Glass manufacturing – Processes of manufacturing fibers – filaments – or preforms – With measuring – controlling – sensing – programming – timing,...
Reexamination Certificate
1998-08-13
2001-10-16
Hoffmann, John (Department: 1731)
Glass manufacturing
Processes of manufacturing fibers, filaments, or preforms
With measuring, controlling, sensing, programming, timing,...
C065S382000, C065S412000
Reexamination Certificate
active
06301934
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to methods of making optical fiber having longitudinally varying optical properties. Optical fibers made in accordance with the invention may include dispersion decreasing and dispersion managed fiber. Such fibers may be used for soliton pulse transmission, in which an optical soliton pulse maintains its original shape as it travels along the optical fiber. However, the invention is not limited to this application.
Dispersion refers to the spreading out of light pulses as they travel in an optical fiber. Such spreading of a soliton pulse causes attenuation losses as the pulse travels along the fiber. Dispersion may be compensated for by changing the optical properties of the fiber so as to reduce the total dispersion. Two types of fiber which compensate for dispersion are dispersion decreasing fiber and dispersion managed fiber.
Dispersion decreasing fiber has a slow change in dispersion over the length of the fiber. This gradually decreases the dispersion in the fiber and thus decreases the effect of attenuation losses on the transmission of a soliton pulse traveling along the fiber.
Dispersion managed fiber is characterized by sections of positive and negative dispersion, with relatively sharp transitions between each section. Dispersion managed fiber strives to create a fiber where the overall dispersion of the fiber is zero, but the dispersion at any one point is either slightly positive or negative. Such a scheme minimizes the effects of four-wave mixing, self phase modulation and other nonlinear optical effects that are produced by transmitting data pulses at the zero dispersion point, while still effectively compensating for the chromatic dispersion effects that occur over the length of the fiber link.
The present invention is directed to methods of making dispersion decreasing and dispersion managed fiber by axially changing the optical properties of the fiber.
Prior art methods of making fiber, having axially changing optical properties, each have associated disadvantages. For example, changing the core-clad ratio, by either machining or chemically etching the consolidated preform or core cane, alters the optical properties of the fiber. Unfortunately, this method adds additional processing steps and additional select losses associated with these steps. Changing the draw tension may also change the optical properties of the fiber axially, but, this method fails to maintain the advantages of drawing fiber in a particular tension regime. Another alternative, altering the optical properties of the fiber by drawing a fiber having a non-constant outer diameter, creates unwanted connectorization and splicing issues. Theoretically, the optical properties of the fiber can be changed by placing multiple overclad compositions on the fiber to obtain stress effects in the drawn fiber. However this method would alter the existing laydown and consolidation processes to such an extent that it would not likely provide a viable manufacturing process.
Thus, there is a need for a method of changing the optical properties of fiber that does not have the disadvantages associated with these prior art methods.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method of making dispersion decreasing and dispersion managed fiber without additional manufacturing steps or the select losses associated with such additional steps.
It is a further object of the present invention to provide a method of making dispersion decreasing and dispersion managed fiber which maintains a particular tension regime during the draw process.
It is an object of the present invention to provide a method of making dispersion decreasing and dispersion managed fiber having a constant outside diameter.
It is a further object of the present invention to provide a method of making dispersion decreasing and dispersion managed fiber which does not alter existing laydown and consolidation processes.
It is an object of the present invention to provide a method of making dispersion decreasing and dispersion managed fiber which allows the axial location of change in the dispersion in the fiber to be determined.
The disadvantages and limitations of other methods of changing the optical properties of fiber are overcome by the present invention, which provides a method for separately controlling and varying the input, into a furnace, of core and clad material, and thereby controlling the core diameter of the product which exits the furnace, i.e. either core or fiber, e.g. by drawing a rod and tube simultaneously using separate downfeeds.
REFERENCES:
patent: 3909110 (1975-09-01), Marcuse
patent: 4049413 (1977-09-01), French
patent: 4578096 (1986-03-01), Siegmund
patent: 42 33 869 (1993-11-01), None
Corning Incorporated
Hoffmann John
Krogh Timothy R.
Servilla Scott S.
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