Other methods known in the prior art include the Outside Vapor Deposition Process (“OVD”) disclosed by U.S. Pat. No. 3,737,292 to Keck and U.S. Pat. No. 3,932,162 to Blakenship, and the Vapor Axial Deposition (“VAD”) process disclosed by, for example, U.S. Pat. Nos. 4,062,665 and 4,224,04, both to Izawa et al. The present inventors, though, have identified that the processes and methods as disclosed by the above-listed patents have various shortcomings including, for example, the necessity for performing separate steps for sintering or consolidation of the deposited silica.
Still other known methods for making preforms include the method of sleeving and collapsing a tube or tubes on a primary preform using, for example, a plasma torch, as disclosed by U.S. Pat. No. 5,578,106 to Fleming et al., or an oxygen-hydrogen torch, as disclosed by U.S. Pat. No. 4,596,589 to Perry and U.S. Pat. No. 4,820,322 to Baumgart. The present inventors have identified shortcomings with all of these methods, including, for example, the requirement for a jacketing process.
The prior art also includes the overcladding process as disclosed by U.S. Pat. No. 5,522,007 to Drourt. These methods include the steps of building up a large diameter preform by depositing cladding glass onto a primary preform, using a plasma torch. A typical shortcoming of overcladding is its necessary addition of one or more additional steps, namely that the primary preform be made first, followed by adding the overcladding layers, which adds time and equipment costs.
It is known in the optical fiber industry that one method for lowering cost, and for increasing processing rate, is to make larger preforms. For example, as reported by Glodis et al. in U.S. Pat. No. 6,105,396 (“the '396 patent”), a preform can be made which generates approximately 400 kilometers of fiber.
The benefits of making larger preforms manifest in at least two stages, or steps, of manufacturing fiber—the preform fabrication step and the fiber draw step. Regarding the first step, the immediate benefit that is seen from using a larger preform is that the larger the preform the greater the length of fiber that it produces.
For example, the set-up and inspection time for making the larger preform should not be substantially longer than the set-up and inspection time for making smaller preforms. This is an important consideration because the initial set-up for fabricating a preform, together with the post-processing inspections, occupy a significant percentage of the time required to fabricate a preform. Therefore, more net increase in manufacturing efficiency is gained when using a larger preform if the set-up and inspection times during its manufacture are kept substantially the same as those for a smaller preform.
Improved fiber quality is another benefit gained by using a larger preform. This is because drawing fiber is basically a stretching of the preform volume. A larger diameter preform has a greater volume per unit length and, therefore, when compared to a smaller diameter preform, a shorter linear section of the preform is required to form the same length of fiber. The optical qualities of a preform typically vary along its length. Therefore, since the larger preform requires less length to produce a given length of fiber, fiber drawn from it has a correspondingly lower rate of variation per unit length than would be seen in fiber drawn from a smaller preform.
There are other objectives that must be met when fabricating larger preforms so that the larger size provides a practical, usable increase in manufacturing efficiency. Low equipment cost is one of these objectives. Namely, the decrease in cost that can be obtained by fabricating larger preforms will be maximized by a method that requires minimum purchase and installation of new equipment.
Another problem relating to MCVD processes, and to making larger preforms, is the incomplete oxidation of dopants flowing through the hollow or void in the tube. A reason is that the base glass chemical, such as SiCl
4
, and the dopant chemicals, such as GeCl
4
, POCl
3
and SF
6
, flow together into the hollow. Because of the plurality of reactants present, there are multiple chemical reactions that result. A typical effect of the multiple reactions is that only one is essentially completed, this frequently being the reaction of SiCl
4
vapors with O
2
. In contrast, the dopant oxidation reactions are frequently not complete. For example, in the conventional MVCD manufacturing of germanium doped silica, a large fraction of the dopant appears in the gaseous effluent in the form of GeCl
4
. Published reports such as “Germanium Chemistry in the MCVD Process for Optical Fiber Fabrication,” J. of Lightwave Technology, LT-5, no.2, 1987, 277-285, show that as much as 70% of the initial germanium flowing into the hollow is present in the effluent as GeCl
4
.
SUMMARY OF THE INVENTION
The present invention provides an apparatus and method for making an optical fiber preform using plasma deposition on a silica tube, where at least a portion of the process performs concurrent deposition, consolidation, or deposition/consolidation of silica on the inside and the outside of the tube. Certain steps within the described embodiments deposit soot, without consolidation, on one of the inner and outer surfaces of the tube, concurrent with simultaneous deposition and consolidation of soot on the other of the inner and outer surface. Other steps perform concurrent deposition, without consolidation, followed by concurrent consolidation, with or without deposition of additional soot during the concurrent consolidation pass. The total deposition rate is increased over the prior art due to the concurrent deposition of soot on the inner and outer surfaces of the tube. The deposition rate is also increased by the invention setting the rate of tra
Aslami Mohd A.
Danilov Eugenie B.
Guskov Mikhail I.
Hammerle Wolfgang
Wu Dau
FiberCore, Inc.
Griffin Steven P.
Lopez Carlos
Patton & Boggs LLP
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