Anti-PMD system for optical fibers
An anti-PMD system comprises a pulley which oscillates in rotation and applies a torsion torque alternately in the clockwise direction and in the counterclockwise direction to an optical fiber during drawing of the optical fiber to reduce its PMD. A portion of a peripheral external surface of the pulley intended to be in contact with the optical fiber during drawing is convex.
1. An anti-PMD system comprising:
an optical fiber being drawn;
a pulley having an outermost peripheral external surface over which the optical fiber rolls during the drawing of the optical fiber, said pulley being rotatable so as to oscillate in rotation and to apply a torsion torque alternately in the clockwise direction and in the counterclockwise direction to the optical fiber during drawing of said optical fiber to reduce its PMD, wherein the outermost peripheral external surface of said pulley in contact with said optical fiber during drawing is toroidal, convex surface.
2. The anti-PMD system claimed in claim 1 wherein a ratio r/R of a radius r of curvature of the convex portion of said peripheral external surface of said pulley to a radius R of the pulley is in the range of 1/2 to 1.
3. The anti-PMD system claimed in claim 1 wherein a ratio r/R of a radius r of curvature of the convex portion of said peripheral external surface of said pulley to a radius R of the pulley is in the range of 1/4 to 1/2 when R is greater than 50 mm.
4. The anti-PMD system claimed in claim 1 wherein a ratio r/R of a radius r of curvature of the convex portion of said peripheral external surface of said pulley to a radius R of the pulley is in the range of 1 to 2 when R is less than 50 mm.
5. The anti-PMD system claimed in claim 1 wherein the radius of curvature of the convex portion of said peripheral external surface of said pulley is constant over the whole of said convex portion of said peripheral external surface of said pulley.
6. The anti-PMD system claimed in claim 1 wherein all of said peripheral external surface of said pulley is convex.
7. The anti-PMD system claimed in claim 1 wherein the radius of said pulley is less than or equal to 100 mm.
8. The anti-PMD system claimed in claim 1 wherein the radius of said pulley is greater than or equal to 25 mm.
9. The anti-PMD system claimed in claim 1 wherein said pulley has no guide rims.