Method of controlling the polarization mode dispersion of an optical fiber during fiber drawing
An optical fiber drawing installation is equipped with an oscillating pulley that applies torsion to the fiber alternately in one rotation direction and then in the opposite direction. To control the torsion applied to the fiber, images are formed of the fiber and the pulley. The images are analyzed to determine the position of the fiber relative to the pulley. The torsion is calculated from the calculated position, on the assumption that the fiber rolls on the pulley.
1. A method of controlling polarization mode dispersion of an optical fiber during fiber drawing, said method comprises the steps of:
applying torsion to said fiber by displacement of said fiber relative to a member,
capturing at least one image of said fiber and said member,
analyzing said image to determine the position of said fiber relative to said member, and
calculating said torsion applied to said fiber from said determined position.
2. The method claimed in claim 1 wherein said step of applying torsion to said fiber comprises the displacement in rotation of said member relative to said fiber and said step of analyzing said at least one image comprises determining the angular position of said fiber relative to said member.
3. The method claimed in claim 2 wherein said step of applying torsion to said fiber comprises periodic movement of said member.
4. The method claimed in claim 3 wherein said step of capturing at least one image of said fiber and said member is executed periodically, with a period different from that of said movement of said member.
5. The method claimed in claim 1 wherein said step of calculating said torsion applied to said fiber comprises calculating the number of turns through which said fiber rolls on said member.
6. The method claimed in claim 5 wherein said step of calculating said torsion applied to said fiber comprises calculating the mean position of said fiber by integrating its positions.