Method for fabricating a low polarization mode dispersion optical fiber
The method of fabricating an optical waveguide fiber from a preform having a centerline aperture which includes reducing the pressure in the centerline aperture, then increasing the pressure in the centerline aperture to a pressure in order to improve uniformity, circularity, and/or symmetry around the centerline aperture region.
1. A method of forming a preform for use in making an optical waveguide fiber, the method comprising:
providing a consolidated preform having an outer surface with an outside diameter and an inner surface with an inside diameter, the inner surface defining a centerline aperture therein;
exposing the inner surface to a first pressure, less than the pressure at the outer surface, while at least part of the preform is at a first temperature for a time sufficient to contract without fully collapsing the aperture and without pulling on the preform; and
after the aperture is contracted, exposing the inner surface to a second pressure, greater than the first pressure, while at least part of the preform is at a second temperature and for a time sufficient to further contract the aperture.
2. The method of claim 1 wherein the first temperature is less than the consolidation temperature of the preform.
3. The method of claim 1 wherein the first temperature is between the consolidation temperature and the draw temperature of the preform.
4. The method of claim 1 wherein the first temperature is between about 1450° C. and about 1950° C.
5. The method of claim 1 wherein the first temperature is between about 1300° C. and about 1600° C.
6. The method of claim 1 wherein the first temperature is between about 1650° C. and about 2200° C.
7. The method of claim 1 wherein the first pressure is less than about 10 Torr.
8. The method of claim 1 wherein the first pressure is less than about 100 Torr.
9. The method of claim 1 wherein the first pressure is less than about 500 Torr.
10. The method of claim 1 wherein the second temperature is greater than the first temperature.
11. The method of claim 1 wherein the aperture is fully collapsed.
12. The method of claim 1 wherein the second pressure is greater than 500 Torr.
13. The method of claim 1 wherein the second pressure is greater than 700 Torr.
14. The method of claim 1 wherein the second pressure is greater than 760 Torr.
15. The method of claim 1 wherein the preform is fabricated via an OVD process.